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Seated and semi-recumbent positioning of the ventilated intensive care patient – Effect on gas exchange, respiratory mechanics and hemodynamics
Heart & Lung 43 (2014) 105e111
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Seated and semi-recumbent positioning of the ventilated intensive care patient e Effect on gas exchange, respiratory mechanics and hemodynamics Peter Thomas, BPhty (Hons), PhD, FACP a, *, Jennifer Paratz, MPhty, PhD, FACP b, Jeffrey Lipman, MBBCh, DA (SA), FFA (SA), FFA (CritCare), FCICM b, c a
Department of Physiotherapy, Royal Brisbane and Women’s Hospital, Brisbane, Australia Burns Trauma and Critical Care Research Centre, University of Queensland, Brisbane, Australia c Department of Intensive Care Medicine, Royal Brisbane and Women’s Hospital, Brisbane, Australia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 April 2013 Received in revised form 25 November 2013 Accepted 26 November 2013
Objectives: To compare the effect of semi-recumbent and sitting positions on gas exchange, respiratory mechanics and hemodynamics in patients weaning from mechanical ventilation. Background: Upright positions are encouraged during rehabilitation of the critically ill but there effects have not been well described. Methods: A prospective, randomized, cross-over trial was conducted. Subjects were passively mobilized from supine into a seated position (out of bed) and from supine to a semi-recumbent position (>45 backrest elevation in bed). Arterial blood gas (PaO2/FiO2, PaO2, SaO2, PaCO2 and Aea gradient), respiratory mechanics (VE, VT, RR, Cdyn, RR/VT) and hemodynamic measurements (HR, MABP) were collected in supine and at 5 min and 30 min after re-positioning. Results: Thirty-four intubated and ventilated subjects were enrolled. The angle of backrest inclination in sitting (67 5 ) was greater than gained with semi-recumbent positioning (50 5 , p < 0.001). There were no clinically important changes in arterial blood gas, respiratory mechanic or hemodynamic values due to either position. Conclusions: Neither position resulted in significant changes in respiratory and hemodynamic parameters. Both positions can be applied safely in patients being weaned from ventilation. Crown Copyright Ó 2014 Published by Elsevier Inc. All rights reserved.
Keywords: Intensive care Respiratory mechanics Posture Semi-recumbent Weaning
Introduction
Abbreviations: Aea gradient, alveolar gas to arterial blood oxygen tension difference; ALI, acute lung injury; APACHE, acute physiological and chronic health evaluation II score; BMI, body mass index; Cdyn, dynamic lung compliance; CV, closing volume; FiO2, fraction of inspired oxygen; FRC, functional residual capacity; HR, heart rate; MABP, mean arterial blood pressure; MLI, Murray lung injury; P, linear mixed model main effect analysis for position (sitting or semi-recumbent); P T, linear mixed model analysis for position and time interaction; PaCO2, partial pressure of carbon dioxide in arterial blood; PaO2, partial pressure of oxygen in arterial blood; PIPaw, peak inspiratory airway pressure; RR, respiratory rate; RR/VT, shallow breathing index; SaO2, arterial hemoglobin oxygen saturation; SOFA, sepsis-related organ failure assessment; SpO2, pulse oximeter oxygen saturation; T, liner mixed model main effect analysis for time; T0, time of measurement, baseline starting position; T5, time of measurement, 5 min post intervention; T30, time of measurement, 30 min post intervention; VE, minute ventilation; VT, tidal volume. Conflicts of interest: All authors have none to declare. * Corresponding author. Tel.: þ61 (0)7 3646 7288; fax: þ61 (0)7 3646 1665. E-mail address: [email protected] (P. Thomas).
The practice of early mobilization of the intensive care patient is considered to be safe1,2 and appears to positively influence intensive care outcomes. For example, a focus on early mobilization can improve the functional ability of patients during the intensive care period3,4 and at hospital discharge.1 Additionally, it may increase ventilator-free days1 and reduce intensive care and hospital length of stay.5 As part of these early mobilization strategies, the positioning of patients upright in bed or out of bed is encouraged in order to overcome possible respiratory and/or cardiovascular complications of immobility.1 Positioning patients semi-recumbent up to 60 is usually well tolerated hemodynamically, with minimal impact on cardiac output6,7 and 45 semi-recumbent positioning has been shown to significantly reduce the incidence of ventilatorassociated pneumonia.8 Outside of the intensive care unit, research involving subjects from both normal and diseased populations have shown significant improvement in pulmonary function associated with movement from a supine to an erect semi-recumbent (in bed)
0147-9563/$ e see front matter Crown Copyright Ó 2014 Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.hrtlng.2013.11.011
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or seated position (out of bed).9e14 These benefits include increases in functional residual capacity (FRC),10e12 lung compliance14,15 and adoption of large tidal volume-low respiratory rate patterns of breathing.14 In some people, the changes in lung volume and mechanics on moving from a supine to seated position may result in improvement in the partial pressure of oxygen in arterial blood (PaO2) and other indices of gas exchange.10,11 Knowledge of the influence of position on gas exchange and/or respiratory mechanics is important during weaning from mechanical ventilation. If adoption of a seated or semi-recumbent position results in improved gas exchange, lung compliance and/or tidal volume and a reduction in respiratory rate and work of breathing, their utilization may prevent respiratory muscle fatigue and shorten the weaning process. Additionally, there could be advantages in moving a patient out of bed and into a seated position. Investigation in normal subjects suggests that positioning a patient into a seated posture may result in greater improvements in FRC than are gained with a semi-recumbent position.13 Maintaining a patient in a semirecumbent position can be challenging in clinical practice16e18 and if patients slide out of a semi-recumbent position into a slumped position it may further reduce lung volume.13 Several studies have examined the effect of a semi-recumbent or seated position on gas exchange and/or respiratory mechanics in specific intensive care populations including patients with acute lung injury,19e22 abdominal distension23 and post-operative abdominal surgery.24,25 However, only two studies have recruited patients specifically during the stages of weaning from mechanical ventilation.26,27 These two studies report no significant deleterious effects of sitting or semi-recumbent positions. However, respiratory effort may be higher in sitting26; and sitting may result in smaller improvements in inspiratory muscle strength.27 Neither study has reported the effect on arterial blood gas measurements. Changes in compliance may account for increased respiratory effort,26 and have previously been hypothesized to impact on changes in oxygenation indices.20,22 The aim of this study was to compare the effects of sitting out of bed and semi-recumbent positioning in bed when applied in ventilated (>48 h) intensive care patients. The null hypothesis was that a change in position from supine to either a seated or semirecumbent position would not affect gas exchange, respiratory mechanics, or hemodynamic values. Methods A prospective, randomized, cross-over trial design was used with concealed allocation to the first position examined. Ethical approval for this study was gained from the relevant institutional human research ethics committee. Written informed consent to participation was gained from participants and/or their authorized legal guardian. Participants were recruited from
the intensive care unit of a tertiary-referral, university-affiliated, metropolitan centre. Patients receiving mechanical ventilation for more than 48 h were screened and consent for participation sought if there were no absolute contraindications to sitting and their cardiovascular and respiratory parameters were stable according to the criteria outlined in Table 1. As there was limited published data investigating the effect of upright positioning on arterial blood gas measurements and respiratory mechanics in patients weaning from mechanical ventilation, an interim analysis was conducted after enrollment of 20 patients and was used to estimate the standard deviation for paired differences in PaO2/FiO2 and VE from supine to sitting and semirecumbent positioning. A sample size estimate of 34 patients was calculated to detect moderate effect sizes and clinically significant changes in PaO2/FiO2 (difference ¼ 20, s ¼ 35, a ¼ 0.05, power ¼ 0.9) and VE (sample estimate ¼ 27, difference ¼ 1 L/min, s ¼ 1.55 L/min, a ¼ 0.05, power ¼ 0.9) in a repeated measures design.28 Admission diagnosis, demographic information, sepsisrelated organ failure assessment (SOFA) scores29 and Murray lung injury (MLI) scores30 were calculated from data collected on the day of the study. Automated calculations for acute physiological and chronic health evaluation II (APACHE) scores31 were obtained from the intensive care unit’s clinical information system. Ventilator settings and respiratory mechanics (respiratory rate (RR), tidal volume (VT), minute ventilation (VE), peak inspiratory airway pressure (PIPaw), dynamic lung compliance (Cdyn) were recorded via electronic transfer of data from the serial port of the ventilator (Mallinckrodt Puritan Bennet 7200Ò or 840Ô ventilator), which were calibrated according to manufacturer’s recommendations. A shallow breathing index was also calculated as RR/VT. Ventilator measurement of pressure, volume and flow are considered to be accurate and have low variability.32,33 However, at each data collection point, 5-min periods of respiratory mechanic measurements were collected and averaged to reduce any breath-tobreath variability of measurements.34,35 Variations in gas exchange were monitored through arterial blood gas sampling (ABL 700 Series machines e Radiometer, Copenhagen, Denmark) and analysis of the ratio of PaO2 to FiO2 (PaO2/FiO2), PaO2, the partial pressure of carbon dioxide in arterial blood (PaCO2), arterial hemoglobin oxygen saturation (SaO2), and alveolar gas to arterial blood oxygen tension difference (Aea gradient). Heart rate (HR), MABP and SpO2 were recorded from the patient monitoring system (Philips Intellivue). For MABP measurements, arterial blood pressures were manually checked for accuracy/calibration against sphygmomanometer readings prior to data collection and the arterial line transducer placement was re-zeroed prior to each recording.
Table 1 Study inclusion and exclusion criteria. Inclusion criteria
Exclusion criteria
Age >18 years Intubated and receiving mechanical ventilation (>48 h) Suitable candidates to mobilize into either the seated or semi-recumbent position. To ascertain this, clinical characteristics had to include: PaO2 >60 mm Hg FiO2 <0.6 PIPaw <40 cm H2O Stable hemodynamic parameters HR 60e130 beats/min MABP 70e120 mm Hg
Signs of new or sustained sepsis on the day of enrollment Hemoglobin <70 g/L Platelets <30 109/L
Arrhythmias (if present) stable and not compromising blood pressure
Vasopressor or neuromuscular blockade medications Nitric oxide Pulmonary barotrauma (e.g. flail chest, untreated pneumothorax) Burn injuries Dialysis Contraindications to upright positioning (e.g. unstable spinal column fractures or spinal cord injury) Intracranial pressure monitoring
P. Thomas et al. / Heart & Lung 43 (2014) 105e111
A goniometer/protractor was used to measure the angle of backrest inclination achieved36 and a tape measure was used to determine the static maintenance of the two upright positions over the study period. The reference points measured were the distance between a patient’s popliteal crease and the bed end (semi-recumbent positioning) or the chair base (sitting). All goniometer and tape measure recordings were taken by the primary investigator. The study period began with a minimum of 2 h during which ventilator settings were left unchanged, other interventions limited and a 30 min period in the supine position immediately prior to data collection. The dose of sedative medications was not altered during the study period. To attain the semi-recumbent position, the patient’s bed was simply adjusted from a horizontal position to having the head of bed elevated. The seated position was achieved by transferring the patient out of bed (via sliding board) into a HaustedÒ chair (APC series, Hausted Medina, Ohio). Neither position required the patient to actively assist or contribute to the transfer and/or change in position. Both the HaustedÒ chair and beds used were able to have their backrest adjusted through a 0e80 range. With either position, a minimum of 45 backrest elevation was targeted, with higher elevations used when reported comfortable by the patient. This reflected clinical practice. Patients were maintained in either position for 30 min, at which point, data collection finished. Patients were later returned supine, with a minimum of 30 min supine before the alternate position was studied. For each position, data was collected at three time points including the baseline supine position (T0), then 5 min post implementation of the semi-recumbent or sitting position (T5) and/or at 30 min post implementation (T30). Arterial blood gas samples were taken at T0 and T30 only. Respiratory mechanics, HR, BP and SpO2 measurements were collected at T0, T5 and T30. Goniometer and tape measure recordings were taken at T5 and T30. During the data collection periods, the position was ceased if intolerance to either position was noted. This was defined by: a >10% increase in fraction of inspired oxygen (FiO2) required to maintain pulse oximeter oxygen saturation (SpO2) >90% or the partial pressure of oxygen in arterial blood (PaO2) >60 mm Hg; the alteration of heart rate by 30 beats/min; the onset of a new arrhythmia or ischemic electrocardiograph changes or a reduction in blood pressure due to arrhythmia; or change in mean arterial blood pressure (MABP) by 30 mm Hg). Additionally, occurrences of any adverse events (e.g. accidental extubation, removal of indwelling catheters) were recorded. If any intolerance or adverse event occurred, medical staff were notified immediately and appropriate action taken. An intention-to-treat analysis was used for this study. Continuous variables were assessed for normality of distribution, transformed as appropriate and analyzed using a linear mixed model (within subject main effects: position (sitting or semi-recumbent) (P) and time (T) and their interaction (P T); subjects were random effects). Incorporated into this model was assessment for an order effect, and analysis of covariates, which included a subjects’ age, body mass index (BMI), extent of lung pathology (determined from the chest radiograph rating of the MLI score), degree of hypoxemia (determined from the respiratory system rating of the SOFA score) and 24-h fluid balance for the day of the study. Paired sample t-tests were used to compare the angle of inclination and displacement out of position measured between the two positions. Results are expressed as mean standard deviation and a significance level of <0.05 was used. Results Thirty-four patients were enrolled in the study. Diagnostic and demographic information is presented in Table 2.
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Table 2 Baseline characteristics of the patients. Characteristic
Value
Age (years) Female e N (%) Body mass index (kg/m2) APACHE IIa Primary diagnosis e N Gastrointestinal (post-operative) Gastrointestinal (non-surgical) Multi-trauma (post-operative) Cardiovascular (post-operative) Respiratory Neurological (post-operative) Neurological (non-surgical) Cardiovascular Metabolic/renal (non-surgical) Diabetic ketoacidosis Drug overdose Glasgow coma score e median Eye Motor Verbal Total SOFA scoreb Respiratory Coagulation Liver Cardiovascular Central nervous system Renal Total SOFA score MLI scoreb Days prior to enrollment of: Hospital admission ICU admission Mechanical ventilation Tracheostomy e N (%) Ventilator mode e N SIMV (volume controlled) Pressure support ventilation FiO2 Pressure support (cm H20) PEEP (cm H20) Hemoglobin (g/L) 24-h fluid balance (L)
65.5 14.4 13 (38%) 28.6 6.9 23.2 6.7
Range 18e87 18.7e50.8 10e37
9 2 2 3 7 1 3 4 1 1 1 4 6 3 13 2.29 0.24 0.44 0.44 0.85 0.59 4.85 1.25
3e4 1e6 1e5 5e15
0.58 0.65 0.82 0.56 0.89 1.0 2.0 0.6
16.4 9.3 12.8 8.7 12.5 8.5 21 (62%) 6 28 0.35 11.5 5.7 90.2 0.20
0.06 2.8 1.44 13.7 1.5
1e3 0e3 0e3 0e3 0e4 0e4 1e9 0e2.7 5e36 3e36 3e36
0.25e0.5 8e20 5e10 70e141 3.4e2.1
a
APACHE II scores were collated from admission data. SOFA scores and MLI scores were calculated from data collected on the day of the study. b
Recruitment of patients during the weaning period from mechanical ventilation is reflected by the majority of patients being ventilated on pressure support ventilation (Table 2), and only eight (24%) of patients receiving sedative or opioid infusions (two patients received Propofol, six patients received Fentanyl). At the time of enrollment, nine patients (26%) had previously sat out of bed on days prior to recruitment to the study. The randomization procedure resulted in three of these patients being examined first in the semi-recumbent position and six in the seated position. The median time between assessment of the semi-recumbent and seated positions was 2.5 h (inter-quartile range ¼ 1e3.5 h). Three patients completed only one part of the protocol, resulting in 33 assessments in the seated position and 32 in the semi-recumbent position. Reasons for non-completion of the entire protocol were elective extubation prior to completion (N ¼ 2) and the onset of hemodynamic instability requiring commencement of inotropes (N ¼ 1), which occurred more than 3 h after the first intervention. Review by the investigators and attending medical staff determined that there was no direct temporal or causal relationship with this deterioration and the study protocol. No patients required cessation
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P. Thomas et al. / Heart & Lung 43 (2014) 105e111
position (50 5 , range 40e60 ; t(30) ¼ 14.1, p < 0.001). After 30 min in an upright position, patients in the semi-recumbent position were observed to have moved out of the position more than in the seated position (4 4 cm (range 0e16 cm) versus 1 1 cm (range 0e6 cm) respectively, t(20) ¼ 4.5, p < 0.001).
Table 3 Variables with significant effects due to order. Value
Order
p value
First PaO2/FiO2 PaO2 PaCO2 MAPaw
240 80.5 37.4 10.1
Second
58 11.6 6.0 2.1
245 84.0 36.6 9.7
68 15.7 5.9 2.0
O
OT
OP
0.012 0.009 0.036 <0.001
0.672 0.996 0.789 0.976
0.844 0.695 0.222 0.334
Discussion
Mean standard deviation. Units: PaO2/FiO2 (), PaO2 (mm Hg), PaCO2 (mm Hg), MAPaw (cm H2O). Abbreviations: O ¼ order, O T ¼ order time interaction, O P ¼ order position sequence interaction.
To our knowledge, this is the first study that has compared the effects of positioning a patient in a seated versus semi-recumbent position on arterial blood gas measurements, during weaning from mechanical ventilation. Our results demonstrated that in this population, the semi-recumbent position and seated position are safe interventions, which have minimal effect on gas exchange and respiratory mechanics. The seated position enabled a higher angle of inclination to be attained, and was more easily maintained over the 30-min period studied. In some populations, moving subjects from a supine to seated position may result in improvements in oxygenation or in other indices of gas exchange.10,11 However, improvements in oxygenation in the ventilated patients enrolled in our study were negligible and the magnitude of the reduction in PaCO2 when in semirecumbent or sitting positions was of little clinical importance. Previous investigations in intensive care populations have also found no significant improvements in gas exchange as a result of semi-recumbent positioning (60 ) in patients who were intubated, but weaned from mechanical ventilation24; patients with acute lung injury (ALI) receiving ventilation and neuromuscular blockades who were positioned in 30 and 45 semi-recumbent positions20; ventilated post-operative abdominal surgery patients after walking and sitting out of bed25; and in both ventilated and nonventilated chronic critically ill patients after being passively tilted to 70 .37 The absence of clinically significant effects on gas exchange in this and prior studies of intensive care patients may be related to reductions in FRC and increased alveolar closing volumes (CV) in this population. CV is the lung volume during expiration at which the flow from the lower parts of the lungs becomes severely reduced or stops because of airway closure (before residual volume is reached).38 When moving from a seated position into supine reduces FRC and results in CV exceeding FRC, airway closure begins to occur during normal tidal breathing and a fall in PaO2 may
of the positioning interventions during testing according to the safety criteria. Despite randomized assignment and concealed allocation to the two study positions, an order effect was detected. Values for PaO2/ FiO2 and PaO2 were lower and PaCO2 and MAPaw were higher at all time points during the patient’s first positioning trial (Table 3). Additionally, values obtained for PaO2/FiO2, PaO2, SaO2 and PIPaw were higher throughout examination of the of supine e seated test sequence versus the supine e semi-recumbent sequence (Tables 4 and 5). However, there were no observed effects related to changing a patient’s position over time (T0eT30) for these variables. Changes in position over T0eT30 had no effect on any indices of oxygenation (Table 4). There was a significant effect of time on PaCO2 regardless of the upright posture studied (T0: 37.4 6.0 > T30: 36.6 5.9 mm Hg, t(92) ¼ 4.0, p < 0.001). Respiratory mechanics were unchanged after institution of either upright position (Table 4). The hemodynamic response to attaining the upright position was similar between the two positions (Table 4), with an increase in MABP at T5 (T0: 87.8 12.9 < T5: 92.3 14.3 mm Hg, t(150) ¼ 3.0, p ¼ 0.003) occurring without a significant change in HR. At T30, the rise in MABP had dissipated and returned to baseline levels (T0: 87.8 12.9 ¼ T30: 87.7 15.8 mm Hg, t(150) ¼ 0.6, p ¼ 0.559). There was no significant effect on gas exchange and respiratory mechanic measurements through inclusion of the covariates of age, BMI, extent of lung pathology, degree of hypoxemia or 24-h fluid balance. The angle of inclination achieved in the seated position (67 5 , range 55e80 ) was greater than achieved in the semi-recumbent
Table 4 Response in gas exchange indices, respiratory mechanics and hemodynamics at T0, T5 and T30. Value
Semi-recumbent sequence T0
PaO2/FiO2 PaO2 SaO2 Aea gradient PaCO2 SpO2 RR VT VE Cdyn PIPaw MAPaw RR/VT MABP HR
234 79.0 96.0 125 37.2 96.5 25.2 0.56 13.48 42.7 19.1 9.9 53.4 88.6 94.9
64 11.1 1.8 52 5.8 2.4 7.3 0.16 3.64 14.6 3.5 2.1 22.9 12.8 15.3
Sitting out of bed sequence
T5
T30
e e e e e 96.4 25.8 0.55 13.61 44.5 18.7 9.9 54.7 92.2 95.3
237 80.5 96.3 124 36.6 96.5 26.7 0.55 13.96 44.6 19.3 9.9 54.2 90.9 96.8
2.3 7.0 0.13 3.49 15.7 4.6 2.2 23.1 12.8 17.2
T0
64 12.5 1.5 50 5.9 2.5 7.1 0.14 3.48 15.0 3.8 2.1 24.6 11.9 18.6
244 83.1 96.5 120 37.7 96.5 24.5 0.56 12.82 42.9 19.70 9.9 51.1 87.0 95.6
62 12.9 1.6 49 6.2 2.0 7.5 0.15 3.64 14.0 3.34 2.1 23.5 13.1 16.8
p value
T5
T30
e e e e e 97.3 25.7 0.56 13.78 42.5 20.35 10.0 54.0 92.4 99.7
253 86.0 96.6 119 36.5 97.1 25.8 0.55 13.81 42.4 19.77 9.9 54.9 84.4 99.9
2.3 8.1 0.15 4.22 15.0 3.97 2.2 25.8 15.8 17.7
63 17.1 1.7 47 6.0 2.1 7.6 0.13 4.17 13.8 3.53 1.9 20.7 18.6 17.0
T
P
PT
0.931 0.928 0.697 0.560 0.001c 0.459 0.112 0.746 0.152 0.869 0.062 0.066 0.696 0.013b 0.339
0.015a 0.003a 0.016a 0.164 0.659 0.065 0.980 0.588 0.789 0.111 <0.001a 0.133 0.947 0.324 0.121
0.184 0.813 0.773 0.094 0.208 0.268 0.618 0.658 0.290 0.579 0.671 0.952 0.886 0.096 0.361
Mean standard deviation. Units: PaO2/FiO2 (), PaO2 (mm Hg), SaO2 (%), Aea gradient (mm Hg), PaCO2 (mm Hg), SpO2 (%); RR (breaths/min), VT (L), VE (L), Cdyn (L/cm H2O), PIPaw (cm H2O), MAPaw (cm H2O), RR/VT (); MABP (mm Hg), HR (beats/min). Abbreviations: T ¼ time, P ¼ position sequence, P T ¼ position sequence time interaction. a Sitting > semi-recumbent sequence, see Table 5. b T5 > T0, T30. c T0 > T30.
P. Thomas et al. / Heart & Lung 43 (2014) 105e111 Table 5 Variables with significant effects due to position sequence. Value
Supine e semi-recumbent
PaO2/FiO2 PaO2 SaO2 PIPaw
236 79.8 96.1 19.0
64 11.8 1.7 4.0
Supine e seated 249 84.6 96.6 20.0
62 15.1 1.6 3.6
p value 0.018 0.003 0.015 0.007
Mean standard deviation. Units: PaO2/FiO2 (), PaO2 (mm Hg), SaO2 (%), PIPaw (cm H2O).
arise.10,39 However, when FRC volume is significantly reduced, or CV significantly increased so that CV exceeds (FRC þ VT) in both the seated and supine position, significant airway closure is present in both positions. Subsequently, changes in regional alveolar ventilation may be small and diminish any potential for upright positioning to induce a change in oxygenation.10,39 Factors that are known to decrease the elastic recoil of the lung and subsequently increase CV include advancing age, smoking, respiratory disease and/or obesity.10,11,39 Alternatively, FRC may be reduced by the presence of: respiratory failure40,41; mechanical ventilation, anesthesia and paralysis42,43; ALI44; major chest X-ray abnormalities45; a low FEV1/FVC ratio11; and abdominal surgery.46 Many of these conditions were features of the subjects in this study and the wider intensive care population. The decision to mobilize a patient out of bed who is weaning from mechanical ventilation can be delayed due to concerns of the effort involved by the patient and the impact this may have on respiratory system function. In this study, the change to either upright position resulted in no significant effect on RR, VT, VE, or RR/ VT. Deye et al26 also found no change in these variables after 15 min of supine, semi-recumbent positioning and a seated position in bed. As seated positions produce negligible changes in RR, VT, VE, or RR/ VT, they could be utilized during the weaning of patients from mechanical ventilation in order to promote arousal, function and interaction of patients with their environment. However, Deye et al26 also measured work of breathing and respiratory effort and found them to be slightly lower with semi-recumbent positioning. Subsequently, they concluded that the semi-recumbent position is useful in difficult to wean patients in order to unload (rest) the respiratory muscles. While this unloading may be important when recovery is required, the benefits of early mobilization in the critically ill have been gained by mobilizing patients out of bed and incrementally loading (training) the respiratory system. These benefits have also been demonstrated in patients who are slow to wean.5,47,48 Therefore, the utilization of seated positioning could instead be viewed as an important component of early rehabilitation strategies in order to slightly increase respiratory effort and/or provide a stable and more optimal position for rehabilitation exercises. When periods of sitting are well tolerated, progression may then occur to standing or tilt table rehabilitation, which are more demanding and generate increases in VT and/or VE.25,37 A reduction in compliance with the use of upright positioning was not observed in this study. Variations in compliance have been observed in ventilated patients with ALI when positioned from supine to a 30 or 45 semi-recumbent position20 but not with seated positions in bed.19 Differences in the level of sedation and/ or use of neuromuscular blocking agents may account for the differences observed. In heavily sedated and/or paralyzed patients compliance is decreased because spontaneous diaphragmatic contractions are reduced and diaphragmatic excursion is reliant on the positive pressure ventilation to overcome resistance from the abdominal compartment. We encountered no adverse events during the application of the semi-recumbent or seated position in patients who met our study criteria and only a small increase in MABP was evident immediately
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after positioning in to the upright position. Prior investigations also appear to support the safety specifically of sitting and/or semirecumbent positioning,20,22 with no adverse event reported and/ or no requirement for additional sedation, neuromuscular blockade or vasoactive drugs.20 Bourdin et al49 reported the frequent use of sitting out of bed in 20 patients receiving mechanical ventilation, and concluded it to be safe with minimal changes in HR or MABP. Other studies have assessed hemodynamic changes with semirecumbent positioning in patients who are hemodynamically stable, ventilated and/or receiving vasoactive drugs with results indicating that altering position from supine to a semi-recumbent position up to 60 is generally well tolerated, with minimal change to cardiac output.6,7 Moving a patient in to a semi-recumbent position is easier and involves less staff compared to sitting a patient out of bed. However, discomfort may contribute to the ability to sustain the semirecumbent position and several authors have outlined the difficulties of implementing and/or maintaining the semi-recumbent position in clinical practice.16e18 While we did not record the level of comfort experienced by patients in either position, we believe comfort was the main factor that limited achievement of higher backrest elevations with semi-recumbent positioning. Additionally, the results of this study suggest that an advantage of seated positions is the ability to achieve a greater angle of inclination and to remain stable in the position. This may have significant implications for patient safety and comfort and considerations in pressure area management with the use of upright positioning. Erect postures enhance the mechanics of the thoracic cage and increase the caudal excursion of the diaphragm.50 As patients slide out of the semi-recumbent position, they assume a slumped posture. As the degree of kyphosis increases, lung volumes and chest wall mechanics may be adversely affected. For example, in normal subjects, a slumped semi-recumbent position significantly reduces FRC13 and a slumped sitting position has been shown to decrease VE and VT.50 Therefore, it is possible, that with a longer duration of semi-recumbent positioning, adverse effects of pulmonary function may have become evident in this population. The results of this study support clinicians to implement early mobilization strategies, in that the adoption of seated positions out of bed can be commenced with the knowledge that short applications of 30 min are generally not detrimental to a patient’s respiratory or cardiovascular status. Additionally, clinicians should not expect improvements in oxygenation indices to routinely occur when utilizing upright positions in patients that are weaning from mechanical ventilation. While a potential benefit of passively moving patients out of bed into specialized chairs is that patients may not slide out of the upright position, clinicians should be aware of the risk that static positioning also poses to skin integrity and therefore the duration of seated upright positioning may need to be limited and/or guided by a patient’s skin tolerance. A limitation of this study was the short period of data collection. Thirty minutes in the upright position was chosen for the convenience and ability to complete data collection for both positions in close proximity, in an environment where various interventions and investigations compete for time. Similar and/or shorter time periods have been used in prior research in this population and detected significant changes in respiratory function.13,20,24,25 The median time between the position sequences was 2.5 h and an order effect was observed. While the magnitude of these changes were small and would not be clinically significant, it may indicate that small improvements in respiratory function occur through the repeated utilization of these position changes. A longer time period for data collection and the effect of repeated applications of upright position may have been able to detect significant changes in respiratory function. Variation in respiratory responses to upper limb
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exercise has been found when ventilated patients are compared with non-ventilated patients.14 As patients were still supported on mechanical ventilation, if any detrimental effect of either position arose, the impact of the change on respiratory function may have been lessened.51 Therefore, replication of this study in patients who have been recently extubated, are undergoing a slow weaning process or are undergoing spontaneous breathing trials may yield differing results. In addition to investigating the effect of utilizing upright positions over longer time periods and/or during different phases of ventilator support, more specific measures of a patients lung volume, work of breathing and fatigue are required in future studies to direct prescription of seated positions under varying circumstances. For example, if the success or duration of a T-piece trial in a difficult to wean patient was known to be affected by semirecumbent or seated positions, then positions that benefit lung volumes or work of breathing or reduce fatigue could be utilized during the trial. Positions that may provide an additional challenge to the respiratory system e.g. by increasing work of breathing may be utilized at different times to a T-piece trial, to prevent overloading the respiratory system of the slow to wean patient. Further investigation into the variety of real and/or perceived barriers to mobilizing patients out of bed is also warranted52 including patient factors (e.g. comfort, arousal, dyspnea) and environmental factors (e.g. equipment, sedation practices). By increasing our understanding of the impact of positioning practices throughout various stages of critical illness, clinicians will be able to refine early rehabilitation strategies that include the appropriate timing and application of upright positioning. Acknowledgments Warren Stanton, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane. Ross Darnell, Statistician, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane. Financial support for this project was gained from the Australian Physiotherapy Association, Dorothy Hopkins Award for clinical research. References 1. Schweickert WD, Pohlman MC, Pohlman AS, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet. 2009;373(9678):1874e1882. 2. Bailey P, Thomsen GE, Spuhler VJ, et al. Early activity is feasible and safe in respiratory failure patients. Crit Care Med. 2007;35(1):139e145. 3. Nava S. Rehabilitation of patients admitted to a respiratory intensive care unit. Arch Phys Med Rehabil. 1998;79(7):849e854. 4. Thomsen GE, Snow GL, Rodriguez L, Hopkins RO. Patients with respiratory failure increase ambulation after transfer to an intensive care unit where early activity is a priority. Crit Care Med. 2008;36(4):1119e1124. 5. Morris PE, Goad A, Thompson C, et al. Early intensive care unit mobility therapy in the treatment of acute respiratory failure. Crit Care Med. 2008;36(8): 2238e2243. 6. Lambert CW, Cason CL. Backrest elevation and pulmonary artery pressures: research analysis. Dimens Crit Care Nurs. 1990;9(6):327e335. 7. Doering L. The effect of positioning on hemodynamics and gas exchange in the critically ill: a review. Am J Crit Care. 1993;2(3):208e216. 8. Drakulovic MB, Torres A, Bauer TT, Nicolas JM, Nogue S, Ferrer M. Supine body position as a risk factor for nosocomial pneumonia in mechanically ventilated patients: a randomised trial. Lancet. 1999;354(9193):1851e1858. 9. Behrakis PK, Baydur A, Jaeger MJ, Milic-Emili J. Lung mechanics in sitting and horizontal body positions. Chest. 1983;83(4):643e646. 10. Craig DB, Wahba WM, Don HF, Couture JG, Becklake MR. “Closing volume” and its relationship to gas exchange in seated and supine positions. J Appl Physiol. 1971;31(5):717e721. 11. Hardie JA, Morkve O, Ellingsen I. Effect of body position on arterial oxygen tension in the elderly. Respiration. 2002;69(2):123e128. 12. Ibanez J, Raurich JM. Normal values of functional residual capacity in the sitting and supine positions. Intensive Care Med. 1982;8(4):173e177.
13. Jenkins SC, Soutar SA, Moxham J. The effects of posture on lung volumes in normal subjects and in patients pre- and post- coronary artery surgery. Physiotherapy. 1988;74(10):492e496. 14. Vitacca M, Clini E, Spassini W, Scaglia L, Negrini P, Quadri A. Does the supine position worsen respiratory function in elderly subjects? Gerontology. 1996;42(1):46e53. 15. Lorino AM, Atlan G, Lorino H, Zanditenas D, Harf A. Influence of posture on mechanical parameters derived from respiratory impedance. Eur Respir J. 1992;5(9):1118e1122. 16. Cook DJ, Meade MO, Hand LE, McMullin JP. Toward understanding evidence uptake: semirecumbency for pneumonia prevention. Crit Care Med. 2002;30(7):1472e1477. 17. Grap M, Munro C, Bryant S, Ashtiani B. Predictors of backrest elevation in critical care. Intensive Crit Care Nurs. 2003;19(2):68e74. 18. van Nieuwenhoven C, Vandenbroucke-Grauls C, van Tiel F, et al. Feasibility and effects of the semirecumbent position to prevent ventilator-associated pneumonia: a randomized study. Crit Care Med. 2006;34(2):396e402. 19. Dellamonica J, Lerolle N, Sargentini C, et al. Effect of different seated positions on lung volume and oxygenation in acute respiratory distress syndrome. Intensive Care Med. 2013;39(6):1121e1127. 20. Bittner E, Chendrasekhar A, Pillai S, Timberlake GA. Changes in oxygenation and compliance as related to body position in acute lung injury. Am Surg. 1996;62(12):1038e1041. 21. Hoste EAJ, Roosens CDVK, Bracke S, et al. Acute effects of upright position on gas exchange in patients with acute respiratory distress syndrome. J Intensive Care Med. 2005;20(1):43e49. 22. Richard JC, Maggiore SM, Mancebo J, Lemaire F, Jonson B, Brochard L. Effects of vertical positioning on gas exchange and lung volumes in acute respiratory distress syndrome. Intensive Care Med. 2006;32(10):1623e1626. 23. Burns S, Egloff M, Ryan B, Carpenter R, Burns J. Effect of body position on spontaneous respiratory rate and tidal volume in patients with obesity, abdominal distention and ascites. Am J Crit Care. 1994;3(2):102e106. 24. Bonnet F, Bourgain JL, Matamis D, Tesseire B, Viars P. The influence of position on ventilation-perfusion distribution after abdominal surgery. Acta Anaesthesiol Scand. 1988;32(7):585e589. 25. Zafiropoulos B, Alison JA, McCarren B. Physiological responses to the early mobilisation of the intubated, ventilated abdominal surgery patient. Aust J Physiother. 2004;50(2):95e100. 26. Deye N, Lellouche F, Maggiore SM, et al. The semi-seated position slightly reduces the effort to breathe during difficult weaning. Intensive Care Med. 2013;39(1):85e92. 27. Chang MY, Chang LY, Huang YC, Lin KM, Cheng CH. Chair-sitting exercise intervention does not improve respiratory muscle function in mechanically ventilated intensive care unit patients. Respir Care. 2011;56(10): 1533e1538. 28. Dupont WD, Plummer WD. Power and sample size calculations: a review and computer program. Control Clin Trials. 1990;11:116e128. 29. Vincent JL, Moreno R, Takala J, et al. The SOFA (sepsis-related organ failure assessment) score to describe organ dysfunction/failure. Intensive Care Med. 1996;22(7):707e710. 30. Murray JF, Matthay MA, Luce JM, Flick MR. An expanded definition of the adult respiratory distress syndrome. Am Rev Respir Dis. 1988;138(3): 720e723. 31. Knauss WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13:818e829. 32. Banner MJ, Blanch PB, Kirby RR. Imposed work of breathing and methods of triggering a demand-flow, continuous positive pressure system. Crit Care Med. 1993;21(2):183e190. 33. Gammage GW, Banner MJ, Blanch PB, Kirby RR. Ventilator displayed tidal volume e what you see may not be what you get [abstract]. Crit Care Med. 1988;16:454. 34. Petrini MF, Evans J, Wall MA, Norman JR. Variability, reproducibility and datacollection time of pulmonary bedside monitoring. Biomed Instrum Technol. 1998;32:273e281. 35. Tobin MJ. Respiratory monitoring in the intensive care unit. Am Rev Respir Dis. 1988;138:1625e1642. 36. Hummel R, Grap M, Sessler C, Munro C, Corley M. Continuous measurement of backrest elevation in critical care: a research strategy. Crit Care Med. 2000;28(7):2621e2625. 37. Chang AT, Boots RJ, Hodges PW, Thomas PJ, Paratz JD. Standing with the assistance of a tilt table improves minute ventilation in chronic critically ill patients. Arch Phys Med Rehabil. 2004;85(12):1972e1976. 38. Stedman TL. Stedman’s Medical Dictionary. Philadelphia: Lippincott Williams and Wilkins; 2000. 39. Leblanc P, Ruff F, Milic-Emili J. Effects of age and body position on “airway closure” in man. J Appl Physiol. 1970;28(4):448e451. 40. Katz JA, Ozanne GM, Zinn SE, Fairley HB. Time course and mechanisms of lungvolume increase with PEEP in acute pulmonary failure. Anesthesiology. 1981;54(1):9e16. 41. Ramachandran PR, Fairley HB. Changes in functional residual capacity during respiratory failure. Can Anaesth Soc J. 1970;17(4):359e369. 42. Hedenstierna G, Strandberg A, Brismar B, Lundquist H, Tokics L. What causes the lowered FRC during anaesthesia? Clin Physiol. 1985;5:S133eS141. 43. Wahba RW. Perioperative functional residual capacity. Can J Anaesth. 1991;38(3):384e400.
P. Thomas et al. / Heart & Lung 43 (2014) 105e111 44. Rylander C, Hogman M, Perchiazzi G, Magnusson A, Hedenstierna G. Functional residual capacity and respiratory mechanics as indicators of aeration and collapse in experimental lung injury. Anesth Analg. 2004;98(3):782e789. 45. Wiren JE, Lindell SE, Hellekant C. Pre- and postoperative lung function in sitting and supine position related to postoperative chest X-ray abnormalities and arterial hypoxaemia. Clin Physiol. 1983;3(3):257e266. 46. Meyers JR, Lembeck L, O’Kane H, Baue AE. Changes in functional residual capacity of the lung after operation. Arch Surg. 1975;110(5):576e583. 47. Burtin C, Clerckx B, Robbeets C, et al. Early exercise in critically ill patients enhances short-term functional recovery. Crit Care Med. 2009;37(9):2499e2505. 48. Clini EM, Crisafulli E, Antoni FD, et al. Functional recovery following physical training in tracheotomized and chronically ventilated patients. Respir Care. 2011;56(3):306e313.
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49. Bourdin G, Barbier J, Burle JF, et al. The feasibility of early physical activity in intensive care unit patients: a prospective observational one-center study. Respir Care. 2010;55(4):400e407. 50. Landers M, Barker G, Wallentine S, McWhorter W, Peel C. A comparison of tidal volume, breathing frequency, and minute ventilation between two sitting postures in healthy adults. Physiother Theory Pract. 2003;19: 109e119. 51. El-Khatib MF, Jamaleddine GW, Khoury AR, Obeid MY. Effect of continuous positive airway pressure on the rapid shallow breathing index in patients following cardiac surgery. Chest. 2002;121(2):475e479. 52. Mendez-Tellez PA, Dinglas VD, Colantuoni E, et al. Factors associated with timing of initiation of physical therapy in patients with acute lung injury. J Crit Care. 2013;28(6):980e984.
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Seated and semi-recumbent positioning of the ventilated intensive care patient e Effect on gas exchange, respiratory mechanics and hemodynamics Peter Thomas, BPhty (Hons), PhD, FACP a, *, Jennifer Paratz, MPhty, PhD, FACP b, Jeffrey Lipman, MBBCh, DA (SA), FFA (SA), FFA (CritCare), FCICM b, c a
Department of Physiotherapy, Royal Brisbane and Women’s Hospital, Brisbane, Australia Burns Trauma and Critical Care Research Centre, University of Queensland, Brisbane, Australia c Department of Intensive Care Medicine, Royal Brisbane and Women’s Hospital, Brisbane, Australia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 April 2013 Received in revised form 25 November 2013 Accepted 26 November 2013
Objectives: To compare the effect of semi-recumbent and sitting positions on gas exchange, respiratory mechanics and hemodynamics in patients weaning from mechanical ventilation. Background: Upright positions are encouraged during rehabilitation of the critically ill but there effects have not been well described. Methods: A prospective, randomized, cross-over trial was conducted. Subjects were passively mobilized from supine into a seated position (out of bed) and from supine to a semi-recumbent position (>45 backrest elevation in bed). Arterial blood gas (PaO2/FiO2, PaO2, SaO2, PaCO2 and Aea gradient), respiratory mechanics (VE, VT, RR, Cdyn, RR/VT) and hemodynamic measurements (HR, MABP) were collected in supine and at 5 min and 30 min after re-positioning. Results: Thirty-four intubated and ventilated subjects were enrolled. The angle of backrest inclination in sitting (67 5 ) was greater than gained with semi-recumbent positioning (50 5 , p < 0.001). There were no clinically important changes in arterial blood gas, respiratory mechanic or hemodynamic values due to either position. Conclusions: Neither position resulted in significant changes in respiratory and hemodynamic parameters. Both positions can be applied safely in patients being weaned from ventilation. Crown Copyright Ó 2014 Published by Elsevier Inc. All rights reserved.
Keywords: Intensive care Respiratory mechanics Posture Semi-recumbent Weaning
Introduction
Abbreviations: Aea gradient, alveolar gas to arterial blood oxygen tension difference; ALI, acute lung injury; APACHE, acute physiological and chronic health evaluation II score; BMI, body mass index; Cdyn, dynamic lung compliance; CV, closing volume; FiO2, fraction of inspired oxygen; FRC, functional residual capacity; HR, heart rate; MABP, mean arterial blood pressure; MLI, Murray lung injury; P, linear mixed model main effect analysis for position (sitting or semi-recumbent); P T, linear mixed model analysis for position and time interaction; PaCO2, partial pressure of carbon dioxide in arterial blood; PaO2, partial pressure of oxygen in arterial blood; PIPaw, peak inspiratory airway pressure; RR, respiratory rate; RR/VT, shallow breathing index; SaO2, arterial hemoglobin oxygen saturation; SOFA, sepsis-related organ failure assessment; SpO2, pulse oximeter oxygen saturation; T, liner mixed model main effect analysis for time; T0, time of measurement, baseline starting position; T5, time of measurement, 5 min post intervention; T30, time of measurement, 30 min post intervention; VE, minute ventilation; VT, tidal volume. Conflicts of interest: All authors have none to declare. * Corresponding author. Tel.: þ61 (0)7 3646 7288; fax: þ61 (0)7 3646 1665. E-mail address: [email protected] (P. Thomas).
The practice of early mobilization of the intensive care patient is considered to be safe1,2 and appears to positively influence intensive care outcomes. For example, a focus on early mobilization can improve the functional ability of patients during the intensive care period3,4 and at hospital discharge.1 Additionally, it may increase ventilator-free days1 and reduce intensive care and hospital length of stay.5 As part of these early mobilization strategies, the positioning of patients upright in bed or out of bed is encouraged in order to overcome possible respiratory and/or cardiovascular complications of immobility.1 Positioning patients semi-recumbent up to 60 is usually well tolerated hemodynamically, with minimal impact on cardiac output6,7 and 45 semi-recumbent positioning has been shown to significantly reduce the incidence of ventilatorassociated pneumonia.8 Outside of the intensive care unit, research involving subjects from both normal and diseased populations have shown significant improvement in pulmonary function associated with movement from a supine to an erect semi-recumbent (in bed)
0147-9563/$ e see front matter Crown Copyright Ó 2014 Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.hrtlng.2013.11.011
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or seated position (out of bed).9e14 These benefits include increases in functional residual capacity (FRC),10e12 lung compliance14,15 and adoption of large tidal volume-low respiratory rate patterns of breathing.14 In some people, the changes in lung volume and mechanics on moving from a supine to seated position may result in improvement in the partial pressure of oxygen in arterial blood (PaO2) and other indices of gas exchange.10,11 Knowledge of the influence of position on gas exchange and/or respiratory mechanics is important during weaning from mechanical ventilation. If adoption of a seated or semi-recumbent position results in improved gas exchange, lung compliance and/or tidal volume and a reduction in respiratory rate and work of breathing, their utilization may prevent respiratory muscle fatigue and shorten the weaning process. Additionally, there could be advantages in moving a patient out of bed and into a seated position. Investigation in normal subjects suggests that positioning a patient into a seated posture may result in greater improvements in FRC than are gained with a semi-recumbent position.13 Maintaining a patient in a semirecumbent position can be challenging in clinical practice16e18 and if patients slide out of a semi-recumbent position into a slumped position it may further reduce lung volume.13 Several studies have examined the effect of a semi-recumbent or seated position on gas exchange and/or respiratory mechanics in specific intensive care populations including patients with acute lung injury,19e22 abdominal distension23 and post-operative abdominal surgery.24,25 However, only two studies have recruited patients specifically during the stages of weaning from mechanical ventilation.26,27 These two studies report no significant deleterious effects of sitting or semi-recumbent positions. However, respiratory effort may be higher in sitting26; and sitting may result in smaller improvements in inspiratory muscle strength.27 Neither study has reported the effect on arterial blood gas measurements. Changes in compliance may account for increased respiratory effort,26 and have previously been hypothesized to impact on changes in oxygenation indices.20,22 The aim of this study was to compare the effects of sitting out of bed and semi-recumbent positioning in bed when applied in ventilated (>48 h) intensive care patients. The null hypothesis was that a change in position from supine to either a seated or semirecumbent position would not affect gas exchange, respiratory mechanics, or hemodynamic values. Methods A prospective, randomized, cross-over trial design was used with concealed allocation to the first position examined. Ethical approval for this study was gained from the relevant institutional human research ethics committee. Written informed consent to participation was gained from participants and/or their authorized legal guardian. Participants were recruited from
the intensive care unit of a tertiary-referral, university-affiliated, metropolitan centre. Patients receiving mechanical ventilation for more than 48 h were screened and consent for participation sought if there were no absolute contraindications to sitting and their cardiovascular and respiratory parameters were stable according to the criteria outlined in Table 1. As there was limited published data investigating the effect of upright positioning on arterial blood gas measurements and respiratory mechanics in patients weaning from mechanical ventilation, an interim analysis was conducted after enrollment of 20 patients and was used to estimate the standard deviation for paired differences in PaO2/FiO2 and VE from supine to sitting and semirecumbent positioning. A sample size estimate of 34 patients was calculated to detect moderate effect sizes and clinically significant changes in PaO2/FiO2 (difference ¼ 20, s ¼ 35, a ¼ 0.05, power ¼ 0.9) and VE (sample estimate ¼ 27, difference ¼ 1 L/min, s ¼ 1.55 L/min, a ¼ 0.05, power ¼ 0.9) in a repeated measures design.28 Admission diagnosis, demographic information, sepsisrelated organ failure assessment (SOFA) scores29 and Murray lung injury (MLI) scores30 were calculated from data collected on the day of the study. Automated calculations for acute physiological and chronic health evaluation II (APACHE) scores31 were obtained from the intensive care unit’s clinical information system. Ventilator settings and respiratory mechanics (respiratory rate (RR), tidal volume (VT), minute ventilation (VE), peak inspiratory airway pressure (PIPaw), dynamic lung compliance (Cdyn) were recorded via electronic transfer of data from the serial port of the ventilator (Mallinckrodt Puritan Bennet 7200Ò or 840Ô ventilator), which were calibrated according to manufacturer’s recommendations. A shallow breathing index was also calculated as RR/VT. Ventilator measurement of pressure, volume and flow are considered to be accurate and have low variability.32,33 However, at each data collection point, 5-min periods of respiratory mechanic measurements were collected and averaged to reduce any breath-tobreath variability of measurements.34,35 Variations in gas exchange were monitored through arterial blood gas sampling (ABL 700 Series machines e Radiometer, Copenhagen, Denmark) and analysis of the ratio of PaO2 to FiO2 (PaO2/FiO2), PaO2, the partial pressure of carbon dioxide in arterial blood (PaCO2), arterial hemoglobin oxygen saturation (SaO2), and alveolar gas to arterial blood oxygen tension difference (Aea gradient). Heart rate (HR), MABP and SpO2 were recorded from the patient monitoring system (Philips Intellivue). For MABP measurements, arterial blood pressures were manually checked for accuracy/calibration against sphygmomanometer readings prior to data collection and the arterial line transducer placement was re-zeroed prior to each recording.
Table 1 Study inclusion and exclusion criteria. Inclusion criteria
Exclusion criteria
Age >18 years Intubated and receiving mechanical ventilation (>48 h) Suitable candidates to mobilize into either the seated or semi-recumbent position. To ascertain this, clinical characteristics had to include: PaO2 >60 mm Hg FiO2 <0.6 PIPaw <40 cm H2O Stable hemodynamic parameters HR 60e130 beats/min MABP 70e120 mm Hg
Signs of new or sustained sepsis on the day of enrollment Hemoglobin <70 g/L Platelets <30 109/L
Arrhythmias (if present) stable and not compromising blood pressure
Vasopressor or neuromuscular blockade medications Nitric oxide Pulmonary barotrauma (e.g. flail chest, untreated pneumothorax) Burn injuries Dialysis Contraindications to upright positioning (e.g. unstable spinal column fractures or spinal cord injury) Intracranial pressure monitoring
P. Thomas et al. / Heart & Lung 43 (2014) 105e111
A goniometer/protractor was used to measure the angle of backrest inclination achieved36 and a tape measure was used to determine the static maintenance of the two upright positions over the study period. The reference points measured were the distance between a patient’s popliteal crease and the bed end (semi-recumbent positioning) or the chair base (sitting). All goniometer and tape measure recordings were taken by the primary investigator. The study period began with a minimum of 2 h during which ventilator settings were left unchanged, other interventions limited and a 30 min period in the supine position immediately prior to data collection. The dose of sedative medications was not altered during the study period. To attain the semi-recumbent position, the patient’s bed was simply adjusted from a horizontal position to having the head of bed elevated. The seated position was achieved by transferring the patient out of bed (via sliding board) into a HaustedÒ chair (APC series, Hausted Medina, Ohio). Neither position required the patient to actively assist or contribute to the transfer and/or change in position. Both the HaustedÒ chair and beds used were able to have their backrest adjusted through a 0e80 range. With either position, a minimum of 45 backrest elevation was targeted, with higher elevations used when reported comfortable by the patient. This reflected clinical practice. Patients were maintained in either position for 30 min, at which point, data collection finished. Patients were later returned supine, with a minimum of 30 min supine before the alternate position was studied. For each position, data was collected at three time points including the baseline supine position (T0), then 5 min post implementation of the semi-recumbent or sitting position (T5) and/or at 30 min post implementation (T30). Arterial blood gas samples were taken at T0 and T30 only. Respiratory mechanics, HR, BP and SpO2 measurements were collected at T0, T5 and T30. Goniometer and tape measure recordings were taken at T5 and T30. During the data collection periods, the position was ceased if intolerance to either position was noted. This was defined by: a >10% increase in fraction of inspired oxygen (FiO2) required to maintain pulse oximeter oxygen saturation (SpO2) >90% or the partial pressure of oxygen in arterial blood (PaO2) >60 mm Hg; the alteration of heart rate by 30 beats/min; the onset of a new arrhythmia or ischemic electrocardiograph changes or a reduction in blood pressure due to arrhythmia; or change in mean arterial blood pressure (MABP) by 30 mm Hg). Additionally, occurrences of any adverse events (e.g. accidental extubation, removal of indwelling catheters) were recorded. If any intolerance or adverse event occurred, medical staff were notified immediately and appropriate action taken. An intention-to-treat analysis was used for this study. Continuous variables were assessed for normality of distribution, transformed as appropriate and analyzed using a linear mixed model (within subject main effects: position (sitting or semi-recumbent) (P) and time (T) and their interaction (P T); subjects were random effects). Incorporated into this model was assessment for an order effect, and analysis of covariates, which included a subjects’ age, body mass index (BMI), extent of lung pathology (determined from the chest radiograph rating of the MLI score), degree of hypoxemia (determined from the respiratory system rating of the SOFA score) and 24-h fluid balance for the day of the study. Paired sample t-tests were used to compare the angle of inclination and displacement out of position measured between the two positions. Results are expressed as mean standard deviation and a significance level of <0.05 was used. Results Thirty-four patients were enrolled in the study. Diagnostic and demographic information is presented in Table 2.
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Table 2 Baseline characteristics of the patients. Characteristic
Value
Age (years) Female e N (%) Body mass index (kg/m2) APACHE IIa Primary diagnosis e N Gastrointestinal (post-operative) Gastrointestinal (non-surgical) Multi-trauma (post-operative) Cardiovascular (post-operative) Respiratory Neurological (post-operative) Neurological (non-surgical) Cardiovascular Metabolic/renal (non-surgical) Diabetic ketoacidosis Drug overdose Glasgow coma score e median Eye Motor Verbal Total SOFA scoreb Respiratory Coagulation Liver Cardiovascular Central nervous system Renal Total SOFA score MLI scoreb Days prior to enrollment of: Hospital admission ICU admission Mechanical ventilation Tracheostomy e N (%) Ventilator mode e N SIMV (volume controlled) Pressure support ventilation FiO2 Pressure support (cm H20) PEEP (cm H20) Hemoglobin (g/L) 24-h fluid balance (L)
65.5 14.4 13 (38%) 28.6 6.9 23.2 6.7
Range 18e87 18.7e50.8 10e37
9 2 2 3 7 1 3 4 1 1 1 4 6 3 13 2.29 0.24 0.44 0.44 0.85 0.59 4.85 1.25
3e4 1e6 1e5 5e15
0.58 0.65 0.82 0.56 0.89 1.0 2.0 0.6
16.4 9.3 12.8 8.7 12.5 8.5 21 (62%) 6 28 0.35 11.5 5.7 90.2 0.20
0.06 2.8 1.44 13.7 1.5
1e3 0e3 0e3 0e3 0e4 0e4 1e9 0e2.7 5e36 3e36 3e36
0.25e0.5 8e20 5e10 70e141 3.4e2.1
a
APACHE II scores were collated from admission data. SOFA scores and MLI scores were calculated from data collected on the day of the study. b
Recruitment of patients during the weaning period from mechanical ventilation is reflected by the majority of patients being ventilated on pressure support ventilation (Table 2), and only eight (24%) of patients receiving sedative or opioid infusions (two patients received Propofol, six patients received Fentanyl). At the time of enrollment, nine patients (26%) had previously sat out of bed on days prior to recruitment to the study. The randomization procedure resulted in three of these patients being examined first in the semi-recumbent position and six in the seated position. The median time between assessment of the semi-recumbent and seated positions was 2.5 h (inter-quartile range ¼ 1e3.5 h). Three patients completed only one part of the protocol, resulting in 33 assessments in the seated position and 32 in the semi-recumbent position. Reasons for non-completion of the entire protocol were elective extubation prior to completion (N ¼ 2) and the onset of hemodynamic instability requiring commencement of inotropes (N ¼ 1), which occurred more than 3 h after the first intervention. Review by the investigators and attending medical staff determined that there was no direct temporal or causal relationship with this deterioration and the study protocol. No patients required cessation
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position (50 5 , range 40e60 ; t(30) ¼ 14.1, p < 0.001). After 30 min in an upright position, patients in the semi-recumbent position were observed to have moved out of the position more than in the seated position (4 4 cm (range 0e16 cm) versus 1 1 cm (range 0e6 cm) respectively, t(20) ¼ 4.5, p < 0.001).
Table 3 Variables with significant effects due to order. Value
Order
p value
First PaO2/FiO2 PaO2 PaCO2 MAPaw
240 80.5 37.4 10.1
Second
58 11.6 6.0 2.1
245 84.0 36.6 9.7
68 15.7 5.9 2.0
O
OT
OP
0.012 0.009 0.036 <0.001
0.672 0.996 0.789 0.976
0.844 0.695 0.222 0.334
Discussion
Mean standard deviation. Units: PaO2/FiO2 (), PaO2 (mm Hg), PaCO2 (mm Hg), MAPaw (cm H2O). Abbreviations: O ¼ order, O T ¼ order time interaction, O P ¼ order position sequence interaction.
To our knowledge, this is the first study that has compared the effects of positioning a patient in a seated versus semi-recumbent position on arterial blood gas measurements, during weaning from mechanical ventilation. Our results demonstrated that in this population, the semi-recumbent position and seated position are safe interventions, which have minimal effect on gas exchange and respiratory mechanics. The seated position enabled a higher angle of inclination to be attained, and was more easily maintained over the 30-min period studied. In some populations, moving subjects from a supine to seated position may result in improvements in oxygenation or in other indices of gas exchange.10,11 However, improvements in oxygenation in the ventilated patients enrolled in our study were negligible and the magnitude of the reduction in PaCO2 when in semirecumbent or sitting positions was of little clinical importance. Previous investigations in intensive care populations have also found no significant improvements in gas exchange as a result of semi-recumbent positioning (60 ) in patients who were intubated, but weaned from mechanical ventilation24; patients with acute lung injury (ALI) receiving ventilation and neuromuscular blockades who were positioned in 30 and 45 semi-recumbent positions20; ventilated post-operative abdominal surgery patients after walking and sitting out of bed25; and in both ventilated and nonventilated chronic critically ill patients after being passively tilted to 70 .37 The absence of clinically significant effects on gas exchange in this and prior studies of intensive care patients may be related to reductions in FRC and increased alveolar closing volumes (CV) in this population. CV is the lung volume during expiration at which the flow from the lower parts of the lungs becomes severely reduced or stops because of airway closure (before residual volume is reached).38 When moving from a seated position into supine reduces FRC and results in CV exceeding FRC, airway closure begins to occur during normal tidal breathing and a fall in PaO2 may
of the positioning interventions during testing according to the safety criteria. Despite randomized assignment and concealed allocation to the two study positions, an order effect was detected. Values for PaO2/ FiO2 and PaO2 were lower and PaCO2 and MAPaw were higher at all time points during the patient’s first positioning trial (Table 3). Additionally, values obtained for PaO2/FiO2, PaO2, SaO2 and PIPaw were higher throughout examination of the of supine e seated test sequence versus the supine e semi-recumbent sequence (Tables 4 and 5). However, there were no observed effects related to changing a patient’s position over time (T0eT30) for these variables. Changes in position over T0eT30 had no effect on any indices of oxygenation (Table 4). There was a significant effect of time on PaCO2 regardless of the upright posture studied (T0: 37.4 6.0 > T30: 36.6 5.9 mm Hg, t(92) ¼ 4.0, p < 0.001). Respiratory mechanics were unchanged after institution of either upright position (Table 4). The hemodynamic response to attaining the upright position was similar between the two positions (Table 4), with an increase in MABP at T5 (T0: 87.8 12.9 < T5: 92.3 14.3 mm Hg, t(150) ¼ 3.0, p ¼ 0.003) occurring without a significant change in HR. At T30, the rise in MABP had dissipated and returned to baseline levels (T0: 87.8 12.9 ¼ T30: 87.7 15.8 mm Hg, t(150) ¼ 0.6, p ¼ 0.559). There was no significant effect on gas exchange and respiratory mechanic measurements through inclusion of the covariates of age, BMI, extent of lung pathology, degree of hypoxemia or 24-h fluid balance. The angle of inclination achieved in the seated position (67 5 , range 55e80 ) was greater than achieved in the semi-recumbent
Table 4 Response in gas exchange indices, respiratory mechanics and hemodynamics at T0, T5 and T30. Value
Semi-recumbent sequence T0
PaO2/FiO2 PaO2 SaO2 Aea gradient PaCO2 SpO2 RR VT VE Cdyn PIPaw MAPaw RR/VT MABP HR
234 79.0 96.0 125 37.2 96.5 25.2 0.56 13.48 42.7 19.1 9.9 53.4 88.6 94.9
64 11.1 1.8 52 5.8 2.4 7.3 0.16 3.64 14.6 3.5 2.1 22.9 12.8 15.3
Sitting out of bed sequence
T5
T30
e e e e e 96.4 25.8 0.55 13.61 44.5 18.7 9.9 54.7 92.2 95.3
237 80.5 96.3 124 36.6 96.5 26.7 0.55 13.96 44.6 19.3 9.9 54.2 90.9 96.8
2.3 7.0 0.13 3.49 15.7 4.6 2.2 23.1 12.8 17.2
T0
64 12.5 1.5 50 5.9 2.5 7.1 0.14 3.48 15.0 3.8 2.1 24.6 11.9 18.6
244 83.1 96.5 120 37.7 96.5 24.5 0.56 12.82 42.9 19.70 9.9 51.1 87.0 95.6
62 12.9 1.6 49 6.2 2.0 7.5 0.15 3.64 14.0 3.34 2.1 23.5 13.1 16.8
p value
T5
T30
e e e e e 97.3 25.7 0.56 13.78 42.5 20.35 10.0 54.0 92.4 99.7
253 86.0 96.6 119 36.5 97.1 25.8 0.55 13.81 42.4 19.77 9.9 54.9 84.4 99.9
2.3 8.1 0.15 4.22 15.0 3.97 2.2 25.8 15.8 17.7
63 17.1 1.7 47 6.0 2.1 7.6 0.13 4.17 13.8 3.53 1.9 20.7 18.6 17.0
T
P
PT
0.931 0.928 0.697 0.560 0.001c 0.459 0.112 0.746 0.152 0.869 0.062 0.066 0.696 0.013b 0.339
0.015a 0.003a 0.016a 0.164 0.659 0.065 0.980 0.588 0.789 0.111 <0.001a 0.133 0.947 0.324 0.121
0.184 0.813 0.773 0.094 0.208 0.268 0.618 0.658 0.290 0.579 0.671 0.952 0.886 0.096 0.361
Mean standard deviation. Units: PaO2/FiO2 (), PaO2 (mm Hg), SaO2 (%), Aea gradient (mm Hg), PaCO2 (mm Hg), SpO2 (%); RR (breaths/min), VT (L), VE (L), Cdyn (L/cm H2O), PIPaw (cm H2O), MAPaw (cm H2O), RR/VT (); MABP (mm Hg), HR (beats/min). Abbreviations: T ¼ time, P ¼ position sequence, P T ¼ position sequence time interaction. a Sitting > semi-recumbent sequence, see Table 5. b T5 > T0, T30. c T0 > T30.
P. Thomas et al. / Heart & Lung 43 (2014) 105e111 Table 5 Variables with significant effects due to position sequence. Value
Supine e semi-recumbent
PaO2/FiO2 PaO2 SaO2 PIPaw
236 79.8 96.1 19.0
64 11.8 1.7 4.0
Supine e seated 249 84.6 96.6 20.0
62 15.1 1.6 3.6
p value 0.018 0.003 0.015 0.007
Mean standard deviation. Units: PaO2/FiO2 (), PaO2 (mm Hg), SaO2 (%), PIPaw (cm H2O).
arise.10,39 However, when FRC volume is significantly reduced, or CV significantly increased so that CV exceeds (FRC þ VT) in both the seated and supine position, significant airway closure is present in both positions. Subsequently, changes in regional alveolar ventilation may be small and diminish any potential for upright positioning to induce a change in oxygenation.10,39 Factors that are known to decrease the elastic recoil of the lung and subsequently increase CV include advancing age, smoking, respiratory disease and/or obesity.10,11,39 Alternatively, FRC may be reduced by the presence of: respiratory failure40,41; mechanical ventilation, anesthesia and paralysis42,43; ALI44; major chest X-ray abnormalities45; a low FEV1/FVC ratio11; and abdominal surgery.46 Many of these conditions were features of the subjects in this study and the wider intensive care population. The decision to mobilize a patient out of bed who is weaning from mechanical ventilation can be delayed due to concerns of the effort involved by the patient and the impact this may have on respiratory system function. In this study, the change to either upright position resulted in no significant effect on RR, VT, VE, or RR/ VT. Deye et al26 also found no change in these variables after 15 min of supine, semi-recumbent positioning and a seated position in bed. As seated positions produce negligible changes in RR, VT, VE, or RR/ VT, they could be utilized during the weaning of patients from mechanical ventilation in order to promote arousal, function and interaction of patients with their environment. However, Deye et al26 also measured work of breathing and respiratory effort and found them to be slightly lower with semi-recumbent positioning. Subsequently, they concluded that the semi-recumbent position is useful in difficult to wean patients in order to unload (rest) the respiratory muscles. While this unloading may be important when recovery is required, the benefits of early mobilization in the critically ill have been gained by mobilizing patients out of bed and incrementally loading (training) the respiratory system. These benefits have also been demonstrated in patients who are slow to wean.5,47,48 Therefore, the utilization of seated positioning could instead be viewed as an important component of early rehabilitation strategies in order to slightly increase respiratory effort and/or provide a stable and more optimal position for rehabilitation exercises. When periods of sitting are well tolerated, progression may then occur to standing or tilt table rehabilitation, which are more demanding and generate increases in VT and/or VE.25,37 A reduction in compliance with the use of upright positioning was not observed in this study. Variations in compliance have been observed in ventilated patients with ALI when positioned from supine to a 30 or 45 semi-recumbent position20 but not with seated positions in bed.19 Differences in the level of sedation and/ or use of neuromuscular blocking agents may account for the differences observed. In heavily sedated and/or paralyzed patients compliance is decreased because spontaneous diaphragmatic contractions are reduced and diaphragmatic excursion is reliant on the positive pressure ventilation to overcome resistance from the abdominal compartment. We encountered no adverse events during the application of the semi-recumbent or seated position in patients who met our study criteria and only a small increase in MABP was evident immediately
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after positioning in to the upright position. Prior investigations also appear to support the safety specifically of sitting and/or semirecumbent positioning,20,22 with no adverse event reported and/ or no requirement for additional sedation, neuromuscular blockade or vasoactive drugs.20 Bourdin et al49 reported the frequent use of sitting out of bed in 20 patients receiving mechanical ventilation, and concluded it to be safe with minimal changes in HR or MABP. Other studies have assessed hemodynamic changes with semirecumbent positioning in patients who are hemodynamically stable, ventilated and/or receiving vasoactive drugs with results indicating that altering position from supine to a semi-recumbent position up to 60 is generally well tolerated, with minimal change to cardiac output.6,7 Moving a patient in to a semi-recumbent position is easier and involves less staff compared to sitting a patient out of bed. However, discomfort may contribute to the ability to sustain the semirecumbent position and several authors have outlined the difficulties of implementing and/or maintaining the semi-recumbent position in clinical practice.16e18 While we did not record the level of comfort experienced by patients in either position, we believe comfort was the main factor that limited achievement of higher backrest elevations with semi-recumbent positioning. Additionally, the results of this study suggest that an advantage of seated positions is the ability to achieve a greater angle of inclination and to remain stable in the position. This may have significant implications for patient safety and comfort and considerations in pressure area management with the use of upright positioning. Erect postures enhance the mechanics of the thoracic cage and increase the caudal excursion of the diaphragm.50 As patients slide out of the semi-recumbent position, they assume a slumped posture. As the degree of kyphosis increases, lung volumes and chest wall mechanics may be adversely affected. For example, in normal subjects, a slumped semi-recumbent position significantly reduces FRC13 and a slumped sitting position has been shown to decrease VE and VT.50 Therefore, it is possible, that with a longer duration of semi-recumbent positioning, adverse effects of pulmonary function may have become evident in this population. The results of this study support clinicians to implement early mobilization strategies, in that the adoption of seated positions out of bed can be commenced with the knowledge that short applications of 30 min are generally not detrimental to a patient’s respiratory or cardiovascular status. Additionally, clinicians should not expect improvements in oxygenation indices to routinely occur when utilizing upright positions in patients that are weaning from mechanical ventilation. While a potential benefit of passively moving patients out of bed into specialized chairs is that patients may not slide out of the upright position, clinicians should be aware of the risk that static positioning also poses to skin integrity and therefore the duration of seated upright positioning may need to be limited and/or guided by a patient’s skin tolerance. A limitation of this study was the short period of data collection. Thirty minutes in the upright position was chosen for the convenience and ability to complete data collection for both positions in close proximity, in an environment where various interventions and investigations compete for time. Similar and/or shorter time periods have been used in prior research in this population and detected significant changes in respiratory function.13,20,24,25 The median time between the position sequences was 2.5 h and an order effect was observed. While the magnitude of these changes were small and would not be clinically significant, it may indicate that small improvements in respiratory function occur through the repeated utilization of these position changes. A longer time period for data collection and the effect of repeated applications of upright position may have been able to detect significant changes in respiratory function. Variation in respiratory responses to upper limb
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exercise has been found when ventilated patients are compared with non-ventilated patients.14 As patients were still supported on mechanical ventilation, if any detrimental effect of either position arose, the impact of the change on respiratory function may have been lessened.51 Therefore, replication of this study in patients who have been recently extubated, are undergoing a slow weaning process or are undergoing spontaneous breathing trials may yield differing results. In addition to investigating the effect of utilizing upright positions over longer time periods and/or during different phases of ventilator support, more specific measures of a patients lung volume, work of breathing and fatigue are required in future studies to direct prescription of seated positions under varying circumstances. For example, if the success or duration of a T-piece trial in a difficult to wean patient was known to be affected by semirecumbent or seated positions, then positions that benefit lung volumes or work of breathing or reduce fatigue could be utilized during the trial. Positions that may provide an additional challenge to the respiratory system e.g. by increasing work of breathing may be utilized at different times to a T-piece trial, to prevent overloading the respiratory system of the slow to wean patient. Further investigation into the variety of real and/or perceived barriers to mobilizing patients out of bed is also warranted52 including patient factors (e.g. comfort, arousal, dyspnea) and environmental factors (e.g. equipment, sedation practices). By increasing our understanding of the impact of positioning practices throughout various stages of critical illness, clinicians will be able to refine early rehabilitation strategies that include the appropriate timing and application of upright positioning. Acknowledgments Warren Stanton, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane. Ross Darnell, Statistician, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane. Financial support for this project was gained from the Australian Physiotherapy Association, Dorothy Hopkins Award for clinical research. References 1. Schweickert WD, Pohlman MC, Pohlman AS, et al. Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomised controlled trial. Lancet. 2009;373(9678):1874e1882. 2. Bailey P, Thomsen GE, Spuhler VJ, et al. Early activity is feasible and safe in respiratory failure patients. Crit Care Med. 2007;35(1):139e145. 3. Nava S. Rehabilitation of patients admitted to a respiratory intensive care unit. Arch Phys Med Rehabil. 1998;79(7):849e854. 4. Thomsen GE, Snow GL, Rodriguez L, Hopkins RO. Patients with respiratory failure increase ambulation after transfer to an intensive care unit where early activity is a priority. Crit Care Med. 2008;36(4):1119e1124. 5. Morris PE, Goad A, Thompson C, et al. Early intensive care unit mobility therapy in the treatment of acute respiratory failure. Crit Care Med. 2008;36(8): 2238e2243. 6. Lambert CW, Cason CL. Backrest elevation and pulmonary artery pressures: research analysis. Dimens Crit Care Nurs. 1990;9(6):327e335. 7. Doering L. The effect of positioning on hemodynamics and gas exchange in the critically ill: a review. Am J Crit Care. 1993;2(3):208e216. 8. Drakulovic MB, Torres A, Bauer TT, Nicolas JM, Nogue S, Ferrer M. Supine body position as a risk factor for nosocomial pneumonia in mechanically ventilated patients: a randomised trial. Lancet. 1999;354(9193):1851e1858. 9. Behrakis PK, Baydur A, Jaeger MJ, Milic-Emili J. Lung mechanics in sitting and horizontal body positions. Chest. 1983;83(4):643e646. 10. Craig DB, Wahba WM, Don HF, Couture JG, Becklake MR. “Closing volume” and its relationship to gas exchange in seated and supine positions. J Appl Physiol. 1971;31(5):717e721. 11. Hardie JA, Morkve O, Ellingsen I. Effect of body position on arterial oxygen tension in the elderly. Respiration. 2002;69(2):123e128. 12. Ibanez J, Raurich JM. Normal values of functional residual capacity in the sitting and supine positions. Intensive Care Med. 1982;8(4):173e177.
13. Jenkins SC, Soutar SA, Moxham J. The effects of posture on lung volumes in normal subjects and in patients pre- and post- coronary artery surgery. Physiotherapy. 1988;74(10):492e496. 14. Vitacca M, Clini E, Spassini W, Scaglia L, Negrini P, Quadri A. Does the supine position worsen respiratory function in elderly subjects? Gerontology. 1996;42(1):46e53. 15. Lorino AM, Atlan G, Lorino H, Zanditenas D, Harf A. Influence of posture on mechanical parameters derived from respiratory impedance. Eur Respir J. 1992;5(9):1118e1122. 16. Cook DJ, Meade MO, Hand LE, McMullin JP. Toward understanding evidence uptake: semirecumbency for pneumonia prevention. Crit Care Med. 2002;30(7):1472e1477. 17. Grap M, Munro C, Bryant S, Ashtiani B. Predictors of backrest elevation in critical care. Intensive Crit Care Nurs. 2003;19(2):68e74. 18. van Nieuwenhoven C, Vandenbroucke-Grauls C, van Tiel F, et al. Feasibility and effects of the semirecumbent position to prevent ventilator-associated pneumonia: a randomized study. Crit Care Med. 2006;34(2):396e402. 19. Dellamonica J, Lerolle N, Sargentini C, et al. Effect of different seated positions on lung volume and oxygenation in acute respiratory distress syndrome. Intensive Care Med. 2013;39(6):1121e1127. 20. Bittner E, Chendrasekhar A, Pillai S, Timberlake GA. Changes in oxygenation and compliance as related to body position in acute lung injury. Am Surg. 1996;62(12):1038e1041. 21. Hoste EAJ, Roosens CDVK, Bracke S, et al. Acute effects of upright position on gas exchange in patients with acute respiratory distress syndrome. J Intensive Care Med. 2005;20(1):43e49. 22. Richard JC, Maggiore SM, Mancebo J, Lemaire F, Jonson B, Brochard L. Effects of vertical positioning on gas exchange and lung volumes in acute respiratory distress syndrome. Intensive Care Med. 2006;32(10):1623e1626. 23. Burns S, Egloff M, Ryan B, Carpenter R, Burns J. Effect of body position on spontaneous respiratory rate and tidal volume in patients with obesity, abdominal distention and ascites. Am J Crit Care. 1994;3(2):102e106. 24. Bonnet F, Bourgain JL, Matamis D, Tesseire B, Viars P. The influence of position on ventilation-perfusion distribution after abdominal surgery. Acta Anaesthesiol Scand. 1988;32(7):585e589. 25. Zafiropoulos B, Alison JA, McCarren B. Physiological responses to the early mobilisation of the intubated, ventilated abdominal surgery patient. Aust J Physiother. 2004;50(2):95e100. 26. Deye N, Lellouche F, Maggiore SM, et al. The semi-seated position slightly reduces the effort to breathe during difficult weaning. Intensive Care Med. 2013;39(1):85e92. 27. Chang MY, Chang LY, Huang YC, Lin KM, Cheng CH. Chair-sitting exercise intervention does not improve respiratory muscle function in mechanically ventilated intensive care unit patients. Respir Care. 2011;56(10): 1533e1538. 28. Dupont WD, Plummer WD. Power and sample size calculations: a review and computer program. Control Clin Trials. 1990;11:116e128. 29. Vincent JL, Moreno R, Takala J, et al. The SOFA (sepsis-related organ failure assessment) score to describe organ dysfunction/failure. Intensive Care Med. 1996;22(7):707e710. 30. Murray JF, Matthay MA, Luce JM, Flick MR. An expanded definition of the adult respiratory distress syndrome. Am Rev Respir Dis. 1988;138(3): 720e723. 31. Knauss WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13:818e829. 32. Banner MJ, Blanch PB, Kirby RR. Imposed work of breathing and methods of triggering a demand-flow, continuous positive pressure system. Crit Care Med. 1993;21(2):183e190. 33. Gammage GW, Banner MJ, Blanch PB, Kirby RR. Ventilator displayed tidal volume e what you see may not be what you get [abstract]. Crit Care Med. 1988;16:454. 34. Petrini MF, Evans J, Wall MA, Norman JR. Variability, reproducibility and datacollection time of pulmonary bedside monitoring. Biomed Instrum Technol. 1998;32:273e281. 35. Tobin MJ. Respiratory monitoring in the intensive care unit. Am Rev Respir Dis. 1988;138:1625e1642. 36. Hummel R, Grap M, Sessler C, Munro C, Corley M. Continuous measurement of backrest elevation in critical care: a research strategy. Crit Care Med. 2000;28(7):2621e2625. 37. Chang AT, Boots RJ, Hodges PW, Thomas PJ, Paratz JD. Standing with the assistance of a tilt table improves minute ventilation in chronic critically ill patients. Arch Phys Med Rehabil. 2004;85(12):1972e1976. 38. Stedman TL. Stedman’s Medical Dictionary. Philadelphia: Lippincott Williams and Wilkins; 2000. 39. Leblanc P, Ruff F, Milic-Emili J. Effects of age and body position on “airway closure” in man. J Appl Physiol. 1970;28(4):448e451. 40. Katz JA, Ozanne GM, Zinn SE, Fairley HB. Time course and mechanisms of lungvolume increase with PEEP in acute pulmonary failure. Anesthesiology. 1981;54(1):9e16. 41. Ramachandran PR, Fairley HB. Changes in functional residual capacity during respiratory failure. Can Anaesth Soc J. 1970;17(4):359e369. 42. Hedenstierna G, Strandberg A, Brismar B, Lundquist H, Tokics L. What causes the lowered FRC during anaesthesia? Clin Physiol. 1985;5:S133eS141. 43. Wahba RW. Perioperative functional residual capacity. Can J Anaesth. 1991;38(3):384e400.
P. Thomas et al. / Heart & Lung 43 (2014) 105e111 44. Rylander C, Hogman M, Perchiazzi G, Magnusson A, Hedenstierna G. Functional residual capacity and respiratory mechanics as indicators of aeration and collapse in experimental lung injury. Anesth Analg. 2004;98(3):782e789. 45. Wiren JE, Lindell SE, Hellekant C. Pre- and postoperative lung function in sitting and supine position related to postoperative chest X-ray abnormalities and arterial hypoxaemia. Clin Physiol. 1983;3(3):257e266. 46. Meyers JR, Lembeck L, O’Kane H, Baue AE. Changes in functional residual capacity of the lung after operation. Arch Surg. 1975;110(5):576e583. 47. Burtin C, Clerckx B, Robbeets C, et al. Early exercise in critically ill patients enhances short-term functional recovery. Crit Care Med. 2009;37(9):2499e2505. 48. Clini EM, Crisafulli E, Antoni FD, et al. Functional recovery following physical training in tracheotomized and chronically ventilated patients. Respir Care. 2011;56(3):306e313.
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49. Bourdin G, Barbier J, Burle JF, et al. The feasibility of early physical activity in intensive care unit patients: a prospective observational one-center study. Respir Care. 2010;55(4):400e407. 50. Landers M, Barker G, Wallentine S, McWhorter W, Peel C. A comparison of tidal volume, breathing frequency, and minute ventilation between two sitting postures in healthy adults. Physiother Theory Pract. 2003;19: 109e119. 51. El-Khatib MF, Jamaleddine GW, Khoury AR, Obeid MY. Effect of continuous positive airway pressure on the rapid shallow breathing index in patients following cardiac surgery. Chest. 2002;121(2):475e479. 52. Mendez-Tellez PA, Dinglas VD, Colantuoni E, et al. Factors associated with timing of initiation of physical therapy in patients with acute lung injury. J Crit Care. 2013;28(6):980e984.