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Manual hyperinflation: a description of the technique
o RI
GI N A L ARTICLE
nu I D
f h The aim of this study was to describe the technique of manual hyperinflation as applied by physiotherapists. Ten physiotherapists volunteered to manually hyperinflate a test lung. The protocol randomlyaltered resuscitation circuits (Laerdal and MacgiU} and respiratory compliance conditions. Measurements of tidal volume airway pressure, inflation flow rate and inflation rate were recorded during each test condition. The therapists applied a mean (SO) tidal volume of 1.4(0.2)Lwithamean (SO) airway pressure of 20.6 (6.6) cmHzO. The technique was significantly different between each test condition and between all therapists. Therapists were obseNed to hypeNentilate the testJung and also apply positive end expiratory pressure with the Macgill circuit. A description of the technique applied to patients is required prior to evaluation of the technique in determining its effect on patients. [McCarren B and Chow CM: Manual hyperinflation: a description of the technique. Australian Journal of Physiotherapy 42: 203-208] J
Key words: lung; Respiration; Resuscitation; Ventilation BMcCarren BSe, GradDipPhty, GradDipPhty (Cardiothoracics) isalecturerin cardiothoracies in the School of Physiotherapy, The University of Sydney. CM Chow SSe, PhD is a lecturer in respiratory physiology in the Faculty of HealthScienees, The University of Sydney. Correspondence: Bredge McCarren, School of Physiotherapy, Faculty of Health Sciences, The University of Sydney, East Street, Lidcombs, NSW2141.
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anual hyperinflation (MH) is a technique that uses a ~% resuscitation circuit to provide a larger than baseline tidal volume to the lungs of the patient who is intubated. Manual hyperinflation has been shown to open collapsed lungs and improve gas exchange in animal studies (Laver et al 1964, Mead and Collier 1959) and surgical patients (Bendixen·et al 1963, Egbert et .al 1963, Levine et al 1972). However, in these studies the volume, airway pressure, flow rate and inflation rate (number ofbreaths per minute) of the technique were not reported.. Conversely barotrauma/ volumetrauma may occur with the application of MH.Barotrauma/ volumetrauma that causes leakage of air, protein and fluid into lung tissue has been shown to occur with large tidal volumes and airway pressure, resulting in an increased stiffness of the lung and decreased gas exchange (Dreyfuss et al 1985 ,Dreyfuss et al 1988, Parker et al 1990). There has been no documented evidence reporting barotrauma\ volumetrauma occurring with MH in the .clinical setting. However, it is important that the possible occurrence of barotrauma during the widely used technique of MH is investigated.
This paperwas presented atthe Fourth National APA Cardiothoracic Conference in Melbourne (1995) and the 12th International Congress of the World Confederation far Physical Therapy in Washington OC(1995).
Physiotherapists have not documented the parameters of their technique .of MR. Therefore it is unknown whether the above reported changes occur as a result of the physiotherapist's technique. The aim of this study was to obtain a description of the technique of MH in terms of tidal volume, airway pressure, flow rate and inflation rate. A definition is required prior to critical evaluation of the effectiveness of the technique. This study obtains a definition of MH using a test lung as a simulated patient lung..
ethodology Subjects were recruited via letters sent to physiotherapists in the major teaching hospitals of Sydney. Only physiotherapists who had a minimum of three years clinical experience and were either cardiopulmonary clinical educators or had practised in intensive care units were included in the study. Prior to the testing procedure, the physiotherapists were asked to provide a written description of the technique they used in the clinic. The physiotherapists were then asked to manually hyperinflate the test lung (Vent Aid training/test lung model 1600, Michigan Instruments Inc.. ) as they would a patient with acute atelectasis and no history of secretions. In the testing procedure, the therapists were instructed to apply a constant large size breath with an inspiratory hold, to minimise variation. The physiotherapists were given two
ORIGINAl ARTIClE
AUSTRAliAN PHYSIOTHERAPY
determined by the integration of the flow rate. Airway pressure was measured via a Validyne DP45 low pressure transducer (Validyne Engineering Corporation, Northbridge CA) placed betwe~n the bagging circuit and the airway that represented the trachea. The airway pressure was recorded on a strip chart recorder. Calibration of the pressure transducer involved applying a range (5-50 cmH20) oflmown pressures through the transducer at 5 cmH20 increments. The deflections were recorded on the strip chart recorder. A calibration curve was derived from the data. This procedure was performed prior to testing each
therapist. The accuracy of the Validyne pressure transducer is ± 0.25 per cent full scale (FS) (Validyne Engineering Corporation, 1990). The inflation rate was estimated by counting the number of breaths for every minute of manual hyperinflation using the airway pressure recording from the strip chart recorder.
From Page 203
minutes' practice to familiarise themselves with the circuit and the testing condition. There were four testing conditions; two lung compliance settings and two resuscitation circuits. One compliance setting (0.05 L/cmHzO) reflected that of an intubated and ventilated patient with no atelectasis (Oh 1990) and the other (0.035 L/cmHzO) a decrease in compliance as might occur with atelectasis. In all the testing conditions, the resistance of the test lung was maintained at a 2.33 ± 0.05 em HzOIL/s at 1 L/s representing that of a 9mm endotracheal tube (Michigan Instruments Inc., 1981). The two resuscitation circuits, the Macgill (2L) and Laerdal self inflating (1.6L) circuits are commonly used in the hospitals of Sydney. A random crossover design was employed. The physiotherapists were blind to the lung compliance settings.
Measurements/equipment The measurements of tidal volume (VT), airway pressure (P a), inflation flow rate (VT/T]) and inflation rate (RR) were recorded. In each testing condition 10 measurements or one minute recording of each variable was taken in order to improve the reliability of the measurements. Tidal volume and inflation flow rate were measured with the Pulsys (a pulmonary data acquisition and analysis system). The Pulsys (Version 1.2) is a software system that uses a Hans Rudolph heated linear pneumotachograph 8300 (Model 3813, Hans Rudolph Inc., Kansas City) and Pulsys pressure transducer/signal conditioner to measure flow rate (Clinical Engineering Solutions, Sydney). Calibration of the pneumotachograph was performed with a 3L syringe, according to the American Thoracic Society 1979 guidelines (pierce 1986), prior to a new subject and after every 10 minutes of continual testing with each subject. The reliability of the Hans Rudolph pneumotachograph to measure flow rate is 0.02 cmHzOIL/min (Hans Rudolph Inc., 1988). The volume is
Statistical analyses The raw data of each of the therapists' technique in each test condition was used for all statisical analyses except where noted. The mean and standard deviation OfVT, VT/TI, P a and RR of all four testing conditions were calculated. To determine the effects of
AUSTRAliAN PHYSIOTHERAPY
ORIGINAL ARTICLE
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The effects of resuscitation circuit and lung compliance on the mean (SD) values of tidal volume, airway pressure and inflation flow rate. *There is a significant difference between circuits.
figure 2. The individual responses of 10 therapists in all four testing conditions. There is a significant difference between therapists.
S There is a significant difference between compliance settings.
compliance and different circuits on the technique of MH, ANOVA of repeated measures were performed on the combined data. One way analysis of variance with a post-hoc Scheffe test (p < 0.05) was performed to determine if a difference existed between the mean of each therapist's technique (VT, VT/TI and P J in the four testing conditions. The statistical package SPSS for MS Windows Release 6.0 was used for the data analyses.
Results Ten physiotherapists volunteered in response to the 15 letters sent to the major teaching hospitals in Sydney. The mean years of experience was 5.2 years with a range of 4-8 years. Four of the physiotherapists had experience of the Laerdal circuit only, two were experienced with both the Laerdal and Macgill. The other four physiotherapists used a hospital black anaesthetic bag (the characteristics of
this circuit are similar to the Macgill without a valve or with a hospital designed expiratory valve). The written description provided by the physiotherapists revealed that they all used a two handed technique and aimed for "slow" inflation flow rates. However, within a clinical treatment session, the physiotherapists varied the size of the tidal volume delivered and the use of inspiratory hold. Some delivered three to five large tidal
o RI GIN A L ART Ie lE
from
205
volumes followed by three to five smaller tidal volumes, whilst others delivered two to five breaths with an inspiratory hold followed by two to five breaths without an inspiratory hold. The rationale given for the variation was to minimise the increase in airway pressure. The duration of the technique was dependent on the reversal of the patient's signs and symptoms and on the patient's tolerance of the treatment. The mean (SD) OfVT, Paand VT/TI of the individual test conditions and of the combined results of the four testing conditions are listed in Table lw There was a significant difference in VT (p
Discussion This study documents the first qualitative description of MHin terms ?f tid~l volume, airway pressure, Inflatlon flow rate and inflation rate as applied by physiotherapists using the test lung. The technique varied under the different conditions of lung compliance settings and resuscitation circuits. The individual therapists modifie<;l their technique appropriately when lung compliance decreased in order to prevent barotrauma or volumetrauma. The different physical characteristics ofthe resuscitation circuit influenced the technique of MH. The major consideration with this study is the use of the test lung. The test lung has a fixed compliance throughout the respiratory cycle, whereas the human lung demonstrates hysteresis or dynamically changing compliance (Nunn 1987). Lung compliance varies with position changes, spontaneous and ventilator breaths, recent ventilatory history and within the treatment itself. It is likely that the technique of MH changes significantly in response to the dynamically changing respiratory system. Therefore this description may not be representative of the technique that is performed on patients. Nevertheless this definition of MH of the test lung has provided physiotherapists with a broad range of values that were not available previously, so the technique of physiotherapists may now be compared with the technique described in earlier literature. The mean (SD) tidal volume applied by physiotherapists was 1481.5 (242) mL.This volume is approximately ISOto 200 per cent greater than the tidal volume delivered by a mechanical ventilator and two to three times the resting tidal volume of a. normal subject (Oh 1990). Larger tIdal volumes (two to five times resting) have been noted to improve overall gas exchange and compliance in intubated and ventilated patients (Levine et al 1972) and dogs (Laver et aI1964). Tidal volumes ofl.5 times
AUSTRAliAN PHYSIOTHERAPY
the baseline, when combined with 100 per cent oxygen, prevent the deleterious effects ofsuctioning (Goodnough 1985). Therefore it may be deduced that the large tidal volumes achieved in this study may be an effective form of treatment. However ' this needs to be confirmed. Increased airway·pressure is required to overcome the increased elastic recoil of the underinflated or collapsed alveolar units. The mean (SD) peak airway pressure of20.7 (6.6) cmHzO achieved in this study is consistent with the values (20-40cmH20) reported in other studies. Hyperinflation to pressures of 20,-40 cmH20 have been demonstrated to improve the compliance of the lung (Egbert etal 1963, Mead and Collier 1959). Improved oxygenation occurred at 20 cmH20 (Bendixenet al 1963) while alveolar recruitment occurred at 30 cmH20 (Lum et al 1990)w High airway pressuresandlor large inflation volumes have also been implicated in barotrauma/ volumetrauma. The mean airway pressures achieved using the test lung are unlikely to result in the pathological changes that were demonstrated to occur with barotrauma in the· animal studies (Dreyfusset a11988, Parkeretal 1990, Peevy et al 1990). However, it is important to note that some physiotherapists in this study did reach peak values of between 30 and 40 .cmH20. In animal studies barotrauma has been demonstrated to occur within this pressure range, resulting in a decrease in.compliance and gas exchange and disruption of the alveoli epithelium and capillary endothelium (Dreyfuss etall985, Egan 1982, Tsuno etal 1990). Therefore barotrauma may occur during treatment by physiotherapists. Investigation of the physiotherapist's technique ofMH is required to evaluate the likelihood of barotrauma occurring. The physiotherapists' mean (SD) inflation rate of 13 (2.3) per minute was high, especially if the large tidal volume is considered. The calculated mean minute ventilation was
AUSTRAliAN PHYSIOTHERAPY
OR I GIN A l
ART Ie 1 E
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Macgill Circuit
laerdal Circuit
Figure 3.
An exampie of one therapist's recording lNhich compan!s the effect of MacgiU and laerdal circuH on airwavpressure dlu~ing end inspirator.y hold (an"ows) and at end
expiration.
19.3 L/min. This is higher than the normal minute ventilation of a spontaneously breathing patient or ofa mechanically ventilated patient (Oh 1990). Physiotherapists need to consider the possibility of overventilation and modify their technique to match the baseline minute ventilation of the patient. The technique of MH was significantly influenced by the type of resuscitation.circuit used. The tidal volumes, inflation flow rates and airway pressures were significantly different between the two circuits. Hess and associates (1989 and 1990) also noted that the resuscitator brand had a significant effect on the inflation volumes applied. The Macgill circuit applied a significantly higher tidal 'volume and airway pressure than the Laerdal circuit. The flow rates were '!lisa significantly lower with the ,Macgillcircuit.The most obvious 'explanation for the differences is in the physical characteristics of the two circuits. The inflation capacity, compliance of the bag, type of ,¢Jpiratoryvalveand the gas source port are the more notable differences. The Macgill circuit has a 2Lcapacity, <~hile the Laerdal has a 1.6L capacity. 'The more compliant Macgill rubber bag allows the therapist to
more gas into the lung. The expiratory fishmouth valve on the Laerdal circuit allows the gas to leak during the end inspiratory hold and therefore there is a loss of volume and pressure. In contrast, with the Macgill circuit both the operator manipulated valve and the proximal position of the gas port allows continuous filling of the gas into the lung thus permitting the volume and airway pressure to increase at end inspiration. These physical differences account for the variations in the description of the technique. This suggests that it is important to note the resuscitation circuit used when evaluating the effects of MH. Most of the physiotherapists applied a mean positive end expiratory pressure (PEEP) of3.31 (3.71) cmHzO (range 0-13.75 cmHzO) while using the Macgill circuit. This may be related to manipulation of the expiratory valve, which increases airway resistance thereby prolonging expiratory time. Thus PEEP is produced on reinflation of the test lung prior to complete deflation. A consequence of adding PEEP is the increase in the maximal airway pressure consistent with the observed higher airway pressures in the Macgill circuit. Another parameter that is known to
affect the technique of MHis lung compliance, which is defined asa unit change in volume·to a unit change in pressure (Nunn 1987). Common clinical conditions that result in a decrease incompliance of the lung include atelectasis, pneumonia, adult respiratory distress· syndrome and pulmonary oedema. The decrease in compliance altered the physiotherapists' technique with an increased airway pressure despite the decrease in tidal volume. The results of this study confirm the conclusions of Hess et al.(1993) that an increase in impedance resulted in a significant decrease in inflation volume. This appropriate modification of the technique should minimise the occurrence of barotrauma/ volumetrauma. The expected decrease in inflation flow rates did not occur with decreased compliance. Slow inflation flow rates increase the time available for ventilation of the less compliant alveoli and therefore improve the distribution of ventilation and gas exchange (Baker 1977, Pillet et aI1993). Another factor that influences the description of the MH is the individual's technique. The wide variation between the individual operator's technique of MHhas also been noted by other .authors (Hess et al 1989, Hess and Spahr 1990). Significant determinants that influence the volume and therefore peak pressure of MH are the number of hands (one versus two) and hand size (Hess et al 1989). Other important determinants that account for the variation ofperformance include the therapist's·past experience of the circuit and the method learned during skill acquisition~ Before physiotherapists can evaluate the effects of MH and its individual components, a description of the technique currently used on patients is required. Physiotherapists will then be able to assess the effects of their technique on ventilation, perfusion, gas exchange, compliance, reversing/ preventing respiratory problems and overall patient outcome.· This study has
OR I GIN ALAR TIC LE
From Page 201 highlighted the following issues. It is important to recognise that different circuits and therapists will significantly alter the technique. A possible recommendation is for therapists to obtain objective measures of their technique and of the circuit they use. Inflationary volume could be measured with a Wright Respirometer (Clement Clarke International Ltd., London) or portable computerised spirometer that measures tidal volume. Both of these instruments are commonlyfound in physiotherapy departments or intensive care units. Airway pressure can be easily measured. A blood pressure manometer, the pressure manometer of positive expiratory pressure (PEP) circuit or airway cuff pressure manometer can be inserted into the circuit, enabling physiotherapists to measure peak airway pressure and PEEP. Physiotherapists can also determin.e and apply the appropriate inflation rate. This will facilitate the use ofslow inflation flow rates in patients who have low lung compliance or high .airway resistance. There are advantages and disadvantages of both circuits tested in the present study. If a therapist has a choice between circuits, recognising the advantages of the circuit chosen for a given patient will allow such knowledge to beincorporated into the clinical decision making process. However, if there is no choice the therapist should modify the technique to enhance the benefits and minimise the disadvantages in order to improve the patient's outcome. One of the roles of physiotherapists in intensive care is to teach inexperienced physiotherapists and/or students the technique of MH using a resuscitation circuit. A worthwhile practice may be to measure the components of MH while the therapists learn and.practise the technique. This should improve their learning and assist the understanding of the effects of the technique in various pathologies ofthe respiratory and cardiovascular system.
In conclusion, this study has provided a description of theMH technique. This provides a starting point for further investigation into the effects of MH.
References Baker AB, Colliss]Eand Cowie RW(1977): Effects of varying inspiratory flow waveform and time in intermittent positive pressure ventilation. ll:various physiologicalvariables. British Journal ofAnaesthesia 49: 1221-1233. Bendixen llH, Hedley...;Whyte],ChirB and Laver MB (1963): Impaired oxygenation in surgical patients during general anesthesia with controlledventilation. Aconceptofatelectasis. New England Journal of Medicine 269: 991-996. Dreyfuss D, BassetG, Soler P and SaumonG (1985): Intermittent positive-pressure ventilation with high inflation pressures produces pulmonary microvascular injury in rats. American Review of Respiratory Disease 132 880-884. Dreyfuss D, Soler P, BassetG and Saumon G (1988): High inflation pulmonary edema. Respective effects of high airway pressure, high tidal volume, andpositive end- expiratory pressure. AmericanReviewofRespiratory Disease 137: 1159-1164. Egan EA (1982): Lung inflation, lung solute permeability, and alveolar edema. Journal of Applied Physiology 53: 121-125. Egbert LD,Laver ME and BendixenHH (1963): Intermittent deep breaths and compliance during anesthesia in man. Anesthesiology 24: 57-60. GoodnoughSK(1985):The effects of oxygen and hyperinflation on arterial tension after endotracheal suctioning. Heart and Lung 14: 11-17. Hans Rudolph Inc. (1989): Service and Instruction Manual for Rudolph Pneumotachs (PTM), Kansas City. Hess D, GoffG,and]ohnsonK(1989): The effect ofhand size, resuscitor brand,and use of two hands on volumes delivered duringadult bag.,. valve ventilation. Respiratory Care 34: 805-810. Hess D and Spahr C (1990): An evaluation of volumes delivered by selected adult disposable resuscitators: The effect ofhand size, number ofhands used, and use ofdisposable medical gloves. Respiratory Care 35: 801-805. Hess D, SimmonsM, Blakovitch S, Lightner D and Doyle T (1993): An evaluation of the effects of fatigue, impedence, and use of two hands on volumes delivered during bag-valve ventilation. Respiratory Care 38: 271-275. Laver MB, Morgan ],Bendixen HHand Radford Jr EP (1964): Lung volume, compliance, and arterial oxygen tensions during controlled ventilation. Journal.of Applied Physiology 19: 725-733.
AUSTRAliAN PHYSIOTHERAPY
Levine M, Gilbert Rand Auchincloss]H(1972): A comparison of the effects ofsighs, large tidal volumes, andpositive end expiratory pressure in assisted ventilation. ScandinavianJournal of Respiratory Disease 53: 101-108. LumH, Huang I and Mitzner W (1990): M 0 rphoi 0 gicalevidence foralveo Iar recruitment athigh transpulmonary pressure. Journal ofApplied Physiology 68: 2280-2286. Mead] and Collier C (1959): Relation of volume history of lungs to respiratory mechanics .in anesthetized dogs. Journal ofAppliedPhysiology 14: 669-678. Nunn F] (1987): Applied Respiratory Physiology (3rd ed.) London: Butterworth, pp. 23-45. Dh TE (1990): Mechanical ventilatory support. In Oh TE(Ed.) Intensive Care ManuaI. Sydney: Butterworth, pp. 155-161. OhTE (1990): Respiratory physiology. Symbols and normal values. InOh TE (Ed.) Intensive Care Manual. Sydney: Butterworth, pp.679-681. Parker]C, Hernandez LA, Longnecker GL, Peevy K] andJohnson W (1990): Lung edema caused by high peak pressures in dogs. Role of microvascular filtration pressure and permeability. American Review of Respiratory Disease 142: 321-328. PeevyK], Hernandez LA, Moise AAand Parker]C (1990): Barotrauma and microvascular injury in lungs of nonadult rabbits: Effects of ventilation pattern. Critical Care Medicine 18:634,..637. Pierce R] (1986): Spirometryand lung volumes. A review of method, indication, normal values and reproducibility. Volume 6 (supplement): 1~22.
Pillet 0, Choukroun ML and Castaing Y (1993): Effects ofinspiratoty flow rate alterations on gas exchange during mechanical ventilation in nonnallungs. Efficiency ofend-inspiratory pause. Chest 103: 1161-1165. Tsuno K, Prato P and Kolobow T (1990): Acute lung injury from mechanical ventilation at moderately high airway pressures. Journal of Applied Physiology 69: 956-96 L Validyne Engineering Corp. (1990): Instruction Manual. California.
GI N A L ARTICLE
nu I D
f h The aim of this study was to describe the technique of manual hyperinflation as applied by physiotherapists. Ten physiotherapists volunteered to manually hyperinflate a test lung. The protocol randomlyaltered resuscitation circuits (Laerdal and MacgiU} and respiratory compliance conditions. Measurements of tidal volume airway pressure, inflation flow rate and inflation rate were recorded during each test condition. The therapists applied a mean (SO) tidal volume of 1.4(0.2)Lwithamean (SO) airway pressure of 20.6 (6.6) cmHzO. The technique was significantly different between each test condition and between all therapists. Therapists were obseNed to hypeNentilate the testJung and also apply positive end expiratory pressure with the Macgill circuit. A description of the technique applied to patients is required prior to evaluation of the technique in determining its effect on patients. [McCarren B and Chow CM: Manual hyperinflation: a description of the technique. Australian Journal of Physiotherapy 42: 203-208] J
Key words: lung; Respiration; Resuscitation; Ventilation BMcCarren BSe, GradDipPhty, GradDipPhty (Cardiothoracics) isalecturerin cardiothoracies in the School of Physiotherapy, The University of Sydney. CM Chow SSe, PhD is a lecturer in respiratory physiology in the Faculty of HealthScienees, The University of Sydney. Correspondence: Bredge McCarren, School of Physiotherapy, Faculty of Health Sciences, The University of Sydney, East Street, Lidcombs, NSW2141.
inti BIll
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anual hyperinflation (MH) is a technique that uses a ~% resuscitation circuit to provide a larger than baseline tidal volume to the lungs of the patient who is intubated. Manual hyperinflation has been shown to open collapsed lungs and improve gas exchange in animal studies (Laver et al 1964, Mead and Collier 1959) and surgical patients (Bendixen·et al 1963, Egbert et .al 1963, Levine et al 1972). However, in these studies the volume, airway pressure, flow rate and inflation rate (number ofbreaths per minute) of the technique were not reported.. Conversely barotrauma/ volumetrauma may occur with the application of MH.Barotrauma/ volumetrauma that causes leakage of air, protein and fluid into lung tissue has been shown to occur with large tidal volumes and airway pressure, resulting in an increased stiffness of the lung and decreased gas exchange (Dreyfuss et al 1985 ,Dreyfuss et al 1988, Parker et al 1990). There has been no documented evidence reporting barotrauma\ volumetrauma occurring with MH in the .clinical setting. However, it is important that the possible occurrence of barotrauma during the widely used technique of MH is investigated.
This paperwas presented atthe Fourth National APA Cardiothoracic Conference in Melbourne (1995) and the 12th International Congress of the World Confederation far Physical Therapy in Washington OC(1995).
Physiotherapists have not documented the parameters of their technique .of MR. Therefore it is unknown whether the above reported changes occur as a result of the physiotherapist's technique. The aim of this study was to obtain a description of the technique of MH in terms of tidal volume, airway pressure, flow rate and inflation rate. A definition is required prior to critical evaluation of the effectiveness of the technique. This study obtains a definition of MH using a test lung as a simulated patient lung..
ethodology Subjects were recruited via letters sent to physiotherapists in the major teaching hospitals of Sydney. Only physiotherapists who had a minimum of three years clinical experience and were either cardiopulmonary clinical educators or had practised in intensive care units were included in the study. Prior to the testing procedure, the physiotherapists were asked to provide a written description of the technique they used in the clinic. The physiotherapists were then asked to manually hyperinflate the test lung (Vent Aid training/test lung model 1600, Michigan Instruments Inc.. ) as they would a patient with acute atelectasis and no history of secretions. In the testing procedure, the therapists were instructed to apply a constant large size breath with an inspiratory hold, to minimise variation. The physiotherapists were given two
ORIGINAl ARTIClE
AUSTRAliAN PHYSIOTHERAPY
determined by the integration of the flow rate. Airway pressure was measured via a Validyne DP45 low pressure transducer (Validyne Engineering Corporation, Northbridge CA) placed betwe~n the bagging circuit and the airway that represented the trachea. The airway pressure was recorded on a strip chart recorder. Calibration of the pressure transducer involved applying a range (5-50 cmH20) oflmown pressures through the transducer at 5 cmH20 increments. The deflections were recorded on the strip chart recorder. A calibration curve was derived from the data. This procedure was performed prior to testing each
therapist. The accuracy of the Validyne pressure transducer is ± 0.25 per cent full scale (FS) (Validyne Engineering Corporation, 1990). The inflation rate was estimated by counting the number of breaths for every minute of manual hyperinflation using the airway pressure recording from the strip chart recorder.
From Page 203
minutes' practice to familiarise themselves with the circuit and the testing condition. There were four testing conditions; two lung compliance settings and two resuscitation circuits. One compliance setting (0.05 L/cmHzO) reflected that of an intubated and ventilated patient with no atelectasis (Oh 1990) and the other (0.035 L/cmHzO) a decrease in compliance as might occur with atelectasis. In all the testing conditions, the resistance of the test lung was maintained at a 2.33 ± 0.05 em HzOIL/s at 1 L/s representing that of a 9mm endotracheal tube (Michigan Instruments Inc., 1981). The two resuscitation circuits, the Macgill (2L) and Laerdal self inflating (1.6L) circuits are commonly used in the hospitals of Sydney. A random crossover design was employed. The physiotherapists were blind to the lung compliance settings.
Measurements/equipment The measurements of tidal volume (VT), airway pressure (P a), inflation flow rate (VT/T]) and inflation rate (RR) were recorded. In each testing condition 10 measurements or one minute recording of each variable was taken in order to improve the reliability of the measurements. Tidal volume and inflation flow rate were measured with the Pulsys (a pulmonary data acquisition and analysis system). The Pulsys (Version 1.2) is a software system that uses a Hans Rudolph heated linear pneumotachograph 8300 (Model 3813, Hans Rudolph Inc., Kansas City) and Pulsys pressure transducer/signal conditioner to measure flow rate (Clinical Engineering Solutions, Sydney). Calibration of the pneumotachograph was performed with a 3L syringe, according to the American Thoracic Society 1979 guidelines (pierce 1986), prior to a new subject and after every 10 minutes of continual testing with each subject. The reliability of the Hans Rudolph pneumotachograph to measure flow rate is 0.02 cmHzOIL/min (Hans Rudolph Inc., 1988). The volume is
Statistical analyses The raw data of each of the therapists' technique in each test condition was used for all statisical analyses except where noted. The mean and standard deviation OfVT, VT/TI, P a and RR of all four testing conditions were calculated. To determine the effects of
AUSTRAliAN PHYSIOTHERAPY
ORIGINAL ARTICLE
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Figure t.
The effects of resuscitation circuit and lung compliance on the mean (SD) values of tidal volume, airway pressure and inflation flow rate. *There is a significant difference between circuits.
figure 2. The individual responses of 10 therapists in all four testing conditions. There is a significant difference between therapists.
S There is a significant difference between compliance settings.
compliance and different circuits on the technique of MH, ANOVA of repeated measures were performed on the combined data. One way analysis of variance with a post-hoc Scheffe test (p < 0.05) was performed to determine if a difference existed between the mean of each therapist's technique (VT, VT/TI and P J in the four testing conditions. The statistical package SPSS for MS Windows Release 6.0 was used for the data analyses.
Results Ten physiotherapists volunteered in response to the 15 letters sent to the major teaching hospitals in Sydney. The mean years of experience was 5.2 years with a range of 4-8 years. Four of the physiotherapists had experience of the Laerdal circuit only, two were experienced with both the Laerdal and Macgill. The other four physiotherapists used a hospital black anaesthetic bag (the characteristics of
this circuit are similar to the Macgill without a valve or with a hospital designed expiratory valve). The written description provided by the physiotherapists revealed that they all used a two handed technique and aimed for "slow" inflation flow rates. However, within a clinical treatment session, the physiotherapists varied the size of the tidal volume delivered and the use of inspiratory hold. Some delivered three to five large tidal
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volumes followed by three to five smaller tidal volumes, whilst others delivered two to five breaths with an inspiratory hold followed by two to five breaths without an inspiratory hold. The rationale given for the variation was to minimise the increase in airway pressure. The duration of the technique was dependent on the reversal of the patient's signs and symptoms and on the patient's tolerance of the treatment. The mean (SD) OfVT, Paand VT/TI of the individual test conditions and of the combined results of the four testing conditions are listed in Table lw There was a significant difference in VT (p
Discussion This study documents the first qualitative description of MHin terms ?f tid~l volume, airway pressure, Inflatlon flow rate and inflation rate as applied by physiotherapists using the test lung. The technique varied under the different conditions of lung compliance settings and resuscitation circuits. The individual therapists modifie<;l their technique appropriately when lung compliance decreased in order to prevent barotrauma or volumetrauma. The different physical characteristics ofthe resuscitation circuit influenced the technique of MH. The major consideration with this study is the use of the test lung. The test lung has a fixed compliance throughout the respiratory cycle, whereas the human lung demonstrates hysteresis or dynamically changing compliance (Nunn 1987). Lung compliance varies with position changes, spontaneous and ventilator breaths, recent ventilatory history and within the treatment itself. It is likely that the technique of MH changes significantly in response to the dynamically changing respiratory system. Therefore this description may not be representative of the technique that is performed on patients. Nevertheless this definition of MH of the test lung has provided physiotherapists with a broad range of values that were not available previously, so the technique of physiotherapists may now be compared with the technique described in earlier literature. The mean (SD) tidal volume applied by physiotherapists was 1481.5 (242) mL.This volume is approximately ISOto 200 per cent greater than the tidal volume delivered by a mechanical ventilator and two to three times the resting tidal volume of a. normal subject (Oh 1990). Larger tIdal volumes (two to five times resting) have been noted to improve overall gas exchange and compliance in intubated and ventilated patients (Levine et al 1972) and dogs (Laver et aI1964). Tidal volumes ofl.5 times
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the baseline, when combined with 100 per cent oxygen, prevent the deleterious effects ofsuctioning (Goodnough 1985). Therefore it may be deduced that the large tidal volumes achieved in this study may be an effective form of treatment. However ' this needs to be confirmed. Increased airway·pressure is required to overcome the increased elastic recoil of the underinflated or collapsed alveolar units. The mean (SD) peak airway pressure of20.7 (6.6) cmHzO achieved in this study is consistent with the values (20-40cmH20) reported in other studies. Hyperinflation to pressures of 20,-40 cmH20 have been demonstrated to improve the compliance of the lung (Egbert etal 1963, Mead and Collier 1959). Improved oxygenation occurred at 20 cmH20 (Bendixenet al 1963) while alveolar recruitment occurred at 30 cmH20 (Lum et al 1990)w High airway pressuresandlor large inflation volumes have also been implicated in barotrauma/ volumetrauma. The mean airway pressures achieved using the test lung are unlikely to result in the pathological changes that were demonstrated to occur with barotrauma in the· animal studies (Dreyfusset a11988, Parkeretal 1990, Peevy et al 1990). However, it is important to note that some physiotherapists in this study did reach peak values of between 30 and 40 .cmH20. In animal studies barotrauma has been demonstrated to occur within this pressure range, resulting in a decrease in.compliance and gas exchange and disruption of the alveoli epithelium and capillary endothelium (Dreyfuss etall985, Egan 1982, Tsuno etal 1990). Therefore barotrauma may occur during treatment by physiotherapists. Investigation of the physiotherapist's technique ofMH is required to evaluate the likelihood of barotrauma occurring. The physiotherapists' mean (SD) inflation rate of 13 (2.3) per minute was high, especially if the large tidal volume is considered. The calculated mean minute ventilation was
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(/11{1 (
Macgill Circuit
laerdal Circuit
Figure 3.
An exampie of one therapist's recording lNhich compan!s the effect of MacgiU and laerdal circuH on airwavpressure dlu~ing end inspirator.y hold (an"ows) and at end
expiration.
19.3 L/min. This is higher than the normal minute ventilation of a spontaneously breathing patient or ofa mechanically ventilated patient (Oh 1990). Physiotherapists need to consider the possibility of overventilation and modify their technique to match the baseline minute ventilation of the patient. The technique of MH was significantly influenced by the type of resuscitation.circuit used. The tidal volumes, inflation flow rates and airway pressures were significantly different between the two circuits. Hess and associates (1989 and 1990) also noted that the resuscitator brand had a significant effect on the inflation volumes applied. The Macgill circuit applied a significantly higher tidal 'volume and airway pressure than the Laerdal circuit. The flow rates were '!lisa significantly lower with the ,Macgillcircuit.The most obvious 'explanation for the differences is in the physical characteristics of the two circuits. The inflation capacity, compliance of the bag, type of ,¢Jpiratoryvalveand the gas source port are the more notable differences. The Macgill circuit has a 2Lcapacity, <~hile the Laerdal has a 1.6L capacity. 'The more compliant Macgill rubber bag allows the therapist to
more gas into the lung. The expiratory fishmouth valve on the Laerdal circuit allows the gas to leak during the end inspiratory hold and therefore there is a loss of volume and pressure. In contrast, with the Macgill circuit both the operator manipulated valve and the proximal position of the gas port allows continuous filling of the gas into the lung thus permitting the volume and airway pressure to increase at end inspiration. These physical differences account for the variations in the description of the technique. This suggests that it is important to note the resuscitation circuit used when evaluating the effects of MH. Most of the physiotherapists applied a mean positive end expiratory pressure (PEEP) of3.31 (3.71) cmHzO (range 0-13.75 cmHzO) while using the Macgill circuit. This may be related to manipulation of the expiratory valve, which increases airway resistance thereby prolonging expiratory time. Thus PEEP is produced on reinflation of the test lung prior to complete deflation. A consequence of adding PEEP is the increase in the maximal airway pressure consistent with the observed higher airway pressures in the Macgill circuit. Another parameter that is known to
affect the technique of MHis lung compliance, which is defined asa unit change in volume·to a unit change in pressure (Nunn 1987). Common clinical conditions that result in a decrease incompliance of the lung include atelectasis, pneumonia, adult respiratory distress· syndrome and pulmonary oedema. The decrease in compliance altered the physiotherapists' technique with an increased airway pressure despite the decrease in tidal volume. The results of this study confirm the conclusions of Hess et al.(1993) that an increase in impedance resulted in a significant decrease in inflation volume. This appropriate modification of the technique should minimise the occurrence of barotrauma/ volumetrauma. The expected decrease in inflation flow rates did not occur with decreased compliance. Slow inflation flow rates increase the time available for ventilation of the less compliant alveoli and therefore improve the distribution of ventilation and gas exchange (Baker 1977, Pillet et aI1993). Another factor that influences the description of the MH is the individual's technique. The wide variation between the individual operator's technique of MHhas also been noted by other .authors (Hess et al 1989, Hess and Spahr 1990). Significant determinants that influence the volume and therefore peak pressure of MH are the number of hands (one versus two) and hand size (Hess et al 1989). Other important determinants that account for the variation ofperformance include the therapist's·past experience of the circuit and the method learned during skill acquisition~ Before physiotherapists can evaluate the effects of MH and its individual components, a description of the technique currently used on patients is required. Physiotherapists will then be able to assess the effects of their technique on ventilation, perfusion, gas exchange, compliance, reversing/ preventing respiratory problems and overall patient outcome.· This study has
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From Page 201 highlighted the following issues. It is important to recognise that different circuits and therapists will significantly alter the technique. A possible recommendation is for therapists to obtain objective measures of their technique and of the circuit they use. Inflationary volume could be measured with a Wright Respirometer (Clement Clarke International Ltd., London) or portable computerised spirometer that measures tidal volume. Both of these instruments are commonlyfound in physiotherapy departments or intensive care units. Airway pressure can be easily measured. A blood pressure manometer, the pressure manometer of positive expiratory pressure (PEP) circuit or airway cuff pressure manometer can be inserted into the circuit, enabling physiotherapists to measure peak airway pressure and PEEP. Physiotherapists can also determin.e and apply the appropriate inflation rate. This will facilitate the use ofslow inflation flow rates in patients who have low lung compliance or high .airway resistance. There are advantages and disadvantages of both circuits tested in the present study. If a therapist has a choice between circuits, recognising the advantages of the circuit chosen for a given patient will allow such knowledge to beincorporated into the clinical decision making process. However, if there is no choice the therapist should modify the technique to enhance the benefits and minimise the disadvantages in order to improve the patient's outcome. One of the roles of physiotherapists in intensive care is to teach inexperienced physiotherapists and/or students the technique of MH using a resuscitation circuit. A worthwhile practice may be to measure the components of MH while the therapists learn and.practise the technique. This should improve their learning and assist the understanding of the effects of the technique in various pathologies ofthe respiratory and cardiovascular system.
In conclusion, this study has provided a description of theMH technique. This provides a starting point for further investigation into the effects of MH.
References Baker AB, Colliss]Eand Cowie RW(1977): Effects of varying inspiratory flow waveform and time in intermittent positive pressure ventilation. ll:various physiologicalvariables. British Journal ofAnaesthesia 49: 1221-1233. Bendixen llH, Hedley...;Whyte],ChirB and Laver MB (1963): Impaired oxygenation in surgical patients during general anesthesia with controlledventilation. Aconceptofatelectasis. New England Journal of Medicine 269: 991-996. Dreyfuss D, BassetG, Soler P and SaumonG (1985): Intermittent positive-pressure ventilation with high inflation pressures produces pulmonary microvascular injury in rats. American Review of Respiratory Disease 132 880-884. Dreyfuss D, Soler P, BassetG and Saumon G (1988): High inflation pulmonary edema. Respective effects of high airway pressure, high tidal volume, andpositive end- expiratory pressure. AmericanReviewofRespiratory Disease 137: 1159-1164. Egan EA (1982): Lung inflation, lung solute permeability, and alveolar edema. Journal of Applied Physiology 53: 121-125. Egbert LD,Laver ME and BendixenHH (1963): Intermittent deep breaths and compliance during anesthesia in man. Anesthesiology 24: 57-60. GoodnoughSK(1985):The effects of oxygen and hyperinflation on arterial tension after endotracheal suctioning. Heart and Lung 14: 11-17. Hans Rudolph Inc. (1989): Service and Instruction Manual for Rudolph Pneumotachs (PTM), Kansas City. Hess D, GoffG,and]ohnsonK(1989): The effect ofhand size, resuscitor brand,and use of two hands on volumes delivered duringadult bag.,. valve ventilation. Respiratory Care 34: 805-810. Hess D and Spahr C (1990): An evaluation of volumes delivered by selected adult disposable resuscitators: The effect ofhand size, number ofhands used, and use ofdisposable medical gloves. Respiratory Care 35: 801-805. Hess D, SimmonsM, Blakovitch S, Lightner D and Doyle T (1993): An evaluation of the effects of fatigue, impedence, and use of two hands on volumes delivered during bag-valve ventilation. Respiratory Care 38: 271-275. Laver MB, Morgan ],Bendixen HHand Radford Jr EP (1964): Lung volume, compliance, and arterial oxygen tensions during controlled ventilation. Journal.of Applied Physiology 19: 725-733.
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Levine M, Gilbert Rand Auchincloss]H(1972): A comparison of the effects ofsighs, large tidal volumes, andpositive end expiratory pressure in assisted ventilation. ScandinavianJournal of Respiratory Disease 53: 101-108. LumH, Huang I and Mitzner W (1990): M 0 rphoi 0 gicalevidence foralveo Iar recruitment athigh transpulmonary pressure. Journal ofApplied Physiology 68: 2280-2286. Mead] and Collier C (1959): Relation of volume history of lungs to respiratory mechanics .in anesthetized dogs. Journal ofAppliedPhysiology 14: 669-678. Nunn F] (1987): Applied Respiratory Physiology (3rd ed.) London: Butterworth, pp. 23-45. Dh TE (1990): Mechanical ventilatory support. In Oh TE(Ed.) Intensive Care ManuaI. Sydney: Butterworth, pp. 155-161. OhTE (1990): Respiratory physiology. Symbols and normal values. InOh TE (Ed.) Intensive Care Manual. Sydney: Butterworth, pp.679-681. Parker]C, Hernandez LA, Longnecker GL, Peevy K] andJohnson W (1990): Lung edema caused by high peak pressures in dogs. Role of microvascular filtration pressure and permeability. American Review of Respiratory Disease 142: 321-328. PeevyK], Hernandez LA, Moise AAand Parker]C (1990): Barotrauma and microvascular injury in lungs of nonadult rabbits: Effects of ventilation pattern. Critical Care Medicine 18:634,..637. Pierce R] (1986): Spirometryand lung volumes. A review of method, indication, normal values and reproducibility. Volume 6 (supplement): 1~22.
Pillet 0, Choukroun ML and Castaing Y (1993): Effects ofinspiratoty flow rate alterations on gas exchange during mechanical ventilation in nonnallungs. Efficiency ofend-inspiratory pause. Chest 103: 1161-1165. Tsuno K, Prato P and Kolobow T (1990): Acute lung injury from mechanical ventilation at moderately high airway pressures. Journal of Applied Physiology 69: 956-96 L Validyne Engineering Corp. (1990): Instruction Manual. California.