Comparison of Pulmonary Artery Pressure Measurements in the Supine and 60° Lateral Positions

lomparison of Pulmonary Artery Pressure Measurements in the S u ~ i n eand 60"Lateral Positions A

Leanne is continuing this research in her doctoral studies.

nne M Aitken Abstract Pulmonary artery pressure monitoring with the patient in both the supine and lateml positions, is an essential element in the assessment o f critically ill patients. Previous work offers conflicting results regarding the accuracy o f measurements obtained with the patient in the lateml position. The purpose o f this study was to determine i f accurate pulmonary artery pressure measurements can be obtained in the cardiac surgical patient. Thirty-Rve patients underwent repositioning between the supine and both the left and right 60" lateral position while being mechanically ventilated and then breathing spontaneously. Pulmonary artery pressure measurements were recorded prior to, two minutes following and ten minutes following repositioning. Despite some variation in results the pulmonary capillary wedge pressure measurement was reliable ten minutes after repositioning in both the spontaneously breathing and mechanically ventilated patient. Other pulmonary artery pressure measurements were not so reliable in the lateral position. This study concludes that clinical practitioners can obtain accurate pulmonary capillary wedge pressure measurements in postaperative cardiac surgical patients positioned in either the lei? or right 60" lateml position. Further research is however required, with larger

RN- IC Cert. B.HSclNurs' Hans* position has been questioned since N A MRC the early use of pulmonary artery of Philoscophy Stuclent, . ,, . aculry or Nursng. 11 Melbourne Institute of Technology. I V Clinical Nurse Consultant wacic lntt?nsiveGalre Unit lyal Hobart HospitalI a.

IUI I I

Accepted:

..

May 7 99'4 OctobeF 7995

numbers h m all subgroups o f the critical care population. Physiological and pathophysiological characteristics which preclude reliable pulmonary artery pressure measurements need to be identified. Haemodynamic monitoring, including pulmonary artery pressure monitoring, constitutes an essential component of the continuous assessment of a critically ill patient. Accurate and reliable use of this information enables acquisition of diagnostic information regarding the patient's haemodynamic status, in particular left ventricular function. It also allows assessment of the patient's response to therapeutic interventions. Several authors have found that information from pulmonary artery catheters has prompted a major change in therapy in approximately 50% of patients studied(1, 2, 3). In order to ensure these changes in therapy are optimal for the patient it is essential that reliable pressure measurements are obtained.

Literature Review The reliability of measuring pulmonary artery pressures while patients are positioned in the lateral

catheters (4). Previous work has not yet provided a clear response to this issue. Kennedy et al. (5) and Guenther et al. (6) investigated medical patients being turned from the supine to the 90" right and left lateral position and found no difference in pulmonary capillary wedge pressure. Whitman (7) had similar findings in a post-operative cardiac surgical group of patients turned to the 20" lateral position. In contrast others (8.9,10) found differences in pulmonary artery pressures between the supine and varying (45" - 90") lateral positions. More recently Groom et al. (I I) studied both medical and surgical intensive care patients and found variations between the two subgroups of patients. The surgical patients generally demonstrated no statistical or clinical difference in pulmonary artery pressures, while medical patients showed both statistical and clinical differences in all parameters measured. When interpreting previous work it is difficultto compare one study with another. Some studies have small subject numbers @,lo),from both specific (5,7,8.11) and varied (6,l O,I I) subgroups of the critical care population. Researchers recorded the pressure measurements at differing time intervals after lateral repositioning, and perhaps most significantly used differing transducer zeroing positions. Additionally, minimal control of the modifying variables of mechanical ventilation and the position of the pulmonary artery catheter tip was exercised. The extent of lateral repositioning also varied in previous work between

Steri-Cath Closed Ventilation Suction System For F The Steri-Cath Closed Ventilation Suction System allows the maintenance of ventilator pressures during suctioning of mechanically ventilated patients.

Steri-Cath also reduces the risk of cross contamination because it offers a CLOSED system which fully protects both the user, and the patient. The system comprises of four major components. 1.

A protective sleeve which encloses the catheter.

2.

A lightweight clear T-Piece which connects the tracheal or tracheostomy tube t o the breathing system.

3.

A unique finger operated suction control valve for maximum suction control and prevention of contamination of the user.

4.

An irrigation line designed t o deliver fluid at the tip of the suction catheter t o accurately direct lavage and provide effective irrigation.

NEW CONCEPT I N SUCTIONI NG

utine Suctioning Of Mechanically Ventilated Patients

Steri-Cath is an innovative system which offers major benefits over standard suctioning. -

Ventilator pressure can be maintained throughout suctioning because no disconnection of the circuit is required.

-

Cross contamination is reduced because the system is totally closed. The carefully designed suction control valve isolates the user from any contract w i t h suctioned material.

-

Irrigation can be accurately delivered t o loosen secretions and t o clean the system if required.

-

The catheter can be reintroduced at anytime over a 24 hour period as often as required t o eliminate the build up of secretions.

CONCEPT I N SUCTIONI NG The Boots Company (Australia) Pty Ltd

A.C.N. 000 071 278

PO Box 120, Carlingford 2118 21 Loyalty Road, North Rocks, NSW Facsimile: (02) 842 7224 Toll Free: 008 226 766 Telephone: (02) 842 7222

I

COMPARISON OF PULMONARY ARTERY PRESSURE MEASUREMENTS IN THE SUPINE AND 60" LATERAL POSITIONS

20" (7) and 90" (6,8.14). Lateral positioning of the critically ill patient is encouraged to improve patient comfort, to maintain skin integrity, and to alter ventilation/perfusion ratios. Maximum elimination of sacral and trochanteric pressure is achieved with a 30" lateral position (15). Optimal improvement in ventilation/perfusion ratios, particularly in unilateral lung disease, is achieved in the 90" lateral decubitous position (16.17). Critically ill patients are frequently placed in the 60" lateral position as this tends to be most comfortable for the majority of patients, while providing benefits to both the skin and the lungs. After review of the literature and extensive discussions with colleagues in the health care profession the following lack of consensus became apparent. It is agreed that the phlebostatic axis (mid-plane of the thorax at the level of the fourth intercostal space [ I 81) is accepted as the zero level for haemodynamic monitoring when the patient is in the supine position. Interpretation of whether this represents the level of the left or right atrium varies widely among both authors and clinicians, however Winsor and Burch clearly describe the phlebostatic axis as passing "through the openings of the venae cavae into the right auricle" (18, p.168). In addition, the use of this zero reference level provided relatively little variation in venous pressure measurements, "even though the thickness of the chests varied considerably" (18, p.165). Unfortunately there exists no equivalent consensus regarding the appropriate zero reference level when the patient is in the lateral position. Winsor and Burch did make the point that "although an anatomic landmark is necessary, the validity of this landmark must be based upon physiologic data" (18, p.168). While the phlebostatic axis identifies the horizontal plane (i.e. the

mid-point of the thorax) to be used to identify the zero reference level no work has identified the appropriate vertical plane in humans. This additional plane is necessary for zero referencing of the monitoring system when the patient is in the lateral position. For the purpose of this study it was decided to use a mathematically derived mid-point of the thorax on both the horizontal and vertical plane to identify an appropriate zero reference point. The anatomical landmark which corresponded to this point was identified in each individual subject and used as the level of zero for the monitoring system. The second part of the study then set out to determine the appropriateness of this zero reference level, from a physiologicalviewpoint. Following consideration of previous work this study was developed to attempt to answer the following question. Is there a difference in pulmonary artery systolic (PAS), pulmonary artery diastolic (PAD), pulmonary artery mean (PAM) and pulmonary capillary wedge pressure (PCWP) measurements obtained in the 60" lateral position when com-

I

pared to those measurements obtained in the supine position in post-operative cardiac surgical spontaneously breathing and mechanically ventilated patients? The influence of the position of the pulmonary artery catheter tip was also analysed.

Method Sample

Thirty-five subjects were enrolled in this prospective correlational study. All patients in the Cardiothoracic ,IntensiveCare Unit of a large teaching hospital in Tasmania, who had a balloon-tipped pulmonary artery catheter (American Edwards Laboratories - 93A-131H-7F or Biosensors International - TD1704H) in situ were eligible for entry. Subjects were admitted to the study by means of convenience sampling in association with the specified inclusion (Table 1) and exclusion (Table 2) criteria. 80% of subjects had undergone coronary artery bypass grafting, while the remaining 20% had undergone a valve repair or replacement. No effort was made to control for age (except that all subjects were adult), gender, or primary diagnoses other than all

Table 1

INCLUSION CRITERIA 1. Pulmonary artery catheter insitu for general monitoring purposes

2. Subjects post Cardiac Surgery: Coronary Artery Bypass Grafting Valve Repair /Replacement Atrial / Ventricular Septa1 Defect Repair

Table 2

EXCLUSION CRITERIA 1. inconclusive Pulmonary Artery or Pulmonary Capillary Wedge recording 2. Repositioning of patients taking greater than five minutes

3. Monitoring equipment other than those models stated 4. Contraindications/inabilityto reposition patient in either lateral position.

5. Changes in patient treatment required in the time period between the first and third pressure recordings

COMPARISON OF PULMONARY ARTERY PRESSURE MEASUREMENTS IN THE SUPINE AND 60"LATERAL POSITIONS

patients being in the acute postoperative stage following cardiac surgery. Permission to conduct this study was obtained from the relevant hospital Ethics Committee. Level of Zero Reference

The pressure monitoring transducer was levelled and zeroed to the phlebostatic axis when the subject was in the supine position. Pulmonary artery pressure measurements were then recorded. While in the supine position patients had one pillow under their head, and the head of the bed elevated up to 45". This degree of elevation remained constant for lateral positioning. Prior to lateral repositioning, the open end of tubing from two additional transducers was attached to each lateral aspect of the subject's thorax in the fourth intercostal space, midway between the anterior and posterior thoracic surfaces. Both these transducers, when open to atmosphere, read zero, thus ensuring they were level. The subject was then placed in the 60" lateral position, where the angle was measured with a compass and protractor and maintained with pillows. The height of the transducers was then realigned so that they each read the same absolute value, for example 9 mmHg, with the upper tubing being negative (-9mmHg)and the lower tubing being positive (+9mmHg). This transducer position then identified the level of the midpoint of the thorax and provided the zero point for obtaining the pulmonary artery pressure measurements in the lateral position (See Figure 1 above) On each subject the surface landmark which corresponded with the mid-point of the thorax was then identified. This landmark was recorded on the data collection forms and marked on the subject's thorax so as to ensure consistency in transducer positions at future data collection times.

Figure 1 -Transducer levelling in the lateral position.

Pressure Measurements All subjects underwent repositioning between the supine and both the right and the left 60" lateral position on two occasions each, once while receiving mechanical ventilation and once while breathing spontaneously. Mechanical ventilation included both controlled mandatory ventilation and synchronised intermittent mandatory ventilation (SIMV). When SIMV was in use pressure measurements were obtained at the end of ventilated

breaths. Spontaneously breathing patients were receiving no ventilatory assistance other than oxygen therapy via a face mask. Subjects on whom less than four sets of data were obtained were removed from the study in order to prevent bias in the results. The timing of repositioning of the subjects was dictated by their condition and by the nurse co-ordinating their care. Pressure recordings were obtained using any of four Siemens

Starship CHILDREN'S HEALTH

Staff Nurses Paediatric Intensive Care Starship Children's Health, New Zealand's leading paediatric hospital, is seeking a number of enthusiastic, motivated Staff Nurses to work in our Paediatric Intensive Care Unit. You will need to be an experienced Paediatric Intensive Care Nurse (a paediatric intensive care certificate is desirable), have a commitment to Whanau/family centred nursing and the ability to work in a bicultural environment. We can offer you a comprehensive 10 week orientation programme with the support of an experienced Nurse Educator and a commitment to professional development. Closing date: 26 January 1996. WrittenApplications with CV to Human Resource Adviser, Starship Children's Health, Private Bag 92024, Auckland 1, New Zealand.

Auckland Healthcare Te Tokn Ornngn 0 Tnrnnki Mnkn~rRen

I

COMPARISON OF PULMONARY ARTERY PRESSURE MEASUREMENTS IN THE SUPINE AND 60" LATERAL POSITIONS

Sirecust 1281 physiological monitors maintained according to hospital and manufacturer guidelines with annual biomedical services, including calibration. Pressure measurements were recorded immediately prior to, two minutes following and ten minutes following repositioning of the subject. The monitoring system was rezeroed to the level of the mid-point of the thorax prior to obtaining each set of pressure recordings. Systolic, diastolic and mean pressure measurements were obtained using the digital readouts supplied by the monitor, except in those situations where a respiratory swing was apparent. In these instances the pressure recording was frozen on the screen and each of the pressure measurements were obtained at end expiration using the inbuilt cursor. Pulmonary capillary wedge pressure measurements were always obtained using the latter method. Where possible, the subject received no changes of treatment during the time period between the first and third pressure recordings. If

alterations to current treatment were required for optimisation of the subject's condition the set of data affected was removed from the study. Correct position of the catheter tip was confirmed radiologically on a routine post-operative chest x-ray and by a correctly identifiable pulmonary artery waveform. Additional information obtained from the chest x-ray was the position of the catheter in either the left or the right lung. Data Collection Data collection was performed by the author and two other data collectors over an eight week period. Training took place prior to the study to ensure the principles of patient positioning and pressure measurement were the same for each of the data collectors. Differences between measurements obtained by the author and each data collector within one minute of each other, were assessed during the study using a paired t-test. The p values ranged from 0.22 - 0.76 which indicated no

Table 3

SURFACE LANDMARK OF THE MIDPOINT OF THE THORAX LEm LATERAL POSITION

n = 35 Anatomical Landmark

Number CX)of subjects

Left rnidclavicular line

29 (83%)

2crn left of sternal border Left anterior axillary line

4 (11%) 2 (6%)

Table 4

SURFACE LANDMARK OF THE MIDPOINT OF THE THORAX RIGHT LATERAL POSITION n = 35 Anatomical Landmark

Number

of subjects

Right rnidclavicular line

26 (74%)

2crn right of sternal border Right anterior axillary line Right sternal border

5 (14%) 3 (9%) 1 (3%)

significant difference in pressure measurements recorded. Statistical Analysis Repeated measures ANOVA (Statistical Analysis System, Release 6.03) was used to analyse the significance of differences for each subject between PAS, PAD, PAM and PCWP measurements. This analysis was conducted once for the pressure measurements obtained while the patient was being mechanically ventilated and once for those pressure measurements obtained while the patient was spontaneously breathing. Analysis was repeated taking into account the position of the pulmonary artery catheter tip. For all analyses p<0.05 was considered statistically significant.

Results Of the 35 subjects enrolled in the study, seven were excluded from analysis of pulmonary artery pressure measurements due to non-attainment of four sets of complete data. Analysis of the surface landmark representing the mid-point of the thorax was carried out on all 35 subjects. The mid-point of the thorax corresponded to three and four different surface landmarks in the left and right 60" lateral positions respectively (Tables 3 and 4). These surface landmarks ranged from the dependent sternal border to the dependent anterior axillary line at the level of the fourth intercostal space. From these data it can be seen that the use of the dependent mid-clavicular line as the zero point for pulmonary artery pressure monitoring transducers will accurately reflect the mid-point of the thorax in 74% of subjects in the right and 83% of subjects in the left lateral position. Pulmonary artery pressure measurements varied between the supine and the left and right 60" lateral position on specific occasions. Subjects who were breathing spon-

COMPARISON OF PULMONARY ARTERY PRESSURE MEASUREMENTS IN THE SUPINE AND 60"LATERAL POSITIONS

taneously demonstrated statistically significant differences in PAS, PAD, PAM and PCWP measurements obtained two minutes following latera1 repositioning. Each of these differences had resolved ten minutes after repositioning (Table 5). During mechanical ventilation subjects demonstrated a wider variety of responses while in the lateral position. PAS, PAD and PAM pres-

ing from the time of one chest x-ray to the next. Repeated measures ANOVA was therefore performed on all patients in whom the pulmonary artery catheter tip was in the right lung, as they were positioned in the right lateral position. Despite the previously mentioned limitation the trend suggested improving accuracy in pulmonary artery pressure measurements when pulmonary artery

Table 5

PULMONARY ARTERY PRESSURE MEASUREMENTS SPONTANTEOUSLY BREATHING SUBJECTS Pressure

Lateral Position

Supine (mmHg)

2 Minutes (mmHg)

Minutes (mmHg)

10

F Supine 2Mies-

F Supine 2-8

-

F Supine lOMhks

10M-a

17.91'

2.96

8.78*

4.27,

2.80

23.32

11.07*

12.60*

0.28

16.25

14.57

10.27"

7.89'

0.89

32.58

36.86

34.75

10.21.

14.03*

3.36

RIGHT

15.11

16.07

15.11

3.14

PAM

RIGHT

22.93

24.54

23.21

7.18*

9.63.

0.41

PCWP

RIGHT

14.93

16.82

14.93

7.25.

12.27

0.00

PAS

LEFT

34.36

38.75

35.57

PAD

L W

15.25

16.39

14.57

PAM

LEFT

23.04

23.04

PCWP

LER

14.89

PAS

RIGHT

PAD

13.42'

NB: For Tables 5 , 6 & 7 -where a non-significant F statistic is available for overall analysis (eg: PAD / Right Lateral Position above) further analysis based on time has not been ~erformed.

sure measurements demonstrated differences ten minutes after repositioning to the right lateral position. However PCWP measurements taken ten minutes after repositioning to either lateral position were not different to those pressure measurements taken in the supine position (Table 6 Page 28). Analysis of the influence of the position of the pulmonary artery catheter tip in either the dependent or the non-dependent lung was possible only in a limited form. This was because only four pulmonary artery catheters were positioned in the left lung, twenty-two in the right lung and two either indeterminate or vary-

catheters were positioned in the dependent lung (Table 7 Page 28).

Discussion The dependent mid-clavicular line at the level of the fourth intercostal space was the surface landmark that most frequently corresponded with the mid-point of the thorax. This landmark is midway between the previously utilised landmarks of midsternum (5,6,10) and dependent mid-axillary line (I I). Also worth noting is that inclusion of those patients where the level of the mid-point of the thorax was 2cm to the dependent side of the sternal border would introduce a variation of approximately 3cm in the height of the

transducer. This would increase the represented group of patients to 94% and 88% in the left and right 60" lateral positions respectively. Variation of 3cm in the transducer height equates to 2.2mmHg pressure variation. This variation is considered normal fluctuation in pulmonary artery pressure measurements in the critically ill (19). Additionally, it is probably clinically insignificant in the adult post-operative cardiac population. The use of the mid-clavicular landmark as the zero reference point in this study when it has not been used in previously documented studies has eventuated as a result of a basic methodological difference. Previous authors have attempted to identify a surface landmark that corresponded to the left atrium when the patient was in the lateral position. In contrast, this author has identified a surface landmark with the same zero value in the lateral position as that commonly used in the supine position. The belief that this zero reference point is physiologically valid is an integral assumption underlying the comparisons between pulmonary artery pressure measurements in the supine and lateral positions made in this study. The clinical applicability of the results is obviously also dependent on this assumption. Analysis of pulmonary artery pressure measurements provides some significant patterns that will allow incorporation of the findings into clinical practice. Although a variety of statistical differences in all pulmonary artery pressure measurements were present two minutes after lateral repositioning of the patients the PCWP uniformly showed no significant difference ten minutes after repositioning.This was consistent for both spontaneously breathing and mechanically ventilated patients. This uniformity was not true for the PAS, PAD or PAM pressure measurements. It should be noted at this

COMPARISON OF PULMONARY ARTERY PRESSURE MEASUREMENTS IN THE SUPINE AND 60"LATEXAL POSITIONS Table 6

PULMONARY ARTERY PRESSURE MEASUREMENTS MECAHNICALLY VENTILATED SUBJECTS n = 28 Pressure

F Supine -

F Supine

-

Supine

-

10-

PAS

LEFT

29.61

PAD

LEFT

14.57

PAM

LEFT

21.64

PCWP

LEFT

11.07

PAS

RIGHT

30.61

PAD

RIGHT

15.00

PAM

RIGHT

21.29

PCWP

RIGHT

10.43

Table 7

PULMONARY ARTERY PRESSURE MEASUREMENTS PULMONARY ARTERY CATHETER POSITIONED IN RIGHT LUNG

I

I

-

Supine -

Supine

2M i s

10 Minules

SPONTANEOUSLY BREATHING: RIGHT 33.45 RIGHT

14.91

RIGHT

22.68

RIGHT

14.73

MECHAP CALLY VENTILATED RIGHT 30.05 PAD PAM

RIGHT

PCWP

RIGHT

10.41

point that the power of the study is low (PAS - 0.40, PAD - 0.50, PAM 0.40, PCWP - 0.70 varying because of differing effect size) as a result of the small subject numbers and small pressure differences which existed at ten minutes. As such the results should be interpreted with caution and the need for further studies in this area, as discussed in Implications For Nursing Practice, should be acknowledged. The most probable explanation

for the presence of the difference at two minutes, and the resolution by ten minutes, lies in the physiological stress a subject experiences when undergoing a position change. This stress apparently disperses to an acceptable level in less than ten minutes. Atthough these findings differ from previous literature it should be noted that only two previous authors have studied a population consisting exclusively of cardiac surgical

patients (7, 11). The differing zero reference point for the pressure transducers may also account for differing findings. As a result of the small number of pulmonary artery catheters positioned in the left lung no conclusions could be made in relation to the influence of the position of the pulmonary artery catheter tip. However, the trends are in line with a significant portion of the literature that stresses the need for the pulmonary artery catheter to be in West's zone 3 (20, 2 1 , ~ ~Previous ). work in this area has centred on the patient being positioned in the supine position. However, it is reasonable to assume the same physiological principles of blood flow apply when the patient is positioned in the lateral position. Further work with larger patient numbers will be required to confirm or refute this assumption. The above findings are subject to certain limitations, which arise primarily from the acute nature of the patient's condition. There has been no control of the influence of vasoactive drugs, particularly inotropic and vasodilator agents. The specific effect of each of these drugs on pulmonary artery pressures, particularly in the setting of repositioning of the patient, is not known. The underlying haemodynamic stability of the patient has also not been incorporated into analysis. These limitations may be responsible for some of the variable results, such as the significant PAS, PAD and PAM pressure measurements in mechanically ventilated patients in the right lateral position at ten minutes. Additionally, although patients were removed from the study if they received active treatment between the first and third pressure measurements, it was not possible to detect all minor changes in haemodynamic status. These changes may have occurred as a result of their condition rather than the change in position. Assessment of the position of the pulmonary artery catheter tip was open to possible inaccuracy as a

I

COMPARISON OF PULMONARY ARTERY PRESSURE MEASUREMENTS IN THE SUPINE AND 60"LATERAL POSITIONS

result of catheter movement between the time of the chest x-ray and the measurement of pulmonary arterv * .rsressures. This interval ranaed from one to twenty-four hours. Catheter manipulation, in the event of a non-clearly defined pulmonary capillary wedge trace, was allowed.

-

Implications for Nursing Practice The findings of this study will provide some guidance for nurses caring for post-operative cardiac surgical patients. In the short-term it should be accepted that accurate PCWP measurements can be obtained in patients ten minutes after repositioning them in the 60" lateral position. This accuracy is not repeated in other pulmonary artery pressure measurements. This knowledge will allow promotion of increased periods of sleep by facilitating lengthier side positioning. Secondly, it will also lead to improved respiratory function by allowing enhancement of ventilation1 perfusion ratios. Thirdly, it will decrease tissue breakdown as a result of the diminished need for long periods of time in the supine position. Finally, unnecessary utilisation of nursing and paramedical time spent repositioning patients to the supine position for regular pressure measurements will increase the time available for other aspects of patient management. However these results should be accepted only as an interim measure until further research in this area is conducted. Although this study has provided some early guidelines for monitoring the cardiac surgical patient it should be repeated with larger numbers, and also expanded to cover other sub-groups of the critical care populations. There remains a need to identify the physiological and pathophysiological characteristics which preclude accurate pulmonary artery pressure measurements with the patient in the lateral position.

The need to identify the specific management variables, such as the use of vasoactive drugs, mode of ventilation and PEEP. as well as the position of the pulmonary artery catheter tip, still remains. A final area that, although difficult to assess, may provide some revealing information is measurement of the variation between nursing practitioners in their subjective determination of the position of the mid-clavicular line at the level of the fourth intercostal space in a range of subjects. Conceivably, this variation may be greater than the variation between surface landmarks representing the mid-point of the thorax in a cross-section of subjects.

Acknowledgements I would like to acknowledge the assistance of Lisa Gurner and Michael Sullivan in data collection, Tony Bell in statistical analysis and Carl Moller for his ongoing support and guidance throughout the study.

References 1. Connors AF, McCaffree DR, Gray BA. Evaluation of Right-Heart Catheterization in the critically ill patient without acute myocardial infarction. N Eng J Med 1983; 308(5):263-267 2. Celoria G, Steingrub JS, Vickers-Lahti M, et al. Clinical assessment of hemodynamic values in two surgical intensive care units: effects on therapy Arch Surg 1990; 125:1036-1039 3. Eisenberg PR, Jaffe AS, Schuster DP Clinical evaluation compared to pulmonary artery catheterization in the hemodynamic assessment of critically ill patients Crit Care Med 1984; 12(7): 549-553 4. Pace NL A critique of flow-directed pulmonary arterial catheterization Anesthesiology 1977; 47:455-465 5. Kennedy GT, Bryant A, Crawford MH The effects of lateral body positioning on measurements of pulmonary artery and pulmonary artery wedge pressures Heart Lung 1984; 13(2):155-158 6. Guenther NR, Kay J, Cheng EY, Lauer KK Comparing pulmonary artery catheter measurements in supine, prone and lateral positions (abstract) Crit Care Med 1987; 15(4):383 Z Whitman, GR Comparison on pulmonary artery catheter measurements in 20" supine and 20" right and left lateral recumbent positions (Abstract) Proceedings of the AACN International lntensive Care Nursing Conference. 1982

I

8. Lange RA, Katz J, McBride W, Moore DM, Hills LD Effects of supine and lateral positions on cardiac output and intracardiac pressures Am J Cardiol 1988; 62330-333 9. Nakao S. Come PC. Miller MJ, et al Effects of supine and lateral positions on cardiac output and intracardiac pressures: an ex~erimentalstudv Circulation 1986: 73(3):579-585 10.Keating D, Bolyard K. Eichler E, Reed J Effect of sidetying positions on pulmonary artery pressures Heart Lung 1986; 15(6):605-610 11.Groom L, Frisch SR. Elliott M Reproducibility and accuracy of pulmonary artery pressure measurement in supine and lateral positions Heart Lung 1990; 19(2):147-151 12.Wild L, Effect of lateral recumbent positions on measurement of pulmonary artery and pulmonary artery wedge pressures in critically ill adults (Abstract) Heart Lung 1984; 13 (3):305 13.Cason CL, Lambert CW Position and reference level for measuring right atrial pressure Critical Care Nursing Quarterly 1990; 12 (4):77 - 86 14.Bryant A, Kennedy GT The effects of lateral body position on pulmonary artery and pulmonary capillary wedge pressure measurements (Abstract) Circulation 1982; 66 (part 11):9 15.Seilor WO, Allen S, Stahelin HB lnfluence of the 30" laterally inclines position and the 'Super-soft' 3-piece mattress on skin oxygen tension on areas of maximum pressure - implications for pressure sore prevention Gerontology 1986; 32:158 166 16. Prokocimer P, Garbino J, Wolf M, Regnier B Influence of posture on gas exchange in artificially ventilated pat~entswith focal lung disease lntensive Care Med 1983; 9:69 72 17.G1llespieDJ, Rehder K. Body position and ventilation-perfusionrelationships in unilateral pulmonary disease Chest 1987; 91(1):75 - 79 18.Winsor T, Burch GE Phlebostatic Axis and Phlebostatic Level, Reference Levels for Venous Pressure Measurements in Man Proceedingsof the Society for Experimental Biology and Medicine 1945; 58:165 169. 19.Nemens EJ, Woods SL Normal fluctuations in pulmonary artery and pulmonary capillary wedge pressures In acutely ill patients Heart Lung 1982; 11(5):393-398 20.Raper R, Sibbald WJ Misled by the wedge? The Swan-Ganzcatheter and left ventricular preload Chest 1986; 89(3):427-434 21 .Quaal SJ, Quality assurance in hemodynamic monitoring AACN Clinical Issues In Critical Care Nursing 1993; 4(1):197-206 22.Gardner PE, Pulmonary Artery Pre-,sure Monitoring AACN Clinical Issues In Criiical Care Nursing 1993; 4(1):98-I19