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Body Position and Ventilation-Perfusion Relationships in Unilateral Pulmonary
BOdy Position and Ventilation-Perfusion Relationships in Unilateral Pulmonary Disease* Delmar]. Gillespie, M.D., Ph.D., F.C.C.P.;t and Kai Rehder, M.D.
The effect of positional change (right vs left lateral decubitus) on the distribution of ventilation and perfusion ratios was determined in four patients with respiratory failure and chest roentgenographic 6ndings of unilateral pulmonary disease. In these patients with a unilateral interstitial pattern, improvement in oxygenation which occurred when the "good" side was dependent (down) was associated with changes in the patterns of ventilationperfusion distribution; two patients showed a predominant
decrease in rigbt-to-Ieft intrapulmonary shunt, and two showed an improvement in ventilation-perfusion equality. Therefore, when unilateral interstitial pulmonary disease was present, positional change resulted in changes in rightto-left intrapulmonary shunt or low ventilation-perfusion ratios or both. Variability between patients can be explained by the nonhomogeneity of pulmonary disease in patients with respiratory failure.
~Y position can influence pulmonary volume and
patients with unilateral pulmonary disease in response to changes in body position. In particular; we were interested in the influence of body position on right-toleft intrapulmonary shunting and ventilation-perfusion mismatching.
regional ventilation-perfusion relationships.I" In patients with pulmonary disease, body position can have significant effects on gas exchange."?" In adult patients with unilateral pulmonary disease lying in the lateral decubitus position, gas exchange is improved when the normal lung is dependent (down.)11-13 This pattern may be reversed in infants." Current explanations for this improvement in gas exchange are hypothetical and based on data from studies in animals' and normal man.3.5.6.15.16 In patients with unilateral pulmonary disease who require mechanical ventilation for respiratory failure, attempts have been made to correlate changes in gas exchange with intrapulmonary shunt," respiratory system compliance," pulmonary perfusion," or angiography," but no detailed analysis of gas exchange has been reported. Because various methods of treatment such as differential pulmonary ventilation 18.19 and selective positive end-expiratory pressure (PEEP)51D have been advocated, more information is needed about the ventilation-perfusion relationships during positional change in the patient with unilateral pulmonary disease. The multiple inert-gas elimination technique has been used to characterize changes in pulmonary gas exchange in various diseases21-23 and during anesthesia. If In this study the technique was used to define mechanisms of changes in efficiency of gas exchange in *From the Division of Thoracic Diseases and Internal Medicine and Critical Care Service, and the Departments of Anesthesiology and Physiology and Biophysics, Mayo Clinic and Mayo Foundation, Boehester, Minn. Supported in part by research grants HL-2l584 and HL-00708 from the National Institutes of Health. tRecipient of clinical investigator award HL-00708 from the National Heart, Lung, and Blood Institute. Reprint requem: Dr: Gillespie, Mayo Clinic, Rochester, MN 55905
MATERIALS AND METHODS All studies were conducted in medical or surgical intensive care units. Four patients who required prolonged mechanical ventilation for respiratory failure and showed chest roentgenographic evidence of unilateral pulmonary disease were studied after obtaining informed consent. The study was approved by the institutional review
board.
Table l-ChtJracteriatica rf Patients with Bapiratory Failure Who Required MechtJnktJl Ventilation and Fintlinga on Chat Roentgenogram Casel Age, yr
Diagnosis
1/83 Aspiration, right lung 2/78 Postoperative repair, thoracoabdominal aneurysm 3/76 Postoperative left upper lobectomy, retained secretions 4/68 Postoperative repair, thoracoabdominal aneurysm
Chest MV Roentgenogram Mode*
PEE~
em
Flo.
H.D
Infiltrate, right lung Infiltrate, left lung
IMV8
0.52
0
AlC 8
0.51
3
Infiltrate, left lung
AlC 14
0.50
5
Infiltrate, atelectasis, left lung
IMV8
0.40
3
Mechanical ventilation; IM~ intermittent mandatory ventilation; and AlC, assist control.
*M~
CHEST I 91 I 1 I JANUARY, 1987
75
Table 2-ArteriGl Blood GGa Leve&, Ventilation, and Hemodynamic VariGbles· Case and Position of "Good" Side
Mean Pressure, mm Hg
Umin
VE,
Umin
Pulmonary Arterial
Pulmonary Arterial Wedge
44 44
3.64 3.24
9.41 7.58
27 23
12 12
59 103
49 51
2.84 2.87
5.81 6.46
20 22
13 12
Down
74 131
40 36
3.86 3.00
10.95 10.83
25
30
11 10
Down
64 111
49
48
3.01 2.84
5.93
36
16 13
*Q, Cardiac output; and VE,
minute ventilation.
PaO., mmHG
PaCO s, mmHG
49 61
Down
Case 1
Up Down Case 2 Up
Case 3 Up
Case 4 Up
Q,
Patients were stable when studied. For this study the same settings on the ventilator were used as for the clinical management; that is, no adjustments in minute ventilation, PEE~ or inspired oxygen fraction (Flo.) were made. All patients had a Swan-Gam (J French) pulmonary arterial catheter and radial arterial catheter previously in place for clinical management Each patient was studied in both lateral decubitus positions, with the initial position of the abnormal side alternated between dependent (down) or nondependent (up) and the two sides studied in succession. The study was started by constant intravenous infusion (5.6 mllmin) of six "inert" gases (dissolved in a solution of 5 percent dextrose in water). Samples of arterial and mixed venous blood were obtained after 20 minutes of infusion by simultaneous withdrawal of 5 ml and 15 ml of blood from the pulmonary and radial arteries, respectively. A mixed sample of expired gas was also obtained by collecting expired gas after it bad passed through a 12.7-L heated mixing chamber. The sample of gas was drawn after appropriate delay for the gas to pass through the heating system. In addition, mean expired minute volume was calculated from timed collection of expiredgas. Samples of arterial and mixed venous blood and expired gas were obtained after an additional five minutes of infusion. Between the time that the two sets of samples ofblood and gas were obtained, arterial oxygen (PaO.) and carbon dioxide (PaCO.) ten-
5.74
40
sions were determined (electrodes), with appropriate temperature correction. After the infusion was completed, cardiac output was determined in triplicate by thermal dilution; and right arterial, pulmonary arterial, pulmonary arterial occlusion, and systemic arterial pressures were recorded. The mean of the three measurements of cardiac output is reported. The solubility of the six inert gases was analyzed by gas chromatography by using a modification of the technique described by Wagner et al.15 By using the ratio of arterial and mixed venous partial pressure to represent retention and the ratio of expired gas and mixed venous partial pressure to represent excretion, the method of Evans and WagnerlS was used to determine the continuous distribution of ventilation and perfusion as related to the ventilationperfusion ratio (VAlQ). RESULTS
Four patients with respiratory failure who required mechanical ventilation and had chest roentgenographic findings of a unilateral infiltrate were included in the study (Table 1). All of the patients had a history of smoking. In all patients with an interstitial process, turning the "good" side to the dependent position
Table 3-EJfect cfBodt/ POIrition ora VAlQ Dtatribution Relative to Blood Flow and ventilation· Case and Position of
QslQ,
percent
Mean
VAlQ
In SO
VONT, percent
Mean
PaO/Flo.
VAlQ
lnSD
94 117
32.3 19.4
0.67 0.39
1.12 1.06
37.8 33.5
3.25 3.83
1.13 1.46
116 202
12.6 14.9
0.41 0.41
1.80 1.39
21.4 30.1
2.37 1.95
0.99 0.93
Down
148 262
10.6 2.1
0.48 0.44
1.83 1.89
23.1 22.9
3.41 3.99
1.20 1.23
Down
160 278
0 0
0.24 0.31
1.98 1.44
41.8 44.6
2.13 1.19
1.40 1.41
"Oood" Side
Case 1 Up Down Case 2 Up Down Case 3 Up Case 4 Up
*QslQ, Venous admixture; VAlQ, ventilation/perfusion ratio; 10 SO, 78
Ventilation
Blood Flow
log standard deviation; and VoNT, inert gas dead space. Unilateral Pulmonary Dt8eMe(Gllesple, Rehder)
la
.80
Ib Dead
~~~
.80
AO
AO
,jI~
......t 32.3%
0
Slwnt '''4%
0 2a
1.
2b
.60
DMd
30
Spoce
30.1%
~
0
..J LL
.30
.I~
Shunt 14.• %
0
0 0
..J
CD
0
I
0
0
.60
3a
3b
Z
.60
C(
s ~ C(
.30
.30
0
0
..J ~ Z
4a
4b
O..d
~ .60
apac.
44.'%
.60 .30
0
0
.....
.30
M
0.0%
QOI
QI
1.0
10
100
0
0
0.01
VENTILATION - PERFUSION
01
RATIO
(down) improved oxygenation (Table 2). This improvement in oxygenation was not associated with a significant change in PaCO I • Cardiac output decreased in three of the four patients when the abnormal side was nondependent (up), without significant change in mean pulmonary arterial or mean wedge pressure. Table 3 and Figures 1 and 2 show the ventilationperfusion and retention-excretion data for all patients with the "good" side either dependent (down) or nondependent (up). The improvement in oxygenation noted in patients 1 and 3 was mainly the result of a decrease in right-to-Ieft intrapulmonary shunt. In patient 2, the oxygenation improved despite a small increase in right-to-left shunt by a decrease in very low ventilation-perfusion ratios and an improvement in overall ventilation-perfusion matching. Patient 4 had no measurable right-to-left shunt in either position, but perfusion of areas with low ventilation-perfusion ratios (0.01 to 0.1) decreased when the "good" side was dependent (down). DISCUSSION
The proposed mechanisms which define gas exchange in patients with unilateral pulmonary disease are primarily based on studies of normal lungs involving awake l.3.15 or anesthetized-paralyzed volunteers. 5,6 Most investigators have speculated that the improvement in oxygenation noted when the abnormal lung is
1.0
10
tOO
FIGURE 1. Distribution of ventilation-perfusion ratios for four patients with respiratory failure and unilateral pulmonary disease on chest roentgenogram, with "good" side nondependent (up) (a) or dependent (down) (b).
nondependent (up) is the result of improvement in ventilation-perfusion equality or shunt or both;9-13 however; the specific mechanisms remain unclear. In this study of patients with unilateral pulmonary disease, we verified the underlying causes responsible for improved oxygenation noted when the abnormal lung is up; however; the series is small and may not explain all mechanisms of improved gas exchange in patients with unilateral pulmonary disease. Studies on the influence of body position on gas distribution in normal lungs have shown that differences between the awake and anesthetized-paralyzed state are attributable to changes in the mechanical properties of the respiratory system. Inspiratory gas distribution in awake spontaneously breathing subects lying in the lateral decubitus position is preferential to the dependent (down) lung at volumes above functional residual capacity,5,15 but with anesthesia-paralysis and mechanical ventilation, preferential gas distribution is to the nondependent (up) lung." This is because of the differences in impedance between the two hemithoraces. In the awake state the vertical pleural pressure gradient favors gas distribution to the dependent zone because of higher compliance and larger excursion of the diaphragm. With mechanical ventilation after anesthesia-paralysis, diaphragmatic movement is passive and has greater displacement in the nondependent zone, and the dependent hemiCHEST I 91 I 1 I JANUARY, 1987
77
1.0 la
II»
R
R
0.1
§ Z 0
i=a&&JI
0.0
LO la
., , "
a:~
O.
xI
~ICUJ
ZI Co _%
;1 0
i=
0.0
..
.... '
'
,,
.
,,
,.,
LOse
Z
"'0 ~8
R
R
R
R
,,
IIJ
E 0.5
~:
ZI 0
,
i=
0.0
C a:
LO
0
I&-
..
4e
,i
2. Retention and excretion vs blood-gas partition coefficient for six inert gases for four patients with respiratory failure and unilateral pulmonary disease on chest roentgenogram, with "good" side nondependent (up) (a) or dependent (down) (b).
., , "
FIGURE
,~
0.0 .... '
R
R
,,""
"
,;1
,,
ODOI ().()I
thorax is less compliant. 5,6 In this study, patients were mechanically ventilated but did not receive anesthesiaparalysis; therefore, the chest wall and diaphragm would playa major role in gas distribution relative to the difference in impedance between the two hemithoraces. In contrast to gas distribution, blood flow to the lungs is mainly determined by gravitational forces, with the greatest flowto the dependent regions. 3 Blood How may also be inHuenced by nongravity-related factors, but these are still not completely defined. rr Distribution of pulmonary perfusion can be inHuenced by changes in cardiac output and by alveolar pressure." Although hypoxemia has been shown to influence regional blood How distribution, gravitational forces are not overcome by hypoxemia in the lateral decubitus position, and flow is not directed to the good lung when it is nondependent (up).16 The distribution of ventilation-perfusion ratios by the multiple inert-gas technique has shown, not surprisingly, that the causes for improved gas exchange with change in body position are not clearly defined by clinical findings or laboratory data. Quantitation of the ventilation-perfusion distribution showed no consistent changes in pattern between patients; that is, the changes in gas exchange were not solely attributable to either improvement in the matching of ventilation and perfusion or to a decrease in right-to-Ieft intrapulmonary shunting. All patients had a bimodal ventilation-perfusion 78
,
,,
,,~' 0.1
LO
10
100
1000
o.oot
,," _-
"
001
0.1
1.0
10
100
1000
BLOOD-GAS PARTITION COEFFICIENT
pattern when the "good" side was down. This is in accord with previous observations in patients whose lungs were mechanically ventilated." In two patients the biomodal pattern disappeared when the "good" side was up. In these patients (patients 2 and 3), a broad-based pattern of ventilation-perfusion ratios existed which may be the result of chronic obstructive pulmonary disease in the "good" lung. 29 Nevertheless, the pattern of ventilation-perfusion distribution (that is, bimodal vs broad-based pattern when the "good" side was up) did not relate to the causes responsible for the improvement in gas exchange. The major cause for improved oxygenation was a decrease in right-to-Ieft shunting in patients 1 and 3 and improved ventilation-perfusion matching in patients 2 and 4. In patient 2, the percentage of shunt increased slightly when the "good" side was dependent; however, combined shunt and very low ventilation-perfusion ratio (V/Q) «0.01) decreased from 16.8 percent to 14.9 percent. Changes in cardiac output or dead space did not contribute to the changes in gas exchange. In conclusion, we verified the causes by which improved oxygenation occurs when the "good" side is dependent (down) in patients with unilateral pulmonary disease. Distribution of ventilation-perfusion ratios determined by the multiple inert-gas technique shows variability between patients but indicates that either improved right-to-left shunt or improved ventilation-perfusion matching is predominant. This variUnilateral Pulmonary Disease (GIllespie, Rehder)
ability may result from the nonhomogeneity of pulmonary disease among patients; however, both mechanisms respond the same clinically with oxygenation, improving when the "good" lung is dependent (down). ACKNOWLEDGMENTS: We thank Ms. Ellen A. Graupmann for secretarial assistance and Mrs. Donna M. Meyer, Mrs. Lynn M. Loosbrock, and Mr. Mark W. Wignes for their valuable technical help.
REFERENCES 1 Blair E, Hickam JB. The effect of change in body position on lung volume and intrapulmonary gas mixing in normal subjects. J Clin Invest 1955; 34:383-89 2 Bryan AC, Bentivoglio LG, Beerel It: MacLeish H, Zidulka A, Bates D~ Factors affecting regional distribution of ventilation and perfusion in the lung. J Appl Physioll964; 19:395-402 3 Kaneko x, Mwc-Emw }, Dolovich MB, Dawson A, Bates D~ Regional distribution ofventilation and perfusion asa function of body position. J Appl Physioll966; 21:767-77 4 Katori R, Amorim D deS, Theye RA, Wood EH. Influence of body position on regional pulmonary arterial-venous shunts in intact dogs. J Appl Physioll970; 29:288-96 5 Rehder Ie, Hatch DJ, Sessler AD, Fowler WS. The function of each lung of anesthetized and paralyzed man during mechanical ventilation. Anesthesiology 1972; 37:16-26 6 Rehder K, Sessler AD, Rodarte JR. Regional intrapulmonary gas distribution in awake and anesthetized-paralyzed man. J Appl Physioll977; 42:391-402 7 Piehl MA, Brown RS. Use of extreme position changes in acute respiratory failure. Crit Care Med 1976; 4:13-4 8 Douglas ww, Rehder K, Beynen FM, Sessler AD, Marsh HM. Improved oxygenation in patients with acute respiratory failure: the prone position. Am Rev Respir Dis urn; 115:559-66 9 Prokocimer ~ Garbino J, Wolff M, Regnier B. Influence of posture on gas exchange in artificially ventilated patients with focal lung disease. Intensive Care Med 1983; 9:69-72 10 Zack MB, Pontoppidan H, Kazemi H. The effect of lateral positions on gas exchange in pulmonary disease: a prospective evaluation. Am Rev Respir Dis 1974; 110:49-55 11 Katz JD, Barash PG. Positional hypoxaemia following posttraumatic pulmonary insufficiency. Can Anaesth Soc J 1977;
24:346-52
12 Ibanez J, Raurich JM, Abizanda R, Claramonte R, Ibanez ~ Bergada J. The effect of lateral positions on gas exchange in patients with unilateral lung disease during mechanical ventilation. Intensive Care Med 1981; 7:231-34 13 Remolina C, Khan AU, Santiago ~ Edelman NH. Positional hypoxemia in unilateral lung disease. N Eng) J Med 1981;
304:523-25
14 Davies H, Kitchman R, Gordon I, Helms ~ Regional ventilation in infancy: reversal of adult pattern. N Engl J Med 1985; 313: 1626-28 15 Lillington GA, Fowler WS, Miller RD, Helmholz HF Jr. Nitrogen clearance rates of right and left lungs in different positions. J Clin Invest 1959; 38:2026-34 16 Arborelius M J~ Lundin G, Svanberg L, Defares JG. Influence of unilateral hypoxia on blood Row through the lungs in man in lateral position. J Appl Physioll960; 15:595-97 17 Kanarek DJ, Shannon DC. Adverse effect of positive endexpiratory pressure on pulmonary perfusion and arterial oxygenation. Am Rev Respir Dis 1975; 112:457-59 18 Carlon GC, Kahn R, Howland WS, Baron R, Ramaker J. Acute life-threatening ventilation-perfusion inequality: an indication for independent lung ventilation. Crit Care Moo 1978; 6:380-83 19 Pawner D}, Eross 8, Grenvik A. Dif£erentiallung ventilation with PEEP in the treatment of unilateral pneumonia. Crit Care Med 1977; 5:170-72 20 Carlon GC, Ray C J~ Klein R, Goldiner PL, Miodawnik S. Criteria for selective positive end-expiratory pressure and independent synchronized ventilation of each lung. Chest 1978; 74:501-07 21 Dantzker DR, Bower JS. Mechanisms of gasexchange abnormality in patients with chronic obliterative pulmonary vascular disease. J Coo Invest 1979; 64:1050-55 22 Dantzker DR, Brook CJ, Dehart ~ Lynch J~ Weg JG. Ventilation-perfusion distributions in the adult respiratory distress syndrome. Am Rev Respir Dis 1979; 120:1039-52 23 Dantzker DR, Patten GA, Bower JS. Gas exchange at rest and during exercise in adults with cystic fibrosis. Am Rev Respir Dis 1982; 125:400-05 24 Rehder K, Knopp TJ, Sessler AD, Didier E:e Ventilationperfusion relationship in young healthy awake and anestbetizedparalyzed man. J Appl Physioll979; 47:745-53 25 Wagner PD, Naumann PF, Laravuso RB. Simultaneous measurement of eight foreign gases in blood by gas chromatography. J Appl Physioll974; 36:600-05 26 Evans JW, Wagner PD. Limits on VAlQ distributions from analysis of experimental inert gas elimination. J Appl Physiol 1977; 42:889-98 27 Beck ICC,Rehder K. Regional differences in blood pressure-Row properties of canine lung parenchyma independent of gravity. Fed Proc 1985; 44: 1754 28 Rehder IC, Wenthe FM, Sessler AD. Function of each lung during mechanical ventilation with ZEEP and with PEEP in man anesthetized with thiopental-meperidine. Anesthesiology 1973; 39:597-606 29 Wagner PO, Dantzker DR, Dueck R, Clausen JL, West JB. Ventilation-perfusion inequality in chronic obstructive pulmonary disease. J Clin Invest 1977; 59:203-16
CHEST I 91 I 1 I JANUARY. 1987
71
The effect of positional change (right vs left lateral decubitus) on the distribution of ventilation and perfusion ratios was determined in four patients with respiratory failure and chest roentgenographic 6ndings of unilateral pulmonary disease. In these patients with a unilateral interstitial pattern, improvement in oxygenation which occurred when the "good" side was dependent (down) was associated with changes in the patterns of ventilationperfusion distribution; two patients showed a predominant
decrease in rigbt-to-Ieft intrapulmonary shunt, and two showed an improvement in ventilation-perfusion equality. Therefore, when unilateral interstitial pulmonary disease was present, positional change resulted in changes in rightto-left intrapulmonary shunt or low ventilation-perfusion ratios or both. Variability between patients can be explained by the nonhomogeneity of pulmonary disease in patients with respiratory failure.
~Y position can influence pulmonary volume and
patients with unilateral pulmonary disease in response to changes in body position. In particular; we were interested in the influence of body position on right-toleft intrapulmonary shunting and ventilation-perfusion mismatching.
regional ventilation-perfusion relationships.I" In patients with pulmonary disease, body position can have significant effects on gas exchange."?" In adult patients with unilateral pulmonary disease lying in the lateral decubitus position, gas exchange is improved when the normal lung is dependent (down.)11-13 This pattern may be reversed in infants." Current explanations for this improvement in gas exchange are hypothetical and based on data from studies in animals' and normal man.3.5.6.15.16 In patients with unilateral pulmonary disease who require mechanical ventilation for respiratory failure, attempts have been made to correlate changes in gas exchange with intrapulmonary shunt," respiratory system compliance," pulmonary perfusion," or angiography," but no detailed analysis of gas exchange has been reported. Because various methods of treatment such as differential pulmonary ventilation 18.19 and selective positive end-expiratory pressure (PEEP)51D have been advocated, more information is needed about the ventilation-perfusion relationships during positional change in the patient with unilateral pulmonary disease. The multiple inert-gas elimination technique has been used to characterize changes in pulmonary gas exchange in various diseases21-23 and during anesthesia. If In this study the technique was used to define mechanisms of changes in efficiency of gas exchange in *From the Division of Thoracic Diseases and Internal Medicine and Critical Care Service, and the Departments of Anesthesiology and Physiology and Biophysics, Mayo Clinic and Mayo Foundation, Boehester, Minn. Supported in part by research grants HL-2l584 and HL-00708 from the National Institutes of Health. tRecipient of clinical investigator award HL-00708 from the National Heart, Lung, and Blood Institute. Reprint requem: Dr: Gillespie, Mayo Clinic, Rochester, MN 55905
MATERIALS AND METHODS All studies were conducted in medical or surgical intensive care units. Four patients who required prolonged mechanical ventilation for respiratory failure and showed chest roentgenographic evidence of unilateral pulmonary disease were studied after obtaining informed consent. The study was approved by the institutional review
board.
Table l-ChtJracteriatica rf Patients with Bapiratory Failure Who Required MechtJnktJl Ventilation and Fintlinga on Chat Roentgenogram Casel Age, yr
Diagnosis
1/83 Aspiration, right lung 2/78 Postoperative repair, thoracoabdominal aneurysm 3/76 Postoperative left upper lobectomy, retained secretions 4/68 Postoperative repair, thoracoabdominal aneurysm
Chest MV Roentgenogram Mode*
PEE~
em
Flo.
H.D
Infiltrate, right lung Infiltrate, left lung
IMV8
0.52
0
AlC 8
0.51
3
Infiltrate, left lung
AlC 14
0.50
5
Infiltrate, atelectasis, left lung
IMV8
0.40
3
Mechanical ventilation; IM~ intermittent mandatory ventilation; and AlC, assist control.
*M~
CHEST I 91 I 1 I JANUARY, 1987
75
Table 2-ArteriGl Blood GGa Leve&, Ventilation, and Hemodynamic VariGbles· Case and Position of "Good" Side
Mean Pressure, mm Hg
Umin
VE,
Umin
Pulmonary Arterial
Pulmonary Arterial Wedge
44 44
3.64 3.24
9.41 7.58
27 23
12 12
59 103
49 51
2.84 2.87
5.81 6.46
20 22
13 12
Down
74 131
40 36
3.86 3.00
10.95 10.83
25
30
11 10
Down
64 111
49
48
3.01 2.84
5.93
36
16 13
*Q, Cardiac output; and VE,
minute ventilation.
PaO., mmHG
PaCO s, mmHG
49 61
Down
Case 1
Up Down Case 2 Up
Case 3 Up
Case 4 Up
Q,
Patients were stable when studied. For this study the same settings on the ventilator were used as for the clinical management; that is, no adjustments in minute ventilation, PEE~ or inspired oxygen fraction (Flo.) were made. All patients had a Swan-Gam (J French) pulmonary arterial catheter and radial arterial catheter previously in place for clinical management Each patient was studied in both lateral decubitus positions, with the initial position of the abnormal side alternated between dependent (down) or nondependent (up) and the two sides studied in succession. The study was started by constant intravenous infusion (5.6 mllmin) of six "inert" gases (dissolved in a solution of 5 percent dextrose in water). Samples of arterial and mixed venous blood were obtained after 20 minutes of infusion by simultaneous withdrawal of 5 ml and 15 ml of blood from the pulmonary and radial arteries, respectively. A mixed sample of expired gas was also obtained by collecting expired gas after it bad passed through a 12.7-L heated mixing chamber. The sample of gas was drawn after appropriate delay for the gas to pass through the heating system. In addition, mean expired minute volume was calculated from timed collection of expiredgas. Samples of arterial and mixed venous blood and expired gas were obtained after an additional five minutes of infusion. Between the time that the two sets of samples ofblood and gas were obtained, arterial oxygen (PaO.) and carbon dioxide (PaCO.) ten-
5.74
40
sions were determined (electrodes), with appropriate temperature correction. After the infusion was completed, cardiac output was determined in triplicate by thermal dilution; and right arterial, pulmonary arterial, pulmonary arterial occlusion, and systemic arterial pressures were recorded. The mean of the three measurements of cardiac output is reported. The solubility of the six inert gases was analyzed by gas chromatography by using a modification of the technique described by Wagner et al.15 By using the ratio of arterial and mixed venous partial pressure to represent retention and the ratio of expired gas and mixed venous partial pressure to represent excretion, the method of Evans and WagnerlS was used to determine the continuous distribution of ventilation and perfusion as related to the ventilationperfusion ratio (VAlQ). RESULTS
Four patients with respiratory failure who required mechanical ventilation and had chest roentgenographic findings of a unilateral infiltrate were included in the study (Table 1). All of the patients had a history of smoking. In all patients with an interstitial process, turning the "good" side to the dependent position
Table 3-EJfect cfBodt/ POIrition ora VAlQ Dtatribution Relative to Blood Flow and ventilation· Case and Position of
QslQ,
percent
Mean
VAlQ
In SO
VONT, percent
Mean
PaO/Flo.
VAlQ
lnSD
94 117
32.3 19.4
0.67 0.39
1.12 1.06
37.8 33.5
3.25 3.83
1.13 1.46
116 202
12.6 14.9
0.41 0.41
1.80 1.39
21.4 30.1
2.37 1.95
0.99 0.93
Down
148 262
10.6 2.1
0.48 0.44
1.83 1.89
23.1 22.9
3.41 3.99
1.20 1.23
Down
160 278
0 0
0.24 0.31
1.98 1.44
41.8 44.6
2.13 1.19
1.40 1.41
"Oood" Side
Case 1 Up Down Case 2 Up Down Case 3 Up Case 4 Up
*QslQ, Venous admixture; VAlQ, ventilation/perfusion ratio; 10 SO, 78
Ventilation
Blood Flow
log standard deviation; and VoNT, inert gas dead space. Unilateral Pulmonary Dt8eMe(Gllesple, Rehder)
la
.80
Ib Dead
~~~
.80
AO
AO
,jI~
......t 32.3%
0
Slwnt '''4%
0 2a
1.
2b
.60
DMd
30
Spoce
30.1%
~
0
..J LL
.30
.I~
Shunt 14.• %
0
0 0
..J
CD
0
I
0
0
.60
3a
3b
Z
.60
C(
s ~ C(
.30
.30
0
0
..J ~ Z
4a
4b
O..d
~ .60
apac.
44.'%
.60 .30
0
0
.....
.30
M
0.0%
QOI
QI
1.0
10
100
0
0
0.01
VENTILATION - PERFUSION
01
RATIO
(down) improved oxygenation (Table 2). This improvement in oxygenation was not associated with a significant change in PaCO I • Cardiac output decreased in three of the four patients when the abnormal side was nondependent (up), without significant change in mean pulmonary arterial or mean wedge pressure. Table 3 and Figures 1 and 2 show the ventilationperfusion and retention-excretion data for all patients with the "good" side either dependent (down) or nondependent (up). The improvement in oxygenation noted in patients 1 and 3 was mainly the result of a decrease in right-to-Ieft intrapulmonary shunt. In patient 2, the oxygenation improved despite a small increase in right-to-left shunt by a decrease in very low ventilation-perfusion ratios and an improvement in overall ventilation-perfusion matching. Patient 4 had no measurable right-to-left shunt in either position, but perfusion of areas with low ventilation-perfusion ratios (0.01 to 0.1) decreased when the "good" side was dependent (down). DISCUSSION
The proposed mechanisms which define gas exchange in patients with unilateral pulmonary disease are primarily based on studies of normal lungs involving awake l.3.15 or anesthetized-paralyzed volunteers. 5,6 Most investigators have speculated that the improvement in oxygenation noted when the abnormal lung is
1.0
10
tOO
FIGURE 1. Distribution of ventilation-perfusion ratios for four patients with respiratory failure and unilateral pulmonary disease on chest roentgenogram, with "good" side nondependent (up) (a) or dependent (down) (b).
nondependent (up) is the result of improvement in ventilation-perfusion equality or shunt or both;9-13 however; the specific mechanisms remain unclear. In this study of patients with unilateral pulmonary disease, we verified the underlying causes responsible for improved oxygenation noted when the abnormal lung is up; however; the series is small and may not explain all mechanisms of improved gas exchange in patients with unilateral pulmonary disease. Studies on the influence of body position on gas distribution in normal lungs have shown that differences between the awake and anesthetized-paralyzed state are attributable to changes in the mechanical properties of the respiratory system. Inspiratory gas distribution in awake spontaneously breathing subects lying in the lateral decubitus position is preferential to the dependent (down) lung at volumes above functional residual capacity,5,15 but with anesthesia-paralysis and mechanical ventilation, preferential gas distribution is to the nondependent (up) lung." This is because of the differences in impedance between the two hemithoraces. In the awake state the vertical pleural pressure gradient favors gas distribution to the dependent zone because of higher compliance and larger excursion of the diaphragm. With mechanical ventilation after anesthesia-paralysis, diaphragmatic movement is passive and has greater displacement in the nondependent zone, and the dependent hemiCHEST I 91 I 1 I JANUARY, 1987
77
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thorax is less compliant. 5,6 In this study, patients were mechanically ventilated but did not receive anesthesiaparalysis; therefore, the chest wall and diaphragm would playa major role in gas distribution relative to the difference in impedance between the two hemithoraces. In contrast to gas distribution, blood flow to the lungs is mainly determined by gravitational forces, with the greatest flowto the dependent regions. 3 Blood How may also be inHuenced by nongravity-related factors, but these are still not completely defined. rr Distribution of pulmonary perfusion can be inHuenced by changes in cardiac output and by alveolar pressure." Although hypoxemia has been shown to influence regional blood How distribution, gravitational forces are not overcome by hypoxemia in the lateral decubitus position, and flow is not directed to the good lung when it is nondependent (up).16 The distribution of ventilation-perfusion ratios by the multiple inert-gas technique has shown, not surprisingly, that the causes for improved gas exchange with change in body position are not clearly defined by clinical findings or laboratory data. Quantitation of the ventilation-perfusion distribution showed no consistent changes in pattern between patients; that is, the changes in gas exchange were not solely attributable to either improvement in the matching of ventilation and perfusion or to a decrease in right-to-Ieft intrapulmonary shunting. All patients had a bimodal ventilation-perfusion 78
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pattern when the "good" side was down. This is in accord with previous observations in patients whose lungs were mechanically ventilated." In two patients the biomodal pattern disappeared when the "good" side was up. In these patients (patients 2 and 3), a broad-based pattern of ventilation-perfusion ratios existed which may be the result of chronic obstructive pulmonary disease in the "good" lung. 29 Nevertheless, the pattern of ventilation-perfusion distribution (that is, bimodal vs broad-based pattern when the "good" side was up) did not relate to the causes responsible for the improvement in gas exchange. The major cause for improved oxygenation was a decrease in right-to-Ieft shunting in patients 1 and 3 and improved ventilation-perfusion matching in patients 2 and 4. In patient 2, the percentage of shunt increased slightly when the "good" side was dependent; however, combined shunt and very low ventilation-perfusion ratio (V/Q) «0.01) decreased from 16.8 percent to 14.9 percent. Changes in cardiac output or dead space did not contribute to the changes in gas exchange. In conclusion, we verified the causes by which improved oxygenation occurs when the "good" side is dependent (down) in patients with unilateral pulmonary disease. Distribution of ventilation-perfusion ratios determined by the multiple inert-gas technique shows variability between patients but indicates that either improved right-to-left shunt or improved ventilation-perfusion matching is predominant. This variUnilateral Pulmonary Disease (GIllespie, Rehder)
ability may result from the nonhomogeneity of pulmonary disease among patients; however, both mechanisms respond the same clinically with oxygenation, improving when the "good" lung is dependent (down). ACKNOWLEDGMENTS: We thank Ms. Ellen A. Graupmann for secretarial assistance and Mrs. Donna M. Meyer, Mrs. Lynn M. Loosbrock, and Mr. Mark W. Wignes for their valuable technical help.
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