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Overinflation of pneumatic antishock garments in the elderly
Overinflation of Pneumatic Antishock Garments in the Elderly John A. Savino, MD, Ihsan Jabbour, MD, Nanakram Agarwal, MD, and Dan Byrne, BA, Valhalla, New York
With the increased longevity of the American population, more elderly persons continue to drive motor vehicles b e y o n d the age of 65 years and, consequently, a greater p r o p o r t i o n are involved in motor vehicle accidents. T h e incidence of cardiac risk factors progressively increases with age, t h e r e b y placing elderly persons at greater risk if subjected to blunt t r a u m a [1,2]. T h e p n e u m a t i c antishock g a r m e n t has been utilized in the prehospital setting to t r e a t hypovolemic shock, stabilize fractures, and provide compressive hemostasis. M a n y studies have been performed to d e t e r m i n e the h e m o d y n a m i c effects of the compressive trousers in normovolemic and hypotensive, hypovolemic young volunteers, t r a u m a victims, and animals [2-7]. Since elderly patients have become more i n v o l v e d in vehicular trauma, perhaps the need for utilization of p n e u m a t i c antishock garm e n t s for their resuscitation has increased. Because the literature is devoid of evaluations on older patients, the purpose of this s t u d y is to determine the effects of the p n e u m a t i c antishock garments on their myocardial p e r f o r m a n c e and the optimal level of inflation in order to avoid detrimental hemodynamic effects.
Material and Methods Ten patients (8 men and 2 women) with a mean age of 66.5 4- 6.4 years (mean 4- standard deviation) were admitted to the preoperative hemodynamic assessment unit at the Westchester County Medical Center, Valhalla, N e w York to evaluate cardiac performance prior to major abdominal or thoracic operation. The primary diagnoses requiring operation included lung cancer (three patients), rectal cancer (two patients), and colon cancer (two patients), as well as benign gastrointestinal disease (two patients) and biliary disease (one patient). From the Department of Surgery, New York Medical College, Valhalla, New York. Requests for reprints should be addressed to John A. Savino, MD, New York Medical College, Valhalla, New York 10595.
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All patients had 7 F. flow-directed pulmonary artery and radial artery catheters inserted, and were placed on continuous electrocardiographic and blood pressure monitoring. Cardiac outputs were measured in triplicate by the thermodilution technique using a cardiac output computer (model 9520, Edwards Laboratories, Santa Ana, CA). All measurements were made during relatively stable periods when the patients did not exhibit anxiety or restlessness. Collected data consisted of height, body weight, body temperature, cardiac output, mean peripheral arterial pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, right atrial pressure, percentage of oxygen concentration of inspired air, hemoglobin concentration, and arterial and mixed venous blood gases. The following hemodynamic variables were calculated from standard formulas: body surface area, cardiac index, left ventricular stroke work, right ventricular stroke work, total peripheral resistance, pulmonary vascular resistance, arteriovenous oxygen difference, and oxygen consumption. In order to assess left ventricular function, Sarnoff curves were utilized to plot left ventricular stroke work against pulmonary capillary wedge pressure. The pneumatic antishock garments (supplied by Jobst Institute, Toledo, OH) were placed over the lower extremities initially in an uninflated position. Hemodynamic data were then obtained. The trousers were then inflated to 50 m m Hg for 15 minutes, at which time data were collected. The trousers were deflated for 15 minutes and then inflated to 75 mm Hg for 15 minutes, at which time data were again collected. The measurements of the cardiorespiratory variables were obtained after 15 minutes of inflation in order to allow for equilibration of the physioi logic effects. All data were expressed as the mean 4- standard deviation. Statistical comparisons between data obtained under the various conditions were made using the Student's t test for paired distribution. Differences were considered significant at p >0.05. The protocol was approved by the Committee for Protection o f Human Subjects of the Westchester County Medical Center and New York Med-
The American Journal of Surgery
Pneumatic A n t i s h o c k Garments in the Elderly
TABLE I
Hemodynamlc Data Using Pneumatic Antlshock Garment Compression (mean 4- standard deviation) 0 mm Hg
RAP (mr, Hg) MPAP (mm Hg) PCWP (mm Hg) MAP (mm Hg) CI (liter/min/m 2) LVSW (g/m/m -2) TPR (dyne/s/cm-S/m 2) A.VO2 (ml/dl) VO2 (ml/min/m 2) PVR (dyne/slcm-Slm 2) RVSW (g/m/m -2)
6.1 17.9 11.1 98 3.5 51 2,285 4.75 159 173 6.8
4- 3.1 -I- 3.6 4- 1.6 4- 11.4 4. 0.98 4- 14.7 4- 664 4- 1.3 4- 45 .,L 94 4- 2.3
50 mm Hg 9.4 -4- 2.2 20.3 4- 3.2 14.9 4- 3.1~ 106-I- 16.3 3.4 -;- 0.93 49.1 4- 14.9 2,489 4- 980 4.7 -I- 1.5 153 -4- 37 143 4- 70.2 6.26 4- 2.8
75 mm Hg 11.5 -1- 4t 21.7 -t- 3* 14.4 4- 3.3* 109 4- 11.8 3.45 4- 0.89 52.3 4- 16.9 2,482 4- 846 4.59 4- 1.37 149 4- 40 181 -I- 59.7 5.8 4- 2.7
* p <0.05 when compared with values with trousers uninflated. 1 p <0.01 when compared with values with trousers uninflated. Ave2 = arteriovenous oxygen difference; CI = cardiac index; LVSW = left ventricular stroke work; MAP = mean peripheral arterial pressure; MPAP = mean pulmonary artery pressure; PCWP = pulmonary capillary wedge pressure; PVR = pulmonary vascular resistance; RAP = right atrial pressure; RVSW = right ventricular stroke work; TPR = total peripheral resistance; VO2 = oxygen consumption.
ical College. Before each study, informed consent was obtained from each patient after the procedure was carefully explained. Results
The data accumulated in the uninflated state, after 15 minute compression of the lower extremities at 50 mm Hg, and after 15 minute compression of the lower extremities at 75 mm Hg are summarized in Table I. Prior to inflation of the pneumatic antishock garment, all patients were relatively normotensive, with mean values grossly within normal limits (peripheral arterial blood pressure 98 -F 11.4 mm Hg). After inflation of the pneumatic antishock garment, significant increases in the right atrial pressure (89 percent, p <0.01), pulmonary capillary wedge pressure (34 percent, p <0.01), and mean pulmonary artery pressure (21 percent, p <0.05) were noted (Figure 1). The mean peripheral arterial pressure increased by 11.2 percent, total peripheral resistance by 9 percent, and pulmonary vascular resistance by 5 percent; however, these incremental increases were not statistically significant. There were minimal changes in the cardiac index and left ventricular stroke work, a 14 percent decrease in right ventricular stroke work, and a 6 percent decrease in oxygen consumption. The 10 patients were divided into two groups based on an increase or decrease in left ventricular stroke work. In Group B, the left ventricular stroke work progressively diminished from baseline levels with inflation of the pneumatic antishock garment (Table II). Group A patients demonstrated a 26.5 percent increase in left ventricular stroke work levels (p <0.05), whereas the levels in the Group B patients decreased by 20 percent (p <0.05). Also noted in Group B was an 18 percent decrease in cardiac index (p <0.05) and a 16.4 percent decrease in right ventricular stroke work, with associated Volume 155, April 1988
increases in total peripheral resistance (26 percent, p <0.05) and pulmonary vascular resistance' (18 peri cent) (Figure 2). The patients in Group B demonstrated a 43 percent decrease (p <0.05) in the ratio of left ventricular stroke work to pulmonary capillary wedge pressure at 50 mm Hg compression and a 37 percent decrease in the ratio of left ventricular stroke work to pulmonary capillary wedge pressure at 75 mm Hg compression (p ~0.05) (Figure 3). Comparison of identical parameters in Groups A and B revealed no statistically significant differences. Plots of the left ventricular stroke work and pulmonary capillary wedge pressure ventricular function curves revealed a progressive decrease in ventricular function in these patients with inflation of the pneumatic antishock garment to 50 mm Hg and 75 mm Hg (Figure 4). With the trousers inflated t o 50 mm Hg, all of the Group B patients and one of the Group A patients demonstrated diminished ventricular function. With inflation to 75 mm Hg, 8 of the 10 patients demonstrated diminished ventricular function. All patients returned to baseline hemodynamic levels when the pneumatic antishock garment was returned to the deflated state after 15 minutes of compression at 50 m m Hg and subsequent to 15 minutes compression at 75 mm Hg. Comments The results of this study reflect an 11 percent increase in mean arterial pressure in these relatively normovolemic patients. The total peripheral resistance increased approximately 9 percent. Perhaps this factor of increased afterload contributed to the modest increase in blood pressure. The statistically significant increase in right atrial pressure, mean pulmonary artery pressure, and pulmonary capillary wedge pressure, hemodynamic variables that
573
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reflect augmented preload and pulmonary vasoconstriction, probably did not result from increased intrathoracic pressure produced by external counterpressure on the abdomen since that portion of the pneumatic antishock garment was not utilized. However, the increase in these pressures may reflect increased right and left ventricular pressures secondary to a modest increase in total peripheral resistance and pulmonary vascular resistance or it may be secondary to autotransfusion into the central circulation. Current studies have refuted the concept of autotransfusion of volume into the central circulation. Gaffney et al [8] studied volunteer subjects and demonstrated that pneumatic antishock garment inflation increased blood pressure without an increase in stroke volume or cardiac output. Abraham et al [9] concluded that pneumatic antishock garment inflation increased blood pressure through its effects on peripheral resistance without evidence of an autotransfusion effect in a group of critically ill patients. Skillman et al [10] similarly demonstrated an increase in pulmonary capillary wedge pressure without a significant increase in cardiac output in a group of preoperative patients scheduled to undergo elective abdominal aortic operations. Either by direct mechanical compression or by induction of a general pressor response, inflation of the trousers decreases the diameter of the compressed vessels under the suit, and as consistent with Poiseuille's law, a small decrease in vessel radius leads to a significant decrease in blood flow and a large increase in vessel resistance [11]. More significant in our group of elderly patients was the effect of the pneumatic antishock garment on left ventricular function. Based on an increase or decrease in left ventricular stroke work, the patients were divided into two groups of five. In Group B, an increase in total peripheral resistance and pulmonary vascular resistance was reflected by a decrease in cardiac index, left ventricular stroke work, and right ventricular stroke work (Figure 2). This group of patients demonstrated approximately a 43 percent decrease in the left ventricular stroke work to pulmonary capillary wedge pressure ratio, indicat-
p < O Ol 12
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50 75 P A S G (mmH 9) Figure 1. Note the effects of pneumatic ant/shock garment (PASG) inflation at 50 mm Hg and 75 mm Hg for 15 minutes on right atrial pressure (RAP), mean pulmonary artery pressure ( MPAP), and pulmonary capillary wedge pressure ( PCWP).
TABLE II
0
Hemodynamic Data of the two Groups Based on Left Ventricular Stroke Work ( L V S W ) Using Pneumatic Antlshock Garment Compression (mean -I- standard deviation)
Parameter CI (liter/m/n) LVSW (g/m/m -2) TPR (dynels/cm-S lm 2) RVSW (g/m/m -2) PVR (dyne/s/cm-S/m 2)
Group A 3.23 46.3 2,366.8 7.4 209.8
0 mm H9 Group B
-I- 0.26 3.78 -I- 1.38 4- 6.2 55.8 4- 19.7 4- 282.5 2,203.4 4- 945.9 4- 2 6.1 4- 2.6 4- 80.4 136.2 4- 94.8
Group A 3.60 54.5 2,243 6.4 164.9
50 mm Hg Group B
4- 0.86 3.25 4- 1.06 4- 13.4 44.7 4- 15.9 4- 368.8 2,651.2 4- 1,221.5 4- 2.8 5.7 4- 3 4- 74.2 125.5 4- 69.7
Group A 3.70 58.6 2,181 6.48 201.4
75 mm Hg Group B
4- 0.75 4- 14.9" 4- 352.5 4- 3.04 4- 73.4
3.11 45.9 2,783 5.1 160.2
4- 1.08" 4- 1.78" -I- 1,122.5" 4- 2.4 4- 61.1
* p <0.05 when compared with values with trousers uninflated in respective groups. CI = cardiac index; PVR = pulmonary vascular resistance; RVSW = right ventricular stroke work; TPR = total peripheral resistance.
574
The American Journalof Surgery
Pneumatic Antishock Garments in the Elderly
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Figure 2. Note the effects of pneumatic antlshock garment (PASG) Inflation at 50 mm Hg and 75 mm Hg. Secondary to Increases In total peripheral resistance (TPR) and pulmonary vascular resistance (PVR), the cardiac Index (CI), left ventrlcular stroke work (L VSW), and right ventrlcular stroke work (RVSW) decreased In 5 of the 10 patients (Group B).
ing decreased left ventricular function with inflation of the pneumatic antishock garment. Group A patients demonstrated increased left ventricular stroke work, but more significantly, no significant changes in the left ventricular stroke work to pulmonary capillary wedge pressure ratio. When the effect of the compression was reviewed graphically on Sarnoff ventricular function curves, 8 of the 10 patients demonstrated diminished left ventricular performance when the extremities were compressed for 15 minutes at 75 mm Hg. Left ventricular stroke volume is a function of left ventricular segment length, the relationship being reflected schematically as a ventricular function curve [12]. 1988
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V o l u m e 155, April
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5O 75 PASG (mmHg) Figure 3. Inflation of the pneumatic an#shock garment ( PASG) to 50 mm Hg and 75 mm Ng had no effect on the left ventricular stroke work (LVSW) to pulmonary capillary wedge pressure (PCWP) ratio In five patients (Group A), but caused approximately a 40 percent decrease In the ratio In the other five patients (Group B).
The operating point for the left ventricle in normovolemia is on the flat portion of the curve, and changes in preload have little effect on cardiac output under this circumstance [13]. Thus, an increase in segment length caused by pneumatic antishock garment inflation will have little effect on stroke volume. In fact, the increase in left ventricular afterload associated with the increase in peripheral vascular resistance will cause a decrease in left ventricular function and a resultant decrease in stroke volume and cardiac output. A normal ventricle, however, will respond to an increase in afterload by homeometric autoregulation, the resulting increase in contractility restoring stroke volume to normal [14]. The impressive observation in the patients in the present study was the lack of autoregulation on the part of the ventricle, which revealed poor myocardial muscular reserve. The situation is different in the hypovolemic, hypotensive circumstance because the left ventricle is operating at the steeper portion of the ventricular function curve, and there is also some evidence to indicate impaired coronary perfusion [15]. Inflation of the pneumatic antishock garment can increase stroke volume by increasing both segment length and coronary flow. There will be little change in ventricular afterload to counter the increase in cardiac function since there is minimal change in systemic resistance. Controversially, some studies indicate that the increase in cardiac output results from a sudden increase in preload rather than an
575
Savino et al
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Figure 4. Left ventricular function curves demonstrating decreased function In 6 of 10 patients with 50 mrn Hg inflation of the pneumatic antishock garment and in 8 of 10 patients with 75 turn Hg Inflation. L VSW = left ventricular stroke work; PCWP =
pulmonary capillary wedge pressure,
increase in peripheral resistance, particularly in hypovolemic animals [12]. Inflation of the trousers to 50 mm Hg precipitated decreased left ventricular function in 6 of 10 patients and in 8 of 10 patients, with compression to 75 mm Hg. Review of the data in these relatively normovolemic patients revealed no advantageous effect on any parameter with compression of the lower extremities to 75 mm Hg. Other reports in the literature have confirmed this impression that an optimal blood pressure and cardiac output response can be obtained without recourse to high inflation pressures, presumably because the volume of blood translocated initially by inflation is minimally increased by higher inflation pressures [16-18]. Higher inflation pressures appear to be unnecessary unless tamponade of arterial bleeding is ~he ultimate goal. Certainly, extremity injuries secondary to
576
massive muscle necrosis could potentially be averte d if the lowest pressure combination on the extremities and the abdomen are utilized to produce optimal clinical improvement [19]. In elderly patients, indiscriminate inflation of the trousers to increased pressures could be particularly dangerous, especially when fluid replacement has overly compensated for hypovolemic deficits. We conclude that in patients with poor myocardial reserve, application of the pneumatic antishock garment precipitated decreased left ventricular function. Despite relatively normal cardiac indices after application of the pneumatic antishock garment, the effect on myocardial performance was variable and unpredictably detrimental in the elderly patients with unknown myocardial reserve. There was no significant benefit derived from inflation pressures greater than 50 mm Hg in this group of patients; therefore, the lowest combination of pressures producing the most efficacious results should be used. Summary The hemodynamic effects of pneumatic antishock garment application in high-risk elderly patients were examined in 10 preoperative patients (mean age 66.5 4- 6.4 years) with the pneumatic antishock garments uninflated, after 15 minutes of inflation to 50 mm Hg, and after 15 minutes of inflation to 75 mm Hg. After inflation, significant increases in right atrial pressure (89 percent), pulmonary capillary wedge pressure (34 percent), and mean pulmonary artery pressure (21 percent) were noted. Mean peripheral arterial pressure increased 11.2 percent. Depression of the cardiac index (18 percent), left ventricular stroke work (20 percent), and right ventricuiar stroke work (16.4 percent) with associated increases in total peripheral resistance (26 percent) and pulmonary vascular resistance (18 percent) occurred in 5 of 10 patients. Left ventricular function curves revealed a progressive decrease in ventricular function at 50 mm Hg and 75 mm Hg. We have concluded that the effect of the pneumatic antishock garment on myocardial function is variable and unpredictably dangerous in the elderly patient with diminished myocardial reserve. As no significant benefit was derived from inflation pressures greater than 50 mm Hg in these patients, the lowest combination of pressures producing the most efficacious results should be used. References 1. Savino JA, Del Guercio LRM. Preoperative assessment of high-risk surgical patients. Surg Ciin North Am 1985; 65: 763-91. 2. Kaback KR, Sanders AB, Meislin HW. Mast suit update. JAMA 1984; 252: 2598-603. 3. Ferrario CM, Nadzam G, Fernandez LA. Effects of pneumatic compression on the cardiovascular dynamics in the dog
The American Journal of Surgery
Pneumatic Antishock Garments in the Elderly
after hemorrhage. Aerospace Med 1970; 41:411-5. 4. Shenasky JH, Gillenwater JY. Renal hemodynamic and function effects of external counterpressure. Surg Gynecol Obstet 1972; 134: 253-8. 5. Zippe C, Burchard WK, GannDS. Trendelenberg versus PASG application on moderate hemorrhagic hypoperfusion. J Trauma 1985; 25: 923-31. 6. Holcroft JW, Link FP, Lantz BMT,Green JF, Weber CJ. Venous return and the pneumatic antishock garment in hypovolemic baboons. J Trauma 1984; 240: 928-35. 7. Palafox BA, Johnson MN, McEgen DK, Gazzarga AB. ICP changes following application of the mast suit. J Trauma 1981; 21: 55-62. 8. Gaffney FA, Thai ER, Taylor WF, et al. Hemodynamic effects of medical anti-shock trousers (mast garment). J Trauma 1981; 21: 931-7. 9. Abraham E, Cobo JC, Bland RD, Shoemaker WC. Cardlorespiratory effects of pneumatic trousers in critically ill patients. Arch Surg 1984; 119: 912-5. 10. Skillman JJ, Rajnikant CP, Klick JM. Cardiac performance testing by volume loading and lower-extremity compression. Arch Surg 1982; 117:1009-11. 11. Wangensteen SL, Ludewig RM, Eddy DM, The effect of external counter pressure on the intact circulation. Surg Gynecol
Volume 155, April 1988
Obstet 1968; 127: 253-8. 12. Bellamy RF, Deguzman LR, Pederson DC. Immediate hemodynamic consequences of mast inflation in normo and hypovolemic anesthetiz#d swine. J Trauma 1984; 24: 889-95= 13. Braunwald E, Ross J. Control of ca,rdiac performance. In: Berne RM, ed. Handbook of phySiology. Section 2: the cardiovascular systern, the heart. Bethesda, MD: The American Physiological Society, 1979; 1: 536-7. 14. Sarnoff SJ, Mitchell JH, Gilmore JP. Homeometric autoregulation of the heart. Circ Res 1960; 8: 1077-91. 15. Downey JM. Myocardial contractile force as a function of coronary blood flow. Am J Physiol 1976; 230: 1-6. 16. Roberts VC. External compression and femoral vein flow. Lancet 1971; 1: 136-8. 17. Thirsk RB, Kamm RD, Shapiro AH. Changes in venous blood volume produced by external compression of the lower leg. Med Biol Eng Comput 1980; 18: 650-6. 18. Burchard KW, Slotman GJ, Jed E, Singh AK, Gann DS. Positive pressure respirations and pneumatic antishock garment application: hemodynamic response. J Trauma 1985; 25: 83-9. 19. Godbout B, Burchard KW, Scotman GJ, Gann DS. Crush syndrome with death following pneumatic antishock garment application. J Trauma 1984; 24: 1052-6.
577
With the increased longevity of the American population, more elderly persons continue to drive motor vehicles b e y o n d the age of 65 years and, consequently, a greater p r o p o r t i o n are involved in motor vehicle accidents. T h e incidence of cardiac risk factors progressively increases with age, t h e r e b y placing elderly persons at greater risk if subjected to blunt t r a u m a [1,2]. T h e p n e u m a t i c antishock g a r m e n t has been utilized in the prehospital setting to t r e a t hypovolemic shock, stabilize fractures, and provide compressive hemostasis. M a n y studies have been performed to d e t e r m i n e the h e m o d y n a m i c effects of the compressive trousers in normovolemic and hypotensive, hypovolemic young volunteers, t r a u m a victims, and animals [2-7]. Since elderly patients have become more i n v o l v e d in vehicular trauma, perhaps the need for utilization of p n e u m a t i c antishock garm e n t s for their resuscitation has increased. Because the literature is devoid of evaluations on older patients, the purpose of this s t u d y is to determine the effects of the p n e u m a t i c antishock garments on their myocardial p e r f o r m a n c e and the optimal level of inflation in order to avoid detrimental hemodynamic effects.
Material and Methods Ten patients (8 men and 2 women) with a mean age of 66.5 4- 6.4 years (mean 4- standard deviation) were admitted to the preoperative hemodynamic assessment unit at the Westchester County Medical Center, Valhalla, N e w York to evaluate cardiac performance prior to major abdominal or thoracic operation. The primary diagnoses requiring operation included lung cancer (three patients), rectal cancer (two patients), and colon cancer (two patients), as well as benign gastrointestinal disease (two patients) and biliary disease (one patient). From the Department of Surgery, New York Medical College, Valhalla, New York. Requests for reprints should be addressed to John A. Savino, MD, New York Medical College, Valhalla, New York 10595.
572
All patients had 7 F. flow-directed pulmonary artery and radial artery catheters inserted, and were placed on continuous electrocardiographic and blood pressure monitoring. Cardiac outputs were measured in triplicate by the thermodilution technique using a cardiac output computer (model 9520, Edwards Laboratories, Santa Ana, CA). All measurements were made during relatively stable periods when the patients did not exhibit anxiety or restlessness. Collected data consisted of height, body weight, body temperature, cardiac output, mean peripheral arterial pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, right atrial pressure, percentage of oxygen concentration of inspired air, hemoglobin concentration, and arterial and mixed venous blood gases. The following hemodynamic variables were calculated from standard formulas: body surface area, cardiac index, left ventricular stroke work, right ventricular stroke work, total peripheral resistance, pulmonary vascular resistance, arteriovenous oxygen difference, and oxygen consumption. In order to assess left ventricular function, Sarnoff curves were utilized to plot left ventricular stroke work against pulmonary capillary wedge pressure. The pneumatic antishock garments (supplied by Jobst Institute, Toledo, OH) were placed over the lower extremities initially in an uninflated position. Hemodynamic data were then obtained. The trousers were then inflated to 50 m m Hg for 15 minutes, at which time data were collected. The trousers were deflated for 15 minutes and then inflated to 75 mm Hg for 15 minutes, at which time data were again collected. The measurements of the cardiorespiratory variables were obtained after 15 minutes of inflation in order to allow for equilibration of the physioi logic effects. All data were expressed as the mean 4- standard deviation. Statistical comparisons between data obtained under the various conditions were made using the Student's t test for paired distribution. Differences were considered significant at p >0.05. The protocol was approved by the Committee for Protection o f Human Subjects of the Westchester County Medical Center and New York Med-
The American Journal of Surgery
Pneumatic A n t i s h o c k Garments in the Elderly
TABLE I
Hemodynamlc Data Using Pneumatic Antlshock Garment Compression (mean 4- standard deviation) 0 mm Hg
RAP (mr, Hg) MPAP (mm Hg) PCWP (mm Hg) MAP (mm Hg) CI (liter/min/m 2) LVSW (g/m/m -2) TPR (dyne/s/cm-S/m 2) A.VO2 (ml/dl) VO2 (ml/min/m 2) PVR (dyne/slcm-Slm 2) RVSW (g/m/m -2)
6.1 17.9 11.1 98 3.5 51 2,285 4.75 159 173 6.8
4- 3.1 -I- 3.6 4- 1.6 4- 11.4 4. 0.98 4- 14.7 4- 664 4- 1.3 4- 45 .,L 94 4- 2.3
50 mm Hg 9.4 -4- 2.2 20.3 4- 3.2 14.9 4- 3.1~ 106-I- 16.3 3.4 -;- 0.93 49.1 4- 14.9 2,489 4- 980 4.7 -I- 1.5 153 -4- 37 143 4- 70.2 6.26 4- 2.8
75 mm Hg 11.5 -1- 4t 21.7 -t- 3* 14.4 4- 3.3* 109 4- 11.8 3.45 4- 0.89 52.3 4- 16.9 2,482 4- 846 4.59 4- 1.37 149 4- 40 181 -I- 59.7 5.8 4- 2.7
* p <0.05 when compared with values with trousers uninflated. 1 p <0.01 when compared with values with trousers uninflated. Ave2 = arteriovenous oxygen difference; CI = cardiac index; LVSW = left ventricular stroke work; MAP = mean peripheral arterial pressure; MPAP = mean pulmonary artery pressure; PCWP = pulmonary capillary wedge pressure; PVR = pulmonary vascular resistance; RAP = right atrial pressure; RVSW = right ventricular stroke work; TPR = total peripheral resistance; VO2 = oxygen consumption.
ical College. Before each study, informed consent was obtained from each patient after the procedure was carefully explained. Results
The data accumulated in the uninflated state, after 15 minute compression of the lower extremities at 50 mm Hg, and after 15 minute compression of the lower extremities at 75 mm Hg are summarized in Table I. Prior to inflation of the pneumatic antishock garment, all patients were relatively normotensive, with mean values grossly within normal limits (peripheral arterial blood pressure 98 -F 11.4 mm Hg). After inflation of the pneumatic antishock garment, significant increases in the right atrial pressure (89 percent, p <0.01), pulmonary capillary wedge pressure (34 percent, p <0.01), and mean pulmonary artery pressure (21 percent, p <0.05) were noted (Figure 1). The mean peripheral arterial pressure increased by 11.2 percent, total peripheral resistance by 9 percent, and pulmonary vascular resistance by 5 percent; however, these incremental increases were not statistically significant. There were minimal changes in the cardiac index and left ventricular stroke work, a 14 percent decrease in right ventricular stroke work, and a 6 percent decrease in oxygen consumption. The 10 patients were divided into two groups based on an increase or decrease in left ventricular stroke work. In Group B, the left ventricular stroke work progressively diminished from baseline levels with inflation of the pneumatic antishock garment (Table II). Group A patients demonstrated a 26.5 percent increase in left ventricular stroke work levels (p <0.05), whereas the levels in the Group B patients decreased by 20 percent (p <0.05). Also noted in Group B was an 18 percent decrease in cardiac index (p <0.05) and a 16.4 percent decrease in right ventricular stroke work, with associated Volume 155, April 1988
increases in total peripheral resistance (26 percent, p <0.05) and pulmonary vascular resistance' (18 peri cent) (Figure 2). The patients in Group B demonstrated a 43 percent decrease (p <0.05) in the ratio of left ventricular stroke work to pulmonary capillary wedge pressure at 50 mm Hg compression and a 37 percent decrease in the ratio of left ventricular stroke work to pulmonary capillary wedge pressure at 75 mm Hg compression (p ~0.05) (Figure 3). Comparison of identical parameters in Groups A and B revealed no statistically significant differences. Plots of the left ventricular stroke work and pulmonary capillary wedge pressure ventricular function curves revealed a progressive decrease in ventricular function in these patients with inflation of the pneumatic antishock garment to 50 mm Hg and 75 mm Hg (Figure 4). With the trousers inflated t o 50 mm Hg, all of the Group B patients and one of the Group A patients demonstrated diminished ventricular function. With inflation to 75 mm Hg, 8 of the 10 patients demonstrated diminished ventricular function. All patients returned to baseline hemodynamic levels when the pneumatic antishock garment was returned to the deflated state after 15 minutes of compression at 50 m m Hg and subsequent to 15 minutes compression at 75 mm Hg. Comments The results of this study reflect an 11 percent increase in mean arterial pressure in these relatively normovolemic patients. The total peripheral resistance increased approximately 9 percent. Perhaps this factor of increased afterload contributed to the modest increase in blood pressure. The statistically significant increase in right atrial pressure, mean pulmonary artery pressure, and pulmonary capillary wedge pressure, hemodynamic variables that
573
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Say/no et al
16
reflect augmented preload and pulmonary vasoconstriction, probably did not result from increased intrathoracic pressure produced by external counterpressure on the abdomen since that portion of the pneumatic antishock garment was not utilized. However, the increase in these pressures may reflect increased right and left ventricular pressures secondary to a modest increase in total peripheral resistance and pulmonary vascular resistance or it may be secondary to autotransfusion into the central circulation. Current studies have refuted the concept of autotransfusion of volume into the central circulation. Gaffney et al [8] studied volunteer subjects and demonstrated that pneumatic antishock garment inflation increased blood pressure without an increase in stroke volume or cardiac output. Abraham et al [9] concluded that pneumatic antishock garment inflation increased blood pressure through its effects on peripheral resistance without evidence of an autotransfusion effect in a group of critically ill patients. Skillman et al [10] similarly demonstrated an increase in pulmonary capillary wedge pressure without a significant increase in cardiac output in a group of preoperative patients scheduled to undergo elective abdominal aortic operations. Either by direct mechanical compression or by induction of a general pressor response, inflation of the trousers decreases the diameter of the compressed vessels under the suit, and as consistent with Poiseuille's law, a small decrease in vessel radius leads to a significant decrease in blood flow and a large increase in vessel resistance [11]. More significant in our group of elderly patients was the effect of the pneumatic antishock garment on left ventricular function. Based on an increase or decrease in left ventricular stroke work, the patients were divided into two groups of five. In Group B, an increase in total peripheral resistance and pulmonary vascular resistance was reflected by a decrease in cardiac index, left ventricular stroke work, and right ventricular stroke work (Figure 2). This group of patients demonstrated approximately a 43 percent decrease in the left ventricular stroke work to pulmonary capillary wedge pressure ratio, indicat-
p < O Ol 12
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50 75 P A S G (mmH 9) Figure 1. Note the effects of pneumatic ant/shock garment (PASG) inflation at 50 mm Hg and 75 mm Hg for 15 minutes on right atrial pressure (RAP), mean pulmonary artery pressure ( MPAP), and pulmonary capillary wedge pressure ( PCWP).
TABLE II
0
Hemodynamic Data of the two Groups Based on Left Ventricular Stroke Work ( L V S W ) Using Pneumatic Antlshock Garment Compression (mean -I- standard deviation)
Parameter CI (liter/m/n) LVSW (g/m/m -2) TPR (dynels/cm-S lm 2) RVSW (g/m/m -2) PVR (dyne/s/cm-S/m 2)
Group A 3.23 46.3 2,366.8 7.4 209.8
0 mm H9 Group B
-I- 0.26 3.78 -I- 1.38 4- 6.2 55.8 4- 19.7 4- 282.5 2,203.4 4- 945.9 4- 2 6.1 4- 2.6 4- 80.4 136.2 4- 94.8
Group A 3.60 54.5 2,243 6.4 164.9
50 mm Hg Group B
4- 0.86 3.25 4- 1.06 4- 13.4 44.7 4- 15.9 4- 368.8 2,651.2 4- 1,221.5 4- 2.8 5.7 4- 3 4- 74.2 125.5 4- 69.7
Group A 3.70 58.6 2,181 6.48 201.4
75 mm Hg Group B
4- 0.75 4- 14.9" 4- 352.5 4- 3.04 4- 73.4
3.11 45.9 2,783 5.1 160.2
4- 1.08" 4- 1.78" -I- 1,122.5" 4- 2.4 4- 61.1
* p <0.05 when compared with values with trousers uninflated in respective groups. CI = cardiac index; PVR = pulmonary vascular resistance; RVSW = right ventricular stroke work; TPR = total peripheral resistance.
574
The American Journalof Surgery
Pneumatic Antishock Garments in the Elderly
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Figure 2. Note the effects of pneumatic antlshock garment (PASG) Inflation at 50 mm Hg and 75 mm Hg. Secondary to Increases In total peripheral resistance (TPR) and pulmonary vascular resistance (PVR), the cardiac Index (CI), left ventrlcular stroke work (L VSW), and right ventrlcular stroke work (RVSW) decreased In 5 of the 10 patients (Group B).
ing decreased left ventricular function with inflation of the pneumatic antishock garment. Group A patients demonstrated increased left ventricular stroke work, but more significantly, no significant changes in the left ventricular stroke work to pulmonary capillary wedge pressure ratio. When the effect of the compression was reviewed graphically on Sarnoff ventricular function curves, 8 of the 10 patients demonstrated diminished left ventricular performance when the extremities were compressed for 15 minutes at 75 mm Hg. Left ventricular stroke volume is a function of left ventricular segment length, the relationship being reflected schematically as a ventricular function curve [12]. 1988
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V o l u m e 155, April
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5O 75 PASG (mmHg) Figure 3. Inflation of the pneumatic an#shock garment ( PASG) to 50 mm Hg and 75 mm Ng had no effect on the left ventricular stroke work (LVSW) to pulmonary capillary wedge pressure (PCWP) ratio In five patients (Group A), but caused approximately a 40 percent decrease In the ratio In the other five patients (Group B).
The operating point for the left ventricle in normovolemia is on the flat portion of the curve, and changes in preload have little effect on cardiac output under this circumstance [13]. Thus, an increase in segment length caused by pneumatic antishock garment inflation will have little effect on stroke volume. In fact, the increase in left ventricular afterload associated with the increase in peripheral vascular resistance will cause a decrease in left ventricular function and a resultant decrease in stroke volume and cardiac output. A normal ventricle, however, will respond to an increase in afterload by homeometric autoregulation, the resulting increase in contractility restoring stroke volume to normal [14]. The impressive observation in the patients in the present study was the lack of autoregulation on the part of the ventricle, which revealed poor myocardial muscular reserve. The situation is different in the hypovolemic, hypotensive circumstance because the left ventricle is operating at the steeper portion of the ventricular function curve, and there is also some evidence to indicate impaired coronary perfusion [15]. Inflation of the pneumatic antishock garment can increase stroke volume by increasing both segment length and coronary flow. There will be little change in ventricular afterload to counter the increase in cardiac function since there is minimal change in systemic resistance. Controversially, some studies indicate that the increase in cardiac output results from a sudden increase in preload rather than an
575
Savino et al
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Figure 4. Left ventricular function curves demonstrating decreased function In 6 of 10 patients with 50 mrn Hg inflation of the pneumatic antishock garment and in 8 of 10 patients with 75 turn Hg Inflation. L VSW = left ventricular stroke work; PCWP =
pulmonary capillary wedge pressure,
increase in peripheral resistance, particularly in hypovolemic animals [12]. Inflation of the trousers to 50 mm Hg precipitated decreased left ventricular function in 6 of 10 patients and in 8 of 10 patients, with compression to 75 mm Hg. Review of the data in these relatively normovolemic patients revealed no advantageous effect on any parameter with compression of the lower extremities to 75 mm Hg. Other reports in the literature have confirmed this impression that an optimal blood pressure and cardiac output response can be obtained without recourse to high inflation pressures, presumably because the volume of blood translocated initially by inflation is minimally increased by higher inflation pressures [16-18]. Higher inflation pressures appear to be unnecessary unless tamponade of arterial bleeding is ~he ultimate goal. Certainly, extremity injuries secondary to
576
massive muscle necrosis could potentially be averte d if the lowest pressure combination on the extremities and the abdomen are utilized to produce optimal clinical improvement [19]. In elderly patients, indiscriminate inflation of the trousers to increased pressures could be particularly dangerous, especially when fluid replacement has overly compensated for hypovolemic deficits. We conclude that in patients with poor myocardial reserve, application of the pneumatic antishock garment precipitated decreased left ventricular function. Despite relatively normal cardiac indices after application of the pneumatic antishock garment, the effect on myocardial performance was variable and unpredictably detrimental in the elderly patients with unknown myocardial reserve. There was no significant benefit derived from inflation pressures greater than 50 mm Hg in this group of patients; therefore, the lowest combination of pressures producing the most efficacious results should be used. Summary The hemodynamic effects of pneumatic antishock garment application in high-risk elderly patients were examined in 10 preoperative patients (mean age 66.5 4- 6.4 years) with the pneumatic antishock garments uninflated, after 15 minutes of inflation to 50 mm Hg, and after 15 minutes of inflation to 75 mm Hg. After inflation, significant increases in right atrial pressure (89 percent), pulmonary capillary wedge pressure (34 percent), and mean pulmonary artery pressure (21 percent) were noted. Mean peripheral arterial pressure increased 11.2 percent. Depression of the cardiac index (18 percent), left ventricular stroke work (20 percent), and right ventricuiar stroke work (16.4 percent) with associated increases in total peripheral resistance (26 percent) and pulmonary vascular resistance (18 percent) occurred in 5 of 10 patients. Left ventricular function curves revealed a progressive decrease in ventricular function at 50 mm Hg and 75 mm Hg. We have concluded that the effect of the pneumatic antishock garment on myocardial function is variable and unpredictably dangerous in the elderly patient with diminished myocardial reserve. As no significant benefit was derived from inflation pressures greater than 50 mm Hg in these patients, the lowest combination of pressures producing the most efficacious results should be used. References 1. Savino JA, Del Guercio LRM. Preoperative assessment of high-risk surgical patients. Surg Ciin North Am 1985; 65: 763-91. 2. Kaback KR, Sanders AB, Meislin HW. Mast suit update. JAMA 1984; 252: 2598-603. 3. Ferrario CM, Nadzam G, Fernandez LA. Effects of pneumatic compression on the cardiovascular dynamics in the dog
The American Journal of Surgery
Pneumatic Antishock Garments in the Elderly
after hemorrhage. Aerospace Med 1970; 41:411-5. 4. Shenasky JH, Gillenwater JY. Renal hemodynamic and function effects of external counterpressure. Surg Gynecol Obstet 1972; 134: 253-8. 5. Zippe C, Burchard WK, GannDS. Trendelenberg versus PASG application on moderate hemorrhagic hypoperfusion. J Trauma 1985; 25: 923-31. 6. Holcroft JW, Link FP, Lantz BMT,Green JF, Weber CJ. Venous return and the pneumatic antishock garment in hypovolemic baboons. J Trauma 1984; 240: 928-35. 7. Palafox BA, Johnson MN, McEgen DK, Gazzarga AB. ICP changes following application of the mast suit. J Trauma 1981; 21: 55-62. 8. Gaffney FA, Thai ER, Taylor WF, et al. Hemodynamic effects of medical anti-shock trousers (mast garment). J Trauma 1981; 21: 931-7. 9. Abraham E, Cobo JC, Bland RD, Shoemaker WC. Cardlorespiratory effects of pneumatic trousers in critically ill patients. Arch Surg 1984; 119: 912-5. 10. Skillman JJ, Rajnikant CP, Klick JM. Cardiac performance testing by volume loading and lower-extremity compression. Arch Surg 1982; 117:1009-11. 11. Wangensteen SL, Ludewig RM, Eddy DM, The effect of external counter pressure on the intact circulation. Surg Gynecol
Volume 155, April 1988
Obstet 1968; 127: 253-8. 12. Bellamy RF, Deguzman LR, Pederson DC. Immediate hemodynamic consequences of mast inflation in normo and hypovolemic anesthetiz#d swine. J Trauma 1984; 24: 889-95= 13. Braunwald E, Ross J. Control of ca,rdiac performance. In: Berne RM, ed. Handbook of phySiology. Section 2: the cardiovascular systern, the heart. Bethesda, MD: The American Physiological Society, 1979; 1: 536-7. 14. Sarnoff SJ, Mitchell JH, Gilmore JP. Homeometric autoregulation of the heart. Circ Res 1960; 8: 1077-91. 15. Downey JM. Myocardial contractile force as a function of coronary blood flow. Am J Physiol 1976; 230: 1-6. 16. Roberts VC. External compression and femoral vein flow. Lancet 1971; 1: 136-8. 17. Thirsk RB, Kamm RD, Shapiro AH. Changes in venous blood volume produced by external compression of the lower leg. Med Biol Eng Comput 1980; 18: 650-6. 18. Burchard KW, Slotman GJ, Jed E, Singh AK, Gann DS. Positive pressure respirations and pneumatic antishock garment application: hemodynamic response. J Trauma 1985; 25: 83-9. 19. Godbout B, Burchard KW, Scotman GJ, Gann DS. Crush syndrome with death following pneumatic antishock garment application. J Trauma 1984; 24: 1052-6.
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