Calculated Preoperative Mean Left

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1 Calculated Preoperative Mean Left Atrial Pressure as a Guide to Volume Load at the Termination of Aortocoronary Bypass Operation Daniel A. Goor, M.D., Rephael Mohr, M.D., Jacob Lavee, M.D., and Aram Smolinsky, M.D. ABSTRACT The routine use of an arbitrary fixed left atrial (LA) pressure during volume load after aortocoronary bypass operation was compared with use of an individualized postoperative target LA pressure according to a calculated preoperative LA pressure in two groups of consecutive patients. The preoperative LA pressure of each patient was calculated from the preoperative left ventricular enddiastolic pressure (LVEDP) by the formula: mean LA pressure = 1.16 x LVEDP Left atrial pressure, mean arterial pressure, mean right atrial pressure, and cardiac output were measured simultaneously on arrival at the intensive care unit and 60 minutes later. Cardiac index (CI) and systemic vascular resistance (SVR) were calculated from the variables already mentioned. Results indicated a significantly higher CI and significantly lower SVR in patients in whom volume load was aimed at the calculated preoperative LA pressure. It was concluded that the optimal postoperative LA pressure is specific for each patient and depends on the preoperative LVEDP. The ideal mean left atrial (LA) pressure during volume load at the termination of an open-heart operation is still controversial and, therefore, confusing, especially in coronary bypass procedures [l-lo]. Some authors routinely use a mean LA pressure ranging from 7 to 15 mm Hg (namely, low LA pressures) [I, 2, 6, 91, while others routinely use a mean LA pressure ranging from 15 to 25 mm Hg (namely, high LA pressures) [3-5, 7, 8, lo]. No reference could be found in the English-language literature regarding an attempt to individualize and match the From the Department of Cardiac Surgery, Chaim Sheba Medical Center, Tel Hashomer, and the Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel. Accepted for publication Apr 30, Address reprint requests to Dr. Goor, Department of Cardiac Surgery, Chaim Sheba Medical Center, Tel Hashomer 52621, Israel. mean LA pressure to the specific demand of each patient. In the present study, it was observed that the optimal mean LA pressure can be calculated for each patient undergoing a coronary operation from the preoperative left ventricular end-diastolic pressure (LVEDP). Material and Methods For the evaluation of optimal LA pressure, two methods of volume replacement during the early period following cardiopulmonary bypass were compared in 30 consecutive patients who underwent aortocoronary bypass grafting in the early part of In 14 patients (Group l), replacement of volume was aimed at arriving at a mean LA pressure of 7 to 15 mm Hg. Volume load was withheld when mean arterial pressure reached 90 to 100 mm Hg. In the remaining 16 patients (Group 2), volume load was aimed at reaching the calculated preoperative mean LA pressure. Calculation of the preoperative mean LA pressure is based on the patient s LVEDP noted during heart catheterization. When the LVEDP is less than 15 mm Hg (normal LVEDP), the mean LA pressure is considered equal to the LVEDP [ll-191. If the LVEDP is equal to or greater than 15 mm Hg (left ventricular dysfunction), the mean LA pressure is calculated using the formulas of Falicov and Resnekov [20] as follows: LVEDP = 0.88 x PAEDP PAWMP = 1.02 x PAEDP where PAEDP = pulmonary artery end-diastolic pressure and PAWMP = pulmonary arterial wedge mean pressure (all values expressed in mm Hg). In the absence of mitral or pulmonary vascular block, the mean LA pressure is equal to the PAWMP (14, 15, 21, 221 and is expressed as a function of LVEDP by: Mean LA pressure = 1.16 x LVEDP

2 381 Goor et al: Calculated Preoperative Mean Left Atrial Pressure Table 1. Data for the Two Patient Groupsa Variable Group 1 Group 2 A (N = 5) B(N = 9) A (N = 9) B(N = 7) Mean age (yr) 48.2 (40-56) 55.8 (39-65) 51.7 (38-65) 54.1 (36-60) Medwomen Type of angina Unstable 5 (100%) 9 (100%) 7 (77.8%) 4 (57.1%) Stable (22.2%) 3 (42.9%) Previous MI 2 (40%) 6 (66.7%) 5 (55.6%) 4 (57.1%) Hypertension 3 (60%) 7 (77.8%) 5 (55.6%) 6 (85.7%) Preop LV functionb Good (EF 50%) 4 (80%) 6 (66.7%) 7 (77.8%) 6 (85.7%) Fair (EF 35-50%) 1(20%) 3 (33.3%) 2 (22.2%) 0 Poor (EF 30-35%) (14.3%) LVEDP (mm Hg) 11.2 (10-12) 20.8 (15-30) 10.2 (8-13) 19.1 (15-30) Left main lesion (>50%) 1(20%) 3 (33.3%) 1 (11.1%) 0 Grafts per patient Bypass time (min) 104 (89-120) (79-155) 91.9 (39-128) (92-126) Aortic cross-clamp time (min) 47 (35-63) 42.2 (29-60) 36.1 (12-53) 43.6 (28-60) awhen numbers in parentheses are shown without percent sign, they represent a range; with the percent sign, they indicate gercentage of patients. Good = no impairment of contractibility on cardiac catheterization; Fair = impairment of Contractibility of one or two surfaces of the ventricle; Poor = poor global left ventricular dysfunction. MI = myocardial infarction; LV = left ventricular; EF = ejection fraction; LVEDP = left ventricular end-diastolic pressure. The two major groups were further subdivided according to the preoperative LVEDP. Subgroups 1A and 2A included patients with an LVEDP of less than 15 mm Hg, and subgroups 1B and 2B included patients with an LVEDP equal to or greater than 15 mm Hg. All patients were similar with regard to age, type of preoperative angina, number of preoperative infarctions, hypertension, number of grafts, bypass time, and duration of aortic cross-clamping. The pertinent clinical, catheterization, and operative data of both groups are summarized in Table 1. Conventional techniques of heart-lung bypass were used, including moderate hypothermia (26" to 28"C)* and clear fluid prime. Saphenous vein grafts were used for bypass in all instances. All anastomoses were performed on cardiopulmonary bypass, with those distal per- *We currently use deep hypothermia for all patients undergoing coronary operation [=]. formed first. During distal anastomoses, the aorta was single cross-clamped, the heart was cooled with a hyperkalemic cardioplegic solution, and venting was done through the pulmonary vein of the right upper lobe. No patient in either group required catecholamine support. In 2 patients from Group 1B and 1 from Group 2A, afterload reduction with nitroprusside was used during the study period. Mean LA pressure, mean arterial pressure, mean right atrial pressure, and cardiac output were measured simultaneously on the patient's arrival at the intensive care unit (ICU) (time zero) and 60 minutes later. Mean LA pressure was measured using a vinyl catheter placed in the left atrium; the midaxillary line was used as the zero reference point for the mean LA pressure and the mean arterial pressure. Cardiac output was measured by thermodilution with the cardiac output computer 601 by Instrument Laboratory. Systemic vascular resistance (SVR) was cal-

3 382 The Annals of Thoracic Surgery Vol 35 No 4 April 1983 Table 2. Calculated and Measured Mean Left Atrial Pressure Measured Mean Pressure Significance Calculated Preop Mean Pressure 0 Time in ICU 60 Minutes in ICU Preop vs Preop vs Group (mmhg) (mm Hg) (mm Hg) 0 Time in ICU 60 Minutes in ICU 1A 11.2 f f * 1.2 p < p < B 15.6 f p < p < A 10.2 f f 2.8 NS NS f f f 2.7 NS NS ICU = intensive care unit; 0 Time in ICU = measurements taken on arrival at ICU; 60 Minutes in 1CU = measurements taken 60 minutes after arrival at ICU; NS = not significant. Table 3. Postoperative Cardiac lndex and Systemic Vascular Resistance Time of Group 1 Group 2 Significance Measurement (min postop) A B A B 1A vs 2A 1B vs 28 CARDIAC INDEX^ 0 Time in ICU 1.86 f f * 0.36 p < 0.05 p < Minutes in ICU 1.75 f f ? p < 0.01 p < 0.02 SYSTEMIC VASCULAR RESISTANCE 0 Time in ICU 2,188 f 306 2,351 f 444 1, ,667? 339 p < 0.05 p < Minutes in ICU 2, ,327 f 494 1,636 f 337 1, p < 0.01 p < 0.02 The p value of 1A versus 1B and 2A versus 28 was not significant for measurements taken on arrival at ICU (0 Time in ICU) or 60 minutes after arrival at ICU (60 Minutes in ICU) for either cardiac index or systemic vascular resistance. bmeasured in liters per minute per square meter of body surface area. Measured in dynes per second per ent ti meter-^. ICU = intensive care unit. culated by the first of the following formulas and cardiac index (CI) by the second: SVR = 80(MAP - MRAP)/CO CI = CO/BSA where MAP = mean arterial pressure, MRAP = mean right atrial pressure, CO = cardiac output, and BSA = body surface area. All results were compared by the Student t test (nonpaired, two-tailed). Results Postoperative mean LA pressure on arrival at the ICU and 60 minutes later was significantly lower than the calculated preoperative mean LA pressure in all patients in Group 1. It equaled the calculated preoperative mean LA pressure in all patients in Group 2 (Table 2). Postoperative CI was significantly higher in patients in Group 2 than those in Group 1 (Table 3). Thus, in patients with left ventricular dys- function who were managed by a fixed target mean LA pressure (Group lb), the CI on arrival at the ICU and 60 minutes later was 1.86? 0.33 and 1.89 k 0.34 L/min/m2, respectively, compared with 2.33 & 0.36 and L/min/ m2, respectively, in similar patients who were managed according to the individual preoperative calculated mean LA pressure (Group 2B). Systemic vascular resistance was significantly lower in Group 2 patients than in Group 1 patients (e.g., 2,351? 444 and 1,667? 339 dynes sec cm- in Groups 1B and 2B, respectively, on arrival at the ICU (see Table 3). No significant difference in CI and SVR was found between patients in subgroups A and B in either of the two study groups. There were no surgical deaths or perioperative infarctions in either group. Comment It is common knowledge that hypertrophic cardiac chambers require high filling pressures.

4 383 Goor et al: Calculated Preoperative Mean Left Atrial Pressure Therefore, patients who have valvular disease that results in left ventricular hypertrophy are commonly treated with high LA pressures. Patients undergoing a coronary artery operation, however, are not considered under this rule. Despite the fact they they show LVEDPs ranging from 10 to 35 mm Hg at heart catheterization, they are usually treated according to the individual preferences of the surgeon rather than their individual needs. Perusal of the literature on optimal LA pressure at the termination of coronary bypass operation reveals confusing figures. On one hand, there are those who prefer LA pressures in the range of 7 to 15 mm Hg, namely, low LA pressures [I, 2,6,9]; on the other hand, some prefer values of 15 to 25 mm Hg, namely, high LA pressures [3-5, 7, 8, 101. The common denominator of these two approaches is the surgeon s preference for a target mean LA pressure. The present study shows that the target mean LA pressure should not be a fixed value, but rather should depend on the individual features of the patient s left ventricular hemodynamics. Thus, there is a place for low and high LA pressures, depending on the patient s preoperative LVEDPs. It is shown here that the CI in patients whose postoperative volume load was aimed at the preoperative calculated mean LA pressure (Group 2) was significantly higher than in the group whose volume load was aimed at a fixed target mean LA pressure (Group 1). One of the limitations of this study is that the preoperative calculated mean LA pressure was compared with that lower than the calculated mean LA pressure. In our past experience, a mean LA pressure higher than the preoperative calculated mean LA pressure seemed risky; therefore, during this study no attempts were made to surpass the calculated mean LA pressure. In fact, our cautious approach to high LA pressures was recently supported by the report of Ellis and associates (21 showing that an overly high postoperative LA pressure has a deleterious effect on cardiac output. Starling s law of the heart states that the work of the ventricle is a function of diastolic fiber length, which, in turn, is determined largely by the effective filling pressure [24]. Based on Starling s law and on the work of Sarnoff and Berg- lund [18], it is evident that each heart has a certain filling pressure at which its function curve reaches the optimum. Filling pressures below this value cause markedly decreased stroke work [ 181. Excessive filling pressures reduce stroke work [18, 241, especially in ischemic hearts in which an increase in LVEDP may result in increased myocardial oxygen demand and decreased subendocardial perfusion [25, 261. Moreover, it has been shown [27, 281 that patients with coronary artery disease fall into a wide range of functional categories, not necessarily correlated with their anatomical patterns. Thus, some patients with severe coronary artery disease show left ventricular function curves that are entirely normal, while others with similar anatomical disease show abnormal left ventricular function curves, as evidenced by the high left ventricular filling pressure. Therefore, an arbitrarily fixed optimal filling pressure cannot be assigned to all patients with ischemic heart disease. For this reason we believe that maintenance of optimal cardiac output during the postoperative period in the patient undergoing a coronary bypass operation would be better achieved if volume replacement were aimed at the patient s own optimal filling pressure rather than at an arbitrary value. Based on studies showing that a coronary bypass operation does not change the variables in ventricular performance in the early postoperative period [29-311, we assumed that for each heart the preoperative optimal filling pressure (mean LA pressure) should also be optimal in the postoperative period. As the preoperative mean LA pressure cannot be measured directly, we calculated it from the measured LVEDP (see Material and Methods section). As shown by Forsberg [14], Sarnoff and Berglund [ls], Braunwald [12, 131, OIdham [17], Mitchell [16], Bouchard [ll], Wallace [19], Kaltman [15], and their associates, the mean LA pressure is equal to the LVEDP in patients with normal left ventricular function (Group 2A). In patients with left ventricular dysfunction, the mean LA pressure is lower than the LVEDP because the left atrial kick augments the LVEDP [ll, 13, 16, 20, 221. In the latter group (Group 2B), preoperative mean LA pressure is calculated from the LVEDP using the formulas of Falicov and Resnekov [20].

5 384 The Annals of Thoracic Surgery Vol 35 No 4 April 1983 In conclusion, although the fundamental concepts of filling pressures are fairly well known, in this report it is shown for perhaps the first time that volume load at the termination of coronary artery bypass grafting should suit the individual hemodynamic features of each patient and should equal the calculated preoperative mean LAP. References 1. Crexells C, Chatterjee K, Forrester JS, et al: Optimal level of filling pressure in the left side of the heart in acute myocardial infarction. N Engl J Med 289:1263, Ellis RJ, Mangano DT, Van Dyke DC: Relationship of wedge pressure to end diastolic volume in patients undergoing myocardial revascularization. J Thorac Cardiovasc Surg 78:605, Fishman NH, Hutchinson JC, Roe BB: Controlled atrial hypertension: a method for supporting cardiac output following open heart surgery. J Thorac Cardiovasc Surg 52:777, Kirklin JW, Theye RA: Cardiac performance after open intracardiac surgery. Circulation 28:1061, Kouchoukos NT, Sheppard LC, Kirklin JW: Effect of alternations in arterial pressure on cardiac performance early after open intracardiac operations. J Thorac Cardiovasc Surg 64:563, Mangano DT, Van Dyke DC, Ellis RJ: The effect of increasing preload on ventricular output and ejection in man: limitations of the Frank-Starling mechanism. Circulation 62:535, Rastelli GG, Kirklin JW: Hemodynamic state early after prosthetic replacement of mitral valve. Circulation 34:448, Russel RO, Rackley CE, Pombo J, et al: Effects of increasing left ventricular filling pressure in patients with acute myocardial infarction. J Clin Invest 49:1538, Sarin CL, Yalav E, Clement AJ, Braimbridge MV: The necessity for measurement of left atrial pressure after cardiac valve surgery. Thorax 25385, Tarhan S, White RD, Moffitt EA: Anesthesia and postoperative care for cardiac operations. Ann Thorac Surg 23:173, Bouchard RJ, Gault JH, Ross J: Evaluation of pulmonary arterial end diastolic pressure as an estimate of left ventricular end-diastolic pressure in patients with normal and abnormal left ventricular performance. Circulation , Braunwald E, Brockenbrough EC, Frahm CJ, Ross J: Left atrial and left ventricular pressures in subjects without cardiovascular disease. Circulation 24:267, Braunwald E, Frahm CJ: Studies on Starling s law of the heart: IV. Observations on the hemody- namic functions of the left atrium in man. Circulation 24:633, Forsberg SA: Relations between pressure in pulmonary artery, left atrium and left ventricle with special reference to events at end diastole. Br Heart J 33:494, Kaltman AJ, Herbert WH, Conroy RJ, Kossman CE: The gradient in pressure across the pulmonary vascular bed during diastole. Circulation 34:377, Mitchell JH, Gilmore JP, Sarnoff SJ: The transport function of the atrium: factors influencing the relation between mean left atrial pressure and left ventricular end diastolic pressure. Am J Cardiol 9:237, Oldham HN, Wechsler AS, Wolfe WG, et al: Left ventricular filling pressure after aorto-coronary grafting. J Thorac Cardiovasc Surg 65343, Samoff SJ, Berglund E: Ventricular function: I. Starling s law of the heart studied by means of simultaneous right and left ventricular function curves in the dog. Circulation 9:706, Wallace AG, Mitchell JH, Skinner NS, Sarnoff SJ: Hemodynamic variables affecting the relation between mean left atrial and left ventricular enddiastolic pressures. Circ Res 13:261, Falicov RE, Resnekov L: Relationship of the pulmonary artery end diastolic pressure to the left ventricular end diastolic and mean filling pressures in patients with and without left ventricular dysfunction. Circulation 42:65, Lappas D, Lell WA, Gabel JC, et al: Indirect measurement of left atrial pressure in surgical patients: pulmonary-capillary wedge and pulmonary-artery diastolic pressures compared with left-atrial pressure. Anesthesiology 38:394, Rahimtoola SH, Loeb HS, Ehsani A, et al: Relationship of pulmonary artery to left ventricular diastolic pressures in acute myocardial infarction. Circulation 46:283, Goor DA, Lavee J: Enhanced protection of myocardial function by systemic deep hypothermia (20 C) during cardioplegic arrest in multiple coronary bypass grafting. J Thorac Cardiovasc Surg 84:237, Starling EH: The Linacre Lecture on the Law of the Heart (presented at Cambridge University, 1915). London, Longmans, Green, Hirshhorn S, Kaiser GA: The effects of changes in left ventricular end diastolic pressure on the distribution of coronary blood flow and on the electrical activity of the heart. Curr Top Surg Res 2:463, Salisbury PF, Cross CE, Rieben PA: Acute ischemia of inner layers of ventricular wall. Am Heart J 66:650, Bristow JD, Van Zee BE, Judkins MP: Systolic and diastolic abnormalities of the left ventricle in coronary artery disease. Circulation Q219, 1970

6 385 Goor et al: Calculated Preoperative Mean Left Atrial Pressure 28. Linhart JW, Hildner FJ, Barold SS, Samet P: Myocardial function in patients with coronary artery disease. Am J Cardiol23:379, Bolooki H, Mallon S, Ghahramani A, et al: Objective assessment of the effects of aortocoronary bypass operation on cardiac function. J Thorac Cardiovasc Surg 66:916, Bolooki H, Rubinson RM, Michie DD, Jude JR Assessment of myocardial contractibility after coronary bypass grafts. J Thorac Cardiovasc Surg 62543, Spencer FC, Green GE, Tice DA, et al: Coronary artery bypass grafts for congestive heart failure. J Thorac Cardiovasc Surg 62:529, 1971