Evaluation of Central Venous Pressure as a Guide to Volume Replacement in Children Following Cardiopulmonary Bypass

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1 Evaluation of Central Venous Pressure as a Guide to Volume Replacement in Children Following Cardiopulmonary Bypass Alan B. Gazzaniga, M.D., Charles L. Byrd, M.D., David R. Stewart, M.D., and Nicholas E. O Connor, M.D. ABSTRACT After cardiopulmonary bypass in three groups of children whole blood was replaced on the basis of measured intraoperative losses; intraoperative losses plus the deficit recorded by direct blood volume measurement; and intraoperative losses plus eievation of central venous pressure (CVP) to double preoperative levels. Blood replacement by intraoperative losses alone led to blood volume deficits and low creatinine clearances postoperatively. Adequate replacement was achieved by direct measurement of blood volume or by maintaining an elevated CVP immediately after bypass. A n increase in whole-body venous tone after cardiopulmonary bypass has been demonstrated by Reid and associates [5] from a study of their patients. Normal central venous pressures were noted despite measured blood volume deficits. Increases in venornotor tone, therefore, would limit the value of central venous pressure (CVP) as a means of detecting postoperative hypovolemia. The purpose of this study is to define the usefulness of CVP as a guide to volume replacement following intracardiac operations in children. Materials and Methods Serial observations were made on 9 boys and 2 girls aged 6 to 14 years and weighing an average of 42 (range, 20 to 68) kg. The average time on cardiopulmonary bypass was 52 (range, 22 to 88) minutes. None of the patients were on digitalis or had congestive heart failure. Operation was performed using the disc oxygenator primed with fresh whole blood, 5% dextrose and water, and mannitol to give a priming hematocrit of 32%. Patients were divided into three groups. Group I patients received blood From the Departments of Thoracic and Cardiovascular Surgery, The Children s Hospital Medical Center, Boston, Mass., and the University of California, Irvine, Calif. Accepted for publication June 17, Address reprint requests to Dr. Gauaniga, Department of Surgery, the University of California, Irvine, Calif THE ANNALS OF THORACIC SURGERY

2 CVP and Volume Replacement in Children equal to intraoperative and chest tube losses and on the basis of clinical manifestations of hypovolemia. Group I1 patients received replacement equal to chest tube and intraoperative blood losses as well as deficits recorded by direct blood volume measurements. Group I11 patients received their measured intraoperative and subsequent chest tube losses, and in addition they were transfused immediately after bypass to achieve a stable CVP approximately double preoperative levels (never more than 18 cm. H20). The CVP was monitored in all groups using a polyethylene catheter inserted into the superior vena cava through the left brachial or external jugular vein. Zero base line was 5 cm. below the suprasternal notch. On the day prior to operation total blood volume (TBV) was measured with the Volemetron as previously described [2]. Five microcuries of 1311 radioactive albumin was used, and the isotope equilibration period was 15 minutes. In the Group I and I1 patients blood volume determinations were made preoperatively, immediately postoperatively, and at 6 to 8, 32 to 36, and 72 hours postoperatively. In the Group I11 patients blood volume was measured preoperatively and at 2 to 4, 32 to 36, and 72 hours postoperatively. Postoperative blood samples were drawn from the central venous catheter. Large vessel hematocrit (LVH), using the microhematocrit technique,* was determined in duplicate, and no corrections were allowed for trapped plasma. Plasma volume (PV) and red cell mass (RV) were calculated using the LVH, TBV, and formula TBV = PV/(lOO - Hct). All patients underwent a preoperative 12-hour cumulative creatinine clearance test. Serum osmolality and creatinine concentrations were determined using blood samples drawn at the end of each collection period. After operation urine was collected at separate intervals every 6 hours for 24 hours, then every 24 hours for two days. These collections were measured for volume, creatinine concentration, and osmolality. Serum osmolality and creatinine concentrations were determined for blood samples drawn at the end of each collection period. Serum and urine osmolality were measured by freezing point depression,t and creatinine concentrations were determined with the photoelectric colorimeter (adaptation of Folin's method). The creatinine, osmolar, and free water clearances were calculated according to standard formulas [7]. R esu 1 ts GROUP I Blood Volume, Hematocrit, and Replacement. The data indicate a consistent deficit in both the RV and PV fractions postoperatively, despite what appeared to be correct intraoperative transfusion replacement (Table 1). The hypovolemia initially was reflected in the plasma fraction, but 36 'International Hematocrit Centrifuge, International Equipment Co., Boston, Mass.?Advanced Instrument Co. Osmometer, Newton Highlands, Mass.

3 L or 0 TABLE 1. MEAN CHANGES IN TOTAL BLOOD VOLUME, PLASMA VOLUME, RED CELL VOLUME, AND HEMATOCRIT Postoperatively Preoperatively 0-1 Hr. 6-8 Hr Hr. 72 Hr. Patients TBV PV RV Hct TBV PV RV Hct TBV PV RV Hct TBV PV RV Hct TBV PV RV HCI (n=3) 2,047 1, , , ,823 1, ,970 1, (n=3) 3,350 1,973 1, ,530 1,438 1, ,063 1,804 1, ,137 1,940 1, ,300 2,066 1,234 Group 111 Group I1 Group I (n = 5) 2,206 1, ,187 1, ,136 1, ,180 1, TBV = total blood volume (ml.); PV = plasma volume (ml.); RV =red cell volume (m13; Hct = hematoait (percent).

4 CVP and Volume Replacement in Children hours after operation PV was near preoperative levels. There was a continuing mean RV deficit of approximately 150 ml. 36 hours after operation. The mean hematocrit rose immediately after operation, and with the increase in PV the hematocrit fell to 34 on the third postoperative day. Blood replacement was required primarily during the first 8 hours after operation. These patients received an average of 200 ml. more than chest tube losses. This was considered adequate replacement as judged by clinical signs and urine output. Creatinine Clearance. Creatinine clearance, although adequate during the initial 6 hours after operation, fell to the lowest level during the next 12 hours (Figure). Creatinine clearance was abnormal (normal, 60 to 80 ml. per minute per square meter of body surface area) in all 3 patients for the first 48 hours after operation. Two of the 3 patients had low-normal clearances 48 to 72 hours after operation, and 1 continued to have a reduced clearance. Free Water Clearance. Free water clearance was negative preoperatively since collections were made on overnight fasting patients (Table 2). Negative free water clearance was maximal during the 6- to 12-hour period after operation. Thereafter the clearance fell but remained negative throughout the study. Central Venous Pressure. Postoperative CVPs in this group were generally unchanged from preoperative levels and were in the range of 7 to 10 cm. HzO. GROUP I1 Blood Volume, Hematocrit, and Replacement. There was an immediate 800 ml. mean postoperative blood volume deficit. This loss was primarily 90 -I N E 80 \.- E 70 u a g 60 0 Groupm GrouplI e W OP. t Hours Post -op Changes in creatinine clearance following cardiopulmonary bypass. Group Z patients had persistently low creatinine clearances. VOL. 13, NO. 2, FEBRUARY,

5 2 TABLE 2. MEAN FREE WATER CLEARANCE (ml./min./m.z) s E! n Postoperatively z Patients Preopera tively 0-6 Hr Hr Hr Hr Hr Hr. E Group I.e (n = 3) Group I1 (n = 3) Group I11 (n = 5)

6 CVP and Volume Replacement in Children in PV, although RV was also diminished (see Table 1). Six to 8 hours later the TBV deficit was approximately 300 ml. and the PV was near preoperative levels. The patients received an average of 600 ml. of whole blood beyond chest tube losses. Creatinine Clearance. Creatinine clearance was in the normal range during the entire postoperative period (see Figure). Free Water Clearance. These patients also had a negative free water clearance preoperatively (Table 2). Postoperatively the mean clearance remained negative throughout the study but reached the lowest levels 6 hours after operation. Between the 48- and 72-hour period, 2 of the 3 patients underwent diuresis with a positive free water clearance. Central Venous Pressure. Postoperative CVP ranged between 8 and 12 cm. HzO and was the same as or higher than preoperative levels. GROUP I11 Blood Volume, Hematocrit, and Replacement. Blood volume in this group was virtually unchanged during the 2- to 4-hour measurement period immediately postoperatively (Table 1). The PV was nearly identical and the RV was slightly greater. Hematocrit changed very little postoperatively. Intraoperative whole-blood replacement was 400 to 600 ml. greater than measured losses. Postoperative blood replacement generally matched chest tube losses. Creatinine Clearance. Creatinine clearance in this group was normal at all collection periods (see Figure). Free Water Clearance. Mean clearance was negative preoperatively, reached a peak between the 0- and 6-hour period postoperatively, and gradually fell but was still negative between the 48- and 72-hour period after operation (see Table 2). Central Venous Pressure. Mean CVP rose from a preoperative value of 8.4 cm. HzO to a high of 15 cm. HzO 1 hour postoperatively, then fell to 12 cm. HzO at 30 hours postoperatively and was still at this level at 72 hours. Comment In this study, intraoperative and postoperative transfusion therapy based on replacement of measured losses produced blood volume deficits similar to those observed by other investigators [l, 4, 51. Hypovolemia was not obvious during clinical examination of the patients, and normal CVPs were frequently encountered despite a measured blood volume deficit. Reid and associates [5] reported a reduced TBV and a reduced venous blood volume after cardiopulmonary bypass in their patients. This occurred with an elevated CVP and could be explained on the basis of increased venomotor tone. They also showed an increase in central blood volume due to redistribution. These alterations appear to occur after bypass is com- vor4. 13, NO. 2, FEBRUARY,

7 GAZZANIGA ET AL. pleted [3]. The increase in venomotor tone is not adequately explained by the current studies. There may be changes in the shape and distensibility of the veins [5]. Alterations in the release of neurohumoral substances such as catecholamines and serotonin might also be a factor [61. The inadequacy of blood volume replacement by use of measured losses alone is reflected in the creatinine clearance study of the Group I patients. These clearances were consistently below normal, which indicates a reduction in the glomerular filtration rate (GFR) and were probably the result of hypovolemia. On the other hand, creatinine clearances remained normal during the entire study in the other two groups. Negative free water clearance in the presence of a normal GFR gives an indirect indication of antidiuretic hormone (ADH) activity. ADH is released primarily in the presence of hypovolemia or dehydration [81. Negative free water clearances were observed in all patients during the initial 48 hours after operation. There were no positive clearances in any of the patients receiving blood by measured intraoperative and chest tube losses. Positive free water clearances occurred in 2 of the 3 patients whose replacement was based on direct blood volume measurement during the 48- to 72-hour period postoperatively. Two of the 5 patients transfused to an elevated CVP had a zero clearance between the 48- and 72-hour period. These results indicate adequate volume replacement in the Group I1 and I11 patients. Central venous pressure measurement can be used as a guide for blood volume replacement after cardiopulmonary bypass in children if it is realized that during the initial 24 hours after operation CVP can be normal or slightly elevated in the presence of hypovolemia. References 1. Berger, R. L., Polanzak, M. L., and Ryan, T. J. Central venous pressure and blood volume pattern following open-heart surgery. Ann. Thorac. Surg. 6:57, Gazzaniga, A. B., Replogle, R. L., and Gross, R. E. Blood volume changes following closure of intracardiac left-to-right shunts. J.A.M.A. 198:989, Giannelli, S., Ayres, S. M., Fleming, P., Conrad, W., Schwartz, M. S., and Gould, H. Peripheral vascular volumes and whole body hematocrit during human heart lung bypass. Circulation 41:629, McClenahan, J. B., Yamauchi, H., and Roe, B. B. Blood volume studies in cardiac surgery patients. J.A.M.A. 195:356, Reid, D. J., Digerness, S. B., and Kirklin, J. W. Changes in whole body venous tone and distribution of blood after open intracardiac surgery. Am. J. Cardiol. 22:621, Replogle, R., Levy, M., DeWall, R. A., and Lillehei, R. C. Catecholamine and serotonin response to cardiopulmonary bypass. J. Thorac. Cardiovasc. Surg. 44:638, Smith, H. W. Principles of Renal Physiology. New York: Oxford University Press, Verney, E. B. Some aspects of water and electrolyte excretion. Surg. Gynecol. Obstet. 106:441, THE ANNALS OF THORACIC SURGERY