Comparison of pulsatile and non-pulsatile cardiopulmonary bypass on regional renal blood flow in sheep

OBJECTIVE--The purpose of the present study was to evaluate the effects of pulsatile cardiopulmonary bypass (CPB) on sheep regional renal blood flow by comparing pulsatile and non-pulsatile perfusion at two different flow rates. DESIGN--Seven female Suffolk sheep were used and the animals were perfused with pulsatile and non-pulsatile CPB at flow rates of 60 and 100 ml/min/kg. Regional renal blood flow was measured by the colored microsphere method. General linear model ANOVA was performed to analyze the data. RESULTS--Regional renal blood flow was significantly higher in both outer and middle cortices of pulsatile CPB compared with non-pulsatile CPB (outer cortex: pulsatile CPB, 381+/-192 ml/min/100 g, non-pulsatile CPB, 255+/-151 ml/min/100g, p=0.002; middle cortex: pulsatile CPB, 239+/-114 ml/min/100 g, non-pulsatile CPB, 176+/-80 ml/min/100 g, p=0.02). The increase of flow rate from 60 to 100 ml/min/kg improved renal cortical blood flow significantly. CONCLUSION--The regional renal blood flow was significantly higher in both outer and middle cortices of pulsatile CPB compared with the non-pulsatile CPB.     

The effects of pulsatile and non-pulsatile cardiopulmonary bypass on renal blood flow and function

The physiologic effects of pulsatile and non-pulsatile flow in cardiopulmonary bypass were compared in terms of the relationship between different flow rates and what effects these had on pulsatile and non-pulsatile flow. Forty adult mongrel dogs were used in this study and divided into 5 groups, each comprised of 8 animals, according to the flow rate during cardiopulmonary bypass, namely; 40, 60, 80, 100, or 120 ml/kg/min. The animals were perfused with either pulsatile or non-pulsatile flow for 1 hour, given randomly at the same mean flow rate. At flow rates of 80 and 100 ml/kg/min, the mean arterial blood pressure and total peripheral vascular resistance were significantly lower in pulsatile flow than in non-pulsatile flow, and the renal blood flow was significantly greater in pulsatile flow than in non-pulsatile flow. The renal arterial-venous lactate difference was significantly less in pulsatile flow than in non-pulsatile flow at a flow rate of 80 ml/kg/min, and the renal lactate extraction was significantly higher in pulsatile flow than in non-pulsatile flow at the same flow rate. The renal excess lactate was significantly lower in pulsatile flow than in non-pulsatile flow at a flow rate of 100 ml/kg/min. There were no significant differences in these parameters between the two types of perfusion at flow rates of 40, 60 or 120 ml/kg/min. Pulsatile flow was therefore apparently advantageous, when compared to non-pulsatile flow, in terms of hemodynamics, renal circulation, and metabolism of the kidney at flow rates of 80 and 100 ml/kg/min. However, when the flow rate was 120 ml/kg/min, pulsatile flow and non-pulsatile flow had the same effects.     

The effects of pulsatile and non-pulsatile cardiopulmonary bypass on renal blood flow and function

The physiologic effects of pulsatile and non-pulsatile flow in cardiopulmonary bypass were compared in terms of the relationship between different flow rates and what effects these had on pulsatile and non-pulsatile flow. Forty adult mongrel dogs were used in this study and divided into 5 groups, each comprised of 8 animals, according to the flow rate during cardiopulmonary bypass, namely; 40, 60, 80, 100, or 120 ml/kg/min. The animals were perfused with either pulsatile or non-pulsatile flow for 1 hour, given randomly at the same mean flow rate. At flow rates of 80 and 100 ml/kg/min, the mean arterial blood pressure and total peripheral vascular resistance were significantly lower in pulsatile flow than in non-pulsatile flow, and the renal blood flow was significantly greater in pulsatile flow than in non-pulsatile flow. The renal arterial-venous lactate difference was significantly less in pulsatile flow than in non-pulsatile flow at a flow rate of 80 ml/kg/min, and the renal lactate extraction was significantly higher in pulsatile flow than in non-pulsatile flow at the same flow rate. The renal excess lactate was significantly lower in pulsatile flow than in non-pulsatile flow at a flow rate of 100 ml/kg/min. There were no significant differences in these parameters between the two types of perfusion at flow rates of 40, 60 or 120 ml/kg/min. Pulsatile flow was therefore apparently advantageous, when compared to non-pulsatile flow, in terms of hemodynamics, renal circulation, and metabolism of the kidney at flow rates of 80 and 100 ml/kg/min. However, when the flow rate was 120 ml/kg/min, pulsatile flow and non-pulsatile flow had the same effects.     

Brain tissue pH, oxygen tension, and carbon dioxide tension in profoundly hypothermic cardiopulmonary bypass. Comparative study of circulatory arrest, nonpulsatile low-flow perfusion, and pulsatile low-flow perfusion

The pH, oxygen tension, and carbon dioxide tension of canine brain tissue were experimentally examined during profoundly hypothermic cardiopulmonary bypass. After core cooling, a 60-minute period of circulatory arrest was performed in group 1 (n = 8), a 120-minute nonpulsatile low-flow perfusion (25 ml/kg/min) in group 2 (n = 8), and a 120-minute pulsatile low-flow perfusion (25 ml/kg/min) in group 3 (n = 8). When the animal was rewarmed, the core temperature was raised to 32 degrees C. Brain tissue pH kept decreasing in group 1, but it showed a delayed recovery in group 2 and a rapid recovery in group 3 during core rewarming. Brain tissue oxygen tension decreased significantly in group 1. Brain tissue carbon dioxide tension increased irreversibly in group 1, increased to about 100 mm Hg and recovered to 89.9 +/- 15.3 mm Hg in group 2, and reached a plateau of about 85 mm Hg and recovered to 55.4 +/- 6.7 mm Hg in group 3. We concluded that a 120-minute period of nonpulsatile low-flow perfusion provides more protection from brain damage than a 60-minute period of circulatory arrest. Furthermore, pulsatile flow will increase the safety margin of cardiopulmonary bypass even if the flow rate is reduced to 25 ml/kg/min.     

Pulsatile perfusion versus conventional high-flow nonpulsatile perfusion for rapid core cooling and rewarming of infants for circulatory arrest in cardiac operation.

Thirty consecutive infants undergoing hypothermia and circulatory arrest for repair of ventricular septal defect, transposition of the great vessels, or atrioventricular canal defects were alternately selected for conventional high flow nonpulsatile perfusion or pulsatile perfusion during core cooling and rewarming. All received morphine anesthesia, 30 mg/kg of Solu-Medrol, and 10 to 15 mcg/kg of phentolamine. Those receiving nonpulsatile flow were perfused at a rate of 160 to 180 cc/kg/min with a roller pump and oxygenator with arterial pressure of 50 to 55 mm Hg. In the pulsatile flow group, a roller pump and oxygenator were used, and an especially constructed Datascope PAD (pulsatile assist device) was interposed in the arterial line to provide pulsatile perfusion with 75/40 mm Hg pressure at slightly reduced flow (150 cc/kg/min). The average rectal, esophageal, and tympanic membrane temperatures were reduced to approximately 16 degrees C prior to circulatory arrest. Following repair, perfusion was resumed until these temperatures returned to 37 degrees C. Cooling and rewarming were enhanced by pulsatile perfusion, with over 30% reduction in total pump time. Additionally, the larger patients in the pulsatile group cooled almost as rapidly as the smaller. The rates of decline and subsequent rise of rectal, esophageal, and tympanic membrane temperatures were equal in the pulsatile group, but the rectal temperature lagged far behind in the nonpulsatile group. Urine production during bypass was 100% greater in the pulsatile group. The plasma free hemoglobin was similar in both groups. The average postrewarming pH was 7.31 in the nonpulsatile group and 7.42 in the pulsatile group. Infants receiving pulsatile flow awakened more quickly, were more alert, and required less postoperative mechanical ventilation. We suggest that pulsatile perfusion for core cooling and rewarming of infants is safe and is more rapid and physiological than conventional high-flow nonpulsatile perfusion.     

Peripheral vascular resistance and angiotensin II levels during pulsatile and no-pulsatile cardiopulmonary bypass.

The effects of pulsatile and non-pulsatile cardiopulmonary bypass (CPB) on levels of peripheral vascular resistance and plasma angiotensin II (AII) have been studied in 24 patients submitted to elective cardiac surgical procedures. Twelve patients had conventional non-pulsatile perfusion throughout the period of CPB (non-pulsatile group), while 12 had pulsatile perfusion during the central period of total CPB, using the Stockert pulsatile pump system (pulsatile group). There were no significant differences between the groups in respect of age, weight, bypass time, cross-clamp time, or in mean pump flow or mean perfusion pressure at the onset of CPB. Peripheral vascular resistance index (PVRI) and plasma AII levels were measured at the onset of total CPB and at the end of total CPB. In the non-pulsatile group PVRI rose from 19.6 units to 29.96 units during perfusion. In the pulsatile group PVRI showed little change from 20.89 units to 21.45 units during perfusion (P less than 0.001). Plasma AII levels (normal less than 35 pg/ml) rose during perfusion from 49 pg/ml to 226 pg/ml in the non-pulsatile group. The rise in the pulsatile group from 44 pg/ml to 98 pg/ml was significantly smaller than that in the non-pulsatile group (P less than 0.01). These results indicate that pulsatile cardiopulmonary bypass prevents the rise in PVRI associated with non-pulsatile perfusion, and that this effect may be achieved by preventing excessive activation of the renin-angiotensin system, thus producing significantly lower plasma concentrations of the vasoconstrictor angiotensin II.     

Optimal perfusion flow rate for the brain during deep hypothermic cardiopulmonary bypass at 20 degrees C. An experimental study

The relationship between the perfusion flow rate and cerebral oxygen consumption during deep hypothermic cardiopulmonary bypass at 20 degrees C was investigated in dogs. In 10 dogs the perfusion flow rate was decreased in steps from 100 to 60, 30, and 15 ml/kg/min every 30 minutes. Although cerebral blood flow decreased as perfusion flow rate decreased, the ratio of cerebral blood flow to the perfusion flow rate increased significantly (p less than 0.05) at a perfusion flow rate of 15 ml/kg/min compared to that at a perfusion flow rate of 100 or 60 ml/kg/min. The arterial-sagittal sinus blood oxygen content difference increased as perfusion flow rate decreased. Consequently, cerebral oxygen consumption did not vary significantly at perfusion flow rates of 100 (0.48 +/- 0.10), 60 (0.43 +/- 0.14), and 30 ml/kg/min (0.44 +/- 0.12 ml/100 gm/min), and it decreased significantly to 0.31 +/- 0.22 ml/100 gm/min at a perfusion flow rate of 15 ml/kg/min. In five dogs the perfusion flow rate was decreased in one step from 100 to 15 ml/kg/min, and after 60 minutes' perfusion at a perfusion flow rate of 15 ml/kg/min, the perfusion flow rate was returned to 100 ml/kg/min. Cerebral oxygen consumption decreased significantly during 60 minutes' perfusion at a perfusion flow rate of 15 ml/kg/min and did not return to its initial value after the perfusion flow rate was returned to 100 ml/kg/min. These data indicate that the optimal perfusion flow rate for the brain during deep hypothermic cardiopulmonary bypass at 20 degrees C appears to be 30 ml/kg/min, with a possible oxygen debt in the brain resulting in anaerobic metabolism if the perfusion flow rate is kept at 15 ml/kg/min or less.     

Brain tissue pH, oxygen tension, and carbon dioxide tension in profoundly hypothermic cardiopulmonary bypass. Pulsatile assistance for circulatory arrest, low-flow perfusion, and moderate-flow perfusion

The brain tissue pH, oxygen tension, and carbon dioxide tension were experimentally examined during profoundly hypothermic cardiopulmonary bypass with core cooling and core rewarming. Sixty-minute circulatory arrests (n = 28, group I), 120-minute low-flow perfusions (25 ml/kg/min; n = 16, group II), and 120-minute moderate-flow perfusions (50 ml/kg/min; n = 16, group III) were accomplished with and without pulsatile flow. In group I, progressive brain tissue acidosis and hypercapnia were recovered with pulsatile assistance. In group II, brain tissue acidosis and hypercapnia were recovered completely with pulsatile assistance but incompletely without it. In group III mild acidosis was eliminated with pulsatile assistance where the pH was significantly higher than in groups I and II, and brain tissue carbon dioxide pressure was significantly lower than in groups I and II with and without pulsatile assistance. Brain tissue hypoxia was severe in group I, slight in group II, but not found in group III. We concluded that a perfusion flow rate will decide the safe period, and a pulsatile assistance will promote brain protection at any flow rate in profoundly hypothermic cardiopulmonary bypass.     

Pulsatile assistance for profoundly hypothermic circulatory arrest, low-flow perfusion, and moderate-flow perfusion: comparative study of brain tissue pH, PO2, and PCO2

The pH, oxygen tension, and carbon dioxide tension of canine brain tissue were experimentally examined during profoundly hypothermic cardiopulmonary bypass with and without pulsatile assistance. After core cooling, a 60-minute of circulatory arrest was performed in group 1 (n = 16), a 120-minute of low-flow perfusion (25 ml/kg/min) in group 2 (n = 16), and 120 minute of moderate-flow perfusion (50 ml/kg/min) in group 3 (n = 16). The core rewarming was done to the temperature above 32 degrees C. Each group was divided into two subgroups with and without pulsatile assistance (subgroup-p; n = 8, subgroup-c; n = 8). In group 1, progressive brain tissue acidosis and hypercapnea were recovered by use of pulsatile assistance. In group 2, brain tissue acidosis and hypercapnea were recovered completely with pulsatile assistance, but incompletely without it. In group 3, mild acidosis and hypercapnea were eliminated with pulsatile assistance. Brain tissue hypoxia was severe in group 1, slight in group 2, but not found in group 3. We conclude that a pulsatile assistance provides brain protection at any flow-ratio, and that the less flow-ratio and the longer perfusion period will make the pulsatile assistance the more necessary.     

Plasma vasopressin levels and urinary flow during cardiopulmonary bypass in patients with valvular heart disease: effect of pulsatile flow.

The effect of pulsatile flow on plasma vasopressin levels during cardiopulmonary bypass (CPB) was studied in 20 patients undergoing open valve replacement. Routine bypass was used in 10 patients and the AVCO pulsatile bypass pump was utilized in the other 10. In Group I (nonpulsatile) during CPB, the vasopressin level was markedly elevated (3.1 +/- 2 to 80 +/- 22 pg/ml) as was urine flow (0.6 +/- 0.2 to 5.9 +/- 2 ml/min) and urine Na+ concentration (69 +/- 19 to 116 +/- 7 mEq/L). In Group II (pulsatile) during CPB, the vasopressin level (3.8 +/- 3 to 54 +/- 14 pg/ml), urine flow (0.6 +/- 0.1 to 16.2 +/- 4.8 ml/min), and urine Na+ concentrations (61 +/- 13 to 97 +/- 10 mEq/L) were also elevated. The rise in vasopressin and urine Na+ was less in the pulsatile group (p less than 0.05) whereas the urine flow was higher (p less than 0.05). To maintain comparable blood pressure, the pulsatile flow group required significantly higher flows (4.5 +/- 0.2 compared to 3.8 +/- 0.2; p less than 0.05). These data suggest that CPB produces a marked vasopressin stress response which is beyond the physiological range for an antidiuretic effect on the kidney. At these levels vasopressin can exert a vasopressor effect to maintain resistance and affect renal blood flow, as well as producing an Na+ diuresis. The addition of pulsatile flow creates a more physiological situation attenuating the vasopressin response and producing a decrease in systemic resistance and a less pronounced Na+ diuresis.     

Superior results of ketone body ratio in pulsatile normothermic cardiopulmonary bypass; comparison with non-pulsatile cardiopulmonary bypass

Sixteen patients undergoing aortocoronary bypass surgery under normothermic cardiopulmonary bypass were divided into 2 groups according to the either addition or none of pulsatility induced by intra-aortic balloon pumping (IABP). In those patients, hepatic blood flow was measured 3 times before, during and after cardiopulmonary bypass. Additionally, arterial and hepatic ketone body ratios [(AKBR) and (HKBR)], and hepatic venous saturation (ShvO2) were measured throughout and after the surgery. RESULTS: The hepatic blood flows measured at 3 different times at the surgery were much more in the pulsatile group (p < 0.05). The values of AKBR, indicator of mitochondrial redox potential in hepatocytes, were maintained in nearly normal in the pulsatile group, but were suppressed in the non-pulsatile group. This trend was much more obvious in the values of HKBR. The significantly lower ShvO2 levels were observed in the non-pulsatile group during the cardiopulmonary bypass (p < 0.05). CONCLUSIONS: Pulsatile normothermic cardiopulmonary bypass induced by IABP provides better liver perfusion and results in a better hepatic metabolism than non-pulsatile cardiopulmonary bypass.     

Cerebral perfusion during canine hypothermic cardiopulmonary bypass: effect of arterial carbon dioxide tension

Cerebral blood flow (radioactive microspheres), intracranial pressure (subdural bolt), and retinal histopathology were examined in 20 dogs undergoing 150 minutes of hypothermic (28 degrees C) cardiopulmonary bypass to compare alpha-stat (arterial carbon dioxide tension, 40 +/- 1 mm Hg; n = 10) and pH-stat (arterial carbon dioxide tension, 61 +/- 1 mm Hg; n = 10) techniques of arterial carbon dioxide tension management. Pump flow (80 mL.kg-1.min-1), mean aortic pressure (78 +/- 2 mm Hg), and hemoglobin level (87 +/- 3 g/L [8.7 +/- 0.3 g/dL]) were maintained constant. During bypass, intracranial pressure progressively increased in the alpha-stat group from 6.0 +/- 1.0 to 13.9 +/- 1.8 mm Hg (p less than 0.05) and in the pH-stat group from 7.7 +/- 1.1 to 14.7 +/- 1.4 mm Hg (p less than 0.05), although there was no evidence of loss of intracranial compliance or intracranial edema formation as assessed by brain water content. With cooling, cerebral blood flow decreased by 56% to 62% in the alpha-stat group (p less than 0.05) and by 48% to 56% in the pH-stat group (p less than 0.05). However, 30 minutes after rewarming to 37 degrees C, cerebral blood flow in both groups failed to increase and remained significantly depressed compared with baseline values. Both groups showed similar amounts of ischemic retinal damage, with degeneration of bipolar cells found in the inner nuclear layer in 67% of animals. We conclude that, independent of the arterial carbon dioxide tension management technique, (1) cerebral perfusion decreased comparably during prolonged hypothermic bypass, (2) intracranial pressure increases progressively, (3) ischemic damage to retinal cells occurs despite maintenance of aortic pressure and flow, and (4) a significant reduction in cerebral perfusion persists after rewarming.     

Pediatric physiologic pulsatile pump enhances cerebral and renal blood flow during and after cardiopulmonary bypass

Controversy over benefits of pulsatile flow after pediatric cardiopulmonary bypass (CPB) continues. Our study objectives were to first, quantify pressure and flow waveforms in terms of hemodynamic energy, using the energy equivalent (EEP) formula, for direct comparisons, and second, investigate effects of pulsatile versus nonpulsatile flow on cerebral and renal blood flow, and cerebral vascular resistance during and after CPB with deep hypothermic circulatory arrest (DHCA) in a neonatal piglet model. Fourteen piglets underwent perfusion with either an hydraulically driven dual-chamber physiologic pulsatile pump (P, n = 7) or a conventional nonpulsatile roller pump (NP, n = 7). The radiolabeled microsphere technique was used to determine the cerebral and renal blood flow. P produced higher hemodynamic energy (from mean arterial pressure to EEP) compared to NP during normothermic CPB (13 +/- 3% versus 1 +/- 1%, p < 0.0001), hypothermic CPB (15 +/- 4% versus 1 +/- 1%, p < 0.0001) and after rewarming (16 +/- 5% versus 1 +/- 1%, p < 0.0001). Global cerebral blood flow was higher for P compared to NP during CPB (104 +/- 12 ml/100g/min versus 70 +/- 8 ml/100g/min, p < 0.05). In the right and left hemispheres, cerebellum, basal ganglia, and brainstem, blood flow resembled the global cerebral blood flow. Cerebral vascular resistance was lower (p < 0.007) and renal blood flow was improved fourfold (p < 0.05) for P versus NP, after CPB. Pulsatile flow generates higher hemodynamic energy, enhancing cerebral and renal blood flow during and after CPB with DHCA in this model.     

Comparison of regional myocardial blood flow and metabolism distal to a critical coronary stenosis in the fibrillating heart during alternate periods of pulsatile and nonpulsatile perfusion

The effect of pulsatile cardiopulmonary bypass on intramyocardial gas tensions and regional myocardial blood flow was studied in 10 mongrel dogs. Following application of a critical stenosis to the circumflex coronary artery (CIRC), animals were placed on total bypass with vented, fibrillating hearts. During three 45 minute periods of perfusion, animals alternately received pulsatile or linear flow with perfusion pressure carefully maintained at 80 mm. Hg. In myocardium supplied by the stenosed CIRC, intramyocardial oxygen tension (PO2) rose from 13 +/- 3 to 19 +/- 5 mm. Hg when a period of linear flow was followed by a period of pulsatile flow (p less than 0.025). Similarly in the CIRC-supplied area, intramyocardial carbon dioxide (PCO2) decreased from 128 +/- 12 to 99 +/- 12 mm. Hg (p less than 0.005) with conversion from linear to pulsatile flow. Myocardial blood flow (microsphere technique) to endocardial and epicardial layers of the CIRC-supplied area was significantly greater (p less than 0.05) during pulsatile than during linear perfusion. In contrast, when periods of pulsatile bypass were followed by periods of linear perfusion, myocardial PO2 fell from 25 +/- 6 to 9 +/- 3 (less than 0.02) and myocardial PCO2 rose from 82 +/- 12 to 154 +/- 12 mm. Hg (p less than 0.001). These data suggest that (1) fibrillation-induced regional ischemia distal to a critical coronary stenosis can be reduced by pulsatile perfusion during bypass and (2) the mechanism for the reduction in regional ischemia is improved myocardial blood flow.     

Cerebral blood flow rate during cardiopulmonary bypass and optimal cerebral perfusion flow rate during separated brain perfusion--a clinical study

There is no established theory to determine the cerebral blood flow rate (CBF) during not only the standard cardiopulmonary bypass but during the cardiopulmonary bypass with separated brain perfusion. This study was carried out to answer the following questions. (1) what is the relationship during the cardiopulmonary bypass between CBF and systemic flow rate or blood pressure?. (2) what is the optimal flow rate to the innominate artery during the separated brain perfusion? Twenty-one patients were selected for this study, who were operated under the cardiopulmonary bypass with a standard roller pump and a membrane oxygenator under moderate hypothermia (nasopharyngeal temperature of 26-28 degrees C). Systemic flow rate was maintained between 40 and 70 ml/kg/min. CBF before the cardiopulmonary bypass was 30.6 +/- 5.5 ml/100 g brain/min, and increased to 33.8 +/- 8.9 ml/100 g brain/min during the cardiopulmonary bypass. CBF was proportional to systemic flow rate (r = 0.62, p less than 0.01) and showed poor association with blood pressure ranged from 35 to 94 mmHg. As for the relationship between innominate arterial and cerebral blood flow rate, CBF linearly followed the decrease of innominate arterial flow rate to below about 9 ml/kg/min, but showed almost no changes when innominate arterial flow rate was over 9 ml/kg/min. It was observed that cerebral oxygen consumption did not decrease significantly under moderate hypothermia (26-28 degrees C), as far as CBF of 25 ml/100 g brain/min was maintained. Based on the relationship between innominate arterial and cerebral blood flow rate, it was shown that the innominate arterial flow rate to provide CBF of 25 ml/100 g brain/min was 5.5 ml/kg/min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Critical oxygen delivery during cardiopulmonary bypass in dogs: pulsatile vs. non-pulsatile blood flow

BACKGROUND AND OBJECTIVE: To determine the minimal oxygen delivery and pump flow that can maintain systemic oxygen uptake during normothermic (37 degrees C) pulsatile and non-pulsatile cardiopulmonary bypass in dogs. METHODS: Eighteen anaesthetized dogs were randomly assigned to receive either non-pulsatile (Group C; n = 9) or pulsatile bypass flow (Group P; n = 9). Oxygen delivery was reduced by a progressive decrease in pump flow, while arterial oxygen content was maintained constant. In each animal, critical oxygen delivery was determined from plots of oxygen uptake vs. oxygen delivery and from plots of blood lactate vs. oxygen delivery using a least sum of squares technique. Critical pump flow was determined from plots of lactate vs. pump flow. RESULTS: At the critical point, oxygen delivery obtained from oxygen uptake was 7.7 +/- 1.1 mL min(-1) kg(-1) in Group C and 6.8 +/- 1.8 mL min(-1) kg(-1) in Group P (n.s.). These values were similar to those obtained from lactate measurements (Group C: 7.8 +/- 1.6 mL min(-1) kg(-1); Group P: 7.6 +/- 2.0 mL min(-1) kg(-1)). Critical pump flows determined from lactate measurements were 55.6 +/- 13.8 mL min(-1) kg(-1) in Group C and 60.8 +/- 13.9 mL min(-1) kg(-1) in Group P (n.s.). CONCLUSIONS: Oxygen delivery values greater than 7-8 mL min(-1) kg(-1) were required to maintain oxygen uptake during normothermic cardiopulmonary bypass with either pulsatile or non-pulsatile blood flow. Elevation of blood lactate levels during bypass helps to identify inadequate tissue oxygen delivery related to insufficient pump flow.     

Biologically variable pulsation improves jugular venous oxygen saturation during rewarming

BACKGROUND: Conventional pulsatile (CP) roller pump cardiopulmonary bypass (CPB) was compared to computer controlled biologically variable pulsatile (BVP) bypass designed to return beat-to-beat variability in rate and pressure with superimposed respiratory rhythms. Jugular venous O2 saturation (SjvO2) below 50% during rewarming from hypothermia was compared for the two bypass techniques. A SjvO2 less than 50% during rewarming is correlated with cognitive dysfunction in humans. METHODS: Pigs were placed on CPB for 3 hours using a membrane oxygenator with alpha-stat acid base management and arterial filtration. After apulsatile normothermic CPB was initiated, animals were randomized to CP (n = 8) or BVP (roller pump speed adjusted by an average of 2.9 voltage output modulations/second; n = 8), then cooled to a nasopharyngeal temperature of 28 degrees C. During rewarming to stable normothermia, SjvO2 was measured at 5 minute intervals. The mean and cumulative area for SjvO2 less than 50% was determined. RESULTS: No between group difference in temperature existed during hypothermic CPB or during rewarming. Mean arterial pressure, arterial partial pressure O2, and arterial partial pressure CO2 did not differ between groups. The hemoglobin concentration was within 0.4 g/dL between groups at all time periods. The range of systolic pressure was greater with BVP (41 +/- 18 mm Hg) than with CP (12 +/- 4 mm Hg). A greater mean and cumulative area under the curve for SjvO2 less than 50% was seen with CP (82 +/- 96 versus 3.6% +/- 7.3% x min, p = 0.004; and 983 +/- 1158 versus 42% +/- 87% x min; p = 0.004, Wilcoxon 2-sample test). CONCLUSIONS: Computer-controlled BVP resulted in significantly greater SjvO2 during rewarming from hypothermic CPB. Both mean and cumulative area under the curve for SjvO2 less than 50% exceeded a ratio of 20 to 1 for CP versus BVP. Cerebral oxygenation is better preserved during rewarming from moderate hypothermia with bypass that returns biological variability to the flow pattern.     

Effects of phentolamine on tissue perfusion in pediatric cardiac surgery

OBJECTIVE: To evaluate whether the deleterious effects of cardiopulmonary bypass (CPB) can be overcome by phentolamine-induced pharmacologic vasodilation in pediatric patients with congenital heart disease. DESIGN: Prospective, randomized, clinical study. SETTING: Single university hospital. PARTICIPANTS: Forty-three pediatric patients undergoing open cardiac surgery for repair of congenital heart disease. INTERVENTIONS: Patients were randomly allocated into two groups. Patients in group 1 (n = 22) received 0.2 mg/kg of phentolamine during the cooling and rewarming periods of CPB. Group 2 patients (n = 21) did not receive phentolamine. Temperature measurements (rectal [R], nasopharyngeal [N], and toe [P]) and serum lactate values were obtained before, during, and after CPB; systemic oxygen consumption was evaluated during CPB. MEASUREMENTS AND MAIN RESULTS: At the end of the CPB period and at the end of the operation, lactate values of group 1 (1.87+/-0.37 and 1.8+/-0.39 mmol/L, respectively) were significantly lower than values of group 2 (2.24+/-0.28 and 2.33+/-0.33 mmol/L; p < 0.05 and p < 0.05, respectively). At the beginning of the rewarming period N-R temperature gradients of group 1 (0.14 degrees C+/-0.92 degrees C) were lower than group 2 (-0.58 degrees C+/-1.84 degrees C) values (p < 0.05). Central-peripheral temperature gradients of group 1 obtained at the end of the CPB period (N-R = 2.18 degrees C+/-0.69 degrees C; N-P = 7.84 degrees C+/-1.54 degrees C; R-P = 5.66 degrees C+/-1.70 degrees C) were significantly lower than the values of group 2 (N-R = 2.80 degrees C+/-0.91 degrees C, N-P = 9.97 degrees C+/-2.02 degrees C; R-P = 7.18 degrees C+/-2.10 degrees C; p < 0.05; p < 0.001; p < 0.05). At the end of the operation values of group 1 (N-R = 0.48 degrees C+/-0.31 degrees C; N-P = 6.30 degrees C+/-1.23 degrees C; R-P = 5.82 degrees C+/-1.16 degrees C) were significantly lower than the values of group 2 (N-R = 0.94 degrees C+/-0.56 degrees C; N-P = 8.69 degrees C+/-0.28 degrees C; R-P = 7.75 degrees C+/-2.15 degrees C; p < 0.05; p < 0.001; p < 0.001). The systemic oxygen consumption values of group 1 were higher than group 2 (6.26+/-1.82 v 5.17+/-1.05 mL/min/kg; p < 0.05) after complete rewarming. Mean arterial pressure (MAP) values of group 1 (58.9+/-6.4 mmHg) were lower than group 2 (63.4+/-6.7 mmHg) at the period after CPB (p = 0.03). CONCLUSION: The results suggest that the use of phentolamine during CPB is associated with limited systemic anaerobic metabolism and more uniform body perfusion.     

The Effects of Pulsatile Versus Nonpulsatile Perfusion on Blood Viscoelasticity Before and After Deep Hypothermic Circulatory Arrest in a Neonatal Piglet Model

Blood trauma increases blood viscoelasticity by increasing red cell aggregation and plasma viscosity and by decreasing cell deformability. During extracorporeal circulation, the mode of perfusion (pulsatile or nonpulsatile) may have a significant impact on blood trauma. In this study, a hydraulically driven dual chamber pulsatile pump system was compared to a standard nonpulsatile roller pump in terms of changes in the blood viscosity and elasticity during cardiopulmonary bypass (CPB) and pre and post deep hypothermic circulatory arrest (DHCA). Piglets, with an average weight of 3 kg, were used in the pulsatile (n = 5) or nonpulsatile group (n = 5). All animals were subjected to 25 min of hypothermia, 60 min of DHCA, 10 min of cold reperfusion, and 40 min of rewarming with a pump flow of 150 ml/kg/min. A pump rate of 150 bpm, pump ejection time of 120 ms, and stroke volume of 1 ml/kg were used during pulsatile CPB. Arterial blood samples were taken pre-CPB (36 degrees C), during normothermic CPB (35 degrees C), during hypothermic CPB (25 degrees C), pre-DHCA (18 degrees C), post-DHCA (19 degrees C), post-rewarming (35 degrees C), and post-CPB (36 degrees C). Viscosity and elasticity were measured at 2 Hz and 22 degrees C and at strains of 0.2, 1, and 5 using the Vilastic-3 Viscoelasticity Analyzer. Results suggest that the dual chamber neonate-infant pulsatile pump system produces less blood trauma than the standard nonpulsatile roller pump as indicated by lower values of both viscosity and elasticity during CPB support.