Relationship of brain blood flow and oxygen consumption to perfusion flow rate during profoundly hypothermic cardiopulmonary bypass. An experimental study

A study was made of the relation of brain blood flow and oxygen consumption to changes in perfusion flow rate during cardiopulmonary bypass at 20 degrees C in nine cynomolgus monkeys. Four perfusion flow rates varying from 0.25 to 1.75 L X min-1 X m-2 were randomly instituted, each for a 10 minute period. At the end of each period, brain arteriovenous oxygen content difference was measured and 15 mu radioactive microspheres were injected into the arterial perfusion line. The brain was then removed and section into anatomic regions and radioactivity was counted. Regional and total brain blood flows were calculated, as was whole brain oxygen consumption. Brain perfusion continued in all areas at all perfusion flow rates. Whole brain blood flow decreased (p less than 0.0001) as perfusion flow rate was reduced (45 +/- 6.5, 41 +/- 7.9, and 23 +/- 2.8 ml X min-1 X 100 gm-1 at 1.5, 1.0, and 0.5 L X min-1 X m-2, respectively). The proportion of the total perfusion delivered to the brain increased (p = 0.003) with decreasing perfusion flow rates (5.4% +/- 0.78%, 7.1% +/- 1.24%, and 8.2% +/- 1.11% at 1.5, 1.0, and 0.5 L X min-1 X m-2, respectively). Brain blood flow resistance remained unchanged (p = 0.4) while that of the remaining body increased (p less than 0.0001). There was a greater reduction of blood flow in the cortical white matter (p = 0.01) than in other regions of the brain. Brain oxygen consumption was the same (p = 0.5) at all perfusion flow rates, related to an increasing percent oxygen extraction with decreasing perfusion flow rate (p less than 0.0001). The data indicate that all areas of the brain remain perfused, even at low perfusion flow rates, during profoundly hypothermic cardiopulmonary bypass, and that brain oxygen consumption is maintained in part by increased oxygen extraction and in part by redistribution of the perfusate from the remaining body to the brain.     

Partial brachiocephalic perfusion under hypothermic cardiopulmonary bypass. An experimental study.

We studied electrophysiological, oxygen metabolic, and histological variables in dogs to establish the reliability and safety of partial brachiocephalic perfusion (PBP) under hypothermic cardiopulmonary bypass (CPB) at 23 degrees-25 degrees C. Sixteen mongrel dogs were divided into two groups. Six (control group) underwent typical hypothermic CPB for 90 min, and 10 (PBP group) underwent PBP under hypothermic CPB for 90 min. During core cooling on the CPB, a progressive reduction in voltage and slowing of frequency of the electroencephalogram (EEG) was observed. At around 23 degrees C nasopharyngeal temperature the tracing became almost flat and remained so throughout the hypothermic CPB or the PBP under hypothermic CPB. Consistent recovery of the EEG was, however, observed during the period of rewarming on the CPB, and the voltage and frequency of the EEG recovered to control levels on weaning off CPB at 36 degrees C in both groups. In the PBP group, the cerebral arteriovenous oxygen (AVO2) difference was 12.4 +/- 4.0 vol% before beginning the CPB, and it was 5.6 +/- 2.7, 5.7 +/- 3.1, 5.4 +/- 3.3, and 4.9 +/- 2.9 vol% at 10, 30, 60, and 90 min respectively after commencement of the PBP under hypothermic CPB. The cerebral AVO2 difference measured 10 min after commencement of the PBP was significantly less than that in the control group (P less than 0.05), but otherwise there were no significant differences between cerebral AVO2 differences in the two groups. Concentration of serum creatine kinase-BB (CK-BB) gradually increased in proportion to the duration of CPB in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Optimal blood flow for cooled brain at 20 degrees C.

BACKGROUND: Optimal conditions for deep hypothermic perfusion and protective brain blood flow remain unclear. METHODS: Dogs (n = 52) underwent 120 minutes of cardiopulmonary bypass at 20 degrees C with perfusion flow rates of 2.5, 5, 10, 20, 40, and 100 mL x kg(-1) x min(-1). We examined the effect of the various flow rates and different perfusion pressures on brain blood flow, metabolism, and intracellular pH. RESULTS: The brain was ischemic and acidotic when the perfusion flow rate was less than 5 mL kg(-1) x min(-1) and pressure was less than 10 mm Hg. When perfusion pressure was higher than 10 mm Hg, cerebral cortex blood flow was more than 9 mL x 100 g(-1) x min(-1) and intracellular pH, higher than 6.95. The cerebral metabolic rate for oxygen decreased at a flow rate of 2.5 mL x kg(-1) min(-1). The cerebral metabolic ratio of glucose to oxygen and the cerebral vascular resistance were lowest when perfusion pressure was 10 to 30 mm Hg. Full-flow (100 mL x kg(-1) x min(-1)) perfusion caused paradoxical brain acidosis; a flow of 40 mL x kg(-1) x min(-1) provided the best results. CONCLUSIONS: Both extremely low-flow perfusion and excessive perfusion cause brain acidosis. Low-flow perfusion at a pressure of 20 mm Hg provides cerebral vasorelaxation and aerobic metabolism during operations at 20 degrees C.     

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)     

Experimental determination of the safe minimum perfusion flow rate for low-flow hypothermic cardiopulmonary bypass

This study investigated the safe minimum perfusion flow rate for low-flow hypothermic cardiopulmonary bypass in a canine model. The adequacy of cerebral oxygenation was determined from the adenosine concentration, the oxygen saturation of cerebral venous blood and brain oxyhemoglobin level. In experiment 1, nine beagles were cooled on bypass to a nasopharyngeal temperature of 18 degrees C and the perfusion flow rate was reduced in a stepwise fashion every 30 min from 100 to 50, 30, 20 and 10 ml/kg per min. In experiment 2, six beagles were cooled on bypass as in experiment 1, and flow was maintained at 30 ml/kg per min for 120 min. At a perfusion flow rate of 30 ml/kg per min, adequate cerebral oxygenation was maintained for 120 min. In contrast, perfusion flow rates of 20 and 10 ml/kg per min were associated with cerebral ischemia.     

Determination of optimal perfusion flow rate for deep hypothermic cardiopulmonary bypass in the adult based on distributions of blood flow and oxygen consumption.

To determine the optimal perfusion flow in deep hypothermic cardiopulmonary bypass at 20 degrees C in human beings, we studied the relationship of perfusion flow to the whole body and to regional oxygen consumption. In adult patients (n = 11, average age 54 years) with valvular or coronary heart disease, the distributions of perfusion flow rate and oxygen consumption were analyzed by dividing into the superior and inferior vena caval areas. Measurements (n = 39) were made at various perfusion flow rates (perfusion flow rate in the superior vena caval area plus that in the inferior vena caval area equals whole-body perfusion flow rate: 0.4 to 2.2 L/min/m2) in a setting of average hemoglobin levels of 8.1 gm/dl. Between whole-body perfusion flow rate and oxygen consumption (total oxygen consumption equals superior plus inferior vena caval oxygen consumption), there was a hyperbolic correlation (r = 0.73; p less than 0.001; asymptote = 29.0 ml/min/m2). A positive linear correlation was found between whole-body perfusion flow rate and inferior vena caval oxygen consumption (r = 0.75; p less than 0.001), whereas no significant relation was seen between whole-body perfusion flow rate and superior vena caval oxygen consumption. For distributional changes in inferior vena caval perfusion flow rate/whole body perfusion flow rate and inferior vena caval oxygen consumption/whole body oxygen consumption, the broken-line regression analysis showed respective critical points where both parameters started to drop when whole-body perfusion flow rate was gradually reduced: 1.2 L/min/m2 for inferior vena caval perfusion flow rate/whole-body perfusion flow rate and 0.8 L/min/m2 for inferior vena caval oxygen consumption/whole-body oxygen consumption. The results indicate that (1) the oxygen consumption to the superior vena caval area was maintained independent of the perfusion in a relatively wide range in contrast to that for the inferior vena caval area and (2) when the redistribution of oxygen consumption is considered as undesirable under low-flow perfusion, the optimal perfusion flow for 20 degrees C deep hypothermic cardiopulmonary bypass appeared to be 0.8 L/min/m2.     

Cerebrovascular and cerebral metabolic effects of alterations in perfusion flow rate during hypothermic cardiopulmonary bypass in man.

Recent experimental and clinical investigations provide conflicting evidence regarding the effects of changes in the systemic flow rate from the pump oxygenator on cerebral blood flow and the cerebral metabolic rate of oxygen consumption. However, the results of existing clinical studies are difficult to interpret because of the confounding effects of differences in management of arterial carbon dioxide tension and use of anesthetic and vasoactive agents during cardiopulmonary bypass. To clarify the relationship among perfusion flow rate, cerebral blood flow, and cerebral metabolic rate of oxygen consumption in man during hypothermic cardiopulmonary bypass, we varied perfusion flow rate in random order to either 1.75 or 2.25 L.min-1.m-2 and studied cerebral blood flow (measured by clearance of xenon 133) and cerebral metabolic rate of oxygen consumption (estimated as the product of cerebral blood flow and the cerebral arteriovenous oxygen content difference) in patients managed with both the alpha-stat (group 1) and the pH-stat (group 2) methods of pH and arterial carbon dioxide tension adjustment. We measured the cerebral arteriovenous oxygen content difference using radial arterial and jugular venous bulb blood samples. In each patient other variables known to exert effects on cerebral blood flow and cerebral metabolic rate of oxygen consumption, including temperature, arterial carbon dioxide tension, arterial oxygen tension, mean arterial pressure, and hematocrit, were maintained constant between measurements. In both groups, mean arterial pressure at both pump flow rates was similar because of spontaneous reciprocal alterations in systemic vascular resistance, that is, as perfusion flow rate declined, systemic vascular resistance increased; as perfusion flow rate increased, systemic vascular resistance declined. Under these tightly controlled conditions, pump flow variation per se exerted no effect on cerebral blood flow or cerebral metabolic rate of oxygen consumption in either group.     

The optimal flow rate for antegrade cerebral perfusion during deep hypothermic circulatory arrest

The aim of this study is to compare cerebral protection using antegrade cerebral perfusion (ACP) with various flow rates during deep hypothermic circulatory arrest (DHCA) in a piglet model. Twenty‐three piglets were randomized to five groups: the control group (n = 3), DHCA group (n = 5), ACP25 group (n = 5), ACP50 group (n = 5), and ACP80 group (n = 5). Three control piglets did not undergo operations. Twenty piglets underwent cardiopulmonary bypass (CPB) and DHCA for 60 min at 20°C. ACP was conducted at 0, 25, 50, and 80 mL/kg/min in the DHCA, ACP25, ACP50, and ACP80 group, respectively. Serum S‐100B protein and neuron‐specific enolase were monitored, and brain tissues were assayed for the activities of caspase‐3 and stained for the evidence of apoptotic cellular injury. Rise in serum S‐100B level (post‐CPB—pre‐CPB) in the ACP50 group was significantly lower than that in the ACP80 group (P = 0.001). Caspase‐3 levels were significantly elevated in the ACP80 group compared with the ACP25 (P = 0.041) and ACP50 group (P = 0.01), while positive terminal deoxyneucleotidyl transferase‐mediated biotin‐dUTP nick end labeling reaction scores in the ACP80 group were significantly higher than those in the ACP25 (P = 0.043) and ACP50 group (P = 0.023). Cerebral protection effects of ACP at 25 and 50 mL/kg/min were superior to that of ACP at 80 mL/kg/min as determined by cerebral markers, immunology, and histology.     

A clinical study on brain perfusion during cardiopulmonary bypass

The purpose of this study was to determine the optimum cerebral perfusion flow rate and pressure of the selective cerebral perfusion. Blood flows of the brachiocephalic and left common carotid artery in 34 patients were continuously monitored by means of electromagnetic flow meter during cardiac operations. Radial and common carotid arterial pressure were monitored simultaneously. Arterial and internal jugular venous blood were sampled and cerebral oxygen consumption was calculated. During steady state hypothermic cardiopulmonary bypass (CPB), mean cerebral perfusion flow was about 600 ml/min at CPB flow of 2.4 L/min/m2. Cerebral oxygen consumption was decreased to 50% of the prebypass level during steady state hypothermic CPB and then it returned to prebypass level after CPB. Common carotid arterial pressure was about 10 mmHg lower than radial arterial pressure during CPB. When CPB flow was remained at 2.4 L/min/m2, left common carotid arterial flow was not affected by common carotid arterial pressure within the range of 40 to 80 mmHg. Cerebral autoregulation might be preserved at this pressure level of the common carotid artery. When CPB flow was reduced from 2.4 L/min/m2, cerebral oxygen consumption was remained constant level until the flow reached to 1.6 L/min/m2, at which cerebral perfusion flow was about 400 ml/min. Data suggest that optimum cerebral perfusion flow during the selective cerebral perfusion may be about 600 ml/min although cerebral oxygen consumption was maintained when cerebral perfusion flow was reduced to 400 ml/min. Optimum cerebral perfusion pressure was 40-80 mmHg of carotid arterial pressure and when monitored in radial artery, more than 10 mmHg higher pressure should be required.     

Metabolism of the heart and brain during hypothermic cardiopulmonary bypass

The alterations in tissue metabolism induced by hypothermic cardiopulmonary bypass are not completely known. Phosphorus-31 nuclear magnetic resonance spectroscopy was used to determine the effect of hypothermic cardiopulmonary bypass on energy states and intracellular pH of the heart and brain. Sheep were instrumented for cardiopulmonary bypass and had a radiofrequency coil placed over either the heart or skull. The animals were placed in a 4.7-T magnet at 37 degrees C and spectra obtained. The animals were cooled on cardiopulmonary bypass to either 26 degrees C (n = 17) or 18 degrees C (n = 14) for brain studies and to 26 degrees C (n = 12) for heart studies. Hypothermia increased the phosphocreatine/adenosine triphosphate ratio in the heart (2.38 +/- 0.23 versus 3.18 +/- 0.37, 37 degrees versus 26 degrees C, respectively, p = 0.03). The brain phosphocreatine/adenosine triphosphate ratio increased from 1.70 +/- 0.09 at 37 degrees C to 2.00 +/- 0.12 at 26 degrees C (p = 0.009) and 2.10 +/- 0.07 at 18 degrees C (p = 0.0001). Intracellular pH increased during hypothermia (heart: 7.05 +/- 0.02 to 7.18 +/- 0.02, 37 degrees versus 26 degrees C, p = 0.0001; and brain: 7.07 +/- 0.02 versus 7.32 +/- 0.02, 37 degrees versus 18 degrees C, p = 0.0001). The adenosine triphosphate resonance position is known to be sensitive to magnesium binding as well as temperature and was shifted upfield (p less than 0.01) in both the heart and brain. This effect could be totally explained by the temperature dependence of this process.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral blood flow and oxygen metabolism during cardiopulmonary bypass with moderate hypothermic selective cerebral perfusion

Cerebral blood flow was measured using transcranial doppler during cardiopulmonary bypass in nine patients with selective cerebral perfusion for surgery of arch aorta (group S). For comparison, 11 adult open heart patients (group C) were also measured. The authors' selective cerebral perfusion at 28 degrees C resulted in moderate hypothermia and antegrade perfusion using independent pumps for three branches. Total flow in the three branches was 500 ml/min. A Labodop DP-100 doppler ultrasound velocimeter was used to measure middle cerebral arterial blood flow velocity. Hemoglobin concentration and oxygen saturation were also measured in arterial and jugular venous blood. The arteriovenous oxygen content difference (Ca-vO2) was calculated and multiplied by the middle cerebral arterial blood flow velocity value, which resulted in the cerebral metabolic rate for oxygen (CMRO2). The cerebral perfusion pressure of group S was lower than in group C, and the arterial carbon-dioxide tension (PaCO2) of group S was higher than in group C during cardiopulmonary bypass. Middle cerebral arterial blood flow velocity values of both groups remained constant before, during and after cardiopulmonary bypass. The CMRO2 decreased during cardiopulmonary bypass and showed no difference between the two groups. The changes in PaCO2 might be significant factors in the increase in cerebral blood flow during selective cerebral perfusion. This study supports the conclusion that, compared with our routine open heart surgery procedures, our selective cerebral perfusion procedures had the same cerebral blood flow and oxygen metabolism during cardiopulmonary bypass.     

深低温低流量灌注与降温期血气管理对乳猪脑保护的对照研究

目的：在深低渐体外循环中比较降温期pH稳态血气管理和深低温阶段低流量灌注对脑保护的作用能力。方法：24头乳猪根据不同的体外循环脑保护处理方法分成4组，A组：深低温停循环、降温期alpha稳态血气管理；B组：深低温停循环、降温期pH稳态血气管理；C组：深低温低流量、降温期alpha稳态血气管理；D组：深低温低流量、降温期pH稳态血气管理。比较不同脑保护方法和体外循环阶段对脑血流（CBF）、脑氧代谢率（CMRO2）、脑乳酸含量、脑水含量和脑电图（EEG）的影响。结果：B组、D组降温末CBF均高于A组、C组；而CMRO2则低于A组、C组；B组、D组降温期EEC平坦波出现早。C组、D组复温期CBF、CMRO2和EEG恢复好于A组、B组。复温末A组、B组颈内静脉乳酸含量显著高于C组、D组，脑水含量组间差异无显著性。结论：深低温体外循环流量灌注对脑保护的作用能力强于降温期pH稳态血气管理，两种方法配合应用具有脑保护的协同作用。     

Changes in hemodynamic variables during hypothermic cardiopulmonary bypass. Effects of flow rate, flow character, and arterial pH

During hypothermic cardiopulmonary bypass, the effects on hemodynamic variables of alternating pump flow rate between 1.5 and 2.0 L.min-1.m-2, flow character between nonpulsatile and pulsatile perfusion, and acid-base management between pH- and alpha-stat control were studied in a crossover factorial experiment. Twenty-four patients who were undergoing elective coronary artery bypass grafting were studied during stable hypothermic (27 degrees to 29 degrees C) cardiopulmonary bypass. A minimum of two (when time allowed, three) consecutive 10-minute periods (period 1, 2, or 3) were investigated. Only stage of the study period during cardiopulmonary bypass, flow rate, and interaction between stage and acid-base management were found to have significant effects on mean arterial pressure. In all patients, there were average increases in mean arterial pressure from period 1 to period 2 of 9.4 (95% confidence interval 5.8, 13.0) mm Hg, from period 2 to period 3 of 6.3 (95% confidence interval 1.2, 11.4) mm Hg, and from period 1 to period 3 of 15.7 (95% confidence interval 10.6, 20.9) mm Hg. At 2.0 L.min-1.m-2, mean arterial pressure was 7.2 (95% confidence interval 1.6, 12.9) mm Hg higher than at 1.5 L.min-1.m-2. Peripheral vascular resistance was significantly affected only by stage and flow rate. There were, in all patients, mean increases in peripheral vascular resistance from period 1 to period 2 of 239 (95% confidence interval 135, 343) dynes.sec.cm-5, from period 2 to period 3 of 85 (-64, 234) dynes.sec.cm-5, and from period 1 to period 3 of 324 (95% confidence interval 175, 473) dynes.sec.cm-5. At 1.5 L.min-1.m-2, the peripheral vascular resistance was 316 (95% confidence interval 152, 480) dynes.sec.cm-5 higher than at 2.0 L.min-1.m-2. Alteration in flow rate, but not flow character or arterial pH, had a significant effect on peripheral vascular resistance. It is hypothesized that the increase in peripheral vascular resistance during the course of cardiopulmonary bypass results from an active capillary mechanism, whereas the increase that is associated with reduction in flow rate reflects a passive mechanism. The increase in peripheral vascular resistance with decrease in flow rate indicates impaired tissue perfusion, unlike that occurring with stage.     

幼猪深低温低流量体外循环心脏手术中脑损伤的实验研究

目的 评价长时间深低温低流量体外循环( cardiopulmonary bypass,CPB)心脏手术对幼猪未成熟脑的影响及其机制.方法 北京长白幼猪15只,按随机数字表法分为实验组(10只)和对照组(5只).实验组麻醉后正中开胸,常规建立CPB,体温降至25℃后,开始低流量循环(50 ml· kg-1· min-1),主动脉阻断120 min后开放,停机后观察120 min取脑海马组织;对照组麻醉后开胸,取脑海马组织.实验组分别在麻醉诱导后即刻(T1)、停机后5 min (T2)、120 min(T3)取静脉血,酶联免疫吸附法(ELISA)检测白细胞介素-6(interleukin-6,IL-6)、肿瘤坏死因子-α(tumor necrosis factor-α,TNF-α).实验组、对照组脑海马组织行HE染色病理检查;ELISA法测海马神经元特异性烯醇化酶(neuron-specific enolase,NSE)、S100蛋白β亚型(S100 protein beta subtypes,S100β).结果 实验组1只死于CPB停机后心脏骤停,余9只和对照组5只完成至实验结束.与T1比较,实验组T2的IL-6、TNF-α分别升高7.01％(P＜0.05)、3.52％(P＜0.05);T3的IL-6、TNF-α分别升高5.10％(P＜0.05)、1.47％(P＞0.05).与对照组比较,实验组可见脑损伤病理学改变,NSE、S100β分别升高40.08％ (P＜0.05)、29.66％( P＜0.05). 结论 深低温低流量CPB心脏手术可造成幼猪脑组织损伤,并证实炎症反应是脑损伤的可能机制之一.     

Tissue heat content and distribution during and after cardiopulmonary bypass at 17 degrees C.

We measured afterdrop and peripheral tissue temperature distribution in eight patients cooled to approximately 17 degrees C during cardiopulmonary bypass and subsequently rewarmed to 36.5 degrees C. A nasopharyngeal probe evaluated trunk and head temperature and heat content. Peripheral tissue temperature (arm and leg temperature) and heat content were estimated using fourth-order regressions and integration over volume from 30 tissue and skin temperatures. Peripheral tissue temperature decreased to 19.7+/-0.9 degrees C during bypass and subsequently increased to 34.3+/-0.7 degrees C during 104+/-18 min of rewarming. The core-to-peripheral tissue temperature gradient was -5.9+/-0.9 degrees C at the end of cooling and 4.7+/-1.5 degrees C at the end of rewarming. The core-temperature afterdrop was 2.2+/-0.4 degrees C and lasted 89+/-15 min. It was associated with 1.1+/-0.7 degrees C peripheral warming. At the end of cooling, temperatures at the center of the upper and lower thigh were (respectively) 8.0+/-5.2 degrees C and 7.3+/-4.2 degrees C cooler than skin temperature. On completion of rewarming, tissue at the center of the upper and lower thigh were (respectively) 7.0+/-2.2 degrees C and 6.4+/-2.3 degrees C warmer than the skin. When estimated systemic heat loss was included in the calculation, redistribution accounted for 73% of the afterdrop, which is similar to the contribution observed previously in nonsurgical volunteers. IMPLICATIONS: Temperature afterdrop after bypass at 17 degrees C was 2.2+/-0.4 degrees C, with approximately 73% of the decrease in core temperature resulting from core-to-peripheral redistribution of body heat. Cooling and rewarming were associated with large radial tissue temperature gradients in the thigh.     

Effect of perfusion flow rate on tissue oxygenation in newborn piglets during cardiopulmonary bypass

BACKGROUND: Our knowledge of the best perfusion flow rate to use during cardiopulmonary bypass (CPB) in order to maintain tissue oxygenation remains incomplete. The present study examined the effects of perfusion flow rate and patent ductus arteriosus (PDA) during normothermic CPB on oxygenation in several organ tissues of newborn piglets. METHODS: The experiments were performed on 12 newborn piglets: 6 with PDA ligation (PDA-L), and 6 without PDA ligation (PDA-NL). CPB was performed through the chest at 37 degrees C. During CPB, the flow rate was changed at 15-minute intervals, ranging from 100 to 250 ml/kg/min. Tissue oxygenation was measured by quenching of phosphorescence. RESULTS: For the PDA-L group, oxygen in the brain did not change significantly with changes in flow rate. In contrast, for the PDA-NL group, oxygen was dependent upon the flow rate. Statistically significant decreases in cortical oxygen were observed with flow rates below 175 ml/kg/min. Within the myocardium, liver, and intestine, there were no significant differences in the oxygen levels between the PDA-L and PDA-NL groups. In these tissues, the oxygen decreased significantly as the flow rate decreased below 150 ml/kg/min, 125 ml/kg/min, and 175 ml/kg/min, respectively. Oxygen pressure in skeletal muscle was not dependent on either PDA ligation or flow rate. CONCLUSIONS: In newborn piglets undergoing CPB, the presence of a PDA results in reduced tissue oxygenation to the brain but not to other organs. In general, perfusion flow rates of 175 ml/kg/min or greater are required in order to maintain normal oxygenation of all organs except muscle.     

Microvascular permeability after cardiopulmonary bypass. An experimental study

Microvascular permeability is presumed to increase during cardiopulmonary bypass, but this has not been directly demonstrated. Method: Therefore, a controlled experimental study was performed in dogs in which the permeability ratio of the small intestinal microvasculature was determined. Shortly after 120 minutes of cardiopulmonary bypass (experimental group, n = 7) or a sham procedure (control group, n = 7), the superior mesenteric venous pressure was raised in a stepwise fashion until the intestinal lymph/plasma protein concentration stabilized at a minimum value. Data: Minimal lymph/plasma concentration ratio (permeability ratio) of the total proteins and each of six protein fractions was greater in dogs that had been on bypass than in control dogs (p = 0.01 for total proteins and less than 0.05 for five of the fractions). The variability in this regard was large in both groups, and in some animals subjected to bypass the permeability ratio was more than twice the maximum value for the control group. The increase in permeability ratio was greater for large molecules. Inferences: Cardiopulmonary bypass results in a variable increase in microvascular permeability. This results primarily from an increase in the size of large pores in the microvascular barrier.