Perfusion characteristics during cardiopulmonary bypass and subsequent changes in alveolar-arterial oxygen tension gradients

In 11 elective coronary artery bypass graft (CABG) recipients, changes in alveolar-arterial O2 tension difference (deltaAaDO2) from 5 minutes before to 30 minutes after cardiopulmonary bypass (CPB) ranged from -54.9 to +63.1 torr and exhibited significant linear correlation (r = 0.77, p less than 0.01) with the mean arterial perfusion pressure (MAPP) during CPB multiplied by the duration (T) of CPB divided by the body surface area (BSA) of the patient. The regression equation (deltaAaDO2 = 0.015 MAPP divided by BSA X T -50) enables estimation of the delta AaDO2 to result from a given episode of CPB. Mural edema of airways and pulmonary vasculature, developing during CPB, may be a mechanism underlying this correlation.     

Reduced oxygen tension during cardiopulmonary bypass limits myocardial damage in acute hypoxic immature piglet hearts

Objectives.

Cardiopulmonary bypass (CPB) is usually instituted in a hyperoxic fashion (oxygen tension (pO₂) 300–500 mmHg), which may expose cyanotic infants to potential reoxygenation damage. Oxygen free radicals play an important role in this injury. The rate of production of this highly reactive toxic oxygen species is dependent on the oxygen level during reoxygenation. This study tested the hypothesis that reduction of the oxygen in the bypass prime and in blood cardioplegia (BCP) to normoxic levels can reduce reoxygenation injury and will result in improved contractility.

Methods.

We operated on 19 Duroc-Yorkshire piglets (2–3 weeks, 3–5 kg). Five underwent 30 min of BCP arrest during 1 h of CPB without hypoxia (control). Fourteen underwent 120 min of hypoxia (arterial pO₂ 20–30 mmHg) on ventilator before reoxygenation on CPB. Reflecting the clinical routine procedure, nine of them were reoxygenated on CPB for 5 min with high pO₂ (350–450 mmHg) followed by 30 min of BCP arrest (high pO₂) and 25 min of reoxygenation/reperfusion on CPB with high pO₂ levels (NoRx). Five others were put on CPB with pO₂ reduced to normoxic levels (pO₂ 100 mmHg) in CPB and BCP (Rx). Functional and biochemical measurements were made before hypoxia, as well as during and after reoxygenation.

Results.

In contrast to controls, NoRx resulted in a 40% decrease in antioxidant reserve capacity (P<0.01) at 4 mM t-butyl hydroperoxide (t-BHP), a 1212% increase in moycardial conjugated diene production during BCP induction (P<0.0003), a 1000% during reperfusion (P<0.002), a 36.1% and a 37.0% increase in coronary sinus blood conjugated dienes at 35 min (P<0.05) and 60 min (P<0.05) of reoxygenation. These biochemical changes were accompanied by a 79% reduction of left ventricular contractility (P<0.0003). Conversely, Rx led to an improvement in antioxidant reserve capacity (939±212 vs 1342±177 nmol/g protein; P<0.003), less conjugated diene production during BCP induction (15.5±6.1 vs 42.1±8.8 A₂₃₃nm/min per 100 g; P<0.003) and reperfusion (1.8±3.9 vs 22.0±5.5 A₂₃₃nm/min per 100 g; P<0.005), and to a significantly improved post bypass LV contractility (58±25 vs 21±5; P<0.0003).

Conclusions.

These data document that hypoxemic/reoxygenation injury occurs in acute hypoxic immature piglet hearts when reoxygenated on CPB with hyperoxic pO₂ (normal clinical practice). By lowering the antioxidant reserve capacity, hypoxemia seems to render the developing heart susceptible to reoxygenation damage, which occurs with the reintroduction of molecular oxygen, and is associated with free radical production, subsequent lipid peroxidation, and depressed post bypass LV function. Reduction of pO₂ during the initial reoxygenation period and during BCP arrest to normoxic levels resulted in a significant reduction of this oxygen-related damage and in much improved myocardial performance.     

Hierarchy of regional oxygen delivery during cardiopulmonary bypass

BACKGROUND: Relative to the nonbypass state, cardiopulmonary bypass may decrease whole-body oxygen (O2) delivery. We predicted that during cardiopulmonary bypass, a hierarchy of regional blood flow and O2 delivery could be characterized. METHODS: In 8 46.5 +/- 1.2-kg pigs, fluorescent microspheres were used to determine blood flow and O2 delivery to five organ beds before and during 37 degrees C cardiopulmonary bypass at four randomized bypass flows (1.4, 1.7, 2.0, and 2.3 L/min/m2). At completion, 18 tissue samples were obtained from the cerebral cortex (n = 4), renal cortex (n = 2), renal medulla (n = 2), pancreas (n = 3), small bowel (n = 3), and limb muscle (n = 4) for regional blood flow determination. RESULTS: At conventional cardiopulmonary bypass flow (2.3 L/min/m2), whole-body O2 delivery was reduced by 44 +/- 6% relative to the pre-cardiopulmonary bypass state (p < 0.05). Over a range of cardiopulmonary bypass flows (2.3 to 1.7 L/min/m2), brain and kidney maintained their perfusion. Blood flow and O2 delivery to both regions were reduced when the cardiopulmonary bypass flow was reduced to 1.4 L/min/m2. However, perfusion and O2 delivery to other visceral organs (pancreas, small bowel) and skeletal muscle showed pump flow dependency over the range of flows tested. CONCLUSIONS: This study characterizes the organ-specific hierarchy of blood flow and O2 distribution during cardiopulmonary bypass. These dynamics are relevant to clinical decisions for perfusion management.     

Subcutaneous tissue oxygen tension after coronary revascularisation with and without cardiopulmonary bypass

Directly measured subcutaneous tissue oxygen tension reflects the adequacy of regional tissue oxygenation and influences wound infection and healing. We tested the hypothesis that off-pump coronary artery bypass would increase subcutaneous tissue oxygen tension by minimizing cardiopulmonary bypass-induced systemic inflammation. Ten consecutive patients scheduled for off-pump coronary artery bypass were compared with 10 undergoing conventional cardiopulmonary bypass. All patients had a tissue oxygen sensor implanted longitudinally into the subcutaneous tissue of the leg in the saphenous vein harvest wound. Data were collected from closure of the saphenous vein wound for 20 h postoperatively. Although more off-pump patients had only one coronary artery grafted, postoperative subcutaneous tissue oxygen tension was significantly higher in off-pump patients throughout the 20-h study. Absolute mean (SD) differences ranged from 2.3 kPa in the first 2 h [14.4 (2.3) vs. 12.1 (2.4) kPa in off-pump and cardiopulmonary bypass, respectively, p = 0.04] to 4.6 kPa at 8-10 h [14.0 (3.5) vs. 9.3 (2.7) kPa, p = 0.007]. In contrast, there were no significant differences in arterial oxygen tension values over this period. Mean arterial pressure and haemoglobin were transiently higher in off-pump patients at 8 h only. We conclude that postoperative subcutaneous tissue oxygen tension was higher for 20 h after off-pump compared with conventional cardiopulmonary bypass.     

Heparin monitoring during cardiopulmonary bypass in congenital heart surgery

The Hepcon/HMS system automatically provides the activated clotting time and a whole blood heparin concentration. It also provides the adequate protamine dose by titration of protamine to heparin. 45 patients undergoing congenital heart surgery with cardiopulmonary bypass (CPB) were studied by the Hepcon/HMS device. We measured the heparin dose response before heparin administration, and the ration between the dose of protamine (ml) which was necessary for heparin neutralization at the termination of CPB and the dose of total heparin (ml) in each patient. The value of heparin dose response ranged 120-390 (mean 228) IU/kg. The ratio between protamine dose and heparin dose varied 0.11-0.99 (mean 0.55). There was a statistically significant correlation between the duration of CPB and this ratio (r = -0.51, n = 45, p = 0.0005). From the standpoint of variances in the value of heparin dose response, conventional way of the heparin administration according to the patient's body weight alone may cause inadequacy of anticoagulation during CPB. A dose of protamine determined by Hepcon device that is smaller than a conventional dose of protamine prevents inadvertent overdose and, therefore, can reduce the adverse effects excessive protamine has.     

Dobutamine increases oxygen consumption during constant flow cardiopulmonary bypass

We have studied the effects of flow and dobutamine on systemic haemodynamic variables, oxygen delivery (DO2) and oxygen consumption (VO2) in 20 patients during cardiopulmonary bypass (CPB) with mild hypothermia (34 degrees C). In a subgroup of seven patients, we also studied the effects on gastric microcirculatory blood flow (MCF) using laser Doppler flowmetry. During CPB, measurements were made before and after two interventions: the first consisted of increasing flow from 2.4 to 3.0 litre min-1 m-2 for 10 min; the second consisted of an infusion of dobutamine at a rate of 6 micrograms kg-1 min-1 for 10 min during constant flow CPB. There were no significant differences in DO2, VO2 or haemodynamic variables between the two baseline measurements. The increase in flow raised DO2 (27%, P < 0.001), mean arterial pressure (P < 0.01) and MCF (P < 0.01), but failed to increase VO2. In contrast, dobutamine infusion increased VO2 (11%, P < 0.001) during constant flow CPB without significant changes in DO2, systemic haemodynamic variables or MCF. These results indicate that increases in VO2 during dobutamine may be flow-independent.      

Hypoxemia after intraluminal oxygen line obstruction during cardiopulmonary bypass

A patient sustained an episode of hypoxemia during cardiopulmonary bypass. Investigation of the extracorporeal circuit after successful resolution of the problem showed that a white, crystalline substance later identified as mannitol occluded the oxygen supply line to a bubble oxygenator. The management and subsequent investigation of the problem are presented.     

Splanchnic blood flow and oxygen uptake during cardiopulmonary bypass

OBJECTIVE: To measure splanchnic blood flow (SBF) with 2 indicator dilution techniques during and after cardiopulmonary bypass (CPB), to compare the results with transesophageal echocardiography Doppler-measured right hepatic vein (RHV) flow, and to study gastric tonometry data in the same patients. DESIGN: Single-arm prospective study. SETTING: University hospital operating room and intensive care unit. PARTICIPANTS: Ten adult patients undergoing cardiac surgery. INTERVENTIONS: SBF was measured using constant rate infusion of indocyanine green dye and low-dose ethanol from induction of anesthesia until end of hypothermic CPB. The infusion of ethanol was continued, and SBF was measured postoperatively at 2, 3, and 4 hours after CPB. Simultaneously, RHV flow, splanchnic oxygen delivery and uptake, and gastric mucosal pH were calculated. MEASUREMENTS AND MAIN RESULTS: SBF, RHV flow, and gastric mucosal pH remained unchanged during the study period. SBF measured with indocyanine green was 765 +/- 88 (SEM) mL/min after induction of anesthesia. SBF before CPB measured with ethanol was 985 +/- 218 mL/min. There was no significant difference between the methods. RHV flow was 450 +/- 87 mL/min after induction of anesthesia. There was no correlation between individual values of RHV flow and SBF. Splanchnic oxygen uptake was 52 +/- 7.8 mL/min after induction of anesthesia and decreased to 28 +/- 2.6 mL/min during CPB. Gastric mucosal pH was 7.32 +/- 0.02 after induction of anesthesia and showed no correlation to SBF or to splanchnic oxygen uptake. CONCLUSION: SBF did not decrease during CPB. SBF could be measured with ethanol with reasonable accuracy. Transesophageal echocardiography assessment of RHV flow was not suitable to quantify SBF in the individual patient, but could be used to follow relative changes.     

Whole-body oxygen consumption at different temperatures during cardiopulmonary bypass

For evaluation of the adequacy of tissue perfusion during cardiopulmonary bypass (CPB), whole-body oxygen consumption rates at different body weights and temperatures are basic and important data. But few studies have analyzed the oxygen consumption estimated from real-time data during CPB in clinical situations. We analyzed retrospectively the oxygen consumption at different body weights (BW) during normothermia (VO2 37) and the oxygen consumption ratio at different body temperatures (BT; %VO2X; X = BT) from the CPB charts of 189 cases. From these charts, 877 data points for oxygen consumption during total CPB were calculated by Fick's law. By statistical analysis of these data, we derived the following formulae: VO2 37 (ml/kg/min) = 7.6481 x BW0.0679, R2 = 1.0 (BW < 8 kg) VO2 37 (ml/kg/min) = 32.394 x BW-0.625, R2 = 0.92 (BW > or = 8 kg) %VO2X (%) = 4 x 10(-5) x BT4.0777, R2 = 0.42. These formulae indicate that (1) the whole-body oxygen consumption during total CPB can be measured by subtracting the oxygen consumption associated with circulatory and respiratory processes from the oxygen consumption derived from the basal metabolism; and (2) although the change in oxygen consumption induced by hypothermia is variable depending on body weight, the rate of change shows no difference regardless of the patient's weight.     

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)     

温度对体外循环期间氧代谢的影响

目的　观察温度对体外循环心肺转流 (CPB)期间氧代谢的影响。方法　成年健康杂种犬 11只 ,随机分为低温组 (H组 ,n =5 )和常温组 (N组 ,n =6)。H组采用 4℃改良托马氏停搏液间断灌注 ,最低鼻咽温度 2 8～ 3 0℃ ;N组采用氧合温血持续灌注 ,最低鼻咽温度 3 5 3～ 3 7 1℃。主动脉阻断 60分钟、CPB90分钟。分别测定麻醉稳定后CPB前、CPB3 0分钟、CPB90分钟、CPB后 60分钟时的动脉血氧饱和度 (SaO2 )、动脉氧分压 (PaO2 )、混合静脉血氧饱和度 (S vO2 )、混合静脉血氧分压(P vO2 )、血红蛋白浓度 (Hb)、红细胞压积 (Hct)、股静脉乳酸 (La)浓度 ,并计算氧供给 (DO2 )、氧消耗(VO2 )、氧摄取率 (ERO2 )。结果　与CPB前相比 ,CPB中两组的DO2 明显降低 (P <0 0 1) ,CPB后60分钟两组SaO2 、PaO2 、S vO2 都有不同程度的降低 (P <0 0 5或P <0 0 1) ,La、ERO2 增高 ;CPB过程中H组DO2 、VO2 低于N组 (P <0 0 5或P <0 0 1)。结论　在过度血液稀释情况下 ,常温和低温CPB后都存在低氧血症 ,但常温CPB期间氧利用明显优于低温CPB。     

心肺转流时利多卡因对脑氧代谢的影响

目的　观察心肺转流 (CPB)时利多卡因对脑氧代谢的影响,探讨脑保护措施。方法　二尖瓣膜置换手术20例,随机均分为对照组 (Ⅰ组)和利多卡因组(Ⅱ组)。Ⅱ组在麻醉后用微量泵输入利多卡因150μg·kg 1·min 1。α稳态处理血气,通过桡动脉和颈内静脉球部血液的动态血气分析及乳酸浓度测定,计算全身动脉及颈内静脉的血氧含量、动 颈内静脉血氧含量差、脑氧摄取率和动 颈内静脉血乳酸浓度差。分析CPB时利多卡因对脑氧代谢的影响。结果　CPB开始后,两组的动脉血氧含量、动 颈内静脉血氧含量差和脑氧摄取率下降,随着复温又升高。CPB降温至 26℃时,Ⅱ组的动 颈内静脉血氧含量差、脑氧摄取率明显低于Ⅰ组(P<0 .01)。两组的乳酸浓度均升高,降温后动 颈内静脉血的乳酸浓度差无明显变化。停CPB时,两组的动 颈内静脉血氧含量差仍明显低于CPB前水平(P<0 .01)。结论　CPB中利多卡因能降低脑氧耗,有利于改善大脑氧供需平衡和保护CPB中缺血脑细胞的功能。     

乌司他丁对心肺转流心脏手术病人脑氧代谢的影响

目的探讨乌司他丁对心肺转流（CPB）心脏手术病人脑氧代谢的影响。方法选择24例择期行心脏瓣膜置换术病人,随机分为乌司他丁组（U组）和对照组（C组）,每组12例。U组共给予乌司他丁2．4万U／kg,其中1．2万U／kg于麻醉诱导后静脉推注,0．6万U／kg加入CPB预充液中,随转流进人体内,0．6万U／kg于主动脉开放前约5min加入CPB机内。C组用等量的生理盐水代替。于麻醉后手术前（T1）、低温稳定期（T2）、复温至36℃（Ts）、CPB结束后60min（Tt）、CPB结束后6h（T5）同时抽取动脉血与颈静脉球血,进行血气分析和动脉血、颈静脉球血乳酸（AL、VL）测定并计算动脉血氧含量（CaO2）、动脉-颈内静脉血氧含量差（Ca-jvO2）、脑乳酸生成量（AVDL）与乳酸氧指数（LOI）。结果C组Ca-jvO2于T2至T5、U组于T2至T4均有不同程度降低（P〈0．05）;两组AL、VL于T2至T5进行性升高,AVDL、LOI于T4、L高于T1至L3两组间CaO2各时点无显著性差异;U组颈静脉球血氧饱和度（SjvO2）、AL、VL、AVDL、LOI于T4、T5时明显低于C组（P〈0．05或P〈0．01）;U组Ca—jvO2于T4、T5时明显高于C组（P〈0．05或P〈0．01）。结论乌司他丁可以减轻CPB引起的脑无氧代谢,改善脑氧摄取与利用。