母体体外循环过程中胎儿有创监测动物模型的建立

目的 建立孕羊体外循环过程中胎羊有创监测模型,探讨母体体外循环对胎儿温度、血流动力学的影响.方法 20头健康孕羊随机分为对照组、常温组、浅低温组和中低温组4组,每组5头.常规建立体外循环,转流降温.监测孕羊和胎羊的温度、心率、平均动脉压.结果 中低温组1头孕羊转流后发生室颤导致孕羊和胎羊死亡.降温期胎羊温度始终高于孕羊的温度.复温期孕羊、胎羊温度回升,转流结束后胎羊温度低于孕羊温度.降温期胎羊心率逐渐减慢,血压下降,复温期逐渐恢复正常.结论 母体体外循环影响胎儿温度、血压和心率,但变化是可逆的.母体常温或浅低温体外循环对胎儿的影响最小,临床上可以安全应用.     

The effects of deep hypothermic cardiopulmonary bypass and total circulatory arrest on cerebral blood flow in infants and children

Cardiopulmonary bypass management in infants and children involves extensive alterations in temperature, hemodilution, and perfusion pressure, with occasional periods of circulatory arrest. Despite the use of these biologic extremes of temperature and perfusion, their effects on cerebral blood flow are unknown. This study was designed to examine the relationship of mean arterial pressure and nasopharyngeal temperature to cerebral blood flow during deep hypothermic cardiopulmonary bypass (18 degrees to 22 degrees C) with and without periods of total circulatory arrest. Cerebral blood flow was measured before, during, and after deep hypothermic cardiopulmonary bypass using xenon clearance techniques in 25 children, aged 2 days to 60 months. Fourteen patients underwent repair with circulatory arrest. There was a highly significant correlation of cerebral blood flow with temperature during cardiopulmonary bypass (p = 0.007). During deep hypothermic bypass there was a significant association between cerebral blood flow and mean arterial pressure (p = 0.027). In infants undergoing repair with deep hypothermia alone, cerebral blood flow returned to prebypass levels in the rewarming phase of bypass. However, in patients undergoing repair with circulatory arrest, no significant increase in cerebral blood flow during rewarming or even after bypass was observed (p = 0.01). These data show that deep hypothermic cardiopulmonary bypass significantly decreases cerebral blood flow because of temperature reduction. Under conditions of deep hypothermia, cerebral pressure-flow autoregulation is lost. This study also demonstrates that cerebral reperfusion after deep hypothermia is impaired if the patient is exposed to a period of total circulatory arrest.     

The effect of hypothermic cardiopulmonary bypass and total circulatory arrest on cerebral metabolism in neonates, infants, and children

Cardiopulmonary bypass management in neonates, infants, and children often requires the use of deep hypothermia at 18 degrees C with occasional periods of circulatory arrest and represents marked physiologic extremes of temperature and perfusion. The safety of these techniques is largely dependent on the reduction of metabolism, particularly cerebral metabolism. We studied the effect of hypothermia on cerebral metabolism during cardiac surgery and quantified the changes. Cerebral metabolism was measured before, during, and after hypothermic cardiopulmonary bypass in 46 pediatric patients, aged 1 day to 14 years. Patients were grouped on the basis of the different bypass techniques commonly used in children: group A--moderate hypothermic bypass at 28 degrees C; group B--deep hypothermic bypass at 18 degrees to 20 degrees C with maintenance of continuous flow; and group C--deep hypothermic circulatory arrest at 18 degrees C. Cerebral metabolism significantly decreased under hypothermic conditions in all groups compared with control levels at normothermia, the data demonstrating an exponential relationship between temperature and cerebral metabolism and an average temperature coefficient of 3.65. There was no significant difference in the rate of metabolism reduction (temperature coefficient) in patients cooled to 28 degrees and 18 degrees C. From these data we were able to derive an equation that numerically expresses a hypothermic metabolic index, which quantitates duration of brain protection provided by reduction of cerebral metabolism owing to hypothermic bypass over any temperature range. Based on this index, patients cooled to 28 degrees C have a predicted ischemic tolerance of 11 to 19 minutes. The predicted duration that the brain can tolerate ischemia ("safe" period of deep hypothermic circulatory arrest) in patients cooled to 18 degrees C, based on our metabolic index, is 39 to 65 minutes, similar to the safe period of deep hypothermic circulatory arrest known to be tolerated clinically. In groups A and B (no circulatory arrest), cerebral metabolism returned to control in the rewarming phase of bypass and after bypass. In group C (circulatory arrest), cerebral metabolism and oxygen extraction remained significantly reduced during rewarming and after bypass, suggesting disordered cerebral metabolism and oxygen utilization after deep hypothermic circulatory arrest. The results of this study suggest that cerebral metabolism is exponentially related to temperature during hypothermic bypass with a temperature coefficient of 3.65 in neonates infants and children. Deep hypothermic circulatory arrest changes cerebral metabolism and blood flow after the arrest period despite adequate hypothermic suppression of metabolism.     

Hypothermia and the Approximate Entropy of the Electroencephalogram

Background: The electroencephalogram is commonly used to monitor the brain during hypothermic cardiopulmonary bypass and circulatory arrest. No quantitative relationship between the electroencephalogram and temperature has been elucidated, even though the qualitative changes are well known. This study was undertaken to define a dose-response relationship for hypothermia and the approximate entropy of the electroencephalogram.

Methods: The electroencephalogram was recorded during cooling and rewarming in 14 patients undergoing hypothermic cardiopulmonary bypass and circulatory arrest. Data were digitized at 128 Hz, and approximate entropy was calculated from 8-s intervals. The dose-response relationship was derived using sigmoidal curve-fitting techniques, and statistical analysis was performed using analysis of variance techniques.

Results: The approximate entropy of the electroencephalogram changed in a sigmoidal fashion during cooling and rewarming. The midpoint of the curve averaged 24.7[degrees]C during cooling and 28[degrees]C (not significant) during rewarming. The temperature corresponding to 5% entropy (T0.05) was 18.7[degrees]C. The temperature corresponding to 95% entropy (T0.95) was 31.3[degrees]C during cooling and 38.2[degrees]C during rewarming (P < 0.02).     

Power spectral analysis of EEG during simple deep hypothermia under ether anesthesia

Power spectral analysis of electroencephalogram was performed during simple deep hypothermia under ether anesthesia, compared with that during hypothermic cardiopulmonary bypass under morphine anesthesia. In ether anesthesia group, EEG isoelectricity developed at average esophageal temperature of 27.2 degrees C which is higher than the temperature previously reported. This remarkable depression of the EEG may be due to deep ether anesthesia, because severe hypotension episodes were not associated with this and no neurological complication was noticed post-operatively. In cardiopulmonary bypass group, EEG activity persisted throughout the procedures even at the lowest esophageal temperature reached of 22.3 degrees C. In ether anesthesia group, the temperature at which EEG activity reappeared correlated with the duration of circulatory arrest. During simple deep hypothermia under ether anesthesia, the EEG is not useful to detect brain ischemia during cooling period, because EEG activity was lost in the early course of cooling, but during rewarming period the EEG demonstrated depression of cerebral function due to total circulatory arrest.     

Hypothermia and the approximate entropy of the electroencephalogram

BACKGROUND: The electroencephalogram is commonly used to monitor the brain during hypothermic cardiopulmonary bypass and circulatory arrest. No quantitative relationship between the electroencephalogram and temperature has been elucidated, even though the qualitative changes are well known. This study was undertaken to define a dose-response relationship for hypothermia and the approximate entropy of the electroencephalogram. METHODS: The electroencephalogram was recorded during cooling and rewarming in 14 patients undergoing hypothermic cardiopulmonary bypass and circulatory arrest. Data were digitized at 128 Hz, and approximate entropy was calculated from 8-s intervals. The dose-response relationship was derived using sigmoidal curve-fitting techniques, and statistical analysis was performed using analysis of variance techniques. RESULTS: The approximate entropy of the electroencephalogram changed in a sigmoidal fashion during cooling and rewarming. The midpoint of the curve averaged 24.7 degrees C during cooling and 28 degrees C (not significant) during rewarming. The temperature corresponding to 5% entropy (T 0.05 ) was 18.7 degrees C. The temperature corresponding to 95% entropy (T 0.95 ) was 31.3 degrees C during cooling and 38.2 degrees C during rewarming ( P < 0.02). CONCLUSIONS: Approximate entropy is a suitable analysis technique to quantify the electroencephalographic changes that occur with cooling and rewarming. It demonstrates a delay in recovery that is of the same magnitude as that seen with conventional interpretation of the analog electroencephalogram and extends these observations over a greater range of temperatures.     

Reduced jugular venous oxygen saturation during rewarming from deep hypothermic circulatory arrest: cerebral overextraction?

Deep hypothermic circulatory arrest may impair cerebral cellular functions, and physiological parameters following circulatory arrest may deviate from the normal. The intention of this study was to monitor jugular venous oxygen saturation during cardiopulmonary bypass before and after deep hypothermic circulatory arrest. Jugular venous oxygen saturation were obtained on 18 patients by using a retrograde jugular vein catheter during replacement of the ascending aorta. Indications for operations were ascending aortic dilatation (n=15) and acute aortic dissection (n=3). Hypothermic cardiopulmonary bypass (233+/-60 min), cardioplegic arrest (105+/-37 min) and circulatory arrest (22+/-7 min) were utilized during the operations. Jugular venous oxygen saturation increased during hypothermia and decreased during rewarming. Compared with cooling, jugular venous oxygen saturation during the initial part of rewarming were significantly lower (87+/-5% vs. 97+/-1%, 89+/-4% vs. 95+/-2%, 81+/-4% vs. 87+/-5% at 16, 20 and 24 degrees C respectively, p<0.05). One patient required re-exploration because of bleeding. All patients were found neurologically normal before being discharged from the hospital (mean 14+/-7 days). In conclusion, jugular venous oxygen saturation is inversely related to the body temperature in patients undergoing hypothermic cardiopulmonary bypass. Significantly decreased jugular venous oxygen saturation during the initial part of rewarming may signify an increased cerebral extraction of oxygen.     

Safety of deliberate intraoperative and postoperative hypothermia for patients undergoing coronary artery surgery: a randomized trial

BACKGROUND: Hypothermia in the perioperative period is associated with adverse effects, particularly bleeding. Before termination of cardiopulmonary bypass, rewarming times and perfusion temperatures are often increased to avoid post-cardiopulmonary bypass hypothermia and the presumed complications. This practice may, however, also have adverse effects, particularly cerebral hyperthermia. We present safety outcomes from a trial in which patients undergoing coronary artery surgery were randomly assigned to normothermia or hypothermia for the entire surgical procedure. METHODS: Consenting patients over the age of 60 years presenting for a first, elective coronary artery surgery with cardiopulmonary bypass were randomly assigned to having their nasopharyngeal temperature maintained at either 37 degrees C (group N; 73 patients) or 34 degrees C (group H; 71 patients) throughout the intraoperative period, with no rewarming before arrival in the intensive care unit. All received tranexamic acid. RESULTS: There was no clinically important difference in intraoperative blood product or inotrope use. Temperatures on arrival in the intensive care unit were 36.7 degrees C +/- 0.38 degrees C and 34.3 degrees C +/- 0.38 degrees C in groups N and H, respectively. Blood loss during the first 12 postoperative hours was 596 +/- 356 mL in group N and 666 +/- 405 mL in group H (mean difference +/- 95% confidence interval, 70 +/- 126 mL; P =.28). There was no significant difference in blood product utilization, intubation time, time in the hospital, myocardial infarction, or mortality. The mean time in the intensive care unit was 8.4 hours less in the hypothermic group (P =.02). CONCLUSIONS: Our data support the safety of perioperative mild hypothermia in patients undergoing elective nonreoperative coronary artery surgery with cardiopulmonary bypass. These findings suggest that complete rewarming after hypothermic cardiopulmonary bypass is not necessary in all cases.     

Hippocampal neuronal death following deep hypothermic circulatory arrest in dogs: involvement of apoptosis.

This study was undertaken to evaluate the histological nature of brain damage caused by deep hypothermic circulatory arrest during cardiopulmonary bypass. Total body cooling to 15 degrees C and rewarming were performed with a conventional cardiopulmonary bypass technique using the femoral artery and vein. Dogs were assigned to one of three groups. In group 1 (n = 4), cardiopulmonary bypass was maintained in a state of deep hypothermia (15 degrees C) for 90 min, group 2 animals (n = 5) underwent 60 min of deep hypothermic circulatory arrest at 15 degrees C, and group 3 (n = 6) underwent 90 min of deep hypothermic circulatory arrest at 15 degrees C. All dogs were killed by perfusion fixation 72 h after cardiopulmonary bypass. The CA1 regions of the hippocampi were examined by light and electron microscopy. Biotinylated dUTP was used for nick-end labeling of apoptotic cells mediated by terminal deoxytransferase. No morphological change was observed in group 1 dogs, and very little in group 2 dogs. More severe neuronal damage was observed in group 3. The nuclei of many cells were shrunken and showed nick-end labeling. Dense chromatin masses were detected electron microscopically in the nuclei of CA1 pyramidal cells. Neuronal cell death observed in CA1 pyramidal cells 72 h after 90 min of deep hypothermic circulatory arrest at 15 degrees C involves apoptosis. Therefore, according to this model, the maximum duration of deep hypothermic circulatory arrest should not be allowed to exceed 60 min.     

Deep accidental hypothermia and cardiac arrest rewarming with forced air

Background : During the last two cold winters we have treated 5 severely hypothermic patients (temperature below 30C) with active external rewarming rather than with extracorporal circulation and heat exchanger.
Patients : Two patients were found in cardiac arrest, and 3 victims of mountain accidents suffered deep hypothermia without arrest. In one of them, ventricular fibrillation (VF) was converted successfully to a sinus rhythm at a core temperature of 25.9C. Both arrested patients developed an adequate hemodynamic state during resuscitation although they were at very low temperature. All the patients were warmed with a convective cover inflated with warm air of about 38A°C (Bair Hugger). The core temperature increased by approximately 1°C/h in all patients. During rewarming we observed neither an initial drop of the core temperature (afterdrop) nor cardiac arrhythmias. The outcome of all 5 patients was good without neurological sequelae.
Conclusion : We conclude that external rewarming with forced air is a feasible alternative to cardiopulmonary bypass in severely hypothermic patients with electrical activity. This method can be used even in patients with VF because defibrillation can be successfully performed in deep hypothermia. Although afterdrop during external rewarming is feared, we did not observe this phenomenon. Rewarming with forced air is inexpensive, easy to perform and direct access to the patient is possible at any time. It does not require heparinisation and can be used in hospitals where they do not have cardiopulmonary bypass facilities. Thus, this method is particularly useful in situations when the hypothermic patient cannot be transferred to a major medical center.     

Jugular bulb temperature compared with non-invasive temperatures and cerebral arteriovenous oxygen saturation differences during open heart surgery

Limited information is available about the correlation between cerebral temperature and routine temperature measurements during cardiopulmonary bypass in infants. Nasopharyngeal, tympanic membrane and rectal temperatures were compared with jugular bulb temperature in ten infants operated on with moderate or deep hypothermia. The cerebral arteriovenous saturation differences were correlated with the temperatures at the four measurement sites. The jugular bulb and nasopharyngeal temperatures showed the most rapid response during cooling and rewarming. The tympanic temperature response varied in an unpredictable way. Rectal temperature, which was the target for rewarming, lagged behind during both cooling and rewarming. Overwarming at the end of cardiopulmonary bypass, seen as jugular bulb and nasopharyngeal temperatures exceeding 38 degrees C, was common after deep hypothermia. A high correlation was found between the cerebral arteriovenous oxygen saturation differences and the jugular bulb temperature (r = 0.81) and the nasopharyngeal and the tympanic temperature (r = 0.79), whereas the correlation with rectal temperature was weaker (0.66).     

Oxygenator exhaust capnography: a method of estimating arterial carbon dioxide tension during cardiopulmonary bypass.

An in vivo study was undertaken during hypothermic (28 degrees C) cardiopulmonary bypass to compare oxygenator exhaust capnography as a means of estimating arterial carbon dioxide tension (PaCO2) with bench blood gas analysis. A total of 123 pairs of measurements were made in 40 patients. Oxygenator exhaust capnographic measurements systematically underestimated PaCO2 measured by a bench blood gas analyzer. During the cooling and stable hypothermic phases of cardiopulmonary bypass, the relationship was reasonably accurate, but became far more variable during rewarming. Oxygenator exhaust capnography could be used as an inexpensive means of continuously monitoring PaCO2 during the cooling and stable hypothermic phases of cardiopulmonary bypass but should not be used during rewarming.     

Effects of deep hypothermic circulatory arrest with retrograde cerebral perfusion on electroencephalographic bispectral index and suppression ratio

OBJECTIVE: No systematic study has been conducted to investigate effects of deep hypothermic circulatory arrest (DHCA) on electroencephalographic bispectral index (BIS) and suppression ratio (SR). Thus, the effects of DHCA were evaluated on BIS and SR. DESIGN: A prospective clinical study. SETTING: University hospital (single institute). PARTICIPANTS: Twenty consecutive patients undergoing thoracic aortic surgery using DHCA under narcotics-sevoflurane anesthesia. INTERVENTIONS: BIS and SR were monitored during cardiopulmonary bypass, simultaneously with nasopharyngeal temperature (NPT). MEASUREMENTS AND MAIN RESULTS: BIS decreased to 0 with induction of deep hypothermia and rose again with rewarming, although rates of BIS changes in response to cooling and rewarming varied widely among patients. Typically, BIS decreased slowly until NPT reached 26 degrees C during cooling and then it began to decrease rapidly and reached 0 at 17 degrees C, in inverse proportion to SR, which increased rapidly with deep hypothermia and reached 100% at 17 degrees C. When SR was 50% or more, BIS was determined by SR according to the expression: BIS = 50-SR/2. With rewarming, BIS rose again and returned to precooling baseline levels. Time to the beginning of the BIS recovery significantly correlated with duration of DHCA. CONCLUSIONS: With induction of deep hypothermia, BIS decreased in a biphasic manner to 0 at rates varying among patients. With rewarming, BIS rose again at rates extremely widely varying among patients. The rate of BIS recovery was related to duration of DHCA. BIS may be capable of conveniently tracing suppression and recovery of a part of cerebral electrical activity before, during, and after DHCA.     

Comparative analysis of alpha-stat and pH-stat strategies with a membrane oxygenator during deep hypothermic circulatory arrest in young pigs

Using young pigs, this study compared the strategies of alpha-stat and pH-stat during deep hypothermic circulatory arrest (DHCA) for the cooling time of brains during the induction of hypothermia and rewarming time with cardiopulmonary bypass (CPB); the cerebral perfusion rate and metabolism rate, and the ratio of these 2 rates; and the extent of the cerebral edema development after circulatory arrest. Fourteen young pigs were assigned to 1 of 2 strategies of gas management. Cerebral blood flow was measured with a cerebral venous outflow technique. With CPB, core cooling was initiated and continued until the nasopharyngeal temperature fell below 20 degrees C. The flow rate was set at 2,500 ml/min. Once the temperature reached below 20 degrees C, the animals were subjected to DHCA for 40 min. During the cooling period, the acid-base balance was maintained using either alpha-stat or pH-stat strategy. After DHCA, the body was rewarmed to the normal body temperature. The animals then were sacrificed, and we measured the brain water content. The cerebral perfusion and metabolism rates were measured before the onset of CPB, before cooling, before DHCA, 15 min after rewarming, and upon the completion of rewarming. The cooling time was significantly shorter with alpha-stat than with pH-stat strategy while no significant differences were observed in the rewarming time between groups. Also, no significant differences were found in cerebral blood flow volume, metabolic rate, or flow/metabolic rate ratio between groups. In each group, the cerebral blood flow volume, metabolic rate, and flow/metabolic rate ratio showed significant differences in body temperature. Brain water content showed no significant differences between the 2 groups. In summary, this study found no significant differences between alpha-stat and pH-stat strategies, except in the cooling time. The cooling time was rather shorter with the alpha-stat than with the pH-stat strategy.     

孕羊低温体外循环对胎羊血流动力学以及碳水化合物代谢的影响

目的 探讨孕羊低温体外循环(CPB)对胎羊血流动力学以及碳水化合物代谢的影响.方法 孕羊20头,随机分成对照组,开胸不建立体外循环;常温CPB组(35～36℃)、浅低温组CPB(32～34℃)和中低温CPB组(28～31℃),建立常规体外循环,转流降温、复温30 min.分别监测孕羊和胎羊的心率、平均动脉压、胎羊脐动脉和颈内动脉的搏动指数(pulse index,PI),孕羊与胎羊血糖、乳酸含量和HCO-3值的变化.结果 母羊和胎羊平均动脉压差异无统计学意义(P＞0.05).浅低温组和中低温组颈内动脉PI值较对照组和常温组显著增高(P＜0.05),脐动脉PI值组间差异无统计学意义,但随体外循环时间的延长而增高.血糖水平胎羊各组间差异无统计学意义(P＞0.05),但中低温CPB组中胎羊显著低于孕羊(P＜0.05).中低温CPB组胎羊血乳酸随时间延长有上升趋势(P＜0.05),而且显著高于孕羊(P＜0.05),但各CPB组间血乳酸差异无统计学意义.结论 孕羊低温体外循环降温时,胎羊心率明显下降,复温后胎羊心率能回复正常,体外循环对胎羊平均动脉压无明显影响,但低温降低胎羊脑部和脐动脉的血流;低温体外循环导致胎羊血糖水平降低,而血乳酸浓度显著增高.

Abstract：

Objective To evaluate effects of maternal hypothermic cardiopulmonary bypass on fetal homodynamic and carbohydrate metabolism. Methods Twenty pregnant sheep were divided into four groups randomly: control group(n=5),normothermic group (35-36℃)(n=5), mild hypothermic group(32-34℃)(n=5) and moderate hypothermic group (28-31℃)(n=5).Thoracotomy was performed without CPB in the control group. Routine CPB was established with different temperature in other three groups. The temperature of normothermic group was kept normal; the left two groups were cooled down to the set point of temperature and then rewarmed back to normal level. Fetal and maternal temperatures, heart rate,mean blood pressure(BP), pulse index (PI) of fetal umbilical artery (UA) and internal carotid artery (CA) were evaluated at cooling and rewarming stages. Biochemical indicators including blood glucose and lactic acid were also measured at the same time. Results There are no differences in mesn BP of ewas and fetal lambs between the different groups (P＞0.05). CA PI value of mild hypothermic group and moderate hypothermic group were significantly higher than those of control group and normothermic group (P＜0.05). There was no difference of UA PI in the four groups, but PI increased following the prolonged duration of CPB. There was no difference change of blood glucose in the four group of fetus, which was significantly lower than the ewe groups. An upward trend of fetal blood lactic acid with time was observed in three CPB groups. The whole level of fetal blood lactic acid was much higher than that of maternal blood of lactic acid. Conclusion Cooling of maternal bypsss decreases fetal heart rate significantly,and fetal heart rate recovered to base line following rewarming phase. There was no signicant effect of CPB on fetal mean BP. However, CPB impacted on the blood flow of fetal brain and umbilical artey. Hypothermia CPB can increase fetal blood glucose and blood lactic acid dramatically.     

Halothane solubility in blood during cardiopulmonary bypass: the effect of haemodilution and hypothermia.

The influence of haemodilution and cooling on the solubility of halothane in blood during cardiopulmonary bypass was studied in six normothermic and six hypothermic patients undergoing open-heart operations. The solubility of halothane in blood was 2.17 at 30 degrees C and 1.34 at 37 degrees C. There was also an increase in the blood/gas partition coefficient of about 8.7 per cent for each degree celsius of temperature fall. These changes in haemodiluted blood explain the different anaesthetic requirements observed in patients undergoing cardiopulmonary bypass, either at normal temperature or at moderate hypothermia.     

Regional oxygenation and systemic inflammatory response during cardiopulmonary bypass: influence of temperature and blood flow variations

OBJECTIVE: To evaluate the role of target temperature (28 degrees or 34 degrees C) in cardiac surgery on regional oxygenation during hypothermia and rewarming and systemic inflammatory response. DESIGN: Prospective, controlled, and randomized clinical study. SETTING: University hospital. PARTICIPANTS: Elderly patients (mean age 70 +/- 2 years) with acquired heart disease with an anticipated bypass time exceeding 120 minutes (n = 30). INTERVENTIONS: The patients were cooled to either 28 degrees C (n = 15) or 34 degrees C (n = 15). At hypothermia, bypass blood flow was reduced twice from full flow (2.4 L/min/m(2) body surface area [BSA]) to 2.0 L/min/m(2). MEASUREMENTS AND MAIN RESULTS: Hepatic and jugular venous oxygen tension and saturation were higher at 28 degrees C than at 34 degrees C. In comparison with the preoperative values, at 28 degrees C hepatic venous values were higher; whereas at 34 degrees C, they were lower. The reduction of pump blood flow during hypothermia, from 2.4 to 2.0 L/min/m(2)was accompanied by reductions of central, jugular, and hepatic oxygenation at both target temperatures. During rewarming, central and regional venous oxygenation decreased irrespective of the preceding temperature. The decrease was most pronounced in hepatic venous blood, with the lowest individual values <10%. Serum concentrations of C3a and IL-6 increased during hypothermia and increased further during rewarming irrespective of the preceding temperature. CONCLUSION: During cardiopulmonary bypass, hypothermia at 28 degrees C increases regional and central venous oxygenation better than at 34 degrees C. In contrast, venous oxygenation decreases during rewarming irrespective of the preceding temperature. No significant difference in the systemic inflammatory response associated with target temperature was detected.     

Blood flow distribution in infant pigs subjected to surface cooling, deep hypothermia, and circulatory arrest. Deleterious effects in pigs with left-to-right shunts

Surface cooling, deep hypothermia and circulatory arrest have been used effectively for correction of congenital heart defects in infancy. Which patients are best suited for this technique has not been addressed. The addition of surface cooling to deep hypothermia and circulatory arrest provides homogeneous cooling and avoids swelling due to reperfusion injury after circulatory arrest. However, surface cooling in patients with large left-to-right shunts causes increased peripheral resistance and increased shunting which can result in decreased perfusion of vital organs. The purpose of this study is to measure the effect of a large left-to-right shunt on total organ blood flow distribution in infant piglets during surface cooling, deep hypothermia, and circulatory arrest. Eleven 2-week-old piglets had surface cooling, deep hypothermia, and circulatory arrest for 45 minutes, followed by rewarming and weaning from cardiopulmonary bypass. Microspheres (15 mu) were injected before surface cooling, at 28 degrees C, at 15 degrees C, and after weaning from cardiopulmonary bypass. Group I (five piglets) was the control. Group II (six piglets) had a large (6 mm) left-to-right aortopulmonary shunt established before microsphere injection. Cardiac outputs in both Groups I and II decreased with surface cooling. The distribution of cardiac output in Group I did not change with surface cooling; however, Group II pigs showed marked change in distribution of cardiac output, resulting in decreased renal, visceral, and pulmonary flow (p less than 0.05). Amylase determinations before and after surface cooling, deep hypothermia, and circulatory arrest were unchanged in Group I but elevated in Group II (p less than 0.05). These observations suggest altered cellular metabolism in visceral organs during the period of surface cooling which may be compounded by circulatory arrest and rewarming.     

Auditory brainstem evoked responses and temperature monitoring during pediatric cardiopulmonary bypass

PURPOSE: To examine the effects of temperature on auditory brainstem responses (ABRs) in infants during hypothermic cardiopulmonary bypass for total circulatory arrest (TCA). The relationship between ABRs (as a surrogate measure of core-brain temperature) and body temperature as measured at several temperature monitoring sites was determined. METHODS: In a prospective, observational study, ABRs were recorded non-invasively at normothermia and at every 1 or 2 degrees C change in ear-canal temperature during cooling and rewarming in 15 infants (ages: 2 days to 14 months) that required TCA. The ABR latencies and amplitudes and the lowest temperatures at which an ABR was identified (the threshold) were measured during both cooling and rewarming. Temperatures from four standard temperature monitoring sites were simultaneously recorded. RESULTS: The latencies of ABRs increased and amplitudes decreased with cooling (P < 0.01), but rewarming reversed these effects. The ABR threshold temperature as related to each monitoring site (ear-canal, nasopharynx, esophagus and bladder) was respectively determined as 23 +/- 2.2 degrees C, 20.8 +/- 1.7 degrees C, 14.6 +/- 3.4 degrees C, and 21.5 +/- 3.8 degrees C during cooling and 21.8 +/- 1.6 degrees C, 22.4 +/- 2.0 degrees C, 27.6 +/- 3.6 degrees C, and 23.0 +/- 2.4 degrees C during rewarming. The rewarming latencies were shorter and Q10 latencies smaller than the corresponding cooling values (P < 0.01). Esophageal and bladder sites were more susceptible to temperature variations as compared with the ear-canal and nasopharynx. CONCLUSION: No temperature site reliably predicted an electrophysiological threshold. A faster latency recovery during rewarming suggests that body temperature monitoring underestimates the effects of rewarming in the core-brain. ABRs may be helpful to monitor the effects of cooling and rewarming on the core-brain during pediatric cardiopulmonary bypass.     

The effects of cardiopulmonary bypass and profound hypothermic circulatory arrest on anterior fontanel pressure in infants

The Ladd transducer was used to measure anterior fontanel pressure in 23 infants undergoing cardiopulmonary bypass and profound hypothermic circulatory arrest for surgical correction of congenital heart disease. Mean (+/- SD) minimum oesophageal and rectal temperatures of 11.3 +/- 1.5 degrees C and 18.1 +/- 2.2 degrees C respectively were achieved with a mean duration of arrest of 53.4 +/- 13.9 minutes. During reperfusion cardiopulmonary bypass after circulatory arrest, mean anterior fontanel pressure (18.3 +/- 6.4 mmHg) increased above baseline pre-bypass values (10.6 +/- 2.9 mmHg) (p less than 0.005). Mean arterial blood pressure decreased significantly from pre-bypass values (57.0 +/- 11.8 mmHg) during both cooling (38.8 +/- 8.4 mmHg) and rewarming cardiopulmonary bypass (45.8 +/- 8.9 mmHg) (p less than 0.005). These changes were associated with a significant decrease in cerebral perfusion pressure during cooling (27.3 +/- 11.0 mmHg) and rewarming cardiopulmonary bypass (27.5 +/- 10.6 mmHg), compared with baseline pre-bypass values (46.5 +/- 12.3 mmHg) (p less than 0.005). The data demonstrate significant but transient decreases in cerebral perfusion pressure during cooling and rewarming bypass.