Prevention of cerebral hyperthermia during cardiac surgery by limiting on-bypass rewarming in combination with post-bypass body surface warming: a feasibility study

Cerebral hyperthermia is common during the rewarming phase of cardiopulmonary bypass (CPB) and is implicated in CPB-associated neurocognitive dysfunction. Limiting rewarming may prevent cerebral hyperthermia but risks postoperative hypothermia. In a prospective, controlled study, we tested whether using a surface-warming device could allow limited rewarming from hypothermic CPB while avoiding prolonged postoperative hypothermia (core body temperature <36 degrees C). Thirteen patients undergoing primary elective coronary artery bypass grafting surgery were randomized to either a surface-rewarming group (using the Arctic Sun thermoregulatory system; n = 7) or a control standard rewarming group (n = 6). During rewarming from CPB, the control group was warmed to a nasopharyngeal temperature of 37 degrees C, whereas the surface-warming group was warmed to 35 degrees C, and then slowly rewarmed to 36.8 degrees C over the ensuing 4 h. Cerebral temperature was measured using a jugular bulb thermistor. Nasopharyngeal temperatures were lower in the surface-rewarming group at the end of CPB but not 4 h after surgery. Peak jugular bulb temperatures during the rewarming phase were significantly lower in the surface-rewarming group (36.4 degrees C +/- 1 degrees C) compared with controls (37.7 degrees C +/- 0.5 degrees C; P = 0.024). We conclude that limiting rewarming during CPB, when used in combination with surface warming, can prevent cerebral hyperthermia while minimizing the risk of postoperative hypothermia[corrected].     

Postoperative ventilatory and circulatory effects of extended rewarming during cardiopulmonary bypass

Postoperative effects of extended rewarming (ECR) after hypothermic cardiopulmonary bypass (CPB) were studied. All (n = 28) patients were rewarmed to a nasopharyngeal temperature exceeding 38 degrees C before terminating CPB. In 12 patients (control group) the rectal temperature (Tre) was 33.8 +/- 1.7 degrees C (mean +/- sd) at termination of CPB. In sixteen patients (ECR group) rewarming during CPB was continued to a Tre of 36.8 +/- 0.5 degrees C. Postoperative body temperatures, heat content, shivering, oxygen uptake, CO2 production and haemodynamic variables were measured. ECR reduced the heat gain required to complete core rewarming to 665 +/- 260 kJ, compared with 1037 +/- 374 kJ in the control group (p less than 0.01). The incidence of shivering was reduced (p less than 0.05) as well as shivering intensity and duration. In seven non-shivering ECR group patients this coincided with significantly reduced metabolic and ventilatory demands but these improvements were not valid for the group as a whole. The required ventilation temporarily during postoperative rewarming in both groups increased to 250 per cent of the basal need. Extending CPB rewarming (to at least 36 degrees C Tre) was inefficient when used as the sole measure to reduce the untoward effects of residual hypothermia during recovery after cardiac surgery with hypothermic CPB.     

Determinants of core temperature at the time of admission to intensive care following cardiac surgery

OBJECTIVE: To determine the predictors of core temperature on arrival in the intensive care unit (ICU) after cardiac surgery. DESIGN: Prospective, randomized trial.SETTING: Tertiary care medical center, operating rooms (ORs), and ICU.PATIENTS: 72 patients presenting for coronary artery bypass surgery.INTERVENTIONS: Randomized assignment for ambient OR temperature (16-18 degrees C vs. 21-23 degrees C) and rewarming endpoint on cardiopulmonary bypass (CPB; nasopharyngeal and urinary bladder temperatures >/=36.5 degrees C and 34.0 degrees C, respectively, vs. nasopharyngeal and urinary bladder temperatures >/=37.5 degrees C and 36.0 degrees C, respectively) at the time of separation from bypass.MEASUREMENTS AND MAIN RESULTS: The best (and only significant) predictor of core temperature on arrival in the ICU was rewarming endpoint at the time of separation from CPB (p = 0.004). Patient weight, height, body habitus, and nitroprusside administration did not significantly predict core temperature. Ambient temperature affected only body temperature when the duration of time in the OR after separation from bypass was prolonged (>90 min). A weighted average body temperature was a better predictor of complete rewarming than was any single monitoring site.CONCLUSIONS: To reduce the incidence of hypothermia after cardiac surgery, the most important variable is rewarming endpoint achieved before separation from bypass. A warm ambient temperature (>21 degrees C) may be beneficial if the duration of time in the OR after bypass is prolonged (>90 min).     

Site of temperature monitoring and prediction of afterdrop after open heart surgery

To determine which of the commonly used "core" temperature sites, remote from the brain, best indicates total body rewarming, the temperatures in the rectum (RT), urinary bladder (UBT) and the pulmonary artery (PAT) at the termination of cardiopulmonary bypass (CPB) were correlated with the decrease in nasopharyngeal temperature (NPT) after CPB (afterdrop) in 29 patients. The amount of afterdrop is inversely related to the adequacy of total body rewarming, smaller values indicating better rewarming. All patients had uncomplicated cardiac surgery and received high pump flows during rewarming on CPB. The UBT showed the best correlation with afterdrop (p less than 0.001) compared with the other temperature sites, the durations of CPB and rewarming during CPB, and the time that the NPT was greater than 37 degrees C during rewarming. The urinary bladder is a simple, non-invasive monitoring site when a urinary catheter is required and our results indicated that the UBT is a better monitor of the adequacy of total body rewarming on CPB than NPT alone. The study also suggested that rewarming to a UBT in excess of 36.2 degrees C prior to the termination of CPB is unlikely to further reduce afterdrop.     

Heating efficacy of external heat supply during and after open-heart surgery with hypothermia

Heat balance after cardiac surgery with hypothermic cardiopulmonary bypass (CPB) was studied in 156 patients. In spite of rewarming during CPB there was residual hypothermia at the end of operation. This heat deficit could not be prevented by intraoperative use of a heating mattress at 38 degrees C and/or heated (39 degrees C) humidified inspired gases. Postoperatively, in four groups of patients, the core and finger skin temperatures were recorded and the mean skin and mean body temperatures and heat balance were calculated. Heating of humidified inspired gases (n = 22) gave little improvement in the time course of the temperatures and heat balance as compared with that in a control group with no external warming postoperatively (n = 49). A thermal ceiling (a low-temperature radiator suspended above the bed and providing radiant heat (n = 35] significantly increased the measured temperatures, which were restored to normal earlier than those in the controls. Also, with this radiant heat postoperative shivering was almost abolished. With a combination of radiant heat and heated, humidified gases (n = 50), the postoperative heat balance was improved somewhat further. For patients treated with radiant heat, postoperative rewarming was accomplished in a shorter time and almost without active endogenous muscular thermogenesis, as was evident by the great reduction in postoperative shivering.     

The effects of two rewarming strategies on heat balance and metabolism after coronary artery bypass surgery with moderate hypothermia

BACKGROUND: Postoperative hypothermia is common in cardiac surgery with hypothermic cardiopulmonary bypass (CPB). This trial was designed to evaluate whether rewarming over the normal bladder temperature (over 37 degrees C) at the end of hypothermic CPB combined with passive heating methods after CPB might result in a better heat balance, lower energy expenditure (EE) and decrease of disturbances in oxygen balance compared to only rewarming the patients to a bladder temperature of 35-37 degrees C. METHODS: A prospective, randomized controlled clinical study was performed in 38 patients scheduled for elective coronary artery bypass surgery. Twenty patients (group C) were rewarmed to a bladder temperature of 35-37 degrees C at the end of hypothermic (28 degrees C) CPB. Eighteen patients (group W) were rewarmed to a bladder temperature of 37-38.5 degrees C. RESULTS: At the end of CPB, the bladder temperature was 36.2+/-0.7 degrees C (mean+/-SD) in group C and 37.9+/-0.5 degrees C in group W. After half an hour's stay in the ICU, the mean body temperature (MBT) was 35.1+/-0.6 degrees C in group C and 36.6+/-0.7 degrees C in group W. During the following five hours, MBT increased to 37.4+/-0.8 degrees C in group C and to 38.0+/-0.6 degrees C in the other group. The peak value of EE in the ICU was 1.73+/-0.44 (group C) vs 1.35+/-0.29 (W/kg) (group W) (P=0.003). EE was significantly (P=0.044) higher in group C than in the other group between 1.5 and 5.5 h in the ICU. The increased energy expenditure due to heat production was associated with an increase in O2 consumption (VO2) 61.6+/-30.4% vs 25.2+/-24.1%, (peak values) compared to the basal values of the two groups measured before anesthesia (between groups P<0.001). Between 1.5 and 5.5 h in the ICU, group C had significantly higher VO2 (P=0.026), CO2 production (P=0.017), venous pCO2 (P<0.001) and minute ventilation (p=0.014) than group W. Venous pH was lower (P<0.001) in group C. The peak value of oxygen extraction was also higher (P=0.045) in group C. On the other hand, the lowest value of venous oxygen saturation was higher (P=0.04) in group W. CONCLUSION: With rewarming the patients at the end of CPB to a bladder temperature of over 37 degrees C combined with passive heating methods after CPB, it was possible to decrease EE and VO2 compared to the control group (rewarmed to bladder temperature of 35-37 degrees C) after coronary artery bypass surgery with moderate hypothermia.     

The rewarming rate and increased peak temperature alter neurocognitive outcome after cardiac surgery.

Neurocognitive dysfunction is a common complication after cardiac surgery. We evaluated in this prospective study the effect of rewarming rate on neurocognitive outcome after hypothermic cardiopulmonary bypass (CPB). After IRB approval and informed consent, 165 coronary artery bypass graft surgery patients were studied. Patients received similar surgical and anesthetic management until rewarming from hypothermic (28 degrees -32 degrees C) CPB. Group 1 (control; n = 100) was warmed in a conventional manner (4 degrees -6 degrees C gradient between nasopharyngeal and CPB perfusate temperature) whereas Group 2 (slow rewarm; n = 65) was warmed at a slower rate, maintaining no more than 2 degrees C difference between nasopharyngeal and CPB perfusate temperature. Neurocognitive function was assessed at baseline and 6 wk after coronary artery bypass graft surgery. Univariable analysis revealed no significant differences between the Control and Slow Rewarming groups in the stroke rate. Multivariable linear regression analysis, examining treatment group, diabetes, baseline cognitive function, and cross-clamp time revealed a significant association between change in cognitive function and rate of rewarming (P = 0.05). IMPLICATIONS: Slower rewarming during cardiopulmonary bypass (CPB) was associated with better cognitive performance at 6 wk. These results suggest that a slower rewarming rate with lower peak temperatures during CPB may be an important factor in the prevention of neurocognitive decline after hypothermic CPB.     

Thermogenic effect of amino acids not demonstrated in heart surgery with cardiopulmonary bypass

BACKGROUND: In abdominal surgery and in healthy volunteers, amino acids increased thermogenesis. In this double-blind study we investigated if a similar effect would ensue in heart surgery and accelerate the rewarming process postoperatively. METHODS: Thirty-four patients undergoing coronary artery bypass grafting or aortic valve replacement were randomized into two groups, and received either 500 ml of amino acids or Ringer's solution intravenously during 4 h. The infusion was started approximately 30 min before the end of a cardiopulmonary bypass (CPB), performed at a temperature of 34 degrees C with rewarming to 36-37 degrees C. The lowest pulmonary artery (PA) temperature after the CPB and the time interval until the temperature reached 37 degrees C were recorded. Oxygen uptake was calculated from cardiac output (thermodilution) and the pulmonary av-difference of oxygen after induction of anaesthesia, at the end of surgery, and 1 and 2 h after the CPB. RESULTS: Demographic data, medication including beta-blockers, CPB data and case mix were similar. The lowest temperature after the CPB was 35.9 +/- 0.1 degrees C in the amino acid group and 35.6 +/- 0.2 degrees C in the control group, and the increase per hour was 0.6 +/- 0.1 degrees C and 0.6 +/- 0.0 degrees C, respectively, with no differences between the groups. During the infusion, oxygen uptake was higher in the amino acid group, 115 +/- 4 ml m(-2), than in the controls, 102 +/- 3 ml m(-2) (P < 0.05). No adverse effects of the infusions were noted. CONCLUSION: The lack of a thermal effect of the amino acids in the heart surgery was most probably due to the temperature gradients between the different body compartments, and also may have been due to the use of beta-blockers.     

Errors in thermodilution cardiac output measurements caused by rapid pulmonary artery temperature decreases after cardiopulmonary bypass.

When systemic cooling and rewarming are performed during cardiopulmonary bypass (CPB), the pulmonary artery temperature typically decreases after CPB. This decrease may be rapid enough to cause substantial underestimation of cardiac output (CO) measured by thermodilution, due to changing baseline temperature during the thermodilution measurement. In 16 patients undergoing CPB for coronary artery grafts, digital recording of pulmonary artery temperature was done during room-temperature thermodilution CO (TDCO) injections. TDCO were computed with and without correction for baseline temperature decrease. Prior to CPB, the temperature change was -0.013 degrees C/min, producing no significant effect on CO measurements; the coefficient of variation of CO measurements was 5.1%. One minute after CPB the temperature change was -0.144 degrees C/min, producing a CO measurement error of -0.57 +/- 0.52 l/min (SD), or about 11% of the average CO; the range of the error was 0.05 to -2.0 l/min. Ten minutes after CPB the temperature change was -0.063 degrees C/min, and CO error was -0.31 +/- 0.36 (0.15 to -1.20) l/min. At 30 min the temperature change was -0.012 degrees C/min (not significant), and CO error was -0.13 +/- 0.14 l/min. Duration of CPB was 104 +/- 30 min, with rewarming for 44 +/- 13 min; the average minimum bladder temperature was 25.1 +/- 2.3 degrees C during cooling and 36.7 +/- 0.7 degrees C at the end of CPB. Under these conditions TDCO measurements within the first 10 min after CPB often underestimate the true CO.     

Rewarming from moderate to deep hypothermia: plasma catecholamine content, metabolism and circulatory function. 2 case reports

Two patients were rewarmed from hypothermia (esophageal temperature 27.2 degrees C, 27.5 degrees C respectively). The first case suffered from head-injury after alcohol ingestion and was deeply comatose. A metabolic or cardiovascular regulatory response to cold was not observed in this patient. The relationship between esophageal temperature and whole-body-oxygen consumption was quantified with a Q10 of 2.75 during rewarming (27.2-37.2 degrees C). His epinephrine levels were greatly elevated to 1,000 pg/ml whereas norepinephrine levels were only moderately increased to 250 pg/ml. Premature ventricular contractions (PVCs) during intubation or from the pulmonary artery catheter were not observed. The second patient was a 87 year old man with accidental hypothermia. He exhibited shivering at an esophageal temperature of 27.5 degrees C which indicated persistent thermoregulation. In contrast to the first case his norepinephrine levels were elevated to 1,500 pg/ml and his epinephrine levels only to 450 pg/ml. After onset of surface rewarming an additional increase in norepinephrine levels was observed and an increasing rate of PVC's (15/min) recorded, which ceased when temperature returned to normal. Our observations indicate that part of the cardiac complications during rewarming from deep hypothermia may result from thermoregulation and additional catecholamine liberation.     

Core cooling by central venous infusion of ice-cold (4 degrees C and 20 degrees C) fluid: isolation of core and peripheral thermal compartments

BACKGROUND: Central venous infusion of cold fluid may be a useful method of inducing therapeutic hypothermia. The aim of this study was to quantify systemic heat balance and regional distribution of body heat during and after central infusion of cold fluid. METHODS: The authors studied nine volunteers, each on two separate days. Anesthesia was maintained with use of isoflurane, and on each day 40 ml/kg saline was infused centrally over 30 min. On one day, the fluid was 20 degrees C and on the other it was 4 degrees C. By use of a tympanic membrane probe core (trunk and head) temperature and heat content were evaluated. Peripheral compartment (arm and leg) temperature and heat content were estimated with use of fourth-order regressions and integration over volume from 18 intramuscular thermocouples, nine skin temperatures, and "deep" hand and foot temperature. Oxygen consumption and cutaneous heat flux estimated systemic heat balance. RESULTS: After 30-min infusion of 4 degrees C or 20 degrees C fluid, core temperature decreased 2.5 +/- 0.4 degrees C and 1.4 +/- 0.2 degrees C, respectively. This reduction in core temperature was 0.8 degrees C and 0.4 degrees C more than would be expected if the change in body heat content were distributed in proportion to body mass. Reduced core temperature resulted from three factors: (1) 10-20% because cutaneous heat loss exceeded metabolic heat production; (2) 50-55% from the systemic effects of the cold fluid per se; and (3) approximately 30% because the reduction in core heat content remained partially constrained to core tissues. The postinfusion period was associated with a rapid and spontaneous recovery of core temperature. This increase in core temperature was not associated with a peripheral-to-core redistribution of body heat because core temperature remained warmer than peripheral tissues even at the end of the infusion. Instead, it resulted from constraint of metabolic heat to the core thermal compartment. CONCLUSIONS: Central venous infusion of cold fluid decreases core temperature more than would be expected were the reduction in body heat content proportionately distributed. It thus appears to be an effective method of rapidly inducing therapeutic hypothermia. When the infusion is complete, there is a spontaneous partial recovery in core temperature that facilitates rewarming to normothermia.     

Thermal energy balance as a measure of adequate rewarming from hypothermic cardiopulmonary bypass

OBJECTIVE: To determine whether the amount of heat (thermal energy) used actively to rewarm patients on cardiopulmonary bypass (CPB) was a better indicator of adequate rewarming from hypothermic CPB than core temperature. DESIGN: Prospective study. SETTING: Single hospital. PARTICIPANTS: Fifty-four sequential patients undergoing hypothermic CPB. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Thermal energy balance (TEB) (net heat supplied to or removed from the body, from initiation to termination of CPB) was measured using previously validated apparatus. Adequacy of rewarming was assessed by measuring the coldest postoperative core (tympanic membrane) temperature and the time to rewarm postoperatively to a core temperature of 37.0 degrees C. Core temperature on termination of CPB did not correlate with the degree of postoperative hypothermia as judged by time to rewarm postoperatively to 37.0 degrees C (r = 0.14; p = 0.33), but did correlate with coldest postoperative core temperature (r = 0.47; p = 0.0003). TEB correlated better with time to rewarm to 37.0 degrees C (r = 0.43; p = 0.001) and coldest postoperative core temperature (r = 0.58, p = 0.0001). CONCLUSION: TEB is a better predictor than corresponding values of core temperature on termination of CPB in predicting the coldest postoperative temperature and time to rewarm to 37 degrees C.     

Body morphology and the speed of cutaneous rewarming

BACKGROUND: Infants and children cool quickly because their surface area (and therefore heat loss) is large compared with their metabolic rate, which is mostly a function of body mass. Rewarming rate is a function of cutaneous heat transfer plus metabolic heat production divided by body mass. Therefore, the authors tested the hypothesis that the rate of forced-air rewarming is inversely related to body size. METHODS: Isoflurane, nitrous oxide, and fentanyl anesthesia were administered to infants, children, and adults scheduled to undergo hypothermic neurosurgery. All fluids were warmed to 37 degrees C and ambient temperature was maintained near 21 degrees C. Patients were covered with a full-body, forced-air cover of the appropriate size. The heater was set to low or ambient temperature to reduce core temperature to 34 degrees C in time for dural opening. Blower temperature was then adjusted to maintain core temperature at 34 degrees C for 1 h. Subsequently, the forced-air heater temperature was set to high (approximately 43 degrees C). Rewarming continued for the duration of surgery and postoperatively until core temperature exceeded 36.5 degrees C. The rewarming rate in individual patients was determined by linear regression. RESULTS: Rewarming rates were highly linear over time, with correlations coefficients (r2) averaging 0.98+/-0.02. There was a linear relation between rewarming rate (degrees C/h) and body surface area (BSA; m2): Rate (degrees C/h) = -0.59 x BSA (m2) + 1.9, r2 = 0.74. Halving BSA thus nearly doubled the rewarming rate. CONCLUSIONS: Infants and children rewarm two to three times faster than adults, thus rapidly recovering from accidental or therapeutic hypothermia.     

Postoperative ventilatory and circulatory effects of heating after aortocoronary bypass surgery

Twenty-four patients with stable angina pectoris were studied after aortocoronary bypass surgery with hypothermic cardiopulmonary bypass (CPB). Twelve patients (radiant heat supply group) were rewarmed during CPB to a nasopharyngeal temperature of at least 38 degrees C and a mean rectal temperature of 34.4 degrees C. Postoperatively they received radiant heat supply from a thermal ceiling. In addition, a heating water mattress was used during the end of the operation and heated, humidified inspired gases were administered intra- and postoperatively. The other 12 patients (combination heat supply group) had the rewarming during CPB extended until the rectal temperature exceeded 36 degrees C, but otherwise received the same treatment as the radiant heat supply group. The combination of extended rewarming during CPB and postoperative radiant heat supply significantly reduced oxygen uptake, carbon dioxide production and the required ventilation volumes during early recovery as compared with the values in the radiant heat supply group. The reduced metabolic demands were accompanied by lower cardiac index and oxygen delivery, which, however, were sufficient for adequate tissue perfusion as judged by the similarity in oxygen extraction and arterial base excess values in the two groups. The metabolic demands and ventilatory requirements were reduced to a level at which safe early extubation is possible.     

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.     

异丙酚对中低温体外循环脑氧合的影响

目的观察异丙酚对中低温体外循环心肺转流术(CPB)期间脑氧合的影响。方法心内直视手术患者17例随机分为芬太尼组和异丙酚组,通过监测动脉、颈内静脉血和混合静脉血氧含量以及乳酸浓度,计算全身和脑动静脉氧含量差、氧摄取率和动静脉乳酸浓度差,分析异丙酚对CPB期间脑氧合的影响。结果两组复温过程中动静脉氧含量差和氧摄取率均较低温时升高;异丙酚组在CPB过程中动脉-颈内静脉血氧含量差和脑的氧摄取率要高于芬太尼组(P<0.05),动脉-混合静脉血氧含量差和全身的氧摄取率两组差异无显著意义(P>0.05)。CPB全过程中两组血乳酸浓度均进行性升高。结论CPB期间应用异丙酚麻醉并不能明显改善脑氧合。CPB期间脑保护机理有其复杂性一面,不能仅停留于氧代谢平衡方面。     

Profound hypothermia (less than 10 degrees C) compared with deep hypothermia (15 degrees C) improves neurologic outcome in dogs after two hours' circulatory arrest induced to enable resuscitative surgery

Deaths from uncontrollable hemorrhage might be prevented by arresting the circulation under protective hypothermia to allow resuscitative surgery to repair these injuries in a bloodless field. We have shown previously that in hemorrhagic shock, circulatory arrest of 60 minutes under deep hypothermia (tympanic membrane temperature, Ttm = 15 degrees C) was the maximum duration of arrest that allowed normal brain recovery. We hypothesize that profound cerebral hypothermia (Ttm less than 10 degrees C) could extend the duration of safe circulatory arrest. In pilot experiments, we found that the cardiopulmonary system did not tolerate arrest at a core (esophageal) temperature (Tes) of less than 10 degrees C. Twenty-two dogs underwent 30-minute hemorrhagic shock (mean arterial pressure 40 mm Hg), rapid cooling by cardiopulmonary bypass (CPB), blood washout to a hematocrit of less than 10%, and circulatory arrest of 2 hours. In deep hypothermia group 1 (n = 10), Ttm was maintained at 15 degrees C during arrest. In profound hypothermia group 2 (n = 12), during cooling with CPB, the head was immersed in ice water, which decreased Ttm to 4 degrees-7 degrees C. The Tes was 10 degrees C in all dogs during arrest. Reperfusion and rewarming were by CPB for 2 hours. Controlled ventilation was to 24 hours, intensive care to 72 hours. In the 20 dogs that followed protocol, best neurologic deficit scores (0% = normal, 100% = brain death) at 24-72 hours were 23% +/- 19% in group 1 and 12% +/- 8% in group 2 (p = 0.15). Overall performance categories and histologic damage scores were significantly better in group 2 (p = 0.04 and p less than 0.001, respectively). We conclude that profound cerebral hypothermia with CPB plus ice water immersion of the head can extend the brain's tolerance of therapeutic circulatory arrest beyond that achieved with deep hypothermia.     

Do Standard Monitoring Sites Reflect True Brain Temperature When Profound Hypothermia Is Rapidly Induced and Reversed?

Background: Brain temperature is closely approximated by most body temperature measurements under normal anesthetic conditions. However, when thermal autoregulation is overridden, large temperature gradients may prevail. This study sought to determine which of the standard temperature monitoring sites best approximates brain temperature when deep hypothermia is rapidly induced and reversed during cardiopulmonary bypass.

Methods: Twenty-seven patients underwent cardiopulmonary bypass and deep hypothermic circulatory arrest in order for each to have a giant cerebral aneurysm surgically clipped. Brain temperatures were measured directly with a thermocouple embedded in the cerebral cortex. Eight other body temperatures were monitored simultaneously with less invasive sensors at standard sites.

Results: Brain temperature decreased from 32.6 + 1.4 degrees Celsius (mean plus/minus SD) to 16.7 plus/minus 1.7 degrees Celsius in 28 plus/minus 7 min, for an average cerebral cooling rate of 0.59 + 0.15 degree Celsius/min. Circulatory arrest lasted 24 plus/minus 15 min and was followed by 63 + 17 min of rewarming at 0.31 plus/minus 0.09 degree Celsius/min. None of the monitored sites tracked cerebral temperature well throughout the entire hypothermic period. During rapid temperature change, nasopharyngeal, esophageal, and pulmonary artery temperatures corresponded to brain temperature with smaller mean differences than did those of the tympanic membrane, bladder, rectum, axilla, and sole of the foot. At circulatory arrest, nasopharyngeal, esophageal, and pulmonary artery mean temperatures were within 1 degree Celsius of brain temperature, even though individual patients frequently exhibited disparate values at those sites.     

Changes in forehead and sole tissue temperature during cardiopulmonary bypass for acquired cardiac disease]

The forehead tissue temperature (FT-T) and the sole tissue temperature (ST-T) were measured and recorded by a deep body thermometer (Terumo Corp.) during open heart surgery. The changes in FT-T and ST-T after cardiopulmonary bypass (CPB) showed two characteristic patterns; the convergence pattern and the dissociation pattern. It is said that the dissociation pattern can notes a poor peripheral circulation. The deverging point of the two patterns was studied in 65 patients with acquired cardiac disease. We divided the patients into two groups taking 3.5 degrees C of the FT-T and ST-T difference (DT) after 2 hour weaning from CPB. The number of the patients in convergence group (group I) was 42, and that in the dissociation group (group II) was 23. The two groups were compared with the DT and the time required for the rise in each temperature from CPB rewarming to CPB weaning. There was no intergroup difference in the DT when the FT-T began to rise upon CPB rewarming. However, the DT was 3.8 +/- 2.3 (mean +/- SD) degrees C in group I and 7.1 +/- 1.8 degrees C in group II when the ST-T began to rise, and 4.2 +/- 2.5 degrees C in group I and 6.9 +/- 1.4 degrees C in group II when the FT-T reached its peak; the figures were significantly lower in group I (P < 0.01). The time required for the rise in ST-T was significantly shorter in group I (14.8 +/- 17.1 min) than in group II (25.8 +/- 14.7 min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Gastroschisis: a 17-year experience

From 1970 to 1987, 23 neonates with gastroschisis were treated at Kobe Children's Hospital. One patient died and 22 survived (96%). Seven patients were hypothermic upon arrival at the hospital, with body temperatures of 31.8 to 35.4 degrees C. Six patients were successfully managed by warm saline bathing (40 to 42 degrees C for one minute) to improve hypothermia. One patient who did not receive this rewarming procedure (body temperature, 31.8 degrees C) died of intractable metabolic disorders related to hypothermia. Ten patients were treated by primary fascial closure of the abdominal wall defect, eight by the skin flap method with secondary closure of the deliberately created abdominal hernia, and five by the silastic sac technique. Two patients required creation of intestinal stomas for ileal atresia. After surgery, 19 patients required ventilatory care with total paralysis (average 6.0 days). Nine patients required total parenteral nutrition (TPN), while 13 tolerated enteral feeding on days 3 to 11 (average, 6.0 days). In the latter 13 patients, intravenous fluid therapy was discontinued on day 11. Our experience suggests that (1) rewarming in a saline bath is effective treatment for hypothermia, (2) ventilatory assistance with total paralysis is mandatory, and (3) TPN can be avoided in 60% of the patients.