Afterdrop after hypothermic cardiopulmonary bypass: the value of tympanic membrane temperature monitoring

Temperature control after cardiac arrest

Managing temperature is an important part of post-cardiac arrest care. Fever or hyperthermia during the first few days after cardiac arrest is associated with worse outcomes in many studies. Clinical data have not determined any target temperature or duration of temperature management that clearly improves patient outcomes. Current guidelines and recent reviews recommend controlling temperature to prevent hyperthermia. Higher temperatures can lead to secondary brain injury by increasing seizures, brain edema and metabolic demand. Some data suggest that targeting temperature below normal could benefit select patients where this pathology is common. Clinical temperature management should address the physiology of heat balance. Core temperature reflects the heat content of the head and torso, and changes in core temperature result from changes in the balance of heat production and heat loss. Clinical management of patients after cardiac arrest should include measurement of core temperature at accurate sites and monitoring signs of heat production including shivering. Multiple methods can increase or decrease heat loss, including external and internal devices. Heat loss can trigger compensatory reflexes that increase stress and metabolic demand. Therefore, any active temperature management should include specific pharmacotherapy or other interventions to control thermogenesis, especially shivering. More research is required to determine whether individualized temperature management can improve outcomes.

Comparison of Effects of Propofol and Isosorbide Dinitrate during Rewarming on Cardiopulmonary Bypass

OBJECTIVES

Comparison of effects of propofol and isosorbide dinitrate during rewarming on cardiopulmonary bypass in patients undergoing coronary artery bypasses grafting.

METHODS

It was randomized prospective clinical trial. One hundred and twenty patient (120) undergoing CABG surgery were included in this study. Group-I (Study group, n=60): in which only propofol infusion used during rewarming and Group-II (control Group, n=60) in which isosorbide dinitrate and propofol infusion combination was used during rewarming. The data was entered and analyzed through SPSS Version 19. Independent sample T-test and chi-square test were used for data analysis. P value of ≤ 0.05 was taken as significant.

RESULTS

Mean arterial pressures during rewarming were 63.41±3.61 mmHg in propofol group versus 60.80±4.86 mmHg in control group (p-value 0.001). Core temperature on weaning from cardiopulmonary bypass was 37.11±0.49 °C in propofol group and 37.00±0.18 °C in control group. After drop in core temperature was little more in propofol group (1.02±0.36 °C) versus 0.96±0.37 °C in control group but this difference was not statistically significant (p-value 0.41). Mean Ventilation time after surgery in propofol group was 4.65±0.65 hours versus 5.03±0.81 hours in control group (p-value 0.006).

CONCLUSION

Propofol alone is capable of fulfilling the requirements of adequate rewarming during Cardiopulmonary bypass and can produce more hemodynamic stability and early post-operative recovery.

Oxygen consumption after hypothermic cardiopulmonary bypass: the effect of continuing a propofol infusion postoperatively

OBJECTIVE

To evaluate the effect of a fixed rate of infusion of propofol on total body oxygen consumption during the postoperative rewarming phase after cardiopulmonary bypass.

DESIGN

Prospective, randomized, controlled study.

SETTING

Cardiac intensive care unit, university hospital.

PARTICIPANTS

Twenty-four male and female patients undergoing elective first-time coronary artery bypass graft surgery.

INTERVENTIONS

Total body oxygen consumption was measured using a pulmonary artery catheter and thermodilution during postoperative rewarming. Twelve patients had propofol infused at 2 mg/kg/h for 4 hours or until rewarmed.

MEASUREMENTS AND MAIN RESULTS

Total body oxygen consumption was reduced in the propofol group compared with the control group. Oxygen consumption was a median of 30.0 mL/min/m(2) less in the patients receiving propofol (p = 0.01). One patient receiving propofol shivered compared with 4 in the control group (p = 0.14).

CONCLUSION

Administration of propofol during postoperative rewarming reduces total body oxygen consumption and may reduce shivering.

A prospective comparison of three heat preservation methods for patients undergoing hypothermic cardiopulmonary bypass

OBJECTIVE

To prospectively compare 3 methods of body heat preservation in patients undergoing surgery requiring the use of hypothermic cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, and nonblinded.

SETTING

University teaching hospital.

PARTICIPANTS

Adult cardiac surgery patients (n = 101).

INTERVENTIONS

Subjects were randomly assigned to 1 of 3 treatment groups: Group 1 (n = 33) used a fluid-filled warming blanket, group 2 (n = 31) used a heated and humidified breathing circuit, and group 3 (n = 37) used intravenous fluid warmers for the administration of all fluids. Treatments started on separation from CPB and concluded at the end of the intraoperative experience. Anesthetic technique, minute ventilation, conduct of CPB, and room temperature in the operating room were standardized.

MEASUREMENTS AND MAIN RESULTS

Blood temperature was measured at its nadir on CPB, on separation from CPB, and just before departure from the operating room. No differences were found among groups for CPB duration, coldest venous temperature on CPB, rewarming time, rate of rewarming, room temperature, or blood temperature on separation from CPB. There were no significant differences found in post-CPB temperature afterdrop among groups.

CONCLUSIONS

This study suggests that there is no statistically significant disparity in the effectiveness of these 3 intraoperative heat preservation methods. Ease of use and cost-effectiveness should guide the choice of warming method post-CPB.

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.

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.