Tissue heat content and distribution during and after cardiopulmonary bypass at 31 degrees C and 27 degrees C

Heating and Cooling Rates With an Esophageal Heat Exchange System

BACKGROUND

The Esophageal Cooling Device circulates warm or cool water through an esophageal heat exchanger, but warming and cooling efficacy in patients remains unknown. We therefore determined heat exchange rates during warming and cooling.

METHODS

Nineteen patients completed the trial. All had general endotracheal anesthesia for nonthoracic surgery. Intraoperative heat transfer was measured during cooling (exchanger fluid at 7°C) and warming (fluid at 42°C). Each was evaluated for 30 minutes, with the initial condition determined randomly, starting at least 40 minutes after induction of anesthesia. Heat transfer rate was estimated from fluid flow through the esophageal heat exchanger and inflow and outflow temperatures. Core temperature was estimated from a zero-heat-flux thermometer positioned on the forehead.

RESULTS

Mean heat transfer rate during warming was 18 (95% confidence interval, 16-20) W, which increased core temperature at a rate of 0.5°C/h ± 0.6°C/h (mean ± standard deviation). During cooling, mean heat transfer rate was -53 (-59 to -48) W, which decreased core temperature at a rate of 0.9°C/h ± 0.9°C/h.

CONCLUSIONS

Esophageal warming transferred 18 W which is considerably less than the 80 W reported with lower or upper body forced-air covers. However, esophageal warming can be used to supplement surface warming or provide warming in cases not amenable to surface warming. Esophageal cooling transferred more than twice as much heat as warming, consequent to the much larger difference between core and circulating fluid temperature with cooling (29°C) than warming (6°C). Esophageal cooling extracts less heat than endovascular catheters but can be used to supplement catheter-based cooling or possibly replace them in appropriate patients.

2016 survey about temperature management during extracorporeal circulation in China

Objective:

In order to assess the current status of temperature management during cardiopulmonary bypass (CPB) in China and, thereby, implement standardized management protocols, the authors carried out a national survey about institutions performing CPB.

Method:

The survey was carried out from September 2015 to February 2016 and was supported by the Chinese Society of ExtraCorporeal Circulation. A total of 114 institutions participated, accounting for 15.64% (114/729) of the total of germane Chinese institutions, whereby, 80.85% (38/47) of the institutions had an annual surgical volume of more than 1000 cases.

Results:

The most common sites of temperature measurement were nasopharyngeal (NP) (99.12%) and rectal (92.98%) while oxygenator blood temperature was less popular (28%). Rectal temperature as the core temperature was chosen by 78.95% of the institutions; 92.11% of the institutions chose nasopharyngeal temperature to represent the cerebral temperature. During deep hypothermia circulatory arrest (DHCA) when there was no cerebral perfusion, 18 to 22℃ was the most common indication of circulatory arrest. However, with cerebral perfusion, more than 40% of the institutions maintained a lowest temperature of 22 to 25℃ for adult and pediatric patients. A NP temperature of 36 to 37℃ was chosen by 70.18% of the institutions while 81.79% chose a rectal temperature of 35 to 36.5℃ as the indication to wean from CPB. The majority of the institutions chose a difference of 10℃ between the water tank and core temperatures as the temperature gradient during rewarming. Auxiliary heat preservation techniques and equipment were used in 91.23% of the institutions, whereas 35.58% of them would lower the indications to wean from CPB.

Conclusions:

This survey accurately reflects the current situation of temperature management during CPB in institutions with an annual surgical volume of >500 cases, but has, hereby, failed to properly represent the institutions with a lower annual surgical volume.

Optimal Conditions for Cardiopulmonary Bypass

There is no single optimal set of conditions for cardio pulmonary bypass. What is optimal is determined by patient factors, surgical need, and the mechanics of perfusion. Additionally, the best way to manage bypass typically varies over its course.

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.

Perioperative thermoregulation and temperature monitoring

Traditionally, hypothermia has been thought of and used perioperatively as a presumptive strategy to reduce cerebral and myocardial tissue sensitivity to ischemia. Evidence, however, is mounting that maintenance of perioperative normothermia is associated with improved outcomes in patients undergoing all types of surgery, even cardiac surgery. Ambient environmental temperature is sensed by free nerve endings in the dermal and epidermal layers of the skin, which are the axonal extensions of thermosensitive neurons found in the dorsal root ganglia. Free nerve endings in the skin, by means of transient receptor ion channels that are specifically thermosensitive, also may directly sense environmental temperature. This information is transmitted to the preoptic/anterior hypothalamic region of the brainstem, which coordinates efferent responses to abnormal temperature deviation. People have evolved a highly integrated thermoregulatory system that maintains core body temperature in a relatively narrow temperature range. This system, though, is impaired by the stress of regional and general anesthesia, and the added exposure that occurs during the surgical procedure. When combined, these factors can lead to unwanted thermal disturbances. In a cold operating room environment, hypothermia is the usual perioperative consequence; however, hyperthermia is more dangerous and demands immediate diagnosis. Intraoperative hypothermia usually develops in three phases. The first is a rapid decrease in core temperature following anesthetic induction, which mostly results from redistribution of heat from the core thermal compartment to the outer shell of the body. This is followed by a slower, linear reduction in the core temperature that may last several hours. Finally, a core temperature plateau is reached, after which core temperature remains virtually unchanged for the remainder of the procedure. The plateau can be passive or result from re-emergence of thermoregulatory control in patients becoming sufficiently hypothermic. Mild hypothermia in the perioperative period has been associated with adverse outcomes, including impaired drug metabolism, prolonged recovery from anesthesia, cardiac morbidity, coagulopathy, wound infections, and postoperative shivering. Perioperative temperature monitoring devices vary by transducer type and site monitored. More important than the specific device is the site of temperature monitoring. Sites that are accessible during surgery and give an accurate reflection of core temperature include esophageal, nasopharynx, bladder, and rectal sites. Core temperature also may be estimated reasonably using axillary temperature probes except under extreme thermal conditions. Rather than taking a passive approach to thermal management, anesthesiologists need to be proactive in monitoring patients in cold operating rooms and use available technology to prevent gross disturbances in the core temperature. Various methods are available to achieve this. Prewarming patients reduces redistribution hypothermia and is an effective strategy for maintaining intraoperative normothermia. Additionally, forced-air warming and circulating water garments also have been shown to be effective. Heating intravenous fluids does not warm patients, but does prevent fluid-induced hypothermia in patients given large volumes of fluid. This article examined the evolutionary adaptations people possess to combat inadvertent hypothermia and hyperthermia. Because thermal disturbances are associated with severe consequences, the standard of care is to monitor temperature during general anesthesia and to maintain normothermia unless otherwise specifically indicated.

Core and skin surface temperature course after normothermic and hypothermic cardiopulmonary bypass and its impact on extubation time

BACKGROUND AND OBJECTIVE

Cardiopulmonary bypass is associated with temperature pertubations that influence extubation time. Common extubation criteria demand a minimum value of core temperature only. The aim of this prospective study was to test the hypothesis that changes in core and skin surface temperature are related to extubation time in patients following normothermic and hypothermic cardiopulmonary bypass.

METHODS

Forty patients undergoing cardiac surgery were studied; 28 patients had normothermic cardiopulmonary bypass (nasopharyngeal temperature >35.5 degrees C) and 12 had hypothermic cardiopulmonary bypass (28-34 degrees C). In the intensive care unit, urinary bladder temperature and skin surface temperature gradient (forearm temperature minus fingertip temperature: >0 degrees C = vasoconstriction, < or =0 degrees C = vasodilatation) were measured at 30-min intervals for 10 h postoperatively. At the same intervals, the patients were evaluated for extubation according to common extubation criteria.

RESULTS

On arrival in the intensive care unit the mean urinary bladder temperature was 36.8 +/- 0.5 degrees C in the normothermic group and 36.4+/-0.3 degrees C in the hypothermic group (P = 0.014). The skin surface temperature gradient indicated severe vasoconstriction in the both groups. The shift from vasoconstriction to vasodilatation was faster in normothermic cardiopulmonary bypass patients (138+/-65 min) than in patients after hypothermic cardiopulmonary bypass (186+/-61 min, P = 0.034). There was a linear relation between the time to reach a skin surface temperature gradient = 0 degrees C and extubation time (r2 = 0.56, normothermic group; r2 = 0.82, hypothermic group).

CONCLUSIONS

The transition from peripheral vasoconstriction to vasodilatation is related to extubation time in patients following cardiac surgery under normothermic as well as hypothermic cardiopulmonary bypass.

Cardiopulmonary bypass temperature and brain function

A debate has emerged in recently published studies about the optimum cardiopulmonary bypass temperature for good neurological outcome - warm vs. cold, i.e. normothermic vs. hypothermic. Although many comparative studies have been performed, the results of these studies are inconclusive and are difficult to interpret. Brain function has been studied in terms of neurological and neuropsychological outcome, protein S100beta levels as a marker of brain damage, and cerebral oxygenation using jugular bulb oximetry and near-infrared spectroscopy. The studies produce no conclusive proof of the superiority of warm or cold cardiopulmonary bypass. However, it appears that any degree of bypass hypothermia (< 35 degrees C) may protect the brain. On the other hand, even a slight increase in bypass temperature to > 37 degrees C may cause marked brain injury.

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.

Effectiveness of a circulating-water warming garment in rewarming after pediatric cardiac surgery using hypothermic cardiopulmonary bypass

OBJECTIVE

To evaluate the effectiveness and safety of the ALLON 2001 microprocessor-based thermoregulation system in pediatric patients undergoing cardiac surgery requiring hypothermic cardiopulmonary bypass compared with the routine thermal care.

DESIGN

Prospective randomized clinical study.

SETTING

Single tertiary academic medical center.

PARTICIPANTS

Infants (0-1 year) who underwent congenital heart surgery requiring hypothermic cardiopulmonary bypass (n = 18). Patients with open wounds and/or patients treated with an investigational drug or device within 30 days of surgery were excluded.

INTERVENTIONS

Randomized use of thermoregulation system (warming garment, n = 9) or routine thermal care (control, n = 9) after separating from cardiopulmonary bypass until the arrival to the pediatric intensive care unit (PICU).

MEASUREMENTS AND MAIN RESULTS

There were no statistically significant differences in the demographic data, cardiopulmonary bypass time, operating room time, incidence of deep hypothermic circulatory arrest, and cooling temperature between the groups. The nasopharyngeal temperature was significantly higher in the warming garment group after separation from cardiopulmonary bypass. Nasopharyngeal temperature at 20 minutes was 36.5 degrees C versus 35.01 degrees C (p = 0.0047), at 40 minutes was 36.98 degrees C versus 35.30 degrees C (p = 0.034), and at admission to the PICU was 36.09 degrees C versus 35.31 degrees C (p = not significant). There was no difference in the core-to-peripheral temperature gradient (nasopharyngeal-to-skin temperature) between the 2 study groups at any time point. No adverse events related to the use of the warming garment thermoregulation system were observed.

CONCLUSION

The investigated thermoregulation system was effective in preventing the after-drop of temperature that occurs after cardiopulmonary bypass in small infants compared with routine warming methods.

A pilot study of evaluation of cerebral function by S100? protein and near-infrared spectroscopy during cold and warm cardiopulmonary bypass in infants and children undergoing open-heart surgery

Cerebral injury in children undergoing cardiopulmonary bypass (CPB) remains a major source of morbidity. The effect of cardiopulmonary bypass temperature on cerebral function in terms of serum S100beta protein level and cerebral oxygenation monitored by near infrared spectroscopy (NIRO-300) in children is not known. In this study, 18 children undergoing open-heart surgery at the Hospital for Sick Children in London were equally assigned by minimisation to warm (35 +/- 1 degrees C) or cold (25 +/- 1 degrees C) CPB. Changes in S100beta protein and cerebral oxygenation were studied in both groups. S100beta protein serum level increased significantly after CPB in both groups. There was no significant difference in serum S100beta protein concentrations between the two groups. However, cerebral oxygenation in terms of tissue oxygen index (TOI) was significantly impaired during rewarming from cold CPB. Five patients were desaturated (TOI < 50%) during rewarming in the cold bypass group compared to two in the warm patients. This study supports the use of warm CPB in children undergoing open-heart surgery, although further studies recruiting more patients are warranted.

Prediction of excessive bleeding after coronary artery bypass graft surgery: the influence of timing and heparinase on thromboelastography

OBJECTIVE

To compare the ability of thromboelastography, when done at either 10 or 60 minutes after protamine reversal of heparin, to predict excessive bleeding after coronary artery bypass graft (CABG) surgery and to investigate, with the use of heparinase, whether heparin contamination was responsible for the difference, if any.

DESIGN

Prospective study.

SETTING

University hospital, single institution.

PARTICIPANTS

Patients undergoing elective CABG surgery (n = 40).

INTERVENTIONS

Blood samples for thromboelastography and routine coagulation tests were collected before induction of anesthesia and at 10 and 60 minutes after protamine reversal of heparin. Blood loss and blood product use were recorded postoperatively.

MEASUREMENTS AND MAIN RESULTS

Of 40 patients undergoing elective CABG surgery, 10 fulfilled the criteria for excessive postoperative bleeding. The sensitivity of thromboelastography to identify patients who bled was better at 60 minutes than at 10 minutes after protamine reversal of heparin (100% v 70%). There was greater specificity (83% v 40% at 10 minutes; 73% v 20% at 60 minutes) and positive predictive value (58% v 28% at 10 minutes; 55% v 29% at 60 minutes) when heparinase was added. At both times, thromboelastography showed only moderate correlation with total blood loss and the use of fresh frozen plasma or platelets or both. Conventional coagulation tests did not predict excessive postoperative bleeding.

CONCLUSION

This study suggests that timing and the use of heparinase influence the predictive ability of thromboelastography, but its usefulness as a sole predictor of post-CABG surgery bleeding is limited.

Use of the Cobra catheter for targeted temperature management during cardiopulmonary bypass in swine

BACKGROUND

The purpose of this investigation was to determine whether temperatures of the aortic arch and descending aortic circulations could be controlled independently during cardiopulmonary bypass with a cannula possessing an endoaortic baffle (Cobra; Cardeon, Cupertino, Calif).

METHODS

After Institutional Animal Care and Use Committee approval, 12 pigs weighing 60 kg were started on bypass through a sternotomy. A dual-lumen endoaortic cannula with a deployable baffle was used for arterial cannulation. Bypass was initiated at 37 degrees C, and control measurements were obtained. The baffle was then inflated with saline solution, segmenting blood flow along the greater and lesser curvatures of the aortic arch. Parallel heat exchangers were used to independently control temperature of the arch and descending aortic perfusates. Cerebral and systemic temperatures were recorded continuously.

RESULTS

During cardiopulmonary bypass, mean flow and arterial pressure were maintained at 2.4 to 2.6 L x min(-1) x m(-2) and 60 to 70 mm Hg, respectively. With aortic flow distributed by the baffle, a 5 degrees C temperature differential between brain (30 degrees C) and body (35 degrees C) was established in a mean of 5 +/- 2 minutes. Mean brain and corporeal temperatures of 27 degrees C and 35 degrees C were then maintained over 60 minutes. Relative to control, internal jugular and inferior vena cava oxygen saturations increased during targeted temperature control with the device.

CONCLUSIONS

The Cobra cannula allows for independent control of brain and body temperature while providing satisfactory hemodynamics. Application of this temperature management strategy may offer cerebral protection and the advantages of warm systemic bypass temperature.

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.

Effectiveness of resistive heating compared with passive warming in treating hypothermia associated with minor trauma: a randomized trial

OBJECTIVES

To determine the occurrence of hypothermia in patients with minor trauma, to test the hypotheses that resistive heating during transport is effective treatment for hypothermia and that this treatment reduces patients' thermal discomfort, pain, and fear, and to evaluate the accuracy of oral temperatures obtained at the scene of injury.

PATIENTS AND METHODS

In December 1999 and January 2000, 100 patients with minor trauma were randomly assigned to passive warming or resistive heating. All patients were covered with a carbon-fiber resistive warming blanket and a wool blanket, but the warming blanket was activated only in those assigned to resistive heating. Core (tympanic membrane) and oral temperatures, heart rate, pain, fear, and overall satisfaction of patients were compared between the 2 groups on arrival at a hospital.

RESULTS

Hypothermia was noted in 80 patients at the time of rescue. Mean initial core temperatures were 35.4 degrees C (95% confidence interval [CI], 35.2 degrees C - 35.6 degrees C) in the patients who received passive warming and 35.3 degrees C (95% CI, 35.1 degrees C - 35.5 degrees C) in those who received resistive heating. From the time of rescue until arrival at the hospital, mean core temperature decreased 0.4 degrees C/h (95% CI, 0.3 degrees C/h - 0.5 degrees C/h) with passive warming, whereas it increased 0.8 degrees C/h (95% CI, 0.7 degrees C/h - 0.9 degrees C/h) with resistive heating. Oral and tympanic membrane temperatures were similar. Mean heart rate decreased 23 beats/min in those assigned to resistive heating but remained unchanged in those assigned to passive warming. Patients in the resistive heating group felt warmer, had less pain and anxiety, and overall were more satisfied with their care.

CONCLUSIONS

Oral temperatures are sufficiently accurate for field use. Hypothermia is common even in persons with minor trauma. Resistive heating during transport augments thermal comfort, increases core temperature, reduces pain and anxiety, and improves overall patient satisfaction.

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.

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).

Differential perfusion: a new technique for isolated brain cooling during cardiopulmonary bypass

BACKGROUND

The purpose of this study was to determine the feasibility of differential perfusion of the aortic arch and descending aorta during cardiopulmonary bypass using a cannula designed for aortic segmentation.

METHODS

Pigs weighing 57 kg (n = 8), underwent cardiopulmonary bypass using the dual lumen aortic cannula. An inflatable balloon separated proximal (aortic arch) and distal (descending aorta) ports. During differential perfusion, the aorta was segmented and the arch and descending aorta perfused differentially using parallel heat exchangers. Ability to independently control brain and body temperature, cardiopulmonary bypass flow rate and mean arterial blood pressure was determined.

RESULTS

During differential perfusion cerebral hypothermia (27 degrees C) with systemic normothermia (38 degrees C) was established in 23 minutes. Independent control of arch and descending aortic flow and mean arterial blood pressure was possible. Analysis of internal jugular venous O2 saturation data indicated an increase in the ratio of cerebral O2 supply to demand during differential perfusion.

CONCLUSIONS

A cannulation system segmenting the aorta allows independent control of cerebral and systemic perfusion. This device could provide significant cerebral protection while maintaining the advantages of warm systemic cardiopulmonary bypass temperatures.

Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: A randomized controlled trial

STUDY OBJECTIVE

We study a resistive-heating blanket in a volunteer model of severe accidental hypothermia to evaluate differences in rates of rewarming, core temperature afterdrop, and body heat content and distribution during active and passive rewarming.

METHODS

Eight volunteers participated in a crossover design on 2 days. The volunteers were anesthetized and cooled to 33 degrees C (91.4 degrees F); anesthesia was subsequently discontinued, and shivering was prevented with meperidine. On one randomly assigned day, the volunteers were rewarmed passively with reflective foil (passive insulation), whereas on the other they were covered with a carbon fiber-resistive heating blanket set to 42 degrees C (107.6 degrees F; active rewarming). Trunk and head temperature and heat content were calculated from core (tympanic membrane) temperature. Peripheral (arm and leg) tissue temperature and heat content were estimated by using fourth-order regressions and integration over volume from 30 tissue and skin temperatures.

RESULTS

Core heat content increased 73+/-14 kcal (mean+/-SD) during 3 hours of active warming, but only 31+/-24 kcal with passive insulation, a difference of 41+/-20 kcal (95% confidence interval [CI] 27 to 55 kcal; P <. 001). Peripheral tissue heat content increased linearly by 111+/-16 kcal during active warming but only by 38+/-31 kcal during passive warming, a difference of 74+/-34 kcal (95% CI 50 to 97; P <.001). Consequently, total body heat increased 183+/-22 kcal during active warming but only 68+/-54 kcal with passive insulation, a difference of 115+/-42 kcal (95% CI 86 to 144 kcal; P <.001). Core temperature increased from 32.9 degrees C+/-0.2 degrees C to 35.2 degrees C+/-0. 4 degrees C during 3 hours of active warming, a difference of 2.3 degrees C+/-0.4 degrees C. In contrast, core temperature with foil insulation only increased from 32.9 degrees C+/-0.2 degrees C to 33. 8 degrees C+/-0.5 degrees C, a difference of only 0.8 degrees C+/-0. 4 degrees C. The difference in the core temperature increase between the two treatments was thus 1.5 degrees C+/-0.4 degrees C (95% CI 1. 2 degrees C to 1.7 degrees C; P <.001 between treatments). Active warming was not associated with an afterdrop, whereas the afterdrop was 0.2 degrees C+/-0.2 degrees C and lasted a median of 45 minutes (interquartile range, 41 to 64 minutes) with passive insulation.

CONCLUSION

Resistive heating more than doubles the rewarming rate compared with that produced by reflective metal foil and does so without producing an afterdrop. It is therefore likely to be useful in the prehospital setting.

Forced-air warming decreases vasodilator requirement after coronary artery bypass surgery

Postoperative hypothermia is common and associated with adverse hemodynamic consequences, including adrenergically mediated systemic vasoconstriction and hypertension. Hypothermia is also a known predictor of dysrhythmias and myocardial ischemia in high-risk patients. We describe a prospective, randomized trial designed to test the hypothesis that forced-air warming (FAW) provides improved hemodynamic variables after coronary artery bypass graft. After institutional review board approval and written informed consent, 149 patients undergoing coronary artery bypass graft were randomized to receive postoperative warming with either FAW (n = 81) or a circulating water mattress (n = 68). Core temperature was measured at the tympanic membrane. A weighted mean skin temperature was calculated. Heart rate, mean arterial blood pressure, central venous pressure, cardiac output, and systemic vascular resistance were monitored for 22 h postoperatively. Mean arterial blood pressure was maintained by protocol between 70 and 80 mm Hg by titration of nitroglycerin and sodium nitroprusside. The two groups had similar demographic characteristics. Tympanic and mean skin temperatures were similar between groups on intensive care unit admission. During postoperative rewarming, tympanic temperature was similar between groups, but mean skin temperature was significantly greater in the FAW group (P < 0.05). Heart rate, mean arterial pressure, central venous pressure, cardiac output, and systemic vascular resistance were similar for the two groups. The percent of patients requiring nitroprusside to achieve the hemodynamic goals was less (P < 0.05) in the FAW group. In conclusion, aggressive cutaneous warming with FAW results in a higher mean skin temperature and a decreased requirement for vasodilator therapy in hypothermic patients after cardiac surgery. This most likely reflects attenuation of the adrenergic response or opening of cutaneous vascular beds as a result of surface warming. IMPLICATIONS Forced-air warming after cardiac surgery decreases the requirement for vasodilator drugs and may be beneficial in maintaining hemodynamic variables within predefined limits.

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.