Surgical hypothermia

The forgotten art of cold therapeutic properties in cancer: A comprehensive historical guide

Cold therapy has been used for centuries, from Julius Caesar to Mohandas Gandhi, as a potent therapeutic approach. However, it has been largely forgotten in modern medicine. This review explores the history of cold therapy and its potential application as a therapeutic strategy against various diseases, including cancer. We examine the different techniques of cold exposure and the use of other therapeutical approaches, such as cryoablation, cryotherapy, cryoimmunotherapy, cryothalectomy, and delivery of cryogen agents. While clinical trials using cold therapy for cancer treatment are still limited, recent research shows promising results in experimental animal cancer models. This area of research is becoming increasingly significant and warrants further investigation.

Preliminary evaluation of the Arctic Sun temperature-controlling system during off-pump coronary artery bypass surgery

BACKGROUND

Maintaining normothermia during off-pump coronary artery bypass (OPCAB) surgery is a challenge not met by currently available medical devices and strategies. The purpose of this study was to determine the efficacy of a new thermoregulatory device, the Arctic Sun temperature-controlling circulating fluid adhesive pad system, in preventing hypothermia during OPCAB surgery.

METHODS

Thirteen consenting patients undergoing OPCAB had their temperature managed using the Arctic Sun system. They were matched with 23 consenting control OPCAB patients whose temperature was maintained with standardized, conventional therapy (elevated ambient operating room temperature, warmed intravenous fluids, and a convective forced air warming system placed under the surgical drapes). Nasopharyngeal temperature (recorded at 1-minute intervals) was compared between the two groups by analysis of both the time and area under the curve for a temperature less than 36 degrees C.

RESULTS

Multivariate linear regression analysis revealed that the average amount of hypothermia in the Arctic Sun group was significantly less than in the control group, both for time spent less than 36 degrees C (20.7 vs 121.3 minutes, p = 0.0004) and for area under the curve less than 36 degrees C (11.8 degrees C vs 78.1 degrees C x minutes, p = 0.0001).

CONCLUSIONS

The Arctic Sun temperature-controlling system is more effective than conventional warming methods in preventing hypothermia during OPCAB surgery.

The effect of fluoride and hypothermia on the in vitro metabolism of mivacurium

IMPLICATIONS

The fluoride inhibition of mivacurium hydrolysis by pseudocholinesterase increases in hypothermia, but it will very rarely occur in clinical practice because it requires rather large fluoride concentrations (>50 micromol/L) and very low temperatures (<28 degrees C).

Vecuronium pharmacokinetics and pharmacodynamics during hypothermic cardiopulmonary bypass in infants and children

PURPOSE

To determine the effect of moderate and deep hypothermic cardiopulmonary bypass (CPB) on the pharmacokinetic and pharmacodynamic behaviour of vecuronium in infants and children.

METHODS

We studied 12 patients undergoing surgery for congenital heart disease under narcotic-nitrous oxide anesthesia. Neuromuscular blockade was maintained constant (TI 4-10% by Datex electromyograph) by adjusting a vecuronium infusion. Plasma vecuronium concentrations (Cpss) were analysed by HPLC to describe a pseudosteady-state during each of the pre-CPB, CPB and post-CPB phases. Paired arterial blood samples were taken 20 min apart after at least 20 min of constant infusion.

RESULTS

Nine cases were analysed, mean age 20 mo, mean weight 9 kg. Three patients had deep and six moderate hypothermia. In the pre-CPB phase Cpss fell into two groups (mean +/- SD: 330 +/- 42 ng x ml(-1); 127 +/- 27 ng x ml(-1); P < 0.001); similarly the clearances showed a bimodal distribution (mean +/- SD: 5.08 +/- 0.94; 11.51 +/- 0.2 ml x min(-1) x kg(-1) P < 0.001), although in different patients. During CPB this bimodal distribution disappeared. Vecuronium infusion rate (VIR) decreased by 84% and 92% from pre-CPB to CPB phase in deep and moderate hypothermia groups respectively (P < 0.05), paralleled by decreases in Cpss of 36% (P > 0.05) and 52% (P < 0.05).

CONCLUSION

Changes in vecuronium requirements and plasma concentrations during CPB demonstrate that vecuronium pharmacokinetics and pharmacodynamics are both affected by hypothermic CPB in infants. The finding of bimodal distributions for plasma vecuronium and vecuronium clearance highlights the need for individual monitoring of neuromuscular blockade in this age group.

The physiological response to norepinephrine during hypothermia and rewarming

Our purpose was to determine if core hypothermia influences physiological responses to norepinephrine (NE); and if rewarming reverses these effects. Animals were instrumented to measure mean arterial pressure (MAP) and cardiac output (CO). Core temperature was manipulated from 37.5 degrees C (normothermia), to 30 degrees C (hypothermia) and the back to 37.5 degrees C (rewarming) using an external arterial-venous femoral shunt. At each of these temperatures, baseline CO and MAP were measured. Norepinephrine (NE) was infused at rates to deliver 0.2, 1.0, or 5 microg kg(-1) per h. At each dose CO and MAP was measured again. Systemic vascular resistance (SVR) was calculated using the formula (SVR = (MAP/CO) x 80). Eight animals underwent all three phases of the protocol. The response to NE during normothermia was a significant increase in MAP to doses of 1 microg kg(-1) per min (P < 0.01) and 5 microg kg(-1) per min (P < 0.01) and SVR to doses of 1 microg kg(-1) per min (P < 0.01) and 5 microg kg(-1) per min (P < 0.01). The response to NE during hypothermia was a significant increase in MAP only at doses of 1 microg kg(-1) per min (P = 0.03) and 5 microg kg(-1) per min (P = 0.01). The response to NE after rewarming was a significant increase in MAP only at a dose of 5 microg kg(-1) per min (P = 0.03). This study shows that core hypothermia causes a change in physiological response to NE that rewarming does not reverse.

The management of temperature during hypothermic cardiopulmonary bypass: II--Effect of prolonged hypothermia

In animals mild hypothermia (32-35 degrees C) reduces ischaemic brain injury, but this has not been investigated in humans. During hypothermic cardiopulmonary bypass (CPB) patients are made hypothermic (usually to 30-32 degrees C) but are then rewarmed at a time when they are still at risk of ischaemic brain injury. We investigated the feasibility and safety of maintaining mild hypothermia throughout the CPB period. Thirty adult cardiac surgical patients were randomized to either rewarming to 36-37 degrees C or to maintaining temperature at 34 degrees C without rewarming. On arrival in the recovery room, patients in the hypothermic group had a mean bladder temperature of 33.8 +/- 0.45 degrees C compared with 35.4 +/- 0.58 degrees C (mean +/- SD, P < 0.05) in the rewarmed patients. There were no differences between groups in intra- or postoperative blood loss or blood use, inotrope use, dysrhythmias, or myocardial infarction. The hypothermic group received more muscle relaxant for the treatment of shivering postoperatively. Our results suggest that mild hypothermia following CPB did not increase morbidity although larger studies are needed for confirmation.

The management of temperature during cardiopulmonary bypass: effect on neuropsychological outcome

Laboratory studies demonstrate that mild degrees of brain cooling (2 degrees C to 5 degrees C) confer substantial protection from ischemic brain injury, and that mild elevation of brain temperature can be markedly deleterious. During hypothermic cardiopulmonary bypass (CPB) patients are made hypothermic and then rewarmed at a time when they are exposed to neurological insults. Our studies show that during rewarming, peak brain temperatures near 39 degrees C often are achieved inadvertently. We hypothesize that maintaining brain temperature < or = 34 degrees C during and after CPB will reduce the incidence of postoperative neuropsychological deficits. We present safety data from a study of 30 patients assigned either to conventional hypothermic CPB with rewarming or a protocol where brain temperature is raised only to 34 degrees C at the time of separation from CPB. There was no difference in bleeding, cardiac morbidity, or time to extubation between groups. We designed a neuropsychological test battery to detect postoperative neuropsychological deficits and tested its usefulness in a preliminary sample of 15 patients undergoing hypothermic CPB. We found patient acceptability and compliance were good. Sensitivity also seemed adequate in that 30% of patients were identified as having deteriorated at 1 week postoperatively compared to preoperatively, a result similar to that reported by others. Clinical trials of the efficacy of mild hypothermia in modulating brain injury in humans are needed before techniques of CPB can be designed to optimize neuroprotection.

The effect of acute hypothermia and serum potassium concentration on potassium cardiotoxicity in anesthetized rats

We examined the effects of hypothermia on serum K+ concentration and the interaction of body temperature and K+ load on cardiac toxicity in anesthetized rats. Serum K+ concentration significantly decreased to 2.61 +/- 0.13, 2.59 +/- 0.19 and 2.39 +/- 0.14 mmol/l at 31.0 degrees C, 28.0 degrees C and 25.0 degrees C, respectively, from the control value of 2.80 +/- 0.15 mmol/l at 37.0 degrees C. We used a 300% increase in baseline QRS duration as evidence of cardiac toxicity. Serum K+ concentrations of 4.95 +/- 0.12, 4.71 +/- 0.10, 4.45 +/- 0.14 and 4.07 +/- 0.14 mmol/l resulted in cardiac toxicity at 37.0 degrees C, 31.0 degrees C, 28.0 degrees C, and 25.0 degrees C, respectively. These data indicate that the level at which an elevation of serum K+ concentration causes cardiac toxicity diminishes with progressive hypothermia. We conclude that hypothermia induces hypokalemia, possibly through redistribution, and that the myocardium appears to be more sensitive to the toxic effects of K+ as hypothermia deepens.

Hypothermic protection following middle cerebral artery occlusion in the rat

The effects of deep hypothermia on ischemic neuronal injury were examined using a permanent middle cerebral artery occlusion model in the rat. Animals were maintained at temporalis temperatures of either 24 degrees C or 36 degrees C and killed 6 hours after arterial occlusion. Normothermic rats displayed an average infarct volume of 25.1% +/- 1.6% of the right hemisphere, whereas hypothermic rats had an average infarct volume of 4.1% +/- 1.3% (p less than 0.001). The right/left hemispheric ratio was 1.05 +/- 0.02 in the normothermic group and 1.00 +/- 0.02 in the hypothermic group (p less than 0.05). These results suggest that hypothermia to 24 degrees C may reduce cerebral infarction and edema formation following middle cerebral artery occlusion in the rat.