We evaluated the usefulness of a novel earphone-type infrared tympanic thermometer (IRT) during cardiac surgery with cardiopulmonary bypass. Tympanic membrane temperature (T(Tym)) was monitored using the IRT inserted into the right ear canal of 12 adult patients (ASA III) who had been scheduled for elective cardiac surgery with cardiopulmonary bypass under general anesthesia. Rectum (T(Rec)) and nasopharyngeal temperatures (T(Naso)) were also monitored, and all temperatures were recorded at 5-min intervals during cardiopulmonary bypass. Operating room temperature was kept at 20°-27°C; a conductive warming/cooling system was used to control the patient's body temperature. Of 265 measurements obtained, body temperature range was 31.6°-37.6°C. No complications were related to site of insertion of the monitoring probe. Significant correlations were seen between T(Tym) and T(Naso) (r = 0.971, P < 0.001), and T(Tym) and T(Rec) (r = 0.759, P < 0.001). A Bland-Altman plot showed that average temperature of T (Tym) was 0.06°C above T(Naso) (±0.66°C, 2 SD) and 0.12°C below T(Rec) (±1.78°C, 2 SD). We conclude that an earphone-type IRT is noninvasive and hygienic and could continuously evaluate selective cerebral temperature during cardiopulmonary bypass in adults.

Background We previously reported that each 100 mg dL − 1 reduction in blood glucose over the range from ≈90 to > 300 mg dL − 1 decreases the shivering threshold (triggering core temperature) in rabbits by 1 °C. However, the effects of lower blood glucose concentrations has yet to be evaluated. We thus evaluated the relationship between the shivering threshold and blood glucose concentration over the mild-to-severe hypoglycemic range. Methods Thirty-nine rabbits were lightly anaesthetized with isoflurane and randomly assigned to one of the three groups: 1) severe hypoglycemia, insulin and dextrose infusions titrated to achieve blood glucose concentration at 45–75 mg dL − 1 ; 2) mild hypoglycemia, insulin and dextrose infusions titrated to achieve blood glucose concentration at 75–100 mg dL − 1 ; and 3) saline infusion. Cooling by colonic perfusion of water at 10 °C was continued until shivering occurred or esophageal core temperatures reached to 34 °C. Results The shivering threshold in the severe hypoglycemic rabbits was 35.7 ± 1.1 °C (mean ± SD); the thresholds in the mild hypoglycemic rabbits was 37.0 ± 0.7 °C; and the threshold in the control rabbits was 37.9 ± 1.0 °C. The shivering threshold increased linearly with blood glucose concentration: shivering threshold (°C) = 0.032 ∙ [blood glucose concentration (mg dL − 1 )] + 34.1, R 2 = 0.45. The shivering threshold thus decreased by approximately 1 °C for each 31 mg dL − 1 decrease in blood glucose concentration. Conclusions There was a linear relationship between blood glucose and the shivering threshold over the range from severe hypoglycemia to normoglycemia. Blood glucose perturbations in the hypoglycemic range reduced the shivering threshold about three times as much as previously reported for the hyperglycemic range.

Hyperglycemia increases the threshold for shivering, whereas hypoglycemia lowers the threshold on rabbits.

Shivering after surgery or during therapeutic hypothermia can lead to serious complications, such as myocardial infarction and respiratory failure. Although several anesthetics and opioids are shown to have anti-shivering effects, their sedative and respiratory side effects dampen the usefulness of these drugs for the prevention of shivering. In the present study, we explored the potential of a novel ultrashort-acting benzodiazepine, remimazolam, in the prevention of shivering using a rabbit model of hypothermia. Adult male Japanese white rabbits were anesthetized with isoflurane. The rabbits received saline (control), remimazolam (either 0.1 or 1 mg/kg/h), or remimazolam + flumazenil, a selective γ-aminobutyric acid (GABA) type A receptor antagonist (n = 6 each). Thirty minutes after discontinuation of the drugs, cooling was initiated by perfusing 10°C water via a plastic tube positioned in the colon until the animal shivered. Core body temperature and hemodynamic and physiological parameters were recorded. Remimazolam at 1 mg/kg/h significantly lowered the core temperature change during shivering (−2.50 ± 0.20°C vs. control: −1.00 ± 0.12°C, p = 0.0009). The effect of 1 mg/kg/h remimazolam on the core temperature change was abolished by flumazenil administration (−0.94 ± 0.16°C vs. control: −1.00 ± 0.12°C, p = 0.996). Most of the hemodynamic and physiological parameters did not differ significantly among groups during cooling. Remimazolam at a clinically relevant dose successfully suppressed shivering in rabbits via the GABA pathway even after its anesthetic effects likely disappeared. Remimazolam may have the potential to prevent shivering in patients undergoing surgery or therapeutic hypothermia.