Low incidence of shivering with chronic propranolol therapy

"The magnitude and associated factors of intraoperative shivering after cesarean section delivery under Spinal anesthesia'': A cross sectional study

Background

Shivering is an involuntary, spontaneous, and repetitive contraction of the skeletal muscle and increases patients’ discomfort, oxygen-consuming, wound infection; increased surgical bleeding, and morbid cardiac events. The aim of this study was to determine the magnitude and associated factors of intraoperative shivering after cesarean section delivery

Methodology

An institution-based cross-sectional study was conducted. A total of 326 willing patients were included in the study after obtaining ethical consent and we have used consecutive sampling techniques. Axillary temperature was recorded preoperatively and in the intra-operative period every 5 min. Descriptive statistics, cross-tabs, and binary logistic regression analysis were performed to identify the association shivering and independent variables. The strength of the association was presented using an adjusted odds ratio with a 95% confidence interval and a p-value<0.05 was considered as statistically significant.

Results

The overall incidence of intraoperative shivering after cesarean section delivery under spinal anesthesia was 51.8% (95% CI: 46.3, 57.1). The majority of the patients who developed shivering were after 20 min of spinal anesthesia. In this study body temperature, mean arterial pressure of the patient, and duration of surgery were significantly associated with shivering.

Conclusion

In this study duration of surgery, hypothermia and hypotension were the independent associated risk factors for intraoperative shivering.

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The incidence of post spinal anesthesia shivering after cesarean section delivery was 51.8% in the study area.

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More than 45% patients were developed Grade III shivering.

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Hypothermia, hypotension and duration of surgery were affected shivering.

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Most patients were developed shivering after 20 min of spinal anesthesia.

Independent risk factors for postoperative shivering

Postoperative shivering (PAS) is uncomfortable for patients and potentially risky. In this observational trial we sought to identify independent risk factors for PAS after general anesthesia. Potential risk factors for PAS were recorded in 1340 consecutive patients. Signs of shivering, peripheral and core temperature, and thermal comfort were recorded in the postanesthetic care unit. The data were split into an evaluation data set (n = 1000) and a validation data set (n = 340). The first was used to identify independent risk factors for PAS and to formulate a risk score using backward-elimination logistic regression analysis. The proposed model was subsequently tested for its discrimination and calibration properties using receiver operating characteristic (ROC)-curve analysis and linear correlation between the predicted and the actual incidences of PAS in the validation group. The incidence of PAS was 11.6%. There were three major risk factors: young age, endoprosthetic surgery, and core hypothermia, with age being the most important. The risk score derived from this analysis had a reasonable discriminating power, with an area under the ROC-curve of 0.69 (95% confidence interval, 0.60-0.78; P < 0.0001). Furthermore the equation of the calibration curve (y = 0.69x + 6; R2= 0.82; P < 0.05) indicated a good and statistically significant agreement between predicted and actual PAS incidence. Postoperative shivering can be predicted with acceptable accuracy using the four risk factors identified in the present study. The presented model may serve as a clinical tool to help clinicians to rationally administer prophylactic antishivering drugs.

Postanaesthetic shivering: epidemiology, pathophysiology, and approaches to prevention and management

Along with nausea and vomiting, postanaesthetic shivering is one of the leading causes of discomfort for patients recovering from general anaesthesia. The distinguishing factor during electromyogram recordings between patients with postanaesthetic shivering and shivering in fully awake patients is the existence of clonus similar to that recorded in patients with spinal cord transection. Clonus coexists with the classic waxing and waning signals associated with cutaneous vasoconstriction (thermoregulatory shivering). The primary cause of postanaesthetic shivering is peroperative hypothermia, which sets in because of anaesthetic-induced inhibition of thermoregulation. However, shivering associated with cutaneous vasodilatation (non-thermoregulatory shivering) also occurs, one of the origins of which is postoperative pain. Apart from causing discomfort and aggravation of pain, postanaesthetic shivering increases metabolic demand proportionally to the solicited muscle mass and the cardiac capacity of the patient. No link has been demonstrated between the occurrence of shivering and an increase in cardiac morbidity, but it is preferable to avoid postanaesthetic shivering because it is oxygen draining. Prevention mainly entails preventing peroperative hypothermia by actively rewarming the patient. Postoperative skin surface rewarming is a rapid way of obtaining the threshold shivering temperature while raising the skin temperature and improving the comfort of the patient. However, it is less efficient than certain drugs such as meperidine, clonidine or tramadol, which act by reducing the shivering threshold temperature.

When asleep, one is cooler on beta-blockade than on placebo. A study of pulmonary arterial blood temperature and skeletal muscle heat production in anaesthetized man

The effect of beta 1-adrenergic blockade on body temperature was studied during general anaesthesia by means of a thermistor in an indwelling pulmonary arterial catheter. Metoprolol (200 mg daily) or placebo was given double-blind preoperatively for at least 2 weeks to 27 hypertensive patients undergoing abdominal surgery. A significantly greater temperature fall was observed in the metoprolol group compared with the placebo group. Heat production in the rectus abdominis muscle, measured by direct microcalorimetry, was significantly lower after metoprolol. The hypothermic effect of beta-adrenergic blockade during anaesthesia deserves special attention.