Prophylactic Tramadol Versus Magnesium Sulphate for Prevention of Post-Spinal Shivering

This randomized controlled trial was conducted to compare the effectiveness of prophylactic intravenous tramadol with intravenous magnesium sulphate for prevention of post-spinal shivering in women undergoing elective cesarean section under spinal anesthesia. The study was conducted in the Department of Anaesthesia, Punjab Rangers Teaching Hospital, Lahore, over a period of six months from 10 October 2024 to 10 April 2025.

Spinal anesthesia is widely used for cesarean section because of its rapid onset, reliability, avoidance of airway manipulation, and favorable maternal and neonatal safety profile. However, post-spinal shivering is a relatively common complication and may cause considerable discomfort and anxiety for the patient. Shivering may also interfere with monitoring and may increase oxygen consumption and metabolic demand. Various pharmacological agents have therefore been investigated for prevention and treatment of shivering associated with neuraxial anesthesia. Tramadol has been used as an anti-shivering agent because of its central effects on serotonergic and noradrenergic pathways, while magnesium sulphate may reduce shivering by influencing neuromuscular transmission and lowering the shivering threshold. Previous comparative studies have reported conflicting results regarding the effectiveness of these agents in patients undergoing cesarean section under spinal anesthesia. The present study was therefore undertaken to compare the two agents under standardized perioperative conditions.

A total of 106 pregnant women scheduled for elective cesarean section were enrolled after obtaining ethical approval and written informed consent. Eligible participants were women aged 18 to 40 years undergoing elective cesarean section under spinal anesthesia. Participants were selected through non-probability consecutive sampling. Patients were excluded if they had severe systemic disease involving the cardiopulmonary, renal, or hepatic systems; thyroid disorders; pre-eclampsia or eclampsia; psychiatric illness; morbid obesity; significant intraoperative blood transfusion or excessive fluid administration; abnormal placental attachment; or allergy to any of the study medications.

After enrollment, participants were randomly allocated into two equal groups of 53 patients each. Group A received tramadol at a dose of 0.5 mg/kg intravenously, while Group B received magnesium sulphate at a dose of 30 mg/kg intravenously. In both groups, the assigned study medication was diluted in 100 mL isotonic saline and administered after establishment of spinal anesthesia. Standardized drug doses and similar perioperative conditions were used to ensure comparability between the treatment groups.

All participants received standard preoperative medications and anesthetic management according to the institutional protocol. Preoperative medications included oral ranitidine 150 mg and metoclopramide 10 mg on the night before surgery, with intravenous medications administered before anesthesia as per protocol. Spinal anesthesia was performed in the sitting position using a 25- or 26-gauge Quincke needle at the L3-L4 or L4-L5 intervertebral level. A dose of 2.0-2.2 mL of 0.5% hyperbaric bupivacaine was used for the spinal block. Ringer lactate was administered as a co-load at 10 mg/kg according to the study protocol. The operating-room temperature was maintained at approximately 24-25°C.

Standard monitoring was applied throughout the perioperative period, including electrocardiography, non-invasive blood pressure, pulse oximetry, pulse rate, and temperature monitoring. A senior consultant supervised the anesthetic procedures. Data collection was performed by the resident responsible for assessment and documentation according to the study proforma. Standardized anesthesia and monitoring protocols were used in both groups to minimize potential confounding.

The primary outcome was the occurrence of post-spinal shivering after administration of the study medication. Shivering was defined as involuntary, spontaneous muscular activity lasting for more than 15 seconds and reaching a score of 2 or higher on the Crossley and Mahajan shivering scale. The presence or absence of shivering was recorded during the observation period. In patients who developed shivering, the grade of shivering was documented. The severity categories included Grade II, Grade III, and Grade IV in accordance with the scale used in the study.

Secondary assessments included the severity of post-spinal shivering and the occurrence of perioperative adverse effects. Adverse effects monitored during the study included nausea, vomiting, bradycardia, arrhythmia, and hypotension. Patients who developed shivering were managed according to the institutional clinical protocol, including external warming, oxygen supplementation, and rescue pharmacological treatment such as pethidine or dexmedetomidine when clinically indicated.

Baseline demographic and clinical characteristics were recorded for all participants, including age, body mass index (BMI), American Society of Anesthesiologists (ASA) physical status, and parity. Age was categorized into 18-30 years and 31-40 years for subgroup analysis. BMI was categorized into normal-weight and overweight/obese groups. ASA physical status was categorized as ASA-I or ASA-II. Parity was categorized as parity ≤2 or >2.

The sample size was calculated using the WHO sample size calculator with an assumed statistical power of 80% and a significance level of 5%. The calculation was based on previously reported shivering frequencies of 7.7% in patients receiving tramadol and 30.8% in patients receiving magnesium sulphate. The resulting sample consisted of 106 participants, with 53 participants allocated to each treatment group.

Data were entered, coded, and analyzed using SPSS version 26. Continuous variables were assessed for distribution and summarized as mean ± standard deviation, while categorical variables were presented as frequencies and percentages. Baseline demographic and clinical characteristics were compared between the two groups to assess their comparability. The independent-samples t-test was used for comparison of continuous variables where appropriate. The chi-square test was used for comparison of categorical variables, while Fisher's exact test was applied where expected cell frequencies were small. The primary outcome, occurrence of post-spinal shivering, was compared between the two treatment groups using the chi-square or Fisher's exact test, as appropriate. Shivering severity grades and perioperative adverse effects were also compared between groups using appropriate categorical tests. A two-sided p-value of ≤0.05 was considered statistically significant.

Stratified analysis was performed to assess whether the frequency of post-spinal shivering varied according to important baseline characteristics. Comparisons were stratified by age, BMI, ASA physical status, and parity. The chi-square test or Fisher's exact test was applied as appropriate within each subgroup. All statistical tests were two-sided, and a p-value of ≤0.05 was considered statistically significant.