European Journal of Cardiovascular Medicine

Spinal anaesthesia is widely used for lower abdominal, pelvic, perineal, and lower-limb procedures because it provides reliable neural blockade while avoiding airway instrumentation and reducing exposure to systemic anaesthetic agents. Despite these advantages, neuraxial blockade disrupts normal thermoregulatory control and predisposes surgical patients to heat redistribution and hypothermia. Core temperature in healthy adults is normally maintained within a narrow range through behavioural and autonomic responses, principally vasoconstriction, sweating, and shivering. Anaesthesia widens the interthreshold range within which these defences are not activated, thereby increasing vulnerability to perioperative temperature decline.[1-4]

Shivering following spinal anaesthesia is clinically important because it is both distressing and physiologically demanding. Neuraxial sympathetic blockade causes vasodilatation below the level of the block and promotes redistribution of heat from central to peripheral compartments. At the same time, vasoconstriction and shivering are impaired in blocked regions, while altered afferent thermal input changes central thermoregulatory processing.[1,2,9] Exposure to a cool operating-room environment, surgical exposure, administration of unwarmed intravenous fluids, and prolonged procedures further increase heat loss. Although hypothermia is a major trigger, shivering can also occur in normothermic patients, indicating that non-thermoregulatory mechanisms such as pain, altered spinal reflex activity, and perioperative neurohumoral changes contribute to its development.[3-5]

Postanaesthetic shivering increases oxygen consumption and carbon dioxide production and can intensify sympathetic activity, discomfort, and postoperative pain. These effects are particularly undesirable in patients with limited cardiopulmonary reserve. Perioperative hypothermia itself has broader consequences, including delayed recovery, altered drug metabolism, coagulopathy, and increased susceptibility to postoperative complications.[1,3,5,14] Earlier observational work has demonstrated substantial variation in shivering incidence, reflecting differences in patient characteristics, anaesthetic technique, temperature-management practices, and definitions of shivering.[6-8,11] In patients receiving neuraxial anaesthesia, reported rates have ranged from low single-digit values to more than half of untreated control populations.[2,6] Such variation makes locally generated data relevant for routine perioperative practice, especially in institutions where patient warming strategies and operating-room conditions differ from those represented in controlled trials.

Identifying perioperative factors that predict shivering can allow anaesthesiologists to select patients for closer temperature surveillance and timely preventive measures. Temperature at baseline and during surgery, extent of sensory blockade, duration of surgery, and intravenous fluid exposure are plausible determinants, yet their relative contribution remains incompletely defined in heterogeneous adult surgical populations. Therefore, the present study was conducted to determine the prevalence and severity of postoperative shivering among adult surgical patients receiving spinal anaesthesia and to evaluate perioperative predictors associated with its occurrence, with particular attention to hypothermia, surgical duration, sensory block level, and intraoperative fluid administration.

study was conducted in the Department of Anaesthesiology at Konaseema Institute of Medical Sciences and Research Foundation, Amalapuram, Andhra Pradesh, India, from January 2020 to June 2020.

Study population: Patients aged 18 years or older with American Society of Anesthesiologists (ASA) physical status I or II who underwent elective surgery under spinal anaesthesia were eligible. Patients with contraindications to spinal anaesthesia, pre-existing fever or clinically significant hypothermia, known disorders affecting thermoregulation, requirement for conversion to general anaesthesia, refusal to participate, or incomplete perioperative temperature or shivering observations were excluded.

Sample size and sampling: The sample size was estimated using the single-proportion formula n = Z²p(1-p)/d². A previously published prospective observational study reported a post-spinal shivering prevalence of 8.15%.[6] With a 95% confidence level and an absolute precision of 6%, the calculated minimum sample was approximately 80 participants. Consecutive eligible patients were enrolled during the study period until the required sample was obtained.

Anaesthetic procedure and monitoring: Routine monitoring included non-invasive blood pressure, electrocardiography, and pulse oximetry. Spinal anaesthesia was administered under aseptic precautions according to institutional practice using hyperbaric bupivacaine, with dose and interspace selected by the attending anaesthesiologist. Sensory block level was assessed clinically and the highest achieved level was recorded. Intravenous fluid administration and duration of spinal anaesthesia and surgery were documented. Perioperative warming and fluid administration followed routine institutional practice; no study-specific warming or pharmacological antishivering intervention was imposed before outcome assessment.

Temperature and shivering assessment: Temperature was measured using a calibrated tympanic thermometer and treated as the perioperative core-temperature estimate. Baseline temperature was recorded before spinal anaesthesia and repeated during the perioperative period, including at the end of surgery. Hypothermia was defined as a recorded temperature below 36.0°C.[1,14] Shivering was assessed during early postoperative recovery using a clinically graded scale adapted from Crossley and Mahajan, ranging from no shivering to progressively more extensive muscular activity.[10] For analysis, observed episodes were categorized as mild, moderate, or severe. The primary outcome was occurrence of postoperative shivering; secondary outcomes included severity and associated perioperative predictors.

Statistical analysis: Continuous variables were summarized as mean ± standard deviation and categorical variables as frequency and percentage. Between-group comparisons used an independent-samples t-test for continuous variables and Chi-square or Fisher’s exact test for categorical variables, as appropriate. Variables with clinical relevance or evidence of association on univariate analysis were entered into multivariable logistic regression. Adjusted odds ratios (aORs) with 95% confidence intervals (CIs) were reported. A two-sided p-value <0.05 was considered statistically significant.

Ethical considerations: Necessary Permissions were obtained before starting the study. Written informed consent was obtained from all participants in accordance with the Declaration of Helsinki.

Participant flow and baseline characteristics

A total of 86 adult patients scheduled for surgery under spinal anaesthesia were assessed for eligibility during the study period. Six patients were excluded: three did not satisfy the predefined eligibility criteria, two declined participation, and one had incomplete perioperative temperature recordings. Consequently, 80 patients were included in the final analysis. Complete intraoperative and immediate postoperative observations regarding shivering were available for all included participants.

The mean age of the study population was 44.9 ± 13.2 years, and 46 (57.5%) participants were males. The mean body mass index (BMI) was 25.5 ± 3.6 kg/m². Forty-five (56.3%) patients were classified as ASA physical status I and 35 (43.8%) as ASA II. The mean duration of surgery was 87.6 ± 28.9 minutes, while the mean volume of intraoperative intravenous fluid administered was 1248 ± 416 mL. The mean baseline core temperature was 36.7 ± 0.3°C (Table 1).

Table 1. Baseline demographic and perioperative characteristics of the study participants (n=80)

Values are presented as mean ± standard deviation or n (%), as appropriate.

Prevalence and severity of postoperative shivering

Postoperative shivering was observed in 28 of 80 patients, giving an overall prevalence of 35.0%. The remaining 52 (65.0%) patients did not develop shivering during the observation period. Among the 28 patients who developed shivering, 8 (28.6%) experienced mild shivering, 12 (42.9%) had moderate shivering, and 8 (28.6%) developed severe shivering. Thus, moderate-to-severe shivering occurred in 20 patients, representing 25.0% of the entire study population (Table 2).

Table 2. Prevalence and severity of postoperative shivering

Comparison between patients with and without postoperative shivering

Patients who developed postoperative shivering had a significantly lower mean baseline core temperature than those who did not develop shivering (36.5 ± 0.3°C vs 36.8 ± 0.3°C; p<0.001). The mean duration of surgery was also longer among patients with shivering (101.8 ± 29.5 vs 79.9 ± 25.6 minutes; p=0.001). A sensory block level of T6 or above was observed more frequently among patients who developed shivering than among those who did not (57.1% vs 28.8%; p=0.014). Similarly, patients with shivering received a greater volume of intravenous fluids intraoperatively (1438 ± 421 vs 1146 ± 380 mL; p=0.003). Age, sex, BMI, and ASA physical status were not significantly associated with postoperative shivering (Table 3).

Table 3. Comparison of perioperative characteristics according to postoperative shivering status

Values are expressed as mean ± SD or n (%).

Perioperative temperature changes

The mean core temperature decreased progressively following spinal anaesthesia. In patients who subsequently developed shivering, the reduction in temperature was more pronounced than in those without shivering. At the end of surgery, the mean core temperature was 35.9 ± 0.4°C in the shivering group compared with 36.3 ± 0.3°C in the non-shivering group (p<0.001). Perioperative hypothermia, defined as a core temperature <36.0°C, was documented in 21 of 28 patients (75.0%) who developed shivering compared with 13 of 52 patients (25.0%) without shivering (p<0.001) (Table 4).

Table 4. Temperature-related findings according to postoperative shivering status

Predictors of postoperative shivering

Variables demonstrating clinically relevant or statistically significant associations on univariate analysis were entered into a multivariable logistic regression model. After adjustment for potential confounding factors, perioperative hypothermia, longer duration of surgery, and a higher sensory block level remained independently associated with postoperative shivering. Perioperative hypothermia was the strongest predictor, with affected patients having approximately four times greater odds of developing postoperative shivering (aOR 4.18; 95% CI: 1.42–12.31; p=0.009). Surgery lasting more than 90 minutes was independently associated with increased shivering risk (aOR 2.74; 95% CI: 1.03–7.29; p=0.043), while a sensory blockade extending to T6 or above was also significant (aOR 2.86; 95% CI: 1.05–7.80; p=0.040) (Table 5).

Table 5. Multivariable logistic regression analysis of predictors of postoperative shivering

Overall, postoperative shivering occurred in approximately one-third of patients undergoing spinal anaesthesia and was most strongly associated with perioperative hypothermia, prolonged surgery, and a higher level of sensory blockade.

In this prospective observational study, postoperative shivering occurred in 35.0% of adults undergoing surgery under spinal anaesthesia, with moderate-to-severe shivering affecting one-quarter of the study population. This prevalence falls within the broad range reported for neuraxial anaesthesia, although substantial variation exists across studies. Crowley and Buggy reported a median incidence of approximately 55% across control groups in neuraxial studies, whereas Luggya et al. documented a prevalence of 8.15% after spinal anaesthesia and Wódarski et al. reported shivering in 21.9% of women undergoing caesarean section.[2,6,7] Differences in surgical population, ambient temperature, warming practices, block characteristics, and definitions of shivering probably account for much of this heterogeneity. Earlier recovery-room observations also demonstrated that postoperative shivering frequency changes markedly according to anaesthetic technique and patient characteristics.[11]

Perioperative hypothermia was the strongest independent predictor in the present analysis. Three-quarters of patients who shivered developed a temperature below 36°C, compared with one-quarter of those without shivering. This finding is physiologically consistent with the well-established effect of spinal anaesthesia on thermoregulation. Neuraxial blockade reduces vasoconstrictor and shivering thresholds, blocks thermoregulatory responses in anaesthetized dermatomes, and permits redistribution of body heat from the core to peripheral tissues.[1,4,9] Luggya et al. similarly identified hypothermia as an important associated factor after spinal anaesthesia.[6] Furthermore, active warming and warmed intravenous fluids have been shown to decrease both hypothermia and shivering during spinal anaesthesia, supporting the clinical relevance of temperature preservation.[12]

Longer surgery was independently associated with shivering, with procedures exceeding 90 minutes showing higher adjusted odds. Prolonged exposure to the operating-room environment extends the period during which radiant, convective, conductive, and evaporative heat losses exceed metabolic heat production.[1,4] The shivering group also received a larger volume of intravenous fluids. Although fluid volume did not remain statistically significant after adjustment, greater exposure to unwarmed fluid can increase thermal loss and could interact with surgical duration. These observations support careful temperature surveillance when procedures are prolonged or fluid requirements rise.

A sensory block level at T6 or above was another independent predictor. A more extensive sympathetic block produces wider vasodilatation and reduces the body region capable of effective vasoconstriction and shivering, providing a plausible mechanism for the observed association.[2,9] Baseline temperature was also lower among patients who subsequently shivered, suggesting that even small preoperative thermal differences can influence the margin before the shivering threshold is reached. In contrast, age, sex, BMI, and ASA physical status were not significant in this cohort. This differs from Eberhart et al., who identified younger age among predictors after general anaesthesia, emphasizing that risk profiles vary by anaesthetic technique and population.[8]

The findings have practical implications. Simple attention to preoperative temperature, maintenance of normothermia, judicious warming of fluids, and closer observation during longer procedures or higher spinal blocks could reduce postoperative shivering burden. Pharmacological treatments are effective once shivering occurs,[13] but prevention through thermal management remains preferable because hypothermia is itself associated with adverse perioperative outcomes.[3,5,14]

LIMITATIONS

This study has several limitations. It was conducted at a single centre with a modest sample size and only 28 shivering events, which limits the stability and external applicability of the multivariable estimates. Temperature assessment relied on tympanic measurements rather than an invasive reference method. Operating-room temperature, exact warming exposure, and intrathecal drug dose were not incorporated into the predictor model, leaving potential residual confounding.

Postoperative shivering was common after spinal anaesthesia, affecting 35.0% of the studied adult surgical patients, with one-quarter experiencing moderate-to-severe episodes. Perioperative hypothermia emerged as the strongest independent predictor, while surgery lasting more than 90 minutes and sensory blockade extending to T6 or above were also independently associated with shivering. Lower baseline temperature and greater intravenous fluid administration characterized patients who developed shivering. These findings support systematic temperature monitoring throughout the perioperative period and focused preventive strategies for patients undergoing prolonged procedures or higher spinal blocks. Maintaining normothermia, minimizing avoidable heat loss, and ensuring timely recognition and treatment of shivering can improve patient comfort and perioperative physiological stability after spinal anaesthesia.

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