BODY MASS INDEX AND SPREAD OF LOCAL ANAESTHETIC IN SUB ARACHNOID BLOCK:AN OBSERVATIONAL STUDY

Abstract

Background: Subarachnoid block (SAB), commonly known as spinal anaesthesia, is a widely utilized regional anaesthetic technique for abdomen and lower limbs surgery. The effectiveness and distribution of local anaesthetic agents administered via SAB are influenced by a range of physiological and demographic factors, with body mass index (BMI) being a significant contributor. Elevated BMI, particularly in obese individuals, has been associated with changes in cerebrospinal fluid (CSF) volume and flow dynamics, which can alter the spread, onset, and duration of the anaesthetic effect. These alterations may result in unpredictable anaesthetic responses, underscoring the importance of assessing the role of BMI in determining the characteristics and efficacy of spinal anaesthesia. Aim: To compare the spread, onset, and recovery characteristics of local anaesthetic in spinal anaesthesia between obese and non-obese patients undergoing elective lower abdominal surgeries. Material & Methods: A comparative study involving 110 patients aged 18 to 59 years and classified as ASA physical status I–II was conducted at R.L. Jalappa Hospital and Research Centre. The participants were stratified into two groups based on body mass index (BMI): Group 1 included patients with BMI <25 kg/m² (n=55), and Group 2 comprised those with BMI >25 kg/m² (n=55). Spinal anaesthesia was administered uniformly. Key anaesthetic parameters—including the onset time of sensory and motor blockade, time to achieve maximum block height, and duration of block recovery—were systematically recorded. Data analysis was performed using SPSS version 26.0, with statistical significance set at a p-value less than 0.05. xx Results: Obese patients (Group 2) demonstrated a significantly longer onset time and duration for both sensory and motor blocks compared to non-obese patients (p<0.05). However, there was no significant difference in the duration of surgery or anaesthesia between the two groups. Conclusion: BMI significantly influences the pharmacodynamics of spinal anaesthesia. Obese patients exhibit delayed onset and prolonged duration of spinal block, highlighting the need for individualized anaesthetic dosing and monitoring to enhance patient safety and efficacy of spinal anaesthesia in higher BMI populations