Spinal anaesthesia is a simple, reliable, and most common anaesthetic technique practiced worldwide for lower limb, lower abdominal surgeries.^1,2However, spinal anaesthesia is associated with side effects such as hypotension, bradycardia, and shivering.^3,4Hypotension after spinal anesthesia is initially due to a blockade of sympathetic fibers leading to a drop in systemic vascular resistance.^5,6Spinal-induced bradycardia is multifactorial but is in part due to the Bezold–Jarisch reflex. This reflex is mediated by serotonin receptors within the wall of the ventricle in response to systemic hypotension. It is thought that the stimulation of these peripheral 5-hydroxytryptamine subtype 3 (5-HT₃) receptors results in increased parasympathetic activity and decreased sympathetic activity, resulting in bradycardia, vasodilatation, and hypotension. Serotonin is an additive trigger for BJR in hypovolemic patients. Ondansetron being one of the 5-HT3 receptor antagonist being widely used as an antiemetic agent, has been safely used to blunt the Bezold–Jarisch reflex, resulting in less bradycardia and hypotension in humans undergoing spinal anesthesia.^3,7

Also, Shivering is a common, undesirable perioperative event in patients under spinal anesthesia.^8,9 Perioperative shivering has a multitude of deleterious effects. These include patients’ discomfort, an increase in oxygen consumption up to 500%, and increased risk of myocardial ischemia.¹⁰ Shivering also induces artifacts in intraoperative monitoring especially with electrocardiogram (ECG), noninvasive blood pressure monitoring, and pulse oximetry.¹¹
The mechanism of spinal anesthesia-induced shivering is poorly understood. One proposed mechanism is that during spinal anesthesia, there is a block in sympathetic flow which leads to peripheral vasodilatation and increased cutaneous blood flow below the level of block.¹² There is, subsequently, a core-to-periphery heat redistribution with an increased heat loss to the environment. With a drop in body core temperature, the anterior hypothalamic thermoregulatory thermostat is reset and shivering response is triggered above the level of block with the aim of raising metabolic heat production and core body temperature.¹²

Even though spinal anaesthesia is a simple and safe procedure, rare complications such as unresponsive hypotension, bradycardia and shivering are real anaesthetic challenges. It is preferred to prevent hypotension rather than treating it. Hence, in the recent past, most of the studies are focusing on prophylactic management of hypotension and shivering; ondansetron is such a drug gaining popularity in the prevention of hypotension and shivering in patients who underwent subarachnoid block.