Effect of Ondansetron on the Incidence of Spinal Anaesthesia-Induced Hypotension in Elderly Patients Undergoing Fracture Hip Surgery

Spinal anesthesia is widely used for fracture hip surgery because it provides effective surgical anesthesia while avoiding many physiological effects associated with general anesthesia. However, spinal anesthesia-induced hypotension (SIH), defined as a mean arterial pressure (MAP) decrease >20% from baseline or systolic blood pressure (SBP) <90 mmHg or a >20% decrease from baseline, is one of its most common complications. It primarily results from sympathetic blockade, causing vasodilation, reduced venous return, decreased cardiac output, and subsequent arterial hypotension. This may be particularly significant in elderly patients because of reduced cardiovascular, arterial, and autonomic reserve, together with a higher prevalence of cardiovascular disease and polypharmacy.

A sudden reduction in left-ventricular preload may activate cardiac mechanoreceptors and trigger the Bezold-Jarisch reflex (BJR). Serotonin-sensitive 5-HT3 receptors located on intracardiac vagal nerve endings may enhance vagal activity, contributing to bradycardia defined as heart rate (HR) < 50 beat per minute (bpm) and hypotension.

Ondansetron, a selective 5-HT3 receptor antagonist widely used as an antiemetic, has been investigated to attenuate the BJR and reduce SIH. Several randomized trials and meta-analyses have reported that prophylactic intravenous ondansetron, commonly given at 4-8 mg shortly before spinal injection, reduces post-spinal hypotension, bradycardia, and rescue vasopressor requirements, including in elderly surgical patients. An exploratory analysis suggested a greater preventive effect in patients aged ≥65 years.

However, the elderly subgroup was small and a 8 mg dose was used, leaving uncertainty regarding the optimal dose.

Spinal anesthesia technique The conduct of spinal anesthesia will be standardized across the two groups. On arrival to the operating room, standard ASA monitors including a pulse oximetry, electrocardiography and non-invasive blood pressure will be applied and the patients will be continuously monitored.

Baseline hemodynamics will be recorded at one, three, and five minutes before the studied drug administration, and the average will be taken as a baseline.

After an intravenous (IV) access is secured, all patients will receive an intraoperative infusion of 5-10 ml/kg Ringer's lactate or Normal saline solution per hour.

With the parturient in a sitting position, spinal anaesthesia will be conducted using the midline or paramedian approach after proper antiseptic cleaning and draping in the lumbar vertebral interspace of L3-L4 or a level below using a 25 or 22-gauge Quincke needle. After confirming free flow of cerebrospinal fluid, a 3 mL of hyperbaric bupivacaine 0.5% will be injected intrathecal in both Groups the same dose, Then all patients will be then made to lie supine.

Block-level will be tested every five minutes using a frozen plastic ampule of sterile water along the midclavicular line to check the response to cold, and the highest sensory level obtained will be registered.

Motor level will be assessed every five minutes using the Modified Bromage Scale, where Grade 0 indicates full movement of the hip, knee, and ankle; Grade 1 indicates inability to raise the extended leg while retaining the ability to flex the knee and move the ankle; Grade 2 indicates inability to flex the knee while retaining ankle movement; and Grade 3 indicates complete motor block with inability to move the hip, knee, or ankle. The highest Modified Bromage grade obtained will be recorded.

Surgeons will be allowed to proceed with surgery after attaining a block level of at least up to T10.

Data collection

1. Patient characteristics including, age, sex, weight, height, and ASA status.

2. Hemodynamic parameters including heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and oxygen saturation (SpO2) will be recorded at the following time points:

   • Before injection of the study drug (baseline);
   • At interval of 0 (baseline) and 5 minutes after the study drug administration and before intrathecal injection;
   • At two-minutes intervals up to 20 minutes after intrathecal injection,
   • Every 5 minutes until end of surgery.
   • Postoperative hemodynamics at 2, 4, 6, 8, 12, 24 hours after surgery.

3. Bradycardia (HR <50 bpm) will be treated with atropine 0.5 mg. Clinically significant hypotension, defined as MAP fall > 20% from baseline, or systolic blood pressure < 90 mmHg / fall > 20% from baseline, and if developed will be treated with IV ephedrine sulfate boluses of 6 mg as required. Amount of atropine and ephedrine required, sensory level achieved at 15 min of Spinal anaesthesia.

4. Duration of surgery (minutes), total fluid intake (ml), and length of PACU stay (minutes).

5. Side effects including hypotension (defined as MAP fall > 20% from baseline, or systolic blood pressure < 90 mmHg / fall > 20% from baseline), hypertension, bradycardia (HR < 50 bpm), tachycardia (HR > 100 bpm), hypoxemia (defined as a SpO2 level of less than 94% with a need for oxygen supplementation), respiratory depression, hallucinations, nystagmus, postoperative nausea and vomiting (PONV), and shivering will be treated and recorded.

The incidence of postoperative nausea and vomiting (PONV) episodes will be assessed in the first 24 h (at 2, 4, 6, 8, 12, 24 hours after surgery).

Patients who will develop shivering will be warmed with heated blankets.