Influence of Injection Rate of Intrathecal Mixture of Local Anesthesia on Hypotension in Cesarean Section

Overview

Hypotension is the most common complication of neuraxial anesthesia in obstetric patients and its prevalence in cesarean section is about 50-90%. Maternal hypotension causes unpleasant symptoms such as nausea, vomiting, loss of consciousness, respiratory depression, and cardiac arrest. Hypotension may reduce placental perfusion and result in fetal acidosis and neurological injury. Several techniques have been proposed to prevent hypotension. The recommended spinal block height to ensure patient comfort for Cesarean delivery is T4-6. Clinically, it is desirable that the spread of local anesthetic through the cerebrospinal fluid (CSF) achieves a sensory level no higher than the T4 dermatome to avoid extensive sympathetic block. It is also important that the spinal block level be no lower than T6 to avoid patient discomfort during peritoneal manipulation and uterine exteriorization. The effect of injection speed on spread of spinal anesthesia is controversial. Several studies have demonstrated more extensive spread with faster injection while others report either greater spread with slower injection, or no difference. Slow injection of hyperbaric bupivacaine 10 mg over 60 and 120 sec has been shown to reduce the incidence and severity of hypotension during Cesarean delivery under spinal anesthesia.

Patients admitted to undergo elective c-section under spinal anesthesia will be randomized using the sealed envelope technique to Group I who will receive intrathecal injection in a slow speed 1ml in 15 sec and group II who will receive 1ml in 5 sec. The baseline pulse rate, blood pressure, respiratory rate, and oxygen saturation will be recorded intraoperatively. The presence of preoperative hypotension, nausea and vomiting, and level of block at 5 and 10 mins post intrathecal injection will be assessed .