The Efficacy of the Volume of Hyperbaric Bupivacaine Used and Its Influence on Spinal Anaesthesia Induced Hypotension during Caesarean Section

Aims: To audit the spinal anaesthesia practice among physician anaesthetists and to determine the lowest effective volume of hyperbaric bupivacaine that could minimise the incidence of spinal anaesthesia induced hypotension during caesarean section.

Study Design: It was a prospective observational study of patients undergoing caesarean section. Patient recruitment was by convenient sampling.

Place and Duration of Study: The study was carried out at the Obstetric theatre of the University of Calabar Teaching Hospital, Calabar, Nigeria between March and June 2015.

Methodology: One hundred and thirty one (131) patients who met the inclusion criteria were recruited for the study. Patients with antepartum haemorrhage, pregnancy-induced hypertension or patients on any antihypertensive agents and those with contraindications to spinal anaesthesia were excluded. The spinal anaesthesia was instituted at L3 L4 interspace in the sitting position. The maximum height of sensory block and the number of patients that were hypotensive (systolic blood pressure less than 90 mmHg) in relation to the volume of hyperbaric bupivacaine used were noted. Simple descriptive and inferential statistics was used to determine the association between the volumes of hyperbaric bupivacaine used, the height of block and incidence of hypotension.

Results: The volumes of 0.5% hyperbaric bupivacaine used ranged from 1.5– 2.7 millilitres (mls). Sixty-eight (51.9%) patients received treatment for hypotension. The incidence of hypotension was related to volume of bupivacaine used and height of sensory block. The incidence of hypotension was more in patient that had 2 mls (62.9%). Less than 2mls was associated with lower incidence of hypotension (32.5%) but with a high risk of intraoperative analgesic requirement (22.5%). A block height below T6 was a risk factor for supplementary intraoperative analgesic requirement and above T6 risk factor for hypotension. The maximum height of sensory block did not have any significant relationship with the volume of the hyperbaric bupivacaine used, (P = 0.1).

Conclusion: Spinal anaesthesia-induced hypotension is a complication that may not be eliminated. The incidence during caesarean section in this study was influenced more by height of block than volume of the drug used. The used of 1.5 mls (7.5 mg) of 0.5% hyperbaric bupivacaine and a block height of T6 could provide adequate anaesthesia for caesarean section and reduce the incidence of hypotension.