Minimum effective volume of bupivacaine in spinal anesthesia for elective cesarean section. Does it differ with height? A non-randomized parallel study

Background
Spinal anesthesia is the preferred anesthetic technique for elective Cesarean deliveries. Hypotension is the most common side-effect and has both maternal and neonatal consequences. This study aims to determine the minimum effective volume of hyperbaric bupivacaine 0.5% with fentanyl in 90% of parturients (MEV90) with different height groups undergoing cesarean section.
Patients and Methods
Parturients scheduled for elective cesarean section under spinal anesthesia were divided into 3 groups according to their height (ht), group 1 including those with height between 150 and 159 cm, group 2 with ht between 160 and 169 cm and group 3 patients with ht between 170 and 179 cm. The starting volumes were 2.5, 2.6 and 2.7 ml respectively. We identified 3 responses to the injected volume and the volume given to each parturient depends on the response of the previous one. Every patient was assessed for hemodynamics, degree of sensory and motor blocks.
Results
Demographically, all the groups were comparable. The study was completed after recruiting 201 patients. The MEV90 for group 1 was approximately 2.62 ml (95% CI, 2.59–2.65 ml), 2.76 ml for group 2 (95% CI, 2.73–2.77 ml) and 2.80 for group 3 (95% CI, 2.76–2.81 ml). None of the babies had an Apgar score below 7 at 1 and 5 min after birth in the 3 groups.
Conclusion
The volumes of hyperbaric 0.5% bupivacaine with fentanyl which produced effective spinal block in 90% of parturients undergoing cesarean deliveries were 2.62, 2.76 and 2.8 ml in the 3 different height groups respectively.