Norepinephrine and Phenylephrine for Spinal Anesthesia-induced Hypotension.

Spinal anesthesia-induced hypotension is a frequent complication during spinal anesthesia for cesarean section. The incidence of spinal anesthesia-induced hypotension is as high as 62.1-89.7% if prophylactic measures are not taken. The 2016 ASA guidelines for obstetric anesthesia suggest avoiding hypotension following spinal anesthesia in women and emphasize the use of vasopressors, specifically alpha-receptor agonists, as the preferred strategy to prevent and manage spinal anesthesia-induced hypotension. The prophylactic vasopressor strategy is more effective in enhancing hemodynamic stability and reducing adverse events such as nausea and vomiting during cesarean section, compared to rescue strategy. However, it does not demonstrate significant advantages in neonatal outcomes such as umbilical artery pH and Apgar score. The impact of various vasopressor application patterns on neonatal outcomes after cesarean section lacks further supporting evidence. Therefore, this study aims to explore the effects of different application modes (prophylactic and rescue strategy) of norepinephrine and norepinephrine on neonate umbilical artery pH undergoing cesarean section through a multicenter, single-blind, 2*2 crossover and cluster randomized trial.

Inclusion criteria

• 18-45 years
• Primipara or multipara
• Singleton pregnancy ≥37 weeks
• American Society of Anesthesiologists physical status classification II
• Scheduled for cesarean section under spinal anesthesia

Exclusion criteria

• Body height < 150 cm
• Body weight > 100 kg or body mass index (BMI) ≥ 40 kg/m2
• Eclampsia or chronic hypertension or baseline blood pressure ≥140 mmHg
• Hemoglobin < 7g/dl
• Fetal distress, or known fetal developmental anomaly