Role of the atrial natriuretic factor in obstetric spinal hypotension

In recent years, the concept of prophylactic volume expansion to prevent hypotension caused by spinal anesthesia has been challenged. Investigators have reevaluated the concept of prehydration in the obstetric patient and the physiologic mechanisms involved. This article addresses whether the hypotensive effects attributed to the atrial natriuretic factor are the reason for the apparent failure of prehydration.

Atrial natriuretic factor was measured before (baseline) and 10 min after spinal anesthetic drug injection (control) in 48 healthy pregnant patients scheduled for elective cesarean section. Sixteen patients received hydration with 15 ml/kg crystalloid immediately before spinal anesthesia, 16 patients received the same volume starting with the spinal anesthetic injection, and the remaining 16 patients received no prehydration (control). Blood pressure, heart rate, ephedrine requirements, infused fluids, and urine output were measured.

Atrial natriuretic factor concentrations increased significantly in prehydrated patients but not in the control group. There was a significant correlation in the change in atrial natriuretic factor concentrations and urine output but no correlation in the control atrial natriuretic factor concentrations and blood pressure or ephedrine requirements. Ephedrine requirements and blood pressure did not differ significantly among study groups.

Atrial natriuretic factor is a potent endogenous diuretic in the pregnant patient but does not appear to be involved in short-term cardiovascular homeostasis after spinal anesthesia. Prehydration appears to be an ineffective measure to prevent post spinal hypotension in the obstetric patient [corrected].