Minimum effective fluid volume of colloid to prevent hypotension during caesarean section under spinal anesthesia using a prophylactic phenylephrine infusion: An up-down sequential allocation study.

STUDY OBJECTIVE

The aim of this study was to de termine the minimum effective fluid volume (MEFV) of hydroxyethyl starch 130/0.4 (HES) infused in a preload fashion which would prevent hypotension in 50% of parturients undergoing caesarean section. A secondary objective was to measure the hemodynamic effect of fluid loading on the subjects.

DESIGN

This is a prospective, double-blinded, dose-finding study using an up-down sequential allocation design.

SETTING

In the operating room.

PATIENTS

Thirty healthy parturients undergoing caesarean section under spinal anesthesia using a prophylactic phenylephrine infusion were included in this study.

INTERVENTION

The initial HES volume infused in the first patient was 500 mL. A failure of treatment to HES preload was defined as a single episode of systolic hypotension below 20% of baseline value. The next patient in the sequence was given a volume of HES adjusted by either an increment or a decrement of 100 mL according to the previous subject response to fluid preload.

MEASUREMENTS

Stroke volume and cardiac output were measured with a bioreactance-based non-invasive cardiac output monitor (NICOM).

MAIN RESULTS

The MEFV of HES was 733 mL (95% CI: 388-917 mL). Fluid loading before the administration of the spinal anesthesia resulted in an increase in stroke volume and cardiac output. The combined effect of spinal anesthesia and a phenylephrine infusion reduced the maternal heart rate and cardiac output, but not the stroke volume.

CONCLUSION

Our study is the first to investigate variable fluid loading volumes in this population. A HES preload of approximatively 700 mL prevented maternal hypotension in 50% of the parturients under the conditions of this study. We suggest that up-down sequential allocation design is a useful tool to compare different fluid loading regimens in this setting.