Mini-fluid challenge predicts fluid responsiveness during spontaneous breathing under spinal anaesthesia

BACKGROUND The ability to predict fluid responsiveness in spontaneously breathing patients under spinal anaesthesia is desirable. OBJECTIVE The objective of this study was to test whether variations in stroke volume (SV) in response to a fixed mini-fluid challenge (ΔSV100) measured by thoracic impedance cardiography (ICG) can predict fluid responsiveness in spontaneously breathing patients under spinal anaesthesia. DESIGN A prospective observational study. SETTING Anaesthesiology department in a university hospital. PARTICIPANTS Seventy-three patients monitored by ICG during surgery under spinal anaesthesia. INTERVENTIONS Patients received a 100 ml fluid challenge followed by volume expansion with 500 ml of crystalloid. MAIN OUTCOMES MEASURES Haemodynamic variables and bioimpedance indices [blood pressure, SV, cardiac output (CO)] were measured before and after fluid challenge and before and after volume expansion. Responders were defined as those with >15% increase in SV after volume expansion. RESULTS SV increased by at least 15% in 27 (37%) of the 73 patients. ΔSV100 predicted fluid responsiveness with an area under the receiver operating characteristic (AUC) curve of 0.93 [95% confidence interval (95% CI) 0.8 to 0.97, P < 0.001]. The cut-off was 7% and a grey zone ranging between 3 and 8% was observed in up to 14% of patients. SVbaseline was a poor predictor of fluid responsiveness [AUC of 0.69 (95% CI 0.57 to 0.79, P = 0.002)]. CONCLUSION ΔSV100 greater than 7% accurately predicted fluid responsiveness during surgery with a grey zone ranging between 3 and 8%.