RESUMO
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. SV baseline 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%.