Correlation of absolute nil-per-oral status with inferior vena cava collapsibility index and post-spinal hypotension...

Prolonged pre-operative fasting is considered as a risk factor for hypovolaemia and spinal anaesthesia-induced hypotension (SAIH). However, physiological compensatory mechanisms may offset fasting-related hypovolaemia. We aimed to examine relationships among absolute nil-per-os (NPO) duration, inferior vena cava collapsibility index (IVCCI), and SAIH in patients under spinal anaesthesia.

This prospective, non-randomised observational study enroled adults scheduled for infra-umbilical surgery. Absolute NPO duration was calculated after adjusting for maintenance intravenous fluids. Pre-operative IVCCI was measured with ultrasonography. SAIH was defined as a >20% reduction in mean blood pressure from baseline. Spearman's rank correlation, receiver operating characteristic (ROC) analysis, and multivariable logistic regression were performed to assess associations and predictors of SAIH.

Data from 51 patients were analysed. IVCCI increased significantly with longer absolute NPO duration (P < 0.001). Absolute NPO duration showed limited ability to discriminate SAIH [area under the ROC curve (AUROC) 0.61, P = 0.17], and IVCCI demonstrated moderate discriminatory ability within this cohort (AUROC 0.70, P = 0.016). In multivariable analysis, IVCCI was the only independent predictor of SAIH [adjusted odds 1.07 per 1% increase, (95% confidence interval: 1.00, 1.15); P = 0.049]. Absolute NPO duration correlated negatively with minimum inferior vena cava diameter (ρ = -0.36, P = 0.009) and positively with IVCCI (ρ = 0.61, P < 0.001).

While absolute NPO duration is related to IVCCI, our findings show that only IVCCI independently predicts SAIH. Implementing pre-operative IVCCI assessment might guide individualised fluid optimisation and prevent SAIH, particularly in patients undergoing prolonged pre-operative fasting.