Abstract
INTRODUCTION: Arterial hypotension is the most common adverse event following subarachnoid block (SAB). Numerous studies have attempted to predict its occurrence, but the results remain inconclusive. The use of 'preloading' with intravenous fluids as a preventive measure remains controversial. Ultrasonographic assessment of the inferior vena cava (IVC) may be useful for evaluating volemia; however, its role as a predictor of hypotension in SAB has not been thoroughly investigated. OBJECTIVE: To describe the correlation between IVC parameters derived (IVC-PD), the collapsibility index (IVCCI), and the distensibility index (IVCDI), and the development of hypotension following SAB. METHODS: This was a prospective, analytical study of diagnostic technology involving 70 patients undergoing SAB. Baseline ultrasonographic measurements of IVC parameters were recorded. The evaluated IVC parameters included the end-expiratory diameter (IVCe > 2 cm), IVCCI (≥ 40%), and IVDI (≥ 18%). Hypotension was defined as systolic blood pressure (SBP) < 90 mmHg, mean arterial pressure (MAP) < 60 mmHg, or a decrease in SBP or MAP ≥ 25% in patients with arterial hypertension. Correlation strength was evaluated using Spearman's index (rho), and simple and binomial linear regression analyses were performed to assess other factors associated with hypotension. RESULTS: The correlation between IVC parameters and post-SAB hypotension was weak and negative (rho = -0.058). Linear regression analysis did not yield statistically significant results (p > 0.05), and the coefficients obtained were negative. A history of arterial hypertension and a sensory block level below T4 were identified as risk factors for hypotension. DISCUSSION: The incidence of arterial hypotension was 27.14%, aligning with the upper range of previous studies. Risk factors such as a sensory block above T4 and a history of arterial hypertension were significantly associated with hypotension. However, no significant correlation was found between pre-anesthetic IVC-PD measurements and post-SAB hypotension, consistent with some prior findings. Variability across studies may relate to differences in patient characteristics and ventilation status. CONCLUSION: While confirming established hypotension risk factors, this study did not support IVC-based prediction, contrasting with some literature. Further research should address limitations like sample size and single-center design to clarify IVC's role in spontaneously ventilating patients.