Heart rate variability assessment to stratify risk of autonomic imbalance during subarachnoid block: A prospective...

Hypotension after subarachnoid block is a common adverse event which can be predicted by simple, safe and indirect measure of autonomic activity.

Heart rate variability has been accepted as an indirect measure of autonomic activity.

It was to evaluate preoperatively risk of hypotension after subarachnoid block.

This is controlled, randomized blind prospective study.

One hundred adult patients of either sex in the age group of 25 to 60 years belonging to ASA physical status of I to III, scheduled for elective infra-umbilical surgery, were enrolled for this randomized prospective study. During preanesthetic check their HRV was analyzed for time domain and frequency domain parameters. They were classified into two groups of 50 patients each depending on their low to high frequency ratios (LF/HF). Group I included patients with LF/HF <2.5 and Group II included patients with LF/HF >2.5. Sensitivity of LF/HF for prediction of hypotension greater than 20% of baseline was tested.

The present study showed significant differences of systolic blood pressure (SBP) after subarachnoid block, depending on baseline LF/HF. Patients with low LF/HF showed lowest SBP of 106.08 ± 3.19 (15.22% fall of base line SBP) as compared to high LF/HF which showed 87.62 ± 8.71 (30.26% fall of base line SBP). Baseline LF/HF parameter correlated significantly with proportionate decrease in SBP after subarachnoid blocks.

Hemodynamic parameter was analyzed by using student t test on statgraphic version 5.1.

Analysis of low and high frequency ratio, reflect autonomic control and may be used as an indirect measure for risk stratification of hypotension after subarachnoid block with high sensitivity.