RESUMO
INTRODUCTION: Spinal anaesthesia consists of administering a local anaesthetic in the subarachnoid space, thus causing sensory, motor, and autonomic nerve conduction block. Currently, recovery from spinal anaesthesia is evaluated by the return of motor function, without considering the autonomic blockade, which is responsible for most complications of the technique. Heart rate variability (HRV) is an indirect method to measure the autonomic nervous system and may be useful in assessing autonomic recovery after spinal anaesthesia. The study objective was to evaluate the autonomic function, through HRV, at the moment of return of motor function in patients who received spinal anaesthesia when clonidine is used as an adjuvant. MATERIAL AND METHODS: This was a randomised, double-blind clinical trial. The sample consisted of 64 ASA I-II patients who underwent spinal anaesthesia and were divided into 2 groups. Group C received 20 mg of bupivacaine with 75 mcg of clonidine, and group B received 20 mg of bupivacaine. HRV was evaluated at rest (T1) and at the time of motor function recovery (T2). Data were collected using a Polar V800® heart rate monitor and then analysed and filtered using Kubios 3.0® software. RESULTS: There was no difference in the values of the low-frequency/high-frequency (LF/HF) ratio, Poincaré plot standard deviation (SD2/SD1), detrended fluctuation analysis (DFAα1, DFAα2), or correlation dimension (D2) indices in any of the groups between the 2 moments. In the clonidine group, there was a difference only in approximate entropy (ApEn), where a P of 0.0124 was obtained considering a 95% confidence interval ranging from 17.83 to 141.47. CONCLUSIONS: There was no significant difference between the duration of sympathetic blockade and motor blockade in spinal anaesthesia.