Cardiorespiratory coupling during spinal anesthesia assessed via causal squared coherence

Spinal anesthesia is an alternative to general anesthesia in lower abdominal surgery. Despite its impact on sympathetic control, little is known on the influence of spinal anesthesia on cardiorespiratory coupling (CRC) as evaluated from the concomitant analysis of heart period (HP) variability and respiration (RESP). The study aims to assess CRC before (PRE) and after (POST) spinal anesthesia in 14 patients (age: 59 ± 12 yrs, 3 females, 11 males, ASA physical status I-II) undergoing lower abdominal surgery. Anesthetic was injected below T8. In POST fluids were administered to the patient to prevent hypotension. CRC was assessed via the computation of model-based causal squared coherence assessing the strength of interactions from RESP to HP and vice versa. HP mean, variance, the power of HP series at the respiratory rate, and the breathing frequency remained stable in POST compared to PRE. Regardless of the directionality of the interactions, CRC did not vary in POST and this result held regardless of the direction of the interactions. The steady values of HP variability and CRC markers suggest that spinal anesthesia performed at a relatively low level (i.e., below T8) and associated with fluid administration might have minimal impact on the cardiac control.