Influence of local anesthetic type, dose, and patient characteristics on spinal anesthesia motor and sensory block durations

Objectives. This study aims to evaluate the impact of local anesthetic type and dose on the duration of motor and sensory blocks, while also examining the influence of patient characteristics (age, height, weight, gender) and ASA score.
Methods. In this prospective cohort study, 42 patients undergoing ambulatory surgery received low-dose spinal anesthesia. One group was administered 40 mg of hyperbaric prilocaine, and the other 20 mg of isobaric chloroprocaine. Motor block was assessed using the Bromage scale, and sensory block duration was evaluated with the ice test across different dermatomes.
Results. Of the 42 patients (22 males, 20 females) with a median age of 42 (IQR=21), 41 successfully completed surgery; one patient in the chloroprocaine group required conversion to general anesthesia. Median motor block duration was significantly longer in the prilocaine group (60 minutes, IQR=53) compared to the chloroprocaine group (48 minutes, IQR=14, p=0.018). Median sensory block duration was also significantly longer in the prilocaine group (155 minutes, IQR=38) compared to the chloroprocaine group (110 minutes, IQR=53, p=0.003). Sensory block height was higher in the prilocaine group, with 47.7% of patients reaching T10 or higher, compared to 5% in the chloroprocaine group (p=0.004). Similarly, 71.4% of prilocaine patients achieved a Bromage score of 2 or higher, compared to 30% in the chloroprocaine group (p=0.004). No significant effects of patient characteristics (age, height, weight, gender, or ASA score) on block duration were found.
Conclusions. Both low-dose prilocaine and ultra-low-dose chloroprocaine were effective for spinal anesthesia. However, chloroprocaine resulted in significantly shorter motor and sensory block durations compared to prilocaine, which provided more dense blocks and higher sensory block levels. Patient characteristics and ASA scores did not significantly affect block duration in either group.