Comparison of two atracurium dosing regimens in dogs undergoing ophthalmic surgery

To compare two atracurium intravenous dosing protocols, intermittent boluses (BOL) and variable rate infusion (VRI), for total dose, neuromuscular blockade depth and recovery, need for reversal, and extubation times in dogs undergoing ophthalmic surgery.

A total of 48 anaesthetic records (24 per group) were retrospectively analysed from dogs meeting predefined inclusion criteria. Extracted data included total atracurium dose, dose rate, train-of-four count (TOFC) and ratio (TOFR), duration within TOFR 0.2-0.7, time to recover 0.9TOFR, extubation time, and reversal requirement. Data were analysed with Welch's t-tests, Wilcoxon rank-sum, or Fisher's exact tests. Effect estimates for reversal requirements were expressed as risk ratios (RRs), risk differences (RDs), odds ratios, and number needed to treat. Significance was set at p < 0.05.

Total atracurium dose did not differ between BOL (0.42 ± 0.26 mg kg^-1) and VRI (0.38 ± 0.12 mg kg^-1; p = 0.500). When normalised to surgical duration, atracurium dose rate was higher in BOL (5.51 ± 2.14 μg kg^-1 minute^-1) than VRI (4.16 ± 1.24 μg kg^-1 minute^-1; p = 0.010). Dogs receiving VRI spent longer within a TOFR 0.2-0.7. Time to 0.9TOFR was shorter in VRI compared with BOL (12.5 ± 6.3 versus 41.5 ± 14.4 minutes; p < 0.001), as was extubation time (31.1 ± 29.3 versus 62.0 ± 21.2 minutes; p < 0.001). Neostigmine reversal was required in 2/24 dogs in VRI (8%) and 7/24 dogs in BOL (29%) (p = 0.140), corresponding to a RR of 0.29 (95% confidence interval 0.07-1.24) and a RD of -21% (95% confidence interval -42-0).

Atracurium VRI was associated with lower dose rate, more stable neuromuscular blockade depth, faster recovery, and shorter extubation times than BOL injection. These findings support the potential clinical advantages of VRI in canine ophthalmic anaesthesia.