Abnormalities of contrast sensitivity and electroretinogram following sevoflurane anaesthesia

Background and objective: We tested the hypothesis that disturbances of the visual pathway following sevoflurane general anaesthesia (a) exist and persist even after clinical discharge criteria have been met and (b) are associated with decreased contrast sensitivity. Methods: We performed pattern and full-field flash electroretinograms (ERG) in 10 unpremedicated ASA I patients who underwent nitrous oxide/sevoflurane anaesthesia. ERG and contrast sensitivity were recorded preoperatively, immediately after discharge from the recovery room and 2 h after discontinuation of sevoflurane. The time at which the Post Anaesthesia Discharge Score first exceeded 9 was also noted. Data were analysed using paired, one-tailed t-tests and Pearson's correlation coefficient. Results: On the full-field photopic ERG, b-wave latency was greater at each postoperative time point (31.6 ± 1.1 and 30.8 ± 1.1 ms) compared topreoperatively (30.1 ± 1.1 ms, P < 0.001 and P = 0.03, respectively). Oscillatory potential latencies were greater on discharge from the recovery room compared with preanaesthetic values (23.1 ± 3.1 vs. 22.4 ± 3.3 ms, P = 0.01) and returned to baseline by 2 h after emergence from anaesthesia. Also at 2 h after emergence from anaesthesia: (a) P50 latency on the pattern ERG was greater than at baseline (81.5 ± 17.9 vs. 51.15 ± 22.6 ms, P = 0.004); (b) N95 amplitude was less compared to preanaesthetic values (2.6 ± 0.5 vs. 3.3 ± 0.4 μV, P = 0.003) and (c) contrast sensitivity was less compared to baseline values (349 ± 153 vs. 404 ± 140, P = 0.048). A positive correlation was demonstrated between contrast sensitivity and both N95 amplitude and b-wave latency (r = 0.99 and r = -0.55 at significance levels of P < 0.005 and P < 0.05, respectively). Conclusions: Postoperative ERG abnormalities and associated decreases in contrast sensitivity are consistently present in patients who have undergone nitrous oxide/sevoflurane anaesthesia. These abnormalities persist beyond the time at which standard clinical discharge criteria have been met.