PROPOFOL INFLUENCES THE ELECTRORETINOGRAM TO A LESSER DEGREE THAN THIOPENTONE

Background: The Electroretinogram (ERG) is used clinically to assess t he function of retina. Anaesthetic agents are known to affect ERG, and as anaesthesia is often needed in children and uncooperative patients , knowledge about its effects is of clinical importance. Barbiturates selectively depress ERG components, and we compared thiopentone with p ropofol to assess if the latter preserved retinal function better. Met hods: Ten pigs, average weight 17 kg ( SD +/- 2 kg) were anaesthetized randomly with propofol 10 mg kg(-1) or thiopentone 30 mg kg(-1). Anae sthesia was maintained by 65% nitrous oxide in oxygen and continuous i nfusion of the induction agent, i.e. 10 mg kg(-1) h(-1) of propofol, o r 10 mg kg(-1) h(-1) for the first hour, then 5 mg kg(-1) h(-1) of thi opentone, with doses being based on pilot studies. After an interval o f one week the programme was repeated using the other agent. After 30 minutes dark-adaptation, responses to single flashes of graded intensi ties from a xenon flashlamp were recorded at five-minute intervals. Th e a- and b-wave amplitudes and implicit times (time to peak), and a-wa ve slopes were determined. Results: The b-wave implicit time was signi ficantly shorter during propofol anaesthesia than when using thiopento ne. The effect was most pronounced at the lowest intensities (P < 0.01 ). No statistically significant differences were found in the amplitud es of the b-waves. The a-wave appeared at lower stimulus intensity (P < 0.05) and the a-wave slopes were significantly steeper (P < 0.01) du ring propofol anaesthesia. Conclusion: Propofol accordingly appeared t o preserve the photoreceptor response better than thiopentone, and may therefore he considered to be more suitable for ERG recordings than t hiopentone.