The Effect of Non-Depolarising Muscle Relaxants on Ocular Pulse Amplitude and Intraocular Pressure

Aim: In general anaesthesia (GA) for ocular surgery the chosen non-depolarising muscle relaxant has a high influence on the fluctuations of intraocular pressure (IOP) and ocular pulse amplitude (OPA). Patients and Methods: In 229 patients, who needed GA for their ophthalmic surgery, OPA and IOP were measured with the dynamic contour tonometer (DCT) before and 5 minutes after intubation. For GA, three groups of non-depolarising muscle relaxants, namely, mivacurium (n=71), atracurium (n=91) and rocuronium (n=67) were used. Results: The IOP decreased by about 4.0 +/- 2.3mmHg using mivacurium in GA, by about 6.1 +/- 2.2mmHg using atracurium and by about 7.4 +/- 1.7mmHg using rocuronium (p<0.001). The relative decrease of the IOP was 20% for mivacurium, 31% for atracurium and 37% for rocuronium. For mivacurium the OPA decreased from 3.4 +/- 1.5mmHg to 2.2 +/- 1.1mmHg (p<0.001) in contrast to atracurium (decrease from 3.6 +/- 1.5mmHg to 1.8 +/- 0.8mmHg; p<0.001) and rocuronium (decrease from 3.1 +/- 1.6mmHg to 1.7 +/- 0.9mmHg; p<0.001). Mean OPA reduction was lowest with mivacurium (1.3mmHg) and the highest with atracurium (1.7mmHg). The mean relative decrease of the OPA was 34% with mivacurium, 46% with atracurium and 43% with rocuronium (p<0.001). There was no linear correlation between the relative OPA decrease and the relative IOP decrease. Conclusion: Risks for ophthalmic surgery may be minimised by avoiding mivacurium in general anaesthesia. Due to its negative effects on IOP and OPA mivacurium does not seem to be suitable for operations with a large opening in the eye such as penetrating keratoplasty and block excision. Rocuronium can be used because it induces a favourised intraoperative decrease of the IOP.