Intraocular pressure changes following laryngoscopy and intubation- McCoy versus Macintosh laryngoscope

Background
We compared intraocular pressure changes following laryngoscopy and intubation with conventional Macintosh blade and McCoy laryngoscope.

Methods
Sixty adult patients were randomly assigned to study group or control group. Study group - (Group A, n=30) - McCoy laryngoscope was used for laryngoscopy. Control group (Group B, n=30) - conventional Macintosh laryngoscope was used for laryngoscopy. Pre-medication was given in the form of tablet alprazolam 0.25mg orally at bed time and two hours prior to surgery. Preoperative baseline intraocular pressure was measured with Schiotz tonometer after instillation of 4% xylocaine drops in the right eye. Injection thiopentone sodium 5 mgkg-1 over 20 seconds was used for induction followed by injection vecuronium 0.1mgkg-1 for intubation. All patients were manually ventilated using oxygen 33%, nitrous oxide 67% and halothane 0.5% for three minutes and ETCO₂ was kept below 40mmHg. Laryngoscopy was done as per group protocol. Size 7mm ID cuffed endotracheal tube was used for female patients and size 8mm ID for male patients in both the groups. Intraocular pressure and haemodynamic parameters were recorded just before induction of anaesthesia (baseline), just before laryngoscopy and intubation and 1 and 3 minutes after intubation.

Results
Patient characteristics, baseline haemodynamic parameters and baseline IOP were comparable in the two groups. Following induction (T₀), there was statistically significant fall in IOP in both groups. One minute after intubation (T₁), there was significant rise in IOP in both the groups and remained so even at three minutes after intubation (T₃). When compared in between the groups at one minute after intubation, the rise in intraocular pressure was significantly less in the study group (A).

Conclusion
We conclude that McCoy laryngoscope in comparison to Macintosh laryngoscope results in significantly less rise in IOP and clinically less marked increase in haemodynamic response to laryngoscopy and intubation.

DOI: http://dx.doi.org/10.4038/slja.v20i2.3213