Mandel R, Ali N, Chen J, Galic IJ, Levesque L: Nitrous oxide analgesia during retinopathy screening: a randomised controlled trial. Arch Dis Child Fetal Neonatal Ed 2012, 97(2):F83-87.
My colleagues and friends Romain Mandel and Nabeel Ali performed a blinded randomized trial of nitrous oxide (laughing gas) for analgesia during routine ophthalmologic eye screening for retinopathy of prematurity. They started the study while I was the chief at the Royal Victoria Hospital in Montreal, and I think the publication downplays what a pain it was to get all the procedures accepted. They had to scavenge the gases because we didn’t want anyone assisting the procedure to be anesthetized (a nurse or ophthalmologist falling over unconscious would have unblinded the trial). Despite what should have been a good administration of a good concentration of N2O, there was no apparent effect on pain responses. I was very happy that Drs Mandel and Ali pursued the trial, despite the difficulties, as I really thought it would work; but unfortunately, even with experienced gentle ophthalmologists, there was no difference in any of the pain indices.
This adds to the literature of things that don’t work very well for the pain responses to ophthalmologic exams. Including sucrose and topical anesthesia. A recent systematic review noted that these measures are either wholly or relatively ineffective. Kandasamy Y, Smith R, Wright IMR, Hartley L. Pain relief for premature infants during ophthalmology assessment. Journal of American Association for Pediatric Ophthalmology and Strabismus. 2011;15(3):276-80. http://www.sciencedirect.com/science/article/pii/S1091853111003326
On the other hand a humane approach I think should lead to the use of topical anesthetics even if they don’t work very well (until we find something that works better), and the pain scores in the Mandel et al study were lower than other studies, perhaps reflecting the fact that a combined approach with sucrose, topical agents and swaddling the infants was used in both groups. Allowing the baby to suck during the procedure seems to help a little, so a soother or bottle could be added. Maybe the best thing would be change the method of screening, there is some evidence that using a digital fundus camera leads to less tachycardia, (see Mukherjee et al) or, even better, just avoiding the use of a speculum (Mehta et al below).
Mukherjee AN, Watts P, Al-Madfai H, Manoj B, Roberts D: Impact of Retinopathy of Prematurity Screening Examination on Cardiorespiratory Indices: A Comparison of Indirect Ophthalmoscopy and Retcam Imaging. Ophthalmology 2006, 113(9):1547-1552. http://www.sciencedirect.com/science/article/pii/S0161642006005641
Mehta M, Adams GGW, Bunce C, Xing W, Hill M: Pilot study of the systemic effects of three different screening methods used for retinopathy of prematurity. Early Human Development 2005, 81(4):355-360. http://www.sciencedirect.com/science/article/pii/S0378378204001562