Anesthetic Impacts on the Oculocardiac Reflex: Evidence from a Large, Observational Study

Abstract

Background The oculocardiac reflex (OCR) is a sudden vagal bradycardia that can be elicited by traction on an extraocular muscle. Bradycardia is highly variable from case to case necessitating a large sample size to observe small to moderate impact on OCR. While the surgeon’s tissue manipulation has immediate impact on OCR and individual patients may have some proclivity to OCR, we sought to characterize the impact on OCR by the anesthesiologist. Methods From 1992 to 2019, during routine, community outpatient general anesthetic strabismus surgery, oculocardiac reflex was prospectively observed utilizing a uniform 10-second, 200 gram square wave tension on each extraocular muscle. Anesthetic parameters were recorded and analyzed with double-cohort design and non-parametric statistics and correlations. We define %OCR as the maximally tension-altered heart rate and a percent of stable pre-tension heart rate. Results The median (IQR) confidence intervals OCR for 2527 initial cases was 89% (67% to 97%) without anticholinergic, and 99% (95% to 100%) in 165 patients with anticholinergic. OCR was 81% (62% to 96%) in 1034 with opioids and to 75% (60% to 95%) in 59 with dexmedetomidine and in 189 with IV dexamethasone to 72% (56% to 92%) There was a significant (p<0.01 Kruskal–Wallis) impact on OCR by various opioids, muscle relaxants and inhalational agents. Linear regression showed significant inhibitory impact on OCR by increased inhalational agent depth and by lower exhaled CO 2 . Conclusion The anesthesiologist can block OCR with sufficient anticholinergics, deeper inhalational agents and robust ventilation, and can augment OCR with opioids, dexmedetomidine and apparently also with dexamethasone. Clinical Trials Registry NCT04353960.

The Oculocardiac Reflex: A Review

“…There is a profound influence on OCR by anticholinergic (Mann–Whitney z=11.0, P<0.01), age (Kruskal–Wallis X 2 (2)=85, p<0.01), type of extraocular rectus muscle (Kruskal–Wallis X 2 (3)=8.0, p<0.05) and the use of opioid (Kruskal–Wallis X 2 (6)=57.6, p<0.01). 21 Adults have less OCR than preschool and school-aged children. 22 …”

“… 118 Uniformly elicited OCR expressed as percent of stable pre-tension heart rate was least with cisatracurium 97%, then succinyl choline 96%, then atracurium 92%, then vecuronium 88%, then mivacurium 82% and most OCR for muscle relaxant rocuronium 78%. 21 In a recent retrospective logistic regression analysis of strabismus surgery in children, the 37 who received rocuronium were 3.1 times less likely to have 20% OCR than the 49 who did not get neuromuscular blockade. 85 …”

“…The anesthesiologist has a profound influence on OCR with ability to reduce or prevent bradycardia with anticholinergic medications if a sufficient dose is delivered in advance of ocular manipulation. 21 Certain anesthetics can also potentiate OCR.…”

“…Some authors define OCR as any ECG change 18 , 34 , 35 or, like the Alaska OCR study, report each case as a percent change in heart rate. 22 , 36–39 For a patient with pre-tension heart rate of 120 bpm dropping to 80 bpm with EOM tension, the percent change in heart rate has been reported as the amount of drop (−33%) or the OCR heart rate as a percent of pre-heart rate 21 , 22 (66%). The reciprocal of the percent heart rate is related to prolongation of the R-R interval.…”

“… 68 With uniformly elicited OCR defined as the percent of stable pre-tension heart rate, 165 initial cases with intravenous anticholinergic (atropine and glycopyrrolate) had much reduced OCR (99%, CI 70%, 103%) compared to 2527 initial, age-matched non-anticholinergic cases (85%, CI 39%, 102%). 21 The Alaska OCR study prioritizes cases without anticholinergic if determined safe by the anesthesiologist. 117…”