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 CO2.

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.

Keywords: anticholinergics; dexamethasone; dexmedetomidine; oculocardiac reflex; opioids; strabismus surgery; trigeminovagal.

Conflict of interest statement

Dr. Arnold is President of Glacier Medical Software that markets cloud-based NICU software ROP Check. Dr. Arnold is President of PDI Check that makes a vision screening game for Nintendo 3DS. Dr. Arnold coordinates the Alaska Blind Child Discovery that has received discounted vision screen technology from several vendors. Dr. Arnold is an investigator and protocol developer for the NIH-supported Pediatric Eye Disease Investigator Group. Dr Robert Arnold has a patent pending for PDI Check; and he serves on non-paid advisory boards for plusoptiX, GoCheck Kids, Adaptica and iScreen amblyopia screening. The authors report no other conflicts of interest in this work.

© 2021 Arnold et al.

Figures

Figure 1

Timeline of the Alaska OCR Study. Uniform elicitation of oculocardiac reflex (OCR) consistent with routine strabismus surgery has employed 10-second, 200-gram square wave tension on rectus extraocular muscles (EOM). Years are to the left and numbers of patients are listed at the bottom. The Alaska study mirrored two prior studies at Mayo Clinic and Indiana University. Publications and presentations of OCR data are listed to the right of the timeline.

Figure 2

Frequency distribution of oculocardiac reflex showing anesthetic impacts. Oculocardiac reflex (OCR) defined as the maximally tension altered heart rate as a percent of stable, pre-tension baseline heart rate (H.R.). Uniform stimulus is 10-second, 200 gram tension on an extraocular rectus muscle. Impacts of various anesthetic agents indicated by box and whisker plots defining interquartile range, 95% range with bar to define median. S.D. is standard deviation and S.E.M. is standard deviation of the mean.

Figure 3

Linear correlation between first and second oculocardiac reflex (OCR). OCR is defined as the tension-modified heart rate as a percent of stable baseline elicited by uniform 10-second, 200 gram tension on an extraocular muscle in 1524 initial unique strabismus adult and pediatric patients with no anticholinergic.