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.
ABSTRACT
PURPOSE: The oculocardiac reflex (OCR) is a trigeminovagal bradycardia elicited by tension on an extraocular muscle (EOM). Using three decades of observational data, we investigated whether or not individual strabismus patients are prone to oculocardiac reflex. PATIENTS AND METHODS: All patients undergoing strabismus surgery from 1992 to 2019 had deliberate 10-second, 200-gram square-wave tension on extraocular rectus muscles with anesthetic variables recorded. OCR was defined as the maximally tension-altered heart rate as a percent of stable baseline heart rate. RESULTS: OCR was compared in 2532 original cases with 323 re-operations. The 169 cases that used anticholinergics (99% OCR) were excluded from the analysis. The median OCR, a 15% drop, was found to be 85% (95% CI 39%, 102%,; range 5-151%). Factors that showed a significant effect on the OCR were the type of EOM with lateral rectus least (Kruskal-Wallis X2(3)=8, p<0.05), and adults had less OCR compared to the children (X2(2)=105, p<0.01). Factors that showed an augmenting effect on the OCR were peri-operative opioids (X2(6)=62, p<0.01) and Caucasian race (X2(4)=12, p<0.02). Gender and iris color were not found to have an impact on OCR. Re-operations and first-degree relatives did not differ from age-matched controls, but EOM- and opioid-adjusted re-operations correlated with their initial cases (r=0.37). CONCLUSION: We confirmed the previously published blocking effect of atropine, augmenting impact of opioids, and an inverse relationship of age on OCR. There was a weak proclivity for individuals to be prone to OCR. We found an impact of race with Caucasians having more OCR.
ABSTRACT
BACKGROUND: We reported that premedication with nasal dexmedetomidine was associated with a more intense oculocardiac reflex (OCR). In this study we performed an intrasubject, intravenous comparison to test our hypothesis that this alpha-adrenergic agonist potentiates the trigemino-vagal reflex. METHODS: OCR (greatest change heart rate/baseline heart rate) was prospectively monitored with 10-second, square-wave 200 g tension on the inferior rectus or other muscles during strabismus surgery. Between the first and second muscle, intravenous dexmedetomidine 0.5 µg/kg was delivered. RESULTS: All patients had no anticholinergic agents. A total 842 historic control patients (median age, 5.5 years) with no dexmedetomidine between muscles experienced the first OCR of 75% ± 24% (SD) and the second OCR of 77% ± 22%. The 33 study patients (median age, 5.6 years) experienced the first OCR 84% ± 16% and dexmedetomidine second OCR of 66% ± 25% for a bradycardia augmentation of 18% ± 19% (P < 0.01 [Mann-Whitney]). CONCLUSIONS: Similar to the effect of fentanyl, intravenous fast-push dexmedetomidine augmented the bradycardia associated with extraocular muscle traction.
