241: Brachial plexus strain is minimally affected when asynclitism is resolved by operative vaginal delivery

RESOLVED BY OPERATIVE VAGINAL DELIVERY EDITH GUREWITSCH, VANESSA LAPOINTE, MICHELLE HARRAN, LINDSAY KRANKER, TARA JOHNSON, ROBERT ALLEN, Johns Hopkins University, Gynecology & Obstetrics, Baltimore, Maryland, Johns Hopkins University, Biomedical Engineering, Baltimore, Maryland OBJECTIVE: Asynclitism (AS) is treatable by operative vaginal delivery (OVD), yet it is unknown if OVD increases brachial plexus (BP) strain already conferred by lateral deviation (LD) of the head, or if instrument type matters. Using a birthing simulator, we compared maximal BP strain between AS and non-AS, low and outlet forceps (F) and vacuum (V) deliveries. STUDY DESIGN: One operator performed 193 simulated low and outlet OpVD. LOA position at either station varied randomly between normal (20 10°) and AS (50 10° [anterior parietal presentation]) and Luikart-Simpson F or KiwiTM V. Neck extension (NE) and anterior BP strain at Erb’s point were recorded from application through head-out. Mean maximal deformations were compared pairwise among F-normal, F-AS, V-normal & V-AS using t-tests; correction of AS (resumption of normal orientation) was compared between F & V using 2 (p 0.05 significant). RESULTS: Pooled data for anterior BP strain is shown, all p 0.001. Significance remained when station was analyzed separately. NE was minimal ( 0.6cm) in all OVD. Correction of AS occurred in 16/50 F and 16/48 V OVD (p 0.89), and was no more likely during low (8/27 F-AS vs. 8/25 V-AS [p 0.85] than outlet (8/23 F-AS vs. 8/23 V-AS [p 1.00]) OVD (p 0.78). Maximal BP strain was similar in corrected and uncorrected AS OVD (13.5 2.3% vs. 12.6 2.2%, p 0.09). CONCLUSION: In simulated OpVD, fetal NE is negligible, regardless of F or V, station or LD. AS OVD produces greater anterior BP strain than normal. Correction of AS is equally likely to be achieved with either F or V, regardless of station, but does not reduce strain. While F produces greater maximal anterior BP strain than V, neither is likely to produce BP injury, regardless of station or LD.