Effect of clinician applied maneuvers on fetal brachial plexus strain during shoulder dystocia delivery

Abstract

516 517 EFFECT OF CLINICIAN APPLIED MANEUVERS ON FETAL BRACHIAL PLEXUS STRAIN DURING SHOULDER DYSTOCIA DELIVERY BERNARD GONIK, RICHARD COSTELLO, NING ZHANG, MICHELE GRIMM, Wayne State University, Ob/Gyn, Detroit, MI Wayne State University, Biomedical Engineering, Detroit, MI OBJECTIVE: To objectively study the impact of suprapubic pressure (SPP), oblique fetal shoulder displacement (OSD), and posterior arm delivery (PAD) on brachial plexus (BP) strain during a shoulder dystocia (SD) event. STUDY DESIGN: A computer software crash dummy model (MADYMO) was modified based on establishedmaternal and fetal anatomic specifications to simulate vaginal delivery after anterior impaction of the fetal shoulder behind the symphysis pubis. The BP was modeled as a spring, using mechanical properties from previously reported data. Exogenously applied axial loading force was used to accomplish delivery. SPP was modeled by a compressive force applied superior to the anterior fetal shoulder. OSD was modeled by repositioning of the fetal torso within the maternal pelvis prior to applying extraction force. PAD was modeled by circumducting the fetal posterior arm prior to applying force. BP deformation was assessed as percent strain in the nerve (change in length/original length3100). RESULTS: With lithotomy pelvic positioning, 75 N of exogenous force was required to achieve delivery. This was associated with 14% BP strain. Applying graded SPP reduced the needed delivery forces and subsequent BP strain. An 80 N SPP resulted in a delivery force of 60 N and a BP strain of 9.8%. Rotating the fetal shoulders to an oblique position decreased delivery force to 50 N and BP strain to 9.8%. Delivering the posterior arm decreased the bisacromial diameter resulting in a reduction in required force to 30 N and a BP strain of 5.3%. CONCLUSION: Vaginal delivery associated with SD results in measurable BP strain. Use of established maneuvers for the management of SD such as SPP, OSD or PAD can result in an objective reduction in needed exogenous delivery force and BP strain. Although computer modeling did not allow for interexperiment variability and therefore statistical comparisons of strain differences, overall BP strain was reduced from 30-62 % with these maneuvers. December 2003 Am J Obstet Gynecol S200 SMFM Abstracts