Pressure and traction on a model fetal head and neck associated with the use of forceps, Kiwi™ ventouse and the BD Odon Device™ in operative vaginal birth: a simulation study

OBJECTIVE: To determine the pressure and traction forces exerted on a model fetal head by the BD Odon Device, forceps and Kiwi ventouse during simulated births. DESIGN: Simulation study. SETTING: Simulated operative vaginal birth. POPULATION OR SAMPLE: 84 simulated operative vaginal births. METHODS: A bespoke fetal mannequin with pressure sensors around the head and strain gauge across the neck was used to investigate pressure applied over the head, and traction across the neck during 84 simulated births using the BD Odon Device, non-rotational forceps and Kiwi ventouse. MAIN OUTCOME MEASURES: Peak pressure on the fetal face and lateral aspects of the head during correct use of the BD Odon Device and forceps. Peak pressure on orbits and neck during misplacement of the BD Odon Device and forceps. Peak traction force generated until instrument failure using the BD Odon Device, forceps and Kiwi ventouse. RESULTS: When correctly sited and using 80kPa inflation pressure on the cuff, the BD Odon Device generated a lower peak pressure on the fetal head than forceps (83kPa vs 146kPa). When instruments were purposefully misplaced over the orbits the BD Odon Device generated a lower peak pressure on the orbits than forceps (70kPa vs 123kPa). When purposefully misplaced over the neck the BD Odon Device, compared to forceps, generated a greater peak pressure on the anterio-lateral aspect of the neck (56kPa vs 17kPa) and a lower peak pressure on the posterior aspect of the neck (76kPa vs 93kPa) than forceps. In cases of true cephalic disproportion the BD Odon Device ‘popped-off’ at a lower traction force than forceps (208N vs 270N). CONCLUSIONS: In simulated assisted vaginal birth with correctly placed instruments the peak pressure exerted on the fetal head by a BD Odon Device is lower than pressure exerted by non-rotational forceps. In cases in which delivery of the fetal head is not possible due to cephalo-pelvic disproportion lower traction forces could be applied using the BD Odon Device than with forceps before the procedure was abandoned due to device failure.