Intrauterine pressure catheter performance in an in vitro uterine model: A simulation of problems for intrapartum monitoring

Objective: To compare pressure recordings from fluid-filled and sensor-tip catheters under varying intrauterine conditions in a uterine model. Methods: The uterine model was a 4.1-L dual-walled polyurethane bladder with ports for dual catheter insertion. “Contractions,” generated by a programmable pump, were analyzed by computer. The first three experiments used an internal volume of normal saline and included either “normal” catheter placement, distal end of the catheter coated with petroleum jelly, or distal end of the catheter kinked at 150°. The fourth and fifth experiments were similar to the first except that the internal volume was either pea soup or bovine blood. Each study had at least 20 consecutive pressure waveform sequences with peaks of 100, 60, and 20 mmHg, and a resting baseline of 10 mmHg. Ascent and descent phases were each 25 seconds. Peak and baseline pressure phases were each 10 seconds. Results: Each catheter generated satisfactory pressure waveforms, which were similar in all experiments except for the one involving simulated meconium. In this trial, significant waveform damping occurred when pea soup filled the fluid catheter line (P < .05, t test). Conclusions: In most extreme experimental conditions, the catheter types behaved similarly when detecting “intrauterine” pressure. The sole exception, thick meconium simulation, suggests that fluid-filled catheters would be less reliable in this condition unless flushed continuously with saline.