Characteristics of the Tsui Test and Pressure Waveform to Confirm Epidural Catheter Placement in Parturients With BMI ≥50 kg/m2

The stimulator is set at frequency of 1Hz with 0.2 msec pulse width and the current output ranging from 0 to 20 mA. The current output will be carefully increased from zero until motor activity is detected up to a maximum of 20 mA.

A pressurized 500ml normal saline bag will be connected to a pressure transducer kit and the transducer will be connected to a portable monitor with the scale set at 0-40 mmHg or to optimum scale. The transducer will be levelled with the heart approximated at the patient's manubrio-sternal angle, with the patient in the sitting position. Sterile tubing will be connected to the epidural needle and attached to transducer. The tubing connection will be filled with saline to ensure proper reflection of the pressure transducer tracing. Test will be considered positive in case of pulsatile waveform is observed in synchrony with heart rate.