PATIENT-TRIGGERED VENTILATION - A COMPARISON OF TIDAL VOLUME AND CHESTWALL AND ABDOMINAL MOTION AS TRIGGER SIGNALS

Patient-triggered synchronized ventilation requires reliable and early detection of the infant's inspiratory effort. Several trigger methods have been developed that frequently lack the sensitivity to detect in spiration in small preterm infants (trigger failure), or show a high r ate of breaths triggered by artifacts in the respiratory signal (autot rigger). The purpose of this study was to determine the effectiveness of the following trigger signals: abdominal movement sensed by a newly developed induction technique, chestwall motion detected by changes i n transthoracic impedance, and tidal volume measured by anemometry at the endotracheal tube connector. Ten preterm infants (birth weight, 58 0-1,424 g; median weight, 943 g; study weight, 535-1,415 g; median wei ght, 838 g; gestation age, 26-32 weeks, median gestational age, 28 wee ks, study age, 1-50 days, median study age, 11 days) were included in the study. A Sechrist SAVI ventilator was triggered by one of three si gnals: chestwall or abdominal movement,or tidal Volume generated by th e infants. Response time between beginning of inspiratory flow, the oc currence of the trigger signal (signal delay), and the onset of the tr iggered breath (trigger delay) were determined for each of the three s ignals. The signal response time was -13.5 msec (95% CI, -33 to -2 mse c) for the abdominal movement signal, indicating that it started befor e inspiratory flow; 0.0 msec for the volume signal; and 44.0 msec (95% CI, 29-73 msec) for the chestwall signal (P < 0.002); this long delay was Secondary to chestwall distortion and a subsequent delay in outwa rd ribcage movement in many infants. The trigger delay for the abdomin al signal was 90.0 msec (95% CI, 55-104 msec), 135.5 msec (95% CI: 82- 186 msec) for the volume signal, and 176.5 msec (95% CI: 165-232 msec) for the chestwall signal, indicating that there was a difference in t he rise time of signal voltage between the three methods (P < 0.01). T he rate of autotriggered breaths was 3.2% (95% CI, 0.3-9.3%) when usin g the abdominal signal, 0.55% (95% CI, 0.0-2.1%) for the tidal volume signal, and 11.25% (95% CI, 0.5-27.8%) for the chestwall signal (P < 0 .05). The incidence of trigger failure was low with all three-signals and was not significantly different between the techniques. In summary , the chestwall signal had a long trigger delay and was highly suscept ible to false triggering. It is, therefore, not a reliable trigger sig nal for synchronized mechanical ventilation in preterm infants. In con trast, tidal volume and abdominal movement signals had an acceptable t rigger delay and a low rare of autotriggering, making them useful clin ical trigger signals. (C) 1996 Wiley-Liss, Inc.