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Lack of relationship between the true airway pressure and the pressure displayed with an infant ventilator
A Sola1, D Fariña, S Rodriguez
1Division of Neonatology, Hospital de Pediatría J.P. Garrahan, Buenos Aires, Argentina.
Objective:
To establish if the pressure indicated in the manometer of an infant ventilator (IV 100B, Sechrist, Anaheim, CA) reflects the true pressure delivered to the proximal airway during mechanical ventilation in the neonatal ICU.
Design:
With approval of our Institutional Research Board, data were collected prospectively. Peak inspiratory pressure and end-expiratory pressure were measured at the "Y" piece of the breathing tubing. Pressure readings from the conventional ventilator's manometer were compared with simultaneously obtained measurements using an electronic monitor.
Setting:
This study was conducted in a 45-bed neonatal ICU, admitting 700 to 750 newborns per year.
Patients:
Twelve neonates who required mechanical ventilation were included in the study.
Interventions:
Specific interventions were not made by study design. Measurements routinely obtained were compared.
Measurements And Main Results:
Two hundred seventy-five simultaneous measurements of peak inspiratory pressure and positive end-expiratory pressure were compared. Peak inspiratory pressure values were higher with the electronic monitor in 273 (99%) of 275 measurements and the mean of the differences between the electronic monitor and ventilator's manometer was statistically significant (p less than .001). For positive end-expiratory pressure measurements, values indicated by the electronic monitor were lower in 152 (55%) of 275 determinations, equal in 65 (23%), and higher in 58 (21%) determinations. Percent variations between methods ranged from 0% to 140% for peak inspiratory pressures and from 0% to 500% for positive end-expiratory pressure.
Conclusions:
These data demonstrate that it is impossible to know the true pressure delivered to the proximal airway of a neonate during mechanical ventilation by observing the ventilator pressure manometer. The manometer readings consistently underestimate the true peak inspiratory pressure values and are very unpredictable regarding positive end-expiratory pressure values. These findings support the use of other methods to monitor the proximal airway pressure besides the ventilator's manometer in the neonatal ICU. Furthermore, mean airway pressure should not be calculated from the pressure readings obtained from the tested ventilator's manometer.