Correction of compliance and resistance altered by endotracheal tube leaks.

OBJECTIVE

Measurements of lung compliance and resistance are influenced by endotracheal tube leaks. To keep compliance and resistance reliable, we developed an algorithm to correct inspiratory and expiratory volume and flow mathematically.

DESIGN

Prospective, clinical study.

SETTING

University research laboratory and neonatal intensive care unit.

MODEL

A ventilated lung model with a linear pressure-volume relationship and with adjustment of an increasing endotracheal tube leak was investigated.

PATIENTS

A total of 21 ventilated premature neonates (median weight, 1220 g; range, 640-2160 g; median leak, 32%; range, 24-56%) were studied.

MEASUREMENTS AND MAIN RESULTS

Compliance and resistance were calculated from the recordings of flow, volume, and airway pressure over time employing linear regression of the equation of motion to obtain compliance and resistance. Compliance and resistance altered by leaks were corrected and compared with measurements without leak. Compliance and resistance of the lung model could be corrected up to an endotracheal tube leak size of 86%. Compliance and resistance without leak and after leak correction did not differ significantly for all infants using the linear regression method (p >.05). For the correction of compliance in 15 and for the correction of resistance in 12 of the 21 infants, the coefficients of variation of ten measured breaths without leak were greater or equal to the differences of the values of compliance and resistance between conditions of no leak and corrected leak, respectively.

CONCLUSION

Pulmonary compliance and resistance can be reliably corrected even in the presence of a substantial endotracheal tube leak, which makes pulmonary function tests more reliable.