Effect of continuous positive airway pressure on the rapid shallow breathing index in patients following cardiac surgery.
OBJECTIVE
To compare the rapid shallow breathing index (RSBI) under different ventilatory support settings prior to extubation trials.


METHODS
Prospective study.


METHODS
Cardiac surgery unit at a university hospital.


METHODS
A total of 33 coronary artery bypass grafting patients ready for extubation.


METHODS
Enrolled patients received a continuous positive airway pressure (CPAP) trial of 5 cm H(2)O and fraction of inspired oxygen (FIO(2)) of 40% (condition 1), a CPAP trial of 5 cmH(2)O and FIO(2) of 21% (condition 2), and a 1-min spontaneously breathing room air trial without ventilatory support (condition 3). These trials were applied in random order.


RESULTS
Average values of respiratory frequency and tidal volume were measured under the three experimental conditions in all patients immediately prior to extubation. The RSBIs were determined for each patient under each condition; the average RSBIs under conditions 1, 2, and 3 were compared for significance. The average RSBIs (+/- SD) were significantly smaller under condition 1 (34 +/- 13) and condition 2 (36 +/- 14) compared to condition 3 (71 +/- 24). There was no significant difference in RSBI between conditions 1 and 2.


CONCLUSIONS
The administration of 5 cm H(2)O of CPAP can influence the determination of the RSBI. In contrast, changes in FIO(2) have no effect on RSBI determination. We speculate that using the RSBI during CPAP may mislead the clinician into premature discontinuation of mechanical ventilation. Consequently, different threshold values for the RSBI should be derived for different ventilatory support levels.
El-Khatib
Mohamad F
MF
Department of Anesthesiology, School of Medicine, American University of Beirut, Beirut, Lebanon. mk05@aub.edu.lb
Jamaleddine
Ghassan W
GW
Khoury
Andre R
AR
Obeid
Mounir Y
MY
D001026:Coronary Artery Bypass; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D011184:Postoperative Period; D011446:Prospective Studies; D012143:Respiratory Physiological Phenomena; D013990:Tidal Volume