Effects of inspiratory flow waveforms on lung mechanics, gas exchange, and respiratory metabolism in COPD patients during mechanical ventilation.
OBJECTIVE
The clinical usefulness of varying inspiratory flow waveforms during mechanical ventilation has not been adequately studied. The aim of this study was to compare the effects of three different respiratory waveforms on the pulmonary mechanics, gas exchange, and respiratory metabolism of ventilated patients with COPD.


METHODS
A randomized and comparative trial of consecutive patients.


METHODS
Medical ICUs of a 2,000-bed university hospital.


METHODS
Fifty-four patients with COPD were enrolled.


METHODS
Constant, decelerating, and sine waveforms were applied to each patient in a random order.


RESULTS
With tidal volume, inspiratory time, and inspiratory frequency being kept constant, the decelerating waveform produced statistically significant reductions of peak inspiratory pressure, mean airway resistance, physiologic dead space ventilation (VD/VT), PaCO(2), and symptom score. There was also a significant increase in alveolar-arterial oxygen pressure difference with the decelerating flow waveform, but there were no significant changes in mean airway pressure, arterial oxygenation, heart rate, mean BP, and other hemodynamic measurements. In addition, assessment on the work of breathing (WOB) revealed that ventilator WOB values were reduced with the decelerating waveform. Oxygen consumption and carbon dioxide output were virtually not affected by changing inspiratory flow waveforms. Except for VD/VT, the effects of constant square and sine waveforms were similar to each other and could not be separated statistically.


CONCLUSIONS
The most favorable flow pattern for ventilated patients with COPD appeared to be the decelerating waveform. There are possibilities for the improvement of ventilation in these patients by selecting an appropriate inspiratory flow.
Yang
Shieh Ching
SC
Pulmonary Function Laboratory, Department of Laboratory Medicine, 2F, National Taiwan University Hospital, 21 Alley 2, Lane 65, Section 2 Chung-Shan N. Road, Taipei, Taiwan.
Yang
Sze Piao
SP
D000368:Aged; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000628:therapy*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial; D012143:Respiratory Physiological Phenomena; D013990:Tidal Volume; D014939:Work of Breathing / Q000502:physiology
D002245:Carbon Dioxide; D010100:Oxygen