Am. J. Respir. Crit. Care Med., Vol 150, No. 3, 09 1994, 766-769.
Use of flow-volume curves in detecting secretions in ventilator- dependent patients
A Jubran and MJ Tobin
Division of Pulmonary and Critical Care Medicine, Edward Hines Jr. Veterans Administration Hospital, Hines, Illinois 60141.
A noninvasive means of detecting airway secretions in ventilator- dependent
patients is desirable because endotracheal suctioning can result in
life-threatening complications. In a patient who had copious secretions, we
observed a sawtooth pattern on his flow-volume curve that disappeared after
suctioning. Accordingly, we systematically examined the usefulness of a
sawtooth pattern on flow-volume curves in detecting secretions in
ventilator-dependent patients and compared its accuracy with clinical
examination. Flow-volume curves were recorded in 50 ventilator-dependent
patients over 1 min of spontaneous breathing. In 15 of these patients,
clinical examination was performed by three clinicians to determine its
accuracy in detection of secretions. Endotracheal suctioning was then
performed to determine the presence or absence of secretions. Subsequently,
the flow-volume curves of all 50 patients were played back on a video
screen, and three observers, who were unaware of the results of suctioning,
made a decision regarding the presence or absence of a sawtooth pattern.
The sensitivity of the sawtooth pattern in detecting secretions ranged from
0.76 to 0.86, and specificity ranged from 0.86 to 0.90. The likelihood
ratio of a positive test ranged from 5.55 to 7.97, whereas the likelihood
ratio of a negative test ranged from 0.16 to 0.27. Interobserver agreement,
assessed by the kappa statistic, was excellent: 0.76, 0.76, and 0.84. In
the subgroup of patients evaluated by both clinical examination and
flow-volume curve analysis, clinical examination was less accurate in 11 of
the 15 patients. In conclusion, detection of a sawtooth pattern strongly
suggests the presence of secretions, and the absence of this pattern
suggests that secretions are unlikely to be present.
