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The Effect of Flexible Bronchoscopy on End-Expiratory Lung Volumes in Intubated Patients on Mechanical Ventilation

Beth Israel Medical Center, New York City, NY

PURPOSE: Flexible bronchoscopy (FB) in intubated patients on mechanical ventilation (MV) increases airway resistance. During FB, two ventilatory strategies are possible: maintaining tidal volume (TV) while maintaining baseline PaCO₂ or allowing reduction of TV while permitting hypercapnea. Lawson (Chest 2000; 118:824-831) reported significant hyperinflation due to expiratory flow limitation with FB in an intubated lung model particularly with small endotracheal tubes. We studied end expiratory lung volume (EELV) during FB in intubated patients while limiting TV and permitting hypercapnea.

METHODS: Changes in EELV were measured using respiratory inductance plethysmography (RIP). We studied 12 intubated patients on MV requiring bronchoscopy with calibrated RIP. Patients were sedated and paralyzed. MV settings: A/C, FIO₂ 1.0, pressure limit 60cm H₂O, Peak Flow 60 Lpm ramp. TV, PEEP level, respiratory rate settings were constant. RIP, SaO₂, cycling pressure, EKG, BP were measured continuously with pre/post bronchoscopy respiratory mechanics and ABG.

RESULTS: On insertion of FB, there was pressure limiting with resultant marked decrease in TV. There was no increase in EELV in any patient during intubated bronchoscopy. There were multiple episodes of decrease in EELV that coincided with suctioning (max 1250cc decrement). In patients with diffuse lung disease, loss of EELV coincided with marked transient desaturation. Vital signs were stable. Respiratory mechanics were unchanged. PaO₂/FIO₂ ratio decreased 66+/-43 (mean+/-SD) and PaCO2 increased by 12+/-9mmHg (mean+/-SD) pre/post bronchoscopy.

CONCLUSIONS: No elevation of EELV occurred during bronchoscopy in intubated patients. TV was reduced by peak pressure limit protecting the patient against hyperinflation though with consequent increase in PaCO₂. Suctioning during bronchoscopy caused reduction of EELV.

CLINICAL IMPLICATIONS: Increase in EELV during bronchoscopy in intubated patients does not occur when tidal volume is limited. Permissive hypercapnea during bronchoscopy appears to be well tolerated. Suctioning should be limited, especially in patients vulnerable to derecruitment effect. To reduce hyperinflation risk during FB, the approach of permissive hypercapnea is appropriate and may be especially applicable to patients who have small diameter ET tubes.

DISCLOSURE: E. Shakespeare, None.