Influence of fiberoptic bronchoscopy through the endotracheal tube on ventilation parameters during mechanical ventilation

Background and goal of study

Fiberoptic bronchoscopy (FOB) is widely used in intensive care unit practice for percutaneous tracheostomy, for diagnostic evaluation and for toilet of the tracheobronchial tree. The risk of hypoventilation, and even life-threatening airway obstruction due to use of FOB is known. The aim of this study was to estimate the influence of flow, ratio between the endotracheal tube (ETT) and FOB diameter (RTBD), respiratory rate, tidal volume and pulmonary compliance, on mechanical ventilation parameters.

Materials and methods

Simulation experiment tests were done on a training/test lung (Model 5601l, adult TTL; Michigan Instruments Inc.). In the first series standard mechanical ventilation through the ETT (7.5, 8, 9) with stable parameters and different lung compliance was performed. In the second series, experiments with the same ETT and ventilation parameters were done with addition of FOB (pediatric and adult) that was inserted inside the ETT to simulate the process of FOB during mechanical ventilation. The increases in mean intrapulmonary pressure (MIPP) and in the positive end expiratory pressure (PEEP) values were estimated during the simulated procedure. The increase in the integrated MIPP and PEEP values after stabilization of the system was determined by computing the area between the desired and the measured intrapulmonary pressure and PEEP. This area was calculated using an image analysis software (ImagePro 4.5). A multivariate regression method was applied and a predictive formula was computed using the regression coefficients of the statistically significant independent predictors of MIPP.

Results and discussion

For each ETT permissible size of FOB and optimal rate respirations were estimated. Possible deviations in ventilation parameters due to discrepancy between the size of the ETT and the size of FOB were studied. The MIPP was best predicted by the respiratory rate and RTBD. The increase in the respiratory rate and the simultaneous decrease of the RTBD determined the rise of MIPP and PEEP values.

Conclusion

Our study found the reasons for undesirable deviations of ventilation parameters connected with the insertion of FOB in the ETT during mechanical ventilation. Hence, it is possible to improve the airway management by the rational choice of FOB size and ventilation parameters in relation to patients' respiration rate and diameter of ETT.