High Airway Resistance

Increased airway resistance due to the patient biting the endotracheal tube

In pressure control mode, specific changes in the flow-time scalar can indicate increased airway resistance during inspiration. These include:

1) A sharp spike in flow at the onset of inspiration

2) Loss of the normal exponential decay with a more horizontal or flattened inspiratory flow pattern

3) Failure of the flow to return to baseline by the end of the inspiratory phase.

Similarly, signs of increased expiratory resistance include:

1) A flow spike at the beginning of expiration

2) A flattened expiratory flow curve instead of the typical exponential decay

3) Failure of the expiratory flow to reach the baseline before the next breath, a phenomenon known as air trapping or auto-PEEP.

When increased resistance is observed during both inspiration and expiration, potential causes include:

1) Severe bronchospasm

2) Endotracheal tube obstruction from mucus or blood clots

3) Tube kinking or patient biting the tube

In the case discussed, the cause was identified as the patient biting the endotracheal tube, confirmed on physical examination. If such increased resistance goes unrecognized while pressure control settings remain unchanged, it can lead to dangerously reduced tidal volumes. This may result in severe hypercapnia, respiratory acidosis, and even sudden cardiac arrest.