Which condition indicates impending ventilatory failure?

Decreased vital capacity is a significant indicator of impending ventilatory failure. Vital capacity reflects the maximum amount of air a person can forcibly exhale after maximal inhalation, and a decrease suggests that the respiratory system is struggling to maintain adequate ventilation. This reduction can point to various respiratory issues, such as muscle fatigue, airflow obstruction, or restrictive lung disease, all of which may compromise the ability to ventilate effectively.

In contrast, stable PaCO2 levels suggest that the patient's ventilation is adequate and that carbon dioxide is being effectively removed from the body. Increasing tidal volume indicates that the patient may have a compensatory mechanism to enhance ventilation, which could be a positive sign rather than an indicator of failure. Consistent PEEP levels do not necessarily imply failure; rather, they are a strategy used to improve oxygenation and alveolar recruitment. Therefore, a decreased vital capacity is a more direct sign of the potential for ventilatory failure, as it implicates a compromised ability to exchange air adequately.