During mechanical ventilation, the most common cause of patient-ventilator asynchrony in a patient on Assist-Control Ventilation is inadequate management of which of the following parameters?

Explanation

## Patient-Ventilator Asynchrony in ACV **Key Point:** Inspiratory flow rate and trigger sensitivity are the most common parameters responsible for patient-ventilator asynchrony in ACV mode. ### Mechanisms of Asynchrony **High-Yield:** Patient-ventilator asynchrony occurs when: - **Trigger sensitivity is too high (insensitive):** Patient effort is not recognized; delayed breath delivery causes frustration and "fighting the ventilator" - **Inspiratory flow rate is inadequate:** Patient's inspiratory demand exceeds ventilator flow delivery; sensation of air hunger and dyspnea - **Flow rate is excessive:** Premature breath termination; patient feels "pushed" and uncomfortable ### Types of Asynchrony in ACV | Type | Cause | Clinical Sign | | --- | --- | --- | | **Trigger asynchrony** | Insensitive trigger (high threshold) | Patient effort not detected; delayed breath | | **Flow asynchrony** | Inadequate inspiratory flow | Air hunger; patient "chasing" ventilator | | **Cycling asynchrony** | Mismatch in breath termination | Premature or delayed end-inspiration | | **Double-triggering** | High sensitivity + short expiration | Two breaths in one cycle | ### Clinical Pearl The most frequent complaint from patients experiencing asynchrony is "I can't get a breath" or "the ventilator is fighting me." This is almost always due to either an insensitive trigger (patient effort not recognized) or insufficient inspiratory flow (patient's demand exceeds delivery). Adjusting these two parameters resolves >80% of asynchrony complaints. ### Management Algorithm ```mermaid flowchart TD A[Patient reports dyspnea on ACV]:::outcome --> B{Trigger delay observed?}:::decision B -->|Yes| C[Increase trigger sensitivity<br/>Reduce trigger threshold]:::action B -->|No| D{Air hunger sensation?}:::decision D -->|Yes| E[Increase inspiratory flow rate<br/>Consider PSV for weaning]:::action D -->|No| F[Check sedation, pain control<br/>Reassess mode]:::action C --> G[Reassess synchrony]:::outcome E --> G F --> G ``` **Mnemonic:** **FITS** = **F**low, **I**nspiratory, **T**rigger, **S**ensitivity (the top two asynchrony culprits in ACV). [cite:Gupta & Sharma Critical Care Medicine Ch 12]