How would you control patient synchrony in mechanical ventilation?

Controlling Patient Synchrony in Mechanical Ventilation

To optimize patient-ventilator synchrony, adjust triggering sensitivity, match inspiratory flow to patient demand, set appropriate cycling-off criteria, and consider proportional modes (PAV or NAVA) when conventional adjustments fail to achieve synchrony. 1, 2

Recognition of Asynchrony

Patient-ventilator asynchrony is associated with prolonged mechanical ventilation duration, increased morbidity and mortality. 1, 3 Detection requires:

• Systematic inspection of pressure, volume, and flow waveforms displayed on modern ventilators to identify specific patterns of dyssynchrony 4, 5, 6
• Recognition that clinicians typically have low ability to detect asynchronies by observation alone, though automated AI-based software is emerging to improve detection 3

Stepwise Approach to Optimize Synchrony

1. Address Patient Factors First

• Reverse conditions elevating respiratory drive: Treat pain, anxiety, fever, metabolic acidosis, and hypoxemia to reduce excessive ventilatory demands 6
• Minimize dynamic hyperinflation: In obstructive disease, use longer expiratory times (I:E ratio 1:4 or 1:5), lower respiratory rates, and consider PEEP 3-5 cmH₂O to offset intrinsic PEEP 1, 7
• Optimize sedation strategy: Light sedation with dexmedetomidine preserves circadian rhythm and improves sleep efficiency better than midazolam or propofol, which can worsen synchrony 1

2. Optimize Ventilator Settings

Triggering:

• Set sensitive trigger thresholds to minimize patient effort required to initiate breaths 6
• Avoid excessively long expiratory times that create prolonged "lock-out" periods preventing patient-triggered breaths 1

Flow Delivery:

• Match inspiratory flow rate to patient demand (typically 60-100 L/min in distressed patients) to prevent flow starvation 1, 6
• Ensure delivered flow satisfies peak inspiratory flow requirements to avoid patient "fighting" the ventilator 6

Cycling-Off Criteria:

• Match machine inspiratory time to neural inspiratory time to prevent premature or delayed breath termination 6
• Adjust flow-cycling thresholds in pressure support to align with patient's neural timing 1

3. Mode Selection Based on Synchrony Needs

For patients with persistent asynchrony despite optimization:

• Consider Proportional Assist Ventilation (PAV): Delivers pressure proportional to inspiratory muscle effort based on respiratory mechanics, improving synchrony and potentially reducing sleep fragmentation 1, 2
• Consider Neurally Adjusted Ventilatory Assist (NAVA): Delivers pressure proportional to diaphragmatic electrical activity, providing superior patient-ventilator interaction and suppressing asynchrony 1, 2

Evidence shows both proportional modes improve synchrony compared to conventional pressure support, though effects on clinical outcomes remain under investigation 1, 2

4. Adjust Pressure Support Level Carefully

• Titrate pressure support to meet patient demands without over-assistance: The level of assistance must balance reducing work of breathing while avoiding hyperventilation 1, 7
• Avoid excessive pressure support: High PS levels can cause central apneas during sleep, particularly in heart failure patients, leading to major sleep fragmentation 1, 7
• Target normocapnia: Avoid PaCO₂ <35 mmHg, especially during sleep, as hypocapnia triggers central apneas 7

Critical Pitfalls to Avoid

• Over-sedation: Deep continuous sedation abolishes circadian rhythm and worsens sleep architecture, potentially increasing asynchrony 1
• Inadequate expiratory time: Causes breath stacking (auto-PEEP) leading to hyperinflation, barotrauma, and hemodynamic compromise 1
• Ignoring waveform analysis: Failure to inspect ventilator graphics prevents identification of specific asynchrony patterns requiring targeted interventions 4, 5
• Excessive backup rates in assist modes: May override patient efforts and worsen synchrony rather than improve it 1

When Conventional Measures Fail

If standard adjustments fail to achieve synchrony:

• Trial proportional modes (PAV or NAVA) as they fundamentally change the patient-ventilator interaction paradigm 1, 2
• Consider brief neuromuscular blockade only in the most severely ill patients requiring very high ventilator settings, as this eliminates the synchrony problem by removing patient effort entirely 1
• Recognize that some degree of asynchrony (particularly reverse triggering with low inspiratory efforts) may actually prevent diaphragm dysfunction and could be beneficial 3