Optimal Mechanical Ventilation Settings

Introduction to Mechanical Ventilation Parameters

The American Thoracic Society recommends that mechanical ventilation settings should prioritize patient-ventilator synchrony by appropriately configuring inspiratory trigger, expiratory trigger, bias flow, PS rise time, inspiratory time, and inspiratory pause based on underlying respiratory mechanics and disease pathophysiology 1, 2

Pressure triggering requires the patient to generate a negative pressure (typically -1 to -2 cmH2O) to initiate a breath, and is recommended by the European Respiratory Society 1
In patients with intrinsic PEEP (PEEPi), additional effort is required to trigger the ventilator as PEEPi must be counterbalanced before triggering can occur, as suggested by the American College of Chest Physicians 3, 1
Adding external PEEP (typically 5 cmH2O) can help offset PEEPi and reduce triggering effort in obstructive diseases, according to the British Thoracic Society 1, 2

Flow cycling: Ventilator switches to expiration when inspiratory flow decreases to a set percentage (typically 20-80%) of peak inspiratory flow, as recommended by the American Association for Respiratory Care 1
Time cycling: Inspiration ends after a predetermined inspiratory time, and is suggested by the Society of Critical Care Medicine 1, 4
For obstructive diseases (COPD, asthma): Earlier cycling (25-30% of peak flow) to allow adequate expiratory time and prevent dynamic hyperinflation, as recommended by the Global Initiative for Chronic Obstructive Lung Disease 4, 5

For obstructive diseases: Slower rise time (200-300 ms) to prevent excessive initial flow and potential discomfort, as suggested by the European Respiratory Society 5
For restrictive diseases: Faster rise time (100-150 ms) to meet higher inspiratory demand, according to the American Thoracic Society 5

Should be set based on respiratory system mechanics and underlying disease, as recommended by the Society of Critical Care Medicine 6
Can be calculated based on respiratory rate and desired I:E ratio, and is suggested by the American Association for Respiratory Care 4
Typical I:E ratios:
- Normal lungs: 1:2 ratio, as recommended by the American College of Chest Physicians 4
- Obstructive disease: 1:3 or greater to allow adequate expiratory time, according to the Global Initiative for Chronic Obstructive Lung Disease 4, 5
- Restrictive disease: 1:1 to 1:1.5 to optimize inspiratory time, as suggested by the European Respiratory Society 4

Achieving optimal patient-ventilator synchrony requires proper adjustment of all parameters above, as recommended by the American Thoracic Society 1, 5
Common asynchronies: Trigger asynchrony, flow asynchrony, and cycle asynchrony, and are identified by the Society of Critical Care Medicine 1
Monitoring for asynchrony: Observe pressure-time and flow-time scalars, monitor patient comfort and respiratory rate, and consider measuring transpulmonary pressure in complex cases, as suggested by the European Respiratory Society 1, 6, 5

The British Thoracic Society notes that bi-level ventilators employing flow sensors for triggering have been widely adopted due to improved patient comfort 7

In patients with severe COPD where PEEPi may reach high levels, flow triggering combined with external PEEP helps offset intrinsic PEEP and improves triggering 8
For patients with insufficient respiratory effort, timed or assist-control modes may be necessary regardless of trigger type 7

The American Thoracic Society recommends that ventilators for acute NIV should have "sensitive flow triggers" as an essential feature 9
Some modern ventilators allow adjustable inspiratory trigger sensitivity, which is listed as a desirable feature for hospital NIV 9, 8
Portable ventilators may have inferior triggering systems compared to ICU ventilators, impacting patient adaptation and required sedation levels 10