What are the appropriate ventilator modes and settings for patients in the Intensive Care Unit (ICU) with various respiratory conditions, such as Acute Respiratory Distress Syndrome (ARDS), Chronic Obstructive Pulmonary Disease (COPD), and asthma?

Ventilator Modes and Settings for ICU Patients with Various Respiratory Conditions

For ICU patients with respiratory failure, ventilator mode selection should be based on the specific underlying condition, with low tidal volume ventilation (4-8 ml/kg predicted body weight) and plateau pressure <30 cmH2O as the foundation for most patients, particularly those with ARDS. 1

General Principles for Mechanical Ventilation

• Use lower tidal volumes (4-8 ml/kg predicted body weight) and lower inspiratory pressures (plateau pressure ≤30 cmH2O) for all patients with ARDS to reduce mortality 1
• Pressure-controlled ventilation may have slightly lower mortality compared to volume-controlled ventilation in ARDS patients 2
• Target oxygen saturation of 88-92% for most patients to avoid oxygen toxicity while maintaining adequate oxygenation 3, 4
• Consider permissive hypercapnia (pH 7.1-7.4, pCO2 5-12 kPa) when necessary to avoid ventilator-induced lung injury 4
• Implement computerized protocols for low tidal volume ventilation to improve adherence to best practices 5

Condition-Specific Ventilation Strategies

For ARDS Patients

• Use low tidal volume ventilation (4-8 ml/kg predicted body weight) with plateau pressure <30 cmH2O 1
• For moderate to severe ARDS, use higher PEEP (typically 10-15 cmH2O) 1
• Consider recruitment maneuvers in patients with moderate or severe ARDS 1
• For severe ARDS, implement prone positioning for more than 12 hours per day 1
• Avoid routine use of high-frequency oscillatory ventilation 1
• Consider extracorporeal membrane oxygenation (ECMO) for severe refractory ARDS 1

For COPD Patients

• Non-invasive ventilation (NIV) should be the first-line ventilatory support for COPD exacerbations with respiratory acidosis 3, 1
• For NIV, use bi-level pressure support with initial IPAP of 10-15 cmH2O and EPAP of 4-8 cmH2O 3
• Maintain a pressure difference between IPAP and EPAP of at least 5 cmH2O 3
• Set backup respiratory rate of 10-14 breaths/min 3
• If invasive ventilation becomes necessary, use assist-control mode initially with tidal volumes of 6-8 ml/kg 3
• Set PEEP between 4-8 cmH2O to offset intrinsic PEEP and improve triggering 3
• Allow adequate expiratory time (I:E ratio of approximately 1:2 or 1:3) to prevent air trapping 3

For Asthma Patients

• NIV should be used cautiously in asthma and only in an HDU or ICU where immediate intubation is available 1
• If invasive ventilation is required, use low respiratory rates and longer expiratory times to prevent air trapping 4
• Accept permissive hypercapnia to avoid barotrauma 4
• Monitor for auto-PEEP and adjust ventilator settings to minimize it 1

Non-Invasive Ventilation Approaches

CPAP (Continuous Positive Airway Pressure)

• CPAP is primarily used to correct hypoxemia by recruiting underventilated lung areas 1
• It increases mean airway pressure similar to PEEP in intubated patients 1
• CPAP unloads inspiratory muscles and reduces work of breathing 1
• In COPD, CPAP can offset intrinsic PEEP, reducing ventilatory work and potentially decreasing PaCO2 1
• Flow generators need to maintain desired pressure throughout the respiratory cycle 1

Bi-level Pressure Support

• Combines pressure support (IPAP) for ventilation with CPAP (EPAP) for lung recruitment 1
• IPAP provides inspiratory assistance while EPAP recruits underventilated lung and offsets intrinsic PEEP 1
• EPAP also serves to vent exhaled gas through the exhaust port 1
• Most effective mode of NIV for COPD patients 3

Proportional Assist Ventilation (PAV)

• Alternative technique that independently adjusts flow (to counter resistance) and volume (to counter compliance) 1
• May improve patient comfort and compliance with acute NIV 1

Monitoring and Adjustments

• Recheck arterial blood gases after 30-60 minutes of ventilation or if clinical deterioration occurs 3
• For NIV failure, check for technical issues and optimize ventilator settings before considering intubation 1
• Consider intubation if there is persistent or deteriorating acidosis despite optimized NIV 1
• Monitor for barotrauma, which has similar incidence between pressure-controlled and volume-controlled ventilation 2
• Regularly assess respiratory mechanics, as static respiratory system compliance can be highly variable in conditions like COVID-19 ARDS (ranging from 24 to 49 ml/cmH2O) 6

Common Pitfalls to Avoid

• Excessive oxygen therapy leading to worsening hypercapnia in COPD patients - maintain target saturation of 88-92% 3
• Inadequate expiratory time causing dynamic hyperinflation and auto-PEEP, especially in obstructive lung diseases 3
• Excessive tidal volumes increasing risk of ventilator-induced lung injury - adhere to lung-protective strategies 5
• Insufficient PEEP leading to atelectasis and worsening V/Q mismatch 3
• Delayed escalation to invasive ventilation when NIV is failing - monitor closely for worsening ABGs 3, 1

Ventilator Specifications for NIV

• Essential features include pressure control capability of at least 30 cmH2O, support for inspiratory flows of at least 60 L/min, assist-control and bi-level pressure support modes, and disconnection alarms 1
• Desirable features include adjustable pressure rise time, inspiratory and expiratory triggers, and internal battery backup 1
• For acute respiratory failure, ventilators with inspiratory pressure as the controlled variable (bi-level devices) are preferred 1