What are the recommended mechanical breath types for adult patients with respiratory failure, considering their underlying condition and respiratory mechanics?

Mechanical Breath Types for Adult Patients with Respiratory Failure

For patients requiring mechanical ventilation, volume-cycled ventilation using assist-control mode is the appropriate initial choice, delivering low tidal volumes (4-8 ml/kg predicted body weight) with plateau pressures ≤30 cmH2O. 1, 2

Initial Ventilator Mode Selection

Assist-Control (AC) Mode - First-Line Choice

• Volume-cycled assist-control ventilation is recommended at the outset of mechanical ventilation for complete ventilatory support 1
• This mode delivers a preset number of breaths while allowing patient-triggered breaths, with all respirations fully supported by the ventilator 3
• AC mode is indicated for patients who can initiate respiration but cannot maintain adequate spontaneous ventilation 3
• It reduces work of breathing and redirects blood flow to vital organs, which is particularly critical in ARDS and sepsis-related respiratory failure 1

Alternative Modes with Similar Support

• Intermittent mandatory ventilation (IMV) can achieve similar degrees of respiratory support 1
• Pressure-regulated volume-controlled ventilation is also acceptable 1
• No mode of ventilation has proven superior to others in terms of mortality outcomes in sepsis-related respiratory failure 1

Breath Type Characteristics

Volume-Targeted vs Pressure-Targeted Breaths

• Volume targeting guarantees set minute ventilation but does not limit inspiratory pressure 4
• Pressure targeting limits inspiratory pressure and may synchronize better with patient effort, but provides no control over delivered volume 4
• Both approaches can effectively provide lung-protective ventilation when properly managed 4
• Operator expertise impacts outcomes more than the specific breath design features 4

Dual-Control (Adaptive Pressure Control) Modes

• These modes combine pressure-controlled breaths with closed-loop control to maintain minimum tidal volume 5
• They reduce peak inspiratory pressure compared to volume control 5
• A critical limitation is that the ventilator cannot distinguish between improved compliance and increased patient effort, potentially leading to inappropriate adjustments 5

Condition-Specific Breath Delivery

For ARDS Patients

• All ARDS patients require low tidal volume ventilation (4-8 ml/kg predicted body weight) with plateau pressure <30 cmH2O 1, 2, 6
• Tidal volume should be calculated based on ideal body weight: men = 50 + 2.3(height in inches - 60); women = 45.5 + 2.3(height in inches - 60) 1
• For moderate to severe ARDS, apply higher PEEP (typically 10-15 cmH2O) 1, 2, 7
• For severe ARDS (PaO2/FiO2 <150 mmHg), implement prone positioning for >12 hours daily 1, 2, 6
• Strong recommendation AGAINST routine use of high-frequency oscillatory ventilation 1, 2

For COPD Exacerbations

• Non-invasive ventilation (NIV) with bi-level pressure support is first-line for COPD exacerbations with respiratory acidosis (pH <7.35) 1, 2
• Initial settings: IPAP 10-15 cmH2O, EPAP 4-8 cmH2O, with pressure difference ≥5 cmH2O 2
• Backup respiratory rate of 10-14 breaths/min 2
• If invasive ventilation becomes necessary, use assist-control mode with tidal volumes 6-8 ml/kg 2
• Set PEEP 4-8 cmH2O to offset intrinsic PEEP and improve triggering 2
• Allow adequate expiratory time (I:E ratio approximately 1:2 or 1:3) to prevent air trapping 2

Critical Ventilator Parameters

Oxygen Targets

• Target arterial oxygen saturation approximately 90% (PaO2 ~60 mmHg) 1
• For most patients, maintain SpO2 88-92% to avoid oxygen toxicity 2, 6

PEEP Application

• PEEP ameliorates changes in closing volume and lung derecruitment, providing dramatic improvements in PaO2 1
• Maintain PEEP ≥5 cmH2O as baseline, titrating to ≥10 cmH2O for moderate-severe ARDS 2, 6

Permissive Hypercapnia

• Allowing pCO2 to rise while reducing tidal volume prevents alveolar overdistension and has been shown safe and effective at reducing mortality 1

Common Pitfalls to Avoid

Volume Delivery Errors

• Avoid high tidal volumes (>8 ml/kg predicted body weight) as this increases mortality through ventilator-induced lung injury 1, 2
• Never allow plateau pressures to exceed 30 cmH2O 1
• Use ideal body weight, not actual body weight, for tidal volume calculations 1

Synchrony Issues

• Inadequate expiratory time causes dynamic hyperinflation and auto-PEEP, especially in obstructive diseases 2
• Poor ventilator-patient synchrony increases work of breathing and can occur at triggering, post-trigger inflation, or inspiration-expiration switchover 8
• Careful iterative adjustments are required to minimize work of breathing 8

Mode Selection Errors

• Controlled mechanical ventilation (CMV) without patient triggering is only indicated for patients with severe neurological alterations, deep sedation, shock, or severe respiratory failure 3
• Using protocols for ventilator settings without individualized assessment can lead to alveolar overdistention and increased mortality risk 8

NIV-Specific Pitfalls

• Delayed escalation to invasive ventilation when NIV is failing—monitor ABGs at 1-2 hours and intubate if worsening, or at 4 hours if no improvement 1, 2
• NIV contraindications include respiratory arrest, cardiovascular instability, impaired mental status, copious secretions, and recent facial surgery 1

Monitoring Requirements

• Recheck arterial blood gases after 30-60 minutes of ventilation or with clinical deterioration 2
• Monitor plateau pressure, driving pressure, and dynamic compliance continuously 6
• Assess weaning readiness daily through spontaneous breathing trials, which reduce time to extubation by 81% and ventilator mortality by 49% 6