5 Mechanical Ventilation

Purpose and bedside priorities

Mechanical ventilation supports gas exchange but can also cause harm. Bedside care must assess the patient as well as the ventilator, respond promptly to alarms, check the airway and circuit, and watch for complications. Ventilator settings and alarm limits should follow patient-specific orders and facility policy; involve respiratory therapy and the medical team when concerns arise.

Ventilation modes

Modes differ in how breaths are initiated and delivered. In Assist-control ventilation, the ventilator provides a minimum respiratory rate and delivers the set mandatory breath when either the ventilator or the patient triggers it. A patient with a high spontaneous rate may therefore receive many assisted breaths.

In SIMV, mandatory breaths are synchronized with the patient’s effort, while spontaneous breaths between them may receive pressure support. Pressure-support ventilation requires spontaneous patient effort. CPAP supports spontaneous breathing with continuous baseline pressure and no assisted breaths.

Ventilator settings and lung protection

Volume control targets a set tidal volume, while airway pressure may vary. Pressure control targets inspiratory pressure, so delivered tidal volume can vary as lung compliance or airway resistance changes. If compliance worsens during pressure-controlled ventilation, delivered tidal volume may decrease, all else being equal. Assess the patient and trends in delivered volume and pressures, and report concerning changes.

For lung-protective ventilation, use tidal volume based on predicted body weight rather than actual body weight. The recommended assessment includes tidal volume in the range of $4\text{–}8\ \text{mL/kg}$ predicted body weight, plateau pressure, PEEP, and auto-PEEP. In ARDS, a commonly used approach starts near $6\ \text{mL/kg}$ predicted body weight and aims to keep plateau pressure at or below $30\ \text{cm H}_2\text{O}$, with individual adjustment by the clinical team.

Respiratory rate mainly affects minute ventilation and carbon dioxide removal. FiO₂ and PEEP are key settings affecting oxygenation. Titrate oxygen and PEEP to the prescribed oxygenation target; do not make setting changes independently of the patient’s condition, orders, and clinical team.

Responding to ventilator alarms

For every alarm, assess the patient first, then promptly check the airway and circuit. Do not simply silence, disable, or widen alarm limits without an authorized clinical reason.

A high-pressure alarm may result from coughing, biting, secretions, bronchospasm, a kinked circuit, or reduced lung compliance. Assess the patient and rapidly look for correctable causes. If ventilation is ineffective or the patient deteriorates, summon help and provide support according to emergency protocol.

A low-pressure or low-volume alarm may indicate a disconnection, leak, or airway displacement. These problems can rapidly compromise ventilation. Check the patient and equipment promptly; if effective ventilation is not restored, call for assistance and follow emergency procedures. If needed, use a manual resuscitation bag within scope and protocol.

Routine patient and equipment assessment

Routine care combines patient findings with ventilator and airway checks. Assess respiratory effort, chest movement, breath sounds, oxygenation, synchrony, airway position and securement, secretions, the circuit, and relevant trends. AARC recommends assessing tidal volume, plateau pressure, PEEP, and auto-PEEP, as well as airway placement and securement. Verify cuff pressure using a manometer according to policy.

Maintain humidification and provide airway and oral care according to the care plan and facility protocol. Monitor for skin injury and signs of infection, and avoid unnecessary disconnections. Do not deflate an endotracheal-tube cuff at regular intervals without an order.

Interpreting ventilation and oxygenation

Rising PaCO₂ with falling pH suggests worsening respiratory acidosis and inadequate alveolar ventilation. Promptly report the trend and review the patient and ventilator plan with the responsible clinician. Respiratory rate and tidal volume influence minute ventilation, but changes must be guided by the patient’s condition, orders, and clinical team. FiO₂ and PEEP are adjusted primarily to support oxygenation; they do not directly correct elevated PaCO₂ in the same way.

Acute deterioration and complications

Sudden hypotension and tachycardia, a new rise in peak airway pressure, and markedly diminished breath sounds on one side are concerning for tension pneumothorax, an emergency. Urgently summon the clinical team while supporting oxygenation and ventilation; do not delay escalation while waiting for routine tests.

Positive-pressure ventilation can contribute to barotrauma, ventilator-associated lung injury, hypotension, and auto-PEEP. Recognize concerning changes promptly and escalate them.