Mechanical Ventilation

Critical Role of Ventilatory Support in Emergencies

Mechanical ventilation is a life-saving intervention in the emergency department (ED) for patients with respiratory failure. For the Certified Emergency Nurse (CEN) exam, understanding ventilator settings, modes, monitoring, and troubleshooting is essential. Mastery of these concepts ensures safe, effective care and improves patient outcomes in critical situations.^[1]

Parameters and Modes in Mechanical Ventilation

Basic Ventilator Parameters

Tidal Volume (Vt): Volume of air delivered with each breath (usually 6–8 mL/kg ideal body weight).^[2]
Respiratory Rate (RR): Number of breaths per minute set by the clinician or patient.
Fraction of Inspired Oxygen (FiO₂): Percentage of oxygen delivered (0.21–1.00).
Positive End-Expiratory Pressure (PEEP): Pressure maintained in the airways at end-expiration to prevent alveolar collapse.^[3]
Peak Inspiratory Pressure (PIP): Highest pressure during inspiration; reflects airway resistance.
Plateau Pressure (Pplat): Pressure during a pause at end-inspiration; reflects lung compliance.

Common Ventilator Modes

Assist-Control (AC): Delivers a set Vt with each breath (patient- or time-triggered). Common in initial stabilization.^[1]
Synchronized Intermittent Mandatory Ventilation (SIMV): Allows spontaneous breaths between mandated breaths, reducing patient-ventilator dyssynchrony.
Pressure Support Ventilation (PSV): Augments spontaneous breaths with a preset pressure; used for weaning.
Pressure Controlled Ventilation (PCV): Delivers a preset inspiratory pressure; Vt varies with compliance and resistance.

Indications for Ventilation and Physiologic Targets

Indications for Mechanical Ventilation

Acute respiratory failure (PaO₂ < 60 mmHg or PaCO₂ > 50 mmHg with acidosis).^[4]
Inability to protect the airway (GCS < 8, loss of gag reflex).
Severe respiratory distress (accessory muscle use, retractions, tachypnea).
Apnea or impending respiratory arrest.

Physiologic Goals

Oxygenation: Maintain SpO₂ ≥ 92% (or PaO₂ ≥ 60 mmHg) using appropriate FiO₂ and PEEP.^[3]
Ventilation: Maintain PaCO₂ 35–45 mmHg and pH 7.35–7.45 by adjusting RR and Vt.
Reduce Work of Breathing: Unload respiratory muscles to prevent fatigue and allow recovery.^[1]

Initial Ventilator Settings (Example for a 70-kg patient)

Mode: AC, Vt = 420–560 mL (6–8 mL/kg), RR = 12–16 breaths/min.
FiO₂ = 1.0 then wean to maintain SpO₂ > 92%.
PEEP = 5 cmH₂O (may increase in hypoxemic respiratory failure).
I:E ratio = 1:2 or 1:3 to allow adequate exhalation.^[2]

Indications for Intubation and Ventilator-Associated Complications

Indications for Intubation and Ventilation

Respiratory arrest or agonal breathing.
Hypoxemia unresponsive to high-flow oxygen.
Hypercapnia with acidosis (pH < 7.25).^[4]
Excessive work of breathing (RR > 35, use of accessory muscles).
Inability to clear secretions or protect airway.

Complications to Recognize

Barotrauma: High airway pressures causing pneumothorax or subcutaneous emphysema.
Ventilator-Associated Pneumonia (VAP): Prevention includes HOB elevation ≥ 30°, oral care with chlorhexidine, daily sedation vacations.^[5]
Ventilator dyssynchrony: Patient “fighting” the ventilator; assess for pain, anxiety, or improper settings.
Hemodynamic compromise: High intrathoracic pressure reduces venous return → hypotension.^[1]

Monitoring Ventilation: ABGs, Waveforms, and Alarms

Bedside Monitoring

Continuous SpO₂, ETCO₂, and waveform analysis.^[3]
Arterial blood gas (ABG) interpretation: pH, PaCO₂, PaO₂, HCO₃, and base excess.
Check plateau pressure (normal < 30 cmH₂O) to assess lung compliance.

Alarm Interpretation (High-Yield for CEN)

High pressure alarm: Indicates increased resistance (e.g., kinked tube, secretions, bronchospasm) or decreased compliance (e.g., pneumothorax, pulmonary edema).^[2]
Low pressure alarm: Usually a leak in the circuit (disconnection, cuff leak, or extubation).
Low minute ventilation alarm: Assess for hypoventilation, apnea, or disconnection.

Nursing Interventions and Spontaneous Breathing Trials

Nursing Management

Confirm tube placement (auscultation, ETCO₂ waveform, CXR).^[1]
Secure endotracheal tube and document depth at teeth.
Provide sedation and analgesia (e.g., propofol, fentanyl) to reduce anxiety and dyssynchrony.^[5]
Suction only when clinically indicated (not routinely).
Perform oral care every 2-4 hours with chlorhexidine for VAP prevention.

Weaning from Mechanical Ventilation

Assess readiness: PaO₂/FiO₂ > 200, hemodynamic stability, no sedative infusions.
Perform a spontaneous breathing trial (SBT) on PSV or T-piece for 30–120 minutes.^[4]
Monitor for signs of failure: RR > 35, SpO₂ < 90%, tachycardia, diaphoresis, use of accessory muscles.
If SBT passed, consider extubation; ensure adequate cough and minimal secretions.

Safety Measures and Complication Prevention in Ventilation

Barotrauma prevention: Keep plateau pressure < 30 cmH₂O; use lung-protective ventilation (low Vt, adequate PEEP).^[3]
VAP bundle: HOB ≥ 30°, daily sedation interruption, peptic ulcer prophylaxis, DVT prophylaxis, oral chlorhexidine.^[5]
Circuit management: Check for condensate in tubing; drain away from patient to prevent aspiration.
Emergency equipment: Always have a bag-valve-mask, suction, and backup ventilator at bedside.

Critical Concepts for CEN Examination Success

Know your ABGs: Recognize acute respiratory acidosis vs. compensated states.
Alarm algorithms: Practice the “Low Minute Ventilation” and “High Pressure” alarm steps—commonly tested.
Mnemonic for VAP prevention: “HEAD” – Head of bed, Elevate, Antibiotics (only when indicated), Daily sedation vaca.
Weaning criteria: Remember the RSBI (Rapid Shallow Breathing Index) < 105 is favorable.^[4]
Sedation scale: Use Richmond Agitation-Sedation Scale (RASS) to target light sedation.