16.3 Mechanical Ventilation Basics

Mechanical ventilation is a crucial life-saving intervention for patients with respiratory failure. It involves using machines to assist or replace spontaneous breathing, improving gas exchange and reducing the work of breathing. Understanding the basics is essential for nurses providing care to ventilated patients.

This section covers the fundamentals of mechanical ventilation, including goals, settings, and modes. It also explores potential complications and the critical role of nursing care in managing ventilated patients. Proper assessment, monitoring, and interventions are key to ensuring patient safety and optimal outcomes.

Mechanical ventilation principles

Fundamentals and goals

• Mechanical ventilation assists or replaces spontaneous breathing in patients with respiratory failure
• Primary goals improve gas exchange, reduce work of breathing, and reverse life-threatening hypoxemia or acute respiratory acidosis
• Key components include ventilator machine, patient circuit, humidifier, monitors, and alarms
• Patient interface can be invasive (endotracheal tube or tracheostomy) or non-invasive (face mask or nasal prongs)

Ventilator settings and variables

• Settings include tidal volume, respiratory rate, fraction of inspired oxygen (FiO2), positive end-expiratory pressure (PEEP), and inspiratory pressure
• Pressure, volume, and flow serve as main variables controlled by mechanical ventilators to deliver breaths
• Respiratory cycle consists of four phases inspiration, inspiratory pause, expiration, and expiratory pause
• Tidal volume typically set between 6-8 mL/kg of ideal body weight (IBW)
• FiO2 ranges from 21% (room air) to 100% oxygen

Patient assessment and monitoring

• Regular assessment of vital signs includes respiratory rate, heart rate, blood pressure, and oxygen saturation
• Chest auscultation evaluates breath sounds and detects abnormalities (crackles, wheezes)
• Work of breathing assessment observes use of accessory muscles and chest wall movement
• Arterial blood gas (ABG) analysis monitors pH, PaO2, PaCO2, and HCO3- levels
• Continuous pulse oximetry measures oxygen saturation (SpO2)

Ventilation modes and indications

Volume-controlled modes

• Assist-Control (AC) mode delivers set number of breaths with specified tidal volume or pressure
  • Allows patient to trigger additional breaths
  • Indicated for patients with minimal respiratory effort (post-operative, neuromuscular disorders)
• Synchronized Intermittent Mandatory Ventilation (SIMV) provides set number of breaths while allowing spontaneous breathing
  • Useful for weaning patients off mechanical ventilation
  • Combines mandatory breaths with patient-initiated breaths

Pressure-controlled modes

• Pressure Support Ventilation (PSV) provides preset pressure to support spontaneous breathing efforts
  • Often used with SIMV or as standalone mode for patients with stronger respiratory drive
  • Pressure level adjusted based on patient's work of breathing and tidal volume goals
• Continuous Positive Airway Pressure (CPAP) maintains constant positive pressure throughout respiratory cycle
  • Supports alveolar recruitment and improves oxygenation
  • Commonly used in non-invasive ventilation (sleep apnea, mild respiratory distress)

Advanced modes

• Pressure Regulated Volume Control (PRVC) combines features of volume and pressure-controlled ventilation
  • Adjusts inspiratory pressure to deliver set tidal volume
  • Beneficial for patients with changing lung compliance (ARDS, pulmonary edema)
• Airway Pressure Release Ventilation (APRV) applies continuous positive airway pressure with intermittent releases
  • Facilitates CO2 removal and improves oxygenation
  • Indicated for acute respiratory distress syndrome (ARDS) or severe oxygenation difficulties
• High-Frequency Oscillatory Ventilation (HFOV) delivers very small tidal volumes at high frequencies
  • Used in neonates and some adults with severe ARDS
  • Employed when conventional modes prove ineffective

Complications of ventilation

Infectious and pulmonary complications

• Ventilator-Associated Pneumonia (VAP) develops in mechanically ventilated patients
  • Often results from aspiration of oral or gastric contents
  • Prevention measures include elevated head of bed, oral care, and subglottic suctioning
• Barotrauma refers to lung injury caused by excessive airway pressure
  • Can lead to pneumothorax, pneumomediastinum, or subcutaneous emphysema
  • Monitored through chest x-rays and physical assessment
• Volutrauma occurs when excessive tidal volumes cause alveolar overdistension
  • Results in alveolar damage and inflammation
  • Prevented by using lung-protective ventilation strategies (low tidal volumes)

Systemic and physiological complications

• Oxygen toxicity results from prolonged exposure to high oxygen concentrations
  • Can cause absorption atelectasis and oxidative stress to lung tissues
  • Managed by using lowest effective FiO2 to maintain adequate oxygenation
• Hemodynamic compromise occurs due to increased intrathoracic pressure
  • Potentially reduces venous return and cardiac output
  • Monitored through blood pressure, heart rate, and cardiac output measurements
• Respiratory muscle atrophy develops during prolonged mechanical ventilation
  • Complicates weaning efforts and prolongs ventilator dependence
  • Mitigated through early mobilization and spontaneous breathing trials

Psychological complications

• Anxiety, delirium, and post-traumatic stress disorder common in mechanically ventilated patients
• Communication difficulties due to endotracheal tube placement exacerbate psychological stress
• Interventions include sedation management, reorientation techniques, and family involvement in care

Nursing care for ventilated patients

Assessment and monitoring

• Perform regular respiratory assessments including chest auscultation and work of breathing evaluation
• Monitor ventilator settings and alarms ensuring appropriateness for patient's condition
• Assess and document vital signs (respiratory rate, heart rate, blood pressure, oxygen saturation) at regular intervals
• Evaluate patient-ventilator synchrony and address any signs of dyssynchrony or distress

Airway management and infection prevention

• Maintain proper positioning of patient to optimize ventilation (head of bed elevated 30-45 degrees)
• Provide oral care and subglottic suctioning as per protocol to reduce ventilator-associated pneumonia risk
• Manage endotracheal tube or tracheostomy care including cuff pressure monitoring (20-30 cmH2O)
• Implement ventilator bundle interventions (daily sedation interruption, daily weaning assessment)

Medication administration and complication prevention

• Administer prescribed medications including sedatives, analgesics, and neuromuscular blocking agents
• Monitor for medication side effects and efficacy adjusting as needed in collaboration with healthcare team
• Implement deep vein thrombosis prophylaxis (compression devices, anticoagulation as ordered)
• Provide stress ulcer prevention through medication administration and enteral nutrition as appropriate
• Initiate early mobilization when appropriate to prevent muscle atrophy and promote weaning readiness

Patient and family support

• Provide emotional support and education to patients and families regarding mechanical ventilation
• Facilitate communication between ventilated patients and healthcare team (communication boards, eye blink systems)
• Involve family in care activities when appropriate to reduce patient anxiety and promote comfort
• Document all assessments, interventions, and patient responses accurately in medical record