What physiological effects can airway manipulation have on the body?

Physiological Effects of Airway Manipulation

Airway manipulation can cause significant physiological changes affecting multiple body systems, primarily through alterations in intrathoracic pressure, airway reflexes, and hemodynamic responses, which can impact morbidity and mortality outcomes.

Respiratory System Effects

Airway Pressure Changes

• Manipulation of airway pressure through techniques like PEEP (Positive End-Expiratory Pressure) and manual hyperinflation (MHI) directly affects:
  • Alveolar recruitment and prevention of atelectasis
  • Improved oxygenation through increased mean airway pressure 1
  • Enhanced secretion clearance by facilitating movement of secretions toward central airways 1
  • Increased lung compliance 1

Ventilation-Perfusion Matching

• Airway pressure manipulation can improve V/Q matching by:
  • Recruiting collapsed alveoli
  • Redistributing pulmonary blood flow
  • Maintaining patency of previously recruited lung units 1

Potential Adverse Effects

• Barotrauma and volutrauma risk when airway pressures exceed 40 cmH2O 1
• Hypo- or hyperventilation during manual techniques 1
• Risk of oxygen toxicity with prolonged high FiO2 (should maintain FiO2 < 0.60) 1

Cardiovascular System Effects

Hemodynamic Changes

• Increased intrathoracic pressure from airway manipulation can cause:
  • Decreased venous return
  • Reduced cardiac output, particularly with positive pressure ventilation 2
  • Arterial hypotension (sometimes >30% decrease) 2
  • Marked hemodynamic changes during manual hyperinflation due to large fluctuations in intrathoracic pressure 1

Cerebrovascular Effects

• CPAP and increased airway pressure can:
  • Decrease cerebral blood flow velocity 3
  • Increase cerebrovascular resistance (measured by pulsatility index) 3
  • Increase intracranial pressure, though cerebral perfusion pressure typically remains stable 1

Airway Reflexes and Protection

Exaggerated Reflexes

• Airway manipulation can trigger:
  • Breath holding, coughing, and bucking (forceful protracted cough) 1
  • Laryngospasm - protective exaggeration of normal glottic closure reflex 1
  • Increases in arterial pressure, venous pressure, and heart rate 1

Reduced Reflexes

• Residual anesthesia or neuromuscular blockade after airway manipulation can lead to:
  • Reduced pharyngeal tone causing airway collapse and obstruction 1
  • Impaired protective laryngeal reflexes increasing aspiration risk 1
  • Train-of-four ratios of 0.7-0.9 associated with impaired pharyngeal function 1

Complications of Reflex Responses

• Laryngospasm may progress to:
  • Complete airway obstruction
  • Post-obstructive pulmonary edema (negative pressure pulmonary edema) 1
  • Hypoxic cardiac arrest if not promptly addressed 1

Special Considerations for Different Techniques

Manual Hyperinflation (MHI)

• Involves slow deep inspiration with manual resuscitator bag, inspiratory hold, and quick release
• Benefits include improved secretion clearance and lung compliance 1
• Risks include hemodynamic instability and barotrauma 1
• Should be used cautiously in hemodynamically unstable patients 1

Airway Suctioning

• Can cause:
  • Hypoxemia
  • Cardiovascular instability
  • Increased intracranial pressure 1
• Pre-oxygenation, sedation, and reassurance can minimize adverse effects 1

Extubation

• Physiological responses during extubation include:
  • Potential for laryngospasm
  • Cardiovascular stress response (increased blood pressure and heart rate)
  • Risk of post-obstructive pulmonary edema if airway obstruction occurs 1

Clinical Implications and Risk Mitigation

Monitoring Requirements

• Continuous monitoring of:
  • Oxygen saturation (pulse oximetry)
  • Hemodynamic parameters
  • Airway pressures during manual techniques (using pressure manometer) 1

Risk Reduction Strategies

• Maintain airway pressures within safe limits (<40 cmH2O) 1
• Pre-oxygenate before airway suctioning 1
• Use propofol-based techniques when appropriate to reduce exaggerated airway reflexes 1
• Ensure adequate reversal of neuromuscular blockade before extubation 1
• Position patients appropriately to optimize airway patency and secretion clearance 1

Patient-Specific Considerations

• Patients with brain injury: Monitor for increased ICP during airway manipulation 1
• Hemodynamically unstable patients: Use caution with techniques that increase intrathoracic pressure 1
• Obese patients and those with OSA: Higher risk of airway obstruction with reduced reflexes 1

Understanding these physiological responses allows for safer airway management and improved patient outcomes by anticipating and mitigating potential adverse effects of airway manipulation.