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Mechanical Ventilation

Process by which oxygen is moved in and out of the lungs using a mechanical ventilator.
 Purpose: Not curative – supports patient until they can breathe on their own.

Bag Valve Mask

  • Bag-Valve-Mask or BVM (also called Ambu bag) = lifesaving tool for immediate manual ventilation in emergencies.
  • It is a hand-held device used to provide positive pressure ventilation to patients who are not breathing or not breathing adequately.
  • Commonly used in emergency situations, CPR, anesthesia, and patient transport.
  • Oxygen Delivery in Room air = 21% and with O₂ supply = up to 100%.
  • Nursing Role →
    • Ensure proper mask seal.
    • Connect oxygen.
    • Always check for effective chest rise = adequate ventilation.
    • Prevent complications.
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Types of Ventilation

Based on Mechanism

  1. Positive Pressure Ventilation (PPV)
    • Air is pushed into the lungs using positive pressure.
    • Commonly used in critical care.
    • Examples: Mechanical ventilator, Ambu bag, CPAP.
  2. Negative Pressure Ventilation (NPV)
    • Air is drawn into the lungs by creating negative pressure around the chest.
    • Mimics normal breathing physiology.
    • Example: Iron lung (historical use).
    • Bulky, less practical, rarely used now.

Based on Control Variable

  1. Volume-Controlled Ventilation (VCV)
    • Delivers a preset tidal volume with each breath.
    • Airway pressure vary depending on lung compliance & resistance.
  2. Pressure-Controlled Ventilation (PCV)
    • Delivers a preset inspiratory pressure during each breath.
    • Tidal volume varies with compliance & resistance.

Modes of positive pressure ventilation:

1. Controlled mandatory ventilation (CMV)
  • Full control by ventilator
  • Spontaneous respiratory effort is “locked out.”
  • Patient is sedated or paralyzed
2. Assist-control ventilation (ACV)
  • When Patient initiates a spontaneous breath, preset volume of breath is delivered.
  • Minimum Ventilator respiratory rate is set, to avoid Hypoventilation
3. Synchronized intermittent mandatory ventilation(SIMV)
  • Weaning mode
  • Patient breaths spontaneously, Intermittently Ventilator delivers preset volume breath
  • Works in Synchrony with patient breath
4. Pressure support ventilation
  • Pressure is set while volume of gas varies as per patient
5. Bi-PAP [Bilevel positive airway pressure]
  • Two levels of positive pressure support
    • Higher inspiratory pressure
    • Lower expiratory pressure.
6. C – PAP [Continuous positive airway pressure]
  • Most effective treatment for obstructive sleep apnea
  • Because the positive pressure keeps the airway open during sleep.
  • To use CPAP, the patient must be breathing independently.
  • It allows a lower percentage of O² to be used with a similar effect.
  • Low O2 – More effect
BIPAP & CPAP – Both are non – invasive

Ventilator Alarms

High-Pressure Alarm:
Possible Obstruction
Causes:
  • Patient coughing
  • Kinked or plugged airway tube
  • Decreased lung compliance (e.g., pulmonary edema, ARDS)
Low-Pressure Alarm:
Possible leak
Causes:
    • Leak in ventilator tubing or circuit
    • Disconnection of tubing
    • Loose cuff on endotracheal tube
    • Loose humidifier connections
    • Increased lung compliance. (Emphysema – COPD type, Aging lungs)

Complications of Mechanical Ventilation

                Mechanical ventilation, while lifesaving, is associated with several complications involving respiratory system, gastrointestinal system, cardiovascular system, and overall patient outcomes.

1. Infection – Ventilator-Associated Pneumonia (VAP):
    • Usually develops more than 48 hours of mechanical ventilation.
    • Clinical features include fever, increased secretions, and a change in the color or odor of sputum.
2. Barotrauma
  • Caused by excessive airway pressure
  • May result in alveolar rupture and pneumothorax (collection of air between the pleura and lung).
  • Signs include sudden drop in SpO₂, decreased or absent breath sounds, and respiratory distress.
  • Severe cases can lead to tension pneumothorax (life-threatening emergency).
3. Volutrauma
  • Caused by high tidal volume.
  • Leads to alveolar overdistension and collapse.
4. Alveolar Collapse (Atelectasis)
  • May occur due to inadequate ventilation, mucus plugging, or inappropriate ventilator settings.
  • Results in impaired oxygen exchange.
  • Prevention: recruitment maneuvers, adequate PEEP (positive end-expiratory pressure), and suctioning.
5. Hypoventilation and Hyperventilation
  • Hypoventilation: insufficient ventilation, can lead to hypercapnia (High PaCO₂).
  • Hyperventilation: excessive ventilatio, can lead to hypocapnia (Low PaCO₂).
  • Both can lead to acid–base imbalance and altered patient outcomes.
6. Patient–Ventilator Asynchrony
  • Mismatch between patient effort and ventilator.
  • Increases work of breathing and discomfort.
7. Stress Ulcers (Gastrointestinal Complication)
  • Common in critically ill patients.
  • Stress Ulcers c an cause GI bleeding.
  • Prevent with H₂ blockers (Ranitidine) or PPIs (Pantoprazole).
8. Respiratory Muscle Weakness and Atrophy
  • Prolonged ventilation can  cause diaphragm and muscle atrophy.
  • Can make weaning from the ventilator difficult.
9. Cardiovascular Complications
  • Positive pressure ventilation increases intrathoracic pressure.
  • This reduces venous return (preload) causing decreased cardiac output leading to hypotension.
  • Patients with hypovolemia or cardiac dysfunction are more vulnerable.

Nursing Care

To prevent infection 
  • HOB elevation at  a minimum of 30 to 45 degrees
  • No routine changes of the patient’s ventilator circuit tubing    
  • Strict hand washing & using sterile gloves always
To reduce secretion
  • Assess for the presence of secretions by lung auscultation at least every 2 to 4 hours
  • Turn the patient every 1 to 2 hours,
  • Providing chest physiotherapy to  lung areas with increased secretions
  • Suctioning:
      • Not required routinely as it can damage the airway mucosa
      • Suction only when there is excess secretions 
Managing alarms
  • If,at any time, the ventilator is malfunctioning  (e.g., failure of O2 supply)
    • Disconnect the patient from the  machine 
    • Manually ventilate with a BVM and 100% O2 until  the ventilator is fixed
Ventilator asynchrony
  • If a patient breathes out of synchrony due to anxiety or pain, sit with the patient and verbally coach them to breathe with the ventilator.
  • Paralyze the patient with a neuromuscular blocking agent to provide more effective synchrony, as advised
  • Remember that the paralyzed patient can hear, see, think, and feel. It is very important to administer IV sedation and analgesia concurrently when the patient is paralyzed.
  • Restraints always come last.
  • Although appearing to be asleep, sedated, or paralyzed, always address them as if they were awake and alert
ETcO2 (Capnography)
  • End-tidal carbon dioxide  monitoring 
  • Used for confirmation of ET tube placement & ventilation
  • Normal CO2 value – 35-45mmHg
    • >45 – Hypoventilation
    • <35 – Hyperventilation
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