Mechanical Ventilation

Introduction and Indications for Mechanical Ventilation

Mechanical ventilation is a life-saving supportive therapy that physically moves air in and out of the lungs when a patient cannot maintain adequate spontaneous breathing. It does not cure disease; rather, it buys time for underlying medical or surgical conditions to resolve through treatment. In Nigerian clinical settings, patients often arrive at emergency departments or intensive care units in severe respiratory distress from conditions like late-stage malaria with pulmonary complications, severe trauma, tetanus, or acute exacerbations of asthma.

• Acute Respiratory Failure: Inability to exchange oxygen and carbon dioxide effectively, seen in severe pneumonia or acute respiratory distress syndrome (ARDS).
• Hypoxemic Failure: Low blood oxygen levels despite high-flow oxygen delivery, often caused by pulmonary edema or massive atelectasis.
• Hypercapnic Failure: Elevated carbon dioxide levels due to pump failure, common in central nervous system depression, drug overdose, or severe neuromuscular disease like myasthenia gravis.
• Airway Protection: Inability to protect the airway due to decreased level of consciousness, head injury, or cardiac arrest.

Modes of Mechanical Ventilation

Ventilator modes dictate how the machine interacts with the patient's respiratory effort. Choosing the correct mode depends on the patient's level of consciousness, respiratory drive, and muscle strength.

• Control Mode (CMV): The ventilator delivers a preset volume or pressure at a fixed rate, completely ignoring any breathing effort from the patient. Rarely used unless the patient is heavily sedated or paralyzed.
• Assist-Control (AC): Every breath is delivered by the machine, either at a set timed rate or triggered by the patient's own weak inhalation effort. Ensures a minimum minute ventilation.
• Synchronized Intermittent Mandatory Ventilation (SIMV): Delivers preset mandatory breaths synchronized with the patient's inspiratory effort, but allows the patient to breathe spontaneously between mandatory breaths without machine assistance.
• Pressure Support Ventilation (PSV): The patient triggers every breath, and the ventilator provides a set amount of positive pressure during inspiration to reduce the work of breathing.

Ventilator Settings and Parameters

Configuring the ventilator requires balancing physiological needs with lung protection. Incorrect settings can cause barotrauma, volutrauma, or oxygen toxicity.

A common misconception is that higher tidal volumes ensure better oxygenation; however, excessive volume overdistends alveoli and triggers dangerous inflammatory responses known as ventilator-induced lung injury.

Nursing Assessment and Patient Monitoring

Continuous surveillance of a mechanically ventilated patient prevents life-threatening complications such as accidental extubation, circuit disconnection, or tension pneumothorax. Nurses must perform both machine checks and physical assessments.

Begin every shift by verifying that operational alarms are active, manual resuscitation bags with masks are present at the bedside, and emergency airway equipment is ready. Assess chest symmetry, bilateral breath sounds, and endotracheal tube depth markings every two to four hours. Monitor vital signs closely, noting any sudden spikes in peak inspiratory pressure which can signal tube obstruction, coughing, bronchospasm, or decreased lung compliance. Observe the patient's level of sedation and comfort using standardized behavioral pain scales, ensuring they do not fight the ventilator cycle.

Airway Management and Securing the Endotracheal Tube

Maintaining a patent artificial airway is a core nursing responsibility. Endotracheal tubes (ETTs) bypass natural upper airway filtration and humidification, making meticulous care mandatory to prevent infections and displacement.

• Tube Positioning: Confirm the centimeter mark at the lip or teeth every shift and note it on the nursing chart.
• Securing: Use specialized tape or commercial tube holders to prevent accidental movement. Two nurses should participate when repositioning the tube or changing ties to prevent extubation.
• Suctioning: Perform endotracheal suctioning only when clinically indicated by coarse breath sounds, visible secretions, or coughing—not routinely. Pre-oxygenate the patient and limit suction passes to ten to fifteen seconds to avoid severe hypoxemia and cardiac arrhythmias.
• Oral Care: Provide regular chlorhexidine mouth rinses and brush teeth every twelve hours to minimize ventilator-associated pneumonia risk.

Complications of Mechanical Ventilation and Preventive Care

Prolonged mechanical ventilation exposes patients to significant physical risks. Nurses implement evidence-based care bundles to mitigate these hazards.

• Ventilator-Associated Pneumonia (VAP): Prevent by elevating the head of the bed between 30 and 45 degrees, performing daily sedation vacation assessments, and maintaining oral hygiene protocols.
• Barotrauma and Volutrauma: Result from high airway pressures or excessive volumes, causing pneumothorax or subcutaneous emphysema. Minimized by low tidal volume strategies.
• Oxygen Toxicity: Caused by high FiO2 levels over prolonged periods, leading to free radical damage and pulmonary fibrosis. Titrate oxygen downward as soon as arterial blood gases allow.
• Diaphragm Atrophy: Inactivity of respiratory muscles leads to rapid weakening. Daily spontaneous breathing trials help preserve muscle mass.

Weaning Protocols and Extubation

Weaning is the gradual transition from mechanical ventilatory support to spontaneous breathing. The process begins as soon as the acute phase of illness resolves and the patient meets specific clinical criteria.

Screen daily for readiness: stable cardiovascular status, adequate oxygenation without high PEEP or FiO2, reversal of the underlying disease process, and active spontaneous breathing efforts. Once criteria are met, conduct a Spontaneous Breathing Trial (SBT) using a T-piece or low pressure support for 30 to 120 minutes. Monitor the patient for signs of fatigue, tachypnea, tachycardia, or diaphoresis. Successful trials lead to extubation. Following tube removal, provide humidified oxygen, encourage deep breathing and coughing, and monitor closely for upper airway stridor or respiratory exhaustion.