Complications associated with mechanical ventilation are primarily due to the effects positive pressure has on the lungs and cardiovascular system. Positive pressure not only damages sensitive lung tissue but also may inhibit blood flow returning to the heart. Each of these effects can then go on to affect other organ systems such as the kidneys and brain. These hazards are briefly reviewed here as well as additional hazards related to mechanical ventilation.
Ventilator induced lung injury (VILI) occurs when the alveoli capillary membrane is damaged during mechanical ventilation. VILI can be the result of barotrauma, volutrauma, atelectrauma, and biotrauma.
Barotrauma occurs when high ventilatory pressures rupture the small airways and alveoli. Barotrauma may become life threatening if it leads to tension pneumothorax. A tension pneumothorax is a condition in which air enters the pleural space with each breath but cannot exit.
Volutrauma occurs when normal alveoli are over distended and can occur even when using low tidal volume ventilation. As gas enters the lungs it naturally follows the path of least resistance. Therefore, gas enters a diseased lung, the healthy regions of the lung may receive the bulk of the tidal volume as compared to the diseased non-compliant regions of the lung.
Atelectrauma occurs when collapsed alveoli are repeatedly snapped open with each breath only to then re-collapse again after exhalation. This creates shearing forces which damage the epithelial cells of the alveoli. As a result, cellular proteins leak into the extracellular fluid leading to pulmonary edema.
Biotrauma occurs when aforementioned traumas fill the alveoli with cytokines, proteins, white blood cells, and neutrophils. These bio-elements cause further damage to the alveolar-capillary membrane by allowing bacteria into the bloodstream. This leads to an even more severe systemic inflammatory response as a result.
Oxygen toxicity can occur when a high fio2 is used for a prolonged period of time. Free radicals are released which damage the epithelial cells of the alveolus. Current medical literature suggests exposing the patient to an fio2 less than 0.60 may decrease the risk of oxygen toxicity.
Absorption atelectasis may also occur due to high fio2 use as nitrogen is washed out of the alveoli with a high oxygen concentration. When the fio2 is high, gas uptake from the alveolus to the bloodstream may occur faster than gas can enter the alveoli. The alveoli may then collapse as a result.
Neonatal retinopathy is associated with exposure to high FiO2. Premature neonates are at particular risk of retinopathy.
Hypotension and decreased cardiac output may occur when increased intra-thoracic pressure from positive pressure ventilation and PEEP use decreases venous blood returning to the right atrium.
Increased pulmonary vascular resistance also may result as a response to the reduced cardiac output caused by PPV and the use of PEEP. The use of PEEP increases pressure applied to the alveoli and may compress pulmonary vasculature.
Neurological & Neuromuscular Hazards
Increased intracranial pressure is common in patients with traumatic brain injury or stroke. The use of PEEP during mechanical ventilation may increase ICP by reducing central venous blood return leaving the brain. Increased carbon dioxide levels may decrease cerebral blood flow and increase ICP as a result.
Cerebral hypo perfusion can occur when high mean airway pressures are used during mechanical ventilation. This may occur when high mean airway pressure (MAP) decreases overall blood pressure.
Delirium is a common hazard of mechanical ventilation and often the result of benzodiazepine use during mechanical ventilation.
Poly neruopathy and myopathy is a common occurrence in patient’s receiving mechanical ventilation. This may make weaning difficult due to diaphragmatic dysfunction.
Ventilator Associated Pneumonia (VAP) occurs when oropharyngeal secretions slip past the endotracheal tube cuff and are aspirated into the lungs. Though, VAP is really more the result of artificial airway use rather than mechanical ventilation.
The definition and diagnosis of VAP has evolved over the years. Currently, VAP is defined as a pneumonia occurring greater than 48 hours after initiation of invasive mechanical ventilation.
Some general guidelines for VAP prevention include:
- Maintain good oral hygiene by brushing the teeth, suctioning excess oral secretions and providing an antiseptic mouth rinse such as chlorhexidine for example.
- Avoid breaking (opening) and routinely changing the ventilator circuit.
- Minimize unnecessary transports. Transports have been associated with contamination of the airway and an increased risk of VAP.
- Maintain the head of the bead greater than a 30 degree angle.
- Using endotracheal tubes with subglottic suction ports can help remove secretions pooling on top of the cuff before they can be aspirated.
- Use PEEP
Impaired mucocilliary clearance during mechanical ventilation due to the use of an artificial airway may lead to increased secretion retention and buildup in the lungs.
Trauma and edema may also result from the use of artificial airways. A rare but serious complication of long term mechanical ventilation can create a connection between the trachea and the esophagus known as a tracheo-esophageal fistula. Gastric distention may then result as air passes into the esophagus rather than solely the trachea.
Hypervolemia (fluid overload) can occur as a result of decreased cardiac output associated with positive pressure ventilation. Decreased cardiac output decreases perfusion of the kidneys which also decreases the production of urine as a result.
Stress ulcers may occur in the GI system of patients receiving mechanical ventilation for greater than 48 hours.
Gastric distention may occur during non-invasive ventilation when using high inspiratory pressures.
Mechanical malfunctions during mechanical ventilation may include:
- Loss of power or gas source
- Accidental disconnection from the ventilator
- Ventilator circuit leaks
Did we miss anything here? What mechanical ventilation hazards would you like to hear more about? Let us know in the comments below!