critical care medicine
Overview of Mechanical Ventilation
Complications of mechanical ventilation and safeguards
Complications of mechanical ventilation can be divided into those resulting from Endotracheal intubation Mechanical ventilation itself Prolonged immobility and inability to eat normally The presence of an endotracheal tube causes risk of sinusitis (which is rarely of clinical importance), Ventilator-Associated Pneumonia , tracheal stenosis, vocal cord injury, and, very rarely, tracheal-esophageal or tracheal-vascular fistula. Purulent tracheal aspirate in a febrile patient who has an elevated white blood cell count Complications of ongoing mechanical ventilation itself include Pneumothorax and pneumatoceles, oxygen toxicity, hypotension, and ventilator-associated lung injury. Oxygen toxicityrefers to inflammatory changes, alveolar infiltration, and, eventually, pulmonary fibrosis that can develop following prolonged exposure to high FIO2 (eg,>0.6). Toxicity is both concentration- and time-dependent. An FIO2>0.6 should be avoided unless necessary for survival. An FIO2 < 0.6 is well tolerated for long periods. Ventilator-associated lung injury(VALI), sometimes termed ventilator-induced lung injury, is alveolar and/or small airway injury related to mechanical ventilation. Possible mechanisms include alveolar overdistention (ie, volutrauma) and the shear forces created by repetitive opening and collapse of alveoli (ie, atelectotrauma), leading to release of inflammatory mediators resulting in increased alveolar permeability, fluid accumulation, and loss of surfactant. develops in a mechanically ventilated patient, particularly when it is accompanied by tachycardia and/or a sudden increase in peak inspiratory pressure, Pneumothorax (Tension) must always be considered; patients with such findings should immediately have a chest examination and a chest x-ray (or immediate treatment if examination is confirmatory). More commonly, however, hypotension is a result of sympathetic lysis caused by sedatives or opioids used to facilitate intubation and ventilation. Hypotension can also be caused by decreased venous return due to high intrathoracic pressure in patients receiving high levels of PEEP or in those with high levels of intrinsic PEEP due to asthma or COPD. If there are no physical findings suggesting tension pneumothorax, and if ventilation-related causes of hypotension are a possible etiology, pending a portable chest x-ray, the patient may be disconnected from the ventilator and gently bagged manually at 2 to 3 breaths/minute with 100% oxygen while fluids are infused (eg, 500 to 1000 mL of 0.9% saline in adults, 20 mL/kg in children). An immediate improvement suggests a ventilation-related cause, and ventilator settings should be adjusted accordingly. Relative immobility increases the risk of venous thromboembolic disease (eg, Deep Venous Thrombosis (DVT) , Most hospitals have standardized protocols to reduce complications. Elevating the head of the bed to > 30° decreases risk of Ventilator-Associated Pneumonia , and routine turning of the patient every 2 hours decreases the risk of skin breakdown (see The most effective way to reduce complications of mechanical ventilation is to limit its duration. Daily “sedation vacations” and spontaneous breathing trials help determine the earliest point at which the patient may be Liberation from Mechanical Ventilation . 