Near-Fatal Asthma

By Mark D. Siegel, MD, FCCP

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Mechanical Ventilation

Complications

Complications associated with intubation are similar for NFA and other critical illnesses, and include nosocomial pneumonia, stress gastritis, deep venous thrombosis (DVT), pulmonary embolism, and malnutrition. Patients requiring prolonged mechanical ventilation may be predisposed to sepsis and multiple organ dysfunction.⁴ Appropriate measures to avoid complications include using agents to neutralize gastric acid secretion (most commonly a histamine-receptor blocker), DVT prophylaxis (usually low-dose subcutaneous heparin), appropriate bed positioning, and timely extubation when the patient improves. Enteral feeds should be started when feasible.

Complications specifically associated with NFA include shock and barotrauma, even when optimal ventilator techniques are used. Though difficult, it is critical to differentiate shock related to DHI from tension pneumothorax. Physical examination findings (eg, unilateral hyperresonance, decreased breath sounds, and tracheal shift) that might be expected in tension pneumothorax may be difficult to detect. Although a definitive diagnosis may require a chest radiograph, rapid deterioration in the patient's condition may not allow enough time to obtain one.

If hypotension and increased airway pressure occur, the patient should be immediately disconnected from the ventilator and bagged slowly (eg, 2 or 3 breaths/min) or not at all (if the patient's oxygen saturation is adequate, temporary apnea is generally tolerated).^5,56 If the hypotension is a result of DHI, blood pressure should improve quickly, often within seconds. The patient can then be reconnected to the ventilator with a decrease in the E.

Hypotension resulting from tension pneumothorax should not respond to hypoventilation. The side with the pneumothorax can sometimes be identified by a combination of findings, including decreased breath sounds, hyperresonance, and tracheal shift. If the patient has a reasonable blood pressure and oxygen saturation, it is acceptable to wait for a chest radiograph before decompressing the presumed pneumothorax.⁵⁶ However, if the patient is unstable, decompression must precede definitive testing; the physician should recognize that both hemithoraces may need to be treated or that, in some cases, the wrong diagnosis may be made.

The use of neuromuscular blockade is associated with several potential complications, including prolonged mental status depression due to the high levels of sedation required, skin breakdown, and increased risk of DVT. Prolonged neuromuscular weakness is particularly common and can be prevented only partially by monitoring the quantity of neuromuscular blockade given and the use of peripheral nerve stimulators.⁶⁷ The concurrent use of neuromuscular blockade and high-dose corticosteroids is strongly associated with a severe myopathy, occurring in approximately 30% of patients, with clinical manifestations that can range from mild weakness to quadriparesis that may take weeks or longer to resolve.^68-70 The development of myopathy is strongly associated with the duration of neuromuscular blockade.⁷⁰ Neuromuscular blockade should therefore be discontinued as soon as it is safe to do so.

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