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Clinical Findings

Hypoxemic Respiratory Failure (arterial O2 saturation < 90% while receiving an inspired O2 fraction > 0.6)

This represents a wide A-a gradient that is relatively resistant to supplemental oxygen. Frequently there are opacities on chest x-ray that represent fluid-filled aveoli. Common causes are pneumonia, pulmonary edema, and diffuse pneumonitis of various types, including aspiration, and diffuse lung injury due to sepsis, trauma, and shock. Cause is frequently multifactorial. Additional causes are atelectasis, tumor masses, and pleural disease.

Hypercarbic Respiratory Failure (respiratory acidosis with pH < 7.30)

Patients with carbon dioxide (CO2) retention are often stable and compensate for it. A compensating metabolic acidosis returns the pH to near normal. Acute respiratory acidosis is characterized by CO2 retention above the patient’s normal baseline and low pH on arterial or venous blood gas. Hypercarbia represents inadequate ventilation of the aveoli. A number of diseases that cause this condition do not show opacity of the lung tissue on chest x-ray. Common causes of CO2 retention include drugs that suppress respiration, weakness of the muscles of respiration, and diseases of the lung that reduce its elasticity or obstruct the airways. Conditions outside the lungs such as obesity or distension of the abdomen may contribute. Depression of consciousness frequently leads to inadequate ventilation from depression of respiratory drive or from airway obstruction by the tongue against the posterior pharynx.


Upon diagnosis of respiratory failure, supplemental oxygen is not adequate treatment, and the patient requires positive pressure to support respiration. Hypoglycemia should be corrected and opiate toxicity should be reversed before initiating ventilator support. Obstruction such as inspissated secretions should be suctioned and cleared from the upper airways.

Noninvasive Positive-Pressure Ventilation

Noninvasive positive-pressure ventilation (NIPPV) includes continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BiPAP). CPAP is applied throughout the respiratory cycle of a spontaneously breathing patient and is physiologically identical to constant positive end-expiratory pressure (PEEP). Emergency medical system (EMS) providers commonly use CPAP. BiPAP combines CPAP with an inspiratory pressure. BiPAP can provide modes nearly identical with standard ICU ventilators, such as pressure, volume, and assist control. Patients who are cooperative and can manage and protect their airways are candidates for NPPV, which avoids complications that result from an endotracheal tube (ETT). Endotracheal intubation is necessary for the patient who is fully comatose or who is unable to manage the airway or secretions.

Expectation for recovery plays a role in the decision to use invasive versus noninvasive management. Patients with asthma or acute heart failure are candidates for noninvasive airway management since bronchodilators and diuretics may effect a rapid reversal of respiratory distress. Pneumonia and other ...

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