Respiratory acidosis
Respiratory acidosis is an acid-base disturbance characterized by reduced alveolar ventilation and manifested by hypercapnia (partial pressure of arterial carbon dioxide [Paco2] greater than 45 mm Hg). It can be acute (resulting from sudden failure in ventilation) or chronic (resulting from long-term pulmonary disease).
The prognosis depends on the severity of the underlying disturbance and the patient’s general clinical condition.
Causes
Factors that predispose a patient to respiratory acidosis include:
drugs, such as narcotics, anesthetics, hypnotics, and sedatives, which depress the respiratory control center’s sensitivity
central nervous system (CNS) trauma such as medullary injury, which may impair ventilatory drive
chronic metabolic alkalosis, which may occur when respiratory compensatory mechanisms attempt to normalize pH by decreasing alveolar ventilation
neuromuscular diseases, such as Guillain-Barrè syndrome, myasthenia gravis, and poliomyelitis, in which respiratory muscles fail to respond properly to respiratory drive, reducing alveolar ventilation.
In addition, respiratory acidosis can result from an airway obstruction or parenchymal lung disease that interferes with alveolar ventilation or from chronic obstructive pulmonary disease (COPD), asthma, severe adult respiratory distress syndrome, chronic bronchitis, large pneumothorax, extensive pneumonia, and pulmonary edema.
Key abnormal test values in respiratory acidosis
The following arterial blood gas values help confirm a diagnosis of respiratory acidosis:
Paco2 above the normal 45 mm Hg
pH typically below the normal range of 7.35 to 7.45
normal HCO3–levels (22 to 26 mEq/L) in acute respiratory acidosis but elevated above 26 mEq/L in chronic respiratory acidosis.
Complications
Acute or chronic respiratory acidosis can produce shock and cardiac arrest.
Assessment
The patient may initially complain of headache and dyspnea. He may also have a predisposing condition for respiratory acidosis. On inspection, you may see that he’s dyspneic and diaphoretic. He may report nausea and vomiting.
Palpation may detect bounding pulses. Auscultation may reveal rapid, shallow respirations, tachycardia and, possibly, hypotension.
Ophthalmoscopic examination may uncover papilledema. Neurologic examination may disclose a level of consciousness (LOC) ranging from restlessness, confusion, and apprehension to somnolence, with a fine or flapping tremor (asterixis) and depressed reflexes.
