Respiratory Acidosis

SOURCE

Source: Devlin JW, Matzke GR. Acid–base disorders. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146062232. Accessed August 12, 2017.

DEFINITION

• Acid–base disorder characterized by increase in PaCO₂ that leads to decrease in pH.

ETIOLOGY

• Occurs when lungs fail to excrete carbon dioxide (CO₂) including (Table 1):

  • Disorders that restrict ventilation or increase CO₂ production.

  • Airway and pulmonary abnormalities.

  • Neuromuscular abnormalities.

  • Mechanical ventilator problems.

PATHOPHYSIOLOGY

• Restricted breathing or increased CO₂ production result in lower pH.

  • Acute respiratory acidosis with hypoxemia, hypercarbia, and acidosis is life-threatening.

  • Chronic respiratory acidosis seen with disorders that produce increase in PaCO₂ and hypoxemia compatible with life (eg, chronic obstructive pulmonary disease [COPD]).

• Compensatory response:

  • Chemical buffering occurs early.

  • If prolonged respiratory acidosis (>12–24 hours), metabolic compensation occurs.

    • Serum HCO₃^– increases raising pH to normal by:

      • Proximal tubular HCO₃^– reabsorption.

      • Ammoniagenesis.

      • Distal tubular H⁺ secretion.

RISK FACTORS

• Mechanical ventilation.

• COPD

CLINICAL PRESENTATION

• Patient is usually symptomatic.

SIGNS AND SYMPTOMS

• Confusion.

• Difficulty thinking.

• Headache.

• Severe cases:

  • Central nervous system (CNS) symptoms include:

    • Altered mental status.

    • Abnormal behavior.

    • Seizures.

    • Stupor.

    • Coma.

  • Increased cardiac output.

  • Hypercapnia can mimic stroke or CNS tumor by producing:

    • Headache.

    • Papilledema.

    • Focal paresis.

    • Abnormal reflexes.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• Primary tools for determining cause of acid–base disorders and designing therapy:

  • Blood gases.

  • Serum electrolytes.

  • Medical history.

  • Clinical condition.

LABORATORY TESTS

• Metabolic panel.

  • Serum potassium may be modestly increased.

• Arterial blood gases (ABG) measured to determine oxygenation and acid–base status.

DESIRED OUTCOMES

• Maintain patent airway and adequate oxygenation.

TREATMENT: GENERAL APPROACH

• Treatment dependent on chronicity of condition.