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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.

TABLE 1.Causes of Acute Respiratory Acidosis

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.

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