The nurse draws a blood sample on an anxious patient that is hyperventilating. The arterial blood gas will most likely show


• Hyperventilation is an increase in respiratory rate and/or volume which causes a decrease in PCO2. This in turn raises the pH to cause respiratory alkalosis

• Hyperventilation is often a response to hypoxia, increased metabolic demands from fever or illness, to pain, anxiety, or as part of a compensatory mechanism to when a patient has metabolic acidosis.

• Though hyperventilation is seen in some cases of metabolic acidosis, this answer is incorrect. On the NCLEX, only consider the information given. Unless information is presented to support other possible conditions (e.g. "three day hx of diarrhea and now hyperventilation), don't "read into" the question.

Respiratory Acidosis:
• Respiratory system is the cause
• Increase in PCO2, decrease in pH
• Compensation - Kidneys reabsorb Bicarb (HCO3).

Metabolic Acidosis:
• Caused by loss of bicarb or build up of acids: lactic acidosis, diarrhea, renal failure, ketones, ammonium intoxication; not caused by respiration.
• HCO3 decreases, pH decreases
• Compensation - hyperventilation to eliminate CO2

Respiratory Alkalosis:
• Caused by excessive ventilation
• Decrease in PCO2, increase in pH
• Compensation - Kidneys excrete HCO3.

Metabolic Alkalosis
• Acid (H+) lost from emesis, diuretics. Retention of HCO3 from medications, hyperaldosteronism.
• Increase in HCO3, Increase in pH
• Compensation - Respiratory centers are not stimulated, which leads to hypoventilation and CO2 retention.

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