Internal Medicine

P1: SBT

0521779407-02 CUNY1086/Karliner 0 521 77940 7 June 7, 2007 19:18

Acute Respiratory Alkalosis 57

■Lightheadedness, confusion

■May be asymptomatic

■Respiratory rate and/or depth of inspiration increased by definition,

but not always detected on exam

tests

Laboratory

■Arterial blood gases are diagnostic – PCO2 <35 mmHg, pH >7.50 (see

below for rule of thumb for [HCO3−])

differential diagnosis

■Conditions to distinguish from Acute Respiratory Alkalosis

➣Metabolic acidosis

➣Mixed disorders

Metabolic acidosis and respiratory alkalosis

Metabolic alkalosis and chronic respiratory alkalosis

■Rule of Thumb

➣Expected [HCO3−] in acute respiratory alkalosis:

➣[HCO3−](expected)=24 mEq/L−0.2×(40−PCO2, mmHg)

Observed [HCO 3 – ] should be within 4 mEq/L of the expected value

in uncomplicated acute respiratory alkalosis.

■Causes of Acute Respiratory Alkalosis

➣Hypoxemia

➣Pneumonia

➣Congestive heart failure

➣Pulmonary embolism

➣CNS disorders – infection, trauma

➣Sepsis, particularly with gram negative organisms

➣Anxiety-hyperventilation syndrome

➣Drugs – salicylate intoxication

management

■Determine cause of hyperventilation – e.g., hypoxemia, pulmonary

injury, metabolic acidosis, before intervening

■Ensure adequate oxygen delivery

specific therapy

■For anxiety-hyperventilation syndrome, recirculating device to

increase PCO2 (e.g., paper bag) should produce immediate relief

from symptoms

➣Side effects – if diagnosis incorrect can worsen hypoxemia or

acidemia