Tests
1st tests to order
arterial blood gas
serum bicarbonate
pulse oximetry
Test
May be used to suggest the presence of alveolar hypoventilation, but does not confirm the diagnosis and should not be used to decide when to measure PaCO₂.[40]
Result
SaO₂ <90%
hematocrit (Hct)
Test
Indicated in all patients with suspected or documented daytime and/or nocturnal hypoxemia.
May be used to suggest the presence of alveolar hypoventilation, but is not routinely done.
Result
Hct >45%
Tests to consider
pulmonary function tests
Test
In patients with neuromuscular disease, sleep-disordered breathing is evident when the FVC declines to <65% of predicted.[30] This is associated with the development of sleep-disordered breathing and alveolar hypoventilation.[42] In patients with obesity hypoventilation syndrome, the restrictive pattern is accompanied by a decrease in the expiratory reserve volume.[31]
Result
restrictive pattern on spirometry with reduced total lung capacity
respiratory muscle strength
Test
Known to be decreased in patients with restrictive thoracic disorders, which correlates with the development of sleep-disordered breathing.[16] Also decreased in patients with obesity hypoventilation syndrome due to a combination of abnormal respiratory mechanics and weak respiratory muscles.[32]
Result
decrease in maximal inspiratory and expiratory pressures
CXR
Test
Used to exclude other causes of hypoxemia. In patients with chest wall deformities such as kyphoscoliosis, a Cobb angle >120° (used to measure the spinal curvature) is associated with the development of nocturnal hypoventilation and the development of respiratory symptoms.[43]
Result
normal CXR in most cases; may show signs of congestive heart failure or lower respiratory tract infection if these complicate the condition
polysomnogram
Test
Indicated in patients with chest wall abnormalities and neuromuscular disease to identify patients who would benefit from nocturnal ventilation.[33][34][35][36][37]
Identifies associated obstructive sleep apnea (OSA) in patients with obesity hypoventilation syndrome (OHS).[2] In addition, it may identify patients with OHS prior to developing awake elevations in PaCO₂.[38]
In congestive heart failure with a left ventricular ejection fraction <45% and disturbed sleep, identifies Cheyne-Stokes respiration.[5][6][7][8]
Used in patients with COPD who have suspected overlap syndrome (associated OSA), but use to identify REM-associated hypoventilation is undefined.
Result
demonstrates hypoventilation, particularly during REM sleep; may show obstructive or central apneas; sleep architecture is fragmented with an increase in arousals during the night
echocardiogram
Test
Documents the development of pulmonary hypertension in patients with obesity hypoventilation syndrome, neuromuscular disease, and COPD. In patients with Cheyne-Stokes respiration, documents the severity of left ventricular dysfunction.[3][5][6][7][8][39]
In patients with congestive heart failure and left ventricular ejection fraction <45%, Cheyne-Stokes respiration is reported in 33% to 42% of patients, with a prevalence as high as 56% in inpatients awaiting cardiac transplantation.[5][6][7][8]
Result
demonstrates pulmonary hypertension (mean pulmonary artery pressure >25 mmHg)
thyroid-stimulating hormone
Test
Indicated in patients with hypercapnia who are suspected of having or who have symptoms/signs of hypothyroidism.
Result
elevated if primary hypothyroidism
PHOX2B gene
Test
If there is a clinical suspicion for congenital central alveolar hypoventilation, mutations in the paired-like homeobox 2B (PHOX2B) gene should be evaluated, as mutations are noted in up to 91% of these patients.[24] Suspected instances include newborns with signs of hypoventilation, or patients who present later in life with signs of hypoventilation following anesthesia or a pulmonary infection.[27]
Result
heterozygous mutation
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