Diagnosis and Management of Obesity Hypoventilation Syndrome during Labor

Table 2

Impact of physiologic changes of pregnancy on diagnostic findings associated with obesity hypoventilation syndrome.

Diagnostic finding	Pertinent physiologic changes of pregnancy	Impact of pregnancy on likelihood of meeting diagnostic criteria
BMI >30 kg/m^2	Healthy weight gain in pregnancy, which can be up to 40 pounds	Increased likelihood
Awake hypercapnia, PaCO2 >45 mm Hg	Progesterone-mediated 40–50% increase in minute ventilation causing respiratory alkalosis	Decreased likelihood
Awake hypoxemia, PaO2 <70 mm Hg	PaO2 increases 10 mm Hg during normal pregnancy due to hyperventilation, a lower PaCO2, and a smaller drop in venous oxygen concentration due to increased cardiac output	Decreased likelihood
Elevated serum bicarbonate ≥27 mEq/L	Respiratory alkalosis with renal compensation, which decreases plasma bicarbonate	Decreased likelihood
Polycythemia, hemoglobin >16 g/dL	Physiologic anemia of pregnancy, 30% increase in plasma volume with lower increase in red cell mass	Decreased likelihood
Restrictive lung pattern on PFT, FVC <80% predicted	Lung restriction due to enlarged uterus	Increased likelihood
Elevation diaphragm on chest X-ray	Elevation of diaphragm due to enlarged uterus	Increased likelihood

BMI, body mass index; FVC, forced vital capacity; kg, kilogram; L, liter; m, meter; mEq, milliequivalent; mm Hg, millimeter of mercury; P_aCO₂, partial pressure of carbon dioxide; P_aO₂, partial pressure of oxygen; PFT, pulmonary function test.