Acid-Base Disorders with Elevated Serum CO2

Clinical Interpretation

A serum total CO2 level of 43 mEq/L represents a marked elevation requiring urgent evaluation, according to the American Journal of Kidney Diseases 1
Patients with chronic CO2 retention, particularly those with COPD, may have chronic compensated respiratory acidosis, characterized by high PaCO2, high bicarbonate, and near-normal pH, as noted by the Thorax journal 2
The kidneys retain bicarbonate over hours to days to buffer chronic elevation in PaCO2 in patients with COPD, leading to compensatory bicarbonate elevation, as reported in the Thorax journal 2
In COPD patients, 47% have PaCO2 >45 mmHg, and chronic retention leads to compensatory bicarbonate elevation, according to the Thorax journal 3

Primary metabolic alkalosis is less common with this degree of elevation, but would show elevated pH, elevated bicarbonate, and compensatory mild respiratory acidosis, as noted by the Thorax journal 2
Causes of primary metabolic alkalosis include volume depletion, diuretic use, vomiting, or mineralocorticoid excess, as reported in the Thorax journal 3

Obtaining an arterial blood gas analysis is critical to differentiate the underlying disorder, according to the Thorax journal 2
If pH is normal or mildly acidotic (7.35-7.40) with elevated PaCO2 (>46 mmHg), it may indicate chronic compensated respiratory acidosis, as noted by the Thorax journal 2
If pH is elevated (>7.45) with normal or mildly elevated PaCO2, it may indicate primary metabolic alkalosis, according to the Thorax journal 2
Target oxygen saturation of 88-92% rather than normal ranges in patients with COPD or suspected chronic CO2 retention, as recommended by the Thorax journal 4

Excessive oxygen (PaO2 >75 mmHg or 10 kPa) in CO2 retainers increases the risk of worsening respiratory acidosis, as reported in the Thorax journal 3
Controlled oxygen delivery via Venturi mask at 28% or nasal cannula at 1-2 L/min is recommended, according to the Thorax journal 3

Altered mental status, confusion, or decreased consciousness may suggest severe hypercapnia or acidosis, requiring urgent intervention, as noted by the Thorax journal 3
Severe respiratory acidosis (arterial pH <7.25 with elevated PaCO2) may require possible ventilatory support, according to the Thorax journal 3