Patients with respiratory disease are at risk for inadequate lung ventilation and inadequate tissue oxygenation. Arterial blood gas sampling will provide information about lung ventilation through interpretation of the PCO₂ and tissue oxygenation through interpretation of the PO₂. Patients with certain metabolic diseases and selected drug overdoses are at risk for acid-base abnormalities. Acid base problems are diagnosed through interpretation of arterial pH, PCO₂ and HCO₃ levels.