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.