Other Results on the Arterial Blood Gas

Other results are detailed below.

• Potassium: when low, this indicates a possible metabolic alkalosis [5]
• Chloride : this also has a bearing on metabolic acid-base disorders and is required for calculating the anion gap
• Lactate: immensely important in the diagnosis of sepsis and global hypoperfusion. Remember, an elevated lactate in the presence of abdominal pain suggests ischaemic bowel
• Glucose: remember raised glucose with acidosis can indicate ketoacidosis. Glucose is also an important target in the Surviving Sepsis Campaign: it should be maintained above the lower limit of normal, but less than 8.3 mmol/l
• Haemoglobin: if the Hb is low, there is less O₂ carrying capacity within the blood
• Carboxyhaemoglobin : carbon monoxide (CO) binds to Hb to form carboxyhaemoglobin (COHb); it binds 230-270 times more strongly than O₂ and causes a leftward shift in the oxyhaemoglobin dissociation curve (see above), so less oxygen is available to hypoxic tissues. The main early symptom is headache which occurs when levels reach around 10%. But when levels reach 50-70%, seizures and death can result. When breathing air, CO has a half-life of 3-4 hours, but only 30-90 minutes when breathing 100% O₂. Hyperbaric oxygen reduces this further [9]
• A raised COHb level: is typically seen in patients with smoke inhalation, poisoning from faulty central heating boilers and in cigarette smokers where levels may reach as high as 15% [10]. Car exhaust fumes now contain far lower levels of CO since the conversion to unleaded fuel