BLOOD GAS ANALYSIS REVISION SHARON HARVEY 5/10/04

REVISION n PaO 2 n PaCO 2 n pH n Partial pressure of oxygen normal 10.8 –13.0 kpa n Partial pressure of carbon dioxide normal 4.0 – 6.0 kpa n Normal 7.35 – 7.45

REVISION n HCO 3 n BE n Concentration of bicarbonate normal mmol l -1 n Base excess – the quantity of strong acid or base required to restore pH to normal. Normal range +2mmol l -1 to – 2mmol l -1 a positive BE indicates an excess of base while a negative value indicates a deficit of base.

QUESTIONS TO ASK YOURSELF I. ASSESS OXYGENATION Is the patient hypoxic? II. DETERMINE STATUS OF THE pH pH> 7.45 = alkalosis pH< 7.35 = acidosis III. DETERMINE RESPIRATORY COMPONENT PaCO 2 > 6.0 kpa = respiratory acidosis PaCO 2 < 4.0 kpa = respiratory alkalosis IV. DETERMINE METABOLIC COMPONENT HCO 3 < 22 mmol l -1 = metabolic acidosis HCO 3 > 26 mmol l -1 =metabolic alkalosis

BLOOD GAS ANALYSIS n A 60 year old man is admitted with exacerbation of chronic obstructive pulmonary disease. His arterial blood gases on air showed:- n pH = 7.29 n PaCO 2 = 8.5 kpa n PaO 2 = 8.0 kpa n HCO 3 = 30.5 mmol l -1 n What is the acid-base disturbance and what is the medical management of this patient?

BLOOD GAS ANALYSIS n Answer n This patient has an acidosis wit a high PaCO 2 and normal HCO 3. This is common in exacerbation of COPD. Treatment would usually involve nebulisers, steroids and antibiotics and possible non-invasive ventilation

BLOOD GAS ANALYSIS n A 30 year old man is admitted with status epilepticus. He is given intravenous diazepam. Arterial blood gases on 15 l/min via a reservoir bag mask showed:- n pH = 7.05 n PaCO 2 = 8 kpa n PaO 2 = 15 kpa n HCO 3 = 16 mmol l -1 n What is his acid-base disturbance and why?

BLOOD GAS ANALYSIS n Answer n The patient has an acidosis with both a high PaCO 2 and a high HCO 3. The PaO 2 is lower than expected because the patient was breathing around 70% oxygen. He has a lactic acidosis from prolonged fitting and a respiratory acidosis from intravenous diazepam.

QUESTIONS????