BLOOD GAS ANALYSIS REVISION

SHARON HARVEY

5/10/04

REVISION

PaO2

PaCO2

pH

Partial pressure of oxygen normal 10.8 –13.0 kpa

Partial pressure of carbon dioxide normal 4.0 – 6.0 kpa

Normal 7.35 – 7.45

REVISION

HCO3

BE

Concentration of bicarbonate normal 22-26 mmol l-1

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 YOURSELFI. ASSESS OXYGENATION

Is the patient hypoxic?II. DETERMINE STATUS OF THE pH

pH> 7.45 = alkalosispH< 7.35 = acidosis

III. DETERMINE RESPIRATORY COMPONENTPaCO2 > 6.0 kpa = respiratory acidosis

PaCO2 < 4.0 kpa = respiratory alkalosisIV. DETERMINE METABOLIC COMPONENT

HCO3 < 22 mmol l-1 = metabolic acidosis

HCO3 > 26 mmol l-1 = metabolic alkalosis

BLOOD GAS ANALYSIS

A 60 year old man is admitted with exacerbation of chronic obstructive pulmonary disease. His arterial blood gases on air showed:-

pH = 7.29 PaCO2 = 8.5 kpa PaO2 = 8.0 kpa HCO3 = 30.5 mmol l-1

What is the acid-base disturbance and what is the medical management of this patient?

BLOOD GAS ANALYSIS

Answer This patient has an acidosis wit a high

PaCO2 and normal HCO3. This is common in exacerbation of COPD. Treatment would usually involve nebulisers, steroids and antibiotics and possible non-invasive ventilation

BLOOD GAS ANALYSIS

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:-

pH = 7.05 PaCO2 = 8 kpa PaO2 = 15 kpa HCO3 = 16 mmol l-1

What is his acid-base disturbance and why?

BLOOD GAS ANALYSIS

Answer The patient has an acidosis with both a

high PaCO2 and a high HCO3. The PaO2 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????