Lab Case 13 – Interpretation

Critically unwell patient with

1. Altered GCS

2. Shock

3. Tissue hypoxia

4. Possible airway and ventilation compromise


Burns – airway, skin

Hypoxic brain inury

Poisoning – CO, CN

Other injury – head injury, blast injury …

Medical causes – hypoglycaemia, CVA, AMI

Future work and income related

pH – acidaemia

pCO2 high – respiratory acidosis –

Causes – hypoventilation, hypoxic brain injury, head injury

HCO3 low – metabolic acidosis

Causes – shock – tissue hypoxia, CO, CN, trauma

so, mixed respiratory and metabolic acidosis

pO2 144 – lower than expected on 15 litre non rebreather – severe hypoxia

A-a gradient : (760-47)FiO2 -1.25(pCO2) – pO2 = 713*0.8 – 1.25*56 – 160 = 340

extremely high – VQ mismatch, shunt present due to airway burns, lung injury (chemical injury, aspiration, lung contusion, haemopneumothorax), exacerbation of underlying chronic lung disease.

Interpretation – Mixed respiratory and metabolic acidosis with altered mental state requiring urgent airway control and optimizing of ventilation. This patient requires urgent RSI and intubation with 100% oxygen (likely to have high CO levels).

Caution with intubation – Airway burns and oedema, shock (requires fluid preload, use cardioprotective strategy to induce, possible C spine injury. Muscle relaxant – suxamethonium should be ok in acute burns (check K ), consider Rocuronium. Anticipate ventilation difficulty.

Oxygen delivery:

low flow systems – nasal prongs (NP), hudson mask, non rebreather

high flow systems – CPAP/BiPAP, ventilator, high flow NP

Nasal prongs – provide 24-40% oxygen at 1-5 litres/min

Face mask – provides 28-60% oxygen at 5-10 litres/min

Non Rebreather – provides up to max of 80% at 15litres/min