Lab Case 347 Interpretation

36 year old male presents to ED with swelling and discolouration of his foot after stepping on a piece of coral 1 week ago. The patient reports fever and vomiting.

O/E HR 160 BP 120/70 Temp 37 RR 24 Sats 99 FiO2 .4

CPR  >5 seconds, peripherally shut down with mottled skin

Left foot – swollen, grey/blue in colour extending up to groin. Pulses present


pH 7.30                                              Na 138mmol/l

pCO2 25mmHg                                K 4.0 mmol/l

pO2 156mmHg                                 Cl 102 mmol/l

HCO3 13mmol/l                                 Cr 415 umol/l

B/E -11                                               Lactate 9.5 mmol/l


  1. Describe and interpret the ABG?
  2. What is necrotising fasciitis and how is it managed?



Metabolic Acidosis – pH 7.30 HCO3 13

Compensation – expected PCO2 = HCO3 x 1.5 +8 = 27.5

AG = Na – (Cl+HCO3) = 23

Delta Ratio = change in AG/ Change in HCO3 = 1

Expected PAO2 = (713xFiO2) – (pCO2x1.25) = 285.2 -31.25 =253.95

A-a gradient =PAO2-PaO2 = 97.95

The above ABG shows a compensated HAGMA with a raised A-a gradient. There is a markedly raised creatinine and lactate.

In this clinical context the patient is severely unwell with multiorgan failure likely secondary to a skin infection from the coral wound. The HAGMA is likely due to the lactic acidosis from shock, as well as acute renal failure. The large A-a gradient is likely related to an underlying ARDS. Given the colour of the skin and the clinical picture the patient most likely has necrotising fasciitis.

Necrotising Fasciitis is a rapidly progressive inflammatory infection of the fascia and secondary necrosis of the subcutaneous tissues. The causes of necrotising fasciitis are mixed. Staph aureus and group A haemolytic streptococci are frequently the initiating infecting bacteria, but other aerobic and anaerobic pathogens are present. In lesions sustained in salt water, there is frequently associated Vibrio species

This condition is a surgical emergency and management will include

  • Resuscitation – fluids, respiratory support
  • Antibiotics – as per eTG – meropenem, vancomycin and clindamycin (add cipro/doxy to cover for vibrio species
  • Supportive management – pain relief, aDT
  • Urgent surgical referral and debridement.