Lab Case 197 Interpretation

50 year old male with ROSC,

Metabolic Acidosis – pH 7.16 and HCO3 16mmol/l

Compensation – Expected PCO2 = 1.5 X HCO3 +8 = 32mmHg

AG = Na- (Cl+HCO3) =19

Delta Gap = (AG-12)/(24-HCO3) =0.875

Expected PAO2 = (713xFiO2) – (pCO2 x1.25) =656mmHg

A-a gradient = 656-137 =518

The above patient has a metabolic acidosis with inadequate respiratory compensation or an underlying respiratory acidosis. There is also a raised anion gap and a delta gap of 0.875 indicating that a pure HAGMA exists. There is also a large A-a gradient of 518mmHg.  The patient’s glucose is mildly elevated and lactate moderately elevated. The sodium is on the lower end of normal and the potassium mildly decreased.

In this clinical context of cardiac arrest, the HAGMA is most likely secondary to a lactic acidosis, which is caused by a decreased oxygen delivery from shock and hypoxia.  Toxins in this case also need to be considered as a cause for the HAGMA, as well as the cardiac arrest. The patient is being mechanically ventilated. Hypoventilation in this context can lead to an underlying respiratory acidosis and inadequate compensation. The PCO2 will be high post cardiac arrest because of the lack of ventilation. The very large A-a gradient could be due to an underlying primary problem that has led the patient to arrest, for example PE, pneumonia, pulmonary oedema. It could also be due to a complication from the actual resuscitation and intubation – main bronchus intubation with collapse, pneumothorax.

Post Resuscitation care involves supportive management as well as searching for and treating the cause of the cardiac arrest, and complications of the resuscitation. An ABCDE approach should be used.

A and B – secure definitive airway, confirm ETT placement, ventilate according to underlying lung condition,  maintain sats 94-98%, pass NGT, CXR to see ETT and NGT position and look for complications of resuscitation.

C-IVI access, art line, Fluids as indicated, maintain MAP>65mmHg, and urine output of 0.5ml/kg/hr, 12 lead ECG and bloods to look for cause of arrest

D-assess GCS and pupils, drugs- inotropes, sedation, drugs to treat underlying cause, replace potassium

E-top to toe examination to assess for cause and complications,  maintain BSL between 4-10mmol/l, targeted temperature control

Targeted Temperature Management – the latest ILCOR recommendations for TTM are as follows

  • Maintain temperature between 32-36 C
  • It is recommended for adults after out of hospital cardiac arrest with an initial shockable rhythm who remain unresponsive post ROSC
  • It is suggested for adults post out of hospital cardiac arrest with an initial non shockable rhythm who remain unresponsive after ROSC
  • It is suggested for all adults after in hospital cardiac arrest with any initial rhythm who is unresponsive after ROSC