# Lab case 389 interpretation

Question 1:

PH = 7.349, that is mild acidaemia

HCO3 = 18 mmHg. so we have metabolic acidosis.

Since we have metabolic acidosis then we need to calculate the compensation and the anion gap.

To calculate the compensation we will use Winter’s formula, that is:

Expected pCO2 = 1.5 x HCO3 + 8 (+/-2).

Accordingly, expected pCO2 = 1.5 x 18 + 8 (+/-2) = 35 (33-37). This patients pCO2 is within the expected range..

(This calculation is for arterial blood gases. Since these results were venous then the expected pCO2 should be higher. Normal arterial gas pCO2 is 40 while normal venous gas pCO2 is 48. Most probably this patient had additional respiratory alkalosis).

Next, we will calculate the anion gap, that is Na – (Cl +HCO3) = 14. So, we have HAGMA.

Since we have HAGMA then we need to calculate the Delta Ratio, that is:

Delta Ratio = (AG – 12) / (24 -HCO3) = 0.33. So we have NAGMA… That usually means hyperchloraemic metabolic acidosis. (This patients chloride is 112 mmol/L).

Other abnormal findings:

Cl = 112 mmol/L, that is hyperchloraemia

Lactate = 9.7 mmol/l, that is severe hyperlactataemia.

Creatinine = 149 umol/L. So we have acute kidney injury.

Final conclusion, this patient had mild hyperchloraemic HAGMA possibly associated with respiratory alkalosis. With associated hyperlactataemia and acute kidney injury.

In the presence of Tachycardia, blood pressure to the low side and high temperature, we should expect and treat the patient as a case of sepsis until proven otherwise.

Other possible causes:

• Thyrotoxicosis
• Sympathomimetic toxicity
• Neuroleptic malignant syndrome
• Serotonin syndrome
• Sunstroke
• We should consider exercise induced syncope causes (HOCM or severe AS).

This patient had sunstroke as he had hot and dry skin in addition to high temperature and confusion (a neurological abnormality).

• 2 large bore cannulas with aggressive IV hydration using normal saline.
• Cooling techniques
• Evaporative cooling by sponging or spraying the skin with lukewarm water and putting fans onto the patient.
• Ice packs in the axillae, groin and around the neck.
• Cooling blankets can also be used, caution with wrapping in cool wet towels as they heat up and insulate quickly, avoid this method.
• Immersion in cold water baths if possible, but beware in patients with altered consciousness / confusion. Ice water baths are recommended but may not be tolerated by conscious patients (and may not be practical in sicker patients).
• For severe cases and very sick patients central active cooling can be used, with cold water lavage via:
• urinary catheter
• nasogastric tube or rectal tube
• thoracic or peritoneal lavage
• cardiopulmonary bypass (if available) has also been used for life-threatening cases.
• Close haemodynamic monitoring. Vasopressors may be needed for hypotension (dopamine is preferred as catecholamines may impair heat dissipation).
• There is no role for antipyretics like paracetamol or ibuprofen. Dantrolene has also been shown to be ineffective.
• Consider broad spectrum antibiotics until sepsis is excluded.

Thanks to Dr Paul Koh for providing the details for this case.

Reference:

** Heat Related Illnesses. Emergency Care Institute/ NEW SOUTH WALES. Heat Related Illness | Emergency Care Institute (nsw.gov.au)