Lab case 351 interpretation

Question 1:

PH = 7.53, that is mild alkalaemia

pCO2 = 25 mmHg, that is low (<40), so we have respiratory alkalosis.

Next we check for compensation. From the history of the case the condition looks acute. For acute respiratory alkalosis, we expected the HCO3 to drop by 2 for every 10 pCO2 below 40. Here, pCO2 is 15 mmHg below 40.

Accordingly expected HCO3 is 24 – (15 x 0.2) = 21 mmHg. SO we have well compensated acute respiratory alkalosis.

AG = 137 – (110 + 21) = 6, that is normal.

The other abnormal finding in these blood gases was lactate of 4 mmol/L. That was found to be caused by the excessive doses of Salbutamol that this patient was using.

The final conclusion was: Well compensated acute respiratory alkalosis.

We figured the cause of high lactate by looking at the causes of hyperlactataemia.

Type A hyperlactataemia.

  • Shock / reduce organs perfusion
  • Severe hypoxia
  • Severe anaemia
  • CO poisoning

Type B hyperlactataemia (We use the mnemonic BLACK MIST)

  • B = beta agonists
  • L = liver failure
  • A = alcohol, anticonvulsants (Valproate)
  • C = cyanide
  • K = ketoacidosis
  • M = metformin
  • I = inborn error of metabolism
  • S = salicylate / sepsis
  • T = thiamine deficiency

 Question 2:

Features of severe asthma

On history and examination

  • Laboured respiration
  • Tachycardia > 110 / min
  • RR > 25 / min
  • Unable to complete a sentence in 1 breath / speaks in words

Bed side investigation

  • SPO2 < 90 on room air
  • PEFR < 200 L/min
  • FEV1/PEFR is < 40 or patient was unable to perform the test

 Features of life threatening asthma

 On history and examination

  • Exhaustion
  • Confusion or coma
  • Cyanosis
  • Silent chest
  • Inability to speak
  • Poor respiratory effort
  • Dysrhythmia/ Bradycardia
  • Hypotension

 Bed side investigation

  • SPO2 < 90 despite supplemental O2
  • FEV1/ PEFR is inappropriate

The expected blood gas finding in patient with asthma is respiratory alkalosis. The presence of normal PH usually indicates severe asthma. Acute respiratory acidosis in asthmatic patient is an indication for intubation.

Question 3:

This patient had mild asthma and anxiety.

In addition to the usual treatment of asthma (Bronchodilators and steroids), this patient was given a dose of diazepam. Diazepam calmed patient anxiety and led to total relieve of the patient symptoms.

The hyperventilation associated with anxiety is associated with deleterious effect during asthmatic episodes. Asthmatic patients have problem with exhalation, tachypnoea, will prevent the patient from exhaling completely, this will lead to gas trapping and increase feeling of shortness of breath and more difficulties in ventilation.