Question 9.3

Last updated 09/08/2022 - 15:36
 Topic: Acid-Base Disorders
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A 25-year-old patient presents with significant wheeze and shortness of breath after accidental inhalation of vapour whilst cleaning a bathroom. On arrival in the Emergency Department continuous nebulized salbutamol was commenced.

This arterial blood gas was taken 6 hours into the treatment.

Parameter

Patient Value

Adult Normal Range

FiO2

0.4

pH

7.27

7.35 – 7.45

pO2

70 mmHg (9.2 kPa)

pCO2

36.0 mmHg (4.7 kPa)

35.0 – 45.0 (4.7 – 6.0)

SpO2

93%

Bicarbonate

16.0 mmol/L*

22.0 – 26.0

Lactate

8.8 mmol/L*

0.5 – 1.3

Sodium

145 mmol/L

135 – 145

Potassium

2.9 mmol/L*

3.5 – 5.0

Chloride

111 mmol/L*

95 – 105

Glucose

9.7 mmol/L*

3.5 – 6.0

Explain the results and give reasons for the abnormalities, showing your calculations where appropriate.    (30% marks)

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College answer

Not available.

Discussion

The abnormalities are:

  • The A-a gradient is raised: (713 × 0.4) - (36  / 0.8) - 70 = 170. 
  • There is mild acidaemia
  • There is a metabolic acidosis; the SBE is not offered, but the bicarbonate is 16.
  • The CO2 is slightly more than expected. We cannot apply the SBE equation here, but empirical rules for respiratory compensation in metabolic acidosis suggest the CO2 should be (1.5×16)+8 = 32 58.5 mmHg, i.e. there is also a very mild respiratory acidosis here.
  • The anion gap is raised,  (145-(111+16))= 18
  • The delta ratio is (18-12)/(24-16) = 0.7, suggestive of a mixed normal anion gap and high anion gap acidosis
  • There are also electrolyte abnormalities:
    • Hyperlactataemia
    • Hypokalemia
    • Hyperglycaemia

The possible explanations are:

  • Hypoxia is due to some alveolar injury from the cleaning product vapours (clearly this patient mixed a chlorinated bleach with an acid like household ammonia or vinegar, liberating a cloud of chlorine gas) 
  • The chlorine absorption can also account for the elevated chloride, contributing to the NAGMA component of the metabolic acidosis
  • The hyperglycaemia and hyperlactataemia are due to the salbutamol, and the lactate is contributing to the HAGMA component of the metabolic acidosis)

References

Jones, Frederick L. "Chlorine poisoning from mixing household cleaners." JAMA 222.10 (1972): 1312-1312.

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