Question 9.1

A 75-year-old patient presents with diarrhoea, vomiting and abdominal discomfort. There is a history of previous ingestion of a homemade health tonic.

a) Explain the following results and provide a rationale for the abnormalities. (30% marks)

Parameter	Patient Value	Adult Normal Range
FiO2	0.21
pH	7.00*	7.35 – 7.45
pO2	101 mmHg (13.4 kPa)
pCO2	20.0 mmHg (2.6 kPa)*	35.0 – 45.0 (4.7 – 6.0)
SpO2	97%
Bicarbonate	6.0 mmol/L*	22.0 – 26.0
Base Excess	-22 mmol/L*	-2 to +2
Lactate	1.0 mmol/L	0.5 – 1.3
Sodium	120 mmol/L*	135 – 145
Potassium	5.1 mmol/L*	3.5 – 5.0
Chloride	90 mmol/L*	95 – 105
Urea	41.7 mmol/L*	3.0 – 8.0
Creatinine	1284 μmol/L*	45 – 90

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College answer

Not available.

Discussion

This homemade tonic. Was it antifreeze? Be honest. Whatever it was, it has caused acute renal failure and severe metabolic acidosis, which means the possibilities are endless.

These results demonstrate:

A relatively normal oxygenation
There is a severe metabolic acidosis
The CO₂ is appropriately depressed (the expected CO₂ is around 18 using the SBE method, or (1.5×6)+8 = 17 using the classical Boston calculations).
The anion gap is raised, (120-(90+6) = 24
The delta ratio is therefore (24-12)/(24-6) = 0.66, i.e. a mixed metabolic acidosis exists (both high and normal anion gap components are present)
There is renal failure, which is clearly subacute, in the sense that it takes a few days for the urea to climb to 40.

This does not fall neatly into any specific toxidrome, except perhaps for ethylene glycol toxicity, where there would be both renal failure and a high anion gap. But that would typically give a spuriously elevated lactate, and anyway people do not usually regard antifreeze as a "health tonic", suggesting some other explanation is required. Salicylate toxicity is probably a better choice, as it could legitimately occur as the result of drinking an infusion of willow bark, which probably contributed to the death of Ludwig von Beethoven.

Broadly, there are two possibilities: either something has either attacked the kidneys directly, or merely caused diarrhoea and vomiting so severe that the patient is severely dehydrated and has developed pre-renal failure. In case the reader is interested, Gabardi et al (2007) and Claure-Del Granado et al (2021) list numerous nephrotoxic complimentary medicines, such as:

Chromium picolinate
Creatine monohydrate
L-lysine
Larrea tridentate (Chaparral)
Pausinystalia yohimbe (Yohimbe)
Salix daphnoides (Willow Bark)
Tripterygium wilfordii (Thunder God Vine)
Uncaria tomentosa (Cat's Claw)

Thus, a plausible rationale for the abnormalities could be:

Self-poisoning with a nephrotoxin
Acute renal failure due to this
A period of dehydration due to diarrhoea and vomiting which has exacerbated this

References

Gabardi, Steven, Kristin Munz, and Catherine Ulbricht. "A review of dietary supplement–induced renal dysfunction." Clinical Journal of the American Society of Nephrology 2.4 (2007): 757-765.

Claure-Del Granado, Rolando, and María Espinosa-Cuevas. "Herbal Nephropathy." Nephrology and Public Health Worldwide 199 (2021): 143-154.

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