A 44-year-old patient is admitted post thyroidectomy for Graves’ disease. Seven years ago, the patient had gastric bypass surgery for obesity. Shortly after admission, the serum biochemical findings are:
|
Parameter |
Patient Value |
Adult Normal Range |
|
Sodium |
136 mmol/L |
135 – 145 |
|
Potassium |
5.0 mmol/L |
3.5 – 5.0 |
|
Chloride |
103 mmol/L |
95 – 105 |
|
Bicarbonate |
23.0 mmol/L |
22.0 – 26.0 |
|
Glucose |
5.8 mmol/L |
3.5 – 6.0 |
|
Urea |
5.5 mmol/L |
3.0 – 8.0 |
|
Creatinine |
80 μmol/L |
45 – 90 |
|
Magnesium |
0.60 mmol/L* |
0.75 – 0.95 |
|
Albumin |
35 g/L |
35 – 50 |
|
Protein |
74 g/L |
60 – 80 |
|
Total bilirubin |
12 μmol/L |
< 26 |
|
Aspartate aminotransferase (AST) |
34 U/L |
< 35 |
|
Alanine aminotransferase (ALT) |
40 U/L* |
< 35 |
|
Alkaline phosphatase (ALP) |
188 U/L* |
30 – 110 |
|
γ-Glutamyl transferase (GGT) |
45 U/L* |
< 40 |
|
Calcium corrected |
1.80 mmol/L* |
2.12 – 2.62 |
|
Phosphate |
0.7 mmol/L* |
0.8 – 1.5 |
a) List two potential explanations for the abnormalities seen. (1 mark)
b) List the clinical features which may be associated with these abnormalities? (2 marks)
c) Outline your specific management of the biochemical abnormalities. (3 marks)
Syllabus topic/section:
2.1.7 Renal Intensive Care / Acid-Base and Electrolyte Disorders. L1
Discussion:
This is a core knowledge question which was generally answered well. This is an SAQ with simple lists of hypo and hypercalcaemia issues to complete. Candidates are reminded to only list the number of things asked for. If more than a stipulated number of responses is given (for example part b) asks for three differentials) the examiner will only mark the top three. It is not the responsibility of the examiner to pick the most appropriate of the answers given. This is a requirement of the candidate.
Several candidates omitted part/all of the question. Consider time management strategies to optimise the opportunity to address every question with enough time. We recommend practicing timed answers and practicing answering more than one SAQ consecutively during your preparation.
This is a deliberately timed examination designed to test recall and prioritisation as these are transferrable skills to senior, independent Intensive Care clinical practice. Every question is important for overall success. Candidates who have allocated enough time to address every question of the written paper have a statistically significant higher chance of successful participation and are more likely to be able to demonstrate the standard required on the journey to becoming a transitional fellow of the CICM
To go through this in detail:
So, there is hypomagnesemia, hypophosphataemia, hypocalcemia. Possible explanations for this include:
B) clinical features will mostly be those of hypocalcemia:
The magnesium and phosphate are not low enough to cause clinical features
c) Management, for 3 marks, consists mostly of:
Acute replacement
Medium term replacement
Refractory hypocalcemia
Vetter, Thorsten, and Martin J. Lohse. "Magnesium and the parathyroid." Current opinion in nephrology and hypertension 11.4 (2002): 403-410.
Sutton, R. A. L. "Plasma magnesium concentration in primary hyperparathyroidism." Br Med J 1.5695 (1970): 529-533.
King, R. G., and S. W. Stanbury. "Magnesium metabolism in primary hyperparathyroidism." Clinical Science 39.2 (1970): 281-303.
Hardwick, Laurie L., et al. "Magnesium absorption: mechanisms and the influence of vitamin D, calcium and phosphate." The Journal of nutrition 121.1 (1991): 13-23.
Moe, Sharon M. "Disorders involving calcium, phosphorus, and magnesium." Primary Care: Clinics in Office Practice 35.2 (2008): 215-237.
Cooper, Mark S., and Neil JL Gittoes. "Diagnosis and management of hypocalcaemia." BMJ: British Medical Journal 336.7656 (2008): 1298.
Tohme, J. F., and J. P. Bilezikian. "Hypocalcemic emergencies." Endocrinology and metabolism clinics of North America 22.2 (1993): 363-375.
Wang, Haiyuan, Peter Bua, and Jillian Capodice. "A comparative study of calcium absorption following a single serving administration of calcium carbonate powder versus calcium citrate tablets in healthy premenopausal women." Food & nutrition research 58.1 (2014): 23229.
McKenzie, Travis J., et al. "Recalcitrant hypocalcemia after thyroidectomy in patients with previous Roux-en-Y gastric bypass." Surgery 154.6 (2013): 1300-1306.