Chemical Path, Long Answer and Short Answer

--- ## *SECTION 1: SODIUM DISORDERS* ### *Long Essay Question* *Question 1.1* A 72-year-old man with a history of chronic obstructive pulmonary disease (COPD) is admitted with pneumonia. He is started on intravenous antibiotics. On day 3 of admission, he becomes increasingly confused and drowsy. Laboratory investigations reveal: - Serum Sodium: 118 mmol/L - Serum Potassium: 4.1 mmol/L - Serum Urea: 3.2 mmol/L - Serum Creatinine: 68 μmol/L - Serum Osmolality: 248 mOsm/kg - Urine Sodium: 45 mmol/L - Urine Osmolality: 520 mOsm/kg *a)* What is the primary electrolyte abnormality and classify its severity? (2 marks) *b)* Based on the clinical presentation and laboratory findings, what is the most likely diagnosis? Explain the pathophysiology. (5 marks) *c)* Discuss the principles of management for this condition, including rate of correction and potential complications of inappropriate treatment. (8 marks) --- ### *Short Answer Questions* *Question 1.2* A 45-year-old woman on lithium therapy presents with confusion. Her serum sodium is 158 mmol/L. *a)* Name two causes of hypernatremia in this patient. (2 marks) *b)* What is the formula to calculate free water deficit? (1 mark) *c)* State two neurological complications of rapid correction. (2 marks) --- *Question 1.3* List four causes of hyponatremia with:*a)* Low serum osmolality (2 marks)*b)* Normal serum osmolality (pseudohyponatremia) (2 marks) --- ## *SECTION 2: POTASSIUM DISORDERS* ### *Long Essay Question* *Question 2.1* A 58-year-old woman with type 2 diabetes and hypertension presents to the emergency department with progressive muscle weakness over 48 hours. She is on metformin, ramipril, and spironolactone. She recently started NSAIDs for osteoarthritis. Laboratory results: - Serum Potassium: 7.2 mmol/L - Serum Creatinine: 245 μmol/L (baseline 95 μmol/L) - Serum Bicarbonate: 18 mmol/L - ECG: Tall peaked T waves, widened QRS complexes *a)* What is the electrolyte disorder and classify its severity? (2 marks) *b)* Explain THREE mechanisms contributing to hyperkalemia in this patient. (6 marks) *c)* Outline the emergency management of this condition, including specific treatments and their mechanisms of action. (7 marks) --- ### *Short Answer Questions* *Question 2.2* A patient with severe diarrhea has a serum potassium of 2.3 mmol/L. *a)* List three ECG changes associated with hypokalemia. (3 marks) *b)* Name two factors that affect the distribution of potassium between intracellular and extracellular compartments. (2 marks) --- *Question 2.3* *a)* What is the transcellular shift? Give two examples of conditions causing potassium to shift into cells. (3 marks) *b)* Calculate the potassium deficit in a 70 kg patient with serum K+ of 2.5 mmol/L (assume normal is 4.0 mmol/L). (2 marks) --- ## *SECTION 3: ACID-BASE DISORDERS* ### *Long Essay Question* *Question 3.1* A 19-year-old woman with known type 1 diabetes mellitus presents to the emergency department with a 2-day history of nausea, vomiting, and abdominal pain. She admits to missing her insulin injections. On examination, she is dehydrated, has deep rapid breathing (Kussmaul respiration), and her breath has a fruity odor. Arterial blood gas: - pH: 7.12 - PaCO₂: 22 mmHg - PaO₂: 95 mmHg - HCO₃⁻: 8 mmol/L - Base Excess: -18 mmol/L Biochemistry: - Serum Glucose: 28 mmol/L - Serum Sodium: 132 mmol/L - Serum Potassium: 5.8 mmol/L - Serum Chloride: 98 mmol/L - Serum Creatinine: 145 μmol/L - Serum Ketones: 5.2 mmol/L *a)* Interpret the arterial blood gas results and identify the primary acid-base disorder. Is there appropriate respiratory compensation? (4 marks) *b)* Calculate the anion gap and explain its significance in this case. (4 marks) *c)* Discuss the pathophysiology of diabetic ketoacidosis and outline the principles of management. (7 marks) --- ### *Short Answer Questions* *Question 3.2* A patient's arterial blood gas shows: pH 7.50, PaCO₂ 48 mmHg, HCO₃⁻ 36 mmol/L. *a)* Identify the primary acid-base disorder. (1 mark) *b)* List three possible causes of this disorder. (3 marks) *c)* What is the expected respiratory compensation for a primary metabolic alkalosis? (1 mark) --- *Question 3.3* *a)* Define the anion gap and provide the formula for its calculation. (2 marks) *b)* List four causes of high anion gap metabolic acidosis. (2 marks) *c)* What is the difference between type A and type B lactic acidosis? (1 mark) --- *Question 3.4* A patient with chronic kidney disease has the following results:pH 7.32, PaCO₂ 38 mmHg, HCO₃⁻ 18 mmol/L *a)* What is the primary disorder? (1 mark) *b)* Use Winter's formula to determine if respiratory compensation is appropriate. (2 marks) *c)* Name the type of renal tubular acidosis most commonly seen in CKD. (2 marks) --- ## *SECTION 4: CALCIUM DISORDERS* ### *Long Essay Question* *Question 4.1* A 68-year-old woman presents with fatigue, constipation, polyu