Water And Electrolyte Balance Case Study

UNIVERSTIY OF MALAWI

COLLEGE OF MEDICINE FACULTY OF MEDICINE Bsc MEDICAL LAB TECHNOLOGY YEAR 4 CLINICAL CHEMISTRY CASE REPORT 2 WATER, ELECTROLYTES AND ACID BASE BALANCE GROUP 2 PATRIC MBULAJE (MC/MLT/06/32) ENOCH MAULANA (MC/MLT/06/31) CHIFUNDO SOKO (MC/MLT/06/36) DATE OF SUBMISSION 19TH June 16, 2009

Clinical presentation A 56 year old man diagnosed with oat cell carcinoma of the lung develops progressive lethargy and confusion.

Laboratory findings Laboratory investigation produced the following results. ELEMENT MEASURED

RESULT OBTAINED

NORMAL RANGE

Sodium

119 mmol/l

135-145 mmol/l

Potassium

4.6 mmol/l

3.6-5.0 mmol/l

Urea

5.0 mmol/l

3.3-6.7 mmol/l

Chloride

77 mmol/l

98-107 mmol/l

Bicarbonate

26 mmol/l

22-30 mmol/l

Glucose

6.2 mmol/l

2.0-6.7 mmol/l

Ur osmolality

857 mOsm/kg

300-900 mOsm/kg

Comment on laboratory findings Plasma sodium levels are low and urine osmolality is close to upper limit. This is suggestive of hyponatremia.

Possible causes of the abnormality In health sodium concentration in the body is controlled by Antideuretic Hormone secreted by the pituitary gland in the hypothalamus. Increase in plasma osmolality which is mainly due to sodium concentration in the blood is sensed by osmo-receptors in the hypothalamus. This induces secretion of Antideuretic hormone (ADH) by the pituitary gland. The hormone act on the distal convoluted tubule of the kidney. This makes the kidney to retain water in the blood thus diluting the ECF and bringing plasma osmolality to normal. In oatcell carcinoma the cancer cells contain neurosecretory bodies which secrete Antideuretic Hormone and other hormones like Adenocorticotrophic Hormone (ACTH) and calcitonin.

This abnormal (ectopic) secretion of ADH causes unnecessary water retention by the kidney leading to dilution of Extra Cellular Fluid. Retention of water by the kidneys explains the excretion of urine of high osmolality by the patient. According to the evidence found the patient has dilutional hyponatremia due to inappropriate ADH secretion.

Clinical and laboratory evidence Lethargy and confusion are typical symptoms of hypomatremia. Low concentration of sodium in the brain ECF result in lethargy. Confusion is due to water intoxication.

Additional laboratory investigation Sodium is the main determinant of plasma osmolality, in dilutional hyponatremia plasma osmolality should be low. Plasma osmolality= 2[Na+]+[urea]+[glucose] 2[119] +5+6.2 =249mOsmo/kg From the calculations plasma osmolality of the patient is lower than the minimum normal level. This is 282 mOsmo/kg. This evidence support the fact that water is being retained thus diluting the ECF. To be certain that this is dilutional hyponatrenia, the patient should have. 1. Normal renal createnine clearance rate. 2. To confirm the dilution of plasma, albumin concentration should be measured and should be low.

Relevant information No clinical evidence of fluid overload (edema) because in dilutional hyponatrenia the excess of fluid is shared equally between the extra cellular compartment and Intracellular compartment.

Reference • • •

Marjorie J. Williams, Robert N. Barnes et al. Hyponatremia, Antidiuretic Hormone Secretion and Oat Cell Carcinoma of the Lung. www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Fluid_retention?OpenD ocument Clinical chemistry WJ Marshall SK Bangert 6th edition (29-31, 149-153)