Question

A 70 kg 68 y/o male sees his cardiologist for a follow-up following his myocardial infarction 3 months earlier. He has been taking digoxin and Lisinopril^TM since his MI. At the follow-up, he complains of shortness of breath and has to sleep sitting up in his recliner. He also complains of fatigability and swelling of his ankles and hands. A physical examination finds that he has distended jugulars and pitting edema in the lower legs. His breathing was rapid 22 breaths/min) and rales were heard in the both sides at the base of the lungs. He does not have a fever, but his pulse is 116 bpm and his blood pressure is 110/80. The physician immediately admits him and orders a blood and urine analyses with the results as follows:

Blood			Urine
[Na+]	128 mEq/L		[Na+]	150 mEq/L
[K+]	3.0 mEq/L		[K+]	65 mEq/L
[Cl-]	98 mEq/L		[Cl-]	120 mEq/L
[HCO3-]	21 mEq/L		[HCO3-]	15 mEq/L
Creatinine	1.2 mg/dl		Creatinine	128 mg/dl
PCO2	24 mmHg		24 hr volume	750 ml
pH	7.51		Osmolality	600 mOsm

a) Calculate the volumes of ECF and ECV in this Px assuming the total body osmoles of the Px is 12 Osm. Do these volumes have any impact on the symptoms the Px is exhibiting and what is the cause of these changes (ie, what is the pathology)?

b)   How does this pathology alter the renal sodium handling in this Px and what are the mechanism(s) for developing hyponatremia?

c)   The physician orders an infusion of 2L of 3% saline with 40 mg of Lasix^® given twice a day for three days. Calculate how this treatment would impact the Px’s symptoms assuming the osmolarity of the urine dropped to 400 mOsm?

d) What are the renal mechanisms affected by this treatment. Does this treatment impact the Px’s hypokalemia? If so, why?

Answer 1

The patient described in the question is suffering from heart failure. The symptoms are classic for the condition.

1. First of all, let's calculate the ECF volume of the patient. ECF can be calculated as 20% body weight. Thus ECF= 0.2 x 70 = 14L. Now, Effective Circulating Volume is a dynamic indicator of arterial blood currently perfusing the body tissues I.e the part of ECF within vascular spaces.
2. Although patients with cardiac failure have edema, the body perceives that there is less fluid because less amount of blood pressure is sensed by the baroreceptors and chemoreceptors and also the renal afferent Arterioles. Thus, by the neurohumoral mechanism of body fluid adjustment, the body tries to retain sodium and water so that the perceived state of low body water disappears. This is done by secretion of ADH/Vasopressin. It is a type of dilutional hyponatremia vecause it occurs as a result of impaired renal water excretion.
3. Lasix is actually Furosemide which is a loop Diuretic drug. It acts on the Na-K+-2Cl- transporter in thick ascending loop of Henle. It causes sodium, potassium and chloride loss in urine. This treatment will reduce the edema of the patient and thus breathlessness too.
4. It acts on the thick ascending loop of Henle to reversibly inhibity the soiduk potassium chloride transporter and inhibits the reabsorption of these ions. Extensive use of any Diuretic can lead to electrolytes imbalance and this is also the care here. Lasix causes hypokalemia but not as much when compared to the this idea diuretics. Thus, it is a better choice here.