0071643192.pdf

ENDOCRINE, METABOLIC, FLUID, AND

ELECTROLYTE DISORDERS

Digoxin directly inhibits the

Na+/K+pump. Severe

hypokalemic and

hypercalcemic states increase

digoxin’s inotropic effect on

myocardium.

■ Rehydration should commence immediately and can usually be safely

done with isotonic 0.9 NS, at least initially, with one-half of the deficit

given to the patient over the first 24 hours.

ELECTROLYTE PUMP PHYSIOLOGY

■ While water freely moves between cells, it follows the gradient set up by
electrolyte cell pumps.
■ Pumps can be active (requiring ATP) or passive. The most important ones
to be familiar with are:
■ Na+/K+ion pump: The major active pump in the human body ex-
changes 3 Na+for 2 K+. This creates Na+and K+gradients across the
cell membrane and also an electrical gradient that is used for many
processes from neurotransmitters to myocardium.
■ H+/K+ion pump
■ In acidosis, H+is pumped intracellularly in place of K+to act as a buffer
for the cell.
■ This is why patients with diabetic ketoacidosis are initially hyperkalemic.
With longstanding DKA, K+is lost in the urine. When the acidosis is cor-
rected, the hypokalemia is unmasked. This only occurs with organic acids
such as ketones that do not freely cross the cell membrane, not with lac-
tate or alcohol.

A 59-year-old male with a history of CHF presents to the ED altered with

pitting edema and crackles in his lungs. His sodium is 114 mEq/L. What

therapies should you initiate?

This patient needs water restriction, diuresis with furosemide, hypertonic

saline and treatment of his underlying CHF. Consider dialysis if he has end-stage

renal disease.

SODIUM

■ Sodium is the major extracellular cation as opposed to K+and Mg^2 +,
which are the major intracellular cations.
■ Sodium regulation is followed passively by water regulation, hence prob-
lems with sodium usually represent problems with water balance.

TABLE 7.2. Categories of Dehydration

HYPOTONIC ISOTONIC HYPERTONIC

TYPE DEHYDRATION DEHYDRATION DEHYDRATION

Etiology Na+loss>H 2 O loss Na+loss=H 2 O loss Na+loss<H 2 O loss

Common causes Vomiting Vomiting Diarrhea

Diuretics HHNK

Third spacing DI

Adrenocortical Inability to drink

insufficiency