Fluid and Electrolyte Physiology

Posted by e-Medical PPT
Defined as serum [Na+] less than 136 mEq/L
Water shifts into cells causing cerebral edema
125 mEq/L – nausea and malaise
120 mEq/L – headache, lethargy, obtundation
115 mEq/L – seizure and coma

1.  Assess plasma osmolality
2.  Assess volume status of patient
Hypervolemic, Euvolemic, Hypovolemic
3.  Assess Urine Sodium Concentration
Needed for definitive diagnosis, not needed for treatment purposes
4.  Calculate Na+ Deficit
0.6 x weight (kg) x (130 – plasma [Na+])
5.  Correct at no more than 0.5mEq/L per hour or 12 mEq/L per 24 hours

Defined as serum [Na+] greater than 146 mEq/L
Lethargy, weakness, and irritability that progress to seizure, coma, and death
Usually occurs in adults with altered mental status or no access to water

1.  Assess volume status
2.  Measure urine [Na+]
3.  Calculate water deficit
0.6 x weight (kg) x ([Na+]/140 -1)
4.  Correct with free water no faster than 0.5 mEq/L/hour or 12 mEq/L/day

Defined as a serum [K+] greater than 4.6 mEq/L
Changes in cellular transmembrane potentials can lead to lethal cardiac arrhythmias
Most often associated with renal impairment coupled with exogenous K+ administration or drugs that increase K+
Transcellular shifts – acidosis, succinylcholine, insulin deficiency, massive tissue destruction
Massive blood transfusions
Pseudohyperkalemia - Thrombocytosis, hemolysis, leukocytosis
Urine K+ excretion rate can be used to determine exact cause of hyperkalemia

Drugs causing hyperkalemia – K+ sparing diruetics, ACEI, NSAIDs, Heparin, Cyclosporin, Tacrolimus, Bactrim
EKG Changes
5.5 – 6.5 mEq/L – peaked T-waves
6.5 – 7.5 mEq/L – loss of P-waves
> 8.0 mEq/L – widened QRS

Defined as serum [K+] less than 3.6 mEq/L
Occurs in up to 20% of hospitalized patients
2.5 mEq/L – muscular weakness, myalgia
<2.5 mEq/L – cramps, parasthesias, ileus, tetany, rhabdomyolisis, PVCs, A-V block, V-tach, V-fib

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