POTASSIUM HOMEOSTASIS

Mohammed Almeziny BsPharm R,Ph. Msc PhD

Clinical Pharmacist

Introduction

POTASSIUM is required for neuromuscular

tissues.

intracellularly (98%).

approximately 3500 mmol.

50 mmol is located in extracellular.

(Hak & Dunham, 1983; Scribner et al, 1956).

Protective effect of potassium

An antihypertensive effect.

Inhibitory effect on free radical formation.

Reduce the relative risk of stroke mortality.

Offer a protective effect on renal arterioles

Daily requirement

1-2 mmol/kg. (1mmol =1mEq 39.1 mg)

HYPOKALEMIA

DEFINITION

Hypokalemia is defined as a serum

potassium concentration less than 3.5

mmol/L. Normal levels range from 3.5 to 5

mmol/L

(Young & Koda-Kimble, 1988)

CAUSES

The most common cause of hypokalemia is drug therapy.

Shifting of potassium from extracellular to intracellular.

Reduction in potassium intake (Lindman, 1976; Lawson et al, 1979; Nardone et al, 1978;

AMA, 1983)

Blood pH effect

0.1 unit potassium of approximately 0.6 mmol/L;

0.1 unit corresponds to slightly less 0.6mmol/L.

Clinical presentation

Usually are asymptomatic between 3.5-3 mmol/l

Malaise, weakness, fatigue and myalgia.

Renal tubular disorders, myocardial excitability, and metabolic abnormalities

(AMA, 1983; Stanaszek & Romankiewicz, 1985)

Calculate adult K deficit in hypokalemia

1 mmol/L fall in serum potassium from 4 to 3 mmol/L =200 mmol.

< 3mmol/L, = 200 to 400 mmol for each 1 mmol/L

*After correct acid-base status of measured serum level.

June 1, 1998, Volume 55, Issue 11

Most hospitals removing KCl concentrate from patient units

, ISMP reports

Institute for Safe Medication Practices (ISMP).

JAMA / volume:280 (page: 1444)Promoting Patient Safety by Preventing Medical Error Lucian L. Leape, MD; et al October 28, 1998

Treatment and Prevention

Correct coexisting magnesium depletion.

Give potassium salts, primarily by the oral

route.

POTASSIUM CHLORIDE is the

supplement of choice

(Stanaszek & Romankiewicz, 1985; Beck et al, 1982).

Intravenous indication

Intravenous potassium chloride is

indicated primarily when oral therapy is

not feasible.

Also indicated for the treatment of

DIGITALIS-induced arrhythmias.

(Cohen, 1979; McCarron, 1975).

INTRAVENOUS.

POTASSIUM CHLORIDE MUST BE DILUTED BEFORE INFUSION.If serum potassium is > 2.5 mmol/L and neuromuscular and cardiac abnormalities are minimal (and renal function is not impaired),concentrations not exceeding 40 mmol/L and at a rate of 10 to 15 mmol/hour. Doses should not exceed 100 to 300 mmol/day (AMA, 1983).

INTRAVENOUS. Cont’d

If serum potassium is < 2 mmol/L and muscle paralysis or cardiac abnormalities are present.

Concentrations not exceeding 60 mmol/L at a rate of 40 mmol/hour. Doses should not exceed 400 mmol/day (AMA, 1983).

Administration of potassium in high concentration should be given after strict evaluation.

Intravenous Rate of Administration

Should be kept within 10 to 20 mmol/hour. Frequent biochemical and ECG monitoring is necessary when rates >10 mmol/hour.The faster rates should be continued for only short periods of time

(Lawson, 1976; Lawson & Henry, 1977; van der Linde et al, 1977; Porter, 1976; Beeson et al, 1958; Schwartz, 1976; Dipiro et al, 1989).

Potassium infusion I.V. order

I.V fluid Concentration mmol/L

Rout of infusion

Peripheral/ Central

Infusion rate mmol/h

Ward ECG monitoring Yes/no

ORAL

Liquid, enteric-coated, and slow release preparation.Slow release:

1) Sugar-coated (slow-K) or film coated (K-Tab) tablets;

2) KCL incorporated into wax matrix, controlled release tablets (K-Dur)

3) A gelatin capsule containing microencapsulated KCL crystals that are coated with a water polymer

Food, Standard Amount Potassium (mg)

Calories

Sweetpotato, baked, 1 potato (146 g) 694 131

Tomato paste, ¼ cup 664 54

Beet greens, cooked, ½ cup 655 19

Potato, baked, flesh, 1 potato (156 g) 610 145

White beans, canned, ½ cup 595 153

Yogurt, plain, non-fat, 8-oz container 579 127

Tomato puree, ½ cup 549 48

Clams, canned, 3 oz 534 126

Yogurt, plain, low-fat, 8-oz container 531 143

Prune juice, ¾ cup 530 136

Food, Standard Amount Potassium (mg) Calories

Carrot juice, ¾ cup 517 71

Blackstrap molasses, 1 Tbsp 498 47

Halibut, cooked, 3 oz 490 119

Soybeans, green, cooked, ½ cup 485 127

Tuna, yellowfin, cooked, 3 oz 484 118

Lima beans, cooked, ½ cup 484 104

Winter squash, cooked, ½ cup 448 40

Soybeans, mature, cooked, ½ cup 443 149

Rockfish, Pacific, cooked, 3 oz 442 103

Cod, Pacific, cooked, 3 oz 439 89

Bananas, 1 medium 422 105

Food, Standard Amount Potassium (mg) Calories

Spinach, cooked, ½ cup 419 21

Tomato juice, ¾ cup 417 31

Tomato sauce, ½ cup 405 39

Prunes, stewed, ½ cup 398 133

Peaches, dried, uncooked, ¼ cup 398 96

Pork chop, center loin, cooked, 3 oz 382 197

Milk, non-fat, 1 cup 382 83

Apricots, dried, uncooked, ¼ cup   378 78

Rainbow trout, farmed, cooked, 3 oz 375 144

Pork loin, center rib (roasts), lean, roasted, 3 oz

371 190

Food, Standard Amount Potassium (mg) Calories

Buttermilk, cultured, low-fat, 1 cup 370 98

Cantaloupe, ¼ medium 368 47

1%-2% milk, 1 cup 366 102-122

Lentils, cooked, ½ cup 365 115

Honeydew melon, 1/8 medium 365 58

Kidney beans, cooked, ½ cup 358 112

Plantains, cooked, ½ cup slices 358 90

Split peas, cooked, ½ cup 355 116

Orange juice, ¾ cup 355 85

Yogurt, plain, whole milk, 8 oz container

352 138

Continuous Subcutaneous Infusion

Effective in elderly patients who do not need acute potassium repletion.

Monitoring Parameters

Should be monitored at least every two weeks in ambulatory patients with mild deficiencies and in patients requiring prophylactic.

After a pattern is established, monitoring every 3 to 6 months is adequate (Stanaszek & Romankiewicz, 1985).

HYPERKALEMIA

Introduction

Hyperkalemia is a potentially life-

threatening illness, which can be

difficult to diagnose clinically because

of paucity of reliable signs and

symptoms.

Definition

Hyperkalemia is defined as a serum potassium concentration greater than 5.5 mmol/LSome hospitals > 5mmol/L

(Cox, 1981).

Clinical Manifestation

cardiac excitability, possibly

progressing to ventricular fibrillation

and asystole.

Mortality/Morbidity

Reported death rates rate range up to 67% if

severe hyperkalemia is untreated.

Gender: Male = Female

Causes Decreased or impaired potassium excretion.

Acute or chronic renal failure (most common).

Potassium sparing diuretics.Urinary obstruction. Sickle cell disease. Addison disease.Systemic lupus erythematosus (SLE).

Causes cont’d

Additions of potassium into extracellular space:

potassium supplements (eg, PO/IV

rhabdomyolysis,

hemolysis (eg, venipuncture, blood transfusions,

burns, tumor lysis).

Causes cont’d

Transmembrane shifts

Acidosis.

Medication effects (eg, acute digitalis

toxicity, beta-blockers, succinylcholine).

Causes cont’d

Pseudohyperkalemia: Improper blood collection (eg, ischemic

blood draw from venipuncture technique)Laboratory errorLeukocytosisThrombocytosis.

Classification of Hyperkalemia

Serum sodium is usually decreased, and acidosis is usually present.

The relationship between serum potassium and symptoms is not consistent.

Classification of Hyperkalemia cont’d

MINIMAL TOXICITY - < 6.5 mmol/L. MODERATE TOXICITY - 6.5-8 mmol/L give lassitude, fatigue, and weakness.SEVERE TOXICITY - >8 mmol/L, complete neuromuscular paralysis may dominate the clinical picture. Death from cardiac arrest occurs usually at 10 to 12 mmol/L. It may occur at lower levels if cellular potassium is severely depleted.

Treatment

Urgency of therapy depends on EKG findings and level of serum potassium.

If serum K is greater than 8 mmol/L. If the EKG shows the changes of

hyperkalemia.If the patient is extremely symptomatic.

Goal of therapy

stabilizing the myocardium

Shifting potassium from the extracellular to the intracellular compartment.

Promoting the renal excretion and GI loss of potassium.

CALCIUM

The first drug to be used for severe hyperkalemia (> 7.0 mmol/L) when the ECG also manifests significant abnormalities.

Antagonizes cardiac toxicity.

onset < 5 min and lasts 30-60 min.

Calcium chloride is the preferred salt.

Calcium chloride is very irritating, and should only be given via a central venous catheter.

Enhance the effects of the cardiac glycoside by causing arrhythmias

SODIUM BICARBONATE

Shift potassium intracellularly.

Onset of action is within minutes and lasts approximately 15-30 min.

Blood pH should be monitored to avoid excess alkalosis.

INSULIN/DEXTROSE

Enhances intracellular potassium shift.

This regimen will lower serum potassium by 1 to 2 mmol/L within 30 to 60 minutes with the decrease lasting for several hours (Saxena, 1989).

ADULT DOSE

Administer 25 g of dextrose (250 ml of a 10% solution) I.V + 10 units of regular insulin over 30 minutes, and then continue the infusion at a slower rate. (Saxena, 1989).

Or, 50 ml of a 50% dextrose solution with 5 to 10 units of regular insulin may be administered I.V over 5 minutes.

PEDIATRIC DOSE

0.5 to 1 g/kg/dose followed by 1 unit of regular insulin intravenously for every 4 grams of glucose infused; may repeat every 10 to 30 minutes (Barkin, 1986).

HYPEROSMOLARITY

It must be remembered that 50% dextrose (2525 mOsm/L) , and even 25% dextrose (1330 mOsm/L) , are very hyperosmolar and may be sclerosing to peripheral veins (Chameides, 1988).

Peripheral veins can tolerate up to (900 mOsm/L).

Administration of hypertonic solutions via central lines is preferred, if possible.

SODIUM POLYSTYRENE SULFONATE

SPS is a cation exchange resin.

Onset 2-12 h, (longer when administered rectally).

SORBITOL is added to combat the constipating effect of the cation-exchange resin (Gilman et al, 1990)

Multiple doses of SPS are usually necessary.

BETA-2-AGONIST

Appears to be a safe and reasonably effective means of treatment while waiting for dialysis or other potassium removing therapies to be initiated.

Use with caution in hyperthyroidism, diabetes mellitus, or cardiovascular disorders.

Diuretics

Effects of diuretics are slow and frequently take an hour to begin.

Avoid use in patients with anuria

HEMODIALYSIS

Peritoneal and hemodialysis are effective methods.

Slow to be practical in treatment of acute poisoning.

Patients who cannot tolerate fluids or have kidney dysfunction may benefit from dialysis (Ellenhorn & Barceloux, 1988).

Summary

Chronic Vs Acute

Symptomatic Vs Asymptomatic

Level

Questions?