Download potassium homeostasis

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

Rout of infusion Ward

Concentration

Peripheral Infusion rate / Central ECG monitoring

mmol/L

mmol/h

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

136

530

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 lifethreatening 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/L Some 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 error Leukocytosis Thrombocytosis.

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?