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?