4. Potassium homeostasis
.
The ratio of intracellular to extracellular
potassium determines the cellular membrane
potential.
Small changes - profound effects on the function
of the cardiovascular and neuromuscular systems.
5. Cellular K+ Content
Intracellular K+ affects intra to extracellular K+
With K+ depletion ,
K+ loss from ECF > ICF loss
causing increased Ki + / Ke+
K+ depletion : hyperpolarization
K+ retention : depolarization
9. Factors modifying transcellular
K+ distribution
Acid base status
Pancreatic hormones : insulin , glucagon
Catecholamines
Aldosterone
Plasma Osmolality
Exercise
Cellular K+ content
10. Acid Base Status
Alkalemia promotes K+ uptake by cells
Acidemia diminishes K+ uptake by cells
H+ K+
K+ H+
ACIDOSI
S
ALKALOSIS
An oversimplification in acidosis
11.
12. Exercise
Recurrent contraction increases K+ egress from muscle
Modest exercise : high K+ in ECF in local environment
produces vasodilatation & thereby increased regional blood
flow
Severe exercise : increase plasma K+ modestly
Physical training increases Na+K+ATPase activity in skeletal
muscle which helps skeletal muscle to take up K+ again
13. RENAL ADAPTATION
Kidneys adapt to both acute and chronic
alterations in potassium intake.
obligatory renal losses are 10-15 mEq/d.
Maintain potassium homeostasis until the glomerular
filtration rate drops to less than 15-20 mL/min.
In the presence of renal failure, the proportion of
potassium excreted through the gut increases.
However, as renal function worsens, the kidneys may not
be capable of handling an acute potassium load.
19. RENAL ADAPTATION
Excretion is increased by
(1) aldosterone,
(2) high sodium delivery to the collecting duct (eg, diuretics),
(3) high urine flow (eg, osmotic diuresis),
(4) high serum potassium level
20. Invitro studies
Aldosterone stimulates Na+K+ATPase and thereby activating
Na + influx
Aldosterone
21. Hypokalemia
Defined as plasma concentration of K+ < 3.5 mEq/L
Mild Hypokalemia : 3.0 – 3.5 mEq/L : asymptomatic
Moderate Hypokalemia < 3.0 mEq/L : symptomatic
Severe Hypokalemia <2.5 mEq/L
Clinical manifestations of hypokalemia vary greatly between
individual patients &
their severity depends on degree of hypokalemia
23. PSEUDOHYPOKALEMIA
-spurious
"pseudohypokalemia" occurs in acute myelogenous
leukemia
large number of leucocytes in the blood specimen (stored at
room temperature)
sponge-up the extracellular potassium => artefactually low
serum potassium reading
24. Decrease K intake
Dietary – starvation, clay ingestion
IV therapy
26. GI LOSS of K+
Secretory diarrhea
GIT fistula or small bowel enterostomy
malabsorption syndrome
excessive, voluminous vomiting
laxative abuse
27. Transtubular potassium gradient
(TTKG)
To account for the potentially confounding effect of urine
concentration on the interpretation of the urine potassium
the serum-to-tubular fluid ratio of potassium at the level of the
cortical collecting tubule, where potassium is secreted.
TTKG = (Urine potassium/urine osmolality : serum potassium
/serum osmolality)
A value less than 3 suggests that the kidney is not wasting
excessive potassium, while a value greater than 7 suggests a
significant renal loss..
28. DISTAL K+ SECRETION (TTKG>4)
With normal or low blood pressure
1.With alkalosis – Diuretic therapy, Bartters and gitelmans
syndrome
2. With acidosis – RTA type 1& 2, carbonic anhydrase inhibitor
therapy
3. With variable pH – post obstructive diuresis, Recovery after
ATN,Mg depletion,amphotericine B
29. Barrter’s Syndrome
Site of lesion – TAL
Abnormal
NKCC2,ROMK,Cl channel
Na wasting,volume
contraction
RAASNa reabs by
CT
K&H secretion,met
alkalosis,hypokalemia
34. HYPOKALEMIA-TREATMENT
(1) decreasing potassium losses,
(2) replenishing potassium stores,
(3) evaluating for potential toxicities,
(4) determining the cause in order to
prevent future episodes.
35. HYPOKALEMIA-TREATMENT
In treating hypokalemia, the first step is to identify
and stop ongoing losses of potassium.
Discontinue diuretics/laxatives.
Use potassium-sparing diuretics if diuretic therapy is
required (eg, severe heart failure).
Treat diarrhea or vomiting.
Use H2 blockers to decrease nasogastric suction losses.
Control hyperglycemia if glycosuria is present.
36. HYPOKALEMIA-TREATMENT
Repletion of potassium losses is the second step.
As a first approximation, for every decrease in serum
potassium of 1 mEq/L, the potassium deficit is
approximately 200-400 mEq..
Oral potassium is absorbed readily.
Relatively large doses can be given safely.
37. HYPOKALEMIA-TREATMENT
if the hypokalemia is mild-moderate => po
administration potassium chloride should
occur more slowly over several days at 80 -
160 meq/day in divided doses .
38. HYPOKALEMIA-TREATMENT
Intravenous potassium is less well tolerated because
it can be highly irritating to veins and can be given
only in relatively small doses, generally 10 mEq/h.
Under close cardiac supervision in emergent
circumstances, as much as 40 mEq/h can be
administered through a central line.
Oral and parenteral potassium can be used safely
simultaneously.
Take ongoing potassium losses into consideration
39. HYPOKALEMIA-TREATMENT
avoid glucose-containing parenteral fluids to
prevent an insulin-induced shift of potassium into
the cells.
If the patient is acidotic, correct the potassium first
to prevent an alkali-induced shift of potassium into
the cells.
Replete magnesium if low.
Digoxin , liver disease –keep at 4.0 meq/l
40. Potassium replacement
therapy
- cardiac monitoring is necessary in patients with
profound hypokalemia (< 2.5 meq/L), or if cardiac
arrhythmias are present, if IV potassium is planned
- rapid IV bolus administration of potassium is
usually contra-indicated - the body has a limited
ability to rapidly absorb potassium and lethal
cardiac arrhythmias may result
41. Potassium replacement
therapy
- IV potassium diluted in saline solution the
maximum concentration is 40 meq/L (peripheral
lines) or 60 meq/L (central lines)
10 - 20 meq/hour (in the average-sized adult) for
hypokalemia - if po potassium replacement therapy
cannot be tolerated or if a malabsorption syndrome
is suspected
42. IV infusion rate for severe or
symptomatic hypokalemia
10 - 20 meq/hour Standard IV replacement rate
20 - 40 meq/hour Serum potassium < 2.5 meq/L or
moderate-severe symptoms
> 40 meq/hour Serum potassium < 2.0 Meq/L or life-threatening
symptoms