CMPP: Sodium and Potassium Disorders

water balance

hypo-- water EXCESS

hyper --water DEFICIT

hyponatremia/hypernatremia are primarily disorders of...

increased, dilute

hyponatremia results in _____ intravascular water, and the body is unable to excrete a _____ urine

decreased, concentrated

hypernatremia results in _____ intravascular water, and the body is unable to excrete a _____ urine

Hyponatremia

any process that expands the vascular volume around a fixed total body Na and that limits water excretion may result in THIS condition.

increase in intravascular water

inability of the body to appropriately respond by excreting a dilute urine

--> are the kidneys unable to keep up with the primary problem, or are the kidneys the problem?

two factors required for hyponatremia to occur

H2O content rises due to ingested quantity exceeding the normal physiologic capacity of the kidneys to excrete H2O

how does polydipsia cause hyponatremia?

Psychogenic polydipsia

psychiatric craving for excess water

Beer potomania

Hyponatremia in chronic beer drinkers; >4L

antidiuretic hormone (ADH)

primary determinant for renal water handling; secreted by posterior pituitary in response to high serum osmolality

circulating volume

a high serum osmolality indicates a decreased...

euvolemia, normal serum Na

the body prioritizes maintaining _________ over maintaining _________.

the body perceives the decreased effective circulating volume caused by these conditions as a hypovolemic state

--> results in H2O reabsorption and hyponatremia

--> still technically being "appropriately" released

how do diseases with decreased effective circulating volume (CHF, cirrhosis, nephrotic syndrome) result in secretion of ADH?

Syndrome of inappropriate ADH secretion

ADH is secreted despite no perfusion or osmotic-related stmiilu

low, low, euvolemia

the net result of SIADH is a ____ serum Na, ___ serum osmolality in the setting of __________.

inappropriately high osmolality (concentrated urine)

--> urine should be dilute because the body should be interpreting low serum Na as the body having too much water

in SIADH, urine studies yield an...

pneumonia, TB, acute respiratory failure, mechanical ventilation

pulmonary disorders that can cause SIADH

meningitis, encephalitis, CVA, head trauma, acute psychosis

neurologic and psychiatric disorders that can cause SIADH

paraneoplastic syndromes

how does malignancy cause SIADH

narcotics, chemo, TCAs, anti-seizure meds, antipsychotics

what drugs are indicated in causing SIADH

neurologic -- since neurons are VERY sensitive to fluid changes

hyponatremia primarily results in what kinds of symptoms?

serum osmolality, serum Na

the development of symptoms in hyponatremia is due to changes in _________ rather than changes in _______.

Pseudohyponatremia

falsely low serum sodium level with no physiologic consequences because the serum osmolality is normal.

elevated plasma proteins (multiple myeloma)

hypertriglyceridemia

hyperglycemia

common causes of pseudohyponatremia

elevated blood glucose transiently increases serum osmolality

elevated blood glucose causes water to be drawn into the vasculature --> additional H2O drawn into the vasculature dilutes the Na, resulting in hyponatremia

how can hyperglycemia cause a pseudohyponatremia?

pseudohyponatremia -- treat underlying cause

if a patient is hyponatremic, and their measured serum osmolality is normal/high, what is their diagnosis/tx?

determine URINE osmolality

if a patient is hyponatremic, and their measured serum osmolality is low, what is your next step?

psychogenic polydipsia and beer potomaina

--> dilute urine in response to hyponatremia is an APPROPRIATE response, so the kidneys are doing their best by excreting as much free water as possible.

--> true hyponatremia

if a patient is hyponatremic, their measured serum osmolality is low, and their urine osmolality is low, what is the likely diagnosis?

determine the patient's volume status!

if a patient is hyponatremic, their measured serum osmolality is low, and their measured urine osmolality is high, what is your next step?

late-stage CHF, cirrhosis, nephrotic syndrome (body has perceived these conditions as low volume states)

if a patient is hyponatremic, their measured serum osmolality is low, their measured urine osmolality is high, and they are HYPERvolemic, what is their diagnosis?

SIADH

if a patient is hyponatremic, their measured serum osmolality is low, their measured urine osmolality is high, and they are EUvolemic, what is their diagnosis?

Na losses exceed H2O losses

if a patient is hyponatremic, their measured serum osmolality is low, their measured urine osmolality is high, and they are HYPOvolemic, what is their diagnosis?

fix hyponatremia slowly

pseudohyponatremia -- fix underlying cause

how to treat a hyponatremic pt who is asymptomatic

Central pontine myelinolysis

complication of correcting hyponatremia too rapidly in asymptomatic or minimally symptomatic patients

blood becomes very concentrated --> water moves out of cells --> cells lyse and this causes irreversible neuronal damage

how does overly rapid correction of hyponatremia result in CPM?

irreversible dysarthria, dysphagia, flaccid paralysis, and DEATH

CPM can result in...

chronic asymptomatic hyponatremia

--> if you were to treat, do IT SLOWLY OVER SEVERAL DAYS

what is the most common presentation of hyponatremia?

0.9% NS

tx for hypovolemic hyponatremia

treat underlying cause

H2O restriction and administration of a loop diuretic

tx for hypervolemic hyponatremia

water restriction

identify and treat the underlying cause

tx for SIADH

severe neurologic dysfunction (intractable seizures)

severe symptomatic hyponatremia is defined as...

3% hypertonic saline -- rate of collection is slowed once clinical situation improves

tx for severe symptomatic hyponatremia

free H2O deficit

hypernatremia is most commonly secondary to...

hypothalamic osmoreceptors get stimulated, resulting in increased thirst and ADH secretion --> excretion of maximally concentrated urine

how does the body normally try to compensate for hypernatremia?

hypernatremic dehydration

what is the most common cause of hypernatremia?

skin (evaporations and burns)

respiratory tract insensible losses

GI tract (DIARRHEA)

non-renal causes of hypernatremia

Loop diuretics (due to excretion of excess free water)

Osmotic diuresis (extensive free H2O loss -- usually secondary to glycosuria)

DI (results in ADH deficiency)

renal causes of hypernatremia

Central Diabetes Insipidus

impaired ADH secretion from the posterior pituitary

IDIOPATHIC, brain tumors, cranial surgery, head trauma

causes of central diabetes insipidus

nephrogenic diabetes insipidus

kidneys are unable to respond to ADH

intrinsic renal diseases and various meds (LITHIUM)

causes of nephrogenic DI

physical restrictions (institutionalized, handicapped, post-op, intubated)

mentally impaired (delirium, dementia)

hypothalamic dysfunction (primary hypodipsia)

what are some causes of an impaired thirst response?

depends how quickly Na rises -- shrinking of brain cells if it comes on quickly

Focal neurologic deficits

presentation of hypernatremia

polyuria

renal causes of hypernatremia will have concomitant...

increased aldosterone and increased corticosteroid states

if a patient who is hypernatremia is also hypervolemic, the ddx includes...

they are causing the reabsorption of both water and salt -- so there is a TON of salt and a TON of water being retained

why would increased aldosterone/corticosteroid states cause hypernatremia with hypervolemia?

hypokalemic -- secretes K+

what would you expect your serum potassium level to be in one with hyperaldosteronism and in Cushing's snydrome?

kidneys produce a SMALL amount of highly concentrated during with low Na

if a hypernatremic patient is also hypovolemic, what is the appropriate renal response?

the body wants to hold onto water more than it wants to correct the Na issue --> and the best way to retain water is to also retain salt --> so there is little to no Na in the urine

why is the urine produced by the kidneys in a hypernatremic hypovolemic state low in Na?

insensible fluid losses and GI losses (water losses > Na losses)

primary hypodipsia

what are the primary ddx considerations in one with hypernatremia that is hypovolemic

defect in renal H2O conservation -- DI

if a patient who is hypernatremic and hypovolemic is producing high volumes of dilute urine, what does that indicate?

DDAVP test

test that determines the cause of hypernatremia in the setting of hypovolemia and high urine volume; synthetic form of ADH is given intramurally, and it helps to differentiate central DI from nephrogenic DI

increased urine osmolality -- central DI

unchanged urine osmolality -- nephrogenic DI

what are the different results of the DDAVP test what what do these results indicate?

osmotic diuresis -- kidneys are doing their best to put out a concentrated urine in a a highly concentrated environment, but they cannot keep up with the osmotic load (high volume)

if a patient is hypernatremic, what diagnosis should be considered if the urine volume is inappropriately high but the urine osmolality is appropriately high?

overly aggressive tx can lead to rapid fluid shifts and excess H2O entering the brain cells -- cerebral edema

why is rapid correction of hypernatremia dangerous?

Idiogenic osmoles

Osmotically active substances generated in neurons. The neuron can increase or decrease the number of idiogenic osmoles to balance its osmolarity against that of plasma and the extracellular fluid; can occur when hypernatremia develops gradually.

manage underlying disease

tx for hypervolemic hypernatremia

by mouth/NG tube -- reduces risk of iatrogenic complications

it is safest to administer H2O...

0.9 NS (properly functioning kidneys will excrete the excess Na)

tx for unstable hypernatremia

once hemodynamic status is stablized

in one with unstable hypernatremia, when should fluid be changed to 0.45 NS

intranasal DDAVP

tx for central DI

low Na diet + thiazide diuretic

tx for nephrogenic DI

within the cells

where is most potassium located in the body?

aldosterone allows for K+ to get secreted at the collecting duct in exchange for Na

how does aldosterone help to maintain K homeostasis?

They INCREASE the serum K, since it blocks the component of the RAAS system that allows for K+ to be secreted

how do ACEi/ARBs affect the serum K?

decreased K intake

increased net K loss

shift of K from intravascular space into the cells

what are the three general causes of hypokalemia?

GI losses (N/V/D)

Evaporative losses

what are some non-renal causes of increased net K loss?

MORE COMMON!

--> diuretic use or osmotic diuresis (glycosuria)

--> primary hyperaldosteronism

--> secondary hyperaldosteronism

--> Cushing's syndrome

what are some renal causes of increased net K loss?

alkalemia (HCO3)

exogenous insulin

SABA

what are some causes of transcellular shift in hypokalemia?

Hypokalemic periodic paralysis

rare genetic disease that result in transcellular K shifts and episodic weakness

prominent effects on muscles (cramps) and cardiac rhythm (dysrhythmias)

--> can lead to hypoventilation, paralysis, ileus, constipation

presentation of hypokalemia

the body tries to correct metabolic alkaloses by exchanging H ions for K ions

H ions enter vasculature in exchange for K ions which enter the cell

--> primary hypokalemia can also result in a metabolic alkalosis

how does the body's method of compensation for metabolic alkaloses lead to hypokalemia?

Mg

low K and low __ often occur together.

increased urinary K excretion

what would indicate an inappropriate renal response to hypokalemia?

prominent U wave

what is the EKG change associated with hypokalemia?

replace potassium -- oral is safer, but sometimes may HAVE to give IV

--> SLOWLY, as rapid administration can lead to fatal dysrhythmias

tx for hypokalemia

if imminently life-threatening or oral route not possible

--> do not mix with dextrose

when is IV K+ indicated?

Pseudohyperkalemia

falsely elevated K+ level that is caused by the movement of K out of the cells during a "traumatic" venipuncture "hemolyzed specimen"

movement of K out of the cells during a "traumatic" venipuncture "hemolyzed specimen"

what can cause pseudohyperkalemia?

decreased renal function (#1 cause)

transcellular shift

increased intake of K-rich foods

what are the three major causes of hyperkalemia?

hyperaldosteronism (not properly secreting K+)

adrenal insufficiency

what are some conditions that can cause hyperkalemia due to decreased renal excretion (of K+)?

insulin deficiency, metabolic acidosis, muscle relaxants/paralytics

Rhabdo -- K released from damaged muscles

Tumor lysis syndrome -- lysis always leads to more K

--> These conditions cause a release of K+ from ICF stores to ECF

what are some conditions/meds that can cause transcellular shift/hyperkalemia?

usually only occurs if the pt has concomitant renal dx

when would increased K intake lead to hyperkalemia?

Renin inhibitors, ACEis, ARBs, K-sparing diuretics, NSAIDs (decrease GFR)

--> occurs with these meds b/c most of them prevent aldosterone from secreting K+ in collecting duct

--> usually occurs ONLY in setting of underlying kidney dx

what medications can cause hyperkalemia?

dysrhythmias/cardiac issues -- palpitations, syncope, sudden death!

hyperkalemia presentation

Sine wave (QRS merging with T wave) -- pre-arrest rhythm

peaked T waves

--> can quickly degenerate into Vfib/asystole

EKG findings with hyperkalemia

calcium gluconate

if a hyperkalemic pt's cardiac rhythm is UNSTABLE, what is the initial drug of choice?

decreases membrane excitability

calcium gluconate MOA

Insulin, SABAs, IV HCO3

what are some secondary tx for hyperkalemia

Insulin

if a pt is hyperkalemic and hyperglycemic, what is the only med indicated?

Causes K to shift into the cells -- actively transported with glucose -- temporarily lowering serum level

insulin MOA for hyperkalemia