Lecture 18 Fluid & Electrolyte Balance

maintenance of fluid volume and osmolality is the job of..

kidneys (main Na+ and water balance)

normal plasma Na+

135-145 mEq/L

normal plasma osmolality (concentration of solutes in a solution)

280-300 mOsm/kg

osmosis

water moves from an area of lower solute conc to higher solute conc

isotonic volume contraction in which sodium and water are lost in equal proportions - give what fluid?

(dec in total fluid V, no change in serum osmolality)
Labs: Na+=135-145, plasma osmolality=280-300 (normal lab values)

isotonic fluids (Lactated ringers, 0.9% sodium chloride)

causes of isotonic fluid loss

vomiting, diarrhea, surgery, burns, diuretic overuse

nursing considerations when giving isotonic fluids

replenish slowly to prevent pulmonary edema; monitor pt for fluid overload

loss of water exceeds loss sodium = hypertonic contraction - give what fluids?

reduced extracellular fluid volume and inc osmolality

Labs: Na+ >145, osmolality >300

hypotonic fluid replacement (0.45% sodium chloride, or fluids that contain no solutes at all (D5W))

but treat initially w/ drinking water

causes of hypertonic contraction

hypernatremia related to excessive sweating, osmotic diuresis, CNS disorders (Diabetes insipidus)

nursing considerations when giving hypotonic fluids

monitor for changes LOC related to cerebral edema, seizures, confusion

^overhydration

loss of sodium exceeds loss of water = hypotonic contraction - give what fluids?

both volume and osmolality of extracellular fluid are reduced

labs-hyponatremia is present: sodium level <135, serum osmolality <380

isotonic fluids and in severe cases hypertonic fluids (3%), restrict oral fluids

causes of hypotonic expansion of cells

hyponatremia r/t: diuretic therapy, chronic renal insufficiency, SIADH=lack of aldosterone

causes of fluid overload

overdose w/ therapeutic fluid (iatrogenic)

disease states (congestive HF, renal failure, cirrhosis w/ ascites)

tx for fluid overload

diuretics;

dialysis for renal failure, paracentesis for ascites

acid-base balance is maintained by

respiratory system (immediate rxn-blowing off CO2 raises pH) and kidneys (long-term, slower response)

normal Arterial Blood Gas values

pH 7.35-7.45

PCO2 35-45

HCO3 22-26

Respiratory alkalosis

ph>7.45, PCO2<35

Respiratory alkalosis cause

hyperventilation - decrease in CO2

Respiratory alkalosis tx

mild: none

severe: rebreathe CO2 - paper bag

respiratory acidosis

ph<7.35, PCO2>45

respiratory acidosis causes

hypoventilation - retention of CO2

• depression of medullary respiratory center

• pathologic changes in lungs

respiratory acidosis tx

correction of respiratory impairment; ventilation support PRN

infusion of sodium bicarbonate (NaHCO3) ONLY if SEVERLY low pH

metabolic alkalosis

pH>7.45, HCO3>26

metabolic alkalosis causes

excessive loss of gastric acid (vomiting, or suctioned out)
too much admin of alkalinizing salts (NaHCO3)

metabolic alkalosis tx

tx of cause, IV solution of NaCl and KCl

metabolic acidosis causes

chronic renal failure, loss of bicarbonate during severe diarrhea, metabolic disorders, poisoning by methanol

metabolic acidosis tx

correction of unlerying cause

severe: alkalizing salt (sodium bicarb)

renal dialysis

normal potassium levels

3.5-5 mEq/L

most abundant ICF cation

potassium fx

conduct nerve impulses

maintaining electrical excitability of muscle

regulating acid-base balance

regulation of K+

primarily by kidneys

renal excretion inc by aldosterone

excretion also inc by most diuretics

influenced by extracellular pH:

• alkalosis: K+ uptake enhanced

• acidosis: K+ exits cells

hypokalemia causes

most common cause: use of thiazide or loop diuretic

less common: excessive insulin, alkalosis

mild hypokalemia tx

oral potassium chloride: sustained-release has fewer GI effects

should be taken w/ meals or water

severe hypokalemia tx

IV potassium chloride

• must be diluted and infused slowly (no faster than 10 mEq/hr)

• NEVER ADMIN BY IV PUSH - results in cardiac arrest

• large molecules -- irritating

hyperkalemia

>5 mEq/dL

hyperkalemia causes

renal disease

severe tissue trauma - burns

untreated Addison’s disease

acute acidosis

misuse of potassium-sparing diuretics

overdose w/ IV K+

hyperkalemia consequences

disruption of electrical activity of the heart - heart dysrhythmias, chest pain (T wave heightens, PR prolonged)

noncardiac signs: confusion, anxiety, dyspnea, weakness, numbness

hyperkalemia tx

withhold foods that contain K+

withhold meds like potassium-sparing diuretics, K+ supplements

lower extracellular levels of potassium:

• calcium salt

• infuse glucose and insulin

• oral/rectal admin of Kayexalate (binds w/ K+ and excreted)

normal Magnesium levels

1.5-2.5 mEq/L

magnesium purpose

binding of mRNA to ribosomes, regulates neurochemical transmission and excitability of muscle

hypomagnesemia causes

diarrhea, hemodialysis, kidney disease, prolonged IV feeding, chronic alcoholism

hypomagnesemia tx

mild - magnesium oxide

severe - magnesium sulfate IV

hypermagnesemia causes

renal insufficiency

magnesium-containing antacids or cathartics

hypermagnesemia manifestations

dec HR, muscle weakness, hypotension, resp paralysis, cardiac arrest

hypermagnesemia tx

avoid Mg-based antacids and laxatives

IV calcium gluconate

renal dialysis

restrict dietary intake of Mg

hypocalcemia causes

acute pancreatitis, hypoparathyroidism, chronic renal failure, vit D deficiency, alkalotic states, hypoalbuminemia

hypocalcemia tx

calcium gluconate or calcium chloride, Vit D replacement

signs of hypocalcemia

Trousseau’s sign: involuntary spasm of hand

Chvostek’s sign: tap → facial nerve → twitch