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What is normal plasma osmolality?
Osmolarity vs osmolality
- Osmolarity- the # of osmoles of solute per liter (L) of solution. osmol/L or Osm/L.
- Osmolality- the # of osmoles of solute per kilogram of solvent. osmol/kg or Osm/kg.
What mechanisms regulate water balance?
- (1) Thirst sensation
- (2) Control of renal H20 excretion by ADH
Where is fluid gained and lost from?
Gained from oral fluid and solid food, insensible gain of oxidative metabolism. Lost through urine and stool, insensible losses through lungs and skin.
Na - function
Principal cation in ECF, f(x) as osmotic determinant in regulating ECF volume and water dis'n in body. Determines membrane potential of cells and the active transport of molecules across cell membranes.
Na - regulation
By kidneys. Aldosterone is an important system, regulated by rennin-angiotensin. Other systems include the SNS, atrial natriuretic peptide, kallikrein-kinin system, various intrarenal mechanisms, and factors that affect renal and medullary blood flow.
Na - deficiency
- Hyponatremia s/s: HA. n/v, m. cramps, lethargy, restlessness, disorientation, depressed reflexes.
- Repletion - the targeted rate is 5-10 mEq/kg/d to prevent osmotic demyleniation
Na - drug interactions
Lasix cause low Na
Na - toxicity
- s/s - SNS dysfxn
- N most at risk - AMS, intubated pts, infants, elderly
- Represents a h20 deficit in relation to Na stores
- Correction should not exceed 10 mEq/L/d to prevent cerebral edema and neurological impairment
Na - Adult TPN
Na - Preterm TPN
Na - Infant TPN
Na - Adolescent TPN
Na adult lab range
Na pediatric lab range
- Preemie: 13-140 mEq/L
- Older: 135-146 mEq/L
Total body stored 3K-4K mEq. 98% total K+ stored in cells.
K+ - function
Major intracellular cation, critical role in protein and glycogen synthesis, Na-K+ ATPase; muscle activity especially cardiac muscle; acid/base equilibrium
K+ - deficiency
- <3.6, typically asymptomatic
- 3.0-3.6; weakness, lethargy, constipation; almost always induced by abnormal
- loss urine/feces. Severe s/s – m. necrosis, ascending paralysis, arrhythmias,
- Oral correction safer, 40-100mEq/d
- divided in 2 - 4 doses
- IV: 10-20mEq/h, should not exceed 240-400mEq/d
- avoid giving in dextrose (stimulates
- K+ shifting d/t insulin); Correct Mag which may result from hypokalemia IV: 10-20mEq/h, should not exceed 240-400mEq/d
- avoid giving in dextrose (stimulates K+ shifting d/t insulin); Correct Mag which may result from hypokalemia
K+ - drug interactions
- 1) digoxin toxicity w/hypokalemia
- 2) insulin: causes K+, Mg, Phos to shift into cells (intracellular) hence causing low K+, Mg, and Phos
- 3) tacromalus cause high K+ and elevated glucose
- 4) dextrose and sodium bicarb also move K+ intracellular hence hypokalemia
K+ - toxicity
- s/s often asymptomatic until >5.5mEq/L, then present as m. twitching, cramping, weakness, ascending paralysis, changes in EKG, arrhythmias.
- Give IV Ca2+ gluconate to symptomatic pts or those with EKG changes to restore resting membrane excitability.
K+ - Adult TPN
K+ - Preterm TPN
K+ - Infant TPN
K+ - Adolescent TPN
K+ adult lab range
- requires Na-K+ATPase pump; absorbed in distal jejunum/ileum
- total body Ma ~ 25g, Mg 50-60% in bones;
- serum mag is 33% protein bound, mostly albumin.
MAG - function
Cofactor for ATP, muscle contraction, nerve conduction; predominantly in ICF; Important regulation of intracellular K+, needed for glc, FA, DNA, pro metabolisms. Regulator of Na-K pump, cell membrane action potential
MAG - deficiency
- Neuromuscular hyperexcitability, latent tetany, often comborbid w/ hypokalemia and hypocalcemia.
- Mild-mod 1.0-1.5  give 8-32mEq, up to 1.0mEq/kg
- severe: <1.0  ,give 32-64mEq, up to 1.5mEq/kg;
MAG - drug interactions
- Causing hypomag-
- thiazide and loop diuretics
- amphotericin B
MAG - toxicity
- Occurs w/ renal insufficiency and increased mag intake.
- s/s - neurological, neuromuscular ,cardiac, when exceed 4.8 mg/dL
MAG Preterm/ Infant TPN
MAG - Adolescent TPN
MAG adult lab range
1.8 - 2.3 mg/dL
MAG peds lab ranges
1.3 - 2.0 mg/dL
Ca - general
- Accounts for 1-2% body weight
- Absorbed in duodenum and upper jejunum
- 3 forms: complexed, protein bound, ionized (most important);
- increased protein intake increases Ca secretion (decrease to 1g pro/kg)
- hypoalbuminemia decreases serum ca but d/n affect ionized ca.
Ca - function
Bone metabolism, blood coagulation, neuromuscular activity (nerve transmission
Ca - deficiency
- Caused by dec vit D or PTH, (e.g. acute pancreatitis, hypomag)
- s/s - cardiovascular (hypotensive, dec myocardial contractility, , LQT) or neuromuscular
- asymptomatic hypocalcaemia d/t hypoalbminemia d/n need repletion.
- Total serum ca  >7.5mL/dL or ionized >0.9 mmol/L give 1g Ca chloride OR 3 g Ca gluconate over 10 min. infusion rates should not exceed 0.8 to 1.5 mEq/min d/t arrhythmia risk
- If hyperphosphatameia is present, tx w/ phosphate binders first to resume soft tissue calcification
Ca - drug interactions
- Causing hypocalcaemia-
- hypercalcemia � digoxin toxicity
Ca - toxicity
- >10.2, hyperparathyroidism and bone cancer;
- mild hypercalcemia? responds to hydration and ambulation;
- Severe: IV hydration 0.9% NaCl start promptly 200-300ml/h then furosemide 40-100mg IV;
Ca - Infant TPN
Ca - Adolescent TPN
Ca - adult lab range
- Serum - 8.5-10.5 mg/D:
- Ionized -4.56-5.4 mg/dL
Ca peds lab ranges
- <1 week Serum
- – 6/10 mg/DL preemie, 7-12 term, 8-10.5 child:
- < 7 d Ionized
- -4.52-6.32 mg/dL
Phos - function
Source of ATP; regulates CHO, pro and fat metab, essential for cell membranes, nucleic acids, phosphoproteins; majority in bones/tissues; glucose utilization and glycolysis
Phos - deficiency
- s/s - neurologic, neuromuscular, cardiopulmonary or hematologic
- Chronic alcoholism, critical illness; critical illness
- administration of CHO loads or PN ? causes inadequate phosphorus;
- mild: [2.3-2.7] ? give 0.08-.16mmol/kg
- mod [1.5- 2.2] ? give 0.16-0.32mmol/kg
- severe:[ <1.5] give="" 0="" 32-0="" 64="" br="">not >7mmol/kg;
Phos - drug interactions
digoxin toxicity with hypo
Phos - toxicity
- Hyper: CRI, massive trauma ? ECF;
- Hyperphosphatemia -> hypocalcaemia -> metastatic calcification in tissues
Phos - Adult TPN
Phos Preterm TPN
Phos - Infant TPN
Phos - Adolescent TPN
Phos - adult lab range
3=2.6 - 4.5 mg/dL
Phos peds lab ranges
- 0-5 d – 4.8 – 8.2 mg/d:
- 1-3 yo – 3.8-6.5
- 4-11yo – 3.7 – 5.6
- 12-15 yo- 2.9-5.4
- 16-19 yo 2.7-4.7
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