5. Sodium (Na+)
• Bulk cation of extracellular fluid change in SNa reflects
change in total body Na+
• Principle active solute for the maintenance of intravascular &
interstitial volume
• Absorption: throughout the GI system via active Na,K-ATPase
system
• Excretion: urine, sweat & feces
• Kidneys are the principal regulator
5
6. Sodium (Na+)
• Kidneys are the principal regulator
– 2/3 of filtered Na+ is reabsorbed by the proximal convoluted tubule,
increase with contraction of extracellular fluid
– Countercurrent system at the Loop of Henle is responsible for Na+
(descending) & water (ascending) balance – active transport with Cl-
– Aldosterone stimulates further Na+ re-absorption at the distal
convoluted tubules & the collecting ducts
– <1% of filtered Na+ is normally excreted but can vary up to 10% if
necessary
6
7. Sodium (Na+)
• Normal SNa: 135-145
• Major component of serum osmolality
– Sosm = (2 x Na+) + (BUN / 2.8) + (Glu / 18)
– Normal: 285-295
• Alterations in SNa reflect an abnormal water regulation
7
8. Sodium (Na+)
• Hypernatremia: Causes
– Excessive intake
» Improperly mixed formula
» Exogenous: bicarb, hypertonic saline, seawater
– Water deficit:
» Central & nephrogenic DI
» Increased insensible loss
» Inadequate intake
8
11. Sodium (Na+)
• Hypernatremia Treatment
– Rate of correction for Na+ 1-2 mEq/L/hr
– Calculate water deficit
» Water deficit = 0.6 x wt (kg) x [(current Na+/140) – 1]
– Rate of correction for calculated water deficit
» 50% first 12-24 hrs
» Remaining next 24 hrs
11
34. Potassium (K+)
• Normal range: 3.5-4.5
• Largely contained intra-cellular SK does not reflect total
body K
• Important roles: contractility of muscle cells, electrical
responsiveness
• Principal regulator: kidneys
34
35. Potassium (K+)
• Daily requirement 1-2 mEq/kg
• Complete absorption in the upper GI tract
• Kidneys regulate balance
– 10-15% filtered is excreted
• Aldosterone: increase K+ & decrease Na+ excretion
• Mineralocorticoid & glucocorticoid increase K+ &
decrease Na+ excretion in stool
35
36. Potassium (K+)
• Solvent drag
– Increase in Sosmo water moves out of cells K+ follows
– 0.6 SK / 10 of Sosmo
– Evidence of solvent drag in diabetic ketoacidosis
• Acidosis
– Low pH shifts K+ out of cells (into serum)
– Hi pH shifts K+ into cells
– 0.3-1.3 mEq/L K+ change / 0.1 unit change in pH in the opposite
direction
36
49. Potassium (K+)
• Hypokalemia Presentation
– Usually asymptomatic
– Skeletal muscle: weakness & cramps; respiratory failure
– Flaccid paralysis & hyporeflexia
– Smooth muscle: constipation, urinary retention
ECG changes
» Flattened or inverted T-wave
» U wave: prolonged repolarization of the Purkinje fibers
» Depressed ST segment and widen PR interval
» Ventricular fibrillation can happen
49
50. Potassium (K+)
Hypokalemia
- Flattened or inverted T-wave
- U wave: prolonged
repolarization of the Purkinje
fibers
- Depressed ST segment and
widen PR interval
- Ventricular fibrillation can
happen
50
51. Potassium (K+)
• Hypokalemia Treatment
– Address the causes & underlying condition
– Dietary supplements : leafy green vegetables, tomatoes, citrus fruits,
oranges or bananas
– Oral K replacement preferred
– IV: KCl 0.5-1 mEq/kg over 1 hr (rate of 10 mEq/hr)
– K Acetate or K Phos as alternative
– Add K sparing diuretics
– Correct hypomagnesemia
51
53. Bicarb (HCO3
--)
• Normal range: 25-35
• Important buffer system in acid-base homeostasis
• Increased in metabolic alkalosis or compensated respiratory
acidosis
• Decreased in metabolic acidosis or compensated respiratory
alkalosis
• 0.15 pH change/10 change in bicarb in uncompensated
conditions
53
66. Calcium
• Normal range: 8.8-10.1 with half bound to albumin
• Ionized (free or active)calcium: 4.4-5.4 – relevant for cell
function
• Majority is stored in bone
• Hypoalbuminemia falsely decreased calcium
– Cac = Cam + [0.8 x (Albn – Alb m)]
66
67. Calcium
• Roles:
– Coagulation
– Cellular signals
– Muscle contraction
– Neuromuscular transmission
• Controlled by parathyroid hormone and vitamin D
67
68. Calcium
• Hypercalcemia: Causes
– Excess parathyroid hormone, lithium use
– Excess vitamin D
– Malignancy
– Renal failure
– High bone turn over
» Prolonged immobilization
» Hyperthyroidism
» Thiazide use, vitamin A toxicity
» Paget’s disease
» Multiple myeloma
68
75. Magnesium
• Normal range: 1.5-2.3
• 60% stored in bone
• 1% in extracellular space
• Necessary cofactor for many enzymes
• Renal excretion is primary regulation
75
83. Phosphorus
• Normal range: 2.3 - 4.8
• Most store in bone or intracellular space
• <1% in plasma
• Intracellular major anion, most in ATP
• Concentration varies with age, higher during early childhood
• Necessary for cellular energy metabolism
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