Correction Made Easy 
By Adrian Paul J. Rabe, MD
Clinically Relevant Electrolytes
• H2O – intracellular
• Na – extracellular
• K – intracellular
• Ca – intracellular
• Mg – intracellular
Water
• ICF: 55-75%
• ECF: 25-45%
• Intravascular: Extravascular (1:3)
• Total Body Water
• 60% of Body weight (men)
• 50% of Body weight (women, elderly)
• Osmolar Loss vs Free Water Loss
osmolality+ BUN/2.8
= 275-290+mosm/kg
• PPlasma
Glucose/18
osm = 2(Na+K)
• water
2(Na+K)
• Free
deficit+ BUN/2.8
(L) = TBW+ Glucose/18
x ([Actual Na/140]-1)
• Na is the major determinant of osmolality
Water: Exercise
• 55/F with diarrhea
• Poor skin turgor, thirst
• 45 kg
Na 167
K 3.1
Cl 111
Ca 2.1
• Is there water loss?
• Is it osmolar loss or free water loss?
• Posm = 346 mOsm/kg
• Free water deficit = 4.34 L
Mg 0.55
BUN 2.13
Crea 115
Gluc 3.4
Na: Low
Posm
High
N
Low
Urine output
Non-maximal
ECF Volume
Hyperglycemia
Hyperproteinemia
Hyperlipidemia
Mannitol
Bladder irrigation
Corrected Na (mg/dL) = Na + ((Gluc – 100)/100)
if Gluc > 100
Maximal
Primary Polydipsia
Reset osmostat
Na: Low
ECF
Inc
N
Dec
Urine Na
< 10 mmol/L
Extra-renal Na loss
Remote diuretic use
Remote vomiting
SIADH
Heart
Failure
Hypothyroidism
Hepatic
Cirrhosis
Adrenal
NephroticInsufficiency
Syndrome
Renal Insufficiency
> 20 mmol/L
Na-wasting Nephropathy
Hypoaldosteronism
Diuretics
Vomiting
Na: Low
• Goals
• Restrict water intake
• Promote water loss
• Correct underlying disorder
• ECF volume increased
• Isotonic saline: removes stimulus for AVP release
• Water restriction to less than urine output
• Loop diuretics
• ECF volume N
• Dietary water restriction
Na: Low
• ECF volume decreased or symptomatic hyponatremia
• Correct!
• Na deficit = TBW X (Desired – Actual Na)
• Liters per day = (Na def)/(Infusate Na)
•
Osmotic Demyelination Syndrome – neurologic disorder with flaccid paralysis, dysarthria and dysphagia
5% NaCl
855
3% NaCl
513
0.9% NaCl
154
0.45% NaCl
77
0.2% NaCl
34
Plain LR
130
D5W
0
Na: Low
• ECF volume decreased or symptomatic hyponatremia
• Correct!
• Na deficit = TBW X (Desired – Actual Na)
• Liters per day = (Na def)/(Infusate Na)
• But… correct at 10-12 mmol/L per day (e.g. correct from Na 100 to 110-112)
• In a 50 kg female = 12 x TBW = 12 x 25 = 300
5% NaCl
855
3% NaCl
513
0.9% NaCl
154
0.45% NaCl
77
0.2% NaCl
34
Plain LR
130
D5W
0
Hyponatremia: Exercise
• 65/M hypertensive patient
• Deterioration in sensorium
• 60 kg, xerosis, dry armpits
Na 110
K 2.9
Cl 88
Ca 1.99
5% NaCl
3% NaCl
0.9% NaCl
Mg 0.46
BUN 2.13
Crea 120
855
Gluc 51312.22
154
• Na corrected = 111.2
• ECF: decreased
• Posm = 242.6 mOsm/kg
0.2% NaCl
• 34
Na def: 900
0.45% NaCl
Plain LR
D5W
77
• 130
Daily Correction: 360
0
Na: High
ECF
Increased
Not increased
Urine output
Non-minimal
Urine Osmolality
Give hypertonic solutions
Minimal
Water losses
(hypertonic NaCl or NaHCO3)
(GI, insensible, remote renal)
Uosm = 2 (Na + K) + BUN + RBS
Na: High
Uosm
> 750
< 750
DDAVP response
Uosm increase
Central DI
Uosm decrease
Diuretics
Osmotic Diuresis
Nephrogenic DI
Na: High
• Goals
• Stop ongoing water loss
• Correct water deficit
• Safest is oral correction
• D5W or pNSS are alternative solutions
• Water deficit = ([Actual Na/140]-1)x TBW
• Change in serum Na/L = (infusate Na-serum Na)
(TBW + 1)
• -12/H2O def = (infusate Na-serum Na)
(TBW + 1)
• (-12/H2O def)(TBW +1) = infusate Na – serum Na
• Infusate Na = (-12/H2O def)(TBW +1) +serum Na
• -12(TBW +1)/(Infusate Na-serum Na) = Liters
Na: High
• Goals
• Stop ongoing water loss
• Correct water deficit
• Safest is oral correction
• D5W or pNSS are alternative solutions
• Water deficit = ([Actual Na/140]-1)x TBW
• Change in serum Na/L = (infusate Na-serum Na)
(TBW + 1)
• Na 162 in a 40 y/o 50 kg female
• Deficit: 3.93 L = 4 cycles
• -12/4 = (x-162)/(TBW+1)
• -3(25+1) + 162 = x
• -78+162 = 84
0.9% NaCl
154
0.45% NaCl
77
0.2% NaCl
34
Plain LR
130
D5W
0
Hypernatremia: Exercise
• 21/M with vomiting
• 60 kg, dry buccal mucosa, UO 30cc/3h
Na 180
K 3.1
Cl 115
Ca 2.4
Mg 1.1
BUN 3.46
Crea 120
Gluc 18.9
• Na corrected = 182.4
• ECF: decreased
• Posm = 388.6
• UO: minimal
• Free H20 deficit = 10.9L
• Given infusate pLR: 8L/day for 3 days,
4L/day on the 4th day
K: Low
Urine K excretion
> 15 mmol/d
Acid-base?
Acidosis
TTKG
>4
LowerAcid-base
GI K loss
< 15 mmol/d
TTKG?
(Urine K/Plasma K)
(Uosm /Posm)
TTKG
Alkalosis
<2
use
NaRemote
wastingdiuretic
nephropathy
Remote
Osmoticvomiting
diuresis
Sweat
losses
Diuretic
Acidosis
DKA
RTA
Amphotericin B
Vomiting
Alkalosis
Bartter’s/Liddle’s
Hypomagnesemia
K: Low
• Goals
• Correct deficit
• Minimize losses
• K deficit = (Desired – actual)/0.27 – academic only
• K depletion DOES NOT correlate well with plasma K
• For every decrement in serum K mmol = 200-400 mmol deficit
• If ~3.0 to correct to 4.0, give 200-400 mEqs of K
• < 3.0 = >600 mmol
K: Low
• Oral correction
• Bananas, fruits
• Oral KCL = 40 mEqs/30 cc
• IV correction (ideally, in saline)
• 60 mEqs if via central line
• 40 mEqs if via peripheral line
• Not more than 20 mmol/h unless with paralysis or malignant ventricular arrhythmias
K: High
• Goals
• Depends on ECG and weakness
• Measures
• Ca gluconate 10% in 10 mL over 2-3 minutes
• NaHCO3 3 vials in saline solution
• Glucose-Insulin solution
• B-adrenergic drugs
• Diuretics
• Dialysis
Ca: High
• Goals
• Rule out hyperalbuminemia as a cause
• Corrected Ca = (40-alb) x 0.02 + Ca
• Take intact PTH
• Measures
• Forced saline diuresis (e.g. Furosemide 200 mg + pNSS 1L x 6 hours)
• Bisphosphonates (Pamidronate 60-90 mg IV x 2-4 hours)
• Calcitonin
• Phosphate IV
• Glucocorticoids – decrease Vit D production
• Dialysis
Ca: Low
• Goals
• Rule out hypoalbuminemia as a cause
• Corrected Ca = (40-alb) x 0.02 + Ca
• Take intact PTH
• Measures
• Ca gluconate 10% solution 10 mL + D5 50 cc x 5min
• Ca gluconate drip
• Ca CO3 500 mg BID with meals
• Vit D 2 ug/day
Mg: Low
• Goals
• Correct K concentration
• Correct Ca concentration
• Measures
• 1g = 0.10 increase in Mg
• MgSO4 3 g in D5W 250 cc x 240 = increase by 0.3
11 Equations to memorize!
•
Posm = 2(Na+K) + BUN/2.8 + Glucose/18
•
Uosm = 2 (Na + K) + BUN/2.8 + Glucose/18
•
Corrected Na (mg/dL) = Na + ((Gluc – 100)/100) for Gluc > 100
•
Na deficit = TBW X (Desired – Actual Na)
•
Liters per day = (Na def x 1000)/(Infusate Na)
•
Water deficit = ([Actual Na/140]-1) x TBW
•
Change in serum Na/L = (infusate Na-serum Na)
(TBW + 1)
•
TTKG = (Urine K/Plasma K)/(Uosm /Posm)
•
K deficit = (Desired – actual)/0.27
•
Corrected Ca = (40-alb) x 0.02 + Ca
•
Creatinine Clearance = [(140-age) x weight in kg] x 88.4; multiply by 0.85 for females
[72 x Creatinine in umol]
•
BUN:Creatinine Ratio = (BUN/Crea) in umol x 247
*TBW fraction: 0.6 in males, 0.5 in females and elderly
Before starting any calculation
• Correct everything (Na, Calcium)
• Get TBW
• Get BUN:Crea ratio and Creatinine Clearance
• Get Plasma Osmolality
Exercises
• 49 y/o female diabetic
• 45 kg
• Vomiting, decreased sensorium
• Dry buccal mucosa, drowsy
• BUN 13.6, Crea 223, Na 168, K 2.2, Cl 110, Mg 0.55, Ca 1.24, alb 23, RBS 21.3
• TBW: 22.5
• Creatinine Clearance: 19
• BUN:Crea Ratio: 15
• Corrected Na: 170.8
• Corrected Calcium: 1.58
• Plasma Osmolality: 380.9 (high)
Exercises
• 49 y/o female diabetic
• 45 kg
• Vomiting, decreased sensorium
• Dry buccal mucosa, drowsy
• BUN 5.6, Crea 223, Na 168, K 2.2, Cl 110, Mg 0.55, Ca 1.24, alb 23, RBS 21.3
0.9% NaCl
154
0.45% NaCl
77
0.2% NaCl
34
• Change in Na for 1L pLR: -1.74
Plain LR
130
• Daily: ~7L for 2 days then 3.5 L for the 3rd day
D5W
• Hypernatremia
• Free water deficit: 4.95 L
• Hypokalemia: > 600 mEqs correction
• Hypomagnesemia: MgSO4 4g in D5W 250cc x 12-24h
• Hypocalcemia: Ca Gluconate 1 amp SIVP or drip
0
Exercises
• 58 y/o male with diarrhea, previously with Lung CA
• 62 kg
• Watery non-bloody diarrhea, poor urine output
• Awake, poor skin turgor, complaining of thirst
• BUN 21.6, Crea 254, Na 128, K 1.8, Cl 97, Mg 0.67, Ca 2.51, alb 16, RBS 8.7
• TBW: 37.2
• Creatinine Clearance: 25
• BUN:Crea Ratio: 21
• Corrected Na: 128.6
• Corrected Calcium: 2.99 (mild)
• Plasma Osmolality: 291 (normal to high)
Exercises
• 58 y/o male with diarrhea, previously with Lung CA
• 62 kg
• Watery non-bloody diarrhea, poor urine output
• Awake, poor skin turgor, complaining of thirst
• BUN 22.3, Crea 254, Na 128, K 1.8, Cl 97, Mg 0.67, Ca 2.51, alb 16, RBS 8.7
• Hyponatremia
• Sodium deficit: 424.08 mEqs
• Daily Sodium correction: 446.4
• pNSS: 2.9L/day
• Hypokalemia: >600 to 1200 mEqs
• Hypomagnesemia: MgSO4 3g in D5W 250cc x 12
• Hypercalcemia: Forced saline diuresis, Pamidronate
5% NaCl
855
3% NaCl
513
0.9% NaCl
154
0.45% NaCl
77
0.2% NaCl
34
Plain LR
130
D5W
0