SODIUM - Royal Children's Hospital · ISSUES ARISING FROM THIS CASE 1) Really low Na is scary. 2)...
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Transcript of SODIUM - Royal Children's Hospital · ISSUES ARISING FROM THIS CASE 1) Really low Na is scary. 2)...
ISSUES ARISING FROM THIS CASE
1) Really low Na is scary.
2) Replacement rate- acute/ chronic
3) Loss of weight/ hydration assessment
4) Rate of Na rise
5) What was the metabolic abnormality
6) Neurological risk
Hyponatraemia
• Pseudo: lipid/ proteins/ glucose• Excess water intake• Reduced renal water excretion
– ARF/ CRF– CCF/ NS/ CLD– Def. G’corticoid/ T4– SIADH
• Excess Na loss: renal, GI, Cutan, 3rd space
RENAL NA LOSS
• MCC resistance/ def.• Diuretics• Salt-wasting renal dis./ ARF• Bartter’s S./ Gitelman’s S.
What was going on?
Low Na, high K, low HCO3
=Functional hypoaldosteronism.
Causes: endocrine/ renal
Renal = RTA 4 ie Aldo doesn’t work on distal tubule.
Scenarios: obstruction, pyelonephritis and especially…obstruction with pyelonephritis!
Replacement requires fluid, Na and often HCO3.
PRINCIPLES OF TREATMENT
1) Work out the fluids and level of dehydration.
Acute dehydration is = LOW in isotonic fluid (0.9% NaCl)
2) Work out the excess Na: H2O loss.
Na is primarily an extracellular ion so its distribution volume is estimated by total body water (TBW) as
TBW*0.5
where TBW is estimated as Wt*0.6 and wt is IBW
ie Na volume = Wt*0.6*0.5
3) Work out the desired rate by clinical considerations.
DEFICIT
Na
LOW (KG=Litres)
LOW= 0.9%NaCl
ie LOW(kg)*150
+
Correction for low Na
(140-Se.Na)* 0.6*0.5*Wt
FLUIDS
FLUIDS Na
MAINTENANCE Usual calculation:
100ml/kg/ 1-10kg
50ml/kg/10-20kg
20ml/kg/20kg up
2-3 mmol/kg/day
Modify fluids according to U/O: anuric vs polyuric.
FLUIDS Na
LOSSES Vomit/ Diarrhoea V/D~ 0.45% NaCl
Check U. Na-
if Na < 40 and dehydrated suggest there is some avid reabsorption. ?Oligoanuric.
If Na >70 likely tubular wasting and will need U/O replaced or already Na replenished. ?Polyuric.
Guides the ongoing losses replacement: volume and Na!
DEFICIT
Na
LOW (KG=Litres)
LOW= 0.9%NaCl
ie LOW(kg)*150
+
Correction for low Na
(140-Se.Na)* 0.6*0.5*Wt
FLUIDS
MAINTENANCE Usual calculation 2-3 mmol/kg/day
LOSSES Vomit/ Diarrhoea V/D~ 0.45% NaCl
Check U. Na (<40)
FLUIDS Na
LOW(kg)*150
=90 mmol
+
(140-107)*0.6*0.5*6.5 = 65 mmol
DEFICIT LOW 600ml
MAINTENANCE 600 ml/ 24 hr =20 mmol/day
0 mmol
U. Na (6 mmol/L)LOSSES 0 ml
TOTAL 1200 ml/day 175 mmol/day
Mx Hyponatraemia
• Symptomatic requires urgent Rxraise Na 5mmol/L, 3% NaCl, 3mmol/hr.
– 5 * TBW = Na mmol (* 2 = ml of 3% NaCl)• Asymptomatic (Na level irrespective), no
need for hypertonic saline.• Raise Na above potential symptomatic
range (at least 120-125)
Mx Hyponatraemia
• Acute: cell swelling by osmotic mvt in. • Chronic: organic osmols within the cell are
transported out to decrease osmolality. Water leaves cell again.
• If too rapid correction, sudden cell shrinkage- osmotic demyelination in brain.
• Correct slowly (12-15mmol/L/d) if had symptomatic or profound asymptomatichypoNa of chronic duration.
So, if calculating correction from 107 mmol/L AND asymptomatic, would aim to be really gentle eg over 60 hrs
(12-15 mmol/d will raise Na 30-40 mmol over 60 hrs)
CALCULATION:
60 HRS FLUID TOTAL = 600 + (2.5*600) = 2100
60 HRS Na TOTAL 90 + 65 + (2.5*20) = 205
Na req’t = 205/2100 = 97 mmol/L Na
Rate req’d = 2100/60 = 35 ml/hr
ie 35 ml/hr 0.6% NaCl.
Remembering calculations don’t take everything into account, but this formula usually applies:
Frequency of blood monitoring is directly proportional to the extent of the biochemical derangement
so this child will need 2-4 hrly Se. Na and watch that does not develop more rapid elevation of Na
ALTERNATIVELY, could make a case to acutely raise the Se. Na 5 mmol/L to get him out of the immediate S/Z danger.
5*TBW (0.5*0.6*6.5) = 10 mmol
= 20 ml 3%NaCl or 65 ml 0.9% NaCl over 1 hour
NOTE recheck Na before continuing.
Then presuming Na perfectly responds and is 112 mmol/L, continue by calculating as shown previously, but subtract Na and fluid already given:
ie 205-10/ 2100-65 = 96 mmol/L… ~ 0.6% NaCl at 34ml/hr.
BOTTOM LINE: GENTLER RISE IS SAFEST, SO IF UNSURE GO WITH THE 0.45% NaCl and 2 hrly Na.
ALTERNATIVELY, giving 0.9% NaCl (40 + 80) 120 ml bolus followed by infusion at 20 ml/hr:
over 10 hr can expect to give
320 ml fluid
48 mmol Na
This will raise Na: 48 = (X-107)*0.6*0.5*6.5
X= 48/(0.5*0.6*6.5) +107
X = 131 mmol/L
Raised 24 mmol in 10 hrs if only distributed in ECF and if no sig U Na loss.
This would be dangerously quick- safeguards:
1. Close monitoring of blood and urine Na!
2. Rapid response to progressive Na changes.
3. Seek advice - ICU, Nephrology.
6 MTH WITH I/C ILLNESS
• Sodium: 173 mmol/L • Potassium: 4.2 mmol/L • Chloride: 129 mmol/L • TCO2: 27 mmol/L • Urea: 4.4 mmol/L • Creatinine: 0.05 mmol/L
• Serum Osmolality: 344 • Urine Osmolality: 133• U/O- 1000ml/d (Polyuria= 1200ml/m2)
• Falling off percentiles last 2 months (weaned).
FAMILY HISTORY
• Father- angloceltic. Nil abN on Hx. • Mother- Greek origin. On probing, used to
drink a lot and get up O/N. Rarely now.• First morning urine osmolality- 154.• Mat GM well, nil abN on Hx.• Mat GF used to drink a lot, now deceased.• Male cousins not unwell.
DIAGNOSIS
• Diabetes insipidus.• Classic presentation for nephrogenic DI.• How to distinguish from central DI
• Give DDAVP.
NUMBERS
• Need to know net water deficit• Current weight 5kg and appears mildly
dehydrated-- trap of hypernatraemic dehydration (“doughy”).
• Estimate at least 700 ml deficit on growth percentiles, history and examination.
• Aiming to decr Na 0.5 mmol/hr.
NUMBERS
• Free water deficit formula:[Current Na/ desired Na * TBW]- TBW
• TBW for Na = 0.5*0.6*Wt (1.5L).• SO: [173/145 *1.5] - 1.5 = 290ML• Isotonic deficit = net deficit - 290 ml
410 ml• Correct deficit slowly eg over 48 hr.
So what Fluid
• Deficit: total of 700 ml/ 48hr15 ml/hr of roughly 0.45% NaCl
• Ongoing losses ie U/O with 5% Dextrose.• Insensible losses = 30ml/kg/d (180 ml)
7.5ml/hr with 5% Dextrose• Summary: 0.45%NaCl /5% Dex. 15ml/hr
5% Dextrose 7.5 ml/hr + U/O
DIAGNOSIS CONFIRMATION
• Start the fluids, give IN DDAVP and check Na (Urine and blood) 2-4 hourly to titrate fluids.
NEPHROGENIC DI
• Congenital- Rare. 30 families in Holland-15 million population.
• Secondary/ acquired. Commoner.– CRF– Drugs- Li, Tetracyclines– Metabolic- High Ca, low K– Obstruction/ dysplasia/ chronic PN
• Renal insensitivity to ADH/ VP.
Congenital NDI
• Present from birth onwards, breast feeding, may delay presentation (lower solute).
• PC: dehydration, seizures (> with Rx), constipation, fever. Enuresis/nocturia later.
• Usu have mild FTT- ? LOA due to fluid volumes required.
• Cognitive impairment if unRx’d.• Dx- Polyuria. NDI- U. osm <200 (N>800)
Hypernatraemic dehydration
• Hypertonicity leads to osmotic water loss from cells
• Cells produce organic osmols to resist cell shrinkage.
• These organic osmols are removed by metabolism once fluid deficit corrected, but this is gradual-danger: rapid rehydration!