SODIUM

Dr. Joshua KausmanRenal Fellow, RCH.

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

TOTAL FLUIDS = 1200 ml/ 24 hr

TOTAL Na = 175 mmol/24hr

BUT, CHALLENGE IS RATE!!!

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.

ON THE OTHER HAND

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.

IMMEDIATE ISSUES

• ? Diagnosis.• Fluid management

DIAGNOSIS

• Diabetes insipidus.• Classic presentation for nephrogenic DI.• How to distinguish from central DI

• Give DDAVP.

FLUID MANAGEMENT

• Harder!• What fluids?• What rate?

PROGRESS

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)

Congenital NDI

• Genetics.• 90% XLR (Xq28). V2 receptor defect.• 10% AR>>AD. AQP2 channel defect.

PHYSIOLOGY

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!

Hypernatraemic dehydration

• Clinical features.• Can be signs of ECF dehydration.• In addition: doughy texture to skin, which

can mask usual changes in skin turgor.• Severe: neuromuscular irritation.• Excessive rehydration rate: S/Z’s, ICH.