sp r training 2012 salt and water
TRANSCRIPT
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Salt and Water
SpR training July 2012
Roderick Warren
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Salt and water physiology
Aldosterone Vasopressin Where they act What they do What happens with the crisps and beer
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Collecting duct principal cell – aldosterone and ADH receptors
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ADH release:
• Osmolality (responds to 1% change)
• Effective blood volume (responds to 5-10% change)
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Aldosterone release:
• Potassium
• Effective blood volume (detected at JGA)
ENaC – epithelial sodium channel
NCCT – sodium-chloride cotransporter
NKCC2 – sodium-chloride-potassium cotransporter
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Other natriuresis pathways
ANP Release: atrial distension (and other triggers) Effects: increases GFR (affects renal blood
flow); decreases Na resorption by NCCT
BNP Similar to ANP
Pressure natriuresis
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In the pub
1. Eat crisps and nuts
2. Feel thirsty, drink beer
3. Go to loo
Salt intakeIncreased osmolalityADH release
Fluid intakeIncreased volumeAldosterone suppressed
Excrete salt and water
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Sodium balance
Recommended intake <100 mmol per day– 6g sodium chloride per day– 2.4g sodium per day
Average intake 150-200 mmol per day
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Water
Salt
Sodium balance
IN
2 litres water
150 mmol salt
OUT
2 litres water
150 mmol salt
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Causes of hyponatraemia
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Pseudohyponatraemia?
Incorrect measurement due to presence of lots of lipid or protein
e.g. hypertriglyceridaemia
Often wrongly used to mean hyponatraemia due to another osmotic substance
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Non-hypotonic hyponatraemia
Glucose Urea Mannitol Ethylene glycol
All draw water into blood Reduce serum osmolality
Detect by discrepancy between calculated and actual osmolality
(PS basically, serum osmo = plasma osmo)Bunting et al, Crit Care Med 1986; 14: 650
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Calculated versus actual osmolality
Na 122 K 4.0 Urea 3.4 Gluc 4.5 Osmo = (122+4) x 2
+ 3.4 + 4.5
= 260
Measured osmo 320
Gap 370-240=60
Ethylene glycol intoxication
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When to measure osmolality
Reasonable practice in all cases But remember what it’s for:
– to diagnose a non-measured solute– ethanol– methanol– ethylene glycol
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Hyperglycaemia
Osmotic effect of high glucose draws water into blood, and dilutes sodium (and everything else)
Correction factor– 1 mmol/L Na = 3.5 mmol/L glucose
Possibly more pronounced at glucose > 25 mmol/L– 1 mmol/L Na = 1.4 mmol/L glucose
Ref Hiller et al, Am J Med, 1999; 106: 399. Penne et al Diabetes Care 2010; 33: e91.
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Hyperglycaemia
Admission – simple hyperglycaemia
Na 124
Glucose 45
Urea 8.2
After IV insulin
Na 139
Admission – HONK
Na 146
Glucose 45
Urea 28.2
After IV insulin
Na 160
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Hypotonic hyponatraemia: causes
Shout them out
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Diuretics
Primary adrenal failure
Primary renal disease
Pseudohypoaldosteronism
SIADH
Glucocorticoid deficiency
Pregnancy
Reset osmostat
Excess water intake
Heart failure
Cirrhosis
Nephrotic syndrome
GI loss (vomiting, diarrhoea)
Skin loss (burns, sweating)
Third space (pancreatitis)
Dietary deficiency (anorexia)
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Hypovolaemic Euvolaemic Hypervolaemic
Renal sodium loss
Diuretics
Primary adrenal failure
Primary renal disease
Pseudohypoaldosteronism
SIADH
Glucocorticoid deficiency
Pregnancy
Reset osmostat
Excess water intake
Heart failure
Cirrhosis
Nephrotic syndrome
Other sodium loss
GI (vomiting, diarrhoea)
Skin (burns, sweating)
Third space (pancreatitis)
Dietary deficiency (anorexia)
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Assessing volume status
Either: obvious or euvolaemic
Think you can do better? Two expert nephrologists
carefully reviewed 58 patients with hyponatraemia
Clinical judgement compared with response to IV saline
Actual
Dry Normal
ClinicalDry 7 22
Normal 8 21
For detecting volume depletion:
• sensitivity 47%
• specificity 49%
Chung et al Am J Med 1987; 83: 905
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Hypovolaemic hyponatraemia
Cause Clue
Diuretic Obvious
Primary adrenal Symptoms, signs, cortisol
Primary renal Renal failure, urine dipstick
D&V Usually obvious from history
Anorexia Usually obvious
Skin loss Usually obvious from context
“Third space” Uncommon
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If in doubt
Renal sodium loss
Diuretics
Primary adrenal failure
Primary renal disease
Pseudohypoaldosteronism
Urine Na not low
Other sodium loss
GI (vomiting, diarrhoea)
Skin (burns, sweating)
Third space (pancreatitis)
Dietary deficiency (anorexia)
Urine Na low (<20 mmol/L)
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Diuretic-induced hyponatraemia
Gitelman syndrome (like thiazide treatment) – hypokalaemia, alkalosis, hypocalciuria, hypomagnesaemia
Bartter syndrome (like loop diuretic) – alkalosis, hypokalaemia, hypovolaemia, hypercalciuria
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Diuretic-induced hyponatraemia
94% of reported cases are with thiazides Rapid onset (hours-days) – longer with loops Why? Possible causes:
– patients on thiazides are in water balance or slight water excess (perhaps due to ADH release)
– short half-life of loop diuretics (brief electrolyte excretion, then avid retention)
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Adrenal failure
Aldosterone deficiency– normally protects sodium (at expense of
potassium)
Cortisol deficiency– tonic inhibition of ADH– profound cortisol deficiency causes SIADH-like
picture
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Hypervolaemic hyponatraemia
Usually clinically obvious Said to be dilutional (though I think poorly
understood) ADH stimulated by reduced stretch receptor
stimulus due to...– poor cardiac output– reduced intravascular volume
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Hypothyroidism is not a cause
Serum sodium distribution in 1000 hypothyroid patients and 5000 controls
95% ranges:132-144 (hypothyroid)134-144 (control)
Hypothyroidism lowers serum Na by 0.48 mmol/L
Warner et al, Clin Endo 2006; 64: 596.
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Syndrome of inappropriate antiduretic hormone
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Causes of SIADH
Drug causes Non-drug causes
Tricyclic antidepressants;Selective serotonin reuptake
inhibitors;Opioids;Antipsychotics (e.g. haloperidol,
chlorpromazine, flupentixol, trifluoperazine);
Dopamine agonists;Nicotine;MDMA (Ecstasy).Anti-epileptics (carbamazepine,
valproate);
Malignancy: most, but especially lung.Infections: pulmonary (pneumonia,
TB, empyema); cerebral (e.g. meningitis,
abscesses).Nervous system disease: haemorrhage; infarction; demyelination (e.g. MS,
Guillain-Barré).
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Normal ADH release
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a – Random
b – Non-suppressible basal ADH levels, but normal response to raised plasma osmolality
c – Reset osmostat. ADH rises in response to plasma osmolality, but is always higher than it should be.
Patterns of SIADH
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What happens in SIADH?
Syndrome of inappropriate antidiuretic hormone
Why doesn’t the patient swell up?
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What happens in SIADH?
Water
Salt
Normal state
Inappropriate ADH
Water
Salt
Hyponatraemia
Tendency to hypervolaemia
Compensatory mechanisms – aldosterone etc
Water
Salt
Hyponatraemia
Euvolaemia
Water retention
Salt and water
excretion
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Experimental SIADH
Leaf et al 1953 J Clin Invest 1953; 32: 868
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Experimental SIADH
Leaf et al 1953 J Clin Invest 1953; 32: 868
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SIADH in theory
24-hour urine
sodium excretion
Serum sodium concentration
Onset Maintenance Recovery
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SIADH in theory
1. Fluid intake is required to become hyponatraemic
2. During onset, urine sodium excretion is high
3. SIADH = euvolaemia with total sodium deficit
4. In steady state, urine sodium = sodium intake
5. Sodium intake is required to correct hyponatraemia
6. In recovery, urine sodium is low (as for recovery from hyponatraemia of any cause)
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Limitations: urinary sodium
Range of sodium intake 60-250 mmol Range of water intake 1200-4000 mL Urinary sodium concentration
– from 15 mmol/L to 208 mmol/L
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Limitations: urinary osmolality
“Urine osmolality < serum osmolality excludes SIADH”
Average protein intake 70g/d = 350 mmol urea Average sodium + chloride = 300 mmol Average potassium = 60 mmol
Total about 700 mmol Average urine osmo = about 3-400 mOsm/kg
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710023044_1971023044.pdf
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SIADH may be steady state
24-hour urine
sodium excretion
Serum sodium concentration
Onset Maintenance Recovery
Average urine osmo about
3-400
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Average urine osmo = about 3-400 mOsm/kg
Maybe 6-800 on waking Maybe 200 after drinking
Limitations: urinary osmolality
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So how can we diagnose SIADH?
By ruling out other diagnoses.
But you can exclude if: random urine osmolality <100 mOsm/kg random urine sodium <20 mmol/L except in the recovery phase
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Low urine Na (and osmo) during recovery phase
24-hour urine
sodium excretion
Serum sodium concentration
Onset Maintenance Recovery
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Example 1
76-year old admitted with chest infection.
Clinically euvolaemic.Day 1 2 3 4 5 6 7
S Na 130 125 118 117 119
S Osmo 260 250
S Urea 5.6 4.3 4.0 4.8
S Creat 65 68 58 63
S Cort 680
U Na 76
U Osmo 420
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Example 1
Hyponatraemia Clinically euvolaemic No renal failure Normal cortisol Non-low urine sodium and osmolality Could well be SIADH
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Example 2
45-year old admitted with D&V.
Looks dry.Day 1 2 3 4 5 6 7
S Na 130 125 118 117 119
S Osmo 260 250
S Urea 5.6 6.3 8.0 9.8
S Creat 65 68 98 123
S Cort 680
U Na <20
U Osmo 180
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Example 2
Hyponatraemia Clinically hypovolaemic Degree of renal failure Normal cortisol Low urine sodium and osmolality History of GI loss
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Example 3
76-year old admitted with chest infection.
Clinically euvolaemic.Day 1 2 3 4 5 6 7
S Na 130 125 118 117 119 124 130
S Osmo 260 250
S Urea 5.6 4.3 4.0 5.8 6.9 5.8 5.7
S Creat 65 68 58 73 76 68 65
S Cort 680
U Na <20
U Osmo
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Example 3
Hyponatraemia Clinically euvolaemic No renal failure Normal cortisol Low urine sodium DURING RECOVERY Uninterpretable
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Example 4
66-year old with heart failure.
Oedematous.Day 1 2 3 4 5 6 7
S Na 126 127 125
S Osmo 260 260
S Urea 9.6 11.3 12.0
S Creat 124 136 140
S Cort 680
U Na 40
U Osmo
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Example 4
Clinical picture is heart failure So that’s the diagnosis Non-low urine sodium excludes GI loss In steady-state, urine sodium = sodium intake,
including if hypervolaemic Fluid restriction is appropriate even if SIADH
superimposed
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Treatment of hyponatraemia
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Treatment of hypotonic, hypovolaemic hyponatraemia
Hypovolaemic
Renal sodium loss
Diuretics
Primary adrenal failure
Primary renal disease
Pseudohypoaldosteronism
Other sodium loss
GI (vomiting, diarrhoea)
Skin (burns, sweating)
Third space (pancreatitis)
Dietary deficiency (anorexia)
Treatment:
• Salt and water
• +/- Glucocorticoids
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Treatment of hypotonic, hypervolaemic hyponatraemia
Treat underlying cause:
• e.g. rate control, digoxin
• e.g. sepsis
Remove fluid:
• paracentesis
• diuretics?
Fluid restrict
Hypervolaemic
Renal sodium loss
Heart failure
Cirrhosis
Nephrotic syndrome
Other sodium loss
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Treatment of hypotonic, euvolaemic hyponatraemia
Euvolaemic
Renal sodium loss
SIADH
Glucocorticoid deficiency
Pregnancy
Reset osmostat
Excess water intake
Other sodium loss
Treat cause of SIADH:
• e.g. stop drug
• e.g. antibiotics or chemotherapy
Fluid restrict:
Give drugs:
• demeclocycline
• vaptan
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When is acute treatment needed?
Sodium Effect
130-135 Usually asymptomatic
120-130 Non-specific malaise
<120 Confusion, ataxia, headache
Lower Depressed consciousness, seizures, death
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When is acute treatment needed?
Acute vs chronic (> or < 48 hr) Acute: increased risk of cerebral oedema Chronic: increased risk of CPM
Condition Confusion, seizures, other neurology
Sodium concentration 120 mmol/L is a common threshold
Pragmatism Availability of HDU/ICU, and of hypertonic saline
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What is acute treatment?
Boluses of hypertonic saline If neurologically obtunded 100mL bolus of 3% saline, up to three times Will raise serum Na by 5-6 mmol/L
Infusion of hypertonic saline 0.5 ml/kg/hr Will raise serum Na by 7-10 mmol/L/24 hr
Mohmand et al Clin J Am Soc Nephrol 2007; 2: 1110
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What about normal saline?
Exacerbates hyponatraemia…?
Infusion of 2 litres normal saline
Mean pre-treatment Na 126; n=17
Saline seems to help if urine osmolality <500
Musch et al Q J Med 1998; 91: 749
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What do you do in a normal UK hospital?
Serum sodium = 117 mmol/L If significant neurological symptoms,
definitely admit to ICU Otherwise:
– send serum osmo, cortisol, urine osmo early– zero oral fluid– give 1 litre 0.9% saline initially– monitor Na frequently
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Rate of correction
Urgent correction needed e.g. seizures 5-8 mmol/L in the first hour
First day 8-12 mmol/L
First 48 hours 12-18 mmol/L
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Fluid restriction
In milder cases, begin at one litre More liberal restriction may be OK if previous
fluid intake was high
Very tight restriction may be needed E.g. 500ml or zero
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Fluid restriction
Needs to be strict and tight Must be thirsty, or ineffective Will cause rise in urea/creatinine
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What happens in SIADH?
Water
Salt
Normal state
Inappropriate ADH
Water
Salt
Hyponatraemia
Tendency to hypervolaemia
Compensatory mechanisms – aldosterone etc
Water
Salt
Hyponatraemia
Euvolaemia
Water retention
Salt and water
excretion
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What happens in fluid restriction?
Water
Salt
Normal state (but a bit dry)
Fluid restriction
Water
Salt
Hyponatraemia
Euvolaemia
Water
Salt
Hyponatraemia
Hypovolaemia
Aldosterone ↑
ANP, BNP ↓
Dehydration Salt and water retention
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Demeclocycline
Dose 600-1200mg daily Induces nephrogenic DI in 70% of cases Usually 2-3 days to take effect
– but can be dramatic onset
Problems Avoid if eGFR<30 Can cause irreversible nephrotoxicity Nausea Photosensitivity Hypersensitivity to tetracyclines (anaphylaxis, urticaria)
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Vaptans
V2-receptor antagonists Directly inhibit ADH
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Vaptans
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Tolvaptan
SALT-1 and SALT-2 trials 448 patients with hyponatraemia Euvolaemic or hypervolaemic CCF, cirrhosis, SIADH Randomized to:
– placebo– tolvaptan 15mg od, increased as needed
Schrier et al N Eng J Med 2006; 355: 2099.
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Vaptans
Schrier et al N Eng J Med 2006; 355: 2099.
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Vaptans
Problems Few side effects – thirst, dry mouth Cost:
– £75-£150 per day– £27,000 to £54,000 per year– to raise serum Na by about 5 mmol/L
Restricted use– recurrent profound hyponatraemia
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Urea
Osmotic diuretic Rapid entry into cells – avoids sudden plasma
volume explansion Barely penetrates brain – avoids cerebral oedema 0.5 – 1 g/kg/day
Unavailable in UK 10 cans of baked beans 1kg meat
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Why treat chronic hyponatraemia?
No decent long-term therapy Why bother? Long-term adaptation to hyponatraemia?
But possibly: Gait disturbance Falls Osteoporosis
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Gait and hyponatraemia
Centre of pressure path, while walking right to left•Before correction (Na 124)•After correction (Na 135)
Renneboog et al Am J Med 2006 119 e1-8
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Profound cortisol deficiency
Causes SIADH-like picture (or just SIADH?) Cortisol is tonic inhibitor of ADH secretion
Acute reversal with glucocorticoid Rapid excretion of free water Rapid rise in serum sodium Risk of myelinolysis
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Profound hyponatraemia needs intensive monitoring
Frequent checks of serum sodium Meticulous fluid balance If rising too rapidly consider:
– stop saline– give dextrose– desmopressin
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Cerebral salt wasting
Described in neurosurgical patients Thought to be mediated by BNP (SIBNP?) Hyponatraemia post SAH Cue scratching of heads Is it SIADH? Is it CSW?
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SIADH CSW
1. ADH ↑ 1. BNP ↑
causing water retention causing salt and water loss
2. Renin, aldo ↓ 2a. ADH ↑
causing salt and water loss causing water retention
2b. Renin, aldo ↑
salt and water retention
What’s the difference?
Fluid replete Potentially fluid deplete
Urine sodium ↑ or normal Urine sodium ↑ or normal
Maybe renin, aldo ↓ Maybe renin, aldo ↓
Treatment: fluid restrict or saline
Treatment: saline
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Prevalence? 3/23 in a study from Kuwait
CXR In all
Further investigation e.g. CT If persistent If other symptoms/signs
SIADH and lung cancer
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Serum osmolality Low (<270) High-treat cause-urea, glucose, toxins
Fluid volume status
Deplete-history of D&V?-diuretics?-cortisol?
Replete Overloaded- treat cause- CCF, liver
Check cortisol, urine osmo, urine Na
Low urine osmoLow urine NaLook for GI loss
RepleteNon-low urine osmoNon-low urine NaNormal cortisolProbable SIADH – fluid restrict