Neuroanaesthesia Flashcards
What is the normal serum sodium concentration
135-145 mmol/L
What is the normal serum osmolality
280-295 mOsm/kg
What is the main determinant of serum osmolality
Serum sodium concentration
List the hyponatraemia severity classification
Mild 130-135 mmol/L
Moderate 126-130 mmol/L
Severe <125 mmol/L
List the symptoms of hyponatraemia
Lethargy
Nausea/vomiting
Anorexia
Headache
Muscle weakness
List the hypernatraemia severity classification
Mild 146-149 mmol/L
Moderate 150-159 mmol/L
Severe >160 mmol/L
What neurosurgical patient groups have high propensity to developing hyponatraemia
High grade SAH
Anterior circulation aneurysms
Hydrocephalus
What are the most common new causes of hyponatraemia after brain injury
SIADH
CSWS
List the medications that can cause hyponatraemia
ASM - carbamazepine, oxcarbazepine, levetiracetam, sodium valproate
Antipsychotics - phenothiazines, butyrophenones
Antidepressants - SSRI, SNRI, TCA
Diuretics - thiazides (bendroflumethiazide), indapamide
Antineoplastic - cyclophosphamide, cisplatin, vincristine, ifosfamide
V2 receptor agonist - desmopressin, vasopressin, oxytocin
Hypotonic fluids - compound sodium lactate solution
Others - NSAIDs, nicotine, clofibrate, amphetamine, PPis
What is cerebral salt wasting syndrome
Centrally-mediated increases in renal sodium loss causing hyponatraemia, polyuria, dehydration
List the causes of hypovolaemic, euvolaemic, and hypervolaemic hyponatraemia
Hypovolaemic
* Cerebral salt wasting syndrome
* Hypokalaemia
* Diuretics
* Primary adrenal insufficiency
* Ketonuria
* Diarrhoea/vomitting
* Blood loss
Euvolaemic
* SIADH
* Hypothyroidism
* Secondary adrenal insufficiency
* Cancers with brain met
Hypervolaemic
* SIADH
* Congestive heart failure
* Cirrhosis
* Acute/chronic renal failure
* Anaphylaxis
* Pregnancy
Management of hyponatraemia - increases in serum sodium concentration should not exceed how much
10 mmol/L in 24h
(osmotic demyelination syndrome)
In what patient groups is the risk of osmotic demyelination increased
Malignancy
Malnutrition
Liver failure
What sodium disorder usually present within 48h of pituitary surgery
Cranial diabetes insipidus
Contrast the biochemical features in SIADH vs CSWS
SIADH
* Plasma hypo-osmolality
* Eu/hypervolaemia
* Urinary sodium >20mmol/L
* Urine osmolality normal
CSWS
* Plasma hyper-osmolality
* Hypovolaemia
* Urinary sodium >40mmol/L
* Urine osmolality high
List the management approaches for SIADH vs CSWS
SIADH - restrict fluid intake (1.5L, not <750mL in 24h)
CSWS - replace with isotonic sodium containing fluids
Give the management approach for SIADH/CSWS in serum sodium <125mmol/L or severe symptoms
150mL hypertonic saline through CVC over 20mins
Check serum sodium concentration - aim for 5mmol/L increase in serum sodium in the first hour
Another 150mL HTS over 20mins while awaiting results
List the symptoms in hypernatraemia
Thirst
Lethargy
Irritability
Restlessness
Muscle weakness
Confusion
Contrast the signs of CDI vs dehydration
CDI
* Low CVP (<5mmHg)
* High urine output (>1000mL in 4h)
* Low specific gravity (<1.005)
* Normal urinary sodium (20-60mmol/L)
* High serum osmolality (>305mOsm/kg)
* Low urine osmolality (<350mOsm/kg)
Dehydration
* Low CVP (<5mmHg)
* Low urine output (<0.5 ml/kg/h)
* High specific gravity (>1.020)
* Tachy/hypotension
List the management approaches for CDI
0.2-0.4mg desmopressin IV/IM initially if urine osmolality inappropriately low
Further desmopressin if urine osmolality <100mOsm/kg
Serum sodium monitoring every 4h until stable
Consider 5% dextrose IV if serum sodium >155mmol/L
