Polyuria and Traumatic Brain Injury
OVERVIEW
- polyuria following TBI is common
- multiple causes, some of which imply a poor prognosis
- Goal is to identify and treat the cause and any complications
DIFFERENTIAL
Common and important causes
- Alcohol induced diuresis
- Osmotic diuresis (mannitol therapy)
- Cerebral salt wasting
- Diabetes insipidus
- Hypertonic saline administration
- Hypertensive diuresis (e.g. vasopressors to maintain CPP)
- Appropriate response to fluid therapy or diuretics
- Hyperglycaemia
- Cold-induced hypothermia (either due to exposure or therapeutic hypothermia)
- Co-existent renal disorder (e.g. polyuric phase of acute kidney injury)
HISTORY
- recent osmotherapy (mannitol or hypertonic saline)
- fluid balance and diuretic use
- vasopressor use for CPP management
- diabetes, hypertension, renal disease
- ETOH
- hypothermia
EXAMINATION
- volume status
- urine colour and volume
- BP
- temperature
- evidence of DM, HTN or renal disease
INVESTIGATIONS
Serum
- Na+
- osmolality
- ETOH level
- osmolar gap calculation
Urinary
- osmolality
- Na+
Consider further investigation of renal disease if appropriate (e.g. UEC, ultrasound)
MANAGEMENT
Alcohol induced diuresis
- high ETOH level
-> replace fluid loss
Osmotic diuresis (mannitol therapy)
- high osmolar gap, osmolality and urinary osmolality
-> monitor for hypovolaemia
-> cease mannitol if osmolality > 320mosmol/kg
-> replace electrolytes
Cerebral salt wasting (mimics SIADH biochemically but hypovolemic)
- high urinary osmolality
- low plasma Na+
- plasma osmolality may be high or normal
-> monitor for hypovolaemia, give normal saline
Diabetes insipidus
- high Na+
- low urinary osmolality (<350)
- high plasma osmolality
-> replace H2O or D5W
-> DDAVP 0.5mcg
Hypertonic saline administration
- high serum and urine Na+
Hypertensive diuresis
- normal Na+ and osmolality
-> monitor
Appropriate response to fluid therapy
- normal Na+ and osmolality
-> monitor
Diuretics
- +/- low serum Na, metabolic alkalosis, high urine Na
-> monitor, give fluids if needed; consider acetazolamide
Hyperglycaemia
- high glucose
- glycosuria
-> insulin
Cold-induce diuresis
- hypothermia
-> monitor, rewarm if appropriate, maintain euvolemia
References and Links
CCC Neurocritical Care Series
Emergencies: Brain Herniation, Eclampsia, Elevated ICP, Status Epilepticus, Status Epilepticus in Paeds
DDx: Acute Non-Traumatic Weakness, Bulbar Dysfunction, Coma, Coma-like Syndromes, Delayed Awakening, Hearing Loss in ICU, ICU acquired Weakness, Post-Op Confusion, Pseudocoma, Pupillary Abnormalities
Neurology: Anti-NMDA Encephalitis, Basilar Artery Occlusion, Central Diabetes Insipidus, Cerebral Oedema, Cerebral Venous Sinus Thrombosis, Cervical (Carotid / Vertebral) Artery Dissections, Delirium, GBS vs CIP, GBS vs MG vs MND, Guillain-Barre Syndrome, Horner’s Syndrome, Hypoxic Brain Injury, Intracerebral Haemorrhage (ICH), Myasthenia Gravis, Non-convulsive Status Epilepticus, Post-Hypoxic Myoclonus, PRES, Stroke Thrombolysis, Transverse Myelitis, Watershed Infarcts, Wernicke’s Encephalopathy
Neurosurgery: Cerebral Salt Wasting, Decompressive Craniectomy, Decompressive Craniectomy for Malignant MCA Syndrome, Intracerebral Haemorrhage (ICH)
— SCI: Anatomy and Syndromes, Acute Traumatic Spinal Cord Injury, C-Spine Assessment, C-Spine Fractures, Spinal Cord Infarction, Syndomes,
— SAH: Acute management, Coiling vs Clipping, Complications, Grading Systems, Literature Summaries, ICU Management, Monitoring, Overview, Prognostication, Vasospasm
— TBI: Assessment, Base of skull fracture, Brain Impact Apnoea, Cerebral Perfusion Pressure (CPP), DI in TBI, Elevated ICP, Limitations of CT, Lund Concept, Management, Moderate Head Injury, Monitoring, Overview, Paediatric TBI, Polyuria incl. CSW, Prognosis, Seizures, Temperature
ID in NeuroCrit. Care: Aseptic Meningitis, Bacterial Meningitis, Botulism, Cryptococcosis, Encephalitis, HSV Encephalitis, Meningococcaemia, Spinal Epidural Abscess
Equipment/Investigations: BIS Monitoring, Codman ICP Monitor, Continuous EEG, CSF Analysis, CT Head, CT Head Interpretation, EEG, Extradural ICP Monitors, External Ventricular Drain (EVD), Evoked Potentials, Jugular Bulb Oxygen Saturation, MRI Head, MRI and the Critically Ill, Train of Four (TOF), Transcranial Doppler
Pharmacology: Desmopressin, Hypertonic Saline, Levetiracetam (Keppra), Mannitol, Midazolam, Sedation in ICU, Thiopentone
MISC: Brainstem Rules of 4, Cognitive Impairment in Critically Ill, Eye Movements in Coma, Examination of the Unconscious Patient, Glasgow Coma Scale (GCS), Hiccoughs, Myopathy vs Neuropathy, Neurology Literature Summaries, NSx Literature Summaries, Occulocephalic and occulovestibular reflexes, Prognosis after Cardiac Arrest, SIADH vs Cerebral Salt Wasting, Sleep in ICU
- Brain Trauma Foundation Guidelines – Guidelines for the Management of Severe TBI
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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