302 Autonomic mechanisms: postural hypotension Flashcards
What is transient loss of consciousness?
Real or apparent loss of consciousness with loss of awareness, characterised by amnesia for the period of unconsciousness, abnormal motor control, loss of responsiveness and a short duration
What is syncope?
Transient loss of consciousness due to cerebral hypoperfusion, characterised by a rapid onset, short duration and spontaneous complete recovery
What are some causes of loss of consciousness?
-Syncope
Reflex syncope, orthostatic hypotension, cardiac
-Epileptic seizures
-Psychogenic
Psychogenic pseudo syncope (PPS), psychogenic non-epileptic seizures (PNES)
-Rare causes
Subclavian steal syndrome, vertebrobasilar TIA, Subarachnoid haemorrhage, Cyanotic breath holding spell
What are some causes of low cardiac output?
-Reflex bradycardia
Eg. cardioinhibitory reflex syncope
-Cardiovascular causes
Eg. arrhythmia, structural heart disease, pulmonary hypertension
-Inadequate venous return due to volume depletion or venous pooling
-Chronotropic and inotropic incompetence through autonomic failure
What are some types of reflex (neurally mediated) syncope’s?
-Vaso-vagal
Eg. orthostatic, emotional
-Situational
Eg. micronutrition, GI stimulation, Cough, sneeze, post exercise
-Carotid sinus syndrome
-Non-classical stimulation
What is carotid sinus syndrome?
A ventricular pause lasting >3 s and/or a fall in systolic BP of >50 mmHg
Requires the reproduction of spontaneous symptoms and, in addition, that patients have syncope of unknown origin compatible with a reflex mechanism
Carotid sinus hypersensitivity may be non-specific as it is present in up to 40% of older population
Risk of provocation of TIA – should be undertaken with caution in patients with previous TIA, stroke or known carotid stenosis >70%
What is the treatment for reflex syncope?
-Lie down when you feel it coming on
-Perform counter manoeuvres
-Drink enough water
-Inform others of what to do during a spell
What are the causes of syncope due to orthostatic hypotension?
-Drug induced orthostatic hypotension
Eg. vasodilators, diuretics, antidepressants
-Volume depletion
Eg. haemorrhage, diarrhoea, vomiting
-Primary autonomic failure (neurogenic OH)
Eg. pure autonomic failure, multisystem atrophy, Parkinsons disease
-Secondary autonomic failure
Eg. Diabetes, amyloidosis, spinal cord injury, kidney failure
What is the orthostatic challenge test?
The tilt test
Measuring blood pressure while sitting and standing to look for drop
What is the treatment for orthostatic hypotension?
-Patients should be instructed to have a sufficient salt and water intake, targeting 2–3 L of fluids per day and 10 g of sodium chloride
-Rapid ingestion of cool water is reported to be effective in combating orthostatic intolerance and postprandial hypotension
-Consider modification or discontinuation of hypotensive drug regimen
-Midodrine
-Fludrocortisone
What is the Valsalva manoeuvre?
The action of attempting to exhale with the nostrils and mouth, or the glottis, closed. This increases pressure in the middle ear and the chest, as when bracing to lift heavy objects, and is used as a means of equalizing pressure in the ears
What are some causes of cardiac syncope?
Arrhythmia as the primary cause
-Bradycardia or tachycardia
Structural cardiac causes
Eg. aortic stenosis, acute MI, cardiomyopathy, cardiac masses, congenital anomalies
Cardiopulmonary and great vessels
Eg. pulmonary embolus, acute aortic dissection, pulmonary hypertension
What are some conditions that may be incorrectly diagnosed as syncope?
-Generalised seizures
-Psychogenic pseudo syncope
-Falls without TLOC
-Cerebral haemorrhage
-Carotid TIA
-Cataplexy
-Intoxication
-Coma
-Cardiac arrest
-Metabolic disorders Eg. hypoxia, hypoglycaemia
