DSA34 - Transient Loss of Consciousness

What in the CNS is responsible for maintaining the complex process/continuum of "consciousness"?

Reticular Activating System (RAS)

What parts make up the RAS?

-Brainstem reticular formations

-Thalamic Intralaminar connections

-Projection of thalamic tracts to the global cerebral cortex

Where is the RAS located?

Central brainstem from midbrain to caudal pons

What factors must be maintained for the cerebral cortex and the RAS to function properly (to maintain consciousness)?

-Glucose

-O2

-CBF = 55 ml/100 g/min

-pCO2 and pH at normal levels

What issues can interfere with the necessary factors for the RAS & Cortex?

-Reduction of brain perfusion

-Focal reduction of perfusion to RAS

-Hypoxemia

-Severe Anemia

-Toxicity (barbiturates, narcotics)

-Seizures

-Trauma (concussion/TBI)

What is the lifetime incidence of JUST vasovagal syncope?

At least 35%

Define Syncope

To swoon or faint; ALWAYS implies that the underlying pathophysiological mechanism is global cerebral hypoperfusion

What is the question you must ask to determine the Dx of LOC?

Is there evidence for global cerebral hypoperfusion (syncope) or for seizure, or is there some other associated event?

Define Cause of Transient LOC:

Most COMMON cause of "passing out"; Referred to as neurocardiogenic or reflex syncope - intrinsic cardiovascular reflexes are misfiring, resulting in sudden drop in BP (vasodepressor effect) in conjunction with a paradoxical bradycardia (vagal effect).

-Hx: Recurrent; more common in ELDERLY, PHYSICALLY IMPAIRED (esp if inactive and on multiple meds); Can triggered by prolonged standing, heat, crowds, EtOH; May be a/w brief gen convulsive activity

-Sx: Occurs while standing/sitting erect; lasts seconds to minutes; A/w = light-headed, sweating, feeling hot or cold, pallor; Precip events = strong emotion, pain, fatigue, coughing, urinating, vomiting, swallowing, defecating, hunger, nausea, palpitations

-PE: +/- OH; DURING = pale, diaphoretic, tachycardic/bradycardic, hypotensive

-Dx: Likely Normal

Vasovagal/Vasodepressor Syncope

T/F - Vasovagal syncope is the most common cause of syncope

True

What is the pathophysiological mechanism behind Vasovagal Syncope?

Paradoxical, autonomic reflex triggered by stimulus --> SUDDEN increased sympathetic surge --> Activate Beta 2 receptors in large muscles ==> SHUNTS BLOOD & increases (for a moment) venous pooling in LEs, while simultaneously INCREASING CONTRACTILITY of an EMPTY VENTRICLE --> Decreased Venous Return --> Stimulates mechanoreceptors in atria to stimulate vagal nerve to SLOW HEART (with low SV) = Decreased CO (low cerebral perfusion)

Define Cause of Transient LOC:

Global cerebral hypoperfusion caused by specific cardiac structural defects or arrhythmia (ex: aortic stenosis/sick sinus syndrome with episodic bradycardia)

-Hx: Hx HD, Palpitations, Angina (more than non-cardiac)

-Sx: Unrelated to posture, LOC rarely leads to injury, tongue biting/incontinence rare

-PE: Brief post-ictal period; Normal but more abns than with non-cardiac

-Dx: CXR (Cardiomegaly), ECG Abns (may need 21 day holter monitor/EP studies/ECHO/Cardiac CT or MRI)

-Tx: Depends on etiology

Cardiogenic Syncope

Define Cause of Transient LOC:

Increased electrical activity may "short circuit" RAS and/or decreased CBF with sympathetic overdrive

-Hx: Any age or gender; No specific bodily position; LOC may lead to injury; FHx, +/- Hx Head Trauma and/or neuropsych Hx

-Sx: Occurs in any position; Duration for several minutes; Common convulsive activity; Tongue biting & incontinence common

-PE: Prolonged post-ictal period; Some abns in neuro-psych exam; Skin lesions in neurocutaneous syndromes (Tuberous sclerosis, NF, etc); evidence of injury

-Dx: Abn BRAIN MRI + EEGbo

Seizure

Define Cause of Transient LOC:

Injury to VB system and RAS causes this to occur (can either be unilateral or to entire part)

-Hx: Hx of focal neuro sx + Vascular risks

-Sx: Duration for minutes to hours; No relationship to position; No triggers

-PE: Focal Neuro findings - may have CROSSED SX (ex: Vertical Diplopia, Dysarthria, bilateral weakness AND/OR unilateral facial numbness or weakness with contralateral limb numbness or weakness) + HTN +/- AFib +/- Bruits

-Dx: Brain MRI

Brainstem TIA

Define Cause of Transient LOC:

Anxiety --> Hyperventilation --> Resp Alkalosis ==> Cerebral Vasoconstriction

-Hx: Hx of anxiety or hyperventilation

-Sx: Perioral tingling/cramping + fingers/hands tingling during hypervent + Anxiety + Air Hunger (can't get full breath); unrelieved by recumbency

-PE: Normal, but appears anxious

-Dx: Normal

-Tx: Breath thru paper bag, lie flat, anti-anxiety meds, counseling

Psychogenic Syncope

Define Cause of Transient LOC:

-Hx: Rare in non-diabetics with pancreatic neoplasm

-Sx: Duration is prolonged

-PE: Normal aside from event; DURING = diaphoretic, mydriasis, tachycardia; Diabetic signs

-Dx: Low BS during event (<50 meq/l, often < 30 meq/l)

-Tx: IV/ORAL GLUCOSE!! + Adjust diabetes treatment

Hypoglycemic LOC

What are the first steps when providing first aid to someone who faints?

-Keep them recumbent

-Place something soft under head

-Turn head to side

-Check VSS

-Keep recumbent until all post-ictal sx subside

-Slowly stand/sit them up