ANS Phys & Pharm Flashcards
(65 cards)
ANS Reflexes - CNS:
Cushing’s Triad
1) Increased ICP
2) Bradycardia
3) Hypertension
Intracranial HTN leads to SNS mediated systemic HTN. Activation of the PSNS medullary centers via baroreflex slows HR (but not enough to reduct HTN!). This results in increased blood flow to brain & further increased ICP.
ANS Reflexes - CNS:
Autonomic HYPERreflexia
1) Disruption of efferent impulses down the SC from T5 or higher.
2) Exaggerated SNS response to bowel, bladder, or surgical stimuli d/t receptor sensitivity 2/2 denervation
3) Loss of inhibitory impulses results in pure SNS response (HTN!)
Anesthesia impact: mgmt of quads/paras consists of spinal or GA with careful manipulation of BP due to alterations in ANS.
ANS Reflexes - CNS:
Thermogenesis Reflex
1) Sweating controlled by cholinergic fibers (blocked by atropine or nerve blocks)
2) Shivering decreased in elderly, absent in newborns, blocked by NMDR’s
3) GA impair thermogenesis
All GA ________ thermogenesis reflexes.
All GA impair thermogenesis reflexes.
Sweating threshold is increased and vasoconstriction and shivering thresholds are markedly decreased. Can lead to hypothermia during surgery if heat loss thorugh radiation, convection, conduction, and evaporation are not minimized.
ANS Reflexes - Cardiac:
Baroreceptor
- stretch receptors in aorta and carotid arteries sense increased pressure
- send signals via Hering Nerve & Vagus (CNX) to medulla
- decreased HR, decreased BP, decreased contractility, decreased PVR
- Phenylephrine (a1-agonist) increases BP and reflex decreases HR
ANS Reflexes - Cardiac:
Chemoreceptor
- Instead of sensing BP (baroreflex), chemoreceptors sense increased arterial CO2 and decreased arterial pH.
- HYPERcarbia increases minute ventilation.
- Peripheral in carotid body respond to decreased PO2.
- N. Hering and Vagus increase RR and TV which increases minute ventilation
- may also see increased HR and CO.
ANS Reflexes - Cardiac:
Bainbridge Reflex
- increasd CVP activates stretch receptors in the atria
- afferent impulses through vagus inhibit PSNS output resulting in tachycardia
- seen during labor when contractions autotransfuse and increase CVP
ANS Reflexes - Cardiac:
Bezold-Jarisch
1. hypotension
2. bradycardia
3. coronary dilation
- noxious stimuli (chemical or mechanical) sensed in cardiac ventricles
- unmyelinated -fibers of vagus send signals to 1) enhance baroreflex, 2) inhibit sympathetic output and 3) decrease PVR to make it easier for heart to pump.
- increased blood flow to the myocardium to decrease the work of the heart (cardioprotective)*
ANS Reflexes - Cardiac:
Oculocardiac (Five & Dime Reflex)
- afferent impulses to pressure on the eye or pulling on eye muscle
- efferent slowing of HR via Vagus N
- muscarinic response can be blocked by atropine or glycopyrolate (so surgeon can proceed with procedure)
Five & Dime
- Afferent through CN V
- Efferent through CN X Vagus
= five and dime
Anesthetic Interactions:
A2 agonists are _______ and reduce anesthetic needs.
A2 agonists are inhibitory and reduce anesthetic needs.
Anesthetic Interactions:
Fentanyl _______ SNS tone and _______ vagal activation.
Fentanyl depresses SNS tone and promotes vagal activation.
Anesthetic Interactions:
Des _____ the ANS and _____ the SNS (so we see HTN and tachycardia)
Des depresses the ANS and stimulates the SNS
Comorbid Implications:
Aging
- HTN and orthostasis
- temperature regulation
- increased circulating NE (receptor downregulation and decreased responses to exogenous catecholamines)
- decreased renin, decreased aldosterone, increased ANP = salt wasting!
Comorbid Implications:
DM
- 20-40% IDDM have neuropathies (ANS)
- labile BP, gastroparesis, altered thermoregulation, ?vagal dysfunction
- increased aspiration risk, aggressive temp maintenance, increased CO
Comorbid Implications:
Dysautonomia
- Shy-Drager syndrome, Guillain Barre, Lambert-Eaton, Postural Orthostatic Hypotension, HR variability, BP lability
dysautonomia - umbrella term used to describe several different medical conditions that cause a malfunction of the Autonomic Nervous System.
Endogenous Catecholamines
- EPi
- NE
- Dopamine
Epi
- produced in adrenal medulla (80% Epi, 20% NE)
- Adrenal standard secretion rates:
0. 2 mcg/kg/min Epi
0. 05 mcg/kg/min NE
- Exogenous Infusion Rate:
2-10mcg/kg/min (B1, B2)
>10mcg/kg/min (A1)
Anaphylaxis 0.2-0.5 mg sub-Q
NE
- NE has >A1 and no B2 effects than Epi
- 4-12 mcg/min (A1, B)
At Low Dose: B1 dominates & BP increases 2/2 increased CO
At High Dose: A1 dominates and BP increases, but HR and CO may decrease 2/2 baroreflex
- beware effect on pulm A1 and possible pulm HTN and R HF
Dopamine
- precursor to Epi and NE
- Exogenous dopamine does not cross BBB (L-dopa for parkinson’s)
Low Dose: 1-3 mcg/kg/min = D1 activation (coronary, renal, mesenteric vasodilation)
Moderate Dose: 3-10 mcg/kg/min = B1
High: >10 mcg/kg/min = A1
Metabolism of catecholamines
- COMT is intracellular
- MAO in nerve terminal mitochondria
- Exogenous catecholamines may resist COMT and MAO metabolism
- MAOIs will cause more of these to be available*
Exogenous Catecholamines:
Dopamine D1 Receptor Agonists - Fenoldopam
- minimal D-2, a or b effects
- 10x potency of dopamine
- dosed 0.1-0.8 mcg/kg/min
- 0.1-0.2 mcg/kg/min = renal vasodilation, increased renal blood flow and GFR, and Na+ excretion
- improved outcome in CABG pts w less renal failure!
Exogenous Catecholamines:
a1 receptor agonists
- increase BP and MVO2 supply
- decrease hr
- variable CO
- this is good! increased BP and decreased HR = better perfusion to coronaries!
phenylephrine
- almost pure A agonist
- > venoconstriction than arterial (increases venous return, maintains CO, HR decreases 2/2 baroreceptors)
- NOT contraindicated in OB (but not necessarily better than ephedrine)
- neosynephrine nasal spray
