CV Phys & Vasopressors

Question 1

Drugs of choice for mild hypotension from general or regional anesthesia? (2)

Answer 1

Phenylephrine
Dose: 50-200 mcg
Infusion: 20-200 mcg/min

Ephedrine
Dose: 2.5-10 mg

Question 2

Concentration: 1:1,000 epi

Answer 2

Dose Equivalent & Percent

1 mg/ml = 0.1%

Question 3

Concentration: 1:10,000 epi

Answer 3

Dose Equivalent & Percent

0.1 mg/ml = 0.01%

Question 4

Concentration: 1:100,000 epi

Answer 4

Dose Equivalent & Percent

0.01 mg/ml = 0.001%

Question 5

Concentration: 1:200,000 epi

Answer 5

Dose Equivalent & Percent

0.005 mg/ml = 0.0005%

Question 6

How many mg of epi are in 5mL of a 1:10,000 (g/mL) solution?

Answer 6

Convert 1:10,000 into mg/mL
1:10,000 = 1000mg/10,000mL = 0.1 mg/mL
5mL x 0.1 mg/mL = 0.5 mg

Question 7

chronotropy

Answer 7

HR

Question 8

inotropy

Answer 8

contractility

Question 9

dromotropy

Answer 9

conduction velocity

Question 10

lusitropy

Answer 10

rate of myocardial relaxation

Question 11

Endothelial Vasodilators

Answer 11

NO and prostacyclin

Question 12

Endothelial vasoconstrictors

Answer 12

thromboxane A2, leukotrienes, endothelin 1, ACE

Question 13

(vascular) resistance is most affected by?

Answer 13

radius^4

Question 14

PCWP is a good approximation of?

Answer 14

LA pressure and reflects the filling pressure of the L side of the heart

Question 15

Bainbridge reflex

Answer 15

-atrial stretch can increase HR which may help match CO to venous return

Question 16

Baroreceptor response

Answer 16

receptors in carotid sinus and aortic arch are activated by increased SBP that stimulates stretch receptors and sends signals through the vagus and glossopharyngeal nerves to CNS

Question 17

Carotid sinus chemoreceptors

Answer 17

-stimulation due to atrial hypoxemia results in SNS stimulation

Question 18

How low is too low of a decrease in BP in a healthy patient?

Answer 18

20-30% below baseline in normal healthy patient may be OKAY

hypotensive situations: keep MAP greater than 2/3 of normotensive MAP to prevent cerebral ischemia

Question 19

Patient position and BP

Answer 19

blood pressure decreases 2 mmHg for every 2.5 cm (1 in) height above the point of measurement

BP in brain of a sitting pt is about 12-16 mmHg lower than the upper arm measurement

Question 20

Endogenous catecholamine synthesis pathway:

Answer 20

phenylalanine > tyrosine > L-dopa > dopamine > norepi > epi

Question 21

Common synthesized catecholamines:

Answer 21

dobutamine
isoproterenol
phenylephrine

Question 22

Vasopressin Dose

Answer 22

• 0.01-0.04 units/min IV infusion for vasodilatory shock
• 1-8 unit bolus
• elimination t1/2 10-20 min

Question 23

Great for refractory hypotension due to ACE/ARB-induced hypotension

Answer 23

Vasopressin

1-8 units IV push

Question 24

Epi Dose

Answer 24

20-100 mcg IV bolus

0.01-.1 mcg/kg/min infusion

Question 25

Dopamine Dose

Answer 25

1-30 mcg/kg/min IV infusion Dopaminergic = 0.5-2 Beta 1 = 2-10 alpha = > 10

Question 26

Phenylepherine Dose

Answer 26

50-200 mcg IV bolus to treat BP that accompanies SNS blockade produced by anesthesia 20-200 mcg/min for continuous infusion or if weight based infusion then 0.25-1 mcg/kg/min

Question 27

Ephedrine Dose

Answer 27

2. 5-10 mg IV adults 0. 1 mg/kg IV peds - longer onset due to indirect effects - tachyphylaxis possible on repeat doses

Question 28

Dobutamine Dose

Answer 28

high dose (cardiac stress tests) = 10-20 m/kg /min low dose infusions: 5 mcg/kg/min

Question 29

Milrinone Dose

Answer 29

50 mcg/kg IV bolus over 10-30 min 0.375-0.75 mcg/kg/min infusion

Question 30

What kind of patients should NOT be subjected to hypotension

Answer 30

``` known carotid stenosis known valve disorders known heart failure known fixed CO known severe CAD ```

Question 31

Factors that directly affect MAP

Answer 31

CO & SVR

Question 32

Factors that directly affect CO

Answer 32

SV & HR

Question 33

Factors that directly affect SV

Answer 33

Preload & Inotropy

Question 34

Factors that directly affect Preload

Answer 34

Blood volume & venous compliance

Question 35

What neurohumoral factors affect the physiology of blood pressure?

Answer 35

neural (autonomic) and humoral (circulating or hormonal) factors regulate the heart and vasculature ANS = SNS & PSNS Humoral = Renal Na+ and H2o handling by renin-angiotensin-aldosterone system (also circulating catecholamines, vasopressin (ADH), ANP, and endothelin)

Question 36

Volatile agents general effects on hemodynamics (HR, Preload, Afterload, Contractility)

Answer 36

HR - decrease Preload - vasodilation reduces volume return to heart Afterload - vasodilation reduces SVR Contractility - depress

Question 37

Blood pressure control is due to 4 main factors including?

Answer 37

1. intrinsic factors (frank starling, SA/AV node) 2. nervous system (SNS, PSNS) 3. reflexes (baroreceptor, chemoreceptor, atrial receptor/bainbridge) 4. humoral factors (RAAS)

Question 38

As anesthetists how can we control Frank-Starling Mechanism?

Answer 38

maintain optiumum preload

Question 39

As anesthetists how can we affect SA & AV nodes?

Answer 39

antiarrhythmics

Question 40

As anesthetists how can we affect nervous system factors?

Answer 40

sympathomimetics, anticholinergics, cholinergic

Question 41

As anesthetists how can we affect baroreceptor reflexes?

Answer 41

be aware of bradycardia with pure alpha agonists

Question 42

As anesthetists how can we affect chemoreceptor reflexes?

Answer 42

maintain optimal oxygen saturation, etco2, pH

Question 43

As anesthetists how can we affect the atrial receptor (bainbridge) reflex?

Answer 43

maintain optimum preload

Question 44

As anesthetists how can we affect humoral factors?

Answer 44

vasopressin

Question 45

Describe the RAAS system

Answer 45

The renin-angiotensin-aldosterone system (RAAS) plays an important role in regulating blood volume and systemic vascular resistance, which together influence cardiac output and arterial pressure. As the name implies, there are three important components to this system: 1) renin, 2) angiotensin, and 3) aldosterone. Renin, which is released primarily by the kidneys, stimulates the formation of angiotensin in blood and tissues, which in turn stimulates the release of aldosterone from the adrenal cortex.

Question 46

3 things that stimulate renin release by the kidneys

Answer 46

1) sympathetic nerve activation (acting through β1-adrenoceptors) 2) renal artery hypotension (caused by systemic hypotension or renal artery stenosis) 3) decreased sodium delivery to the distal tubules of the kidney.

Question 47

Diagram how we get from renin to ATII

Answer 47

Circulating Renin --> angiotensinogen --> angiotensin I --> [ACE enzyme in lungs] --> angiotensin II renin is released into the blood, it acts upon a circulating substrate, angiotensinogen, that undergoes proteolytic cleavage to form the decapeptide angiotensin I. Vascular endothelium, particularly in the lungs, has an enzyme, angiotensin converting enzyme (ACE), that cleaves off two amino acids to form the octapeptide, angiotensin II

Question 48

How can dopamine cause both vasodilation and vasoconstriction?

Answer 48

Low doses - vasodilation via activation of DA1 receptors and inhibition of NE by activation of DA2 receptors High doses - vasoconstriction via activation of alpha1 & alpha2 adrenoceptors on the postjunctional cell

Question 49

non-catecholamine alpha1 agonist?

Answer 49

phenylephrine

Question 50

Norepi dose

Answer 50

0.1 mcg/kg IV push bolus 2-20 mcg/min infusion 0.01-3 mcg/kg/min weight based infusion

Question 51

Describe autoregulation of BP

Answer 51

-the intrinsic ability of circulation to maintain a constant blood flow despite changes in perfusion pressure (MAP), vessel resistance is the regulated variable to keep flow constant

Question 52

Describe Critical closing pressure

Answer 52

pressure at which vessels collapse and blood flow stops, this is what makes diastolic blood pressure an important variable

Question 53

How do peripheral chemoreceptors regulate blood pressure?

Answer 53

They are sensitive to Pao2, Paco2, & pH -decreased Pao2/incresaed Co2 causes co-activation of SNS and PNS causing SNS vasoconstriction and PNS decrease in HR

Question 54

How do central chemoreceptors regulate blood pressure?

Answer 54

- exposed to CSF and not blood - stimulated by H+ concentrations in the CSF (not blood) and not PCo2/Po2 - they do so via the products (increase in H+) of the henderson-hasselbalch equation that occurs with an increase in arterial PCo2 occurs leading to a reduction in pH.