Vasopressin & SNP

Question 1

Arginine vasopressin

Answer 1

endogenous hormone

Question 2

ADH

Answer 2

produced in hypothalamus stores in posterior pituitary

Question 3

ADH role

Answer 3

osmoregulation: release stimulated by increased osmolarity and hypovolemia
potent vasoconstrictor, but dilates renal afferent, pulmonary and cerebral arterioles

Question 4

3 Types Vasopressin Receptors

Answer 4

V1, V2, V3

Question 5

V1

Answer 5

mediates vasoconstriction (vasculature)

Question 6

V2

Answer 6

mediates water reabsorption in the renal collecting ducts (kidney)

Question 7

V3

Answer 7

found in CNS and stimulates modulation of corticotrophin secretion

Question 8

Vasopressin Uses

Answer 8

post cardiopulm bypass shock 
refractory hypotension (ACE & ARB DOS) 
Reduce bleeding in VWB disease 
anti-diuresis in DI 
treatment of enuresis

Question 9

Vasopressin Dosage

Answer 9

low dose infusion: 0.03-0.04 units/min, max 0.1 units/min
bolus IV 1-2 units
onset: 1-5 min 
DOA: 10-30 min 
peak effect: 5 min

Question 10

Vasopressin Complications

Answer 10

only seen at dosages >0.04 units/min
GI ischemia
decreased CO
skin or digital necrosis

Question 11

Peripheral Vasodilators: SNP

Answer 11

direct acting, nonselective peripheral vasodilator
relaxation of arterial and venous VSM
lacks significant effects on nonvascular SM and cardiac muscle

Question 12

SNP MOA

Answer 12

SNP interacts with oxyhemoglobin to form methemoglobin, NO and cyanide
NO activates guanylate cyclase (increasing cGMP)

Question 13

SNP Metabolism

Answer 13

transfer of an electron from iron of oxyhemoglobin to SNP yields metHgb and an UNSTABLE SNP radical, this breaks down to release 5 cyanide ions.
ONE cyanide ion interacts with metHGB to form cyano-methemoglobin (nontoxic)
remainder metabolized in liver and kidney and converted to thiocyanate

Question 14

SNP Toxicity

Answer 14

occurs due to the effects of high plasma concentrations of THIOCYANATE

Question 15

Cyanide Toxicity

Answer 15

occurs at rates >2mcg/kg/min for LONG PERIODS
suspect this when patients have resistance to hypotensive effects or previously responsive patient who is unresponsive (tachyphylaxis) rates >2-10 mcg/kg/min
May precipitate tissue anoxia, anaerobic metabolism and lactic acidosis

Question 16

Thiocyanate Toxicity

Answer 16

rare, cleared by kidney in 3-7 days
less toxic than cyanide
S/S: N/V tinnutis, fatigue, CNS hyperrflexia, confusion, psychosis, miosis, seizure and coma

Question 17

SNP Dosage

Answer 17

0.3 mcg/kg/min- 10 mcg/kg/min IV 
do not infuse >10 min 
immediate onset, short DOA 
extremely potent, monitor BP with aline 
requires continuous IV admin to maintain therapeutic effect

Question 18

SNP Effects CV

Answer 18

venous and arterial vasodilation 
decreased venous capacitance d/t VR 
Increase HR (baroreflex) 
decrease SBP, SVR, PVR
increased contractility 
decreased diastolic BP, reduced coronary perfusion

Question 19

Clinical uses SNP

Answer 19

controlled hypotension: 0.3-0.5 mcg/kg/min (max 2mcg/kg/min)
hypertensive crisis: infusion 1-2mcg/kg IV (bolus also)
cardiac disease: decreases LV afterload, benefits management of MR or AR, CHF, and HF
consider coronary steal

Question 20

cGMP role

Answer 20

inhibits calcium entry into VSMC but increases uptake of calcium into the smooth ER.
Results in vasodilation via NO

Question 21

Cyanide Toxicity Tx

Answer 21

D/C SNP ASAP
100% FIO2 (even though sat is good)
Sodium bicarb
Sodium thiosulfate 150mg/kg over 15 min (sulfur donor to convert cyanide to thiocyanate
sodium nitrate 5mg/kg for SEVERE TOXICITY (coverts hemoglobin to metHgb which converts cyanide to cyanometHemoglobin

Question 22

SNP Effects CNS

Answer 22

increased CBF and ICP

modest decrease in MAP or with greater decrease in MAP can reduce CBF (caution with carotid disease)

Question 23

SNP Effects Pulmonary

Answer 23

attenuation of HPV

Question 24

SNP Effects Blood

Answer 24

increased intracellular cGMP leads to inhibition of platelet aggregation and increase bleeding time.

Question 25

Methemoglobinemia

Answer 25

rare, consider differential diagnosis with pts having impaired oxygenation despite adequate CO and arterial oxygenation

Question 26

Phototoxicity

Answer 26

SNP mix with 5% glucose in water, protect from light
if exposed to light, SNP converts to something that releases hydrogen cyanide
wrap in foil or dark plastic bag

Question 27

Toxicity

Answer 27

in the presence of renal disease and liver disease