Flashcards in Periph Vasodilators Deck (51)
What do peripheral vasodilators facilitate?
Forward flow in AR, MR or HF
When do we use peripheral vasodilators?
For controlled hypotension and to treat hypertensive ccrisis
Two most common peripheral vasodilators we use?
Nipride and NTG
Approximately what is the goal MAP in cases that use controlled hypotension?
When would we NOT use controlled hypotension?
Severe CVD, SCI or TBI. They all really need perfusion.
Where does nipride lack significant effects?
nonvascular smooth muscle and cardiac muscle (DOES NOT DILATE THE CORONARIES)
Does nipride relax arterial or venous?
Is nipride direct or indirect and selective or nonselective?
What is the MOA of nipride?
Nipride interacts with oxyhemoglobin which dissociates immediately to form methemoglobin and the release of NO and cyanide. NO activates the guanylate cyclase (in the vascular muscle) increasing cGMP. cGMP inhibits calcium entry into the vascular smooth musle but increases the uptake of Ca into the sER. RESULTS IN VASODILATION!
How is nipride metabolized?
The transfer of an election from Fe to nipride yields metHgb and an unstable nipride radical where all 5 cyanide ions are released. One of these cyanide ions reacts with metHgb to form cyano-methemoglobin. The remainder of cyanide ions are metabolized in the liver and kidney are are converted to thiocyanate which is cleared by the kidney.
Why do we care about the metabolism of nipride?
When can cyanide toxicity occur?
At rates over 2mcg/kg/min for long periods.
When do we start to suspect cyanide toxicity?
When a patient starts demonstrating resistance to effects, previous responsive patient could now be unresponsive at rates over 2-10mcg/kg/min.
Why is cyanide toxicity so bad?
The cyanide ion interferes with the tissues ability to uptake oxygen which may precipitate tissue anoxia, anaerobic metabolism, and lactic acidosis (see a lactate like 10 instead of the normal 1-3)
What can occur as a result of cyanide toxicity?
CNS dysfunction, mental status changes and seizures.
How do we treat cyanide toxicity?
Immediately discontinue nipride, 100% FiO2 admin despite their O2 sat. Sodium bicarb to correct metabolic acidosis. Sodium thiosulfate acts as a sulfur donor to convert cyanide to thiocyanate. Sodium nitrate 5mg/kg if severe toxicity (converts hemoglobin to metHgb which converts cyanide to cyanomethemoglobin).
Do we worry about thiocyanate toxicity?
It is rare seeing as thiocynate (which is the result of the livers conversion of a cyanide ion) is cleared by the kidney in 3 to 7 days. It is less toxic than cyanide.
What are some symptoms of thiocyanate toxicity?
N/V, tinnitus, fatigue, CNS hyperreflexia, confusion, psychosis, miosis, seizure and coma.
What about methemoglobinemia?
It is also rare but should be considered as a differential diagnosis in patients with impaired oxygenation despite adequate CO and arterial oxygenation.
What happens when nipride is exposed to light?
With continuous exposure to light nipride is converted to aquapentacyanoferrate in the presence of light and the release of hydrogen cyanide.
What should nipride be mixed in?
5% glucose in water.
What is the dose of nipride?
The max dose of nipride should not be infused for greater than how long?
What is the onset and DOA of nipride?
Immediate onset and a short duration of action.
What considerations do we have regarding the use of nipride?
Requires a continuous IV administration to maintain a therapeutic effect. Extremely potent use and aline.
What kind of affects does nipride have on the CV system?
Direct venous arterial vasodilation, decreased venous capacitance and decreased preload. We can see a baroreceptor mediated reflex in HR. We decrease our SBP, SVR, PVR while we increase contractility. There is an intracoronary steal in areas of damage associated with MI.
What is coronary steal?
Coronary steal (with its symptoms termed cardiac steal syndrome) is a phenomenon where an alteration of circulation patterns lead to a reduction in the blood directed to the coronary circulation. It is caused when there is narrowing of the coronary arteries and a coronary vasodilator is used - "stealing" blood away from those parts of the heart. This happens as a result of the narrowed coronary arteries being always maximally dilated to compensate for the decreased upstream blood supply. Thus, dilating the resistance vessels in the coronary circulation causes blood to be shunted away from the coronary vessels supplying the ischemic zones, creating more ischemia.
What CNS effects do we see when we use nipride?
Increased cerebral blood flow and ICP
What pulmonary effects do we see when we use nipride?
Attenuation of hypoxic vasoconstriction.