Nitrates, Desaturation & pulmonary shunting

ChelleChelle · Sep 4, 2007

One of the complications of nipride as well as nitrates is pulmonary shunting. Some patients are more sensitive than others.

I can even remember a patient that we used hurricaine (benzocaine) spray (back in the dark ages) to numb up the back of an intubated patients throat. That's when I learned that benzocaine spray can increase intrapulmonary shunting in some patients! Turns out that the patients family thought that if a little benzocaine spray was good........ALOT was better. Every time the staff left the room, they squirted a little more in!!!!!

If you notice the QS/QT is increasing on any of your patients.......or the 02 sat is dropping.........always good to figure out why.

Was the patient receiving NTG IV? Large or small amounts?

Here is an excerpt from "Circulation"

"We conclude that the decrease in arterial PO2 following sublingual nitroglycerin is caused by redistribution of pulmonary blood flow with imbalance in ventilation-perfusion relationships or shunting."

The complete reference may be found at: http://www.circ.ahajournals.org/cgi/content/abstract/57/1/106

It's kind of an old article............but do a google search or a medical library search and I'm sure you can access more information.

Here's another excerpt from another source.

"The intravenous nitrodilators nitroglycerine (TNG) and sodium nitroprusside (SNP), may cause hypoxemia by increasing the blood flow to alveoli with a low V/Q ratio"

Complete reference may be found at: http://users.otenet.gr/~fkanak/shunt.html

http://www.springerlink.com/content/v62167562l27205p/

Hope that helps

loafin' · Sep 7, 2007

One of the complications of nipride as well as nitrates is pulmonary shunting. Some patients are more sensitive than others.
I can even remember a patient that we used hurricaine (benzocaine) spray (back in the dark ages) to numb up the back of an intubated patients throat. That's when I learned that benzocaine spray can increase intrapulmonary shunting in some patients! Turns out that the patients family thought that if a little benzocaine spray was good........ALOT was better. Every time the staff left the room, they squirted a little more in!!!!!
If you notice the QS/QT is increasing on any of your patients.......or the 02 sat is dropping.........always good to figure out why.
Was the patient receiving NTG IV? Large or small amounts?
Here is an excerpt from "Circulation"
"We conclude that the decrease in arterial PO2 following sublingual nitroglycerin is caused by redistribution of pulmonary blood flow with imbalance in ventilation-perfusion relationships or shunting."
The complete reference may be found at: http://www.circ.ahajournals.org/cgi/content/abstract/57/1/106
It's kind of an old article............but do a google search or a medical library search and I'm sure you can access more information.
Here's another excerpt from another source.
"The intravenous nitrodilators nitroglycerine (TNG) and sodium nitroprusside (SNP), may cause hypoxemia by increasing the blood flow to alveoli with a low V/Q ratio"
Complete reference may be found at: http://users.otenet.gr/~fkanak/shunt.html

http://www.springerlink.com/content/v62167562l27205p/

Hope that helps

Actually, with nitrates and topical anesthetics that you mentioned as well as others can cause methemoglobinemia. They can change the structure of hemoglobin to where it cannot hold o2, thus causing sats to rapidly decrease. If methemoglobin levels are high enough the patient can die. The antidote is methylene blue.

ChelleChelle · Sep 7, 2007

I agree about the methemoglobinemia................but there is also a component with the vasodilators that increases perfusion to non-ventilated alveoli which contributes to the increased shunt or VQ mismatch.

loafin' · Sep 7, 2007

I agree about the methemoglobinemia................but there is also a component with the vasodilators that increases perfusion to non-ventilated alveoli which contributes to the increased shunt or VQ mismatch.

I agree, just adding more info.

berry · Sep 10, 2007

If a patient is on some form of the nitrate drug classification, why might they experience desaturation and I am also trying to understand why they might cause pulmonary shunting.
Any help with understanding the above would be greatly appreciated. Thanks!

Hypoxic pulmonary vasoconstriction(HPV) is a physiological response in which pulmonary arteries constrict in the presence of hypoxia without hypercapnia. This leads to redirecting blood flow to alveoli with higher oxygen tension. If a patient is on drugs that vasodilate HPV is blunted meaning hypoxic alveoli have increased perfusion.