Question: I was faced the other day with a question by one of my fellow peers in regards to the administration of nitroglycerine. As a contraindication, it states that we cannot administer nitro of the SBP drops by one third or more of its initial value after nitro is administered. This can be interpreted in 2 different ways, as brought to my attention by my fellow peer so now ever since, I second guess myself. So my question is, this "initial value," is it the very first BP we take even before the first dose of nitro, or is it referring to the initial BP you take AFTER the first dose of nitro. It is such a simple answer I am sure but if I can get clarification so I can also relay the message to my fellow peer that would be great.
This is an important question to clarify. The initial value is the BP reading that is taken prior to the administration of the first dose of NTG. As per the medical directive for NTG use in cardiac ischemia, the conditions for its use include a HR between 60-159, as well as the presence of normotension. We know from this that the BP needs to be taken before the administration of NTG.
With respect to the contraindication of a drop in SBP by one third or more of its initial value after NTG is administered, this pertains to a comparison of blood pressures. In this case you are comparing the blood pressure you obtained before nitro use and the BP you obtain afterwards. The purpose of this is to determine if the use of nitroglycerin is causing the patient to vasodilate to the extent that they become hypotensive, which would prompt you to stop using nitroglycerin.
If the BP post nitro use is used as a baseline to determine if it is causing hypotension, then you are using a value that the nitro has already had an effect on and is not representative of the patients baseline BP. Administering nitro in this case may lead to significant hypotension for the patient and subsequent morbidity. Please inform your peer of this answer.