Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

Chart Version – Fentanyl in the out-of-hospital setting: variables associated with hypotension and hypoxemia

Some charts for a more visual assessment of what I wrote in – Fentanyl in the out-of-hospital setting: variables associated with hypotension and hypoxemia.[1]

In this study, hypotension was defined as a systolic blood pressure less than 90 mm/Hg. The numbers in these charts are doses and not patients. A total of 1,055 doses were given to 500 patients.

If the patient was already hypotensive there was a 53% chance that the patient would still be hypotensive after a dose of fentanyl.

That means a 47% chance that the hypotensive patient would no longer be hypotensive after a dose of fentanyl.

There were only 45 doses given to hypotensive patients, so we do not have a lot of data. We also do not know what the specific blood pressures were for each dose (before and after). A patient with a blood pressure of 72/50 before a dose of fentanyl, and a blood pressure of 88/56 after fentanyl is still hypotensive. A patient with a blood pressure of 88/56 before a dose of fentanyl, and a blood pressure of 90/56 after fentanyl is no longer hypotensive. I could go on for a while with the possibilities, but we do not have the raw data, so it is all just speculation. Similarly, a patient could be given fluids or pressors, but that does not appear to be the case in this study.

If this were a treatment for hypotension and with a much larger number of patients and about half had their hypotension resolve after fentanyl, then this might be an impressive treatment for hypotension. A lot of ifs. A lot of correlation.

What about the possibility of new hypotension after a dose of fentanyl?

Out of 1010 doses, there were only 28 cases of new hypotension. We do not know if some of these were patients who were hypotensive before a dose of fentanyl, but had their blood pressure rise after receiving that earlier dose of fentanyl. Would these be considered new hypotension? Were there any cases of this? We don’t know.

We do know that they were giving fentanyl to patients with lower pressures than 90 systolic.

What is the risk of new hypotension in a patient with a blood pressure of at least 90, who is given a dose of fentanyl?

Very low. Less than 3%.

If only all of our treatments were this safe.

When should we expect hypotension after giving a dose of fentanyl?

When the patient is already hypotensive.

A different way of looking at this chart –

Likelihood of no hypotension after a dose of fentanyl:

97+% if no hypotension at the time of the dose.

47% if there is already hypotension at the time of the dose.

What about a chart of hypoxemia after fentanyl?

No hypoxemia after fentanyl.

Zero cases.

Should we ignore the possibility of hypoxemia or hypotension after fentanyl?

No, but we should not avoid using fentanyl due to exaggerated possibilities from people who are not familiar with fentanyl.

Footnotes:

[1] Fentanyl in the out-of-hospital setting: variables associated with hypotension and hypoxemia
Rogue Medic
Article

This refers to the paper below and the podcast below that –

Fentanyl in the out-of-hospital setting: variables associated with hypotension and hypoxemia.
Krauss WC, Shah S, Shah S, Thomas SH.
J Emerg Med. 2011 Feb;40(2):182-7. Epub 2009 Mar 27.
PMID: 19327928 [PubMed – in process]

Full Text PDF Download at medicalscg.

Fentanyl Study: EMS Research Episode 9
EMS Research Podcast
Podcast

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