Thread by @HarrietHopfMD

Took me a while, but in response to @AmyPearsonMD tweet of my talk last week @uihealthcare, a thread on ⬆️FiO2 and #SSI.

@scruff888 @DrMikeAziz @MPOGASPIRE @APSForg @woundheal #infectionprevention 1/15

Whether intraoperative high inspired oxygen is beneficial is not a settled question.* This thread explains why I routinely use it unless there is a contraindication. bit.ly/2gexBIz

*The evidence that it is NOT harmful is overwhelming.

Impetus to investigate high-inspired O2 grew out of in vitro, animal, human volunteer, & patient studies (1960s-90s): wound hypoxia associated with⬆️#SSI & peripheral vasoconstriction resulting from SNS activation is common source of wound hypoxia. bit.ly/2H9SlfS
2/15

Volunteer & patient studies showed preventing SNS activation prevented or corrected wound #hypoxia. RCTs demonstrated preventing/correcting wound hypoxia by preventing SNS activation (e.g. by perioperative active warming bit.ly/2LUcCYN ) improved wound outcomes.
3/15

These studies raised the question: would increasing FiO2 reduce wound hypoxia & thus dec SSI?

Here’s where it gets complicated. In animal studies, increasing FiO2 increases wound oxygen ONLY when perfusion is adequate ncbi.nlm.nih.gov/pubmed/3677745
4/15

So increased FiO2 would only be expected to increase wound oxygen (thus decrease SSI) if perfusion is adequate. This assumption is supported by a recently published mathematical model (bit.ly/2LV2fnG)* figure

*side note: publishing in JTB = pinnacle of my career
5/15

Greif (2000, bit.ly/31UBo0x) 1st to study FiO2 0.8 vs. 0.3 for⬇️SSI in colon surgery (high SSI risk).

Anesthetic management designed to maintain wound perfusion (normothermia, 15-20 mg/kg/h crystalloid)

Outcome: SSI⬇️~50% (11% to 5%)
6/15

What was special about Greif et al 2000?

They measured whether the oxygen got to its target (the wound).

⬆️oxygen➡️⬆️wound O2: ~85% intraop & 35% in PACU in 0.8 group. bit.ly/31UBo0x

No study since has measured wound oxygen, although most demonstrated⬇️SSI.
7/15

Let’s consider largest negative trial (PROXI 2009) bit.ly/31VYF22. What differed?

*abdominal surgery (mixed risk)
*anesthetic management not standardized
*very restricted fluid (~1100 mL cryt + ~500 ml colloid, no weight gain)

Outcome: no difference (20 vs. 19%)
8/15

So what?
*Wound oxygen measurements would have been useful in PROXI.
*The result is the *expected* result if⬆️inspired oxygen didn’t get to the wound.
*There is no way to know if that explains the result—or if the results “disprove” the value of increased oxygen.
9/15

2015 Cochran review:
bit.ly/2VlbOiJ
•No evidence harm:
Not associated w all-cause mortality, resp insufficiency, serious adverse events, or LOS

•Some benefit:
In patients w preop abx*
In colorectal surgery patients

*most abx are oxygen-dependent for effect
10/15

My take home:

The most important thing for wound oxygen is to minimize sympathetic nervous system activation. Once you have done that, additional oxygen likely beneficial in surgeries w high SSI risk.
11/15

How do you optimize peripheral perfusion? (I)
Preop and intraop active warming (bit.ly/2ILc7hR)

12/15

How do you optimize peripheral perfusion? (II)
"Adequate" or "appropriate" fluid management (bit.ly/2IwJHrt )
Yeah, I don’t know the correct answer either, but⬆️evidence severe fluid restriction is problematic.
13/15

How do you optimize peripheral perfusion? (III)

Pain and stress both⬇️wound oxygen & impair healing. No RCTs on benefit of pain control & stress reduction, but they do seem like a good idea, anyway.
14/15

Summary

Also, please, please, please wash your hands early and often. #handhygiene #5moments

15/15