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Does atelectasis cause post-operative fever?
I occasionally hear atelectasis listed in the differential diagnosis for early post-op fever (EPF) but this idea has never made much physiologic sense to me.
Let's explore this question in the following #tweetorial.
Does atelectasis cause post-operative fever?
I occasionally hear atelectasis listed in the differential diagnosis for early post-op fever (EPF) but this idea has never made much physiologic sense to me.
Let's explore this question in the following #tweetorial.
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Like many US medical students, I first learned this central dogma of post-op fever on my surgical clerkship through the perpetuation of a rather cumbersome and inelegant mnemonic involving the letter W.
Like many US medical students, I first learned this central dogma of post-op fever on my surgical clerkship through the perpetuation of a rather cumbersome and inelegant mnemonic involving the letter W.
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Despite its ubiquity, however, there is little published evidence to support this idea. One of the largest systematic reviews on the topic found that in 7 of 8 studies there was no significant association between atelectasis and early post-op fever.
PMID: 21527508
Despite its ubiquity, however, there is little published evidence to support this idea. One of the largest systematic reviews on the topic found that in 7 of 8 studies there was no significant association between atelectasis and early post-op fever.
PMID: 21527508
4/
The only study to show any association suffered from methodological flaws since it compared fever on post-op day (POD) 1 or 2 with atelectasis looked for on POD 4.
Using fever as a diagnostic test for atelectasis in this manner was poor (sensitivity of 25%).
PMID: 3350683
The only study to show any association suffered from methodological flaws since it compared fever on post-op day (POD) 1 or 2 with atelectasis looked for on POD 4.
Using fever as a diagnostic test for atelectasis in this manner was poor (sensitivity of 25%).
PMID: 3350683
5/
Another study of 100 cardiac surgery patients evaluated with daily chest x-rays and continuous bladder thermometry revealed that both fever and atelectasis are common after surgery, but were actually inversely related.
PMID: 7813318
Another study of 100 cardiac surgery patients evaluated with daily chest x-rays and continuous bladder thermometry revealed that both fever and atelectasis are common after surgery, but were actually inversely related.
PMID: 7813318
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The incidence of atelectasis increased from 43% on POD 0 ➡️79% on POD2 while the incidence of fever decreased from 37% on POD0 ➡️ 17% on POD2.
The incidence of atelectasis increased from 43% on POD 0 ➡️79% on POD2 while the incidence of fever decreased from 37% on POD0 ➡️ 17% on POD2.
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If the data correlation between atelectasis and EPF is poor, where does this idea originate from?
It’s unclear exactly, but there are animal studies as far back as the 1920s examining the physiologic effects of inducing massive atelectasis.
If the data correlation between atelectasis and EPF is poor, where does this idea originate from?
It’s unclear exactly, but there are animal studies as far back as the 1920s examining the physiologic effects of inducing massive atelectasis.
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It should be noted however that the descriptions of post-operative atelectasis, as given below by Dr. Shields in 1949, may have differed from our modern nosology and may sound more like what we today would classify as post-obstructive pneumonia.
It should be noted however that the descriptions of post-operative atelectasis, as given below by Dr. Shields in 1949, may have differed from our modern nosology and may sound more like what we today would classify as post-obstructive pneumonia.
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Many recent papers cite Lansing and Jamieson in 1963 as the modern scientific basis for this idea of atelectasis causing fever. In this study they anesthetized dogs, occluded their bronchi with cotton plugs, and measured the physiologic responses.
Many recent papers cite Lansing and Jamieson in 1963 as the modern scientific basis for this idea of atelectasis causing fever. In this study they anesthetized dogs, occluded their bronchi with cotton plugs, and measured the physiologic responses.
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Unsurprisingly, the dogs developed tachypnea, tachycardia, and pyrexia. When the plugs were removed the dogs returned to normal within 12 hours but “thick mucopurulent exudates” were noted distal to the obstruction in all cases.
Unsurprisingly, the dogs developed tachypnea, tachycardia, and pyrexia. When the plugs were removed the dogs returned to normal within 12 hours but “thick mucopurulent exudates” were noted distal to the obstruction in all cases.
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Interestingly, some dogs received antibiotics during the experiment. These dogs failed to mount the same physiologic response suggesting that they were more likely observing the effects of a pyogenic infection such as post-obstructive pneumonia rather than simple atelectasis.
Interestingly, some dogs received antibiotics during the experiment. These dogs failed to mount the same physiologic response suggesting that they were more likely observing the effects of a pyogenic infection such as post-obstructive pneumonia rather than simple atelectasis.
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In another modern study, rats undergoing ligation of a main stem bronchus were found to have ⬆️ IL-1/TNF levels. This is difficult to interpret as the tissue injury from a thoracotomy and infracting lung tissue likely confounds any affect of atelectasis alone.
PMID: 8457016
In another modern study, rats undergoing ligation of a main stem bronchus were found to have ⬆️ IL-1/TNF levels. This is difficult to interpret as the tissue injury from a thoracotomy and infracting lung tissue likely confounds any affect of atelectasis alone.
PMID: 8457016
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So if atelectasis does not directly cause fevers, is there a more plausible explanation for noninfectious early post-operative fever?
Enter every internist's favorite hand-waiving explanation: cytokines!
So if atelectasis does not directly cause fevers, is there a more plausible explanation for noninfectious early post-operative fever?
Enter every internist's favorite hand-waiving explanation: cytokines!
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To be more specific, it may be that the "danger model of immunity", as proposed in a recent opinion paper by Crompton et al. in JAMA Surgery, may provide an alternative explanation for EPF.
PMID: 30840058
To be more specific, it may be that the "danger model of immunity", as proposed in a recent opinion paper by Crompton et al. in JAMA Surgery, may provide an alternative explanation for EPF.
PMID: 30840058
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In this model, damage-associated molecular patterns (DAMPs) released from the tissue damage caused during surgery itself may activate innate immune cells which then release pyrogenic cytokines such as IL-1, Il-6 and, TNF that lead the hypothalamus to generate a fever.
In this model, damage-associated molecular patterns (DAMPs) released from the tissue damage caused during surgery itself may activate innate immune cells which then release pyrogenic cytokines such as IL-1, Il-6 and, TNF that lead the hypothalamus to generate a fever.
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While not definitive, this model intuitively makes more physiologic sense. It may provide a satisfactory explanation for the phenomenon of non-infectious EPF and help to relieve the existential discomfort most doctors feel when a fever has no obvious infectious cause.
While not definitive, this model intuitively makes more physiologic sense. It may provide a satisfactory explanation for the phenomenon of non-infectious EPF and help to relieve the existential discomfort most doctors feel when a fever has no obvious infectious cause.
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I'll conclude with a few 🔑 takeaways:
🔘Fever and atelectasis are both common after surgery but are poorly correlated
🔘Animal studies of atelectasis and fever are plagued by confounding
🔘 The danger model of immunity may provide a plausible alternative explanation for EPF
I'll conclude with a few 🔑 takeaways:
🔘Fever and atelectasis are both common after surgery but are poorly correlated
🔘Animal studies of atelectasis and fever are plagued by confounding
🔘 The danger model of immunity may provide a plausible alternative explanation for EPF
As requested by the tweetorial master himself, @tonybreu, please see the links below (in order of reference above) for my “Works Cited”:
ncbi.nlm.nih.gov/pubmed/21527508
ncbi.nlm.nih.gov/pubmed/3350683
ncbi.nlm.nih.gov/pubmed/7813318
jamanetwork.com/journals/jamas…
jamanetwork.com/journals/jamas…
ncbi.nlm.nih.gov/pubmed/21527508
ncbi.nlm.nih.gov/pubmed/3350683
ncbi.nlm.nih.gov/pubmed/7813318
jamanetwork.com/journals/jamas…
jamanetwork.com/journals/jamas…
