Title: Prophylactic negative pressure wound dressing (NPWD)
after caesarean – an extended debate to include surgical aspects
Re: Hyldig N, Joergensen JS,
Lamont RF, Moller S, Vinter CA. Prophylactic negative pressure wound
therapy in obese women undergoing caesarean section: a commentary on new
evidence that fuels the debate. BJOG 2021;
https://doi.org/10.1111/1471-0528.16750.
Dear Editor,
The “surgical” issue of caesarean wound infection seems a tussle
between opposing biostatisticians.1,2 Tuuli et
al2 may rightly defend statistical validity of their
much larger invaluable RCT showing definitive evidence of
ineffectiveness of NPWD, contrary to claim.1 The major
reproducibility/replication crisis in medicine illustrates limitations
of our tools/methodologies (not wrong but incomplete). Fred
Bookstein,3 Professor of Statistics and Life Sciences
at Washington and Vienna Universities elucidated principles for drawing
conclusions from experimental/trial data - biological plausibility,
dose-response relationships, broad evidence (including consilience),
adjustments for measurement error and potential confounders and
(last/least important) statistical significance. The statistical tests
simply cannot prove the actual hypothesis (H1) e.g.
whether NPWD is effective; which is circumvented by disproving a
substitute null-hypothesis (H0).4 This
can introduce a big difference (e.g. the intriguing prosecutor’s
fallacy) as the renowned data-scientist from Washington University
reiterated that if the original hypothesis is very weak/unlikely; then
even if a study shows ‘statistical significance’, the original
hypothesis is still very likely to be false (difference due to chance or
confounders).4
Are the hypotheses underlying NPWD very weak with misemployment of
laboratory research? Application of suction to skin-surface dressing is
claimed to bring-in more blood and oxygen but take away the lymph! The
last thing pregnant women (higher blood-volume and massive
estrogens/progestogens) have is poor vascularity/tissue-hypoxia of
abdominal wall, even with high BMI. In contrast, the underlying problems
are hematomas, contusion and serosanguinous collections providing nidus
for microbes. The shearing movements between the incised adipose layers
in overweight women being prevented by superficial NPWD seems
unreasonable/unwarranted as opposed to careful suturing technique.
Unfortunately, the discussion about good surgical techniques
(benefitting low and high BMI women) is unglamorous/unfashionable,
summarily rejected as ‘anecdotal opinion’. The obstetricians are
discouraged from even thinking about the pros-cons of the surgical
techniques but simply copy their colleagues.
The author has performed about 150-200 caesareans/year for 35 years with
one wound infection in a woman of 68 BMI. This is immaterial or he
simply didn’t know his patients with wound infection is not a valid
argument. Moreover, anyone can achieve <1% rate with similar
technique. He has specifically avoided application of brute blunt force
for abdominal entry. The meme of Joel-Cohen-technique became prematurely
entrenched from small trials and got increasingly exaggerated to
excessive indiscriminate blunt force of non-surgical-precision. Such
force causes widespread tissue-trauma (unseen beyond the incision),
inflammation and hematomas. Paradoxically, more sharp and limited
focussed blunt dissection constitute good
tissue-handling/surgical-principle. This paradox goes unnoticed; the
last thing fish may notice is water. Meticulous abdominal closure is
also important. Most of the depth of adipose tissue, particularly in
overweight women, should be approximated by robust interrupted layer/s
of sutures to minimize shearing movements. Placing a fine (3-5mm)
vacuum-drain above the sheath for a few days in overweight women will
drain any exudate (also provide twenty-times cheaper and superior
negative pressure).
Prophylactic NPWD seems wastefully expensive and ineffective.
Judiciously designed large trials of surgical techniques are required,
mindful that same surgeons may not be able to switch between contrasting
techniques.
Disclosure of interests: No conflict of interest or funding to
declare.