Our study has limitations that need to be addressed for
interpretation of the results. (1) The number of patients
included in the study is limited, and the results should
be interpreted with this in mind. However, the sample
size was enough to detect the large differences that
occurred in the respiratory and morphological variables.
(2) We used fixed levels of inspiratory pressures for
recruitment maneuver and PEEP. (3) We used fixed tidal
volumes of 10 ml/kg predicted body weight; therefore,
different effects of higher or lower tidal volumes cannot
be excluded. (4) We studied our patients in the supine
position; however, beach chair position has been shown
to effectively improve respiratory mechanics and oxygenation
in obese patients during anesthesia, especially
in combination with PEEP.36 (5) We used conventional
volume-controlled ventilation, and recent studies have
shown promising results with improved gas-exchange
and respiratory mechanics while using biologically variable
ventilation.37 (6) The majority of the patients included
in the study were female, the most common
population of patients undergoing bariatric surgery.20
(7) We did not study children, although obesity in children
is a growing problem and poses great challenges in
airway and ventilatory treatment with increased risk of
desaturation and airway management problems.38 (8)
We did not evaluate hemodynamics in detail in these
patients undergoing conventional bariatric surgery. (9)
We minimized the number of CT scans for each patient
as requested by the ethical committee at Uppsala University,
Sweden, and in line with good clinical and research
practice.16 (10) The anesthesia was induced with
100% O2, which promotes formation of atelectasis; however,
this is a standard procedure in patients with high
risk of difficult intubation and hypoxemia at the time of
induction of anesthesia.39,40 (11) We chose to perform
the recruitment maneuver in pressure control to optimize
its effects. Not all ventilators used in anesthesia are
made to enable such a maneuver. However, these techniques
are very common in ventilators used in intensive
care units, and we believe that future technical development
is needed to improve anesthesia ventilators. (12)
The changes in lung volumes were most likely caused by
induction of anesthesia and paralysis, but another possible
explanation is that during spontaneous breathing the
patient did not comprehend the instructions given, thus
failing to make an end-expiratory breath-hold. However
we believe this to be unlikely; careful instructions were
given, and each patient was observed to make a breathhold
during the CT scanning.
In conclusion, this study has demonstrated that anesthesia
in morbidly obese patients induces atelectasis
formation and impairment in oxygenation. A recruitment
maneuver followed by PEEP was sufficient to reduce
the amount of atelectasis and improve oxygenation
for a prolonged period of time. Conversely, PEEP or
recruitment maneuver alone was not effective to reach a
sustained improvement of respiratory function.
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