Minimizing atelectasis formation during general anaesthesia—oxygen washout is a non-essential supplement to PEEP

Abstract

BackgroundFollowing preoxygenation and induction of anaesthesia, most patients develop atelectasis. We hypothesized that an immediate restoration to a low oxygen level in the alveoli would prevent atelectasis formation and improve oxygenation during the ensuing anaesthesia.MethodsWe randomly assigned 24 patients to either a control group (n = 12) or an intervention group (n = 12) receiving an oxygen washout procedure directly after intubation. Both groups were, depending on body mass index, ventilated with a positive end-expiratory pressure (PEEP) of 6–8 cmH2O during surgery. The atelectasis area was studied by computed tomography before emergence. Oxygenation levels were evaluated by measuring blood gases and calculating estimated venous admixture (EVA).ResultsThe atelectasis areas expressed as percentages of the total lung area were 2.0 (1.5–2.7) (median [interquartile range]) and 1.8 (1.4–3.3) in the intervention and control groups, respectively. The difference was non-significant, and also oxygenation was similar between the two groups. Compared to oxygenation before the start of anaesthesia, oxygenation at the end of surgery was improved in the intervention group, mean (SD) EVA from 7.6% (6.6%) to 3.9% (2.9%) (P = .019) and preserved in the control group, mean (SD) EVA from 5.0% (5.3%) to 5.6% (7.1%) (P = .59).ConclusionAlthough the oxygen washout restored a low pulmonary oxygen level within minutes, it did not further reduce atelectasis size. Both study groups had small atelectasis and good oxygenation. These results suggest that a moderate PEEP alone is sufficient to minimize atelectasis and maintain oxygenation in healthy patients.

Effect of positive end-expiratory pressure on gastric insufflation during induction of anaesthesia when using pressure-controlled ventilation via a face mask

“…Recently, two studies have demonstrated that a PEEP level of 6 to 7 cmH 2 O as a single intervention in nonobese patients results in an ‘open lung’ with minimal atelectasis, as investigated by computed tomography immediately before emergence from anaesthesia. 32,33 Extrapolating from these two studies and the current study, the following implication might evolve: If pre-oxygenation starts, using first a CPAP of 6 to 7 cmH 2 O and then a PEEP of the same magnitude during induction of anaesthesia, this should both give the respiratory advantages and definitely be safe in healthy, fasting patients, such as in this study, as long as PIP is no higher than 15 cmH 2 O. This is assuming that the risk for gastric insufflation with lower PEEP at equal PIP per se is not higher than with PEEP of 10 cmH 2 O.…”

A simple method to provide positive end expiratory pressure to treat hypoxaemia in an anaesthetised Asian Elephant (Elephas maximus)

“…The resulting FiO 2 was 33%, although a FiO 2 of 42% is reported by the manufacturer (In Case of Anaesthesia, n.d.). As high FiO 2 is associated with increased shunt fraction in other species, the lower FiO 2 provided by this ventilator may have been beneficial in preventing further atelectasis (De Monte et al 2013;Osbertg et al 2017).…”

What is the best strategy for one-lung ventilation during thoracic surgery?

“…In addition, trained personnel and a functioning pre-and a post-anesthesia care unit are mandatory. CPAP ventilation within the scope of regular preoxygenation and immediately after extubation is feasible in any case without further technical effort, but might not be this effective (12). Especially for high-risk patients (FEV1 <70%) and for patients requiring postoperative intensive care, continued CPAP ventilation is highly recommended.…”