Our study found that providing a recruitment manoeuvre post-intubation or a continuous positive pressure during induction significantly decreased lung atelectasis as quantified by lung ultrasound compared to conventional ventilation in children under ten years old undergoing laparoscopic surgeries. The benefit of recruitment manoeuvre followed by increased PEEP over conventional ventilation is also reflected in the study by Acosta et al. in children undergoing laparoscopic surgeries. They found only 19% of their recruitment group to have significant atelectasis compared to 80% of their control group [7]. However, while Acosta et al. found that their recruitment manoeuvre decreased the atelectasis significantly during and after capnoperitoneum, this was not reflected in our study. This may be attributed to the fact that Acosta et al. did not measure LUS post recruitment as opposed to our study. We believe that the increased PEEP had a significant benefit for the lung aeration as opposed to the recruitment manoeuvre alone.While there was a decrease in loss of aeration post recruitment in our study, it was not absolute. Song et al. also found the consolidation and B-line scores in their recruitment group were significantly lower at surgical closure than the control group [11].

Recruitment manoeuvres and application of increased PEEP are some of the methods to combat lung atelectasis. A recruitment manoeuvre is performed to improve the transpulmonary pressure beyond that offered by tidal volume ventilation. It maximises the number of alveoli participating in the gas exchange to decrease shunt fraction and stabilise lung volume [4]. To be effective, a recruitment manoeuvre must apply sufficient inspiratory pressure to open collapsed areas of the lung, followed by an adequate level of PEEP to keep the alveoli open. The use of PEEP itself has decreased loss of FRC, airway closure, and atelectasis formation. Without PEEP, the lung mechanics shift to the less compliant part of the pressure–volume curve where lung collapse may occur. The optimal PEEP level helps keep the alveoli aerated and thus preserves FRC without compromising the hemodynamics [1].

We found that the lung ultrasound score at surgical wound closure was significantly higher than that post recruitment in the RM group despite being considerably lower than that in the CG group. This indicates that while the recruitment manoeuvre and increased PEEP does not prevent atelectasis altogether, it does contribute to a higher degree of protection from atelectasis than that offered by conventional ventilation. This is also supported by the study of Song et al., who witnessed juxta pleural consolidation in all infants at the end of surgery despite giving them an ultrasound-guided recruitment manoeuvre. While they suggested that a PEEP of 5 may not be sufficient to prevent collapse post recruitment manoeuvre, our study had similar findings despite a fixed higher PEEP [10] Similar results were also reported by Acosta et al., who found that in 4 out of the six children who underwent laparoscopy, a recruitment manoeuvre and a subsequent sustained higher PEEP failed to obliterate atelectasis [7]. We hypothesise that possibly an individualised titrated PEEP, as opposed to a standard PEEP post recruitment, may be more successful in preventing atelectasis.

In our study, the lung ultrasound scores of the CPAP group were comparable to the RM group at all time points. This indicates that a continuous positive pressure of 10 cm H2O during induction is beneficial in countering the loss of aeration caused by the pneumoperitoneum. However, there was still a significant increase in lung atelectasis during pneumoperitoneum and during closure than that during induction.

We chose to measure arterial blood gases for a more accurate representation of the oxygenation and carbon dioxide present in the blood. Repeat measurements helped provide a trend of the same over the course of laparoscopy. As far as the authors know, this is the first study to document this trend in laparoscopic paediatric surgeries. The PaO2/FiO2ratio post development of pneumoperitoneum was significantly less in the CG group than in the RM and CPAP group. This indicates the development of more shunts and dead space in the CG group instead of the RM and CPAP group. Although all the ratios were more than 300, indicating optimum ventilation and perfusion, this difference might become clinically significant in children with coexisting pulmonary disease.

The driving pressure of the CG group was significantly more than that of either the RM or CPAP group during pneumoperitoneum. This was probably secondary to the fact that the RM and CPAP group had a higher PEEP than the CG group, resulting in already distended alveoli and the requirement of lower pressures for ventilation. On the other hand, the driving pressures required after induction and post-intubation across all three groups were similar.

No child in the recruitment group suffered significant hypotension, and the recruitment could be completed in all children successfully. Hence, the recruitment manoeuvre and a PEEP of 10 were tolerated well by all children without compromising their hemodynamics. In previous studies, too, recruitment manoeuvres did not lead to significant hypotension, deeming them safe to be used in ASA 1 and 2 patients. In the study by Acosta et al., they did not find any hemodynamic compromise in any of their cases [7]. Similarly, none of the infants in the study by Song et al. showed any hemodynamic instability [10]. In a study done in 32 ventilated paediatric patients in the critical care unit; Duff et al. reported transient bradycardia in 2/93 recruitment performed and increased intracranial compliance in three subjects [12]. Although they concluded that manoeuvres are safe and beneficial in critically ill children, these side effects should be considered, and use of manoeuvres and elevated PEEP should be judiciously administered in the setting of ASA 3 and 4 patients. Large scale population studies in children with comorbidities can better establish the safety and efficacy of these recruitment strategies under general anaesthesia.

In our study, the same anaesthetist performed lung ultrasound in all the patients to exclude inter-observer variability. We used an established lung ultrasound score to quantify atelectasis objectively. Repeated scans were done at different times during the surgery that helped establish a more apparent trend to understand the components leading to atelectasis. By performing concurrent blood gas analysis, objectivity was added to the study.

Our study has a few limitations. We did not obtain a baseline LUS before induction and assumed that all the children recruited in the study had normal lung aeration. An awake child is unlikely to be cooperative in the preoperative period without premedication. Hence, we did not obtain a preoperative image. Also, hyperinflation is not detected by lung ultrasound. We limited the peak inspiratory pressure to avoid the same. The assessor was not blinded to the ventilatory strategy as the ultrasound images were obtained and assessed in real-time during the surgery. Fluid balance in critically ill patients has been seen to affect the lung ultrasound, although its effect on surgical paediatric population is not well studied.We did not study the correlation of fluid balance with lung ultrasound scores.

Our study can pave the way for future research. A larger-scale study may help establish the superiority of one ventilation strategy over the other. Titration of PEEP to detect optimum PEEP per patient may provide a more effective method for preventing atelectasis per patient. Ultrasound-guided recruitment strategies may also be investigated to decrease atelectasis that has set in during induction. The efficacy and safety of these ventilation strategies need to be tested in ASA 3 and 4 patients.