Abstract: Background Baby body plethysmography is the gold standard for testing the functional residual volume and airway resistance, making it important for the evaluation of infant respiratory physiology. Objective To explore the influence of improving the operation skills of pulmonary function test (PFT) in plethysmography on the success rate of PFT. Design Quality improvement study. Methods PFTs were performed using the Jaeger MasterScreen BabyBody device (Erich Jaeger GmbH, v4.65, Würzburg, Germany) to examine tidal breathing flow volume loop (TBFVL) and plethysmographic functional residual capacity (FRCP). Before the improvement, the protocol of PFT were in accordance with the recommendations published by the American Thoracic Society (ATS) and the European Respiratory Society (ERS). On the basis of the previous protocol, improvement was described as increasing the dosage of sedatives (oral chloral hydrate) , touching or massaging the baby for 5 minutes before the test, and placing a slope pillow with 15 degree supine position. Continuous cases of PFT in pulmonary function room from January 2017 to January 2019 were included, and children with severe pneumonia caused by acute lower respiratory tract infection (ALRI) were excluded. The date of January 1, 2018 was set as the timing to differentiate before and after improvement. They were divided into neonatal pneumonia group and ALRI group. ALRI group was divided into the wheeze and non-wheezing subgroups. Main outcome measures The success rate of TBFVL and FRCP, and the failure rate of sedation. Results Totally 120 cases of neonatal pneumonia and 477 cases of ALRI were included. There were 31 cases failing to fall asleep after sedation, 3 cases with neonatal pneumonia and 28 cases with ALRI for both 14 cases in the wheezing and non-wheezing subgroups. Among 23 cases in the early awakening group who did not finish the PFT, there were 6 cases with neonatal pneumonia and 17 cases with ALRI for 5 cases in the wheezing and 12 cases in the non-wheezing subgroup. Although the success rate of TBFVL and FRCP had been improved with decreased rate of sedation failure in the neonatal pneumonia group, there was no significant difference compared with that before the improvement on PFT protocol. The success rate of TBFVL and FRCP had been improved with decreased rate of sedation failure in the non- wheezing and the wheezing subgroups after improvement on PFT protocol with statistical significance. Conclusion Improving the quality of PFT protocol of Baby body plethysmography can significantly increase the success rate of FRCP and TBFVL and reduce the failure rate of sedation.

Key words: Plethysmography, Improving the quality, Pulmonary, Infants, Neonates