Evaluation of Respiratory Dynamics in an Asymmetric Lung Compliance Model / 대한구급학회지

BACKGROUND: Unilateral lung hyperinflation develops in lungs with asymmetric compliance, which can lead to vital instability. The aim of this study was to investigate the respiratory dynamics and the effect of airway diameter on the distribution of tidal volume during mechanical ventilation in a lung model with asymmetric compliance. METHODS: Three groups of lung models were designed to simulate lungs with a symmetric and asymmetric compliance. The lung model was composed of two test lungs, lung1 and lung2. The static compliance of lung1 in C15, C60, and C120 groups was manipulated to be 15, 60, and 120 ml/cmH₂O, respectively. Meanwhile, the static compliance of lung2 was fixed at 60 ml/cmH₂O. Respiratory variables were measured above (proximal measurement) and below (distal measurement) the model trachea. The lung model was mechanically ventilated, and the airway internal diameter (ID) was changed from 3 to 8 mm in 1-mm increments. RESULTS: The mean ± standard deviation ratio of volumes distributed to each lung (VL1/VL2) in airway ID 3, 4, 5, 6, 7, and 8 were in order, 0.10 ± 0.05, 0.11 ± 0.03, 0.12 ± 0.02, 0.12 ± 0.02, 0.12 ± 0.02, and 0.12 ± 0.02 in the C15 group; 1.05 ± 0.16, 1.01 ± 0.09, 1.00 ± 0.07, 0.97 ± 0.09, 0.96 ± 0.06, and 0.97 ± 0.08 in the C60 group; and 1.46 ± 0.18, 3.06 ± 0.41, 3.72 ± 0.37, 3.78 ± 0.47, 3.77 ± 0.45, and 3.78 ± 0.60 in the C120 group. The positive end-expiratory pressure (PEEP) of lung1 was significantly increased at airway ID 3 mm (1.65 cmH₂O) in the C15 group; at ID 3, 4, and 5 mm (2.21, 1.06, and 0.95 cmH₂O) in the C60 group; and ID 3, 4, and 5 mm (2.92, 1.84, and 1.41 cmH₂O) in the C120 group, compared to ID 8 mm (P < 0.05). CONCLUSIONS: In the C15 and C120 groups, the tidal volume was unevenly distributed to both lungs in a positive relationship with lung compliance. In the C120 group, the uneven distribution of tidal volume was improved when the airway ID was equal to or less than 4 mm, but a significant increase of PEEP was observed.

Evaluation of Respiratory Dynamics in an Asymmetric Lung Compliance Model / 대한중환자의학회지

BACKGROUND: Unilateral lung hyperinflation develops in lungs with asymmetric compliance, which can lead to vital instability. The aim of this study was to investigate the respiratory dynamics and the effect of airway diameter on the distribution of tidal volume during mechanical ventilation in a lung model with asymmetric compliance. METHODS: Three groups of lung models were designed to simulate lungs with a symmetric and asymmetric compliance. The lung model was composed of two test lungs, lung1 and lung2. The static compliance of lung1 in C15, C60, and C120 groups was manipulated to be 15, 60, and 120 ml/cmH₂O, respectively. Meanwhile, the static compliance of lung2 was fixed at 60 ml/cmH₂O. Respiratory variables were measured above (proximal measurement) and below (distal measurement) the model trachea. The lung model was mechanically ventilated, and the airway internal diameter (ID) was changed from 3 to 8 mm in 1-mm increments. RESULTS: The mean ± standard deviation ratio of volumes distributed to each lung (VL1/VL2) in airway ID 3, 4, 5, 6, 7, and 8 were in order, 0.10 ± 0.05, 0.11 ± 0.03, 0.12 ± 0.02, 0.12 ± 0.02, 0.12 ± 0.02, and 0.12 ± 0.02 in the C15 group; 1.05 ± 0.16, 1.01 ± 0.09, 1.00 ± 0.07, 0.97 ± 0.09, 0.96 ± 0.06, and 0.97 ± 0.08 in the C60 group; and 1.46 ± 0.18, 3.06 ± 0.41, 3.72 ± 0.37, 3.78 ± 0.47, 3.77 ± 0.45, and 3.78 ± 0.60 in the C120 group. The positive end-expiratory pressure (PEEP) of lung1 was significantly increased at airway ID 3 mm (1.65 cmH₂O) in the C15 group; at ID 3, 4, and 5 mm (2.21, 1.06, and 0.95 cmH₂O) in the C60 group; and ID 3, 4, and 5 mm (2.92, 1.84, and 1.41 cmH₂O) in the C120 group, compared to ID 8 mm (P < 0.05). CONCLUSIONS: In the C15 and C120 groups, the tidal volume was unevenly distributed to both lungs in a positive relationship with lung compliance. In the C120 group, the uneven distribution of tidal volume was improved when the airway ID was equal to or less than 4 mm, but a significant increase of PEEP was observed.

Relationship between pre-extubation positive endexpiratory pressure and oxygenation after coronary artery bypass grafting / Relação entre a pressão expiratória positiva final pré-extubação e a oxigenação após revascularização cirúrgica do miocárdio

AbstractIntroductionAfter removal of endotracheal tube and artificial ventilation, ventilatory support should be continued, offering oxygen supply to ensure an arterial oxygen saturation close to physiological.Objective:The aim of this study was to investigate the effects of positive-end expiratory pressure before extubation on the oxygenation indices of patients undergoing coronary artery bypass grafting.Methods:A randomized clinical trial with seventy-eight patients undergoing coronary artery bypass grafting divided into three groups and ventilated with different positive-end expiratory pressure levels prior to extubation: Group A, 5 cmH2O (n=32); Group B, 8 cmH2O (n=26); and Group C, 10 cmH2O (n=20). Oxygenation index data were obtained from arterial blood gas samples collected at 1, 3, and 6 h after extubation. Patients with chronic pulmonary disease and those who underwent off-pump, emergency, or combined surgeries were excluded. For statistical analysis, we used Shapiro-Wilk, G, Kruskal-Wallis, and analysis of variance tests and set the level of significance at P<0.05.ResultsGroups were homogenous with regard to demographic, clinical, and surgical variables. There were no statistically significant differences between groups in the first 6 h after extubation with regard to oxygenation indices and oxygen therapy utilization.Conclusion:In this sample of patients undergoing coronary artery bypass grafting, the use of different positive-end expiratory pressure levels before extubation did not affect gas exchange or oxygen therapy utilization in the first 6 h after endotracheal tube removal.

ResumoIntrodução:Após a remoção do tubo endotraqueal e ventilação artificial, o suporte ventilatório deve ser continuado, oferecendo suprimento de oxigênio para garantir uma saturação arterial de oxigênio próxima da fisiológica.Objetivo:O objetivo deste estudo foi investigar os efeitos da pressão expiratória positiva final antes de extubação nos índices de oxigenação de pacientes submetidos à cirurgia de revascularização miocárdica.Métodos:Ensaio clínico randomizado com 78 pacientes submetidos à cirurgia de revascularização do miocárdio, divididos em três grupos e ventilados com diferentes níveis de pressão expiratória positiva final antes da extubação: Grupo A, 5 cmH2O (n=32); Grupo B, 8 cm H2O (n=26); e grupo C, 10 cmH2O (n=20). Dados do índice de oxigenação foram obtidos a partir de amostras de gases sanguíneos arteriais coletados em 1, 3 e 6 h após a extubação. Pacientes com doença pulmonar crônica e aqueles que foram submetidos à cirurgia sem circulação extracorpórea, de emergência ou combinadas foram excluídos. Para a análise estatística, foram utilizados Shapiro-Wilk, G, Kruskal-Wallis, e análise dos testes de variância e definição do nível de significância em P<0,05.Resultados:Os grupos foram homogêneos em relação às variáveis ​​demográficas, clínicas e cirúrgicas. Não houve diferenças estatisticamente significativas entre os grupos nas primeiras 6 h após extubação no que diz respeito aos índices de oxigenação e a utilização de oxigenoterapia.Conclusão:Nesta amostra de pacientes submetidos à revascularização do miocárdio, o uso de diferentes níveis de pressão expiratória positiva final antes da extubação não afetou as trocas gasosas ou utilização de oxigenoterapia nas primeiras 6h após a remoção do tubo endotraqueal.