CCCF Academy

Morimoto, Kenji¹; Kodani, Tadashi¹; Saito, Osamu¹; Shimizu, Naoki¹

¹Department of Paediatric Emergency and Critical Care Medicine, Tokyo Metropolitan Children’s Medical Centre, Tokyo, JAPAN

[Introduction]
Lower respiratory tract disease caused by respiratory syncytial virus (RSV) is characterised by narrowing the airways resulting in increased airway resistance, air-trapping and respiratory difficulty. However, if measured value of respiratory system resistance reflects the actual severity or not is unclear. 
[Objectives]
To clarify the relationship between measured airway resistance and clinical severity in intubated patients with RSV bronchiolitis.
[Methods]
From December 2015 to January 2016, Mechanically ventilated infants with respiratory failure caused by RSV in pediatric intensive care unit (PICU) were enrolled. Respiratory system mechanics including respiratory system resistance were measured by ARFEL® (AIVISION Inc.). Data were assessed by Pearsin’s correlation coefficient.
[Results]
Nine patients were enrolled. The results were age: 9.9 (5.5-9.9) month-old, body weight: 7.2(5.9, 8.9) kg, paCO₂: 49.0(43.0, 55.5)torr, airway resistance 127 .0(104.5, 255.0) cmH₂O/L/sec, the product of DP (driving pressure) and paCO₂  1323(1044, 1554), mechanically ventilated duration 9.0(7.0, 9.5) days and the length  of PICU stay 10(9.0, 11.5)days (median, IQR).  Each of the correlation coefficient with respiratory system resistance was ICU length of stay: r = -0.691(p=0.039), mechanically ventilated duration: r = -0.656(p=0.055), paCO2: r = 0.31(p=0.417), PIP (peak inspiratory pressure): r = 0.660, the product of paCO2 and DP: r = 0.933(p<0.001).
This study shows that respiratory system resistance can be an index of the severity in acute bronchiolitis patients. Deterioration of symptoms due to acute bronchiolitis requires a step-up of the treatment, such as HFO (high-frequency oscillatory ventilation) and ECMO (Extracorporeal membrane oxygenation). These treatments are more invasive and have more risks.
It is proved that respiratory system resistance has a correlation with paCO₂ and the product of the DP and paCO₂  which objectively reflects the severity of respiratory infections, while it has an inverse correlation with the PICU length of stay and the duration of mechanical ventilation. 
It is possible that these results are related with patient age and are confounding factors. 
By adjustment with linear regression analysis, the resistance had a clear association with the paCO₂ and the product of DP and paCO₂, and there is no relationship between the product of DP and paCO₂ and the PICU length of stay and the duration of mechanical ventilation. 
In infancy, since the age (physique) is associated with airway diameter, the age of patients probably were confounders. It should be noted that, when it needs high PIP in the respiratory management for acute bronchiolitis patients, we provide management to tolerate high paCO₂ content, and the paCO₂ reflected the clinical state in this study.
Conclusion]
Respiratory system resistance of RSV patients could be used as an indicator of clinical severity.