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Title: Ventilatory ratio : a simple bedside index to monitor ventilatory efficiency
Author: Sinha, Pratik
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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A lack of a simple index that monitors ventilatory efficiency at the bedside has meant that oxygenation has been the predominant variable that is used to monitor adequacy of ventilatory strategies and disease severity in mechanically ventilated patients. Due to complexities in its measurement, deadspace ventilation, the traditional method to track ventilatory failure, has failed to become integral in the management of mechanically ventilated patients. Ventilatory ratio (VR) is an easy to calculate index that uses variables measured at the bedside: [Mathematical equation appears here. To view, please open pdf attachment] where [Symbols appears here. To view, please open pdf attachment] is taken to be 100 based on predicted body weight and [Symbols appears here. To view, please open pdf attachment] is taken to be 5 kPa. Physiological analysis of VR dictates that it is influenced by deadspace fraction and CO2 production. Physiological analysis of VR was validated in a benchside lung model and a high fidelity computational cardiopulmonary physiology model. The impact of CO2 production on VR was investigated in patients undergoing laparoscopic surgery who received exogenous intraperitoneal CO2. This showed that delta values of the 2 variables were linear. The variability of CO2 production was examined in ICU patients and results of the study showed that variability of CO2 production was small. In an ICU population correlation of VR was stronger with deadspace in comparison to CO2 production. Of these two variables, deadspace had the greater effect on VR. The clinical uses of VR were examined in 4 databases of ICU patients. VR was significantly higher in non-survivors compared to survivors. Higher values of VR were associated with increased mortality and more ventilator days. A rising values of VR over time was also associated with worse outcome. VR is a simple bedside index that provides clinicians with useful information regarding ventilatory efficiency and is associated with outcome.
Supervisor: Takata, Masao ; Soni, Neil Sponsor: Westminster Hospital Medical School
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral