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Open Access 01-02-2013 | Research

Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside

Authors: Pratik Sinha, Nicholas J Fauvel, Pradeep Singh, Neil Soni

Published in: Critical Care | Issue 1/2013

Abstract

Introduction

Due to complexities in its measurement, adequacy of ventilation is seldom used to categorize disease severity and guide ventilatory strategies. Ventilatory ratio (VR) is a novel index to monitor ventilatory adequacy at the bedside.

VR = ({\dot{V}}_{E m e a s u r e d} \times P a_{C O_{2 m e a s u r e d}}) / ({\dot{V}}_{E p r e d i c t e d} \times P a_{C O_{2 i d e a l}})

{\dot{V}}_{E p r e d i c t e d}

is 100 mL.Kg^-1.min^-1 and

P a_{C O_{2 i d e a l}}

is 5 kPa. Physiological analysis shows that VR is influenced by dead space (V_D/V_T) and CO2 production

(\dot{V} C O_{2})

. Two studies were conducted to explore the physiological properties of VR and assess its use in clinical practice.

Methods

Both studies were conducted in adult mechanically ventilated ICU patients. In Study 1, volumetric capnography was used to estimate daily V_D/V_T and measure

\dot{V} C O_{2}

in 48 patients. Simultaneously, ventilatory ratio was calculated using arterial blood gas measurements alongside respiratory and ventilatory variables. This data was used to explore the physiological properties of VR. In Study 2, 224 ventilated patients had daily VR and other respiratory variables, baseline characteristics, and outcome recorded. The database was used to examine the prognostic value of VR.

Results

Study 1 showed that there was significant positive correlation between VR and VD/VT (modified r = 0.71) and

\dot{V} C O_{2}

(r = 0.14). The correlation between VR and V_D/V_T was stronger in mandatory ventilation compared to spontaneous ventilation. Linear regression analysis showed that V_D/V_T had a greater influence on VR than

\dot{V} C O_{2}

(standardized regression coefficient 1/1-V_D/V_T: 0.78,

\dot{V} C O_{2}

: 0.44). Study 2 showed that VR was significantly higher in non-survivors compared to survivors (1.55 vs. 1.32; P < 0.01). Univariate logistic regression showed that higher VR was associated with mortality (OR 2.3, P < 0.01), this remained the case after adjusting for confounding variables (OR 2.34, P = 0.04).

Conclusions

VR is an easy to calculate bedside index of ventilatory adequacy and appears to yield clinically useful information.

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Title: Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside
Authors: Pratik Sinha
Nicholas J Fauvel
Pradeep Singh
Neil Soni
Publication date: 01-02-2013
Publisher: BioMed Central
Published in: Critical Care / Issue 1/2013
Electronic ISSN: 1364-8535
DOI: https://doi.org/10.1186/cc12541

Keynote webinar | Spotlight on medication adherence

Springer Medicine

Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside

Abstract

Introduction

Methods

Results

Conclusions

Keynote webinar | Spotlight on medication adherence

Springer Medicine

Abstract

Introduction

Methods

Results

Conclusions

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