Elsevier

Nutrition

Volume 25, Issues 11–12, November–December 2009, Pages 1106-1114
Nutrition

Applied nutritional investigation
Influence of different ventilator modes on Vo2 and Vco2 measurements using a compact metabolic monitor

https://doi.org/10.1016/j.nut.2009.01.018Get rights and content

Abstract

Objective

We assessed the influence of different ventilator modes on carbon dioxide elimination (Vco2) and oxygen uptake (Vo2) using a new compact modular metabolic monitor (E-COVX) and its impact on calculated respiratory quotient (RQ) and resting energy expenditure (REE) in critically ill children.

Methods

Sequential 30-min ventilation by pressure-regulated volume controlled ventilation (PRVC), synchronized intermittent mandatory ventilation (SIMV), and biphasic intermittent positive airway pressure/airway pressure release ventilation (BiVent) in mechanically ventilated critically-ill children was assessed. To determine within- or between-day variations, 30-min Vo2 and Vco2 measurements were repeated at four separate occasions.

Results

A total of 3960 pulmonary 1-min gas exchange measurements were recorded in the 44 sessions for the three ventilator modes. Vo2, Vco2, and REE did not differ significantly among the PRVC, SIMV, and BiVent sequence of measurements. RQ (0.86 ± 0.1) in the SIMV and Vco2 (113 ± 55 mL/min) in the BiVent mode had a higher trend compared with PRVC (0.82 ± 0.01, P < 0.05, and 103 ± 49 mL/min, P < 0.2, respectively). All three modes displayed good agreement and there were no significant differences between the first and second same-day or between the first- and second-day measurements or sequentially changed ventilator modes. Bland-Altman plots comparing the means of sequential REE, Vo2, Vco2, and RQ during the PRVC, SIMV, and BiVent modes of ventilation indicated that the average paired differences were <  5.5%.

Conclusion

The influence of different ventilator modes on Vo2 and Vco2 measurements in adequately sedated critically ill children is not significant. The E-COVX metabolic module is suitable for repeated measurements in well-sedated mechanically ventilated children with stable respiratory patterns using the PRVC, SIMV, or BiVent modes of ventilation.

Introduction

The E-COVX (GE Healthcare/Datex-Ohmeda, Helsinki, Finland) is a simple metabolic non-invasive monitor incorporated into existing anaesthetic and critical care monitoring systems. It uses the practical method of breath-by-breath monitoring of metabolic gas exchange by relating flow measurements made at the mouth by pneumotachography to measurements of inspired and expired gas compositions. Compared with the Deltatrac II (Datex Ohmeda 2000, Helsinki, Finland) [1], [2], [3] or metabolic monitors integrated into ventilators using different methodologies [4], [5], this compact modular monitor has shown variable results.

Pressure regulated controlled ventilation (PRVC), synchronized intermittent mandatory ventilation (SIMV), and biphasic intermittent positive airway pressure/airway pressure release ventilation (BiPAP or BiVent/APRV) are usually used for fully supporting or weaning patients gradually from a ventilator. BiPAP or BiVent is an effective mode of mechanical ventilation similar to APRV, but it also applies continuous positive airway pressure to maintain adequate lung volume and promote alveolar recruitment and adds a time-cycled release phase to lower set pressure. In addition, spontaneous breathing can be integrated and is independent of the ventilator cycle. Because the degree of impact on oxygen uptake (Vo2) and carbon dioxide elimination (Vco2) might vary according to the minute volume, the BiPAP or BiVent/APRV ventilation mode of ventilation, used in some studies, may have been a factor influencing the accuracy of measurements by E-COVX [6]. Accordingly, it has been suggested that the ventilator mode is extremely important when using the breath-by-breath method for measuring gas exchange [6]. The performance and reproducibility of the E-COVX, however, has not been studied in controlled clinical settings under different modes of ventilation, especially those considered more suitable for progressive respiratory muscle reloading [7].

The primary aim of our study was to clinically assess the influence of different ventilator modes on airway Vco2 and Vo2 using a simple compact modular metabolic monitor (E-COVX) and its impact on calculated respiratory quotient (RQ) and resting energy expenditure (REE) in stable critically ill children under controlled heat and moisture conditions and respiratory frequency. A secondary aim was to access the longitudinal reproducibility of these measurements, only in adequately sedated patients, in each ventilatory modality.

Section snippets

Patient population

Mechanically ventilated, critically ill children admitted to the pediatric intensive care unit at the University Hospital of Heraklion, Crete, from January 2007 through December 2007 were studied prospectively. The ethics committee of the institutional review board approved the study, and parents or guardians gave informed, written consent.

All hemodynamically stable (Advanced Pediatric Life Support range for systolic blood pressure and heart rate), adequately sedated (Ramsey scale ≥3),

Patients

Eleven patients (seven boys, four girls) were studied. Mean age ± SD was 7.8 ± 4.9 y (range 0.9–14); mean weight at admission was 30.9 ± 27.5 kg, and mean height was 120 ± 28 cm. Mean length of stay in the pediatric intensive care unit was 27.8 ± 32 d and mean duration of mechanical ventilation was 25 ± 33 d. Four patients were admitted after an elective procedure; the remaining patients were admitted as a result of an acute illness or injury. Three of the patients had severe respiratory distress associated

Discussion

The most accurate method for monitoring of Vo2 and Vco2 and determining REE in hospitalized patients is indirect calorimetry [15]. Recently developed instruments are fully computerized and perform the calculations and often have built-in algorithms for detection and deletion of aberrant periods of energy expenditure resulting from an abnormal breathing period or movement of the limbs. Accurate determination of energy needs in hospitalized patients is vital because underfeeding and overfeeding

Conclusions

We have shown that the influence of different ventilator modes under controlled heat and moisture conditions and respiratory frequency on Vo2 and Vco2 measurements in adequately sedated critically ill children is not significant. The E-COVX metabolic module is suitable for repeated measurements in well-sedated mechanically ventilated children with stable respiratory patterns using the PRVC, SIMV, or BiVent modes of ventilation.

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