ABSTRACT
In recent years, there has been an increasing interest in knowing the consequences of the patient–ventilator interaction in non-invasive mechanical ventilation. Therefore, several ventilator manufacturers have incorporated into their devices the possibility to monitor ventilation on-line and download the data stored in their internal memories. However, there is not a consensus as to how these data should be presented, and said devices have still not been sufficiently validated to be used systematically in clinical practice.
The objective of the present study is to develop a critical, argumentative analysis of the technical characteristics for determining the monitor variables used in the different software programs incorporated in commercial ventilators. Likewise, the study contemplates the presentation of the measurements on the screen display, emphasizing the advantages and defects of each one and analyzing their behavior in common clinical practice situations, such as changes in the interface or the presence of accidental leaks. In addition, solution mechanisms are proposed for establishing future directives for the parameters that are important for clinicians, as well as the manner for providing and interpreting said information.
RESUMEN
En los últimos años ha aumentado el interés por conocer las consecuencias de la interacción paciente-ventilador sobre la mecánica pulmonar en ventilación no invasiva. Es por ello que diversas empresas fabricantes de ventiladores han incorporado a los mismos la posibilidad de monitorización de la ventilación on-line y de descarga de los datos almacenados en su memoria interna. Sin embargo, no existe consenso en la forma de presentación de estos datos, y dichos dispositivos aún no están lo suficientemente validados como para ser empleados de forma sistemática en la práctica clínica.
El presente trabajo tiene por objetivo efectuar un análisis crítico y argumentado de las características técnicas de la determinación de variables de monitorización en uso en los diferentes software incorporados a ventiladores comerciales y de las formas de presentación de estas mediciones en pantalla, enfatizando los defectos y las virtudes de cada una de ellas y analizando su comportamiento en situaciones comunes en la práctica clínica, como los cambios en la interfase o la presencia de fugas accidentales. Asimismo, se proponen vías de solución para establecer las directrices futuras acerca de los parámetros que pueden resultar de importancia para el clínico y la forma de proporcionar e interpretar dicha información.
Introduction
The use of non-invasive mechanical ventilation (NIMV) at home as treatment for patients with chronic respiratory failure was initiated in Spain at the beginning of the nineties.1 The main pathologies in which this therapy has been applied have been neuromuscular and ribcage diseases,2 obesity-associated hypoventilation syndrome3 and chronic obstructive pulmonary disease (COPD).4 The proportion of patients affected by each of these diseases among those treated with home mechanical ventilation, however, is different in several European countries in the latest published study that compiles the patterns of home NIMV use in Europe, which was published in 2005 with data from the two previous years. Thus, while in some countries, such as Italy, the proportion of ventilated patients with airway pathologies (mainly COPD) reaches 50% of the total, in others, such as Spain, this does not surpass 20%.5 The increased use of non-invasive ventilation in clinical pulmonology observed in this last decade, however, may have substantially modified these territorial patterns of prescription.
In recent years, coinciding with the technical improvements that different respirators have been incorporating, there has been increased interest in understanding the consequences of patient–ventilator interaction on lung mechanics, and more specifically the effects of different ventilator modes and ventilation parameters that are modifiable by clinicians on these same mechanics. Therefore, several companies that manufacture ventilators have incorporated in their products the possibility to monitor ventilation on-line and to download the data stored in the internal memory. Along these lines, a recent publication6 recommends the use of monitoring systems for patients who receive home NIMV, especially in those in whom respiratory failure is not sufficiently corrected. It also identifies the need to validate the built-in software developed and introduced by manufacturers that provide the possibility to download the data stored in the internal memory of the ventilator. Nevertheless, the literature about the reliability of these software programs is limited. There is only one very recent study done in a simulation setting that explores the reliability of the leak and tidal volume calculations.7
The objective of this present study is to develop a critical and argumentative analysis of the technical characteristics of monitored variable determinations used in the different software programs incorporated in commercial ventilators, as well as the forms of presentation of these measurements on the screen, emphasizing the defects and the virtues of each one. The data presented here have been obtained by acquiring tracings, with actual patients, in a controlled simulation setting (Simulator IngMar Medical 2000 SL, Pittsburgh, PA, USA and PowerLab/16SP, ADInstruments, Sydney, Australia), and these have been compared with those provided by the commercial software incorporated in each ventilator. Thus, this paper intends to reflect on where the monitoring of patients with home NIMV should be headed.
On-screen Presentation of Ventilator Data; System Requirements
The first NIMV monitoring systems appeared in the market more than 10 years ago as an adaptation aimed at improving control over treatment compliance and its effectiveness in patients with sleep apnea syndrome and treatment with positive airway pressure by using a device fitted to the back of the ventilator. One of the first commercial models with this novelty (VPAP III, ResMed, Sydney, Australia) was able to download data, not only for compliance, but also for minute volume, respiratory rate, obstructive episodes and values for unintentional leaks. Its design incorporated a pulse-oximeter that was able to synchronize the data for lung mechanics with oxyhemoglobin saturation. Fig. 1 shows a tracing from this device.
