The high prevalence of respiratory diseases has led to an increasing demand of assistance services in recent years. This increase also introduced a gradual rise in the admission of patients, what it is particularly important in the case of the respiratory diseases, whose prevalence is high and expected to grow in a near future. Acute lung injury, acute respiratory failure and its most severe form, the acute respiratory distress syndrome, are relatively common in the intensive care unit setting and have a high morbidity and mortality. Chronic obstructive pulmonary disease, for example, affects about 210 million people globally and causes some 3 million deaths annually. These diseases are a major drain on healthcare budgets with 50% of costs accounted for by hospital admissions, much of which could be avoided through development of more responsive models of care allowing earlier recognition and a better treatment. Almost all most critical patients admitted in a Critical Care Unit necessitate ventilatory support. Despite a research shift to non-invasive respiratory support, mechanical ventilation remains an essential tool in the care of the critically ill. The availability of a variety of respiratory modes and somewhat confusing terminology presents a daunting challenge for the physician. But, above all, many of the available treatment modes have not been adequately evaluated and their efficacy appears not completely assessed, by only judging the extent of recent literature reporting experimental evaluations in vivo and in vitro. In addition, there is paucity of information on the relative merits of those ventilatory strategies that have been studied. From an analysis of recent literature, mechanical, pneumatic, fluid-dynamic and thermo-hygrometric phenomena taking place in the system connecting the patient to the pulmonary ventilator (breathing circuit) seem to influence, and in a not always repeatable way, the pneumatic parameter values actually applied to the patient, the thermo-hygrometric state of the gas mixture, the response time to patient's inspiration effort and the assessment of patient respiratory parameters. Just to give an example, in the last decade, measurement of gas volume (air and oxygen) actually delivered to patient's lungs during mechanical ventilation, especially in case of neonatal ventilation, has received the attention of several scientific authors. The main outcome of this research is that the value of the delivered volume displayed by the ventilator monitoring unit significantly differs from the actual volume that reaches patient's airways. These observations assume increasing importance because of the low mortality associated with ventilation with reduced tidal volumes. It has to be considered that mechanical ventilation is always an interactive process between the machine (pulmonary ventilator, humidifier, breathing circuit) and the patient (characteristics of the respiratory system, kind of patient and pathology, etc.), also if the patient is completely passive. Thus, it appears interesting to investigate the above described measurement systems for monitoring and control of mechanical quantities, as it is common practice with other instruments utilized in other fields of science. Moreover, several parameters of patient's pulmonary mechanics are deduced from these measurements. Thus, clinicians figure out quantitative evaluation of the mechanical status of the respiratory system, i.e. respiratory system compliance, airway resistance, work of breathing, from numerical quantities provided by the ventilator monitoring unit and from the observation of the shape of respiratory loops. However, there is no assurance that the air flow and pressure actually delivered to the patient as a function of time correspond to the respiratory pattern set by the physicians. Probably, in order to better understand the reliability and clinical significance of monitoring results, it is necessary to address the study of pulmonary ventilation by considering the system ventilator-circuit-patient as a whole. This chapter, which is intended to represent a food for though for the clinician and researcher dealing with pulmonary ventilation, has the aim to briefly address some causes of possible misleading information which can be obtained from these complex though fascinating machines for vital support. © 2011 Nova Science Publishers, Inc. All rights reserved.
Pulmonary ventilators as monitoring instruments: Measurements and common issues
Silvestri S.
2011-01-01
Abstract
The high prevalence of respiratory diseases has led to an increasing demand of assistance services in recent years. This increase also introduced a gradual rise in the admission of patients, what it is particularly important in the case of the respiratory diseases, whose prevalence is high and expected to grow in a near future. Acute lung injury, acute respiratory failure and its most severe form, the acute respiratory distress syndrome, are relatively common in the intensive care unit setting and have a high morbidity and mortality. Chronic obstructive pulmonary disease, for example, affects about 210 million people globally and causes some 3 million deaths annually. These diseases are a major drain on healthcare budgets with 50% of costs accounted for by hospital admissions, much of which could be avoided through development of more responsive models of care allowing earlier recognition and a better treatment. Almost all most critical patients admitted in a Critical Care Unit necessitate ventilatory support. Despite a research shift to non-invasive respiratory support, mechanical ventilation remains an essential tool in the care of the critically ill. The availability of a variety of respiratory modes and somewhat confusing terminology presents a daunting challenge for the physician. But, above all, many of the available treatment modes have not been adequately evaluated and their efficacy appears not completely assessed, by only judging the extent of recent literature reporting experimental evaluations in vivo and in vitro. In addition, there is paucity of information on the relative merits of those ventilatory strategies that have been studied. From an analysis of recent literature, mechanical, pneumatic, fluid-dynamic and thermo-hygrometric phenomena taking place in the system connecting the patient to the pulmonary ventilator (breathing circuit) seem to influence, and in a not always repeatable way, the pneumatic parameter values actually applied to the patient, the thermo-hygrometric state of the gas mixture, the response time to patient's inspiration effort and the assessment of patient respiratory parameters. Just to give an example, in the last decade, measurement of gas volume (air and oxygen) actually delivered to patient's lungs during mechanical ventilation, especially in case of neonatal ventilation, has received the attention of several scientific authors. The main outcome of this research is that the value of the delivered volume displayed by the ventilator monitoring unit significantly differs from the actual volume that reaches patient's airways. These observations assume increasing importance because of the low mortality associated with ventilation with reduced tidal volumes. It has to be considered that mechanical ventilation is always an interactive process between the machine (pulmonary ventilator, humidifier, breathing circuit) and the patient (characteristics of the respiratory system, kind of patient and pathology, etc.), also if the patient is completely passive. Thus, it appears interesting to investigate the above described measurement systems for monitoring and control of mechanical quantities, as it is common practice with other instruments utilized in other fields of science. Moreover, several parameters of patient's pulmonary mechanics are deduced from these measurements. Thus, clinicians figure out quantitative evaluation of the mechanical status of the respiratory system, i.e. respiratory system compliance, airway resistance, work of breathing, from numerical quantities provided by the ventilator monitoring unit and from the observation of the shape of respiratory loops. However, there is no assurance that the air flow and pressure actually delivered to the patient as a function of time correspond to the respiratory pattern set by the physicians. Probably, in order to better understand the reliability and clinical significance of monitoring results, it is necessary to address the study of pulmonary ventilation by considering the system ventilator-circuit-patient as a whole. This chapter, which is intended to represent a food for though for the clinician and researcher dealing with pulmonary ventilation, has the aim to briefly address some causes of possible misleading information which can be obtained from these complex though fascinating machines for vital support. © 2011 Nova Science Publishers, Inc. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
