Anwendung von Notfallbeatmungsgeräten zur invasiven und nicht-invasiven Beatmung an einem Versuchsmodell - resultierende Beatmungsgrößen und gastrale Insufflation

Abstract

Background: Respiratory insufficiency and therapy are central problems in emergency and critical care medicine. If ventilation is necessary, a possible treatment could be invasive (e.g. via tracheal tube) or non-invasive (e.g. via face mask). Both application forms have advantages and disadvantages. Non-invasive ventilation is associated with insufficient tidal volumes and aspiration, but could avoid harmful consequences of invasive procedures for the patient. To estimate the risk of invasive and non-invasive ventilation with emergency ventilators physical basics are useful to know, as well as results of different ventilation parameters. Methods: We constructed an experimental set-up with an artificial lung and an esophagus sphincter model, consisting of a rubber tube under a water column of 33 cm. A spirometer measured the volume that passes the sphincter to calculate gastric insufflations. Airway pressure and flow curves were recorded. With this model invasive and non-invasive ventilation could be simulated by adding or removing the sphincter model. As emergency ventilators we used the Oxylator® EM-100, the Medumat® Standard a, the Ambu® Bag Mark III® and the Smart Bag®. All devices were tested in invasive and non-invasive ventilation with different parameter settings. Lung parameters were adjusted in five different combinations of compliance and resistance. The Oxylator® is used in an automatic and a manual mode. With the Medumat® we readjust the measured results of the ventilation with the Oxylator® in order to compare both devices. Medumat® and hand bag devices were tested with standard parameters as well (tidal volume 500 ml and 1000 ml, frequency of breath 12 per minute). Additionally, we checked the influence of PEEP with an Evita 2, an intensive care ventilator, systematically. Results: Exceeding esophagus sphincter pressure with airway pressure leads to higher gastric insufflations. This can be verified by ventilation with all devices. If the Oxylator® is operated in automatic mode, it ventilates with a very high variation of ventilations parameters. In this case exceeding sphincter pressure leads to a rise in inspiratory time and volume. The risk of gastric insufflations is higher than applying the Medumat® with the same settings of tidal volume and frequency in the automatic mode. Using these standard parameters only seems to become harmful for the patient, when 1000 ml are applied in a highly reduced lung compliance (here tested 0,02 l/mbar). We can illustrate that lung compliance and inspiratory pressure are coherent. The lung compliance has more influence on inspiratory pressure and gastric insufflations than the lung resistance. With constant high inspiratory flow there are no lower gastric insufflations than using sinus formed flow. If PEEP is lower than the sphincter pressure, there is no significant rise of gastric insufflations by use of the PEEP itself (tested from 0 to 6 mbar). Conclusions: The primary goal should be avoiding exceeding the sphincter pressure in order to limit gastric insufflations. Using the Medumat® seems to be more secure than using the Oxylator®. The use of pressure controlled ventilation in an unprotected airway without sufficient limited inspiratory volume could increase gastric insufflations. Related to gastric insufflations or possible pulmonary barotrauma tidal volumes of 1000 ml should be avoided if lung compliance is very low. Sinusoidal flow is not more dangerous than using constant flow form, accordingly using hand bag devices is not coherent with higher gastric insufflations automatically. The positive effect of PEEP can be used without increase gastric insufflations if PEEP is below sphincter pressure.