The extended application area of capnography was verified in a bench test study and clinical investigation.
The in vitro study involving artificial lungs with different mechanical properties gave insight into the eneven ventilation distribution driven by the markedly altered resistive and/or elastic properties of the individual sides. These findings contributed to a better understanding of
ventilation heterogeneities in a lung, including compartments with different time constants.
Due to the high reproduction number of SARS-CoV-2 virus, there may be a sudden increase in
the number of patients requiring mechanical ventilation. This can lead to an acute shortage of ventilators in critical care. Using capnogaphy in Study I., we demonstrated that the adequacy of ventilator splitting can be verified. However, ventilator splitting can only be considered as a rescue intervention to provide adequate tidal volumes without collateral airflow for two subjects
with different respiratory systems. Our experimental results support that this split ventilation
modality can be applied without the risk of diminishing patient safety if emergencies arise due
to temporal shortages of mechanical ventilators. Therefore, the risk of non-ventilation is higher
than that of controlled shared ventilation in terms of morbidity. Moreover, goal-oriented
capnography can serve as a bedside approach to ensure the adequacy of tidal volumes on both
lungs during this life saving intervention. Capnography as a routinely available monitoring modality may help in emergencies (i.e. in pandemics or combat hospitals) when there is a lack of equipment and/or health care professionals. From this aspect, ventilator sharing can be
regarded as a lifesaving manoeuvre in catastrophe medicine. This alternative may have importance during the exacerbation of an upcoming epidemic wave, or devastating war-related
tragic events when intensive care specialists may be faced with a shortage of ventilators. Study II. demonstrated that, diabetes affects airway function and the elastic properties of the
respiratory tissues, leading to ventilation heterogeneities. This inhomogenous alveolar emptying was confirmed by capnography showing an elevated phase III slope. These intrinsic mechanical and ventilation abnormalities in diabetes were counterbalanced by the increased
contractile response of the pulmonary vasculature to hypoxic stimuli, which was able to maintain the normal intrapulmonary shunt fraction and oxygenation ability of the lungs. On the
other hand, obesity similarly deteriorated the global respiratory mechanics, and the external
trigger worsened gas exchange. The simultaneous presence of diabetes and obesity had additive effects on the worsened respiratory resistance. This synergistic effect may be related to the combination of the external mechanical overload exerted by the upward shift of the diaphragm
in obesity, and the enhanced susceptibility of the alveoli to collapse subsequent to type II pneumocyte dysfunction in the presence of diabetes secretion. These pathophysiological
changes highlight the importance of lung protective ventilation with high PEEP and low VTs not only in obesity, but also in patients with diabetes.
Taking together the findings of the two studies may have clinical relevance. Since a high proportion of the critically ill COVID-19 patients are diabetic and/or obese, detailed information obtained by capnography may help to optimize mechanical ventilation in the case of a necessity for shared ventilation in a population overwhelmed by diabetic and/or obese patients.