This chapter reviews the current status of combining the new evolving technologies of CO2 monitoring and non-invasive positive pressure ventilation (NPPV). It explores the advantages as well as the challenges that prompt further research. The non-invasive character of both NPPV and capnography make the combination attractive for the clinical management of acute and chronic respiratory failure. Several different types of patient interfaces are available for the delivery of non-invasive ventilation, including full face masks, complete face masks, nasal masks, sealed helmets, nasal pillows, mouthpieces and custom-fabricated masks. Sidestream gas measurement offers a number of sampling locations, including: inside the mask, at the mask outlet, or with the nasal cannula at or near the patient's nostrils. It is plausible that the synergies between NPPV and time/volumetric capnography will help the clinician to more rapidly identify therapeutic pressure levels that optimize CO2 elimination and patient work of breathing-key objectives for non-invasive ventilation.

The range of measurements for the CO2 fraction (FCO2) or the corresponding partial pressure (PCO2) in the breathing gas is identical in neonates and adults. The much lower amount of exhaled CO2 makes capnography in neonates more difficult, because there are objective limits for the size of the analyzer chamber or the magnitude of suction flow used with sidestream devices. For intraoperative monitoring, time-based capnography is commonly used, and the shape of the capnogram provides robust qualitative data and the PETCO2. In emergency medicine, critically ill infants often require tracheal intubation before transportation to the hospital. Capnography is a simple, non-invasive technique used to obtain information on alveolar ventilation and the deadspaces of the respiratory system. Compared with the more simple, time-based capnography, volumetric capnography measurements have a much higher informative potential, and enable the calculation of the different airway deadspaces.

Volumetric capnography (VC) provides valuable insights into lung collapse-recruitment physiology in a noninvasive and real-time manner, and thus lends itself to monitoring cyclic recruitment maneuvers at the bedside. Lung recruitment is a pressure-dependent phenomenon. Positive end-expiratory pressure (PEEP) needed to prevent the lung from recollapse after the recruitment maneuver is higher in patients with pulmonary diseases. Lung recruitment improves CO2 elimination by increasing the area of the alveolar-capillary membrane available for gas exchange. Lung recruitment affects the last two processes, mainly as a consequence of opening previously collapsed pulmonary capillaries and alveoli. Data from VC during lung recruitment can be grouped and analyzed in four principal ways according to CO2 kinetics: lung perfusion; gas exchange; lung ventilation; and gas transport within the airways. The sensitivity and specificity of non-invasive VC can be enhanced by supplemental invasive measurements of gas exchange.

This chapter focuses on the use of capnography to optimize and minimize the length of mechanical ventilation. Mechanical ventilation can be divided into three phases: acute stabilization, pre-weaning, and weaning/ extubation readiness testing. Alveolar minute ventilation is determined from the volumetric capnogram. Liberation from mechanical ventilation implies the use of an extubation readiness test to withdraw mechanical ventilation as soon as the patient meets extubation criteria regardless of the level of ventilatory support. A myriad of adversities make weaning and liberation from mechanical ventilation an extremely important clinical issue. With the majority of intensive care unit (ICU) patients requiring mechanical ventilation, minimizing the duration of mechanical ventilation while optimizing the potential for successful extubation is crucial in the management of critically ill patients. Capnography, both time-based and volumetric, allows mechanical ventilatory strategies to be designed with clear, precise, objective criteria.