Tidal capnography is a non-invasive method to continuously measure exhaled carbon dioxide (CO₂) via a CO₂ sensor which is placed between the endotracheal tube (ETT) and the ventilator circuit. Historically, there has been some scepticism on the accuracy of capnography in neonatal care, based on technological limitations rising from the very small tidal volumes and high breathing rates of neonates, especially the more preterm ones. Recent advances have largely addressed these limitations and have enabled more widespread use of capnography within neonatal care (1).

Maintenance of CO₂ within the desired range is clinically important in the newborn to avoid the adverse outcomes associated with too high or too low CO₂ levels (2, 3). As CO₂ is a potent moderator of cerebral vascular tone, both extremes can lead to detrimental side effects such as intraventricular haemorrhage (IVH) and periventricular leucomalacia (4). Moreover, fluctuations of CO₂ during the early days of life or during initial stabilisation in the delivery room have been strongly associated with the development of IVH (5).

Waveform capnography can provide information over and above a solitary value of exhaled carbon dioxide, and it is important that clinicians at the bedside can interpret the contemporaneous and stored/trend information which can be provided by the capnography waveform (6). Clinical real-time interpretation of waveforms may identify life threatening complications of mechanical ventilation such as dislodged or blocked ETT (7), or describe established or impending lung pathologies (8). The CO₂ waveforms are more useful when evaluated with the concurrent flow, volume and pressure waveforms (9), although not all ventilators present them at a synchronous scale. This short overview aims to cover the practical basics of neonatal capnography, providing an aid for clinicians asking the following question: “In newborn infants requiring mechanical ventilation, what value does the capnography waveform have in supporting diagnosis and clinical troubleshooting?”

We present some graphic representations of commonly seen time-based capnograms, based on observed patterns.

We have presented a practical approach to neonatal tidal capnography used as a clinical adjunct to respiratory monitoring at the cot-side. With the emergence of continuous tidal capnography as a reliable monitoring tool in neonatal intensive care, we believe that the general neonatal audience would benefit from this targeted education on the interpretation of CO₂ waveforms.

It is interesting to note that similarly to the clinical estimation of the work of breathing and the utilisation of blood gases and chest radiographs, waveform monitoring holds unique information that describes the respiratory condition of a single subject at a specific time point (1). For example, the slope of phase III of a time capnogram, holds information on ventilation inhomogeneity which is not available from the waveforms of flow, volume or pressure, chest radiograms or blood gas analysis. Although interpretation of the CO₂ waveforms can be undertaken taking into consideration the concurrent waveforms of pressure, flow and volume (7), this approach is not always possible in everyday clinical practice as some ventilators do not display the CO₂ traces in synchrony with volume and flow, while some other units display the CO₂ traces in the monitoring screen rather that the ventilator display.

We should note that unlike some other methods of respiratory monitoring, tidal capnography is non-invasive and provides real-time breath by breath information.

Since CO₂ fluctuations during initial stabilisation in the labour ward have been associated with IVH (5), there is significant potential in using capnography as part of standard monitoring after birth. In the current era, furthermore, the majority of preterm infants are managed mostly on non-invasive respiratory support, and during this period high levels of CO₂ can be implicated in impaired oxygenation (15). There is scope, thus, in expanding the use of CO₂ monitoring during non-invasive support, which will require the future development of novel interfaces and lighter capnographs.

Tidal capnography is arguably not the only way to monitor CO₂ and is not possible in high frequency modes due to very high breathing rates. An alternative monitoring method is via transcutaneous CO₂ measurement, which measures CO₂ at the tissue level and the value is thus closer to the arterial one (16). Tidal CO₂ measurements can be influenced by the settings and mode of ventilation as a high breathing frequency may exceed the capnograph's response capabilities, while a significant ETT leak, high airway resistance and respiratory rate may also decrease the accuracy of the measurement (17).

In conclusion, we have described patterns of clinical scenarios where tidal capnography can be useful in diagnosis and troubleshooting at the cot-side.