Indeed, the gradient has been utilised in adult intensive as an index of severity in acute respiratory distress syndrome (Yousuf et al 2017). Nevertheless, knowledge of the gradient between pCO 2 and EtCO 2 could provide valuable clinical information compared to standalone values of pCO 2 and EtCO 2. Concern has arisen within the neonatal population due to the often-reported poor agreement between pCO 2 and EtCO 2, especially in infants with severe lung disease (Trevisanuto et al 2012, Mehta et al 2014, Scrivens et al 2019, Williams et al 2020). The adoption of EtCO 2 as a surrogate for the partial pressure of blood (arterial/capillary) carbon dioxide (pCO 2) has, however, been questioned, especially for very low birth weight infants (Scrivens et al 2019). Within the paediatric setting, non-invasive end-tidal CO 2 (EtCO 2) monitoring has been utilised to provide a reliable assessment of the effectiveness of mechanical ventilation (McDonald et al 2002). Tidal capnography on the other hand allows for non-invasive, real-time continuous measurement of exhaled CO 2. The gold standard for measurement, blood gas analysis, is invasive and cannot be utilised to provide continuous values of CO 2, hence often leaving infants with periods of time during which CO 2 is unmonitored. The National Institute for Health and Care Excellence (NICE) has set out limits of CO 2 levels to target during the first 72 h and thereafter in mechanically ventilated prematurely born infants (NICE 2019). The results of end-tidal capnography monitoring have the potential to predict blood carbon dioxide values within the neonatal population.Ĭarbon dioxide (CO 2) levels are routinely monitored on the neonatal unit, especially in those requiring invasive respiratory support as both hypercapnia and hypocapnia can have adverse effects on the developing brain (Wong et al 2021). In infants born at less than 32 completed weeks of gestation, pCO 2 levels were independently associated with EtCO 2, day after birth, birthweight and fraction of inspired oxygen (FiO 2) (model r 2 = 0.52, p < 0.001). The ∆P-EtCO 2 for infants born less than 32 weeks of gestation was significantly higher (1.4 kPa) compared to infants born at greater than 32 weeks of gestation (0.8 kPa) ( p < 0.001). Overall, there was moderate correlation between pCO 2 and EtCO 2 levels ( r = 0.65, p < 0.001). The infants had a median gestational age of 33.3 (range 22.3–42.0) weeks and birth weight of 1880 (395–5520) grams. A total of 4697 blood gas results from one hundred and fifty infants were analysed. End-tidal capnography monitoring was performed using the Microstream sidestream Filterline H set capnograph.
Ventilatory settings corresponding to the time of each blood gas assessment were noted. Daily pCO 2 and EtCO 2 levels were recorded and the difference (gradient: ∆P-EtCO 2) between the pairs were calculated. An observational study of routinely monitored newborn infants requiring mechanical ventilation in the first 28 d after birth was undertaken. Furthermore, to assess whether pCO 2 levels could be predicted from continuous EtCO 2 monitoring. To determine factors which influenced the relationship between blood carbon dioxide (pCO 2) and end-tidal carbon dioxide (EtCO 2) values in ventilated, newborn infants.
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