Evaluation of a new end‐tidal carbon monoxide monitor from the bench to the bedside

INTRODUCTION Elevated levels of end-tidal carbon monoxide corrected for inhaled carbon monoxide (ETCOc) have been correlated with blood carboxyhemoglobin corrected for inhaled carbon monoxide (COHbc) and increased bilirubin production in both healthy newborn infants and those with haemolysis. Elevated bilirubin production has also been reported in infants born premature, born to mothers with diabetes, with bruising or birth trauma, with iso-immune haemolytic disorders, such as maternal–fetal blood group incompatibilities with ABO, Rh, or other minor groups, glucose6-phosphate dehydrogenase (G6PD) deficiency, structural and functional red blood cell abnormalities and perinatal sepsis (1–6). The 2004 American Academy of Pediatrics (AAP) guideline (7) specifically recommends that ETCOc measurements be used to identify the presence of haemolysis in infants and their subsequent risk for hyperbilirubinemia based on observations that haeme degradation from senescing red blood cells leads to the equimolar production of carbon monoxide (CO) and bilirubin in the absence of exposure to high ambient CO or active tissue injury (8). Recently, the US Food and Drug Administration approved a newly developed portable bedside device, the CoSense CO Monitor (Capnia Inc., Redwood City, CA, USA), for measuring ETCOc levels. The CoSense Monitor is equipped with an electrochemical sensor that measures ETCOc using single breath and ambient air sampling. ETCOc values are measured with a sensitivity of 0.1 parts per million (ppm or lL/L). In this report, we evaluated the accuracy and imprecision of this point-of-care device using bench tests and conducted a limited clinical study, in control and newborns with haemolytic disease, to correlate ETCOc levels with blood COHbc. For bench studies, a custom-made dynamic breathing simulator (supplied by Capnia, Inc.) was used to mimic breathing rates of 48 and 45 breaths per minute (bpm) and breath volumes of 12.6 and 25.5 mL representing a preterm and a term infant, respectively. Two gas mixtures (Airgas, Redwood City, CA, USA) with significantly different CO concentrations 2.38 ppm CO, 50.0 ppm hydrogen (H2), 5.06% carbon dioxide (CO2), balance nitrogen (N2) and 5.07 ppm CO, 52.3 ppm H2, 5.01% CO2, balance N2 were used to evaluate the accuracy and imprecision of three different monitors as well as the effect of H2 concentrations on the measurements of CO. Both gas mixtures were certified by Airgas against National Institute of Standards and Technology test standards to 1% accuracy of CO concentrations. The test gases were selected based on prior data that defined the level of haemolysis (9). Devices were tested simultaneously using tape-bundled nasal cannulas inserted 5 mm into the simulator outlet tube for interdevice and intradevice accuracy and imprecision with ten consecutive measurements taken for each gas mixture. Because all measurements are corrected to ambient CO levels automatically by the device to yield ETCOc, we needed to add back the ambient CO measured as the test gas measurements are unaffected by ambient CO and, therefore, do not need to be corrected. For bedside studies, ETCOc measurements were determined in patients born or readmitted to the Lucile Salter Packard Children’s Hospital at Stanford, CA, USA, in 2013–2014. The study was approved by the Stanford Institutional Review Board. A convenience sample, comprising of 83 newborns ≥30 weeks of gestational age with birthweights ≥1500 g, minimum plasma total bilirubin levels ≥5 mg/dL and a postnatal age of <5 days after birth, was recruited. Exclusion criteria were as follows: neonates