Carbon dioxide monitors, exhaled gas

Performance of capnometry in non-intubated infants in the pediatric intensive care unit

Background

Assessing the ventilatory status of non-intubated infants in the Pediatric Intensive Care Unit (PICU) is a constant challenge. Methods to evaluate ventilation include arterial blood gas analysis (ABG), which is invasive and intermittent, and transcutaneous carbon dioxide monitoring (P_tcCO2), which, while non-invasive, is also intermittent. A method that is non-invasive and continuous would be of great benefit in this population. We hypothesized that non-invasive capnometry via sidestream monitoring of exhaled carbon dioxide (CO₂) would provide an acceptable measurement of ventilatory status when compared to ABG or P_tcCO2.

Methods

Preliminary prospective study of infants less than one year of age admitted to the PICU in a large urban teaching hospital. Infants not intubated and not requiring non-invasive ventilation were eligible. A sidestream CO₂ reading was obtained in a convenience sample of 39 patients. A simultaneous ABG was collected in those with an arterial catheter, and a P_tcCO2 was obtained in those without.

Results

Correlation of sidestream CO₂ with ABG was excellent (r² = 0.907). Sidestream correlated less well with P_tcCO2 (r² = 0.649). Results were not significantly altered when weight and respiratory rate were added as independent variables. Bland-Altman analysis revealed a bias of -2.7 with a precision of ±6.5 when comparing sidestream CO₂ to ABG, and a bias of -1.7 with a precision of ±9.9 when comparing sidestream CO₂ to P_tcCO2.

Conclusions

Performance of sidestream monitoring of exhaled CO₂ is acceptable clinical trending to assess the effectiveness of ventilation in non-intubated infants in the PICU.

Effects of IV Pentobarbital With and Without Fentanyl on End-Tidal Carbon Dioxide Levels During Deep Sedation of Pediatric Patients Undergoing MRI

OBJECTIVE

IV pentobarbital is used in radiology departments for sedating pediatric patients undergoing diagnostic imaging. To our knowledge, no published studies have documented end-tidal carbon dioxide levels during sedation with IV pentobarbital. The purpose of this prospective study was to determine the effects of different doses of IV pentobarbital with or without fentanyl on end-tidal carbon dioxide levels during deep sedation of pediatric patients undergoing MRI.

SUBJECTS AND METHODS

One hundred sixty-five patients (70 girls, 95 boys) having a mean age of 3.4 years received IV pentobarbital sedation with or without fentanyl for undergoing MRI from January through March 2002. Each child was sedated with 2-6 mg/kg of body weight of IV pentobarbital and an additional 1-3 micro g/kg of fentanyl if needed. After the administration of sedation, a 28-ft (8.5 m) nasal cannula with capnography capability was applied to each patient, and capnogram tracings and values were recorded every 5 min.

RESULTS

Mean values of end-tidal carbon dioxide were between 37 and 42 mm Hg during 60 min of sedation for both groups. When IV pentobarbital was used alone, no significant difference was seen between patients who received 3-5 mg of pentobarbital and those who received more than 5 mg (p = 0.97, F test).

CONCLUSION

End-tidal carbon dioxide levels remain within normal clinical range during sedation with IV pentobarbital with or without fentanyl. Our sedation protocol produced no significant deviations from normal respiratory parameters.

Microstream capnograpy technology: a new approach to an old problem

Significant technical limitations inherent in black-body infrared technology used in conventional sidestream and mainstream capnography have hindered the acceptance and growth of capnography as a monitoring tool outside the operating room environment. We describe a new technology (Microstream) for CO2 monitoring, based on molecular correlation spectroscopy, which results in a highly efficient and selective emission of a spectrum of discrete wavelengths exactly matching those for CO2 absorption. The CO2 specific emissions allow for an extremely small sample cell (15 microl), which in turn, permits the use of a very low sample flow rate (50 ml/min) without compromising waveform integrity or end-tidal CO2 accuracy. Design and technology features of the CO2 emission source, sample cell, and breath sampling circuits are described.