Noninvasive monitoring of end-tidal CO2 via nasal cannulas in spontaneously breathing children during the perioperative period.

OBJECTIVE: To determine the correlation between end-tidal CO2 and PaCO2 values measured via nasal cannulas in spontaneously breathing children during the perioperative period. DESIGN: Prospective evaluation. SETTING: Pediatric intensive/intermediate care unit in a tertiary care referral center. PATIENTS: Thirty postoperative surgical and trauma patients aged < or = 18 yrs (average age 7.8 yrs [range 6 months to 16 yrs] and average weight 28.3 kg (range 8.5 to 69). MEASUREMENTS AND MAIN RESULTS: Spontaneously breathing, nonintubated patients with an arterial cannula in place were selected for study. End-tidal CO2 was sampled from nasal cannulas by a sidestream aspirator and was estimated by infrared spectroscopy. The difference between PaCO2 and end-tidal CO2 was compared using linear regression analysis. A total of 55 blood gas measurements were obtained on the 30 patients. The PaCO2 to end-tidal CO2 gradient was < or = 4 torr in 54 of the 55 samples. The mean PaCO2 was 39.5 +/- 3.3 torr (5.27 +/- 0.44 kPa) with a mean end-tidal CO2 value of 39.7 +/- 3.8 torr (5.29 +/- 0.51 kPa). Linear regression analysis of arterial vs. end-tidal CO2 yielded a slope of 0.992 and p = .0001. CONCLUSIONS: End-tidal CO2 measurement by infrared spectroscopy provided an accurate estimation of PaCO2 in this patient population. Its use may limit the need for invasive monitoring and/or repeated arterial blood gas analysis.

Dissolved organic matter and heterotrophic microneuston in the surface microlayers of the north atlantic.

Dissolved organic carbon, carbohydrates, and adenosine triphosphate in the size fractions 0.2 to 3 micrometers and 3 to 1000 micrometers are significantly enriched in the upper 150-micrometer surface layer compared to subsurface water, mean enrichment factors being 1.6, 2.0, 2.5, and 3.1, respectively. When calculated as a 0.1-micrometer microlayer of wet surfactants, the mean concentration of organic matter was 2.9 grams per liter, of which carbohydrates accounted for 28 percent. The data for plant pigments and particulate adenosine triphosphate indicated that bacterioneuston was enriched at seven of nine stations while phagotrophic protists were enriched at five stations. Instances of enrichment and inhibition were verified by cultural data for bacteria and amoebas. The observations indicate that the surface microlayers are largely heterotrophic microcosms, which can be as rich as laboratory cultures, and that an appreciable part of the dissolved organic carbon is carbohydrate of phytoplankton origin, released and brought to the surface by migrating and excreting phagotrophic protists.