Relationship between arterial carbon dioxide and end-tidal carbon dioxide when a nasal sampling port is used

Abstract

End-tidal carbon dioxide (ETCO2) values obtained from awake nonintubated patients may prove to be useful in estimating a patient's ventilatory status. This study examined the relationship between arterial carbon dioxide tension (PaCO2) and ETCO2 during the preoperative period in 20 premedicated patients undergoing various surgical procedures. ETCO2 was sampled from a 16-gauge intravenous catheter pierced through one of the two nasal oxygen prongs and measured at various oxygen flow rates (2, 4, and 6 L/min) by an on-line ETCO2 monitor with analog display. Both peak and time-averaged values for ETCO2 were recorded. The results showed that the peak ETCO2 values (mean = 38.8 mm Hg) correlated more closely with the PaCO2 values (mean = 38.8 mm Hg; correlation coefficient r = 0.76) than did the average ETCO2 values irrespective of the oxygen flow rates. The time-averaged PaCO2-ETCO2 difference was significantly greater than the PaCO2-peak ETCO2 difference (P less than 0.001). Values for subgroups within the patient population were also analyzed, and it was shown that patients with minute respiratory rates greater than 20 but less than 30 and patients age 65 years or older did not differ from the overall studied patient population with regard to PaCO2-ETCO2 difference. A small subset of patients with respiratory rates of 30/min or greater (n = 30) did show a significant increase in the PaCO2-ETCO2 difference (P less than 0.001). It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Agreement between arterial partial pressure of carbon dioxide and saturation of hemoglobin with oxygen values obtained by direct arterial blood measurements versus noninvasive methods in conscious healthy and ill foals

“…In theory, this should not occur, but this finding has been reported in similar studies 5,6,9,23,29,30 on people, horses, and dogs. This detail may have contributed to the small Paco 2 -Petco 2 gradient documented in our study.…”

Physiologic effects of nasopharyngeal administration of supplemental oxygen at various flow rates in healthy neonatal foals

“…1 This can potentially result in elevated airway pressure with both positive (increased functional residual capacity, alveolar recruitment, and improvement in ventilation-perfusion matching) and negative (retention of carbon dioxide and hypercapnia) consequences, especially at high oxygen flow rates. 1,21 The relationship and correlation between Paco 2 and Petco 2 has been examined in various studies [22][23][24] in efforts to use Petco 2 as a less invasive means of monitoring Paco 2 in clinical cases such as emergency room admissions and during anesthesia; overall correlation between these 2 variables has been high in several studies [22][23][24] in people. Likewise, a significant correlation between Paco 2 and Petco 2 was determined in the healthy neonatal foals used in the present study.…”

Concordance Between Capnography and Arterial Blood Gas Measurements of Carbon Dioxide in Acute Asthma

“…However, PaCO 2 values may not have to be temperature corrected when PetCO 2 values are also uncorrected. 12 Third, we have not reported the intraclass correlation coefficient as a measure of agreement between the 2 methods. Our decision to omit this was based on evidence that, although intraclass correlation is commonly used to demonstrate the interchangeability of measurements, it is inappropriate for this purpose.…”