Relationship of End tidal PCO2 a n d Arterial PCO2 in Acute Critically Ill Patients

Jung, In Chul; Yang, Ji Ah; Park, Do Young; Lee, Be Ahn; Lee, Sung Woo; Hong, Yun Sik

Abstract

BACKGROUND
The CO2 concentration in exhaled gases is intrinsically linked to tissue metabolism, ventilation, and pulmonary circulation. In hemodynamically stable patients, the end-tidal CO2(PetCO2) is known to be a good index of arterial CO2 (PaCO2). However, the PetCO2 has some limitations in predicting PaCO2 in emergent patients with unstable vital signs.
OBJECTIVE
We evaluated the relationship of PetCO2 and PaCO2 and the validity of the difference between PetCO2 and PaCO2(PaCO2-PetCO2) for various clinical situations. MATERIAL AND METHOD: A prospective analysis was performed in endotracheally intubated patients, who presented at the Korea University Emergency Medical Center during a 14-month period from January 2003 to February 2004. Patients were divided into three groups; respiratory insufficiency of cardiopulmonary cause (Group A), respiratory insufficiency of extracardiopulmonary cause (Group B), cardiac arrest with any cause (Group C). Group A was subdivided into two subgroups; A1 with a history of chronic lung disease disease and A2 with no history of chronic lung disease history. In each group, the mean of PaCO2-PetCO2 was calculated and multiple comparison was performed in each groups by using a one-way ANOVA test, and the 95% confidence interval of PaCO2 - PetCO2 was calculated. P a C O2 and PetCO2 were evaluated by using a linear regression analysis. The calculation was performed using the SPSS for windows version 10.0, and p values of less than 0.05 were considered significant. RESULT: A total of 59 patients were included in this study. Twenty-five patients were in Group A, (18 in A1 and 7 in A2), 26 in Group B, and 8 in Group C. The linear regression data showed the relation between PaCO2 and PetCO2 to be statistically significant in the Groups A2, B, and C. The values of the difference of PaCO2-PetCO2 were 22.1+/-3.26 mmHg in Group A, 33.7+/-7.21 mmHg in Group A1, 17.6+/-3.06 mmHg in Group A2, 5.3+/-1.45 mmHg in Group B, and 21.2+/-4.73 mmHg in Group C. The 95% confidence intervals of PaCO2-PetCO2 were 15.37- 28.81 mmHg in Group A, in group A1, 16.07-51.35 mmHg in group A1, 11.11-24.03 mmHg in Group A2, 2.33-8.31 mmHg in Group B, and 10.03-32.42 mmHg in Group C.
CONCLUSION
In patients with chronic pulmonary disease, who are endotracheally intubated for assisted ventilation, the PetCO2 do not reflect the PaCO2 and also the value of PaCO2-PetCO2 is not a good parameter for determining pathological status. However, in patients with acute cardiopulmonary disease and during cardiopulmonary resusciatation, the PetCO2 does not reflect the quantitative value of PaCO2, but may be used in predicting the tendency of PaCO2 to increase. In endotracheally intubated patients with extracardiopulmonary cause, PetCO 2 reflects the quantitative index of PaCO2 and the value of PaCO2-PetCO2 may be a good index for monitoring pathological conditions.