In the past few decades, assessment of exhaled CO2 in both intubated and non-intubated patients has evolved into an essential component in many aspects of patient monitoring. Besides the basic assessment of ventilation, exhaled CO2 monitoring can provide valuable patient safety information and critical physiologic data in regard to the ventilation and perfusion matching in the lungs, cardiac output, and metabolic rate. Despite these important clinical monitoring benefits and widespread availability, exhaled CO2 monitoring is often underutilized. The purpose of this paper is to review the importance and present the extensive body of knowledge to support the use of exhaled CO2 monitoring in various areas of clinical practice. Advanced application concepts and the future development of exhaled CO2 monitoring will also be discussed.

BACKGROUND: Calculation of physiologic dead space (dead space divided by tidal volume [V D / V T ]) using the Enghoff modification of the Bohr equation requires measurement of the partial pressure of mean expired CO 2 (P E CO 2 ) by exhaled gas collection and analysis, use of a metabolic analyzer, or use of a volumetric CO 2 monitor. The Dräger XL ventilator is equipped with integrated volumetric CO 2 monitoring and calculates minute CO 2 production (V CO 2 ). We calculated P E CO 2 and V D /V T from ventilator derived volumetric CO 2 measurements of V CO 2 and compared them to metabolic analyzer and volumetric CO 2 monitor measurements. METHODS: A total of 67 measurements in 36 subjects recovering from acute lung injury or ARDS were compared. Thirty-one ventilator derived measurements were compared to measurements using 3 different metabolic analyzers, and 36 ventilator derived measurements were compared to measurements from a volumetric CO 2 monitor. RESULTS: There was a strong agreement between ventilator derived measurements and metabolic analyzer or volumetric CO 2 monitor measurements of P E CO 2 and V D /V T. The correlations, bias, and precision between the ventilator and metabolic analyzer measurements for P E CO 2 were r ‫؍‬ 0.97, r 2 ‫؍‬ 0.93 (P < .001), bias ؊1.04 mm Hg, and precision ؎ 1.47 mm Hg. For V D /V T the correlations were r ‫؍‬ 0.95 and r 2 ‫؍‬ 0.91 (P < .001), and the bias and precision were 0.02 ؎ 0.04. The correlations between the ventilator and the volumetric CO 2 monitor for P E CO 2 were r ‫؍‬ 0.96 and r 2 ‫؍‬ 0.92 (P < .001), and the bias and precision were ؊0.19 ؎ 1.58 mm Hg. The correlations between the ventilator and the volumetric CO 2 monitor for V D /V T were r ‫؍‬ 0.97 and r 2 ‫؍‬ 0.95 (P < .001), and the bias and precision were 0.01 ؎ 0.03. CONCLUSIONS: P E CO 2 , and therefore V D /V T , can be accurately calculated directly from the Dräger XL ventilator volumetric capnography measurements without use of a metabolic analyzer or volumetric CO 2 monitor.

We studied the feasibility of routine diagnostic testing for HIV-1 RNA at a publicly funded testing site. HIV-1 RNA was determined with a commercial polymerase chain reaction assay in pooled seronegative blood samples submitted for HIV testing to a public health laboratory. Recovery of HIV-1 RNA from the samples was estimated as at least 8% of viral RNA that was found in freshly prepared plasma. We estimated that screening for HIV-1 RNA in serum pools would result in the identification of blood specimens from more than 95% of acutely infected patients. The frequency of HIV-1 RNA in seronegative blood samples was estimated to be between 19 and 601 per 10(6) submitted specimens. The ratio of HIV-1 RNA positive and seronegative samples to specimens with HIV-1 antibodies confirmed by Western blot was estimated to be between 0.2% and 6.6%. The reagent costs for identifying 1 HIV-infected blood sample were 10-fold higher with the commercially available HIV-1 RNA assay compared with the HIV antibody enzyme-linked immunosorbent assay. Diagnostic testing for HIV-1 RNA may be warranted in high-risk populations since acutely infected patients may benefit most from anti-retroviral therapy and are thought to contribute disproportionately to the HIV epidemic.