Selected topic: Prehospital careA Sudden Increase in Partial Pressure End-Tidal Carbon Dioxide (PETCO2) at the Moment of Return of Spontaneous Circulation
Introduction
Outcome of advanced life support (ALS) is determined by many factors, including severity of the primary insult, time elapsed between cardiac arrest and beginning of the basic life support (BLS) and ALS itself, the efficiency of BLS and ALS, cause of the cardiac arrest, patient's general state of health, and environmental circumstances. Of these factors, only ALS efficiency is under the control of the care providers. Therefore, any information regarding efficiency of ALS during its delivery is desirable, especially because frequent pulse checking and electrocardiogram (ECG) rhythm analysis may negatively interfere with the efficiency of ALS (1).
The partial pressure end-tidal carbon dioxide (PETCO2) level reflects tissue metabolism, tissue and lung perfusion, and alveolar ventilation. Under constant ventilation, PETCO2 reflects the level of circulation and intensity of the body's aerobic metabolism. Spontaneous circulation (SC) has been reported to be more effective in comparison with chest compression in the level of cardiac output reached (2). This provided a rationale for the observation by Kalenda that an increase of PETCO2 occurs after ROSC (3). This has been confirmed in both experimental and clinical studies (4, 5, 6, 7). Two experimental and one clinical study demonstrated a linear relationship between the cardiac output and PETCO2 (8, 9, 10). Some other studies on out-of-hospital and hospital resuscitations also confirmed that PETCO2 level after ROSC is higher than before ROSC (6, 11, 12). Other studies have been aimed at using PETCO2 to discriminate between patients suffering cardiac arrest with a chance for ROSC from those destined to die (13, 14, 15, 16, 17, 18). These studies have concluded that a PETCO2 value of 10 mm Hg may serve as such a threshold value.
The ILCOR (International Liaison Committee on Resuscitation) Consensus on Science and Treatment Recommendations in 2005 mentioned the use of capnometry as a possible early indicator of ROSC (19).
A principle goal of the present study was to analyze changes in PETCO2 levels around the ROSC point with an ultimate goal of determining whether an increase in PETCO2 level could be used as a reliable indicator of ROSC.
Section snippets
Study Design
This was a retrospective case control study. PETCO2 was continuously monitored during out-of-hospital ALS delivered to patients in cardiac arrest. Subsequently, the PETCO2 recordings were analyzed in two extreme groups of cases: the first group of patients were those with a single uncomplicated ROSC followed by stable SC; the second group of patients were those with an unsuccessful ALS resuscitation without any sign of ROSC, who died at the scene. Collected data were also used to compare PETCO2
Results
A summary of data on the 108 analyzed cases of ALS, subdivided into two groups, is presented (Table 1).
The mean duration of PETCO2 recordings in 59 cases with ROSC was 18 min before ROSC and 33 min after ROSC. The average of the mean levels of PETCO2 was 26.65 ± 12.00 mm Hg (3.55 ± 1.6 kPa) before ROSC and 36.60 ± 12.44 mm Hg (4.8 ± 1.66 kPa) after ROSC (p < 0.0001). Results of the paired t-test, comparing PETCO2 after ROSC to its level before ROSC in individual cases, indicated that the
Discussion
This study applied PETCO2 monitoring to out-of hospital resuscitation (ALS) of patients with cardiac arrest who were intubated and had constant lung ventilation maintained by an automatic device. The latter procedure is important because any fluctuation in the alveolar ventilation (for example, by using a self-inflating bag) may be expected to interfere with PETCO2 as indicator of the cardiac output, because principle variables affecting PETCO2 values are the entire body metabolism, cardiac
Conclusions
The study demonstrates that constantly ventilated patients undergoing ALS in out-of-hospital conditions have a significantly higher PETCO2 of about 10 mm Hg (1.33 kPa) after ROSC than before ROSC. It also shows that an increase in PETCO2 > 10 mm Hg (1.33 kPa), coming relatively suddenly, is likely to indicate ROSC. Consequently, the rule of 10 mm Hg may be extended to include the utilization of a sudden increase of more than 10 mm Hg in continuously recorded PETCO2 as an indicator of likelihood
Acknowledgment
This work is a part of the study “Sudden cardiac arrest in out-of-hospital care. Analysis of causes and comparison of different methods recommended for circulatory restoration.” The study was financially supported from the grant IGA NR/7970-3 provided by the Ministry of Health of the Czech Republic and by the project MSM 0021620806 of the Ministry of Education, Youth and Sports of the Czech Republic. The authors would like to acknowledge all contributors, Drs.: T. Garnol, M. Sykorova, A.
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