• Prehospital ETCO2 predicts in-hospital mortality and metabolic disturbances

    by Alan Batt. Last modified: 12/03/14

    etco2

    Summary

    • Retrospective cohort study over 2 years
    • 1328 records reviewed
      • 1088 patients had hospital discharge data, ETCO2, and 6 prehospital vital signs recorded:
        • ETCO2, Respiratory Rate, Systolic BP, Diastolic BP, Pulse, SpO2
      • ETCO2 was collected via Microstream capnography in both intubated and non-intubated patients.
      • Low ETCO2 levels were the strongest predictor of mortality in the overall group.
      • Low ETCO2 levels were the strongest predictor of mortality in subgroup analysis excluding prehospital cardiac arrest.
    • Sensitivity of abnormal ETCO2 for predicting mortality was 93%; specificity was 44%.
    • Negative predictive value was 99%.
    • Significant associations between ETCO2 and serum bicarbonate levels, anion gap and lactate levels.
    • Of all prehospital vital signs, ETCO2 was the most predictive and consistent for mortality

    Limitations:

    • Study observed patients presenting to a single emergency medical service, who were transported to a single hospital.
    • Study was performed retrospectively and thus is subject to selection bias. Retrospective studies also cannot show temporal relationship.
    • ETCO2 was monitored by paramedics only in patients requiring advanced life support care, patients deemed to require only basic life support were excluded.
    • Collection of ETCO2 and vital signs occured only at a single point of time during care – unknown how continuous capnography and repeated vital signs may have clarified the role each plays in outcome prediction.

    Sensitivity & Specificity

    • Sensitivity (also called the true positive rate) relates to a test’s ability to identify a condition correctly – it measures the proportion of actual positives which are correctly identified as such (e.g. the percentage of sick people who are correctly identified as having the condition).
      • Negative result in a test with high sensitivity is useful for ruling out disease – the test is reliable when its result is negative, since it rarely misdiagnoses those who have the disease.
    • Specificity (sometimes called the true negative rate) relates to a test’s ability to exclude a condition correctly – it measures the proportion of negatives which are correctly identified as such (e.g. the percentage of healthy people who are correctly identified as not having the condition).
      • Positive result in a test with high specificity is useful for ruling in disease – the test will rarely gives positive results in healthy patients.

     

     
    Hunter CL1, Silvestri S2, Ralls G2, Bright S3, Papa L4. The sixth vital sign: prehospital end-tidal carbon dioxide predicts in-hospital mortality and metabolic disturbances. Am J Emerg Med. 2014 Feb;32(2):160-5. PMID: 24332900.

    Abstract

    Objective

    To determine the ability of prehospital end-tidal carbon dioxide (ETCO2) to predict in-hospital mortality compared to conventional vital signs.

    Methods

    We conducted a retrospective cohort study among patients transported by emergency medical services during a 29-month period. Included patients had ETCO2 recorded in addition to initial vital signs. The main outcome was death at any point during hospitalization. Secondary outcomes included laboratory results and admitting diagnosis.

    Results

    Of 1328 records reviewed, hospital discharge data, ETCO2, and all 6 prehospital vital signs were available in 1088 patients. Low ETCO2 levels were the strongest predictor of mortality in the overall group (area under the receiver operating characteristic curve (AUC of 0.76, 95% confidence interval [CI] 0.66-0.85), as well as subgroup analysis excluding prehospital cardiac arrest (AUC of 0.77, 95% CI 0.67-0.87). The sensitivity of abnormal ETCO2 for predicting mortality was 93% (95% CI 79%-98%), the specificity was 44% (95% CI 41%-48%), and the negative predictive value was 99% (95% CI 92%-100%). There were significant associations between ETCO2 and serum bicarbonate levels (r = 0.429, P < .001), anion gap (r = -0.216, P < .001), and lactate (r = -0.376, P < .001).

    Conclusion

    Of all prehospital vital signs, ETCO2 was the most predictive and consistent for mortality, which may be related to an association with metabolic acidosis.

    References

     
    1.

    Hunter CL1, Silvestri S2, Ralls G2, Bright S3, Papa L4. The sixth vital sign: prehospital end-tidal carbon dioxide predicts in-hospital mortality and metabolic disturbances. Am J Emerg Med. 2014 Feb;32(2):160-5. PMID: 24332900.

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    Alan Batt

    Alan Batt

    Paramedic, educator, researcher
    Alan is a critical care paramedic, paramedic educator and prehospital researcher, currently working around the world as an educator and researcher. He has previously worked and studied across Europe, North America and the Middle East. He holds a Graduate Certificate in Intensive Care Paramedic Studies, and an MSc in Critical Care. His main interests are in care of the elderly, end-of-life care, patient safety, professionalism (including role and identity), and paramedic education.

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    One thought on “Prehospital ETCO2 predicts in-hospital mortality and metabolic disturbances

    • Cody says:

      What is the point in which we see a sudden increase in mortality. What levels of Etco2 should I start worrying about my patient as a paramedic in the field? 25? 20? Or even lower?

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