Capnography offers an indirect method to detect metabolic acidosis. EtCO2 measurements have been shown to closely estimate arterial partial pressure of carbon dioxide (pCO2) in healthy patients and also in the presence of metabolic derangements such as acidosis. Bou Chebl et al illustrated that lower pCO2 values correspond to lower pH and bicarbonate values in hyperglycemic diabetic patients, which is in line with the known pathophysiology of acid-base disturbances.⁴ In more severe cases of underlying metabolic acidosis, one would expect an increase in compensatory tachypnea and, therefore, lower EtCO2 readings. But how low buys you an insulin drip and a costly ICU bed? According to recent data (see Table 1) among patients with screening Accu-Cheks greater than 550 mg/dL, an EtCO2 of 35 or greater virtually guarantees that the patient is not in DKA with a sensitivity of 100 percent.⁴ On the other hand, EtCO2s of ≤21 and ≤26 are 100 percent and 96 percent specific for DKA, respectively.⁴ Among patients with a blood glucose (BG) >250 mg/dL, an EtCO2 greater or less than 24.5 is both 90 percent sensitive and 90 percent specific for ^DKA.5 In a pediatric population with hyperglycemia, similar cutoff points were delineated: an EtCO2 of >29 and ≥36 were 83 percent and 100 percent sensitive in ruling out DKA, respectively, while an EtCO2 of 6.

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Table 1. Determining the Likelihood of DKA with Capnography

There is no current consensus regarding which EtCO2 levels can be used consistently in practice to rule in or rule out metabolic acidosis, and therefore DKA, in the right clinical setting; however, utilizing end-tidal capnography in the evaluation of diabetic patients with suspected DKA is a quick and noninvasive method both to approximate the presence and severity of metabolic acidosis and to guide your initial treatment and the patient’s ultimate disposition. While no formal consensus exists, a screening EtCO2 of ≥36 in your next hyperglycemic diabetic patient can rule out ketoacidosis and spare your patient an invasive ABG test.

End-Tidal to Monitor COPD Exacerbations

People across the world continue to smoke despite the best efforts of the Truth campaign. COPD exacerbations seem as prominent as ever among ED visits and thus lead to difficult clinical decisions regarding treatment plans, intubation, and disposition. Many emergency physicians rely on ABG analysis in conjunction with their physical assessments to make the appropriate disposition for patients with COPD exacerbation. Could EtCO2 also be the answer for COPD or just another far-fetched fairy tale?