Capnography as a tool to detect metabolic changes in patients cared for in the emergency setting.
Francisco José Cereceda-Sánchez, Jesús Molina-Mula
PMID 28513767WHAT IT FOUND
Exhaled CO2 readings tracked blood gas values well in children with diabetic ketoacidosis or gastroenteritis, but adult emergency studies were inconsistent.
It may help screen severe illness, not replace blood tests.
Key findings
01In children with diabetic ketoacidosis, no child with end-tidal CO2 above 30 mmHg had diabetic ketoacidosis, with sensitivity 1.0 and specificity 0.86.
02In adults with diabetic ketoacidosis, end-tidal CO2 above 24.5 mmHg was outside the interval for diabetic ketoacidosis, with sensitivity 0.90 and specificity 0.90.
03In adults with dyspnea, one study found a mean deviation of 12 mmHg between end-tidal CO2 and arterial CO2, and another found weak agreement ranging from -10 mmHg to +26 mmHg.
STILL TO COME
How it was doneWhat they foundWhat it means for RNs
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What it does not show
The review included observational correlation studies, not trials of capnography-guided treatment. Sample sizes were small and convenience sampling was used in most included studies. The included studies used different capnograph models, sensors, cannulas and measurement durations, making direct comparison difficult. Eight studies did not report the duration of capnography measurement, and some did not report the cannula type. Many adult studies involved patients with chronic respiratory or cardiac disease, which can alter end-tidal CO2 independently of metabolic status. The review could not recommend precise end-tidal CO2 cutoff values for clinical decisions.
The easy way to misread this
Do not treat capnography as a stand-alone diagnostic test for metabolic acidosis. The review found inconsistent correlations and concordance in adult emergency studies, and it could not recommend precise cutoff values.