![]() ![]() The researchers found that “ end-tidal CO 2 could provide a highly sensitive predictor of return of spontaneous circulation during cardiopulmonary resuscitation (MPR)” (p.791, Cantineau et al, 1996). For example, the authors of the article “ End-tidal carbon dioxide during cardiopulmonary resuscitation in humans presenting mostly with asystole: a predictor of outcome” investigated 120 French patients during non-traumatic cardiac arrest. Their conclusion was, “End-tidal CO(2) is linearly related to HCO(3) and is significantly lower in children with DKA” (Fearon & Steele, 2002).Įxpired end-tidal CO 2 values are considered by many emergency professionals as an accurate predictor (life/death) of cardiac arrest. They start this publication with, “ Patients with diabetic ketoacidosis (DKA) hyperventilate, lowering their alveolar (PACO(2)) and arterial carbon dioxide (PaCO(2))”. Thus, the heart patients with the more serious heart problems had lower CO 2 levels and, therefore, heavier breathing in terms of minute ventilation.Īmerican scientists from the Brown Medical School in Providence recently published a study on End-tidal carbon dioxide that predicts the presence and severity of acidosis in children with diabetes (Fearon & Steele, 2002). The investigation of over 100 patients (Tanabe et al, 2001) with different degrees of chronic heart failure revealed that class I patients (light degree) had about 34.5 mm Hg etCO 2 pressure, class II patients: 32.5 mm Hg, and class III patients: 30.8 mm Hg. What also follows from many studies is that with the deterioration of health etCO 2 tension gets even lower. Indeed, people who breathe more should generally show smaller CO 2 concentrations in expired air. 35 mm Hg corresponds to 4.6% CO 2 at sea level (see Appendix 2 to find the relationships between aCO 2% and absolute aCO 2 pressure at different altitudes).Īll previously quoted studies (section 1.1) indicating hyperventilation should find abnormally low etCO 2 for tested patients. According to “Handbook on physiology” (Severinghaus JW, 1965), “A PCO 2 below 35 mm Hg is indicative of alveolar hyperventilation” (p.1476). The normal alveolar CO 2 pressure is about 40 mm Hg pressure (Guyton, 1984 Ganong, 1995) or partial pressure of 5.3% of normal air at sea level. The level of CO 2 gradually rises during exhalation showing an approximate equalization with the CO 2 value in alveoli in the lungs (hence, the phrase “end-tidal”). A device called a “capnometer” can continually measure CO 2 levels in the expired air. This last phenomenon will be discussed in the next section.Īs a result, many professional researchers, when investigating respiration, often measure etCO 2 (end-tidal CO 2) as a more accurate characteristic reflecting CO 2 content of the lungs. ![]() Inaccuracies occur in cases of small body weight (found, for example, in children), irregular or very shallow breathing found in some obese patients, and obstruction of airways leading to partial or total closure of some lung areas. ![]() Minute ventilation, although a very important respiratory parameter, needs special equipment and does not always indicate hyperventilation and small aCO 2. There is incredible utility in using EtCO2 in CPR.BPT (Buteyko Practitioner Training) Module How Buteyko practitioners can measure changes in breathing of their students The correlation between serum pCO2 and EtCO2 is also less understood animal studies do not show much correlation, and as you would expect with CPR, there will likely be some dead space and/or V/Q mismatch. The utility of EtCO2 in patients who are receiving bag mask ventilation (BVM) or have a laryngeal mask airway (LMA) is less understood and researched. The PQRST mnemonic should be applied to patients with an ETT. Approximately 20 minutes into a resuscitation, the likelihood of ROSC is significantly higher if EtCO2 >20 mm Hg and much less if EtCO2 <10 mm Hg. Termination (T)ĮtCO2 may provide an additional data point when deciding whether it is appropriate to terminate CPR. This can be seen in bronchospasm or a kinked or blocked ETT or circuit. This is an example of a waveform that looks like a “sharkfin,” which indicates expiratory obstruction. ![]()
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