[Simultaneous measurement of arterial and end-expiratory carbon dioxide before, during and after voluntary...

Hyperventilation syndrome is considered an established diagnosis if it is confirmed that the patient's complaints correlate with arterial hypocapnia. In the diagnostic criteria set up by a group in Nijmegen, paCO2 is determined indirectly by measuring the end tidal CO2. Values below 4 kPa measured at rest and 10 or more minutes after deliberate hyperventilation are classified positive diagnostic criteria for hyperventilation syndrome. However, it has not been proven that end tidal pCO2 agrees well with paCO2 during the entire manoeuvre. We performed simultaneous measurements of both parameters in 10 healthy non-smokers, before, during and after 3 minutes of deliberate hyperventilation. A comparison of the values employed for diagnosing a hyperventilation syndrome (during normal respiration before and 10 and more minutes after hyperventilation) yields a mean difference of 0.39 kPa according to the statistical computation described by Bland and Altman (limits of the range of agreement between 0.98 and -0.18). The end tidal CO2 values measured during the normal respiratory phase as well as 10 and more minutes after hyperventilation, agree well with the arterial values (the arterial values being slightly higher). During and shortly after hyperventilation the values obtained by both methods differ from one another, so that the exact degree of hypocapnia during a hyperventilation period cannot be assessed by measuring the end tidal CO2.