Mesure de l'espace mort physiologique (VD/VT) chez des patients intubés en ventilation mécanique: comparaison entre la chambre mixique et la calorimétrie indirecte

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In critically ill patients, an increase in the dead space (VD) to tidal volume (VT) ratio, known as ‘physiologic dead space’ (VD/VT) can lead to hypercapnia and to an increase in the workload of the respiratory muscles. Measuring VD can thus be of help to the ICU physician in guiding therapeutic options. Purpose of the study To compare two methods of VD determination, i.e., the Douglas bag technique and indirect calorimetry. Patients and methods VD was assessed with both methods, at baseline and after adding 100 and 175 mL of external dead space. Results (mean ± SD) Sixteen patients (age 59 ± 15 years), were enrolled in the study. At baseline, VD was 316 ± 21 mL and 338 ± 23 mL, as measured by the Douglas bag and indirect calorimetry, respectively. With 100 and 175 mL of external dead space added, values were 356 ± 22 and 407 ± 24 mL with the Douglas bag and 378 ± 21 and 419 ± 22 mL with indirect calorimetry. Correlation between both methods was excellent ( r 2 = 0.95, r = 0.98). Mean bias between both techniques (Bland and Altman method) was Conclusions Both the Douglas bag method and indirect calorimetry can be used to measure VD in intubated and mechanically ventilated patients.