The aim of this study was to determine typical values for non-invasive volumetric capnography (VCap) parameters for healthy volunteers and anesthetized individuals. VCap was obtained by a capnograph connected to the airway opening. We prospectively studied 33 healthy volunteers 32 ± 6 years of age weighing 70 ± 13 kg at a height of 171 ± 11 cm in the supine position. Data from these volunteers were compared with a cohort of similar healthy anesthetized patients ventilated with the following settings: tidal volume (VT) of 6-8 mL/kg, respiratory rate 10-15 bpm, PEEP of 5-6 cmH₂O and FiO₂ of 0.5. Volunteers showed better clearance of CO₂ compared to anesthetized patients as indicated by (median and interquartile range): (1) an increased elimination of CO₂ per mL of VT of 0.028 (0.005) in volunteers versus 0.023 (0.003) in anesthetized patients, p < 0.05; (2) a lower normalized slope of phase III of 0.26 (0.17) in volunteers versus 0.39 (0.38) in anesthetized patients, p < 0.05; and (3) a lower Bohr dead space ratio of 0.23 (0.05) in volunteers versus 0.28 (0.05) in anesthetized patients, p < 0.05. This study presents reference values for non-invasive volumetric capnography-derived parameters in healthy individuals. Mechanical ventilation and anesthesia altered these values significantly.

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BACKGROUND: The difference between Bohr and Enghoff dead space are not well described in ARDS patients. We aimed to analyze the effect of PEEP on the Bohr and Enghoff dead spaces in a model of ARDS. METHODS: 10 pigs submitted to randomized PEEP steps of 0, 5, 10, 15, 20, 25 and 30 cm H 2 O were evaluated with the use of lung ultrasound images, alveolar-arterial oxygen difference (P (A-a)O 2), transpulmonary mechanics, and volumetric capnography at each PEEP step. RESULTS: At PEEP > 15 cm H 2 O, atelectasis and P (A-a)O 2 progressively decreased while endinspiratory transpulmonary pressure (P L), end-expiratory P L , and driving P L increased (all P < .001). Bohr dead space (V D Bohr /V T), airway dead space (V D aw /V T), and alveolar dead space (V D alv /V T alv) reached their highest values at PEEP 30 cm H 2 O (0.69 ؎ 0.10, 0.53 ؎ 0.13 and 0.35 ؎ 0.06, respectively). At PEEP <15 cm H 2 O, the increases in atelectasis and P (A-a)O 2 were associated with negative end-expiratory P L and highest driving P L. V D Bohr /V T and V D aw /V T showed the lowest values at PEEP 0 cm H 2 O (0.51 ؎ 0.08 and 0.32 ؎ 0.08, respectively), whereas V D alv /V T alv increased to 0.27 ؎ 0.05. Enghoff dead space and its derived V D alv /V T alv showed high values at low PEEPs (0.86 ؎ 0.02 and 0.79 ؎ 0.04, respectively) and at high PEEPs (0.84 ؎ 0.04 and 0.65 ؎ 0.12), with the lowest values at 15 cm H 2 O (0.77 ؎ 0.05 and 0.61 ؎ 0.11, respectively; all P < .001). CONCLUSIONS: Bohr dead space was associated with lung stress, whereas Enghoff dead space was partially affected by the shunt effect.

ObjectivesThe effectiveness of the active humidification systems (AHS) in patients already weaned from mechanical ventilation and with an artificial airway has not been very well described. The objective of this study was to evaluate the performance of an AHS in chronically tracheostomized and spontaneously breathing patients.MethodsMeasurements were quantified at three levels of temperature (T°) of the AHS: level I, low; level II, middle; and level III, high and at different flow levels (20 to 60 L/minute). Statistical analysis of repeated measurements was performed using analysis of variance and significance was set at a P<0.05.ResultsWhile the lowest temperature setting (level I) did not condition gas to the minimum recommended values for any of the flows that were used, the medium temperature setting (level II) only conditioned gas with flows of 20 and 30 L/minute. Finally, at the highest temperature setting (level III), every flow reached the minimum absolute humidity (AH) recommended of 30 mg/L.ConclusionAccording to our results, to obtain appropiate relative humidity, AH and T° of gas one should have a device that maintains water T° at least at 53℃ for flows between 20 and 30 L/m, or at T° of 61℃ at any flow rate.