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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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Rationale: Acute hypoxemic respiratory failure is a condition that comprises a wide array of entities. Obtaining a histological lung sample might help reach a diagnosis and direct an appropriate treatment in a select group of patients. Objective: To describe our experience in the use of cryobiopsy for the diagnosis of acute hypoxemic respiratory failure of undetermined origin.

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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.