Capnography may provide useful non-invasive bedside information concerning heterogeneity in lung ventilation, ventilation–perfusion mismatching and metabolic status. Although the capnogram may be recorded by mainstream and sidestream techniques, the capnogram indices furnished by these approaches have not previously been compared systematically. Simultaneous mainstream and sidestream time and volumetric capnography was performed in anaesthetized, mechanically ventilated patients undergoing elective heart surgery. Time capnography was used to assess the phase II (S_II,T) and III slopes (S_III,T). The volumetric method was applied to estimate phase II (S_II,V) and III slopes (S_III,V), together with the dead space values according to the Fowler (V_DF), Bohr (V_DB), and Enghoff (V_DE) methods and the volume of CO₂ eliminated per breath ($VCO2$). The partial pressure of end-tidal CO₂ ($PETCO2$) was registered. Excellent correlation and good agreement were observed in S_III,T measured by the mainstream and sidestream techniques [ratio=1.05 (sem 0.16), R²=0.92, P<0.0001]. Although the sidestream technique significantly underestimated $VCO2$ and overestimated S_III,V [1.32 (0.28), R²=0.93, P<0.0001], V_DF, V_DB, and V_DE, the agreement between the mainstream and sidestream techniques in the difference between V_DE and V_DB, reflecting the intrapulmonary shunt, was excellent [0.97 (0.004), R²=0.92, P<0.0001]. The $PETCO2$ exhibited good correlation and mild differences between the mainstream and sidestream approaches [0.025 (0.005) kPa]. Sidestream capnography provides adequate quantitative bedside information about uneven alveolar emptying and ventilation–perfusion mismatching, because it allows reliable assessments of the phase III slope, $PETCO2$ and intrapulmonary shunt. Reliable measurement of volumetric parameters (phase II slope, dead spaces, and eliminated CO₂ volumes) requires the application of a mainstream device.

Levosimendan has a calcium-sensitizing effect in the myocardium and opens ATP-sensitive potassium channels (K_ATP) in vascular smooth muscle. Because airway smooth muscle also expresses K_ATP, we characterized the protective potential of levosimendan against increased airway and respiratory tissue resistances. Animals were administered levosimendan alone ( group L), levosimendan after pretreatment with a K_ATPchannel blocker (glibenclamide, group LG), glibenclamide only ( group G), or solvent alone (dextrose, group C). Airway resistance (R_aw), tissue damping, and elastance were determined by forced oscillations under baseline conditions and following provocation tests with intravenous methacholine (MCh). Cardiac output (CO) was assessed by transpulmonary thermodilution. The same sequence of measurements was then repeated during intravenous infusion of levosimendan in groups L and LG or glucose in groups G and C. Sham treatments in groups C and G had no effect on lung responsiveness. However, levosimendan treatment in group L elevated CO and inhibited the MCh-induced airway responses [R_awchanges of 87.8 ± 83% (SD) vs. 24.4 ± 16% at 4 μg·kg⁻¹·min⁻¹MCh, P < 0.001], and in G (35.2 ± 12.7 vs. 25.2 ± 12.9%, P < 0.05). The preventive affect of levosimendan against lung constriction vanished in the LG group. Levosimendan exerts a K_ATP-mediated potential to prevent bronchoconstriction and may prohibit adverse lung peripheral changes both in the small bronchi and the pulmonary parenchyma. The identification of a further pleiotropic property of levosimendan that is related to the pulmonary system is of particular importance for patients with decreased cardiorespiratory reserves for which simultaneous circulatory support is complemented with prevention of adverse respiratory events.

Crystalloids are first line in fluid resuscitation therapy, however there is a lack of evidence-based recommendations on the volume to be administered. Therefore, we aimed at comparing the systemic hemodynamic and respiratory effects of volume replacement therapy with a 1:1 ratio to the historical 1:3 ratio. Anesthetized, ventilated rats randomly included in 3 groups: blood withdrawal and replacement with crystalloid in 1:1 ratio (Group 1, n = 11), traditional 1:3 ratio (Group 3, n = 12) and a control group with no interventions (Group C, n = 9). Arterial blood of 5% of the total blood volume was withdrawn 7 times, and replaced stepwise with different volume rations of Ringer’s acetate, according to group assignments. Airway resistance (Raw), respiratory tissue damping (G) and tissue elastance (H), mean arterial pressure (MAP) and heart rate (HR) were assessed following each step of fluid replacement with a crystalloid (CR1-CR6). Lung edema index was measured from histological samples. Raw decreased in Groups 1 and 3 following CR3 (p < 0.02) without differences between the groups. H elevated in all groups (p < 0.02), with significantly higher changes in Group 3 compared to Groups C and 1 (both p = 0.03). No differences in MAP or HR were present between Groups 1 and 3. Lung edema was noted in Group 3 (p < 0.05). Fluid resuscitation therapy by administering a 1:1 blood replacement ratio revealed adequate compensation capacity and physiological homeostasis similar with no lung stiffening and pulmonary edema. Therefore, considering this ratio promotes the restrictive fluid administration in the presence of continuous and occult bleeding.