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Capnography, the non-invasive monitoring of the CO2 partial pressure in the exhaled gas provides information on lung ventilation and perfusion. The reference mainstream (MS) method measures CO2 directly at the airway opening. Sidestream (SS) devices analyse a gas sample aspirated through a tube, distorting the capnogram in an unclarified manner and degree. We investigated the influence of sampling rate on the shape factors of the SS capnogram. Measurements were made simultaneously with MS and SS capnographs, the latter being equipped with adjustable sampling flow in 6 anaesthetised, ventilated patients. Phase 2 and 3 slopes (S2 and S3) were derived from time capnograms. S2 describes the transition between the emptying of bronchial and alveolar gas, S3 reflects the heterogeneity of alveolar ventilation. To assess the effects of sampling flow on capnogram shape, we analysed correlations between the sampling flow and the difference of SS and MS parameters (S2diff, S3diff). By increasing sampling flow from 100 to 400 ml/min in 3 steps, S2diff exhibited monotonous, linear decrease (R2=0.47, p Our results highlight that changes in sampling flow rate bias the shape factors derived from SS capnogram. Increasing the sampling flow from 200 to 400-500 ml/min improves the accuracy of SS capnographic parameter estimations, approaching those obtained by the MS method. In clinical practice, however, the feasibility of increasing the sampling flow is limited by the loss of tidal volume, which is of great importance in paediatric patients. Supported by OTKA grant K115253.

The lung function deterioration to cardiopulmonary bypass (CPB) can be alleviated by recruitment manoeuvres (RM), elevating the positive end-expiratory pressure (PEEP), and/or bronchodilator therapies. We aimed at comparing the efficiency of these treatment strategies. Airway resistance (Raw), respiratory compliance (C), capnogram phase III slope (S III ), and Horowitz coefficient (HQ) were measured in anaesthetized, mechanically ventilated patients undergoing cardiac surgeries. Five different therapeutic interventions were compared to the standard post-CPB lung management with 4 cmH 2 O PEEP: i) application of elevated PEEP (8 cmH 2 O), ii) administration of 1 MAC sevoflurane (SEV) during either PEEP4 or iii) PEEP8, iv) a RM followed by PEEP8, and v) concomitant use of a RM, PEEP8, and SEV. The Raw decreased significantly in all groups, with the greatest drop after the combined application of RM, PEEP and SEV (-60±21[SD]%, p III decreased in all patients; elevated PEEP and SEV induced the greatest changes (-32±16%, p Supported by OTKA grant K115253.