In:
Anesthesia & Analgesia, Ovid Technologies (Wolters Kluwer Health), Vol. 122, No. 5 ( 2016-05), p. 1412-1420
Abstract:
Although the mechanical status of the lungs affects the shape of the capnogram, the relations between the capnographic parameters and those reflecting the airway and lung tissue mechanics have not been established in mechanically ventilated patients. We, therefore, set out to characterize how the mechanical properties of the airways and lung tissues modify the indices obtained from the different phases of the time and volumetric capnograms and how the lung mechanical changes are reflected in the altered capnographic parameters after a cardiopulmonary bypass (CPB). METHODS: Anesthetized, mechanically ventilated patients ( n = 101) undergoing heart surgery were studied in a prospective consecutive cross-sectional study under the open-chest condition before and 5 minutes after CPB. Forced oscillation technique was applied to measure airway resistance (Raw), tissue damping (G), and elastance (H). Time and volumetric capnography were performed to assess parameters reflecting the phase II (S II ) and phase III slopes (S III ), their transition (D 2min ), the dead-space indices according to Fowler, Bohr, and Enghoff and the intrapulmonary shunt. RESULTS: Before CPB, S II and D 2min exhibited the closest ( P = 0.006) associations with H (0.65 and −0.57; P 〈 0.0001, respectively), whereas S III correlated most strongly ( P 〈 0.0001) with Raw ( r = 0.63; P 〈 0.0001). CPB induced significant elevations in Raw and G and H ( P 〈 0.0001). These adverse mechanical changes were reflected consistently in S II , S III , and D 2min , with weaker correlations with the dead-space indices ( P 〈 0.0001). The intrapulmonary shunt expressed as the difference between the Enghoff and Bohr dead-space parameters was increased after CPB (95% ± 5% [SEM] vs 143% ± 6%; P 〈 0.001). CONCLUSIONS: In mechanically ventilated patients, the capnographic parameters from the early phase of expiration (S II and D 2min ) are linked to the pulmonary elastic recoil, whereas the effect of airway patency on S III dominates over the lung tissue stiffness. However, severe deterioration in lung resistance or elastance affects both capnogram slopes.
Type of Medium:
Online Resource
ISSN:
0003-2999
DOI:
10.1213/ANE.0000000000001185
Language:
English
Publisher:
Ovid Technologies (Wolters Kluwer Health)
Publication Date:
2016
detail.hit.zdb_id:
2018275-2
Bookmarklink