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Br J Anaesth. 2018 Nov;121(5):1156-1165. doi: 10.1016/j.bja.2018.03.022. Epub 2018 Apr 24.

Lung volumes, respiratory mechanics and dynamic strain during general anaesthesia.

Author information

1
Department of Anesthesiology and Intensive Care Medicine, Catholic University of the Sacred Heart, Fondazione "Policlinico Universitario A. Gemelli", Rome, Italy. Electronic address: dlgrieco@outlook.it.
2
Department of Anesthesiology and Intensive Care Medicine, Catholic University of the Sacred Heart, Fondazione "Policlinico Universitario A. Gemelli", Rome, Italy.

Abstract

BACKGROUND:

Driving pressure (ΔP) represents tidal volume normalised to respiratory system compliance (CRS) and is a novel parameter to target ventilator settings. We conducted a study to determine whether CRS and ΔP reflect aerated lung volume and dynamic strain during general anaesthesia.

METHODS:

Twenty non-obese patients undergoing open abdominal surgery received three PEEP levels (2, 7, or 12 cm H2O) in random order with constant tidal volume ventilation. Respiratory mechanics, lung volumes, and alveolar recruitment were measured to assess end-expiratory aerated volume, which was compared with the patient's individual predicted functional residual capacity in supine position (FRCp).

RESULTS:

CRS was linearly related to aerated volume and ΔP to dynamic strain at PEEP of 2 cm H2O (intraoperative FRC) (r=0.72 and r=0.73, both P<0.001). These relationships were maintained with higher PEEP only when aerated volume did not overcome FRCp (r=0.73, P<0.001; r=0.54, P=0.004), with 100 ml lung volume increases accompanied by 1.8 ml cm H2O-1 (95% confidence interval [1.1-2.5]) increases in CRS. When aerated volume was greater or equal to FRCp (35% of patients at PEEP 2 cm H2O, 55% at PEEP 7 cm H2O, and 75% at PEEP 12 cm H2O), CRS and ΔP were independent from aerated volume and dynamic strain, with CRS weakly but significantly inversely related to alveolar dead space fraction (r=-0.47, P=0.001). PEEP-induced alveolar recruitment yielded higher CRS and reduced ΔP only at aerated volumes below FRCp (P=0.015 and 0.008, respectively).

CONCLUSIONS:

During general anaesthesia, respiratory system compliance and driving pressure reflect aerated lung volume and dynamic strain, respectively, only if aerated volume does not exceed functional residual capacity in supine position, which is a frequent event when PEEP is used in this setting.

KEYWORDS:

functional residual capacity; positive end-expiratory pressure; respiratory mechanics

PMID:
30336861
DOI:
10.1016/j.bja.2018.03.022
[Indexed for MEDLINE]

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