Alveolar recruitment versus hyperinflation: A balancing act.
OBJECTIVE
To address lung recruitment according to pressure/volume curves, along with regional recruitment versus hyperinflation evidence from computed tomography and electrical impedance tomography.


RESULTS
Cyclical tidal volume recruitment of atelectatic lung regions causes acute lung injury, as do large breaths during pneumonectomy. Using the lower inflection point on the static pressure/volume inflation curve plus 2 cmH2O as a positive end-expiratory pressure setting limits hyperinflation in acute lung injury, but may not provide enough positive end-expiratory pressure to avoid cyclical recruitment/derecruitment injury in more severe acute lung injury regions. Both computed tomography and electrical impedance tomography can help titrate positive end-expiratory pressure in these regions, thereby assuring an 'open lung' ventilatory pattern. Regional pressure/volume curves show that adequate positive end-expiratory pressure for severe acute lung injury regions may not be reliably determined from whole lung pressure/volume curves. Balancing positive end-expiratory pressure requires both arterial PO2 and PCO2 values to determine at what level hyperinflated regions become seriously underperfused (develop very high ventilation-perfusion ratios), adding to the hypercarbia from increased deadspace.


CONCLUSIONS
Positive end-expiratory pressure levels must be high enough to minimize recruitment/derecruitment cycling. Balancing recruitment versus overdistension may require thoracic tomography, to assure sufficient improvement in oxygenation while limiting hypercarbia.
Dueck
Ron
R
Department of Anesthesiology, University of California, San Diego, California, USA. rdueck@ucsd.edu
D000818:Animals; D045422:Continuous Positive Airway Pressure / Q000009:adverse effects; D006612:High-Frequency Ventilation / Q000009:adverse effects; D006801:Humans; D008176:Lung Volume Measurements; D010992:Plethysmography, Impedance / Q000379:methods; D011175:Positive-Pressure Respiration / Q000009:adverse effects; D011650:Pulmonary Alveoli / Q000000981:diagnostic imaging / Q000503:physiopathology*; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy; D012121:Respiration, Artificial / Q000009:adverse effects; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy; D015656:Respiratory Mechanics; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed / Q000379:methods