Pressure-volume curve variations after a recruitment manoeuvre in acute lung injury/ARDS patients: implications for the understanding of the inflection points of the curve.
OBJECTIVE
Although the pressure-volume (P-V) curve has been proposed in the management of mechanically ventilated patients, its interpretation remains unclear. Our aim has been to study the variations of the P-V curve after a recruitment manoeuvre (RM). Our hypothesis was that the lower inflection point (LIP) represents the presence of compressive atelectases, so it should not change after lung recruitment, while the upper inflection point (UIP) reflects reabsorptive atelectases, and an effective recruitment should result in changes at this level.


METHODS
Two P-V curves (quasi-static method) separated by an RM (40 cmH2O, two consecutive manoeuvres) were plotted in 35 postoperative patients with criteria of acute lung injury/acute respiratory distress syndrome (ARDS). LIP, UIP and expiratory inflection point (EIP) were defined as the first point where the curve consistently starts to separate from the line.


RESULTS
One to six measurements were obtained per patient (73 procedures). Neither the lower nor the EIPs varied significantly after the RM (P = 0.11 and 0.35, respectively). An UIP was observed in 18 curves (25%) before the RM and disappeared on nine occasions after the recruitment. Similar results were obtained when first measurements only were analysed, and when the cause (pulmonary vs. extrapulmonary), severity of lung injury or duration of mechanical ventilation at first measurement were studied.


CONCLUSIONS
An RM does not modify the LIP significantly, but induces the disappearance of the UIP in 50% of the cases in which this point is found.
Pestaña
D
D
Hospital Universitario La Paz, Servicio de Anestesia-Reanimación, Residencia General, Madrid, Spain. dpestana.hulp@salud.madrid.org
Hernández-Gancedo
C
C
Royo
C
C
Pérez-Chrzanowska
H
H
Criado
A
A
D000368:Aged; D005500:Follow-Up Studies; D006801:Humans; D008170:Lung Compliance / Q000502:physiology; D010100:Oxygen / Q000008:administration & dosage / Q000097:blood; D011175:Positive-Pressure Respiration / Q000379:methods*; D011650:Pulmonary Alveoli / Q000503:physiopathology; D001261:Pulmonary Atelectasis / Q000503:physiopathology; D012128:Respiratory Distress Syndrome / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology*
D010100:Oxygen