The upper inflection point of the pressure-volume curve. Influence of methodology and of different modes of ventilation.
OBJECTIVE
The pressure-volume (P/V) curve has been proposed as a tool to adjust the ventilatory settings in cases of acute respiratory distress syndrome (ARDS). The aim of this study was to test the influence of P/V tracing methodology on the presence and value of the upper inflection point (UIP).


METHODS
In 13 medical ARDS patients, the interruption and the automated low flow inflation methods were compared while the patients were ventilated at conventional (10-12 ml/kg) and at low (5-6 ml/kg) tidal volume (Vt). Two levels of inspiratory flow and insufflation time were used (3 and 6 s).


RESULTS
No significant difference in UIP was found between the static and the dynamic methods, whatever the flow used. At Vt 10-12 ml/kg, the static and dynamic UIPs were 22.4 +/- 4.4 cmH(2)O and 22.1 +/- 4.5 cmH(2)O ( p = 0.86), respectively; at Vt of 5-6 ml/kg, the static and dynamic UIPs were 26.6 +/- 4.1 cmH(2)O and 25.5 +/- 5 cmH(2)O ( p = 0.34), respectively. Significant differences in UIP were found, in the static and dynamic conditions, between the two levels of Vt ( p < 0.005): it was lower with the higher Vt, suggesting that UIP is dependent on previous tidal alveolar recruitment.


CONCLUSIONS
Interruption and continuous flow techniques gave similar results, but the previous Vt influences the pressure value of the UIP.
Servillo
Giuseppe
G
Dipartimento Universitario di Scienze Chirurgiche, Anestesiologiche, Rianimatorie e dell'Emergenza, Università degli Studi di Napoli Federico II, Via Pansini n.5, 80131 Napoli, Italy. servillo@unina.it
De Robertis
Edoardo
E
Maggiore
Salvatore
S
Lemaire
François
F
Brochard
Laurent
L
Tufano
Rosalba
R
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007558:Italy; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology / Q000628:therapy*; D013990:Tidal Volume