![]() ![]() As extrapolation to time zero was shown to overestimate Pcap, we used extrapolation to 0.2 s after occlusion for the fitting period comprised between 0.3 and 2 s. We fitted an exponential curve to the pressure signal at two different time periods after occlusion, 0.3–2.0 s as proposed by Hakim (Fig. We superimposed one non-occluded pulmonary artery pressure curve to the occluded curve and defined the moment of occlusion as the moment when the occluded pressure deviated below the non-occluded tracing (Fig. The mathematical method chosen has been validated against the double occlusion method. This method has been validated and used experimentally and clinically. Three intensive care specialists estimated Pcap using the visual inspection method (Fig. Static pressures were measured and static compliance of the respiratory system calculated at each ventilator setting by the occlusion method. Pcap measurements were made only at setVt, by occluding the pulmonary artery in triplicate for a minimum of 6 s during an end-expiratory pause. Protocolįour PEEP levels (6, 9, 12 and 15 cmH 2O) were used for the assessment of respiratory mechanics and, at each PEEP level, three tidal volumes (Vt) were used (setVt, a 20% higher Vt and a 20% lower Vt). A physiologic recording system (Direc, Raytech Instruments, Canada) was used. Systemic and pulmonary artery pressures (SAP, PAP) and central venous pressure (CVP) were obtained from a patient monitor (AS3, Datex-Ohmeda, Finland). Volume was obtained by digital integration of the flow signal. The reproducibility and between-method variability of computed Pcap were evaluated.Ī heated pneumotachometer (Fleisch No2, Switzerland) and two differential pressure transducers (Validyne, MP45, ☒.0 and ☑00.0 cmH 2O CA) were used for flow and airway opening pressure measurements. Pcap was determined using two different methods. In addition, we assessed the effect of PEEP on Pcap and Pcap−PAOP. We evaluated the evolution of Pcap and Pcap−PAOP from early to established ARDS. We hypothesized that, in ARDS, Pcap−PAOP varies over time and with PEEP level. Since Pcap−PAOP is not constant, hydrostatic pressure in the capillaries may be grossly underestimated in the clinical setting. The effect of PEEP on Pcap and on Pcap−PAOP remains unsettled. The protective approach to ventilation in ARDS advocates high positive end-expiratory pressure (PEEP) levels and low tidal volumes. Although it is physiologically obvious that PAOP is not a surrogate for Pcap in these circumstances, Pcap is seldom assessed and PAOP is commonly used to guide fluid management in ARDS. Evidence exists that reduction of Pcap may improve lung edema in the acute respiratory distress syndrome (ARDS). In ARDS, the gradient between Pcap and pulmonary artery occlusion pressure (PAOP) (Pcap−PAOP), as well as capillary permeability are increased. Since Pcap is a major determinant of fluid leakage, its importance is emphasized in the presence of increased permeability. Indirect methods seek to assess the pressure in the sites where fluid leakage occurs. ![]() Pulmonary capillary pressure (Pcap) cannot be measured directly. Pcap can be estimated at the bedside by either the visual or mathematical methods. The high variability in Pcap−PAOP increases the risk for underestimation of filtration pressures and consequently the risk for lung edema. Pulmonary capillary pressure cannot be predicted from PAOP during early and established ARDS. Higher PEEP levels were associated with increased PAPd, Pcap and PAOP, as well as with larger Pcap−PAOP throughout ARDS. Pcap−PAOP (6.3☒.7 mmHg) did not change throughout ARDS. PAPd, Pcap and PAOP tended to decrease from early to late ARDS ( p=0.128, 0.265, 0.121). The visually determined Pcap showed a bias of 2.5☒.1 mmHg as compared to the mathematical estimation. Diastolic pulmonary artery pressure (PAPd) and pulmonary artery occlusion pressure (PAOP) were measured. Pcap was determined for every occlusion trace by three observers (visual method) and a mathematical model. Pulmonary artery occlusions were made in triplicate at each PEEP level. Four PEEP levels (6, 9, 12 and 15 cmH 2O) were studied. Pulmonary arterial pressures were measured during routine respiratory mechanics measurements throughout ARDS. Nine ARDS patients, according to the ARDS Consensus Conference criteria. Intensive care unit in a teaching institution. (1)To describe the evolution of pulmonary capillary pressure (Pcap) and of the pressure drop across the pulmonary venous bed from early to established acute respiratory distress syndrome (ARDS), (2) to assess Pcap under different levels of positive end-expiratory pressure (PEEP) and (3) to compare the visual method and a mathematical model to determine Pcap. ![]()
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