Mechanical ventilation may promote overdistension-induced pulmonary lesions in patients with acute respiratory distress syndrome (ARDS). The static pressure-volume (P-V) curve of the respiratory system can be used to determine the lung volume and corresponding static airway pressure at which lung compliance begins to diminish (the upper inflection point, or UIP). This fall in compliance may indicate overdistension of lung units. We prospectively studied 42 patients receiving mechanical ventilation with an FIO2 of 0.5 or more for at least 24 h. According to the Lung Injury Score (LIS), 25 patients were classified as having ARDS (LIS > 2.5), while 17 patients constituted a non-ARDS control group. The P-V curve was obtained every 2 d. Mechanical ventilation initially used standard settings (volume-control mode, a positive end-expiratory pressure [PEEP] adjusted to the lower inflection point on the P-V curve, and a tidal volume [VT] of 10 ml/kg). The end-inspiratory plateau pressure (Pplat) was compared to the UIP, and VT was lowered when the Pplat was above the UIP. In the range of lung volume studied on the P-V curves (up to 1600 ml), a UIP could be shown in only one control patient (at 23 cm H2O). By contrast, a UIP was present on the P-V curve obtained from all patients with ARDS, corresponding to a mean airway pressure of 26 +/- 6 cm H2O, a lung volume of 850 +/- 200 ml above functional residual capacity and 610 +/- 235 ml above PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)

The controller allows the automated delivery of propofol and remifentanil and maintains BIS values in predetermined boundaries during general anesthesia better than manual administration.

The aim of this work was to analyze changes in cerebral hemodynamics and intracranial pressure (ICP) evoked by mean systemic arterial pressure (SAP) and arterial CO(2) pressure (Pa(CO(2))) challenges in patients with acute brain damage. The study was performed by means of a new simple mathematical model of intracranial hemodynamics, particularly aimed at routine clinical investigation. The model was validated by comparing its results with data from transcranial Doppler velocity in the middle cerebral artery (V(MCA)) and ICP measured in 44 tracings on 13 different patients during mean SAP and Pa(CO(2)) challenges. The validation consisted of individual identification of 6 parameters in all 44 tracings by means of a best fitting algorithm. The parameters chosen for the identification summarize the main aspects of intracranial dynamics, i.e., cerebrospinal fluid circulation, intracranial elastance, and cerebrovascular control. The results suggest that the model is able to reproduce the measured time patterns of V(MCA) and ICP in all 44 tracings by using values for the parameters that lie within the ranges reported in the pathophysiological literature. The meaning of parameter estimates is discussed, and comments on the main virtues and limitations of the present approach are offered.

RRI used in the immediate POP after cardiac surgery with CPB enabled prediction of delayed AKI and anticipation of its severity.

The classic model of the respiratory system (RS) is comprised of a Newtonian resistor in series with a capacitor and a viscoelastic unit including a resistor and a capacitor. The flow interruption technique has often been used to study the viscoelastic behavior under constant inspiratory flow rate. To study the viscoelastic behavior of the RS during complete respiratory cycles and to quantify viscoelastic resistance (Rve) and compliance (Cve) under unrestrained conditions, we developed an iterative technique based on a differential equation. We, as others, assumed Rve and Cve to be constant, which concords with volume and flow dependency of model behavior. During inspiration Newtonian resistance (R) was independent of flow and volume. During expiration R increased. Static elastic recoil showed no significant hysteresis. The viscoelastic behavior of the RS was in accordance with the model. The magnitude of Rve was 3.7 +/- 0.7 cmH2O.l-1 x s, i.e., two times R. Cve was 0.23 +/- 0.051 l/cmH2O, i.e., four times static compliance. The viscoelastic time constant, i.e., Cve.Rve, was 0.82 +/- 0.11s. The work dissipated against the viscoelastic system was 0.62 +/- 0.13 cmH2O x 1 for a breath of 0.56 liter, corresponding to 32% of the total energy loss within the RS. Viscoelastic recoil contributed as a driving force during the initial part of expiration.