Data on respiratory variables in critically ill patients with acute respiratory failure placed on proportional assist ventilation with load adjustable gain factors (PAV+).

The data show respiratory variables in 108 critically ill patients with acute respiratory failure placed on proportional assist ventilation with load adjustable gain factors (PAV+) after at least 36 h on passive mechanical ventilation. PAV+ was continued for 48 h until the patients met pre-defined criteria either for switching to controlled modes or for breathing without ventilator assistance. Data during passive mechanical ventilation and during PAV+ are reported. Data are acquired from the whole population, as well as from patients with and without acute respiratory distress syndrome. The reported variables are tidal volume, driving pressure (ΔP, the difference between static end-inspiratory plateau pressure and positive end-expiratory airway pressure), respiratory system compliance and resistance, and arterial blood gasses. The data are supplemental to our original research article, which described individual ΔP in these patients and examined how it related to ΔP when the same patients were ventilated with passive mechanical ventilation using the currently accepted lung-protective strategy "Driving pressure during assisted mechanical ventilation. Is it controlled by patient brain?" [1].

Driving pressure during assisted mechanical ventilation: Is it controlled by patient brain?

Tidal volume (VT) is the controlled variable during passive mechanical ventilation (CMV) in order to avoid ventilator-induced-lung-injury. However, recent data indicate that the driving pressure [ΔP; VT to respiratory system compliance (Crs) ratio] is the parameter that best stratifies the risk of death. In order to study which variable (VT or ΔP) is controlled by critically ill patients, 108 previously studied patients were assigned to receive PAV+ (a mode that estimates Crs and permits the patients to select their own breathing pattern) after CMV, were re-analyzed. When patients were switched from CMV to PAV+ they controlled ΔP without constraining VT to narrow limits. VT was increased when the resumption of spontaneous breathing was associated with an increase in Crs. When ΔP was high during CMV, the patients (n=12) decreased it in 58 out of 67 measurements. We conclude that critically ill patients control the driving pressure by sizing the tidal volume to individual respiratory system compliance using appropriate feedback mechanisms aimed at limiting the degree of lung stress.

Effects of propofol on sleep quality in mechanically ventilated critically ill patients: a physiological study.

PURPOSE: To access the effect of propofol administration on sleep quality in critically ill patients ventilated on assisted modes. METHODS: This was a randomized crossover physiological study conducted in an adult ICU at a tertiary hospital. Two nights' polysomnography was performed in mechanically ventilated critically ill patients with and without propofol infusion, while respiratory variables were continuously recorded. Arterial blood gasses were measured in the beginning and at the end of the study. The rate of propofol infusion was adjusted to maintain a sedation level of 3 on the Ramsay scale. Sleep architecture was analyzed manually using predetermined criteria. Patient-ventilator asynchrony was evaluated breath by breath using the flow-time and airway pressure-time waveforms. RESULTS: Twelve patients were studied. Respiratory variables, patient-ventilator asynchrony, and arterial blood gasses did not differ between experimental conditions. With or without propofol all patients demonstrated abnormal sleep architecture, expressed by lack of sequential progression through sleep stages and their abnormal distribution. Sleep efficiency, sleep fragmentation, and sleep stage distribution (1, 2, and slow wave) did not differ with or without propofol. Compared to without propofol, both the number of patients exhibiting REM sleep (p = 0.02) and the percentage of REM sleep (p = 0.04) decreased significantly with propofol. CONCLUSIONS: In critically ill patients ventilated on assisted modes, propofol administration to achieve the recommended level of sedation suppresses the REM sleep stage and further worsens the poor sleep quality of these patients.

Estimation of inspiratory muscle pressure in critically ill patients.

BACKGROUND: Recently, a new technology has been introduced aiming to monitor and improve patient ventilator interaction (PVI monitor). With the PVI monitor, a signal representing an estimation of the patient's total inspiratory muscle pressure (Pmus(PVI)) is calculated from the equation of motion, utilizing estimated values of resistance and elastance of the respiratory system. OBJECTIVE: The aim of the study was to prospectively examine the accuracy of Pmus(PVI) to quantify inspiratory muscle pressure. METHODS AND INTERVENTIONS: Eleven critically ill patients mechanically ventilated on proportional assist ventilation with load-adjustable gain factors were studied at three levels of assist (30, 50 and 70%). Airway, esophageal, gastric and transdiaphragmatic (Pdi) pressures, volume and flow were measured breath by breath, whereas the total inspiratory muscle pressure (Pmus) was calculated using the Campbell diagram. RESULTS: For a given assist, Pmus(PVI) throughout inspiration did not differ from the corresponding values calculated using the Pdi and Pmus signals. Inspiratory and expiratory time did not differ among the various methods of calculation. Inspiratory muscle pressure decreased with increasing assist, and the magnitude of this decrease did not differ among the various methods of pressure calculation. CONCLUSIONS: A signal generated from flow, volume and airway pressure may be used to provide breath-by-breath quantitative information of inspiratory muscle pressure.

Is proportional-assist ventilation with load-adjustable gain factors a user-friendly mode?

OBJECTIVES: The aim of this study was to compare the number of interventions (ventilator settings and sedatives, analgesics and vasoactive medication dose manipulations) between critically ill patients on proportional-assist ventilation with load-adjustable gain factors (PAV+) and those on pressure support (PS). DESIGN: Retrospective analysis of data from a previous randomized clinical trial. METHODS: A total of 208 patients who were mechanically ventilated on controlled modes and met criteria for assisted breathing were randomized to receive either PS (n = 100) or PAV+ (n = 108). Changes in ventilator settings and in the dose of sedatives, analgesics, and vasoactive medications were identified during the period in which the patients were ventilated either with PS (30.4 +/- 17.4 h) or PAV+ (30.0 +/- 18.1 h) and classified as changes to facilitate weaning (CFW) or changes to respond to deterioration (CD). RESULTS: The mean number of changes in ventilator settings was significantly higher with PS than that with PAV+ (10.7 +/- 5.7 vs. 8.9 +/- 4.6). With PS the proportion of these changes classified as CFW was significantly lower than that with PAV+ (59.8% vs. 69.2%). Dyssynchrony as a cause of CD was more likely to occur with PS than with PAV+ (42 vs. 3%). The mean number of changes in the dose of sedatives, analgesics, and vasoactive medications was higher with PS than with PAV+, the difference being significant only for sedatives (4.06 +/- 3.8 vs. 2.82 +/- 3.4). CONCLUSIONS: Compared to PS, PAV+ is associated with fewer intervention in terms of ventilator settings and sedative dose changes.

Short-term cardiorespiratory effects of proportional assist and pressure-support ventilation in patients with acute lung injury/acute respiratory distress syndrome.

BACKGROUND: Recent data indicate that assisted modes of mechanical ventilation improve pulmonary gas exchange in patients with acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Proportional assist ventilation (PAV) is a new mode of support that amplifies the ventilatory output of the patient effort and improves patient-ventilator synchrony. It is not known whether this mode may be used in patients with ALI/ARDS. The aim of this study was to compare the effects of PAV and pressure-support ventilation on breathing pattern, hemodynamics, and gas exchange in a homogenous group of patients with ALI/ARDS due to sepsis. METHODS: Twelve mechanically ventilated patients with ALI/ARDS (mean ratio of partial pressure of arterial oxygen to fractional concentration of oxygen 190 +/- 49 mmHg) were prospectively studied. Patients received pressure-support ventilation and PAV in random order for 30 min while maintaining mean airway pressure constant. With both modes, the level of applied positive end-expiratory pressure (7.1 +/- 2.1 cm H2O) was kept unchanged throughout. At the end of each study period, cardiorespiratory data were obtained, and dead space to tidal volume ratio was measured. RESULTS: With both modes, none of the patients exhibited clinical signs of distress. With PAV, breathing frequency and cardiac index were slightly but significantly higher than the corresponding values with pressure-support ventilation (24.5 +/- 6.9 vs. 21.4 +/- 6.9 breaths/min and 4.4 +/- 1.6 vs. 4.1 +/- 1.3 l . min . m, respectively). None of the other parameters differ significantly between modes. CONCLUSIONS: In patients with ALI/ARDS due to sepsis, PAV and pressure-support ventilation both have clinically comparable short-term effects on gas exchange and hemodynamics.

Pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease.

OBJECTIVES: To study the pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD). DESIGN: A prospective physiological study. SETTING: A 12-bed Intensive Care Unit. PATIENTS: Ten patients with acute exacerbation of COPD. INTERVENTIONS: At three levels of positive end-expiratory pressure (PEEP, 0, 5 and 10 cm H(2)O) tracheal (Ptr) and airway pressures, flow (V') and volume (V) were continuously recorded during volume control ventilation and airway occlusions at different time of expiration. MEASUREMENTS AND RESULTS: V-V' curves during passive expiration were obtained, expired volume was divided into five equal volume slices and the time constant (tau) and dynamic deflation compliance (Crs(dyn)) of each slice was calculated by regression analysis of V-V' and post-occlusion V-Ptr relationships, respectively. In each volume slice the existence or not of flow limitation was examined by comparing V-V' curves with and without decreasing Ptr. For a given slice total expiratory resistance was calculated as tau/Crs(dyn), whereas expiratory resistance (Rrs) and time constant (tau(rs)) of the respiratory system were subsequently estimated taken into consideration the presence of flow limitation. At zero PEEP, tau(rs) increased significantly toward the end of expiration due to an increase in Rrs. PEEP significantly decreased Rrs at the end of expiration and resulted in a faster and relatively constant rate of lung emptying. CONCLUSIONS: Patients with COPD exhibit a decrease in the rate of lung emptying toward the end of expiration due to an increase in Rrs. PEEP decreases Rrs, resulting in a faster and uniform rate of lung emptying.