Computerized lung acoustic monitoring can help to differentiate between various chest radiographic densities in critically ill patients.

BACKGROUND: Complementary bedside lung monitoring modalities are often sought in order to assist in the differentiation between several lung opacities in the intensive care unit (ICU). OBJECTIVES: To evaluate the use of computerized lung acoustic monitoring as a complementary approach in the differentiation between various chest radiographic densities in critically ill patients. METHODS: Lung vibration intensity was assessed in 82 intensive care patients using vibration response imaging. Patients were classified according to their primary findings on chest radiography (CXR): consolidation (n = 35), congestion (n = 10), pleural effusion (n = 15), atelectasis/hypoinflation (n = 10) and normal findings (n = 12). Sixty patients were mechanically ventilated and 22 patients were spontaneously breathing. RESULTS: Significantly elevated vibration intensity was detected in patients with consolidation, as opposed to pleural effusion, atelectasis and normal CXR (p < 0.01, Mann-Whitney U test). Vibration intensity was also increased for congestion, but this increase was not significant. The positive predictive value of CXR lung opacity in combination with increased vibration intensity to detect consolidations and/or congestions was 95% (20/21). Furthermore, vibration intensity was significantly higher in mechanically ventilated patients compared to spontaneously breathing patients (p = 0.001, Mann-Whitney U test). Differences related to gender, age and body position were not significant. CONCLUSIONS: Computerized lung acoustic monitoring at the bedside was found to be a useful, readily available, noninvasive, adjunctive tool in the differentiation between various CXR densities in critically ill patients.

Changes in regional distribution of lung sounds as a function of positive end-expiratory pressure.

INTRODUCTION: Automated mapping of lung sound distribution is a novel area of interest currently investigated in mechanically ventilated, critically ill patients. The objective of the present study was to assess changes in thoracic sound distribution resulting from changes in positive end-expiratory pressure (PEEP). Repeatability of automated lung sound measurements was also evaluated. METHODS: Regional lung sound distribution was assessed in 35 mechanically ventilated patients in the intensive care unit (ICU). A total of 201 vibration response imaging (VRI) measurements were collected at different levels of PEEP between 0 and 15 cmH2O. Findings were correlated with tidal volume, oxygen saturation, airway resistance, and dynamic compliance. Eighty-two duplicated readings were performed to evaluate the repeatability of the measurement. RESULTS: A significant shift in sound distribution from the apical to the diaphragmatic lung areas was recorded when increasing PEEP (paired t-tests, P < 0.05). In patients with unilateral lung pathology, this shift was significant in the diseased lung, but not as pronounced in the other lung. No significant difference in lung sound distribution was encountered based on level of ventilator support needed. Decreased lung sound distribution in the base was correlated with lower dynamic compliance. No significant difference was encountered between repeated measurements. CONCLUSIONS: Lung sounds shift towards the diaphragmatic lung areas when PEEP increases. Lung sound measurements are highly repeatable in mechanically ventilated patients with various lung pathologies. Further studies are needed in order to fully appreciate the contribution of PEEP increase to diaphragmatic sound redistribution.

Prediction of extubation outcome: a randomised, controlled trial with automatic tube compensation vs. pressure support ventilation.

INTRODUCTION: Tolerance of a spontaneous breathing trial is an evidence-based strategy to predict successful weaning from mechanical ventilation. Some patients may not tolerate the trial because of the respiratory load imposed by the endotracheal tube, so varying levels of respiratory support are widely used during the trial. Automatic tube compensation (ATC), specifically developed to overcome the imposed work of breathing because of artificial airways, appears ideally suited for the weaning process. We further evaluated the use of ATC in this setting. METHODS: In a prospective study, patients who had received mechanical ventilation for more than 24 hours and met defined criteria for a weaning trial, underwent a one-hour spontaneous breathing trial with either ATC (n = 87) or pressure support ventilation (PSV; n = 93). Those tolerating the trial were immediately extubated. The primary outcome measure was the ability to maintain spontaneous, unassisted breathing for more than 48 hours after extubation. In addition, we measured the frequency/tidal volume ratio (f/VT) both with (ATC-assisted) and without ATC (unassisted-f/VT) at the start of the breathing trial as a pretrial predictor of extubation outcome. RESULTS: There were no significant differences in any of the baseline characteristics between the two groups apart from a significantly higher Acute Physiology and Chronic Health Evaluation (APACHE) II score in the ATC group (p = 0.009). In the PSV group, 13 of 93 (14%) patients failed the breathing trial compared with only 6 of 87 (6%) in the ATC group; this observed 8% difference, however, did not reach statistical significance (p = 0.12). The rate of reintubation was not different between the groups (total group = 17.3%; ATC = 18.4% vs. PSV = 12.9%, p = 0.43). The percentage of patients who remained extubated for more than 48 hours was similar in both groups (ATC = 74.7% vs. PSV = 73.1%; p = 0.81). This represented a positive predictive value for PSV of 0.85 and ATC of 0.80 (p = 0.87). Finally, the ATC-assisted f/VT was found to have a significant contribution in predicting successful liberation and extubation compared with the non-significant contribution of the unassisted f/VT (unassisted f/VT, p = 0.19; ATC-assisted f/VT, p = 0.005). CONCLUSIONS: This study confirms the usefulness of ATC during the weaning process, being at least as effective as PSV in predicting successful extubation outcome and significantly improving the predictive value of the f/VT. TRIAL REGISTRATION: Current Controlled Trials ISRCTN16080446.

Extubation outcome following a spontaneous breathing trial with automatic tube compensation versus continuous positive airway pressure.

OBJECTIVE: We hypothesized that the additional use of automatic tube compensation (ATC) during a spontaneous breathing trial with continuous positive airway pressure (CPAP), by minimizing respiratory work, would result in more patients undergoing successful extubation. DESIGN: Prospective, randomized, controlled study. SETTING: A ten-bed, general intensive care department at a tertiary-care hospital. PATIENTS: Adult patients (n=99) who had undergone mechanical ventilation for >24 hrs and met defined criteria for a weaning trial. INTERVENTIONS: Patients were randomized to undergo a 1-hr spontaneous breathing trial with either ATC with CPAP (ATC group, n=51) or CPAP alone (CPAP group, n=48). ATC was provided by commercially available mechanical ventilators. Patients tolerating the spontaneous breathing trial underwent immediate extubation. The primary outcome measure was successful extubation, defined as the ability to maintain spontaneous breathing for 48 hrs after discontinuation of mechanical ventilation and extubation. MEASUREMENTS AND MAIN RESULTS: There were no significant differences in demographic, respiratory, or hemodynamic characteristics between the two groups at the start of the spontaneous breathing trial. There was a trend for more patients in the ATC group to tolerate the breathing trial and undergo extubation (96% vs. 85%; p=.08). The rate of reintubation was 14% in the ATC group and 24% in the CPAP group (p=.28). Significantly more patients in the ATC group thus met the criteria for successful extubation (82% vs. 65%; p=0.04). CONCLUSION: This is the largest single-center study to date assessing the use of commercially available ATC and suggests that this might be a useful mode for performing a spontaneous breathing trial preceding extubation in a general intensive care population.

Initial experience with a mechanical ventilation weaning unit.

BACKGROUND: While increasing numbers of patients require prolonged mechanical ventilation, resources for weaning are either limited (ICU beds) or inadequate (general wards). OBJECTIVES: To report on our initial experience over a 7 month period with an eight-bed mechanical ventilation weaning unit. METHODS: Sixty-nine patients requiring MV for > 10 days were admitted to the unit (nurse:patient ratio 1:4). Data collected included reason for MV, duration of hospital stay, and MVWU course. Outcome results (successful weaning and mortality) were compared to those in historic controls (patients ventilated in the general wards over a 4 month period prior to the MVWU; n = 100). RESULTS: The mean age of the patients was 68 +/- 16.6 years and hospital stay prior to MVWU admission 28.6 +/- 24.2 days (range 10-72). The main reasons for MV included acute exacerbation of chronic obstructive pulmonary disease (31%) and recent pneumonia (28%). Mean MVWU stay was 13.5 +/- 15.7 days (range 1-72 days). Thirty-four patients (49%) underwent tracheostomy. Fourteen patients required admission to the ICU due to deterioration in their status. Twenty-nine patients (42%) were successfully weaned and discharged to the wards. A further 20 patients were transferred to the chronic ventilation unit of a regional geriatric rehabilitation hospital, where 5 were subsequently weaned and 15 required prolonged ventilation. Compared to controls (matched for age and reason for mechanical ventilation), more MVWU patients underwent successful weaning (49% vs. 12%, P < 0.001) and their mortality rate (n = 12) was significantly lower (17% vs. 88%, P < 0.001). CONCLUSION: The higher level of care possible in a MVWU may result in a significantly improved rate of weaning and lower mortality. The assessment of long-term outcome in patients discharged to pulmonary rehabilitation centers requires further investigation.

Automatic tube compensation-assisted respiratory rate to tidal volume ratio improves the prediction of weaning outcome.

OBJECTIVE: To assess whether the respiratory rate to tidal volume ratio (RVR) measured while receiving automatic tube compensation (ATC) [RVRATC] would have a better predictive value as a weaning measure than unassisted RVR. DESIGN: Prospective cohort study. SETTING: General ICU of a tertiary-care university hospital. PATIENTS: Forty-three patients who received mechanical ventilation for > 24 h and were considered ready for weaning. INTERVENTIONS: All patients underwent a 60-min spontaneous breathing trial (SBT) [positive end-expiratory pressure of 5 cm H(2)O; ATC, 100%]. Patients tolerating the trial (n = 35) were extubated immediately. The following parameters were measured at the onset and end of the SBT: RVR, RVRATC, peak airway pressure (Paw), airway occlusion pressure, and minute ventilation. The outcome measure was successful extubation (ability to maintain spontaneous breathing for > 48 h). MEASUREMENTS AND RESULTS: Median age was 55 years (range, 25 to 88 years), median APACHE (acute physiology and chronic health evaluation) II score was 15.5 (range, 3 to 29), and median duration of mechanical ventilation prior to the SBT was 7 days (range, 1 to 40 days). Extubation was successful in 25 patients (72%). There were no significant differences in baseline characteristics between patients successfully extubated (group 1) and those requiring reintubation. On multivariate analysis, RVRATC measured at 60 min (RVR(60)ATC) was most predictive of successful extubation (p = 0.03). The area under the receiver operator characteristic curve was also highest for RVR(60)ATC (0.81 +/- 0.03) as compared to RVR (0.77 +/- 0.03), RVRATC (0.75 +/- 0.04), and RVR measured at 60 min (0.69 +/- 0.05). The ratio of RVR(60)ATC to Paw was the best predictor (0.84 +/- 0.02). CONCLUSIONS: RVRATC measured at the end of the SBT was the best predictor of successful extubation. A new ratio (ratio of RVRATC to Paw) was most predictive and deserves further study.