Automatic detection of reverse-triggering related asynchronies during mechanical ventilation in ARDS patients using flow and pressure signals.

Asynchrony due to reverse-triggering (RT) may appear in ARDS patients. The objective of this study is to validate an algorithm developed to detect these alterations in patient-ventilator interaction. We developed an algorithm that uses flow and airway pressure signals to classify breaths as normal, RT with or without breath stacking (BS) and patient initiated double-triggering (DT). The diagnostic performance of the algorithm was validated using two datasets of breaths, that are classified as stated above. The first dataset classification was based on visual inspection of esophageal pressure (Pes) signal from 699 breaths recorded from 11 ARDS patients. The other classification was obtained by vote of a group of 7 experts (2 physicians and 5 respiratory therapists, who were trained in ICU), who evaluated 1881 breaths gathered from recordings from 99 subjects. Experts used airway pressure and flow signals for breaths classification. The RT with or without BS represented 19% and 37% of breaths in Pes dataset while their frequency in the expert's dataset were 3% and 12%, respectively. The DT was very infrequent in both datasets. Algorithm classification accuracy was 0.92 (95% CI 0.89-0.94, P < 0.001) and 0.96 (95% CI 0.95-0.97, P < 0.001), in comparison with Pes and experts' opinion. Kappa statistics were 0.86 and 0.84, respectively. The algorithm precision, sensitivity and specificity for individual asynchronies were excellent. The algorithm yields an excellent accuracy for detecting clinically relevant asynchronies related to RT.

Transpulmonary pressure and gas exchange during decremental PEEP titration in pulmonary ARDS patients.

BACKGROUND: Selection of the PEEP associated with the best compliance of the respiratory system during decremental PEEP titration can be used for the treatment of patients suffering from ARDS. We describe changes in transpulmonary pressure (Ptp) and gas exchange during a decremental PEEP titration maneuver in subjects with pulmonary ARDS. METHODS: Eleven subjects with early ARDS were included. After a recruitment maneuver they were ventilated in volume-controlled ventilation and PEEP was decreased from 30 to 0 cm H2O by steps of 3 cm H2O. Static airway pressure (Paw), esophageal pressure (Pes), Ptp (Paw - Pes), the ratio of dead space to tidal volume (VD/VT), and PaO2 were recorded at each step. RESULTS: A linear correlation was found between Paw and Ptp. Expiratory Ptp became negative in all subjects when PEEP decreased below 8.9 ± 5.2 cm H2O. VD/VT was 0.67 ± 0.06 with 30 cm H2O of PEEP, and decreased 15.4 ± 8.5% during the maneuver, when PEEP and expiratory Ptp were 10.6 ± 4.1 cm H2O and 1.2 ± 2.8 cm H2O, respectively. VD/VT was significantly higher during ventilation at high (> 18 cm H2O), compared to low, inspiratory Ptp values (P < .001). PaO2 decreased when expiratory Ptp became negative (P < .001). CONCLUSIONS: During decremental PEEP titration we sequentially observed high inspiratory Ptp that stressed lung tissue and increased VD/VT, and negative Ptp, indicating high risk of alveolar collapse, explaining worse oxygenation. PEEP selection based on Ptp and VD/VT in ARDS may help to avoid these situations.

Muscle weakness in septic patients requiring mechanical ventilation: protective effect of transcutaneous neuromuscular electrical stimulation.

PURPOSE: The aim of this study was to evaluate the effect of transcutaneous neuromuscular electrical stimulation (NMES) on muscle strength in septic patients requiring mechanical ventilation (MV). METHODS: Sixteen septic patients requiring MV and having 1 or more organ failure other than respiratory dysfunction were enrolled within 48 hours from admission to the intensive care unit. Neuromuscular electrical stimulation was administered twice a day on brachial biceps and vastus medialis (quadriceps) of 1 side of the body until MV withdrawal. Blinded investigators measured arm and thigh circumferences, biceps thickness by ultrasonography, and muscle strength after awakening with Medical Research Council scale. RESULTS: Two patients died before strength evaluation and were excluded from the analysis. Neuromuscular electrical stimulation was applied for 13 days (interquartile range, 7-30 days). Biceps (P = .005) and quadriceps (P = .034) strengths were significantly higher on the stimulated side at the last day of NMES. Improvement was mainly observed in more severe and weaker patients. Circumference of the nonstimulated arm decreased at the last day of NMES (P = .015), whereas no other significant differences in limb circumferences or biceps thickness were observed. CONCLUSION: Neuromuscular electrical stimulation was associated with an increase in strength of the stimulated muscle in septic patients requiring MV. Neuromuscular electrical stimulation may be useful to prevent muscle weakness in this population.

Effects of recruitment manoeuvres on haemodynamics, oxygen exchange and oxygen delivery in patients with acute lung injury and acute respiratory distress syndrome.

OBJECTIVE: To evaluate the impact of a recruitment manoeuvre (RM) on haemodynamics, gas exchange, and oxygen transport in patients with acute lung injury (ALI) an acute respiratory distress syndrome (ARDS) under mechanical ventilation. DESIGN, SETTING AND PARTICIPANTS: Prospective interventional study in the intensive care unit of a teaching hospital in Buenos Aires, Argentina. The study was carried out between June 2002 and March 2003. Eleven consecutive patients with ALI and ARDS who required an RM were included. Haemodynamic measurements and blood samples were taken before and during the RM, and at 2 and 30 minutes after the RM. INTERVENTION: After baseline measurements, positive end-expiratory pressure (PEEP) was set at 40cmH(2)O for 45 seconds. MAIN OUTCOME MEASURES: Systemic haemodynamics, oxygen exchange and oxygen delivery. RESULTS: Mean PEEP before the RM was 14 (SD, 3) cmH(2)O, and was maintained after the RM. The RM did not modify the arterial partial pressure of oxygen (PaO(2)) but did induce small but significant changes in the mean arterial partial pressure of carbon dioxide (Pa-ETCO(2)) and arterial minus end-tidal PCO(2) gradient (PaCO(2)) at 2 minutes and 30 minutes after the RM (P<0.05). The mean cardiac index dropped from 3.08 (SD, 0.84) to 2.37 (SD, 0.75) L/min/m(2) (P<0.001) during the RM and then returned to baseline values. Mean systolic blood pressure also fell transitorily during the RM, from 131 (SD, 15) to 104 (SD, 25) mmHg, but diastolic and mean arterial pressures remained unchanged. Oxygen consumption and the arterial mixed venous oxygen content gradient increased after the RM (P<0.05). CONCLUSION: In our small series of patients with ALI/ARDS ventilated with high levels of PEEP, the RM failed to improve oxygen exchange and induced deleterious effects on haemodynamics.