Expiratory Muscle Activity Counteracts Positive End-Expiratory Pressure and Is Associated with Fentanyl Dose in Patients with Acute Respiratory Distress Syndrome.

Rationale: Hypoxemia during mechanical ventilation might be worsened by expiratory muscle activity, which reduces end-expiratory lung volume through lung collapse. A proposed mechanism of benefit of neuromuscular blockade in acute respiratory distress syndrome (ARDS) is the abolition of expiratory efforts. This may contribute to the restoration of lung volumes. The prevalence of this phenomenon, however, is unknown. Objectives: To investigate the incidence and amount of end-expiratory lung impedance (EELI) increase after the administration of neuromuscular blocking agents (NMBAs), clinical factors associated with this phenomenon, its impact on regional lung ventilation, and any association with changes in pleural pressure. Methods: We included mechanically ventilated patients with ARDS monitored with electrical impedance tomography (EIT) who received NMBAs in one of two centers. We measured changes in EELI, a surrogate for end-expiratory lung volume, before and after NMBA administration. In an additional 10 patients, we investigated the characteristic signatures of expiratory muscle activity depicted by EIT and esophageal catheters simultaneously. Clinical factors associated with EELI changes were assessed. Measurements and Main Results: We included 46 patients, half of whom showed an increase in EELI of >10% of the corresponding Vt (46.2%; IQR, 23.9-60.9%). The degree of EELI increase correlated positively with fentanyl dosage and negatively with changes in end-expiratory pleural pressures. This suggests that expiratory muscle activity might exert strong counter-effects against positive end-expiratory pressure that are possibly aggravated by fentanyl. Conclusions: Administration of NMBAs during EIT monitoring revealed activity of expiratory muscles in half of patients with ARDS. The resultant increase in EELI had a dose-response relationship with fentanyl dosage. This suggests a potential side effect of fentanyl during protective ventilation.

Cycling-off modes during pressure support ventilation: effects on breathing pattern, patient effort, and comfort.

PURPOSE: Expiratory asynchrony during pressure support ventilation (PSV) has been recognized as a cause of patient discomfort, increased workload, and impaired weaning process. We evaluated breathing pattern, patient comfort, and patient effort during PSV comparing 2 flow termination criteria: fixed at 5% of peak inspiratory flow vs automatic, real-time, breath-by-breath adjustment within the range of 5% to 55%. MATERIALS AND METHODS: Randomized crossover clinical trial. Sixteen awake patients, in the process of weaning, under PSV for more than 24 hours were subjected to 3 phases of PSV, each lasting 1 hour and using 1 of the 2 aforementioned termination criteria. RESULTS: Effective pressure support during automatic adjustment (AA) was 12.5±3.2 cm H2O vs 12.5±3.9 cm H2O (P=.9) with the fixed termination criterion, and external positive end-expiratory pressure was 6.2±1.8 vs 6.8±2 (P<.05). The effective termination criterion was higher during AA (31% [23-39] vs 12% [6-23]; P<.01), but without producing premature breath terminations. Pressure overshoots and alternative cycling-off were also decreased. Throughout the AA period, we observed a higher respiratory rate (24±8 breaths/min vs 19±6 breaths/min; P<.001), lower tidal volume (484 ± 88 mL vs 518±102 mL; P<.001), and shorter inspiratory times (1.0±0.3 seconds vs 1.3±0.3 seconds; P<.001). Automatic adjustment was associated with lower airway occlusion pressure after 0.1 second (P0.1) (1.8±0.9 cm H2O vs 2.4±1 cm H2O; P<.01), lower pressure-time product to trigger the ventilator, and lower subjective discomfort (visual analog scale, 3.7±1.3 vs 4.5±1.2; P<.001). CONCLUSIONS: When compared with a fixed termination criterion, the use of a variable, real-time-adjusted termination criterion improved some indices of patient-ventilator synchrony, producing better breathing pattern, less discomfort, and slightly lower patient effort during PSV.

Prediction of chronic critical illness in a general intensive care unit / Predição de doença crítica crônica em uma unidade geral de cuidados intensivos resumo

OBJECTIVE: To assess the incidence, costs, and mortality associated with chronic critical illness (CCI), and to identify clinical predictors of CCI in a general intensive care unit. METHODS: This was a prospective observational cohort study. All patients receiving supportive treatment for over 20 days were considered chronically critically ill and eligible for the study. After applying the exclusion criteria, 453 patients were analyzed. RESULTS: There was an 11% incidence of CCI. Total length of hospital stay, costs, and mortality were significantly higher among patients with CCI. Mechanical ventilation, sepsis, Glasgow score < 15, inadequate calorie intake, and higher body mass index were independent predictors for cci in the multivariate logistic regression model. CONCLUSIONS: CCI affects a distinctive population in intensive care units with higher mortality, costs, and prolonged hospitalization. Factors identifiable at the time of admission or during the first week in the intensive care unit can be used to predict CCI.

OBJETIVO: Avaliar a incidência, custos e mortalidade relacionados a doença crítica crônica (DCC) e identificar seus preditores clínicos em uma unidade de terapia intensiva geral. MÉTODOS: Trata-se de uma coorte observacional prospectiva. Todos pacientes que recebiam tratamento de suporte por mais de 20 dias eram considerados doentes críticos crônicos. Permaneceram 453 pacientes após a aplicação dos critérios de exclusão. RESULTADOS: A incidência de DCC foi de 11%. Permanência hospitalar, custos e mortalidade foram significativamente maiores na população com DCC. Ventilação mecânica, sepse, Glasgow escore < 15, inadequada ingestão calórica e elevado índice de massa corporal foram preditores independentes para dcc em um modelo multivariado de regressão logística. CONCLUSÃO: DCC abrangeumadistintapopulaçãonasunidadesde terapiaintensiva apresentando maiores mortalidade, custos e permanência hospitalar. Alguns fatores presentes na admissão ou durante a primeira semana na unidade de terapia intensiva podem ser usados como preditores de DCC.

Prediction of chronic critical illness in a general intensive care unit.

OBJECTIVE: To assess the incidence, costs, and mortality associated with chronic critical illness (CCI), and to identify clinical predictors of CCI in a general intensive care unit. METHODS: This was a prospective observational cohort study. All patients receiving supportive treatment for over 20 days were considered chronically critically ill and eligible for the study. After applying the exclusion criteria, 453 patients were analyzed. RESULTS: There was an 11% incidence of CCI. Total length of hospital stay, costs, and mortality were significantly higher among patients with CCI. Mechanical ventilation, sepsis, Glasgow score <15, inadequate calorie intake, and higher body mass index were independent predictors for CCI in the multivariate logistic regression model. CONCLUSIONS: CCI affects a distinctive population in intensive care units with higher mortality, costs, and prolonged hospitalization. Factors identifiable at the time of admission or during the first week in the intensive care unit can be used to predict CCI.

Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome.

RATIONALE: The hypothesis that lung collapse is detrimental during the acute respiratory distress syndrome is still debatable. One of the difficulties is the lack of an efficient maneuver to minimize it. OBJECTIVES: To test if a bedside recruitment strategy, capable of reversing hypoxemia and collapse in > 95% of lung units, is clinically applicable in early acute respiratory distress syndrome. METHODS: Prospective assessment of a stepwise maximum-recruitment strategy using multislice computed tomography and continuous blood-gas hemodynamic monitoring. MEASUREMENTS AND MAIN RESULTS: Twenty-six patients received sequential increments in inspiratory airway pressures, in 5 cm H(2)O steps, until the detection of Pa(O(2)) + Pa(CO(2)) >or= 400 mm Hg. Whenever this primary target was not met, despite inspiratory pressures reaching 60 cm H(2)O, the maneuver was considered incomplete. If there was hemodynamic deterioration or barotrauma, the maneuver was to be interrupted. Late assessment of recruitment efficacy was performed by computed tomography (9 patients) or by online continuous monitoring in the intensive care unit (15 patients) up to 6 h. It was possible to open the lung and to keep the lung open in the majority (24/26) of patients, at the expense of transient hemodynamic effects and hypercapnia but without major clinical consequences. No barotrauma directly associated with the maneuver was detected. There was a strong and inverse relationship between arterial oxygenation and percentage of collapsed lung mass (R = - 0.91; p < 0.0001). CONCLUSIONS: It is often possible to reverse hypoxemia and fully recruit the lung in early acute respiratory distress syndrome. Due to transient side effects, the required maneuver still awaits further evaluation before routine clinical application.

Imbalances in regional lung ventilation: a validation study on electrical impedance tomography.

Imbalances in regional lung ventilation, with gravity-dependent collapse and overdistention of nondependent zones, are likely associated to ventilator-induced lung injury. Electric impedance tomography is a new imaging technique that is potentially capable of monitoring those imbalances. The aim of this study was to validate electrical impedance tomography measurements of ventilation distribution, by comparison with dynamic computerized tomography in a heterogeneous population of critically ill patients under mechanical ventilation. Multiple scans with both devices were collected during slow-inflation breaths. Six repeated breaths were monitored by impedance tomography, showing acceptable reproducibility. We observed acceptable agreement between both technologies in detecting right-left ventilation imbalances (bias = 0% and limits of agreement = -10 to +10%). Relative distribution of ventilation into regions or layers representing one-fourth of the thoracic section could also be assessed with good precision. Depending on electrode positioning, impedance tomography slightly overestimated ventilation imbalances along gravitational axis. Ventilation was gravitationally dependent in all patients, with some transient blockages in dependent regions synchronously detected by both scanning techniques. Among variables derived from computerized tomography, changes in absolute air content best explained the integral of impedance changes inside regions of interest (r(2) > or = 0.92). Impedance tomography can reliably assess ventilation distribution during mechanical ventilation.