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Frailty and multi-morbidity have been associated with increased pressure on Emergency Departments (ED), higher hospital admissions and more risks for patients arising from the ED stay. The advantages of developing specific attention to frailty in ED have been highlighted. The benefits of these approaches are related to patients but also to organizations. The aim is to present how a Program of Care for Frailty (PCF) in an ED impacts on patient flows. Setting: A tertiary, teaching, 550-bed urban hospital, with 80,000 adult patients/year ED attendances (43% ≥ 65 years). The three main axes of the program are (1) an ED geriatrization, implementing multidisciplinary comprehensive geriatric assessment performed by ED professionals (physician, nurses, social worker, pharmacist); (2) an elder-friendly area (EFA) inside the ED was built; (3) The ED integration in a collaborative network with others healthcare providers in the territory for a shared urgent care. Between 2011 and 2017, we observe a progressive increase in ED activity (+ 8.1%), in patient’s age (40.9% vs 42.8% ≥ 65 years), and an increase in ambulance arrivals (+ 25.1%). The admission rate was rising until 2014 (10.8–12%). In 2014, the ED geriatrization began and networking was reinforced, and a decrease in the rate of admission (11.3%) is observed. Despite a progressive increase in ED activity and older people, we have observed a decrease in hospital admissions in parallel with the Program of Care for Frailty development. Systematic application of similar programs in distinct EDs would have an impact on the overall health system.

We read with interest the report by Witjes et al regarding the influence of end-of-life care on organ donor potential (1). The report promotes innovation in management of potential organ donors outside the ICU, particularly in patients admitted to the emergency department (ED) with acute devastating brain injury (DBI) and imminent brain death. This article is protected by copyright. All rights reserved.

Classification algorithms with unbalanced datasets tend to produce high predictive accuracy over the majority class, but poor predictive accuracy over the minority class. This problem is very common in biomedical data mining. This paper introduces a Support Vector Machine (SVM)-based optimized feature selection method, to select the most relevant features and maintain an accurate and well-balanced sensitivity-specificity result between unbalanced groups. A new metric called the balance index (B) is defined to implement this optimization. The balance index measures the difference between the misclassified data within each class. The proposed optimized feature selection is applied to the classification of patients' weaning trials from mechanical ventilation: patients with successful trials who were able to maintain spontaneous breathing after 48h and patients who failed to maintain spontaneous breathing and were reconnected to mechanical ventilation after 30min. Patients are characterized through cardiac and respiratory signals, applying joint symbolic dynamic (JSD) analysis to cardiac interbeat and breath durations. First, the most suitable parameters (C"+,C"-,@s) are selected to define the appropriate SVM. Then, the feature selection process is carried out with this SVM, to maintain B lower than 40%. The best result is obtained using 6 features with an accuracy of 80%, a B of 18.64%, a sensitivity of 74.36% and a specificity of 82.42%.

Weaning from mechanical ventilation is still one of the most challenging problems in intensive care. Unnecessary delays in discontinuation and weaning trials that are undertaken too early are both undesirable. This study investigated the contribution of spectral signals of heart rate variability (HRV) and respiratory flow, and their coherence to classifying patients on weaning process from mechanical ventilation. A total of 121 candidates for weaning, undergoing spontaneous breathing tests, were analyzed: 73 were successfully weaned (GSucc), 33 failed to maintain spontaneous breathing so were reconnected (GFail), and 15 were extubated after the test but reintubated within 48 h (GRein). The power spectral density and magnitude squared coherence (MSC) of HRV and respiratory flow signals were estimated. Dimensionality reduction was performed using principal component analysis (PCA) and sequential floating feature selection. The patients were classified using a fuzzy K-nearest neighbour method. PCA of the MSC gave the best classification with the highest accuracy of 92% classifying GSucc versus GFail patients, and 86% classifying GSucc versus GRein patients. PCA of the respiratory flow signal gave the best classification between GFail and GRein patients (79% accuracy). These classifiers showed a good balance between sensitivity and specificity. Besides, the spectral coherence between HRV and the respiratory flow signal, in patients on weaning trial process, can contribute to the extubation decision.

Objective: Patients with heart failure (HF) seen at the emergency department (ED) are increasingly older and more likely to present delirium. Little is known, however, about the impact of this syndrome on outcome in these patients. We aimed to investigate the prognostic value and risk factors of delirium at admission (prevalent delirium) in ED patients with decompensated HF. Methods and Results: We performed a prospective, observational study, analyzing the presence of prevalent delirium in decompensated HF patients attended at the ED in 2 hospitals in Spain in the context of the Epidemiology Acute Heart Failure Emergency project. We used the brief Confusion Assessment Method to assess the presence of delirium. Patients were followed for 1 month after discharge. Of 239 enrolled patients (81.7 +/- 9.4 years, women 61.1%, long-term care [LTC] 11%), 35 (14.6%) had prevalent delirium (20% LTC vs 9.4% in-home, P = .078). The factors associated with delirium in the multivariate analysis were functional dependence (P = .001) and dementia (P = .005). Prevalent delirium was an independent risk factor of death within 30 days (OR 3.532; 95% CI 1.422-8.769, P = .007) whereas autonomy in basic activities of daily living was a protective factor (OR 0.971; 95% CI 0.956-0.986, P = .001). The area under the ROC curve for our 30-day mortality model was 0.802 (95% CI 0.721-0.883, P = .001). Conclusion: Prevalent delirium in patients with decompensated HF was a predictor of short-term mortality. Routine identification of delirium in patients at risk, particularly those with greater functional dependence, can help emergency physicians in decision-making and enhance care in patients with decompensated HF. (C) 2015 AMDA - The Society for Post-Acute and Long-Term Care Medicine.

Background/Aims The currently recommended treatment for acute variceal bleeding is the association of vasoactive drugs and endoscopic therapy. However, which emergency endoscopic treatment combines better with drugs has not been clarified. This study compares the efficacy and safety of variceal ligation and sclerotherapy as emergency endoscopic treatment added to somatostatin. Methods Patients admitted with acute gastrointestinal bleeding and with suspected cirrhosis received somatostatin infusion (for 5 days). Endoscopy was performed within 6h and those with esophageal variceal bleeding were randomized to receive either sclerotherapy ( N =89) or ligation ( N =90). Results Therapeutic failure occurred in 21 patients treated with sclerotherapy (24%) and in nine treated with ligation (10%) (RR=2.4, 95% CI=1.1–4.9). Failure to control bleeding occurred in 15% vs 4%, respectively ( P =0.02). Treatment group, shock and HVPG >16mmHg were independent predictors of failure. Side-effects occurred in 28% of patients receiving sclerotherapy vs 14% with ligation (RR=1.9, 95% CI=1.1–3.5), being serious in 13% vs 4% ( P =0.04). Six-week survival probability without therapeutic failure was better with ligation ( P =0.01). Conclusions The use of variceal ligation instead of sclerotherapy as emergency endoscopic therapy added to somatostatin for the treatment of acute variceal bleeding significantly improves the efficacy and safety.

Objective To evaluate short- and long-term outcomes of elderly patients (≥ 65 years) treated at an intermediate care unit (IMCU) and to identify outcome predictors.

Traditional time domain techniques of data analysis are often not sufficient to characterize the complex dynamics of respiration. In this paper, the respiratory pattern variability is analyzed using symbolic dynamics. A group of 20 patients on weaning trials from mechanical ventilation are studied at two different pressure support ventilation levels, in order to obtain respiratory volume signals with different variability. Time series of inspiratory time, expiratory time, breathing duration, fractional inspiratory time, tidal volume and mean inspiratory flow are analyzed. Two different symbol alphabets, with three and four symbols, are considered to characterize the respiratory pattern variability. Assessment of the method is made using the 40 respiratory volume signals classified using clinical criteria into two classes: low variability (LV) or high variability (HV). A discriminant analysis using single indexes from symbolic dynamics has been able to classify the respiratory volume signals with an out-of-sample accuracy of 100%.

Objective: The society which hospitals serve is currently undergoing demographic, technological and cultural changes. The Internal Medicine Service (IMS) of the Hospital de la Santa Creu i Sant Pau considers these changes to provide an opportunity for improvement. We present the proposals and methodology applied for the re-engineering of the IMS. Method: The nominal group technique was used to identify and prioritize objectives and to select problems and interventions for implementation. Hospital staff of all levels, residents’ associations in the hospital’s vicinity, health authorities external to the hospital, patients and their families participated in these groups. The redesign was initiated in 1998 and continues to date. Results: The strong points of the IMS were considered to be its multidisciplinary training and adaptability to different situations and needs. The seven objectives selected identified the external and internal clients. Among the five main problems prioritized, three centered on improving process management and two on non-clinical skills training. Finally, 23 end points influencing daily clinical activity were selected. These end-points aim to improve the participation of all the team members in the objectives of the service/hospital and to help in resolving citizen’s problems. Conclusions: Our proposal for remodelling raises two important issues. The first reveals the importance of working with specific and participative methodology. The second identifies objectives, detects problems, proposes courses of action for improvement, and selects a number of end points, which should be incorporated in the redesign of our IMS. The proposed redesign continues to be open and to incorporate improvements.

La enfermedad cardiovascular representa la principal causa de mortalidad entre los adultos de mas de 30 anos de las sociedades industrializadas, y la enfermedad coronaria es la principal causa de esta mortalidad, seguida de los episodios cerebrovasculares. La enfermedad arteriosclerotica ‐habitualmente asintomatica durante decadas‐ subyace en la anatomia y patologia de estas entidades. Siendo una enfermedad cronica relativamente benigna, se transforma en una grave enfermedad aguda que se manifiesta clinicamente como un sindrome coronario agudo (SCA) en forma de angina inestable, infarto agudo de miocardio (IAM) o muerte subita 1 . La fisiopatologia de los SCA es compleja y multifactorial; en ella desempenan un papel importante la inflamacion e infeccion de la pared arterial, la disfuncion endotelial, la desproporcion entre el aporte y la demanda de oxigeno, el metabolismo lipidico, la estenosis coronaria y, finalmente, la erosion o rotura de una placa aterosclerotica vulnerable, que determina la formacion de un trombo intracoronario 3 . El

La utilizacion de sistemas para establecer el pronostico de los pacientes es habitual en las unidades de cuidados intensivos. Su capacidad predictiva es variable y depende de la poblacion a la que se aplica. Entre las poblaciones en las que han demostrado una menor exactitud se encuentra la de los enfermos ventilados mecanicamente Estudio de cohortes de 1.103 pacientes ventilados mecanicamente. Con un analisis de particiones recursivas se determinaron las variables asociadas a la mortalidad, y con un analisis de regresion logistica se construyeron dos modelos predictivos: el primero con el SAPS II y las variables previas al inicio de la ventilacion mecanica, y el segundo con el SAPS II y las variables previas y aparecidas durante la ventilacion mecanica. Para evaluar la prediccion de la mortalidad se realizo una medida de calibracion con el metodo de Lemeshow y Hosmer y una medida de discriminacion calculando el area bajo la curva ROC La mortalidad observada fue de un 42% (IC del 95%, 39-45) frente a una predicha por el SAPS II de un 36%. En el analisis de particiones recursivas, las variables asociadas a la mortalidad fueron: fracaso renal agudo, shock, PaO2/FiO2 En una cohorte de enfermos ventilados mecanicamente, el SAPS II fue un mal predictor de la mortalidad hospitalaria. La inclusion de factores previos al inicio y aparecidos durante la ventilacion mecanica mejora discretamente la exactitud predictiva

Fundamento La ventilacion mecanica es una tecnica fundamental en las unidades de cuidados intensivos (UCI). El objetivo es conocer su utilizacion y las diferencias en su aplicacion en 72 UCI espanolas Metodos Estudio de cohortes de los pacientes ventilados durante mas de 12 h. Se registraron datos demograficos, indicacion de la ventilacion mecanica, parametros ventilatorios, modos de ventilacion y desconexion, y dias de soporte ventilatorio, dias de estancia y situacion al alta Resultados Se incluyo a 1.103 pacientes (29%) de los ingresados, un 66% de varones, con una mediana de edad de 65 anos y del SAPS II de 43. No se observaron diferencias geograficas en la aplicacion de la ventilacion mecanica ni en los desenlaces principales. En el 64% la indicacion de ventilacion fue insuficiencia respiratoria. Al inicio, la modalidad asistida-controlada fue la mas utilizada (90%), con un volumen tidal medio (desviacion estandar [DE]) 8,9 (2,0) ml/kg y PEEP 5,5 (2,2) cmH2O. El 4% recibio ventilacion no invasora, el 68% de los enfermos no preciso intubacion. La duracion de la ventilacion fue 7 (8) dias. El metodo de desconexion mas utilizado fue una prueba unica diaria de respiracion espontanea (58%). La duracion fue de 3 (5) dias. La incidencia de traqueostomia fue 15% y se realizo a los 14 (8) dias. La mortalidad en la UCI fue del 32,8% y en el hospital del 42,8% Conclusiones La comparacion de la utilizacion de la ventilacion mecanica en 72 UCI espanolas evidencia una practica similar, con minimas diferencias en el uso de los modos de ventilacion y desconexion y una similar mortalidad y dias de estancia

Resumen Introduccion El tratamiento de las neumonias adquiridas en la comunidad (NAC) con antibioticos en monoterapia y monodosis (MM) ha demostrado la misma efectividad clinica que las pautas clasicas de antibioterapia fraccionada, a la vez que disminuye la estancia hospitalaria. Esto hace que la MM constituya una opcion de mejora. Objetivo: Comprobar si las caracteristicas del tratamiento de las NAC con MM eran exportables a un hospital diferente de aquellos en los que se habian descrito inicialmente. Material y metodo Estudio de intervencion para la mejora de la calidad, en el periodo de enero a mayo de 1999. Tipo de muestreo: consecutivo. Datos recogidos: edad, sexo, puntuacion APACHE II e indice de Charlson para comorbilidades, tiempo de estancia, mortalidad a 30 dias, reingresos en los 10 dias siguientes del alta hospitalaria, tiempos de enfermeria en preparar y suministrar el tratamiento. En la etapa I se compararon las pautas de MM con levofloxacino o ceftriaxona frente a la pauta clasica de cefotaxima cada 6 h acompanada de un macrolido cada 12 h. En la etapa II se compararon entre si las pautas de MM: levofloxacino frente a ceftriaxona. Durante todo el estudio se aplicaron guias de practica clinica comunes a todos los pacientes con NAC. En la etapa III, segun los resultados obtenidos y a las evidencias bibliograficas, el grupo de expertos selecciono la pauta definitiva. Resultados En la etapa I el tiempo medio ± desviacion estandar (DE) de estancia de las NAC tratadas con MM fue de 151 ± 80,6 h frente a 204 ± 110,4 horas en el tratamiento clasico, siendo la diferencia estadisticamente significativa y clinicamente relevante. No se detectaron diferencias en la mortalidad y reingresos; el tiempo de enfermeria fue de 4 min/paciente/dia en la MM frente a 16 minutos en el tratamiento clasico. En la segunda etapa no se detectaron diferencias entre los dos tipos de MM empleadas, si bien no se alcanzo el tamano adecuado de la muestra. El grupo de expertos selecciono la MM con levofloxacino por permitir un tratamiento secuencial sin cambio de farmaco y porque su biodisponibilidad oral proxima al cien por cien permite iniciar el tratamiento oral rapidamente. Comentario Nuestros resultados ponen de manifiesto que la MM supone una opcion de mejora en nuestro hospital, dado que al disminuir los tiempos de estancia por paciente junto con un ahorro en el tiempo de enfermeria mejora la utilizacion de las camas sin incrementar los riesgos para el paciente.

The purpose of this work is to evaluate characteristics of a respiratory model, RS1 , in the presence of the following stimuli: exercise, hypercapnia and hypoxia. RS1 has a controller where the driving signal optimizes alveolar ventilation and respiratory frequency to minimize the respiratory work output. A comparative study of the steady-state and transient responses with other three models is performed by simulation. Alternative equations to calculate the optimum frequency are evaluated during exercise and a linear average of two of them is proposed and tested for a healthy subject and with restrictive/obstructive pathology. Additionally, the circulatory time delay in gas transport that produces periodic breathing is calculated.

We have read with interest the report by Ramanathan et al regarding a case of ornithine transcarbamylase (OTC) deficiency unmasked post–liver transplantation (1). This serves as a big learning opportunity in clinical organ donor evaluation. A consequence of this disorder is hyperammonemia. Acute high levels in serum ammonia can cause severe neurological findings such as cerebral edema and brain death (2-4). This article is protected by copyright. All rights reserved.

Blood pressure carries a great deal of information about people’s physical attributes. We analyzed the blood pressure signal in healthy subjects considering two positions, supine and sitting. 44 healthy subjects were studied. Parameters extracted from the blood pressure signal, related to time and frequency domain were used to compare the effect of postural position between supine and sitting. In time domain analysis, the time systolic interval and the time of blood pressure interval were higher in supine than in sitting position (p = 0.001 in both case). Parameters related to frequency peak, interquartile range, in frequency domain presented statistically significant difference (p < 0.0005 in both case). The blood pressure variability parameters presented smaller values in supine than in sitting position (p < 0.0005). In general, the position change of supine to sitting produces an increment in the pressure gradient inside heart, reflected in the blood pressure variability.

One of the most challenging problems in intensive care is still the process of discontinuing mechanical ventilation, called weaning process. Both an unnecessary delay in the discontinuation process and a weaning trial that is undertaken too early are undesirable. In this study, we analyzed respiratory pattern variability using the respiratory volume signal of patients submitted to two different levels of pressure support ventilation (PSV), prior to withdrawal of the mechanical ventilation. In order to characterize the respiratory pattern, we analyzed the following time series: inspiratory time, expiratory time, breath duration, tidal volume, fractional inspiratory time, mean inspiratory flow and rapid shallow breathing. Several autoregressive modeling techniques were considered: autoregressive models (AR), autoregressive moving average models (ARMA), and autoregressive models with exogenous input (ARX). The following classification methods were used: logistic regression (LR), linear discriminant analysis (LDA) and support vector machines (SVM). 20 patients on weaning trials from mechanical ventilation were analyzed. The patients, submitted to two different levels of PSV, were classified as low PSV and high PSV. The variability of the respiratory patterns of these patients were analyzed. The most relevant parameters were extracted using the classifiers methods. The best results were obtained with the interquartile range and the final prediction errors of AR, ARMA and ARX models. An accuracy of 95% (93% sensitivity and 90% specificity) was obtained when the interquartile range of the expiratory time and the breath duration time series were used a LDA model. All classifiers showed a good compromise between sensitivity and specificity., Uno de los problemas más difíciles en cuidados intensivos sigue siendo el proceso de interrupción de la ventilación mecánica, denominado proceso de destete. Tanto un retraso innecesario en el proceso de interrupción como un ensayo de destete demasiado precoz son indeseables. En este estudio, analizamos la variabilidad del patrón respiratorio utilizando la señal de volumen respiratorio de pacientes sometidos a dos niveles diferentes de ventilación con presión de soporte (PSV), antes de la retirada de la ventilación mecánica. Para caracterizar el patrón respiratorio, se analizaron las siguientes series temporales: tiempo inspiratorio, tiempo espiratorio, duración de la respiración, volumen corriente, tiempo inspiratorio fraccional, flujo inspiratorio medio y respiración rápida superficial. Se consideraron varias técnicas de modelización autorregresiva: modelos autorregresivos (AR), modelos autorregresivos de medias móviles (ARMA) y modelos autorregresivos con entrada exógena (ARX). Se utilizaron los siguientes métodos de clasificación: regresión logística (LR), análisis discriminante lineal (LDA) y máquinas de vectores soporte (SVM). Se analizaron 20 pacientes en ensayos de destete de la ventilación mecánica. Los pacientes, sometidos a dos niveles diferentes de PSV, se clasificaron como PSV baja y PSV alta. Se analizó la variabilidad de los patrones respiratorios de estos pacientes. Se extrajeron los parámetros más relevantes utilizando los métodos clasificadores. Los mejores resultados se obtuvieron con el rango intercuartílico y los errores finales de predicción de los modelos AR, ARMA y ARX. Se obtuvo una precisión del 95% (93% de sensibilidad y 90% de especificidad) cuando el rango intercuartílico del tiempo espiratorio y las series temporales de duración de la respiración se utilizaron un modelo LDA. Todos los clasificadores mostraron un buen compromiso entre sensibilidad y especificidad.

One objective of mechanical ventilation is the recovery of spontaneous breathing as soon as possible. Remove the mechanical ventilation is sometimes more difficult that maintain it. This paper proposes the study of respiratory flow signal of patients on weaning trials process by autoregressive moving average model (ARMA), through the location of poles and zeros of the model. A total of 151 patients under extubation process (T-tube test) were analyzed: 91 patients with successful weaning (GS), 39 patients that failed to maintain spontaneous breathing and were reconnected (GF), and 21 patients extubated after the test but before 48 hours were reintubated (GR). The optimal model was obtained with order 8, and statistical significant differences were obtained considering the values of angles of the first four poles and the first zero. The best classification was obtained between GF and GR, with an accuracy of 75.3% on the mean value of the angle of the first pole.

Background Weaning patients from mechanical ventilation is an important problem in intensive care units. Weaning is usually conducted in an empirical manner, and a standardized approach has not been developed. Methods We carried out a prospective, randomized, multicenter study involving 546 patients who had received mechanical ventilation for a mean (±SD) of 7.5±6.1 days and who were considered by their physicians to be ready for weaning. One hundred thirty patients had respiratory distress during a two-hour trial of spontaneous breathing. These patients were randomly assigned to undergo one of four weaning techniques: intermittent mandatory ventilation, in which the ventilator rate was initially set at a mean (±SD) of 10.0±2.2 breaths per minute and then decreased, if possible, at least twice a day, usually by 2 to 4 breaths per minute (29 patients); pressure-support ventilation, in which pressure support was initially set at 18.0±6.1 cm of water and then reduced, if possible, by 2 to 4 cm of water at le...

Weaning trials process of patients in intensive care units is a complex clinical procedure. 153 patients under extubation process (T-tube test) were studied: 94 patients with successful trials (group S), 38 patients who failed to maintain spontaneous breathing and were reconnected (group F), and 21 patients with successful test but that had to be reintubated before 48 hours (group R). The respiratory pattern of each patient was characterized through the following time series: inspiratory time (T(I)), expiratory time (T(E)), breathing cycle duration (T(Tot)), tidal volume (V(T)), inspiratory fraction (T(I)/T(Tot)), half inspired flow (V(T)/T(I)), and rapid shallow index (f/V(T)), where ƒ is respiratory rate. Using techniques as autoregressive models (AR), autoregressive moving average models (ARMA) and autoregressive models with exogenous input (ARX), the most relevant parameters of the respiratory pattern were obtained. We proposed the evaluation of these parameters using classifiers as logistic regression (LR), linear discriminant analysis (LDA), support vector machines (SVM) and classification and regression tree (CART) to discriminate between patients from groups S, F and R. An accuracy of 93% (98% sensitivity and 82% specificity) has been obtained using CART classification.

Autonomic nervous system regulates the behavior of cardiac and respiratory systems. Its assessment during the ventilator weaning can provide information about physio-pathological imbalances. This work proposes a non linear analysis of the complexity of the heart rate variability (HRV) and breathing duration (T Tot ) applying recurrence plot (RP) and their interaction joint recurrence plot (JRP). A total of 131 patients on weaning trials from mechanical ventilation were analyzed: 92 patients with successful weaning (group S) and 39 patients that failed to maintain spontaneous breathing (group F). The results show that parameters as determinism (DET), average diagonal line length (L), and entropy (ENTR), are statistically significant with RP for T Tot series, but not with HRV. When comparing the groups with JRP, all parameters have been relevant. In all cases, mean values of recurrence quantification analysis are higher in the group S than in the group F. The main differences between groups were found on the diagonal and vertical structures of the joint recurrence plot.

Several modalities of ventilatory support have been proposed to gradually withdraw patients from mechanical ventilation, but their respective effects on the outcome of weaning from mechanical ventilation are not known. We conducted a randomized trial in three intensive care units in mechanically ventilated patients who met standard weaning criteria. Those who could not sustain 2 h of spontaneous breathing were randomly assigned to be weaned with T-piece trials, with synchronized intermittent mandatory ventilation (SIMV), or with pressure support ventilation (PSV). Specific criteria for performing tracheal extubation were defined for each modality. The number of patients who could not be separated from the ventilator at 21 d (i.e., who failed to wean) was compared between the groups. Patients in whom tracheal intubation was required in a 48-h period following extubation were also classified as failures. Among 456 mechanically ventilated patients who met weaning criteria, 109 entered into the study (35 with T piece, 43 with SIMV, and 31 with PSV). The three groups were comparable in terms of etiology of disease or characteristics at entry in the study. When all causes for weaning failure were considered, a lower number of failures was found with PSV than with the other two modes, with the difference just reaching the level of significance (23% for PSV, 43% for T piece, 42% for SIMV; p = 0.05). After excluding patients whose weaning was terminated for complications unrelated to the weaning process, the difference became highly significant (8% for PSV versus 33% and 39%, p < 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

Little information exists regarding the proportion of patients treated with mechanical ventilation in intensive care units (ICUs), their underlying disease states, the modes of ventilation used, duration of ventilator support, methods and time required for weaning, and mortality in these patients. We carried out a cross-sectional multicenter study in 47 medical-surgical ICUs in Spain to investigate these issues in 290 patients who required mechanical ventilation for at least 24 hs. Relative frequency of different modes was as follows: assist-control ventilation (AC), 55%; synchronized intermittent mandatory ventilation (SIMV), 26%; pressure support ventilation (PSV), 8%; SIMV plus PSV, 8%; pressure-controlled ventilation (PCV), 1%; and continuous positive airway pressure (CPAP), 2%. Overall duration of mechanical ventilation was 27.1±1.1 (SE). A variety of techniques were used for weaning: T-tube trials, 24%; SIMV, 18%; PSV, 15%; SIMV plus PSV, 9%; and some combination of two or more methods in succession in 33% of the patients. Time required for weaning using a combination of SIMV and PSV was longer (17.8 days) than with other techniques (about 5 days, p

One of the most challenging problems in intensive care is the process of discontinuing mechanical ventilation, called weaning process. An unnecessary delay in the discontinuation process and an early weaning trial are undesirable. This paper proposes to analysis the respiratory pattern variability of these patients using autoregressive modeling techniques: autoregressive models (AR), autoregressive moving average models (ARMA), and autoregressive models with exogenous input (ARX). A total of 153 patients on weaning trials from mechanical ventilation were analyzed: 94 patients with successful weaning (group S); 38 patients that failed to maintain spontaneous breathing (group F), and 21 patients who had successful weaning trials, but required reintubation in less than 48 h (group R). The respiratory pattern was characterized by their time series. The results show that significant differences were obtained with parameters as model order and first coefficient of AR model, and final prediction error by ARMA model. An accuracy of 86% (84% sensitivity and 86% specificity) has been obtained when using order model and first coefficient of AR model, and mean of breathing duration.

The process of discontinuing mechanical ventilation is called weaning and is one of the most challenging problems in intensive care. An unnecessary delay in the discontinuation process and an early weaning trial are undesirable. This study aims to characterize the respiratory pattern through features that permit the identification of patients' conditions in weaning trials. Three groups of patients have been considered: 94 patients with successful weaning trials, who could maintain spontaneous breathing after 48 h (GSucc); 39 patients who failed the weaning trial (GFail) and 21 patients who had successful weaning trials, but required reintubation in less than 48 h (GRein). Patients are characterized by their cardiorespiratory interactions, which are described by joint symbolic dynamics (JSD) applied to the cardiac interbeat and breath durations. The most discriminating features in the classification of the different groups of patients (GSucc, GFail and GRein) are identified by support vector machines (SVMs). The SVM-based feature selection algorithm has an accuracy of 81% in classifying GSucc versus the rest of the patients, 83% in classifying GRein versus GSucc patients and 81% in classifying GRein versus the rest of the patients. Moreover, a good balance between sensitivity and specificity is achieved in all classifications.

The process of weaning from mechanical ventilation is one of the challenges in intensive care. 149 patients under extubation process (T-tube test) were studied: 88 patients with successful trials (group S), 38 patients who failed to maintain spontaneous breathing and were reconnected (group F), and 23 patients with successful test but that had to be reintubated before 48 hours (group R). Each patient was characterized using 8 time series and 6 statistics extracted from respiratory and cardiac signals. A moving window statistical analysis was applied obtaining for each patient a sequence of patterns of 48 features. Applying a cluster analysis two groups with the majority dataset were obtained. Neural networks were applied to discriminate between patients from groups S, F and R. The best performance obtained was 84.0% of well classified patients using a linear perceptron trained with a feature selection procedure (that selected 19 of the 48 features) and taking as input the main cluster centroid. However, the classification baseline 69.8% could not be improved when using the original set of patterns instead of the centroids to classify the patients.

The static pressure volume (PV) curve of the total respiratory system is a well established method to assess pulmonary mechanics during respiratory failure. We have tested the impact of auto-PEEP on the PV curve determination in 16 COPD patients. An isovolumic pressure increment (IPI) was found at the beginning of the curve and a close correlation between IPI and auto-PEEP level (r = 0.962) p less than 0.001) was observed. The regression equation was not significantly different from the identity line. We conclude that the appearance of IPI in PV curves is largely determined by auto-PEEP and it is a good estimate of the existing auto PEEP level.

During the early phase of the acute respiratory distress syndrome in adults (ARDS), pulmonary pressure-volume (P-V) curves exhibit a peculiar pattern, with increased hysteresis and an inflection in the ascending limb (Matamis et al, Chest 86:58-661984). End-expiratory lung volume is also markedly reduced. We traced P-V curves using a 2-L syringe in six patients with ARDS (group 2) and five patients without ARDS (group 1). End-expiratory lung volume, measured using the closed circuit helium dilution technique, was markedly reduced in both groups (39% ± 7% predicted in group 1, and 27% ± 7% in group 2). In the ARDS group, P-V curve was grossly abnormal, with an inflection at low lung volume and increased hysteresis: lung volume difference during inflation and deflation at a pressure 10 cm H2O higher than end-expiratory pressure was 803 ± 127 mL in group 2 and was only 450 ± 189 mL in group 1. Compliance measured during deflation was only slightly reduced in group 2. Application of first positive end-expiratory pressure 10, then 20 cm H2O, restored end-expiratory lung volume in all patients, and, in group 2 (ARDS), suppressed the inflection of the ascending limb, reduced hysteresis, and shifted the P-V trace upward and to the left. We conclude that, in ARDS patients, an abnormal pattern of P-V curve is explained by loss of volume, and by increased surface tension, since lung volume was similarly reduced in both groups. Increasing the level of end-expiratory pressure restores the normal pulmonary P-V relationship by suppressing the airway closure.

We studied airway occlusion pressure (P 0.1) and maximal inspiratory pressure (PIMax) in 10 healthy volunteers (Group A), 10 early postsurgical cardiac patients on spontaneous breathing (Group B), 10 patients mechanically ventilated for ARF (Group C), 10 patients weaning from mechanical ventilation after ARF (Group D) and 10 patients extubated after post-ARF (Group E). We calculated the index P 0.1/PIMax in an attempt to link the ventilatory demands and muscle ventilatory reserve. We found that the sensitivity and specificity in diagnosing the need for either full (C), partial (D) or no ventilatory support (A, B, E) by means of the P 0.1 were C = (50%, 95%), D = (70%, 72%) and A + B + E = (83%, 90%) respectively. When the index P 0.1/PIMax was used they were C = (90%, 100%), D = (80%, 87%) and A + B + E = (86%, 90%). We conclude that the index P 0.1/PIMax increases the reliability of P 0.1 alone to correctly classify the patients that will need either full, partial or no ventilatory support in ARF.

One of the challenges in intensive care is the process of weaning from mechanical ventilation. We studied the differences in respiratory pattern variability between patients capable of maintaining spontaneous breathing during weaning trials and patients that fail to maintain spontaneous breathing. In this work, neural networks were applied to study these differences. 64 patients from mechanical ventilation are studied: Group S with 32 patients with Successful trials and Group F with 32 patients that Failed to maintain spontaneous breathing and were reconnected. A performance of 64.56% of well classified patients was obtained using a neural network trained with the whole set of 35 features. After the application of a feature selection procedure (backward selection) 84.56% was obtained using only 8 of the 35 features.

Nonlinear processes of the autonomic nervous system (ANS) can produce breath-to-breath variability in the pattern of breathing. In order to provide assess to these nonlinear processes, nonlinear statistical dependencies between heart rate variability and respiratory pattern variability are analyzed. In this way, auto-mutual information and cross-mutual information concepts are applied. This information flow analysis is presented as a short-term non linear analysis method to investigate the information flow interactions in patients on weaning trials. 78 patients from mechanical ventilation were studied: Group A of 28 patients that failed to maintain spontaneous breathing and were reconnected; Group B of 50 patients with successful trials. The results show lower complexity with an increase of information flow in group A than in group B. Furthermore, a more (weakly) coupled nonlinear oscillator behavior is observed in the series of group A than in B.

Traditional time domain techniques of data analysis are often not sufficient to characterize the nonlinear dynamics of respiration. In this study, the respiratory pattern variability was analyzed using auto mutual information measures. These provide access to nonlinear statistical autodependencies of respiratory pattern variability. A group of 20 patients on weaning trials from mechanical ventilation were studied at two different pressure support ventilation levels, in order to obtain respiratory volume signals with different variability. Time series of breathing duration, inspiratory time, fractional inspiratory time, tidal volume and mean inspiratory flow were analyzed. Different measures based on auto-mutual information were studied to characterize the respiratory pattern variability with regard to its complex organization.

Assessing autonomic control provides information about patho-physiological imbalances. Measures of variability of the cardiac interbeat duration RR(n) and the variability of the breath duration TinfTot/inf(n) are sensitive to those changes. The interactions between RR(n) and TinfTot/inf(n) are complex and strongly non-linear. A study of joint symbolic dynamics is presented as a new short-term non-linear analysis method to investigate these interactions in patients on weaning trials. 78 patients from mechanical ventilation are studied: Group A (patients that failed to maintain spontaneous breathing and were reconnected) and Group B (patients with successful trials). Using the concept of joint symbolic dynamics, cardiac and respiratory changes were transformed into a word series, and the probability of occurrence of each word type was calculated and compared between both groups. Significant differences were found in 13 words, and the most significant pinfn/inf(Winfc010, r010/inf): 0.0041#177; 0.0036 (group A) against 0.0012#177; 0.0024 (group B), p-value = 0.00001. The number of seldom occurring word types (forbidden words) also presents significant differences fwinfcr/inf: 6.9#177; 6.6 against 13.5#177; 5.3, p-value = 0.00004. Joint symbolic dynamics provides an efficient non-linear representation of cardiorespiratory interactions that offers simple physiological interpretations.

To determine the incidence, risk factors, and outcome of barotrauma in a cohort of mechanically ventilated patients where limited tidal volumes and airway pressures were used.Prospective cohort of 361 intensive care units from 20 countries.A total of 5183 patients mechanically ventilated for more than 12 h.Baseline demographic data, primary indication for mechanical ventilation, daily ventilator settings, multiple-organ failure over the course of mechanical ventilation and outcome were collected. Barotrauma was present in 154 patients (2.9%). The incidence varied according to the reason for mechanical ventilation: 2.9% of patients with chronic obstructive pulmonary disease; 6.3% of patients with asthma; 10.0% of patients with chronic interstitial lung disease (ILD); 6.5% of patients with acute respiratory distress syndrome (ARDS); and 4.2% of patients with pneumonia. Patients with and without barotrauma did not differ in any ventilator parameter. Logistic regression analysis identified as factors independently associated with barotrauma: asthma [RR 2.58 (1.05-6.50)], ILD [RR 4.23 (95%CI 1.78-10.03)]; ARDS as primary reason for mechanical ventilation [RR 2.70 (95%CI 1.55-4.70)]; and ARDS as a complication during the course of mechanical ventilation [RR 2.53 (95%CI 1.40-4.57)]. Case-control analysis showed increased mortality in patients with barotrauma (51.4 vs 39.2%; p=0.04) and prolonged ICU stay.In a cohort of patients in whom airway pressures and tidal volume are limited, barotrauma is more likely in patients ventilated due to underlying lung disease (acute or chronic). Barotrauma was also associated with a significant increase in the ICU length of stay and mortality.

The discrepancy in results from different studies regarding outcome of weaning from mechanical ventilation may be due to several factors such as the differences in patient populations and weaning indexes used. In order to analyze the clinical characteristics and weaning indexes in patients undergoing a 2-h T-piece weaning trial and the relationship between the etiology of acute respiratory failure (ARF) and the outcome of this weaning trial, we prospectively studied 217 patients receiving mechanical ventilation who met standard weaning criteria. Successful weaning occurred in 57.6% (125 of 217) of patients: 13 of 33 (39.4%) patients with chronic obstructive pulmonary disease (COPD), 27 of 46 (58.7%) neurologic patients, and 85 of 138 (61.6%) patients with ARF. Ventilatory support was reinstituted in 31.8% (69 of 217) patients: 20 of 33 (60.6%) of patients with COPD, four of 46 (8.7%) neurologic patients, and 45 of 138 (32.6%) patients with ARF (p , 0.001). Reintubation was required in 23 of 148 (15.5%) patients: 15 of 42 (35.7%) neurologic patients, and eight of 93 (8.6%) patients with ARF, whereas no patient with COPD was reintubated (p , 0.001). Using a discriminant analysis, the following variables were selected as the best predictors of outcome: ( 1 ) in the whole population, days of mechanical ventilation before weaning trial (DMV), frequency-to-tidal volume ratio (f/V T ), maximal inspiratory pressure (MIP), airway occlusion pressure (P 0.1 ), maximal expiratory pressure (MEP), and vital capacity (VC); ( 2 ) in patients with ARF, DMV, P 0.1 /MIP, MIP, f/V T , and age; ( 3 ) in patients with COPD, f/V T , P 0.1 , P 0.1 /MIP, MIP, age, and DMV; ( 4 ) in neurologic patients, MIP, MEP, and f/V T ? P 0.1 . Using these predictors, 74.6% of the whole population, 76.1% of patients with ARF, 93.9% of patients with COPD, and 73.9% of neurologic patients were accurately classified as weaning successes or failures. The highest rate of reintubation occurred in neurologic patients. In this group, the ability to cough and clear respiratory secretions, objectively reflected by MEP, may help in clinical decision-making. Vallverdu I, Calaf N, Subirana M, Net A, Benito S, Mancebo J. Clinical characteristics, respiratory functional parameters, and outcome of a two-hour T-piece trial in patients weaning from mechanical ventilation. AM J RESPIR CRIT CARE MED 1998;158:1855‐1862.

Purpose :The purpose of this article is to analyze the effect of a pressure-regulated volume-controlled ventilation mode on lung mechanics and gas exchange in patients with acute respiratory failure. Materials and Methods :We ventilated 10 patients with two pressure-limited modes: pressure-controlled ventilation (PC) and pressure-regulated volume-controlled ventilation (PRVC) in random order, for 1 hour each. Patients were stabilized on volume-controlled ventilation (VC) for 30 minutes before, between, and at the end of PC and PRVC to reach baseline conditions. At the end of every VC period and at 30 and 60 minutes of PC and PRVC, respiratory mechanics, gasometrics, and hemodynamic parameters were collected. Results :We found no significant differences between the three VC periods. Comparing VC with the two pressure-limited ventilation modes, peak pressure decreased from 29.4 ± 9.1 cm H2O (VC) to 25.9 ± 8.4 (PC 60 minutes) and 26.1 ± 8.2 (PRVC 60 minutes), and PaCO2 decreased significantly from 38.6 ± 3.1 mm Hg (VC) to 36.7 ± 2.8 (PC 60 minutes) and 36.8 ± 2.9 (PRVC 60 minutes). Conclusions :Pressure-limited ventilation allows mechanical ventilation for the same tidal volume as VC but results in a lower peak inspiratory pressure and a slightly lower Paco2. The mechanism responsible for this gas exchange effect is unknown but is probably related to a better air distribution of the decelerated flow. The clinical relevance of this phenomenon remains to be established.

In patients with acute exacerbations of chronic obstructive pulmonary disease, noninvasive ventilation may be used in an attempt to avoid endotracheal intubation and complications associated with mechanical ventilation.We conducted a prospective, randomized study comparing noninvasive pressure-support ventilation delivered through a face mask with standard treatment in patients admitted to five intensive care units over a 15-month period.A total of 85 patients were recruited from a larger group of 275 patients with chronic obstructive pulmonary disease admitted to the intensive care units in the same period. A total of 42 were randomly assigned to standard therapy and 43 to noninvasive ventilation. The two groups had similar clinical characteristics on admission to the hospital. The use of noninvasive ventilation significantly reduced the need for endotracheal intubation (which was dictated by objective criteria): 11 of 43 patients (26 percent) in the noninvasive-ventilation group were intubated, as compared with 31 of 42 (74 percent) in the standard-treatment group (P0.001). In addition, the frequency of complications was significantly lower in the noninvasive-ventilation group (16 percent vs. 48 percent, P = 0.001), and the mean (+/- SD) hospital stay was significantly shorter for patients receiving noninvasive ventilation (23 +/- 17 days vs. 35 +/- 33 days, P = 0.005). The in-hospital mortality rate was also significantly reduced with noninvasive ventilation (4 of 43 patients, or 9 percent, in the noninvasive-ventilation group died in the hospital, as compared with 12 of 42, or 29 percent, in the standard-treatment group; P = 0.02).In selected patients with acute exacerbations of chronic obstructive pulmonary disease, noninvasive ventilation can reduce the need for endotracheal intubation, the length of the hospital stay, and the in-hospital mortality rate.

with Special Reference to Ventilator-associated Barotrauma.- Pneumotachographic Recording of Ventilatory Pattern.- Spirometry.- Inspiratory Occluded Airway Pressure.- Transdiaphragmatic Pressure.- Assessment of the Breathing Workload During Mechanical Ventilation.- Assessment of Diaphragmatic Function.- Pulmonary Compliance.- Respiratory Impedance.- Elastance and Resistance of Respiratory System.- Respiratory Inductive Plethysmography.- Closing Volume.- Functional Residual Capacity in Acute Respiratory Failure. Methods of Measurement in the Ventilated Patients and Their Clinical Utility.- FRC and Efficiency of Gas Mixing in the Lung. SF6.- Determination of Lung-Ventilation and Perfusion by Isotope Technique.- Multiple Inert Gas Elimination Technique.- Pulmonary Diffusion Capacity.- Blood Gases.- Pulse Oximetry in the Intensive Therapy Unit.- Transcutaneous Monitoring of Oxygen and Carbon Dioxide.- Mixed Venous Oxygen Saturation Monitoring in Mechanically Ventilated Patients.- Capnography.- Measurement of Oxygen Consumption and Carbon Dioxide Production in Artificially Ventilated Patients.- Bronchoalveolar Lavage.- Measurement of Extrapulmonary Lung Water.- Interactions Between Convective and Diffusive Components of O2 Transport to the Tissues.- Energy Metabolism and Diaphragmatic Function: Applications of Magnetic Resonance Spectroscopy.- The Oxygen Consumption of the Respiratory Muscles.- Clinical Applications of Balloon Occlusion Pulmonary Angiography (BOPA).- Computerized Axial Tomography of the Lung During Acute Respiratory Failure.

Background Ventilator-associated pneumonia is a common complication in ventilated patients. Endotracheal suctioning is a procedure that may constitute a risk factor for ventilator-associated pneumonia. It can be performed with an open system or with a closed system. In view of suggested advantages being reported for the closed system, a systematic review comparing both techniques was warranted. Objectives To compare the closed tracheal suction system and the open tracheal suction system in adults receiving mechanical ventilation for more than 24 hours. Search methods We searched CENTRAL (The Cochrane Library 2006, Issue 1) MEDLINE, CINAHL, EMBASE and LILACS from their inception to July 2006. We handsearched the bibliographies of relevant identified studies, and contacted authors and manufacturers. Selection criteria The review included randomized controlled trials comparing closed and open tracheal suction systems in adult patients who were ventilated for more than 24 hours. Data collection and analysis We included the relevant trials fitting the selection criteria. We assessed methodological quality using method of randomization, concealment of allocation, blinding of outcome assessment and completeness of follow up. Effect measures used for pooled analyses were relative risk (RR) for dichotomous data and weighted mean differences (WMD) for continuous data. We assessed heterogeneity prior to meta-analysis. Main results Of the 51 potentially eligible references, the review included 16 trials (1684 patients), many with methodological weaknesses. The two tracheal suction systems showed no differences in risk of ventilator-associated pneumonia (11 trials; RR 0.88; 95% CI 0.70 to 1.12), mortality (five trials; RR 1.02; 95% CI 0.84 to 1.23) or length of stay in intensive care units (two trials; WMD 0.44; 95% CI -0.92 to 1.80). The closed tracheal suction system produced higher bacterial colonization rates (five trials; RR 1.49; 95% CI 1.09 to 2.03). Authors' conclusions Results from 16 trials showed that suctioning with either closed or open tracheal suction systems did not have an effect on the risk of ventilator-associated pneumonia or mortality. More studies of high methodological quality are required, particularly to clarify the benefits and hazards of the closed tracheal suction system for different modes of ventilation and in different types of patients.

Gentamicin intrapatient pharmacokinetics variations were studied in 40 critically ill medical patients, suffering gram-negative sepsis. These patients were studied in two phases throughout gentamicin treatment: firstly, on the second day of treatment, when aggressive fluid therapy was required, and secondly, five days later, when patients had achieved a more stable clinical condition. Pharmacokinetic parameters were determined using least squares linear regression analysis assuming a one-compartment model using the Sawchuk-Zaske method. The apparent volume of distribution (Vd) in the first phase of the study was 0.43 +/- 0.12 L/kg, while on the seventh day of treatment it was 0.29 +/- 0.17 L/kg (p less than 0.001). Statistically significant differences were also observed for peak serum concentration (p less than 0.001), total dosage recommended (p less than 0.001) and half-life (p less than 0.05), whilst differences were not found for trough levels. From the analysis of the results obtained, we recommend increasing the initial dosage and monitoring plasma levels within the first days of therapy in critically ill patients treated with gentamicin, since important variations in aminoglycoside Vd related to disease, fluid balance and renal function, commonly occur in these patients.

The Simplified Acute Physiology Score III Outcomes Research Group is developing an international multidimensional instrument for the global evaluation of intensive care unit performance. Among its specific objectives are the update of a severity of illness index (Simplified Acute Physiology Score) with a mortality prediction equation, with the hindsight of recent years, and the creation or application of novel instruments in the areas of infections and cost-effectiveness. Some important measurements such as the quality of life and the satisfaction of patients and professionals are not included. A further aim is the achievement of international validation.

ContextThe outcome of patients receiving mechanical ventilation for particular indications has been studied, but the outcome in a large number of unselected, heterogeneous patients has not been reported.ObjectiveTo determine the survival of patients receiving mechanical ventilation and the relative importance of factors influencing survival.Design, Setting, and SubjectsProspective cohort of consecutive adult patients admitted to 361 intensive care units who received mechanical ventilation for more than 12 hours between March 1, 1998, and March 31, 1998. Data were collected on each patient at initiation of mechanical ventilation and daily throughout the course of mechanical ventilation for up to 28 days.Main Outcome MeasureAll-cause mortality during intensive care unit stay.ResultsOf the 15 757 patients admitted, a total of 5183 (33%) received mechanical ventilation for a mean (SD) duration of 5.9 (7.2) days. The mean (SD) length of stay in the intensive care unit was 11.2 (13.7) days. Overall mortality rate in the intensive care unit was 30.7% (1590 patients) for the entire population, 52% (120) in patients who received ventilation because of acute respiratory distress syndrome, and 22% (115) in patients who received ventilation for an exacerbation of chronic obstructive pulmonary disease. Survival of unselected patients receiving mechanical ventilation for more than 12 hours was 69%. The main conditions independently associated with increased mortality were (1) factors present at the start of mechanical ventilation (odds ratio [OR], 2.98; 95% confidence interval [CI], 2.44-3.63; P35 cm H2O), and (3) developments occurring over the course of mechanical ventilation (OR, 8.71; 95% CI, 5.44-13.94; P

We have studied eleven patients ventilated in the assisted mode during recovery from acute respiratory failure. We have measured the effort required to trigger the pressure demand valve for 3 different ventilators, and have measured the occulusion pressure as an index of neuromuscular inspiratory drive. We found a delay in the opening of the demand valve, as previously described by other authors. We also found a close correlation between the effort required to open the demand valve and the occlusion pressure. We conclude that the inspiratory effort required to open the demand valve, in the assist mode, is greater than the preset trigger level and that it is well correlated with the neuromuscular inspiratory drive. This inspiratory effort against the closed demand valve, allows the measurement of the occlusion pressure.

We studied different gas dilution techniques in order to validate an easy method for the measurement of functional residual capacity (FRC) in patients with acute respiratory failure (ARF) undergoing mechanical ventilation (MV). FRC was measured in duplicate using four different techniques in 22 adult patients. The reference technique was the bag-in-a-box (BB) with helium (BB He) which was compared with a BB with nitrogen (BB NO, with helium syringe (He S), and with N 2 syringe N 2 S) techniques. The mean values of FRC (in BTPS units) obtained with the different techniques were 1,108 mL ± 398 mL (BB He), 1,061 mL ± 418 mL (BB N 2 , 1,170 mL ± 431 mL (He S), and 1,050 mL ± 429 mL N 2 S), the differences not being statistically significant. The linear regression equations were BB N 2 = −42 + 0.99 BB He, He S=54 +1.00 BB He, and N 2 S= −66 + 1.00 BB He. The mean difference between duplicate determinations ranged between −1.8 mL and 14 mL. The techniques studied are useful and practical bedside procedures for the estimation of FRC in ARF patients undergoing MV.

The effect of PEEP on the arterial minus end-tidal carbon dioxide gradient (FaCO 2 – PetCO 2 ) was evaluated in 13 adult patients with acute respiratory failure. The morphologic study of the pressure-volume (P-V) curves allowed separation of the patients into two groups: group 1 (n = 7) with initial inflection point in the (P-V) curve, and group 2 without inflection point. We hypothesized that the profile of the PaCO 2 – PetCO 2 gradient would indicate an appropriate PEEP level only in patients with recruitable air spaces. We ventilated group 1 patients with zero end expiratory pressure (ZEEP), PEEP corresponding to inflection point pressure (PEEP Pi ) and PEEP 5 cm H 2 O above PEEP Pi , and group 2 patients with ZEEP, 6 cm H 2 O PEEP and 12 cm H 2 O PEEP. The PaCO 2 – PetCO 2 gradient changed significantly in group 1 (ZEEP: 13.59 mm Hg; PEEP Pi : 8.33 mm Hg; PEEP Pi + 5 cm H 2 O: 10.54 mm Hg), but not in group 2 (ZEEP: 14.15 mm Hg; PEEP 6 cm H 2 O:14.20 mm Hg; PEEP 12 cm H 2 O: 16.53 mm Hg). Our results show that the PaCO 2 – PetCO 2 gradient may be useful in selecting a PEEP level which produces alveolar recruitment, but only in those patients with initial inflection point in the P-V curve.