Airway pressure curve: a good tool to measure neural inspiratory time?

BACKGROUND: Considerable asynchrony during pressure-support ventilation has been reported. While the beginning of active inspiration is usually identifiable in the airway pressure (Paw) curve (the inspiratory trigger), there is still a need for accurate, non-invasive methods to identify the end of inspiration. To test the hypothesis that inspiration, particularly the end of inspiration, can be estimated from the Paw curve, we compared indirect measurements based on Paw with simultaneous direct electromyography of the diaphragm (EMGdi). METHODS: We prospectively studied 10 patients during the weaning period after cardiac surgery. Inspiratory pressure support was set at 20, 15, 10, and 5 cm H(2)O; 25 respiratory cycles were analyzed at each pressure level. Recording of the electromyogram was obtained with electrodes inserted into the diaphragm during surgery. RESULTS: The start and end of inspiration were identified in the Paw curve in 99% and 98% of the 1000 cycles analyzed, respectively, and were coincident with the electromyogram in 62% and 53% of the cycles, respectively. The inspiratory time estimated from the Paw curve was well correlated (r=0.94, P<0.0001) with the electromyogram. CONCLUSION: The end of neural inspiration (EMGdi) can be easily and with little error recognized from the Paw curve alone in patients with normal ventilatory mechanics who receive pressure-support ventilation.

Un método sencillo para ayudar a la comprobacióndel correcto posicionamiento de los tubos endotraquealesde doble luz izquierdos / Correct placement of left-sided double lumen endotracheal tubes: a simple verification

OBJETIVO: Los tubos endobronquiales de doble luz (TDL)se utilizan en cirugía torácica para la intubación selectiva pulmonar,necesaria para la ventilación unipulmonar. La comprobaciónde su correcta colocación se realiza mediante fibrobroncoscopia.Presentamos un método simple y alternativopara ayudar a la comprobación del posicionamiento de losTDL izquierdos, que consiste en pasar una sonda de aspiraciónpor la rama traqueal del TDL. Nuestra hipótesis es quesi la sonda pasa sin dificultad el tubo estaría colocado correctamente.El objetivo de este estudio fue la determinación de lasensibilidad y especificidad de la prueba.MATERIAL Y MÉTODO: Pacientes programados para cirugíatorácica electiva de neumonectomía o lobectomíaizquierdas. Tras pasar la sonda por el TDL izquierdo secomprobó con el fibrobroncoscopio (técnica de referencia),comparándose ambos métodos.RESULTADO: Se incluyeron 100 pacientes. De los casosestudiados, en el 88% se dedujo una correcta posición delTDL por paso de sonda sin resistencia. De estos, en el 84%la fibrobroncoscopia corroboró esta situación mientras queen el 4% restante no fue así y hubo que recolocarlos. En el12% se encontró resistencia al pasar la sonda verificándoseen éstos una mala colocación por fibrobroncoscopio.CONCLUSIONES: Si dominamos esta técnica o si no disponemosde fibrobroncoscopio, esta maniobra puede ser útily de mucha ayuda durante la colocación de los TDLizquierdos. Nuestros resultados apoyan la práctica cotidianade esta maniobra, ya que es un método sencillo y accesible,pero recordando que la comprobación mediantefibrobroncoscopio es la técnica de referencia actualmente (AU)

OBJETIVE: Double lumen endotracheal tubes (DLTs)are used in thoracic surgery for selective bronchialintubation, which is required for single lung ventilation.Correct placement of the tube is checked by means offiberoptic bronchoscopy. We present a simple alternativemethod to help confirm the correct placement of left-sidedDLTs. The method consists of passing a suction catheterthrough the tracheal lumen of the tube. Our hypothesiswas that if the catheter can be inserted without difficulty,the tube is correctly placed. The objective was todetermine the sensitivity and specificity of that criterion.MATERIAL AND METHODS: We studied patients scheduledfor elective left pneumonectomy or lobectomy. After passingthe catheter through the left-sided DLT, placement waschecked by means of fiberoptic bronchoscopy (gold standard)and the results were compared with the placementassessment based on ease of insertion.RESULTS: One hundred patients were included. The DLTwas judged to be correctly placed in 88% of patients inwhom the catheter was inserted without resistance.Bronchoscopy corroborated this finding in 84% of cases;the tube was found to be incorrectly placed in theremaining 4% of cases and had to be reinserted. Resistancewas noted in 12% of cases and bronchoscopy confirmedthat the tube was incorrectly placed in those patients.CONCLUSIONS: This technique can be very useful inplacing left-sided DLTs in situations where fiberopticbronchoscopy is not available and if the anesthesiologisthas a thorough command of the method. Our resultssupport the routine use of this criterion as it is simple andeasy to learn. It should be remembered, however, thatconfirmation of placement by means of fiberopticbronchoscopy is currently the gold standard technique (AU)

[Preoxygenation for anesthesia]. / Preoxigenación en anestesia.

Oxygenation, or rather denitrogenation, prior to apnea during anesthetic induction attempts to replace alveolar nitrogen with oxygen to achieve an intrapulmonary oxygen reserve that will allow apnea to be as prolonged as possible with the least possible desaturation. During apnea, the rate of arterial desaturation depends mainly on the volume of oxygen stored in the lung, on mixed venous oxygen saturation, and on the presence of intrapulmonary shunt. Together, these factors account for the higher rate of desaturation during apnea in children, obese individuals, postoperative patients, and pregnant women. Two approaches to preoxygenation have proven effective to date: ventilation with 100% oxygen at tidal volume for 3 minutes using a well-sealed face mask and the performance of 8 vital capacity maneuvers in 1 minute. The efficacy of preoxygenation can be assessed by expired oxygen fraction or by pulse oximetry. In a healthy adult, both methods described ensure sufficient oxygenation (pulse oximetry 90% to 95%) after a period of apnea lasting between 6 and 10 minutes.

[Post-pneumonectomy edema]. / Edema postneumonectomía.

A 64-year-old man complained of irritable cough of 3 months' duration and 1 episode of hemoptysis and dyspnea related to effort. The radiograph revealed a mass in the upper right lobe. Adenocarcinoma of the lung was diagnosed by mediastinoscopy. After removal of the right lung, the patient was admitted to the recovery unit for 36 hours and transferred out without complications. The clinical course in 48 hours on the ward included increasing dyspnea, tachypnea and greater respiratory effort with hypoxemia in spite of increased FiO2. A radiograph showed pulmonary edema and the patient was readmitted to the recovery unit. We describe this case of postpneumonectomy edema and discuss the possible origins of the clinical picture, differential diagnosis, preventive measures and possible treatments.

Edema postneumonectomía / Post-pneumonectomy edema

Un varón de 64 años consultó por tos irritativa de tres meses de evolución más un episodio de hemoptisis y disnea de esfuerzo. La radiografía mostró una masa en el lóbulo superior derecho y la mediastinoscopia diagnosticó un adenocarcinoma de pulmón. Al paciente se le practicó una neumonectomía derecha, permaneciendo en la unidad de reanimación durante 36 horas, de donde fue dado de alta sin incidencias. A las 48 horas de estancia en sala, desarrolló un cuadro progresivo de disnea, taquipnea y aumento del trabajo respiratorio con hipoxemia a pesar de los aumentos de la FiO2. La radiografía mostró un patrón de edema pulmonar, reingresando en reanimación. Describimos el caso de edema postneumonectomía. Se discute la posible etiología del cuadro clínico, planteándose el diagnóstico diferencial, las medidas para prevenirlo y su posible tratamiento (AU)

[Comparison of patient-ventilator synchronization during pressure support ventilation versus amplified spontaneous pattern in postoperative patients]. / Comparación de la sincronización paciente-ventilador durante la ventilación con presión de soporte y con patrón espontáneo amplificado en pacientes postoperados.

INTRODUCTION: Patient-ventilator desynchronization can develop during weaning from proportional-assist ventilation. Poor adaptation between ventilator assistance and the patient's ventilatory demand is termed asynchrony. OBJECTIVES: Comparative analysis of types and incidence of asynchrony in patients receiving pressure support (PS) ventilation or amplified spontaneous pattern (ASP) ventilation, to determine whether the presence of asynchrony is related to a patient's level of dyspnea or anxiety. PATIENTS AND METHODS: Eighteen patients were studied prospectively after undergoing coronary revascularization. Baseline anxiety was assessed before surgery. A pleural catheter was inserted during surgery. After surgery patients were randomly assigned to ventilation with PS mode or ASP. Flow curves, flow volume, airway pressure and pleural pressure were recorded by a BioCore CP100 monitor once the patient's work of breathing held steady between 0.3 and 0.5 J/l. The curves were recorded for 10 m on a computer for later analysis. After each recording dyspnea and anxiety were assessed. Fifty consecutive cycles per patient were analyzed, signalling in each case the start of inspiration and expiration. RESULTS: Nine hundred ventilatory cycles were analyzed to identify five types of patient-ventilator asynchrony: 1) self-cycled (SC: inspiratory assistance from the ventilator without demand by patient); 2) no effort detected (NED: patient inspiratory effort but no flow response from the ventilator); 3) interrupted support (IS: interruption of ventilatory support during patient inspiration); 4) prolonged mechanical inspiration (PMI: maintenance of ventilatory support during patient expiration), and 5) double-breath, single cycle (DBSC: sequence of inspiration-expiration-inspiration of the patient within a single assisted inspiration). Asynchronic cycles were found in all PS-ventilated patients (84 of 450; 18.7%): 9.1% SC, 4% NED, 2.2% IS, 1.5% PMI and 1.8% DBSC. Asynchronic cycles were seen in only two ASP patients (16 of 450; 3.5%); both cases were NED asynchrony. Levels of anxiety and dyspnea were slightly higher with the PS mode than with ASP but the differences were not significant (p = 0.05). CONCLUSIONS: The incidence of asynchrony during assisted ventilation is very high with the PS mode and is substantially less with ASP. Asynchrony is difficult to detect clinically and is revealed only by advanced cycle-to-cycle monitoring.

Comparación de la sincronización paciente-ventilador durante la ventilación con presión de soporte y con patrón espontáneo amplificado en pacientes postoperados / Comparison of patient-ventilator synchronization with pressure support ventilation versus amplified spontaneous pattern in postoperative patients

Introducción . Durante el destete de la ventilación mecánica usando métodos de soporte ventilatorio parcial puede producirse desincronización paciente-respirador. Denominamos asincronismo a la desadaptación entre la asistencia del respirador y la demanda ventilatoria del paciente.Objetivos. Análisis comparativo de los tipos e incidencia de asincronismos en pacientes ventilados con presión de soporte (PSV) y con patrón espontáneo amplificado (PEA). Observar si su presencia se relaciona con el grado de confort (disnea y ansiedad) del paciente.Pacientes y métodos. Se estudiaron prospectivamente 18 pacientes postoperados de revascularización coronaria. Preoperatoriamente, se valoró el grado de ansiedad basal. Intraoperatoriamente, se colocó un catéter pleural. En el postoperatorio, los pacientes fueron ventilados aleatoriamente con PSV y PEA. Las curvas de flujo, volumen corriente, presión en vía aérea y presión pleural fueron obtenidas con un monitor Bicore CP100, cuando el trabajo respiratorio del paciente fue constante entre 0,3 y 0,5 J/l. Las curvas fueron recogidas durante 10 min en un ordenador para su posterior análisis. Tras cada registro se evaluó la disnea y la ansiedad. Se analizaron 50 ciclos consecutivos por paciente, señalando en cada uno de ellos el inicio de la inspiración y espiración.Resultados. Se analizaron un total de 900 ciclos ventilatorios, detectándose cinco tipos de asincronismo paciente-respirador: 1) autociclado (AC, asistencia inspiratoria del ventilador sin demanda del paciente); 2) esfuerzo no detectado (END, esfuerzo inspiratorio del paciente sin que se produzca respuesta de flujo del ventilador); 3) soporte interrumpido (SI, interrupción del apoyo ventilatorio durante la inspiración del paciente); 4) inspiración mecánica prolongada (IMP, mantenimiento del soporte ventilatorio durante la espiración del paciente), y 5) doble respiración-ciclo único (DRCU, secuencia de inspiración-espiración-inspiración del paciente dentro de una única asistencia inspiratoria). En todos los pacientes con PSV se encontraron ciclos asincrónicos (84 de 450; 18,7 por ciento); un 9,1 por ciento de AC, un 4 por ciento de END, un 2,2 por ciento de SI, un 1,5 por ciento de IMP y un 1,8 por ciento de DRCU. Con PEA se encontraron ciclos asincrónicos sólo en dos pacientes (16 de 450; 3,5 por ciento), siendo todos ellos del tipo END. En nuestro estudio el grado de ansiedad y de disnea con PSV fue algo superior al obtenido con la PEA, pero las diferencias no fueron significativas (p = 0,05).Conclusiones. La incidencia de asincronismos durante la asistencia ventilatoria con PSV es muy elevada y se reduce notablemente con PEA. Clínicamente, los asincronismos son difícilmente detectables y sólo el análisis ciclo a ciclo, mediante monitorización avanzada, los pone de manifiesto (AU)

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