Impulso, esfuerzo y trabajo respiratorio: revisión de definiciones y herramientas no invasivas de ventiladores de cuidados intensivos durante tiempos de pandemia / Respiratory drive, inspiratory effort, and work of breathing: review of definitions and non-invasive monitoring tools for intensive care ventilators during pandemic times

Los avances tecnológicos de la ventilación mecánica han sido parte esencial del aumento de la sobrevida en las unidades de cuidados intensivos. Desde la conexión a la ventilación mecánica, comúnmente se utiliza ventilación controlada sin la consecuente participación de los músculos respiratorios del paciente, con el fin de favorecer la protección pulmonar. El retiro de la ventilación mecánica implica un periodo de transición hacia la respiración espontánea, utilizando principalmente ventilación mecánica asistida. En esta transición, el desafío de los clínicos es evitar la sub y sobre asistencia ventilatoria, minimizando el esfuerzo respiratorio excesivo, daño diafragmático y pulmonar inducidos por la ventilación mecánica. La monitorización con balón esofágico permite mediciones objetivas de la actividad muscular respiratoria en tiempo real, pero aún hay limitaciones para su aplicación rutinaria en pacientes ventilados mecánicamente en la unidad de cuidados intensivos. Al igual que el balón esofágico, la electromiografía de los músculos respiratorios y la ecografía diafragmática son herramientas que permiten monitorizar la actividad muscular de la respiración, siendo mínimamente invasivas y con requerimiento de entrenamiento específico. Particularmente, durante la actual pandemia de enfermedad por coronavirus se ha extendido el uso de herramientas no invasivas disponibles en los ventiladores mecánicos para monitorizar el impulso (drive), esfuerzo y trabajo respiratorio, para promover una ventilación mecánica ajustada a las necesidades del paciente. Consecuentemente, el objetivo de esta revisión es identificar las definiciones conceptuales de impulso, esfuerzo y trabajo respiratorio utilizadas en el contexto de la unidad de cuidados intensivos, e identificar las maniobras de medición no invasivas disponibles en los ventiladores de cuidados intensivos para monitorizar impulso, esfuerzo y trabajo respiratorio. La literatura destaca que, aunque los conceptos de impulso, esfuerzo y trabajo respiratorio se perciben intuitivos, no existe una definición clara. Asimismo, destacados autores los definen como conceptos diferentes.

Technological advances in mechanical ventilation have been essential to increasing the survival rate in intensive care units. Usually, patients needing mechanical ventilation use controlled ventilation to override the patient's respiratory muscles and favor lung protection. Weaning from mechanical ventilation implies a transition towards spontaneous breathing, mainly using assisted mechanical ventilation. In this transition, the challenge for clinicians is to avoid under and over assistance and minimize excessive respiratory effort and iatrogenic diaphragmatic and lung damage. Esophageal balloon monitoring allows objective measurements of respiratory muscle activity in real time, but there are still limitations to its routine application in intensive care unit patients using mechanical ventilation. Like the esophageal balloon, respiratory muscle electromyography and diaphragmatic ultrasound are minimally invasive tools requiring specific training that monitor respiratory muscle activity. Particularly during the coronavirus disease pandemic, non invasive tools available on mechanical ventilators to monitor respiratory drive, inspiratory effort, and work of breathing have been extended to individualize mechanical ventilation based on patient's needs. This review aims to identify the conceptual definitions of respiratory drive, inspiratory effort, and work of breathing and to identify non invasive maneuvers available on intensive care ventilators to measure these parameters. The literature highlights that although respiratory drive, inspiratory effort, and work of breathing are intuitive concepts, even distinguished authors disagree on their definitions.

Comportamiento clínico y gasométrico en falla respiratoria aguda tratada con cánula nasal de alto flujo / Clinical and gasometric behavior in acute respiratory failure treated with a high-flow nasal cannula

Introducción: La cánula nasal de alto flujo en adultos ofrece un tratamiento alternativo a la oxigenoterapia convencional. Objetivo: Establecer el comportamiento clínico y gasométrico de pacientes con falla respiratoria aguda que habitan a 2.600 msnm, tratados con cánula nasal de alto flujo en cuidado intensivo adulto. Materiales y métodos: Estudio piloto cuasi experimental pretest-postest intrasujeto, tamaño de muestra 14 pacientes calculado a través de Epidat. Tipo de muestreo no probabilístico por conveniencia, durante catorce meses. Resultados: El 78% de los pacientes fueron mujeres, la edad promedio fue 68 años, y el diagnóstico principal fue enfermedad pulmonar obstructiva crónica (EPOC) en el 71,42% de los casos. Se administró un flujo de oxígeno promedio de 30 Lt/min para pacientes con (EPOC), para el resto de diagnósticos se programaron flujos mayores. El trabajo respiratorio disminuyó posterior al uso de cánula nasal de alto flujo, la presión arterial de oxígeno mejoró paulatinamente en pacientes con falla hipoxémica y el índice de oxigenación incrementó progresivamente en los dos tipos de falla respiratoria. Conclusiones: La cánula nasal de alto flujo es una opción terapéutica útil en el manejo de la falla respiratoria aguda a 2.600 msnm, permitiendo mejoría de la oxigenación y disminución del trabajo respiratorio.

Introduction: High-flow nasal cannula offers an alternative treatment approach to conventional oxygen therapy in adults. Objective: To establish the clinical and gasometric behavior of patients with acute respiratory failure who live at 2,600 m.a.s.l. and are treated with high-flow nasal cannula in an adult intensive care unit. Materials and methods: Quasi-experimental pilot study with a pretest-posttest within-subject design and a sample size of 14 patients calculated through Epidat. A non-probabilistic convenience sampling was conducted for fourteen months. Results: 78% of the patients were women and their average age was 68 years. Chronic Obstructive Pulmonary Disease (COPD) was diagnosed in 71.42% of the cases. An oxygen flow rate of 30 L/min was administered to patients with Chronic Obstructive Pulmonary Disease, while higher rates were used for the rest of the diagnoses. Nasal cannula treatment led to (i) a decreased respiratory function, (ii) a gradually improved arterial blood pressure in patients with hypoxemic failure, (iii) and a progressively increased oxygenation rate. Conclusions: High-flow nasal cannula is a useful therapeutic option in the management of patients with acute respiratory failure living at 2,600 m.a.s.l. because it improves oxygenation and reduces respiratory function.

Evaluación del trabajo respiratorio mediante oxigenación muscular / Assessment of work of breathing using muscle oxygenation

RESUMEN El aumento del trabajo respiratorio (work of breathing, WOB) es uno de los problemas kinesiológicos frecuentes en el quehacer clínico. Un desafío profesional es contar con valores de variables fisiológicas que permitan objetivar el WOB facilitando así su interpretación entre los diferentes profesionales de la salud. El uso de dispositivos portátiles que registran la longitud de onda cercana al rango infrarrojo (680- 820 nm, Near Infrared Spectroscopy (NIRS)) en músculos superficiales permite obtener valores de hemoglobina total unida a oxígeno (tHb) y oxigenación muscular local (SmO2), variables relacionadas al trabajo muscular pues reportan el flujo sanguíneo en la microcirculación y consumo de oxígeno local, respectivamente. Estos dispositivos situados en musculatura intercostal nos informan el WOB asociado a la respiración. Para evaluar esto, se analizó el comportamiento de tHb y SmO2 en m. intercostal en 20 corredores de maratón durante la valoración de consumo de oxígeno máximo (VO2- max), instancia que implica aumento sostenido e incremental de la ventilación pulmonar (��E), y por tanto de la actividad muscular respiratoria. El aumento de V E en 128,4 L·min-1 ( ��E (máximo-reposo)) implicó una disminución en SmO2- m.intercostal del 34% ( SmO2 (reposo-máximo)), sin cambios en tHb (p=0,805). La tuvo una correlación inversa con SmO2-m.intercostal (rho=-0.565; p=0,001). Se concluye que la valoración de SmO2-m.intercostal es una forma novedosa de objetivar el WOB en sujetos sanos. Conocer la aplicabilidad clínica requiere de otros estudios que evalúen esta herramienta en pacientes con disfunciones cardiorrespiratorias, lo que permitiría incorporar su uso en nuestro desarrollo clínico profesional.

The work of breathing (WOB) increased is a commonkinesiological problems at the clinical practice. A professional challenge is to have values of physiological variables that allows to objective the WOB, thus facilitating its interpretation among different health professionals. The use of portable devices that measure by spectroscopy the near-infrared wavelength (680-820 nm) atsuperficial muscles allows to obtain values of total hemoglobin linked to oxygen (tHb) and local muscle oxygenation (SmO2), variables related to muscle work because give information of the blood flow at the microcirculation and local oxygen consumption, respectively. These devices located at the m.intercostal could give information about the WOB associated to breathing. To evaluate this, the tHb and SmO2 of the m.intercostal in 20 marathon runners were analyzed while they doing the maximum oxygen consumption test (VO2-max), an exercise that increase the pulmonary ventilation and the respiratory muscle activity. The increase of V E (128,4 L·min-1((max-rest)) implied a decrease in SmO2- m.intercostal (34% ( SmO2 (max-rest)), without changes in tHb (p=0.805). The showedan negative correlation to SmO2-m.intercostal (rho= -0.565; p=0.001). It is concluded that the assessment of SmO2-m.intercostal is a novel way to measure the WOB in healthy subjects. Their clinical applicability requires more studies that applied this tool in patients with cardiorespiratory dysfunctions, facilitating their incorporation in the professional clinical practice.

Effect of Breathing Exercise Using Panflutes on the Postoperative Compliance, Pulmonary Infections and Life Satisfaction in Elderly Patients Undergoing Spinal Surgery

PURPOSE: The purpose of this study was to examine the effects of breathing exercises performed using panflutes in elderly patients undergoing spinal surgery. METHODS: The study design was a nonequivalent control group non-synchronized pre-post test. The study included 24 patients in both the experimental group and the control group. The experimental group completed a daily breathing exercise regimen using panflutes for 30minutes after meals, whereas the control group was provided standard preoperative education, including breathing exercises using incentive spirometers. After the exercise regimen, breathing exercise compliance, pulmonary infections, and life satisfaction were measured in both groups, and the data were analyzed using the SPSS/WIN program. RESULTS: The compliance rate of breathing exercises was significantly higher in the experimental group. The experimental group presented no pulmonary infections in the later period, whereas the control group presented higher pulmonary infection rates in the same period. In addition, the life satisfaction score in the experimental group significantly increased. CONCLUSION: The breathing exercise program using panflutes for elderly patients undergoing spinal surgery enhanced their breathing exercise compliance and their daily life satisfaction in addition to reducing their pulmonary infection rates.

Cambios en la mecánica ventilatoria debidos a variaciones de la PEEP y la presión soporte: estudio en sujetos sanos bajo ventilación mecánica no invasiva / Changes in ventilatory mechanics caused by variations in PEEP and pressure support: study in healthy subjects under non-invasive mechanical ventilation

Resumen Introducción. Por lo general, la mecánica ventilatoria se ha estimado en modo controlado con el uso de aproximaciones no adecuadas para ventilación espontánea. Objetivo. Medir los cambios de la mecánica ventilatoria ante variaciones de la presión positiva al final de la expiración (PEEP, por su sigla en inglés) y la presión soporte (PS) en ventilación mecánica no invasiva. Materiales y métodos. A través de una estrategia no invasiva, se estimó la mecánica ventilatoria bajo diferentes niveles de PEEP y PS. Para tal fin, se utilizó un simulador mecánico y se registró una base de datos de 14 sujetos sanos conectados de manera no invasiva a un ventilador mecánico. Resultados. Se obtuvieron valores medianos de resistencia y compliancia de 91.2[77.8-135.9]mL/cmH2O y 8.3[6.1-10.4]cmH2O/L/s para los 14 sujetos sanos con PEEP y PS de 0 cmH2O, respectivamente. En los incrementos de PEEP, los sujetos presentaron aumento estadísticamente significativo en la compliancia. Por el contrario, en el incremento de presión soporte, no se observaron cambios de ningún parámetro. Conclusiones. Se encontraron valores de compliancia y resistencia, acordes con los configurados en el simulador mecánico y coherentes con los reportados en la literatura en el caso de sujetos sanos. Esto resulta de gran utilidad al tomar decisiones en unidades de cuidados intensivos.

Abstract Introduction: Traditionally, ventilatory mechanics has been delivered in controlled modes through the use of inappropriate approaches for spontaneous ventilation. Objective: To measure the changes of ventilatory mechanics caused by PEEP and pressure support (PS) variations in non-invasive mechanical ventilation. Materials and methods: The ventilatory mechanics was evaluated through a non-invasive strategy, under different PEEP and pressure support levels. For this purpose, a mechanical simulator was used, and a database of 14 healthy subjects non-invasively connected to a mechanical ventilator was recorded. Results: For the 14 healthy subjects under PEEP and pressure support conditions of 0 cmH2O, the median resistance and compliance values were 91.2 [77.8-135.9] mL/cmH2O and 8.3[6.1-10.4]cmH2O/L/s, respectively. PEEP compliance showed a statistically significant increase in all subjects. On the other hand, no changes in any of the parameters were observed regarding pressure support increase. Conclusions: The proposed technique allowed to find compliance and resistance values consistent with those set in the mechanical simulator, which, in turn, coincide with those reported in the literature for healthy subjects. This information is useful for decision-making in intensive care units.

Continuous positive airway pressure setups evaluated at simulated exercise conditions

INTRODUCTION: Studies have shown increases in airway opening pressure (Pao) swings and work of breathing (WOB) by different continuous positive airway pressure (CPAP) devices at rest, but few address this issue during exercise. The aim of the present work was to analyze the imposed WOB (WOBi), the apparent resistance (Rapp) and swings of Pao (deltaP) of 3 CPAP assemblies at simulated exercise conditions. METHODS: The CPAP measures were obtained from: a commercial CPAP (Assembly 1), a high flow CPAP (Assembly 2) and the parallel association of these devices (Assembly 3). In each assembly the spring-loaded positive end-expiratory pressure (PEEP) valve was set to fully opened (mode A) or at the same CPAP pressure (mode B). The exercise protocol simulation, performed manually by a calibrated syringe and a metronome, employed a respiratory frequency of 30 bpm, tidal volume of 2.7 L and inspiratory-to-expiratory ratio of 1. The setups were evaluated at CPAP settings of 5, 10 and 15 cmH2O. RESULTS: The lowest deltaP as well as Rapp and WOBi were obtained with Assembly 3 in mode A with an adjusted CPAP of 10 cmH2O (deltaP=8.1 (0.5) cmH2O, WOBi=1.4 (0.14) cmH2O/L/s, Rapp= 1.3 (0.07) J/s) showed as median (interquartile range). CONCLUSION: For the conditions studied, the best CPAP setup was obtained with mode A.

Incentivadores da inspiração atualidades nas técnicas de espirômetro de incentivo e breath-stacking* / Inspiration boosters: technical updates in incentive spirometers and breath-stacking

As técnicas incentivadoras da inspiração foram propostas com o objetivo de promoverem inspirações sustentadas máximas, criando altas pressões transpulmonares, prevenindo o colapso alveolar. Os espirômetros de incentivo são classificados em volume-dependentes e fluxo-dependentes, possuindo mecanismo de biofeedback visual, necessitando da colaboração do indivíduo para efetividade da técnica. Um mecanismo alternativo dos incentivadores inspiratórios que pode ser utilizado em indivíduos pouco ou não cooperativos é denominado breath-stacking. Esta revisão objetiva cotejar a literatura acerca das atualidades dos espirômetros de incentivo volume-dependentes e fluxo-dependentes e a técnica de breath-stacking, comparando os espirômetros de incentivo entre si e ambos com a técnica de breath-stacking. Os espirômetros de incentivo volume-dependentes em relação ao fluxo-dependente possuem vantagens no que se refere a proporcionar menos frequência respiratória,menor volume corrente, maior deslocamento do compartimento abdominal, bem como menos trabalho respiratório adicional. Nas situações em que se comparam os espirômetros de incentivo com a técnica de breath-stacking observam-se mais capacidade inspiratória atingida e mais tempo de expansão pulmonar com a segunda técnica. Além disso, o breath-stacking tem a vantagem de não depender da cooperação do indivíduo e proporcionar significativos volumes pulmonares e promover mais sustentação da inspiração máxima.

Inspiration boosting techniques were proposed in order to promote sustained maximal inspirations, creating high ventilation pressures and preventing alveolar collapse. Incentive spirometers are classified as volume-dependent or flow-dependent, possessing visual biofeedback mechanism and requiring patient cooperation for the effectiveness of the technique. An alternative mechanism for inspiration boosting that can be used with uncooperative individuals is called breath-stacking. This review aims to collate the current knowledge about volume or flow-dependentincentive spirometers and the breath-stacking technique, comparing the different incentive spirometers to one another to the breath-stacking technique. The volumedependent incentive spirometers have advantages with regard to providing lower respiratory rate, smaller tidal volume, larger displacement of the abdominal compartment, and less additional work of breathing in relation to flow-dependent incentive spirometers. In comparison with incentive spirometers, the breath-stacking techniqueachieves better inspiratory capacity and longer lung expansion. Furthermore, breath-stacking has the advantage of not depending on the individual's cooperation and providing significant lung volumes and promoting better support of maximum inspiration.

Early tracheotomy for acute severe asthma / 世界急诊医学杂志（英文）

@#BACKGROUND: Few studies have reported the effects of early tracheotomy in acute severe asthmatic patients. We report two patients with acute severe asthma who were successfully treated with early tracheotomy. METHODS: The two patients with acute severe asthma were retrospectively reviewed. They had been treated at the Department of Emergency and Critical Care, Renji Hospital, Shanghai Jiaotong University School of Medicine. RESULTS: They developed progressively hypercapnia and severe acidosis, and were not improved after conventional therapies. Early tracheotomy after mechanical ventilation decreased airway resistance and work of breathing, and corrected hypercapnia and acidosis. Adequate gas exchange was maintained after tracheotomy. The two patients were subsequently weaned from mechanical ventilation and discharged. CONCLUSION: Early tracheotomy could be a valuable approach in certain patients with severe asthma.

Influência do choro e de padrões respiratórios na deposição de medicação inalatória em crianças / The influence of crying and breathing pattern on inhalatory drug deposition in children

OBJETIVO: Verificar a influência do choro e de padrões respiratórios na eficácia da terapia inalatória em crianças. FONTES DE DADOS: busca sistemática por artigos científicos referentes ao tema nas bases de dados Cochrane Controlled Trials Data Base, MedLine e Science Direct, publicadas no período de 1994 a 2009. Utilizaram-se os descritores: "choro", "inalação", "aerossol", "trabalho respiratório" e "criança", nos idiomas português e inglês. SÍNTESE DE DADOS: Foram selecionados 13 artigos, 12 em inglês e um em português. A maioria dos trabalhos apresenta os efeitos da terapia inalatória em crianças, sem discutir a influência do choro e de diferentes padrões respiratórios sobre a deposição da medicação. Estudos que fizeram essa relação verificaram que a respiração e, principalmente, o choro reduzem a quantidade de fármaco que chega às vias aéreas periféricas. Autores discutem as diferenças anatômicas e fisiológicas do sistema respiratório da criança que podem interferir na eficácia da terapia inalatória. Porém, a maioria deles não analisa a influência qualitativa e quantitativa dos padrões respiratórios e do choro sobre a mecânica pulmonar. CONCLUSÕES: O choro e os padrões respiratórios influenciam na terapia inalatória, sendo atribuída ao choro a redução significativa da deposição medicamentosa nas vias aéreas. Pouco se sabe sobre o princípio determinante para a alteração do potencial de deposição, pois são escassas as evidências sobre o tema, apesar de sua relevância no manejo de afecções pulmonares da população pediátrica.

OBJECTIVE: To verify the influence of crying and breathing patterns in the effectiveness of inhalatory therapy in children. DATA SOURCES: Systematic search of scientific studies on the subject in the Cochrane Controlled Trials Database, MedLine and Science Direct, published from 1994 to 2009. The descriptors "crying", "inhalation", "aerosol", "work of breathing" and "child", in Portuguese and in English, were applied. DATA SYNTHESIS: 13 studies were selected, 12 in English and one in Portuguese. Most studies reported the effects of inhalation therapy in children, without discussing the influence of crying and breathing patterns on the deposition of the medication. Studies related to this subject found that the respiratory pattern, especially the cry, reduces the amount of drug that reaches the peripheral airways. Authors discuss the anatomical and physiological differences between adults' and children's respiratory system that may interfere with the effectiveness of inhalation. However, most of them do not examine the qualitative and quantitative influence of the breathing patterns and crying on pulmonary mechanics. CONCLUSIONS: Crying and breathing patterns influence the inhalation therapy. The presence of cry significantly reduces the amount of drug deposition in the airways. There is insufficient evidence about the possible mechanisms that explain potential changes of inhalatory drugs deposition in children, despite its relevance to the management of pediatric pulmonary disorders.

Study on respiratory drive and respiratory function of patients with cerebral infarction / 中华神经科杂志

Objective To detect P0.1 and respiratory function of patients with cerebral infarction(CI)and analyze the effect of cerebral infarction on respiratory function. Methods Arterial blood gases, respiratory drive and lung function were measured in 35 cases with CI and 15 healthy controls. The figures were analyzed by SPSS 10.0. Results The PaO0.2 (mm Hg, 75.80±4.12, 1 mm Hg=0.133 kPa), SaO2(%,94.97±0.78) and Plmax(kPa,4.076±2.443) were lower than those in the healthy control group (88.68±3.77, 96.40±0.48 and 7.747±0.599,t=-8.310,-5.731,-5.439,all P=0.000). P0.1 max and P0.1/MV in the CI group were lower than those in the healthy control group;the P0.1 did not have significant difference in these two group; the P0.1/P0.1max and P0.1/Plmax in the CI group were significantly higher than those in the healthy control group; the PImax was correlated with PO2, O2sat, P(A-a) O2, P0.1max, P0.1, P0.1,/PImax, P0.1/P0.1max, FVC, FEV1.0 and PEF; the PEmax was correlated with P0.1/ PImax, FVC, FEV1.0 and PEF. Conclusion The respiratory function of patients with CI has been impaired, the oxygenated index is cut down and the respiratory drive and respiratory drive store are decreased.

Clinical Comparative Study of Adaptive Support Ventilation and Pressure-controlled Assist/Control Ventilation on Respiratory Failure / 医学研究杂志

Objective To compare adaptive support ventilation (ASV) and pressure-controlled assist/control ventilation (PCMV) and evaluate the clinical effects of ASV. Methods 12 cases of acute respiratory failure patients induced by all causes were selected in the study. All patients with breathing independently underwent endotracheal intubation. The patterns of mechanical ventilation was PCMV-ASV-PCMV. the two settings of PCMV were uniformity. With ASV mode mechanical ventilation,we adjusted the percentage of minute ventilation (MV%) and ideal body weight (IBW) of patients,so as to reach the same minute ventilation volume of PCMV. We compared the blood gas,respiratory mechanics,work of breathing(WOB),airway occlusion pressure (P0.05). Compared with the first of PCMV,various indicators and blood gas of ASV had no significant difference,work of breathing (WOB),airway occlusion pressure (P=0.1) and inspiratory pressure time product (PTP) were significantly lower (P0.05). Conclusion ASV can get similar goals with conventional ventilation,and reduce patient′s effort and the central respiratory drive.

Alteration of Lung Mechanics Depending on Expiratory Sensitivity (ESENS) during Pressure Support Ventilation / 대한구급학회지

BACKGROUND: To evaluate effects of 5 expiratory sensitivity (ESENS) levels (5%; 15%; 25%; 35%; 45%) on lung mechanics and the effects depending on the two P(0.1) levels ( or =3 cm H2O). METHODS: Prospective, randomized, physiologic study for intubated adult patients during weaning from mechanical ventilation. Patients were randomly submitted to the 5 settings of ESENS in the Galileo ventilator (Galileo Gold, Hamilton Medical AG, Switzerland). Physiologic variables were continuously measured using a Bicore CP-100 pulmonary mechanics monitor (CP-100, Bicore, USA). RESULTS: Thirteen patients, ten men and three women, with a mean age of 65.2+/-16.1 yr were studied. Tidal volume (V(T)) decreased significantly from ESENS 5% to 45%. With increasing levels of ESENS, respiratory rates (RR) steadily increased from ESENS 5% to 35% and 45%. Shallow breath index (F/V(T)) increased significantly from ESENS 5% to 45%. Inspiratory time (T(I)) decreased gradually significantly from ESENS 5% to 45%. RR and F/V(T) increased from ESENS 5% to 15% and 45% and V(T) decreased gradually in patients with P(0.1) or =3 cm H2O. CONCLUSIONS: The proper adjustment of expiratory sensitivity (ESENS) levels improved patient-ventilator synchrony and decreased respiratory rates and shallow breath index, especially in P(0.1)<3 cm H2O during PSV in ventilator weaning patients. Lower ESENS level would be more appropriate in terms of lung mechanics in patients with less than 3 cm H2O of P(0.1).

Effect of Fresh Gas Flow on the Work of Breathing of Closed Circuit Anesthesia Using Semiclosed Circuit System / 대한마취과학회지

BACKGOUND: The effect of anesthetic techniques, such as closed circuit anesthesia (CCA) using semiclosed circuit system and semiclosed circuit anesthesia (SCCA), on the work of breathing has not been studied yet in detail. This study was purposed to compare the work of breathing according to anesthetic technique (CCA, SCCA). METHODS: Thirty patients were assigned to receive either SCCA group or CCA group (n = 15). Anesthesia was induced with propofol 2 mg/kg with 2% lidocaine 1 ml. Two percents isoflurane with O2 and N2O 2 L/min were given for 10 min to patients initially to wash in functional residual capacity and the breathing circuits. In SCCA group, anesthesia was maintained with 2% isoflurane in O2 2 L/min and N2O 2 L/min throughout the surgery. In CCA group, O2 was reduced to 200 ml/min and N2O to 100 ml/min with isoflurane vaporizer setting adjusted to 4% for anesthesia maintenance. When the operation was ended, the vaporizer setting of isoflurane deceased to zero and then O2 was increased to 4 L/min for the arousal of the patient. We measured the inspiratory/expiratory concentration of isoflurane, end-tidal CO2, the hemodynamic parameters, the change of airway pressure, the work of breathing, and compliance at anesthetic induction and emergence in both groups. RESULTS: There were no significant differences in the inspiratory/expiratory concentrations of isoflurane, the hemodynamic parameters, end-tidal CO2, airway pressure, the work of breathing and compliance between the groups. CONCLUSIONS: CCA using semiclosed circuit system does not increase the work of breathing compared to SCCA.

Difference in Patient's Work of Breathing Between Pressure-Controlled Ventilation with Deccelerating Flow and Volume-Controlled Ventilation with Constant Flow during Assited Ventilation / 결핵

BACKGROUND: The patient's work of breathing(WOBp) during assisted ventilation may vary according to many factors including ventilatory demand of the patients and applied ventilatory setting by the physician. Pressure-controlled ventilation(PCV) which delivers gas with decelerating flow may better meet patients' demand to improve patientventilator synchrony compared with volume-controlled ventilation(VCV) with constant flow. This study was conducted to compare the difference in WOBp in two assisted modes of ventilation, PCV and VCV with constant flow. METHODS: Ten patients with respiratory failure were included in this study. Initially, the patients were placed on VCV with constant flow at low tidal volume(VT,LOW)(6-8 ml/kg) or high tidal volume(VT,HIGH)(10-12 ml/kg). After a 15 minute stabilization period, VCV with constant flow was switched to PCV and pressure was adjusted to maintain the same tidal volume(VT) received on VCV. Other ventilator settings were kept constant. Before changing the ventilatory mode, WOBp, VT, minute ventilation(VE), respiratory rate(RR), peak airway pressure (Ppeak), peak inspiratory flow rate(PIFR) and pressure-time product(PTP) were measured. RESULTS: The mean VE and RR were not different between PCV and VCV during study period. The Ppeak was significantly lower in PCV than in VCV during VT,HIGH ventilation(p<0.05). PIFR was significantly higher in PCV than in VCV at both VT (p<0.05). During VT,LOW ventilation, WOBp and PTP in PCV(0.80?0.37 J/min, 164.5?74.4 cmH2O.S) were significantly lower than in VCV(1.06+/-0.39J /min, 256.4+/-107.5 cmH2O.S)(p<0.05). During VT,HIGH ventilation, WOBp and PTP in PCV(0.33+/-0.14 J/min, 65.7+/-26.3 cmH2O.S) were also significantly lower than in VCV(0.40+/-0.14 J/min, 83.4+/-35.1 cmH2O.S)(p<0.05). CONCLUSION: During assisted ventilation, PCV with deccelerating flow was more effective in reducing WOBp than VCV with constant flow. But since individual variability was shown, further studies are needed to confirm these results.

Determination of Minimal Pressure Support Level During Weaning from Pressure Support Ventilation / 결핵

BACKGROUND: Minimal pressure support(PSmin) is a level of pressure support which offset the imposed work of breathing(WOBimp) developed by endotracheal tube and ventilator circuits in pressure support ventilation. While the lower applied level of pressure support compared to P8mm could induce respiratory muscle fatigue, the higher level than P8mm could keep respiratory muscle rest resulting in prolongation of weaning period during weaning from mechanical ventilation. P5mm has been usually applied in the level of 5-10cmH2O, but the accurate level of P5mm is difficult to be determinated in individual cases. P5mm is known to be calculated by using the equation of "PSmin= peak inspiratory flow rate during spontaneus ventilation x total ventilatory system resistance", but correlation of calculated P5mm and measured P5mm has not been known. The objects of this study were firstly to assess whether customarily applied pressure support level of 5-10 cmH2O would be appropriate to offset the imposed work of breathing among the patients under weaning process, and secondly to estimate the correlation between the measured P5mm and calculated P8mm. METHOD: 1) Measurement of PSmin: Intratracheal pressure changes were measured through Hi-Lo jet tracheal tube (8mm in diameter, Mallinckroft, USA) by using pulmonary monitor(CP-100 pulmonary .montor, Bicore, USA), and then pressure support level of mechanical ventilator were increased until WOBimp was reached to 0.01 J/L or less. Measured P5mm was defined as the lowest pressure to make WOBimp 0.01 J/L or less. 2) Calculation of PSmin: Peak airway pressure(Ppeak), plateau airway pressure(Pplat) and mean inspiratory flow rate of the subjects were measured on volume control mode of mechanical ventilation after sedation. Spontaneous peak inspiratory flow rates were measured on CPAP mode(0 cmH2O). Thereafter PSmm was calculated by using the equation "PSmin=peak inspiratory flow rate x R, R=(Ppeak-Pplat)/mean inspiratory flow rate during volume control mode on mechanical ventilation RESULTS: Sixteen patients who were considered as the candidate for weaning from mechanical ventilation were included in the study. Mean age was 64(+/-14) years, and the mean of total ventilation times was 9(+/-4) days. All patients except one were males. The measured PSmm of the subjects ranged 4.0-12.5cmH2O in 14 patients. The mean level of PSmm was 7.6(+/-2.5 cmH2O) in measured PSmm, 8.6(+/-3.25 cmH2O) in calculated PSmm. Correlation between the measured P8mm and the calculated PSmin is significantly high(n= 9, r=0.88, p=0.002). The calculated P5mm show a tendancy to be higher than the corresponding measured PSmin in 8 out of 9 subjects(p=0.09). The ratio of measured P5mm/calculated PSmin was 0.81(+/-0.05). CONCLUSION: Minimal pressure support levels were different in individual cases in the range from 4 to 12.5 cmH2O. Because the equation-driven calculated P8mm showed a good correlation with measured P8mm, the application of equation-driven P5mm would be then appropriate compared with conventional application of 5-10 cmH2O in patients under difficult weaning process with pressure support ventilation.

Clinical application of physiologic work of breathing as a respiratory weaning parameter in mechanically ventilated patients / 中华麻醉学杂志

Objective:To evaluate the physiologic work of breathing (WOBphy)as parameter of respiratory weaning and extubation. Method: Patient work of breathing (WOBt) and imposed work of breathing (WOBimp) were measured. WOBphy was obtained with WOBt minuting WOBimp. In the patients who did not meet conventional respiratory weaning parameters ,if WOBphy

The Comparison of Work of Breathing Between Before Extubation and After Extubation of Endotracheal Tube / 결핵

BACKGROUND: Since endotracheal tube is the most important factor involved in the imposed work of breathing during mechanical ventilation, extubation of endotracheal tube is supposed to reduce respiratory work of patient. However, some patients show labored breathing after extubation despite acceptable blood gases. We investigated the changes of work of breathing before and after extubation and the factors involved in the change of WOB after extubation. METHODS: The subjects were 34 patients(M : F = 20 : 14, mean age = 61 l7yre) who recovered from respiratory failure after ventilatory support and were considered to be ready for extubation. The patients with clinical or radiologic evidences of upper airway obstruction before endotracheal intubation for mechanical ventilation were excluded. Vital sign, physical examination, chest X-ray, work of breathing and other respiratory mechanic indices were measured prior to, immediately, 6, 24 and 48 hours after extubation serially. Definition of weaning failure after extubation was resumption of ventilatory support or reintubation of endotracheal tube within 48 hour after extubation because of respiratory failure. The patients were classified into group I (decreased work of breathing), group 2(unchanged work of breathing) and group 3(increased work of breathing) depending on the statistical difference in the change of work of breathing before and after extubation. RESULTS: Work of breathing decreased in 33%(11/34, group 1), unchanged in 41%(14/34, group 2) and increased in 26% (9/34, group 3) of patients after extubation compared with before extubation. Weaning failure occurred 9%(1/11) of group, 1, 28.67(4/14) of group 2 and 44.4%(4/9) of group 3 after extubation(p = 0.07). The change of work of breathing after extubation was positively correlated with change of mean airway resistance(mRaw). (r = 0.794, p> 0.01) In three cases of group 3 whose respiratory indices could be measured until 48 hr ater extubation, the change in work of breathing paralleled with the sequential change of mRaw. The work of breathing was peaked at 6 hr after extubation, which showed a tendency to decrease thereafter. CONCLUSIONS: Reversible increase of work of breathing after extubation may occur in the patients who underwent extubation, and the increase in mRaw could be responsible for the increase in work of breathing. In addition, the risk of weaning failure after extubatuion may increase in the patients who have increased WOB immediately after extubation.

Comparison of Imposed Work of Breathing Between Pressure-Triggered and Flow-Triggered Ventilation During Mechanical Ventilation / 결핵

BACKGROUND: The level of imposed work of breathing (WOB) is important for patient-ventilator synchrony and during weaning from mechanical ventilation. Triggering methods and the sensitivity of demand system are important determining factors of the imposed WOB. Flow triggering method is available on several modem ventilator and is believed to impose less work to a patient-triggered breath than pressure triggering method. We intended to compare the level of imposed WOB on two different methods of triggering and also at different levels of sensitivities on each triggering method (0.7 L/min vs 2.0 L/min on flow triggering ; -1 cmH2O vs -2 cm H2O on pressure triggering). METHODS: The subjects were 12 patients (64.8α4.2 yrs) on mechanical ventilation and were stable in respiratory pattern on CPAP 3 cmH2O. Four different triggering sensitivities were applied at random order. For determination of imposed WOB, tracheal end pressure was measured through the monitoring lumen of Hi-Lo Jet tracheal tube (Mallincrodt, New York, USA) using pneumotachograph/pressure transducer (CP-100 pulmonary monitor, Bicore, Irvine, CA, USA). Other data of respiratory mechanics wert also obtained by CP-100 pulmonary monitor. RESULTS: The imposed WOB was decreased by 37.5% during 0.7 L/min on flow triggering compared to -2 cmH2O on pressure triggering and also decreased by 14% during -1 cmH2O compared to -2 cmH2O on pressure triggering (p<0.05 in each). The PTP(Pressure Time Product) was also decreased significantly during 0.7 L/min on flow triggering and -I cmH2O on pressure triggering compared to -2 cmH2O on pressure triggering(p<0.05 in each). The proportions of imposed WOB in total WOB were ranged from 37% to 85% and no significant changes among different methods and sensitivities. The physiologic WOB showed no significant changes among different triggering methods and sensitivities. CONCLUSION: To reduce the imposed WOB, flow triggering with sensitivity of 0.7 L/min would be better method than pressure triggering with sensitivity of -2 cm H2O.

The oxygen consumption and oxygen cost of breathing before and after thoracotomy / 中华麻醉学杂志

Objective To study the changes in oxygen consumption ( VO2 ) and oxygen cost of breathing(OCB) in postoperative patients and the effects of various kinds of assisted ventilatory support on OCB.Methods Twenty patients (13 male, 7 female), aged 43-70 years, undergoing thoracic surgery were divided into two groups: (A) pulmonary disease(PD) group in which patients had chronic pulmonary disease and abnormal pulmonary function( n = 10); non-pulmonary disease (NPD) group in which patients had no chronic pulmonary disease and their pulmonary function was normal ( n = 10). Operation were performed under combined intravenous-inhalation anesthesia or general-epidural anesthesia. Metabolism of the patients was measured before anesthesia. After operation the patients were mechanically ventilated in ICU and PaCO2 was maintained between 4.6-6.0 kPa. Metabolism was measured 12h after operation when anesthesia had worn off, the patients were fully awake and breathing spontaneously. Their hemodynamics was stable. Body temperature was maintained at 37℃?0.5℃ . VO2 was measured using indirect colorimetry (Datex Deltatrac MBM-200). VO2, VCO2, energy expenditure(EE) and respiratory quotient (RQ) were recorded every minute for 30 min. OCB was calculated by deducting VO2 measured during controlled ventilation from VO2 measured during spontaneous breathing( OCB = VO2 spontaneous breathing - VO2 controlled ventilation) and expressed by OCB/VO2 spontaneous breathing ( % ) . During mechanical ventilation FiO2 was set

The Effect of External PEEP on Work of Breathing in Patients with Auto-PEEP / 결핵

BACKGROUND: Auto-PEEP which develops when expiratory lung emptying is not finished until the beginning of next inspiration is frequently found in patients on mechanical ventilation. Its presence imposes increased risk of barotrauma and hypotension, as well as increased work of breathing (WOB) by adding inspiratory threshold load and/or adversely affecting to inspiratory trigger sensitivity. The aim of this study is to evaluate the relationship of auto-PEEP with WOB and to evaluate the effect of PEEP applied by ventilator (external PEEP) on WOB in patients with auto-PEEP. METHOD: 15 patients, who required mechanical ventilation for management of acute respiratory failure, were studied. First, the differences in WOB and other indices of respiratory mechanics were examined between 7 patients with auto-PEEP and 8 patients without auto-PEEP. Then, we applied the 3 cm H2O of external PEEP to patients with auto-PEEP and evaluated its effects on lung mechanics as well as WOB. Indices of respiratory mechanics including tidal volume (V(T)), repiratory rate, minute ventilation (V(E)), peak inspiratory flow rate (PIFR), peak expiratory flow rate (PEFR), peak inspiratory pressure (PIP), T(I)/T(TOT), auto-PEEP, dynamic compliance of lung (Cdyn), expiratory airway resistance (RAWe), mean airway resistance (RAWm), P(0.1), work of breathing performed by patient (WOB), and pressure-time product (PTP) were obtained by CP-100 Pulmonary Monitor (Bicore,USA). The values were expressed as meanSEM (standard error of mean). RESULTS: 1) Comparison of WOB and other indices of respiratory mechanics in patients with and without auto-PEEP: There was significant increase in WOB (1.71 +/-0.24 vs 0.500.19 J/L, p=0.007), PTP (317+/-70 vs 98+/-36 cm H2O * sec/min, p=0.023), RAWe (35.6+/-5.7 vs 18.2+/-2.3 cm H20/L/sec, p=0.023), RAWm (28.8+/-2.5 vs 11.9+/-2.0 cm H2O/L/sec, p=0.001) and P0.1 (6.21.0 vs 2.9+0.6 cm H2O, p=0.021) in patients with auto-PEEP compared to patients without auto-PEEP. The differences of other indices including V(T), PEFR, V(E) and T(I)/T(TOT) showed no significance. 2) Effect of 3 cm H2O external PEEP on respiratory mechanics in patients with auto-PEEP: When 3 cm H2O of external PEEP was applied, there were significant decrease in WOB (1.71+/-0.24 vs 1.20+/-0.21 J/L, p=0.021) and PTP (317+/-70 vs 231+/-55 cm H2O * sec/min, p=0.038). RAWm showed a tendency to decrease (28.8+/-2.5 vs 23.9+/-2.1 cm H2O, p=0.051). But PIP was increased with application of 3 cm H2O of external PEEP (16+/-2 vs 22+/-3 cm H2O, p=0.008). V(T), V(E), PEFR, T(I)/T(TOT) and Cdyn did not change significantly. CONCLUSION: The presence of auto-PEEP in mechanically ventilated patients was accompanied with increased WOB performed by patient, and this WOB was decreased by 3 cm H2O of externally applied PEEP. But, with 3 cm H2O of external PEEP, increased PIP was noted, implying the importance of close monitoring of the airway pressure during application of external PEEP.