RESUMEN

BACKGROUND: Internal redistribution of gas, referred to as pendelluft, is a new potential mechanism of effort-dependent lung injury. Neurally-adjusted ventilatory assist (NAVA) and proportional assist ventilation (PAV +) follow the patient's respiratory effort and improve synchrony compared with pressure support ventilation (PSV). Whether these modes could prevent the development of pendelluft compared with PSV is unknown. We aimed to compare pendelluft magnitude during PAV + and NAVA versus PSV in patients with resolving acute respiratory distress syndrome (ARDS). METHODS: Patients received either NAVA, PAV + , or PSV in a crossover trial for 20-min using comparable assistance levels after controlled ventilation (> 72 h). We assessed pendelluft (the percentage of lost volume from the non-dependent lung region displaced to the dependent region during inspiration), drive (as the delta esophageal swing of the first 100 ms [ΔPes 100 ms]) and inspiratory effort (as the esophageal pressure-time product per minute [PTPmin]). We performed repeated measures analysis with post-hoc tests and mixed-effects models. RESULTS: Twenty patients mechanically ventilated for 9 [5-14] days were monitored. Despite matching for a similar tidal volume, respiratory drive and inspiratory effort were slightly higher with NAVA and PAV + compared with PSV (ΔPes 100 ms of -2.8 [-3.8--1.9] cm H2O, -3.6 [-3.9--2.4] cm H2O and -2.1 [-2.5--1.1] cm H2O, respectively, p < 0.001 for both comparisons; PTPmin of 155 [118-209] cm H2O s/min, 197 [145-269] cm H2O s/min, and 134 [93-169] cm H2O s/min, respectively, p < 0.001 for both comparisons). Pendelluft magnitude was higher in NAVA (12 ± 7%) and PAV + (13 ± 7%) compared with PSV (8 ± 6%), p < 0.001. Pendelluft magnitude was strongly associated with respiratory drive (ß = -2.771, p-value < 0.001) and inspiratory effort (ß = 0.026, p < 0.001), independent of the ventilatory mode. A higher magnitude of pendelluft in proportional modes compared with PSV existed after adjusting for PTPmin (ß = 2.606, p = 0.010 for NAVA, and ß = 3.360, p = 0.004 for PAV +), and only for PAV + when adjusted for respiratory drive (ß = 2.643, p = 0.009 for PAV +). CONCLUSIONS: Pendelluft magnitude is associated with respiratory drive and inspiratory effort. Proportional modes do not prevent its occurrence in resolving ARDS compared with PSV.

RESUMEN

Information about respiratory mechanics such as resistance, elastance, and muscular pressure is important to mitigate ventilator-induced lung injury. Particularly during pressure support ventilation, the available options to quantify breathing effort and calculate respiratory system mechanics are often invasive or complex. We herein propose a robust and flexible estimation of respiratory effort better than current methods. We developed a method for non-invasively estimating breathing effort using only flow and pressure signals. Mixed-integer quadratic programming (MIQP) was employed, and the binary variables were the switching moments of the respiratory effort waveform. Mathematical constraints, based on ventilation physiology, were set for some variables to restrict feasible solutions. Simulated and patient data were used to verify our method, and the results were compared to an established estimation methodology. Our algorithm successfully estimated the respiratory effort, resistance, and elastance of the respiratory system, resulting in more robust performance and faster solver times than a previously proposed algorithm that used quadratic programming (QP) techniques. In a numerical simulation benchmark, the worst-case errors for resistance and elastance were 25% and 23% for QP versus <0.1% and <0.1% for MIQP, whose solver times were 4.7 s and 0.5 s, respectively. This approach can estimate several breathing effort profiles and identify the respiratory system's mechanical properties in invasively ventilated critically ill patients.

Asunto(s)

RESUMEN

Optimal fluid management is critical during mechanical ventilation to mitigate lung damage. Under normovolemia and protective ventilation, pulmonary tensile stress during pressure-support ventilation (PSV) results in comparable lung protection to compressive stress during pressure-controlled ventilation (PCV) in experimental acute lung injury (ALI). It is not yet known whether tensile stress can lead to comparable protection to compressive stress in ALI under a liberal fluid strategy (LF). A conservative fluid strategy (CF) was compared with LF during PSV and PCV on lungs and kidneys in an established model of ALI. Twenty-eight male Wistar rats received endotoxin intratracheally. After 24 h, they were treated with CF (minimum volume of Ringer's lactate to maintain normovolemia and mean arterial pressure ≥70 mmHg) or LF (~4 times higher than CF) combined with PSV or PCV (VT  = 6 ml/kg, PEEP = 3 cmH2 O) for 1 h. Nonventilated animals (n = 4) were used for molecular biology analyses. CF-PSV compared with LF-PSV: (1) decreased the diffuse alveolar damage score (10 [7.8-12] vs. 25 [23-31.5], p = 0.006), mainly due to edema in axial and alveolar parenchyma; (2) increased birefringence for occludin and claudin-4 in lung tissue and expression of zonula-occludens-1 and metalloproteinase-9 in lung. LF compared with CF reduced neutrophil gelatinase-associated lipocalin and interleukin-6 expression in the kidneys in PSV and PCV. In conclusion, CF compared with LF combined with PSV yielded less lung epithelial cell damage in the current model of ALI. However, LF compared with CF resulted in less kidney injury markers, regardless of the ventilatory strategy.

Asunto(s)

RESUMEN

BACKGROUND: In patients with emphysema, invasive mechanical ventilation settings should be adjusted to minimize hyperinflation while reducing respiratory effort and providing adequate gas exchange. We evaluated the impact of pressure-controlled ventilation (PCV) and pressure support ventilation (PSV) on pulmonary and diaphragmatic damage, as well as cardiac function, in experimental emphysema. METHODS: Emphysema was induced by intratracheal instillation of porcine pancreatic elastase in Wistar rats, once weekly for 4 weeks. Control animals received saline under the same protocol. Eight weeks after first instillation, control and emphysema rats were randomly assigned to PCV (n = 6/each) or PSV (n = 6/each) under protective tidal volume (6 ml/kg) for 4 h. Non-ventilated control and emphysema animals (n = 6/group) were used to characterize the model and for molecular biology analysis. Cardiorespiratory function, lung histology, diaphragm ultrastructure alterations, extracellular matrix organization, diaphragmatic proteolysis, and biological markers associated with pulmonary inflammation, alveolar stretch, and epithelial and endothelial cell damage were assessed. RESULTS: Emphysema animals exhibited cardiorespiratory changes that resemble human emphysema, such as increased areas of lung hyperinflation, pulmonary amphiregulin expression, and diaphragmatic injury. In emphysema animals, PSV compared to PCV yielded: no changes in gas exchange; decreased mean transpulmonary pressure (Pmean,L), ratio between inspiratory and total time (Ti/Ttot), lung hyperinflation, and amphiregulin expression in lung; increased ratio of pulmonary artery acceleration time to pulmonary artery ejection time, suggesting reduced right ventricular afterload; and increased ultrastructural damage to the diaphragm. Amphiregulin correlated with Pmean,L (r = 0.99, p < 0.0001) and hyperinflation (r = 0.70, p = 0.043), whereas Ti/Ttot correlated with hyperinflation (r = 0.81, p = 0.002) and Pmean,L (r = 0.60, p = 0.04). CONCLUSIONS: In the model of elastase-induced emphysema used herein, PSV reduced lung damage and improved cardiac function when compared to PCV, but worsened diaphragmatic injury.

RESUMEN

BACKGROUND: Evidence exists that during pressure support ventilation (PSV), the addition of an extrinsic (ie, ventilator-generated) breath-to-breath variability (BBV) of breathing pattern improves respiratory function. If BBV is beneficial per se, choosing the PS level that maximizes it could be considered a valid strategy for conventional PSV. In this study, we evaluated the effect of different PS levels on intrinsic BBV in acutely ill, mechanically ventilated subjects to determine whether a significant relationship exists between PS level and BBV magnitude. METHODS: Fourteen invasively mechanically ventilated subjects were prospectively studied. PS was adjusted at 20 cm H2O and sequentially reduced to 15, 10, and 5 cm H2O. Arterial blood gas analysis and pressure at 0.1 s after the onset of inspiration (P0.1) were measured at each PS level. Airway and esophageal pressure and air flow were continuously recorded. Peak inspiratory flow, tidal volume (VT), breathing frequency, and pressure-time product (PTP) were calculated on a breath-by-breath basis. The breathing pattern variability was assessed by the coefficient of variation of the time series of VT, peak inspiratory flow, and breathing frequency from ∼ 60 consecutive breath cycles at each PS level. A general linear model for repeated measures was applied, with PS as an independent factor. A significance level of .05 was considered. RESULTS: Despite a large inter-individual difference in all measured variables (P < .001), the coefficient of variation was as low as 30%, and no significant differences in the coefficient of variation of peak inspiratory flow, breathing frequency, and VT between PS levels were observed (P > .15). Additionally, a significant increase in P0.1, PTP, and breathing frequency (P < .01) and a reduction in VT (P < .001) were observed with PS reduction. CONCLUSIONS: Despite a significant increase in spontaneous activity with PS reduction, BBV was not influenced by the PS level and was as low as 30% for all evaluated parameters.

Asunto(s)

RESUMEN

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

Asunto(s)

RESUMEN

Introdução: O principal objetivo da ventilação mecânica é a diminuição do trabalho respiratório. Para que isto ocorra, o ciclo mecânico deveria coincidir com o tempo inspiratório neural do paciente. A assincronia paciente ventilador ocorre por fatores relacionados ao paciente e aos parâmetros ventilatórios e podem prolongar o tempo de suporte mecânico e permanência em unidades de terapia intensiva. Objetivos: Revisar a assincronia nas diferentes fases do ciclo respiratório, sua avaliação através dos gráficos e as intervenções capazes de melhorar a interação paciente ventilador em ventilação por pressão de suporte. Resultados/ Discussão: Através de busca em base de dados científicos, foram incluídos 26 artigos que abordavam o tema proposto. Os diferentes tipos de assincronia podem ser observados através de esforços ineficientes, atrasos no disparo, disparos automáticos, disparos duplos, presença de PEEP intrínseca, términos prematuro ou prolongado da inspiração e curvas diferentes do padrão usual. Conclusão: A correta identificação e ajustes conforme a demanda do paciente são pontos importantes na interação paciente ventilador e podem contribuir para a melhora do prognóstico destes pacientes.(AU)

Introduction: The main reason of mechanical ventilation is the decrease the work of breathing. To achieve it, the mechanical breath should coincide with the neural inspiratory time. Patient-ventilator asynchrony may be secondary for the facts related to the patient´s condition or ventilatory settings and may prolong support and UTI stay. Objectives: Review asynchrony in different phases of mechanical breath, the evaluation through ventilator waveforms and the proper settings to improve patient-ventilator interaction in pressure support ventilation. Results/ Discussion: Through research on scientific basis, 26 studies that match the theme were included. Asynchrony may be seen as inefficient efforts, trigger delay, auto-triggering, double triggering, presence of auto-PEEP, premature termination, delayed termination or unusual waveforms. Conclusion: Proper identification and adjustments that coincides with patient´s demand are critical points in patient ventilator interaction and may contribute to improve their prognosis.(AU)

Asunto(s)

RESUMEN

JUSTIFICATIVA E OBJETIVOS: Esta pesquisa justifica-se na necessidade de maior conhecimento a respeito das técnicas de desmame ventilatório utilizadas em pacientes sob ventilação mecânica prolongada. O objetivo deste estudo foi comparar a obtenção do índice de respiração rápida e superficial (IRRS) nas modalidades PSV de 10 cmH2O e PEEP de 5 cmH2O (PSV10); CPAP de 5 cmH2O (CPAP5) e em ventilação espontânea (ESP), correlacionando com sucesso ou insucesso na retirada da ventilação mecânica (VM). MÉTODO: Estudo prospectivo incluindo 54 pacientes em VM há mais de 48 horas, submetidos ao IRRS em três modos ventilatórios: PSV10, CPAP5 e ESP nos momentos pré e pós-nebulização, utilizando tubo-T. Os pacientes foram retirados da VM quando o IRRS era < 105. RESULTADOS: Não houve diferença estatisticamente significativa entre os valores do IRRS obtidos nos momentos pré e pós-nebulização. Houve diferença estatística significativa dos valores do IRRS entre CPAP5 e PSV10 (p = 0,008) e entre a modalidade ESP e PSV10 (p = 0,01) no momento pré-nebulização e dos valores do IRRS obtidos entre CPAP5 e PSV10 (p = 0,01) no momento pós-nebulização. CONCLUSÕES: Neste estudo pode-se observar que o valor do IRRS foi superestimado quando obtido na modalidade PSV10. Foi constatado também que não houve necessidade de nebulização de 30 minutos antes da extubação traqueal quando o desmame é realizado com a técnica de redução gradativa da PSV. Este estudo sugeriu que o IRRS foi capaz de prever o sucesso do desmame; entretanto, incapaz de determinar o insucesso quando seu valor fosse < 105. Recomenda-se que o IRRS seja analisado em associação com outros parâmetros preditivos de desmame.

BACKGROUND AND OBJECTIVES: To compare the attainment of the rapid shallow breathing index (IRRS) in modalities PSV 10 cmH2O and PEEP 5 cmH2O (PSV10), CPAP 5 cmH2O (CPAP5) and spontaneous breathing (SB), correlating them with success on failure in the withdrawal of mechanical ventilation (MV). METHODS: Prospective study including 54 patients in MV > 48 hours, submitted to the IRRS in three ventilatory modalities: PSV10, CPAP5 and SB at the moments before and after T-tube spontaneous breathing. The patients were removed from MV when IRRS was < 105. RESULTS: There wasn't statistically significant difference between IRRS values at the moments before and after T-tube SB. There was statistically significant difference IRRS value between the modalities CPAP5 and PSV10 (p = 0.008), and between the modalities SB and PSV10 (p = 0.01) at the moment before T-Tube SB and of IRRS value, gotten between CPAP5 and PSV10 (p = 0.01) at the moment after T-tube SB. CONCLUSIONS: From this sample, it can be observed that IRRS values are overestimated when gotten in modality PSV10. It was also evidenced that there is no need of a 30 min T-tube SB before extubation, when the weaning is performed with the technique of gradual reduction of PSV. This study suggested that IRRS is able to predict weaning success; however it is not able to determine failure when it was < 105. It is recommended that IRRS must be analyzed in association with other predictive weaning parameters.

Asunto(s)

RESUMEN

JUSTIFICATIVA E OBJETIVOS: A retirada precoce da ventilação mecânica dos pacientes das unidades de terapia intensiva (UTI) é importante para a redução da morbimortalidade, porém na prática, os desmames são realizados aleatoriamente. Face à importância desse procedimento, esse estudo avaliou a implementação de protocolos de desmame e comparou dois métodos distintos. MÉTODO: Foram incluídos no estudo 120 pacientes dependentes de ventilação mecânica por mais de 48 horas. O método de Pressão Suporte + PEEP (PSP), foi aplicado aos pacientes em dias pares, constituindo o grupo 1 (GPSP) e em dias ímpares, utilizou-se o método do Tubo-T (TT), formando o grupo 2 (GTT), RESULTADOS: A resposta dos pacientes à extubação revelou evolução semelhante nos dois grupos, porém deixou claro, pela análise estatística do teste Qui-quadrado, o benefício de se utilizar um protocolo de desmame. De todos os pacientes estudados, 109 (90,83 por cento) tiveram sucesso na extubação não sendo necessário nenhum tipo de ventilação não-invasiva dentro de 24 horas após o desmame, enquanto que apenas 11 pacientes (9,17 por cento) necessitaram de ventilação mecânica não-invasiva ou de re-intubação no mesmo período, caracterizando o insucesso do desmame. CONCLUSÕES: A implementação e a padronização de protocolos de desmame da ventilação mecânica, reduziu significativamente o índice de re-intubação na UTI, diminuindo o período de internação e o índice de morbimortalidade, porém neste estudo, não foram encontradas diferenças estatísticas significativas entre os métodos analisados.

BACKGROUND AND OBJECTIVES: Mechanical ventilation incurs significant morbidity and mortality, weaning intensive care unit patients is highly desirable, although it is usuallyconducted in an empirical manner. Thus, this article assessed a weaning protocol implementation and compared two different methods. METHODS: It was carried out a study involving 120 patients who had received mechanical ventilation for more than 48 hours. These patients were randomlyassigned to undergo one of two weaning techniques: pressure-supportventilation + PEEP (PSP) technique, which was applied to the patients in equal days, forming the PSP group (PSPG) and the T-tube method (TT), applied in odd days and forming the TT group (TTG). Standardized protocols were followedfor each technique RESULTS: The patients response to extubation revealed similar progress in both PSP and TT groups, but after the Chi-square statistical test, the benefits of using a weaning protocol was clear. One hundred nine (90.83 percent) of all patients, had a successful weaning and any noninvasive ventilation type was needed in a span time of 24 hours after extubation, and only eleven (9.17 percent), had an unsuccessful weaning. CONCLUSIONS: Although this study didn't show any difference between the two methods applied, we could conclude that, the implementation of standardized weaning protocols can substantially decrease the patient's reintubation rate, promoting a downward trend in mortality and morbidity for these patients and shortening their hospital and intensive care units length of stay.

Asunto(s)