Comparing three protective mechanical ventilation strategies, HFOV, low-frequency-ventilation, and low-frequency-ventilation with TGI, in an ARDS experimental model

Introdução: Um dos principais objetivos na SARA é encontrar a melhor estratégia protetora de ventilação mecânica que minimize o stress pulmonar e otimize as trocas gasosas. Teoricamente, estas duas metas podem ser obtidas simultaneamente, evitando-se a hiperdistensão e colapso cíclico de unidades alveolares instáveis. Numa tentativa de radicalizar a minimização da hiperdistensão e da pressão motriz inspiratória, duas estratégias podem ser propostas: o uso da ventilação de alta freqüência oscilatória (HFOV) e o uso da insuflação intra-traqueal de gás (TGI), esta última associada à hipercapnia permissiva e baixas freqüências respiratórias. Objetivo: identificar qual (quais) entre as três estratégias de ventilação mecânica, HFOV, TGI e ventilação protetora de baixa freqüência (VP: volume corrente ~6 mL/kg), foi (foram) a (s) mais protetora (s) em um modelo de SARA em coelhos, durante seis horas de ventilação mecânica. Material e métodos: Os animais (n = 45) foram submetidos a repetidas lavagens pulmonar até uma PaO2 < 100 mmHg. Imediatamente após a injuria pulmonar, foi obtida uma curva P/V para calculo do trabalho inspiratório e energia dissipada durante insuflação pulmonar. Em seguida, os animais foram randomizados em um dos três grupos: HFOV, VP ou TGI. O PEEP ou PMEAN ideais foram obtidos através de uma curva PEEP/PaO2 (ou PMEAN/PaO2) que foi precedida por uma manobra de recrutamento. Os animais dos grupos VP e TGI foram inicialmente ventilados em PCV com um delta de pressão = 8 cmH2O e freqüência = 60 resp/min. A única diferença inicial entre os dois foi que o grupo TGI possuía um fluxo traqueal continuo = 1 L/min. Os animais do grupo HFOV foram inicialmente ventilados com uma amplitude de pressão = 45 cmH2O e freqüência = 10 Hz. Todos os animais foram ventilados com uma FiO2 = 1.0. Os deltas de pressão (ou pressão motriz) nos grupos VP e TGI foram reajustados para manter uma PaCO2 = 90-110 mmHg, enquanto no HFOV a amplitude de pressão foi reajustada para manter uma PaCO2 = 45-55 mmHg. No final do experimento, outra curva P/V foi obtida. Amostras do LBA e sangue foram coletados antes e após o período de ventilação para determinar os níveis de IL-8. Amostras do pulmão esquerdo foram processadas para análise histológica e para cálculo da relação peso-úmido/ peso-seco. Resultados: Não foi observada diferença na PaO2 entre os grupos. A PaCO2 foi significantemente menor no grupo HFOV (59 ± 3 mmHg) quando comparado aos grupos VP (99 ± 4 mmHg) e TGI (80 ± 3 mmHg). O volume corrente foi significantemente menor nos grupos TGI e HFOV quando comparado ao grupo VP. Logo após a lesão pulmonar, todos os grupos necessitaram de trabalhos similares para a insuflação pulmonar, mas o grupo VP foi o único que não apresentou melhora (diminuição) deste trabalho expiratório, a estratégia VP foi a única que apresentou aumento ao longo das 6 horas (P<0,001). Os grupos TGI e HFOV também apresentaram maiores concentrações de polimorfonucleares no tecido pulmonar (P=0,008) e tendências a favorecer um maior índice superfície/volume (P=0,14), maior gradiente IL-8 (diferença ente IL-8 no LBA e plasma - P=0,08) e menor relação peso-úmido/peso-seco (P=0,17) ao final das 6 horas de ventilação. Discussão: O menor trabalho requerido na insuflação pulmonar depois de 6 horas de ventilação refletiu uma redução nas pressões críticas de abertura e, provavelmente, uma melhora do edema pulmonar e do sistema surfactante nas estratégias HFOV e TGI. O aumento do trabalho expiratório no grupo VP sugere, inclusive, uma deterioração na qualidade do surfactante neste grupo. Nos grupos TGI e HFO, a maior concentração de polimorfonucleares no tecido pulmonar e a tendência a apresentar maior gradiente de IL8 poderiam se interpretados como uma melhor membrana alvéolo-capilar, resultando na menor liberação de mediadores compartimentalizados no interior dos alvéolos. Além de necessitar volumes correntes mais altos, a estratégia VP necessitou de pressões inspiratórias progressivamente mais altas durante as seis horas de protocolo, devido a reajustes freqüentes, necessários à manutenção das trocas gasosas. Conclusão: Uma redução mais radical das pressões motrizes demonstrou efeitos benéficos num modelo de lesão pulmonar aguda experimental, mesmo quando associada a uma estratégia que já prioriza o recrutamento pulmonar ótimo. O TGI mostrou ser uma alternativa viável à HFOV, apresentando algumas vantagens práticas de implementação e em termos de previsibilidade de resposta nas trocas gasosas.Introduction: One of the major goals in ARDS is to find the best protective mechanical ventilation strategy, which minimizes lung stress and optimizes gas exchange. Theoretically, these two goals can be accomplished by simultaneously avoiding alveolar overdistension and cyclic collapse of unstable alveolar units. Pushing further the rationale of this strategy, two new strategies have been proposed: high frequency oscillatory mechanical ventilation (HFOV) and intra-tracheal gas insufflation (TGI) associated with permissive hypercapnia and conventional frequencies. Objective: To determine which of the three protective modalities of mechanical ventilation, HFOV, low-frequency-protective ventilation (LFV), or LFV associated with tracheal gas insufflation (TGI), was the most protective strategy in an ARDS rabbit model during six hours of mechanical ventilation. Material and methods: The animals (n = 45) were submitted to repeated saline lavage until PaO2 < 100 mmHg. Immediately after lung injury, a P/V curve was obtained to calculate inspiratory/expiratory work and energy dissipated during lung inflation. Thereafter, the animals were randomized into one of three groups: LFV, HFOV or TGI. The optimal PEEP or PMEAN was obtained during a PEEP/PaO2 (or PMEAN/PaO2) curve which was preceded by a recruiting maneuver. The animals of the LFV and TGI groups were initially ventilated in PCV with diving pressure = 8 cmH2O and frequency = 60 b/m. The only initial difference between these two arms was that the TGI group had a continuous tracheal flow = 1 L/min. The animals in the HFOV were initially ventilated with an oscillatory pressure amplitude = 45 cmH2O and frequency = 10 Hz. All animals were ventilated with FiO2 = 1.0. Driving pressure was then adjusted in LFV and TGI groups to maintain a PaCO2 = 90-110 mmHg, while in HFO the pressure amplitude was adjusted to maintain a PaCO2 = 45-55 mmHg. At the end of the experiment, after 6 hours of ventilation, another P/V curve was obtained. BAL and bloods samples were drawn before and after the period of ventilation to determine IL-8 levels. The left lung was processed for histological analysis and for wet weight/dry weight (ww/dw) ratio. Results: We observed no differences in PaO2 among the groups. PaCO2 was significantly lower at HFO (59 ± 3 mmHg) when compared with LFV (99 ± 4 mmHg) and TGI (80 ± 3 mmHg) groups. Tidal volume was significantly lower in TGI and HFO groups when compared with LFV group. Soon after injury, all groups required similar energy for lung inflation (inspiratory work), but the VP group was the only one not presenting any improvement in this parameter after 6 hours (P<0.001). Concerning the expiratory work, the VP strategy was the only one presenting an increase in the expiratory work along the 6 hours (P<0.001). The TGI and HFOV groups showed the highest polymorphonuclear cell concentration in lung tissue (P=0.008) and trends towards a higher surface/volume index (P=0.14), higher IL8 gradient (difference between IL8 in BAL and plasma) and lower ww/dw ratio at the end of 6 hours of ventilation (P=0.17). Discussion: The lower energy for lung inflation after six hours of ventilation reflected the reduction of opening pressures and better surfactant function during ventilation under TGI and HFOV strategies. The increase in expiratory work during the VP strategy further suggests that the surfactant quality deteriorated under this strategy. In the TGI and HFOV groups, the higher concentration of polymorphonuclear cells and the trend towards a higher IL8 gradient between the lung and blood may suggest a better integrity of the alveolar-capillary membrane, leading to less release of compartmentalized mediators within the alveolar space. Besides the higher tidal volumes used during VP, this strategy required inspiratory pressures progressively higher along the hours, due to frequent and necessary adjustments of tidal volumes or pressures according to the gas-exchange requirements. Conclusion: An aggressive reduction of tidal volume and driving pressures was beneficial during protective strategies, even when an optimization of lung recruitment was already in place. The TGI strategy showed to be an attractive alternative to HFOV, presenting some advantages in terms of implementation and predictability of response

Influence of inspiratory muscle training on weaning patients from mechanical ventilation: a systematic review

Introduction: The inability of respiratory muscles to generate force and endurance is recognized as an important cause of failure in weaning patients from invasive mechanical ventilation (IMV). Thus, inspiratory muscle training (IMT) might be an interesting treatment option for patients with prolonged IMV weaning. Objective: The aim of this systematic literature review was to evaluate the effectiveness of inspiratory muscle training in weaning patients from mechanical ventilation and to identify the most effective type of training for this particular purpose. Methods: We searched PubMed, LILACS, PEDro and Web of Science for randomized clinical trials published in English or Portuguese from January 1990 until March 2015. Results: Eighty-nine studies were identified of which five were selected. A total of 267 patients participated in the five randomized clinical trials analyzed here. IMV duration before onset of training varied greatly among subjects. Three studies performed IMT using a threshold device and two studies used adjustments of ventilator pressure sensitivity. Four studies have shown that IMT resulted in a significant increase in inspiratory maximal pressure. Only two studies, however, have reported that IMT resulted in higher success rates in weaning patients from IMV. One study has found that patients showed a shorter ventilator weaning duration after IMT. Conclusion: IMT using pressure threshold devices results in increased inspiratory muscle strength and can therefore be considered a more effective treatment option and with the potential to optimize ventilator weaning success in patients at risk of prolonged IMV

Influence of inspiratory muscle training on weaning patients from mechanical ventilation: a systematic review

Abstract Introduction: The inability of respiratory muscles to generate force and endurance is recognized as an important cause of failure in weaning patients from invasive mechanical ventilation (IMV). Thus, inspiratory muscle training (IMT) might be an interesting treatment option for patients with prolonged IMV weaning. Objective: The aim of this systematic literature review was to evaluate the effectiveness of inspiratory muscle training in weaning patients from mechanical ventilation and to identify the most effective type of training for this particular purpose. Methods: We searched PubMed, LILACS, PEDro and Web of Science for randomized clinical trials published in English or Portuguese from January 1990 until March 2015. Results: Eighty-nine studies were identified of which five were selected. A total of 267 patients participated in the five randomized clinical trials analyzed here. IMV duration before onset of training varied greatly among subjects. Three studies performed IMT using a threshold device and two studies used adjustments of ventilator pressure sensitivity. Four studies have shown that IMT resulted in a significant increase in inspiratory maximal pressure. Only two studies, however, have reported that IMT resulted in higher success rates in weaning patients from IMV. One study has found that patients showed a shorter ventilator weaning duration after IMT. Conclusion: IMT using pressure threshold devices results in increased inspiratory muscle strength and can therefore be considered a more effective treatment option and with the potential to optimize ventilator weaning success in patients at risk of prolonged IMV

Effects of manual chest compression on expiratory flow bias during the positive end-expiratory pressure-zero end-expiratory pressure maneuver in patients on mechanical ventilation

ABSTRACT Objective: To investigate the effects of manual chest compression (MCC) on the expiratory flow bias during the positive end-expiratory pressure-zero end-expiratory pressure (PEEP-ZEEP) airway clearance maneuver applied in patients on mechanical ventilation. The flow bias, which influences pulmonary secretion removal, is evaluated by the ratio and difference between the peak expiratory flow (PEF) and the peak inspiratory flow (PIF). Methods: This was a crossover randomized study involving 10 patients. The PEEP-ZEEP maneuver was applied at four time points, one without MCC and the other three with MCC, which were performed by three different respiratory therapists. Respiratory mechanics data were obtained with a specific monitor. Results: The PEEP-ZEEP maneuver without MCC was enough to exceed the threshold that is considered necessary to move secretion toward the glottis (PEF − PIF difference > 33 L/min): a mean PEF − PIF difference of 49.1 ± 9.4 L/min was achieved. The mean PEF/PIF ratio achieved was 3.3 ± 0.7. Using MCC with PEEP-ZEEP increased the mean PEF − PIF difference by 6.7 ± 3.4 L/min. We found a moderate correlation between respiratory therapist hand grip strength and the flow bias generated with MCC. No adverse hemodynamic or respiratory effects were found. Conclusions: The PEEP-ZEEP maneuver, without MCC, resulted in an expiratory flow bias superior to that necessary to facilitate pulmonary secretion removal. Combining MCC with the PEEP-ZEEP maneuver increased the expiratory flow bias, which increases the potential of the maneuver to remove secretions

Estudo experimental sobre a eficiência e segurança da manobra de hiperinsuflação manual como técnica de remoção de secreção Experimental study on the efficiency and safety of the manual hyperinflation maneuver as a secretion clearance technique

OBJETIVO: Avaliar, em um modelo pulmonar simulando um paciente sob ventilação mecânica, a eficiência e a segurança da manobra de hiperinsuflação manual (HM) com o intuito de remover secreção pulmonar. MÉTODOS: Oito fisioterapeutas utilizaram um ressuscitador manual autoinflável para realizar HM com o objetivo de remover secreções, em duas condições: conforme rotineiramente aplicada durante sua prática clínica, e após receberem instruções verbais baseadas em recomendações de especialistas. Três cenários clínicos foram simulados: função pulmonar normal, doença pulmonar restritiva e doença pulmonar obstrutiva. RESULTADOS: Antes da instrução, o uso de duas compressões sequenciais do ressuscitador era comum, e a pressão proximal (Pprox) foi mais alta em relação à obtida após a instrução. Entretanto, a pressão alveolar (Palv) nunca excedeu 42,5 cmH2O (mediana, 16,1; intervalo interquartil [IQ], 11,7-24,5), mesmo com valores de Pprox de até 96,6 cmH2O (mediana, 36,7; IQ, 22,9-49,4). O volume corrente (VC) gerado foi relativamente pequeno (mediana, 640 mL; IQ, 505-735) e o pico de fluxo inspiratório (PFI) geralmente excedeu o pico de fluxo expiratório (PFE): 1,37 L/s (IQ, 0,99-1,90) e 1,01 L/s (IQ, 0,55-1,28), respectivamente. Uma relação PFI/PFE OBJECTIVE: To evaluate, in a lung model simulating a mechanically ventilated patient, the efficiency and safety of the manual hyperinflation (MH) maneuver as a means of removing pulmonary secretions. METHODS: Eight respiratory therapists (RTs) were asked to use a self-inflating manual resuscitator on a lung model to perform MH as if to remove secretions, under two conditions: as routinely applied during their clinical practice; and after receiving verbal instructions based on expert recommendations. In both conditions, three clinical scenarios were simulated: normal lung function, restrictive lung disease, and obstructive lung disease. RESULTS: Before instruction, it was common for an RT to compress the resuscitator bag two times, in rapid succession. Proximal pressure (Pprox) was higher before instruction than after. However, alveolar pressure (Palv) never exceeded 42.5 cmH2O (median, 16.1; interquartile range [IQR], 11.7-24.5), despite Pprox values as high as 96.6 cmH2O (median, 36.7; IQR, 22.9-49.4). The tidal volume (VT) generated was relatively low (median, 640 mL; IQR, 505-735), and peak inspiratory flow (PIF) often exceeded peak expiratory flow (PEF), the median values being 1.37 L/s (IQR, 0.99-1.90) and 1.01 L/s (IQR, 0.55-1.28), respectively. A PIF/PEF ratio < 0.9 (which theoretically favors mucus migration toward the central airways) was achieved in only 16.7% of the maneuvers. CONCLUSIONS: Under the conditions tested, MH produced safe Palv levels despite high Pprox. However, the MH maneuver was often performed in a way that did not favor secretion removal (PIF exceeding PEF), even after instruction. The unfavorable PIF/ PEF ratio was attributable to overly rapid inflations and low V T

Evaluation of the effectiveness of preoperative outpatient pulmonary preparation in patients undergoing esophageal surgery

<div><p>Abstract Introduction: Preoperative inspiratory muscle training (IMT) can minimize the occurrence of complications after esophagectomy. Objective: To evaluate the effects of preoperative IMT in patients undergoing esophageal surgery by determining respiratory muscle strength (PImax and PEmax), pulmonary function (FEV1, FVC, FEV1/FVC) and functional capacity by the 6-minute walk test (6MWT). Methods: Twenty-two patients were randomized into two groups: a control group (CG; n = 10) and an intervention group (IG; n = 12). Only IG performed IMT for a minimum period of 2 weeks. The assessments were conducted pre- and post-surgery. Results: An increase of PImax was observed in IG, but not in CG, in the second preoperative assessment (p = 0.014). Assessment on postoperative day 1 showed a reduction in maximal respiratory pressures in the two groups, but the reduction was more marked in IG (p < 0.05). Partial recovery of the variables evaluated was observed at discharge in the two groups. These variables had fully returned to initial values on postoperative day 30. The distance walked in the 6MWT was greater in IG, but the difference was not significant (p = 0.166). There was no difference in the frequency of pulmonary complications between groups. Conclusion: Preoperative IMT performed in our study improved inspiratory muscle strength but did not influence the postoperative pulmonary function or functional capacity of patients undergoing esophagectomy.</p></div