Alterações ventilatórias durante o uso de trocadores de calor e umidade em pacientes submetidos à ventilação mecânica com pressão de suporte e ajustes nos parâmetros ventilatórios para compensar estas possíveis alterações: estudo de intervenção autocontrolado em humanos / Ventilatory changes during the use of heat and moisture exchangers in patients submitted to mechanical ventilation with support pressure and adjustments in ventilation parameters to compensate for these possible changes: a self-controlled intervention study in humans

RESUMO Objetivo: Avaliar as possíveis alterações do volume corrente, volume-minuto e frequência respiratória causadas pela utilização de trocadores de calor e umidade em pacientes submetidos à ventilação mecânica na modalidade pressão de suporte, e quantificar a variação da pressão de suporte necessária para compensar o efeito causado pelo trocador de calor e umidade. Métodos: Os pacientes sob ventilação mecânica invasiva na modalidade pressão de suporte foram avaliados utilizando umidificadores aquecidos e trocadores de calor e umidade. Caso o volume encontrado com uso de trocadores de calor e umidade fosse menor que o achado com o umidificador aquecido, iniciava-se o aumento da pressão de suporte, perante o uso de trocadores de calor e umidade, até ser encontrado um valor de pressão de suporte que possibilitasse ao paciente gerar um valor próximo do volume corrente inicial com umidificador aquecido. A análise foi realizada por meio do teste t pareado, e os valores de incremento foram expressos em porcentagem de aumento necessário. Resultados: Foram avaliados 26 pacientes. O uso de trocadores de calor e umidade aumentou a frequência respiratória, e reduziu o volume corrente e o volume-minuto, quando comparados com o uso do umidificador aquecido. Com o uso de trocadores de calor e umidade, os pacientes precisaram de um incremento de 38,13% na pressão de suporte para manter os volumes prévios. Conclusão: O trocador de calor e umidade alterou os parâmetros de volume corrente, volume-minuto e frequência respiratória, sendo necessário um aumento da pressão de suporte para compensar estas alterações.

ABSTRACT Objective: To evaluate the possible changes in tidal volume, minute volume and respiratory rate caused by the use of a heat and moisture exchanger in patients receiving pressure support mechanical ventilation and to quantify the variation in pressure support required to compensate for the effect caused by the heat and moisture exchanger. Methods: Patients under invasive mechanical ventilation in pressure support mode were evaluated using heated humidifiers and heat and moisture exchangers. If the volume found using the heat and moisture exchangers was lower than that found with the heated humidifier, an increase in pressure support was initiated during the use of the heat and moisture exchanger until a pressure support value was obtained that enabled the patient to generate a value close to the initial tidal volume obtained with the heated humidifier. The analysis was performed by means of the paired t test, and incremental values were expressed as percentages of increase required. Results: A total of 26 patients were evaluated. The use of heat and moisture exchangers increased the respiratory rate and reduced the tidal and minute volumes compared with the use of the heated humidifier. Patients required a 38.13% increase in pressure support to maintain previous volumes when using the heat and moisture exchanger. Conclusion: The heat and moisture exchanger changed the tidal and minute volumes and respiratory rate parameters. Pressure support was increased to compensate for these changes.

Evaluating humidity recovery efficiency of currently available heat and moisture exchangers: a respiratory system model study

OBJECTIVES: To evaluate and compare the efficiency of humidification in available heat and moisture exchanger models under conditions of varying tidal volume, respiratory rate, and flow rate. INTRODUCTION: Inspired gases are routinely preconditioned by heat and moisture exchangers to provide a heat and water content similar to that provided normally by the nose and upper airways. The absolute humidity of air retrieved from and returned to the ventilated patient is an important measurable outcome of the heat and moisture exchangers' humidifying performance. METHODS: Eight different heat and moisture exchangers were studied using a respiratory system analog. The system included a heated chamber (acrylic glass, maintained at 37°C), a preserved swine lung, a hygrometer, circuitry and a ventilator. Humidity and temperature levels were measured using eight distinct interposed heat and moisture exchangers given different tidal volumes, respiratory frequencies and flow-rate conditions. Recovery of absolute humidity (%RAH) was calculated for each setting. RESULTS: Increasing tidal volumes led to a reduction in %RAH for all heat and moisture exchangers while no significant effect was demonstrated in the context of varying respiratory rate or inspiratory flow. CONCLUSIONS: Our data indicate that heat and moisture exchangers are more efficient when used with low tidal volume ventilation. The roles of flow and respiratory rate were of lesser importance, suggesting that their adjustment has a less significant effect on the performance of heat and moisture exchangers.

Interaction between intra-abdominal pressure and positive-end expiratory pressure

OBJECTIVE: The aim of this study was to quantify the interaction between increased intra-abdominal pressure and Positive-End Expiratory Pressure. METHODS: In 30 mechanically ventilated ICU patients with a fixed tidal volume, respiratory system plateau and abdominal pressure were measured at a Positive-End Expiratory Pressure level of zero and 10 cm H2O. The measurements were repeated after placing a 5 kg weight on the patients' belly. RESULTS: After the addition of 5 kg to the patients' belly at zero Positive-End Expiratory Pressure, both intra-abdominal pressure (p<0.001) and plateau pressures (p=0.005) increased significantly. Increasing the Positive-End Expiratory Pressure levels from zero to 10 cm H2O without weight on the belly did not result in any increase in intra-abdominal pressure (p=0.165). However, plateau pressures increased significantly (p< 0.001). Increasing Positive-End Expiratory Pressure from zero to 10 cm H2O and adding 5 kg to the belly increased intra-abdominal pressure from 8.7 to 16.8 (p<0.001) and plateau pressure from 18.26 to 27.2 (p<0.001). Maintaining Positive-End Expiratory Pressure at 10 cm H2O and placing 5 kg on the belly increased intra-abdominal pressure from 12.3 +/- 1.7 to 16.8 +/- 1.7 (p<0.001) but did not increase plateau pressure (26.6+/-1.2 to 27.2 +/-1.1 -p=0.83). CONCLUSIONS: The addition of a 5kg weight onto the abdomen significantly increased both IAP and the airway plateau pressure, confirming that intra-abdominal hypertension elevates the plateau pressure. However, plateau pressure alone cannot be considered a good indicator for the detection of elevated intra-abdominal pressure in patients under mechanical ventilation using PEEP. In these patients, the intra-abdominal pressure must also be measured.

O curativo compressivo usado em queimadura de tórax influencia na mecânica do sistema respiratório? / Does the compressive dressing made in burning of thorax influence in the mechanics of the respiratory system?

Introdução: O paciente com queimadura em tórax apresenta restrição torácica pela queimadura e pela dor, levando a uma diminuição de força muscular respiratória. A utilização de curativos cirúrgicos e curativos no leito é de extrema importância para pacientes queimados, pois são utilizados para prevenção de infecção e inflamação da área queimada, porém estes curativos podem contribuir com esta restrição da afecção, levando à formação de atelectasias e outras complicações respiratórias. Objetivo: Verificar a influência do curativo torácico no sistema respiratório. Método: Foram realizadas medidas da Pimax e Pemax, capacidade vital, volume corrente, frequência respiratória, volume minuto e peak flow em 10 indivíduos do sexo feminino, com média de idade média de 23 anos (18-26), saudáveis, sem restrições respiratórias, em três etapas, com e sem curativo oclusivo em tórax e repetidas as mensurações 15 minutos após a colocação do curativo. Resultados: Houve diminuição da força muscular respiratória, do volume corrente, capacidade vital e aumento da frequência respiratória após a colocação do curativo oclusivo em tórax. Conclusão: O uso do curativo compressivo de tórax influenciou nas medidas de mecânica respiratória de indivíduos normais, levando à diminuição da força muscular inspiratória e expiratória, queda no fluxo expiratório e na capacidade vital.

Background: The patient with burning in thorax presents a thorax restriction for burning and for pain, leading to a reduction of respiratory muscular force. The use of surgical dressings and dressings in the stream bed is of extreme importance for burnt patients, therefore infection prevention of and inflammation of the burnt area are used for, however these dressings can contribute with this restriction of the pathology leading the respiratory formation of atelectasis and other complications. Objective: To verify the influence of the thorax dressing in the respiratory system. Methods: They had been carried through measured of the Pimax and Pemax, vital capacity, current volume, respiratory frequency, volume minute and peak flow in 10 individuals of the feminine sex, with average of age average of 23 years (18-26), healthful, without respiratory restrictions, in three stages, with and without occlusive dressing in thorax and repeated the measurement 15 minutes after rank of the dressing. Results: It had a reduction of the respiratory muscular force, of the current volume, vital capacity and increase of the respiratory frequency after the rank of the occlusive dressing in thorax. Conclusion: The use of the compressive dressing of thorax influenced in the measures of respiratory mechanics of normal individuals, taking the reduction of the inspiratory and expiratory muscular force, fall in the expiratory flow and the vital capacity.

Avaliação e comparação de diferentes tipos de trocadores de calor e umidade / Evaluation and comparison among different: heat and moisture exchangers

As tarefas de umidificação e aquecimento do ar inspirado podem ser realizadas por meio de trocadores de calor e umidade (HMEs - Heat and moisture exchangers). Os objetivos do nosso estudo são avaliar e comparar a capacidade de umidificação e aquecimento de oito diferentes tipos de HMEs em um modelo experimental com pulmão animal isolado e avaliar o impacto de cada um dos HMEs na ventilação alveolar em um modelo mecânico do sistema respiratório, com adição de CO2 a um fluxo de 0,65L / When tracheal intubation is necessary during ventilatory support, the physiological mechanisms of heating and humidifying the inspired air are supressed, so it is vital the preconditioning of the inspired gases with the goal of offering water and heat contents similar to those normally provided by the upper airways. These tasks of humidification and heating can be accomplished through the use of heat and moisture exchangers (HMEs). Objectives: 1- Evaluate and compare the humidification and heating capacity of eight different types of HMEs in a respiratory system...