Abstract
Rev Bras Ter Intensiva. 2022;34(1):176-184
DOI 10.5935/0103-507X.20220012-en
Defective management of secretions is one of the most frequent complications in invasive mechanically ventilated patients. Clearance of secretions through chest physiotherapy is a critical aspect of the treatment of these patients. Manual rib cage compression is one of the most practiced chest physiotherapy techniques in ventilated patients; however, its impact on clinical outcomes remains controversial due to methodological issues and poor understanding of its action. In this review, we present a detailed analysis of the physical principles involved in rib cage compression technique performance, as well as the physiological effects observed in experimental and clinical studies, which show that the use of brief and vigorous rib cage compression, based on increased expiratory flows (expiratory-inspiratory airflow difference of > 33L/minute), can improve mucus movement toward the glottis. On the other hand, the use of soft and gradual rib cage compression throughout the whole expiratory phase does not impact the expiratory flows, resulting in ineffective or undesired effects in some cases. More physiological studies are needed to understand the principles of the rib cage compression technique in ventilated humans. However, according to the evidence, rib cage compression has more potential benefits than risks, so its implementation should be promoted.
Abstract
Rev Bras Ter Intensiva. 2021;33(4):537-543
DOI 10.5935/0103-507X.20210081
To compare gas exchange indices behavior by using liberal versus conservative oxygenation targets in patients with moderate to severe acute respiratory distress syndrome secondary to COVID-19 under invasive mechanical ventilation. We also assessed the influence of high FiO2 on respiratory system mechanics.
We prospectively included consecutive patients aged over 18 years old with a diagnosis of COVID-19 and moderate-severe acute respiratory distress syndrome. For each patient, we randomly applied two FiO2 protocols to achieve SpO2 88% - 92% or 96%. We assessed oxygenation indices and respiratory system mechanics.
We enrolled 15 patients. All the oxygenation indices were significantly affected by the FiO2 strategy (p < 0.05) selected. The PaO2/FiO2 deteriorated, PA-aO2 increased and Pa/AO2 decreased significantly when using FiO2 to achieve SpO2 96%. Conversely, the functional shunt fraction was reduced. Respiratory mechanics were not affected by the FiO2 strategy.
A strategy aimed at liberal oxygenation targets significantly deteriorated gas exchange indices, except for functional shunt, in COVID-19-related acute respiratory distress syndrome. The respiratory system mechanics were not altered by the FiO2 strategy.
Abstract
Rev Bras Ter Intensiva. 2021;33(4):572-582
DOI 10.5935/0103-507X.20210084
To evaluate the influences of respiratory muscle efforts and respiratory rate setting in the ventilator on tidal volume and alveolar distending pressures at end inspiration and expiration in volume-controlled ventilation and pressure-controlled ventilation modes in acute respiratory distress syndrome.
An active test lung (ASL 5000™) connected to five intensive care unit ventilators was used in a model of acute respiratory distress syndrome. Respiratory muscle efforts (muscle pressure) were configured in three different ways: no effort (muscle pressure: 0cmH2O); inspiratory efforts only (muscle pressure:-5cmH2O, neural inspiratory time of 0.6s); and both inspiratory and expiratory muscle efforts (muscle pressure:-5/+5cmH2O). Volume-controlled and pressure-controlled ventilation modes were set to deliver a target tidal volume of 420mL and positive end-expiratory pressure of 10cmH2O. The tidal volume delivered to the lungs, alveolar pressures at the end of inspiration, and alveolar pressures at end expiration were evaluated.
When triggered by the simulated patient, the median tidal volume was 27mL lower than the set tidal volume (range-63 to +79mL), and there was variation in alveolar pressures with a median of 25.4cmH2O (range 20.5 to 30cmH2O). In the simulated scenarios with both spontaneous inspiratory and expiratory muscle efforts and with a mandatory respiratory rate lower than the simulated patient's efforts, the median tidal volume was higher than controlled breathing.
Adjusting respiratory muscle effort and pulmonary ventilator respiratory rate to a value above the patient’s respiratory rate in assisted/controlled modes generated large variations in tidal volume and pulmonary pressures, while the controlled mode showed no variations in these outcomes.
Abstract
Rev Bras Ter Intensiva. 2021;33(4):616-623
DOI 10.5935/0103-507X.20210071
Manual hyperinflation is used in neonatal and pediatric intensive care units to promote expiratory flow bias, but there is no consensus on the benefits of the technique. Thus, a review that presents supporting evidence is necessary. This study aims to review the literature on the manual hyperinflation maneuver in neonatal and pediatric intensive care units to analyze the evidence for this technique in terms of the forms of application (associated with other techniques or not), its safety, the performance of manual resuscitators and the influence of the physical therapist’s experience, in addition to evaluating the methodological quality of the identified articles. A search was performed in the following databases: Web of Science, ScienceDirect, PubMedⓇ, Scopus, CINAHL and SciELO. Two researchers independently selected the articles. Duplicate studies were assessed, evaluated by title and abstract and then read in full. The quality of the articles was analyzed using the PEDro scale. Six articles were included, two of which had high methodological quality. The main results provided information on the contribution of the positive end-expiratory pressure valve to increasing lung volumes and the use of chest compressions to optimize expiratory flow bias, the negative influence of operator experience on the increase in peak inspiratory flow, the performance of different manual resuscitators when used with the technique and the safety of application in terms of maintaining hemodynamic stability and increasing peripheral oxygen saturation. The available studies point to a positive effect of the manual hyperinflation maneuver in children who are admitted to intensive care units.
Registration PROSPERO: CRD42018108056.
Abstract
Rev Bras Ter Intensiva. 2021;33(3):428-433
DOI 10.5935/0103-507X.20210068
To build a cost-effectiveness model to compare the use of propofol versus midazolam in critically ill adult patients under mechanical ventilation.
We built a decision tree model for critically ill patients submitted to mechanical ventilation and analyzed it from the Brazilian private health care system perspective. The time horizon was that of intensive care unit hospitalization. The outcomes were cost-effectiveness per hour of intensive care unit stay avoided and cost-effectiveness per hour of mechanical ventilation avoided. We retrieved data for the model from a previous meta-analysis. We assumed that the cost of medication was embedded in the intensive care unit cost. We conducted univariate and probabilistic sensitivity analyses.
Mechanically ventilated patients using propofol had their intensive care unit stay and the duration of mechanical ventilation decreased by 47.97 hours and 21.65 hours, respectively. There was an average cost reduction of US$ 2,998.971 for propofol when compared to midazolam. The cost-effectiveness per hour of intensive care unit stay and mechanical ventilation avoided were dominant 94.40% and 80.8% of the time, respectively.
There was a significant reduction in costs associated with propofol use related to intensive care unit stay and duration of mechanical ventilation for critically ill adult patients.
Abstract
Rev Bras Ter Intensiva. 2021;33(3):445-456
DOI 10.5935/0103-507X.20210060
This systematic review was designed to assess the usefulness of cough peak flow to predict the extubation outcome in subjects who passed a spontaneous breathing trial.
The search covered the scientific databases MEDLINE, Lilacs, Ibecs, Cinahl, SciELO, Cochrane, Scopus, Web of Science and gray literature. The Quality Assessment of Diagnostic Accuracy Studies was used to assess the methodological quality and risk of study bias. The statistical heterogeneity of the likelihood (LR) and diagnostic odds ratios were evaluated using forest plots and Cochran’s Q statistic, and a crosshair summary Receiver Operating Characteristic plot using the multiple cutoffs model was calculated.
We initially retrieved 3,522 references from the databases; among these, 12 studies including 1,757 subjects were selected for the qualitative analysis. Many studies presented an unclear risk of bias in the “patient selection” and “flow and time” criteria. Among the 12 included studies, seven presented “high risk” and five “unclear risk” for the item “reference standard.” The diagnostic performance of the cough peak flow for the extubation outcome was low to moderate when we considered the results from all included studies, with a +LR of 1.360 (95%CI 1.240 - 1.530), -LR of 0.218 (95%CI 0.159 - 0.293) and a diagnostic odds ratio of 6.450 (95%CI 4.490 - 9.090). A subgroup analysis including only the studies with a cutoff between 55 and 65 L/minute showed a slightly better, although still moderate, performance.
A cough peak flow assessment considering a cutoff between 55 and 65L/minute may be useful as a complementary measurement prior to extubation. Additional well-designed studies are necessary to identify the best method and equipment to record the cough peak flow as well as the best cutoff.
Abstract
Rev Bras Ter Intensiva. 2021;33(3):461-468
DOI 10.5935/0103-507X.20210061
Spontaneous breathing can be deleterious in patients with previously injured lungs, especially in acute respiratory distress syndrome. Moreover, the failure to assume spontaneous breathing during mechanical ventilation and the need to switch back to controlled mechanical ventilation are associated with higher mortality. There is a gap of knowledge regarding which parameters might be useful to predict the risk of patient self-inflicted lung injury and to detect the inability to assume spontaneous breathing. We report a case of patient self-inflicted lung injury, the corresponding basic and advanced monitoring of the respiratory system mechanics and physiological and clinical results related to spontaneous breathing. The patient was a 33-year-old Caucasian man with a medical history of AIDS who developed acute respiratory distress syndrome and needed invasive mechanical ventilation after noninvasive ventilatory support failure. During the controlled ventilation periods, a protective ventilation strategy was adopted, and the patient showed clear clinical and radiographic improvement. However, during each spontaneous breathing period under pressure support ventilation, despite adequate initial parameters and a strictly adjusted ventilatory setting and monitoring, the patient developed progressive hypoxemia and worsening of respiratory system mechanics with a clearly correlated radiographic deterioration (patient self-inflicted lung injury). After failing three spontaneous breathing assumption trials, he died on day 29 due to refractory hypoxemia. Conventional basic and advanced monitoring variables in this case were not sufficient to identify the aptitude to breathe spontaneously or to predict the risk and development of patient self-inflicted lung injury during partial support ventilation.
Abstract
Rev Bras Ter Intensiva. 2020;32(1):115-122
DOI 10.5935/0103-507X.20200017
The central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio (Pcv-aCO2/Ca-cvO2) has been proposed as a surrogate for respiratory quotient and an indicator of tissue oxygenation. Some small observational studies have found that a Pcv-aCO2/Ca-cvO2 > 1.4 was associated with hyperlactatemia, oxygen supply dependency, and increased mortality. Moreover, Pcv-aCO2/Ca-cvO2 has been incorporated into algorithms for tissue oxygenation evaluation and resuscitation. However, the evidence for these recommendations is quite limited and of low quality. The goal of this narrative review was to analyze the methodological bases, the pathophysiologic foundations, and the experimental and clinical evidence supporting the use of Pcv-aCO2/Ca-cvO2 as a surrogate for respiratory quotient. Physiologically, the increase in respiratory quotient secondary to critical reductions in oxygen transport is a life-threatening and dramatic event. Nevertheless, this event is easily noticeable and probably does not require further monitoring. Since the beginning of anaerobic metabolism is indicated by the sudden increase in respiratory quotient and the normal range of respiratory quotient is wide, the use of a defined cutoff of 1.4 for Pcv-aCO2/Ca-cvO2 is meaningless. Experimental studies have shown that Pcv-aCO2/Ca-cvO2 is more dependent on factors that modify the dissociation of carbon dioxide from hemoglobin than on respiratory quotient and that respiratory quotient and Pcv-aCO2/Ca-cvO2 may have distinct behaviors. Studies performed in critically ill patients have shown controversial results regarding the ability of Pcv-aCO2/Ca-cvO2 to predict outcome, hyperlactatemia, microvascular abnormalities, and oxygen supply dependency. A randomized controlled trial also showed that Pcv-aCO2/Ca-cvO2 is useless as a goal of resuscitation. Pcv-aCO2/Ca-cvO2 should be carefully interpreted in critically ill patients.
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