Recruit the lung before titrating the right positive end-expiratory pressure to protect it

Good practices for prone positioning at the bedside: Construction of a care protocol

Last year, interest in prone positioning to treat acute respiratory distress syndrome (ARDS) resurfaced with the demonstration of a reduction in mortality by a large randomized clinical trial. Reports in the literature suggest that the incidence of adverse events is significantly reduced with a team trained and experienced in the process. The objective of this review is to revisit the current evidence in the literature, discuss and propose the construction of a protocol of care for these patients. A search was performed on the main electronic databases: Medline, Lilacs and Cochrane Library. Prone positioning is increasingly used in daily practice, with properly trained staff and a well established care protocol are essencial.

Effects of the open lung concept following ARDSnet ventilation in patients with early ARDS

BACKGROUND

Ventilation with low tidal volume (VT) is well recognized as a protective approach to patients with acute respiratory distress syndrome (ARDS), but the optimal level of positive end-expiratory pressure (PEEP) remains uncertain. This study aims to evaluate two protective ventilatory strategies sequentially applied in patients with early ARDS.

METHODS

In this prospective cohort study, fifteen patients were ventilated during 24 h with positive end-expiratory pressure (PEEP) adjusted according to the ARDSnet low-PEEP table (ARDSnet-24 h). During the next 24 h, nine patients with PaO2/FIO2 ratio below 350 mmHg were ventilated with PEEP titrated according to the Open Lung Concept protocol (ARDSnet + OLC). In the other six patients, regardless of their PaO2/FIO2 ratio, the ARDSnet remained for a further 24 h (ARDSnet-48 h). Ventilatory variables, arterial blood-gas and cytokine were obtained at baseline, 24 and 48 h. Additionally, whole-lung-computed tomography was acquired at 24 and 48 h.

RESULTS

A sustained improvement in PaO2/FIO2 ratio (P = 0.008) with a decrease in collapsed regions (P = 0.008) was observed in the ARDSnet + OLC group compared with the ARDSnet-24 h group. A reduction in IL-6 in plasma (P < 0.02) was observed throughout the protocol in the ARDSnet + OLC group. Compared with the ARDSnet-48 h group, the ARDSnet + OLC presented smaller amounts of collapsed areas (P = 0.018) without significant differences in hyperinflated regions and in driving and plateau pressures.

CONCLUSIONS

In this set of patients with early ARDS, mechanical ventilation with an individually tailored PEEP sustained improved pulmonary function with better aeration, without significant increase in hyperinflated areas".

TRIAL REGISTRATION

Brazilian Clinical Trials Registry (ReBec). RBR-5zm9pr. 04th November 2015.

Brazilian recommendations of mechanical ventilation 2013. Part I

Perspectives on invasive and noninvasive ventilatory support for critically ill patients are evolving, as much evidence indicates that ventilation may have positive effects on patient survival and the quality of the care provided in intensive care units in Brazil. For those reasons, the Brazilian Association of Intensive Care Medicine (Associação de Medicina Intensiva Brasileira - AMIB) and the Brazilian Thoracic Society (Sociedade Brasileira de Pneumonia e Tisiologia - SBPT), represented by the Mechanical Ventilation Committee and the Commission of Intensive Therapy, respectively, decided to review the literature and draft recommendations for mechanical ventilation with the goal of creating a document for bedside guidance as to the best practices on mechanical ventilation available to their members. The document was based on the available evidence regarding 29 subtopics selected as the most relevant for the subject of interest. The project was developed in several stages, during which the selected topics were distributed among experts recommended by both societies with recent publications on the subject of interest and/or significant teaching and research activity in the field of mechanical ventilation in Brazil. The experts were divided into pairs that were charged with performing a thorough review of the international literature on each topic. All the experts met at the Forum on Mechanical Ventilation, which was held at the headquarters of AMIB in São Paulo on August 3 and 4, 2013, to collaboratively draft the final text corresponding to each sub-topic, which was presented to, appraised, discussed and approved in a plenary session that included all 58 participants and aimed to create the final document.

Feasibility of titrating PEEP to minimum elastance for mechanically ventilated patients

Background

Selecting positive end-expiratory pressure (PEEP) during mechanical ventilation is important, as it can influence disease progression and outcome of acute respiratory distress syndrome (ARDS) patients. However, there are no well-established methods for optimizing PEEP selection due to the heterogeneity of ARDS. This research investigates the viability of titrating PEEP to minimum elastance for mechanically ventilated ARDS patients.

Methods

Ten mechanically ventilated ARDS patients from the Christchurch Hospital Intensive Care Unit were included in this study. Each patient underwent a stepwise PEEP recruitment manoeuvre. Airway pressure and flow data were recorded using a pneumotachometer. Patient-specific respiratory elastance (E_rs) and dynamic functional residual capacity (dFRC) at each PEEP level were calculated and compared. Optimal PEEP for each patient was identified by finding the minima of the PEEP-E_rs profile.

Results

Median E_rs and dFRC over all patients and PEEP values were 32.2 cmH₂O/l [interquartile range (IQR) 25.0–45.9] and 0.42 l [IQR 0.11–0.87]. These wide ranges reflect patient heterogeneity and variable response to PEEP. The level of PEEP associated with minimum E_rs corresponds to a high change of functional residual capacity, representing the balance between recruitment and minimizing the risk of overdistension.

Conclusions

Monitoring patient-specific E_rs can provide clinical insight to patient-specific condition and response to PEEP settings. The level of PEEP associated with minimum-E_rs can be identified for each patient using a stepwise PEEP recruitment manoeuvre. This ‘minimum elastance PEEP’ may represent a patient-specific optimal setting during mechanical ventilation.

Trial registration

Australian New Zealand Clinical Trials Registry: ACTRN12611001179921.

Electronic supplementary material

The online version of this article (doi:10.1186/s40814-015-0006-2) contains supplementary material, which is available to authorized users.

Brazilian recommendations of mechanical ventilation 2013. Part I

Perspectives on invasive and noninvasive ventilatory support for critically ill patients are evolving, as much evidence indicates that ventilation may have positive effects on patient survival and the quality of the care provided in intensive care units in Brazil. For those reasons, the Brazilian Association of Intensive Care Medicine (Associação de Medicina Intensiva Brasileira - AMIB) and the Brazilian Thoracic Society (Sociedade Brasileira de Pneumologia e Tisiologia - SBPT), represented by the Mechanical Ventilation Committee and the Commission of Intensive Therapy, respectively, decided to review the literature and draft recommendations for mechanical ventilation with the goal of creating a document for bedside guidance as to the best practices on mechanical ventilation available to their members. The document was based on the available evidence regarding 29 subtopics selected as the most relevant for the subject of interest. The project was developed in several stages, during which the selected topics were distributed among experts recommended by both societies with recent publications on the subject of interest and/or significant teaching and research activity in the field of mechanical ventilation in Brazil. The experts were divided into pairs that were charged with performing a thorough review of the international literature on each topic. All the experts met at the Forum on Mechanical Ventilation, which was held at the headquarters of AMIB in São Paulo on August 3 and 4, 2013, to collaboratively draft the final text corresponding to each sub-topic, which was presented to, appraised, discussed and approved in a plenary session that included all 58 participants and aimed to create the final document.

Setting the Ventilator in the NICU

Success in providing respiratory support to the neonate requires a clear understanding of the context in which it is being applied. Perhaps more than for any other age group, the array of different situations in which ventilation is applied to the newborn infant is extremely broad, with in each case different pathophysiological disturbances and often the need to use a specific approach to apply ventilation optimally. Table 42.1 provides a list of the more common situations in which conventional ventilation is used in the neonate and includes some considerations regarding ventilator settings for each situation. For each situation, a suggested mode of ventilation is indicated, along with target ranges for positive end-expiratory pressure (PEEP) and tidal volume (V_T). Further discussion of the physiological rationale and available evidence for ventilator settings is set out below.

Visualisation of time-varying respiratory system elastance in experimental ARDS animal models

BACKGROUND

Patients with acute respiratory distress syndrome (ARDS) risk lung collapse, severely altering the breath-to-breath respiratory mechanics. Model-based estimation of respiratory mechanics characterising patient-specific condition and response to treatment may be used to guide mechanical ventilation (MV). This study presents a model-based approach to monitor time-varying patient-ventilator interaction to guide positive end expiratory pressure (PEEP) selection.

METHODS

The single compartment lung model was extended to monitor dynamic time-varying respiratory system elastance, Edrs, within each breathing cycle. Two separate animal models were considered, each consisting of three fully sedated pure pietrain piglets (oleic acid ARDS and lavage ARDS). A staircase recruitment manoeuvre was performed on all six subjects after ARDS was induced. The Edrs was mapped across each breathing cycle for each subject.

RESULTS

Six time-varying, breath-specific Edrs maps were generated, one for each subject. Each Edrs map shows the subject-specific response to mechanical ventilation (MV), indicating the need for a model-based approach to guide MV. This method of visualisation provides high resolution insight into the time-varying respiratory mechanics to aid clinical decision making. Using the Edrs maps, minimal time-varying elastance was identified, which can be used to select optimal PEEP.

CONCLUSIONS

Real-time continuous monitoring of in-breath mechanics provides further insight into lung physiology. Therefore, there is potential for this new monitoring method to aid clinicians in guiding MV treatment. These are the first such maps generated and they thus show unique results in high resolution. The model is limited to a constant respiratory resistance throughout inspiration which may not be valid in some cases. However, trends match clinical expectation and the results highlight both the subject-specificity of the model, as well as significant inter-subject variability.

Clinical review: Acute respiratory distress syndrome - clinical ventilator management and adjunct therapy

Acute respiratory distress syndrome (ARDS) is a potentially devastating form of acute inflammatory lung injury with a high short-term mortality rate and significant long-term consequences among survivors. Supportive care, principally with mechanical ventilation, remains the cornerstone of therapy - although the goals of this support have changed in recent years - from maintaining normal physiological parameters to avoiding ventilator-induced lung injury while providing adequate gas exchange. In this article we discuss the current evidence base for ventilatory support and adjunctive therapies in patients with ARDS. Key components of such a strategy include avoiding lung overdistension by limiting tidal volumes and airway pressures, and the use of positive end-expiratory pressure with or without lung recruitment manoeuvres in patients with severe ARDS. Adjunctive therapies discussed include pharmacologic techniques (for example, vasodilators, diuretics, neuromuscular blockade) and nonpharmacologic techniques (for example, prone position, alternative modes of ventilation).

Recruitment and PEEP level influences long-time aeration in saline-lavaged piglets: an experimental model

OBJECTIVES

To evaluate aeration/ventilation in saline-lavaged piglets during a 3-h follow-up after a recruitment maneuver (RM)/PEEP titration compared with PEEP 10 cmH2O without a RM.

BACKGROUND

Lung recruitment and PEEP titration are used to find a PEEP preventing repetitive opening/collapsing of lung.

METHODS

Twenty-one lung-lavaged piglets, mean age 7 weeks and mean weight 10 kg; a RM-group and a PEEP10-group, were ventilated at PEEP 5 cmH2O (baseline) followed by zero PEEP ventilation. In the RM-group, tidal elimination of CO2 and dynamic compliance (Cdyn) guided recruitment and PEEP titration, respectively. A final 3-h ventilation followed using PEEP 2 cmH2O above the first decline of Cdyn and end-inspiratory pressure (EIP) for a target tidal volume (VT) of 10 ml · kg(-1). In the PEEP10-group, PEEP 10 cmH2O without a RM was used during the final 3-h ventilation. CT scans and blood gases were repeated every 30 min. Airway pressures, Cdyn and hemodynamics were continuously recorded.

RESULTS

Aeration improved without differences between groups. The RM-group PEEP level of 10 ± 0.6 cmH2O did not differ from the PEEP10-group. Compared to baseline EIP was lower in the RM-group after 3-h ventilation. In both groups, driving pressure (DP) was lower and Cdyn higher than baseline. In the RM-group, final EIP and DP were lower and Cdyn higher than in the PEEP10-group.

CONCLUSIONS

Both RM/PEEP titration and PEEP elevation resulted in improved aeration without differences between groups at the end point. Lung aeration was achieved at lower EIP and DP and higher Cdyn in the RM-group than in the PEEP10-group.

The need for and feasibility of a pediatric ventilation trial: reflections on a survey among pediatric intensivists*

OBJECTIVE

To explore what design would be reasonable, acceptable, and feasible for a pediatric trial investigating the effect of low tidal volume ventilation.

DESIGN

A two-round modified Delphi approach among pediatric intensivists with a visible special interest in mechanical ventilation.

SETTINGS

None.

SUBJECTS

Pediatric intensivists.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

In the first questionnaire "experts" classified 64 items as "important," "not so important" or "not important" (June 2010). The second questionnaire included the 29 items having been classified by more than 50% of the experts as being "important" in the first questionnaire that needed to be ranked in order of importance (August 2010). Twenty-nine of 50 (64%) experts responded to the first questionnaire, and 28 of the 29 initial responders (96.6%) to the second questionnaire. Actual expert opinion favored the following: age of study population 0 yrs to 2 yrs, expected duration of ventilation ≥ 48 hrs, and stratification by the severity of hypoxemia (cutoff PaO(2)/FIO(2) < 200). The two study arms should compare the effect of 6 mL/kg vs. 10 mL/kg on mortality. However, these views of the experts face two major issues. First, 10 mL/kg does not represent standard of care. Second, numerous uncertainties render mortality unsuitable as primary measure of outcome including a large sample size (>1500).

CONCLUSIONS

Actual expert opinion favored investigating the effect of 6 mL/kg vs.10 mL/kg on mortality. Such a design suffers from various serious criticisms. Therefore, and in our opinion, a pediatric Acute Respiratory Distress Syndrome Network trial is not realistic.

Open lung approach vs acute respiratory distress syndrome network ventilation in experimental acute lung injury

Background

Setting and strategies of mechanical ventilation with positive end-expiratory pressure (PEEP) in acute lung injury (ALI) remains controversial. This study compares the effects between lung-protective mechanical ventilation according to the Acute Respiratory Distress Syndrome Network recommendations (ARDSnet) and the open lung approach (OLA) on pulmonary function and inflammatory response.

Methods

Eighteen juvenile pigs were anaesthetized, mechanically ventilated, and instrumented. ALI was induced by surfactant washout. Animals were randomly assigned to mechanical ventilation according to the ARDSnet protocol or the OLA (n=9 per group). Gas exchange, haemodynamics, pulmonary blood flow (PBF) distribution, and respiratory mechanics were measured at intervals and the lungs were removed after 6 h of mechanical ventilation for further analysis.

Results

PEEP and mean airway pressure were higher in the OLA than in the ARDSnet group [15 cmH₂O, range 14–18 cmH₂O, compared with 12 cmH₂O; 20.5 (sd 2.3) compared with 18 (1.4) cmH₂O by the end of the experiment, respectively], and OLA was associated with improved oxygenation compared with the ARDSnet group after 6 h. OLA showed more alveolar overdistension, especially in gravitationally non-dependent regions, while the ARDSnet group was associated with more intra-alveolar haemorrhage. Inflammatory mediators and markers of lung parenchymal stress did not differ significantly between groups. The PBF shifted from ventral to dorsal during OLA compared with ARDSnet protocol [−0.02 (−0.09 to −0.01) compared with −0.08 (−0.12 to −0.06), dorsal–ventral gradients after 6 h, respectively].

Conclusions

According to the OLA, mechanical ventilation improved oxygenation and redistributed pulmonary perfusion when compared with the ARDSnet protocol, without differences in lung inflammatory response.