ERS statement on chest imaging in acute respiratory failure

Chest imaging in patients with acute respiratory failure plays an important role in diagnosing, monitoring and assessing the underlying disease. The available modalities range from plain chest X-ray to computed tomography, lung ultrasound, electrical impedance tomography and positron emission tomography. Surprisingly, there are presently no clear-cut recommendations for critical care physicians regarding indications for and limitations of these different techniques.The purpose of the present European Respiratory Society (ERS) statement is to provide physicians with a comprehensive clinical review of chest imaging techniques for the assessment of patients with acute respiratory failure, based on the scientific evidence as identified by systematic searches. For each of these imaging techniques, the panel evaluated the following items: possible indications, technical aspects, qualitative and quantitative analysis of lung morphology and the potential interplay with mechanical ventilation. A systematic search of the literature was performed from inception to September 2018. A first search provided 1833 references. After evaluating the full text and discussion among the committee, 135 references were used to prepare the current statement.These chest imaging techniques allow a better assessment and understanding of the pathogenesis and pathophysiology of patients with acute respiratory failure, but have different indications and can provide additional information to each other.

Reclassifying Acute Respiratory Distress Syndrome

RATIONALE

The ratio of Pa_O2 to Fi_O2 (P/F) defines acute respiratory distress syndrome (ARDS) severity and suggests appropriate therapies.

OBJECTIVES

We investigated 1) whether a 150-mm-Hg P/F threshold within the range of moderate ARDS (100-200 mm Hg) would define two subgroups that were more homogeneous; and 2) which criteria led the clinicians to apply extracorporeal membrane oxygenation (ECMO) in severe ARDS.

METHODS

At the 150-mm-Hg P/F threshold, moderate patients were split into mild-moderate (n = 50) and moderate-severe (n = 55) groups. Patients with severe ARDS (Fi_O2 not available in three patients) were split into higher (n = 63) and lower (n = 18) Fi_O2 groups at an 80% Fi_O2 threshold.

MEASUREMENTS AND MAIN RESULTS

Compared with mild-moderate ARDS, patients with moderate-severe ARDS had higher peak pressures, Pa_CO2, and pH. They also had heavier lungs, greater inhomogeneity, more noninflated tissue, and greater lung recruitability. Within 84 patients with severe ARDS (P/F < 100 mm Hg), 75% belonged to the higher Fi_O2 subgroup. They differed from the patients with severe ARDS with lower Fi_O2 only in Pa_CO2 and lung weight. Forty-one of 46 patients treated with ECMO belonged to the higher Fi_O2 group. Within this group, the patients receiving ECMO had higher Pa_CO2 than the 22 non-ECMO patients. The inhomogeneity ratio, total lung weight, and noninflated tissue were also significantly higher.

CONCLUSIONS

Using the 150-mm-Hg P/F threshold gave a more homogeneous distribution of patients with ARDS across the severity subgroups and identified two populations that differed in their anatomical and physiological characteristics. The patients treated with ECMO belonged to the severe ARDS group, and almost 90% of them belonged to the higher Fi_O2 subgroup.

A Simple Effective Pharmacological Treatment of Hypoxemia During One-Lung Ventilation

Hypoxemia during one-lung ventilation is a challenge in the clinical practice. Moving from the results of the study conducted by Choi et al., we discuss the possibility to modulate hypoxemia by administering iloprost via inhalation, in the light of the physiological mechanisms.

Different routes and formulations of melatonin in critically ill patients. A pharmacokinetic randomized study

BACKGROUND AND OBJECTIVES

Critically ill patients present reduced endogenous melatonin blood levels, and they might benefit from its exogenous supplementation. The aim of this research was to evaluate the feasibility of different routes of administration and drug formulations of melatonin. The efficiency of absorption was assessed as well as the adequacy in achieving and maintaining the physiological nocturnal blood peak.

METHODS

Twenty-one high-risk critically ill patients were randomly assigned to receive melatonin either: (a) per os, as a standard tablet (ST-OS), (b) per os, as a suspension in solid lipid nanoparticles (SLN-OS) or c) transdermal (TD), by applying a jellified melatonin microemulsion (μE) on the skin (μE-TD). SLN-OS and μE-TD were lipid-based colloidal systems. The endogenous melatonin blood values were observed for 24 hours; subsequently, melatonin 3 mg was administered and pharmacokinetics was studied for 24 hours further.

RESULTS

In both groups that received ST-OS and SLN-OS, the median time-to-peak blood concentration was 0.5 hours; however, the area under the curve (AUC) after administration of SLN-OS was significantly higher than after ST-OS (157386 [65732-193653] vs 44441 [22319-90705] pg/mL*hours, P = 0.048). μE-TD presented a delayed time-to-peak blood concentration (4 hours), a lower bioavailability (AUC: 3142 [1344-14573] pg/mL*hours) and reached pharmacological peak concentration (388 [132-1583] pg/mL).

CONCLUSIONS

SLN-melatonin enterally administered offers favourable pharmacokinetics in critically ill patients, with higher bioavailability with respect to the standard formulation; μE-TD provided effective pharmacological blood levels, with a time-concentration profile more similar to the physiological melatonin pattern.

Clinical review: peripheral muscular ultrasound in the ICU

Muscular weakness developing from critical illness neuropathy, myopathy and muscle atrophy has been characterized as intensive care unit-acquired weakness (ICUAW). This entity occurs commonly during and after critical care stay. Various causal factors for functional incapacity have been proposed. Among these, individual patient characteristics (such as age, comorbidities and nutritional status), acting in association with sustained bed rest and pharmacological interventions (included the metabolic support approach), seem influential in reducing muscular mass. Long-term outcomes in heterogeneous ICUAW populations include transient disability in 30% of patients and persistent disabilities that may occur even in patients with nearly complete functional recovery. Currently available tools for the assessment of skeletal muscle mass are imprecise and difficult to perform in the ICU setting. A valid alternative to these imaging modalities is muscular ultrasonography, which allows visualization and classification of muscle characteristics by cross-sectional area, muscle layer thickness, echointensity by grayscale and the pennation angle). The aim of this narrative review is to describe the current literature addressing muscular ultrasound for the detection of muscle weakness and its potential impact on treatment and prognosis of critically ill patients when combined with biomarkers of muscle catabolism/anabolism and bioenergetic state. In addition, we suggest a practical flowchart for establishing an early diagnosis.

Short-Term Appraisal of the Effects and Safety of Manual Versus Ventilator Hyperinflation in an Animal Model of Severe Pneumonia

BACKGROUND

In patients on mechanical ventilation, lung hyperinflation is often performed to reverse atelectasis and clear retained mucus. We evaluated the effects of manual hyperinflation and ventilator hyperinflation on mucus clearance, gas exchange, pulmonary mechanics, and hemodynamics.

METHODS

Six mechanically ventilated pigs with severe Pseudomonas aeruginosa pneumonia randomly received either 12 manual hyperinflation breaths over a period of 2 min (through a gradual manual compression of a resuscitation bag within 4 s to achieve 40 cm H₂O of airway pressure), or 12 ventilator hyperinflation over 2 min to achieve the same ventilatory end points as in manual hyperinflation. Mucus clearance rate was measured through fluoroscopic tracking of tracheal markers. Prior to each maneuver and 15 min thereafter, we assessed arterial and mixed gas exchange, pulmonary mechanics, and hemodynamics.

RESULTS

Both manual hyperinflation and ventilator hyperinflation significantly decreased inspiratory flow by approximately 16 L/min (P < .001) and increased peak expiratory flow by roughly 44 L/min (P < .001). The median (interquartile range) mucus clearance rate was 1.31 (0.84-2.30) prior to the interventions, and 0.70 (0.00-2.58) and 0.65 (0.45-1.47) during manual hyperinflation and ventilator hyperinflation, respectively (P = .09). Hyperinflations, whether delivered manually or through the ventilator, did not significantly modify pulmonary or hemodynamic parameters.

CONCLUSIONS

In an animal model of severe P. aeruginosa pneumonia, neither manual hyperinflation nor ventilator hyperinflation improved mucus clearance. If confirmed in comprehensive clinical experimentations, these findings should promote reappraisal of indications for both manual hyperinflation and ventilator hyperinflation as a therapeutic technique for mucus clearance and atelectasis reversal.

Pathophysiology and Management of Acute Respiratory Distress Syndrome in Obese Patients

A rising prevalence of obesity is reported over time and throughout the world. At the same time, the acute respiratory distress syndrome (ARDS) remains an important public health problem, accounting for approximately 10% of intensive care unit admissions and leading to significant hospital mortality. Even in the absence of acute illnesses, obesity affects respiratory mechanics and gas exchange in the setting of a restrictive disease. In the presence of ARDS, obesity adds various challenges to a safe and effective management of respiratory support. Difficult airway management, altered lung and chest wall physiology, and positional gas trapping are routinely encountered. The management of such difficult cases is generally empiric, as it is based on small-sized, physiologic studies or on suggestions from the general anesthesia literature. The present review focuses on those cases in which ARDS is coincident with obesity, with the aim of presenting treatment options based on the current evidence. The first part summarizes the epidemiology of obesity and ARDS. Then the diagnostic challenges due to obesity-related artifacts of the different imaging techniques will be presented. A subsequent, detailed description of the altered respiratory anatomy and physiology of obesity will provide help in selecting an optimal, individually tailored strategy of support. Furthermore, we will discuss how esophageal manometry should be used to adjust the settings of positive end-expiratory pressure and tidal volume; the challenges of prone positioning and extracorporeal support; and the optimal strategies for weaning from mechanical ventilation, including when and how to perform a tracheostomy.

Music therapy reduces stress and anxiety in critically ill patients: a systematic review of randomized clinical trials

INTRODUCTION

The underlying clinical condition and the Intensive Care Unit (ICU) environment make critical illness a stressful event. Although the usual management consists of sedation, non-pharmacological interventions such as music therapy have been suggested for their drug-sparing effect. Aim of the present review is to assess the current evidence on the effectiveness of music therapy in reducing stress and anxiety in critically ill, adult patients.

EVIDENCE ACQUISITION

A systematic review of publications was undertaken using MEDLINE, CINAHL, Cochrane Library, Scopus, Web of Science, Indice Italiano di Letteratura di Scienze Infermieristiche. We included studies of critically ill patients that assessed any effect of music therapy on stress and anxiety, which were variably assessed according to each study's definition.

EVIDENCE SYNTHESIS

Eleven studies were included (10 RCTs and one quasi-experimental design), for a total of 959 patients (range 17-373). The overall quality of the studies was satisfactory; several potential sources for bias were identified. Music therapy was generally provided as a single, 30'-intervention, ranging from 15 to 60'. Only in two studies was the intervention repeated more than once daily. The control groups were standard care, relaxation, headphones with no music or noise-cancelling headphones. Music therapy determined a significant reduction in the levels of anxiety and stress, as assessed by self-reported scales and physiologic parameters. Pooled analysis was not performed due to the heterogeneity of the interventions.

CONCLUSIONS

Despite significant heterogeneity in trial designs, timing and features of the intervention, music therapy is consistently associated with a reduction in anxiety and stress of critically ill patients.

In-vitro analysis of a novel 'add-on' silicone cuff to improve sealing properties of tracheal tubes

Leakage of colonised oropharyngeal secretions across the tracheal tube cuff may cause iatrogenic pulmonary infection. We studied a novel 'add-on' cuff, which can be inserted over an existing tracheal tube and advanced into the subglottic region. The physical properties of the novel silicone cuff (BronchoGuard, Ciel Medical, USA) were evaluated in comparison with the Hi-Lo^® tracheal tube. In a bench study, we identified saline inflation volumes required to transmit pressures between 15 and 30 cmH₂ O against artificial tracheas of 18, 20 and 22 mm internal diameter. We computed cuff compliance, and minimal inflation volume to achieve air sealing during mechanical ventilation. Finally, we compared the leakage flow rate of artificial saliva across the novel cuff. On average, the mean (SD) inflation volumes necessary to transmit tracheal pressures of 15, 20, 25 and 30 cmH₂ O were 4.1 (2.2), 4.4 (2.3), 4.6 (2.4) and 4.8 (2.4) ml for the novel cuff and 7.7 (2.5), 8.0 (2.6), 8.4 (2.6) and 8.7 (2.7) ml for the Hi-Lo tube, respectively (p < 0.001). The minimal inflation volumes to achieve air sealing were 3.8 (0.9) and 10.5 (2.1) ml (p < 0.001), which resulted in transmitted tracheal pressures of 8.3 (9.8) and 27.6 (34.8) cmH₂ O (p < 0.001). Compliance was 0.026 (0.004) and 0.616 (0.324) ml.cmH₂ 0^-1 , respectively (p < 0.001). Although massive leak was found when the novel cuff transmitted pressures ≤ 20 cmH₂ O against the trachea, leakage was avoided with pressures ≥ 25 cmH₂ O, owing to optimal contact between the cuff and the tracheal wall. In contrast, the standard cuff consistently leaked irrespective of the pressure. We conclude that the novel cuff has advantageous properties that warrant clinical corroboration.

An in-vitro study to evaluate high-volume low-pressure endotracheal tube cuff deflation dynamics

BACKGROUND

High-volume low-pressure (HVLP) endotracheal tube (ETT) cuffs for critically ill patients often deflate during the course of mechanical ventilation. We performed an in-vitro study to comprehensively assess HVLP cuff deflation dynamics and potential preventive measures.

METHODS

We evaluated 24-hour deflation of seven HVLP cuffs of cylindrical or tapered shape, and made of polyvinylchloride or polyurethane. Experiments were performed within a thermostated chamber set at 37 °C. In the first stage of experiments, the cuff pilot balloon valve was not manipulated. The cuff internal pressure was assessed hourly for 24 hours, via a linear position sensor which monitored cuff deflation displacements. Then, we re-evaluated cuff deflation of the worst-performing ETT cuffs with the cuff pilot balloon valve sealed. Finally, we inflated ETT cuffs within an artificial trachea to evaluate deflation dynamics during mechanical ventilation.

RESULTS

Initial tests showed an exponential decrease in cuff internal pressure in five out of seven cuffs. Cuffs of cylindrical shape and made of polyurethane demonstrated the fastest deflation rates (P<0.050 vs. cuffs of conical shape and made of polyvinylchloride). When the cuff pilot balloon valve was not sealed, the internal cuff pressure deflation rate differed significantly among ETTs (P=0.005). Yet, upon sealing the cuff pilot balloon valve and during mechanical ventilation, cuff deflation rates decreased (P<0.050).

CONCLUSIONS

In controlled in-vitro settings, ETT cuffs consistently deflate over time, and the cuff pilot balloon valve plays a central role in this occurrence. Deflation rate decreases when cuffs are inflated within a plastic artificial tracheal model and mechanical ventilation is activated.

Declining Mortality in Patients With Acute Respiratory Distress Syndrome: An Analysis of the Acute Respiratory Distress Syndrome Network Trials

OBJECTIVES

There has been multiple advances in the management of acute respiratory distress syndrome, but the temporal trends in acute respiratory distress syndrome-related mortality are not well known. This study aimed to investigate the trends in mortality in acute respiratory distress syndrome patients over time and to explore the roles of daily fluid balance and ventilation variables in those patients.

DESIGN

Secondary analysis of randomized controlled trials conducted by the Acute Respiratory Distress Syndrome Network from 1996 to 2013.

SETTING

Multicenter study involving Acute Respiratory Distress Syndrome Network trials.

PATIENTS

Patients with acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASURES AND MAIN RESULTS

Individual patient data from 5,159 acute respiratory distress syndrome patients (excluding the Late Steroid Rescue Study trial) were enrolled in this study. The crude mortality rate decreased from 35.4% (95% CI, 29.9-40.8%) in 1996 to 28.3% (95% CI, 22.0-34.7%) in 2013. By adjusting for the baseline Acute Physiology and Chronic Health Evaluation III, age, ICU type, and admission resource, patients enrolled from 2005 to 2010 (odds ratio, 0.61; 95% CI, 0.50-0.74) and those enrolled after 2010 (odds ratio, 0.73; 95% CI, 0.58-0.92) were associated with lower risk of death as compared to those enrolled before 2000. The effect of year on mortality decline disappeared after adjustment for daily fluid balance, positive end-expiratory pressure, tidal volume, and plateau pressure. There were significant trends of declines in daily fluid balance, tidal volume, and plateau pressure and an increase in positive end-expiratory pressure over the 17 years.

CONCLUSIONS

Our study shows an improvement in the acute respiratory distress syndrome-related mortality rate in the critically ill patients enrolled in the Acute Respiratory Distress Syndrome Network trials. The effect was probably mediated via decreased tidal volume, plateau pressure, and daily fluid balance and increased positive end-expiratory pressure.

Lung recruitment: What has computed tomography taught us in the last decade?

Although chest X-ray remains a fundamental lung imaging technique, through the years, CT scan has significantly improved our knowledge of the pathophysiological process and currently is the reference lung imaging tool for both a visual and quantitative computer-based analysis. The application of lung CT in the early phase of ARDS has led to changes in the clinical management in up of thirty percent of the patients. Although CT requires the transportation of the patient to the radiological department and exposes the patient to high dose of radiation, given the several information that CT can offer, it should be applied at least one time, in the early phase in all ARDS patients. CT plays an irreplaceable role to describe and assess the lung recruitability and to help a more physiological setting of mechanical ventilation.

Enteral versus intravenous approach for the sedation of critically ill patients: a randomized and controlled trial

Background

ICU patients must be kept conscious, calm, and cooperative even during the critical phases of illness. Enteral administration of sedative drugs might avoid over sedation, and would be as adequate as intravenous administration in patients who are awake, with fewer side effects and lower costs. This study compares two sedation strategies, for early achievement and maintenance of the target light sedation.

Methods

This was a multicenter, single-blind, randomized and controlled trial carried out in 12 Italian ICUs, involving patients with expected mechanical ventilation duration > 72 h at ICU admission and predicted mortality > 12% (Simplified Acute Physiology Score II > 32 points) during the first 24 h on ICU. Patients were randomly assigned to receive intravenous (midazolam, propofol) or enteral (hydroxyzine, lorazepam, and melatonin) sedation. The primary outcome was percentage of work shifts with the patient having an observed Richmond Agitation-Sedation Scale (RASS) = target RASS ±1. Secondary outcomes were feasibility, delirium-free and coma-free days, costs of drugs, length of ICU and hospital stay, and ICU, hospital, and one-year mortality.

Results

There were 348 patients enrolled. There were no differences in the primary outcome: enteral 89.8% (74.1–100), intravenous 94.4% (78–100), p = 0.20. Enteral-treated patients had more protocol violations: n = 81 (46.6%) vs 7 (4.2%), p < 0.01; more self-extubations: n = 14 (8.1%) vs 4 (2.4%), p = 0.03; a lighter sedative target (RASS = 0): 93% (71–100) vs 83% (61–100), p < 0.01; and lower total drug costs: 2.39 (0.75–9.78) vs 4.15 (1.20–20.19) €/day with mechanical ventilation (p = 0.01).

Conclusions

Although enteral sedation of critically ill patients is cheaper and permits a lighter sedation target, it is not superior to intravenous sedation for reaching the RASS target.

Trial registration

ClinicalTrials.gov, NCT01360346. Registered on 25 March 2011.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2280-x) contains supplementary material, which is available to authorized users.

Appraisal of systemic inflammation and diagnostic markers in a porcine model of VAP: secondary analysis from a study on novel preventive strategies

Background

We previously evaluated the efficacy of a ventilatory strategy to achieve expiratory flow bias and positive end-expiratory pressure (EFB + PEEP) or the Trendelenburg position (TP) for the prevention of ventilator-associated pneumonia (VAP). These preventive measures were aimed at improving mucus clearance and reducing pulmonary aspiration of bacteria-laden oropharyngeal secretions. This secondary analysis is aimed at evaluating the effects of aforementioned interventions on systemic inflammation and to substantiate the value of clinical parameters and cytokines in the diagnosis of VAP.

Methods

Twenty female pigs were randomized to be positioned in the semirecumbent/prone position, and ventilated with duty cycle 0.33 and without PEEP (control); positioned as in the control group, PEEP 5 cmH₂O, and duty cycle to achieve expiratory flow bias (EFB+PEEP); ventilated as in the control group, but in the Trendelenburg position (Trendelenburg). Following randomization, P. aeruginosa was instilled into the oropharynx. Systemic cytokines and tracheal secretions P. aeruginosa concentration were quantified every 24h. Lung biopsies were collected for microbiological confirmation of VAP.

Results

In the control, EFB + PEEP, and Trendelenburg groups, lung tissue Pseudomonas aeruginosa concentration was 2.4 ± 1.5, 1.9 ± 2.1, and 0.3 ± 0.6 log cfu/mL, respectively (p = 0.020). Whereas, it was 2.4 ± 1.9 and 0.6 ± 0.9 log cfu/mL in animals with or without VAP (p < 0.001). Lower levels of interleukin (IL)-1β (p = 0.021), IL-1RA (p < 0.001), IL-4 (p = 0.005), IL-8 (p = 0.008), and IL-18 (p = 0.050) were found in Trendelenburg animals. VAP increased IL-10 (p = 0.035), tumor necrosis factor-α (p = 0.041), and endotracheal aspirate (ETA) P. aeruginosa concentration (p = 0.024). A model comprising ETA bacterial burden, IL-10, and TNF-α yielded moderate discrimination for the diagnosis of VAP (area of the receiver operating curve 0.82, 95% CI 0.61–1.00).

Conclusions

Our findings demonstrate anti-inflammatory effects associated with the Trendelenburg position. In this reliable model of VAP, ETA culture showed good diagnostic accuracy, whereas systemic IL-10 and TNF-α marginally improved accuracy. Further clinical studies will be necessary to confirm clinical value of the Trendelenburg position as a measure to hinder inflammation during mechanical ventilation and significance of systemic IL-10 and TNF-α in the diagnosis of VAP.

Interpretation of the transpulmonary pressure in the critically ill patient

Mechanical ventilation is a life-saving procedure, which takes over the function of the respiratory muscles while buying time for healing to take place. However, it can also promote or worsen lung injury, so that careful monitoring of respiratory mechanics is suggested to titrate the level of support and avoid injurious pressures and volumes to develop. Standard monitoring includes flow, volume and airway pressure (Paw). However, Paw represents the pressure acting on the respiratory system as a whole, and does not allow to differentiate the part of pressure that is spent di distend the chest wall. Moreover, if spontaneous breathing efforts are allowed, the Paw is the sum of that applied by the ventilator and that generated by the patient. As a consequence, monitoring of Paw has significant shortcomings. Assessment of esophageal pressure (Pes), as a surrogate for pleural pressure (Ppl), may allow the clinicians to discriminate between the elastic behaviour of the lung and the chest wall, and to calculate the degree of spontaneous respiratory effort. In the present review, the characteristics and limitations of airway and transpulmonary pressure monitoring will be presented; we will highlight the different assumptions underlying the various methods for measuring transpulmonary pressure (i.e., the elastance-derived and the release-derived method, and the direct measurement), as well as the potential application of transpulmonary pressure assessment during both controlled and spontaneous/assisted mechanical ventilation in critically ill patients.

Conscious sedation in critically ill patients is associated with stressors perception lower than assessed by caregivers

BACKGROUND

In ICU, the stay is frequently a stressful experience. Caregivers may help to understand patients' perceptions; however, their reliability is uncertain. Despite the recent recommendations of lighter sedation targets, little is known about the impact of "conscious sedation" on ICU patients memories. Purpose of this prospective, observational study is to analyze the stress perception in consciously-sedated ICU-patients, comparing it to caregivers and staff members.

METHODS

Twenty-nine high-risk ICU-patients treated with awake/cooperative sedation were enrolled. Before discharge, patients received a validated questionnaire for ICU stressors evaluation, also administered to their main caregiver (N.=29), to caregivers of other ICU patients not enrolled in the study (N.=33) and to staff members (ICU nurses, attending physicians, residents, medical students, N.=56).

RESULTS

Total stress score was: patients 141±41, patient relatives 210±63, other relatives: 202±73, ICU staff: 232±44, P<0.001. Among patients, older age (P=0.031), longer ICU-stay (P=0.018) and awake-sedation (P=0.022) were associated with lower stress; sex and illness severity had no effect; mechanical ventilation length (P=0.021) and agitation (P=0.029) were associated with higher stress. Nurses tended to overestimate stressors more than attending physicians and trainees. Within staff members, age (P=0.021) and years of experience (P=0.069) were positively associated with overestimation.

CONCLUSIONS

Conscious sedation is associated with stress perception lower than stress assessed by caregivers: relatives and staff members tend to overestimate ICU patient stress, more so with increasing age or expertise. A number of stressors underestimated by staff and families could be target of specific interventions to ameliorate quality of life during ICU stay.

Long Term Evaluation of Gas Exchange and Hydrodynamic Performance of a Heparinized Artificial Lung: Comparison of Two Different Hollow Fiber Pore Sizes

We compared the performance of a heparinized hollow fiber artificial lung (Medtronic, Minimax) featuring standard hollow fibers (Group A) and experimental hollow fibers with a smaller pore size (Group B). Four sheep in each group underwent a veno-venous bypass for 72 hours. Every 6 hours, at 3 different blood flow rates (BFr) (400, 800, 1200 ml/min), at a constant gas flow rate (Gfr = 4 L/min), and at a constant blood inlet PCO2 (45-55 mmHg), we measured the oxygenation performance (O2 transfer = VO2 and blood outlet PO2 = PO2out), CO2 removal (CO2 transfer = VCO2 and PCO2 outlet = PCO2out) and pressure drop across the device (ΔP). A total of about 50 measurement sets were obtained for each group at different time points and blood flow rates. Both groups showed a good oxygenation performance (PO2out always higher than 200 mmHg) and no differences were observed between the two groups (at 1200 ml/min BFr, the average VO2 of all time points was 47 ± 15 ml/min in group A and 44 ± 11 ml/min in group B, mean ± SD, NS). During the first 24 hours, the VCO2 was higher in Group B than in Group A at each BFr (at 1200 ml/min BFr, 81 ± 18 vs 67 ± 20 ml/min, p<0.01), while no differences were observed during the subsequent 48 hours. Throughout the entire experiment, VCO2 increased with increasing BFr in both groups, (in group B, from 43 ± 14 ml/min at 400 ml/min BFr, to 73 ± 17 ml/min at 1200 ml/min BFr, average of all time points, p<0.01). In both groups the ΔP increased with the increasing BFr, but it was lower in Group B than in Group A at BFr 800 and 1200 ml/min (at 1200 ml/min BFr, 51 ± 15 mmHg vs 65 ± 17 mmHg, p<0.01), and remained stable for the entire experimental period.

A Morphological and Quantitative Analysis of Lung CT Scan in Patients With Acute Respiratory Distress Syndrome and in Cardiogenic Pulmonary Edema

BACKGROUND

The acute respiratory distress syndrome (ARDS) and cardiogenic pulmonary edema (CPE) are both characterized by an increase in lung edema that can be measured by computed tomography (CT). The aim of this study was to compare possible differences between patients with ARDS and CPE in the morphologic pattern, the aeration, and the amount and distribution of edema within the lung.

METHODS

Lung CT was performed at a mean positive end-expiratory pressure level of 5 cm H₂O in both groups. The morphological evaluation was performed by two radiologists, while the quantitative evaluation was performed by a dedicated software.

RESULTS

A total of 60 patients with ARDS (20 mild, 20 moderate, 20 severe) and 20 patients with CPE were enrolled. The ground-glass attenuation regions were similarly present among the groups, 8 (40%), 8 (40%), 14 (70%), and 10 (50%), while the airspace consolidations were significantly more present in ARDS. The lung gas volume was significantly lower in severe ARDS compared to CPE (830 [462] vs 1120 [832] mL). Moving from the nondependent to the dependent lung regions, the not inflated lung tissue significantly increased, while the well inflated tissue decreased (ρ = 0.96-1.00, P < .0001). Significant differences were found between ARDS and CPE mostly in dependent regions. In severe ARDS, the estimated edema was significantly higher, compared to CPE (757 [740] vs 532 [637] g).

CONCLUSIONS

Both ARDS and CPE are characterized by a similar presence of ground-glass attenuation and different airspace consolidation regions. Acute respiratory distress syndrome has a higher amount of not inflated tissue and lower amount of well inflated tissue. However, the overall regional distribution is similar within the lung.

Intensive care unit patients with lower respiratory tract nosocomial infections: the ENIRRIs project

The clinical course of intensive care unit (ICU) patients may be complicated by a large spectrum of lower respiratory tract infections (LRTI), defined by specific epidemiological, clinical and microbiological aspects.

A European network for ICU-related respiratory infections (ENIRRIs), supported by the European Respiratory Society, has been recently established, with the aim at studying all respiratory tract infective episodes except community-acquired ones. A multicentre, observational study is in progress, enrolling more than 1000 patients fulfilling the clinical, biochemical and radiological findings consistent with a LRTI. This article describes the methodology of this study. A specific interest is the clinical impact of non-ICU-acquired nosocomial pneumonia requiring ICU admission, non-ventilator-associated LRTIs occurring in the ICU, and ventilator-associated tracheobronchitis. The clinical meaning of microbiologically negative infectious episodes and specific details on antibiotic administration modalities, dosages and duration are also highlighted. Recently released guidelines address many unresolved questions which might be answered by such large-scale observational investigations. In light of the paucity of data regarding such topics, new interesting information is expected to be obtained from our network research activities, contributing to optimisation of care for critically ill patients in the ICU.

Methodology for the first European network for ICU-related respiratory infections (ENIRRIs) projecthttp://ow.ly/sud930fU1e7

Respiratory support in patients with acute respiratory distress syndrome: an expert opinion

Acute respiratory distress syndrome (ARDS) is a common condition in intensive care unit patients and remains a major concern, with mortality rates of around 30–45% and considerable long-term morbidity. Respiratory support in these patients must be optimized to ensure adequate gas exchange while minimizing the risks of ventilator-induced lung injury. The aim of this expert opinion document is to review the available clinical evidence related to ventilator support and adjuvant therapies in order to provide evidence-based and experience-based clinical recommendations for the management of patients with ARDS.

Tidal volume in acute respiratory distress syndrome: how best to select it

Mechanical ventilation is the type of organ support most widely provided in the intensive care unit. However, this form of support does not constitute a cure for acute respiratory distress syndrome (ARDS), as it mainly works by buying time for the lungs to heal while contributing to the maintenance of vital gas exchange. Moreover, it can further damage the lung, leading to the development of a particular form of lung injury named ventilator-induced lung injury (VILI). Experimental evidence accumulated over the last 30 years highlighted the factors associated with an injurious form of mechanical ventilation. The present paper illustrates the physiological effects of delivering a tidal volume to the lungs of patients with ARDS, and suggests an approach to tidal volume selection. The relationship between tidal volume and the development of VILI, the so called volotrauma, will be reviewed. The still actual suggestion of a lung-protective ventilatory strategy based on the use of low tidal volumes scaled to the predicted body weight (PBW) will be presented, together with newer strategies such as the use of airway driving pressure as a surrogate for the amount of ventilatable lung tissue or the concept of strain, i.e., the ratio between the tidal volume delivered relative to the resting condition, that is the functional residual capacity (FRC). An ultra-low tidal volume strategy with the use of extracorporeal carbon dioxide removal (ECCO₂R) will be presented and discussed. Eventually, the role of other ventilator-related parameters in the generation of VILI will be considered (namely, plateau pressure, airway driving pressure, respiratory rate (RR), inspiratory flow), and the promising unifying framework of mechanical power will be presented.

Heat and moisture exchangers (HMEs) and heated humidifiers (HHs) in adult critically ill patients: a systematic review, meta-analysis and meta-regression of randomized controlled trials

BACKGROUND

The aims of this systematic review and meta-analysis of randomized controlled trials are to evaluate the effects of active heated humidifiers (HHs) and moisture exchangers (HMEs) in preventing artificial airway occlusion and pneumonia, and on mortality in adult critically ill patients. In addition, we planned to perform a meta-regression analysis to evaluate the relationship between the incidence of artificial airway occlusion, pneumonia and mortality and clinical features of adult critically ill patients.

METHODS

Computerized databases were searched for randomized controlled trials (RCTs) comparing HHs and HMEs and reporting artificial airway occlusion, pneumonia and mortality as predefined outcomes. Relative risk (RR), 95% confidence interval for each outcome and I ² were estimated for each outcome. Furthermore, weighted random-effect meta-regression analysis was performed to test the relationship between the effect size on each considered outcome and covariates.

RESULTS

Eighteen RCTs and 2442 adult critically ill patients were included in the analysis. The incidence of artificial airway occlusion (RR = 1.853; 95% CI 0.792-4.338), pneumonia (RR = 932; 95% CI 0.730-1.190) and mortality (RR = 1.023; 95% CI 0.878-1.192) were not different in patients treated with HMEs and HHs. However, in the subgroup analyses the incidence of airway occlusion was higher in HMEs compared with HHs with non-heated wire (RR = 3.776; 95% CI 1.560-9.143). According to the meta-regression, the effect size in the treatment group on artificial airway occlusion was influenced by the percentage of patients with pneumonia (β = -0.058; p = 0.027; favors HMEs in studies with high prevalence of pneumonia), and a trend was observed for an effect of the duration of mechanical ventilation (MV) (β = -0.108; p = 0.054; favors HMEs in studies with longer MV time).

CONCLUSIONS

In this meta-analysis we found no superiority of HMEs and HHs, in terms of artificial airway occlusion, pneumonia and mortality. A trend favoring HMEs was observed in studies including a high percentage of patients with pneumonia diagnosis at admission and those with prolonged MV. However, the choice of humidifiers should be made according to the clinical context, trying to avoid possible complications and reaching the appropriate performance at lower costs.

Paracetamol in fever in critically ill patients-an update

Fever, which is arbitrary defined as an increase in body temperature above 38.3°C, can affect up to 90% of patients admitted in intensive care unit. Induction of fever is mediated by the release of pyrogenic cytokines (tumor necrosis factor α, interleukin 1, interleukin 6, and interferons). Fever is associated with increased length of stay in intensive care unit and with a worse outcome in some subgroups of patients (mainly neurocritically ill patients). Although fever can increase oxygen consumption in unstable patients, on the contrary, it can activate physiologic systems that are involved in pathogens clearance. Treatments to reduce fever include the use of antipyretics. Thus, the reduction of fever might reduce the ability to develop an efficient host response. This balance, between harms and benefits, has to be taken into account every time we decide to treat or not to treat fever in a given patient. Among the antipyretics, paracetamol is one of the most common used. Paracetamol is a synthetic, nonopioid, centrally acting analgesic, and antipyretic drug. Its antipyretic effect occurs because it inhibits cyclooxygenase-3 and the prostaglandin synthesis, within the central nervous system, resetting the hypothalamic heat-regulation center. In this clinical review, we will summarize the use of paracetamol as antipyretic in critically ill patients (sepsis, trauma, neurological, and medical).

Airway driving pressure and lung stress in ARDS patients

Background

Lung-protective ventilation strategy suggests the use of low tidal volume, depending on ideal body weight, and adequate levels of PEEP. However, reducing tidal volume according to ideal body weight does not always prevent overstress and overstrain. On the contrary, titrating mechanical ventilation on airway driving pressure, computed as airway pressure changes from PEEP to end-inspiratory plateau pressure, equivalent to the ratio between the tidal volume and compliance of respiratory system, should better reflect lung injury. However, possible changes in chest wall elastance could affect the reliability of airway driving pressure. The aim of this study was to evaluate if airway driving pressure could accurately predict lung stress (the pressure generated into the lung due to PEEP and tidal volume).

Methods

One hundred and fifty ARDS patients were enrolled. At 5 and 15 cmH₂O of PEEP, lung stress, driving pressure, lung and chest wall elastance were measured.

Results

The applied tidal volume (mL/kg of ideal body weight) was not related to lung gas volume (r² = 0.0005 p = 0.772). Patients were divided according to an airway driving pressure lower and equal/higher than 15 cmH₂O (the lower and higher airway driving pressure groups). At both PEEP levels, the higher airway driving pressure group had a significantly higher lung stress, respiratory system and lung elastance compared to the lower airway driving pressure group. Airway driving pressure was significantly related to lung stress (r² = 0.581 p < 0.0001 and r² = 0.353 p < 0.0001 at 5 and 15 cmH₂O of PEEP). For a lung stress of 24 and 26 cmH₂O, the optimal cutoff value for the airway driving pressure were 15.0 cmH₂O (ROC AUC 0.85, 95 % CI = 0.782–0.922); and 16.7 (ROC AUC 0.84, 95 % CI = 0.742–0.936).

Conclusions

Airway driving pressure can detect lung overstress with an acceptable accuracy. However, further studies are needed to establish if these limits could be used for ventilator settings.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1446-7) contains supplementary material, which is available to authorized users.

Severe hypoxemia: which strategy to choose

BACKGROUND

Acute respiratory distress syndrome (ARDS) is characterized by a noncardiogenic pulmonary edema with bilateral chest X-ray opacities and reduction in lung compliance, and the hallmark of the syndrome is hypoxemia refractory to oxygen therapy. Severe hypoxemia (PaO2/FiO2 < 100 mmHg), which defines severe ARDS, can be found in 20-30 % of the patients and is associated with the highest mortality rate. Although the standard supportive treatment remains mechanical ventilation (noninvasive and invasive), possible adjuvant therapies can be considered. We performed an up-to-date clinical review of the possible available strategies for ARDS patients with severe hypoxemia.

MAIN RESULTS

In summary, in moderate-to-severe ARDS or in the presence of other organ failure, noninvasive ventilatory support presents a high risk of failure: in those cases the risk/benefit of delayed mechanical ventilation should be evaluated carefully. Tailoring mechanical ventilation to the individual patient is fundamental to reduce the risk of ventilation-induced lung injury (VILI): it is mandatory to apply a low tidal volume, while the optimal level of positive end-expiratory pressure should be selected after a stratification of the severity of the disease, also taking into account lung recruitability; monitoring transpulmonary pressure or airway driving pressure can help to avoid lung overstress. Targeting oxygenation of 88-92 % and tolerating a moderate level of hypercapnia are a safe choice. Neuromuscular blocking agents (NMBAs) are useful to maintain patient-ventilation synchrony in the first hours; prone positioning improves oxygenation in most cases and promotes a more homogeneous distribution of ventilation, reducing the risk of VILI; both treatments, also in combination, are associated with an improvement in outcome if applied in the acute phase in the most severe cases. The use of extracorporeal membrane oxygenation (ECMO) in severe ARDS is increasing worldwide, but because of a lack of randomized trials is still considered a rescue therapy.

CONCLUSION

Severe ARDS patients should receive a holistic framework of respiratory and hemodynamic support aimed to ensure adequate gas exchange while minimizing the risk of VILI, by promoting lung recruitment and setting protective mechanical ventilation. In the most severe cases, NMBAs, prone positioning, and ECMO should be considered.

Effect of body mass index in acute respiratory distress syndrome

BACKGROUND

Obesity is associated in healthy subjects with a great reduction in functional residual capacity and with a stiffening of lung and chest wall elastance, which promote alveolar collapse and hypoxaemia. Likewise, obese patients with acute respiratory distress syndrome (ARDS) could present greater derangements of respiratory mechanics than patients of normal weight.

METHODS

One hundred and one ARDS patients were enrolled. Partitioned respiratory mechanics and gas exchange were measured at 5 and 15 cm H2O of PEEP with a tidal volume of 6-8 ml kg(-1) of predicted body weight. At 5 and 45 cm H2O of PEEP, two lung computed tomography scans were performed.

RESULTS

Patients were divided as follows according to BMI: normal weight (BMI≤25 kg m(-2)), overweight (BMI between 25 and 30 kg m(-2)), and obese (BMI>30 kg m(-2)). Obese, overweight, and normal-weight groups presented a similar lung elastance (median [interquartile range], respectively: 17.7 [14.2-24.8], 20.9 [16.1-30.2], and 20.5 [15.2-23.6] cm H2O litre(-1) at 5 cm H2O of PEEP and 19.3 [15.5-26.3], 21.1 [17.4-29.2], and 17.1 [13.4-20.4] cm H2O litre(-1) at 15 cm H2O of PEEP) and chest elastance (respectively: 4.9 [3.1-8.8], 5.9 [3.8-8.7], and 7.8 [3.9-9.8] cm H2O litre(-1) at 5 cm H2O of PEEP and 6.5 [4.5-9.6], 6.6 [4.2-9.2], and 4.9 [2.4-7.6] cm H2O litre(-1) at 15 cm H2O of PEEP). Lung recruitability was not affected by the body weight (15.6 [6.3-23.4], 15.7 [9.8-22.2], and 11.3 [6.2-15.6]% for normal-weight, overweight, and obese groups, respectively). Lung gas volume was significantly lower whereas total superimposed pressure was significantly higher in the obese compared with the normal-weight group (1148 [680-1815] vs 827 [686-1213] ml and 17.4 [15.8-19.3] vs 19.3 [18.6-21.7] cm H2O, respectively).

CONCLUSIONS

Obese ARDS patients do not present higher chest wall elastance and lung recruitability.

Diagnostic workup for ARDS patients

Acute respiratory distress syndrome (ARDS) is defined by the association of bilateral infiltrates and hypoxaemia following an initial insult. Although a new definition has been recently proposed (Berlin definition), there are various forms of ARDS with potential differences regarding their management (ventilator settings, prone positioning use, corticosteroids). ARDS can be caused by various aetiologies, and the adequate treatment of the responsible cause is crucial to improve the outcome. It is of paramount importance to characterize the mechanisms causing lung injury to optimize both the aetiological treatment and the symptomatic treatment. If there is no obvious cause of ARDS or if a direct lung injury is suspected, bronchoalveolar lavage (BAL) should be strongly considered to identify microorganisms responsible for pneumonia. Blood samples can also help to identify microorganisms and to evaluate biomarkers of infection. If there is no infectious cause of ARDS or no other apparent aetiology is found, second-line examinations should include markers of immunologic diseases. In selected cases, open lung biopsy remains useful to identify the cause of ARDS when all other examinations remain inconclusive. CT scan is fundamental when there is a suspicion of intra-abdominal sepsis and in some cases of pneumonia. Ultrasonography is important not only in evaluating biventricular function but also in identifying pleural effusions and pneumothorax. The definition of ARDS remains clinical and the main objective of the diagnostic workup should be to be focused on identification of its aetiology, especially a treatable infection.

The occlusion tests and end-expiratory esophageal pressure: measurements and comparison in controlled and assisted ventilation

Background

Esophageal pressure is used as a reliable surrogate of the pleural pressure. It is conventionally measured by an esophageal balloon placed in the lower part of the esophagus. To validate the correct position of the balloon, a positive pressure occlusion test by compressing the thorax during an end-expiratory pause or a Baydur test obtained by occluding the airway during an inspiratory effort is used. An acceptable catheter position is defined when the ratio between the changes in esophageal and airway pressure (∆Pes/∆Paw) is close to unity. Sedation and paralysis could affect the accuracy of esophageal pressure measurements. The aim of this study was to evaluate, in mechanically ventilated patients, the effects of paralysis, two different esophageal balloon positions and two PEEP levels on the ∆Pes/∆Paw ratio measured by the positive pressure occlusion and the Baydur tests and on the end-expiratory esophageal pressure and respiratory mechanics (lung and chest wall).

Methods

Twenty-one intubated and mechanically ventilated patients (mean age 64.8 ± 14.0 years, body mass index 24.2 ± 4.3 kg/m², PaO₂/FiO₂ 319.4 ± 117.3 mmHg) were enrolled. In step 1, patients were sedated and paralyzed during volume-controlled ventilation, and in step 2, they were only sedated during pressure support ventilation. In each step, two esophageal balloon positions (middle and low, between 25–30 cm and 40–45 cm from the mouth) and two levels of PEEP (0 and 10 cmH₂O) were applied. The ∆Pes/∆Paw ratio and end-expiratory esophageal pressure were evaluated.

Results

The ∆Pes/∆Paw ratio was slightly higher (+0.11) with positive occlusion test compared with Baydur’s test. The level of PEEP and the esophageal balloon position did not affect this ratio. The ∆Pes and ∆Paw were significantly related to a correlation coefficient of r = 0.984 during the Baydur test and r = 0.909 in the positive occlusion test. End-expiratory esophageal pressure was significantly higher in sedated and paralyzed patients compared with sedated patients (+2.47 cmH₂O) and when esophageal balloon was positioned in the low position (+2.26 cmH₂O). The esophageal balloon position slightly influenced the lung elastance, while the PEEP reduced the chest wall elastance without affecting the lung and total respiratory system elastance.

Conclusions

Paralysis and balloon position did not clinically affect the measurement of the ∆Pes/∆Paw ratio, while they significantly increased the end-expiratory esophageal pressure.