Association between tidal volume size, duration of ventilation, and sedation needs in patients without acute respiratory distress syndrome: an individual patient data meta-analysis

Patients with uninjured lungs may also benefit from lung-protective ventilator settings

Although mechanical ventilation is a life-saving strategy in critically ill patients and an indispensable tool in patients under general anesthesia for surgery, it also acts as a double-edged sword. Indeed, ventilation is increasingly recognized as a potentially dangerous intrusion that has the potential to harm lungs, in a condition known as ‘ventilator-induced lung injury’ (VILI). So-called ‘lung-protective’ ventilator settings aiming at prevention of VILI have been shown to improve outcomes in patients with acute respiratory distress syndrome (ARDS), and, over the last few years, there has been increasing interest in possible benefit of lung-protective ventilation in patients under ventilation for reasons other than ARDS. Patients without ARDS could benefit from tidal volume reduction during mechanical ventilation. However, it is uncertain whether higher levels of positive end-expiratory pressure could benefit these patients as well. Finally, recent evidence suggests that patients without ARDS should receive low driving pressures during ventilation.

Effect of inspiratory synchronization during pressure-controlled ventilation on lung distension and inspiratory effort

Background

In pressure-controlled (PC) ventilation, tidal volume (V_T) and transpulmonary pressure (P_L) result from the addition of ventilator pressure and the patient’s inspiratory effort. PC modes can be classified into fully, partially, and non-synchronized modes, and the degree of synchronization may result in different V_T and P_L despite identical ventilator settings. This study assessed the effects of three PC modes on V_T, P_L, inspiratory effort (esophageal pressure–time product, PTP_es), and airway occlusion pressure, P_0.1. We also assessed whether P_0.1 can be used for evaluating patient effort.

Methods

Prospective, randomized, crossover physiologic study performed in 14 spontaneously breathing mechanically ventilated patients recovering from acute respiratory failure (1 subsequently withdrew). PC modes were fully (PC-CMV), partially (PC-SIMV), and non-synchronized (PC-IMV using airway pressure release ventilation) and were applied randomly; driving pressure, inspiratory time, and set respiratory rate being similar for all modes. Airway, esophageal pressure, P_0.1, airflow, gas exchange, and hemodynamics were recorded.

Results

V_T was significantly lower during PC-IMV as compared with PC-SIMV and PC-CMV (387 ± 105 vs 458 ± 134 vs 482 ± 108 mL, respectively; p < 0.05). Maximal P_L was also significantly lower (13.3 ± 4.9 vs 15.3 ± 5.7 vs 15.5 ± 5.2 cmH₂O, respectively; p < 0.05), but PTP_es was significantly higher in PC-IMV (215.6 ± 154.3 vs 150.0 ± 102.4 vs 130.9 ± 101.8 cmH₂O × s × min⁻¹, respectively; p < 0.05), with no differences in gas exchange and hemodynamic variables. PTP_es increased by more than 15% in 10 patients and by more than 50% in 5 patients. An increased P_0.1 could identify high levels of PTP_es.

Conclusions

Non-synchronized PC mode lowers V_T and P_L in comparison with more synchronized modes in spontaneously breathing patients but can increase patient effort and may need specific adjustments.

Clinical Trial Registration Clinicaltrial.gov # NCT02071277

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-017-0324-z) contains supplementary material, which is available to authorized users.

In vivo lung perfusion rehabilitates sepsis-induced lung injury

BACKGROUND

Sepsis is the leading cause of lung injury in adults and can lead to acute respiratory distress syndrome (ARDS). Using a novel technique of isolated in vivo lung perfusion (IVLP), we hypothesized that normothermic IVLP will improve oxygenation and compliance in a porcine model of sepsis-induced lung injury.

METHODS

Mature adult swine (n = 8) were administered lipopolysaccharide (LPS; 50 μg/kg over 2 hours) via the external jugular vein, followed by sternotomy and central extracorporeal membrane oxygenation (ECMO) cannulation (right atrium to ascending aorta). The left pulmonary artery (inflow) and left superior and inferior pulmonary veins (outflow) were dissected out and cannulated to deliver isolated perfusion to the left lung. After 4 hours of normothermic IVLP with Steen solution, the left lung then underwent 4 hours of reperfusion after IVLP decannulation. Airway pressures and lung-specific pulmonary vein blood gases from the right lung (LPS control) and left lung (LPS + IVLP) of the same animal were compared.

RESULTS

All animals demonstrated a significant reduction in the ratio of partial pressure of oxygen in arterial blood (PaO₂)/fraction of inspired oxygen (FiO₂) (P/F ratio) and total lung compliance at 2 hours after the start of LPS infusion (mean, 469 ± 19.7 mm Hg vs 222.2 ± 21.4 mm Hg; P < .0001). After reperfusion, 6 animals (75%) exhibited improved lung function, allowing for ECMO decannulation. Lung-specific oxygenation was superior in the left lung after 4 hours of reperfusion (mean, 310.5 ± 54.7 mm Hg vs 201.1 ± 21.7 mm Hg; P = .01). Similarly, total lung compliance improved after IVLP of the left lung. The lung wet weight to dry weight ratio demonstrated reduced edema in rehabilitated left lungs (mean, 6.5 ± 0.3 vs 7.5 ± 0.4; P = .04).

CONCLUSIONS

IVLP successfully rehabilitated LPS-injured lungs compared to ECMO support alone in this preclinical porcine model.

Mechanical Ventilation: State of the Art

Mechanical ventilation is the most used short-term life support technique worldwide and is applied daily for a diverse spectrum of indications, from scheduled surgical procedures to acute organ failure. This state-of-the-art review provides an update on the basic physiology of respiratory mechanics, the working principles, and the main ventilatory settings, as well as the potential complications of mechanical ventilation. Specific ventilatory approaches in particular situations such as acute respiratory distress syndrome and chronic obstructive pulmonary disease are detailed along with protective ventilation in patients with normal lungs. We also highlight recent data on patient-ventilator dyssynchrony, humidified high-flow oxygen through nasal cannula, extracorporeal life support, and the weaning phase. Finally, we discuss the future of mechanical ventilation, addressing avenues for improvement.

Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications: LAS VEGAS - an observational study in 29 countries

BACKGROUND

Limited information exists about the epidemiology and outcome of surgical patients at increased risk of postoperative pulmonary complications (PPCs), and how intraoperative ventilation was managed in these patients.

OBJECTIVES

To determine the incidence of surgical patients at increased risk of PPCs, and to compare the intraoperative ventilation management and postoperative outcomes with patients at low risk of PPCs.

DESIGN

This was a prospective international 1-week observational study using the 'Assess Respiratory Risk in Surgical Patients in Catalonia risk score' (ARISCAT score) for PPC for risk stratification.

PATIENTS AND SETTING

Adult patients requiring intraoperative ventilation during general anaesthesia for surgery in 146 hospitals across 29 countries.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of patients at increased risk of PPCs based on the ARISCAT score. Secondary outcomes included intraoperative ventilatory management and clinical outcomes.

RESULTS

A total of 9864 patients fulfilled the inclusion criteria. The incidence of patients at increased risk was 28.4%. The most frequently chosen tidal volume (VT) size was 500 ml, or 7 to 9 ml kg predicted body weight, slightly lower in patients at increased risk of PPCs. Levels of positive end-expiratory pressure (PEEP) were slightly higher in patients at increased risk of PPCs, with 14.3% receiving more than 5 cmH2O PEEP compared with 7.6% in patients at low risk of PPCs (P < 0.001). Patients with a predicted preoperative increased risk of PPCs developed PPCs more frequently: 19 versus 7%, relative risk (RR) 3.16 (95% confidence interval 2.76 to 3.61), P < 0.001) and had longer hospital stays. The only ventilatory factor associated with the occurrence of PPCs was the peak pressure.

CONCLUSION

The incidence of patients with a predicted increased risk of PPCs is high. A large proportion of patients receive high VT and low PEEP levels. PPCs occur frequently in patients at increased risk, with worse clinical outcome.

TRIAL REGISTRATION

The study was registered at Clinicaltrials.gov, number NCT01601223.

Fifty Years of Research in ARDS. Is Acute Respiratory Distress Syndrome a Preventable Disease?

Despite significant advances in our understanding and management of patients with acute respiratory distress syndrome (ARDS), the morbidity and mortality from ARDS remains high. Given the limited number of effective treatments for established ARDS, the strategic focus of ARDS research has shifted toward identifying patients with or at high risk of ARDS early in the course of the underlying illness, when strategies to reduce the development and progression of ARDS and associated organ failures can be systematically evaluated. In this review, we summarize the rationale, current evidence, and future directions in ARDS prevention.

Protective intraoperative ventilation with higher versus lower levels of positive end-expiratory pressure in obese patients (PROBESE): study protocol for a randomized controlled trial

BACKGROUND

Postoperative pulmonary complications (PPCs) increase the morbidity and mortality of surgery in obese patients. High levels of positive end-expiratory pressure (PEEP) with lung recruitment maneuvers may improve intraoperative respiratory function, but they can also compromise hemodynamics, and the effects on PPCs are uncertain. We hypothesized that intraoperative mechanical ventilation using high PEEP with periodic recruitment maneuvers, as compared with low PEEP without recruitment maneuvers, prevents PPCs in obese patients.

METHODS/DESIGN

The PRotective Ventilation with Higher versus Lower PEEP during General Anesthesia for Surgery in OBESE Patients (PROBESE) study is a multicenter, two-arm, international randomized controlled trial. In total, 2013 obese patients with body mass index ≥35 kg/m² scheduled for at least 2 h of surgery under general anesthesia and at intermediate to high risk for PPCs will be included. Patients are ventilated intraoperatively with a low tidal volume of 7 ml/kg (predicted body weight) and randomly assigned to PEEP of 12 cmH₂O with lung recruitment maneuvers (high PEEP) or PEEP of 4 cmH₂O without recruitment maneuvers (low PEEP). The occurrence of PPCs will be recorded as collapsed composite of single adverse pulmonary events and represents the primary endpoint.

DISCUSSION

To our knowledge, the PROBESE trial is the first multicenter, international randomized controlled trial to compare the effects of two different levels of intraoperative PEEP during protective low tidal volume ventilation on PPCs in obese patients. The results of the PROBESE trial will support anesthesiologists in their decision to choose a certain PEEP level during general anesthesia for surgery in obese patients in an attempt to prevent PPCs.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02148692. Registered on 23 May 2014; last updated 7 June 2016.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Incidence and Prognostic Impact of Respiratory Support in Patients With ST-Segment Elevation Myocardial Infarction

Data addressing the use of respiratory support in acute coronary syndromes are lacking. To address this evidence gap, we characterized prognostic impact and trends in utilization of invasive mechanical ventilation (IMV) and noninvasive ventilation (NIV) in patients hospitalized with ST-segment elevation myocardial infarction (STEMI) from 2002 through 2013 using the National Inpatient Sample. Multivariate logistic regression was performed to identify patient, hospital, and clinical characteristics associated with requiring IMV or NIV within 24 hours of hospitalization. Multivariate Cox proportional hazards regression was used to quantify the magnitude of in-hospital mortality associated with IMV and NIV use. From 2002 to 2013, we identified 1,867,114 patients with STEMI. Age, gender, higher co-morbidity burden, and chronic pulmonary disease were significantly associated with need for respiratory support. The use of IMV and NIV increased at average annual rates of 6.6% and 14.3%, respectively (p_trend <0.001). Age- and gender-adjusted mortality rates are high but declined for patients with STEMI requiring IMV (44.7% in 2002 to 37.6% in 2013, p_trend = 0.002) and NIV (11.6% in 2002 to 6.8% in 2013, p_trend <0.001). Compared to patients with STEMI with no ventilation need, a requirement for IMV or NIV was associated with increased adjusted in-hospital mortality (hazard ratio 2.5, p <0.001 and 1.7, p <0.001, respectively). In conclusion, approximately 1 in 23 patients hospitalized with STEMI will require respiratory support in the form of IMV or NIV. Patients with STEMI who require respiratory support have a high risk of death, although rates of in-hospital mortality have decreased over time.

Protective mechanical ventilation in United Kingdom critical care units: A multicentre audit

Lung protective ventilation is becoming increasingly used for all critically ill patients being mechanically ventilated on a mandatory ventilator mode. Compliance with the universal application of this ventilation strategy in intensive care units in the United Kingdom is unknown. This 24-h audit of ventilation practice took place in 16 intensive care units in two regions of the United Kingdom. The mean tidal volume for all patients being ventilated on a mandatory ventilator mode was 7.2(±1.4) ml kg^-1 predicted body weight and overall compliance with low tidal volume ventilation (≤6.5 ml kg^-1 predicted body weight) was 34%. The mean tidal volume for patients ventilated with volume-controlled ventilation was 7.0(±1.2) ml kg^-1 predicted body weight and 7.9(±1.8) ml kg^-1 predicted body weight for pressure-controlled ventilation (P < 0.0001). Overall compliance with recommended levels of positive end-expiratory pressure was 72%. Significant variation in practice existed both at a regional and individual unit level.

Association between ventilatory settings and development of acute respiratory distress syndrome in mechanically ventilated patients due to brain injury

PURPOSE

In neurologically critically ill patients with mechanical ventilation (MV), the development of acute respiratory distress syndrome (ARDS) is a major contributor to morbidity and mortality, but the role of ventilatory management has been scarcely evaluated. We evaluate the association of tidal volume, level of PEEP and driving pressure with the development of ARDS in a population of patients with brain injury.

MATERIALS AND METHODS

We performed a secondary analysis of a prospective, observational study on mechanical ventilation.

RESULTS

We included 986 patients mechanically ventilated due to an acute brain injury (hemorrhagic stroke, ischemic stroke or brain trauma). Incidence of ARDS in this cohort was 3%. Multivariate analysis suggested that driving pressure could be associated with the development of ARDS (odds ratio for unit increment of driving pressure 1.12; confidence interval for 95%: 1.01 to 1.23) whereas we did not observe association for tidal volume (in ml per kg of predicted body weight) or level of PEEP. ARDS was associated with an increase in mortality, longer duration of mechanical ventilation, and longer ICU length of stay.

CONCLUSIONS

In a cohort of brain-injured patients the development of ARDS was not common. Driving pressure was associated with the development of this disease.

Associations between positive end-expiratory pressure and outcome of patients without ARDS at onset of ventilation: a systematic review and meta-analysis of randomized controlled trials

Background

The aim of this investigation was to compare ventilation at different levels of positive end-expiratory pressure (PEEP) with regard to clinical important outcomes of intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) at onset of ventilation.

Methods

Meta-analysis of randomized controlled trials (RCTs) comparing a lower level of PEEP with a higher level of PEEP was performed. The primary outcome was in-hospital mortality.

Results

Twenty-one RCTs (1393 patients) were eligible. PEEP ranged from 0 to 10 cmH₂O and from 5 to 30 cmH₂O in the lower PEEP and the higher PEEP arms of included RCTs, respectively. In-hospital mortality was not different between the two PEEP arms in seven RCTs (risk ratio [RR] 0.87; 95% confidence interval [CI] 0.62–1.21; I² = 26%, low quality of evidence [QoE]), as was duration of mechanical ventilation in three RCTs (standardized mean difference [SMD] 0.68; 95% CI −0.24 to 1.61; I² = 82%, very low QoE). PaO₂/FiO₂ was higher in the higher PEEP arms in five RCTs (SMD 0.72; 95% CI 0.10–1.35; I² = 86%, very low QoE). Development of ARDS and the occurrence of hypoxemia (2 RCTs) were lower in the higher PEEP arms in four RCTs and two RCTs, respectively (RR 0.43; 95% CI 0.21–0.91; I² = 56%, low QoE; RR 0.42; 95%–CI 0.19–0.92; I² = 19%, low QoE). There was no association between the level of PEEP and any hemodynamic parameter (four RCTs).

Conclusion

Ventilation with higher levels of PEEP in ICU patients without ARDS at onset of ventilation was not associated with lower in-hospital mortality or shorter duration of ventilation, but with a lower incidence of ARDS and hypoxemia, as well as higher PaO₂/FiO₂. These findings should be interpreted with caution, as heterogeneity was moderate to high, the QoE was low to very low, and the available studies prevented us from addressing the effects of moderate levels of PEEP.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0208-7) contains supplementary material, which is available to authorized users.

Epidemiological characteristics, practice of ventilation, and clinical outcome in patients at risk of acute respiratory distress syndrome in intensive care units from 16 countries (PRoVENT): an international, multicentre, prospective study

BACKGROUND

Scant information exists about the epidemiological characteristics and outcome of patients in the intensive care unit (ICU) at risk of acute respiratory distress syndrome (ARDS) and how ventilation is managed in these individuals. We aimed to establish the epidemiological characteristics of patients at risk of ARDS, describe ventilation management in this population, and assess outcomes compared with people at no risk of ARDS.

METHODS

PRoVENT (PRactice of VENTilation in critically ill patients without ARDS at onset of ventilation) is an international, multicentre, prospective study undertaken at 119 ICUs in 16 countries worldwide. All patients aged 18 years or older who were receiving mechanical ventilation in participating ICUs during a 1-week period between January, 2014, and January, 2015, were enrolled into the study. The Lung Injury Prediction Score (LIPS) was used to stratify risk of ARDS, with a score of 4 or higher defining those at risk of ARDS. The primary outcome was the proportion of patients at risk of ARDS. Secondary outcomes included ventilatory management (including tidal volume [V_T] expressed as mL/kg predicted bodyweight [PBW], and positive end-expiratory pressure [PEEP] expressed as cm H₂O), development of pulmonary complications, and clinical outcomes. The PRoVENT study is registered at ClinicalTrials.gov, NCT01868321. The study has been completed.

FINDINGS

Of 3023 patients screened for the study, 935 individuals fulfilled the inclusion criteria. Of these critically ill patients, 282 were at risk of ARDS (30%, 95% CI 27-33), representing 0·14 cases per ICU bed over a 1-week period. V_T was similar for patients at risk and not at risk of ARDS (median 7·6 mL/kg PBW [IQR 6·7-9·1] vs 7·9 mL/kg PBW [6·8-9·1]; p=0·346). PEEP was higher in patients at risk of ARDS compared with those not at risk (median 6·0 cm H₂O [IQR 5·0-8·0] vs 5·0 cm H₂O [5·0-7·0]; p<0·0001). The prevalence of ARDS in patients at risk of ARDS was higher than in individuals not at risk of ARDS (19/260 [7%] vs 17/556 [3%]; p=0·004). Compared with individuals not at risk of ARDS, patients at risk of ARDS had higher in-hospital mortality (86/543 [16%] vs 74/232 [32%]; p<0·0001), ICU mortality (62/533 [12%] vs 66/227 [29%]; p<0·0001), and 90-day mortality (109/653 [17%] vs 88/282 [31%]; p<0·0001). V_T did not differ between patients who did and did not develop ARDS (p=0·471 for those at risk of ARDS; p=0·323 for those not at risk).

INTERPRETATION

Around a third of patients receiving mechanical ventilation in the ICU were at risk of ARDS. Pulmonary complications occur frequently in patients at risk of ARDS and their clinical outcome is worse compared with those not at risk of ARDS. There is potential for improvement in the management of patients without ARDS. Further refinements are needed for prediction of ARDS.

FUNDING

None.

Mechanical Ventilation Alters the Development of Staphylococcus aureus Pneumonia in Rabbit

Ventilator-associated pneumonia (VAP) is common during mechanical ventilation (MV). Beside obvious deleterious effects on muco-ciliary clearance, MV could adversely shift the host immune response towards a pro-inflammatory pattern through toll-like receptor (TLRs) up-regulation. We tested this hypothesis in a rabbit model of Staphylococcus aureus VAP. Pneumonia was caused by airway challenge with S. aureus, in either spontaneously breathing (SB) or MV rabbits (n = 13 and 17, respectively). Pneumonia assessment regarding pulmonary and systemic bacterial burden, as well as inflammatory response was done 8 and 24 hours after S. aureus challenge. In addition, ex vivo stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed S. aureus were performed. Data were expressed as mean±standard deviation. After 8 hours of infection, lung injury was more severe in MV animals (1.40±0.33 versus [vs] 2.40±0.55, p = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, p = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (p = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed S. aureus (e.g., TNF-α: 1656±166 vs. 1005±89; p = 0.014). Moreover, MV induced TLR2 overexpression in both lung and spleen tissue. MV hastened tissue injury, impaired lung bacterial clearance, and promoted a systemic inflammatory response, maybe through TLR2 overexpression.

Nebulized heparin for patients under mechanical ventilation: an individual patient data meta-analysis

Pulmonary coagulopathy is a characteristic feature of lung injury including ventilator-induced lung injury. The aim of this individual patient data meta-analysis is to assess the effects of nebulized anticoagulants on outcome of ventilated intensive care unit (ICU) patients. A systematic search of PubMed (1966-2014), Scopus, EMBASE, and Web of Science was conducted to identify relevant publications. Studies evaluating nebulization of anticoagulants in ventilated patients were screened for inclusion, and corresponding authors of included studies were contacted to provide individual patient data. The primary endpoint was the number of ventilator-free days and alive at day 28. Secondary endpoints included hospital mortality, ICU- and hospital-free days at day 28, and lung injury scores at day seven. We constructed a propensity score-matched cohort for comparisons between patients treated with nebulized anticoagulants and controls. Data from five studies (one randomized controlled trial, one open label study, and three studies using historical controls) were included in the meta-analysis, compassing 286 patients. In all studies unfractionated heparin was used as anticoagulant. The number of ventilator-free days and alive at day 28 was higher in patients treated with nebulized heparin compared to patients in the control group (14 [IQR 0-23] vs. 6 [IQR 0-22]), though the difference did not reach statistical significance (P = 0.459). The number of ICU-free days and alive at day 28 was significantly higher, and the lung injury scores at day seven were significantly lower in patients treated with nebulized heparin. In the propensity score-matched analysis, there were no differences in any of the endpoints. This individual patient data meta-analysis provides no convincing evidence for benefit of heparin nebulization in intubated and ventilated ICU patients. The small patient numbers and methodological shortcomings of included studies underline the need for high-quality well-powered randomized controlled trials.

Donor to recipient sizing in thoracic organ transplantation

Donor-to-recipient organ size matching is a critical aspect of thoracic transplantation. In the United States potential recipients for lung transplant and heart transplant are listed with limitations on donor height and weight ranges, respectively. Height is used as a surrogate for lung size and weight is used as a surrogate for heart size. While these measures are important predictors of organ size, they are crude surrogates that fail to incorporate the influence of sex on organ size. Independent of other measures, a man’s thoracic organs are approximately 20% larger than a woman’s. Lung size can be better estimated using the predicted total lung capacity, which is derived from regression equations correcting for height, sex and age. Similarly, heart size can be better estimated using the predicted heart mass, which adjusts for sex, age, height, and weight. These refined organ sizing measures perform better than current sizing practice for the prediction of outcomes after transplantation, and largely explain the outcome differences observed after sex-mismatch transplantation. An undersized allograft is associated with worse outcomes. In this review we examine current data pertaining to size-matching in thoracic transplantation. We advocate for a change in the thoracic allocation mechanism from a height-or-weight-based strategy to a size-matching process that utilizes refined estimates of organ size. We believe that a size-matching approach based on refined estimates of organ size would optimize outcomes in thoracic transplantation without restricting or precluding patients from thoracic transplantation.

New puzzles for the use of non-invasive ventilation for immunosuppressed patients

On October 27, 2015, Lemile and colleagues published an article in JAMA entitled "Effect of Noninvasive Ventilation vs. Oxygen Therapy on Mortality among Immunocompromised Patients with Acute Respiratory Failure: A Randomized Clinical Trial", which investigated the effects of non-invasive ventilation (NIV) in 28-day mortality of 374 critically ill immunosuppressed patients. The authors found that among immunosuppressed patients admitted to the intensive care unit (ICU) with hypoxemic acute respiratory failure, early NIV compared with oxygen therapy alone did not reduce 28-day mortality. Furthermore, different from the previous publications, there were no significant differences in ICU-acquired infections, duration of mechanical ventilation, or lengths of ICU or hospital stays. The study power was limited, median oxygen flow used was higher than used before or 9 L/min, NIV settings provided tidal volumes higher than what is considered protective nowadays or from 7 to 10 mL/kg of ideal body weight and the hypoxemic respiratory failure was moderate to severe (median PaO2/FIO2 was around 140), a group prone to failure in noninvasive ventilatory support. Doubts arose regarding the early use of NIV in immunosuppressed critically ill patients with non-hypercapnic hypoxemic respiratory failure that need to be solved in the near future.

Mechanical ventilation strategies for the surgical patient

PURPOSE OF REVIEW

To summarize clinical evidence for intraoperative ventilation settings, which could protect against postoperative pulmonary complications (PPCs) in surgical patients with uninjured lungs.

RECENT FINDINGS

There is convincing evidence for protection against PPCs by low tidal volumes: benefit was found in several randomized controlled trials, and was recently confirmed in meta-analyses. Evidence for protection against PPCs by high levels of positive end-expiratory pressure (PEEP) is less definite. Although benefit was found in several randomized controlled trials, most of them compared a bundle of low tidal volume and high level of PEEP with conventional ventilation; one recent large randomized controlled trial that compared high with low levels of PEEP showed that ventilation with high level of PEEP did not protect against PPCs but caused intraoperative complications instead. A recent individual patient data meta-analysis of trials comparing bundles of low tidal volume and high levels of PEEP to conventional intraoperative ventilation suggested that protection against PPCs comes from tidal volume reductions, and not from increasing levels of PEEP.

SUMMARY

The understanding on the protective roles of tidal volume and PEEP settings against PPCs has rapidly expanded. During intraoperative ventilation, low tidal volumes are protective, the protective role of high levels of PEEP is uncertain.

Lung-Protective Ventilation With Low Tidal Volumes and the Occurrence of Pulmonary Complications in Patients Without Acute Respiratory Distress Syndrome: A Systematic Review and Individual Patient Data Analysis

OBJECTIVE

Protective mechanical ventilation with low tidal volumes is standard of care for patients with acute respiratory distress syndrome. The aim of this individual patient data analysis was to determine the association between tidal volume and the occurrence of pulmonary complications in ICU patients without acute respiratory distress syndrome and the association between occurrence of pulmonary complications and outcome in these patients.

DESIGN

Individual patient data analysis.

PATIENTS

ICU patients not fulfilling the consensus criteria for acute respiratory distress syndrome at the onset of ventilation.

INTERVENTIONS

Mechanical ventilation with low tidal volume.

MEASUREMENTS AND MAIN RESULTS

The primary endpoint was development of a composite of acute respiratory distress syndrome and pneumonia during hospital stay. Based on the tertiles of tidal volume size in the first 2 days of ventilation, patients were assigned to a "low tidal volume group" (tidal volumes ≤ 7 mL/kg predicted body weight), an "intermediate tidal volume group" (> 7 and < 10 mL/kg predicted body weight), and a "high tidal volume group" (≥ 10 mL/kg predicted body weight). Seven investigations (2,184 patients) were included. Acute respiratory distress syndrome or pneumonia occurred in 23% of patients in the low tidal volume group, in 28% of patients in the intermediate tidal volume group, and in 31% of the patients in the high tidal volume group (adjusted odds ratio [low vs high tidal volume group], 0.72; 95% CI, 0.52-0.98; p = 0.042). Occurrence of pulmonary complications was associated with a lower number of ICU-free and hospital-free days and alive at day 28 (10.0 ± 10.9 vs 13.8 ± 11.6 d; p < 0.01 and 6.1 ± 8.1 vs 8.9 ± 9.4 d; p < 0.01) and an increased hospital mortality (49.5% vs 35.6%; p < 0.01).

CONCLUSIONS

Ventilation with low tidal volumes is associated with a lower risk of development of pulmonary complications in patients without acute respiratory distress syndrome.

Lung anatomy, energy load, and ventilator-induced lung injury

BACKGROUND

High tidal volume can cause ventilator-induced lung injury (VILI), but positive end-expiratory pressure (PEEP) is thought to be protective. We aimed to find the volumetric VILI threshold and see whether PEEP is protective per se or indirectly.

METHODS

In 76 pigs (22 ± 2 kg), we examined the lower and upper limits (30.9-59.7 mL/kg) of inspiratory capacity by computed tomography (CT) scan at 45 cmH2O pressure. The pigs underwent a 54-h mechanical ventilation with a global strain ((tidal volume (dynamic) + PEEP volume (static))/functional residual capacity) from 0.45 to 5.56. The dynamic strain ranged from 18 to 100 % of global strain. Twenty-nine pigs were ventilated with end-inspiratory volumes below the lower limit of inspiratory capacity (group "Below"), 38 within (group "Within"), and 9 above (group "Above"). VILI was defined as death and/or increased lung weight.

RESULTS

"Below" pigs did not develop VILI; "Within" pigs developed lung edema, and 52 % died before the end of the experiment. The amount of edema was significantly related to dynamic strain (edema 188-153 × dynamic strain, R (2) = 0.48, p < 0.0001). In the "Above" group, 66 % of the pigs rapidly died but lung weight did not increase significantly. In pigs ventilated with similar tidal volume adding PEEP significantly increased mortality.

CONCLUSIONS

The threshold for VILI is the lower limit of inspiratory capacity. Below this threshold, VILI does not occur. Within these limits, severe/lethal VILI occurs depending on the dynamic component. Above inspiratory capacity stress at rupture may occur. In healthy lungs, PEEP is protective only if associated with a reduced tidal volume; otherwise, it has no effect or is harmful.

Influence of different degrees of head elevation on respiratory mechanics in mechanically ventilated patients

OBJECTIVE

The positioning of a patient in bed may directly affect their respiratory mechanics. The objective of this study was to evaluate the respiratory mechanics of mechanically ventilated patients positioned with different head angles hospitalized in an intensive care unit.

METHODS

This was a prospective physiological study in which static and dynamic compliance, resistive airway pressure, and peripheral oxygen saturation were measured with the head at four different positions (0° = P1, 30° = P2, 45° = P3, and 60° = P4). Repeated-measures analysis of variance (ANOVA) with a Bonferroni post-test and Friedman analysis were used to compare the values obtained at the different positions.

RESULTS

A comparison of the 35 evaluated patients revealed that the resistive airway pressure values in the 0° position were higher than those obtained when patients were positioned at greater angles. The elastic pressure analysis revealed that the 60° position produced the highest value relative to the other positions. Regarding static compliance, a reduction in values was observed from the 0° position to the 60° position. The dynamic compliance analysis revealed that the 30° angle produced the greatest value compared to the other positions. The peripheral oxygen saturation showed little variation, with the highest value obtained at the 0° position.

CONCLUSION

The highest dynamic compliance value was observed at the 30° position, and the highest oxygenation value was observed at the 0° position.

Intraoperative ventilation strategies to prevent postoperative pulmonary complications: Systematic review, meta-analysis, and trial sequential analysis

For many years, mechanical ventilation with high tidal volumes (V(T)) was common practice in operating theaters because this strategy recruits collapsed lung tissue, improves ventilation-perfusion mismatch, and thus decreases the need for high oxygen fractions. Positive end-expiratory pressure (PEEP) was seldom used because it could cause cardiac compromise. Increasing advances in the understanding of the mechanisms of ventilator-induced lung injury from animal studies and randomized controlled trials in patients with uninjured lungs in intensive care unit and operation room have pushed anesthesiologists to consider lung-protective strategies during intraoperative ventilation. These strategies at least include the use of low V(T), and perhaps also the use of PEEP, which when compared to high V(T) with low PEEP may prevent the occurrence of postoperative pulmonary complications (PPCs). Such protective effects, however, are likely ascribed to low V(T) rather than to PEEP. In fact, at least in nonobese patients undergoing open abdominal surgery, high PEEP does not protect against PPCs, and it can impair the hemodynamics. Further studies shall determine whether a strategy consisting of low V(T) combined with PEEP and recruitment maneuvers reduces PPCs in obese patients and other types of surgery (e.g., laparoscopic and thoracic), compared to low V(T) with low PEEP. Furthermore, the role of driving pressure for titrating ventilation settings in patients with uninjured lungs shall be investigated.

Ventilation and gas exchange management after cardiac arrest

For several decades, physicians had integrated several interventions aiming to improve the outcomes in post-cardiac arrest patients. However, the mortality rate after cardiac arrest is still as high as 50%. Post-cardiac arrest syndrome is associated with high morbidity and mortality due to not only poor neurological outcome and cardiovascular failure but also respiratory dysfunction. To minimize ventilator-associated lung injury, protective mechanical ventilation by using low tidal volume ventilation and driving pressure may decrease pulmonary complications and improve survival. Low level of positive end-expiratory pressure (PEEP) can be initiated and titrated with careful cardiac output and respiratory mechanics monitoring. Furthermore, optimizing gas exchange by avoiding hypoxia and hyperoxia as well as maintaining normocarbia may improve neurological and survival outcome. Early multidisciplinary cardiac rehabilitation intervention is recommended. Minimally invasive monitoring techniques, that is, echocardiography, transpulmonary thermodilution method measuring extravascular lung water, as well as transcranial Doppler ultrasound, might be useful to improve appropriate management of post-cardiac arrest patients.

Prevention of acute respiratory distress syndrome

PURPOSE OF REVIEW

The paucity of effective therapeutic interventions in patients with the acute respiratory distress syndrome (ARDS) combined with overwhelming evidence on the importance of timely implementation of effective therapies to critically ill patients has resulted in a recent shift in ARDS research. Increasingly, efforts are being directed toward early identification of patients at risk with a goal of prevention and early treatment, prior to development of the fully established syndrome. The focus of the present review is on the prevention of ARDS in patients without this condition at the time of their healthcare encounter.

RECENT FINDINGS

The primary thematic categories presented in the present review article include early identification of patients at risk of developing ARDS, optimization of care delivery and its impact on the incidence of ARDS, pharmacological prevention of ARDS, prevention of postoperative ARDS, and challenges and opportunities with ARDS prevention studies.

SUMMARY

Recent improvements in clinical care delivery have been associated with a decrease in the incidence of hospital-acquired ARDS. Despite the initial challenges, research in ARDS prevention has become increasingly feasible with several randomized controlled trials on ARDS prevention completed or on the way.

Mechanical Ventilation and ARDS in the ED: A Multicenter, Observational, Prospective, Cross-sectional Study

BACKGROUND

There are few data regarding mechanical ventilation and ARDS in the ED. This could be a vital arena for prevention and treatment.

METHODS

This study was a multicenter, observational, prospective, cohort study aimed at analyzing ventilation practices in the ED. The primary outcome was the incidence of ARDS after admission. Multivariable logistic regression was used to determine the predictors of ARDS.

RESULTS

We analyzed 219 patients receiving mechanical ventilation to assess ED ventilation practices. Median tidal volume was 7.6 mL/kg predicted body weight (PBW) (interquartile range, 6.9-8.9), with a range of 4.3 to 12.2 mL/kg PBW. Lung-protective ventilation was used in 122 patients (55.7%). The incidence of ARDS after admission from the ED was 14.7%, with a mean onset of 2.3 days. Progression to ARDS was associated with higher illness severity and intubation in the prehospital environment or transferring facility. Of the 15 patients with ARDS in the ED (6.8%), lung-protective ventilation was used in seven (46.7%). Patients who progressed to ARDS experienced greater duration in organ failure and ICU length of stay and higher mortality.

CONCLUSIONS

Lung-protective ventilation is infrequent in patients receiving mechanical ventilation in the ED, regardless of ARDS status. Progression to ARDS is common after admission, occurs early, and worsens outcome. Patient- and treatment-related factors present in the ED are associated with ARDS. Given the limited treatment options for ARDS, and the early onset after admission from the ED, measures to prevent onset and to mitigate severity should be instituted in the ED.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT01628523; URL: www.clinicaltrials.gov.

PReVENT--protective ventilation in patients without ARDS at start of ventilation: study protocol for a randomized controlled trial

BACKGROUND

It is uncertain whether lung-protective mechanical ventilation using low tidal volumes should be used in all critically ill patients, irrespective of the presence of the acute respiratory distress syndrome (ARDS). A low tidal volume strategy includes use of higher respiratory rates, which could be associated with increased sedation needs, a higher incidence of delirium, and an increased risk of patient-ventilator asynchrony and ICU-acquired weakness. Another alleged side-effect of low tidal volume ventilation is the risk of atelectasis. All of these could offset the beneficial effects of low tidal volume ventilation as found in patients with ARDS.

METHODS/DESIGN

PReVENT is a national multicenter randomized controlled trial in invasively ventilated ICU patients without ARDS with an anticipated duration of ventilation of longer than 24 hours in 5 ICUs in The Netherlands. Consecutive patients are randomly assigned to a low tidal volume strategy using tidal volumes from 4 to 6 ml/kg predicted body weight (PBW) or a high tidal volume ventilation strategy using tidal volumes from 8 to 10 ml/kg PBW. The primary endpoint is the number of ventilator-free days and alive at day 28. Secondary endpoints include ICU and hospital length of stay (LOS), ICU and hospital mortality, the incidence of pulmonary complications, including ARDS, pneumonia, atelectasis, and pneumothorax, the cumulative use and duration of sedatives and neuromuscular blocking agents, incidence of ICU delirium, and the need for decreasing of instrumental dead space.

DISCUSSION

PReVENT is the first randomized controlled trial comparing a low tidal volume strategy with a high tidal volume strategy, in patients without ARDS at onset of ventilation, that recruits a sufficient number of patients to test the hypothesis that a low tidal volume strategy benefits patients without ARDS with regard to a clinically relevant endpoint.

TRIAL REGISTRATION

The trial is registered at www.clinicaltrials.gov under reference number NCT02153294 on 23 May 2014.

MECHANICAL VENTILATION FOR THE LUNG TRANSPLANT RECIPIENT

Mechanical ventilation (MV) is an important aspect in the intraoperative and early postoperative management of lung transplant (LTx)-recipients. There are no randomized-controlled trials of LTx-recipient MV strategies; however there are LTx center experiences and international survey studies reported. The main early complication of LTx is primary graft dysfunction (PGD), which is similar to the adult respiratory distress syndrome (ARDS). We aim to summarize information pertinent to LTx-MV, as well as PGD, ARDS, and intraoperative MV and to synthesize these available data into recommendations. Based on the available evidence, we recommend lung-protective MV with low-tidal-volumes (≤6 mL/kg predicted body weight [PBW]) and positive end-expiratory pressure for the LTx-recipient. In our opinion, the MV strategy should be based on donor characteristics (donor PBW as a parameter of actual allograft size), rather than based on recipient characteristics; however this donor-characteristics-based protective MV is based on indirect evidence and requires validation in prospective clinical studies.

Recent advances in mechanical ventilation in patients with acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterised by different degrees of severity and different stages. Understanding these differences can help to better adapt the ventilatory settings to protect the lung from ventilator-induced lung injury by reducing hyperinflation or keeping the lung open when it is possible. The same therapies may be useful and beneficial in certain forms of ARDS, and risky or harmful at other stages: this includes high positive end-expiratory pressure, allowance of spontaneous breathing activity or use of noninvasive ventilation. The severity of the disease is the primary indicator to individualise treatment. Monitoring tools such as oesophageal pressure or lung volume measurements may also help to set the ventilator. At an earlier stage, an adequate lung protective strategy may also help to prevent the development of ARDS.

Recent advances in mechanical ventilation in patients without acute respiratory distress syndrome

While being an essential part of general anesthesia for surgery and at times even a life-saving intervention in critically ill patients, mechanical ventilation has a strong potential to cause harm. Certain ventilation strategies could prevent, at least to some extent, the injury caused by this intervention. One essential element of so-called ‘lung-protective’ ventilation is the use of lower tidal volumes. It is uncertain whether higher levels of positive end-expiratory pressures have lung-protective properties as well. There are indications that too high oxygen fractions of inspired air, or too high blood oxygen targets, are harmful. Circumstantial evidence further suggests that spontaneous modes of ventilation are to be preferred over controlled ventilation to prevent harm to respiratory muscle. Finally, the use of restrictive sedation strategies in critically ill patients indirectly prevents ventilation-induced injury, as daily spontaneous awakening and breathing trials and bolus instead of continuous sedation are associated with shorter duration of ventilation and shorten the exposure to the injurious effects of ventilation.