Effect of nitric oxide on oxygenation and mortality in acute lung injury: systematic review and meta-analysis

H1N1-associated acute respiratory distress syndrome

The worldwide 2009-2010 pandemic of novel H1N1 influenza reminds us that influenza can still be a lethal disease. Acute lung injury and acute respiratory distress syndrome (ARDS) have been the most devastating complications of this pathogen. We present a case of a previously healthy 40-year-old obese man who succumbed to H1N1-associated ARDS. In this focused review, we discuss the pathophysiologic peculiarities and management of acute lung injury/ARDS related to H1N1 infection.

[Burn patients and their respiration problems]

The characteristic features of respiratory disorders in burn patients are presented in a review of the literature. Respiratory disorders in burn patients are related to a direct mechanism, when the bronchial tree is injured by the transfer of thermal energy due to the burn, and/or by an indirect mechanism, when the lung's respiratory and ventilatory function is impaired by localized, regional, or general burns-related phenomena. These respiratory disorders are aggravated by the inhalation of gases contained in smoke. Diagnosis of these disorders is clinical and paraclinical, and has to be performed early and continuously. The patients require various types of therapy, e.g. oxygen therapy, clearing of the airways, improvement of ventilatory mechanics and respiratory function, antibiotic therapy, or surgical correction of sequelae. This taking in charge inevitably has to be multidisciplinary.

Extracorporeal membrane oxygenation in a Scottish intensive care unit

I reflected on the training I had on an extraordinary treatment for profound respiratory failure. The result of training enabled us to successfully treat a young female with the influenza A virus with extracorporeal membrane oxygenation (ECMO). I report the positive outcome that occurred, while continuing to run a busy general intensive care unit (ICU). She was the first of six patients who were all successfully treated with ECMO. Ten trained and experienced critical care nurses and two doctors attended the ECMO training course provided by the national centre in the UK. Five patients had already received ECMO therapy in the Scottish specialist unit (over the period of 8 years). As our Scottish specialist unit purchased exactly the same equipment as the national centre, it was easier for the multidisciplinary team to utilize their new-found knowledge and treat future patients with ECMO. With the predicted swine flu (H1N1) pandemic and the subsequent demand for critical care beds, funding was obtained to facilitate ECMO training. The potential need for increased provision of ECMO therapies was highlighted by recent events in Australia and New Zealand. Their most recent winter produced 68 patients requiring ECMO, whereas the previous year had manifested only three. Using our new equipment and adapted protocols from the national centre, we used these new skills to treat our first patient in October 2009. Johns' reflective practice tool was used to evaluate the care provided. Our patient was on ECMO for 9 days. She went on to make a remarkable recovery and was discharged from the ICU 1 week after ECMO was discontinued. She was discharged to the cardiothoracic high-dependency unit, where she was successfully rehabilitated. We were able to successfully treat a young lady, while providing the care for all other patients. This was a complex treatment, one that uses many resources including time and finance. Now that we have all the equipment, the necessary training and the knowledge, we can continue to deliver this service to the public in our locality.

Acute respiratory distress syndrome

INTRODUCTION

Acute respiratory distress syndrome (ARDS) is characterised by a profound deterioration in systemic oxygenation or ventilation, or both, despite supportive respiratory therapy. ARDS is an acute and progressive respiratory disease of a non-cardiac cause that is associated with progressively diffuse bilateral pulmonary infiltrates, reduced pulmonary compliance, and hypoxaemia. The main causes of ARDS include direct lung injury (e.g., pneumonia, gastric acid aspiration) or indirect lung injury (e.g., sepsis, pancreatitis, massive blood transfusion, non-thoracic trauma). Sepsis and pneumonia account for about 60% of cases. Between one third and one half of people with ARDS die from the disease, but mortality depends on the underlying cause. Some survivors have long-term respiratory or cognitive problems.

METHODS AND OUTCOMES

We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions in adults with acute respiratory distress syndrome? We searched: Medline, Embase, The Cochrane Library, and other important databases up to December 2009 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

RESULTS

We found 20 systematic reviews, RCTs, or observational studies that met our inclusion criteria.

CONCLUSIONS

In this systematic review we present information relating to the effectiveness and safety of the following interventions: corticosteroids, low tidal-volume mechanical ventilation, nitric oxide, prone position, and protective ventilation.

Management of acute lung injury/ARDS

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are disorders of pulmonary inflammation characterized by hypoxemia and respiratory failure. Children have varying incidence of ALI/ARDS from 2.2 to 16 per 100,000 pediatric population associated with high morbidity, mortality, and financial burden. The diagnostic criteria include: acute onset, severe arterial hypoxemia resistant to oxygen therapy alone (PaO₂/FIO₂ ratio ≤ 200 for ARDS and ≤ 300 for ALI), diffuse pulmonary inflammation (bilateral infiltrates on chest radiograph) and No evidence of left atrial hypertension. Management includes ventilatory therapy including lower tidal volume, relatively high PEEP and supportive care. Guidelines for diagnosis, ventilator management, rescue therapies and supportive care are being discussed in the protocol.

Pharmacotherapy for prevention and treatment of acute respiratory distress syndrome: current and experimental approaches

The acute respiratory distress syndrome (ARDS) arises from direct and indirect injury to the lungs and results in a life-threatening form of respiratory failure in a heterogeneous, critically ill patient population. Critical care technologies used to support patients with ARDS, including strategies for mechanical ventilation, have resulted in improved outcomes in the last decade. However, there is still a need for effective pharmacotherapies to treat ARDS, as mortality rates remain high. To date, no single pharmacotherapy has proven effective in decreasing mortality in adult patients with ARDS, although exogenous surfactant replacement has been shown to reduce mortality in the paediatric population with ARDS from direct causes. Several promising therapies are currently being investigated in preclinical and clinical trials for treatment of ARDS in its acute and subacute, exudative phases. These include exogenous surfactant therapy, β₂-adrenergic receptor agonists, antioxidants, immunomodulating agents and HMG-CoA reductase inhibitors (statins). Recent research has also focused on prevention of acute lung injury and acute respiratory distress in patients at risk. Drugs such as captopril, rosiglitazone and incyclinide (COL-3), a tetracycline derivative, have shown promising results in animal models, but have not yet been tested clinically. Further research is needed to discover therapies to treat ARDS in its late, fibroproliferative phase. Given the vast number of negative clinical trials to date, it is unlikely that a single pharmacotherapy will effectively treat all patients with ARDS from differing causes. Future randomized controlled trials should target specific, more homogeneous subgroups of patients for single or combination therapy.

Pulmonary vascular and right ventricular dysfunction in adult critical care: current and emerging options for management: a systematic literature review

INTRODUCTION

Pulmonary vascular dysfunction, pulmonary hypertension (PH), and resulting right ventricular (RV) failure occur in many critical illnesses and may be associated with a worse prognosis. PH and RV failure may be difficult to manage: principles include maintenance of appropriate RV preload, augmentation of RV function, and reduction of RV afterload by lowering pulmonary vascular resistance (PVR). We therefore provide a detailed update on the management of PH and RV failure in adult critical care.

METHODS

A systematic review was performed, based on a search of the literature from 1980 to 2010, by using prespecified search terms. Relevant studies were subjected to analysis based on the GRADE method.

RESULTS

Clinical studies of intensive care management of pulmonary vascular dysfunction were identified, describing volume therapy, vasopressors, sympathetic inotropes, inodilators, levosimendan, pulmonary vasodilators, and mechanical devices. The following GRADE recommendations (evidence level) are made in patients with pulmonary vascular dysfunction: 1) A weak recommendation (very-low-quality evidence) is made that close monitoring of the RV is advised as volume loading may worsen RV performance; 2) A weak recommendation (low-quality evidence) is made that low-dose norepinephrine is an effective pressor in these patients; and that 3) low-dose vasopressin may be useful to manage patients with resistant vasodilatory shock. 4) A weak recommendation (low-moderate quality evidence) is made that low-dose dobutamine improves RV function in pulmonary vascular dysfunction. 5) A strong recommendation (moderate-quality evidence) is made that phosphodiesterase type III inhibitors reduce PVR and improve RV function, although hypotension is frequent. 6) A weak recommendation (low-quality evidence) is made that levosimendan may be useful for short-term improvements in RV performance. 7) A strong recommendation (moderate-quality evidence) is made that pulmonary vasodilators reduce PVR and improve RV function, notably in pulmonary vascular dysfunction after cardiac surgery, and that the side-effect profile is reduced by using inhaled rather than systemic agents. 8) A weak recommendation (very-low-quality evidence) is made that mechanical therapies may be useful rescue therapies in some settings of pulmonary vascular dysfunction awaiting definitive therapy.

CONCLUSIONS

This systematic review highlights that although some recommendations can be made to guide the critical care management of pulmonary vascular and right ventricular dysfunction, within the limitations of this review and the GRADE methodology, the quality of the evidence base is generally low, and further high-quality research is needed.

Acute lung injury in the child

Acute lung injury(ALI) is an important condition in critically ill children, contributing to overall mortality and morbidity. ALI represents the severe spectrum of lower airways disease in children. It is the pathological culmination of diseases such as pneumonia and sepsis. These conditions elicit a host response, which results in a clinically and radiologically defined pulmonary syndrome, leading to additional physiological burden. Despite ALI being well described in the paediatric age group, its management has been largely based on adult studies. Ventilatory support with low tidal volumes, positive end expiratory pressure(PEEP) and permissive hypercapnoea are the pillars of management - derived from adult studies. For those caring for critically unwell children, this review outlines recent paediatric studies, current therapies in the context of available literature and novel emerging approaches.

Therapeutic strategies for severe acute lung injury

OBJECTIVE

In the management of patients with severe acute lung injury and acute respiratory distress syndrome, clinicians are sometimes challenged to maintain acceptable gas exchange while avoiding harmful mechanical ventilation practices. In some of these patients, physicians may consider the use of "rescue therapies" to sustain life. Our goal is to provide a practical, evidence-based review to assist critical care physicians' care for patients with severe acute lung injury and acute respiratory distress syndrome.

DATA SOURCES

We searched the PubMed database for clinical trials that examined the use of the following therapies in severe acute lung injury and acute respiratory distress syndrome: recruitment maneuvers, high positive end-expiratory pressure, prone position, high-frequency oscillatory ventilation, glucocorticoids, inhaled nitric oxide, buffer therapy, and extracorporeal life support.

STUDY SELECTION

All clinical trials that included patients with severe acute lung injury and acute respiratory distress syndrome were included in the review.

DATA SYNTHESIS

The primary author reviewed the aforementioned trials in depth and then disputed findings and conclusions with the other authors until consensus was achieved.

CONCLUSIONS

This article is designed to provide clinicians with a simple bedside definition for the diagnosis of severe acute respiratory distress syndrome; to describe several therapies that can be used for severe acute respiratory distress syndrome with an emphasis on the potential risks and the indications and benefits; and to offer practical guidelines for implementation of these therapies.

Aerosolized prostacyclin for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)

BACKGROUND

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are critical conditions that are associated with high mortality and morbidity. Aerosolized prostacyclin has been used to improve oxygenation despite the limited evidence available so far.

OBJECTIVES

To systematically assess the benefits and harms of aerosolized prostacyclin in critically ill patients with ALI and ARDS.

SEARCH STRATEGY

We identified randomized clinical trials (RCTs) from electronic databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 1); MEDLINE; EMBASE; Science Citation Index Expanded; International Web of Science; CINAHL; LILACS; and the Chinese Biomedical Literature Database (to 31st January 2010). We contacted trial authors and manufacturers in the field.

SELECTION CRITERIA

We included all RCTs, irrespective of blinding or language, that compared aerosolized prostacyclin with no intervention or placebo in either children or adults with ALI or ARDS.

DATA COLLECTION AND ANALYSIS

Two authors independently abstracted data and resolved any disagreements by discussion. We presented pooled estimates of the intervention effects as relative risks (RR) with 95% confidence intervals (CI) for dichotomous outcomes. Our primary outcome measure was all cause mortality. We planned to perform subgroup and sensitivity analyses to assess the effect of aerosolized prostacyclin in adults and children, and on various clinical and physiological outcomes. We assessed the risk of bias through assessment of methodological trial components and the risk of random error through trial sequential analysis.

MAIN RESULTS

We included one paediatric RCT with low risk of bias and involving a total of 14 critically ill children with ALI or ARDS. Aersosolized prostacyclin over less than 24 hours did not reduce overall mortality at 28 days (RR 1.50, 95% CI 0.17 to 12.94) compared with aerosolized saline (a total of three deaths). The authors did not encounter any adverse events such as bleeding or organ dysfunction. We were unable to perform the prespecified subgroups and sensitivity analyses or trial sequential analysis due to the limited number of RCTs. We were also not able to assess the safety and efficacy of aerosolized prostacyclin for ALI and ARDS. We found two ongoing trials, one involving adults and the other paediatric participants. The adult trial has been finalized but the data are not yet available.

AUTHORS' CONCLUSIONS

There is no current evidence to support or refute the routine use of aerosolized prostacyclin for patients with ALI and ARDS. There is an urgent need for more randomized clinical trials.

Special article: rescue therapies for acute hypoxemic respiratory failure

The recent H1N1 epidemic has resulted in a large number of deaths, primarily from acute hypoxemic respiratory failure. We reviewed the current strategies to rescue patients with severe hypoxemia. Included in these strategies are high-frequency oscillatory ventilation, airway pressure release ventilation, inhaled vasodilators, and the use of extracorporeal life support. All of these strategies are targeted at improving oxygenation, but improved oxygenation alone has yet to be demonstrated to correlate with improved survival. The risks and benefits of these strategies, including cost-effectiveness data, are discussed.

Inhaled nitric oxide for acute respiratory distress syndrome (ARDS) and acute lung injury in children and adults

BACKGROUND

Acute hypoxaemic respiratory failure (AHRF), defined as acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), are critical conditions. AHRF results from a number of systemic conditions and is associated with high mortality and morbidity in all ages. Inhaled nitric oxide (INO) has been used to improve oxygenation but its role remains controversial.

OBJECTIVES

To systematically assess the benefits and harms of INO in critically ill patients with AHRF.

SEARCH STRATEGY

Randomized clinical trials (RCTs) were identified from electronic databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 1); MEDLINE; EMBASE; Science Citation Index Expanded; International Web of Science; CINAHL; LILACS; and the Chinese Biomedical Literature Database (up to 31st January 2010). We contacted trial authors, authors of previous reviews, and manufacturers in the field.

SELECTION CRITERIA

We included all RCTs, irrespective of blinding or language, that compared INO with no intervention or placebo in children or adults with AHRF.

DATA COLLECTION AND ANALYSIS

Two authors independently abstracted data and resolved any disagreements by discussion. We presented pooled estimates of the intervention effects on dichotomous outcomes as relative risks (RR) with 95% confidence intervals (CI). Our primary outcome measure was all cause mortality. We performed subgroup and sensitivity analyses to assess the effect of INO in adults and children and on various clinical and physiological outcomes. We assessed the risk of bias through assessment of trial methodological components and the risk of random error through trial sequential analysis.

MAIN RESULTS

We included 14 RCTs with a total of 1303 participants; 10 of these trials had a high risk of bias. INO showed no statistically significant effect on overall mortality (40.2% versus 38.6%) (RR 1.06, 95% CI 0.93 to 1.22; I(2) = 0) and in several subgroup and sensitivity analyses, indicating robust results. Limited data demonstrated a statistically insignificant effect of INO on duration of ventilation, ventilator-free days, and length of stay in the intensive care unit and hospital. We found a statistically significant but transient improvement in oxygenation in the first 24 hours, expressed as the ratio of partial pressure of oxygen to fraction of inspired oxygen and the oxygenation index (MD 15.91, 95% CI 8.25 to 23.56; I(2) = 25%). However, INO appears to increase the risk of renal impairment among adults (RR 1.59, 95% CI 1.17 to 2.16; I(2) = 0) but not the risk of bleeding or methaemoglobin or nitrogen dioxide formation.

AUTHORS' CONCLUSIONS

INO cannot be recommended for patients with AHRF. INO results in a transient improvement in oxygenation but does not reduce mortality and may be harmful.

Pulmonary vascular dysfunction is associated with poor outcomes in patients with acute lung injury

RATIONALE

Despite the recognition that acute lung injury (ALI) can elevate pulmonary artery (PA) pressure and right ventricular afterload, the impact of pulmonary vascular dysfunction on outcomes of these patients is not well defined.

OBJECTIVES

To investigate the impact of pulmonary vascular dysfunction in patients with acute lung injury.

METHODS

Secondary analysis of the Fluid and Catheter Treatment Trial. A total of 501 patients who received a PA catheter were evaluated for associations between increases in transpulmonary gradient (TPG) (PA mean pressure - PA occlusion pressure) or pulmonary vascular resistance index (PVRi) and 60-day mortality, ventilator-, intensive care unit (ICU)-, and cardiovascular-free days (days with mean arterial pressure ≥ 60 mm Hg off vasopressor support).

MEASUREMENTS AND MAIN RESULTS

We were able to measure the TPG in 475 (95%) and the PVRi in 470 (92%) patients. Patients with an elevated baseline TPG had an increased 60-day mortality (30 versus 19%; P = 0.02), and lower numbers of median ventilator- [25-75% quartiles] (15 [0-22] versus 19 [7-24]; P = 0.005), ICU- (14 [0-21] versus 18 [5-22]; P = 0.005), and cardiovascular-free days (23 [12-27] versus 25 [18-27]; P = 0.03). The median PVRi (305 [204-431] dyne s/cm⁵/m²) was elevated early in the course of ALI. PVRi was statistically higher in patients who died (326 [209-518] versus 299 [199-416]; P = 0.01). In individual multivariate models, TPG and PVRi remained independent risk factors for 60-day mortality and decrease in the number of ventilator-, ICU-, and cardiovascular-free days.

CONCLUSIONS

Pulmonary vascular dysfunction is common in ALI, and is independently associated with poor outcomes. Future trials targeting pulmonary vascular dysfunction may be indicated.

Maintenance of nitric oxide inhalation to a patient with hemoperitonium and acute respiratory distress syndrome during anesthesia -A case report-

Inhaled nitric oxide (NO) is occasionally used to treat hypoxemia for patients with acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU). However, it is controversial whether or not to maintain inhalation of NO during general anesthesia because of complications, such as nitrogen dioxide (NO(2)) production, methemoglobinemia, and inhibition of platelet aggregation. In this case, a 67-year-old male fell from a roof and was brought to an emergency care center. During management, he vomited gastric contents and aspirated. In spite of tracheal intubation and mechanical ventilation with high oxygen therapy, the hypoxia did not improve. NO inhalation with mechanical ventilation was performed to treat hypoxemia due to ARDS in the ICU. We maintained the NO inhalation during the surgery for a hemoperitonium. The surgery was completed without intra-operative hemodynamic instability or any complications.

Extracorporeal life support for management of refractory cardiac or respiratory failure: initial experience in a tertiary centre

Introduction

Extracorporeal Life Support (ECLS) and extracorporeal membrane oxygenation (ECMO) have been indicated as treatment for acute respiratory and/or cardiac failure. Here we describe our first year experience of in-hospital ECLS activity, the operative algorithm and the protocol for centralization of adult patients from district hospitals.

Methods

At a tertiary referral trauma center (Careggi Teaching Hospital, Florence, Italy), an ECLS program was developed from 2008 by the Emergency Department and Heart and Vessel Department ICUs. The ECLS team consists of an intensivist, a cardiac surgeon, a cardiologist and a perfusionist, all trained in ECLS technique. ECMO support was applied in case of severe acute respiratory distress syndrome (ARDS) not responsive to conventional treatments. The use of veno-arterial (V-A) ECLS for cardiac support was reserved for cases of cardiac shock refractory to standard treatment and cardiac arrests not responding to conventional resuscitation.

Results

A total of 21 patients were treated with ECLS during the first year of activity. Among them, 13 received ECMO for ARDS (5 H1N1-virus related), with a 62% survival. In one case of post-traumatic ARDS, V-A ECLS support permitted multiple organ donation after cerebral death was confirmed. Patients treated with V-A ECLS due to cardiogenic shock (N = 4) had a survival rate of 50%. No patients on V-A ECLS support after cardiac arrest survived (N = 4).

Conclusions

In our centre, an ECLS Service was instituted over a relatively limited period of time. A strict collaboration between different specialists can be regarded as a key feature to efficiently implement the process.

Nonventilatory strategies for patients with life-threatening 2009 H1N1 influenza and severe respiratory failure

Severe respiratory failure (including acute lung injury and acute respiratory distress syndrome) caused by 2009 H1N1 influenza infection has been reported worldwide. Refractory hypoxemia is a common finding in these patients and can be challenging to manage. This review focuses on nonventilatory strategies in the advanced treatment of severe respiratory failure and refractory hypoxemia such as that seen in patients with severe acute respiratory distress syndrome attributable to 2009 H1N1 influenza. Specific modalities covered include conservative fluid management, prone positioning, inhaled nitric oxide, inhaled vasodilatory prostaglandins, and extracorporeal membrane oxygenation and life support. Pharmacologic strategies (including steroids) investigated for the treatment of severe respiratory failure are also reviewed.

Infection control in mass respiratory failure: preparing to respond to H1N1

The first hints of a global public health crisis emerged with the identification of a new strain of H1N1 influenza A in March and April 2009 in Mexico City. By June 11, the World Health Organization had declared the outbreak of 2009 H1N1 a global pandemic. Now, with the continued growing presence of 2009 H1N1 on the global scene, much attention has been focused on the key role of personal protective equipment in healthcare infection control. Much less emphasis has been placed on specific interventions that may minimize the increased infectious risk commonly associated with critical care delivery. Given the frequency of high-risk respiratory procedures such as intubation and delivery of aerosolized medications in the intensive care unit, the delivery of critical care presents unique infection control challenges and unique opportunities to augment usual infection control practice with specific source-control efforts. Here, we summarize data regarding risks to critical care healthcare workers from previous respiratory virus outbreaks, discuss findings from the early 2009 H1N1 experience that suggest reasons for increased concern for those delivering critical care, and review best available evidence regarding strategies for source control in respiratory and critical care delivery.

The challenge of evidence in clinical medicine

The primary goal of evidence-based medicine (EBM) has been to change the way clinicians make decisions. But EBM has inappropriately privileged the results of clinical research for medical decision making and has undermined the importance of other kinds of medical knowledge, pathophysiologic understanding and clinical experience, to clinical practice. Here, the specific advantages and limitations of each kind of medical knowledge are examined. No particular kind of medical knowledge is necessarily more compelling than the others when it comes to making specific patient care decisions. Several cases where medical knowledge is conflicting are examined to demonstrate the weighting and negotiation necessary for sound clinical judgement. Expert clinicians must utilize a variety of reasons and methods of reasoning in arriving at the best clinical decision or recommendation for an individual patient. The process can be formalized and made explicit, but it cannot be narrowed, simplified and focused only on the results of clinical research.

Pharmacological treatments for acute respiratory distress syndrome

PURPOSE OF REVIEW

Studies of the pharmacologic management of acute respiratory distress syndrome (ARDS) have yielded conflicting results. The purpose of this review is to discuss recent pharmacologic trials in ARDS, using the conceptual framework of ARDS as a heterogeneous disease.

RECENT FINDINGS

Whereas most drug trials in ARDS have been negative, some studies suggest that targeting therapies at subgroups of patients may be successful. Proposed subgroups include early versus late-phase ARDS, direct versus indirect lung injury, and patients with altered coagulation. Corticosteroids have beneficial short-term effects when given at low or moderate doses sooner than 2 weeks but appear to be harmful if initiated later and are of unclear benefit if lung protective ventilation is also used. Surfactant may be helpful in patients with direct lung injury. Anticoagulants and vasodilators may have a greater chance for success in the subset of patients with vascular disease and a high dead-space fraction may identify such a population.

SUMMARY

ARDS is a heterogeneous syndrome. Failure to target subgroups more likely to benefit from specific therapies may be one explanation for largely disappointing trial results so far.

Ventilatory strategies for patients with acute brain injury

PURPOSE OF REVIEW

The ventilation of patients with acute brain injuries can present significant challenges. Frequently, guidelines recommending management strategies for patients with traumatic brain injuries come into conflict with what is now considered best ventilatory practice. In this review, we will explore many of these areas of conflict.

RECENT FINDINGS

The use of ventilatory strategies to control partial pressure of carbon dioxide in patients with traumatic brain injury is associated with the development of acute lung injury. Analysis of the International Mission for Prognosis And Clinical Trial (IMPACT) database has confirmed the association between hypoxia and poor neurological outcome. Although a recent meta-analysis has suggested a survival benefit for steroids in acute lung injury, the use of steroids has been associated with a worsening of outcome in patients with traumatic brain injuries and their effects on the brain have not been fully elucidated.

SUMMARY

There are unlikely to be randomized controlled trials advising how best to ventilate patients with acute brain injuries because of the heterogeneous nature of such injuries. Hypoxia should be avoided. The more widespread use of multimodal brain monitoring, including brain tissue oxygen and cerebral blood flow monitoring, may allow clinicians to tolerate a higher arterial partial pressure of carbon dioxide than has been traditional, allowing a less injurious ventilatory strategy. Modest positive end-expiratory pressure can be used. In severe respiratory failure, most 'rescue' strategies have been attempted in patients with acute brain injuries. Choice of rescue therapy at present is best decided on a case-by-case basis in conjunction with local expertise.

Beyond mortality: future clinical research in acute lung injury

Mortality in National Heart, Lung and Blood Institute-sponsored clinical trials of treatments for acute lung injury (ALI) has decreased dramatically during the past two decades. As a consequence, design of such trials based on a mortality outcome requires ever-increasing numbers of patients. Recognizing that advances in clinical trial design might be applicable to these trials and might allow trials with fewer patients, the National Heart, Lung and Blood Institute convened a workshop of extramural experts from several disciplines. The workshop assessed the current state of clinical research addressing ALI, identified research needs, and recommended: (1) continued performance of trials evaluating treatments of patients with ALI; (2) development of strategies to perform ALI prevention trials; (3) observational studies of patients without ALI undergoing prolonged mechanical ventilation; and (4) development of a standardized format for reporting methods, endpoints, and results of ALI trials.

Sildenafil attenuates pulmonary arterial pressure but does not improve oxygenation during ARDS

Objective

Pulmonary hypertension is a characteristic feature of acute respiratory distress syndrome (ARDS) and contributes to mortality. Administration of sildenafil in ambulatory patients with pulmonary hypertension improves oxygenation and ameliorates pulmonary hypertension. Our aim was to determine whether sildenafil is beneficial for patients with ARDS.

Design

Prospective, open-label, multicenter, interventional cohort study.

Setting

Medical-surgical ICU of two university hospitals.

Patients

Ten consecutive patients meeting the NAECC criteria for ARDS.

Interventions

A single dose of 50 mg sildenafil citrate administered via a nasogastric tube.

Main results

Administration of sildenafil in patients with ARDS decreased mean pulmonary arterial pressure from 25 to 22 mmHg (P = 0.022) and pulmonary artery occlusion pressure from 16 to 13 mmHg (P = 0.049). Systemic mean arterial pressures were markedly decreased from 81 to 75 mmHg (P = 0.005). Sildenafil did not improve pulmonary arterial oxygen tension, but resulted in a further increase in the shunt fraction.

Conclusion

Although sildenafil reduced pulmonary arterial pressures during ARDS, the increased shunt fraction and decreased arterial oxygenation render it unsuitable for the treatment of patients with ARDS.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-010-1754-3) contains supplementary material, which is available to authorized users.

Prone ventilation reduces mortality in patients with acute respiratory failure and severe hypoxemia: systematic review and meta-analysis

BACKGROUND

Prone position ventilation for acute hypoxemic respiratory failure (AHRF) improves oxygenation but not survival, except possibly when AHRF is severe.

OBJECTIVE

To determine effects of prone versus supine ventilation in AHRF and severe hypoxemia [partial pressure of arterial oxygen (PaO(2))/inspired fraction of oxygen (FiO(2)) <100 mmHg] compared with moderate hypoxemia (100 mmHg < or = PaO(2)/FiO(2) < or = 300 mmHg).

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Electronic databases (to November 2009) and conference proceedings.

METHODS

Two authors independently selected and extracted data from parallel-group randomized controlled trials comparing prone with supine ventilation in mechanically ventilated adults or children with AHRF. Trialists provided subgroup data. The primary outcome was hospital mortality in patients with AHRF and PaO(2)/FiO(2) <100 mmHg. Meta-analyses used study-level random-effects models.

RESULTS

Ten trials (N = 1,867 patients) met inclusion criteria; most patients had acute lung injury. Methodological quality was relatively high. Prone ventilation reduced mortality in patients with PaO(2)/FiO(2) <100 mmHg [risk ratio (RR) 0.84, 95% confidence interval (CI) 0.74-0.96; p = 0.01; seven trials, N = 555] but not in patients with PaO(2)/FiO(2) > or =100 mmHg (RR 1.07, 95% CI 0.93-1.22; p = 0.36; seven trials, N = 1,169). Risk ratios differed significantly between subgroups (interaction p = 0.012). Post hoc analysis demonstrated statistically significant improved mortality in the more hypoxemic subgroup and significant differences between subgroups using a range of PaO(2)/FiO(2) thresholds up to approximately 140 mmHg. Prone ventilation improved oxygenation by 27-39% over the first 3 days of therapy but increased the risks of pressure ulcers (RR 1.29, 95% CI 1.16-1.44), endotracheal tube obstruction (RR 1.58, 95% CI 1.24-2.01), and chest tube dislodgement (RR 3.14, 95% CI 1.02-9.69). There was no statistical between-trial heterogeneity for most clinical outcomes.

CONCLUSIONS

Prone ventilation reduces mortality in patients with severe hypoxemia. Given associated risks, this approach should not be routine in all patients with AHRF, but may be considered for severely hypoxemic patients.

Acute lung injury after thoracic surgery

In this review, the authors discussed criteria for diagnosing ALI; incidence, etiology, preoperative risk factors, intraoperative management, risk-reduction strategies, treatment, and prognosis. The anesthesiologist needs to maintain an index of suspicion for ALI in the perioperative period of thoracic surgery, particularly after lung resection on the right side. Acute hypoxemia, imaging analysis for diffuse infiltrates, and detecting a noncardiogenic origin for pulmonary edema are important hallmarks of acute lung injury. Conservative intraoperative fluid administration of neutral to slightly negative fluid balance over the postoperative first week can reduce the number of ventilator days. Fluid management may be optimized with the assistance of new imaging techniques, and the anesthesiologist should monitor for transfusion-related lung injuries. Small tidal volumes of 6 mL/kg and low plateau pressures of < or =30 cmH2O may reduce organ and systemic failure. PEEP may improve oxygenation and increases organ failure-free days but has not shown a mortality benefit. The optimal mode of ventilation has not been shown in perioperative studies. Permissive hypercapnia may be needed in order to reduce lung injury from positive-pressure ventilation. NO is not recommended as a treatment. Strategies such as bronchodilation, smoking cessation, steroids, and recruitment maneuvers are unproven to benefit mortality although symptomatically they often have been shown to help ALI patients. Further studies to isolate biomarkers active in the acute setting of lung injury and pharmacologic agents to inhibit inflammatory intermediates may help improve management of this complex disease.

A low oxygen consumption pneumatic ventilator for emergency construction during a respiratory failure pandemic

The UK influenza pandemic plan predicts up to 750 000 additional deaths with hospitals prioritising patients against inadequate resources. We investigated three prototype low‐cost, gas‐efficient, pneumatic ventilators in a test lung model at different compliance and rate settings. Mean (SD) oxygen consumption was 0.913 (0.198) and 1.119 (0.267) l.min⁻¹ at tidal volumes of 500 ml and 700 ml respectively. Values of F_Io₂ increased marginally as lung compliance reduced, reflecting the increased ventilator workload and consequent increased enrichment of breathing gas by waste oxygen from the pneumatic mechanism. We also demonstrated that a stable nitric oxide concentration could be delivered by this design following volumetric principles. It is possible to make a gas‐efficient ventilator costing less than £200 from industrial components for use where oxygen is available at 2‐4 bar, with no pressurised air or electrical requirements. Such a device could be mass‐produced for crises characterised by an overwhelming demand for mechanical ventilation and a limited oxygen supply.

Acute lung injury and acute respiratory distress syndrome

Every year, more information accumulates about the possibility of treating patients with acute lung injury or acute respiratory distress syndrome with specially designed mechanical ventilation strategies. Ventilator modes, positive end-expiratory pressure settings, and recruitment maneuvers play a major role in these strategies. However, what can we take from these experimental and clinical data to the clinical practice? In this article, we discuss substantial options of mechanical ventilation together with some adjunctive therapeutic measures, such as prone positioning and inhalation of nitric oxide.

Rescue strategies for refractory hypoxemia: a critical appraisal

Mechanical ventilation is the most important aspect of supportive care of patients with severe acute respiratory failure. Most research directed to improving the prognosis of these patients has focused on improving support of the injured lung. In this report, current knowledge on innovative ways to manage refractory hypoxemia and ventilation without further damaging the injured lung is briefly discussed.

Hemoglobin-based red blood cell substitutes and nitric oxide

Hemoglobin-based oxygen carriers (HBOCs) have been studied for decades as red blood cell substitutes. Profound vasoconstrictor effects have limited the clinical utility of HBOCs and are attributable to avid scavenging of nitric oxide (NO). Inhaling NO can charge the body's stores of NO metabolites without producing hypotension and can prevent systemic hypertension induced when HBOCs are subsequently infused. Concurrent breathing of low NO doses can prevent pulmonary vasoconstriction after HBOC infusion without augmenting plasma methemoglobinemia.

Protein S-nitrosylation in health and disease: a current perspective

Protein S-nitrosylation constitutes a large part of the ubiquitous influence of nitric oxide on cellular signal transduction and accumulating evidence indicates important roles for S-nitrosylation both in normal physiology and in a broad spectrum of human diseases. Here we review recent findings that implicate S-nitrosylation in cardiovascular, pulmonary, musculoskeletal and neurological (dys)function, as well as in cancer. The emerging picture shows that, in many cases, pathophysiology correlates with hypo- or hyper-S-nitrosylation of specific protein targets rather than a general cellular insult due to loss of or enhanced nitric oxide synthase activity. In addition, it is increasingly evident that dysregulated S-nitrosylation can not only result from alterations in the expression, compartmentalization and/or activity of nitric oxide synthases, but can also reflect a contribution from denitrosylases, including prominently the S-nitrosoglutathione (GSNO)-metabolizing enzyme GSNO reductase. Finally, because exogenous mediators of protein S-nitrosylation or denitrosylation can substantially affect the development or progression of disease, potential therapeutic agents that modulate S-nitrosylation could well have broad clinical utility.

Pathophysiology, management and treatment of smoke inhalation injury

Smoke inhalation injury continues to increase morbidity and mortality in burn patients in both the third world and industrialized countries. The lack of uniform criteria for the diagnosis and definition of smoke inhalation injury contributes to the fact that, despite extensive research, mortality rates have changed little in recent decades. The formation of reactive oxygen and nitrogen species, as well as the procoagulant and antifibrinolytic imbalance of alveolar homeostasis, all play a central role in the pathogenesis of smoke inhalation injury. Further hallmarks include massive airway obstruction owing to cast formation, bronchospasm, the increase in bronchial circulation and transvascular fluid flux. Therefore, anticoagulants, antioxidants and bronchodilators, especially when administered as an aerosol, represent the most promising treatment strategies. The purpose of this review article is to provide an overview of the pathophysiological changes, management and treatment options of smoke inhalation injury based on the current literature.

Bench-to-bedside review: Inhaled nitric oxide therapy in adults

Nitric oxide (NO) is an endogenous mediator of vascular tone and host defence. Inhaled nitric oxide (iNO) results in preferential pulmonary vasodilatation and lowers pulmonary vascular resistance. The route of administration delivers NO selectively to ventilated lung units so that its effect augments that of hypoxic pulmonary vasoconstriction and improves oxygenation. This 'Bench-to-bedside' review focuses on the mechanisms of action of iNO and its clinical applications, with emphasis on acute lung injury and the acute respiratory distress syndrome. Developments in our understanding of the cellular and molecular actions of NO may help to explain the hitherto disappointing results of randomised controlled trials of iNO.

Inhalational therapies for the ICU

PURPOSE OF REVIEW

Although drug therapy is most commonly delivered via the intravenous route, novel inhaled agents have been introduced for use in the ICU. Additionally, drugs previously delivered intravenously are now being delivered via the respiratory tract in an effort to reduce systemic toxicity and maximize effectiveness.

RECENT FINDINGS

Aerosolized antibiotics have seen increased use in an effort to reduce systemic effects, reduce ventilator-associated pneumonia, and direct high drug concentrations at the site of infection. Drug-resistant pneumonia has also been effectively treated with aerosolized antibiotics. Secretion management includes a host of devices, therapies, and drugs, but the evidence for these is scant. Cardiac drugs via the endotracheal route should be used only when intravenous access is delayed. Inhaled nitric oxide has a defined role in care of infants, although new indications have limited and conflicting data. The use of helium-oxygen mixtures provides symptom relief in a wide variety of scenarios associated with turbulent flow in large airways.

SUMMARY

Inhaled nitric oxide has an established role in neonatal intensive care and a limited role in adult intensive care. Heliox provides symptom relief, but at present cannot be considered routine as a consequence of the multiple technological challenges. Inhaled antimicrobials appear to provide a therapeutic advantage in select individuals with pneumonia. Secretion management is best achieved by adequate humidification and as needed suctioning. The role of inhaled carbon monoxide in critical care holds significant promise, but is currently in early clinical trials.

Prevention of the pulmonary vasoconstrictor effects of HBOC-201 in awake lambs by continuously breathing nitric oxide

BACKGROUND

Hemoglobin-based oxygen-carrying solutions (HBOC) provide emergency alternatives to blood transfusion to carry oxygen to tissues without the risks of disease transmission or transfusion reaction. Two primary concerns hampering the clinical acceptance of acellular HBOC are the occurrence of systemic and pulmonary vasoconstriction and the maintenance of the heme-iron in the reduced state (Fe2+). We recently demonstrated that pretreatment with inhaled nitric oxide prevents the systemic hypertension induced by HBOC-201 (polymerized bovine hemoglobin) infusion in awake mice and sheep without causing methemoglobinemia. However, the impact of HBOC-201 infusion with or without inhaled nitric oxide on pulmonary vascular tone has not yet been examined.

METHODS

The pulmonary and systemic hemodynamic effects of breathing nitric oxide both before and after the administration of HBOC-201 were determined in healthy, awake lambs.

RESULTS

Intravenous administration of HBOC-201 (12 ml/kg) induced prolonged systemic and pulmonary vasoconstriction. Pretreatment with inhaled nitric oxide (80 parts per million [ppm] for 1 h) prevented the HBOC-201--induced increase in mean arterial pressure but not the increase of pulmonary arterial pressure, systemic vascular resistance, or pulmonary vascular resistance. Pretreatment with inhaled nitric oxide (80 ppm for 1 h) followed by breathing a lower concentration of nitric oxide (5 ppm) during and after HBOC-201 infusion prevented systemic and pulmonary vasoconstriction without increasing methemoglobin levels.

CONCLUSIONS

These findings demonstrate that pretreatment with inhaled nitric oxide followed by breathing a lower concentration of the gas during and after administration of HBOC-201 may enable administration of an acellular hemoglobin substitute without vasoconstriction while preserving its oxygen-carrying capacity.

Acute lung injury review

The first report of acute respiratory distress syndrome (ARDS) was published in 1967, and even now acute lung injury (ALI) and ARDS are severe forms of diffuse lung disease that impose a substantial health burden all over the world. Recent estimates indicate approximately 190,000 cases per year of ALI in the United States each year, with an associated 74,500 deaths per year. Common causes of ALI/ARDS are sepsis, pneumonia, trauma, aspiration pneumonia, pancreatitis, and so on. Several pathologic stages of ALI/ARDS have been described: acute inflammation with neutrophil infiltration, fibroproliferative phase with hyaline membranes, with varying degrees of interstitial fibrosis, and resolution phase. There has been intense investigation into the pathophysiologic events relevant to each stage of ALI/ARDS, and much has been learned in the alveolar epithelial, endobronchial homeostasis, and alveolar cell immune responses, especially neutrophils and alveolar macrophages in an animal model. However, these effective results in the animal models are not equally adoptive to those in randomized, controlled trials. The clinical course of ALI/ARDS is variable with the likely pathophysiologic complexity of human ALI/ARDS. In 1994, the definition was recommended by the American-European Consensus Conference Committee, which facilitated easy nomination of patients with ALI/ARDS for a randomized, clinical trial. Here, we review the recent randomized, clinical trials of ALI/ARDS.