Mechanistic scheme and effect of "extended sigh" as a recruitment maneuver in patients with acute respiratory distress syndrome: a preliminary study

Optimizing Mechanical Ventilation in Refractory ARDS

Mechanical ventilation in patients with refractory acute respiratory distress syndrome (ARDS) must provide lung protection. This is achieved by limiting tidal volume (VT) and plateau pressure (Pplat). With the current evidence available VT should be initially set around 6 mL per kg predicted body weight and PPlat maintained below 30 cmH₂O and monitored. Positive end-expiratory pressure (PEEP), which also contributes to lung protection, should be set > 12 cmH₂O, provided oxygenation gets improved, with same Pplat target. Recruitment maneuvers should be used with caution avoiding higher PEEP. Neuromuscular blockade should be started and prone position performed for sessions longer than 16 h. High frequency oscillation ventilation should be used in expert centers only if previous management failed to improve oxygenation.

Analytics with artificial intelligence to advance the treatment of acute respiratory distress syndrome

Artificial intelligence (AI) has found its way into clinical studies in the era of big data. Acute respiratory distress syndrome (ARDS) or acute lung injury (ALI) is a clinical syndrome that encompasses a heterogeneous population. Management of such heterogeneous patient population is a big challenge for clinicians. With accumulating ALI datasets being publicly available, more knowledge could be discovered with sophisticated analytics. We reviewed literatures with big data analytics to understand the role of AI for improving the caring of patients with ALI/ARDS. Many studies have utilized the electronic medical records (EMR) data for the identification and prognostication of ARDS patients. As increasing number of ARDS clinical trials data is open to public, secondary analysis on these combined datasets provide a powerful way of finding solution to clinical questions with a new perspective. AI techniques such as Classification and Regression Tree (CART) and artificial neural networks (ANN) have also been successfully used in the investigation of ARDS problems. Individualized treatment of ARDS could be implemented with a support from AI as we are now able to classify ARDS into many subphenotypes by unsupervised machine learning algorithms. Interestingly, these subphenotypes show different responses to a certain intervention. However, current analytics involving ARDS have not fully incorporated information from omics such as transcriptome, proteomics, daily activities and environmental conditions. AI technology is assisting us to interpret complex data of ARDS patients and enable us to further improve the management of ARDS patients in future with individual treatment plans.

Intracranial-to-central venous pressure gap predicts the responsiveness of intracranial pressure to PEEP in patients with traumatic brain injury: a prospective cohort study

BACKGROUND

Mechanical ventilation (MV) with positive end-expiratory pressure (PEEP) is commonly applied in patients with severe traumatic brain injury (sTBI). However, the individual responsiveness of intracranial pressure (ICP) to PEEP varies. Thus, identifying an indicator detecting ICP responsiveness to PEEP is of great significance. As central venous pressure (CVP) could act as an intermediary to transduce pressure from PEEP to ICP, we developed a new indicator, P_ICGap, representing the gap between baseline ICP and baseline CVP. The aim of the current study was to explore the relationship between P_ICGap and ICP responsiveness to PEEP.

METHODS

A total of 112 patients with sTBI undergoing MV were enrolled in this prospective cohort study. ICP, CVP, cerebral perfusion pressure (CPP), static compliance of the respiratory system (Cst), and end-tidal carbon dioxide pressure (PetCO₂) were recorded at the initial (3 cmH₂O) and adjusted (15 cmH₂O) levels of PEEP. P_ICGap was assessed as baseline ICP - baseline CVP (when PEEP = 3 cmH₂O). The patients were classified into the ICP responder and non-responder groups based on whether ICP increment with PEEP adjusted from 3 cmH₂O to 15 cmH₂O was greater than 20% of baseline ICP. The above parameters were compared between the two groups, and prediction of ICP responsiveness to PEEP adjustment was evaluated by receiver operating characteristic (ROC) curve analysis.

RESULTS

Compared with the non-responder group, the responder group had lower P_ICGap (1.63 ± 1.33 versus 6.56 ± 2.46 mmHg; p <  0.001), lower baseline ICP, and higher baseline CVP. ROC curve analysis suggested that P_ICGap was a stronger predictive indicator of ICP responsiveness to PEEP (AUC = 0.957, 95%CI 0.918-0.996; p <  0.001) compared with baseline ICP and baseline CVP, with favorable sensitivity (95.24, 95%CI 86.91-98.70%) and specificity (87.6, 95%CI 75.76-94.27%), at a cut off value of 2.5 mmHg.

CONCLUSION

The impact of PEEP on ICP depends on the gap between baseline ICP and baseline CVP, i.e. P_ICGap. In addition, P_ICGap is a potential predictor of ICP responsiveness to PEEP adjustment in patients with sTBI.

Effects of Stepwise Lung Recruitment Maneuvers in Patients with Early Acute Respiratory Distress Syndrome: A Prospective, Randomized, Controlled Trial

Since the clinical benefit of lung recruitment maneuvers (LRMs) is still conflicting, we performed this prospective, randomized, controlled study to investigate whether LRMs should be used in the routine management of acute respiratory distress syndrome (ARDS). This trial was conducted in four intensive care units (ICUs) to compare application of a modified stepwise LRMs with solely lung-protective ventilation in patients with moderate to severe ARDS within 72 h from the onset. The primary outcome was 28-day mortality, and the secondary outcomes were ventilator-free days and ICU-free days. We collected data on 120 ARDS patients from 2009 to 2012, and there was no difference in 28-day mortality between the two groups (28.3% vs. 30.0%, p = 0.84). However, among survivors, patients in the LRM group had a significant longer median duration of ventilator-free days (18 vs. 13 days; p = 0.04) and ICU-free days (16 vs. 11 days; p = 0.03) at 28 days than in the control group. The respiratory system compliance was significantly higher in the LRM group from day 1 to day 7. The occurrence rate of barotrauma was similar in both groups. We concluded that LRMs combined with lung-protective ventilation in early ARDS may improve patient outcomes.

Use of Recruitment Maneuvers in Patients With Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a deadly complication in critically ill patients that causes significant morbidity and mortality. Patients with ARDS are seen across intensive care unit settings, with treatment being largely supportive involving techniques through mechanical ventilation. Using low-tidal-volume ventilation is a standard of practice for patients with ARDS, as a lung protection strategy; however, alveolar decruitment may occur. Recruitment maneuvers can recruit collapsed alveoli and promote oxygenation. There are several methods of recruitment maneuvers-each with varying levels and durations of positive end-expiratory pressure. It is still uncertain which method is the best. The evidence for the efficacy of recruitment maneuvers has shown a decrease in intensive care unit mortality, but strong evidence is lacking for its routine use, and the decision to use recruitment maneuvers should be based on individual characteristics and responses. This article reviews management of ARDS, recruitment maneuver techniques, and clinical application through a case study.

Recruitment manoeuvres dislodge mucus towards the distal airways in an experimental model of severe pneumonia

BACKGROUND

Recruitment manoeuvres generate a transient increase in trans-pulmonary pressure that could open collapsed alveoli. Recruitment manoeuvres might generate very high inspiratory airflows. We evaluated whether recruitment manoeuvres could displace respiratory secretions towards the distal airways and impair gas exchange in a porcine model of bacterial pneumonia.

METHODS

We conducted a prospective randomised study in 10 mechanically ventilated pigs. Pneumonia was produced by direct intra-bronchial introduction of Pseudomonas aeruginosa. Four recruitment manoeuvres were applied randomly: extended sigh (ES), maximal recruitment strategy (MRS), sudden increase in driving pressure and PEEP (SI-PEEP), and sustained inflation (SI). Mucus transport was assessed by fluoroscopic tracking of radiopaque disks before and during each recruitment manoeuvre. The effects of each RM on gas exchange were assessed 15 min after the intervention.

RESULTS

Before recruitment manoeuvres, mucus always cleared towards the glottis. Conversely, mucus was displaced towards the distal airways in 28.6% ES applications and 50% of all other recruitment manoeuvres (P=0.053). Median mucus velocity was 1.26 mm min^-1 [0.48-3.89] before each recruitment manoeuvre, but was reversed (P=0.007) during ES [0.10 mm min^-1 [-0.04-1.00]], MRS [0.10 mm min^-1 [-0.4-0.48]], SI-PEEP [0.02 mm min^-1 [-0.14-0.34]], and SI [0.10 mm min^-1 [-0.63-0.75]]. When PaO₂ failed to improve after recruitment manoeuvre, mucus was displaced towards the distal airways in 68.7% of the cases, compared with 31.2% recruitment manoeuvres associated with improved PaO₂ (odds ratio: 4.76 (95% confidence interval: 1.13-19.97).

CONCLUSIONS

Recruitment manoeuvres dislodge mucus distally, irrespective of airflow generated by different recruitment manoeuvres. Further investigation in humans is warranted to corroborate these pre clinical findings, as there may be limited benefits associated with lung recruitment in pneumonia.

Salvage therapies for refractory hypoxemia in ARDS

Acute Respiratory Distress Syndrome (ARDS) is a condition of varied etiology characterized by the acute onset (within 1 week of the inciting event) of hypoxemia, reduced lung compliance, diffuse lung inflammation and bilateral opacities on chest imaging attributable to noncardiogenic (increased permeability) pulmonary edema. Although multi-organ failure is the most common cause of death in ARDS, an estimated 10-15% of the deaths in ARDS are caused due to refractory hypoxemia, i.e.- hypoxemia despite lung protective conventional ventilator modes. In these cases, clinicians may resort to other measures with less robust evidence -referred to as "salvage therapies". These include proning, 48 h of paralysis early in the course of ARDS, various recruitment maneuvers, unconventional ventilator modes, inhaled pulmonary vasodilators, and Extracorporeal membrane oxygenation (ECMO). All the salvage therapies described have been associated with improved oxygenation, but with the exception of proning and 48 h of paralysis early in the course of ARDS, none of them have a proven mortality benefit. Based on the current evidence, no salvage therapy has been shown to be superior to the others and each of them is associated with its own risks and benefits. Hence, the order of application of these therapies varies in different institutions and should be applied following a risk-benefit analysis specific to the patient and local experience. This review explores the rationale, evidence, advantages and risks behind each of these strategies.

How to approach the acute respiratory distress syndrome: Prevention, plan, and prudence

The acute respiratory distress syndrome (ARDS) is typically manifested by refractory hypoxemia with high mortality. A correct diagnosis is the first step to achieve better outcomes. An early intervention to manage modifiable risk factors of ARDS development and the avoidance of aggravating factors that increase disease severity and progression should be carefully addressed. A management plan is necessary at an early stage of ARDS to determine the level of intensive care. It should be carefully decided which therapeutic measures should be performed depending on the patient׳s underlying clinical condition. The clinician׳s considerate prudence is required in decisions of when to apply intensive measures for an ARDS treatment. Mechanical ventilator support should be carefully used depending on the patient׳s severity and pathological phase. Decreasing inappropriate alveolar strain through a low tidal volume under optimal positive end-expiratory pressure is key for ventilator support in ARDS. The extracorporeal membrane oxygenation applied in the experienced centers seems to improve the survival of patients with severe ARDS. A constellation of physical and psychological problems can develop or persist for up to 5 years in patients with ARDS. Therefore, an early mobilization with rehabilitation, even during an intensive care unit stay, should be seriously considered whenever feasible. Lastly, prevention of aspiration, stress ulcers, deep vein thrombosis, catheter-related infection, overhydration, and heavy sedation is essential to achieve better outcomes in ARDS.

Clinical Practice Guideline of Acute Respiratory Distress Syndrome

There is no well-stated practical guideline for mechanically ventilated patients with or without acute respiratory distress syndrome (ARDS). We generate strong (1) and weak (2) grade of recommendations based on high (A), moderate (B) and low (C) grade in the quality of evidence. In patients with ARDS, we recommend low tidal volume ventilation (1A) and prone position if it is not contraindicated (1B) to reduce their mortality. However, we did not support high-frequency oscillatory ventilation (1B) and inhaled nitric oxide (1A) as a standard treatment. We also suggest high positive end-expiratory pressure (2B), extracorporeal membrane oxygenation as a rescue therapy (2C), and neuromuscular blockage for 48 hours after starting mechanical ventilation (2B). The application of recruitment maneuver may reduce mortality (2B), however, the use of systemic steroids cannot reduce mortality (2B). In mechanically ventilated patients, we recommend light sedation (1B) and low tidal volume even without ARDS (1B) and suggest lung protective ventilation strategy during the operation to lower the incidence of lung complications including ARDS (2B). Early tracheostomy in mechanically ventilated patients can be performed only in limited patients (2A). In conclusion, of 12 recommendations, nine were in the management of ARDS, and three for mechanically ventilated patients.

Haemodynamic Effects of Lung Recruitment Manoeuvres

Atelectasis caused by lung injury leads to increased intrapulmonary shunt, venous admixture, and hypoxaemia. Lung recruitment manoeuvres aim to quickly reverse this scenario by applying increased airway pressures for a short period of time which meant to open the collapsed alveoli. Although the procedure can improve oxygenation, but due to the heart-lung and right and left ventricle interactions elevated intrathoracic pressures can inflict serious effects on the cardiovascular system. The purpose of this paper is to give an overview on the pathophysiological background of the heart-lung interactions and the best way to monitor these changes during lung recruitment.

Evaluation of lung recruitment maneuvers in acute respiratory distress syndrome using computer simulation

Introduction

Direct comparison of the relative efficacy of different recruitment maneuvers (RMs) for patients with acute respiratory distress syndrome (ARDS) via clinical trials is difficult, due to the heterogeneity of patient populations and disease states, as well as a variety of practical issues. There is also significant uncertainty regarding the minimum values of positive end-expiratory pressure (PEEP) required to ensure maintenance of effective lung recruitment using RMs. We used patient-specific computational simulation to analyze how three different RMs act to improve physiological responses, and investigate how different levels of PEEP contribute to maintaining effective lung recruitment.

Methods

We conducted experiments on five ‘virtual’ ARDS patients using a computational simulator that reproduces static and dynamic features of a multivariable clinical dataset on the responses of individual ARDS patients to a range of ventilator inputs. Three recruitment maneuvers (sustained inflation (SI), maximal recruitment strategy (MRS) followed by a titrated PEEP, and prolonged recruitment maneuver (PRM)) were implemented and evaluated for a range of different pressure settings.

Results

All maneuvers demonstrated improvements in gas exchange, but the extent and duration of improvement varied significantly, as did the observed mechanism of operation. Maintaining adequate post-RM levels of PEEP was seen to be crucial in avoiding cliff-edge type re-collapse of alveolar units for all maneuvers. For all five patients, the MRS exhibited the most prolonged improvement in oxygenation, and we found that a PEEP setting of 35 cm H₂O with a fixed driving pressure of 15 cm H₂O (above PEEP) was sufficient to achieve 95% recruitment. Subsequently, we found that PEEP titrated to a value of 16 cm H₂O was able to maintain 95% recruitment in all five patients.

Conclusions

There appears to be significant scope for reducing the peak levels of PEEP originally specified in the MRS and hence to avoid exposing the lung to unnecessarily high pressures. More generally, our study highlights the huge potential of computer simulation to assist in evaluating the efficacy of different recruitment maneuvers, in understanding their modes of operation, in optimizing RMs for individual patients, and in supporting clinicians in the rational design of improved treatment strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0723-6) contains supplementary material, which is available to authorized users.

Lung recruitment in acute respiratory distress syndrome: what is the best strategy?

PURPOSE OF REVIEW

Supporting patients with acute respiratory distress syndrome (ARDS) using a low tidal volume strategy is a standard practice in the ICU. Recruitment maneuvers can be used to augment other methods, like positive end-expiratory pressure and positioning, to improve aerated lung volume. Clinical practice varies widely, and optimal method and patient selection for recruitment maneuvers have not been determined.

RECENT FINDINGS

Recent developments include experimental and clinical evidence that a stepwise extended recruitment maneuver may match the improvement in aerated lung volume seen with sustained inflation traditionally used, with less adverse effects. Positioning and other chest wall modifications may be useful adjuncts to recruitment maneuvers. In addition, evidence from clinical studies in the operating room suggests that recruitment maneuvers, as a component of an open lung strategy, may be helpful for mechanically ventilated patients with normal lungs.

SUMMARY

As a component of ventilation strategy for patients with ARDS, the use of recruitment maneuvers, especially a stepwise maneuver, in addition to adequate positive end-expiratory pressure and appropriate positioning, is suggested by currently available data. Until their effect on clinical outcomes is further defined, the use of recruitment maneuvers in ARDS and other settings will continue to be guided by individual clinician experience and patient factors.

Gas exchange in the respiratory distress syndromes

This article describes the gas exchange abnormalities occurring in the acute respiratory distress syndrome seen in adults and children and in the respiratory distress syndrome that occurs in neonates. Evidence is presented indicating that the major gas exchange abnormality accounting for the hypoxemia in both conditions is shunt, and that approximately 50% of patients also have lungs regions in which low ventilation-to-perfusion ratios contribute to the venous admixture. The various mechanisms by which hypercarbia may develop and by which positive end-expiratory pressure improves gas exchange are reviewed, as are the effects of vascular tone and airway narrowing. The mechanisms by which surfactant abnormalities occur in the two conditions are described, as are the histological findings that have been associated with shunt and low ventilation-to-perfusion.

Evaluation of effects of repetitive recruitment maneuvers

Introduction:

acute respiratory failure is manifested clinically as patient with variable degrees of respiratory distress, but characteristically an abnormal arterial blood partial pressure of oxygen or carbon dioxide. The application of mechanical ventilation in this setting can be life saving.

Goals:

The aim of this study is to evaluate the effects of two recruitment maneuvers not only on oxygenation, but on aeration of the lung as well. For that purpose chest x ray and thoracic computed tomography scan (CT) of the lung were used as safe and objective methods for evaluation the impact of recruitment maneuvers on aeration of the lung. CT scan and chest x ray were performed before recruitment maneuvers as confirmation of diagnose and one day after the last recruitment maneuvers.

Material and methods:

Sixty patients who met ar DS criteria of the american european consensus conference were included in this study. This study was conducted in iCU in our hospital between november 2009 and December 2011. Patients were orally intubated, sedated with 0, 2-0, 4 μg/kg /min and midazolam 4 mg/h, and ventilated with evita 2 Dura ventilator (Dragger germany). According to the recom-mendation of the Consensus Conference of the american College of Chest physician all patients had an arterial catheter and cen-tral venous catheter. Hemodynamic data were collected from Data Ohmeda monitors. Gas analyses were mesured from blood samples taken from arteria radialis. Partial pressure of oxygen of mixed blood was messured from blood sample taken from v jugularis interior. We used arterial blood colection syringe Bd preset, and blood samples were analyzed with aVl 995HB blood gas analiser.

Results:

Hemodynamic changes: there wasn’t any differences in heart rate, and mean arterial blood pressure before the recruitment five minutes and sixty minutes after the recruitment in both groups. respiratory mechanics: Highest values of the compliance are achived during the recruitment manouver in both groups. There was better improvment in compliance during the e sigh recruitment maneouver, then in Cpap recruitment maneouver. There was improvement in chest X ray in both groups. 93,4% of patients in the Cpap group and 96,7% in e sigh group. CT scan: in Cpap group there were 8 patients with focal changes and 22 patients with diffusse changes. in e sigh group 29 patients had diffuse changes of the lung and one patient had focal changes. We noticed that there was better improvment in aeration in patients with diffuse changes of the lung 96.7% in e sigh group and 73,3% in Cpapgroup. In patient with focal changes there was improvment in 26,7% in e sigh group and 3,3% in Cpap group. We noticed that there was better improvmnet in aeration in patients with diffuse changes than in patients with focal changes. E sigh maneuver had better impact on aeration of the lung then Cpap recruitment maneuver.

Conclusion:

In our study we proved that e sigh recruitment maneuvers better improved oxygenation in arterial blood than Cpap recruitment maneuver. Repetative e sigh manouvers proved to be essential for arDS patients. They reopened collapsed alveolli and improved aeration of the lung which was confirmed by X ray and CT scan as an objective methods for verification of lung condition.

Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis

BACKGROUND

Pathophysiological changes due to obesity may complicate mechanical ventilation during general anaesthesia. The ideal ventilation strategy is expected to optimize gas exchange and pulmonary mechanics and to reduce the risk of respiratory complications.

METHODS

Systematic search (databases, bibliographies, to March 2012, all languages) was performed for randomized trials testing intraoperative ventilation strategies in obese patients (BMI ≥ 30 kg m(-2)), and reporting on gas exchange, pulmonary mechanics, or pulmonary complications. Meta-analyses were performed when data from at least three studies or 100 patients could be combined.

RESULTS

Thirteen studies (505 obese surgical patients) reported on a variety of ventilation strategies: pressure- or volume-controlled ventilation (PCV, VCV), various tidal volumes, and different PEEP or recruitment manoeuvres (RM), and combinations thereof. Definitions and reporting of endpoints were inconsistent. In five trials (182 patients), RM added to PEEP compared with PEEP alone improved intraoperative PaO2/FIO2 ratio [weighted mean difference (WMD), 16.2 kPa; 95% confidence interval (CI), 8.0-24.4] and increased respiratory system compliance (WMD, 14 ml cm H(2)O(-1); 95% CI, 8-20). Arterial pressure remained unchanged. In four trials (100 patients) comparing PCV with VCV, there was no difference in PaO2/FIO2 ratio, tidal volume, or arterial pressure. Comparison of further ventilation strategies or combination of other outcomes was not feasible. Data on postoperative complications were seldom reported.

CONCLUSIONS

The ideal intraoperative ventilation strategy in obese patients remains obscure. There is some evidence that RM added to PEEP compared with PEEP alone improves intraoperative oxygenation and compliance without adverse effects. There is no evidence of any difference between PCV and VCV.

A comparison between two different alveolar recruitment maneuvers in patients with acute respiratory distress syndrome

Background:

Alveolar recruitment is a physiological process that denotes the reopening of previously gasless lung units exposed to positive pressure ventilation. The current study was aimed to compare two recruitment maneuvers, a high continuous positive airway pressure (CPAP), and an extended sigh in patients with ARDS.

Materials and Methods:

Forty patients with acute respiratory distress syndrome were randomly divided into two groups, 20 patients each. Group I received a CPAP of 40 cm H₂O for 40 seconds and group II received extended sigh (providing a sufficient recruiting pressure × time). In our study, we assessed the effects of both recruitment maneuvers on respiratory mechanics, gas exchange, and hemodynamics. These data were analyzed using two-way analysis of variance (ANOVA) followed by a Student--Newman--Keuls post hoc comparison test. P < 0.05 was considered statistically significant.

Results:

Both methods improved the compliance, increased arterial oxygenation (PaO₂), increased the PaO₂/FiO₂ ratio, and reduced the pulmonary shunt fraction (Q_s/Q_t). However, the extended sigh improved both PaO₂ and PaO₂/FiO₂ ratios more than continuous positive airway pressure. Also the hemodynamic parameters were better maintained during the extended sigh.

Conclusion:

Alveolar recruitment maneuvers are effective in management of mechanically ventilated ARDS patients. We conclude that extended sigh is more effective than continuous positive airway pressure as a recruitment maneuver.

Mechanical ventilation during acute lung injury: current recommendations and new concepts

Despite a very large body of investigations, no effective pharmacological therapies have been found to cure acute lung injury. Hence, supportive care with mechanical ventilation remains the cornerstone of treatment. However, several experimental and clinical studies showed that mechanical ventilation, especially at high tidal volumes and pressures, can cause or aggravate ALI. Therefore, current clinical recommendations are developed with the aim of avoiding ventilator-induced lung injury (VILI) by limiting tidal volume and distending ventilatory pressure according to the results of the ARDS Network trial, which has been to date the only intervention that has showed success in decreasing mortality in patients with ALI/ARDS. In the past decade, a very large body of investigations has determined significant achievements on the pathophysiological knowledge of VILI. Therefore, new perspectives, which will be reviewed in this article, have been defined in terms of the efficiency and efficacy of recognizing, monitoring and treating VILI, which will eventually lead to further significant improvement of outcome in patients with ARDS.

Effect of the alveolar recruitment manoeuvre on haemodynamic parameters in patients with acute respiratory distress syndrome: relationship with oxygenation

BACKGROUND AND OBJECTIVE

Although the alveolar recruitment manoeuvre (ARM) is considered to be an optimal method of recruiting collapsed alveoli in a short period, the haemodynamic effects of the ARM have not been investigated. The aim of this study was to assess whether the ARM causes haemodynamic instability in patients with ARDS, and any relationship this might have with arterial oxygenation.

METHODS

Twenty-eight patients with ARDS (16 responders and 12 non-responders), who were admitted to the medical intensive care unit of a university-affiliated hospital, were enrolled in the study. ARM, using the extended sigh method, was performed within 48 h of the onset of ARDS. Haemodynamic parameters were measured at baseline, during the ARM, and at 2 min, 30 min and 1 h after the ARM.

RESULTS

Responders and non-responders showed no significant changes in blood pressure or cardiac index during or after ARM. Mean pulmonary artery pressure (MPAP), pulmonary vascular resistance index (PVRI) and right ventricular stroke work index (RVSWI) were transiently increased compared with baseline, in responders and non-responders. During and after ARM, the systemic vascular resistance index was significantly higher in non-responders than in responders.

CONCLUSIONS

Some haemodynamic parameters (MPAP, PVRI and RVSWI) changed significantly during ARM. However, these haemodynamic changes were minimal, transient and probably have no clinical significance.

Pros and cons of recruitment maneuvers in acute lung injury and acute respiratory distress syndrome

In patients with acute lung injury and acute respiratory distress syndrome, a protective mechanical ventilation strategy characterized by low tidal volumes has been associated with reduced mortality. However, such a strategy may result in alveolar collapse, leading to cyclic opening and closing of atelectatic alveoli and distal airways. Thus, recruitment maneuvers (RMs) have been used to open up collapsed lungs, while adequate positive end-expiratory pressure (PEEP) levels may counteract alveolar derecruitment during low tidal volume ventilation, improving respiratory function and minimizing ventilator-associated lung injury. Nevertheless, considerable uncertainty remains regarding the appropriateness of RMs. The most commonly used RM is conventional sustained inflation, associated with respiratory and cardiovascular side effects, which may be minimized by newly proposed strategies: prolonged or incremental PEEP elevation; pressure-controlled ventilation with fixed PEEP and increased driving pressure; pressure-controlled ventilation applied with escalating PEEP and constant driving pressure; and long and slow increase in pressure. The efficiency of RMs may be affected by different factors, including the nature and extent of lung injury, capability of increasing inspiratory transpulmonary pressures, patient positioning and cardiac preload. Current evidence suggests that RMs can be used before setting PEEP, after ventilator circuit disconnection or as a rescue maneuver to overcome severe hypoxemia; however, their routine use does not seem to be justified at present. The development of new lung recruitment strategies that have fewer hemodynamic and biological effects on the lungs, as well as randomized clinical trials analyzing the impact of RMs on morbidity and mortality of acute lung injury/acute respiratory distress syndrome patients, are warranted.

Changes of splanchnic perfusion after applying positive end expiratory pressure in patients with acute respiratory distress syndrome

Background:

Positive end-expiratory pressure (PEEP) improves oxygenation and can prevent ventilator- induced lung injury in patients with acute respiratory distress syndrome (ARDS). Nevertheless, PEEP can also induce detrimental effects by its influence on the cardiovascular system. The purpose of this study was to assess the effects of PEEP on gastric mucosal perfusion while applying a protective ventilatory strategy in patients with ARDS.

Materials and Methods:

Thirty-two patients were included in the study. A pressure–volume curve was traced and ideal PEEP, defined as lower inflection point + 2cmH₂O, was determined. Gastric tonometry was measured continuously (Tonocap). After baseline measurements, 10, 15 and 20cmH₂O PEEP and ideal PEEP were applied for 30 min each. By the end of each period, hemodynamics, CO₂ gap (gastric minus arterial partial pressures), and ventilatory measurements were taken.

Results:

PEEP had no effect on CO₂ gap (median [range], baseline: 18 [2–30] mmHg; PEEP 10: 18 [0–40] mmHg; PEEP 15: 17 [0–39] mmHg; PEEP 20: 16 [4–39] mmHg; ideal PEEP: 19 [9–39] mmHg; P = 0.19). Cardiac index also remained unchanged (baseline: 4.7 [2.6–6.2] l min⁻¹ m⁻²; PEEP 10: 4.4 [2.5–7] l min⁻¹ m⁻²; PEEP 15: 4.4 [2.2–6.8] l min⁻¹ m⁻²; PEEP 20: 4.8 [2.4–6.3] l min⁻¹ m⁻²; ideal PEEP: 4.9 [2.4–6.3] l min⁻¹ m⁻²; P = 0.09).

Conclusion:

PEEP of 10–20 cmH₂O does not affect splanchnic perfusion and is hemodynamically well tolerated in most patients with ARDS, including those receiving inotropic supports.

Alveolar recruitment maneuvers in acute lung injury/acute respiratory distress syndrome

Mechanical ventilation can worsen lung damage in acute lung injury and acute respiratory distress syndrome. The use of low tidal volumes is one of the strategies that has been shown to reduce lung injury and improve outcomes in this situation. However, low tidal volumes may lead to alveolar derecruitment and worsening of hypoxia. Recruitment maneuvers along with positive end-expiratory pressure may help to prevent derecruitment. Although recruitment maneuvers have been shown to improve oxygenation, improved clinical outcomes have not been demonstrated. The optimal recruitment strategy and the type of patients who might benefit are also unclear. This review summarizes the impact of recruitment maneuvers on lung mechanics and physiology, techniques of application, and the clinical situations in which they may be useful.

Severe hypoxemic respiratory failure: part 1--ventilatory strategies

Approximately 16% of deaths in patients with ARDS results from refractory hypoxemia, which is the inability to achieve adequate arterial oxygenation despite high levels of inspired oxygen or the development of barotrauma. A number of ventilator-focused rescue therapies that can be used when conventional mechanical ventilation does not achieve a specific target level of oxygenation are discussed. A literature search was conducted and narrative review written to summarize the use of high levels of positive end-expiratory pressure, recruitment maneuvers, airway pressure-release ventilation, and high-frequency ventilation. Each therapy reviewed has been reported to improve oxygenation in patients with ARDS. However, none of them have been shown to improve survival when studied in heterogeneous populations of patients with ARDS. Moreover, none of the therapies has been reported to be superior to another for the goal of improving oxygenation. The goal of improving oxygenation must always be balanced against the risk of further lung injury. The optimal time to initiate rescue therapies, if needed, is within 96 h of the onset of ARDS, a time when alveolar recruitment potential is the greatest. A variety of ventilatory approaches are available to improve oxygenation in the setting of refractory hypoxemia and ARDS. Which, if any, of these approaches should be used is often determined by the availability of equipment and clinician bias.

Acute hemodynamic effects of recruitment maneuvers in patients with acute respiratory distress syndrome

BACKGROUND

The recruitment maneuver (RM) in acute respiratory distress syndrome (ARDS) can cause hemodynamic derangement. We evaluated circulatory and cardiac changes during RMs.

METHODS

We performed sustained inflation (SI) with a pressure of 40 cm H(2)O for 30 seconds as an RM on 22 patients with ARDS. Blood pressure (BP) and heart rate were recorded immediately before, every 10 seconds during, and 30 seconds after the RM. Ventricular dimensions were obtained simultaneously using M-mode echocardiography, and tissue Doppler imaging was performed on the left ventricular wall.

RESULTS

Mean, systolic, and diastolic BP decreased at 20 and 30 seconds during 30-second RMs (mean BP: 92 +/- 12 at baseline to 83 +/- 18 mm Hg at the end of the RM, P < .05) and subsequently recovered. Heart rate decreased at 10 and 20 seconds during the RM, and tended to increase afterward. Both ventricular dimensions decreased significantly during the RM. The left ventricular ejection fraction and peak velocity of the left ventricle during systole remained stable. The fractional changes in mean BP and left ventricular end-diastolic dimension during the RMs were correlated significantly with each other (r(s) = 0.59). Static compliance of the respiratory system (Crs) was lower in patients with mean BP change > or =15% than in patients in whom the change was <15% (P < .05).

CONCLUSIONS

A transient decrease in mean BP was observed during the RM, and its degree was correlated with the preload decrease, while cardiac contractility was maintained.

Prolonged recruitment manoeuvre improves lung function with less ultrastructural damage in experimental mild acute lung injury

The effects of prolonged recruitment manoeuvre (PRM) were compared with sustained inflation (SI) in paraquat-induced mild acute lung injury (ALI) in rats. Twenty-four hours after ALI induction, rats were anesthetized and mechanically ventilated with VT=6 ml/kg and positive end-expiratory pressure (PEEP)=5 cmH(2)O for 1h. SI was performed with an instantaneous pressure increase of 40 cmH(2)O that was sustained for 40s, while PRM was done by a step-wise increase in positive inspiratory pressure (PIP) of 15-20-25 cmH(2)O above a PEEP of 15 cm H(2)O (maximal PIP=40 cmH(2)O), with interposed periods of PIP=10 cmH(2)O above a PEEP=15 cmH(2)O. Lung static elastance and the amount of alveolar collapse were more reduced with PRM than SI, yielding improved oxygenation. Additionally, tumour necrosis factor-alpha, interleukin-6, interferon-gamma, and type III procollagen mRNA expressions in lung tissue and lung epithelial cell apoptosis decreased more in PRM. In conclusion, PRM improved lung function, with less damage to alveolar epithelium, resulting in reduced pulmonary injury.

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

The optimal level of positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome patients is still controversial and has gained renewed interest in the era of 'lung protective ventilation strategies'. Despite experimental evidence that higher levels of PEEP protect against ventilator-induced lung injury, recent clinical trials have failed to demonstrate clear survival benefits. The open-lung protective ventilation strategy combines lung recruitment maneuvers with a decremental PEEP trial aimed at finding the minimum level of PEEP that prevents the lung from collapsing. This approach to PEEP titration is more likely to exert its protective effects and is clearly different from the one used in previous clinical trials.

Efficacy of positive end-expiratory pressure titration after the alveolar recruitment manoeuvre in patients with acute respiratory distress syndrome

Introduction

In acute respiratory distress syndrome (ARDS), adequate positive end-expiratory pressure (PEEP) may decrease ventilator-induced lung injury by minimising overinflation and cyclic recruitment-derecruitment of the lung. We evaluated whether setting the PEEP using decremental PEEP titration after an alveolar recruitment manoeuvre (ARM) affects the clinical outcome in patients with ARDS.

Methods

Fifty-seven patients with early ARDS were randomly assigned to a group given decremental PEEP titration following ARM or a table-based PEEP (control) group. PEEP and inspired fraction of oxygen (FiO₂) in the control group were set according to the table-based combinations of FiO₂ and PEEP of the ARDS network, by which we aimed to achieve a PEEP level compatible with an oxygenation target. In the decremental PEEP titration group, the oxygen saturation and static compliance were monitored as the patients performed the ARM along with the extended sigh method, which is designed to gradually apply and withdraw a high distending pressure over a prolonged period, and the decremental titration of PEEP.

Results

The baseline characteristics did not differ significantly between the control and decremental PEEP titration groups. Initial oxygenation improved more in the decremental PEEP titration group than in the control group. However, dynamic compliance, tidal volume and PEEP were similar in the two groups during the first week. The duration of use of paralysing or sedative agents, mechanical ventilation, stay in the intensive care unit and mortality at 28 days did not differ significantly between the decremental PEEP titration and control groups.

Conclusions

The daily decremental PEEP titration after ARM showed only initial oxygenation improvement compared with the table-based PEEP method. Respiratory mechanics and patient outcomes did not differ between the decremental PEEP titration and control groups.

Trial registration

ClinicalTrials.gov identifier: ISRCTN79027921.

Recruitment maneuvers for acute lung injury: a systematic review

RATIONALE

There are conflicting data regarding the safety and efficacy of recruitment maneuvers (RMs) in patients with acute lung injury (ALI).

OBJECTIVES

To summarize the physiologic effects and adverse events in adult patients with ALI receiving RMs.

METHODS

Systematic review of case series, observational studies, and randomized clinical trials with pooling of study-level data.

MEASUREMENTS AND MAIN RESULTS

Forty studies (1,185 patients) met inclusion criteria. Oxygenation (31 studies; 636 patients) was significantly increased after an RM (PaO2): 106 versus 193 mm Hg, P = 0.001; and PaO2/FiO2 ratio: 139 versus 251 mm Hg, P < 0.001). There were no persistent, clinically significant changes in hemodynamic parameters after an RM. Ventilatory parameters (32 studies; 548 patients) were not significantly altered by an RM, except for higher PEEP post-RM (11 versus 16 cm H2O; P = 0.02). Hypotension (12%) and desaturation (9%) were the most common adverse events (31 studies; 985 patients). Serious adverse events (e.g., barotrauma [1%] and arrhythmias [1%]) were infrequent. Only 10 (1%) patients had their RMs terminated prematurely due to adverse events.

CONCLUSIONS

Adult patients with ALI receiving RMs experienced a significant increase in oxygenation, with few serious adverse events. Transient hypotension and desaturation during RMs is common but is self-limited without serious short-term sequelae. Given the uncertain benefit of transient oxygenation improvements in patients with ALI and the lack of information on their influence on clinical outcomes, the routine use of RMs cannot be recommended or discouraged at this time. RMs should be considered for use on an individualized basis in patients with ALI who have life-threatening hypoxemia.

A comprehensive review of pediatric endotracheal suctioning: Effects, indications, and clinical practice

OBJECTIVE

To provide a comprehensive, evidence-based review of pediatric endotracheal suctioning: effects, indications, and clinical practice.

METHODS

PubMed, Cumulative Index of Nursing and Allied Health Literature, and PEDro (Physiotherapy Evidence Database) electronic databases were searched for English language articles, published between 1962 and June 2007. Owing to the paucity of objective pediatric data, all reports dealing with this topic were examined, including adult and neonatal studies.

RESULTS

One hundred eighteen references were included in the final review. Despite the widespread use of endotracheal suctioning, very little high-level evidence dealing with pediatric endotracheal suctioning exists. Studies of mechanically ventilated neonatal, pediatric, and adult patients have shown that suctioning causes a range of potentially serious complications. Current practice guidelines are not based on evidence from controlled clinical trials. There is no clear evidence that endotracheal suctioning improves respiratory mechanics, with most studies pointing to the detrimental effect it has on lung mechanics. Suctioning should be performed when obstructive secretions are present rather than routinely. There is no clear evidence for the superiority of closed- or open-system suctioning, nor is there clear evidence for appropriate vacuum pressures and suction catheter size. Sterility does not seem to be necessary when suctioning. Preoxygenation has short-term benefits, but the longer-term impact is unknown. Routine saline instillation before suctioning should not be performed. Recruitment maneuvers performed after suctioning have not been shown to be useful as standard practice.

CONCLUSIONS

Endotracheal suctioning is a procedure used regularly in the pediatric intensive care unit. Despite this, good evidence supporting its practice is limited. Further, controlled clinical studies are needed to develop evidence-based protocols for endotracheal suctioning of infants and children, and to examine the impact of different suctioning techniques on the duration of ventilatory support, incidence of nosocomial infection, and length of pediatric intensive care unit and hospital stay.

How best to recruit the injured lung?

Sustained re-opening of collapsed lung tissue (recruitment) requires the application of airway pressures that exceed those of the tidal cycle. The post-maneuver PEEP as well as the duration of high pressure application are also key factors in its success, with their accompanying potential for hemodynamic compromise. Although a wide variety of recruiting maneuvers have been described, the technique that strikes the best balance between efficacy and risk may well vary among patients with differing right heart loading status and lung properties.

Respiratory effects of different recruitment maneuvers in acute respiratory distress syndrome

Introduction

Alveolar derecruitment may occur during low tidal volume ventilation and may be prevented by recruitment maneuvers (RMs). The aim of this study was to compare two RMs in acute respiratory distress syndrome (ARDS) patients.

Methods

Nineteen patients with ARDS and protective ventilation were included in a randomized crossover study. Both RMs were applied in each patient, beginning with either continuous positive airway pressure (CPAP) with 40 cm H₂O for 40 seconds or extended sigh (eSigh) consisting of a positive end-expiratory pressure maintained at 10 cm H₂O above the lower inflection point of the pressure-volume curve for 15 minutes. Recruited volume, arterial partial pressure of oxygen/fraction of inspired oxygen (PaO₂/FiO₂), and hemodynamic parameters were recorded before (baseline) and 5 and 60 minutes after RM. All patients had a lung computed tomography (CT) scan before study inclusion.

Results

Before RM, PaO₂/FiO₂ was 151 ± 61 mm Hg. Both RMs increased oxygenation, but the increase in PaO₂/FiO₂ was significantly higher with eSigh than CPAP at 5 minutes (73% ± 25% versus 44% ± 28%; P < 0.001) and 60 minutes (68% ± 23% versus 35% ± 22%; P < 0.001). Only eSigh significantly increased recruited volume at 5 and 60 minutes (21% ± 22% and 21% ± 25%; P = 0.0003 and P = 0.001, respectively). The only difference between responders and non-responders was CT lung morphology. Eleven patients were considered as recruiters with eSigh (10 with diffuse loss of aeration) and 6 with CPAP (5 with diffuse loss of aeration). During CPAP, 2 patients needed interruption of RM due to a drop in systolic arterial pressure.

Conclusion

Both RMs effectively increase oxygenation, but CPAP failed to increase recruited volume. When the lung is recruited with an eSigh adapted for each patient, alveolar recruitment and oxygenation are superior to those observed with CPAP.

A recruitment manoeuvre performed after endotracheal suction does not increase dynamic compliance in ventilated paediatric patients: a randomised controlled trial

QUESTION

Does a recruitment manoeuvre after suctioning have any immediate or short-term effect on ventilation and gas exchange in mechanically-ventilated paediatric patients?

DESIGN

Randomised controlled trial with concealed allocation, assessor blinding, and intention-to-treat analysis.

PARTICIPANTS

Forty-eight paediatric patients with heterogeneous lung pathology. Fourteen patients were subsequently excluded from analysis due to large leaks around the endotracheal tube.

INTERVENTION

The experimental group received a single standardised suctioning procedure followed five minutes later by a standardised recruitment manoeuvre. The control group received only the single suctioning procedure.

OUTCOME MEASURES

Measurements of ventilation (dynamic lung compliance, expiratory airway resistance, mechanical and spontaneous expired tidal volume, respiratory rate) and gas exchange (transcutaneous oxygen saturation) were recorded, on three occasions before and on two occasions after the recruitment manoeuvre, using a respiratory profile monitor.

RESULTS

There was no difference between the experimental and the control group in dynamic compliance, expired airway resistance, or oxygen saturation either immediately after the recruitment manoeuvre, or after 25 minutes. The experimental group decreased mechanical expired tidal volume by 0.3 ml/kg (95% CI 0.1 to 0.6), increased spontaneous expired tidal volume by 0.3 ml/kg (95% CI 0.0 to 0.6), and increased total respiratory rate by 3 bpm (95% CI 1 to 4) immediately after the recruitment manoeuvre compared with the control group, but these differences disappeared after 25 minutes.

CONCLUSION

There is insufficient evidence to support performing recruitment manoeuvres after suctioning infants and children.

The safety and efficacy of sustained inflations as a lung recruitment maneuver in pediatric intensive care unit patients

OBJECTIVE

To assess the safety and efficacy of sustained inflations (SI) as lung recruitment maneuvers (RMs) in ventilated pediatric intensive care unit (PICU) patients.

DESIGN

Observational, prospective data collection.

SETTING

Tertiary-care PICU.

PATIENTS AND PARTICIPANTS

Thirty-two consecutive ventilated pediatric patients.

INTERVENTIONS

An SI (30-40 cmH(2)O for 15-20 s) was performed following a ventilator disconnection, suctioning, hypoxemia, or routinely every 12 h. Physiologic variables were recorded for 6 h after each SI. All other management was at the attending physician's discretion. The change in variables from pre-SI to post-SI (at 2, 10, and 15 min, 1, 2, 3, 4, 5, and 6 h) was compared using mixed models to account for repeated measures in the same patient.

MEASUREMENTS AND RESULTS

93 RMs were performed on 32 patients (ages 11 days to 14 years). RMs were done after suctioning (58/93, 62%), ventilator disconnect (5/93, 5%), desaturation (8/93, 9%), or routinely (22/93, 24%). Seven of 93 RMs (7.5%) were interrupted for patient agitation, and 2/93 (2.2%) for transient bradycardia. There was no evidence of statistically significant changes in systolic blood pressure, heart rate, or oxygen saturation as measured by pulse oximetry from pre-RM to post-RM, and there were no air leaks. In three patients with altered intracranial compliance, three of eight RM were associated with a spike of intracranial pressure. There was a sustained significant decrease in FiO(2) by 6.1% lasting up to 6 h post-RM.

CONCLUSIONS

RMs (as SI) are safe in ventilated PICU patients and are associated with a significant reduction in oxygen requirements for the 6 h after the RM.

Lung protective ventilatory strategies in acute lung injury and acute respiratory distress syndrome: from experimental findings to clinical application

This review addresses the physiological background and the current status of evidence regarding ventilator-induced lung injury and lung protective strategies. Lung protective ventilatory strategies have been shown to reduce mortality from adult respiratory distress syndrome (ARDS). We review the latest knowledge on the progression of lung injury by mechanical ventilation and correlate the findings of experimental work with results from clinical studies. We describe the experimental and clinical evidence of the effect of lung protective ventilatory strategies and open lung strategies on the progression of lung injury and current controversies surrounding these subjects. We describe a rational strategy, the open lung strategy, to accomplish an open lung, which may further prevent injury caused by mechanical ventilation. Finally, the clinician is offered directions on lung protective ventilation in the early phase of ARDS which can be applied on the intensive care unit.

The Pulmonary and Hemodynamic Effects of Two Different Recruitment Maneuvers After Cardiac Surgery

BACKGROUND

The aim of our study was to evaluate the pulmonary and hemodynamic effects of two different recruitment maneuvers after open heart surgery.

METHODS

Sixty patients undergoing coronary artery bypass surgery were randomized into three groups after operation: recruitment maneuver with continuous positive airway pressure (CPAP) (CPAP-40 group, n = 20), recruitment by positive end-expiratory pressure (PEEP) (PEEP-20 group, n = 20), and 5 cm H2O PEEP (PEEP-5 group, n = 20). In the CPAP-40 group, 40 cm H2O peak inspiratory pressure was applied for 30 s, then PEEP was reduced to 20 cm H2O and ventilation was continued with baseline variables with PEEP decreased until the best Pao2 was achieved. In the PEEP-20 group, 20 cm H2O PEEP was set for 2 min, tidal volume was adjusted to achieve a peak inspiratory airway pressure of 40 cm H2O during the maneuver, then PEEP was decreased until the best Pao2 had been achieved. In the PEEP-5 group, 5 cm H2O PEEP was applied postoperatively.

RESULTS

The mean arterial blood pressure of the CPAP-40 group was lower than that of the PEEP-20 (P < 0.01) and PEEP-5 groups (P < 0.01) during the interventions. Oxygenation was higher in both recruitment groups than in the PEEP-5 group during the mechanical ventilation period. There was no significant difference among the groups beyond that period. The atelectasis score of the PEEP-5 group (1.3 +/- 0.9) on postoperative day 1 was higher than that of the CPAP-40 (0.65 +/- 0.6; P = 0.01) and PEEP-20 (0.65 +/- 0.5; P = 0.01) groups.

CONCLUSIONS

The recruitment techniques with postmaneuver PEEP increased oxygenation and decreased atelectasis equally, whereas PEEP-20 provided more stable hemodynamic conditions than the CPAP maneuver.

Effects of a Sigh on the Respiratory Mechanical Properties in Ali Patients

OBJECTIVES

The application of sighs during baseline ventilation was found to improve alveolar recruitment and oxygenation in patients with acute respiratory distress syndrome (ARDS). The present investigation evaluates if respiratory mechanics can be modified by a sigh.

METHODS

Ten consecutive patients with acute lung injury (ALI) admitted to the University Hospital Intensive Care Unit the were studied during mechanical ventilation. Three sighs were administered to sedated-paralyzed patients during the measurement period. Respiratory mechanics were studied in regular breaths immediately before and after a sigh provided that a steady-state had been reached and by the airway pressure-time curve profile to evaluate the lung recruitment. Viscoelastic constants (elastic, resistive, and time), as well as elastance and resistances, were determined by the single breath method. Arterial blood gases were also determined pre- and post-sigh.

RESULTS

Elastic and resistive components of viscoelasticity decreased after a sigh (20 and 21%, respectively). As a result, the pressure required to overcome viscoelasticity and mechanical inhomogeneities also decreased in these patients (17%). The mechanical changes were associated with alterations in PaO(2).

CONCLUSIONS

The sigh is useful to diminish viscoelastic impedance in ALI patients, thus allowing a smaller inflation pressure. Under the present experimental conditions it seems that viscoelastic mechanical alterations precede their elastic and resistive counterparts.

Cholinergic receptor and cyclic stretch-mediated inflammatory gene expression in intact ASM

We tested the hypothesis that cholinergic stimulation and cyclic stretch regulate inflammatory gene expression in intact airway smooth muscle by measuring mRNA expression in bovine tracheal smooth muscle using limited microarray analysis and RT-PCR. Carbachol (1 microM) induced significant increases in the expression of cyclooxygenase (COX)-1, COX-2, IL-8, and plasminogen activator, urokinase type (PLAU) to levels ranging from 1.3- to 3.1-fold of control. Sinusoidal length oscillation at an amplitude of 10% muscle length and a frequency of 1 Hz induced significant increases in the expression of CCL-2, COX-2, IL-1 beta, and IL-6 to levels ranging from 12- to 206-fold of control. Decreasing the oscillatory amplitude by 50% did not significantly change inflammatory gene expression. In contrast, decreasing the oscillatory frequency by 50% significantly attenuated inflammatory gene expression by 76-93%. Nifedipine (1 microM) had an insignificant effect on carbachol-induced gene expression, but significantly inhibited sinusoidal length oscillation-induced inflammatory gene expression by 40-78%. Correlation analysis revealed two groups of genes with differential responses to sinusoidal length oscillation. The highly responsive group included COX-2, IL-6, and IL-8, which exhibited 45- to 364-fold increases in gene expression in response to sinusoidal length oscillation. The moderately responsive group included CCL2 and PLAU, which exhibited 13- to 19-fold increases in gene expression in response to sinusoidal oscillation. These findings suggest that cyclic stretch regulates inflammatory gene expression in intact airway smooth muscle in an amplitude- and frequency-dependent manner by modulating the activity of L-type voltage-gated calcium channels.

Lung recruitment during mechanical positive pressure ventilation in the PICU: what can be learned from the literature?

A literature review was conducted to assess the evidence for recruitment manoeuvres used in conventional mechanical positive pressure ventilation. A total of 61 studies on recruitment manoeuvres were identified: 13 experimental, 31 ICU, 6 PICU and 12 anaesthesia studies. Recruitment appears to be a continuous process during inspiration and expiration and is determined by peak inspiratory pressure (PIP) and positive end expiratory pressure (PEEP). Single or repeated recruitment manoeuvres may result in a statistically significant increase in oxygenation; however, this is short lasting and clinically irrelevant, especially in late ARDS and pneumonia. Temporary PIP elevation may be effective but only after PEEP loss (for example disconnection and tracheal suctioning). Continuous PEEP elevation and prone positioning can increase P(a)O2 significantly. Adverse haemodynamic or barotrauma effects are reported in various studies. No data exist on the effect of recruitment manoeuvres on mortality, morbidity, length of stay or duration of mechanical ventilation. Although recruitment manoeuvres can improve oxygenation, they can potentially increase lung injury, which eventually determines outcome. Based on the presently available literature, prone position and sufficient PEEP as part of a lung protective ventilation strategy seem to be the safest and most effective recruitment manoeuvres. As paediatric physiology is essentially different from adult, paediatric studies are needed to determine the role of recruitment manoeuvres in the PICU.

Recruitment maneuvers during prone positioning in patients with acute respiratory distress syndrome

OBJECTIVE

To evaluate the interaction of recruitment maneuvers and prone positioning on gas exchange and venous admixture in patients with early extrapulmonary acute respiratory distress syndrome ventilated with high levels of positive end-expiratory pressure. We hypothesized that a sustained inflation performed after 6 hrs of prone positioning would induce sustained improvement in oxygenation (Pao2/Fio2) and venous admixture.

DESIGN

Prospective, interventional study.

SETTING

Tertiary care, postoperative intensive care unit.

PATIENTS

Fifteen patients with early extrapulmonary acute respiratory distress syndrome.

INTERVENTIONS

After 6 hrs of prone positioning, a sustained inflation was performed with 50 cm H2O maintained for 30 secs. Data were recorded in supine position, after 6 hrs of prone positioning, at 3, 30, and 180 mins following the sustained inflation.

MEASUREMENTS AND MAIN RESULTS

A response to prone positioning was observed in nine of 15 patients leading to an improvement of Pao2/Fio2 (147 +/- 37 torr vs. 225 +/- 77 torr, p = .005) and venous admixture (35.4 +/- 8.3% vs. 28.9 +/- 9.8%, p = .001). Six patients did not respond to prone positioning. Following the sustained inflation, the responders to prone positioning showed a further increase of Pao2/Fio2 and decrease of venous admixture at 3 mins (Pao2/Fio2, 225 +/- 77 torr vs. 368 +/- 90 torr, p = .018; venous admixture, 28.9 +/- 9.8% vs. 18.9 +/- 6.7%, p = .05). In all six nonresponders to prone positioning, an improvement of Pao2/Fio2 and venous admixture occurred at 3 mins following the sustained inflation (128 +/- 18 torr vs. 277 +/- 59 torr, p = .03; venous admixture, 34.2 +/- 6.0% vs. 23.8 +/- 6.3%, p = .05). The beneficial effects of the sustained inflation remained significantly elevated over 3 hrs in responders and nonresponders to prone positioning.

CONCLUSION

In patients with early extrapulmonary acute respiratory distress syndrome, a sustained inflation performed after 6 hrs of prone positioning induced further and sustained improvement of oxygenation and venous admixture in both responders and nonresponders to prone positioning.

Intercomparison of recruitment maneuver efficacy in three models of acute lung injury*

OBJECTIVE

To compare the relative efficacy of three forms of recruitment maneuvers in diverse models of acute lung injury characterized by differing pathoanatomy.

DESIGN

We compared three recruiting maneuver (RM) techniques at three levels of post-RM positive end-expiratory pressure in three distinct porcine models of acute lung injury: oleic acid injury; injury induced purely by the mechanical stress of high-tidal airway pressures; and pneumococcal pneumonia.

SETTING

Laboratory in a clinical research facility.

SUBJECTS

Twenty-eight anesthetized mixed-breed pigs (23.8 +/- 2.6 kg).

INTERVENTIONS

The RM techniques tested were sustained inflation, extended sigh or incremental positive end-expiratory pressure, and pressure-controlled ventilation.

PRIMARY MEASUREMENTS

Oxygenation and end-expiratory lung volume.

MAIN RESULTS

The post-RM positive end-expiratory pressure level was the major determinant of post-maneuver PaO2, independent of the RM technique. The pressure-controlled ventilation RM caused a lasting increase of PaO2 in the ventilator-induced lung injury model, but in oleic acid injury and pneumococcal pneumonia, there were no sustained oxygenation differences for any RM technique (sustained inflation, incremental positive end-expiratory pressure, or pressure-controlled ventilation) that differed from raising positive end-expiratory pressure without RM.

CONCLUSIONS

Recruitment by pressure-controlled ventilation is equivalent or superior to sustained inflation, with the same peak pressure in all tested models of acute lung injury, despite its lower mean airway pressure and reduced risk for hemodynamic compromise. Although RM may improve PaO2 in certain injury settings when traditional tidal volumes are used, sustained improvement depends on the post-RM positive end-expiratory pressure value.

Transient hemodynamic effects of recruitment maneuvers in three experimental models of acute lung injury*

OBJECTIVE

Elevated lung volumes and increased pleural pressures associated with recruitment maneuvers (RM) may adversely affect pulmonary vascular resistance and cardiac filling or performance. We investigated the hemodynamic consequences of three RM techniques after inducing acute lung injury.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Hospital research laboratory.

SUBJECTS

Thirteen anesthetized, mechanically ventilated pigs.

INTERVENTIONS

We induced three types of acute lung injury: oleic acid injury (n = 4); ventilator-induced lung injury (n = 4); and pneumonia (n = 5). All three models were designed to initiate a similar severity of oxygenation impairment. RM methods tested were sustained inflation, incremental positive end-expiratory pressure (PEEP) with a limited peak pressure, and pressure-controlled ventilation with increased PEEP and a fixed driving pressure. From a baseline PEEP of 8 cm H2O, all interventions were tested using post-RM PEEP levels of 8, 12, and 16 cm H2O. Cardiac output by thermodilution and systemic and pulmonary artery pressures were measured frequently during the RM and for 15 mins after its completion.

MEASUREMENTS AND MAIN RESULTS

During the RM, cardiac output decreased to a greater extent in the pneumonia model (0.49 of baseline cardiac output) than in the oleic acid injury (0.67 of baseline) or ventilator-induced lung injury (0.79 of baseline) models. Cardiac output recovered to the baseline value by 5 mins post-RM in oleic acid injury and ventilator-induced lung injury models. However, cardiac output remained decreased 15 mins post-RM in the pneumonia model. There were no differences in hemodynamic parameters among RM methods in oleic acid injury and ventilator-induced lung injury models. In the pneumonia model, however, cardiac output decreased to a greater extent during the RM with sustained inflation (to 0.33 of baseline cardiac output) compared with pressure-controlled ventilation (to 0.68 of baseline).

CONCLUSIONS

We conclude that RM transiently but profoundly depressed cardiac output in three models of acute lung injury. The results imply that a lung recruiting maneuver should be used with caution, especially when using sustained inflation in the setting of pneumonia.

Bench-to-bedside review: Recruitment and recruiting maneuvers

In patients with acute respiratory distress syndrome (ARDS), the lung comprises areas of aeration and areas of alveolar collapse, the latter producing intrapulmonary shunt and hypoxemia. The currently suggested strategy of ventilation with low lung volumes can aggravate lung collapse and potentially produce lung injury through shear stress at the interface between aerated and collapsed lung, and as a result of repetitive opening and closing of alveoli. An 'open lung strategy' focused on alveolar patency has therefore been recommended. While positive end-expiratory pressure prevents alveolar collapse, recruitment maneuvers can be used to achieve alveolar recruitment. Various recruitment maneuvers exist, including sustained inflation to high pressures, intermittent sighs, and stepwise increases in positive end-expiratory pressure or peak inspiratory pressure. In animal studies, recruitment maneuvers clearly reverse the derecruitment associated with low tidal volume ventilation, improve gas exchange, and reduce lung injury. Data regarding the use of recruitment maneuvers in patients with ARDS show mixed results, with increased efficacy in those with short duration of ARDS, good compliance of the chest wall, and in extrapulmonary ARDS. In this review we discuss the pathophysiologic basis for the use of recruitment maneuvers and recent evidence, as well as the practical application of the technique.

Evaluation of a recruitment maneuver with positive inspiratory pressure and high PEEP in patients with severe ARDS

BACKGROUND

To evaluate the effect of a recruitment maneuver (RM) with constant positive inspiratory pressure and high positive end-expiratory pressure (PEEP) on oxygenation and static compliance (Cs) in patients with severe acute respiratory distress syndrome (ARDS).

METHODS

Eight patients with ARDS ventilated with lung-protective strategy and an arterial partial pressure of oxygen to inspired oxygen fraction ratio (PaO2/FIO2) < or =100 mmHg regardless of PEEP were prospectively studied. The RM was performed in pressure-controlled ventilation at FIO2 of 1.0 until PaO2 reached 250 mmHg or a maximal plateau pressure/PEEP of 60/45 cmH2O was achieved. The RM was performed with stepwise increases of 5 cmH2O of PEEP every 2 min and thereafter with stepwise decreases of 2 cmH2O of PEEP every 2 min until a drop in PaO2 >10% below the recruitment PEEP level. Data was collected before (preRM), during and after 30 min (posRM).

RESULTS

The PaO2/FIO2 increased from 83 +/- 22 mmHg preRM to 118 +/- 32 mmHg posRM (P = 0.001). The Cs increased from 28 +/- 10 ml cmH2O(-1) preRM to 35 +/- 12 ml cmH2O(-1) posRM (P = 0.025). The PEEP was 12 +/- 3 cmH2O preRM and was set at 15 +/- 4 cmH2O posRM (P = 0.025). The PEEP of recruitment was 36 +/- 9 cmH2O and the collapsing PEEP was 13 +/- 4 cmH2O. The PaO2 of recruitment was 225 +/- 105 mmHg, with five patients reaching a PaO2 > or = 250 mmHg. The FIO2 decreased from 0.76 +/- 0.16 preRM to 0.63 +/- 0.15 posRM (P = 0.001). No major complications were detected.

CONCLUSION

Recruitment maneuver was safe and useful to improve oxygenation and Cs in patients with severe ARDS ventilated with lung-protective strategy.

Effects of recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome ventilated with high positive end-expiratory pressure

OBJECTIVE

Positive end-expiratory pressure (PEEP) and recruitment maneuvers (RMs) may partially reverse atelectasis and reduce ventilation-associated lung injury. The purposes of this study were to assess a) magnitude and duration of RM effects on arterial oxygenation and on requirements for oxygenation support (Fio2/PEEP) in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS) receiving ventilation with low tidal volumes and high levels of PEEP; and b) frequency of adverse respiratory and circulatory events attributable to RMs.

DESIGN

Prospective, randomized, crossover study.

SETTING

Thirty-four intensive care units at 19 hospitals.

PATIENTS

Seventy-two patients with early ALI/ARDS. Baseline PEEP and Fio2 were 13.8 +/- 3.0 cm H2O and 0.39 +/- 0.10, respectively (mean +/- sd).

INTERVENTIONS

We conducted RMs by applying continuous positive airway pressure of 35-40 cm H2O for 30 secs. We conducted sham RMs on alternate days. We monitored oxyhemoglobin saturation by pulse oximetry (SpO2), Fio2/PEEP, blood pressure, and heart rate for 8 hrs after RMs and sham RMs. We examined chest radiographs for barotrauma.

MEASUREMENTS AND MAIN RESULTS

Responses to RMs were variable. Greatest increments from baseline SpO2 within 10 mins after RMs were larger than after sham RMs (1.7 +/- 0.2 vs. 0.6 +/- 0.3 %, mean +/- SEM, p < .01). Systolic blood pressure decreased more +/- 1.1 mm Hg, p < .01). Changes in Fio2/PEEP requirements were not significantly different at any time after RMs vs. sham RMs. Barotrauma was apparent on first radiographs after one RM and one sham RM.

CONCLUSIONS

In ALI/ARDS patients receiving mechanical ventilation with low tidal volumes and high PEEP, short-term effects of RMs as conducted in this study are variable. Beneficial effects on gas exchange in responders appear to be of brief duration. More information is needed to determine the role of recruitment maneuvers in the management of ALI/ARDS.