Higher Mean Airway Pressure Research Articles

Does the use of high PEEP levels prevent ventilator-induced lung injury?

Overdistention and intratidal alveolar recruitment have been advocated as the main physical mechanisms responsible for ventilator-induced lung injury. Limiting tidal volume has a demonstrated survival benefit in patients with acute respiratory distress syndrome and is recognized as the cornerstone of protective ventilation. In contrast, the use of high positive end-expiratory pressure levels in clinical trials has yielded conflicting results and remains controversial. In the present review, we will discuss the benefits and limitations of the open lung approach and will discuss some recent experimental and clinical trials on the use of high versus low/moderate positive end-expiratory pressure levels. We will also distinguish dynamic (tidal volume) from static strain (positive end-expiratory pressure and mean airway pressure) and will discuss their roles in inducing ventilator-induced lung injury. High positive end-expiratory pressure strategies clearly decrease refractory hypoxemia in patients with acute respiratory distress syndrome, but they also increase static strain, which in turn may harm patients, especially those with lower levels of lung recruitability. In patients with severe respiratory failure, titrating positive end-expiratory pressure against the severity of hypoxemia, or providing it in a decremental fashion after a recruitment maneuver, is recommended. If high plateau, driving or mean airway pressures are observed, prone positioning or ultraprotective ventilation may be indicated to improve oxygenation without additional stress and strain in the lung.

Neonatal critical illness and development: white matter and hippocampus alterations in school-age neonatal extracorporeal membrane oxygenation survivors.

To examine the neurobiology of long-term neuropsychological deficits after neonatal extracorporeal membrane oxygenation (ECMO). This cross-sectional study assessed white matter integrity and hippocampal volume of ECMO survivors (8-15y) and healthy children (8-17y) using diffusion tensor imaging (DTI) and structural magnetic resonance imaging (MRI) respectively. Neuropsychological outcome was evaluated in ECMO survivors. Included clinical predictors of white matter integrity: age start ECMO, ECMO duration, highest oxygenation index before ECMO, highest mean airway pressure, and mechanical ventilation duration. ECMO survivors (n=23) had lower global fractional anisotropy than healthy children (n=54) (patients=0.368; comparison group=0.381; p=0.018), but similar global mean diffusivity (p=0.410). ECMO survivors had lower fractional anisotropy in the left cingulum bundle (ECMO survivors=0.345; comparison group=0.399; p<0.001) and higher mean diffusivity in a region of the left parahippocampal cingulum (patients=0.916; comparison group=0.871; p<0.001). Higher global mean diffusivity predicted worse verbal memory in ECMO survivors (n=17) (β=-0.74, p=0.008). ECMO survivors (n=23) had smaller bilateral hippocampal volume than healthy children (n=43) (left, p<0.001; right, p<0.001) and this was related to worse verbal memory (left, β=0.65, p=0.018; right, β=0.71, p=0.006). Neonatal ECMO survivors are at risk for long-term brain alterations, which may partly explain long-term neuropsychological impairments. Neuroimaging may contribute to better risk stratification of long-term impairments.

High-frequency oscillatory ventilation for adult patients with acute respiratory distress syndrome

Background As a new kind of ventilatory mode, high-frequency oscillatory ventilation(HFOV) is characterized by the rapid delivery of small tidal volumes cycling and high mean airway pressure. It has been successfully used in adults with the acute respiratory distress syndrome(ARDS). It has been shown that HFOV has advantages over conventional mechanical ventilation(CMV) in improving oxygenation and reducing the incidence of ventilator associated lung injury(VILI). However, the effect of HFOV on mortality still needs to be characterized. Objective To summarize the trials evaluating HFOV in adults with ARDS and reveal both the strengths and weaknesses of HFOV. Content HFOV is associated with significant improvement in oxygenation and prevention of VILI, however, not associated with reduction of mortality. Further researches are needed to identify optimal patient selection, timing, ventilator settings, and the role of combining HFOV with other interventions. Trend Further researches and explorations are needed to define the role of HFOV in adult ARDS. Key words: High-frequency oscillatory ventilation; Acute respiratory distress syndrome; Adult; Mortality

Airway Pressure Release Ventilation and High-Frequency Oscillatory Ventilation: Potential Strategies to Treat Severe Hypoxemia and Prevent Ventilator-Induced Lung Injury.

Although lifesaving, mechanical ventilation can itself be responsible for damage to lung parenchyma. This ventilator-induced lung injury is especially observed in already injured lungs of patients with ARDS. New ventilatory approaches are needed to safely treat patients with ARDS, and recent studies have suggested the potential utility of open-lung strategies. Airway pressure release ventilation (APRV) and high-frequency oscillatory ventilation (HFOV) are 2 different open-lung strategies that have been proposed to treat refractory hypoxemic respiratory failure while preventing ventilator-induced lung injury. APRV provides increased airway pressure as a potential recruitment mechanism and allows spontaneous breathing, with the potential benefits of decreased sedation, shorter duration of mechanical ventilation, and improvement in cardiac performance. HFOV delivers very small tidal volumes, to prevent volutrauma, at a constant (relatively high) mean airway pressure, thus avoiding atelectrauma. Despite their theoretical benefits, the utility of APRV and HFOV remains unproven and controversial for the routine treatment of ARDS in adult patients. This review is focused on the theoretical and practical aspects of APRV and HFOV, provides an overview of the current evidence, and addresses their possible use in the treatment of ARDS.

Abstract 19663: Failed Delayed Sternal Closure Following Neonatal Cardiac Surgery Predicted by High Mean Airway Pressure and Associated with Increased Post-operative Mortality

Background: Myocardial edema, increased lung water, and anasarca are common following neonatal cardiac surgery with cardiopulmonary bypass and amplify the risk of hemodynamic instability and inadequate ventilation following sternal closure. Delayed sternal closure (DSC) in the intensive care unit one or more days following surgery is a common strategy to mitigate this risk, but has been associated with increased risk of infection. In addition, failed DSC has previously been identified as a risk factor for mortality. This study sought to identify predictor variables and determine impact of failed DSC. Methods: Records of all neonates undergoing DSC in the cardiac intensive care unit (CICU) following surgery with cardiopulmonary bypass between January 2008 and May 2013 were reviewed. Pre-operative, intra-operative and post-operative variables were compared for those patients who failed DSC versus those who did not. Continuous variables were compared utilizing Wilcoxon’s test and categorical variables using Fisher’s exact test. Results: Of 256 neonates undergoing DSC in the CICU, 22 failed first attempt at DSC. No significant difference between the two groups was appreciated in age, weight, or bypass (cross clamp, circulatory arrest, and total) times. Comparing DSC failures to successes, significantly more failures: followed Stage I palliation (63% vs. 31%); occurred later (post-operative day 4.7 vs. 2.8, p = 0.009); and were proceeded by higher mean airway pressures (9 vs. 8 cm H2O, p = 0.04), peak inspiratory pressure (27 vs. 24, p = 0.002), and inotrope score (12.1 vs. 9.6, p = 0.06). There was no association with systolic blood pressure or lactate prior to DSC. Failed DSC was associated with increased duration of mechanical ventilation (41.6 vs 7.4 days, p &lt; 0.001), length of ICU stay (44.3 vs 12.0 days, p &lt; 0.001), and mortality (38 vs 3%, p &lt; 0.001). Conclusions: Mortality for patients who fail the first ICU attempt at delayed sternal closure is significantly higher than for those with successful sternal closure. Ventilatory pressures but not hemodynamic variables prior to DSC differed significantly between the two groups. First attempt at DSC was later in those who failed, suggesting that clinicians had a priori identified these patients as higher risk.

Elective decompression of the left ventricle in pediatric patients may reduce the duration of venoarterial extracorporeal membrane oxygenation.

We aimed to determine the effect of elective left heart decompression at the time of initiation of central venoarterial extracorporeal membrane oxygenation (VA ECMO) on VA ECMO duration and clinical outcomes in children in a single tertiary ECMO referral center with a large pediatric population from a national referral center for pediatric cardiac surgery. We studied 51 episodes of VA ECMO in a historical cohort of 49 pediatric patients treated between the years 1990 and 2013 in the Paediatric Intensive Care Unit (PICU) of the Royal Children's Hospital, Melbourne. The cases had a variety of diagnoses including congenital cardiac abnormalities, sepsis, myocarditis, and cardiomyopathy. Left heart decompression as an elective treatment or an emergency intervention for left heart distension was effectively achieved by a number of methods, including left atrial venting, blade atrial septostomy, and left ventricular cannulation. Elective left heart decompression was associated with a reduction in time on ECMO (128 h) when compared with emergency decompression (236 h) (P = 0.013). Subgroup analysis showed that ECMO duration was greatest in noncardiac patients (elective 138 h, emergency 295 h; P = 0.02) and in patients who died despite both emergency decompression and ECMO (elective 133 h, emergency 354 h; P = 0.002). As the emergency cases had a lower pH, a higher PaCO2 , and a lower oxygenation index and were treated with a higher mean airway pressure, positive end-expiratory pressure, and respiratory rate prior to receiving VA ECMO, we undertook multivariate linear regression modeling to show that only PaCO2 and the timing of left heart decompression were associated with ECMO duration. However, elective left heart decompression was not associated with a reduction in length of PICU stay, duration of mechanical ventilation, or duration of oxygen therapy. Elective left heart decompression was not associated with improved ECMO survival or survival to PICU discharge. Elective left heart decompression may reduce ECMO duration and has therefore the potential to reduce ECMO-related complications. A prospective, randomized controlled trial is indicated to study this intervention further.

Is age at initiation of extracorporeal life support associated with mortality and intraventricular hemorrhage in neonates with respiratory failure?

To describe differences in characteristics among neonates treated with extracorporeal life support (ECLS) in the first week of life for respiratory failure compared with later in the neonatal period and to assess risk factors for central nervous system (CNS) hemorrhage and mortality among the two groups. Review of the Extracorporeal Life Support Organization registry from 2001 to 2010 of neonates ⩽30 days comparing two age groups: those ⩽7 days (Group 1) to those >7 days (Group 2) at ECLS initiation. Among 4888 neonates, Group 1 (n=4453) had significantly lower mortality (17 vs 39%, P<0.001) but greater CNS hemorrhage (11 vs 7%, P=0.02) than Group 2 (n=453). Mortality and CNS hemorrhage improved significantly with increasing gestational age only for Group 1 patients. CNS hemorrhage occurred more frequently in Group 1 patients receiving venoarterial (VA) than with venovenous ECLS (15 vs 7%, P<0.001). In Group 1, lower birth weight and pre-ECLS pH and VA mode were independently associated with mortality. In Group 2, higher mean airway pressure was independently associated with mortality. Complications of ECLS therapy, including CNS hemorrhage and renal replacement therapy were independently associated with mortality for both groups. Neonates cannulated for ECLS after the first week of life had greater mortality despite lower CNS hemorrhage than neonates receiving ECLS earlier. Premature infants cannulated after 1 week had fewer CNS hemorrhages than premature infants treated with extracorporeal membrane oxygenation starting within the first week of life.

Continuous Noninvasive Monitoring of Lung Recruitment during High-Frequency Oscillatory Ventilation by Electrical Impedance Measurement: An Animal Study

Background: Ventilatory pressures should target the range between the upper and lower inflection point of the pressure volume curve in order to avoid atelecto- and volutrauma. During high-frequency oscillatory ventilation (HFOV), this range is difficult to determine. Quadrant impedance measurement (QIM) has recently been shown to allow accurate and precise measurement of lung volume changes during conventional mechanical ventilation. Objectives: To investigate if QIM can be used to determine a static pressure-residual impedance curve during a recruitment-derecruitment manoeuvre on HFOV and to monitor the time course of alveolar recruitment after changing mean airway pressure (MAP). Methods: An incremental and decremental MAP trial (6 cm H₂O to 27 cm H₂O) was conducted in five surfactant-depleted newborn piglets during HFOV. Ventilatory, gas exchange and haemodynamic parameters were recorded. Continuous measurement of thoracic impedance change was performed. Results: Mean residual impedance (RI) increased with each stepwise increase of MAP resulting in a total mean increase of +26.5% (±4.0) at the highest MAP (27 cm H₂O) compared to baseline ventilation at 6 cm H₂O. Upon decreasing MAP levels, RI fell more slowly compared to its ascent; 83.4% (±19.1) and 84.8% (±16.4) of impedance changes occurred in the first 5 min after an increase or decrease in airway pressure, respectively. Conclusions: QIM could be used for continuous monitoring of thoracic impedance and determination of the pressure-RI curve during HFOV. The method could prove to be a promising bedside method for the monitoring of lung recruitment during HFOV in the future.

Airway Pressure Release Ventilation

Airway pressure release ventilation (APRV) is a mode of ventilation that has been around since the 1980s and was originally viewed as a type of continuous positive pressure mode of ventilation. Conceptually, APRV can be thought of as a type of inverse-ratio, pressure-controlled, intermittent mandatory ventilation during which the maintenance of spontaneous breathing and prolonged application of high mean airway pressure contribute to the clinical benefits. The aim of this review article was to familiarize the bedside clinician working in the intensive care unit with the theory and rationale behind this mode of ventilation. The potential advantages and disadvantages of APRV will also be discussed to empower the advance practice clinician and bedside nurse to advocate for their patient diagnosed with the often-high mortality disease of acute respiratory distress syndrome.

Right Ventricular Function during High-Frequency Oscillatory Ventilation, Use of Noninvasive Positive Pressure Ventilation for Acute Lung Injury, and Dexmedetomidine Use for Sedation during Mechanical Ventilation

High-frequency oscillatory ventilation (HFOV) is often used in severe acute respiratory distress syndrome (ARDS), defined as a PaO2/FiO2 ratio of< 100 mmHg. It applies lower tidal volumes with high respiratory frequency and occasionally higher mean airway pressures (mPaw) to achieve oxygenation goals. Although no mortality benefit has been shown, HFOV often results in improved oxygenation (2). The authors hypothesized that higher mPaw during HFOV would negatively affect right ventricular (RV) function in patients with ARDS. Sixteen patients with ARDS with direct lung injury were subjected to a 6-hour period of conventional mechanical ventilation (CMV) with low tidal volume and then switched to HFOV. Three 1-hour periods of HFOV using incremental mPaw of 15, 110, and 115 cm H2O added to mPaw recorded during CMV were administered in randomized order. The mPaw was 18 6 3 cm H2O during CMV and increased progressively up to 336 3 cm H2O on HFOV115. The numbers of patients with RV dysfunction, defined as the ratio of RV end-diastolic area (RVEDA) to left ventricular end diastolic area (LVEDA) . 0.6, on CMV, HFOV15, HFOV110, and HFOV115 were 9 (P , 0.05 vs. HFOV110 and 115), 8, 12, and 15 of 16, respectively. Among these patients, the corresponding numbers with RV failure, defined as RVEDA/LVEDA . 0.9, a subset of dysfunction, were 4 (P , 0.05 versus HFOV115), 4, 6, and 9 of 16. The cardiac index decreased significantly at HFOV115. This is the first study to specifically evaluate RV function during HFOV in ARDS.More than half of the subjects had RV dysfunction at baseline, which significantly worsenedwith increasing mPaw during HFOV. A limitation of the study is that high mPaw onHFOV is usually required over long periods. The acute effects of increased mPaw on RV function may differ with time. The study was performed in a population of patients with ARDS that had a higher incidence of RV dysfunction than has been previously described (3). Whether mPaw-induced RV dysfunction affects patient outcomes should be explored in future studies. Clinicians should be aware that high mPaw during HFOV may precipitate RV failure.

Inspiratory Limb Carbon Dioxide Entrainment During High-Frequency Oscillatory Ventilation: Characterization in a Mechanical Test Lung and Swine Model

High-frequency oscillatory ventilation (HFOV) has been utilized as a rescue oxygenation therapy in adults with ARDS over the last decade. The HFOV oscillating piston can generate negative pressure during the exhalation cycle, which has been termed active exhalation. We hypothesized that this characteristic of HFOV entrains CO(2) into the inspiratory limb of the circuit and increases the total dead space. The purpose of this study was to determine if retrograde CO(2) entrainment occurs and how it is altered by HFOV parameter settings. An HFOV was interfaced to a cuffed endotracheal tube and connected to a mechanical test lung. Negative pressure changes within the circuit's inspiratory limb were measured while HFOV settings were manipulated. Retrograde CO(2) entrainment was evaluated by insufflating CO(2) into the test lung to achieve 40 mm Hg at the carina. Inspiratory limb CO(2) entrainment was measured at incremental distances from the Y-piece. HFOV settings and cuff leak were varied to assess their effect on CO(2) entrainment. Control experiments were conducted using a conventional ventilator. Test lung results were validated on a large hypercapnic swine. Negative pressure was detectable within the inspiratory limb of the HFOV circuit and varied inversely with mean airway pressure (P(-)(aw)) and directly with oscillatory pressure amplitude (ΔP). CO(2) was readily detectable within the inspiratory limb and was proportional to the negative pressure that was generated. Factors that decreased CO(2) entrainment in both the test lung and swine included low ΔP, high mean airway pressure, high oscillatory frequency (Hz), high bias flow, and endotracheal tube cuff leak placement. CO(2) entrainment was also reduced by utilizing a higher bias flow strategy at any targeted mean airway pressure. Retrograde CO(2) entrainment occurs during HFOV use and can be manipulated with the ventilator settings. This phenomenon may have clinical implications on the development or persistence of hypercapnia.

Post transfusion lung injury in the neonatal population

The objective of this study was to examine the changes in level of respiratory support following transfusion in neonates who require intermediate or intensive care. Data on respiratory support were collected retrospectively from the medical record before, during and after transfusion. Neonatal post transfusion lung injury (NPTLI) was defined as an increase in the highest mean airway pressure (MAP) of ≥2 cm H(2)O or FiO(2) >0.15 in the 6-h after transfusion that persisted from 6 to 18 h post transfusion. A total of 373 (330 packed red blood cell) transfusions were given to 108 infants. NPTLI occurred following 31 (8.3%) transfusions in 23 patients. During the first 6 h after transfusion, FiO2 or MAP was increased in 47 transfusions (12.6%) and the changes persisted in 31 transfusions (7.8%). Infants who developed NPTLI were less mature (27.1±0.7 vs 31.0±0.5 weeks; P=0.005) and of lower birth weight (1001±110 vs1692±104 g; P=0.001). Infants who developed NPTLI were more likely to develop necrotizing enterocolitis (6/24 vs 4/85; P=0.002) and die within 24 h of transfusion (5/22 vs 3/85; P=0.003). In neonates receiving intensive or intermediate care, blood transfusion was associated with need for increased respiratory support in a significant number of cases. Development of NPTLI was associated with poorer outcomes.

The Effect of APRV Ventilation on ICP and Cerebral Hemodynamics

Airway pressure release ventilation (APRV) is an alternative approach to the low-tidal volume "open-lung" ventilation strategy. APRV is associated with a higher mean airway pressure than conventional ventilation and has therefore not been evaluated in patients with acute neurological injuries. Case report. We report a patient with severe progressive hypoxemia following a subarachnoid hemorrhage who was converted from pressure-controlled mechanical ventilation to APRV. This change in ventilatory mode was associated with a significant improvement in oxygenation and alveolar ventilation with an associated increase in cerebral blood flow and a negligible increase in intracranial pressure. APRV may safely be applied to neurocritically ill patients, and that this mode of ventilation may increase cerebral blood flow without increasing intracranial pressure.

Right ventricular function during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

To evaluate the effect of mean airway pressure under high-frequency oscillatory ventilation on right ventricular function. Prospective randomized study. Intensive care unit of a tertiary care hospital. Sixteen consecutive patients within the first 48 hrs of mainly pulmonary acute respiratory distress syndrome. After a 6-hr-period of protective conventional mechanical ventilation, patients were submitted to three 1-hr periods of high-frequency oscillatory ventilation (+5, +10, +15) in a randomized order, with a mean airway pressure level determined by adding 5, 10, or 15 cm H2O to the mean airway pressure recorded during conventional mechanical ventilation. Mean airway pressure was 18±3 cm H2O during conventional mechanical ventilation and was increased until 33±3 cm H2O at high-frequency oscillatory ventilation+15. Right ventricular function was assessed using transesophageal echocardiography. During conventional mechanical ventilation, nine patients presented a right ventricular dysfunction (right ventricular end-diastolic area/left ventricular end-diastolic area ratio>0.6) of whom four patients had a right ventricular failure (right ventricular end-diastolic area/left ventricular end-diastolic area ratio>0.9). High-frequency oscillatory ventilation+10 and +15 further worsened right ventricular function, resulting in about a 40% increase in right ventricular end-diastolic area/left ventricular end-diastolic area ratio and a 30% increase in end-diastolic eccentricity index when compared with conventional mechanical ventilation or high-frequency oscillatory ventilation+5 periods. At high-frequency oscillatory ventilation+15, 15 patients had right ventricular dysfunction and nine had right ventricular failure. High-frequency oscillatory ventilation did not improve oxygenation whatever the mean airway pressure level. A significant redistribution of tidal variation to the posterior parts of the lung was observed on electrical impedance tomography measurements when increasing mean airway pressure. However, this redistribution was not observed in patients who presented a worsening of right ventricular function (right ventricular end-diastolic area/left ventricular end-diastolic area increase>40%) at high-frequency oscillatory ventilation+15. In patients with mainly pulmonary acute respiratory distress syndrome, using high mean airway pressure under high-frequency oscillatory ventilation can worsen right ventricular function when compared with protective conventional mechanical ventilation, notably in patients in whom high-frequency oscillatory ventilation produced less alveolar recruitment of the posterior parts of the lungs. This study highlights the interest of monitoring right ventricular function during high-frequency oscillatory ventilation.

Prospective longitudinal evaluation of lung function during the first year of life after repair of congenital diaphragmatic hernia

To evaluate lung function and respiratory morbidity prospectively during the first year of life in patients with congenital diaphragmatic hernia and to study the effect of extracorporeal membrane oxygenation therapy. Prospective longitudinal cohort study. Outpatient clinic of a tertiary-level pediatric hospital. The cohort of 43 infants included 12 patients treated with extracorporeal membrane oxygenation. Evaluation was at 6 and 12 months; 33 infants were evaluated at both time points. None. Maximal expiratory flow at functional residual capacity and functional residual capacity were measured with Masterscreen Babybody. Z-scores were calculated for maximal expiratory flow at functional residual capacity. Mean maximal expiratory flow at functional residual capacity values at 6 and 12 months were significantly below the expected values (mean z-score -1.4 and -1.5, respectively) without a significant change between both time points. Values did not significantly differ between extracorporeal membrane oxygenation and nonextracorporeal membrane oxygenation-treated patients. Functional residual capacity values were generally high, 47% were above the suggested normal range, and did not change significantly over time. Mean functional residual capacity values in extracorporeal membrane oxygenation-treated patients were significantly higher than in nonextracorporeal membrane oxygenation-treated patients (p = .006). The difference (5.1 mL/kg ± 1.8 SE) did not change significantly between the two time points. Higher mean airway pressure and longer duration of ventilation were associated with higher functional residual capacity. None of the perinatal characteristics was associated with maximal expiratory flow at functional residual capacity. Mean weight z-scores were significantly below zero at both time points (p < .001). Mean weight z-score in extracorporeal membrane oxygenation-treated patients were lower than in nonextracorporeal membrane oxygenation-treated patients (p = .046). Infants with congenital diaphragmatic hernia have decreased expiratory flows and increased functional residual capacity within the first year of life. Extracorporeal membrane oxygenation-treated patients with congenital diaphragmatic hernia may have more respiratory morbidity and concomitant growth impairment. Close follow-up beyond the neonatal period is therefore required.

Comparison of poractant alfa and lyophilized lucinactant in a preterm lamb model of acute respiratory distress

A lyophilized formulation of lucinactant has been developed to simplify preparation and dosing. Endotracheal administration of surfactant can be associated with potentially harmful transient hemodynamic changes including decreases in cerebral blood flow and delivery of O2 to the brain. Efficacy and peri-dosing effects of poractant alfa and a lyophilized form of lucinactant were compared in this study. Premature lambs (126-129 d gestation) were delivered by c-section, tracheostomized, ventilated, and instrumented with cerebral laser Doppler flowmetry and tissue PO2 probes. Pulmonary compliance and tidal volumes were monitored continuously and surfactant lung distribution was assessed. Lambs received either poractant alfa or lyophilized lucinactant and were monitored for 3 h after treatment. Both groups showed significant improvements in arterial pCO2, pH, pulmonary compliance, and tidal volume (all P < 0.01), a similar intra-pulmonary distribution profile, and no significant changes in arterial blood pressure or cerebral blood flow. Administration of poractant alfa was associated with higher mean airway pressures from 75 min post-dosing and transiently decreased heart rate and increased brain tissue PO2 during the first 30 min after treatment. In this newborn lamb model of respiratory distress, lyophilized lucinactant results in improved lung function as compared with poractant alfa.

High-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

High-frequency oscillatory ventilation (HFOV) is an attractive alternative to conventional lung protective ventilation. Adequate gas exchange is achieved with very small tidal volumes cycling at a high mean airway pressure. This may prevent injury from inspiratory overdistention and expiratory alveolar collapse. Most patients demonstrate improvements in oxygenation on HFOV though reductions in mortality are lacking. This may be explained by suboptimal technique. In this Opinion, the clinical experience using HFOV in adults in acute respiratory distress syndrome and the evolution of this ventilator technique are reviewed. At some settings, currently available high-frequency ventilators may deliver tidal volumes that approach the magnitude of those delivered during conventional ventilation. Significantly smaller tidal volumes are achieved at higher frequencies (>6 Hz) and are tolerated in most patients. The aggressive use of recruitment maneuvers can significantly improve oxygenation during HFOV. Two large randomized controlled trials are underway that incorporate these findings into their protocols. However, not all patients tolerate HFOV and increased rates of barotrauma have been reported in some studies. Although HFOV is theoretically appealing and may improve outcomes in adults with acute respiratory distress syndrome, it should be reserved for patients failing conventional ventilation until definitive trials are completed.

High-frequency Oscillatory Ventilation From Basics to Evidence, From Evidence to Bedside

Critical care physicians deal every day with patients suffering from acute lung injury and respiratory failure. Acute respiratory distress syndrome (ARDS) is the most severe form of acute lung injury. Mechanical ventilation remains the mainstay of supportive treatment for ARDS. There are patients with ARDS who are unable to achieve adequate gas exchange while receiving conventional mechanical ventilation. In this setting, high-frequency oscillatory ventilation (HFOV) arises as a nonconventional mode of mechanical ventilation with the potential not only of reversing severe hypoxemia, but also of minimizing ventilator-induced lung injury. HFOV is a unique mode of mechanical ventilation characterized by very low tidal volumes, lower than anatomic dead space (1 to 3 mL/kg), and a constant, high mean airway pressure. Ventilation at such low tidal volumes is possible using high respiratory cycle frequencies (3 to 20 Hz). Oxygenation and ventilation can be managed on high-frequency ventilation relatively uncoupled. Changes in oxygenation are addressed by changing mean airway pressure or the oxygen inspiratory fraction. CO2 elimination is dealt with by modifying oscillator pressure amplitude, frequency (inversely), inspiratory to expiratory ratio, and bias flow. High-grade evidence supporting the use of HFOV is scarce. This ventilation technique has proven to be at least as efficient and safe as conventional mechanical ventilation for patients with ARDS. Current literature suggests that it may be useful not only to rescue patients failing on mechanical ventilation, but also to minimize barotrauma, volutrauma, and biotrauma. Selection of candidates for high-frequency oscillation and utilization of the appropriate ventilatory strategies are key issues if benefits from this technique are to be maximized.

Inflammation in utero exacerbates ventilation-induced brain injury in preterm lambs

Cerebral blood flow disturbance is a major contributor to brain injury in the preterm infant. The initiation of ventilation may be a critical time for cerebral hemodynamic disturbance leading to brain injury in preterm infants, particularly if they are exposed to inflammation in utero. We aimed to determine whether exposure to inflammation in utero alters cardiopulmonary hemodynamics, resulting in cerebral hemodynamic disturbance and related brain injury during the initiation of ventilation. Furthermore, we aimed to determine whether inflammation in utero alters the cerebral hemodynamic response to challenge induced by high mean airway pressures. Pregnant ewes received intra-amniotic lipopolysaccharide (LPS) or saline either 2 or 4-days before preterm delivery (at 128 ± 1 days of gestation). Lambs were surgically instrumented for assessment of pulmonary and cerebral hemodynamics before delivery and positive pressure ventilation. After 30 min, lambs were challenged hemodynamically by incrementing and decrementing positive end-expiratory pressure. Blood gases, arterial pressures, and blood flows were recorded. The brain was collected for biochemical and histological assessment of inflammation, brain damage, vascular extravasation, hemorrhage, and oxidative injury. Carotid arterial pressure was higher and carotid blood flow was more variable in 2-day LPS lambs than in controls during the initial 15 min of ventilation. All lambs responded similarly to the hemodynamic challenge. Both 2- and 4-day LPS lambs had increased brain interleukin (IL)-1β, IL-6, and IL-8 mRNA expression; increased number of inflammatory cells in the white matter; increased incidence and severity of brain damage; and vascular extravasation relative to controls. Microvascular hemorrhage was increased in 2-day LPS lambs compared with controls. Cerebral oxidative injury was not different between groups. Antenatal inflammation causes adverse cerebral hemodynamics and increases the incidence and severity of brain injury in ventilated preterm lambs.

Medición del volumen corriente en ventilación de alta frecuencia

Objective To ascertain whether a spirometer can measure tidal volume (TV) during high frequency oscillatory ventilation (HFOV) and high frequency jet ventilation (HFJV), and to analyse the effect of changes in ventilator settings. Methods The study was performed with paediatric porcine lung models submitted to HFOV with a Sensormedics 3100 ventilator and HFJV with a Paravent Pat e R ventilator connected to a D-Fend spirometer. Programmed frequency, amplitude, and mean airway pressure (MAP) were changed in the ventilator, and TV and pressures were recorded using the spirometer. Results The spirometer measured TV in the paediatric lung models and piglets, but could not measure TV less than 8 ml, when the pressure amplitude was higher than 55 cmH 2O or the MAP was higher than 30 cmH 2O. With HFOV there was a correlation between amplitude and tidal volume, and a positive correlation between pressure and TV with HFJV. With both respirators there was a negative correlation between frequency and TV. Conclusions The D-Fend spirometer can measure tidal volume and pressure during HFOV and HFJV. However, it does not work with volumes lower than 8 ml, and high amplitude or mean airway pressure.