Ventilation In Acute Lung Injury Research Articles

First Stabilize and then Gradually Recruit: A Paradigm Shift in Protective Mechanical Ventilation for Acute Lung Injury.

Acute respiratory distress syndrome (ARDS) is associated with a heterogeneous pattern of injury throughout the lung parenchyma that alters regional alveolar opening and collapse time constants. Such heterogeneity leads to atelectasis and repetitive alveolar collapse and expansion (RACE). The net effect is a progressive loss of lung volume with secondary ventilator-induced lung injury (VILI). Previous concepts of ARDS pathophysiology envisioned a two-compartment system: a small amount of normally aerated lung tissue in the non-dependent regions (termed "baby lung"); and a collapsed and edematous tissue in dependent regions. Based on such compartmentalization, two protective ventilation strategies have been developed: (1) a "protective lung approach" (PLA), designed to reduce overdistension in the remaining aerated compartment using a low tidal volume; and (2) an "open lung approach" (OLA), which first attempts to open the collapsed lung tissue over a short time frame (seconds or minutes) with an initial recruitment maneuver, and then stabilize newly recruited tissue using titrated positive end-expiratory pressure (PEEP). A more recent understanding of ARDS pathophysiology identifies regional alveolar instability and collapse (i.e., hidden micro-atelectasis) in both lung compartments as a primary VILI mechanism. Based on this understanding, we propose an alternative strategy to ventilating the injured lung, which we term a "stabilize lung approach" (SLA). The SLA is designed to immediately stabilize the lung and reduce RACE while gradually reopening collapsed tissue over hours or days. At the core of SLA is time-controlled adaptive ventilation (TCAV), a method to adjust the parameters of the airway pressure release ventilation (APRV) modality. Since the acutely injured lung at any given airway pressure requires more time for alveolar recruitment and less time for alveolar collapse, SLA adjusts inspiratory and expiratory durations and inflation pressure levels. The TCAV method SLA reverses the open first and stabilize second OLA method by: (i) immediately stabilizing lung tissue using a very brief exhalation time (≤0.5 s), so that alveoli simply do not have sufficient time to collapse. The exhalation duration is personalized and adaptive to individual respiratory mechanical properties (i.e., elastic recoil); and (ii) gradually recruiting collapsed lung tissue using an inflate and brake ratchet combined with an extended inspiratory duration (4-6 s) method. Translational animal studies, clinical statistical analysis, and case reports support the use of TCAV as an efficacious lung protective strategy.

The Role of Carotid Body Chemoreceptor Afferents in Mediating Abnormal Ventilation in Acute Lung Injury

Background‐Acute lung injury (ALI) induces inflammation that disrupts the normal alveolar‐capillary endothelial barrier which impairs gas exchange to induce hypoxemia that reflexively increases respiration. Increased respiratory rate (RR) usually develops within a few hours to a few days after ALI. This disorder of acute respiratory failure affects approximately 200,000 new cases each year in the US alone and has high morbidity and mortality. The neural mechanisms underlying the respiratory dysfunction after ALI are not fully understood. The purpose of this study involved investigating the role of carotid body chemoreceptor afferents in mediating abnormal ventilation in ALI.Methods and Results‐ALI was induced in male SD rats (200‐250g) using a single intra‐tracheal injection of bleomycin (Bleo) (day 0) and respiratory variables‐ RR, TV (Tidal Volume), and MV (Minute Ventilation) in response to 10% hypoxia (10% O2, 0% CO2) and 5% hypercapnia (21% O2, 5% CO2) were measured weekly from W1‐W4 using whole‐ body plethysmography (WBP). MV at 21% O2 increased from baseline (W0) to W1 and W2 in bleo treated rats (p≤0.01 compared to saline treated sham rats). Changes in MV were due to a significant increase in RR while TV showed no changes. Chemoreflex was assessed by measuring the absolute difference between 21% O2 and hypoxia (10% O2, 0% CO2) & hypercapnia (21% O2, 5% CO2). Chemoreflex activation is a fundamental protective reflex that maintains oxygen homeostasis. Our data indicated a blunted chemoreflex at W1 and a sensitized chemoreflex in W3‐W4 during hypoxia and hypercapnia. We hypothesized that the blunted chemoreflex in W1 could be due to maximal pre‐activation of chemoreceptors, called the ‘ceiling effect’. To test this possibility, 90% hyperoxia (90% O2, 0% CO2) was given to bleo treated rats to inhibit the chemoreflex and our results showed no changes in RR, suggesting absence of the tonic activity at W1 post‐ALI.Conclusions‐These data suggest that chemoreflex activation in response to hypoxia and hypercapnia is blunted at acute stage of lung injury but became sensitized at the recovery stage.

Sodium bicarbonate therapy for acute respiratory acidosis.

Respiratory acidosis is commonly present in patients with respiratory failure. The usual treatment of hypercapnia is to increase ventilation. During the recent surge of COVID-19, respiratory acidosis unresponsive to increased mechanical ventilatory support was common. Increasing mechanical ventilation comes at the expense of barotrauma and hemodynamic compromise from increasing positive end-expiratory pressures or minute ventilation. Treating acute respiratory acidemia with sodium bicarbonate remains controversial. There are no randomized controlled trials of administration of sodium bicarbonate for respiratory acidemia. A recent review concluded that alkali therapy for mixed respiratory and metabolic acidosis might be useful but was based on the conflicting and not conclusive literature regarding metabolic acidosis. This strategy should not be extrapolated to treatment of respiratory acidemia. Low tidal volume ventilation in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) has beneficial effects associated with permissive hypercapnia. Whether the putative benefits will be negated by administration of alkali is not known. Hypercapnic acidosis is well tolerated, with few adverse effects as long as tissue perfusion and oxygenation are maintained. There is a lack of clinical evidence that administration of sodium bicarbonate for respiratory acidosis has a net benefit; in fact, there are potential risks associated with it.

Application of graded airway management during mechanical ventilation in neonates with acute lung injury

Objective To explore the application of graded airway management in mechanical ventilation of neonates with acute lung injury. Methods From June 2016 to June 2018, 84 cases of children with acute lung injury admitted to the neonatology department of this hospital were selected. According to the random number table method, the children were divided into the observation group and the control group, 42 cases of each group.The control group received routine airway management and chest physical therapy every 2 hours.The observation group received airway grading management according to the airway score of children.Acute physiological and chronic health scoreⅡ (APACHEⅡ), qi and blood indexes, mechanical ventilation time, hospital stay and complications were compared between the two groups before and 5 days after treatment. Results After treatment, tidal volume (VT), respiratory rate (f), and blood gas oxygen partial pressure (PaO2)/oxygen concentration (PaO2/FiO2) were significantly improved in the observation group compared with the control group, and the differences were statistically significant(P<0.05). APACHE Ⅱscore was significantly lower than that of the control group, and the difference was statistically significant(P<0.05). Mechanical ventilation time and hospitalization time in observation group were shorter than those in control group, and the differences were statistically significant(P<0.05). The incidence of ventilator-associated pneumonia was significantly lower than that of the control group, and the difference was statistically significant(P<0.05). Conclusions Airway grading management can effectively improve the respiratory function of children with mechanical ventilation in acute lung injury, reduce the incidence of ventilator-associated pneumonia in children, and promote the recovery of children. Key words: Airway grading management; Neonatal; Acute lung injury; Mechanical ventilation; Prognosis

Differences in prevalence of ICU protocols between neurologic and non-neurologic patient populations

PurposeTo compare the differences in the presence of protocols aimed at addressing complications for neurologically injured patients vs. non-neurologic injured patients in a large sample of ICUs across the United States. Materials and methodsProspective observational multi-center cohort study. This was a subgroup analysis of the multi-centered prospective observational cohort study of medical, surgical, and mixed intensive care units from across the country. USCIITG-CIOS study group. ResultsSixty-nine ICUs participated in the study of which 25 (36%) were medical, 24 were surgical (35%) and 20 (29%) were of mixed type, and 64 (93%) were in teaching hospitals. There were 6179 patients across all sites with 1266 (20.4%) with central nervous system diagnoses. Protocol utilization in central nervous system vs. non- central nervous system patients was as follows: Sedation interruption 973/1266 (76.9%) vs. 3840/4913 (78.2%) (p = .32); acute lung injury ventilation 847/1266 (66.9%) vs. 4069/4913 (82.8%) (p < .0001); ventilator associated pneumonia 1193/1266 (94.2%) vs. 4760/4913 (96.9%) (p < .0001); ventilator weaning 1193/1266 (94.2%) vs. 4490/4913 (91.4%) (p = .0009); and early mobility 378/1266 (29.9%) vs. 1736/4913 (35.3%) (p = .0002). ConclusionIn this cohort, we found differences in the prevalence of respiratory illness prevention protocols between critically ill patients with neurologic illness and the general critically ill population.

Mitochondrial damage pathways in ventilator induced lung injury (VILI): an update

Although reduced tidal volumes have improved patient survival during ventilation for acute lung injury, further improvements will require pharmacologic interventions of the cellular pathways for inflammation and injury. We previously reported that pretreatment with mitochondrial targeted mtDNA repair enzymes largely prevented lung injury and inflammation during a protocol for moderately severe ventilation induced lung injury. GSH/GSSG ratios indicated that free radical production had been reduced to baseline levels by treatment. The central role of the alveolar macrophages and cellular mechanisms of injury are discussed. This includes a rapid calcium entry and mitochondrial production of excessive reactive oxygen species. Excessive ROS can then result in activation of the NLRP3 inflammasome and secretion of IL-1 and IL-18 by caspase-1. A simultaneous activation of NFkB to transcribe pro forms of the cytokines is stimulated by damage associated molecular pattern (DAMP) recognition receptors. These are primarily TLR4 responding to various cellular damage products and TLR9 responding to mtDNA fragments that appear to be primarily involved. Intervention in these pathways could result in useful future clinical treatments.

Variability in Usual Care Mechanical Ventilation for Pediatric Acute Respiratory Distress Syndrome: Time for a Decision Support Protocol?

Although pediatric intensivists philosophically embrace lung protective ventilation for acute lung injury and acute respiratory distress syndrome, we hypothesized that ventilator management varies. We assessed ventilator management by evaluating changes to ventilator settings in response to blood gases, pulse oximetry, or end-tidal CO2. We also assessed the potential impact that a pediatric mechanical ventilation protocol adapted from National Heart Lung and Blood Institute acute respiratory distress syndrome network protocols could have on reducing variability by comparing actual changes in ventilator settings to those recommended by the protocol. Prospective observational study. Eight tertiary care U.S. PICUs, October 2011 to April 2012. One hundred twenty patients (age range 17 d to 18 yr) with acute lung injury/acute respiratory distress syndrome. Two thousand hundred arterial and capillary blood gases, 3,964 oxygen saturation by pulse oximetry, and 2,757 end-tidal CO2 values were associated with 3,983 ventilator settings. Ventilation mode at study onset was pressure control 60%, volume control 19%, pressure-regulated volume control 18%, and high-frequency oscillatory ventilation 3%. Clinicians changed FIO2 by ±5 or ±10% increments every 8 hours. Positive end-expiratory pressure was limited at ~10 cm H2O as oxygenation worsened, lower than would have been recommended by the protocol. In the first 72 hours of mechanical ventilation, maximum tidal volume/kg using predicted versus actual body weight was 10.3 (8.5-12.9) (median [interquartile range]) versus 9.2 mL/kg (7.6-12.0) (p < 0.001). Intensivists made changes similar to protocol recommendations 29% of the time, opposite to the protocol's recommendation 12% of the time and no changes 56% of the time. Ventilator management varies substantially in children with acute respiratory distress syndrome. Opportunities exist to minimize variability and potentially injurious ventilator settings by using a pediatric mechanical ventilation protocol offering adequately explicit instructions for given clinical situations. An accepted protocol could also reduce confounding by mechanical ventilation management in a clinical trial.

Translating evidence into practice

Appropriately designed and conducted research is necessary for improving patient care and optimizing health outcomes, but access to best evidence is not enough to make these things happen. In respiratory care, as in other fields, patients do not benefit as much as they should from research findings and evidence-based practice guidelines. Current standards for the diagnosis, staging, and management of chronic obstructive pulmonary disease are based in large part on the results of spirometry, yet most patients carrying this diagnosis have not had this test performed. Despite compelling evidence that it saves lives, reduces complications, and decreases costs in acute respiratory failure complicating chronic obstructive pulmonary disease, noninvasive ventilation is not used in a large proportion of such cases. Lung-protective ventilation for acute lung injury and the acute respiratory distress syndrome also increases survival, decreases complications, and is cost-effective, yet many patients who stand to benefit do not receive it. Clinicians may not be aware of practice guidelines or be familiar with their recommendations; they may not agree with the recommendations, or have insufficient expectation that management according to the guideline will work; they may consider the guideline too complicated or difficult to use in their own practices; patient-related factors may interfere; and changing established practice is often difficult. Overcoming these and other barriers to best practice is the focus of knowledge translation, which recognizes the need for involvement of every aspect of health care and seeks to integrate them effectively. This paper discusses the challenges faced by knowledge translation, provides examples of its successful application in respiratory care, and summarizes what needs to be done if the potential benefits of available evidence are to be realized for both individual patients and the health care system as a whole.

Effect of Inhaled Nitric Oxide on Outcomes in Children With Acute Lung Injury: Propensity Matched Analysis From a Linked Database.

To evaluate the effect of inhaled nitric oxide on outcomes in children with acute lung injury. Retrospective study with a secondary data analysis of linked data from two national databases. Propensity score matching was performed to adjust for potential confounding variables between patients who received at least 24 hours of inhaled nitric oxide (inhaled nitric oxide group) and those who did not receive inhaled nitric oxide (no inhaled nitric oxide group). Linked data from Virtual Pediatric Systems (LLC) database and Pediatric Health Information System. Patients less than 18 years old receiving mechanical ventilation for acute lung injury at nine participating hospitals were included (2009-2014). None. A total of 20,106 patients from nine hospitals were included. Of these, 859 patients (4.3%) received inhaled nitric oxide for at least 24 hours during their hospital stay. Prior to matching, patients in the inhaled nitric oxide group were younger, with more comorbidities, greater severity of illness scores, higher prevalence of cardiopulmonary resuscitation, and greater resource utilization. Before matching, unadjusted outcomes, including mortality, were worse in the inhaled nitric oxide group (inhaled nitric oxide vs no inhaled nitric oxide; 25.7% vs 7.9%; p < 0.001; standardized mortality ratio, 2.6 [2.3-3.1] vs 1.1 [1.0-1.2]; p < 0.001). Propensity score matching of 521 patient pairs revealed no difference in mortality in the two groups (22.3% vs 20.2%; p = 0.40; standardized mortality ratio, 2.5 [2.1-3.0] vs 2.3 [1.9-2.8]; p = 0.53). However, the other outcomes such as ventilation free days (10.1 vs 13.6 d; p < 0.001), duration of mechanical ventilation (13.8 vs 10.1 d; p < 0.001), duration of ICU and hospital stay (15.5 vs 12.2 d; p < 0.001 and 28.0 vs 24.1 d; p < 0.001), and hospital costs ($150,569 vs $102,823; p < 0.001) were significantly worse in the inhaled nitric oxide group. This large observational study demonstrated that inhaled nitric oxide administration in children with acute lung injury was not associated with improved mortality. Rather, it was associated with increased hospital utilization and hospital costs.

Noninvasive ventilation for acute lung injury a meta-analysis of randomized controlled trials

PurposeTo compare the effect of noninvasive ventilation (NIV) and standard oxygen therapy on treating acute lung injury (ALI). MethodsA search on PubMed, Embase, Springer, Cochrane Central Register of Controlled Trials and Clinical Trials was carried out up to Nov 2015 for randomized controlled trials (RCTs) with NIV as cases and standard oxygen therapy as controls. Risk ratios and weight mean difference were used for estimation. ResultsThis meta-analysis included seventeen RCTs. Results showed NIV significantly reduced the intubation rate, length of ICU stay and hospital mortality. The length of hospital stay and ICU mortality were not different. High heterogeneity was found across the studies of intubation rate. The types of acute respiratory failure might be a source of heterogeneity. ConclusionOur results suggest that NIV is effective for ALI in reducing the intubation rate, hospital mortality and length of ICU stay than the standard oxygen therapy.

Factors associated with swallowing assessment after oral endotracheal intubation and mechanical ventilation for acute lung injury.

Endotracheal intubation is associated with postextubation swallowing dysfunction, but no guidelines exist for postextubation swallowing assessments. We evaluated the prevalence, patient demographic and clinical factors, and intensive care unit (ICU) and hospital organizational factors associated with swallowing assessment after oral endotracheal intubation and mechanical ventilation in patients with acute lung injury (ALI). We performed a secondary analysis of a prospective cohort study in which investigators evaluated 178 eligible patients with ALI who were mechanically ventilated via oral endotracheal tube. The patients were recruited from 13 ICUs at four teaching hospitals in Baltimore, Maryland. Patient demographic and clinical factors, types of ICU, and hospital study sites were evaluated for their association with completion of a swallowing assessment both in the ICU and after the ICU stay before hospital discharge. Factors significantly associated with a swallow assessment were evaluated in a multivariable logistic regression model. Before hospital discharge, 79 (44%) patients completed a swallowing assessment, among whom 59 (75%) had their assessments initiated in ICU and 20 (25%) had their assessments initiated on the hospital ward. Female sex (odds ratio [OR] = 2.01; 95% confidence interval [95% CI] = 1.03-3.97), orotracheal intubation duration (OR = 1.13 per day; 95% CI = 1.05-1.22), and hospital study site (Site 3: OR = 2.41; 95% CI = 1.00-5.78) were independently associated with swallowing assessment. Although Site 3 had a twofold increase in swallowing assessments in the ICU, there was no significant difference between hospitals in the frequency of swallowing assessments completed after ICU discharge (P = 0.287) or in the proportion of patients who failed a swallowing assessment conducted in the ICU (P = 0.468) or on the ward (P = 0.746). In this multisite prospective study, female sex, intubation duration, and hospital site were associated with postextubation swallowing assessment. These results demonstrate variability in practice patterns between institutions and highlight the need to determine the appropriate timing and indications for swallowing assessment and to more fully understand swallowing dysfunction after intubation.

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.

Early noninvasive mechanical ventilation in acute lung injury

Esquinas, Antonio MD, PhD, FCCP; Agarwal, Ritesh MD, DM, FACP, FCCP, FRCP(Glasg); Chiumello, Davide MD Author Information

Early noninvasive mechanical ventilation in acute lung injury

Early noninvasive mechanical ventilation in acute lung injury

Analysis of regional compliance in a porcine model of acute lung injury

Lung protective ventilation in Acute Lung Injury (ALI) focuses on using low tidal volumes and adequate levels of positive end-expiratory pressure (PEEP). Identifying optimal pressure is difficult because pressure–volume (PV) relations differ regionally. Precise analysis demands local measurements of pressures and related alveolar morphologies. In a porcine model of surfactant depletion (n=24), we combined measuring static pressures with endoscopic microscopy and electrical impedance tomography (EIT) to examine regional PV loops and morphologic heterogeneities between healthy (control group; CON) and ALI lungs ventilated with low (LVT) or high tidal volumes (HVT). Quantification included indices for microscopy (Volume Air Index (VAI), Heterogeneity and Circularity Index), EIT analysis and calculation of regional compliances due to generated PV loops.We found that: (1) VAI decreased in lower lobe after ALI, (2) electrical impedance decreased in dorsal regions and (3) PV loops differed regionally.Further studies should prove the potentials of these techniques on individual respiratory settings and clinical outcome.

Spontaneous breathing activity in acute lung injury and acute respiratory distress syndrome

We aimed at providing the most recent and relevant evidence regarding spontaneous breathing activity during mechanical ventilation in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Both clinical and experimental data are depicted. The use of unsupported spontaneous breathing has been associated with the most beneficial effects reported to date, but recent data favors also pressure-supported breathing activity in experimental ALI. In patients with ALI/ARDS, unsupported spontaneous breathing in combination with mandatory cycles has been shown to improve lung function, reduce the need for sedation and cardiocirculatory drug therapy, and speed weaning, with no effect on mortality. On the other hand, strong clinical evidence shows that the use of neuromuscular blocking agents in the first 48 h of mechanical ventilation with the volume assist-control ventilation mode reduces morbidity and mortality in severe ARDS compared to placebo. In our opinion, spontaneous breathing activity should be avoided in the first 48 h of mechanical ventilation in patients with severe ARDS (PaO2/FIO2 <120 mmHg), but it may be useful in less severe ARDS and ALI. Clearly, further clinical and experimental investigations on the use of different ventilation modes of supported/unsupported spontaneous breathing in ALI/ARDS are needed.

Starting point to embark on a widespread use of noninvasive positive pressure ventilation in acute lung injury or early acute respiratory distress syndrome?*

Hilbert, Gilles MD, PhD; Vargas, Frederic MD, PhD; Boyer, Alexandre MD; Bui, Hoang-Nam MD Author Information

Early use of noninvasive positive pressure ventilation for acute lung injury

Noninvasive positive pressure ventilation is beneficial for patients with acute respiratory failure. However, its possible benefit for patients with acute lung injury (200 mm Hg < PaO(2)/FIO(2) ≤300 mm Hg) remains unclear. Our aim was to assess the safety and efficacy of noninvasive positive pressure ventilation for patients with acute lung injury and compare this with high-concentration oxygen therapy. A multicentered randomized controlled trial. Ten multipurpose intensive care units. Forty patients who fulfilled the criteria for acute lung injury were included in this study. Patients were randomly allocated to receive either noninvasive positive pressure ventilation (noninvasive positive pressure ventilation group) or high-concentration oxygen therapy through a Venturi mask (control group). Twenty-one patients were assigned to the noninvasive positive pressure ventilation group and 19 were in the control group. At study entry, the patients' characteristics in the two groups were similar. Noninvasive positive pressure ventilation application decreased the respiratory rate and improved PaO(2)/FIO(2) with time. The proportion of patients requiring intubation and the actual number of intubations in the noninvasive positive pressure ventilation group were significantly less than in the control group (one of 21 vs. seven of 19; p = .02, and one of 21 vs. four of 19; p = .04, respectively). Noninvasive positive pressure ventilation showed a trend for reducing inhospital mortality (one of 21 vs. five of 19; p = .09). The total number of organ failures in the noninvasive positive pressure ventilation group was significantly lower than in the control group (three vs. 14; p < .001). Noninvasive positive pressure ventilation is safe for selected patients with acute lung injury. However, a larger randomized trial with need for intubation and mortality as the outcomes of interest is required.

Pulmonary Vascular Resistance and Direct Ventricular Interaction during Mechanical Ventilation in an Oleic Acid Induced Acute Lung Injury Model: A Review

Treatment of patients with Acute Lung Injury (ALI) can be challenging. Mechanical ventilation is often required and can have significant adverse cardiovascular effects. Clinicians and research scientists have been able to utilize an experimental model of ALI/Acute Respiratory Distress Syndrome (ARDS) that can mimic much of the clinical sequelae. This model has provided the opportunity to systematically test best care practices and clarify the important cardiopulmonary interaction during mechanical ventilation. During mechanical ventilation with positive end-expiratory pressure, increased pulmonary vascular resistance (PVR) may adversely affect right ventricular (RV) function, and therefore, left ventricular (LV) function. Thus, increased resistance to RV output can result in decreased LV preload by series interaction, but importantly, also by direct ventricular interaction (DVI) (leftward septal shift). Therefore, if the increase in PVR can be minimized, for example, by volume loading or nitric oxide, the adverse effects of mechanical ventilation on cardiac function may be limited. This paper will review the possible cardiac consequences of elevated PVR through DVI during mechanical ventilation in ALI, and suggest potential benefits of reducing PVR.

Variability in usual care mechanical ventilation for pediatric acute lung injury: the potential benefit of a lung protective computer protocol.

Although pediatric intensivists claim to embrace lung protective ventilation for acute lung injury (ALI), ventilator management is variable. We describe ventilator changes clinicians made for children with hypoxemic respiratory failure, and evaluate the potential acceptability of a pediatric ventilation protocol. This was a retrospective cohort study performed in a tertiary care pediatric intensive care unit (PICU). The study period was from January 2000 to July 2007. We included mechanically ventilated children with PaO(2)/FiO(2) (P/F) ratio less than 300. We assessed variability in ventilator management by evaluating actual changes to ventilator settings after an arterial blood gas (ABG). We evaluated the potential acceptability of a pediatric mechanical ventilation protocol we adapted from National Institutes of Health/National Heart, Lung, and Blood Institute (NIH/NHLBI) Acute Respiratory Distress Syndrome (ARDS) Network protocols by comparing actual practice changes in ventilator settings to changes that would have been recommended by the protocol. A total of 2,719 ABGs from 402 patients were associated with 6,017 ventilator settings. Clinicians infrequently decreased FiO(2), even when the PaO(2) was high (>68 mmHg). The protocol would have recommended more positive end expiratory pressure (PEEP) than was used in actual practice 42% of the time in the mid PaO(2) range (55-68 mmHg) and 67% of the time in the low PaO(2) range (<55 mmHg). Clinicians often made no change to either peak inspiratory pressure (PIP) or ventilator rate (VR) when the protocol would have recommended a change, even when the pH was greater than 7.45 with PIP at least 35 cmH(2)O. There may be lost opportunities to minimize potentially injurious ventilator settings for children with ALI. A reproducible pediatric mechanical ventilation protocol could prompt clinicians to make ventilator changes that are consistent with lung protective ventilation.