Lung injury severity scoring in the era of lung protective mechanical ventilation: the PaO2/FIO2 ratio

Over-distension prediction via hysteresis loop analysis and patient-specific basis functions in a virtual patient model

BACKGROUND AND OBJECTIVE

Recruitment maneuvers (RMs) with subsequent positive-end-expiratory-pressure (PEEP) have proven effective in recruiting lung volume and preventing alveolar collapse. However, a suboptimal PEEP could induce undesired injury in lungs by insufficient or excessive breath support. Thus, a predictive model for patient response under PEEP changes could improve clinical care and lower risks.

METHODS

This research adds novel elements to a virtual patient model to identify and predict patient-specific lung distension to optimise and personalise care. Model validity and accuracy are validated using data from 18 volume-controlled ventilation (VCV) patients at 7 different baseline PEEP levels (0-12cmH₂O), yielding 623 prediction cases. Predictions were made up to ΔPEEP = 12cmH₂O ahead covering 6x2cmH₂O PEEP steps.

RESULTS

Using the proposed lung distension model, 90% of absolute peak inspiratory pressure (PIP) prediction errors compared to clinical measurement are within 3.95cmH₂O, compared with 4.76cmH₂O without this distension term. Comparing model-predicted and clinically measured distension had high correlation increasing to R² = 0.93-0.95 if maximum ΔPEEP ≤ 6cmH₂O. Predicted dynamic functional residual capacity (V_frc) changes as PEEP rises yield 0.013L median prediction error for both prediction groups and overall R² of 0.84.

CONCLUSIONS

Overall results demonstrate nonlinear distension mechanics are accurately captured in virtual lung mechanics patients for mechanical ventilation, for the first time. This result can minimise the risk of lung injury by predicting its potential occurrence of distension before changing ventilator settings. The overall outcomes significantly extend and more fully validate this virtual mechanical ventilation patient model.

A COVID-Positive 52-Year-Old Man Presented With Venous Thromboembolism and Disseminated Intravascular Coagulation Following Johnson & Johnson Vaccination: A Case-Study

The coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Infection by the SARS-CoV-2 increases the risk for systematic multi-organ complications and venous, arterial thromboembolism. The need for an effective vaccine to combat the pandemic prompted the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) to approve a nationwide distribution of the Ad26.COV2.S vaccine manufactured by Johnson & Johnson (J&J). The use of the vaccine was halted after reported cases of cerebral venous sinus thrombosis (CVST) and thrombocytopenia among recipients. Researchers have postulated these rare occurrences as potentially immune-triggered responses associated with complement-mediated thrombotic microangiopathy (TMA). Thrombotic complications and thrombocytopenia increase the risk for blood clot growth due to the inflammation of immune complexes by pro-thrombotic activation of anti-platelet antibodies.

A 52-year-old man presented to the intensive care unit (ICU) with severe dyspnea. He required bilevel positive airway pressure (BiPAP) for supplemental oxygen therapy. Endotracheal intubation was performed due to his worsened respiratory deterioration. Lab results suggested respiratory failure due to decreased partial pressure of oxygen (pO₂) and increased partial pressure of carbon dioxide (pCO₂). Findings of elevated D‐dimer levels with decreased fibrinogen and thrombocytopenia with prolonged prothrombin clotting time were consistent for disseminated intravascular coagulation (DIC). Chest radiography displayed moderate to heavy bilateral airspace consolidations, consistent with multifocal pneumonia suspicious for COVID-19. A computed tomography angiogram (CTA) revealed a mildly enlarged right ventricle and interventricular septum consistent for right heart strain due to a saddle pulmonary embolism (PE) that extended into the main pulmonary lobar segmental arteries bilaterally. The patient was transferred to a higher-level (tertiary) care for radiology intervention to remove the pulmonary embolism found on his lungs.

This patient presented with severe dyspnea secondary to massive PE and deep venous thrombosis (DVT) due to SARS-CoV2 infection following the administration of the J&J vaccine. Bilateral thrombus opacities and pulmonary emboli are consistent among COVID-19 patients by intravascular coagulation with increased prothrombin time and D-dimer concentration with a low platelet count. Adverse emboli growths with increased D-dimer and thrombocytopenia strikes a similarity in recipients of the AstraZeneca vaccine due to vaccine-induced immune thrombotic thrombocytopenia (VITT). Administrative use of the J&J vaccine resumed in May 2021. The FDA's reassurance stemmed from their conclusive findings that the vaccine's benefits far outweigh these rare developments, which account for less than 0.01% of the total recipient population. Nevertheless, a further detailed analysis must be conducted on the adverse thrombotic manifestations following adenoviral-based COVID-19 vaccines (J&J, AstraZeneca) compared to mRNA-based vaccines (Moderna, Pfizer) to assess causality with higher specificity.

Assessment of the SpO2/FiO2 ratio as a tool for hypoxemia screening in the emergency department

Objective

We assessed the performance of the ratio of peripheral arterial oxygen saturation to the inspired fraction of oxygen (SpO₂/FiO₂) to predict the ratio of partial pressure arterial oxygen to the fraction of inspired oxygen (PaO₂/FiO₂) among patients admitted to our emergency department (ED) during the SARS-CoV-2 outbreak.

Methods

We retrospectively studied patients admitted to an academic-level ED in France who were undergoing a joint measurement of SpO₂ and arterial blood gas. We compared SpO₂ with SaO₂ and evaluated performance of the SpO₂/FiO₂ ratio for the prediction of 300 and 400 mmHg PaO₂/FiO₂ cut-off values in COVID-19 positive and negative subgroups using receiver-operating characteristic (ROC) curves.

Results

During the study period from February to April 2020, a total of 430 arterial samples were analyzed and collected from 395 patients. The area under the ROC curves of the SpO₂/FiO₂ ratio was 0.918 (CI 95% 0.885–0.950) and 0.901 (CI 95% 0.872–0.930) for PaO₂/FiO₂ thresholds of 300 and 400 mmHg, respectively. The positive predictive value (PPV) of an SpO₂/FiO₂ threshold of 350 for PaO₂/FiO₂ inferior to 300 mmHg was 0.88 (CI95% 0.84–0.91), whereas the negative predictive value (NPV) of the SpO₂/FiO₂ threshold of 470 for PaO₂/FiO₂ inferior to 400 mmHg was 0.89 (CI95% 0.75–0.96). No significant differences were found between the subgroups.

Conclusions

The SpO₂/FiO₂ ratio may be a reliable tool for hypoxemia screening among patients admitted to the ED, particularly during the SARS-CoV-2 outbreak.

Blood Interleukin-6 Levels Predict Multiple Organ Dysfunction in Critically Ill Patients

BACKGROUND

Predicting multiple organ dysfunction (MOD) in the late phase of critical illnesses is essential. Cytokines are considered biomarkers that can predict clinical outcomes; however, their predictive value for late-phase MOD is unknown. This study aimed to identify the biomarker with the highest predictive value for late-phase MOD.

METHODS

This observational study prospectively evaluated data on adult patients with systemic inflammatory response syndrome, those who presented to the emergency department or were admitted to intensive care units in five tertiary hospitals (n = 174). Seven blood biomarkers levels (interleukin-6 [IL-6], IL-8, IL-10, tumor-necrosis factor-α, white blood cells, C-reactive protein, and procalcitonin) were measured at three timepoints (days 0, 1, and 2). The area under the receiver operating characteristic curve (AUC) was analyzed to evaluate predictive values for MOD (primary outcome, MOD on day 7 [late-phase]; secondary outcome, MOD on day 3 [early-phase]).

RESULTS

Of the measured 7 biomarkers, blood IL-6 levels on day 2 had the highest predictive value for MOD on day 7 using single timepoint data (AUC 0.825, 95% confidence interval [CI] 0.754-0.879). Using three timepoint biomarkers, blood IL-6 levels had the highest predictive value of MOD on day 7 (AUC 0.838, 95% CI 0.768-0.890). Blood IL-6 levels using three timepoint biomarkers had also the highest predictive value for MOD on day 3 (AUC 0.836, 95% CI 0.766-0.888).

CONCLUSION

Of the measured biomarkers, blood IL-6 levels had the highest predictive value for MOD on days 3 and 7. Blood IL-6 levels predict early- and late-phase MOD in critically ill patients.

Effect of zinc supplementation on infants with severe pneumonia

BACKGROUND

Pneumonia is a common respiratory infectious disease in infancy. Previous work shows controversial results on the benefit of zinc supplementation in patients with pneumonia. We conducted this study to investigate serum zinc status amongst infants with severe pneumonia and the clinical impact that zinc supplementation has on those patients with low serum zinc levels.

METHODS

This study design was a non-blinded prospective randomized controlled trial. The study is approved by the Ethics Committees of Beijing Children's Hospital. A total of 96 infants diagnosed with severe pneumonia and hospitalized in the pediatric intensive care unit between November 2011 and January 2012 were enrolled. Enrolled patients were divided into low serum zinc and normal serum zinc group. The low serum zinc group was randomized into treatment and control groups. Only the treatment group received zinc supplementation within 48-72 hours after hospitalization.

RESULTS

The prevalence of zinc deficiency on admission was 76.0%. The low zinc level was most apparent in infants between 1 and 3 months of age. The serum zinc level increased in the zinc treatment group and returned to a normal level (median, 53.20 μmol/L) on day 12±2. There was no statistical difference in the pediatric critic illness score, lung injury score, length of hospital stay, and duration of mechanical ventilation between the zinc treatment group and control group.

CONCLUSION

Zinc deficiency is common in infants with severe pneumonia. Normalization of zinc levels with zinc supplementation did not improve clinical outcomes of infants with pneumonia.

Evaluation of the PaO2/FiO2 ratio after cardiac surgery as a predictor of outcome during hospital stay

BACKGROUND

The arterial partial pressure of O2 and the fraction of inspired oxygen (PaO2/FiO2) ratio is widely used in ICUs as an indicator of oxygenation status. Although cardiac surgery and ICU scores can predict mortality, during the first hours after cardiac surgery few instruments are available to assess outcome. The aim of this study was to evaluate the usefulness of PaO2/FIO2 ratio to predict mortality in patients immediately after cardiac surgery.

METHODS

We prospectively studied 2725 consecutive cardiac surgery patients between 2004 and 2009. PaO2/FiO2 ratio was measured on admission and at 3 h, 6 h, 12 h and 24 h after ICU admission, together with clinical data and outcomes.

RESULTS

All PaO2/FIO2 ratio measurements differed between survivors and non-survivors (p < 0.001). The PaO2/FIO2 at 3 h after ICU admission was the best predictor of mortality based on area under the curve (p < 0.001) and the optimum threshold estimation gave an optimal cut-off of 222 (95% Confidence interval (CI): 202-242), yielding three groups of patients: Group 1, with PaO2/FIO2 > 242; Group 2, with PaO2/FIO2 from 202 to 242; and Group 3, with PaO2/FIO2 < 202. Group 3 showed higher in-ICU mortality and ICU length of stay and Groups 2 and 3 also showed higher respiratory complication rates. The presence of a PaO2/FIO2 ratio < 202 at 3 h after admission was shown to be a predictor of in-ICU mortality (OR:1.364; 95% CI:1.212-1.625, p < 0.001) and of worse long-term survival (88.8% vs. 95.8%; Log rank p = 0.002. Adjusted Hazard ratio: 1.48; 95% CI:1.293-1.786; p = 0.004).

CONCLUSIONS

A simple determination of PaO2/FIO2 at 3 h after ICU admission may be useful to identify patients at risk immediately after cardiac surgery.

Molecular mechanisms of inflammation and tissue injury after major trauma--is complement the "bad guy"?

Trauma represents the leading cause of death among young people in industrialized countries. Recent clinical and experimental studies have brought increasing evidence for activation of the innate immune system in contributing to the pathogenesis of trauma-induced sequelae and adverse outcome. As the "first line of defense", the complement system represents a potent effector arm of innate immunity, and has been implicated in mediating the early posttraumatic inflammatory response. Despite its generic beneficial functions, including pathogen elimination and immediate response to danger signals, complement activation may exert detrimental effects after trauma, in terms of mounting an "innocent bystander" attack on host tissue. Posttraumatic ischemia/reperfusion injuries represent the classic entity of complement-mediated tissue damage, adding to the "antigenic load" by exacerbation of local and systemic inflammation and release of toxic mediators. These pathophysiological sequelae have been shown to sustain the systemic inflammatory response syndrome after major trauma, and can ultimately contribute to remote organ injury and death. Numerous experimental models have been designed in recent years with the aim of mimicking the inflammatory reaction after trauma and to allow the testing of new pharmacological approaches, including the emergent concept of site-targeted complement inhibition. The present review provides an overview on the current understanding of the cellular and molecular mechanisms of complement activation after major trauma, with an emphasis of emerging therapeutic concepts which may provide the rationale for a "bench-to-bedside" approach in the design of future pharmacological strategies.

Claudin-4 levels are associated with intact alveolar fluid clearance in human lungs

The removal of edema from the air spaces is a critical function of the alveolar barrier requiring intact tight junctions. Alveolar fluid clearance contributes to graft function after transplantation and is associated with survival in patients with acute lung injury. Claudin-4 concentrations are known to increase during lung injury and the loss of claudin-4 decreases alveolar fluid clearance in mice. This study was therefore undertaken to evaluate whether differences in lung expression of the tight junction protein claudin-4 are associated with alveolar fluid clearance or clinical measures of lung function. Alveolar fluid clearance rates were measured in ex vivo perfused human lungs not used for transplantation and were compared with histological lung injury and clinical measures of lung injury in the donors. Claudin-4 staining demonstrated a positive correlation with alveolar fluid clearance (Spearman rank correlation [r(s)] = 0.71; P < 0.003); however, claudin-4 staining was not strongly associated with histological measures of lung injury. The expression of other tight junction proteins (including ZO-1) was not associated with alveolar fluid clearance or claudin-4 levels. Claudin-4 staining was lower in lungs from donors with greater impairment in respiratory physiology. These data suggest that claudin-4 may promote alveolar fluid clearance and demonstrate that the amount of claudin-4 expressed may provide specific information regarding alveolar epithelial barrier function that strengthens the link between histological changes and physiological impairment.

[Relationship between PAO2/FIO2 and SATO2/FIO2 with mortality and duration of admission in critically ill children]

OBJECTIVES

The aim of this study is to analyse the relationships and the association between PaO(2)/FiO(2) and SatO(2)/FiO(2with) the duration of admission in Paediatric Intensive Care Units (PICU) and mortality, and to study the relationships between both ratios.

MATERIAL AND METHODS

A retrospective study was conducted on PICU patients in whom a gas analysis was performed in the first twenty-four hours of admission. Demographic, clinical and ventilation variables were collected, and the relationship between PaO(2)/FiO(2) and SatO(2)/FiO(2) with days of admission and mortality was determined. Finally, the best cut-off points of SatO(2)/FiO(2) were determined for PaO(2)/FiO(2) values greater and less than 200.

RESULTS

Of 512 patients admitted during one year, a gas analysis was performed on 358, 65% of those in arterial blood. The median duration of hospitalization was two days and there were 11 patient deaths. There was a low negative correlation between the values of PaO(2)/FiO(2) and SatO(2/)FiO(2) on admission to PICU and with duration of admission, and an inverse association with mortality (P<.01). This association was stronger for the PaO(2)/FiO(2) ratio in patients with heart disease, those undergoing invasive mechanical ventilation, and for arterial blood samples. PaO(2)/FiO(2) and SatO(2)/FiO(2) ratios were significantly correlated with each other. A cut-off of 200 for SatO(2)/FiO(2) had a sensitivity of 97.5% for classifying patients with PaO(2)/FiO(2) values lower or higher than 200.

CONCLUSIONS

PaO(2)/FiO(2) and SatO(2)/FiO(2) index are markers of severity in critically ill patients. In patients who do not have an arterial line, SatO(2)/FiO(2) index can be used for assessment of oxygenation as an indicator of severity in children in critical condition.

Association of dynamic changes in serum cytokine levels with the severity of injury in patients suffering from closed chest traumas complicated with pulmonary contusions

This study aimed to examine the dynamic changes in the serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-10 in patients suffering from closed chest injuries and concomitant pulmonary contusions and their correlation with the Thoracic Trauma Severity Score (TTS) and Injury Severity Score (ISS). Patients with multiple traumas with an ISS ≥16 (n=41) were evaluated in the study. Patients included 21 individuals with trauma complicated by pulmonary contusion and 20 patients with trauma without contusion. Venous blood samples were collected from the patients on days 1, 2, 3, 5 and 7 following trauma to assess serum levels of TNF-α, IL-6 and IL-10, whose correlation with TTS and ISS was analyzed. Levels of TNF-α, IL-6 and IL-10 remained significantly higher in the patients with trauma complicated by contusion compared to the patients with trauma without contusion (P<0.01). These three cytokines were positively correlated with TTS and ISS in the patients with trauma complicated by contusion. Serum TNF-α, IL-6 and IL-10 levels increased significantly in the patients with trauma complicated by pulmonary contusion. In conclusion, both cytokine assays and TTS facilitate the accurate assessment of the severity of chest injury.

Acute lung injury is an independent risk factor for brain hypoxia after severe traumatic brain injury

BACKGROUND

Pulmonary complications are frequently observed after severe traumatic brain injury (TBI), but little is known about the consequences of lung injury on brain tissue oxygenation and metabolism.

OBJECTIVE

We examined the association between lung function and brain tissue oxygen tension (PbtO2) in patients with severe TBI.

METHODS

We analyzed data from 78 patients with severe, nonpenetrating TBI who underwent continuous PbtO2 and intracranial pressure monitoring. Acute lung injury was defined by the presence of pulmonary infiltrates with a PaO2/FiO2 (PF) ratio less than 300 and the absence of left ventricular failure. A total of 587 simultaneous measurements of PbtO2 and PF ratio were examined using longitudinal data analysis.

RESULTS

PbtO2 correlated strongly with PaO2 and PF ratio (P < .05) independent of PaCO2, brain temperature, cerebral perfusion pressure, and hemoglobin. Acute lung injury was associated with lower PbtO2 (34.6 +/- 13.8 mm Hg at PF ratio >300 vs 30.2 +/- 10.8 mm Hg [PF ratio 200-300], 28.9 +/- 9.8 mm Hg [PF ratio 100-199], and 21.1 +/- 7.4 mm Hg [PF ratio <100], all P values <.01). After adjusting for intracranial pressure, Marshall computed tomography score, and APACHE II (Acute Physiology and Chronic Health Evaluation) score, acute lung injury was an independent risk factor for compromised PbtO2 (PbtO2 <20 mm Hg; adjusted odds ratio: 2.13, 95% confidence interval: 1.21-3.77; P < .01).

CONCLUSION

After severe TBI, PbtO2 correlates with PF ratio. Acute lung injury is associated with an increased risk of compromised PbtO2, independent from intracerebral and systemic injuries. Our findings support the use of lung-protective strategies to prevent brain hypoxia in TBI patients.

Clinical aspects and cytokine response in severe H1N1 influenza A virus infection

Introduction

The immune responses in patients with novel A(H1N1) virus infection (nvA(H1N1)) are incompletely characterized. We investigated the profile of Th1 and Th17 mediators and interferon-inducible protein-10 (IP-10) in groups with severe and mild nvA(H1N1) disease and correlated them with clinical aspects.

Methods

Thirty-two patients hospitalized with confirmed nvA(H1N1) infection were enrolled in the study: 21 patients with nvA(H1N1)-acute respiratory distress syndrome (ARDS) and 11 patients with mild disease. One group of 20 patients with bacterial sepsis-ARDS and another group of 15 healthy volunteers were added to compare their cytokine levels with pandemic influenza groups. In the nvA(H1N1)-ARDS group, the serum cytokine samples were obtained on admission and 3 days later. The clinical aspects were recorded prospectively.

Results

In the nvA(H1N1)-ARDS group, obesity and lymphocytopenia were more common and IP-10, interleukin (IL)-12, IL-15, tumor necrosis factor (TNF)α, IL-6, IL-8 and IL-9 were significantly increased versus control. When comparing mild with severe nvA(H1N1) groups, IL-6, IL-8, IL-15 and TNFα were significantly higher in the severe group. In nonsurvivors versus survivors, IL-6 and IL-15 were increased on admission and remained higher 3 days later. A positive correlation of IL-6, IL-8 and IL-15 levels with C-reactive protein and with > 5-day interval between symptom onset and admission, and a negative correlation with the PaO₂:FiO₂ ratio, were found in nvA(H1N1) groups. In obese patients with influenza disease, a significant increased level of IL-8 was found. When comparing viral ARDS with bacterial ARDS, the level of IL-8, IL-17 and TNFα was significantly higher in bacterial ARDS and IL-12 was increased only in viral ARDS.

Conclusions

In our critically ill patients with novel influenza A(H1N1) virus infection, the hallmarks of the severity of disease were IL-6, IL-15, IL-8 and TNFα. These cytokines, except TNFα, had a positive correlation with the admission delay and C-reactive protein, and a negative correlation with the PaO₂:FiO₂ ratio. Obese patients with nvA(H1N1) disease have a significant level of IL-8. There are significant differences in the level of cytokines when comparing viral ARDS with bacterial ARDS.

The impact of continuous lateral rotation therapy in overall clinical and financial outcomes of critically ill patients

BACKGROUND

Significant pulmonary complications are prevalent in intubated and mechanically ventilated patients.

OBJECTIVES

This study was conducted to determine the impact of continuous lateral rotation therapy (CLRT) on patients considered to be at high risk for pulmonary complications. Overall study objectives included hospital length of stay, critical care length of stay, ventilator days, and cost to treat.

METHODS

Patients at risk for pulmonary complications as defined by Pao2/Fio2 ratio < 300, Fio2 > 50% for more than 1 hour, positive end-expiratory pressure > or = 8, or a Predicus score of > or = 5 were compared with a historical comparison group that met the high-risk criteria given above and did not receive CLRT. Patients who received CLRT were separated into 2 groups, early CLRT group (began therapy within 48 hours, n = 49) or late CLRT group (n = 46).

RESULTS

The early CLRT group had a reduction in critical care LOS, (P = .04) as compared with the non-CLRT group. Total hospital costs were reduced (P = .01) in the early intervention group compared to the late intervention group, as well as ICU LOS (P = .02). Nonsignificant trends were seen in reduced ventilator days and hospital LOS. Reintubation rates and readmissions to critical care were also lower in the early intervention group.

CONCLUSIONS

Continuous lateral rotation therapy, when introduced early in course of treatment of high-risk patients, reduces critical care LOS and cost to treat.

Increased permeability-oedema and atelectasis in pulmonary dysfunction after trauma and surgery: a prospective cohort study

BACKGROUND

Trauma and surgery may be complicated by pulmonary dysfunction, acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), but the mechanisms are incompletely understood.

METHODS

We evaluated lung capillary protein permeability non-invasively with help of the 67Ga-transferrin pulmonary leak index (PLI) technique and extravascular lung water (EVLW) by the transpulmonary thermal-dye dilution technique in consecutive, mechanically ventilated patients in the intensive care unit within 24 h of direct, blunt thoracic trauma (n = 5, 2 with ARDS), and within 12 h of indirect trauma by transhiatal oesophagectomy (n = 8), abdominal surgery for cancer (n = 6) and bone surgery (n = 4). We studied transfusion history, haemodynamics, oxygenation and mechanics of the lungs. The lung injury score (LIS, 0-4) was calculated. Plain radiography was also done to judge densities and atelectasis.

RESULTS

The PLI and EVLW were elevated above normal in 61 and 30% of patients, respectively, and the PLI directly related to the number of red cell concentrates given (rs = 0.69, P < 0.001), without group differences. Oxygenation, lung mechanics, radiographic densities and thus the LIS (1.0 [0.25-3.5]) did not relate to PLI and EVLW. However, groups differed in oxygenation and airway pressures and impaired oxygenation related to the number of radiographic quadrants with densities (rs = 0.55, P = 0.007). Thoracic trauma patients had a worse oxygenation requiring higher airway pressures and thus higher LIS than the other patient groups, unrelated to PLI and EVLW but attributable to a higher cardiac output and thereby venous admixture. Finally, patients with radiographic signs of atelectasis had more impaired oxygenation and more densities than those without.

CONCLUSION

The oxygenation defect and radiographic densities in mechanically ventilated patients with pulmonary dysfunction and ALI/ARDS after trauma and surgery are likely caused by atelectasis rather than by increased permeability-oedema related to red cell transfusion.

[Mechanical ventilation induced lung injury]

Mechanical ventilation is associated with important complications, among which production or perpetuation of acute lung injury and product of distant organ injuries of the lung basically through the release of inflammatory mediators to the systemic circulation. There is increasingly greater evidence in both in vitro and in vivo experimental models that show the reality of this lesional mechanism. The main lesional mechanisms are both stretching and rupture of the lung structures (volutrauma) and cyclical opening and closure of the closed alveolar zones (atelectrauma). Studies on the use of protective lung ventilation strategies have shown a beneficial effect in patients with ARDS of the use of open lung ventilation strategies, use of circulating volumes less than 10 ml/kg and of maintaining alveolar pressure under 30 cm of H2O. It should be investigated if these same strategies would be useful in preventing the appearance of ARDS in mechanically ventilated patients for another reason, basically in those with risk factors for the development of this condition.

Indications, management, and outcome of long-term positive-pressure ventilation in dogs and cats: 148 cases (1990-2001)

OBJECTIVE

To determine outcome of positive-pressure ventilation (PPV) for 24 hours or longer and identify factors associated with successful weaning from PPV and survival to hospital discharge in dogs and cats.

DESIGN

Retrospective case series.

ANIMALS

124 dogs and 24 cats that received PPV for 24 hours or longer.

PROCEDURES

Medical records were reviewed for signalment, primary diagnosis, reason for initiating PPV, measures of oxygenation and ventilation before and during PPV, ventilator settings, complications, duration of PPV, and outcome. Animals were categorized into 1 of 3 groups on the basis of the reason for PPV.

RESULTS

Group 1 patients received PPV for inadequate oxygenation (67 dogs and 6 cats), group 2 for inadequate ventilation (46 dogs and 16 cats), and group 3 for inadequate oxygenation and ventilation (11 dogs and 2 cats). Of the group 1 animals, 36% (26/73) were weaned from PPV and 22% (16/73) survived to hospital discharge. In group 2, 50% (31/62) were weaned from PPV and 39% (24/62) survived to hospital discharge. In group 3, 3 of 13 were weaned from PPV and 1 of 13 survived to hospital discharge. Likelihood of successful weaning and survival to hospital discharge were significantly higher for group 2 animals, and cats had a significantly lower likelihood of successful weaning from PPV, compared with dogs. Median duration of PPV was 48 hours (range, 24 to 356 hours) and was not associated with outcome.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that long-term PPV is practical and successful in dogs and cats.

Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody TGN1412

Six healthy young male volunteers at a contract research organization were enrolled in the first phase 1 clinical trial of TGN1412, a novel superagonist anti-CD28 monoclonal antibody that directly stimulates T cells. Within 90 minutes after receiving a single intravenous dose of the drug, all six volunteers had a systemic inflammatory response characterized by a rapid induction of proinflammatory cytokines and accompanied by headache, myalgias, nausea, diarrhea, erythema, vasodilatation, and hypotension. Within 12 to 16 hours after infusion, they became critically ill, with pulmonary infiltrates and lung injury, renal failure, and disseminated intravascular coagulation. Severe and unexpected depletion of lymphocytes and monocytes occurred within 24 hours after infusion. All six patients were transferred to the care of the authors at an intensive care unit at a public hospital, where they received intensive cardiopulmonary support (including dialysis), high-dose methylprednisolone, and an anti-interleukin-2 receptor antagonist antibody. Prolonged cardiovascular shock and acute respiratory distress syndrome developed in two patients, who required intensive organ support for 8 and 16 days. Despite evidence of the multiple cytokine-release syndrome, all six patients survived. Documentation of the clinical course occurring over the 30 days after infusion offers insight into the systemic inflammatory response syndrome in the absence of contaminating pathogens, endotoxin, or underlying disease.

Underuse of lung protective ventilation: analysis of potential factors to explain physician behavior

OBJECTIVE

To determine the frequency of use of low-tidal-volume ventilation in appropriate patients with acute lung injury (ALI) and the factors associated with the choice of tidal volume.

DESIGN

Prospective observational cohort study of patients identified with ALI or acute respiratory distress syndrome from September 2000 to November 2002.

SETTING

Medical and surgical intensive care unit (ICU) at an academic tertiary-care hospital.

MEASUREMENTS AND MAIN RESULTS

Measurements included the proportion for whom the ventilation tidal volume (TV) was <or=7.5 mL/kg predicted body weight (PBW) on days 2, 4, and 7 of ALI and the proportion for whom the ventilation TV was <or=6.5 and <or=8.5 mL/kg/PBW (sensitivity analysis). Demographic and clinical characteristics of patients undergoing ventilation with low and high TV were compared. Of 88 total patients studied, 39% had ventilation with TV <or=7.5 mL/kg/PBW on day 2 of ALI, 49% on day 4, and 56% on day 7. In contrast, 49% of patients had ventilation with TV >8.5 mL/kg/PBW on day 2 of ALI, 30% on day 4, and 24% on day 7. The use of low TV was significantly associated with clinical parameters indicative of worse disease severity, including low values for Pao2 (p = .01), Pao2/Fio2 (p = .08), and static compliance of the respiratory system (p = .006).

CONCLUSIONS

Ventilation with a low TV was used in a minority of patients with ALI, despite results published in 1998 and 2000 supporting this approach. This may be related to clinicians' underrecognition of less severe cases of ALI, their reserving of low-TV ventilation for more severe cases, or both.

The role of the lung in postinjury multiple organ failure

BACKGROUND

Postinjury multiple organ failure (MOF) is a result of a dysfunctional inflammatory response to severe injury and shock. Acute lung injury is thought to promote further organ dysfunction by the systemic release of inflammatory mediators from injured lung tissue. Although clinical evidence supports this model, a clear understanding of the relationship between lung dysfunction and multiple organ failure has yet to be defined. We hypothesized that respiratory dysfunction is an early obligate event in the progression of postinjury MOF.

METHODS

Data were collected prospectively on 1,344 trauma patients at risk for postinjury MOF. Inclusion criteria were age greater than 16 years, trauma intensive care unit admission, Injury Severity Score greater than 15, and survival longer than 48 hours. Isolated head injuries and head injuries with an extracranial abbreviated injury score of less than 2 were excluded. Daily physiologic and laboratory data were collected through surgical intensive care unit day 28 and clinical events were recorded thereafter until death or hospital discharge. Organ failure was characterized using the Denver MOF scale.

RESULTS

Organ dysfunction was observed in 1,011 (75%) of 1,344 patients. Lung dysfunction was observed in 951 (94%) patients with 1 or more organ dysfunctions and 598 (99%) of 605 patients with 2 or more organ dysfunctions. Lung dysfunction preceded heart, liver, and kidney dysfunction by an average of 0.6 +/- 0.2 days, 4.8 +/- 0.2 days, and 5.5 +/- 0.5 days, respectively. The severity of lung dysfunction correlated with the severity of heart, liver, and kidney dysfunction, and the number of other dysfunctional organ systems.

CONCLUSIONS

Postinjury respiratory dysfunction is an obligate event that precedes heart, liver, and kidney failure. The severity of other organ dysfunction is related directly to the severity of respiratory dysfunction. These data implicate lung dysfunction as central to the promotion of pathogenic inflammation and the development of postinjury MOF.

Factors influencing the estimation of extravascular lung water by transpulmonary thermodilution in critically ill patients*

OBJECTIVE

To investigate factors that may influence the estimation of extravascular lung water (EVLW) with a single (cold) indicator compared with assessment using two indicators (thermo-dye dilution).

DESIGN

Post hoc analysis of an electronic hemodynamic database.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

Forty-eight critically ill patients monitored by the thermo-dye dilution technique in the postoperative period.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The EVLW was simultaneously assessed by the thermo-dye dilution technique (EVLWref) and estimated by transpulmonary thermodilution (EVLWest). EVLWref index ranged between 1 and 40 mL/kg (mean 10 +/- 7 mL/kg) and EVLWest between 2 and 39 mL/kg (mean 9 +/- 6 mL/kg). EVLWref was closely correlated (r = .96) with EVLWest. The mean difference (bias) between EVLWref and EVLWest was -0.5 +/- 1.9 mL/kg. The bias was not influenced by the weight, height, body surface area, body mass index, Pao2, intrathoracic blood volume, cardiac output, or dosage of vasoactive agents. In contrast, the bias was slightly but significantly influenced by EVLWref, Pao2/Fio2 ratio, tidal volume, and level of positive end-expiratory pressure.

CONCLUSIONS

In our surgical intensive care unit population, the estimation of EVLW by transpulmonary thermodilution was influenced by the amount of EVLW, the Pao2/Fio2 ratio, the tidal volume, and the level of positive end-expiratory pressure. However, compared with the double indicator method, transpulmonary thermodilution estimation remained clinically acceptable even in patients with severe lung disease.

Prognostic determinants of acute respiratory distress syndrome in adults: impact on clinical trial design

OBJECTIVE

The objective of this study was to review known clinical predictors and biologic markers of adverse clinical outcomes in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) that might be used as selection criteria in clinical trials of novel therapies for ALI/ARDS.

DATA SOURCE

Published studies on clinical predictors and biologic markers of adverse outcomes in ALI/ARDS.

MAIN RESULTS

In large epidemiologic studies, a number of clinical factors have been identified consistently as independent predictors of mortality in ALI/ARDS. These include age, comorbidities, including chronic liver disease and immunosuppression, severity of illness scores, and the degree of multisystem organ failure. Several biologic markers of mortality have also been identified in large studies, including von Willebrand factor antigen, surfactant protein D, protein C, plasminogen activator inhibitor-1, interleukins 6 and 8, and the TNF receptors. The Pao2/Fio2 ratio at the onset of ALI/ARDS does not predict clinical outcome but may be more useful after the first day of ALI/ARDS. A persistently low Pao2/Fio2 ratio is associated with worse outcomes and may be a marker of failure to respond to conventional therapy. Changes in IL-6, IL-8, TNF receptors, and SP-D over the first 3 days of ALI/ARDS are also associated with adverse clinical outcomes. The use of a combination of clinical factors and biologic markers is a promising strategy that needs to be prospectively validated.

CONCLUSIONS

The design of clinical trials for new therapies for ALI and ARDS is a complex problem that ultimately will have a major impact on both trial outcome and generalizability. A number of clinical factors and biologic markers can be used to differentiate groups of patients at highest risk for adverse clinical outcomes. Whether enriching study populations with these sicker patients will increase or decrease the likelihood of a treatment effect for a given therapy is unknown.

Erweitertes h�modynamisches Monitoring mithilfe der transpulmonalen Thermodilution

BACKGROUND

The transpulmonary thermal-dye dilution (TDD) is the clinical gold standard for measurement of intrathoracic blood volume (ITBV) and extravascular lung water (EVLW). Recently, experimental and clinical studies found that ITBV and EVLW can be derived reliably by single transpulmonary thermodilution (TD), however, dependency from various factors of lung function has been discussed.

PATIENTS AND METHODS

We retrospectively analyzed data from 174 critically ill patients who had undergone hemodynamic monitoring by TDD. We calculated the differences of simultaneous TD and TDD determined by ITBV or EVLW measurements. Bias and standard deviations (SD) were calculated and extended Bland-Altman regression analyses were performed. Association of the differences and the potential confounders gender, age, PEEP, p(a)O(2)/F(I)O(2) ratio and the corresponding TDD measurement were analyzed by multiple linear regression and LOWESS regression.

RESULTS

Overall results (bias+/-SD) were 1+/-58 ml/m(2) for ITBV and 0.0+/-1.4 ml/kg bw for EVLW, but TD overestimated TDD results in patients with higher ITBV and underestimated those for lower ITBV values. The deviations were small, and the dependence of ITBV could be explained completely by dependence on PEEP and age. However, low values of EVLW are overestimated by TD.

CONCLUSION

Single transpulmonary thermodilution for estimation of ITBV or EVLW is reliable in patients with severe lung injury for normal and higher values.

Overview of ventilator-induced lung injury mechanisms

PURPOSE OF REVIEW

Mechanical ventilation is the main supportive therapy for patients with acute respiratory distress syndrome. As with any therapy, mechanical ventilation has side effects and may induce lung injury. This review will focus on stretch-dependent activation of alveolar epithelial and endothelial cells and polymorphonuclear leukocytes, and apoptosis/necrosis balance.

RECENT FINDINGS

The past year has seen important research in the area of mechanotransduction and lung native immunity, suggesting further mechanisms of lung inflammation and injury in ventilator-induced lung injury. Research in the past year has also stressed the importance of inflammatory response by alveolar cells and role of polymorphonuclear leukocytes in stretch-induced lung injury and has suggested a role for apoptosis in the maintenance of the alveolar epithelium.

SUMMARY

The proportion of patients receiving protective ventilatory strategies remains modest. If efforts to minimize the iatrogenic consequences of mechanical ventilation are to succeed, there must be a greater understanding of the signal transduction mechanisms and the development of potential pharmacologic targets to modulate the molecular and cellular effects of lung stretch.

Diagnostic measures to evaluate oxygenation in critically ill adults: implications and limitations

Accurate assessment and treatment of disturbances in oxygenation are crucial to optimal outcomes in critically ill patients. Oxygenation is dependent upon adequate pulmonary gas exchange, oxygen delivery, and oxygen consumption. Each of these physiologic processes may vary independently in response to pathophysiologic conditions and therapeutic interventions. The author reviews diagnostic measures available to evaluate pulmonary gas exchange, oxygen delivery, and oxygen consumption in critically ill patients. Currently available tools and their potential value as well as key methodological limitations are addressed. Failure on behalf of clinicians to fully appreciate these limitations can lead to misdiagnoses and inappropriate treatment. The aim of this article is to help advanced practice nurses more fully understand the implications and limitations of these diagnostic measures to ensure accurate assessment and treatment of disturbances in oxygenation.

Mechanical Ventilation

Mechanical ventilation is the second most frequently performed therapeutic intervention after treatment for cardiac arrhythmias in intensive care units today. Countless lives have been saved with its use despite being associated with a greater than 30% in-hospital mortality rate. As life expectancies increase and people with chronic illnesses survive longer, artificial support with mechanical ventilation is also expected to rise. In one survey, over half of senior internal medicine residents reported their training on mechanical ventilation as inadequate, whereas the majority of critical care nurses reported having received no formal education on its use. Technological advances resulting in the availability of sleeker ventilators with graphic waveform displays and new modes of ventilation have challenged the bedside clinicians to incorporate this new data along with evidenced-based research into their daily practice. A review of current thoughts on mechanical ventilation and weaning is presented.