Anne M. Drewry

Mechanisms of Cardiac and Renal Dysfunction in Patients Dying of Sepsis

RATIONALE The mechanistic basis for cardiac and renal dysfunction in sepsis is unknown. In particular, the degree and type of cell death is undefined. OBJECTIVES To evaluate the degree of sepsis-induced cardiomyocyte and renal tubular cell injury and death. METHODS Light and electron microscopy and immunohistochemical staining for markers of cellular injury and stress, including connexin-43 and kidney-injury-molecule-1 (Kim-1), were used in this study. MEASUREMENTS AND MAIN RESULTS Rapid postmortem cardiac and renal harvest was performed in 44 septic patients. Control hearts were obtained from 12 transplant and 13 brain-dead patients. Control kidneys were obtained from 20 trauma patients and eight patients with cancer. Immunohistochemistry demonstrated low levels of apoptotic cardiomyocytes (<1-2 cells per thousand) in septic and control subjects and revealed redistribution of connexin-43 to lateral membranes in sepsis (P < 0.020). Electron microscopy showed hydropic mitochondria only in septic specimens, whereas mitochondrial membrane injury and autophagolysosomes were present equally in control and septic specimens. Control kidneys appeared relatively normal by light microscopy; 3 of 20 specimens showed focal injury in approximately 1% of renal cortical tubules. Conversely, focal acute tubular injury was present in 78% of septic kidneys, occurring in 10.3 ± 9.5% and 32.3 ± 17.8% of corticomedullary-junction tubules by conventional light microscopy and Kim-1 immunostains, respectively (P < 0.01). Electron microscopy revealed increased tubular injury in sepsis, including hydropic mitochondria and increased autophagosomes. CONCLUSIONS Cell death is rare in sepsis-induced cardiac dysfunction, but cardiomyocyte injury occurs. Renal tubular injury is common in sepsis but presents focally; most renal tubular cells appear normal. The degree of cell injury and death does not account for severity of sepsis-induced organ dysfunction.

Sepsis Induces Apoptosis and Profound Depletion of Splenic Interdigitating and Follicular Dendritic Cells

Dendritic cells are a phenotypically diverse group of APC that have unique capabilities to regulate the activity and survival of B and T cells. Although proper function of dendritic cells is essential to host control of invading pathogens, few studies have examined the impact of sepsis on dendritic cells. The purpose of this study was to determine the effect of sepsis on splenic interdigitating dendritic cells (IDCs) and follicular dendritic cells (FDCs) using a clinically relevant animal model. Immunohistochemical staining for FDCs showed that sepsis induced an initial marked expansion in FDCs that peaked at 36 h after onset. The FDCs expanded to fill the entire lymphoid zone otherwise occupied by B cells. Between 36 and 48 h after sepsis, there was a profound caspase 3 mediated apoptosis induced depletion of FDCs such that only a small contingent of cells remained. In contrast to the initial increase in FDCs, IDC numbers were decreased to ∼50% of control by 12 h after onset of sepsis. IDC death occurred by caspase 3-mediated apoptosis. Such profound apoptosis induced loss of FDCs and IDCs may significantly compromise B and T cell function and impair the ability of the host to survive sepsis.

Persistent lymphopenia after diagnosis of sepsis predicts mortality.

ABSTRACT Objective: The objective of this study was to determine whether persistent lymphopenia on the fourth day following the diagnosis of sepsis predicts mortality. Methods: This was a single-center, retrospective cohort study of 335 adult patients with bacteremia and sepsis admitted to a large university-affiliated tertiary care hospital between January 1, 2010, and July 31, 2012. All complete blood cell count profiles during the first 4 days following the diagnosis of sepsis were recorded. The primary outcome was 28-day mortality. Secondary outcomes included development of secondary infections, 1-year mortality, and hospital and intensive care unit lengths of stay. Results: Seventy-six patients (22.7%) died within 28 days. Lymphopenia was present in 28-day survivors (median, 0.7 × 103 cells/&mgr;L; interquartile range [IQR], 0.4–1.1 × 103 cells/&mgr;L) and nonsurvivors (median, 0.6 × 103 cells/&mgr;L; IQR, 0.4–1.1 × 103 cells/&mgr;L) at the onset of sepsis and was not significantly different between the groups (P = 0.35). By day 4, the median absolute lymphocyte count was significantly higher in survivors compared with nonsurvivors (1.1 × 103 cells/&mgr;L [IQR, 0.7–1.5 × 103 cells/&mgr;L] vs. 0.7 × 103 cells/&mgr;L [IQR, 0.5–1.0 × 103 cells/&mgr;L]; P < 0.0001). Using logistic regression to account for potentially confounding factors (including age, Acute Physiology and Chronic Health Evaluation II score, comorbidities, surgical procedure during the study period, and time until appropriate antibiotic administration), day 4 absolute lymphocyte count was found to be independently associated with 28-day survival (adjusted odds ratio, 0.68 [95% confidence interval, 0.51–0.91]) and 1-year survival (adjusted odds ratio, 0.74 [95% confidence interval, 0.59–0.93]). Severe persistent lymphopenia (defined as an absolute lymphocyte count of 0.6 × 103 cells/&mgr;L or less on the fourth day after sepsis diagnosis) was associated with increased development of secondary infections (P = 0.04). Conclusions: Persistent lymphopenia on the fourth day following the diagnosis of sepsis predicts early and late mortality and may serve as a biomarker for sepsis-induced immunosuppression.

Lower tidal volume at initiation of mechanical ventilation may reduce progression to acute respiratory distress syndrome: a systematic review

IntroductionThe most appropriate tidal volume in patients without acute respiratory distress syndrome (ARDS) is controversial and has not been rigorously examined. Our objective was to determine whether a mechanical ventilation strategy using lower tidal volume is associated with a decreased incidence of progression to ARDS when compared with a higher tidal volume strategy.MethodsA systematic search of MEDLINE, EMBASE, CINAHL, the Cochrane Library, conference proceedings, and clinical trial registration was performed with a comprehensive strategy. Studies providing information on mechanically ventilated patients without ARDS at the time of initiation of mechanical ventilation, and in which tidal volume was independently studied as a predictor variable for outcome, were included. The primary outcome was progression to ARDS.ResultsThe search yielded 1,704 studies, of which 13 were included in the final analysis. One randomized controlled trial was found; the remaining 12 studies were observational. The patient cohorts were significantly heterogeneous in composition and baseline risk for developing ARDS; therefore, a meta-analysis of the data was not performed. The majority of the studies (n = 8) showed a decrease in progression to ARDS with a lower tidal volume strategy. ARDS developed early in the course of illness (5 hours to 3.7 days). The development of ARDS was associated with increased mortality, lengths of stay, mechanical ventilation duration, and nonpulmonary organ failure.ConclusionsIn mechanically ventilated patients without ARDS at the time of endotracheal intubation, the majority of data favors lower tidal volume to reduce progression to ARDS. However, due to significant heterogeneity in the data, no definitive recommendations can be made. Further randomized controlled trials examining the role of lower tidal volumes in patients without ARDS, controlling for ARDS risk, are needed.2013 Fuller et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

p53-Dependent and -Independent Pathways of Apoptotic Cell Death in Sepsis

Sepsis induces extensive apoptosis of lymphocytes, which may be responsible for the profound immune suppression of the disorder. Two potential pathways of sepsis-induced lymphocyte apoptosis, Fas and p53, were investigated. Lymphocyte apoptosis was evaluated 20–22 h after sepsis by annexin V or DNA nick-end labeling. Fas receptor-deficient mice had no protection against sepsis-induced apoptosis in thymocytes or splenocytes. p53 knockout mice (p53−/−) had complete protection against thymocyte apoptosis but, surprisingly, had no protection in splenocytes. p53−/− mice had no improvement in sepsis survival compared with appropriately matched control mice with sepsis. We conclude that both p53-dependent and p53-independent pathways of cell death exist in sepsis. This differential apoptotic response of thymocytes vs splenocytes in p53−/− mice suggests that either the cellular response or the death-inducing signal is cell-type specific in sepsis. The fact that p53−/− lymphocytes of an identical subtype (CD8−CD4+) were protected in thymi but not in spleens indicates that cell susceptibility to apoptosis differs depending upon other unidentified factors.

Frontline Science: Defects in immune function in patients with sepsis are associated with PD-1 or PD-L1 expression and can be restored by antibodies targeting PD-1 or PD-L1

Sepsis is a heterogeneous syndrome comprising a highly diverse and dynamic mixture of hyperinflammatory and compensatory anti‐inflammatory immune responses. This immune phenotypic diversity highlights the importance of proper patient selection for treatment with the immunomodulatory drugs that are entering clinical trials. To better understand the serial changes in immunity of critically ill patients and to evaluate the potential efficacy of blocking key inhibitory pathways in sepsis, we undertook a broad phenotypic and functional analysis of innate and acquired immunity in the same aliquot of blood from septic, critically ill nonseptic, and healthy donors. We also tested the ability of blocking the checkpoint inhibitors programmed death receptor‐1 (PD‐1) and its ligand (PD‐L1) to restore the function of innate and acquired immune cells. Neutrophil and monocyte function (phagocytosis, CD163, cytokine expression) were progressively diminished as sepsis persisted. An increasing frequency in PD‐L1+‐suppressor phenotype neutrophils [low‐density neutrophils (LDNs)] was also noted. PD‐L1+ LDNs and defective neutrophil function correlated with disease severity, consistent with the potential importance of suppressive neutrophil populations in sepsis. Reduced neutrophil and monocyte function correlated both with their own PD‐L1 expression and with PD‐1 expression on CD8+ T cells and NK cells. Conversely, reduced CD8+ T cell and NK cell functions (IFN‐γ production, granzyme B, and CD107a expression) correlated with elevated PD‐L1+ LDNs. Importantly, addition of antibodies against PD‐1 or PD‐L1 restored function in neutrophil, monocyte, T cells, and NK cells, underlining the impact of the PD‐1:PD‐L1 axis in sepsis‐immune suppression and the ability to treat multiple deficits with a single immunomodulatory agent.

The presence of hypothermia within 24 hours of sepsis diagnosis predicts persistent lymphopenia.

Objective:To determine whether hypothermia within 24 hours of sepsis diagnosis is associated with development of persistent lymphopenia, a feature of sepsis-induced immunosuppression. Design:Retrospective cohort study. Setting:A 1,200-bed university-affiliated tertiary care hospital. Patients:Adult patients diagnosed with bacteremia and sepsis within 5 days of hospital admission between January 1, 2010, and July 31, 2012. Interventions:None. Measurements and Main Results:Leukocyte counts were recorded during the first 4 days following sepsis diagnosis. Persistent lymphopenia was defined as an absolute lymphocyte count less than 1.2 cells/&mgr;L × 103 present on the fourth day after diagnosis. Of the 445 patients with sepsis included, hypothermia developed in 64 patients (14.4%) (defined as a body temperature < 36.0°C) within 24 hours of sepsis diagnosis. Hypothermia was a significant independent predictor of persistent lymphopenia (adjusted odds ratio, 2.70 [95% CI, 1.10, 6.60]; p = 0.03) after accounting for age, disease severity, comorbidities, source of bacteremia, and type of organism. Compared with the nonhypothermic patients, hypothermic patients had higher 28-day (50.0% vs 24.9%, p < 0.001) and 1-year mortality (60.9% vs 47.0%, p = 0.001). Conclusions:Hypothermia is associated with higher mortality and an increased risk of persistent lymphopenia in patients with sepsis, and it may be an early clinical predictor of sepsis-induced immunosuppression.

Body temperature patterns as a predictor of hospital-acquired sepsis in afebrile adult intensive care unit patients: a case-control study.

IntroductionEarly treatment of sepsis improves survival, but early diagnosis of hospital-acquired sepsis, especially in critically ill patients, is challenging. Evidence suggests that subtle changes in body temperature patterns may be an early indicator of sepsis, but data is limited. The aim of this study was to examine whether abnormal body temperature patterns, as identified by visual examination, could predict the subsequent diagnosis of sepsis in afebrile critically ill patients.MethodsRetrospective case-control study of 32 septic and 29 non-septic patients in an adult medical and surgical ICU. Temperature curves for the period starting 72 hours and ending 8 hours prior to the clinical suspicion of sepsis (for septic patients) and for the 72-hour period prior to discharge from the ICU (for non-septic patients) were rated as normal or abnormal by seven blinded physicians. Multivariable logistic regression was used to compare groups in regard to maximum temperature, minimum temperature, greatest change in temperature in any 24-hour period, and whether the majority of evaluators rated the curve to be abnormal.ResultsBaseline characteristics of the groups were similar except the septic group had more trauma patients (31.3% vs. 6.9%, p = .02) and more patients requiring mechanical ventilation (75.0% vs. 41.4%, p = .008). Multivariable logistic regression to control for baseline differences demonstrated that septic patients had significantly larger temperature deviations in any 24-hour period compared to control patients (1.5°C vs. 1.1°C, p = .02). An abnormal temperature pattern was noted by a majority of the evaluators in 22 (68.8%) septic patients and 7 (24.1%) control patients (adjusted OR 4.43, p = .017). This resulted in a sensitivity of 0.69 (95% CI [confidence interval] 0.50, 0.83) and specificity of 0.76 (95% CI 0.56, 0.89) of abnormal temperature curves to predict sepsis. The median time from the temperature plot to the first culture was 9.40 hours (IQR [inter-quartile range] 8.00, 18.20) and to the first dose of antibiotics was 16.90 hours (IQR 8.35, 34.20).ConclusionsAbnormal body temperature curves were predictive of the diagnosis of sepsis in afebrile critically ill patients. Analysis of temperature patterns, rather than absolute values, may facilitate decreased time to antimicrobial therapy.

Lung-Protective Ventilation Initiated in the Emergency Department (LOV-ED): A Quasi-Experimental, Before-After Trial

Study objective: We evaluated the efficacy of an emergency department (ED)–based lung‐protective mechanical ventilation protocol for the prevention of pulmonary complications. Methods: This was a quasi‐experimental, before‐after study that consisted of a preintervention period, a run‐in period of approximately 6 months, and a prospective intervention period. The intervention was a multifaceted ED‐based mechanical ventilator protocol targeting lung‐protective tidal volume, appropriate setting of positive end‐expiratory pressure, rapid oxygen weaning, and head‐of‐bed elevation. A propensity score–matched analysis was used to evaluate the primary outcome, which was the composite incidence of acute respiratory distress syndrome and ventilator‐associated conditions. Results: A total of 1,192 patients in the preintervention group and 513 patients in the intervention group were included. Lung‐protective ventilation increased by 48.4% in the intervention group. In the propensity score–matched analysis (n=490 in each group), the primary outcome occurred in 71 patients (14.5%) in the preintervention group compared with 36 patients (7.4%) in the intervention group (adjusted odds ratio 0.47; 95% confidence interval [CI] 0.31 to 0.71). There was an increase in ventilator‐free days (mean difference 3.7; 95% CI 2.3 to 5.1), ICU‐free days (mean difference 2.4; 95% CI 1.0 to 3.7), and hospital‐free days (mean difference 2.4; 95% CI 1.2 to 3.6) associated with the intervention. The mortality rate was 34.1% in the preintervention group and 19.6% in the intervention group (adjusted odds ratio 0.47; 95% CI 0.35 to 0.63). Conclusion: Implementing a mechanical ventilator protocol in the ED is feasible and is associated with significant improvements in the delivery of safe mechanical ventilation and clinical outcome.

A Quasi-experimental, Before-after Trial Examining the Impact of an Emergency Department Mechanical Ventilator Protocol on Clinical Outcomes and Lung-protective Ventilation in Acute Respiratory Distress Syndrome

Objectives: To evaluate the impact of an emergency department mechanical ventilation protocol on clinical outcomes and adherence to lung-protective ventilation in patients with acute respiratory distress syndrome. Design: Quasi-experimental, before-after trial. Setting: Emergency department and ICUs of an academic center. Patients: Mechanically ventilated emergency department patients experiencing acute respiratory distress syndrome while in the emergency department or after admission to the ICU. Interventions: An emergency department ventilator protocol which targeted variables in need of quality improvement, as identified by prior work: 1) lung-protective tidal volume, 2) appropriate setting of positive end-expiratory pressure, 3) oxygen weaning, and 4) head-of-bed elevation. Measurements and Main Results: A total of 229 patients (186 preintervention group, 43 intervention group) were studied. In the emergency department, the intervention was associated with significant changes (p < 0.01 for all) in tidal volume, positive end-expiratory pressure, respiratory rate, oxygen administration, and head-of-bed elevation. There was a reduction in emergency department tidal volume from 8.1 mL/kg predicted body weight (7.0–9.1) to 6.4 mL/kg predicted body weight (6.1–6.7) and an increase in lung-protective ventilation from 11.1% to 61.5%, p value of less than 0.01. The intervention was associated with a reduction in mortality from 54.8% to 39.5% (odds ratio, 0.38; 95% CI, 0.17–0.83; p = 0.02) and a 3.9 day increase in ventilator-free days, p value equals to 0.01. Conclusions: This before-after study of mechanically ventilated patients with acute respiratory distress syndrome demonstrates that implementing a mechanical ventilator protocol in the emergency department is feasible and associated with improved clinical outcomes.