Michelle Biehl

Protective versus Conventional Ventilation for Surgery: A Systematic Review and Individual Patient Data Meta-analysis.

Background:Recent studies show that intraoperative mechanical ventilation using low tidal volumes (VT) can prevent postoperative pulmonary complications (PPCs). The aim of this individual patient data meta-analysis is to evaluate the individual associations between VT size and positive end–expiratory pressure (PEEP) level and occurrence of PPC. Methods:Randomized controlled trials comparing protective ventilation (low VT with or without high levels of PEEP) and conventional ventilation (high VT with low PEEP) in patients undergoing general surgery. The primary outcome was development of PPC. Predefined prognostic factors were tested using multivariate logistic regression. Results:Fifteen randomized controlled trials were included (2,127 patients). There were 97 cases of PPC in 1,118 patients (8.7%) assigned to protective ventilation and 148 cases in 1,009 patients (14.7%) assigned to conventional ventilation (adjusted relative risk, 0.64; 95% CI, 0.46 to 0.88; P < 0.01). There were 85 cases of PPC in 957 patients (8.9%) assigned to ventilation with low VT and high PEEP levels and 63 cases in 525 patients (12%) assigned to ventilation with low VT and low PEEP levels (adjusted relative risk, 0.93; 95% CI, 0.64 to 1.37; P = 0.72). A dose–response relationship was found between the appearance of PPC and VT size (R2 = 0.39) but not between the appearance of PPC and PEEP level (R2 = 0.08). Conclusions:These data support the beneficial effects of ventilation with use of low VT in patients undergoing surgery. Further trials are necessary to define the role of intraoperative higher PEEP to prevent PPC during nonopen abdominal surgery.

Lung-Protective Ventilation With Low Tidal Volumes and the Occurrence of Pulmonary Complications in Patients Without Acute Respiratory Distress Syndrome: A Systematic Review and Individual Patient Data Analysis.

Objective:Protective mechanical ventilation with low tidal volumes is standard of care for patients with acute respiratory distress syndrome. The aim of this individual patient data analysis was to determine the association between tidal volume and the occurrence of pulmonary complications in ICU patients without acute respiratory distress syndrome and the association between occurrence of pulmonary complications and outcome in these patients. Design:Individual patient data analysis. Patients:ICU patients not fulfilling the consensus criteria for acute respiratory distress syndrome at the onset of ventilation. Interventions:Mechanical ventilation with low tidal volume. Measurements and Main Results:The primary endpoint was development of a composite of acute respiratory distress syndrome and pneumonia during hospital stay. Based on the tertiles of tidal volume size in the first 2 days of ventilation, patients were assigned to a “low tidal volume group” (tidal volumes⩽ 7 mL/kg predicted body weight), an “intermediate tidal volume group” (> 7 and < 10 mL/kg predicted body weight), and a “high tidal volume group” (≥ 10 mL/kg predicted body weight). Seven investigations (2,184 patients) were included. Acute respiratory distress syndrome or pneumonia occurred in 23% of patients in the low tidal volume group, in 28% of patients in the intermediate tidal volume group, and in 31% of the patients in the high tidal volume group (adjusted odds ratio [low vs high tidal volume group], 0.72; 95% CI, 0.52–0.98; p = 0.042). Occurrence of pulmonary complications was associated with a lower number of ICU-free and hospital-free days and alive at day 28 (10.0 ± 10.9 vs 13.8 ± 11.6 d; p < 0.01 and 6.1 ± 8.1 vs 8.9 ± 9.4 d; p < 0.01) and an increased hospital mortality (49.5% vs 35.6%; p < 0.01). Conclusions:Ventilation with low tidal volumes is associated with a lower risk of development of pulmonary complications in patients without acute respiratory distress syndrome.

Ventilator-Induced Lung Injury: Minimizing Its Impact in Patients With or at Risk for ARDS

Ventilator-induced lung injury (VILI) results from injury to the blood-gas barrier caused by mechanical ventilation. The determinants of VILI are more complex than originally thought, and include the nature, duration, and intensity of the exposure, as well the pattern of initial insult to the lung. Lung-protective mechanical ventilation founded on these basic principles resulted in improved hospital and long-term mortality. The purpose of this review is to provide a comprehensive assessment of the pathogenesis of VILI and its determinants. We also discuss the best preventive approach in patients with or at risk for ARDS and critically appraise the most recent evidence, expert opinion, and implementation of the acquired knowledge to the bedside.

Epidemiology of noninvasive mechanical ventilation in acute respiratory failure - a retrospective population-based study

BackgroundNoninvasive mechanical ventilation (NIV) is a front-line therapy for the management of acute respiratory failure (ARF) in the intensive care units. However, the data on factors and outcomes associated with the use of NIV in ARF patients is lacking. Therefore, we aimed to determine the utilization of NIV for ARF in a population-based study.MethodsWe conducted a populated-based retrospective cohort study, where in all consecutively admitted adults (≥18 years) with ARF from Olmsted County, Rochester, MN, at the Mayo Clinic medical and surgical ICUs, during 2006 were included. Patients without research authorization or on chronic NIV use for sleep apnea were excluded.ResultsOut of 1461 Olmsted County adult residents admitted to the ICUs in 2006, 364 patients developed ARF, of which 146 patients were initiated on NIV. The median age in years was 75 (interquartile range, 60–84), 48% females and 88.7% Caucasians. Eighteen patients (12%) were on Continuous Positive Airway Pressure (CPAP) mode and 128 (88%) were on noninvasive intermittent positive-pressure ventilation (NIPPV) mode. Forty-six (10%) ARF patients were put on NIV for palliative strategy to alleviate dyspnea. Seventy-six ARF patients without treatment limitation were given a trial of NIV and 49 patients succeeded, while 27 had to be intubated. Mortality was similar between the patients initially supported with NIV versus invasive mechanical ventilation (33% vs 22%, P=0.289). In the multivariate analysis, the development of acute respiratory distress syndrome (ARDS) and higher APACHE III scores were associated with the failure of initial NIV treatment.ConclusionsOur results have important implications for a future planning of NIV in a suburban US community with high access to critical care services. The higher APACHE III scores and the development of ARDS are associated with the failure of initial NIV treatment.

Comparison of hospital mortality and long-term survival in patients with acute lung injury/ARDS vs cardiogenic pulmonary edema

BACKGROUND Early differential diagnosis of acute lung injury (ALI) vs cardiogenic pulmonary edema (CPE) is important for selecting the most appropriate therapy, but the prognostic implications of this distinction have not been studied. Accurate prognostic information is essential for providing appropriate informed consent prior to initiation of mechanical ventilation. METHODS This is a long-term follow-up study of a previously established population-based cohort of critically ill adult patients with acute pulmonary edema admitted at a tertiary-care center during 2006 to 2009, in which post hoc expert review had established ALI vs CPE diagnosis. Using logistic and Cox regression, hospital mortality and long-term survival were compared in patients with ALI vs patients with CPE. RESULTS Of 328 patients (ALI = 155, CPE = 173), 240 patients (73%) died during a median follow-up of 160 days. After adjusting for confounders, patients with ALI were significantly more likely to die in the hospital (OR = 4.2, 95% CI = 2.3-7.8, n = 325, P < .001), but among hospital survivors the risk of death during follow-up was the same in both groups (hazard ratio = 1.13, 95% CI = 0.79-1.62, n = 229, P = .50). Independent predictors of mortality included age and APACHE (Acute Physiology and Chronic Health Evaluation) III score. Results were similar when restricting patients with ALI to the subset with ARDS (Berlin definition). In post hoc analyses, the mortality rate in hospital survivors compared with the general US population was significantly higher during the first 2 years but essentially converged by year five. CONCLUSIONS Although hospital mortality is higher in patients with ALI/ARDS compared with patients with CPE, long-term survival is similar in hospital survivors from both groups.

Mild Cognitive Impairment and Risk of Critical Illness

Objectives:Approximately half of ICU admissions are comprised of patients older than 65 years old. Mild cognitive impairment is a common disorder affecting 10–20% of patients in the same age group. A need exists for exploring mild cognitive impairment and risk of critical illness. As mild cognitive impairment may be a contributor to poorer overall health or be a result of it, we sought to determine whether the presence of mild cognitive impairment independently increases the risk of critical illness admissions. Design:Data from the Mayo Clinic Study of Aging were analyzed. All study participants underwent prospective comprehensive cognitive testing and expert panel consensus diagnosis of both cognitive function and clinical state at baseline and subsequent visits. Comparisons were made between those with normal cognitive function and mild cognitive impairment regarding baseline health and frequency of critical illness. Setting:Single-center population-based cohort out of Olmsted County, MN. Participants:All individuals 70–89 years old were screened for prospective enrollment in the Mayo Clinic Study of Aging. Patients with preexisting dementia and ICU admission within 3 years of entry to the study were excluded from this analysis. Interventions:None. Measurements and Main Results:Of 2,425 patients analyzed from the Mayo Clinic Study of Aging, 1,734 patients (71%) were included in the current study. Clinical factors associated with baseline mild cognitive impairment included age, male gender, stroke, and poorer health self-rating. Using a Cox regression model adjusting for these and a priori variables of baseline health, the presence of mild cognitive impairment remained a significant predictor of ICU admission (hazard ratio, 1.50 [1.15–1.96]; p = 0.003). Conclusions and Relevance:The presence of mild cognitive impairment is independently associated with increased critical illness admission. Further prospective studies are needed to analyze the impact of critical illness on cognitive function.

Long-Term Return to Functional Baseline After Mechanical Ventilation in the ICU

Objective: Predictors of long-term functional impairment in acute respiratory failure of all causes are poorly understood. Our objective was to assess the frequency and predictors of long-term functional impairment or death after invasive mechanical ventilation for acute respiratory failure of all causes. Design: Population-based, observational cohort study. Setting: Eight adult ICUs of a single center. Patients: All adult patients from Olmsted County, Minnesota, without baseline functional impairment who received mechanical ventilation in ICUs for acute respiratory failure of all causes from 2005 through 2009. Interventions: None. Measurements and Main Results: In total, 743 patients without baseline functional impairment received mechanical ventilation in the ICU. At 1- and 5-year follow-up, the rates of survival with return to baseline functional ability were 61% (366/597) and 53% (356/669). Among 71 patients with new functional impairment at 1 year, 55% (39/71) had recovered and were alive without functional impairment at 5 years. Factors predictive of new functional impairment or death at 1 year were age, comorbidities, discharge to other than home, mechanical ventilation of 7 days or longer, and stroke. Of factors known at the time of intubation, the following are predictive of new functional impairment or death: age, comorbidities, nonsurgical condition, Acute Physiology and Chronic Health Evaluation III score, stroke, and sepsis. Post hoc sensitivity analyses revealed no significant change in predictor variables in patient populations when stroke was excluded or who received more than 48 hours of mechanical ventilation. Conclusions: At 1- and 5-year follow-up, many patients who received mechanical ventilation for acute respiratory failure from all causes are no longer alive or have new moderate-to-severe functional impairment. Functional recovery between year 1 and year 5 is possible and common. Sepsis, stroke, illness severity, age, and comorbidities predict long-term functional outcome at intubation.

Prediction of critical illness in elderly outpatients using elder risk assessment: a population-based study

Rationale Identifying patients at high risk of critical illness is necessary for the development and testing of strategies to prevent critical illness. The aim of this study was to determine the relationship between high elder risk assessment (ERA) score and critical illness requiring intensive care and to see if the ERA can be used as a prediction tool to identify elderly patients at the primary care visit who are at high risk of critical illness. Methods A population-based historical cohort study was conducted in elderly patients (age >65 years) identified at the time of primary care visit in Rochester, MN, USA. Predictors including age, previous hospital days, and comorbid health conditions were identified from routine administrative data available in the electronic medical record. The main outcome was critical illness, defined as sepsis, need for mechanical ventilation, or death within 2 years of initial visit. Patients with an ERA score of 16 were considered to be at high risk. The discrimination of the ERA score was assessed using area under the receiver operating characteristic curve. Results Of the 13,457 eligible patients, 9,872 gave consent for medical record review and had full information on intensive care unit utilization. The mean age was 75.8 years (standard deviation ±7.6 years), and 58% were female, 94% were Caucasian, 62% were married, and 13% were living in nursing homes. In the overall group, 417 patients (4.2%) suffered from critical illness. In the 1,134 patients with ERA >16, 154 (14%) suffered from critical illness. An ERA score ≥16 predicted critical illness (odds ratio 6.35; 95% confidence interval 3.51–11.48). The area under the receiver operating characteristic curve was 0.75, which indicated good discrimination. Conclusion A simple model based on easily obtainable administrative data predicted critical illness in the next 2 years in elderly outpatients with up to 14% of the highest risk population suffering from critical illness. This model can facilitate efficient enrollment of patients into clinical programs such as care transition programs and studies aimed at the prevention of critical illness. It also can serve as a reminder to initiate advance care planning for high-risk elderly patients. External validation of this tool in different populations may enhance its generalizability.

The Incremental Burden of Acute Respiratory Distress Syndrome: Long-term Follow-up of a Population-Based Nested Case-Control Study

Objective: To evaluate the long‐term survival of patients at similar risk for hospital‐acquired acute respiratory distress syndrome (ARDS) who did and did not develop ARDS. Methods: We conducted long‐term follow‐up of a population‐based nested case‐control study in a consecutive cohort of adult Olmsted County, Minnesota, patients admitted from January 1, 2001, through December 31, 2010. Patients in whom ARDS developed during their hospital stay (cases) were matched to similar‐risk patients without ARDS (controls) by 6 characteristics: age, sex, sepsis, high‐risk surgery, ratio of oxygen saturation to fraction of inspired oxygen, and ARDS risk according to the Lung Injury Prediction Score. Hospital mortality, discharge disposition, and long‐term survival were compared. Results: Patients who developed hospital‐acquired ARDS (n=400) had higher hospital mortality than at‐risk controls (n=400) (35% vs 5%; P<.001). Among hospital survivors (252 matched pairs), ARDS cases were more likely to be discharged to rehabilitation (13% vs 4%) and long‐term care (30% vs 15%) facilities, whereas more controls were discharged home (71% vs 41%). After discharge, differences in survival persisted beyond 90 days (adjusted hazard ratio [HR], 1.76; 95% CI, 1.2‐2.5; P=.002) and 6 months (adjusted HR, 1.73; 95% CI, 1.2‐2.6; P<.001). Conclusion: These results suggest that in a population‐based matched case‐control study of patients with similar characteristics at the time of hospital admission, those who developed hospital‐acquired ARDS had worse long‐term survival.

Interaction between peri-operative blood transfusion, tidal volume, airway pressure and postoperative ARDS: an individual patient data meta-analysis

Background Transfusion of blood products and mechanical ventilation with injurious settings are considered risk factors for postoperative lung injury in surgical Patients. Methods A systematic review and individual patient data meta-analysis was done to determine the independent effects of peri-operative transfusion of blood products, intra-operative tidal volume and airway pressure in adult patients undergoing mechanical ventilation for general surgery, as well as their interactions on the occurrence of postoperative acute respiratory distress syndrome (ARDS). Observational studies and randomized trials were identified by a systematic search of MEDLINE, CINAHL, Web of Science, and CENTRAL and screened for inclusion into a meta-analysis. Individual patient data were obtained from the corresponding authors. Patients were stratified according to whether they received transfusion in the peri-operative period [red blood cell concentrates (RBC) and/or fresh frozen plasma (FFP)], tidal volume size [≤7 mL/kg predicted body weight (PBW), 7-10 and >10 mL/kg PBW] and airway pressure level used during surgery (≤15, 15-20 and >20 cmH2O). The primary outcome was development of postoperative ARDS. Results Seventeen investigations were included (3,659 patients). Postoperative ARDS occurred in 40 (7.2%) patients who received at least one blood product compared to 40 patients (2.5%) who did not [adjusted hazard ratio (HR), 2.32; 95% confidence interval (CI), 1.25-4.33; P=0.008]. Incidence of postoperative ARDS was highest in patients ventilated with tidal volumes of >10 mL/kg PBW and having airway pressures of >20 cmH2O receiving both RBC and FFP, and lowest in patients ventilated with tidal volume of ≤7 mL/kg PBW and having airway pressures of ≤15 cmH2O with no transfusion. There was a significant interaction between transfusion and airway pressure level (P=0.002) on the risk of postoperative ARDS. Conclusions Peri-operative transfusion of blood products is associated with an increased risk of postoperative ARDS, which seems more dependent on airway pressure than tidal volume size.