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Biomedical subjects
Neil R MacIntyre
Publications and source records attributed to Neil R MacIntyre.
Corticosteroid therapy and chronic obstructive pulmonary disease.
Chronic obstructive pulmonary disease is characterized in part by a chronic inflammatory state in the airways (largely from chronic noxious stimuli such as tobacco smoke), punctuated with acute inflammatory exacerbations, which are often infectious. Although pathologically and biochemically different from the inflammation of asthma, the chronic inflammation of chronic obstructive pulmonary disease, especially in subgroups with asthma-like features and especially during exacerbations, might be expected to respond to corticosteroid therapy, as does asthma. Complications from long-term corticosteroid use are important, but they appear less when the corticosteroid is given via the inhaled route. Clinical evidence is particularly strong supporting the use of inhaled corticosteroids to prevent exacerbations and oral corticosteroids to reduce the duration and impact of exacerbations.
Adrenal Cortex Hormones↗
Muscle dysfunction associated with chronic obstructive pulmonary disease.
Skeletal-muscle (both respiratory and limb) abnormalities are common and can have profound effects in patients with chronic inflammatory states such as chronic obstructive pulmonary disease (COPD). Causes include direct inflammatory-mediator effects on muscle function, malnutrition, blood-gas abnormalities, compromised oxygen delivery from right-heart dysfunction, electrolyte imbalances, drugs, and comorbid states. In COPD patients, respiratory muscles are overloaded, which leads to increased fatigue potential, especially during exercise, when hyperinflation worsens. Interestingly, overloaded respiratory muscles develop structural changes that help them adapt to these conditions. In contrast, limb (especially lower extremity) muscles in COPD patients are underloaded as a consequence of disuse, and this leads to muscle atrophy. Treatment is aimed at optimizing lung function, nutritional repletion, aerobic exercise training, and (in certain patients) oxygen therapy. Resistive breathing training is more controversial. Lung-volume-reduction surgery may help with the hyperinflation effects and improve gas exchange and respiratory-muscle function in selected patients.
Breathing Exercises↗
Exercise outcomes after pulmonary rehabilitation depend on the initial mechanism of exercise limitation among non-oxygen-dependent COPD patients.
STUDY OBJECTIVES: Pulmonary rehabilitation (PR) that includes exercise training can improve exercise tolerance and quality of life for patients with COPD. However, the degree of benefit from PR is variable. We hypothesized that the exercise response to PR varies depending on the initial factors that limit exercise. DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS: We retrospectively analyzed the change in exercise capacity after PR in 290 nonhypoxemic patients with COPD. We classified patients into the following subgroups based on the primary limitation seen on initial exercise testing: (1) ventilatory-limited (VL); (2) cardiovascular-limited (CVL); (3) mixed ventilatory/cardiovascular-limited (VLCVL); and (4) non-cardiopulmonary-limited (NL). We compared outcomes among subgroups. RESULTS: In the entire study population, PR led to increased timed walk distance (30.3%; p < 0.0001) and maximal oxygen consumption (VO2max) [84.8 mL/min; p < 0.0001]. Stepwise multiple regression selected age, ventilatory reserve at peak exercise, and exercise arterial oxygen pressure as individual predictors of improvement in VO2max. VO2max increased in the VL subgroup (30.4 mL/min; p = 0.008), the CVL subgroup (109.0 mL/min; p < 0.0001), the mixed VLCVL subgroup (61.3 mL/min; p < 0.0001), and NL subgroups (110.5 L/min; p < 0.0001). The improvement in VO2max was greater in the CVL subgroup than in the VL subgroup (p < 0.0001). Timed walk distance improved to a similar degree in all subgroups (26 to 36%). CONCLUSIONS: Patients with nonventilatory exercise limitations experience the greatest increase in VO2max after PR. However, even patients with severe ventilatory limitation can improve exercise tolerance with PR.
Aged↗
A descriptive evaluation of transfusion practices in patients receiving mechanical ventilation.
STUDY OBJECTIVES: To characterize and compare transfusion practices in a broad sample of patients receiving mechanical ventilation (MV) and not receiving MV in the ICU. DESIGN: Retrospective subgroup analysis from the prospective, multicenter, observational CRIT study. SETTING: Two hundred eighty-four medical, surgical, or medical/surgical ICUs. PATIENTS: Critically ill adults. MAIN RESULTS: Of the 4,892 patients enrolled in the CRIT study, 60% were receiving MV on ICU admission or within 48 h after admission for a median of 4 days. Patients receiving MV had higher baseline APACHE (acute physiology and chronic health evaluation) II scores than patients not receiving MV (22.8 +/- 7.8 and 14.9 +/- 6.4, respectively [mean +/- SD]; p < 0.0001). Despite similar baseline hemoglobin levels (11.0 +/- 2.3 g/dL and 10.9 +/- 2.5 g/dL, p = 0.17), more patients receiving MV underwent transfusions (49% vs 33%, p < 0.0001), and they received significantly more RBCs than patients not receiving MV (p < 0.0001). The principal reason for transfusion in both groups was low hemoglobin level (78.4% and 84.6%, respectively); however, patients receiving MV had higher pretransfusion hemoglobin levels (8.7 +/- 1.7 g/dL) than patients not receiving MV (8.2 +/- 1.7 g/dL, p < 0.0001). Notably, 40.1% of all transfusions in patients receiving MV were administered after day 3 of the ICU stay, compared to 21.2% in patients not receiving MV (p < 0.0001), and a higher percentage of patients receiving MV remaining in the ICU after day 3 underwent transfusions (33.4% vs 18.3%, p < 0.0001). Mortality was higher (17.2% vs 4.5%, p < 0.0001) and mean hospital (15 days vs 10 days, p < 0.0001) and ICU stays (9 days vs 4 days, p < 0.0001) were longer in the subgroup receiving MV. CONCLUSIONS: Mechanical ventilation appears to be an easily identifiable early marker for allogeneic blood exposure risk in ICU patients. While the longer ICU stays account for much of this risk, patients receiving MV also appear to undergo transfusions at higher hemoglobin thresholds than patients not receiving MV, at least early in the ICU stay. Justification of this relatively liberal transfusion practice in patients receiving MV will require further study.
APACHE↗
Current issues in mechanical ventilation for respiratory failure.
The morbidity and mortality associated with respiratory failure is, to a certain extent, iatrogenic. Mechanical ventilation, although the mainstay of treatment for respiratory distress syndrome, can result in physical trauma to lung tissue (ventilator-induced lung injury [VILI]). Strategies to alleviate VILI are often termed lung-protective strategies and are aimed at reducing overstretching and shear stresses associated with repetitive alveolar collapse and reopening. Lower tidal volumes during ventilation, maintenance of positive-end expiratory pressure, and high-frequency ventilation are the best-studied lung-protective strategies that appear to reduce VILI. Faster withdrawal from mechanical ventilation could also improve outcomes and lower the costs associated with care. To enhance the success of weaning from mechanical ventilation, the cooperative efforts of physicians and respiratory therapists are needed. These efforts involve the initiation of spontaneous-breathing trials, implementation of systematic weaning protocols, and optimization of individual patient interventions.
Animals↗
Management of patients requiring prolonged mechanical ventilation: report of a NAMDRC consensus conference.
Patients requiring prolonged mechanical ventilation (PMV) are rapidly increasing in number, as improved ICU care has resulted in many patients surviving acute respiratory failure only to then require prolonged mechanical ventilatory assistance during convalescence. This patient population has clearly different needs and resource consumption patterns than patients in acute ICUs, and specialized venues, management strategies, and reimbursement schemes for them are rapidly emerging. To address these issues in a comprehensive way, a conference on the epidemiology, care, and overall management of patients requiring PMV was held. The goal was to not only review existing practices but to also develop recommendations on a variety of assessment, management, and reimbursement issues associated with patients requiring PMV. Formal presentations were made on a variety of topics, and writing groups were formed to address three specific areas: epidemiology and outcomes, management and care settings, and reimbursement. Each group was charged with summarizing current data and practice along with formulation of recommendations. A working draft of the products of these three groups was then created and circulated among all participants. The document was reworked with input from all concerned until a final product with consensus recommendations on 12 specific issues was achieved.
Chronic Disease↗
Respiratory mechanics in the patient who is weaning from the ventilator.
Ventilator management of the patient recovering from acute respiratory failure must balance competing objectives. On the one hand, aggressive efforts to promptly discontinue support and remove the artificial airway reduce the risk of ventilator-induced lung injury, nosocomial pneumonia, airway trauma from the endotracheal tube, and unnecessary sedation. On the other hand, overly aggressive, premature discontinuation of ventilatory support or removal of the artificial airway can precipitate ventilatory muscle fatigue, gas-exchange failure, and loss of airway protection. To help clinicians balance these concerns, 2 important research projects were undertaken in 1999-2001. The first was a comprehensive evidence-based literature review of the ventilator-discontinuation process, performed by the McMaster University research group on evidence-based medicine. The second was the development (by the American Association for Respiratory Care, American College of Chest Physicians, and Society of Critical Care Medicine) of a set of evidence-based guidelines based on the latter literature review. From those 2 projects, several themes emerged. First, frequent patient-assessment is required to determine whether the patient needs continued ventilatory support, from both the ventilator and the artificial airway. Second, we should continuously re-evaluate the overall medical management of patients who continue to require ventilatory support, to assure that we address all factors contributing to ventilator-dependence. Third, ventilatory support strategies should be aimed at maximizing patient comfort and unloading the respiratory muscles. Fourth, patients who require prolonged ventilatory support beyond the intensive care unit should go to specialized facilities that can provide gradual reduction of support. Fifth, many of these management objectives can be effectively carried out with protocols executed by nonphysicians.
Data Display↗
Ventilator-associated pneumonia: the role of ventilator management strategies.
Ventilator management strategies can affect the risk for ventilator-associated pneumonia in 3 ways: the development of ventilator-induced lung injury; the need for potentially harmful tradeoffs in providing lung-protective ventilatory strategies; and the prolongation of the duration of mechanical ventilation from iatrogenic factors. Strategies to reduce ventilator-induced lung injury include a smaller tidal volume and careful attention to reducing the maximum pressures in the lung. These lung-protective strategies, however, may require tradeoffs with factors that may in themselves produce risks for ventilator-associated pneumonia. Specifically, hypercapnia, discomfort requiring sedation, and atelectasis may all be potential problems with a lung-protective strategy. However, the weight of evidence suggests that beneficial outcomes from lung-protective strategies outweigh any potential harm from these tradeoffs. Finally, properly performed weaning protocols based on clinical evidence should reduce any iatrogenic delays in ventilator weaning and thereby minimize prolongation of unneeded mechanical ventilatory support.
Humans↗
Setting the positive expiratory-end pressure-FIO2 in acute lung injury/acute respiratory distress syndrome.
Airspace collapse is a hallmark of parenchymal lung injury. Strategies to reopen and maintain patency of these regions offer three advantages: improved gas exchange, less ventilator-induced lung injury, and improved lung compliance. Elevations in intrathoracic pressure to achieve these goals, however, may overdistend healthier lung regions and compromise cardiac function. Positive end-expiratory pressure is a widely used technique to maintain alveolar patency, but its beneficial effects must be balanced against its harmful effects. Mechanical approaches to achieve this balance are clinically difficult to do. Thus gas exchange algorithms with modest PaO2 goals are commonly used today. Recruitment maneuvers and long inspiratory time strategies may be useful adjuncts.
Algorithms↗
The "best" tidal volume for managing acute lung injury/acute respiratory distress syndrome.
An inappropriate tidal volume setting can overstretch and injure the lung. Maximal stretch, tidal stretch, frequency of stretch, and rate of stretch are all implicated in such injury. Moreover, the stretch injury produces systemic injury by liberating cytokines and translocating bacteria in the lung. Clinical trials have shown that limiting maximal and tidal stretch improves outcomes, even if gas exchange is partially compromised. Current strategies should focus on limiting tidal and maximal stretch as much as possible.
Animals↗
The CRIT Study: Anemia and blood transfusion in the critically ill--current clinical practice in the United States.
OBJECTIVE: To quantify the incidence of anemia and red blood cell (RBC) transfusion practice in critically ill patients and to examine the relationship of anemia and RBC transfusion to clinical outcomes. DESIGN: Prospective, multiple center, observational cohort study of intensive care unit (ICU) patients in the United States. Enrollment period was from August 2000 to April 2001. Patients were enrolled within 48 hrs of ICU admission. Patient follow-up was for 30 days, hospital discharge, or death, whichever occurred first. SETTING: A total of 284 ICUs (medical, surgical, or medical-surgical) in 213 hospitals participated in the study. PATIENTS: A total of 4,892 patients were enrolled in the study. MEASUREMENTS AND MAIN RESULTS: The mean hemoglobin level at baseline was 11.0 +/- 2.4 g/dL. Hemoglobin level decreased throughout the duration of the study. Overall, 44% of patients received one or more RBC units while in the ICU (mean, 4.6 +/- 4.9 units). The mean pretransfusion hemoglobin was 8.6 +/- 1.7 g/dL. The mean time to first ICU transfusion was 2.3 +/- 3.7 days. More RBC transfusions were given in study week 1; however, in subsequent weeks, subjects received one to two RBC units per week while in the ICU. The number of RBC transfusions a patient received during the study was independently associated with longer ICU and hospital lengths of stay and an increase in mortality. Patients who received transfusions also had more total complications and were more likely to experience a complication. Baseline hemoglobin was related to the number of RBC transfusions, but it was not an independent predictor of length of stay or mortality. However, a nadir hemoglobin level of <9 g/dL was a predictor of increased mortality and length of stay. CONCLUSIONS: Anemia is common in the critically ill and results in a large number of RBC transfusions. Transfusion practice has changed little during the past decade. The number of RBC units transfused is an independent predictor of worse clinical outcome.
Adult↗
Chronic obstructive pulmonary disease: emerging medical therapies.
As many as 10 million Americans have chronic obstructive pulmonary disease and as a consequence experience disabling symptoms, high cost of care, and substantial mortality. Several new approaches are being investigated for possible benefit in managing (or even reversing) chronic obstructive pulmonary disease. This article reviews 4 new approaches that are either in or close to phase III trials: long-acting bronchodilators, phosphodiesterase-4 inhibitors, vasodilators, and retinoids. Of those tiotropium appears to be the closest to receiving clinical approval in the United States. The risk/benefit ratio and the cost-effectiveness of the other compounds are less clear and await additional study.
Animals↗
Respiratory system simulations and modeling.
Simulators and models of the respiratory system range from simple mechanical devices to complex systems that include sophisticated computers. These systems have considerable utility in clinician education, guiding therapies, evaluating new devices and techniques, and in improving our understanding of the cardiorespiratory system. Simulators and models are of 3 types: signs-and-symptoms simulators, anatomic models, and physiologic models. Signs-and-symptoms simulators range from human actors to computer-controlled patient mannequins. Clinical scenarios, from minor abnormalities to catastrophic emergencies, can be simulated. As has been found with aircraft cockpit simulators, improved clinician performance in simulated emergencies should translate into improved performance in real patient-care situations. Anatomic modeling can simulate basic anatomy for training clinicians. Three-dimensional reconstruction of the airways, using real patient data, can help to plan therapy, understand the disease process, and warn of safety issues. Anatomic modeling with radiographs and magnetic resonance images, sometimes created using radiolabeled tracer gases, can create 3-dimensional images of regional lung anatomy and function. Physiologic signals such as carbon dioxide production, oxygen consumption, and washout/washin of various tracer gases can be used to model ventilation-perfusion and ventilation-volume relationships, and those models can improve understanding of disease processes and guide therapies.
Computer Graphics↗
The American Association for Respiratory Care and the National Lung Health Education Program: assuring quality in spirometry.
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Education, Professional↗
Evidence-based ventilator weaning and discontinuation.
Ventilator management of a patient who is recovering from acute respiratory failure must balance competing objectives. Discontinuing mechanical ventilation and removing the artificial airway as soon as possible reduces the risk of ventilator-induced lung injury, nosocomial pneumonia, airway trauma from the endotracheal tube, and unnecessary sedation, but premature ventilator-discontinuation or extubation can cause ventilatory muscle fatigue, gas exchange failure, and loss of airway protection. In 1999 the McMaster University Outcomes Research Unit conducted a comprehensive evidence-based review of the literature on ventilator-discontinuation. Using that literature review, the American College of Chest Physicians, the Society of Critical Care Medicine, and the American Association for Respiratory Care created evidence-based guidelines, which include the following principles: 1. Frequent assessment is required to determine whether ventilatory support and the artificial airway are still needed. 2. Patients who continue to require support should be continually re-evaluated to assure that all factors contributing to ventilator dependence are addressed. 3. With patients who continue to require support, the support strategy should maximize patient comfort and provide muscle unloading. 4. Patients who require prolonged ventilatory support beyond the intensive care unit should go to specialized facilities that can provide more gradual support reduction strategies. 5. Ventilator-discontinuation and weaning protocols can be effectively carried out by nonphysician clinicians.
Evidence-Based Medicine↗
Cognitive and psychological outcomes of exercise in a 1-year follow-up study of patients with chronic obstructive pulmonary disease.
This study evaluated outcomes of self-directed exercise activity on cognitive functioning and psychological well-being among 28 adults with chronic obstructive pulmonary disease (COPD). Participants had completed an intensive 10-week program of exercise training and were given an exercise prescription to follow. One year later, participants completed comprehensive assessments of physical, cognitive, and psychological functioning. At follow-up, 39% (n=11) had continued with a regular program of moderate intensity exercise. Repeated measures analysis of variance indicated that exercise adherent participants maintained gains they had achieved in the initial exercise intervention, but nonexercise participants experienced declines in functional capacity, cognitive performance, and psychological well-being. Continued exercise among patients with COPD is associated with maintenance of physical, cognitive, and psychological functioning.
Aged↗
Pulmonary function testing: coding and billing issues.
Clinicians who conduct pulmonary function tests should understand the principles and rules of the coding and billing system for pulmonary function testing. Certain billing codes will not be paid by most insurance payers. To ensure that your pulmonary function tests are appropriately coded, billed, and paid: (1) obtain a Current Procedural Terminology (CPT) coding book and an International Classification of Diseases 9th Revision (ICD-9) diagnosis book, and understand how they are used in setting coding and billing strategies, (2) know the people in your facility who do the billing and work with them to produce an appropriate coding and billing strategy, (3) make sure the physicians are involved in developing and implementing your coding and billing strategy, and (4) assure that your laboratory is set up properly to follows the Medicare rules for participation, that you have the appropriate testing supervision, that the appropriate administrative structure is in place to assure compliance with all regulations, and that you meet American Thoracic Society testing standards.
Fees and Charges↗