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PubMed2000

Indoor air quality in a middle school, Part I: Use of CO2 as a tracer for effective ventilation.

The overall objective of the study was to evaluate the indoor air quality at a middle school with an emphasis on characterizing baseline conditions. The focus of this article is on the relationship between occupancy and measured concentrations of carbon dioxide, and an evaluation of the use of carbon dioxide as a tracer for ventilation in the school. The school was characterized as having no health complaints, good maintenance schedules, no carpeting within the classrooms or hallways, and no significant remodeling, and its officials had agreed to allow the sampling to take place during school hours. Monitoring followed the guidelines recommended in the "Preliminary Draft: Conceptual Standardized EPA Protocol For Characterizing Indoor Air Quality in School Buildings." Four indoor locations including the cafeteria, a science classroom, an art classroom, and the lobby outside the main office, and one outdoor location were sampled for various environmental comfort and pollutant parameters for one week in February 1997. A consistent relationship between hourly occupancy and corresponding carbon dioxide concentrations was seen. Carbon dioxide concentrations in the cafeteria, art room, and lobby were within specified American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) guidelines for comfort (< 1000 ppm). The science room had the highest concentrations (frequently exceeding 1000 ppm) due to high occupancy and non-functioning unit ventilators. Measured ventilation rates were within specified ASHRAE guidelines for the art room, cafeteria, and lobby. The science room, which relied on natural ventilation only, was not able to meet the ASHRAE guideline on one of the three days studied. The use of a completely mixed space, one compartment mass balance model with estimated CO2 generation rates and measured CO2 concentrations is shown to be a useful method for evaluating ventilation. Modeled effective ventilation, air changes per hour, and mixing factors reflected measured carbon dioxide concentrations and measured ventilation in each room. Mechanical ventilation afforded better mixing than natural ventilation. This study demonstrates the usefulness of collecting indoor CO2 and occupancy data when carrying out indoor air quality evaluations in schools.

Adolescent↗
PubMedDate not supplied

Concepts and application of prehospital ventilation.

Airway management and optimal ventilation are crucial aspects of managing out-of-hospital medical emergencies. The goals in these situations are controlled ventilation and optimized inspiratory time, expiratory time, and airflow. Numerous techniques and devices are available to deliver oxygen-enriched air to patients during resuscitation. The bag-valve-mask (BVM) is one of the most common devices used to provide ventilation, although the American Heart Association ranks BVM devices lower in preference than other ventilation adjuncts, such as emergency and transport ventilators (ETVs) and pocket masks. The clearly documented limitations of BVM ventilation and its widespread use in the United States underscore the need to improve ventilation practices during care provided by emergency medical services (EMS) personnel. As part of that improvement, ETVs clearly have a role in the prehospital setting. These devices should be available on every ambulance, and the ability to use ETVs should be part of each EMS provider's skill set. Furthermore, all patients requiring emergency ventilation must be adequately monitored, including continuous monitoring of end-tidal carbon dioxide concentrations. As with any other skill, ventilation requires attention during initial training, continuing education and skill reinforcement, and quality review.

Carbon Dioxide↗
PubMed1986

Confined spaces--a case for ventilation.

Many exposures, some leading to deaths and injuries, in confined spaces could have been prevented by ventilating the space prior to and during the entry. Current standards and guidelines generally do not require ventilation. Nor do they sufficiently emphasize the need for ventilation or provide guidance on how to ventilate confined spaces. Mechanical ventilation is a positive engineering control action that can usually be taken and that will reduce the hazards of adverse atmospheric conditions inside a confined space. Natural ventilation usually is not sufficiently reliable to serve as a primary means of control. Unfortunately, very little specific information is available for designing and implementing ventilation strategies for confined spaces. More published information is needed, such as examples of effective policy and procedures in use by industry and findings from research on confined space ventilation. Basic and applied research can help to demonstrate effective ventilation actions and develop useful design guidelines. Additional published information should increase hazard awareness and reduce the likelihood of accidents.

Industry↗
PubMed1990

Gestational age: an important influence on the success of patient triggered ventilation.

We have evaluated a new patient triggered (PT) ventilator which has been produced as suitable for neonatal use. This ventilator, the Draeger Babylog 8000, is triggered by airflow changes detected by a hot wire anemometer. Laboratory assessment demonstrated maintenance of tidal volume and absence of inadvertent PEEP at flow rates up to 20 l min-1 and rates of 120 breaths min-1. The ventilator was then used in both conventional and trigger mode in 14 pre-term infants. The results were compared with PT ventilation delivered by the SLE ventilator. At all inflation times studied, using the Draeger ventilator 100% of respiratory efforts were detected in the majority of infants. The trigger delay varied from a median of 80-100 ms and was significantly shorter than the trigger delay of the SLE system (P less than 0.05). Oxygenation improved on Draeger PT compared with conventional ventilation, however, only in infants more mature than 27 weeks gestation. We conclude the Draeger Babylog 8000 is an important advance in patient triggered ventilation, particularly at fast frequencies, but PT ventilation should still be restricted to relatively mature infants.

Gestational Age↗
PubMed1997

Air leaking through the mouth during nocturnal nasal ventilation: effect on sleep quality.

Air leaking through the mouth has been reported in kyphoscoliotic patients receiving nasal ventilation via volume-limited ventilators. This study accessed the frequency of occurrence and effect on sleep quality of air leaking through the mouth during nocturnal nasal ventilation in patients with chest wall and neuromuscular disease using pressure-limited ventilation. Overnight and daytime polysomnography was performed in six stable experienced users of nocturnal nasal noninvasive positive-pressure ventilation (NPPV) who had chronic respiratory failure due to neuromuscular disease or chest wall deformity. All patients used the BiPAP S/T-D ventilatory support system (Respironics, Inc., Murrysville, PA). Measures included sleep scoring, leak quantitation, diaphragm and submental electromyograms (EMGs), and tidal and leak volumes. All patients had air leaking through the mouth for the majority of sleep. Sleep quality was diminished because of poor sleep efficiency and reduced percentages of slow-wave and rapid eye movement (REM) sleep. Air leaking through the mouth was associated with frequent arousals during stages 1 and 2 and REM sleep that contributed to sleep fragmentation, but arousals were infrequent during slow-wave sleep. Despite prevalent leaking, oxygenation was well maintained in all but one patient. Patients used a-combination of passive and active mechanisms to control air leaking. Although nasal ventilation improves nocturnal hypoventilation and symptoms in patients with restrictive thoracic disorders, air leaking through the mouth is very common during use. The leaking is associated with frequent arousals during lighter stages of sleep that interfere with progression to deeper stages, compromising sleep quality. Portable pressure-limited ventilators compensate for leaks, maintaining ventilation and oxygenation, but further studies are needed to determine which interfaces and ventilator techniques best control air leaking and optimize sleep quality.

Adult↗
PubMed1997

Prolonged "phantom" square wave capnograph tracing after patient disconnection or extubation. Potential hazard associated with the Siemens Servo 900c ventilator.

BACKGROUND: The authors report on the appearance of misleading square wave "phantom" capnograph tracings for approximately 3 min after disconnection from the Siemens Servo 900c ventilator. A series of experiments are described to examine the mechanism of this phenomenon. METHODS: Patients were ventilated using the Siemens Servo 900c ventilator with the following settings: minute volume, 5 1/min; respiratory rate, 8 breaths/min; PEEP, 0 cm H2O; trigger sensitivity, 20 cm H2O. The ventilator was connected to the Siemens Servo Evac 180 evacuation system (25 1/min on evacuation flowmeter). Airway pressure and capnography were recorded at the Y piece during ventilation and after disconnection. A back-up ventilator was used to support the patient during disconnection of the ventilator being studied. RESULTS: Initially, the "phantom" capnograph tracing closely resembled the square wave capnograph tracing before disconnection, but the amplitude and shape of the waveform gradually decayed. Based on experiments described in this article, the authors show that the carbon dioxide for the "phantom" capnograph tracing comes from the gas exhaled by the patient in the last breaths before disconnection and which is present in both the expiratory tubing and in the evacuation system. The small pressure gradient between the exhaust reservoir and the atmosphere causes reverse flow of expired gas after disconnection, when both the nonreturn flap valve at the exhaust outlet is open (due to minimal valve incompetence) and when the expiratory servo valve is open (in the absence of positive end-expiratory pressure). This continuous reverse flow is detected by the capnograph but is interrupted intermittently by each attempted positive pressure ventilation, thereby creating a "phantom" capnograph. CONCLUSIONS: After accidental disconnection of the patient from the breathing system, or after accidental extubation of the trachea, the "phantom" capnograph is likely to confuse even an experienced anesthesiologist into the mistaken belief that his rapidly deteriorating patient is being ventilated adequately. Several potential mechanisms to eliminate this phenomenon are outlined, including the avoidance of zero positive end-expiratory pressure. "Phantom" capnography provides an illustration of the dangers of using monitoring techniques, however reliable, as a substitute for vigilant clinical observation.

Capnography↗
PubMed2002

Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study.

BACKGROUND: A number of new microprocessor-controlled mechanical ventilators have become available over the last few years. However, the ability of these ventilators to provide continuous positive airway pressure without imposing or performing work has never been evaluated. METHODS: In a spontaneously breathing lung model, the authors evaluated the Bear 1000, Drager Evita 4, Hamilton Galileo, Nellcor-Puritan-Bennett 740 and 840, Siemens Servo 300A, and Bird Products Tbird AVS at 10 cm H(2)O continuous positive airway pressure. Lung model compliance was 50 ml/cm H(2)O with a resistance of 8.2 cm H(2)O x l(-1) x s(-1), and inspiratory time was set at 1.0 s with peak inspiratory flows of 40, 60, and 80 l/min. In ventilators with both pressure and flow triggering, the response of each was evaluated. RESULTS: With all ventilators, peak inspiratory flow, lung model tidal volume, and range of pressure change (below baseline to above baseline) increased as peak flow increased. Inspiratory trigger delay time, inspiratory cycle delay time, expiratory pressure time product, and total area of pressure change were not affected by peak flow, whereas pressure change to trigger inspiration, inspiratory pressure time product, and trigger pressure time product were affected by peak flow on some ventilators. There were significant differences among ventilators on all variables evaluated, but there was little difference between pressure and flow triggering in most variables on individual ventilators except for pressure to trigger. Pressure to trigger was 3.74 +/- 1.89 cm H(2)O (mean +/- SD) in flow triggering and 4.48 +/- 1.67 cm H(2)O in pressure triggering (P < 0.01) across all ventilators. CONCLUSIONS: Most ventilators evaluated only imposed a small effort to trigger, but most also provided low-level pressure support and imposed an expiratory workload. Pressure triggering during continuous positive airway pressure does require a slightly greater pressure than flow triggering.

Humans↗
PubMed2004

From continuous positive-pressure breathing to ventilator-induced lung injury.

Continuous positive-pressure ventilation in acute respiratory failure. By Kumar A, Falke KJ, Geffin B, Aldredge CF, Laver MB, Lowentein E, Pontoppidan H. N Engl J Med 1970; 283:1430-6. Reprinted with permission. Continuous positive-pressure ventilation was used in eight patients with severe acute respiratory failure. Cardiac output and lung function were studied during continuous positive-pressure ventilation (mean end-expiratory pressure, 13 cm H2O) and a 30-min interval of intermittent positive-pressure ventilation. Although the mean cardiac index increased from 3.6 to 4.5 l/min per square meter of body surface area, the mean intrapulmonary shunt increased by 9% with changeover to intermittent positive-pressure ventilation. Satisfactory oxygenation was maintained in all patients during continuous positive-pressure ventilation with 50% inspired oxygen or less. With intermittent positive-pressure ventilation, arterial oxygen tension promptly fell by 161 mm of mercury, 79% occurring within 1 min. Prevention of air-space collapse during expiration and an increase in functional residual capacity probably explain improved oxygenation with continuous positive-pressure ventilation. In four patients, subcutaneous emphysema or pneumothorax developed. Weighed against the effects of prolonged hypoxemia, these complications were not severe enough to warrant cessation of continuous positive-pressure ventilation.

Acute Disease↗
PubMed1994

Clinical experiences with high-frequency oscillatory ventilation in newborns with severe respiratory distress syndrome.

OBJECTIVE: To generate hypotheses about which subgroups of newborns with severe respiratory distress syndrome might benefit most from high-frequency oscillatory ventilation. DESIGN: Retrospective analysis of a case series of newborns with severe respiratory distress syndrome who were treated in our department with high-frequency oscillatory ventilation. SETTING: Referral center for neonatal and pediatric intensive care medicine. PATIENTS: All newborns (n = 18), admitted between June 1991 and February 1993, of various gestational ages (26 to 41 wks), with severe respiratory distress syndrome caused by various underlying pulmonary diseases who did not respond to conventional therapy and who thus were treated with high-frequency oscillatory ventilation. MAIN OUTCOME MEASURES: Survival until discharge from our unit and persistent improvement of gas exchange. RESULTS: Eight (44%) of 18 patients survived; ten (55%) patients died. Four (22%) survivors showed marked clinical improvement with the initiation of high-frequency oscillatory ventilation. Four (22%) survivors did not respond to high-frequency oscillatory ventilation. The responder group consisted of term or near-term neonates (gestational age at least 35 wks) with pulmonary disease that was complicated by persistent pulmonary hypertension. The group of premature neonates with a gestational age of < 35 wks did not respond to high-frequency oscillatory ventilation. CONCLUSIONS: As a result of our analysis, we hypothesize that term newborns with severe respiratory distress syndrome complicated by persistent pulmonary hypertension and hypercarbia can benefit from high-frequency oscillatory ventilation. Premature neonates with ventilation-induced lung injury are not likely to respond to high-frequency oscillatory ventilation.

Female↗
PubMed1996

Nonrespiratory predictor of mechanical ventilation dependency in intensive care unit patients.

OBJECTIVE: To determine the role of serum albumin concentration as a predictor of mechanical ventilation dependency. DESIGN: Prospective, observation trial. SETTING: Multidisciplinary intensive care unit (ICU) in a university hospital. PATIENTS: One hundred forty-five consecutive patients who required mechanical ventilation for > 72 hrs. INTERVENTIONS: Patients were classified into five different groups based on the cause of respiratory failure. The following parameters were recorded daily: serum albumin concentration; Acute Physiology and Chronic Health Evaluation II (APACHE II) score; and fluid balance. Using multiple regression, multiple logistic regression analysis, and the Anderson-Gill proportional hazards model, we determined the metabolic factors that could help predict weaning success. MEASUREMENTS AND MAIN RESULTS: The mean length of ICU stay was 12.3 +/- 1.0 days. The duration of mechanical ventilation dependency was 10.5 +/- 1.0 days. The initial mean serum albumin concentration was 25.2 +/- 0.6 g/L. The APACHE II score on the first day of ICU stay was 19.1 +/- 0.6. Although albumin concentration was significantly lower and the APACHE II score was significantly higher in ICU nonsurvivors than in ICU survivors, albumin concentration on ICU admission was not a predictor of the length of time spent receiving mechanical ventilation. The profile of albumin concentration changes was different between weaned and mechanical ventilation-dependent patients. At the time of weaning patients from the ventilator, the median albumin concentration was higher than in those patients who continued to be supported by mechanical ventilation. This effect of albumin could not be attributed to patient fluid balance or to the severity of illness since each factor had an independent influence in predicting weaning, using the Anderson-Gill proportional hazards models. CONCLUSIONS: Initial serum albumin concentration did not necessarily predict weaning success. However, when serum albumin concentration was assessed on a daily basis, its trend was important in determining the relative chance of being successfully weaned from the ventilator. This finding suggests that albumin may be an index of the metabolic status of the patient, which could be important in determining the weanability of the patients who are mechanically ventilated for prolonged periods of time.

APACHE↗
PubMed1997

Comparison of pressure- and flow-triggered pressure-support ventilation on weaning parameters in patients recovering from acute respiratory failure.

OBJECTIVE: To compare the effects of pressure- and flow-triggered pressure-support ventilation on weaning parameters during recovery from acute respiratory failure. DESIGN: Prospective, randomized, clinical trial. SETTING: Intensive care unit in a university hospital. PATIENTS: Sixteen orotracheally intubated adult patients recovering from acute respiratory failure of various etiologies, without chronic obstructive pulmonary disease. INTERVENTIONS: Randomized application of pressure- and flow-triggered pressure-support ventilation at 100% and 75% ventilatory support levels in each triggering system. A total of four conditions were applied for 30 mins each in all patients. MEASUREMENTS AND MAIN RESULTS: Ventilatory, respiratory, and hemodynamic data were measured. For the measurement of weaning parameters, pressure and volume signals were directed to a computerized respiratory monitor by means of an esophageal probe and a flow sensor between the "Y" piece of the ventilatory circuit and the endotracheal tube. During both pressure-triggered (trigger sensitivity of -1 cm H2O) and flow-triggered (trigger sensitivity of 0.7 to 2.0 L/min) pressure-support ventilation with a ventilator, peak airway pressures were applied so as to decrease the work of breathing performed by the patient to zero (full ventilatory support). Partial ventilatory support was applied at 75% of the peak airway pressures achieved during full ventilatory support with each triggering system. A total of four experimental conditions were evaluated at identical FiO2 and positive and-expiratory pressure levels during pressure-support ventilation in each patient. Total ventilation volumes, arterial blood gas data, and hemodynamics did not differ among the four experimental conditions. During partial ventilatory support, the work of breathing, rapid shallow breathing index, and esophageal pressure increased significantly with both triggering systems when compared with data obtained at full ventilatory support. The mean data for the weaning parameters during the condition of partial ventilatory support were comparable between pressure- and flow-triggered pressure-support ventilation (i.e., 0.38 +/- 0.24 vs. 0.42 +/- 0.26 joule/L for work of breathing, 2.6 +/- 1.6 vs. 3.3 +/- 1.7 cm H2O for tracheal occlusion pressure, and 40.2 +/- 12.9 vs. 50.4 +/- 18.3 breaths/min/L for rapid shallow breathing index, respectively). CONCLUSIONS: The application of either a pressure- or flow-triggered system during pressure-support ventilation with the ventilator did not significantly affect short-term changes in gas exchange, respiratory mechanics, and inspiratory workload in patients recovering from acute respiratory failure of various etiologies without chronic obstructive pulmonary disease.

APACHE↗
PubMed2001

Experience with a clinical guideline for the treatment of ventilator-associated pneumonia.

OBJECTIVE: To evaluate a clinical guideline for the treatment of ventilator-associated pneumonia. DESIGN: Prospective before-and-after study design. SETTING: A medical intensive care unit from a university-affiliated, urban teaching hospital. PATIENTS: Between April 1999 and January 2000, 102 patients were prospectively evaluated. INTERVENTIONS: Prospective patient surveillance, data collection, and implementation of an antimicrobial guideline for the treatment of ventilator-associated pneumonia. MEASUREMENTS AND MAIN RESULTS: The main outcome evaluated was the initial administration of adequate antimicrobial treatment as determined by respiratory tract cultures. Secondary outcomes evaluated included the duration of antimicrobial treatment for ventilator-associated pneumonia, hospital mortality, intensive care unit and hospital lengths of stay, and the occurrence of a second episode of ventilator-associated pneumonia. Fifty consecutive patients with ventilator-associated pneumonia were evaluated in the before period and 52 consecutive patients with ventilator-associated pneumonia were evaluated in the after period. Severity of illness using Acute Physiology and Chronic Health Evaluation II (25.8 +/- 5.7 vs. 25.4 +/- 8.1, p =.798) and the clinical pulmonary infection scores (6.6 +/- 1.0 vs. 6.9 +/- 1.2, p =.105) were similar for patients during the two treatment periods. The initial administration of adequate antimicrobial treatment was statistically greater during the after period compared with the before period (94.2% vs. 48.0%, p <.001). The duration of antimicrobial treatment was statistically shorter during the after period compared with the before period (8.6 +/- 5.1 days vs. 14.8 +/- 8.1 days, p <.001). A second episode of ventilator-associated pneumonia occurred statistically less often among patients in the after period (7.7% vs. 24.0%, p =.030). CONCLUSIONS: The application of a clinical guideline for the treatment of ventilator-associated pneumonia can increase the initial administration of adequate antimicrobial treatment and decrease the overall duration of antibiotic treatment. These findings suggest that similar types of guidelines employing local microbiological data can be used to improve overall antibiotic utilization for the treatment of ventilator-associated pneumonia.

APACHE↗
PubMedDate not supplied

Ventilator risk management using a programmed monitor.

A computer program was written to improve quality control and risk management of patients on ventilators. The software was designed to run on the new-generation Spacelabs PC Monitor interfaced to the Puritan-Bennett 7200a ventilator. Before the program allows connection of the ventilator to a patient, the ventilator is polled for initial hardware status, alarm statuses and alarm limit settings. If there are no hardware failures, alarm violations, or improperly set alarm limits, the program prompts the clinician to connect the ventilator to the patient. Polling is done periodically after patient ventilation begins, and patient data, alarm conditions, or changes to the ventilator settings are automatically written to disk. In addition, real-time data can be displayed at any time during the ventilation session by using a set of touch-screen options. After the ventilation session is complete, the clinician can print the final report in hard copy or to disk.

Equipment Failure↗
PubMed1997

Weaning from mechanical ventilation.

Use of mechanical ventilation is associated with several major complications despite its lifesaving potential. Timely discontinuation of mechanical ventilation is critical to control of duration of intensive care unit stay and reduction of complications associated with mechanical ventilation. Difficulty in discontinuation (or weaning) of patients from mechanical ventilatory support is in part attributable to inadequate understanding of the mechanisms responsible for unsuccessful outcome and a lack of guidelines regarding the optimal approach to the process of discontinuation of mechanical ventilation. For the first time, results from prospective, randomized, multicenter trials are available comparing common means of discontinuation of mechanical ventilation. In addition, the physiologic basis for a weaning strategy in mechanical ventilation is also coming into better focus. Two recent trials of weaning suggest different optimal modes, one favoring T-piece trials and the other supporting the use of pressure support ventilation. In either case, the above weaning techniques appear to be superior to intermittent mandatory ventilation in separating patients from mechanical ventilatory support. Based on available clinical trials, pressure support ventilation or T-piece trials appear to be the preferred methods for discontinuation of mechanical ventilatory support. A method using a simple T-piece trial technique is described.

Algorithms↗
PubMed2003

High-frequency oscillatory ventilation in adults with acute respiratory distress syndrome.

The last decade has seen increased appreciation of ventilator-induced lung injury. The understanding that the process of mechanical ventilation can itself damage lungs has spurned the search for ventilation strategies that are more lung protective. High-frequency oscillatory ventilation is a mode of high-frequency ventilation that may accomplish all of the current goals of lung protection. Historically, much of the data evaluating high-frequency oscillatory ventilation came from neonatal and pediatric populations. In the past year, a number of provocative and exciting studies have been published that contribute significantly to our understanding of high-frequency oscillatory ventilation, its role in preventing and reducing ventilator-induced lung injury, and its use in the support of adult patients with lung injury. In this article, we discuss the current understanding of high-frequency oscillatory ventilation and highlight the most recent literature addressing its application in adult patients with acute respiratory distress syndrome.

Adult↗
PubMed2005

How to choose a mechanical ventilator.

PURPOSE OF REVIEW: To provide some practical and clinical considerations that may guide users through the decision process when choosing mechanical ventilators RECENT FINDINGS: Although the complexity of mechanical ventilators is steadily increasing, the importance of many devices developed over the course of the technical evolution is still a matter of discussion. Recent data demonstrate that the technical performance of equivalent ventilators (ie, machines of the same generation and category) is pretty similar, suggesting that the different manufacturers keep in step with new developments. Thus, other factors than technical limitations will probably influence the choice of ventilators. Among them the ability of the staff to understand the rationale of the different devices and controls as well as deal with the complexity of the ventilator may be particularly important. SUMMARY: Choosing mechanical ventilators should begin by defining the algorithms of how to ventilate a patient. Once this is done, a ventilator should allow the transformation of specific strategies into practice and the adaptation of the mechanical support to the needs of the individual patient. This procedure is crucially important, because ventilator therapy should always be determined by the physician and based on solid physiologic rationales rather than by the technical features of the machine.

Artificial Intelligence↗
PubMed2005

Clinical use of high-frequency oscillatory ventilation in adult patients with acute respiratory distress syndrome.

OBJECTIVE: High-frequency oscillatory ventilation (HFOV) is an emerging ventilatory strategy for adults that has been used successfully in the neonatal and pediatric population. This modality utilizes high mean airway pressures to maintain an open lung and low tidal volumes at a high frequency that allow for adequate ventilation while at the same time preventing alveolar overdistension. With the current understanding that excessive lung stretch and inadequate end-expiratory ventilatory volume may be injurious to the lungs, HFOV seems to be the ideal lung-protective ventilatory mode. During the past 8 yrs, there have been increasing numbers of studies describing its use in adult patients with acute respiratory distress syndrome. This article aims to review the published studies of HFOV in adults with acute respiratory distress syndrome with regard to its safety and efficacy. DATA SOURCE: To assist us with our review, we did a search of MEDLINE (from 1966 to present) and EMBASE (1980 to present) databases to identify adult, clinical, English-language, research articles related to HFOV use. In addition, we reviewed relevant animal and mechanical ventilation studies. We did not perform a formal systematic review. DATA SYNTHESIS: The application of HFOV was mainly reported as a rescue ventilatory mode in adult patients with acute respiratory distress syndrome who were thought to have failed conventional ventilation. In these patients, HFOV has consistently been shown to improve oxygenation without obvious increases in complications measured. There was only one randomized, controlled trial comparing HFOV with conventional ventilation. This study showed that there was a nonsignificant trend toward a lower mortality rate in the HFOV group. In addition, HFOV was as effective and safe as conventional ventilation. Although there are limitations, multiple studies have shown that earlier initiation of HFOV in patients with severe acute respiratory distress syndrome may also be associated with a lower mortality. CONCLUSIONS: HFOV seems to be safe and effective for adults with severe acute respiratory distress syndrome who have failed conventional ventilation. Further research is needed to determine the ideal patients, timing, and optimal technique with which to provide HFOV. When considering HFOV as an early, lung-protective mode of ventilation, there is still a need to perform an adequately powered, randomized, controlled trial comparing it with the best available form of conventional ventilation. However, we believe that such a trial should wait until we have a better understanding of HFOV in adults.

Adult↗
PubMed2005

Spontaneous breathing affects the spatial ventilation and perfusion distribution during mechanical ventilatory support.

OBJECTIVE: In acute respiratory failure, gas exchange improves with spontaneous breathing during airway pressure release ventilation (APRV). The mechanisms for this improvement are not fully clear. We have shown that APRV with spontaneous breathing reopens nonaerated lung tissue in dorsal juxtadiaphragmatic regions. We hypothesized that spontaneous breathing during APRV may redistribute ventilation and perfusion toward these reopened regions. DESIGN: Prospective, randomized, controlled study. SETTING: Animal research laboratory SUBJECTS: Twenty controlled mechanically ventilated pigs. INTERVENTIONS: Lung injury was induced by injection of oleic acid into the central circulation; thereafter, pigs were randomized to APRV with or without spontaneous breathing. To induce spontaneous breathing during APRV with spontaneous breathing, the mechanical respiratory rate was decreased by 50% in this group. MEASUREMENTS AND MAIN RESULTS: We measured respiratory mechanics, hemodynamics, gas exchange including the multiple inert gas elimination technique, and the spatial ventilation and perfusion distribution using single photon emission tomography. At similar minute ventilation and airway pressures, shunt remained stable during APRV with spontaneous breathing, whereas it increased during APRV without spontaneous breathing during the 2-hr study period (p = .006). Single photon emission tomography showed more ventilation (p < .001) and pulmonary blood (p < .025) flow in dorsal, juxtadiaphragmatic lung regions when spontaneous breathing was present. CONCLUSIONS: The beneficial effects of spontaneous breathing on intrapulmonary shunt and oxygenation are explained both by increased ventilation of aerated dependent lung tissue and by opening up nonaerated tissue so that ventilation is distributed to a larger share of the lung. Redistribution of perfusion is possibly secondary to the altered ventilation. The overall effect is a more efficient use of available lung tissue for gas exchange.

Animals↗