Mechanical Ventilation

Introduction

Galen was the first to describe ventilation of an animal, though it was well over a thousand years later that positive pressure ventilation with a bellows device became an accepted technique for resuscitation of near-drowning victims.  Early in the 19th century, pneumothoraces complicating high pressures and volumes delivered by bellows devices lead to prohibition of the practice early in its clinical development. Negative pressure ventilation techniques, including negative pressure operating rooms, were developed in the 19th and early 20th centuries for clinical use.  The first negative pressure device to gain widespread use, the Drinker-Shaw "iron lung," was developed in 1928.  Later refinements by Emerson during the 1931 polio epidemic resulted in a simplified and less expensive tank respirator which became the mainstay of treatment of paralytic poliomyelitis. In the early 1950s, positive pressure mechanical ventilation emerged following decades of developmental work in animal laboratories and growing clinical experience with cuffed endotracheal tubes in operating rooms.  Clustering of patients with respiratory failure supported on positive pressure ventilators in Copenhagen in 1950s led the way to the development of modern ICUs.  Today, numerous highly sophisticated and refined mechanical ventilators are available for clinical use.  Modern ventilators support various modes of pressure or volume-limited ventilation and provide breath-by-breath estimates of pulmonary mechanics that are valuable for both diagnosis and monitoring responses to therapy.  Recently, mechanical ventilators with closed-loop algorithms for weaning positive pressure have been approved for clinical use, heralding a new era in computerized bedside decision support for the intensivist as other closed-loop devices are sure to follow.

Last updated: August 2009

Search

A web search using the Google^TM search engine yielded 1,180,000 sites for the search term "mechanical ventilation."  The first 100 sites were divided among the four reviewers who selected the top sites from their assigned sites.  One of us (BTT) reviewed all 120 sites.  The reviewers then met and determined the top sites by majority vote.

In general, most of the sites were years out of date and cited relatively few references to support clinical recommendations.  As this is an active field with numerous recent developments, this is a serious shortcoming.  Other sites, including one with a potentially useful ventilator simulator, had broken links that remained nonfunctional even when viewed with three different web browsers (Internet Explorer®, Firefox® and Netscape®).  Most of the sites did not take advantage of the web's potential and were one dimensional with links that simply moved the browser to relevant areas of a single- text document.  Overall, use of multimedia tools was scarce.

We divided our short list of top sites by the intended audience: clinicians and trainees or patients and their families.  The following are our top picks.

Best Websites

A Primer for Mechanical Ventilation

This is part of the online materials for Medicine 683, the fourth-year medical student clerkship in pulmonary medicine at the University of Washington in Seattle. One of the goals of this clerkship is to, “explain the basic modes of mechanical ventilation, choose appropriate initial ventilator settings for a patient and make appropriate adjustments in these settings based on changes in the patient's condition. This website supports that goal. In addition to the online material on mechanical ventilation, there are links to material on pulmonary function testing, pleural effusion and radiology.

1. Authority: The author is David J. Pierson, MD, a noted authority in mechanical ventilation. The author and the supporting institution are clearly identified. Rating: 5

2. Currency: The copyright is 2008. The content is consistent with current evidence. There is no mention of newer modes such as airway pressure release ventilation and proportional assist ventilation, which is appropriate for a primer. Rating: 4

3. Accuracy: The content is accurate for the most part. Terminology related to mechanical ventilation can be confusing and is not consistent from author to author. For example, this author refers to CMV as "Å“controlled mechanical ventilation." The more contemporary definition is "continuous mandatory ventilation" and is synonymous with the term "assist-control ventilation." The author uses the terms volume-targeted and pressure-targeted. This is okay, but in reality the ventilator "controls" the volume or pressure, so volume-controlled and pressure-controlled would be more contemporary terminology. Rating: 4

4. Navigation & Readability: There are some hypertext links to facilitate navigation around the site. Unfortunately, the links to material outside of this page, which includes the tables, requires a university password. The reading level is good, but its appearance is more like that of a textbook and less like a webpage. Rating: 3

5. Utility: The material is up to date. The ten clinical teaching cases are outstanding and cover the breadth of usual clinical cases where mechanical ventilation is needed. The cases are the strength of this site. Rating: 5

Summary: The target audience is medical students. However, the content is equally relevant to residents or others who may encounter mechanical ventilation infrequently in their practice.

Mechanical Ventilation in Critical Care

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1. Authority: This site was developed to help residents during their critical care rotation in the surgical ICU at the University of Pennsylvania. The publisher is clearly identified but not the funding. Rating: 4

2. Currency: The site has not been updated since 2002, though an upgrade was mentioned on the information page for 2007. Rating: 3

3. Accuracy: Content appears correct, though dated with most cited references from the 1990s. Rating: 4

4. Navigation & Readability: This is a very well-organized site with logical subdivisions and easy navigation. The pages are visually appealing with good integration of graphics and text. Rating: 5

5. Utility: This is an extremely useful resource for medical students, residents and perhaps fellows. It includes a number of clinical cases to help integrate the materials presented. Rating: 5

Summary: In summary, this is a well-organized site with intuitive and easy navigation, pleasing graphics and excellent content. With the promised upgrade and additional references the site will be even further ahead of all others in this category.

Overview of Mechanical Ventilation

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1. Authority: The authors and the organization are clearly identified. Although author affiliations are provided, there is no contact information or links. The mission of the organization (the Merck Manual) its history, and editors are clearly identified. While the site is very complete in many ways, there are no cited references. Rating: 3

2. Currency: The most recent review was August 2007. Rating: 4

3. Accuracy: The content is very thorough and discusses many aspects of mechanical ventilation: causes, etiology, diagnosis, management and therapy. Often it is based on large multicenter randomized control trials. However, these references are not explicitly stated. Speculative areas are clearly defined. Rating: 4

4. Navigation & Readability: The presentation of material is straightforward, simple and aesthetically pleasing. Taking advantage of the medium, there are links to other topics within the manual, tables and other graphics in the text, a sidebar with an index for navigation, and even drug names that can be highlighted to show brand names or go to the drug's monograph. The site is primarily for clinicians and provides an excellent overview at a medical student or house staff level. Rating: 4

5. Utility: The website is free and provides a valuable overview for junior physicians. For example, the site clearly describes respiratory system mechanics and ventilator modes. Additionally, the results and practice recommendations from relatively recent high quality studies are incorporated. Rating: 5

Summary: This is a concise and accessible site with up-to-date content. The information is somewhat below the level of experts in the field, however, and relatively limited in scope.

Patient Information Series: Mechanical Ventilation

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1. Authority: This is a series of short explanations of illnesses and procedures commonly encountered in the ICU as well as suggested approaches to decision making for patients and families. This comprehensive site was developed by the Critical Care Assembly. Rating: 5

2. Currency: The sections on mechanical ventilation, weaning from mechanical ventilation, and tracheostomy give up-to-date information though dates are not given. Rating: 4

3. Accuracy: Like most of the patients-centered sites, the evidence base and physiologic principles guiding practice in the ICU are not reviewed in detail, but concepts are presented clearly Rating: 5

4. Navigation & Readability: The site is well organized and cross referenced with hyperlinks. For example, in the section on mechanical ventilation, there are links to sections on respiratory infections, tracheostomy and end-of-life decision making. Rating: 4

5. Utility: This is yet another excellent resource for patients and their surrogate decision makers trying to understand life-threatening illnesses and their treatments. The sections are concise and accessible, thus allowing the reader to gain an extensive overview in a short time frame. The physician "clip and copy" feature allows clinicians to print sections for surrogates without Internet access. Rating: 5

Summary: Overall, this is an excellent site.

ICU-USA Tour; Mechanical Ventilator

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1. Authority: This site is part of the Society of Critical Care Medicine's official patient and family web site, an accessible and thoughtful site that provides information about many aspects of ICU care. The site is endorsed by the American Association of Critical Care Nurses. Rating: 5

2. Currency: The last update is not reported but the material appears timely and up to date. Rating: 4

3. Accuracy: Information is well balanced, accurate and focuses on clinical questions clinicians most often hear from patients and families in the ICU. Rating: 5

4. Navigation & Readability: This is easy to navigate and uses excellent graphics and thoughtful real-life photographs of patients in the ICU to help set expectations and address concerns. Rating: 4

5. Utility: This is an extremely useful source of information for patients undergoing major surgery who are likely to require postoperative ICU care. It is also very useful for visiting family members and surrogate decision makers. Rating: 5

Summary: In conclusion, this site is an outstanding resource for patients and families. It is only one of many helpful sites related to critical care that can be accessed with numerous well placed links.

Should I Receive CPR and Mechanical Ventilation?

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1. Authority: This is a site directed towards patients with life-limiting illnesses who are trying to decide whether they should receive CPR and mechanical ventilation. The author is identified as well as two medical reviewers and their backgrounds. Conflicts of interest are reported for the physician reviewers. There is no contact link to the specific authors. Rating: 4

2. Currency: The last update was July 14, 2008. Rating: 5

3. Accuracy: There is little factual information (only one reference), but very clear explanations of the issues to consider. The possible consequences of choosing mechanical ventilation or not, or CPR or not, are clearly delineated. Also, there is a decision-support tool with questions that can be used to help formulate a decision. Rating: 4

4. Navigation & Readability: Navigation is easy, with many links to other topics within the text. The discussion is easily understandable to patients and families. There is even a poll of users at the beginning to assess the site's usability. Rating: 5

5. Utility: This is a very helpful site for patients and families who anticipate needing intensive care. It helps to raise questions of patients that ultimately will help caregivers and surrogate decision makers know the best course of action if life support is needed. One very unique and potentially useful part of this site is a link to patient testimonials that might help in this decision making. Rating: 5

Summary: Overall, this site appears to be very useful to patients and families trying to make decisions about accepting mechanical ventilation and CPR. There are some useful features, such as a decision-support tool and patient testimonials that make this site unique.

Disclaimer

The author has no personal or financial interest in any of the websites discussed above. The author has no personal or financial interest in any of the websites discussed above. DRH receives royalties from Impact Instrumentation, a manufacturer of mechanical ventilators and other respiratory care products.