Cath Lab Digest - October 2007 - (Page 42)

42 ASK THE CLINICAL INSTRUCTOR OCTOBER 2007 It’s simple, but it requires a little education of the patient before the procedure. They need to be told how to best relax their breathing when you record pressures. Figure 6. pressures cycle with this 5–10 mmHg respiratory variation, because the heart lies within the thorax, just as the lungs do. Ideally, we want to read the pressures at “end-expiration,” which is the point during exhalation before the pressures “dip,” because as soon as the patient begins to inspire, the pressures begin to fall. The next logical question is “How in the heck do we do this?” It’s simple, but it requires a little education of the patient before the procedure. They need to be told how to best relax their breathing when you record pressures. First, try this on yourself. maneuver — bad for pressures and cardiac output. The patient needs to be educated to, upon command, let the air out of their lungs passively and then just “stop” breathing with their glottis still open. This assures that the patient is at the end-expiratory phase as long as possible. Patients can be told to breathe by letting their air out naturally and pausing while you record the pressures, as you will be able to see when they are breathing and when they are at the end-expiratory phase. If you let the patient breathe for 30 seconds between these commands, you will be able to obtain all the pressures of all the chambers within just a few minutes. It must be said that in ventilatorassisted patients, everything we discussed is actually the opposite. That is because air is being forced into the lungs mechanically, instead of through pressure changes in the chest. THAT is a subject for another time. Recording accurate hemodynamics requires you to carefully record and measure cardiac pressures at the right time in the respiratory cycle: end expiration. ■ Figure 7. QUICK — HOLD YOUR BREATH! (wait) relaxed diaphragm allows the expanded lungs to empty, just as when you release an expanded balloon, the air is expelled until the pressures both in and out equalize. Like this empty balloon, the lungs are also most relaxed at the end of expiration. Now that we understand how the mechanisms work, how do we know when to record pulmonary artery catheter pressures and why? When we measure pressures, we want the truest and most accurate readings possible. Assuming that equipment and technique are perfect, we want the most reproducible and relaxed pressure possible. Inspiration is always active because the diaphragm contracts, causing negative pressure within the chest and pulling in air. The point between the end of exhalation and the start of inspiration is the most neutral and relaxed time (Figure 6). This is where the outside pressure and the inside pressures are most equal, and this is where we want to obtain our readings. Figure 7 shows this area on an actual recording. We see the slow cycling of pressure levels during expiration as well as inspiration. Remember, during inspiration, there is more negative pressure in the chest, which correlates to the lower pressure readings. Another way to remember this is that when the diaphragm moves DOWN on inspiration, so do the intracardiac pressures. Actually, all the intracardiac (wait) Did you take a breath in and hold it? Most patients will do the same as well. Doing so creates artificially “high” pressures because of the air pressure against a closed epiglottis (we closed the open-to-air passage). The patient then performs a valsalva-type Acknowledgements: I would like to thank Wes Todd for his contribution to this month’s article. “The only foolish question is one left unasked.” New Staff: Your suggested topics and questions are needed! (You are welcome to remain anonymous.) Email us at: tginapp@rcisreview.com

Table of Contents Feed for the Digital Edition of Cath Lab Digest - October 2007

Saints Medical Center Fibromuscular Dysplasia in Children and Adolescents Cerebral Vascular Accident Following a Pulmonary Embolism: Search for the Hidden Patent Foramen Ovale Contents Clinical Editor’s Corner Meetings Calendar CEU Education Center Radiation Tracking in the Cardiac Catheterization Lab Letter to the Editor Carotid Stenting: An update Release from Stent-jail: Beneficial Snow-Plowing? Patient Management Guidelines Searching for a Cardiovascular Position? Tips for Creating a ‘Stand-Out’ Resume Long-Term Implications of Short-Term Closure Decisions – The Evolution to Vascular Access Management and the Boomerang Catalyst System The Ten-Minute Interview with… Angie Bowles, RN, CCRN CMS Issues Final FY 2008 IPPS Rule ACVP• Membership Page Experience with a New Workhorse Guidewire Ask the Clinical Instructor: Q&A for Those New to Cath Lab A Glimpse of the Future of Clinical Education: Boston Scientific’s SimSuite Bus Visits Carnegie Institute 2007 Educational Fair Held at the Washington Hospital Center Research Update: Original Contribution Abstracts from The Journal of Invasive Cardiology What Do You Think? A Virtual Cath Lab Viewer (VCL): The Development of an Online 3D C-arm Simulator and Coronary Anatomy Viewer Clinical & Industry News Cost-Effectiveness of the Radial versus Femoral Artery Approach to Diagnostic Cardiac Catheterization

Cath Lab Digest - October 2007

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