The issue of patient weight for performance of cardiac catheterization is no trivial matter. The excessive weight of the patient can damage the x-ray table, produce poor quality non-diagnostic images, expose the staff to excess radiation and work-related back injuries (from improper lifting), and is associated with increased procedure complications. We all face this problem at least on a quarterly basis. Obese patients coming to the cath lab have increased in the last decade, with patients weighing above 350 lbs increasing from 1% to nearly 2%, and those greater than 350 lbs from 0 to 0.5%. How should we best manage the morbidly obese patient who truly needs cardiac catheterization?
Equipment Weight Limits
Weight limits for cardiac catheterization laboratories are set to prevent damage to the table machinery that has free-floating tabletop bearings permitting translation in the horizontal, vertical and tilting directions. The x-ray manufacturers provide restrictions by weight on these tables in order to prevent damage to the equipment. A non-functioning table with broken bearings is associated with extra cost of repair, operational downtime and temporarily restricted patient access. Recently, Vanhecke et al, from the cardiology division at William Beaumont Hospital, published “Body weight limitations of United States cardiac catheterization laboratories including restricted access for the morbidly obese.”1 The authors conducted a telephone survey to determine weight limits of 94 cardiac cath labs in the United States. Weight limits for the minimum, mean and maximum patient weights were 160 kg, 198.9 kg, and 250 kg (350 lbs, 437.5 lbs and 550 lbs, respectively). Twenty-one of the 94 labs referred these patients to other institutions when they were deemed to be too heavy. At least 3-5 patients per hospital per year were rejected for being over their lab’s weight limit.
Diagnostic Angiography and Weight
The difficulty with morbidly obese patients occurs not only in the potential for damage to the cath lab equipment, but also in the inability to obtain an adequate study. Non-diagnostic images can lead to wrong or incomplete decisions for further therapy, putting the patient at risk. It is also well-known that coronary artery bypass graft surgery (CABG) may not be possible in some of the extremely obese patients. Complications of the procedure are greater in the morbidly obese patient, with a higher all-cause mortality and morbidity.
The ability of angiographic equipment to produce an adequate study in the obese patient has improved over the years. However, both the image chain and the function of the table for image angulation may not be adequate to provide a diagnostic image. This issue was addressed by Kussmaul et al2 several years ago. As the necessity to cath some of the morbidly obese patients was critical, the authors described a technique of placing a stretcher at 90 degrees to the cath table and placing only the patient’s thorax on the table under the image intensifier. Although successful, views of the coronary tree in both angle and skew were limited. The problem was also taken up by McNulty et al who describe their approach to the morbidly obese with greater use of radial artery access and vascular closure devices.3 Vanhecke and colleagues nicely summarize the strategies (Table 1) that can be employed to address the problem and attain the best result in the morbidly obese patient.
Importantly, as Vanhecke et al note, some patients with highest body mass index (BMI, see Table 2) were less likely to receive procedures despite being below table weight limits due to a number of other difficulties with vascular access, higher potential for procedure complications, poor image acquisition and physical dimensions contributing to the reluctance of providers to perform interventions. The physical dimensions of the patient also increase the risk for falling from the table and staff injury in preventing the occurrence. It goes without saying that morbid obesity may make femoral access nearly impossible. X-ray exposure in the lab is increased for the obese patient. Radiation doses for cineangiography to yield high-quality images for those weighing greater than 180-200 kg (396-440 lbs) require x-ray generators to produce outputs of greater than 100 kV, with a corresponding radiation exposure three to four times out of conventional catheterization for normal body weight.3
What should your lab do with the morbidly obese? Review the strategies outlined above and consider the clinical importance to the patient as to whether the value of the information will be outweighed by the risk and yield of the procedure. From a purely personal point of view, be gentle when discussing the problems of weight and cardiac cath. The patient knows what the problem is, but cannot change things at this point. In the appropriate patient with whom I have established some rapport, I have phrased our dilemma as, “Mrs. Smith, I see you are 5 feet, 2 inches and weigh 285 lbs. The procedure is somewhat more complicated today because you are just too short for your weight. You’ll need to grow 6 or 7 inches for the next time.” It usually puts a smile on their face. Then after explaining the risks and benefits, we proceed with caution.
1. Vanhecke TE, Berman AD, McCullough PA. Body weight limitations of United States cardiac catheterization laboratories including restricted access for the morbidly obese. Am J Cardiol 2008;102:285-286.
2. Kussmaul WG 3rd, Bowers B, Dairywala I. Method for coronary angiography in morbidly obese patients. Catheter Cardiovasc Interv 2005 Jun;65(2):268-270.
3. McNulty PH, Ettinger SM, Field JM, et al. Cardiac catheterization in morbidly obese patients. Catheter Cardiovasc Interv 2002 Jun;56(2):174-177. Dr. Kern welcomes your responses and suggestions for future Editor’s Corner topics and discussions. He can be contacted at mortonkern005@ hotmail.com.