MORBIDLY OBESE PATIENT
Category: Emergency Medicine
Abstract : The Morbidly Obese Patient Obesity is the condition of an excessive
proportion of adipose tissue to total body weight. It is a major health problem,
with the prevalence of obesity in the United States doubling in the past 20
years, such that today over half of all adults are estimated to be overweight.
Since body fat is difficult to measure in the clinical setting, body mass index
(BM
The Morbidly Obese Patient
Obesity is the condition of an excessive
proportion of adipose tissue to total body weight. It is a major health problem,
with the prevalence of obesity in the United States doubling in the past 20
years, such that today over half of all adults are estimated to be overweight.
Since body fat is difficult to measure in the clinical setting, body mass index
(BMI) is frequently utilized.
BMI is calculated by dividing the weight in
kilograms by the square of the height in meters. A BMI greater than 28 kg/m2
defines obesity in both sexes, and morbid obesity is associated with a BMI of 40
kg/m2 or greater.
Morbidly obese patients pose a number of challenges for
emergency health care providers. Prehospital care may be delayed due to problems
in moving and transporting these patients. Appropriate-sized gurneys may not be
readily available. Even providing common amenities, such as hospital gowns or
bedpans of adequate size, can be difficult. In addition, the ED staff must
anticipate and be prepared for challenges in performing technical procedures.
Excess tissue makes access to body fluids and body cavities a formidable task,
while performing imaging procedures can be difficult or impossible. Morbidly
obese patients may also evince changes in cardiopulmonary physiology and
patterns of traumatic injury, which add to the complexity of their
care.
Pathophysiology
The etiology of obesity is heterogeneous,
including increased caloric intake, a low level of habitual physical activity, a
low resting metabolic rate, and possibly high insulin sensitivity. The recent
epidemic in developed countries is felt to be more likely due to inactivity than
increased caloric intake. The recent discovery of leptin, an antiobesity
hormone, has kindled interest in the metabolic pathophysiology of this
disease.
Pregnancy
Obesity will also complicate pregnancy. Body weight
before pregnancy and weight gain during pregnancy both influence labor, and
obese women are more likely to require cesarean sections and to experience
abnormal labor. In addition, these infants tend to be heavier than those born to
nonobese women, increasing the potential for difficult labor and delivery. Other
complications such as hypertension, diabetes, preeclampsia, and eclampsia occur
with increased frequency in pregnant obese women.
Electrocardiogram
Analysis
Host factors such as body mass influence the ease of obtaining and
interpreting an electrocardiogram (ECG). Landmarks for lead placement may be
difficult to determine, and can result in inaccurate lead placement. Variation
in fat deposits surrounding the heart and in the chest wall can lead to
inconsistent voltage changes, although in general, obese patients demonstrate
loss of voltage. Flattening or inversion of the T wave in the inferior or
lateral leads is one consistent change. None of these ECG changes is specific
for obesity, and such abnormalities should not be attributed to obesity
alone.
Sphygmomanometry
Inadequate cuff width and circumference will
artificially elevate pressure readings. However, many morbidly obese patients
are hypertensive, and a high pressure reading cannot always be blamed on
inappropriate equipment. In order to minimize errors in blood pressure
recording, a correct ratio of cuff width to arm circumference, approximately
2:5, should be chosen. The bladder length should be 80 percent of the arm
circumference. The ED should stock a variety of sizes of blood pressure cuffs
specifically for use in the obese population.
Pulse Oximetry
Tissue
thickness can make the transmission of light waves more difficult in the
extremely obese, and thus make pulse oximetry readings unreliable. However,
pulse oximetry in the moderately obese is generally accurate. In morbidly obese
patients, the earlobe could be used instead of the finger for probe placement.
Other potential areas of placement include the fifth digit of the hand or foot,
the nose, lip, or temporal artery.
Imaging
Radiographs have limited
utility in the morbidly obese. Standard film cassettes are too small to
accommodate the entire chest or abdomen, and two or more films may be required.
Excessive soft tissue can result in extremely underpenetrated films. Since
transport is invariably problematic, morbidly obese patients may need to undergo
portable radiography, resulting in lower-quality images.
CT and MRI scans
are clearly superior to radiographs, offering better resolution and greater
penetration. However, many CT scanners have a weight limit of 300 to 350 lb and
a girth limit of 30 in. Most standard MRI scanners have a maximum
shoulder-to-shoulder width of 52 in. and a weight limit of 136 to 159 kg
(300 - 350 lb). Thus many morbidly obese patients will be excluded from undergoing
these studies. There are, however, private companies, veterinary schools, and
zoos that have scanners with a larger capacity.
Weight Limits of Standard
ED and Imaging Equipment
Wheelchairs (16- to 18-in. width) 118 kg (260
lb)
Wheelchairs (20-in. width) 140 kg (310 lb)
Stretchers 227 kg (500
lb)
Radiology table 136 kg (300 lb)
CT table 136 - 159 kg (300 - 350
lb)
MRI table 159 kg (350 lb)
Equipment Problems Specific to ED
Care
From the time the obese patient enters the waiting area until the time
he or she leaves the ED, issues related to the patient's size challenge both
personnel and equipment. Waiting-room chairs may be too small. Most wheelchairs
also have weight limits and are not designed to safely accommodate patients
weighing over 118 kg (260 lb). Gurneys are often too small for the patient if
the protective side rails are in place, and without the side rails, the patient
is not safe.
In addition, collapsible gurneys are not designed to hold
the weight of the morbidly obese patient, leading to instability and concomitant
patient and staff danger. If they are used, keeping the gurney at a lower height
will enhance stability, if the device allows function at this level. Heavy-duty
stretchers (one with additional cross-brace supports) and wheelchairs designed
to hold patients weighing more than 118 kg (260 lb) are available and should be
present in the ED. Metal clamshell transport stretchers are preferable to the
standard wooden stretchers for stability, weight-bearing, and unloading of the
patient.
The comfort and modesty of morbidly obese patients should be
thoughtfully considered during his or her ED stay. The ED should stock oversized
hospital gowns. Patients should also be allowed to wear their own night clothing
as long as it does not obstruct care. Any care that requires lifting or turning
of the obese patient is difficult, as techniques used for average-sized patients
cannot be used. In general, more than two providers should always be utilized to
move the patient. Provision of an overhead trapeze will greatly facilitate
patient-assisted transfers and should be available in the ED.
Lumbar
Puncture in morbidly obese patient
A lumbar puncture is most successfully
performed in the obese patient in the sitting position. With the patient
upright, the midline is easier to estimate and both iliac crests are usually
palpable. Bone encountered after only a few centimeters usually represents
spinous process, and suggests an adjustment in the vertical plane above or below
that point. A deeper bony encounter is likely lamina and requires a medial
adjustment. Ultrasonography has been described as an aid to locating the
vertebra. Despite the excessive tissue, the standard 3-in. needle is adequate
for many obese patients, although this may require pushing the needle hub to the
point of dimpling the skin. The 5-in. needle is sometimes needed. Tight
intervertebral disk spaces are common in this population. The best choice is a
22- or 24-gauge needle, which allows adequate flow and easier passage and
decreases the likelihood of postpuncture headache.
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