Morbidly obese patients are notoriously difficult candidates for intravenous catheterization, venipuncture, or arterial puncture. Anatomy is distorted by subcutaneous fat, and landmark vessels are often not visible or palpable. This leads to multiple attempts, delay in access, and an increased incidence of central line placement with delays in changing a line after admission. All these factors contribute to a higher rate of complications, such as wound infection, pneumothorax, phlebitis, and thrombosis. In addition, standard 1.5-in. needles or catheters may not be long enough to penetrate the subcutaneous tissue and reach the target vessel; 3- or 4-in. needles and catheters are preferred. Locating the radial or femoral artery in order to obtain a sample for arterial blood gas analysis can also be extremely difficult. It may be necessary to change needle lengths on the prepackaged arterial blood gas syringes.
Various techniques can be employed to improve access to the vessel. Application of heat, light tapping over the vessel, active or passive pumping of the extremity, and application of topical nitroglycerin are commonly used to encourage vasodilation. Reactive hyperemia can be created by occluding the circulation for 3 to 4 min, then releasing the sphygmomanometer to 10 to 15 mmHg below the diastolic pressure.
The medial cubital and basilic veins are the first choice in the morbidly obese, since they are large, the antecubital crease is visible, and the skin and subcutaneous tissues are thinner in this area. Branches of the median and basilic veins on the volar surface of the forearm may be too deep to the adipose tissue to be easily accessed. The cephalic vein on the radial aspect of the wrist is a good second choice if it is not also obscured by fat. Another option is the vessels of the dorsum of the hand. The veins of the fingers may be accessible, especially those over the dorsal aspect of the thumb and forefinger. The veins of the feet are usually not good candidates, since they tend to be obscured by fat or the ravages of peripheral vascular disease. However, no vein should be excluded if it is accessible.
If peripheral veins are not available, a cutdown at the forearm veins or an attempt at cannulation of the external jugular vein should be the next choice. Cannulation of the femoral vein is another option, and will be facilitated by placing a towel under the ipsilateral buttock and having an assistant retract the panniculus. Venisection at the saphenous vein, a common alternative in patients of normal weight, will be challenging because of excess adipose tissue. Femoral catheterization is preferred over saphenous venisection in the obese patient with a palpable femoral pulse.
Because of the difficulty of peripheral access in the obese patient, a central line is more frequently required. Unfortunately, central line placement is also challenging.18 Subclavian vein cannulation may be preferable to the internal jugular, since the bony landmarks are more easily palpable and the complication rate is lower than with other central venous access methods. The patient is usually placed in the Trendelenburg position. Change positions gradually while continuing to monitor the ECG and oxygen saturation. In some cases, as when the patient reports the need to sleep upright, the Trendelenburg position may be relatively contraindicated.19 During subclavian line placement, abduction of the arm (as opposed to the standard recommendation of arm adduction) and retraction of chest tissue away from the clavicle may reduce excessive tissue layers at the site. It is common practice to insert a roll under the shoulders or a pillow lengthwise along the spine to improve access.
Ultrasound can facilitate venous cannulation and arterial puncture, allowing a higher success rate with fewer attempts because it is performed independent of landmarks.20
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