ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

8.3. Limitations of the modified Allen test include (6): 1. It cannot be performed properly on unconscious patients, or those with wrist or palm burns. 2. Patients in shock, deeply jaundiced, or pallid present a problem with evaluation of reperfusion. The puncture site and an area at least 2 inches in diameter surrounding the site should be prepared by scrubbing it with an antiseptic. If the technologist is unable to obtain a specimen from a site and another site is chosen, the new site should be prepared in the same way. A new, appropriately sized, sterile needle should be used for each puncture attempt. 10. Sample size depends on the amount and type of anticoagulant and the specific analyzer. A volume smaller than 0.5 ml can be analyzed for pH, Pa CO 2 , and Pa O 2 , but may give false results due to dilution if liquid sodium heparin is used (1, 7). 10.1. Sample size for infants weighing less than 10 kg is no more than 0.5 ml. Assessment of Patients 1. Assess each patient for physical and developmental status to determine if the ability to undergo the test and if special arrangements are required. If there is a language barrier, an interpreter is to be utilized. 2. Ask each patient if he/she has complied with the preparation criteria, or check medical record to assure the preparation criteria have been met. 3. Postponement may be necessary if the patient has not complied with the preparation criteria. The ordering physician is to be contacted to determine if rescheduling is necessary. 4. In order to properly interpret the test results, relevant clinical information (i.e., diagnosis and type of treat- ment) must be provided in writing by the ordering physician. Selection of Site The site of preference is the radial artery (4). Should the radial arteries be ruled out, the brachial artery is the next choice, with the femoral artery the last choice. The radial artery site should not be used if the modified Allen test demonstrates poor ulnar blood flow. Other reasons for excluding the radial artery include inaccessibility due to dressings, casts, and IV lines; hematomas or laceration of tissue due to multiple radial punctures, or the inability to adequately palpate the vessel; or patient statement of previous difficulties with radial punctures. 1. Radial artery 1.1. Although small, it is easily accessible in most patients and the most commonly used site in clinical situations (1). 1.2. Is easily compressed over the firm ligaments of the wrist, and incidence of hematomas is relatively low (1). 1.3. Collateral circulation to the hand is normally provided by the ulnar artery, and the Modified Allen test may be helpful in evaluating this collateral circulation (4). 2. Brachial artery 2.1. May be preferred for larger volumes, but may be more difficult to puncture due to deeper location between muscles and connective tissue (1). 2.2. Proper positioning of arm with hyperextension improves the position of the artery for puncture. 2.3. May be difficult to palpate in obese patients (1). 2.4. Effective compression of the puncture site is more difficult because of the deep location, and inci- dence of hematoma formation may be more common than the radial site (1). 2.5. Not commonly selected as a site in infants and children because of issues with palpation and lack of collateral circulation (1). 9. Site preparation 9.1.

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