Arterial cannulation should be performed when emergency physicians are managing patients with conditions requiring arterial pressure monitoring or repeated arterial blood sampling—for example, hypertensive crisis, cardiogenic shock, and respiratory failure. Although the radial artery is the most frequently employed site, extensive experience using the brachial, femoral, and dorsalis pedis arteries has shown them to be equally satisfactory. In infants and neonates, the temporal or umbilical and dorsalis pedis arteries are most often accessed, although radial artery cannulation is also acceptable. While many operators are most familiar with the radial artery site, use of the femoral artery leaves the arm clear for other procedures and, in the presence of shock, the femoral artery is less difficult to cannulate percutaneously.
Although catheterization of the radial artery is associated with up to a 20 percent incidence of temporary flow obstruction by Doppler study, permanent ischemic complications requiring surgical reanastomosis or amputation are quite rare. Confirmation of collateral flow through a patent ulnar artery can be obtained by performing the Allen test: while the patient clenches the wrist for 1 min the examiner compresses the radial and ulnar vessels with thumb and forefinger. 10 On release of ulnar compression, the patient partially extends the fingers, which are observed for rubor accentuated in comparison to the untested side. Patent ulnar circulation is indicated by return of rubor within 7 s; an equivocal result is 7 to 14 s. Greater than 14 s is considered definitely abnormal. If ulnar cannulation is contemplated, patency of the radial artery can be tested by the same test, with release of that vessel following compression. Percutaneous cannulation of the brachial or femoral arteries may be possible when the radial pulse is absent in a hypotensive patient. The technique is similar to radial artery cannulation, although a careful groin prep, preceded by removal of hair at that site to minimize the risk of infection, is necessary. With profound hypotension, cutdown to the radial artery may be required to cannulate the artery. This is performed through a transverse incision, with the artery punctured by utilizing a technique identical to the percutaneous approach, only under direct vision. The wound should be sutured and the catheter affixed with a silk suture. Serious complications—infection and occlusion—are most closely related to duration of cannulation and are much more common among critically ill patients than among those undergoing monitoring as an adjunct to a surgical procedure. During a typical stay in an intensive care unit, the incidence of local infection can be expected to approach 20 percent, while that of generalized sepsis from primary catheter infection is 4 percent, with little site-dependent variation. Other complications include hematoma formation and hemorrhage requiring transfusion.
The patient's nondominant extremity should be selected for radial artery cannulation. The wrist is placed in mild extension by placing a roll of gauze behind it and taping it to a splint. A sterile prep is applied and the operative area draped. Local infiltration should be performed with a small amount of lidocaine so that the pulse is not obscured. While a 20- or 22-gauge 1.25-in. Teflon catheter over a needle is held in one hand, the radial pulse is palpated with the other. The skin over the radial aspect of the wrist is punctured with the needle pointing proximally and at a 45° angle with the plane of the skin. The needle is advanced into the artery until pulsations appear. The catheter is then slid off the needle into the artery. If pulsatile flow ceases, the catheter may be withdrawn until arterial flow again appears, and a second attempt may be made to advance the catheter. If this is unsuccessful, the procedure must be repeated. After each attempt, care should be taken to apply pressure to the site long enough to prevent hematoma formation. Once in the artery, the catheter is connected to the monitoring system and flushed through a three-way stopcock with a sterile cap. The catheter should then be secured to the skin at its hub using silk or nylon suture. Kits are available for wire-guided arterial catheterization.
If cutdown is necessary to achieve arterial puncture, exposure of the artery is performed in a manner similar to that outlined for venous cutdown above. When 1 cm of artery is visible, the vessel is isolated by passing two lengths of silk suture beneath it, using a hemostat. A catheter through needle device is passed through the skin distal to the area of exposure and advanced into the site. The artery may then be punctured and the catheter advanced. The suture, which is used only to control the artery, may then be removed and the skin incision closed.
SPECIAL PROBLEMS RELATED TO VENOUS ACCESS Complications of Total Parenteral Nutrition
Central venous catheter placement for total parenteral nutrition (TPN) may be done short-term as a part of hospital care or long-term at home or in extended-care facilities. TPN is usually administered through a catheter placed into either the subclavian or jugular vein. The incidence of mechanical and septic complications depends upon the skill, experience, and commitment of both the patient and the nutrition support team.11 Suspicion of line sepsis demands immediate consultation. Most patients should be admitted, although the catheter may not need to be removed in selected cases.
Catheter occlusions occur in approximately 5 percent of patients receiving long-term TPN. If the first-line remedy of flushing the catheter with normal saline or heparin solution fails, thrombolytic agents, such as urokinase, may be used to lyse clots that obstruct the lumen of catheter without obstructing the vessel. The recommended dose of urokinase ranges from 5000 to 15,000 IU, depending on the type of intravascular device and its filling volume. A syringe with 1 to 2 mL of urokinase solution is instilled into the catheter, which is then clamped for 30 min. If no blood return is achieved, the maneuver may be repeated, with urokinase left in the catheter for 60 min. If there is still no return, then a third attempt may be made, this time leaving the urokinase solution in place for 12 h. Failure to clear the catheter after 12 h suggests either organized thrombus or anatomic abnormality; further diagnostic study such as angiography and ultrasound-Doppler duplex scanning may be indicated. Some authors have reported high success rates infusing ethanol (up to 3 mL of 70% solution) for presumed lipid occlusions or hydrochloric acid (HCl, 0.1N, up to 3 mL) to clear presumed mineral oil or other precipitates.
Catheter-related sepsis in patients receiving TPN is usually a result of catheter contamination by organisms colonizing the skin. Gram-negative bacteremia, sepsis syndrome, and fungemia are treated by removal of catheter in association with appropriate antimicrobial therapy. Gram-positive infections can often be managed with the catheter left in place while antibiotic therapy is administered. The delivery of TPN through peripherally inserted central catheters (PICCs) is associated with slightly lower infection rates but a higher rate of mechanical failure. Because there is a considerably increased risk of both infection and thrombosis when femoral lines are used for TPN, this mode of access is less than optimal for patients requiring parenteral nutrition. Other reported complications include pulmonary embolism, line fracture, embolized catheter fragment, mediastinitis, superior vena cava syndrome, pneumothorax, air embolism, and lymphatic duct injury.
It is increasingly common for patients to present to EDs with specialized devices, such as Hickman catheters, which have been placed to provide long-term IV access. Such devices facilitate outpatient treatment in an era of increasing cost-consciousness. Emergency physicians can access these devices to obtain specimens for laboratory study as well as to administer IV fluids and medications.
When indwelling catheters are accessed, meticulous care should be taken to maintain sterility at the site. Depending on the type of device (implanted versus externalized), specialized equipment may be required to obtain access. Five milliliters of either normal saline or heparin flush (100 U/mL) is injected and then withdrawn gently to ensure catheter patency. Blood for laboratory study is collected only after a dead-space volume (5 to 10 mL) has been collected and discarded. Since these devices are heparinized, coagulation studies performed on such samples are unreliable; blood for these studies should be obtained from other sites. After access has been terminated, implanted devices should be flushed with heparin solution of 1000 U/mL strength. Other externalized devices should be flushed using a solution of 100 U/mL strength.
Arteriovenous fistulas and shunts should be used only for access in the most extreme of emergency situations, since complications, including loss of the access site, are common. The smallest needle appropriate to the task at hand should be inserted. Afterward, local pressure should be applied for 5 min or more, and these arterialized sites should be carefully monitored for hemorrhage for 12 h.
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