Technical and Clinical Complications of Intermittent Hemodialysis in the Intensive Care Unit

Vascular Access Problems

Table 154.1 lists the vascular access problems associated with hemodialysis performed to treat AKI in patients receiving intensive care.

At present, double-lumen, noncuffed dialysis catheters are the preferred means of obtaining acute dialysis vascular access. If it is anticipated that a catheter will be needed for more than a week, a tunneled cuffed catheter should be inserted to take advantage of the lower infection rates and higher blood flow rates associated with such catheters. Noncuffed, double-lumen catheters are inserted percutaneously, by means of the Seldinger insertion method, at any of three different deep venous sites: femoral, internal jugular, or subclavian. The anatomic venous site usually is chosen according to the clinical context and the physician's experience. Ideally, such dialysis catheters should be placed in the internal jugular or femoral position, the right internal jugular being the preferred site. Insertion into the right jugular vein is associated with a lower probability of major complications, because there is an almost straight venous path from the insertion site to the right atrium. The subclavian route should be avoided whenever possible, because insertion of subclavian catheters is associated with an unacceptable rate of central venous thrombosis and stenosis, leading to loss of potential sites for future arteriovenous fistulas and grafts. This issue is of particular importance, because it is frequently difficult to determine which patients with AKI need continuous renal replacement therapy either at the time of discharge or in the future. The stenosis that forms in association with a subclavian catheter may be silent until an arteriovenous fistula or graft is created on the ipsilateral arm; the most common clinical presentation in this situation is ipsilateral arm swelling with subclavian vein stenosis. In patients with preexisting cardiovascular implantable electronic devices placed via the subclavian approach, it is easier as well as simpler to place the dialysis catheter on the contralateral side.

The causes of dialysis catheter malfunction depend on the time of introduction. In general, immediate catheter malfunctions are related to catheter position, whereas late malfunctions (more than 2 weeks after insertion) are related more often to thrombus or fibrin sheath formation.

Thrombosed, noncuffed catheters can be exchanged over a guidewire or treated with thrombolytics as long as the exit site and tunnel are not infected. Exit site, tunnel tract, or systemic infections should prompt the removal of noncuffed catheters. The thrombolytic agent used to treat thrombosis of a catheter varies with local practice. In the United States, for example, tissue plasminogen activator (tPA) is used commonly for catheter thrombolysis. This agent may be effective even in low doses of 1 mg per lumen. Thrombosis of cannulated veins is another complication of indwelling catheters. The incidence of venous thrombosis ranges from 20% to 70%, depending on the site and diagnostic modalities used. Deep vein thrombosis develops after activation of the coagulation cascade by an inflammatory process, which is triggered by the presence of the intraluminal foreign body and venous endothelial lesions. The patient has edema of the ipsilateral limb, which may be tender and painful. The presence of venous thrombosis is confirmed by ultrasonography. Treatment consists of catheter removal and anticoagulation.

Air Embolism

With the development of modern hemodialysis machines, the incidence of life-threatening air embolism has diminished. Modern machines contain air bubble detectors, which can stop the pump when air is detected in the system. The two types of air embolism—venous and arterial—are distinguished by the mechanism of air entry and the site where the embolism ultimately lodges.

The two common sites for air entry through the hemodialysis circuit are as follows:

• 1.

  The arterial line, into which air can be sucked because of subatmospheric pressure between the arterial access and the blood pump. Leaks in this segment, which may occur from a loose connector or a crack in the polymeric silicone (Silastic) tubing of the blood pump, may result in air embolism.

• 2.

  Central venous catheters

Occasionally, air in the dialysate fluid may diffuse across the dialysis membrane into the blood, forming bubbles in the venous air trap.

Most causes of air embolism are reported during catheter insertion, incorrect catheter removal, or disconnection of central venous catheters. During dialysis, the air emboli are typically venous. The clinical severity depends on the quantity of the injected air, the rate of air entry, and the site of entry. The patient's body position at the time of embolization determines the clinical manifestations. With the patient in the sitting position, the air first may migrate to the cerebral blood vessels, causing neurologic decompensation and unconsciousness. With the patient in the recumbent position, air reaches the right atrium and right ventricle; foam develops in those chambers and flows into the pulmonary vasculature, which becomes occluded, causing pulmonary hypertension. Symptoms of this complication are dyspnea, chest pain, and cough followed by cardiovascular collapse. In rare cases, air that has entered venous circulation can reach the left heart and then the systemic arterial circulation, where it may provoke coronary and cerebral embolization. Embolization can happen through “paradoxical embolism” via a patent foramen ovale, through passage through physiologic pulmonary arteriovenous shunts, or from incomplete filtering of a large air embolus by the pulmonary capillaries.

Because the majority of affected patients have nonspecific symptoms, air embolism may be difficult to diagnose in the absence of a high level of suspicion for such a possibility. Air embolism should be suspected in dialysis-dependent patients after insertion, manipulation, or removal of a central venous catheter in whom sudden onset of cardiopulmonary or neurologic decompensation develops. Transesophageal echocardiography is a definitive method for detecting intracardiac air. If an air embolism occurs, the venous blood line should be clamped immediately to prevent further entry of air. Management is supportive, with the patient being placed in flat, supine position for arterial air embolism. For venous air embolism, patients may be placed in either a left lateral decubitus position (Durant's maneuver), Trendelenburg position, or left lateral decubitus head down position). Adequate oxygenation is often possible only with an increase in the oxygen concentration of the inspired gas up to 100%. If the patient does not show response within minutes, mechanical ventilation and inotropic support may be needed. If significant foaming has occurred in the right ventricle, causing cardiac arrest, cardiac puncture and aspiration should be performed to remove the foam. Hyperbaric oxygen therapy is an additional aid in treating air embolism. In addition, because chest compressions can force air out of the pulmonary outflow tract and into smaller pulmonary vessels, improving forward blood flow, they can be used as a last-resort maneuver in patients with severe hemodynamic instability.

Hemolysis

Clinically significant hemolysis can occur during the dialysis procedure. There are numerous reported causes of acute hemolysis, including oxidant damage (from chloramines, zinc, copper, or nitrate contamination of the dialysate), reduction injury (from formaldehyde used to disinfect reprocessed dialyzers or water treatment system), osmolar injury (from hypotonic or hypertonic dialysate), thermal injury (from overheated dialysate), and mechanical injury (e.g., kinking of blood lines, narrowed aperture of the blood tubing set, pump malocclusion, and the presence of a blood clot at the tip of a subclavian catheter). Clinical manifestations include headache, abdominal pain, nausea, vomiting, chest or back pain, malaise, shortness of breath, and severe hyperkalemia resulting from hemolysis. Immediately after acute hemolysis is suspected or diagnosed, the blood pump should be stopped, the venous blood lines clamped, and the blood discarded. Dialysis should be restarted as soon as the patient is stable, owing to potential fatal hyperkalemia if it is not.