Performing modified ultrafiltration on pediatric patients

AORN Journal, August, 2002 by Lauren Quattro, Marla Bowser, Adriana Schwendt

Pediatric cardiac surgery is an area of new frontiers. Many infants and children born with congenital heart defects now are discovering an encouraging future. The invention of the heart-lung machine, along with new strides in technology and surgical procedures, has made it possible for cardiac surgeons to provide pediatric patients with new hope for repairing complex defects. One new frontier in pediatric cardiac surgery is the development of the modified ultrafiltration system, which is used during pediatric open-heart procedures to reduce the adverse effects associated with cardiopulmonary bypass (CPB) surgery.

BACKGROUND

To repair most congenital defects in pediatric patients, it is necessary to use CPB, which is not without many risks. One of the challenging problems involved with cardiac surgery is hemodilution. During CPB surgery, the CPB pump must be primed with crystalloid solutions to provide an air-free circuit. During bypass, these crystalloid solutions are introduced into the patient's vascular space, causing hemodilution, and, in turn, a decrease in the patient's hematocrit level, platelets, and clotting factors. This decrease causes increased bleeding, need for transfusions, intubation time, and length of intensive care unit (ICU) stays.

Hemodilution also decreases the patient's colloid osmotic pressure, which causes fluid to move into the extravascular tissues, producing edema. This edema affects many organs, including the brain, kidneys, liver, and lungs. The prime volume to patient blood volume ratio is higher in children than in adults; therefore, it is necessary to use all means possible to reduce this fluid and decrease hemodilution.

MODIFIED ULTRAFILTRATION

Modified ultrafiltration reduces the excess fluid in the patient's vascular system, thus increasing colloid osmotic pressure. This reverses the gradient, causing a decrease in tissue and organ edema and associated morbidity. The modified ultrafiltration technique also allows blood to be returned to the patient in a concentrated form. The maximum charge for the extra supplies needed for modified ultrafiltration range from $150 to $300, making it a cost-effective procedure that results in shorter intubation time and ICU stays.

Patients who have undergone CPB procedures with the modified ultrafiltration technique at Johns Hopkins Hospital, Baltimore, have demonstrated positive results; however, the procedure is associated with some risks, including improper assembly of the modified ultrafiltration pump, introduction of air into the patient's vascular system, line rupture, and hypotension. Neurological deficits also can be associated with modified ultrafiltration if the blood flow through the system is too high, causing a decrease in blood flow to the brain.

To use modified ultrafiltration, the perfusionist who operates the heart-lung machine first modifies the pediatric CPB circuit to incorporate the modified ultrafiltration system. Before priming the CPB circuit, the perfusionist adds a roller head, hemoconcentrator, bubble trap, extra tubing, and connectors to the circuit to incorporate the modified ultrafiltration line. The pump and these extra supplies then are primed to ensure a bubble-free circuit.

At the sterile field, the nurse clamps and cuts the venous line to add a luer-lok connecter. The modified ultrafiltration line coming from the pump will be attached to the luer-lok connector.

Modified ultrafiltration for patients who weigh fewer than 15 kg (33 lbs) is implemented immediately after CPB ceases. It typically is performed for 10 minutes, based on the surgeon's preference. Approximately 10 mL to 20 mL per kg per minute of fluid is removed from the patient, which averages between 400 mL and 600 mL, depending on the patient's weight, amount of time the modified ultrafiltration system is employed, and surgeon preference. Inotropic agents and diuretics, as well as peritoneal dialysis catheters, also are used to decrease the patient's body fluid.

CASE STUDY

Jill, a one-year-old female, was admitted to the OR for repair of a ventricular septal defect (VSD). She was brought to the OR suite at 6:30 AM by her father. The circulating nurse greeted Jill and her father and instructed the father to sit by Jill while masked anesthesia was administered. After Jill was sedated, the circulating nurse encouraged the father to kiss his daughter goodbye and escorted him to the waiting area. The circulating nurse informed Jill's family members that they would be updated regarding the patient's status approximately every one and one-half hours to two hours during the procedure.

In the OR, Jill was intubated, and the anesthesia care provider placed peripheral and central venous lines and a pulse oximeter monitor on Jill's great toe. The physician assistant inserted a 6-Fr Foley catheter, and the circulating nurse placed a grounding pad on Jill's back. Jill was positioned supine for maximum cardiac exposure. The circulating nurse placed a cushioned pad under Jill's head and a small shoulder roll under her shoulders, taking care that her extremities were resting comfortably and that the endotracheal tube was not disrupted.