Society of Cardiovascular Anesthesiologists

Pulmonary function after modified venovenous ultrafiltration in infants: A prospective, randomized trial.

Keenan HT, Thiagarajan R, Stephens KE, Williams G, et al.
J Cardiovasc Thorac Surg; 119:501-507, 2000

Reviewer: Denise Joffe, MD
Children's National Medical Center

Objectives: This study examined the effects of modified ultrafiltration (MUF) on pulmonary compliance, and examined the effects of MUF on several clinical variables including duration of intubation and length of intensive care unit stay in infants having surgery for congenital heart disease.

Study Design: This was a prospective randomized controlled study in a tertiary care facility. Infants less than one year of age, having a variety of cardiac surgical procedures, including complex neonatal repairs were randomized into two groups: a MUF group and a control group. The MUF group underwent veno-venous ultrafiltration for 20 minutes after separation from cardiopulmonary bypass (CPB). The control group underwent no ultrafilration. In each group, the following variables were recorded; baseline static and dynamic pulmonary compliance after induction of anesthesia, but prior to skin incision. Repeat measurements were made within the first hour of PICU admission and then at 24 hours after surgery. In addition, the MUF group had measurements performed after separation from CPB prior to MUF and then at the completion of MUF. Demographic data, length of CPB, the use of hypothermic arrest, complications, hemodynamic support, use of peritoneal dialysis catheters for the relief of abdominal compression, creatinine levels, body weights, duration of intubation and days in the PICU where also recorded.

Results: The study group consisted of a total of 38 patients. In the MUF group a total of 497+/-155 mL was removed. In this group, static and dynamic compliance measurements differed before MUF and immediately post MUF. However, there was no difference in compliance measurements between the MUF and control groups when compared over three time intervals; baseline, PICU admission and 24 hours postop Clinically there was no significant differences in mortality (16%), the number of sternum left open, the use and type of inotropic support, reoperations for bleeding, the use of peritoneal dialysis catheters, the number of hours intubated (MUF 140+/-91 hrs vs control 90+/-58 hrs), the length of PICU stay (MUF 10+/-9.1 days vs control 7.4+/-5.7 days) or the percentage change of weight from preop to postop day 1. The baseline to highest creatinine value was significantly higher in patients in the MUF group (0.4 +/- 0.3 mg/dL versus 0.1 +/- 0.2 mg/dL).

Discussion: The purported advantages of MUF in this patient population are multifold. It has been reported to decrease total body water and total weight gain. In addition, it reduces the number of inflammatory mediators that are thought to be responsible for multiple cardio-pulmonary complications, and coagulopathies.

The authors studied a population of patients who suffer the most complications from CPB because of their young age, low weights, and the complexity of their problems. Presumably these patients are the most likely to benefit from the positive effects of MUF. However, the results of the study do not show any significant positive clinical effects from MUF. With respect to lung function, there was no benefit, beyond the immediate period following MUF, in terms of pulmonary compliance. Furthermore, as stated in the commentary by Dr. Hanley, it is not clear if the improvement of pulmonary compliance was a result of MUF since the control group did not have similar measurements made. Pulmonary compliance improves after bypass and the control group may have shown similar improvements. Of note is that even a comparison of weights on the first post-op day did not differ.

The reason for the lack of lasting positive effects is thought to be the initiation of the inflammatory cascade while on CPB. MUF's short lasting effect (if any exists) could be the result of a temporary depletion of mediators. However, mediators are repleted when MUF is terminated. Some speculate that conventional ultrafiltration (done while on CPB) in combination with MUF may be the most successful at avoiding the initiation of the cascade reaction and removing any mediators formed. In this study MUF alone did not improve cardio-pulmonary outcome.

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