The concept and initial technique for modified ultrafiltration (MUF) were introduced by Elliot et al.1 in 1991 to help ameliorate the well-known increase in total body edema associated with hypothermic, hemodilutional cardiopulmonary bypass (CPB).2,3 Many centers have adopted this technique or modification thereof with generally gratifying results.4–6 Our group has been working to perform all congenital operations, except the Norwood procedure, using 32°C full-flow CPB.7,8 Along with reducing prime volume, we have observed that full-flow 32°C CPB has greatly reduced total body edema as was predicted by Elliot.9 Nonetheless, we have still found MUF to be useful in further removing body water and believe in its metabolic, hematologic, immunologic, and hemodynamic effects.
One negative effect of 32°C full-flow CPB is the tendency for noncoronary collateral circulation and pulmonary bronchial circulation to rewarm the heart and wash out cardioplegia. This can be easily overcome by using multidose cold cardioplegia. To avoid the crystalloid load associated with multidose crystalloid or 4:1 blood cardioplegia, we have opted to use all-blood cardioplegia. This is commercially available through the pediatric modification of the Quest MPS (Quest Medical, Allen, TX).
Having placed the MPS unit within our CPB circuit, we sought to use the MPS to perform MUF. In this manuscript, we will describe our technique and present our results for integration of the Quest MPS for MUF.
The circuit is designed to allow the cardioplegia delivery device to act as a bubble trap and heater/cooler without the need for additional tubing or prime volume. Modified ultrafiltration is achieved using the vent line roller head as the pump. The patient can be transfused through the MPS pump’s connection with the oxygenator/venous reservoir (Figure 1).
The process is initiated by detaching the ultrafilter from the perfusion circuit. The inlet of the hemofilter is attached to a three-way stopcock on the outlet of the vent line. One must then clamp the outlet vent line distally. Next, the outlet of the hemofilter is attached to the three-way stopcock on the Mg++ line turning the stopcock off to Mg++. A clamp is now also applied distal to the three-way stopcock on the inlet vent line. All lines must be primed free of air before initiating MUF. The arterial filter stopcock is turned off to the purge line and opened to the 1/8th-in line. Modified ultrafiltration is begun by turning on the vent line pump slowly, making sure all stopcocks are opened to the circuit. To transfuse volume to the patient during MUF, turn the MPS circuit on to appropriate flow. The cardioplegia line must be pumped free of K+ prior to its attachment to the stopcock in the venous line. The venous line is clamped below the stopcock. If bicaval cannulation is used, the second cannula can be filled with saline as the venous line blood is drained to the circuit for MUF. Vent line volumes should also be returned to the oxygenator/reservoir before beginning MUF.
The charts of 50 consecutive patients were retrospectively reviewed. Patient ages ranged from 3 days to 5 years, and patient weight ranged from 1.7 to 20.4 kg (mean 7.7 kg, standard deviation [SD] 5.6). Nine patients were neonates. Prime volume was 400 cc for patients weighing less than 12 kg and 800 cc for patients weighing more than 12 kg.
Cardiopulmonary bypass time ranged from 32 to 231 minutes (mean 122 minutes, SD 43.1). All patients were perfused at full flow at more than 31 cc except Norwood cases. Modified ultrafiltration time was between 5 and 15 minutes (mean 9.3, SD 1.9). Volumes removed ranged from 100 to 600 cc (mean 236, SD 83.5). There was one mortality (2%), which was unrelated to MUF. No additional prime volume was required to initiate MUF using the Quest MPS.
Since the introduction of MUF in 1991 by Eliot et al.,1 many congenital heart centers have adopted the procedure to help reduce total body edema. Other measures such as reduced hemodilution, mild hypothermia with full flow, and reduced prime volumes are also effective in reducing total body edema. Mild hypothermia with full flow also offers the potential advantage of reduced central nervous system, renal, and inflammatory damage associated with deep hypothermia and reduced-flow CPB with or without circulatory arrest.10–12 Taking this into account, and intrigued by the work of Corno and Lecompte13,14 using normothermic full-flow CPB, our strategy has been to use mildly hypothermic (32°C) full-flow CPB for all pediatric patients, except for Norwood procedures.
When using mild hypothermic full-flow CPB, there is significant noncoronary collateral circulation and bronchial return. Therefore, excellent left ventricular venting and multidose cardioplegia is needed. This has led us to the use of all-blood cardioplegia, which adds no crystalloid load even when used in multidose fashion.
In this article, we have presented a circuit that uses the Quest MPS to deliver multidose all-blood cardioplegia and can be integrated into the MUF circuit. We have demonstrated that this approach is both a safe and effective technique for performing MUF. This study was intended as a safety and feasibility study and is limited by its retrospective nature. The data should not be taken to suggest that this approach is more or less effective than traditional approaches to MUF. Although it is our preference to perform all possible pediatric procedures using mildly hypothermic full-flow CPB as opposed to deep hypothermia with reduced flow CPB with or without circulatory arrest, the data presented here are not intended to support the idea that one technique is superior to the other.
1. Naik SK, Knight A, Elliot MJ: A successful modification of ultrafiltration for cardiopulmonary bypass. Perfusion 6: 41–50, 1991.
2. Kirklin JK, Blackstone EH, Kirklin JW: Cardiopulmonary bypass: studies on its damaging effects. Blood Purif 5: 168–78, 1987.
3. Maehara T, Novak I, Wyse RKH, et al: Perioperative monitoring of total body water by bioelectrical impedance in children undergoing open heart surgery. Eur J Cardiothorac Surg 5: 258–265, 1991.
4. Naik SK, Knight A, Elliot MJ: A prospective randomized study of a modified technique of ultrafiltration during pediatric open heart surgery. Circulation 84(Suppl 3): 422–431, 1991.
5. Bando K, Turrentine MW, Vijay P, et al: Effects of modified ultrafiltration in high-risk patients undergoing operations for congenital heart disease. Ann Thorac Surg 66: 821–828, 1998.
6. Bando K, Turrentine MW, Vijay P, et al: Dilutional and modified ultrafiltration reduces pulmonary hypertension after operations for congenital heart surgery: A prospective randomized study. J Thorac Cardiovasc Surg 115: 517–525, 1998.
7. Gates R: Perfusion and myocardial protection for mild hypothermic 30-32°c full flow CPB in neonatal and low weight infant heart surgery. STS Surgical Motion Pictures, 2003.
8. Gates R, Bleiweis M, Palafox B: Systemic hypothermia for pediatric cardiopulmonary bypass: Do we want it? Do we really need it? WTSA abstract, 2005.
9. Elliot MJ: Modified ultrafiltration and open heart surgery in children [editorial]. Paediatr Anaesth. 9:000–5, 1999.
10. Ungerleider RM, Gaynor JW: The Boston circulatory arrest study: An analysis. J Cardiovsac Surg 127: 1256–1261, 2004.
11. Dittrich S, Priesemann M, Fisher T, et al: Circulatory arrest and renal function in open-heart surgery on infants. Pediatr Cardiol 23: 15–19, 2002.
12. Tassani P, Barankay A, Haas F, et al: Cardiac surgery with deep hypothermic circulatory arrest produces less inflammatory response than low-flow cardiopulmonary bypass in newborns. J Cardiothorac Surg 123: 648–54, 2002.
13. Durandy Y, Hulin S, LeCompte Y: Normothermic cardiopulmonary bypass in pediatric surgery. J Thorac Cardiovasc Surg 123: 194, 2002.
14. Corno AF: What are the best temperature, flow, hematocrit levels for pediatric cardiopulmonary bypass? J Thorac Cardiovasc Surg 124: 856–857, 2002.