Session IV: Pediatric Cardiopulmonary Bypass - What are Best Practices?
By Meghan Whitley
Jamie M. Schwartz, MD (Johns Hopkins) moderated the session on best practices in pediatric cardiopulmonary bypass.
Practice Variation in Cardiopulmonary Bypass
James Reagor, MPS, CCP, FPP
James Reagor, MPS, CCP, FPP (Director of Cardiovascular Perfusion, Cincinnati Children’s Hospital) started the very interesting session with a presentation discussing practice variation in Cardiopulmonary Bypass. Mr. Reagor presented data from the International Pediatric Perfusion Practice Survey from 2011 highlighting institutional differences in ultrafiltration, cardioplegia solutions, and blood gas management strategies. More recently, research performed by the National Pediatric Cardiology Quality Improvement Collaborative in 2018 identified significant variation within institutions that focused exclusively on Stage 1 palliation.
Some of the data presented included significant variation in average pump prime as well as whether steroids were added to the pump prime. Some of the most interesting data presented reviewed variation in oxygenation strategies for initiation of bypass in these patients, with a minority of institutions initiating bypass in a cyanotic state (with PaO2 values less than 70) despite data suggesting this strategy improves cardiac function and reduces damage caused by oxygen radicals. With respect to normothermic Cardiac Index, only 40% of institutions involved in the collaborative targeted 3.0L/min/M2, despite research published from Cincinnati Children’s Hospital noting a 50% reduction in acute kidney injury (AKI) rates when targeting this value.
At Cincinnati Children’s Hospital, Mr. Reagor and his team have implemented methods to decrease practice variation. These strategies are discussed and agreed upon by all team members prior to implementation in an effort to limit variation in outcomes. Utilizing AmSECT (American Society of ExtraCorporeal Technology) Standards and Guidelines to develop institutionally-based protocols, a team perfusion strategy to ensure individuals are following the most up to date agreed upon processes, and initiating practice performance evaluations showing percentage of time within common targets compared to other team members and institutional goals.
At Cincinnati Children’s Hospital, Mr. Reagor mentioned they have real-time alerts when abnormal parameters exist which have led to a 10-fold reduction in time to correct these abnormalities. All of these advances in practice are aimed at targeting specified norms for typical cases, while still allowing for clinical judgement and modifications when necessary.
Finally, Mr. Reagor described an upcoming collaborative network aimed at identifying opportunities for improvement with Cardiopulmonary Bypass which will occur within the next year. He urged those interested to reach out to your perfusion colleagues to join the PediPERForm collaborative.
Cardiopulmonary Bypass and Acute Kidney Injury
Mirela Bojan, MD, PhD
The next lecture on Cardiopulmonary Bypass (CPB) and Acute Kidney Injury (AKI) was given by Dr. Mirela Bojan (Marie Lannelongue Hospital, Le Plessis-Robinson, France). Dr. Bojan started the discussion with the unfortunate fact that 40% of patients will develop cardiac surgery-related acute kidney injury leading to increased length of stay, mechanical ventilation, increased follow-up or mortality. Based on data from the Cardiac and Vascular Surgery-Associated Acute Kidney Injury: The 20th International Consensus Conference of the Acute Disease Quality Initiative Group, several risk factors were identified; including age less than two (3-fold increased risk of AKI) and longer than three hours of bypass (7-fold increased risk) as high predictors. Intraoperative risk factors discussed included AKI related to ischemia/reperfusion, tubular toxicity, and venous congestion.
Dr. Bojan reviewed data on differential renal blood flow and how renal autoregulation is lost at significantly higher pressures than cerebral autoregulation. The risks of CPB were discussed, particularly in relation to cortical and medullary hypoxia as well as the negative effects on autoregulation during hypothermic CPB and rewarming. The increased risk of AKI secondary to anemia, hemolysis, massive transfusion and prolonged blood storage were identified. Based on research regarding AKI following contrast, there does not appear to be a risk of computed tomography angiography (CTA) shortly before CPB in neonates.
Next, Dr. Bojan discussed current and future intraoperative monitoring. With respect to near-infrared spectroscopy (NIRS) monitoring, an increase above the normal somatic-cerebral gradient of 10-15% was noted to be an indicator of sympathetic stimulation and presumed inadequate renal perfusion. The use of urinary oxygen tension as an indicator of medullary oxygen tension was also discussed as a potential clinical indicator which could be further researched.
Based on this data, Dr. Bojan gave some suggestions to attempt to limit the risk of AKI during CPB. With respect to CPB flows, maintaining a perfusion pressure above 40% of baseline MAP for age was identified to limit risk. With respect to the high risk of renal hypoxic injury during rewarming, avoiding cerebral hyperthermia by limiting arterial outlet blood temperature to <37 degrees Celsius and maintaining a rewarming rate of less than 0.5 degrees Celsius per minute were suggested. Moving forward, there could be potential benefits of renal vasodilators and sodium bicarbonate as well as intra and post-operative nitric oxide administration to decrease AKI.
Pro-Con Debate- Pro: Modified Ultrafiltration Should be Used in All Pediatric Patients
Tami M. Rosenthal, BS, MBA, CCP, LP, FFP
Tami Rosenthal, BS, MBA, CCP, LP, FFP (Chief Perfusionist, Children’s Hospital of Philadelphia) started off the Pro-Con Debate on Modified Ultrafiltration advocating for Modified Ultrafiltration (MUF) for all pediatric patients by asking the audience who utilized MUF at their institution. The majority of respondents answered that their institutions did use MUF for all cases.
Ms. Rosenthal discussed the previously documented benefits of decreasing total body water, increasing hematocrit levels and limiting wasted blood in the CPB circuit. To emphasize her point further, Ms. Rosenthal highlighted a number of articles describing the reduction in circulating inflammatory markers, reduction in pulmonary dysfunction, and improvement in hemodynamic variables when MUF was utilized. She highlighted the STS/SCA 2011 Guidelines advocating for MUF in all adult and pediatric cardiac operations using CPB as well as the AmSECT 2019 Guidelines advocating its use to optimize hemodynamics and hematocrit.
Ms. Rosenthal acknowledged some of the concerns raised by those not in favor of MUF, including higher complexity of the circuits, higher prime volumes, concerns regarding cerebral steal, temperature loss, and longer CPB times when it is utilized. However, she debunked these concerns by describing the miniaturized circuit at Children’s Hospital of Philadelphia (CHOP). By utilizing modular pumps (Spectrum Quantum HLM), a mass mounted extension arm, integrated arterial line filters and smaller tubing, they are able to decrease their pump prime to 165ml for children under 4kg. Combined, these practices would not warrant a concern regarding additional volume and potential transfusion. With respect to heat loss and complexity of the MUF circuit, CHOP utilizes a Hotline fluid warmer for MUF to maintain temperature and simplicity with a small prime volume. Ms. Rosenthal described that when monitoring NIRS and staying within flow rate guidelines, the concerns for cerebral steal are limited and the time utilized for MUF likely coincides with transesophageal echocardiography (TEE) and does not increase overall CPB time.
Finally, Ms. Rosenthal highlighted data from CHOP utilizing their miniaturized, combined CPB and MUF circuit. During a five-year period, they noted higher mean hematocrit levels following MUF compared to baseline in patients under 10kg and an increased hematocrit level in all patient STAT categories compared to baseline. She concluded that depending on your institutional MUF/CPB circuits, if you do not need to add additional volume, why would you not MUF?
Pro-Con Debate--CON: Modified Ultrafiltration in Pediatric Cardiac Surgery is no Longer Necessary
Scott Lawson, CCP
Next up, Scott Lawson, CCP (Chief Perfusionist, Children’s Hospital Colorado) debated that MUF in Pediatric Cardiac Surgery is no longer necessary. He described being an early proponent of MUF, but most articles advocating for its use were when circuit sizes and prime volumes were much larger than they are now and acknowledged performing MUF also has potential risks. When a survey was sent to fellow institutions, Mr. Lawson stated that 82% of centers reported “MUF misadventures” which usually included entraining air into the oxygenator or cannulas given the circuitry changes necessary to perform MUF. He advocated that eliminating MUF eliminates these MUF-related errors from occurring.
Mr. Lawson went on to describe observations which were noted with eliminating MUF from his institution. These included a drop in hematocrit with priming the MUF circuit which required an additional 100ml to clear cardioplegia and warm fluid. This hematocrit decrease warranted a second transfusion and donor exposure in 50% of neonates. Simply hemoconcentrating during the rewarming period yielded the same final results when compared to hematocrit values post-MUF in a retrospective study performed at Children’s Hospital Colorado. Mr. Lawson also argued that the MUF hemodynamic improvements and removal of inflammatory mediators with MUF were transient.
Studies have also identified improved ventricular contractility immediately post-bypass when MUF is not performed. Further, eliminating MUF allowed their institution to wean at higher hematocrits given that smaller circuits could be utilized, that bloodless CPB was more likely, and that eliminating MUF did not change inotrope usage. Also, protamine could be administered more quickly leading to earlier hemostasis.
At Children’s Hospital Colorado, their CPB prime is 275ml for children under 12kg, but they are limited in pushing disposable oxygenators to their limits given that they are at higher altitude. In closing, Mr. Lawson declared that eliminating MUF was advisable since it allows for reduced donor exposures, has no effect on outcomes, and allows for there to be no MUF-related errors.