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Ann Thorac Surg 2006;82:1637-1641
© 2006 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Rapid Cardiopulmonary Support in Children With Heart Disease: A Nine-Year Experience

Robert L. Hannan, MDa,b,*, Jorge W. Ojito, CCPa,b, Marion A. Ybarra, BSa,b, Michael C. O'Brien, PA-Ca,b, Anthony F. Rossi, MDa,b, Redmond P. Burke, MDa,b

a Congenital Heart Institute at Miami Children's Hospital, Miami
b Arnold Palmer Hospital, Orlando, Florida

Accepted for publication May 18, 2006.

* Address correspondence to Dr Hannan, Division of Cardiovascular Surgery, Miami Children's Hospital, 3200 S.W. 60 Court, Suite 102, Miami, FL33155-4069. (Email: rhannan001{at}aol.com).

Presented at the Poster Session of the Forty-first Annual Meeting of The Society of Thoracic Surgeons, Tampa, FL, Jan 24–26, 2005.


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 References
 
BACKGROUND: We developed a novel mechanical rapid cardiopulmonary support system (CPS) in 1996 to eliminate what we believed were shortcomings of conventional extracorporeal membrane oxygenation (ECMO) circuits when used in patients with congenital heart disease. We reviewed the use of this system over a nine year period to determine if we had been successful in improving results compared with ECMO and if outcomes have changed over this time.

METHODS: All children supported with CPS (110 procedures) were reviewed. Noncardiac CPS cases (7) were excluded. The study population was divided into two time periods (1995 to 2000 and 2001 to 2004), which correlate with significant differences in intraoperative, postoperative, and CPS management. Patients were further analyzed by age (≤ 30 days or > 30 days), repair complexity (risk adjusted classification for congenital heart surgery [RACHS]-1 category 6 or categories 1 to 5), and length of support.

RESULTS: Overall thirty day survival of cardiac CPS patients was 55% (57 of 103). Overall survival increased from 45% (23 of 51) during the first period to 65% (34 of 52) during the second period [p ≤ 0.005]. Survival rates in neonates improved from 41% (11 of 27) to 56% (15 of 27) and RACHS-1 category 6 survival improved from 38% (5 of 13) to 69% (9 of 13), but neither change reached statistical significance. Intracranial hemorrhage occurred in 6.4% of all CPS patients.

CONCLUSIONS: Cardiopulmonary support is an effective alternative to ECMO for pediatric cardiac support. Further, our experience suggests that patient survival may be improved by CPS compared with reported results for ECMO in cardiac patients.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 References
 
Extracorporeal membrane oxygenation (ECMO) remains the standard of care in most institutions for mechanical support of patients with congenital heart disease [1]. In 1996 we recognized significant shortcomings in the design of conventional ECMO circuits when used in pediatric cardiac patients. These shortcomings included large prime volumes, the need for blood in the prime, long setup times, the requirement for heparinization of acute postoperative patients, and difficulty with transport because of bulky equipment and gravity-dependent venous drainage. To address these shortcomings we designed a new circuit using off-the-shelf components. We designated the new circuit the rapid cardiopulmonary support system (CPS) to distinguish it from conventional ECMO.

In 2000 we reported our experience with the first 23 patients whom we supported with this technique [2]. Since then there have been significant changes in our practice in the operating room, in the intensive care unit, and in the management of patients supported on the CPS circuit. We reviewed 110 consecutive cases of CPS usage from 1995 to 2004 to determine if CPS usage patterns and outcomes have changed as the art of caring for children with congenital heart disease has evolved. We compared these outcomes with literature results reported for ECMO to determine if we had been successful in designing a superior method of support.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 References
 
Patients
We obtained an exemption from the Institutional Review Board for this retrospective study. We reviewed all 110 patients who were managed on CPS from June 1995 through June 2004 by our pediatric cardiac surgery practice. We collected patient information from our departmental database, which has been prospectively maintained on all of our CPS patients. Of the 110 CPS cases, 103 were initiated in cardiac patients and 7 were initiated in noncardiac patients (eg, meconium aspiration). Of the 103 cardiac CPS cases, 83 were surgical patients and 20 were nonsurgical patients (eg, patients with cardiomyopathy). The population of this study is the 103 cardiac patients (both surgical and nonsurgical) that we have supported over the past nine years; the seven noncardiac patients were excluded.

The patient demographic information collected includes diagnosis, age, weight, and time on support. The cardiac diagnoses are shown in Table 1. The ranges and means of the patients' ages, weights, and time on support are shown in Table 2.


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  		Table 1. Cardiac CPS Patient Diagnoses
 

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  		Table 2. Cardiac Cardiopulmonary Support Patient Demographics
 
We divided our study population into two groups based on date of surgery (1995 to 2000 vs 2001 to 2004). The separation of patients into these two time periods reflects the institution of several programmatic changes in management strategies that occurred between late 2000 and early 2001, including intraoperative management, postoperative management, and CPS management. These changes are described in detail below. We have previously described declines in mortality rates between similar time periods both in overall operations (from 3.7% to 1.8%) [3] and in RACHS-1 category 6 procedures (from 29.9% to 11.2%) [4].

We further grouped the patients in each time period by procedure complexity and patient age. The procedure complexity subgroups are derived from the risk adjustment in congenital heart surgery-1 (RACHS-1) method, which categorizes patients undergoing procedures of varying complexities into one of six similar risk groups [5]. Specifically, we compared the high risk RACHS-1 category 6 (CAT 6) patients (stage I palliation for hypoplastic left heart syndrome, stage I palliation for nonhypoplastic left heart syndrome, and Damus-Kaye-Stansel procedures) with lower risk RACHS-1 categories 1 to 5 patients (CAT 1 to 5, all other patients) and with cardiac patients who did not undergo surgery except for CPS cannulation. The age subgroups are neonates (age ≤ 30 days) and all others (age > 30 days).

The CPS Circuit
The CPS circuit and its operation have been described in detail elsewhere [6]. In brief, it is a preassembled, completely heparin-coated circuit (Carmeda; Medtronic, Minneapolis, MN) comprised of arterial and venous tubing, a centrifugal pump, a membrane oxygenator, a flow probe, and a hematocrit-oxygen saturation monitor. The system can be assembled and primed asanguinously (with 250 cc of Plasma-Lyte A [Baxter Healthcare Corp, Deerfield, IL] solution) in less than five minutes. The patient is then cannulated through median sternotomy, neck vessels, or femoral vessels. As long as the patient is not bleeding, heparin is generally bolused (100 IU/kg in preoperative or nonoperative patients and 50 IU/kg in postoperative patients) and then infused to maintain an activated clotting time of 180 to 220 seconds. However, heparin may be deferred for up to 24 hours if required; for instance, in the case of postoperative bleeding. The assembled circuit is compact enough to be attached to a stretcher and is battery-powered. This allows for straightforward transport of the patient within the hospital, by ambulance, or by fixed or rotary wing aircraft.

CPS Management
During the first time period of the study, systemic-to-pulmonary artery shunts were occluded during support and the patients were managed with normal flows, normoxic perfusion, and a partial pressure of oxygen (PO 2) greater than 150. In the second time period, shunts were routinely left open and flows were adjusted upward as necessary to maintain single-ventricle physiology (eg, arterial pH 7.4, PO 2 40, partial pressure of carbon dioxide [PCO 2] 40). Also during the second period, there was an increased use of the circuit as a ventricular assist device (ie, without an oxygenator). This was invariably done in single-ventricle patients who had an initial period of support with an oxygenator in the circuit. Another management strategy instituted during the second period was the routine use of serial lactates to assess the adequacy of systemic perfusion and thus to help guide CPS flow rates.

Patient Management
Between late 2000 and early 2001 several significant changes were made in intraoperative management, postoperative management, and CPS management (detailed above). Intraoperatively we made a programmatic effort to reduce the use of deep hypothermic circulatory arrest (DHCA) by utilizing antegrade cerebral perfusion (ACP) whenever possible [7]. When DHCA was deemed necessary, we increased cooling time prior to DHCA from 15 minutes to a minimum of 20 minutes. Changes in perfusion management included replacing a pure alpha stat pH strategy with a mixed alpha and pH stat strategy [8, 9], increasing hematocrit on bypass [10], and using a hyperoxygenation technique. In addition, we began routinely monitoring cerebral oximetry in 2002.

Postoperative management changes included a programmatic change to goal-directed therapy directed by serial serum lactate determinations, available within two minutes at the bedside with point-of-care testing (i-STAT, East Windsor, NJ) [3], and increased use of afterload reducers (typically milrinone) postoperatively. In addition, based on our evolving experience, there was a decreased threshold for early cardiac catheterization and intervention postoperatively. This was based on our observation that finding treatable lesions in the catheterization laboratory improved survival [11].

Statistics
Statistical analysis, including mean, median, Spearman rank correlation, and the Mann-Whitney rank sum test for significance were conducted using SigmaStat 3.1 Advisory Statistics for Scientists Software (Systat Software, Point Richmond, CA).


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 References
 
CPS Utilization
Over the entire study period there were 2,692 cardiac operations; 1,573 during the first period and 1,119 during the second. During the entire study period we supported 103 cardiac patients on CPS, 83 of whom were surgical cardiac cases (representing 3.1% of total cardiac operations) and 20 of whom were nonsurgical cardiac cases. Between the two time periods we found no significant change in the frequency with which CPS is utilized in the overall cardiac surgical population, in the CAT 6 patient subgroup, or in the neonatal subgroup (see Table 3).


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  		Table 3. Surgical Cardiac CPS Utilization Overall and by Subgroups (Complexity and Age)
 
CPS Outcomes
Thirty day survival of the 103 cardiac CPS patients (surgical and nonsurgical) increased from 45% (23 of 51 patients) during the first time period to 65% (34 of 52 patients) (p ≤ 0.05) during the second time period (Table 4 and Fig 1).


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  		Table 4. Cardiac CPS Survival (30 Day)
 

Figure 1
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  		Fig 1. Kaplan Meier survival curve: all cardiopulmonary support patients (1995 to 2000 vs 2001 to 2004, p ≤ 0.005).

 
Between the two periods we also found increased survival rates in every one of the subgroups studied; the CAT 6 cardiac surgical patients (Table 4 and Fig 2), the CAT 1 to 5 cardiac surgical patients, the cardiac nonsurgical patients, the patients 30 or less days old, and the patients greater than 30 days old. None of these increased rates of survival reached statistical significance (Table 4).


Figure 2
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  		Fig 2. Kaplan Meier survival curve: all cardiopulmonary support risk-adjusted classification for congenital heart surgery-1 category 6 patients (1995 to 2000 vs 2001 to 2004, p = not significant).

 
Most patients were supported for seven days or less (Fig 3). There was no correlation between length of support and probability of survival. The longest support in a survivor was 9 days and in a nonsurvivor was 31 days.


Figure 3
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  		Fig 3. Survival versus duration of cardiopulmonary support (CPS). (Black bar = survivors; grey bar = nonsurvivors.)

 
Among all CPS patients (cardiac and noncardiac) from 1995 to 2004, we have diagnosed an intracranial hemorrhage rate of 6.4% (7 of 110) and a cerebral infarction rate of 2.7% (3 of 110), based on serial head ultrasounds and head computed tomographic (CT) scans when clinically indicated.


   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
References
 
Comparative Data: CPS Versus ECMO
Because pediatric CPS is a novel technique routinely employed by only a handful of institutions, there is little published data of its usage or effectiveness. Therefore, our CPS data are most appropriately compared with those of ECMO studies of similar patient populations.

The largest, most comprehensive study of pediatric cardiac ECMO patients to date was recently presented by Hintz and colleagues [1]. This study evaluated changes in utilization and outcome of neonatal cardiac extracorporeal life support (ECLS) and characterized correlates of survival. It focused on 740 neonates (≤ 30 days old) who were placed on cardiac ECLS from 1996 to 2000, a span nearly contemporaneous with our first study period. The patient population was extracted from the data submitted to the Extracorporeal Life Support Organization Registry, which captures the vast majority of all ECLS cases performed in the United States [12].

We are able to directly compare neonatal survival rates of cardiac CPS and cardiac ECMO patients. Our neonatal CPS survival rate of 41% during the first period increased to 56% during the second period (48% overall). These rates compare to Hintz's [1] overall neonatal survival of 34% (253 of 740) [p ≤ 0.05] (see Table 4). Our pediatric CPS survival rate also increased across periods (from 54% to 76%). The Hintz and colleagues' study [1] does not include pediatric data.

The "complexity" subgroups in the two studies are not strictly comparable because our subgroups are defined by the surgical distinctions made by the RACHS-1 method, whereas the Hintz and colleagues' [1] subgroups are defined by diagnostic criteria; ie, whether or not the patient had hypoplastic left heart syndrome (HLHS). Nevertheless, because HLHS patients usually receive RACHS-1 CAT 6 repairs, we may consider these groups to be analogous, if not equal. In our high complexity CAT 6 patients, survival increased from 38% to 69% between the two periods (54% overall). In Hintz and colleagues' [1] high complexity HLHS group, survival was 28% (33 of 118) [p ≤ 0.025] (see Table 4).

The Hintz and colleagues' study [1] does not address neurologic complications of ECMO. However, our intracranial hemorrhage incidence of 6.4% and cerebral infarct incidence of 2.7% compare favorably with rates reported in the literature of 10% to 28% [13, 14] and of 9% to 14% [15], respectively.

We believe that each of the programmatic changes that we made in late 2000 and early 2001 has had some degree of positive impact on the survival rate of our CPS patients. Although this supposition is difficult to prove, it remains that we have observed a decreasing CPS mortality between the two eras, as well as a decline in overall mortality and in CAT 6 mortality referenced above.

Confounding Variables
The differences in subgroup definitions described above are one barrier to comparing CPS and ECMO data. However, there are numerous other confounding variables that prevent a fully satisfactory comparative analysis of our data and any ECMO study. These include institutional differences in surgical decision making, surgical technique, and medical management both inside and outside the operating room.

An example of a surgical decision making confounder is the threshold for initiating ECLS. Some centers, for instance, choose to electively convert cardiopulmonary bypass (CPB) to ECLS at the conclusion of a repair of complex single-ventricle palliation [16], potentially showing greatly improved survival from ECMO; others (such as ours) choose to initiate ECLS only after a patient proves an inability to wean from CPB, or appears to be failing goal-directed therapy [3]. Intraoperative variables include the relative use of DHCA vs ACP, and differences in perfusion strategy such as pH strategy and hematocrit management.

Finally, there are several differences between the CPS circuit and the ECMO circuit that should be mentioned. Oxygenators have a limited life in the CPS circuit and require replacement every 4 to 7 days. Also, because the CPS circuit uses active venous drainage, identical to the active venous drainage in our operating room circuit [17], the CPS circuit is managed by perfusionists at all times. In contrast, ECMO in many institutions is performed by nurses or respiratory therapists. We believe that having personnel with advanced experience in extracorporeal life support at the bedside is invaluable.

We have accumulated nearly a decade of experience with CPS and have found it to be a valuable therapy for children with congenital heart disease. The survival data of our CPS patients demonstrate that the technique is a safe and effective alternative to ECMO for pediatric cardiac support. Further, our data suggest that pediatric cardiac patients requiring mechanical support may actually have improved survival if supported by CPS rather than by ECMO.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 References
 

  1. Hintz SR, Benitz WE, Colby CE, Sheehan AM, Rycus P, Van Meurs KP, ELSO Registry Utilization and outcomes of neonatal cardiac extracorporeal life support: 1996-2000 Pediatr Crit Care Med 2005;6:33-38.[Medline]
  2. Jacobs JP, Ojito JW, McConaghey TW, et al. Rapid cardiopulmonary support for children with complex congenital heart disease Ann Thorac Surg 2000;70:742-749discussion 749–50.[Abstract/Free Full Text]
  3. Rossi AF, Khan DM, Hannan RL, Bolivar J, Zaidenweber M, Burke R. Goal-directed medical therapy and point-of-care testing improve outcomes after congenital heart surgery Intensive Care Med 2005;31:98-104.[Medline]
  4. Hannan R, Ybarra M, Ojito J, Alonso F, Rossi A, Burke R. Complex neonatal single ventricle palliation using antegrade cerebral perfusion. Presentation at The Society of Thoracic Surgeons, Forty-second Annual Meeting, Chicago, IL. January 2006.
  5. Jenkins KJ, Gauvreau K, Newburger JW, Spray TL, Moller JH, Iezzoni LI. Consensus-based method for risk adjustment for surgery for congenital heart disease J Thorac Cardiovasc Surg 2002;123:110-118.[Abstract/Free Full Text]
  6. Ojito JW, McConaghey T, Jacobs JP, Burke RP. Rapid pediatric cardiopulmonary support system J Extra Corpor Technol 1997;29:96-99.[Medline]
  7. Hannan RL, Ybarra MA, Ojito JW, Alonso FA, Rossi AF, Burke RP. Complex neonatal single ventricle palliation using antegrade cerebral perfusion Ann Thorac Surg 2006;82:1278-1285.[Abstract/Free Full Text]
  8. Bellinger DC, Wypij D, du Plessis AJ, et al. Developmental and neurologic effects of alpha-stat versus pH-stat strategies for deep hypothermic cardiopulmonary bypass in infants J Thorac Cardiovasc Surg 2001;121:374-383.
  9. du Plessis AJ, Jonas RA, Wypij D, et al. Perioperative effects of alpha-stat versus pH-stat strategies for deep hypothermic cardiopulmonary bypass in infants J Thorac Cardiovasc Surg 1997;114:991-1000.[Abstract/Free Full Text]
  10. Jonas RA, Wypij D, Roth SJ, et al. The influence of hemodilution on outcome after hypothermic cardiopulmonary bypass: results of a randomized trial in infants J Thorac Cardiovasc Surg 2003;126:1765-1774.[Abstract/Free Full Text]
  11. Zahn EM, Dobrolet NC, Nykanen DG, Ojito J, Hannan RL, Burke RP. Interventional catheterization performed in the early postoperative period after congenital heart surgery in children J Am Coll Cardiol 2004;43:1264-1269.[Abstract/Free Full Text]
  12. Conrad SA, Rycus PT, Dalton H. Extracorporeal Life Support Registry report 2004 ASAIO J 2005;51:4-10.[Medline]
  13. Hardart GE, Fackler JC. Predictors of intracranial hemorrhage during neonatal extracorporeal membrane oxygenation J Pediatr 1999;134:156-159.[Medline]
  14. De Sanctis JT, Bramson RT, Blickman JG. Can clinical parameters help reliably predict the onset of acute intracranial hemorrhage in infants receiving extracorporeal membrane oxygenation? Radiology 1996;199:429-432.[Abstract/Free Full Text]
  15. Zwischenberger JB, Nguyen TT, Upp Jr JR, et al. Complications of neonatal extracorporeal membrane oxygenationCollective experience from the Extracorporeal Life Support Organization. J Thorac Cardiovasc Surg 1994;107:838-848discussion 848–9.[Abstract/Free Full Text]
  16. Alsoufi B, Shen I, Karamlou T, et al. Extracorporeal life support in neonates, infants, and children after repair of congenital heart disease: modern era results in a single institution Ann Thorac Surg 2005;80:15-21discussion 21.[Abstract/Free Full Text]
  17. Ojito JW, Hannan RL, Miyaji K, et al. Assisted venous drainage cardiopulmonary bypass in congenital heart surgery Ann Thorac Surg 2001;71:1267-1271discussion 1271–2.[Abstract/Free Full Text]

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Invited commentary
Richard G. Ohye
Ann. Thorac. Surg. 2006 82: 1641-1642. [Extract] [Full Text] [PDF]



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R. G. Ohye
Invited commentary
Ann. Thorac. Surg., November 1, 2006; 82(5): 1641 - 1642.
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