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EDITORIAL

Neuraxial Blockade for Pediatric Cardiac Surgery: Lessons Yet to Be Learned

James M. Steven, MD^*, and Francis X. McGowan, Jr., MD

*Department of Anesthesiology, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania; and Department of Anesthesiology, Boston Children’s Hospital, Boston, Massachusetts

Address correspondence and reprint requests to James M. Steven, MD, Department of Anesthesiology, Children’s Hospital of Philadelphia, 34th St. and Civic Center Blvd., Philadelphia, PA 19104-4399.

This issue of Anesthesia & Analgesia contains two reports originating from the Stanford University cardiac anesthesia group that describe their experience with regional anesthetic techniques in pediatric patients having a variety of operations for congenital heart disease (CHD) (1,2). Both studies are retrospective. Although institutional bias precluded any attempt to compare "standard" IV analgesic methods with the neuraxial approaches that are clearly favored by that group, these studies do provide some degree of reassurance regarding efficacy and the infrequency of major complications. These studies also furnish information comparing the various regional techniques, with both suggesting that thoracic epidural catheters are most likely to provide effective and durable analgesia with the fewest complications. However, such comparison between techniques may be premature, because regional techniques have yet to gain wide acceptance in the care of children having open-heart surgery.

Perhaps the greatest obstacle to widespread acceptance of epidural or subarachnoid puncture in this group of patients is concern about the risk of bleeding (e.g. epidural hematoma formation) on heparinization for cardiopulmonary bypass soon after block placement. Other factors that may accentuate this risk in CHD include the presence of collateral vessels, increased venous pressures, and clotting dysfunction associated with cyanosis, venous congestion, or shear stress. Both studies, and particularly the relatively large retrospective series reported by Peterson et al. (1), do help advance the notion that regional techniques can be used with some degree of safety in these patients. The Peterson et al. (1) study contained 220 patients overall, 144 of whom underwent cardiopulmonary bypass; the study by Hammer et al. (2) consisted of 41 additional patients, all of whom required cardiopulmonary bypass. Nine open-heart surgery patients were included in both reports. There was no evidence of "clinical" epidural hematoma formation in either group of patients. As noted in the Peterson et al. (1) study, these numbers only allow one to conclude with 95% confidence that the occurrence rate of epidural hematoma will be less than 1.5% to 2.0% (i.e., the likelihood of an event occurring that was not detected in n patients is approximated with 95% confidence by 3/n) (3). One would have to study at least 3000 patients without one occurrence to assume that the rate was less than 0.1%. What incidence of paraplegia is one willing to accept for shorter duration of mechanical ventilation or some degree of cost reduction? Most clinicians would contend that the first case report of a clinically significant epidural hematoma will negate studies many times the size of these, particularly in absence of comparative studies demonstrating the unique benefits of epidural analgesia.

Nevertheless, clinicians frequently undertake potentially risky procedures and therapies if the benefits are sufficient to warrant them. The major limitation of these studies is the absence of comparative data demonstrating extraordinary benefits. Without this information, we cannot decide if the interventions merit the risk, particularly the low frequency/high morbidity occurrences such as paraplegia or apnea. Nor can we compare them to standard IV analgesia. Reports similar to those presented here were fairly common at the time that regional and neuraxial methods were first being reintroduced into pediatric practice (4–6). These early reports had merit precisely because they represented the initial descriptions of regional techniques in small and/or critically ill infants and children. Few Contemporary clinicians would contend that these techniques are not technically possible or effective. Rather, wider acceptance of regional analgesia for cardiac surgery remains permanently constrained by inadequate demonstration of superior benefits and acceptable safety.

Answers to these questions are not forthcoming. In fact, Hammer et al. (2) suggest that they view the unique benefits of regional anesthesia as so unequivocal that it would be impossible at this point to conduct a proper prospective, large-scale, randomized comparison to "standard" IV techniques. In lieu of direct measurements, enthusiasm for these methods is based on several lines of indirect evidence, many of which remain controversial in children with CHD. These include the following.

Neuraxial Techniques More Effectively Attenuate the Stress Response

There are numerous problems encountered when applying this argument to support the widespread application of neuraxial methods in children undergoing cardiac surgery. Virtually all of the studies indicating that regional techniques provide superior suppression of stress responses have been performed in adults having both cardiac and noncardiac surgery (7,8). As pediatricians and pediatric anesthesiologists, we routinely question the notion that improvements in the outcome of adults with different pathophysiology and undergoing different procedures are likely to apply to this set of pediatric patients. It represents a reasonable hypothesis, but one that needs to be tested.

Although a relationship between anesthetic technique, morbidity, and mortality has been shown in a few high-risk neonatal populations (9,10), more often, effects on surrogate endpoints such as cathecholamines and other stress hormone levels, hemodynamic stability, nitrogen balance, etc, have been used to infer a beneficial effect (11). However, these studies typically compared large-dose IV phenylpiperidine opioid regimens with rather "minimalist" inhaled anesthetics. They were also conducted in high-risk neonatal populations. There is virtually no information in pediatric patients having cardiac surgery that regional techniques significantly affect these surrogate markers. As a result, to apply this argument, one must extrapolate from two discrepant sources: stress hormone responses in patients having noncardiac surgery (11) and older data suggesting a positive association between outcome and these hormone levels in high-risk infants having cardiac surgery (9,10). Recent clinical trials have not validated the link between stress hormone levels and outcome, even in high-risk neonates (12,13). Using these inconsistent results as the basis for assumptions about the beneficial effects of neuraxial analgesia in the lower risk infants and older children who represent typical candidates for these techniques (i.e., for early extubation) would seem highly speculative.

Most major congenital cardiac programs have developed alternative protocols that enable tracheal extubation in the operating room for selected patients. This goal is usually accomplished by limiting IV opioids without detecting any adverse effects on outcome, defined as successful early discharge with no mortality. In contrast to recent practice, numerous congenital cardiac centers routinely tracheally extubate infants early who were formerly considered high risk; in the process, these centers have abandoned therapies aimed at suppression of the stress response. Whether alteration of stress responses represented a surrogate endpoint of little consequence to all but the highest risk patients or other methodological improvements (e.g., modified ultrafiltration) have reduced the impact of the response remains unclear. In summary, there is no evidence in pediatric cardiac patients that regional techniques more effectively suppress the stress response, nor is there sufficient basis for adopting any analgesic techniques to modulate a response that has myriad constituents, a poorly understood role (both beneficial and deleterious), and little evidence of impact on current clinical outcome.

Spontaneous Ventilation and Early Tracheal Extubation Are Better

As referenced in both papers, there have been several reports over the years indicating that early extubation of pediatric cardiac surgery patients is feasible and may help reduce costs. However, little evidence supports the opinion that early tracheal extubation is physiologically superior or leads to better outcome. Based on hemodynamic principles, rather than actual outcome measures, clinicians often contend that Fontan physiology will favor spontaneous ventilation because of lower intrathoracic pressures, thereby augmenting pulmonary flow. Although the work of Penny et al. (14), which is referenced in the article by Peterson et al. (1), actually discusses increased pulmonary blood flow caused by mechanical negative pressure ventilation, there is limited evidence, by using Doppler flow velocity measurements, that pulmonary blood flow changes in Fontan patients with a variety of manipulations during spontaneous and controlled positive pressure ventilation (15,16). Yet, there are no longitudinal Doppler assessments of the same patients immediately before and after tracheal extubation. Similar assertions have been applied to the effects of airway pressure on afterload and ventricular filling in patients with right heart dysfunction. These arguments fail to account for the deleterious effects that hypoventilation, atelectasis, and hypercarbia would exert on pulmonary blood flow and right ventricular afterload in the context of spontaneous ventilation after surgery, sedation, and/or neuraxial opioids. Although respiratory dysfunction may indeed be less prevalent with regional techniques than with IV analgesics, that theoretical benefit has not been confirmed in this population.

However theoretically appealing, there is, alas, no direct evidence for patients with any cardiac lesion, either postoperatively or at any other point, that spontaneous ventilation leads to better hemodynamic function or improves outcome. In fact, tracheal intubation and mechanical ventilation are the mainstays of therapy when these same patients experience severe respiratory or hemodynamic deterioration; likely benefits include diminished work of breathing, improved ventilation and decreased afterload on the systemic ventricle. The perpetually nagging inconsistency of these observations supports the notion that cardiovascular performance reflects a substantially more complicated interplay of physiologic factors that may mislead clinicians who attempt to focus on a single component. We might propose an equally logical argument that all children, after congenital cardiac surgery, would benefit from relief of the burden of spontaneous ventilation during the immediate postoperative period, when they are recovering from the pulmonary, cardiac, and metabolic effects of cardiopulmonary bypass, myocardial ischemia-reperfusion, and various other physiologic insults. Clearly, one can tracheally extubate these patients early, but there is no evidence that it represents the optimal course. It remains to be shown whether early extubation leads to improved physiology, is "physiology-neutral," or is actually a strategy that imposes a tolerable physiologic burden on low- and moderate-risk patients. Finally, the notion, as presented, that regional techniques are essential to the success of early extubation regimens ignores the reality that most congenital cardiac programs have developed general anesthetic regimens that enable prompt tracheal extubation with satisfactory analgesia.

None who has observed the postoperative recovery of children after lateral thoracotomy or witnessed the bilateral thoracosternal ("clamshell") incision used for bilateral lung transplantation would argue that there is no role for regional anesthesia in pediatric cardiac surgery. We simply know that these patients are more comfortable, which has to mean that they are better off. And therein lies the problem. We want to believe that our efforts are good for our patients, and that more effort leads to even greater good. This is the point at which this debate has languished for more than a decade. The central controversy revolves not around efficacy, but whether regional analgesia adjuncts offer unique benefits that merit the rare, but potentially catastrophic, risk. Despite substantial efforts, these investigators will persuade few converts. Although their significant patient population will assuage the anxiety clinicians face, one must address the comparative benefit in a randomized prospective fashion, as Peterson et al. (1) suggest.

One course that might lead to wider acceptance of regional analgesia would emerge from a comparison of preoperative versus postoperative epidural placement. Such a study might provide insight into the importance of preemptive analgesia and whether stress responses play a significant role in measurable outcome. More importantly, it would open the prospect of performing epidural catheter placement once hemostasis is restored and the ability to perform neurologic examination is imminent. Such a modification might permit greater acceptance among the vast majority of practitioners who remain unwilling to assume the risks of preoperative epidural placement without unequivocal demonstrated benefit. We will only be able to advance the discussion, and with it the level of our care, if practitioners on both sides of this debate willingly engage in an appropriate trial comparing regional and IV analgesia in these patients. As things stand now, however, we find ourselves mired at an impasse between fervent believers, resolute in their position and unwilling to test the other point of view.

References

1. Peterson KL, DeCampli WM, Pike NA, et al. Regional anesthesia in pediatric cardiac surgery: report of 220 cases. Anesth Analg 2000;90:1014–9.[Abstract/Free Full Text]
2. Hammer GB, Ngo K, Macario A. A retrospective examination of regional plus general anesthesia in children undergoing open heart surgery. Anesth Analg 2000;90:1020–4.[Abstract/Free Full Text]
3. Hanley JA, Lippman-Hand A. If nothing goes wrong, is everything all right? Interpreting zero numerators. JAMA 1983;249:1743–5.[Abstract/Free Full Text]
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12. Gruber EM, Casta A, Laussen PC, et al. Stress response in infants undergoing cardiac surgery: a randomized study of fentanyl bolus, fantanyl infusion and fentanyl-midazolam infusion [abstract]. Anesthesiology 1999;91:A1284.
13. Casta A, Laussen PC, Gruber EM, et al. A randomized study of fentanyl bolus, fantanyl infusion and fentanyl-midazolam infusion for infant cardiac surgery: clinical outcome [abstract]. Anesthesiology 1999;91:A1285.
14. Penny DJ, Hayek Z, Rawle P, et al. Ventilation with external high frequency oscillation around a negative baseline increases pulmonary blood flow after the Fontan operation. Cardiol Young 1992;2:277–80.
15. Fyfe DA, Kline CH, Sade RM, et al. The utility of transesophageal echocardiography during and after Fontan operations in small children. Am Heart J 1991;122:1403–15.[Web of Science][Medline]
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