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Ann Thorac Surg 2006;82:964-972
© 2006 The Society of Thoracic Surgeons
Division of Cardiovascular-Thoracic Surgery, Children's Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, Illinois
Accepted for publication April 13, 2006.
* Address correspondence to Dr Backer, Department of Cardiovascular-Thoracic Surgery, Children's Memorial Hospital, 2300 Children's Plaza, mc 22, Chicago, IL 60614 (Email: cbacker{at}childrensmemorial.org).
Presented at the Poster Session at the Forty-second Annual Meeting of The Society of Thoracic Surgeons, Chicago, IL, Jan 30–Feb 1, 2006.
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Abstract |
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METHODS: From 1990 to 2006, 11 patients with COA were identified to have inadequate collaterals based on preoperative examination and intraoperative arterial monitoring and test clamp. Left thoracotomy with left atrium-to-descending aorta CPB was used in all. Age ranged from 4.2 to 17.4 years (mean, 8.7 ± 4.6 years). Two were reoperations for recurrent COA, 3 patients had four prior transcatheter balloon dilatations. One patient had aberrant origin of the right subclavian artery. Operative techniques included resection with extended end-to-end anastomosis (n = 6), interposition graft (n = 4), and patch repair (n = 1). During the same period 71 patients older than 1 year of age had COA repair without CPB. Age ranged from 1.1 to 46.1 years (mean, 7.6 ± 7.1 years; p = 0.6).
RESULTS: Preoperative imaging of CPB patients demonstrated absence of collaterals (n = 7), possible collaterals (n = 2), small collaterals (n = 1), and anomalous origin of the right subclavian artery (n = 1). Preoperative arm leg gradient in CPB patients was 36.0 ± 9.0 mm Hg versus 49.9 ± 15 mm Hg in non-CPB patients (p < 0.01). Mean distal femoral artery pressure with aortic test clamp was 34.3 ± 4.8 mm Hg in CPB patients versus 49.8 ± 12.4 mm Hg in non-CPB patients (p < 0.01). Mean CPB flow was 53% ± 7.3% of calculated total flow. Cardiopulmonary bypass time ranged from 17 to 46 minutes (mean, 27.5 ± 9.7 minutes). Aortic clamp time in CPB patients ranged from 15 to 33 minutes (mean, 21.6 ± 6.3 minutes). In the non-CPB group aortic clamp time ranged from 10 to 50 minutes (mean, 23.4 ± 7.5 minutes; p = 0.5). In the CPB group length of stay ranged from 3 to 7 days (mean, 4.9 ± 1.3 days), and in the non-CPB group length of stay ranged from 3 to 12 days (mean, 4.7 ± 1.4 days; p = 0.5). No patient had a neurologic complication. There were no other major complications in the CPB group (eg, bleeding, recurrent laryngeal nerve injury, re-COA).
CONCLUSIONS: Preoperative imaging and a lower arm–to-leg gradient in this series of COA patients suggested inadequate collateral circulation with the potential need for CPB. A femoral artery pressure of less than 45 mm Hg during test clamp was used as an indication for partial CPB. The use of left atrium–to–descending aorta CPB with just over 50% calculated total flow protected the spinal cord in a safe and expeditious fashion. Use of left heart bypass did not affect morbidity or recovery time as compared with COA repair in non-CPB patients.
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Material and Methods |
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Surgical Technique
In all cases monitoring included a right radial arterial line and a femoral arterial line. The index of suspicion for CPB requirement was increased when the gradient between the radial arterial line and the femoral line was smaller. All patients were approached through a left thoracotomy. All patients (CPB and non-CPB) were cooled with surface techniques to a target rectal temperature of 34.5°C. Somatosensory evoked potentials were not monitored. The latissimus dorsi muscle was divided with electrocautery, and the serratus anterior was spared. The initial dissection was in the area of the transverse aortic arch, coarctation, and descending thoracic aorta. After dissecting the arch vessels (left subclavian artery, left carotid artery), a test clamp of the transverse aortic arch proximal to the left subclavian artery was performed. The critical number observed was the mean femoral arterial pressure. If the mean femoral arterial pressure dropped below 45 mm Hg several steps were taken. The clamps were released and the patient's radial pressure was elevated either with fluid administration, inotropic agents, or both. A target upper extremity blood pressure with cross-clamp on was 180 to 200 mm Hg. A repeat test clamp was then performed. In most instances this did not change the distal pressure. If the distal pressure was still less than 45 mm Hg, then we elected to use partial CPB. The perfusionist would at this point begin setting up the extracorporeal circuit (Fig 1).
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Results |
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From January 1990 to March 2006, 209 patients underwent coarctation repair through a thoracotomy at Children's Memorial Hospital. Of these patients 127 were younger than 1 year of age. In general we did not consider the use of CPB for any patient who was younger than 1 year of age. Of the 82 patients older than 1 year of age CPB was used in 11 patients (13.4%). The mean age of the patients who underwent CPB was 8.7 ± 4.6 years (range, 4.2 to 17.4 years). This compared with a mean age of 7.6 ± 7.1 years (range, 1.1 to 46 years) for the non-CPB group (p = 0.6).
The aortic cross-clamp time of the patients having CPB was actually slightly less than that of the non-CPB group. Cross-clamp time in the CPB group was a mean of 21.6 ± 6.3 minutes and in the non-CPB group the mean was 23.4 ± 7.5 minutes (p = 0.5). Comparing the complication rates there were no deaths or paraplegia in either group. The incidence of chylothorax in the non-CPB group was 2 patients, or 2.8%. The incidence of recurrent laryngeal nerve injury in the non-CPB group was 1 (1.4%). The incidence of recoarctation in the non-CPB group was 2 (2.8%). These complication rates were statistically not different from the CPB group. The mean length of stay in the CPB group was 4.9 days, no different from the non-CPB group (4.7 days; p = 0.5).
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Comment |
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There have been many different reported techniques to avoid paraplegia in patients with inadequate collaterals. These include partial left heart CPB as was used in our series [8, 9, 11, 12], partial CPB without an oxygenator [10], CPB with circulatory arrest [13], ascending–to–descending aorta shunts and grafts [14, 15], and temporary intraluminal shunts [16, 17]. All of these techniques have advantages and disadvantages. We only used partial left heart CPB in this series and so cannot compare this with other techniques. In this discussion we review results of other surgeons with our technique, other techniques to avoid paraplegia, and the risk factors associated with paraplegia that should heighten the surgeon's index of suspicion to use CPB.
Partial Left Heart Cardiopulmonary Bypass
The use of partial left heart CPB has been reported by many other authors for the prevention of paraplegia after coarctation repair. Hughes and Reemtsma [8] reported a single patient in 1971. Luosto and colleagues [9] reported a series of 191 patients with coarctation of the aorta. A CPB technique of some form was used in 24 patients with inadequate collateral circulation. In 18 cases they used left atrial–to–descending aorta CPB. In 4 patients they used an intraluminal shunt, and in 2 cases the coarctation was temporarily bypassed using a polyethylene terephthalate fiber (Dacron) prosthesis. These authors made the point that CPB is nearly always needed if during the dissection the thoracotomy can be made without ligation of numerous collaterals. Similar to our approach, they monitored both the direct radial and femoral artery pressures. These authors appear to have experimented with three different techniques but preferred the left atrial–to–femoral artery CPB as used in our series.
Buckels and colleagues [10] reported a series of 47 patients older than 1 year of age undergoing coarctation repair. Twenty-two patients were found to have a distal aortic pressure less than 50 mm Hg and had left heart CPB much as was performed in our current series except no oxygenator was used. There were no cases of paraplegia, but 1 patient had an air embolus. The use of left heart CPB was started after 2 patients remained paraplegic after COA repair.
Wong and associates [12] reported 9 adult patients in whom the distal aortic pressure dropped to less than 20 mm Hg on the temporary application of the aortic cross-clamp. Of interest, 3 of these patients had previous surgical correction or balloon dilatation of the coarctation. The mean pressure gradient preoperatively across the coarctation was 30 mm Hg (ie, a moderate and not severe coarctation). In that series they used left heart CPB with a centrifugal pump cannulating the left pulmonary vein and the descending aorta distal to the coarctation. The mean cross-clamp and CPB times were 36 and 40 minutes, similar to our series. All patients survived, and no patients developed spinal cord complications. Patients were discharged home after a median stay of 6 days. We have not used the pulmonary vein for cannulation because of the potential risk of pulmonary vein stenosis in children.
There is extensive literature on the use of left atrial–to–femoral artery CPB in the prevention of spinal cord ischemia during adult aortic surgery for repair of traumatic lesions or aneurysms of the descending thoracic aorta [7, 18]. An adjunct sometimes used in these patients is cerebral spinal fluid drainage and somatosensory evoked potential monitoring in conjunction with left heart CPB [19]. We have not used cerebral spinal cord fluid drainage or somatosensory evoked potential monitoring in our patients.
Alternative Surgical Techniques for Spinal Cord Protection
Lange and associates [13] from Heidelberg reported the use of CPB and hypothermic circulatory arrest for repair of recoarctation and persistent hypoplastic aortic arch. They reviewed a series of 28 operations performed for recurrent coarctation. Eleven patients were thought to have adequate distal perfusion as assessed by a test clamp with a distal blood pressure greater than 50 mm Hg. In 17 cases, however, there was inadequate collateral circulation as determined by a pressure less than 50 mm Hg. In these cases CPB with circulatory arrest and core cooling to less than 20°C was used. There were no neurologic complications in either group. In comparison with our group of patients this seems to be perhaps more intervention than necessary to prevent paraplegia. The mean CPB time in these patients was 116 minutes, and the mean arrest time was 33 minutes. The mean CPB time in our series was 28 minutes. Proper cannula and clamp placement should allow reconstruction of all but the most difficult recoarctations still using continuous CPB without the disadvantages of circulatory arrest.
Christenson and colleagues [14] from Geneva, Switzerland, have reported a series of 56 patients operated on between 1990 and 2002. They used a temporary bypass from the ascending to the descending aorta, a polytetrafluoroethylene tube between 4 and 8 mm diameter. This was anastomosed to the side of the ascending aorta with a partial occlusion clamp and to the distal descending aorta below the site of the coarctation. The pressures obtained in the distal thoracic aorta were quite good, ranging from 40 to 60 mm Hg. The polytetrafluoroethylene tube was completely excised after coarctation repair. We have not used this technique. One disadvantage with this approach is that there is a limited amount of flow that can be achieved to the descending aorta based on the size of the polytetrafluoroethylene tube, the length of the tube, and the patient's cardiac output. The meta-analysis of spinal cord protection (n = 1,492 patients) published by von Oppell and associates [7] indicated that active augmentation of distal perfusion had the lowest risk of paraplegia when compared with the use of passive shunts. Paraplegia occurred in 8.2% of patients with passive shunts and in only 2.3% of patients with active augmentation of distal perfusion. From a technical standpoint it is our impression that it is easier to cannulate the left atrium and descending thoracic aorta through simple purse-string sutures rather than performing an anastomosis on both the ascending aorta and the distal descending thoracic aorta through partial occlusion clamps. The advantage of the temporary bypass is to obviate the need for a heart-lung machine and the associated (not inexpensive) disposables.
Alexander [16] reported the use of a heparin-bonded intraluminal shunt for spinal cord protection in a 4-year-old child with coarctation. Rommel tourniquets were used to control the proximal and distal portion of the shunt during the anastomosis. Pennington [17] and coworkers also reported use of an intraluminal shunt in 15 patients having subclavian flap arterioplasty. We have not used this technique for several reasons. Again, total blood flow through the shunt is limited by the shunt size and the patient's own intrinsic cardiac output under anesthesia. With the use of partial CPB the blood flow delivered to the lower extremities and the pressure can be regulated in a much more controlled fashion. The intraluminal shunt is somewhat cumbersome and requires a period of aortic cross-clamp without distal spinal cord protection while the coarctation is resected and when the shunt is removed before tying the final sutures. Although we have not attempted this technique, it seems that the actual performance of the anastomosis would be somewhat cumbersome.
The use of partial left heart CPB was very effective in our 11 patients with coarctation and inadequate collateral circulation. We do not think that circulatory arrest is required in the majority of patients. The use of an intraluminal shunt is somewhat technically cumbersome and subject to the passive flow restrictions. Similarly, the temporary ascending–to–descending aorta shunt (Gott shunt) and temporary graft are also limited as to the amount of distal flow that can be achieved. We have not used pulmonary vein cannulation for CPB because of the risk of pulmonary vein stenosis in a small child. The use of left atrium–to–descending thoracic aorta CPB seems to be a compromise on the continuum between passive shunts and hypothermia with circulatory arrest.
Factors Associated With Paraplegia and Their Relationship to the Index of Suspicion for Partial Cardiopulmonary Bypass
Cross-clamp time
Since 1957 at Children's Memorial Hospital, 384 patients have undergone repair of coarctation of the aorta. During that period, a single child (0.26%) has developed paraplegia [20]. This event occurred in 1973 and was related to multiple cross-clamps with a total clamp time of 65 minutes. We are personally aware of 3 patients from other institutions who had postrepair paraplegia (personal communication). Clamp times were 30, 38, and 57 minutes. The series reported by Lerberg and associates [4] discussed 5 patients with postoperative paraplegia. The cross-clamp times in those patients ranged from 40 to 72 minutes (mean, 49 minutes). A predicted long cross-clamp time should elevate a surgeon's index of suspicion for using CPB. A potential limitation of our strategy, which ascribes the absence of paraplegia to the use of CPB, is the short cross-clamp times in our CPB patients. Unfortunately, one never knows how long an anastomosis will take or whether unexpected complications may be encountered during the procedure. One of the patients required 33 minutes for the repair. The use of partial CPB allows one the luxury of not rushing through a procedure, which in many cases results in a shorter operation time. The cutoff time for paraplegia is currently unknown, and there have been patients who have had paraplegia with clamp times for coarctation repair as short as 15 minutes [17].
Distal aortic pressure
Another risk factor for paraplegia is low distal aortic pressure during the procedure [2, 8, 11]. This appears to be directly related to the absence of collaterals. Our experience monitoring the distal aortic pressure in a number of patients has led to the observation that in patients with significant collaterals (typically a patient with a tight coarctation that has developed during a long period) the distal aortic pressure has little if any change during clamp application. In contrast, the patient with a very mild coarctation (ie, 20 to 40 mm Hg gradient) frequently has a dramatic drop in the distal arterial pressure with the test clamp. It is those patients with a dramatic drop in distal aortic pressure who are most troubling for the possible development of paraplegia without the use of partial CPB. Christenson and coworkers [14] observed excellent correlation between preoperative magnetic resonance imaging showing good versus underdeveloped collaterals and intraoperative measurements of the distal pressure. Patients with underdeveloped collaterals had low distal perfusion pressure with aortic clamping. In our series preoperative imaging identified absence of collaterals in 7 of 11 patients. In our series the mean preoperative arm–to-leg gradient was significantly higher in the patients in whom CPB was not needed (49.9 versus 36.1 mm Hg; p < 0.01). Regarding our cutoff point of 45 mm Hg with a test clamp, Hughes and Reemtsma [8] recommended that "protective bypass systems should be available in cases in which surgery for coarctation of the aorta is performed if the distal pressure is less than 50 mm Hg." Watterson and colleagues [11] considered an initial test clamp of a distal pressure of 45 mm Hg or more to be adequate. They noted that during the first 10 minutes of cross-clamping the distal aortic pressure rose by 5 mm Hg. We never use sodium nitroprusside or any other systemic vasodilators during cross-clamp application. This allows a physiologically important increase in the proximal pressure and a resultant rise in distal pressure, presumably owing to increased pressure-dependent flow through high-resistance vessels [21, 22].
Temperature
Crawford and associates [23] in 1984 reported 3 infants who had intraoperative hyperthermia, and all 3 had postoperative paraplegia. These patients were from three different institutions, and had temperatures of 38.7°, 40°, and 39.8°C. Clamp times were 20, 31, and 61 minutes. The patient of Pennington and coworkers [17], who had paraplegia with a 15-minute clamp time, had an intraoperative temperature of 39°C. Based on this report and others we believe that mild intraoperative hypothermia is critically important. We attempt to achieve a rectal or bladder temperature of 34.5°C during the repair with or without CPB. In non-CPB patients we use active cooling, with chest irrigation with cold saline solution if necessary.
Anomalous origin of the right subclavian artery
Another risk factor for paraplegia is anomalous origin of the right subclavian artery from the descending thoracic aorta [4]. One of our patients had this risk factor. The majority of collaterals in patients with coarctation arise from the subclavian arteries. If there is an anomalous right subclavian artery originating below the coarctation, it does not contribute to collateral formation and is occluded during cross-clamp. Lerberg and colleagues [4] described one case of paraplegia among 8 patients who had anomalous origin of the right subclavian artery in coarctation repair. The patient reported by Pennington and associates [17] with a 15-minute cross-clamp time had anomalous origin of the right subclavian artery from the descending aorta. We are aware of another patient with this risk factor who developed paraplegia. We would strongly consider the use of left atrium–to–descending aorta partial CPB in this subgroup of patients.
Relationship of catheter-based techniques for coarctation of the aorta repair
Our strategy for coarctation repair has used (for many reasons) the nearly exclusive use of surgical techniques as the first intervention [24, 25]. For recoarctation, however, we believe that in most instances a transcatheter approach should be the first procedure of choice. An interesting subgroup of patients is those who have had infant balloon dilatation of a coarctation. This occurred in 2 patients in this series. The balloon dilatation of the coarctation reduced the gradient but did not eliminate it. These patients had recurrences requiring some form of reintervention. Because of the prior dilatation the preoperative gradient was small enough that collateral formation did not occur. In these patients the distal aortic pressure dropped precipitously during clamp application and necessitated the use of some form of left heart CPB. It should be noted that paraplegia has been reported as a complication after transcatheter techniques in which a complication required emergent surgical intervention (personal communication). This is a growing population as interventional cardiologists attempt balloon dilatation of native and recurrent coarctation of the aorta. These patients are potential candidates for left atrium–to–descending aorta partial CPB at the time of repair of recurrent coarctation of the aorta.
Conclusions
The use of left atrial–to–descending aorta partial CPB provided protection against spinal cord ischemia in our coarctation patients with minimal collateral circulation. This is helpful particularly in patients with only a mild to moderate native aortic coarctation or in patients who have had a previous balloon dilatation or operation and now have a recurrence.
Our review has not established the necessity of CPB for these patients, but in our opinion the requirement for CPB was highly probable in these patients and the result of an error in omission for these patients results in a devastating complication—paraplegia. The avoidance of paraplegia should be of paramount importance to the surgeon every time a coarctation repair is performed. The index of suspicion for risk of paraplegia should be increased in patients with underdeveloped collaterals based on preoperative imaging, a mild preoperative arm–to-leg gradient, and in patients with aberrant origin of the right subclavian artery from the descending aorta.
We recommend the use of left atrial–to–descending aorta partial CPB in coarctation patients older than 1 year of age if the distal mean arterial blood pressure drops to less than 45 mm Hg with a test clamp of the aorta. In our experience, pump flows of just over 50% of calculated maximum CPB flow are adequate. The use of left heart CPB does not increase morbidity or recovery time after repair of coarctation of the aorta.
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References |
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This article has been cited by other articles:
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  S. P. Setty, C. P. Brizard, and Y. d'Udekem Partial Cardiopulmonary Bypass in Infants With Coarctation and Anomalous Right Subclavian Arteries Ann. Thorac. Surg., August 1, 2007; 84(2): 715 - 715. [Full Text] [PDF]
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C. L. Backer Reply Ann. Thorac. Surg., August 1, 2007; 84(2): 715 - 716. [Full Text] [PDF]
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