Low-flow hypothermic cardiopulmonary bypass protects the brain

Truncus Arteriosus with Interrupted Aortic Arch: Aortic Arch Reconstruction Without Circulatory Arrest

Truncus arteriosus (TA) with interrupted aortic arch (IAA) is a rare congenital cardiac anomaly. Traditionally, IAA would require period of deep hypothermic circulatory arrest (DHCA) for aortic arch reconstruction. DHCA may cause myocardial depression and neuro-developmental dysfunction. IAA repair is presently being performed with hypothermic low-flow selective cerebral perfusion and distal body circulatory arrest. Even though this prevents cerebral adverse effects of DHCA, there is still risk to the spinal cord and kidneys.

Here, we describe the aortic arch reconstruction by maintaining the total body perfusion without any periods of circulatory arrest in a neonate with TA with IAA.

Direct Innominate Artery Cannulation versus Side Graft for Selective Antegrade Cerebral Perfusion during Aortic Hemiarch Replacement

Background  Selective antegrade cerebral perfusion (SACP) has become our preferred method for cerebral protection during open arch cases. While the initial approach involved sewing a graft to the innominate artery as the arterial cannulation site, our access strategy has since evolved to central aortic cannulation with use of a percutaneous cannula in the innominate for SACP. We hypothesized that SACP delivered via direct innominate cannulation using a 12- or 14-Fr cannula results in equivalent outcomes to cases utilizing a side graft.

Methods  This was a single-center, retrospective analysis of 211 adult patients who underwent elective hemiarch replacement using hypothermic circulatory arrest with SACP via the innominate artery between 2012 and 2020. Urgent and emergent cases were excluded.

Results  A side graft sutured to the innominate was utilized in 81% ( n  = 171) of patients, while direct innominate artery cannulation was performed in 19% ( n  = 40) of patients. Baseline patient characteristics were similar between groups aside from a higher baseline creatinine in the direct cannulation group (1.3 vs. 0.9, p  = 0.032). Patients undergoing direct cannulation demonstrated shorter cardiopulmonary bypass time (132.7 vs. 154.9 minutes, p  = 0.020) and shorter circulatory arrest time (8.1 vs. 10.9 minutes, p  = 0.004). Nadir bladder temperature did not significantly differ between groups (27.2°C for side graft vs. 27.6°C for direct cannulation, p  = 0.088). There were no significant differences in postoperative outcomes.

Conclusion  Direct cannulation of the innominate artery with a 12- or 14-Fr cannula for SACP during hemiarch replacement is a safe alternative to using a sutured side graft. While cardiopulmonary bypass and circulatory arrest times appear improved, this is likely attributable to accumulation of experience and proficiency in technique. However, direct innominate artery cannulation may facilitate quicker completion of these procedures by eliminating the time necessary to suture a graft to the innominate artery.

Design of a Physiologic Pulsatile Flow Cardiopulmonary Bypass System for Neonates and Infants

Cardiopulmonary bypass surgical techniques that allow a surgeon to operate on the infant's heart use an extracorporeal circuit consisting of a pump, oxygenator, arterial and venous reservoirs, cannulae, an arterial filter, and tubing. The extracorporeal technique currently used in infants and neonates is sometimes associated with neurologic damage. We are developing a modified cardiopulmonary bypass system for neonates that has been tested in vitro and in one animal in vivo. Unlike other extracorporeal circuits which use steady flow, this system utilizes pulsatile flow, a low prime volume (500ml) and a closed circuit. During in vitro experiments, the pseudo patient's mean arterial pressure was kept constant at 40 mmHg and the extracorporeal circuit pressure did not exceed a mean pressure of 200 mmHg. In our single in vivo experiment, the primary objective was to determine whether physiologic pulsatility with a 10F (3.3 mm) aortic cannula could be achieved. The results suggest that this is possible.

Optimal temperature management in aortic arch operations

Hypothermic circulatory arrest is a critical component of aortic arch procedures, without which these operations could not be safely performed. Despite the use of hypothermia as a protective adjunct for organ preservation, aortic arch surgery remains complex and is associated with numerous complications despite years of surgical advancement. Deep hypothermic circulatory arrest affords the surgeon a safe period of time to perform the arch reconstruction, but this interruption of perfusion comes at a high clinical cost: stroke, paraplegia, and organ dysfunction are all potential-associated complications. Retrograde cerebral perfusion was subsequently developed as a technique to improve upon the rates of neurologic dysfunction, but was done with only modest success. Selective antegrade cerebral perfusion, on the other hand, has consistently been shown to be an effective form of cerebral protection over deep hypothermia alone, even during extended periods of circulatory arrest. A primary disadvantage of using deep hypothermic circulatory arrest is the prolonged bypass times required for cooling and rewarming which adds significantly to the morbidity associated with these procedures, especially coagulopathic bleeding and organ dysfunction. In an effort to mitigate this problem, the degree of hypothermia at the time of the initial circulatory arrest has more recently been reduced in multiple centers across the globe. This technique of moderate hypothermic circulatory arrest in combination with adjunctive brain perfusion techniques has been shown to be safe when performing aortic arch operations. In this review, we will discuss the evolution of these protection strategies as well as their relative strengths and weaknesses.

Cerebral injury during paediatric heart surgery: perfusion issues

Suboptimal neurodevelopmental outcome is common in children who have congenital heart disease. Its aetiology is often multifactorial. This review focuses on the role of cardiopulmonary bypass. Hypothermia is the mainstay of cerebral protection. Low flow and regional low flow are preferred to deep hypothermic circulatory arrest in many situations. Cooling and rewarming, aortopulmonary collaterals, pH, air emboli, the systemic inflammatory response, haematocrit, oxygenation, glucose and ultrafiltration can influence neurodevelopmental outcome. Although no pharmacological agents have been shown to have a beneficial effect on neurodevelopmental outcome in clinical practice in children, animal work on the use of steroids several hours before surgery is encouraging.

Paediatric CPB: Bypass in a High Risk Group

Children and particularly neonates present unique challenges during CPB. Patient age, size, underlying anatomy and surgical strategy influence the perfusion techniques and the construction of the CPB circuit. The normal changes in physiology in the first weeks of life impact upon surgical technique and outcome of repair.

Limited surgical access necessitates alternative cannulation strategies. Deep hypothermia, low flow CPB and circulatory arrest are frequently used. An understanding of the related pathophysiology is therefore required to make the correct choices and to optimise patient outcome.

Implications from neurologic assessment of brain protection for total arch replacement from a randomized trial

OBJECTIVE

The study objective was to perform a randomized trial of brain protection during total aortic arch replacement and identify the best way to assess brain injury.

METHODS

From June 2003 to January 2010, 121 evaluable patients were randomized to retrograde (n = 60) or antegrade (n = 61) brain perfusion during hypothermic circulatory arrest. We assessed the sensitivity of clinical neurologic evaluation, brain imaging, and neurocognitive testing performed preoperatively and 4 to 6 months postoperatively to detect brain injury.

RESULTS

A total of 29 patients (24%) experienced neurologic events. Clinical stroke was evident in 1 patient (0.8%), and visual changes were evident in 2 patients; all had brain imaging changes. A total of 14 of 95 patients (15%) undergoing both preoperative and postoperative brain imaging had evidence of new white or gray matter changes; 10 of the 14 patients had neurocognitive testing, but only 2 patients experienced decline. A total of 17 of 96 patients (18%) undergoing both preoperative and postoperative neurocognitive testing manifested declines of 2 or more reliable change indexes; of these 17, 11 had neither imaging changes nor clinical events. Thirty-day mortality was 0.8% (1/121), with no neurologic deaths and a similar prevalence of neurologic events after retrograde and antegrade brain perfusion (22/60, 37% and 15/61, 25%, respectively; P = .2).

CONCLUSIONS

Although this randomized clinical trial revealed similar neurologic outcomes after retrograde or antegrade brain perfusion for total aortic arch replacement, clinical examination for postprocedural neurologic events is insensitive, brain imaging detects more events, and neurocognitive testing detects even more. Future neurologic assessments for cardiovascular procedures should include not only clinical examination but also brain imaging studies, neurocognitive testing, and long-term assessment.

What is the best method for brain protection in surgery of the aortic arch? Selective antegrade cerebral perfusion

Despite considerable progress in the operative management of lesions involving the transverse aortic arch, replacement of this portion of the vessel remains a surgical challenge and is still associated with mortality and morbidity. This situation is due not only to the technical difficulties of the procedure but, often, to the unsatisfactory preservation of the integrity of the central nervous system during the period of arch exclusion. The techniques of cerebral protection during surgery of the aortic arch can be divided into those aimed at suppressing the metabolic demand of the central nervous system and those aimed at maintaining the metabolic supply during the time of exclusion of the cerebral vessels. Whichever technique is used, it must maintain the normal metabolism of the central nervous system or, at least, allow restoration of the physiologic conditions of its function. In this regard, selective antegrade cerebral perfusion has demonstrated experimentally and clinically its superiority over the other proposed protective techniques.

Surgical management of aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a common and often devastating condition that requires prompt neurosurgical evaluation and intervention. Modern management of aSAH involves a multidisciplinary team of subspecialists, including vascular neurosurgeons, neurocritical care specialists and, frequently, neurointerventional radiologists. This team is responsible for stabilizing the patient on presentation, diagnosing the offending ruptured aneurysm, securing the aneurysm, and managing the patient through a typically prolonged and complicated hospital course. Surgical intervention has remained a definitive treatment for ruptured cerebral aneurysms since the early 1900s. Over the subsequent decades, many innovations in microsurgical technique, adjuvant maneuvers, and intraoperative and perioperative medical therapies have advanced the care of patients with aSAH. This report focuses on the modern surgical management of patients with aSAH. Following a brief historical perspective on the origin of aneurysm surgery, the topics discussed include the timing of surgical intervention after aSAH, commonly used surgical approaches and craniotomies, fenestration of the lamina terminalis, intraoperative neurophysiological monitoring, intraoperative digital subtraction and fluorescent angiography, temporary clipping, deep hypothermic cardiopulmonary bypass, management of acute hydrocephalus, cerebral revascularization, and novel clip configurations and microsurgical techniques. Many of the topics highlighted in this report represent some of the more debated techniques in vascular neurosurgery. The popularity of such techniques is constantly evolving as new studies are performed and data about their utility become available.

Comparison of Three Warming Devices for the Prevention of Core Hypothermia and Post-Anaesthesia Shivering

The efficacy of forced air warming with a surgical access blanket in preventing a decrease in core temperature during anaesthesia and post-anaesthesia shivering (PAS) was compared with two widely used interventions comprising forced air warming combined with an upper body blanket, and a circulating water mattress, in a prospective, randomized double-blind study. A total of 90 patients undergoing total abdominal hysterectomy were studied, 30 in each group. Core temperature was measured 15, 30, 45, 60, 90 and 120 min after induction of anaesthesia. PAS was evaluated every 5 min after emergence from anaesthesia over a period of 1 h. Core temperature fell in all three groups compared with the baseline, but forced air warming using a surgical access blanket was more effective than the other warming methods in ameliorating the temperature decrease. The surgical access blanket was also superior to the circulating water mattress in reducing PAS.

Brain protection by using innominate artery cannulation during aortic arch surgery

The innominate artery cannulation (IAC) through the same sternotomy incision was used for 68 patients with aneurysm, involving the ascending aorta or the aorta arch. The IAC can get adequate flows during cooling and re-warming of cardiopulmonary bypass. It can also provide sufficient antegrade perfusion for brain during hypothermia circulation arrest. There is no relative complication noted for the technique, and we believe it is a simple and effective alternative.

Straight deep hypothermic arrest: experience in 394 patients supports its effectiveness as a sole means of brain preservation

BACKGROUND

The three methods of brain preservation for aortic arch surgery--straight deep hypothermic circulatory arrest (DHCA) without perfusion adjuncts, retrograde cerebral perfusion, and antegrade cerebral perfusion--remain controversial. Patients in this report underwent surgery solely with DHCA.

METHODS

Straight DHCA at 19 degrees C was used in 394 patients (267 males, 127 females) during a 10-year period. Mean age was 61.3 years (range, 15 to 88 years). Eighty-seven cases (22.1%) were urgent or emergencies. Thirty-eight (9.6%) were performed for descending or thoracoabdominal pathology and the rest for ascending/arch (102 hemiarch, 49 total arch). Ninety-one patients (23.1%) had dissections. The head was packed in ice. No barbiturate coma was used.

RESULTS

DHCA lasted a mean of 31.0 minutes (range, 10 to 66 minutes). Reexploration for bleeding was required in 4.5% (18/394). Overall mortality was 6.3% (25/394). Mortality was 3.6% (11/307) for elective cases and 16% (14/87) for emergency cases. The stroke rate was 4.8% (19/394). The seizure rate was 3.1% (12/394). Forty-five patients with high professional cognitive demands (MD, PhD, attorney, etc) performed without detriment postoperatively. Among patients with DHCA exceeding 40 minutes, the stroke rate was 13.1% (8/61); a neuroradiologist's review of brain computed tomography scans found 62.5% of these strokes (5/8) to be embolic and 37.5% (3/8) hypoperfusion related. By multivariable logistic regression, emergency operation and descending location increased morbidity and mortality.

CONCLUSIONS

Straight DHCA without adjunctive perfusion suffices as a sole means of cerebral protection. Stroke and seizure rates are low. Cognitive function, by clinical assessment, is excellent. Especially for straightforward ascending/arch reconstructions, there is little need for the added complexity of brain perfusion strategies.

Effect of prophylactically administered edaravone during antegrade cerebral perfusion in a canine model of old cerebral infarction

OBJECTIVE

Reactive free radical species are thought to be involved in postoperative neurologic dysfunction after antegrade selective cerebral perfusion in brains with old infarction. We assessed the brain protective effect of prophylactically administered edaravone, a free radical scavenger, for antegrade selective cerebral perfusion in brains with or without old infarction in a canine model.

METHODS

A canine model of old cerebral infarction was created by injecting cylindric silicone embolus into the middle cerebral artery. Animals showing obvious neurologic deficits and surviving 4 weeks or longer were included in the model. Deep hypothermia with antegrade selective cerebral perfusion was performed in both intact (non-edaravone, group A; edaravone-treated, group B) and infarcted animals (non-edaravone, group C; edaravone-treated, group D). Serum concentrations of malondialdehyde, hexanoyl-lysine, glutamate, and venous-arterial lactate difference were measured, and central conduction time and amplitude of somatosensory evoked potentials were assessed during the operation.

RESULTS

Compared with the intact groups, serum concentrations of malondialdehyde and hexanoyl-lysine in group C significantly increased at the end of antegrade selective cerebral perfusion, whereas that of glutamate did so in the rewarming phase. Increases in all these biochemical parameters were suppressed in group D. In group C, the venous-arterial lactate difference was significantly greater in the rewarming phase at 28 degrees C compared with intact groups. A significant prolongation of postoperative central conduction time and decrease in neuronal activity were detected in group C, both of which recovered in group D.

CONCLUSION

Prophylactic administration of edaravone exerted a significant protective effect against postoperative neurologic dysfunction after antegrade selective cerebral perfusion in a canine model with old cerebral infarction.

Axillary Cannulation for Proximal Aortic Surgery is as Safe in the Emergent Setting as in Elective Cases

BACKGROUND

Right axillary artery cannulation and selective antegrade cerebral perfusion (SCP) have become well-described strategies in the surgical treatment of proximal aortic disease. Many series report increases in adverse outcomes with SCP used in emergent settings. We compare outcomes in elective and emergent patients.

METHODS

Over 21 months, SCP through right axillary cannulation with a side graft was performed in 61 patients. Thirty-three percent (20 of 61) underwent emergent operation for Stanford type A dissection or intramural hematoma, including 3 of 20 (4.7%) with pericardial tamponade; the remainder of SCP (41 of 61) was elective. The mean follow-up was 9.1 +/- 0.40 months.

RESULTS

Selective antegrade cerebral perfusion was used in 20 of 22 emergent cases (91%), with 2 unsuccessful cannulation attempts, and no peripheral arterial dissections encountered. The SCP flows averaged 16.3 +/- 0.71 cc x kg(-1) x min(-1) for a mean perfusion period of 26.1 +/- 1.9 minutes. The average cardiopulmonary bypass time for all patients was 173 +/- 11 minutes. Average hospital stay was 8.1 +/- 0.80 days. One case (1.3%) of permanent and 3 cases (4.8%) of temporary neurologic dysfunction occurred in SCP patients. The hospital mortality rate for emergent SCP cases (2 of 20, 10%) was not statistically different from the mortality rate for elective SCP cases (3 of 41, 7.3%, p = not significant), with no difference in complication rates. All 3 SCP patients with preoperative tamponade survived without complication. Cerebral oximetry data showed a trend toward decreased left-sided (contralateral) scalp perfusion. There was no association of emergent status with neurologic dysfunction, death, or any other adverse outcome.

CONCLUSIONS

Axillary cannulation and SCP in the surgical treatment of proximal aortic pathology is safe in both elective and emergent settings.

Complex Neonatal Single Ventricle Palliation Using Antegrade Cerebral Perfusion

BACKGROUND

The efficacy of antegrade cerebral perfusion (ACP) during complex neonatal single ventricle palliation requiring arch reconstruction is uncertain. We adapted the use of ACP in early 2001 in a programmatic effort to minimize the use of deep hypothermic circulatory arrest (DHCA).

METHODS

We retrospectively analyzed data of 126 consecutive patients operated on between 1995 and 2004, including stage-one palliation of hypoplastic left heart syndrome, stage-one palliation for nonhypoplastic left heart syndrome, and Damus-Kaye-Stansel procedures. Patients were divided into two groups: those repaired with prolonged DHCA only (n = 67) and those with ACP (n = 59) and usually a shorter period of DHCA. Risk was further stratified into high risk (weight < or = 2.5 kg or other cardiac lesion) and usual risk for each group.

RESULTS

Survival at 30 days in the usual-risk groups was 72.0% DHCA and 93.2% ACP (p < or = 0.025), and in the high-risk groups it was 61.5% DHCA and 80% ACP (not significant). One-year survival in the usual-risk groups was 57.4% DHCA and 84.1% ACP (p < or = 0.01), and in the high-risk groups it was 38.5% DHCA and 46.7% ACP (not significant). Overall survival to date is 52.2% DHCA and 71.2% ACP (p < or = 0.5).

CONCLUSIONS

There is a statistically significant survival advantage for usual-risk patients with the use of ACP. Although there is a trend to improved survival in the high-risk groups, it does not reach statistical significance and long-term outcomes in these patients remains disappointing. We continue to use ACP and believe it contributes to an overall survival advantage in our institution.

Specific bypass conditions determine safe minimum flow rate

BACKGROUND

The purpose of this study is to define a safe minimum flow rate for specific bypass conditions using continuous monitoring with near-infrared spectroscopy and direct observation of the cerebral microcirculation.

METHODS

Two series of experiments (n = 72 in each) were conducted in which piglets were cooled to a temperature of 15 degrees, 25 degrees, or 34 degrees C on cardiopulmonary bypass with hematocrit 20% or 30%, pH-stat management in all, followed by 1 or 2 hours of reduced flow (10, 25, or 50 mL.kg(-1).min(-1)). Animals in series one had a cranial window placed over the parietal cortex to evaluate the microcirculation with intravital microscopy. Plasma was labeled with fluorescein-isothiocyanate-dextran for assessment of functional capillary density (FCD) and microvascular diameter. In series two, near-infrared spectroscopy was utilized to detect tissue oxygenation index (TOI). Outcome measures included histologic and neurologic injury scores.

RESULTS

The TOI during low flow and FCD during rewarming and after weaning from cardiopulmonary bypass were associated with neurologic injury. Failure of FCD to return to baseline during rewarming predicted worse functional and histologic outcome (p < 0.001). Regression analysis indicated that temperature and low-flow rate were multivariable predictors of TOI and FCD during rewarming (p < 0.001).

CONCLUSIONS

Tissue oxygen index derived from near-infrared spectroscopy is a useful real-time monitor for detecting inadequate cerebral perfusion during cardiopulmonary bypass. Minimal safe pump flow rate varies according to the conditions of bypass: using pH stat management and with an hematocrit of either 20% or 30%, a flow rate as low as 10 mL.kg(-1).min(-1) is safe for as long as 2 hours at a temperature of 15 degrees C. However, under the same conditions at 34 degrees C, a flow rate of 10 mL.kg(-1).min(-1) is very likely to be associated with neurologic injury.

Better Protection of Pulmonary Surfactant Integrity With Deep Hypothermia and Circulatory Arrest

BACKGROUND

The influence of deep hypothermia with either circulatory arrest (DHCA) or low-flow (DHLF) perfusion on pulmonary surfactant metabolism in neonates undergoing cardiac surgery remains unknown. This study was conducted to determine the influence of either strategy on surfactant metabolism and pulmonary function with neonatal piglet model.

METHODS

Sixteen piglets underwent 90-minute deep hypothermia, either with circulatory arrest or low-flow perfusion (30 mL.kg(-1).min(-1)) at 18 degrees C. Disaturated phosphatidylcholine, total phospholipids, and total proteins from tracheal aspirates were measured serially until the end of cardiopulmonary bypass. Lung static compliance, airway resistance, and arterial blood oxygen partial pressure to inspired oxygen fraction were also measured.

RESULTS

The DHLF caused more significant decrement of pulmonary static compliance than DHCA (3 +/- 0.4 mL.cmH2O(-1) vs 3.5 +/- 0.3 mL.cmH2O(-1) at 90 minutes of deep hypothermia). Arterial blood oxygen partial pressure to inspired oxygen fraction decreased more significantly after cardiopulmonary bypass in the DHLF group than the DHCA group (205 +/- 84 mm Hg vs 302 +/- 96 mm Hg). The DHLF caused more severe decrement of disaturated phosphatidylcholine total phospholipids (50% +/- 21% vs 67% +/- 23% of baseline at 90 minutes of deep hypothermia) and disaturated phosphatidylcholine total proteins (58% +/- 23% vs 73% +/- 23% of baseline at 90 minutes of deep hypothermia) than DHCA. More significant water retention developed in the lung in the DHLF group than in the DHCA group. The extent of surfactant depletion was statistically correlated with the extent of pulmonary functional deterioration in either group.

CONCLUSIONS

The DHCA induces less injury on pulmonary surfactant metabolism and pulmonary function than DHLF.

Prior deafferentation confers long term protection to CA1 against transient forebrain ischemia and sustains GluR2 expression

Hippocampal CA1 pyramidal neurons undergo delayed neurodegeneration after transient forebrain ischemia, and the phenomenon is dependent upon hyperactivation of l-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) subtype of glutamate receptors, resulting in aberrant intracellular calcium influx. The GluR2 subunit of AMPA receptors is critical in limiting the influx of calcium. The CA1 pyramidal neurons are very sensitive to ischemic damage and attempts to achieve neuroprotection, mediated by drugs, have been unsuccessful. Moreover, receptor antagonism strategies in the past have failed to provide long-term protection against ischemic injury. Long-term protection against severe forebrain ischemia can be conferred by fimbria-fornix (FF) deafferentation, which interrupts the afferent input to CA1. Our study evaluated the long-term protective effect of FF deafferentation, 12 days prior to induction of ischemia, on vulnerable CA1 neurons. Our results indicate that at 7 and 28 days post-ischemia, prior FF deafferentation protected 60% of neurons against ischemic cell death. Furthermore, we sought to evaluate whether FF deafferentation also sustained GluR2 levels in these neurons. GluR2 protein and mRNA expression were sustained by deafferentation at 70% of control following ischemia. Correlation studies revealed a positive correlation between GluR2 protein and mRNA level. These results demonstrate that protection conferred by FF deafferentation was long-term and related to sustained GluR2 expression.

Tissue oxygenation index is a useful monitor of histologic and neurologic outcome after cardiopulmonary bypass in piglets

OBJECTIVE

Tissue oxygenation index is a novel monitoring indicator derived by near-infrared spectroscopy. We hypothesized that tissue oxygenation index could predict a minimum safe flow rate for specific bypass conditions.

METHODS

Thirty-six piglets (age, 43 +/- 5 days; weight, 9.0 +/- 1.1 kg) underwent cardiopulmonary bypass with cerebral near-infrared spectroscopy (NIRO-300; Hamamatsu Photonics K.K., Hamamatsu City, Japan). Animals were cooled for 40 minutes to 15 degrees C, 25 degrees C, or 34 degrees C (pH-stat, hematocrit value of 20% or 30%, and pump flow of 100 mL . kg -1 . min -1), followed by low-flow perfusion (10, 25, or 50 mL . kg -1 . min -1) for 2 hours. Neurologic and behavioral evaluations were determined for 4 days. The brain was then fixed for histologic assessment. Tissue oxygenation index was defined as the average signal during low-flow bypass.

RESULTS

Animals with an average tissue oxygenation index of less than 55% showed cerebral injury, whereas animals with an index of greater than 55% showed minimal or no evidence of injury. Correlations were found between average tissue oxygenation index and histologic score (Spearman rho = -0.65, P < .001) and neurologic deficit score (Pearson r = -0.50, P = .002) on the first postoperative day. Temperature (P < .001), flow rate (P < .001), and hematocrit value (P = .002) were multivariable predictors of tissue oxygenation index, as determined by means of multivariable analysis of variance.

CONCLUSION

Tissue oxygenation index is a useful monitor for defining the minimum safe flow rate during cardiopulmonary bypass. An index value of less than 55% is a strong predictor of neurologic injury.

Reducing risk in infant cardiopulmonary bypass: the use of a miniaturized circuit and a crystalloid prime improves cardiopulmonary function and increases cerebral blood flow

Advances in perfusion strategies have played an important role in improving outcomes following repair of complex congenital heart defects. The influence of cooling strategy, temperature, duration of circulatory arrest, and specific method of cerebral perfusion on neurologic morbidity have been extensively characterized. Similarly, the ability of pharmacologic agents to modulate the post-cardiopulmonary bypass (CPB) inflammatory response has been previously elucidated in both the laboratory and clinical arena. However, modification of the circuit and priming components have received comparably less attention. We recently showed that employment of a miniaturized circuit and a bloodless prime reduce inflammation and have salutary effects on cardiopulmonary function following hypothermic low-flow perfusion (HLF), and that this circuit may also improve cerebral protection following both deep hypothermic circulatory arrest and HLF. The current report, therefore, reviews current strategies utilized to minimize post-CPB inflammation and highlights the empirical evidence from our laboratory demonstrating the beneficial role of a miniaturized extracorporeal circuit in this context.

Comparison of pH management during antegrade selective cerebral perfusion in canine models with old cerebral infarction

OBJECTIVE

We sought to examine the influence on the brain, with or without old infarction, of pH management during antegrade selective cerebral perfusion in a canine model.

METHODS

A cerebral infarct canine model was created by injecting a cylindrical silicone embolus. Dogs that had obvious neurologic deficits and had survived for 4 weeks or more were included in the model. Deep hypothermia with antegrade selective cerebral perfusion was performed in intact mongrel dogs (alpha-stat: group A, n = 6; pH-stat: group B, n = 6) and mongrel dogs with infarctions (alpha-stat: group C, n = 6; pH-stat: group D, n = 6). Maxillary vein saturation of oxygen, venous-arterial lactate difference, and serum concentrations of malondialdehyde and glutamate were measured and central conduction times and amplitude in somatosensory evoked potentials were assessed during the operation.

RESULTS

During the experimental procedure, the maxillary vein saturation of oxygen was significantly less (P <.05), whereas the venous-arterial lactate difference was significantly greater (P <.05) in the cooling phase to 28 degrees C in group C than in the other groups. The pH-stat group showed significantly greater arterial Paco(2) and lower pH than the alpha-stat group during the period between the cooling to 28 degrees C and the rewarming to 28 degrees C (P <.05). Other intraoperative parameters did not show any difference among the groups. In group C the serum concentrations of malondialdehyde and glutamate significantly increased, as did the central conduction time, whereas in both groups C and D the amplitude ratio decreased significantly.

CONCLUSIONS

This experiment suggests that pH-stat management during antegrade selective cerebral perfusion provides more effective protection for a brain with old infarction than alpha-stat management.

Regional low-flow perfusion improves neurologic outcome compared with deep hypothermic circulatory arrest in neonatal piglets

BACKGROUND

Regional low-flow perfusion is an alternative to deep hypothermic circulatory arrest, but whether regional low-flow perfusion improves neurologic outcome after deep hypothermic circulatory arrest in neonates remains unknown. We tested neurologic recovery after regional low-flow perfusion compared with deep hypothermic circulatory arrest in a neonatal piglet model.

METHODS

Sixteen neonatal piglets underwent cardiopulmonary bypass, were randomized to 90 minutes of deep hypothermic circulatory arrest or regional low-flow perfusion (10 mL.kg(-1).min(-1)) at 18 degrees C, and survived for 1 week. Standardized neurobehavioral scores were obtained on postoperative days 1, 3, and 7 (0 = no deficit to 90 = brain death). Histopathologic scores were determined on the basis of the percentage of injured and apoptotic neurons in the neocortex and hippocampus by hematoxylin and eosin and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling (0 = no injury to 4 = diffuse injury). Differences between groups were tested by using the Wilcoxon rank sum test, and results are listed as medians within a range.

RESULTS

There were no significant differences between groups during cardiopulmonary bypass. Postoperative neurobehavioral scores were abnormal in 25% (2/8) of the regional low-flow perfusion animals versus 88% (7/8) of controls. Regional low-flow perfusion animals had significantly less neurologic injury compared with controls on postoperative day 1 (0.00 [range, 0-5] vs 12.5 [range, 0-52]; P <.008). There was a trend for less severe injury in the regional low-flow perfusion group (2.0 [range, 1-4] vs 0.0 [range, 0-50]; P =.08) on hematoxylin and eosin. The degree of apoptosis was significantly less in the regional low-flow perfusion group (0.0 [range, 0-1] vs 2.5 [range, 0-4]; P =.03).

CONCLUSIONS

Regional low-flow perfusion decreases neuronal injury and improves early postoperative neurologic function after deep hypothermic circulatory arrest in neonatal piglets.

Effectiveness of a circulating-water warming garment in rewarming after pediatric cardiac surgery using hypothermic cardiopulmonary bypass

OBJECTIVE

To evaluate the effectiveness and safety of the ALLON 2001 microprocessor-based thermoregulation system in pediatric patients undergoing cardiac surgery requiring hypothermic cardiopulmonary bypass compared with the routine thermal care.

DESIGN

Prospective randomized clinical study.

SETTING

Single tertiary academic medical center.

PARTICIPANTS

Infants (0-1 year) who underwent congenital heart surgery requiring hypothermic cardiopulmonary bypass (n = 18). Patients with open wounds and/or patients treated with an investigational drug or device within 30 days of surgery were excluded.

INTERVENTIONS

Randomized use of thermoregulation system (warming garment, n = 9) or routine thermal care (control, n = 9) after separating from cardiopulmonary bypass until the arrival to the pediatric intensive care unit (PICU).

MEASUREMENTS AND MAIN RESULTS

There were no statistically significant differences in the demographic data, cardiopulmonary bypass time, operating room time, incidence of deep hypothermic circulatory arrest, and cooling temperature between the groups. The nasopharyngeal temperature was significantly higher in the warming garment group after separation from cardiopulmonary bypass. Nasopharyngeal temperature at 20 minutes was 36.5 degrees C versus 35.01 degrees C (p = 0.0047), at 40 minutes was 36.98 degrees C versus 35.30 degrees C (p = 0.034), and at admission to the PICU was 36.09 degrees C versus 35.31 degrees C (p = not significant). There was no difference in the core-to-peripheral temperature gradient (nasopharyngeal-to-skin temperature) between the 2 study groups at any time point. No adverse events related to the use of the warming garment thermoregulation system were observed.

CONCLUSION

The investigated thermoregulation system was effective in preventing the after-drop of temperature that occurs after cardiopulmonary bypass in small infants compared with routine warming methods.

Aortic arch reconstruction without circulatory arrest: review of techniques, applications, and indications

The majority of neonatal intracardiac repairs can now be performed with the use of low-flow cardiopulmonary bypass. However, aortic arch reconstruction still requires a period of circulatory arrest. Recently, a number of surgeons have reported techniques of limiting or completely avoiding circulatory arrest during arch reconstruction in an attempt to reduce the risk of neurologic injury. Several techniques are currently in use that have been successfully applied during biventricular repair and the Norwood operation for a wide range of aortic arch pathology including hypoplastic or interrupted aortic arch, the hypoplastic left heart syndrome, and its equivalents. These techniques maintain continuous low-flow cerebral perfusion via the innominate artery, directly or indirectly. In the last 2 years at the Montreal Children's Hospital (Montreal, Canada) we have consistently used such techniques for all arch reconstructions, including the Norwood operation, completely avoiding the use of circulatory arrest. These techniques are still in evolution with regard to flow rates, temperature, and safe period of low flow. Although the early results are encouraging, long-term follow-up with respect to neurodevelopmental outcome is essential to help us decide which techniques are optimal. This chapter provides an overview of the currently used techniques allowing cerebral perfusion during aortic arch reconstruction and summarizes our early experience at the Montreal Children's Hospital.

Antegrade regional cerebral perfusion

A quiet and bloodless field providing optimal surgical conditions has been a crucial prerequisite for the performance of complex cardiac repairs in early life. The use of deep hypothermic circulatory arrest has fulfilled this role, and has been a catalyst for the development of neonatal and infant cardiac surgery. The recently increased awareness of possibly increased incidence of adverse neurological events and developmental outcome associated with this technique,1–5however, has led to a general trend away from its use. In its place, techniques have been developed to provide cerebral perfusion during reconstruction of the aortic arch and the Norwood operation. Some have described the techniques as regional low-flow perfusion. In our opinion, they are described more accurately as antegrade regional cerebral perfusion. In this review, we discuss the recently described techniques for such antegrade regional cerebral perfusion during surgery on the aortic arch, with emphasis both on the Norwood operation and the observed physiological changes in the cerebral and systemic circulations. The neurologic and developmental outcomes following the use of the technique are still unknown.

Serial proton magnetic resonance spectroscopy of the brain in children undergoing cardiac surgery

We used proton magnetic resonance spectroscopy to study 11 children (age < 8 years) with congenital heart disease undergoing cardiopulmonary bypass to determine whether low (10 +/- 4; n = 6) vs high (20 +/- 4; n = 5) perfusate hematocrits during bypass resulted in changes in brain metabolites which correlate with neurologic injury. Long and short echo time single voxel magnetic resonance spectroscopy in occipital gray matter and neurologic assessment were performed preoperatively and 2 and 5 days postoperatively. We also determined whether prolonged periods at low flow rates during bypass affected spectroscopy variables. We found no significant differences in metabolite ratios between the low vs high hematocrit groups or the lower vs higher flow rate groups (repeated measures analysis of variance of observation ranks converted to normal scores). However, our study was limited by statistical power due to the small sample size, therefore no conclusions could be made. Additional studies involving a greater number of patients are necessary. In all 11 children, magnetic resonance spectroscopy detected a significant decrease in brain N-acetyl-aspartate, and increases in myoinositol and glutamate/glutamine after surgery (Quade test) demonstrating that magnetic resonance spectroscopy is sensitive in detecting subtle postoperative changes in brain metabolites.

Brain injury in children with congenital heart disease

The incidence of neurodevelopmental impairment in children with congenital heart disease is high. Its aetiology is multiple and complex. Prevention and treatment must start during the preoperative period and continue through the intra- and postoperative periods. Research has resulted in a clearer understanding of the relationship between congenital heart disease and the brain, and of the effects of cardiopulmonary bypass, hypothermia and circulatory arrest. This has led to modifications in management which may improve neurological outcome in the future.

Tissue oxygen tension during regional low-flow perfusion in neonates

OBJECTIVE

We examined cerebral cortical and peripheral organ tissue Po(2) values in a neonatal piglet model of regional low-flow perfusion.

METHODS

Twenty-one neonatal piglets were placed on cardiopulmonary bypass, were cooled to 18 degrees C, then underwent either deep hypothermic circulatory arrest or regional low-flow perfusion at 20 or 40 mL/(kg x min) for 90 minutes. Regional low-flow perfusion was carried out by advancing the aortic cannula into the proximal innominate artery. Tissue mean Po(2) and Po(2) distribution were measured in the cerebral cortex, liver, small bowel, and skeletal muscle through the principle of oxygen-dependent quenching of phosphorescence. Measured quantities were compared by analysis of variance or the Fisher exact test.

RESULTS

During regional low-flow perfusion, axillary and femoral arterial pressures, respectively, were 55 +/- 15 and 8 +/- 4 mm Hg at 40 mL/(kg x min) and 37 +/- 10 mm Hg (P =.04) and 17 +/- 5 mm Hg (P =.08) at 20 mL/(kg x min). Venous saturations were 95% +/- 6% at 40 mL/(kg x min) and 84% +/- 6% at 20 mL/(kg x min) (P =.03 at 15, 30, and 45 minutes). Cortical Po(2) was similar to prebypass values during regional low-flow perfusion at 40 mL/(kg x min) (53 +/- 5 mm Hg) but declined during reperfusion and recovery. Cortical Po(2) was lower than before bypass during low-flow perfusion at 20 mL/(kg x min) (38 +/- 7 mm Hg) but increased during reperfusion. Po(2) in liver and bowel was less than 10 mm Hg during low-flow perfusion at both 20 and 40 mL/(kg x min). Fraction of oxygen distribution with Po(2) lower than 15 mm Hg was less during perfusion at 40 mL/(kg x min) than at 20 mL/(kg x min) (P =.001). Three of 6 piglets that received a 40-mL/(kg x min) flow rate had significant upper torso edema, metabolic acidosis, and an unstable recovery period, whereas zero of 6 piglets that received a 20-mL/(kg x min) flow rate did.

CONCLUSIONS

In a piglet model, regional low-flow perfusion at 20 mL/(kg x min) resulted in lower cortical tissue oxygenation but better recovery than did perfusion at 40 mL/(kg x min). Neither flow rate adequately oxygenated organs in the lower torso.

Multimodal protocol influence on stroke and neurocognitive deficit prevention after ascending/arch aortic operations

BACKGROUND

Various techniques are used for brain protection during aortic surgery. Rather than evaluate each factor separately, we evaluated the early outcome of a multimodal protocol (mannitol, thiopental, MgSO4, lidocaine, CO2 field flooding, Leukoguard filter, head ice packing, electroencephalographic arrest at 20 degrees C, alpha-stat, increasing right subclavian artery cannulation, and antegrade/retrograde brain perfusion) for brain protection.

METHODS

Prospectively collected data were analyzed on 403 ascending or arch aortic operations including 199 (49%) arch replacements conducted between July 25, 1991, and September 25, 2001. The mean age was 61.6 years (range 22 to 91 years); 48 (12%) had Marfan syndrome; 141 (35%) had dissection; 134 (33%) had composite grafts inserted; and 138 (34%) had concurrent coronary bypasses performed.

RESULTS

Stroke occurred in 2.0% (8/403) (3 permanent, 5 transient), clinical neurocognitive deficits in 2.5% (10/403) either by testing or patient complaint 2 to 3 weeks after surgery, and 98% (395/403) were 30-day survivors. Univariate predictors of stroke, neurocognitive decline, or death were the following: for stroke, aorta symptom severity grade (1 to 4) (p = 0.001), pump time (p = 0.001), arrest time (p = 0.001), macroscopic atheroma (p = 0.041), concurrent descending/thoracoabdominal aneurysm (p = 0.036), and highest blood rewarming temperature (p = 0.043); for neurocognitive decline, degree of cooling (p = 0.046), pump time (p = 0.001), cooling time (p = 0.001), day extubated (p = 0.042), and antegrade brain perfusion (p = 0.004); for death, pump time (p = 0.001) and clamp time (p = 0.011). The multivariable independent predictors of stroke, neurocognitive decline, or death were the following: for stroke, aorta symptoms grade (p = 0.025), peripheral vascular disease (p = 0.043), and pump time (p = 0.015); neurocognitive decline, preoperative New York Heart Association dyspnea class (p = 0.022), pump time (p = 0.05), arrest time (p = 0.06), day extubated (p = 0.042), and antegrade perfusion (p = 0.023); and for death, pump time (p = 0.018).

CONCLUSIONS

Pump time continues to be the most important predictor of adverse events. The benefit of antegrade or retrograde perfusion remains unproven, partly because of the low event rate (< 2.5%) but may be beneficial for prolonged circulatory arrest. Embolic material either from macroscopic atheroma, descending or thoracoabdominal aneurysms, or associated with peripheral vascular disease, increases the risk of stroke. Preoperative symptoms influence outcome.

Effect of deep hypothermia on cerebral hemodynamics during selective cerebral perfusion with systemic circulatory arrest

OBJECTIVE

We studied the effect of deep hypothermia on cerebral hemodynamics during selective cerebral perfusion with systemic circulatory arrest.

METHODS

Ten anesthesized pigs were placed on cardiopulmonary bypass and cooled to a rectal temperature of 22 degrees C (n = 5) or 15 degrees C (n = 5). During selective cerebral perfusion, the descending aorta was clamped and perfusion of the lower body was discontinued. As the pump flow was changed, we monitored the perfusion pressure, local cerebral blood flow, and local cerebral oxygenation using laser Doppler flowmetry and near-infrared spectroscopy. We also measured the free flow of the left internal thoracic artery during selective cerebral perfusion.

RESULTS

Perfusion pressure and local cerebral blood flow decreased as the pump flow decreased. Oxygenated and deoxygenated hemoglobin in cerebral tissue remained unchanged at a perfusion flow of 10 ml/kg/min, whereas oxygenated hemoglobin decreased and deoxygenated hemoglobin increased progressively and reciprocally as the pump flow decreased. The pump flow for maintaining perfusion pressure above 35 mmHg with stabilized local cerebral oxygenation was significantly higher at 15 degrees C than at 22 degrees C. The internal thoracic artery free flow was higher at 15 degrees C than at 22 degrees C.

CONCLUSIONS

Selective hypothermic cerebral perfusion with systemic circulatory arrest produces an extracranial shunt through the internal thoracic artery, especially under deep hypothermia. Our data suggests that selective cerebral perfusion during deep hypothermia is best managed by perfusion pressure control rather than by flow control.

Brain protection during surgery of the aortic arch

Deep hypothermia with circulatory arrest is the usual method of cerebral protection during replacement of the aortic arch. It has the enormous advantage of allowing the surgical repair to be carried out in a complete bloodless field with no aortic cross-clamping. However, this method only gives the surgeon a limited period of time to carry out the aortic repair. It also requires that cardiopulmonary bypass be prolonged to cool and rewarm the patient which may be the cause of various complications. It has been proposed to improve the efficiency and the results of deep hypothermia, by associating it with retrograde cerebral perfusion of the brain with oxygenated blood through the superior vena cava. This technique improves the tolerance of the brain to cold ischemia and increases the time of repair allowed to the surgeon. Antegrade selective cerebral perfusion has also been in use for more than three decades. When the perfusion is derived from the main arterial line and performed at moderate hypothermia, the aorta must be cross-clamped to perform the repair. In addition, there is some uncertainty as to what constitutes adequate perfusion flow at normal or moderate hypothermic conditions. To reconcile the advantages of both approaches while avoiding their major drawbacks, in 1986 we proposed an original method of selective antegrade brain perfusion. The principle is to perfuse selectively the brain with cold blood (10 to 12 degrees C) while maintaining the central temperature in moderate hypothermia (25-28 degrees C). During the time of the distal anastomosis the cardiopulmonary bypass is stopped, maintaining only the cerebral perfusion at a flow rate of about 400 to 500 mL/mn and a pressure of about 70 mmHg. As soon as the distal anastomosis is completed the main perfusion is resumed. Two hundred and six patients with a mean age of 57 years (22 to 83) were operated on with this technique between October 1984 and March 2001. One hundred forty three patients underwent an elective procedure and 63 patients were operated on in emergency, mainly for acute type A dissection (54 of 63). The hospital mortality was 17% (34 patients). Death was directly related to neurological injury in 9 patients (4.4%). All others patients awoke within 6 to 8 hours and were conscious at 24 hours postoperatively. Thirteen nonfatal neurological complications were observed. The type of lesion, gender, age, duration of CPB, cerebral perfusion, and circulatory arrest had no influence on the neurological outcome of the patients. In our experience, antegrade selective perfusion of the brain with cold blood and moderate hypothermic central temperature constitutes the method of choice for cerebral protection during surgery of the aortic arch as it requires no prolonged CPB and does not limit the time available to perform the aortic repair.

Neonatal aortic arch reconstruction avoiding circulatory arrest and direct arch vessel cannulation

BACKGROUND

Aortic arch reconstruction in neonates routinely requires deep hypothermic circulatory arrest. We reviewed our experience with techniques of continuous low-flow cerebral perfusion (LFCP) avoiding direct arch vessel cannulation.

METHODS

Eighteen patients, with a median age of 11 days (range 1 to 85 days) and a mean weight of 3.2 +/- 0.8 kg, underwent aortic arch reconstruction with LFCP. Seven had biventricular repairs with arch reconstruction, 9 underwent the Norwood operation and 2 had isolated arch repairs. In 1 Norwood and 7 biventricular repair patients, LFCP was maintained by advancing the cannula from the distal ascending aorta into the innominate artery. In 8 of 9 Norwood patients, LFCP was maintained by directing the arterial cannula into the pulmonary artery confluence and perfusing the innominate artery through the right modified Blalock-Taussig shunt fully constructed before cannulation for cardiopulmonary bypass. In 2 patients requiring isolated arch reconstruction, the ascending aorta was cannulated and the cross-clamp was applied just distal to the innominate artery.

RESULTS

LFCP was maintained at 0.6 +/- 0.2 L x min(-1) x m(-2) for 41.0 +/- 13.9 minutes at 18.5 degrees C +/- 1.1 degrees C. In 10 of the 18 patients, blood pressure during LFCP was 15 +/- 8 mm Hg remote from the innominate artery (left radial, umbilical or femoral arteries). In 8 of the 18 patients, right radial pressure during LFCP was 24 +/- 10 mm Hg. The mean mixed-venous saturation was 79.8% +/- 10% during LFCP. Two patients had preoperative seizures, whereas none had seizures postoperatively. One patient died.

CONCLUSIONS

Neonatal aortic arch reconstruction is possible without circulatory arrest or direct arch vessel cannulation. These techniques maintained adequate mixed-venous oxygen saturations with no associated adverse neurologic outcomes.

Experimental study on the effect of antegrade cerebral perfusion on brains with old cerebral infarction

OBJECTIVE

Patients with old cerebral infarction who undergo aortic arch operations are susceptible to postoperative neurologic dysfunction. To verify such susceptibility, we performed this experimental study.

METHODS

A cerebral infarct model was created in mongrel dogs by means of injection of cylindrical silicone embolus through the internal carotid artery. The dogs that had obvious neurologic deficits 1 day later and survived for 4 weeks or more were included in the cerebral infarct model. One month after cerebral infarction was induced, deep hypothermia and selective cerebral perfusion were used in 14 mongrel dogs (infarct group, n = 7; control group, n = 7). During this procedure, serum glutamate concentration and venous-arterial lactate difference were measured. Histopathologic study of the brain was also performed.

RESULTS

Changes in venous-arterial lactate difference in both groups were almost similar, except in the rewarming phase. At 32 degrees C during rewarming, the venous-arterial lactate difference in the infarct group was significantly higher than that in the control group (P =.006). Although pre-cooling concentrations of serum glutamate were similar in both groups, the values in the infarct group at the end of rewarming were significantly higher than those in the control group (P =.046). On histologic examination, the presence of old cerebral infarction with gliosis was confirmed in the infarct group, but neither new cerebral infarction nor destruction of the blood-brain barrier was found.

CONCLUSION

We observed an accelerated anaerobic metabolism and an increased extracellular glutamate release in the infarct group. The brain with old cerebral infarction is more susceptible to ischemia during arch operation than noninfarcted brain.

Cardiopulmonary bypass in infants and children

Cardiopulmonary bypass (CPB) systems have evolved from futuristic visions of surgical pioneers to a safe and efficient tool in the therapy of treatment of cardiac disorders. There are many significant differences in the physiology between neonates and adult patients. There are currently very few congenital cardiac malformations that cannot be addressed effectively with surgical therapy. Yet, the necessity of CPB in the repair of these patients can still result in significant morbidity. A clearer understanding of the effects of CPB, hypothermia, and circulatory arrest is evolving and there is a considerable amount of research in these areas. It seems likely that modification of current CPB systems, minimization of exposure, and surgical techniques to avoid or limit the adverse effects may reduce mortality and morbidity in the future. The problems faced in these complex patients and procedures require that infant and neonatal cardiac surgery be performed in specialized centers with a multidisciplinary approach and specialized personnel. Future improvements in technology will likely result in improved long term outcome for children with congenital cardiac disease. Copyright 2000 by W.B. Saunders Company

Anaesthetic considerations for patients undergoing hypothermic cardiopulmonary bypass for complex neurovascular lesions: case presentation and review

The anaesthetic management of a 38-year-old woman having excision of a meningioma involving the superior sagittal sinus is described. The procedure was performed using low flow moderate hypothermic cardiopulmonary bypass with central cannulation. Relevant literature is reviewed.

Cerebral oxygenation monitoring for total arch replacement using selective cerebral perfusion

BACKGROUND

This study was undertaken to verify the safety of our total arch replacement assisted by selective cerebral perfusion with respect to cerebral oxygenation.

METHODS

Subjects to be evaluated were selected between February 1999 and March 2000 and comprised 13 patients who underwent total arch replacement (TAR) (TAR group) and 18 patients who had undergone coronary artery bypass grafting or valve replacement (control group). They were monitored throughout the operation by two-channel near-infrared spectroscopy. Changes in intracranial oxyhemoglobin and the tissue oxygenation index were compared between the two groups. Additionally, jugular venous oxygen saturation was simultaneously measured in 10 patients from each group. Maximum changes in these variables from baseline in the TAR group were compared with those in the control group. Bilateral oxygenation differences between two hemispheres were also evaluated.

RESULTS

There was no incidence of postoperative cerebral infarction, and no significant difference was observed in the maximum decrease in these variables between the two groups. Bilateral oxygenation differences between the two hemispheres in the TAR group were similar to those in the control group, except for the tissue oxygenation index in the rewarming phase.

CONCLUSIONS

From the standpoint of cerebral oxygenation, our technique of total arch replacement was nearly as safe as an ordinary cardiac operation.

Prospective randomized neurocognitive and S-100 study of hypothermic circulatory arrest, retrograde brain perfusion, and antegrade brain perfusion for aortic arch operations

BACKGROUND

To determine the optimal method of brain protection during deep hypothermic circulatory arrest (DHCA) for arch repair.

METHODS

Of 139 potential aortic arch repairs (denominator), we randomized 30 patients to either DHCA alone (n = 10), DHCA plus retrograde brain perfusion (RBP) (n = 10), or antegrade perfusion (ANTE) (n = 10); a further 5 coronary bypass (CAB) patients were controls. Fifty-one neurocognitive subscores were obtained for each patient at each of four intervals: preoperatively, 3 to 6 days postoperatively, 2 to 3 weeks postoperatively, and 6 months postoperatively. Intraoperative and postoperative S-100 blood levels and electroencephalograms were also obtained.

RESULTS

For the denominator, the 30-day and hospital survival rate was 97.8% (136 of 139) and the stroke rate 2.8% (4 of 139). For the randomized patients, the survival rate was 100% and no patient suffered a stroke or seizure. Circulatory arrest (CA) times were not different (DHCA: RBP:ANTE) for 11 total arch repairs (including 6 elephant trunk; mean, 41.4 minutes; standard deviation, 15). Hemiarch repairs (n = 17) were quickest with DHCA (mean 10.0 minutes; standard deviation, 3.6; p = 0.011) and longest with ANTE (mean 23.8 minutes; standard deviation, 10.28; p = 0.004). Of the patients, 96% had clinical neurocognitive impairment at 3 to 6 days, but by 2 to 3 weeks only 9% had a residual new deficit (1 DHCA, 1 RBP, 1 ANTE), and by 6 months these 3 patients had recovered. Comparison of postoperative mean scores showed the DHCA group did better than RBP patients in 5 of 7 significantly different (p < 0.05) scores and versus 9 of 9 ANTE patients. There were no S-100 level differences between CA groups, but levels were significantly higher versus the CAB controls, particularly at the end of bypass (p < 0.0001); however, these may have been influenced by other variables such as greater pump time, cardiotomy use, and postoperative autotransfusion. Circulatory arrest (p = 0.01) and pump time (p = 0.057) correlated with peak S-100 levels.

CONCLUSIONS

The results of hypothermic arrest have improved; however, there is no neurocognitive advantage with RBP or ANTE. Nevertheless, retrograde brain perfusion may, in a larger study, potentially reduce the risk of strokes related to embolic material. S-100 levels may be artificial. In patients with severe atheroma or high risk for embolic strokes, we use a combination of retrograde and antegrade perfusion on a selective basis.

Hematocrit, volume expander, temperature, and shear rate effects on blood viscosity

Our goal was to determine and predict the effects of temperature, shear rate, hematocrit, and different volume expanders on blood viscosity in conditions mimicking deep hypothermia for cardiac operations. Blood was obtained from six healthy adults. Dilutions were prepared to hematocrits of 35%, 30%, 22.5%, and 15% using plasma, 0.9% NaCl, 5% human albumin, and 6% hydroxyethyl starch. Viscosity was measured over a range of shear rates (4.5-450 s(-1)) and temperature (0 degrees -37 degrees C). A parametric expression for predicting blood viscosity based on the study variables was developed, and its agreement with measured values tested. Viscosity was higher at low shear rates and low temperatures, especially at temperatures less than 15 degrees C (P: < 0.016 for all conditions in comparison with 37 degrees C). Decreasing hematocrit, especially to less than 22.5%, decreased viscosity. Hemodilution with albumin or 0.9% NaCl decreased blood viscosity more than hemodilution with plasma or 6% hydroxyethyl starch (P: < 0.01 for all cases). The derived mathematical model for viscosity as a function of temperature, hematocrit, shear rate, and diluent predicted viscosity values that correlated well with the measured values in experimental samples (r(2) > 0.92, P: < 0.001).

IMPLICATIONS

A theoretical model for blood viscosity predicted independent effects of temperature, shear rate, and hemodilution on viscosity over a wide range of physiologic conditions, including thermal extremes of deep hypothermia in an experimental setting. Moderate hemodilution to a hematocrit of 22% decreased blood viscosity by 30%-50% at a blood temperature of 15 degrees C, suggesting the potential to improve microcirculatory perfusion during deep hypothermia.

Bypass flow, mean arterial pressure, and cerebral perfusion during cardiopulmonary bypass in dogs

OBJECTIVE

To determine if normal cardiopulmonary bypass (CPB) pump flows maintain cerebral perfusion in the context of reduced mean arterial pressure at 33 degrees C.

DESIGN

A prospective investigation.

SETTING

Animal CPB research laboratory.

PARTICIPANTS

Seven dogs that underwent CPB.

INTERVENTIONS

Seven dogs underwent CPB at 33 degrees C using alpha-stat management and a halothane, fentanyl-midazolam anesthetic. Cerebral blood flow was measured using the sagittal sinus outflow technique. After control measurements at 70 mm Hg, cerebral physiologic values were determined under four conditions in random order: (1) mean arterial pressure of 60 mm Hg achieved by a reduction in pump flow, (2) mean arterial pressure of 60 mmHg determined by partial opening of a femoral arterial-to-venous reservoir shunt, (3) mean arterial pressure of 45 mm Hg by reduced pump flow, and (4) mean arterial pressure of 45 mm Hg by shunt. A 9F femoral arterial-to-venous reservoir shunt was controlled by a screw clamp.

MEASUREMENTS AND MAIN RESULTS

Except for the controlled variables of mean arterial pressure and bypass flow, physiologic determinants of cerebral blood flow (temperature, PaCO2 and hematocrit) did not differ under any of the CPB conditions. Pump flow per se was not a determinant of cerebral perfusion. Cerebral blood flow and cerebral oxygen delivery did not differ with changes in pump flow if mean arterial pressure did not differ. Cerebral blood flow depended on mean arterial pressure under all pump flow conditions, however.

CONCLUSIONS

Over the range of flows typical in adult CPB at 33 degrees C, pump flow does not have an effect on cerebral perfusion independent of its effect on mean arterial pressure. A targeted pump flow per se is not sufficient to maintain cerebral perfusion if mean arterial blood pressure is reduced.

Regional low-flow perfusion provides cerebral circulatory support during neonatal aortic arch reconstruction

OBJECTIVE

Because of concerns regarding the effects of deep hypothermia and circulatory arrest on the neonatal brain, we have developed a technique of regional low-flow perfusion that provides cerebral circulatory support during neonatal aortic arch reconstruction.

METHODS

We studied the effects of regional low-flow perfusion on cerebral oxygen saturation and blood volume as measured by near-infrared spectroscopy in 6 neonates who underwent aortic arch reconstruction and compared these effects with 6 children who underwent cardiac repair with deep hypothermia and circulatory arrest.

RESULTS

All the children survived with no observed neurologic sequelae. Near-infrared spectroscopy documented significant decreases in both cerebral blood volume and oxygen saturations in children who underwent repair with deep hypothermia and circulatory arrest as compared with children with regional low-flow perfusion. Reacquisition of baseline cerebral blood volume and cerebral oxygen saturations were accomplished with a regional low-flow perfusion rate of 20 mL x kg(-1) x min(-1).

CONCLUSIONS

Regional low-flow perfusion is a safe and simple bypass management technique that provides cerebral circulatory support during neonatal aortic arch reconstruction. The reduction of deep hypothermia and circulatory arrest time required may reduce the risk of cognitive and psychomotor deficits.

Optimal blood flow for cooled brain at 20 degrees C

BACKGROUND

Optimal conditions for deep hypothermic perfusion and protective brain blood flow remain unclear.

METHODS

Dogs (n = 52) underwent 120 minutes of cardiopulmonary bypass at 20 degrees C with perfusion flow rates of 2.5, 5, 10, 20, 40, and 100 mL x kg(-1) x min(-1). We examined the effect of the various flow rates and different perfusion pressures on brain blood flow, metabolism, and intracellular pH.

RESULTS

The brain was ischemic and acidotic when the perfusion flow rate was less than 5 mL kg(-1) x min(-1) and pressure was less than 10 mm Hg. When perfusion pressure was higher than 10 mm Hg, cerebral cortex blood flow was more than 9 mL x 100 g(-1) x min(-1) and intracellular pH, higher than 6.95. The cerebral metabolic rate for oxygen decreased at a flow rate of 2.5 mL x kg(-1) min(-1). The cerebral metabolic ratio of glucose to oxygen and the cerebral vascular resistance were lowest when perfusion pressure was 10 to 30 mm Hg. Full-flow (100 mL x kg(-1) x min(-1)) perfusion caused paradoxical brain acidosis; a flow of 40 mL x kg(-1) x min(-1) provided the best results.

CONCLUSIONS

Both extremely low-flow perfusion and excessive perfusion cause brain acidosis. Low-flow perfusion at a pressure of 20 mm Hg provides cerebral vasorelaxation and aerobic metabolism during operations at 20 degrees C.