Effect of intermittent deep hypothermic circulatory arrest on brain metabolism

Deep Hypothermia and Circulatory Arrest in Adults

Brain protection during cardiopulmonary bypass has been the subject of intense research. Deep hypothermic circulatory arrest (DHCA) continues to be used for that goal during complex aortic arch and large intracranial aneurysm surgeries. The anesthetic management for adult patients undergoing these types of procedures requires specific knowledge and expertise. Based on our experience and review of the current literature, the authors highlight the key areas of the anesthetic plan, discussing the risk factors associated with adverse neurologic outcome as well as the rationale for decisions regarding specific monitors and medications. In the conclusion an anesthetic protocol for adult patients undergoing DHCA is suggested.

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.

Therapeutic hypothermia applicable to cardiac surgery

OBJECTIVE

To review the beneficial and adverse effects of therapeutic hypothermia (TH) applicable to cardiac surgery with cardiopulmonary bypass (CPB) in the contexts of various temperature levels and techniques for achieving TH.

DATABASES USED

Multiple electronic literature searches were performed using PubMed and Google for articles published from June 2012 to December 2014. Relevant terms (e.g. 'hypothermia', 'cardiopulmonary bypass', 'cardiac surgery', 'neuroprotection') were used to search for original articles, letters and reviews without species limitation. Reviews were included despite potential publication bias. References from the studies identified were also searched to find other potentially relevant citations. Abstracts, case reports, conference presentations, editorials and expert opinions were excluded.

CONCLUSIONS

Therapeutic hypothermia is an essential measure of neuroprotection during cardiac surgery that may be achieved most effectively by intravascular cooling using hypothermic CPB. For most cardiac surgical procedures, mild to modest (32-36 °C) TH will be sufficient to assure neuroprotection and will avoid most of the adverse effects of hypothermia that occur at lower body core temperatures.

Neurodevelopmental outcomes after infant cardiac surgery with circulatory arrest and intermittent perfusion

BACKGROUND

Optimal perfusion strategies for neuroprotection during infant cardiac surgery remain undefined. Despite encouraging experimental data, neurodevelopmental (ND) outcomes after cardiac surgery in neonates and infants using deep hypothermic circulatory arrest (DHCA) with a period of intermittent perfusion have not been reported, and it is not known whether DHCA can be extended while preserving ND outcomes.

METHODS

Cross-sectional ND evaluation with the Bayley Scales of Infant and Toddler Development, Third Edition was conducted at 24 months of age. Retrospective clinical data were extracted from the electronic medical record.

RESULTS

Forty patients underwent cardiac surgery during the first year of life using a period of uninterrupted DHCA (24 patients) or DHCA interrupted by a period of intermittent perfusion (16 patients). Total duration of DHCA ranged from 5 to 74 minutes and did not predict ND scores. Despite a longer exposure to DHCA in the intermittent perfusion group (55 minutes [1,3 interquartile [IQ] 45.3 to 65.5] versus 38 minutes [1,3 IQ 32 to 40.8]), no differences in ND scores were detected. Significant comorbidities, duration of intensive care unit and hospital stay, as well as multiple procedures with DHCA were independent predictors of ND outcomes at 24 months of age.

CONCLUSIONS

Despite extended duration of total DHCA, the use of a period of intermittent perfusion to limit uninterrupted DHCA periods to less than 45 minutes could lead to ND outcomes similar to those of patients exposed to brief periods of DHCA. Deep hypothermic circulatory arrest with intermittent perfusion may facilitate implementation of prospective studies to identify the optimal cerebral perfusion strategy.

Selective cerebro-myocardial perfusion in complex congenital aortic arch pathology: a novel technique

Simultaneous cerebro-myocardial perfusion has been described in neonatal and infant arch surgery, suggesting a reduction in cardiac morbidity. Here reported is a novel technique for selective cerebral perfusion combined with controlled and independent myocardial perfusion during surgery for complex or recurrent aortic arch lesions. From April 2008 to April 2011, 10 patients with arch pathology underwent surgery (two hypoplastic left heart syndrome [HLHS], four recurrent arch obstruction, two aortic arch hypoplasia + ventricular septal defect [VSD], one single ventricle + transposition of the great arteries + arch hypoplasia, one interrupted aortic arch type B + VSD). Median age was 63 days (6 days-36 years) and median weight 4.0 kg (1.6-52). Via midline sternotomy, an arterial cannula (6 or 8 Fr for infants) was directly inserted into the innominate artery or through a polytetrafluoroethylene (PTFE) graft (for neonates <2.0 kg). A cardioplegia delivery system was inserted into the aortic root. Under moderate hypothermia, ascending and descending aorta were cross-clamped, and "beating heart and brain" aortic arch repair was performed. Arch repair was composed of patch augmentation in five, end-to-side anastomosis in three, and replacement in two patients. Average cardiopulmonary bypass time was 163 ± 68 min (71-310). In two patients only (one HLHS, one complex single ventricle), a period of cardiac arrest was required to complete intracardiac repair. In such cases, antegrade blood cardioplegia was delivered directly via the same catheter used for selective myocardial perfusion. Average time of splanchnic ischemia during cerebro-myocardial perfusion was 39 ± 18 min (17-69). Weaning from cardiopulmonary bypass was achieved without inotropic support in three and with low dose in seven patients. One patient required veno-arterial extracorporeal membrane oxygenation. Four patients, body weight <3.0 kg, needed delayed sternal closure. No neurologic dysfunction was noted. Renal function proved satisfactory in all, while liver function was adequate in all but one. The present experience suggests that selective and independent cerebro-myocardial perfusion is feasible in patients with complex or recurrent aortic arch disease, starting from premature newborn less than 2.0 kg of body weight to adults. The technique is as safe as previously reported methods of cerebro-myocardial perfusion and possibly more versatile.

Cerebral metabolism during deep hypothermic circulatory arrest vs moderate hypothermic selective cerebral perfusion in a piglet model: a microdialysis study

BACKGROUND

Few data exist regarding antegrade selective cerebral perfusion (ASCP) and its application in newborn and juvenile patients. Clinical data suggest ASCP alone to be superior to deep hypothermic circulatory arrest (DHCA); however, the effects of moderate hypothermia during ASCP on cerebral metabolism in this patient population are still unclear.

METHODS

After obtaining the approval from animal investigation committee, 16 piglets were randomly assigned to circulatory arrest combined with either ASCP at 27 degrees C or DHCA at 18 degrees C for 90 min. Cerebral oxygen extraction fraction (COEF) from blood as well as cerebral tissue glucose, glycerol, lactate, pyruvate, and the lactate/pyruvate ratio (L/P ratio) by microdialysis were obtained repeatedly.

RESULTS

COEF was lower during cooling and rewarming, respectively, in the DHCA18 group compared to the ASCP27 group (30 +/- 8 vs 56 +/- 13% and 35 +/- 6 vs 58 +/- 7%, respectively). Glucose decreased in both the DHCA18 and ASCP27 groups during the course of cardiopulmonary bypass (CPB), but were higher in the ASCP27 group during ASCP, compared to the DHCA18 group during circulatory arrest (0.7 +/- 0.1 vs 0.2 +/- 0.1 mm.l(-1), P < 0.05). Pyruvate was higher (ASCP27 vs DHCA18: 53 +/- 17 vs 6 +/- 2 microm.l(-1), P < 0.05), and the L/P ratio increased during circulatory arrest in the DHCA18 group, compared to the selective perfusion phase of the ASCP27 group (DHCA18 vs ASCP27: 1891 +/- 1020 vs 70 +/- 28, P < 0.01).

CONCLUSIONS

In this piglet model, both cerebral oxygenation and microdialysis findings suggested a depletion of cerebral energy stores during circulatory arrest in the DHCA18 group, compared to selective cerebral perfusion combined with circulatory arrest in the ASCP27 group.

Neonatal aortic arch surgery

Surgical repair of the aortic arch is entailed in the neonatal period of patients with: hypoplastic left heart syndrome, interrupted aortic arch, hypoplastic aortic arch and complex aortic coarctation. Aortic arch surgery requires a period of circulatory arrest and deep hypothermia. Cerebral selective perfusion has recently been introduced as an alternative to circulatory arrest with the aim of reducing mortality and neurological complications. Moreover, the arch reconstruction phase can be safely performed under moderate hypothermia and with cerebral and myocardial perfusion (on beating heart), thus, completely avoiding cerebral ischemia and completely avoiding or drastically reducing myocardial ischemia.

Moderately hypothermic cardiopulmonary bypass and low-flow antegrade selective cerebral perfusion for neonatal aortic arch surgery

BACKGROUND

Although deep hypothermic circulatory arrest has been extensively used in neonates for aortic arch surgery, the brain and other organs might be adversely affected by prolonged ischemia and deep hypothermia.

METHODS

Between December 1997 and January 2005, 70 consecutive neonates underwent Norwood stage I procedure for hypoplastic left heart syndrome (group A, n = 30), or aortic arch repair for interruption or coarctation with arch hypoplasia (group B, n = 40), with antegrade selective cerebral perfusion (ASCP). Mean weights were 3.0 +/- 0.2 kg and 2.8 +/- 0.07 kg, and mean ages were 10 +/- 3.5 days and 14 +/- 10.6 days in groups A and B, respectively. Only 2 patients were older than 30 days. Core body temperature was lowered to 25 degrees C, and mean pump flow during ASCP was initiated at 10 to 20 mL/(kg x min) and adjusted to guarantee a radial/temporal artery pressure of 30 to 40 mm Hg and venous oxygen saturation of more than 70%. Hematocrit was maintained at 30%.

RESULTS

Early mortality was 17% (group A, 23%; group B, 12.5%; p = 0.19). Six late deaths occurred (3 in each group), and at 36 months, Kaplan-Meier overall survival was 64% +/- 9.2% in group A and 85% +/- 5.7% in group B. One patient had postoperative seizures. Age, weight, sex, prematurity, group A, and ASCP duration did not influence early mortality.

CONCLUSIONS

Antegrade selective cerebral perfusion is a safe and effective procedure and might improve outcome of neonatal aortic arch surgery, minimizing neurologic impact without the need for deep hypothermia.

Regional Low-Flow Perfusion Versus Circulatory Arrest in Neonates: One-Year Neurodevelopmental Outcome

BACKGROUND

Regional low-flow perfusion of the brain is a bypass technique commonly used during stage 1 reconstruction in neonates with hypoplastic left heart syndrome and related variants. The neurodevelopmental outcome of these children is unknown.

METHODS

Twenty-nine infants (22 boys, 7 girls) with hypoplastic left heart syndrome or variant requiring single ventricle palliation and aortic arch reconstruction were studied between 1999 and 2004. Mental Developmental Index (MDI) and Psychomotor Developmental Index were assessed using Bayley Scales of Infant Development and correlated with intraoperative and perioperative variables. Results are reported as mean +/- standard deviation.

RESULTS

Average age at stage 1 operation and at bidirectional Glenn was 7 +/- 8 days and 6.0 +/- 2 months, respectively. The MDI was in the low average range (87.7 +/- 13.2). The Psychomotor Developmental Index was in the mildly delayed range (75.2 +/- 14.5). Regional low-flow perfusion was used in 31% (9 of 29 patients), with an average circulatory arrest time of 23.5 +/- 13.4 minutes. Deep hypothermia and circulatory arrest was used as the primary operative strategy in 69% of patients (20 of 29 patients), with an average circulatory arrest time of 44.3 +/- 15.3 minutes (p = 0.003). No differences in MDI or Psychomotor Developmental Index scores were observed between the regional low-flow perfusion and non-regional low-flow perfusion groups (MDI, 88.0 +/- 12.1 versus 87.6 +/- 14.0; p = 0.93, respectively; Psychomotor Developmental Index, 75.5 +/- 15.1 versus 75.0 +/- 14.6; p = 0.93, respectively). Lowest operative temperature (<16 degrees C) and birth order (<2 versus >3) significantly related to MDI (89.6 versus 72.8; p = 0.047).

CONCLUSIONS

At 1 year of age, neurodevelopmental outcomes of patients undergoing stage 1 using regional low-flow perfusion were similar to outcomes observed in children exposed to circulatory arrest. The association of birth order and MDI suggests that early intervention may benefit these patients.

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.

Neonatal Brain Protection and Deep Hypothermic Circulatory Arrest: Pathophysiology of Ischemic Neuronal Injury and Protective Strategies

Deep hypothermic circulatory arrest (DHCA) has been used for the past 50 years in the surgical repair of complex congenital cardiac malformations and operations involving the aortic arch; it enables the surgeon to achieve precise anatomical reconstructions by creating a bloodless operative field. Nevertheless, DHCA has been associated with immediate and late neurodevelopmental morbidities. This review provides an overview of the pathophysiology of neonatal hypoxic brain injury after DHCA, focusing on cellular mechanisms of necrosis, apoptosis, and glutamate excitotoxicity. Techniques and strategies in neonatal brain protection include hypothermia, acid base blood gas management during cooling, and pharmacologic interventions such as the use of volatile anesthetics. Surgical techniques consist of intermittent cerebral perfusion during periods of circulatory arrest and continuous regional brain perfusion.

Intermittent circulatory arrest for repairing postoperative mycotic pseudoaneurysm in the ascending aorta

Postoperative mycotic pseudoaneurysm in the ascending aorta associated with mediastinitis is one of the most serious complications after cardiovascular surgery. Circulatory arrest is usually needed for repairing this lesion; it is likely that the procedure needs unpredictably prolonged arrest time due to uncontrollable bleeding or serious adhesion. With this reason we employed intermittent circulatory arrest instead. The purpose of this paper is to describe 2 cases which demonstrated the method of intermittent circulatory arrest for repairing postoperative mycotic pseudoaneurysm in the ascending aorta.

Near infrared spectrophotometry reflects cerebral metabolism during hypothermic circulatory arrest in adults

Near-infrared spectrophotometry (NIRS) is assumed to reflect cerebral oxygenation during hypothermic circulatory arrest (HCA). However, the rationale for the use of NIRS as a marker of cerebral metabolism remains to be elucidated. We examined whether cerebral oxygenation measured by NIRS correlated with cerebral metabolic function assessed by cerebral oxygen extraction ratio (OER) during HCA in adults. NIRS was continuously monitored in 14 patients undergoing thoracic aortic surgery using HCA (17.9 +/- 2.9 degrees C esophageal temperature at HCA onset). Jugular venous oxygen saturation and OER were also monitored. OER was significantly reduced from 37.3 +/- 7.2% at the onset of cardiopulmonary bypass to 13.6 +/- 6.2% at the onset of HCA (p < 0.0001). A linear decrease in oxygenated-hemoglobin (oxy-Hb) and increase in deoxygenated-hemoglobin (deoxy-Hb) were found during HCA, which returned to baseline levels after rewarming. The rate of decrease in oxy-Hb and increase in deoxy-Hb were -0.63 +/- 0.45 and 0.51 +/- 0.30 (10(-5) OD/cm per sec), respectively, both of which significantly correlated with OER at the onset of HCA (R2=0.739 and 0.633; p < 0.0001 and p = 0.0007, respectively). NIRS may serve as a reliable diagnostic modality for monitoring cerebral metabolism during aortic surgery using HCA.

Prolongation of total permissible circulatory arrest duration by deep hypothermic intermittent circulatory arrest

OBJECTIVE

We determined whether the duration of permissible circulatory arrest could be prolonged by deep hypothermic intermittent circulatory arrest.

METHODS

Twenty-five beagles were cooled on bypass to 18 degrees C to initiate deep hypothermia that was maintained for 3 hours. Five protocols were then studied: group 1, uninterrupted bypass during hypothermia; group 2, arrest for 40 minutes during hypothermia; group 3, arrest for 60 minutes during hypothermia; group 4, arrest for 80 minutes during hypothermia; and group 5, intermittent circulatory arrest, consisting of six cycles of 20 minutes of arrest followed by 10 minutes of systemic recirculation during hypothermia (total, 120 minutes of arrest). The oxyhemoglobin concentration in the brain was measured with near infrared spectrophotometry.

RESULTS

In groups 2, 3, and 4, the oxyhemoglobin concentration in the brain decreased continuously after arrest, finally reaching a plateau after 24.9 +/- 1.2 minutes. This finding suggested that the available cerebral oxyhemoglobin was depleted. In contrast, the available cerebral oxyhemoglobin was not depleted during hypothermic intermittent arrest in group 5. The mitochondrial respiratory control index was significantly lower in group 4 than in the other groups (p < 0.05). However, there were no significant differences in the respiratory control index for groups 1, 2, 3, and 5. Moreover, the formation of brain edema was significantly lower in group 5 than in the other groups (p < 0.05).

CONCLUSIONS

These results indicate that deep hypothermic intermittent arrest can increase the duration of total permissible circulatory arrest and will be a useful modality when prolonged arrest is anticipated.

Deep hypothermic intermittent circulatory arrest--an adjunct technique for operations on aneurysms involving the aortic arch

Aneurysms involving the aortic arch were repaired in 12 patients using a technique known as deep hypothermic intermittent circulatory arrest (DHICA). This technique consists of repeated cycles of 20 min of circulatory arrest and 10 min of cerebral and systemic reperfusion. Aneurysms were of the following types: 2 true atherosclerotic aneurysm, 8 aortic dissections, and 2 traumatic aneurysm. There were 2 operative deaths caused by coagulopathy as a result of hepatic failure and difficulty with left ventricular venting. The frequency of circulatory arrest ranged from 2 to 5 cycles, and total circulatory arrest ranged from 20 to 71 min (mean 43.6 min). The lowest tympanic temperature ranged from 17.7 to 19.2 degrees C. No permanent cerebral complications occurred in 10 patients. We believe that this adjunct technique offers excellent results in the surgical treatment of aneurysms involving the aortic arch.

Impact of retrograde cerebral perfusion on ascending aortic and arch aneurysm repair

PURPOSE

The effect of retrograde cerebral perfusion on the incidence of stroke and death among patients undergoing repair of aneurysms of the ascending aorta and transverse arch was determined.

MATERIALS AND METHODS

Between January 1991 and March 1995, 161 patients were operated on for aneurysms of the ascending aorta and transverse arch. Thirty-three of the patients (20%) had an aneurysm of the ascending aorta only and 128 (80%) had aneurysms of both the ascending aorta and the transverse arch. All the patients underwent cardiopulmonary bypass, profound hypothermia, and circulatory arrest, and 120 (74%) also underwent retrograde cerebral perfusion. Median pump time was 143 minutes (range, 21 to 461 minutes). Median circulatory arrest time was 42 minutes (range, 8 to 111 minutes), and median myocardial ischemic time was 71 minutes (range, 14 to 306 minutes).

RESULTS

The overall 30-day mortality rate was 6% (9 patients) and the incidence of stroke was 4% (7 patients). The use of retrograde cerebral perfusion demonstrated a protective effect against stroke (3 of 120 patients, or 3%) compared with no retrograde cerebral perfusion (4 of 41 patients, or 9%; odds ratio, 0.24; confidence interval, 0.06 to 0.99; p < 0.049). This was most significant in patients more than 70 years of age; none of the 36 elderly patients who received retrograde cerebral perfusion had a stroke, compared with 3 of the 13 (23%) who did not (p < 0.003). Only pump time was associated with an increased risk of stroke (odds ratio, 1.01; 95% confidence interval, 1.00 to 1.02; p < 0.005). Pump time also was associated with increased mortality (odds ratio, 1.01; 95% confidence interval, 1.00 to 1.02; p < 0.008).

CONCLUSION

Retrograde cerebral perfusion decreased the incidence of stroke in patients undergoing repair of aneurysms of the ascending aorta and transverse arch.

Cerebral hemodynamics after low-flow versus no-flow procedures

Temperature induces depression of cerebral perfusion and cerebral oxygen metabolism in particular, and this seems to explain why a reduced pump flow above a critical level is well tolerated during hypothermic cardiopulmonary bypass with apparent full metabolic recovery afterward. It only partly explains why a longer period of hypothermic circulatory arrest leads to a protracted recovery of cerebral perfusion and cerebral metabolism. This review suggests there is evidence that energy metabolism can easily be compromised during and after rewarming after hypothermic cardiopulmonary bypass with low flow and with circulatory arrest. Although data indicate that cerebral metabolism and cerebral energy state are better after low flow than after circulatory arrest, the risk of energy crises appears imminent with both techniques.