Abstract
Certain neurovascular lesions like complex aneurysms are difficult to treat using conventional neurosurgical techniques due to their size, vascular connections, morphology, or inaccessible location. In these cases, the ability to stop or reduce blood flow through the parent artery allows for reduction of intralesional turgor and subsequent clipping or excision. With recent advances in interventional neuroradiological technology, many of these complex lesions are detected earlier and treated endovascularly. As a result, the use of flow arrest–assisted neurosurgery to treat complex lesions like aneurysms has declined significantly in the past decade. There are institutional and personal variations to anesthestic techniques, with no clear evidence supporting any particular protocol or technique. In this chapter, we present our opinion on techniques and solutions to commonly encountered problems.
Keywords
Adenosine, Cerebral aneurysm, Circulatory-arrest, Deep hypothermic arrest, Rapid ventricular pacing
Outline
Deep Hypothermic Circulatory Arrest 367
Historical Use of Hypothermic Circulatory Arrest in Neuroanesthesia 367
Case Selection and Indications 367
Complications and Associated Postoperative Outcomes 368
Anesthesia Management 368
Adenosine-Assisted Cerebral Blood Flow Arrest 370
Historical Use of Adenosine-Assisted Cerebral Blood Flow Arrest in Neurosurgery 370
Case Selection and Indications 370
Complications and Associated Postoperative Outcomes 371
Anesthesia Management 371
Rapid Ventricular Pacing–Assisted Cerebral Blood Flow Arrest 372
Historical Use of Rapid Ventricular Pacing–Assisted Cerebral Blood Flow Arrest in Neurosurgery 372
Case Selection and Indications 372
Complications and Associated Postoperative Outcomes 372
Anesthesia Management 372
References 373
Deep Hypothermic Circulatory Arrest
Historical Use of Hypothermic Circulatory Arrest in Neuroanesthesia
In 1955, Lougheed et al. demonstrated that cerebral injury due to anoxia from arrest of cerebral circulation in animals could be reduced under hypothermic conditions. In the same year, a case report was published on the use of hypothermic circulatory arrest for excision of a large arteriovenous malformation in a 17-year-old male patient. However, despite showing early signs of good recovery, the patient died on postoperative day 4 due to right vertebral artery thrombosis. In the 1960s, with increasing use of hypothermia for cerebral protection during extracorporeal bypass in cardiac surgery, circulatory arrest with hypothermia was applied in neurosurgical cases. Since then a number of case series have been published, including a large case series in 2011 of 103 patients that reported perioperative morbidity and mortality rates of 18% and 14%, respectively.
Case Selection and Indications
Considering the significant morbidity and mortality associated with deep hypothermic circulatory arrest (DHCA), it should be reserved for complex neurosurgical conditions not amenable to other lower risk techniques like endovascular embolization, flow diversion, or adenosine-induced flow arrest.
Mack et al. identified certain patient and surgical factors that were associated with poor postoperative outcome ( Table 21.1 ). Patient age over 60 years has been repeatedly found to be strongly associated with poor postoperative outcomes. Additional morbidities found in elderly patients and the presence of vascular atherosclerosis may increase complications of cannulation and clipping. Aneurysm size >25 mm (giant aneurysms) , basilar tip location , and intra-aneurysmal thrombosis have also been demonstrated to increase the risk of postoperative complications.
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Complications and Associated Postoperative Outcomes
In a large case series of more than 100 cases, perioperative morbidity and mortality rate were reported at 18% and 14%, respectively. A similar incidence of perioperative mortality (12%) was published in a separate smaller case series of 66 aneurysms in 2008. Most common perioperative complications were death (14%), stroke (7%), and intracranial hematoma formation (2%). Between 59–67% had good functional outcome at discharge (Glasgow Outcome Score ≥ 4), while between 20% and 28% had poor functional outcome (Glasgow Outcome Score ≤ 2).
Anesthesia Management
Preoperative Assessment and Preparation
Preoperative patient selection and team planning : As discussed in earlier sections, appropriate patient selection is vital for good postoperative outcomes. Other appropriate options of alternative techniques should be explored in detail before offering DHCA. A multidisciplinary team meeting including key stakeholders (neurosurgeons, cardiac surgeons, operating room nurses, cardiologists, intensivist, perfusionist and anesthesiologists) well in advance of the operation greatly increases efficiency. An operating theater with adequate space and power outlets to house additional equipment, such as the cardiopulmonary bypass (CPB) machine, should be selected and checked a few weeks before hand to detect previously unidentified issues. Intensive care beds and availability of blood products should be ensured.
Preoperative patient assessment and investigations : In addition to standard preoperative assessment and investigations, the prospective patient should also undergo detailed cardiac evaluation and echocardiogram to determine the presence of conditions such as aortic insufficiency. In the presence of aortic insufficiency, institution of CPB via the femoral route will not be possible and a median sternotomy with left ventricular venting may be needed. Medical conditions identified at this stage should be fully optimized before proceeding with the scheduled operation.
Intraoperative Management
Intraoperative monitors and spinal drains : Along with standard monitoring, arterial vascular access for beat-to-beat blood pressure monitoring, central venous access for administration of vasoactive agents, and external adhesive defibrillation pads for possible cardiac resuscitation should be placed. Since many patients undergoing DHCA for aneurysm clipping do not have major cardiac issues, pulmonary artery catheter placement may be considered after an evaluation of risks versus benefits. In contrast, transesophageal echo (TEE) carries a low risk-to-benefit ratio and may be quite useful intraoperatively. TEE provides (1) real-time assessment of cardiac function, (2) verification of position of bypass cannula, (3) monitoring left and right ventricular distension during CPB, and (4) early detection of air embolism. However, complications of TEE include increased risk of injury to the soft tissue of tongue and esophageal injury. Electroencephalographic (EEG) monitoring is necessary for titrating anesthetic doses to produce burst suppression and can be placed using the traditional intraoperative EEG montage. In addition, use of raw EEG from a bispectral index monitor may also provide adequate data for dose titration.
Spinal drains are used in some centers to improve operative site visualization through cerebrospinal fluid (CSF) drainage. These drains are inserted soon after induction of anesthesia prior to anticoagulation for CPB. Although concerns of developing epidural and spinal hematomas with anticoagulation in DHCA are valid, experienced practitioners of this technique find complications to be uncommon, largely because the drains are inserted and removed under a state of normal coagulation.
Induction and maintenance of anesthesia : Although definitive evidence is lacking, total intravenous anesthesia (TIVA) techniques may produce better postoperative outcomes compared to volatile gas–based anesthesia. Thus, use of TIVA for DHCA aneurysm surgery has become standard practice at the authors’ institutions. During induction, blood pressure surges should be anticipated and managed using antihypertensive agents or by using small boluses of remifentanil, especially in the setting of ruptured or leaking aneurysms. Nitrous oxide may expand the volume of air embolisms and should be used with caution. Intraoperative blood pressure is maintained within 10% of baseline values but further reduced briefly at arterial cannulation for CPB to prevent dissection. After dural opening, burst suppression may be achieved with anesthetic bolus and maintained with increased infusion. Anesthetic administration is maintained at the same dose as cooling occurs, halted at circulatory arrest, and restarted at the same dose during rewarming.
Management of closed chest CPB : A closed chest technique is most commonly used to institute CPB by cannulation of the femoral vessels percutaneously or via cut-down ( Fig. 21.1 ). Closed chest CPB is associated with the following concerns: (1) cardioplegic infusion cannot be used due to inability to cross-clamp the aorta and (2) ventricular distension can occur due to lack of ventricular venting. In the absence of complete asystole and empty ventricles, myocardial protection offered by closed chest CPB may be significantly compromised. Potassium boluses (usually up to three boluses of 20 mEq) can be used as an alternative to cardioplegia when the heart begins to fibrillate on initiation of cooling and CPB. Intraoperative TEE provides verification of bypass cannula position and direct monitoring of ventricular distension. In case of significant left ventricular distension, a sternotomy and ventricular vent insertion may be required. In contrast, right ventricular distension may be treated by augmenting venous drainage through operating table height manipulation relative to the venous reservoir. The greater the extent of aneurysm dissection prior to CPB and DHCA, the shorter the overall arrest time, which is associated with less complications. Core temperatures less than 15°C and DHCA times greater than 30 min are associated with higher complications like hematoma formation and poor postoperative outcomes. At target core temperature of 17°C, circulation is arrested and blood is drained from the venous cannula until the cerebral vasculature appears empty. Blood drainage from the cerebral circulation can result in negative pressure air embolism. Acid–base management during DHCA remains controversial. Although pH-stat management offers theoretical benefit of faster cooling and rewarming as a result of higher flows, there is an increased risk of embolic load. It should also be noted that Murkin et al. found no difference in outcomes between alpha and pH-stat acid–base management strategies when CPB time was less than 90 min. Following clipping, CPB is reestablished and circulatory flow resumed. Integrity of the clipping and hemostasis is observed as flow and pressure increase. However, reinstatement of circulatory arrest may be required to achieve these goals. Prior to separation from CPB, rewarming should proceed at 0.5°C per minute. As normal cardiac electrical activity is established, episodes of ventricular fibrillation may require defibrillation. Inotropes are rarely used to wean off CPB as most of these patients have no cardiac morbidities. Anticoagulation is reversed with protamine (0.75 mg per 100 units of heparin), further blood products, such as coagulating factors and platelets, transfusion should be guided by thromboelastogram and activated clotting time targets (10% of baseline).
