Intraoperative Techniques

Successful surgical outcomes depend upon a clear diagnosis and careful planning. Vascular tumours should be reviewed with the inter-ventional neuroradiologist so that feeding vessels can be identified pre-operatively and if appropriate occluded by glue or coils using endovascular techniques. This can reduce blood loss as well as the length of the operation.

As a consequence of studies such as the International Sub-arachnoid Trial (ISAT) endovascular techniques are becoming increasingly important. The majority of cerebral artery aneurysms are currently being treated by the endovascular route with soft platinum coils rather than by an open operation to clip the aneurysm (Fig. 1). Aneurysms with wider necks and often more complex morphology

Fig. 1 Coiling. Endovascular coiling of aneurysms is frequently the method of choice for the treatment of aneurysm. This prevents rupture and further bleeding from the aneurysm.

may not be suitable for coiling and therefore still require clipping. In this situation temporary clips may be applied to the feeding vessels for a short period of time. Rarely it is necessary to provide a bypass to essential vessels to repair giant non-clippable aneurysms. In this group of patients a bypass anastomosis can be fashioned in a number of ways. The ELANA technique (excimer laser-assisted non-occlusive anastomosis) is a novel and reliable technique to fashion the anastomosis between the external and internal carotid arteries.12 In general, lasers are not regularly used in spite of their early promise.

Proximal control is essential in procedures that may require direct approach to an intracranial aneurysm or an invasive skull base tumour. There should be a clear understanding between surgeon and anaesthetist about the potential blood loss before starting any operation. Central, peripheral and arterial lines are routine. Cranial surgery on an infant should start only once the cross-matched blood has been verified and ensured to be available.

The approach to lesions that are known to be vascular, such as, arteriovenous malformations, meningiomas, or haemangioblastomas should involve preoperative consultation with an interventional neuroradiologist. Temporary aneurysm clips may be used in the situation of an unexpected severe arterial blood loss whilst the intravascular volume is restored. Temporary clips may be safely left on any major artery for two to three minutes, to allow time for dissection of the adjacent structures. A clock is started as soon as the clip is applied and the time counted out. Placing vascular clips blindly into an area of rapid bleeding is rarely, if ever successful. Adequate exposure with brain retractors and suction is essential, so that the surgeon can see and determine the origin of the bleeding. This aspect is in line with other forms of surgery, where adequate exposure and patience remains paramount. In neurosurgery one cannot pack the brain, and the area of applied pressure should be as small as possible. Adequate visualisation can often be accomplished with patties and two suckers. It is not usually possible to sacrifice intracranial or spinal vessels, and they may need to be repaired with fine sutures. In this respect, neu-rosurgery differs from other surgical specialities. Rapid excision of a tumour with surrounding brain is rarely an effective haemostatic technique and is likely to lead to a major neurological deficit. The skill of the surgeon, the position of the lesion, the type of lesion, and the condition of the patient are some of the variables that have to be considered in the risk-benefit equation. Unfortunately, unlike surgery in other areas of the body, closing a bleeding wound over a drain in intracranial surgery is not an option if the patient is to make a useful recovery. The judgment, to take some risk by increasing the speed at which a lesion is removed, is something not easily learned and depends on many variables. A rapid enucleation of a tumour with a finger is not acceptable.

Blood pressure may be decreased as a temporary measure to control bleeding but has a limited role in neurosurgery and can lead to irreversible brain damage because of the reduced cerebral perfusion. Profound hypothermia and cardiac bypass have been employed to access and repair giant cerebral artery aneurysms but these approaches were often complicated by disturbances of clotting and have not proved popular in comparison to the recent advances in endovascular techniques. The period of time and the extent of induced hypotension that can be employed to control bleeding are dependent on the age of the patient and the presence of associated vascular disease.

In certain circumstances a large volume of blood can be unexpectedly lost from venous bleeding. The sagittal sinus may be opened unintentionally during the turning of the bone flap or resection of an invasive meningioma. The elevation of a depressed bone frag-mentfrom the sagittal sinus can also cause major loss of blood. This potential loss can be anticipated and avoided by careful review of the preoperative skull X-rays. One approach to control venous bleeding, whether it is accidental or anticipated, is to consider what would be necessary if the opening were deliberate and planned. The first step is to obtain the necessary exposure and all the borders defined by extending the bone work. The rule that adequate exposure is required, applies to all forms of surgery. Local pressure with surgicell, patties, and wet mastoid swab (with elevation of the head) are usually sufficient to control the venous bleeding, whilst the bone is removed. Cannulation of the venous sinus may be considered necessary, using a small Foley catheter to occlude the lumen by distending the balloon. Only the proximal third of the sagittal sinus can be sacrificed without risk of cerebral infarction. Balloon occlusion of the distal sinus may be temporary, until a decision can be taken on whether the opening can be approximated directly or requires grafting. An assistant is invaluable at this time to control the suction and enable stepwise exposure of the defect involved. A free pericranial flap can be used to graft the defect and maintain patency, but in the majority of cases haemostasis is successful with local tamponade from layers of surgicell and local pressure. A Foley catheter occlusion or a vascular shunt may need to be used if the repair requires considerable time and the defect is difficult to control with local pressure.

In contrast to bleeding from a tumour or a vessel, generalised bleeding from exposed surfaces suggests a coagulopathy, either preexisting to operation or acquired during the operation. It is always difficult to stop an operation and study a problem. Most surgeons have a tendency to continue operating and simply request that the clotting studies be repeated. If the bleeding is deep and could cause compression or displacement of the brain, the surgeon may not have the choice of stopping without endangering the patient. Both situations require laboratory studies to determine the cause, but a surgeon should always remember that uncontrolled or continued bleeding is most often caused by lack of effective local haemostasis rather than by a coagulopathy.

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