Neuro-Anaesthesia
Neurosurgical anesthesia or neuroanesthesia is a branch of anesthesiology which is involved in anesthetizing patients undergoing brain or spinal cord surgery. Neuroanaesthesia continues to develop and expand. It is a speciality where the knowledge and expertise of the anaesthetist may directly influence patient outcome. Evolution of neurosurgical practice for eg. minimally invasive and endoscopic procedure, is accompanied by new challenges for the anesthetist.
The goals of neuroanesthesia are the provision of good operative conditions i.e. a relaxed brain, maintenance of optimum cerebral perfusion and oxygenation throughout surgery, assessment and preservation of neurological function, minimizing interference with intraoperative neuromonitoring and a rapid, high-quality recovery.
Neuroanesthetic management is unique because the very organ the anesthetics act on, is operated upon by the surgeon. Therefore both the surgeon and the anesthetisiologist target the same organ.
The type of anesthesia used depends on the type of surgery being performed.
Intracranial tumor surgery
In case of a standard craniotomy and removal of intracranial tumors the patient is given full general anesthesia. The challenges to the anesthetist are due to different patient positioning to approach the tumor that may be located in various areas of the brain. The patient may be positioned lateral, semi prone and prone apart from usual supine positioning. The risks due to various positioning are cardiovascular and respiratory compromise, peripheral nerve compression, inadequate venous drainage from the brain resulting in brain swelling and venous air embolism to mention a few.
Some tumors because of their location in critical areas of the brain such as in brain stem or if located deep in the white matter are not amenable for curative resection in which case the surgeon may want to do only a biopsy for tissue diagnosis through either a stereotaxy or mini craniotomy. This procedure can be done with either a sedation technique or a complete general anesthesia.
Some tumors in the pituitary or in midline anterior cranial fossa are amenable for trans nasal transphenoidal route. Here the patient is given full general anesthesia with special precautions to protect the airway from blood entering into it during surgery as well as in postoperative period.
Some of the tumors in the ventricles may be removed through endoscopic neurosurgery. Here the patient is given full General Anesthesia with care being taken to monitor and prevent the rise in ICP due to irrigating fluids used during endoscopic neurosurgery.
Finally if the tumor is in an eloquent area of the brain, the surgeon might request for an awake craniotomy. This is the most challenging for the anaesthesiologist. During awake craniotomy, the patient needs to be awake and ready for neurological function testing while at the same time should not have any pain. Therefore the patient receives only light sedation and the patient breathes spontaneously without the aid of artificial airways during the initial part of the procedure until the surgeon reaches the tumor. The patient is made pain free by blocking the nerve supply to the brain and scalp. During the resection of the tumor, the patient is awakened and tested continuously for intact neurological function till the tumor is removed. Once the neurological testing is done, the patient is given sedation once again till the end of surgery.
Neurovascular procedures
Microsurgical clipping of intracranial aneurysms, resection of arteriovenous malformations (AVM) and hemangiomas require full general anesthesia.
Neuroradiological procedures such as coiling of intracranial aneurysms and embolisation of AVMs require full general anesthesia in the neuroradiology suite. Neuroradiology suite poses unique challenges to the anaesthesiologist as it is situated remote from main operating rooms, spatial constraints due to the presence of X-ray machinery and radiation risks to the anaesthesiologist.
Spine surgery
Surgeries in the spine is mostly done in the prone position. The patient needs full general anesthesia. Apart from all the challenges of this position which are already menetioned above, there is risk to the eyes in this position which needs special precautions.
The airway of patients with upper cervical spine pathology may pose special problems during placement of endotracheal tubes which require expert anaesthesiologist to handle special techniques to place the endotracheal tubes.
Magnetic resonance Imaging (MRI)
Most paediatric patients and few adults (with dementia or claustrophobia) who require MRI for disease diagnosis, will need the help of neuroanesthesiologists to make them calm and immobile during MRI. In this instance, patients are given sedation or even a full general anesthesia. The MRI environment poses a big challenge to the anaesthesiologist as it is usually situated away from main OR. The Magnetic environment poses difficulty in monitoring the patients during the procedure. Specialized MRI compatible monitors and machine are required during this procedure.