Introduction

Canine and feline neurosurgical patients are challenging, both for the nurse technician and for the veterinary neurosurgeon. This Nurse Masterclass Series will cover the management of the neurosurgical patient. Items that will be covered are assessment of neurological deficits, basic aspects on advanced imaging techniques for the neurosurgical patient, preparation of the dog and cat for neurosurgery, neurosurgical instrumentation, special considerations during neurosurgery and the short-term postoperative neuro-care which will be the primary responsibility of the nurse technician. But the nurse technician may also be involved in the long-term postoperative care, rehabilitation and physiotherapy of the patient. The nurse technician plays an essential role in the management of the neurosurgical patient, both pre- and postoperatively.

The Masterclass will cover a variety of neurological disorders that require neurosurgical intervention such as: intervertebral disc (IVD) degeneration and herniation, degenerative lumbosacral stenosis ('cauda equina syndrome'), caudal cervical spondylomyelopathy ('wobbler syndrome'), spinal tumours, spinal trauma, surgical brain tumours including pituitary adenomas and surgery of the peripheral nerves.

The Masterclass is aimed at the experienced nurse technician with advanced skills and a learning ambition that goes beyond the standard surgeries. By following this Masterclass the nurse technician will gain new knowledge in the field of the management of the neurosurgical patient which will allow him/her to contribute significantly in the surgical success of these patients.

Neurological Examination

The neurological examination (and not imaging!) is the only examination that can give functional information on the spinal cord in a paretic or paralysed dog. The veterinarian will usually do a neurological grading of the neurosurgical patient. This is especially the case for dogs with intervertebral disc disease (IVDD) that are presented with paresis (reduced voluntary movements) or paralysis of the pelvic limbs (respectively paraparesis and paraparalysis). In case of neurological deficits of all four limbs this is called tetraparesis or tetraparalysis/tetraplegia.

Grading of neurological deficits is based on postural reactions (proprioception = positional stance in space), voluntary motor function (standing and walking from A to B) and conscious nociception (= pain recognition by the brain).

Neurological grading:

 Grade 0 = normal

 Grade 1 = spinal pain, no neurological deficits

 Grade 2 = paresis, decreased proprioception, ambulatory (able to walk from A to B)

 Grade 3 = severe paresis, no proprioception, non-ambulatory (able to stand but not able to walk from A to B)

 Grade 4 = paralysis, no proprioception, non-ambulatory (not able to stand and not able to walk from A to B), decreased bladder function, conscious nociception present

 Grade 5 = paralysis, no proprioception, non-ambulatory (not able to stand and not able to walk from A to B), no bladder function, conscious nociception absent

With some practice, nurse technicians should be able to learn to grade patients using this grading system which will help the veterinary surgeon in the diagnostic work-up and decision tree when to wait, when to treat or when to refer. Also the grading will help to follow the success of treatment over time. Grading should be documented and dated in the medical records. In general, grades 1 and 2 can be treated conservatively (with medication) whereas grades 3, and especially grades 4 and 5 necessitate diagnostic work-up and immediate treatment to prevent further damage to the spinal cord.

Grading can also be used for the prognosis: in general the prognosis will worsen with increasing grade, although many other factors, such as breed, aetiology, onset of disease, duration of deficits, bodyweight and the owner's motivation will influence the final prognosis. In case of grade 5, the prognosis is extremely poor for functional recovery when conscious nociception is absent for a period longer than 48–72 hours.

The Spinal Trauma Patient

The spinal trauma patient may have other organ failures besides an unstable spine and should be approached with the greatest care and special considerations. Dogs with spinal fractures are usually extremely painful (when not completely paralysed) and are usually brought in on stretchers. The pitfalls are omitting to examine these patients for other ailments and failing to do a proper neurological examination the first time the animal enters the clinic. There are usually other trauma than the traumatised spine and these patients may have thoracic trauma (pneumothorax, diaphragmatic herniation, contusion of the heart), abdominal trauma (haemoabdomen, bladder rupture), shock, hypovolaemia or other limb fractures. The grading may be hampered by the inability to examine the animal due to pain.

The first line of treatment is directed at the life-threatening diseases and not at the spinal fracture. The pain should be dealt with immediately with intravenous analgesics and the patient should be immobilised as well as possible (e.g., with a vacuum support cushion or a stretcher with braces). Extreme caution should be taken when giving these patients muscle relaxants since the muscle tone around the spine may be the last stabilising factor in fractures of multiple vertebral compartments. When the patient has been stabilised and the organs have been taken care of, imaging should be performed as soon as possible. However, this presents another dilemma: imaging of the awake patient is usually not possible due to the pain, will lead to low-quality radiographs and may pose a greater risk of dislocation of vertebrae. On the other hand, sedation or anaesthesia will take away muscle tone and therefore may contribute to spinal instability, which may worsen and even transect the spinal cord, when animals are handled without care. In the end, anaesthesia is mandatory when imaging spinal fractures, as it provides analgesia and allows the production of high-quality radiographs. However, it is essential to support the spine, preferably in a vacuum cushion, and the staff should transfer the cushion (with dog) from table to table and not the dog itself. Also, all staff should be informed that the patient has a spinal fracture so accidental traction on the spine in different directions will not occur.

Imaging of the Neurosurgical Patient

Radiography and contrast radiography are still considered valuable diagnostic techniques to diagnose conditions that require neurosurgery. Contrast radiography includes myelography and epidurography. Radiography of the spine is best performed under sedation to produce high-quality radiographs. Oblique views when aiming for optimal ventrodorsal or lateral views make precise radiographic interpretation of the spine very difficult due to overlapping bony structures. Myelography is performed under anaesthesia and the contrast agent is injected in the subarachnoid space around the spinal cord between the skull and C1, or between L4 and L5 or L5 andL6. Especially with cervical myelography, the contrast agent may leak into the brain and cause convulsions when the dog wakes up from anaesthesia. This may be prevented by elevating the head after contrast injection. Myelography may show extradural compression by a space-occupying lesion (like a herniated disc). Myelography is able to image the dynamic nature of a disc herniation, e.g., in case of caudal cervical spondylomyelopathy (CCSM, wobbler disease). Flexion/extension, traction and axial compression views of the cervical region are indicated for confirmation of the diagnosis CCSM.

The developments in veterinary neurosurgery have been advanced by imaging techniques such as computed tomography (CT) and/or magnetic resonance imaging (MRI). These imaging techniques are a neurosurgeon's delight! CT is a radiographic technique producing transverse slices of the spine or skull. Indications for CT are spinal fractures, skull fractures, IVDD, degenerative lumbosacral stenosis, discospondylitis, spinal cord tumour and pituitary and brain tumours. Pituitary tumours are enhanced by a contrast agent because the pituitary gland is outside the blood-brain barrier. Brain tumours are enhanced by a contrast agent because of damage to or loss of the blood-brain barrier by the tumour.

MRI is a technique that depends on the magnetic dipole of the hydrogen proton. MRI involves:

 A hardware component (magnetic field, radio-transmitter that excites the protons, and a radio-receiver that receives radio-signals.

 The contrast agent (magnetisation or spin density of tissue, relaxation times. e.g., T1, T2, and a contrast agent e.g., gadolinium).

 The software component that generates pulse sequences (timing diagram) through mathematical calculations (Fourier transformation) on the radio-signals.

Indications for MRI are IVDD, degenerative lumbosacral stenosis (cauda equina disease), caudal cervical spondylomyelopathy (wobbler disease), discospondylitis, spinal cord tumour and pituitary and brain tumours. In contrast to CT, MRI is able to visualise oedema of spinal cord parenchyma and is diagnostic for spinal cord infarction or fibrocartilaginous thromboembolic myelopathy (FCE). Also, the result of an acute type 1 extrusion of nucleus pulposus in chondrodystrophic dogs (e.g., French Bulldog) that severely damages the spinal cord and starts a negative spiral of oedema, ischaemia and spinal cord necrosis (called myelomalacia), is visible on T2-weighted MRI as a hyperintense signal in the spinal cord parenchyma.

During neurosurgery, the veterinary surgeon usually requires on hand all the available imaging data (radiographs, myelogram, CT and MRI) for localisation of the correct surgical approach and intraoperative feedback of surgical findings in relation to the imaging findings. Also preoperative planning and three-dimensional (3D) measurements on sizes of space-occupying lesions and tumours are an enormous help for the surgeon.

The Brain Patient

The patient that undergoes brain or pituitary surgery requires special care. Apart from the routine monitoring devices, it is imperative in brain surgery to have some type of monitoring of blood pressure and possibly also intracranial pressure. Infusion with mannitol is used to lower the intracranial pressure. The temperature of the surgical unit should be kept below room temperature. A 'cold' brain requires less oxygen. Brain and pituitary surgery requires some type of magnification (operating loupes) or an operating microscope, also for the assisting nurse technician. Postoperative neurosurgical care is done in the intensive care unit and patients are kept sedated for some hours after brain surgery before waking them up. As soon as they are awake the first neurological examination is done to assess brain function. In case of pituitary surgery in dogs for tumours that cause Cushing's disease (the pituitary tumour produces excess adrenocorticotropic hormone (ACTH)) the postoperative monitoring includes electrolytes (sodium, potassium). In the ICU, the dogs are stimulated to drink immediately after surgery to regulate their water balance. The hormonal substitution therapy in dogs after hypophysectomy includes thyroxine, cortisone and desmopressin (a synthetic vasopressin analogue). In cats with acromegaly (the pituitary tumour produces excess growth hormone (GH)) that are undergoing pituitary surgery the same considerations are taken into account as for dogs with Cushing's disease but, in addition, these cats usually have insulin-dependent diabetes mellitus which will resolve quickly after surgery. Therefore continuous monitoring of glucose levels is imperative in the postoperative phase and short-acting insulin medications should be administered to prevent hypoglycaemic events.

Neurosurgical Indications and Procedures

The following diseases are the most common indications for neurosurgery:

 Intervertebral disc disease (IVDD) with cervical disc disease (C2–3, C3–4, C4–5) and thoracolumbar (T11–12, T12–13, T13–L1, L1–2, L2–3) disc disease in chondrodystrophic dogs (e.g., French Bulldog, Dachshund). Disc herniations are usually type 1 (extrusion) herniations of the nucleus pulposus. In the cervical region a ventral approach is used called a ventral fenestration (incision of the annulus fibrosus) and decompression (ventral slot of the vertebral bodies). In the thoracolumbar area a left or right-sided approach is used called hemilaminectomy and lateral fenestration.

 Degenerative lumbosacral stenosis in nonchondrodystrophic dogs (e.g., German Shepherd Dog). Disc herniations are usually type 2 (protrusion) herniations of the annulus fibrosus and nucleus pulposus. In the lumbosacral area the most common approach is dorsal laminectomy, followed by dorsal fenestration of the disc and nucleotomy (removal of the nucleus pulposus).

 Caudal cervical spondylomyelopathy (wobbler disease) in non-chondrodystrophic dogs (e.g., Dobermann). In this disease, the type 2 disc herniation is usually more dynamic in nature and requires decompression but also stabilisation using a variety of techniques such as screw and washer, pins and polymethylmethacrylate (PMMA), or cervical locking plates.

 Atlanto-axial instability in miniature dogs (e.g., Chihuahua). The most common approach is the ventral approach with lag screw fixation. The nurse technician should be aware of postoperative respiratory depression and apnoea in this condition since the respiratory centre is close to the surgical field and may be temporarily affected. Some of these patients need to be ventilated postoperatively for some time.

 Spinal cord tumours. The approach is dependent on the localisation but usually the approach is not a standard technique. In the cervical area and thoracolumbar, lumbar and lumbosacral area spinal tumours are best approached by dorsal laminectomy. In the thoracolumbar area, dorsal laminectomy leads to an unstable spine which requires some type of fixation afterwards e.g., Lubra plates, vertebral plates or pin-PMMA fixation technique.

 Brain tumours. Tumours of the neurocranium can be approached through craniotomy. The term craniectomy is used when the bone flap that is created during craniotomy is not replaced. The location of the tumour dictates the approach. The most common approaches to the calvarium are: rostrotentorial transparietal or transtemporal craniotomy with or without osteotomy of the zygomatic arch; unilateral or bilateral transfrontal sinus craniotomy; caudotentorial craniotomy; or suboccipital craniotomy. Craniotomy approaches can be combined or modified to improve exposure to various aspects of the cerebral hemispheres and cerebellum. Most craniotomies are performed with the cat in sternal recumbency. A head stand, a vacuum cushion and/or surgical tape is used to stabilise the head during the surgical procedure.

 Pituitary tumours. The pituitary tumour is usually approached by the oral route to the brain via a transoral, transnasal microsurgical trans-sphenoidal hypophysectomy. The dogs and cats are in sternal recumbency and the maxilla is supported on a metal bar attached to the operating table. The mandible is reflected downwards and the approach to the base of the skull is through the soft palate, through the nasopharynx and through the sphenoid bone. The surgery is considered a contaminated surgery because the approach is through the mouth and nose.

Special Considerations During Neurosurgery

Neurosurgical instrumentation for the approach and detachment of muscles include periosteal elevators and Gelpi retractors. Laminectomies are performed with an electrical or air-powered burr unit. The advantage of an electrical burr is that the speed of rotations can be fine-tuned. Foot pedal-controlled burring is preferred over hand console-controlled burring since this adds to stability of the burr in the surgeon's hand. Also, irrigation can be automatically integrated in the hand burr but continuous lavage with saline from a syringe by the nurse technician is just as efficient and more reliable than equipment! Copious lavage is a prerequisite in neurosurgery to provide cooling during burring, to remove the bone shavings and to keep the surgical field free of blood. Once the surgeon has entered the spinal canal or the bony calvarium, the spinal cord, nerves and brain are explored with fine ball-tipped neurosurgical probes. Long instruments are preferred which keeps the hands out of the surgical field.

During neurosurgery haemostasis is primarily controlled by bipolar electrocautery. Approaches to the spine require detaching of muscular attachments and this causes profuse bleeding. This can be kept to a minimum by precauterising muscular attachments with bipolar electrocautery before cutting the attachments. Typically a nurse technician can assist and speed up this phase of the surgery. Bipolar electrocautery has the advantage over monopolar electrocautery that the current will pass between the tips of the bipolar forceps and will not affect the adjacent muscle tissue or nerves (or spinal cord). In monopolar electrocautery the current goes from the tip of the monopolar to the contact plate which may cause unwanted twitching and movements of the surgical field.

During most neurosurgical procedures some type of magnification is required to assess the condition of nerves, spinal cord or brain and to assess the sharp margins between normal and affected tissue. Especially in spinal cord and brain tumour surgery, the surgeon is moving on the cutting edge between normal and affected (tumour) tissue. In neurosurgery it may not be possible to take safe margins with tumour excision so the aim is tumour management by debulking (cytoreduction) rather than complete tumour excision. This requires a different mindset than in standard tumour surgery.

Rehabilitation of the Neurosurgical Patient

Neurosurgery is only the first step in recovery of the patient off its legs. Canine rehabilitation should start on the first day after surgery whenever possible and practical. The paralysed patient requires intensive care and its owner requires guidance. Bedding of the patient should be kept dry, clean and soft at all times. The animal should be turned at regular intervals. Paralysed patients frequently have no voluntary urination. 'Bladder' management requires catheterisation or frequent attempts to empty the bladder by manual abdominal pressure. Animals that soil the perineal region with urine and faeces in the postoperative period run a great risk of development of decubitus ulcers or dermatitis in the perineal region. Urine weakens the skin barrier and enables bacteria to enter through the skin and cause redness and infection. As long as the animal is not urinating spontaneously and has to be catheterised, there is an indication to treat with systemic antibiotics. This may even take up to 2 weeks after surgery. Pain medication postoperatively may include non-steroidal anti-inflammatory drugs (e.g., carprofen) and/or morphine-like substances (e.g., oral tramadol or fentanyl patches). The use of postoperative steroids after laminectomies is highly controversial.

Rehabilitation of the paralysed patient may include frequent bathing, muscle massage, exercising standing with support bags, wheelchair walking, hydrotherapy with an underwater treadmill, swimming and exercises for proprioception, etc. The veterinary surgeon may refer the animal to an animal physiotherapist within the practice or outside. A referral letter is made to inform the physiotherapist on the medical history and to provide a channel for feedback on follow-up. Postoperative recovery of conscious nociception is fast (24–48 hours), recovery of motor function may take 6 weeks and recovery of postural reactions (proprioception) may take up to 6 months!