Spinal Anaesthesia for medical students

Introduction
Spinal anaesthesia is induced by injecting small amounts of local anaesthetic into the cerebro-spinal fluid (CSF).
The injection is usually made in the lumbar spine below the level at which the spinal cord ends (L2).
Spinal anaesthesia is easy to perform and has the potential to provide excellent operating conditions for surgery below the umbilicus.
If the anaesthetist has an adequate knowledge of the relevant anatomy, physiology and pharmacology; safe and satisfactory anaesthesia can easily be obtained to the mutual satisfaction of the patient, surgeon and anaesthetist.
The Advantages of Spinal Anaesthesia
Cost. Anaesthetic drugs and gases are costly and the latter often difficult to transport. The costs associated with spinal anaesthesia are minimal.
Patient satisfaction. If a spinal anaesthetic and the ensuing surgery are performed skilfully, the majority of patients are very happy with the technique and appreciate the rapid recovery and absence of side effects.
Respiratory disease. Spinal anaesthesia produces few adverse effects on the respiratory system as long as unduly high blocks are avoided.
Patent airway. As control of the airway is not compromised, there is a reduced risk of airway obstruction or the aspiration of gastric contents. This advantage may be lost if too much sedation is given.
Diabetic patients. There is little risk of unrecognised hypoglycaemia in an awake patient. Diabetic patients can usually return to their normal food and insulin regime soon after surgery as they experience less sedation, nausea and vomiting.
Muscle relaxation. Spinal anaesthesia provides excellent muscle relaxation for lower abdominal and lower limb surgery.
Bleeding. Blood loss during operation is less than when the same operation is done under general anaesthesia. This is because of a fall in blood pressure and heart rate and improved venous drainage with a resultant decrease in oozing.
Splanchnic blood flow. Because it increases blood flow to the gut, spinal anaesthesia may reduce the incidence of anastomotic dehiscence.
Visceral tone. The bowel is contracted during spinal anaesthesia and sphincters are relaxed although peristalsis continues. Normal gut function rapidly returns following surgery.
Coagulation. Post-operative deep vein thromboses and pulmonary emboli are less common following spinal anaesthesia.
Disadvantages of Spinal Anaesthesia
Sometimes it can be difficult to find the dural space and occasionally, it may be impossible to obtain CSF and the technique has to be abandoned. Rarely, despite an apparently faultless technique, anaesthesia is not obtained.
Hypotension may occur with higher blocks and the anaesthetist must know how to manage this situation with the necessary resuscitation drugs and equipment immediately to hand. As with general anaesthesia, continuous, close monitoring of the patient is mandatory.
Some patients are not psychologically suited to be awake, even if sedated, during an operation. They should be identified during the preoperative assessment. Likewise, some surgeons find it very stressful to operate on conscious patients.
Even if a long-acting local anaesthetic is used, a spinal is not suitable for surgery lasting longer than approximately 2 hours. Patients find lying on an operating table for long periods uncomfortable. If an operation unexpectedly lasts longer than this, it may be necessary to convert to a general anaesthetic or supplement the anaesthetic with intravenous ketamine or with a propofol infusion if that drug is available.
When an anaesthetist is learning a new technique, it will take longer to perform than when one is more practised. When one is familiar with the technique, spinal anaesthesia can be very swiftly performed.
There is a theoretical risk of introducing infection into the sub-arachnoid space and causing meningitis. This should never happen if equipment is sterilised properly and an aseptic technique is used. A postural headache may occur postoperatively. This should be rare (see later).
Indications for Spinal Anaesthesia
Spinal anaesthesia is best reserved for operations below the umbilicus e.g. hernia repairs, gynaecological and urological operations and any operation on the perineum or genitalia. All operations on the leg are possible, but an amputation, though painless, may be an unpleasant experience for an awake patient. In this situation it may be appropriate to combine the spinal with a light general anaesthetic.
Spinal anaesthesia is particularly suitable for older patients and those with systemic disease such as chronic respiratory disease, hepatic, renal and endocrine disorders such as diabetes. Many patients with mild cardiac disease benefit from the vasodilation that accompanies spinal anaesthesia except those with stenotic valvular disease or uncontrolled hypertension (see later). It is suitable for managing patients with trauma if they have been adequately resuscitated and are not hypovolaemic. In obstetrics, it is ideal for manual removal of a retained placenta (again, provided there is no hypovolaemia). There are definite advantages for both mother and baby in using spinal anaesthesia for caesarean section. However, special considerations apply to managing spinal anaesthesia in pregnant patients (see later) and it is best to become experienced in its use in the non-pregnant patient before using it for obstetrics.
Contra-indications to Spinal Anaesthesia
Most of the contra-indications to spinal anaesthesia apply equally to other forms of regional anaesthesia.
These include:
Inadequate resuscitation drugs and equipment. No regional anaesthetic technique should be attempted if drugs and equipment for resuscitation are not immediately to hand.
Clotting disorders. If bleeding occurs into the epidural space because the spinal needle has punctured an epidural vein, a haematoma could form and compress the spinal cord. Patients with a low platelet count or receiving anticoagulant drugs such as heparin or warfarin are at risk. Remember that patients with liver disease may have abnormal clotting profiles whilst low platelet counts as well as abnormal clotting can occur in pre-eclampsia.
Hypovolaemia from whatever cause e.g. bleeding, dehydration due to vomiting, diarrhoea or bowel obstruction. Patients must be adequately rehydrated or resuscitated before spinal anaesthesia or they will become very hypotensive.
Patient refusal. Patients may be understandably apprehensive and initially state a preference for general anaesthesia, but if the advantages of spinal anaesthesia are explained they may then agree to the procedure and be pleasantly surprised at the outcome. If, despite adequate explanation, the patient still refuses spinal anaesthesia, their wishes should be respected. Likewise, mentally handicapped patients and those with psychiatric problems need careful pre-operative assessment.
Children. Although spinal anaesthesia has been successfully performed on children, this is a highly specialised technique best left to experienced paediatric anaesthetists.
Sepsis on the back near the site of lumbar puncture lest infection be introduced into the epidural or intrathecal space.
Septicaemia. If a patient is septicaemic, they are at increased risk of developing a spinal abscess. Epidural abscesses can, however, appear spontaneously in patients who have not had spinal/epidural injections especially if they are immuno-deficient: e.g., patients with AIDS, tuberculosis, and diabetes.
Anatomical deformities of the patient's back. This is a relative contraindication, as it will probably only serve to make the dural puncture more difficult.
Neurological disease. The advantages and disadvantages of spinal anaesthesia in the presence of neurological disease need careful assessment. Any worsening of the disease post-operatively may be blamed erroneously on the spinal anaesthetic. Raised intracranial pressure, however, is an absolute contra-indication as a dural puncture may precipitate coning of the brain stem.




Dr NAZIM MOHAMMAD
CONSULTANT ANAESTHESIOLOGIST
K . V . G MEDICAL COLLEGE ., SLUUIA