Complications of neuraxial anaesthesia
Local anaesthetic toxicity
Local anaesthetic drugs are commonly used in obstetrics. These drugs can cause significant neurological and cardiovascular compromise including cardiac arrest if administered in excessive doses or accidentally injected into blood vessels.
Local anaesthetics exert their action by reversibly blocking the transmission of action potential in sensory, motor, and sympathetic nerve fibres. Local anaesthetic molecules inhibit the passage of sodium through voltage-sensitive ion channels in the neuronal membrane. In excessive doses, the molecules can bind to ion channels in other excitable tissues resulting in cardiovascular arrhythmias and cardiac arrest. Neurological side effects include an altered mental state, perioral tingling, and seizures. Neurological adverse effects tend to develop before cardiovascular complications become evident. Local anaesthetic toxicity is a medical emergency and should be treated according to nationally agreed protocols using advanced life support algorithms and intravenous lipid solution (9). The Association of Anaesthetists of Great Britain and Ireland (AAGBI) have produced a safety guideline for the management of severe local anaesthetic toxicity (10). This can be found at the AAGBI website (https://www.aagbi.org/).Postdural puncture headache
Postdural puncture headache is a low-pressure headache that results from a persistent leak of CSF (11). This is usually the consequence of an inadvertent puncture of the dura with the Tuohy needle. The reduction in CSF pressure causes traction on intracranial structures that are pain sensitive. The resultant headache is typically occipitofrontal, and may also involve neck pain. It is intermittent in nature and characteristically improves on lying flat. Many cases will respond to conservative management such as simple analgesics, adequate hydration, and increased caffeine intake. In cases where a severe headache persists, an autologous epidural blood patch may be required.
This procedure involves the aseptic withdrawal of a small volume (typically around 20 mL) of the patient's blood which is then injected into the epidural space. The injected blood reduces the headache by exerting a direct positive volume-pressure effect, and also by forming a clot which effectively ‘patches' the dural puncture site thereby minimizes further CSF leak.High block and respiratory arrest
Regional anaesthesia causes a blockade of the spinal transmission of sensory nerve signals. Motor nerve signals are also blocked to a variable extent. The magnitude of this blockade depends on both the density of the block and also the anatomical level of the block, with higher blocks causing loss of function of more anatomical regions. A block from T4-S5 dermatome levels is required for adequate anaesthesia for caesarean section. At the T4 level, a number of intercostal nerves will be anaesthetized resulting in reduced respiratory function. If the block rises to affect the phrenic nerve roots (C3, C4, C5), respiratory arrest can occur necessitating intubation and temporary mechanical ventilation. The cardio-acceleratory fibres originate from T1-T5 and their blockade results in the bradycardia frequently observed with high neuraxial blockade. A ‘total spinal' occurs when the block is so high that parts of the brainstem are anaesthetized. This causes a loss of consciousness, apnoea, severe hypotension, and bradycardia. Early recognition is important. The management is supportive and may require sedation, mechanical ventilation, haemodynamic support, and intensive care unit admission until the local anaesthetic wears off.