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What is High spinal anaesthesia is characterized by: and explain in detail?
Ans. (d) Hypotension, bradycardiaRef : KDT 6th ed. / 360Systemic Effects (Physiological Alterations) of Central Neu- ralxial BlocksCARDIOVASCULAR SYSTEMThe most prominent effect is hypotension which is because of the following factors:* Venodilatation which is because of sympathetic block which maintains the venous tone.* Dilatation of post arteriolar capillaries which is again because of loss of sympathetic tone.* Decreased cardiac output which is because of:# Decreased venous return: Due to blood pooling in veins of lower limb and lower abdomen.# Bradycardia: Bradycardia can occur as a result of: Decreased atrial pressure because of decrease venous return (Bainbridge reflex) and Direct inhibition of cardioaccelerator fibres (T1 to T4).* Paralysis of nerve supply to adrenal glands with consequently decreased catecholamine release.* Direct absorption of drug into systemic circulation.* Compression of inferior vena cava and aorta by pregnant uterus, abdominal tumors (supine hypotension syndrome).NERVOUS SYSTEM* Autonomic fibres (mediated by C fibres) are most sensitive and they are blocked earliest followed by sensory and then motor fibres. So, sequence of block is Autonomic - Sensory - Motor. The recovery occurs in reverse order although number of studies have suggested return of autonomic activity before sensory.