الفهرس 
Anatomical and physiological considrationOnly 14 pages are availabe for public view
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Abstract
Summary
92
Neuraxial block involves spinal anesthesia, epidural
anesthesia and combined spinal epidural anesthesia. S.A is
used widely for both lower limbs and lower abdominal
surgeries. It gives good sensory and motor block, reduces
incidence of D.V.T and pulmonary embolism, provides
postoperative pain relief and early ambulation. Epidural
anesthesia is used for upper abdominal and thoracic surgeries,
also as a supplement to general anesthesia for providing
excellent control of chronic pain.
Neuraxial block is achieved by sympathetic block which
lead to decrease venous return to the heart and decrease
systemic vascular resistance after blockade of preganglionic
sympathetic fibers that causes hypotension.
Hypotension is defined as systolic blood pressure less
than 90 mmHg or decrease from baseline more than 30%.
Preoperative hypotension should be corrected to reduce
morbidity and mortality.
Prevention of hypotension is of utmost importance.
Several techniques and modalities can be used together as no
single technique proves its efficacy.
Various measures are used such as Trendelenburg
position, leg wrapping, lateral left tilt, volume preloading and
vasopressors.
Fluids used in preloading or co-loading varies between
crystalloids and colloids. Crystalloids have short half- life so
their expansion abilities are limited. While colloids have longer
half-life so they are able to maintain the increase in
intravascular volume. Consequently, less volume is required.
Colloids are more effective than crystalloid in preloading
to prevent hypotension during neuraxial block.
Judicious use of vasopressors such as ephedrine and
phenylephrine will maintain CO and decrease incidence of
hypotension so keep hemodynamics stable.
Ephedrine is a mixed α and β receptor agonist. Its
mechanism is both direct (binds and stimulates receptors) and
indirect (causes release of noradrenaline from presynaptic
vesicles). Ephedrine causes an increase in cardiac contractility,
HR, CO and systolic and diastolic BP. Phenylephrine is
chemically related to adrenaline but pharmacodynamically
similar to noradrenaline. It is a potent, rapidly-acting
vasopressor with a short duration of action. It increases systolic
and diastolic BP in a dose-dependent manner.
Neuraxial block is used for elderly patients with caution
of hypotension to avoid organ hypoperfusion.
Neuraxial block is done widely in obstetric practice to
avoid complication of general anesthesia such as difficult
intubation, aspiration and fetal hypoxia. Correction of
preoperative hemodynamic changes will reduce both maternal
and fetal morbidity and mortality.
Obstetric patients are more susceptible to hypotension
due to aortocaval compression so techniques like left lateral tilt
and co-loading with colloid solutions are widely used.
Good perioperative management of hypertensive patients
by controlling blood pressure will protect patients from end
organ damage due to hypotension which may have detrimental
effects.
Anticipation and early management of hypotension
especially in obstetric, cardiac and hypertensive patients will
improve outcomes and decrease postoperative morbidity,
mortality and hospital stay.