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Hypotensive Anaesthesia

Pulkit Agarwal
Pulkit Agarwal

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Hypotensive Anaesthesia DEFINITION It is a State of induced controlled hypotension during anaesthesia to reduce bleeding and improve the surgical field adjusted to the patients age ,pre-operative blood pressure and past medical history. First used by Cushing in 1917 ADVANTAGES Decreases blood loss during surgery Decreases operative time Provides bloodless operative field PRINCIPLE Reduction in systolic blood pressure to 80 90 mmHg. Decrease in MAP to 50 60 mmHg in normotensive patients. Reduction in MAP by 30% of the baseline values. VITAL ORGAN PHYSIOLOGY Controlled hypotension rarely results in damage because organ blood flow is normally well maintained. Three main organs whose proper functioning is vital which autoregulate their blood pressures include: Brain Kidney Heart CEREBRAL CIRCULATION Many feel that it is the perfusion of the cerebral circulation that is the critical factor that limits MAP reduction. Auto regulation MAP range of 50-150mmHg VARIOUS FACTORS UNDER CONTROL OF ANAESTHETISTS TO MAINTAIN MAP ARE : paCO2 (partial pressure of Arterial CO2) increase in PaCO2 there is an increase in cerebral blood flow paO2 High O2 mainly in hyperbaric range can lead to cerebral damage and thus brain compensates by Vasoconsriction. If O2 below normal then Vasodilation Volatile anaesthetics Volatile anesthetics attenuate or abolish the auto regulation of cerebral blood flow in a dose dependent manner in the following order : halothane > enflurane > isoflurane. (HEI) Vasodilators
CORONARY CIRCULATION Coronary blood flow is dependent upon the aortic diastolic blood pressure and the coronary vascular resistance. RENAL BLOOD FLOW Renal blood flow is controlled in two ways : Extrinsic autonomic and Hormonal mechanisms and Intrinsic auto regulation. BLOOD PRESSURE GOAL The aim of Hypotensive anaesthesia is to reduce blood loss and provide a dry operating field. Hence, the degree of hypotension should be individualized. The hypotension should be considered satisfactory when bleeding appears to be minimal and organ perfusion adequate. Inducing hypotension to a MAP of 30% below a patients usual MAP, with a minimum of 50mmHg in young patients and 80mmHg in the elderly is clinically acceptable. PATIENT LIMITATIONS Cardiac disease Diabetes mellitus Anaemia, haemoglobinopathies, polycythaemia Hepatic disease Ischaemic cerebrovascular disease Renal disease Respiratory insufficiency Severe systemic hypertension Intolerance to drugs available to produce hypotension ANAESTHETIST LIMITATIONS Lack of understanding of the technique. Lack of technical experience. Inability to monitor the patient adequately. TECHNIQUE : MAP = CARDIAC OUTPUT X SYSTEMIC VASCULAR RESISTANCE = (Stroke volume x Heart rate) x SVR Arterial bleed directly prop to MAP beta blockers reduce Stroke volume and Alpha blockers reduce Peripheral vascular resistance Capillary bleed by local adrenaline and hyperventilation to reduce arterial and venous pCO2 Venous Tone reduced by intravenous nitrates, positioning

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Hypotensive Anaesthesia

  • 1. Hypotensive Anaesthesia DEFINITION It is a State of induced controlled hypotension during anaesthesia to reduce bleeding and improve the surgical field adjusted to the patients age ,pre-operative blood pressure and past medical history. First used by Cushing in 1917 ADVANTAGES Decreases blood loss during surgery Decreases operative time Provides bloodless operative field PRINCIPLE Reduction in systolic blood pressure to 80 90 mmHg. Decrease in MAP to 50 60 mmHg in normotensive patients. Reduction in MAP by 30% of the baseline values. VITAL ORGAN PHYSIOLOGY Controlled hypotension rarely results in damage because organ blood flow is normally well maintained. Three main organs whose proper functioning is vital which autoregulate their blood pressures include: Brain Kidney Heart CEREBRAL CIRCULATION Many feel that it is the perfusion of the cerebral circulation that is the critical factor that limits MAP reduction. Auto regulation MAP range of 50-150mmHg VARIOUS FACTORS UNDER CONTROL OF ANAESTHETISTS TO MAINTAIN MAP ARE : paCO2 (partial pressure of Arterial CO2) increase in PaCO2 there is an increase in cerebral blood flow paO2 High O2 mainly in hyperbaric range can lead to cerebral damage and thus brain compensates by Vasoconsriction. If O2 below normal then Vasodilation Volatile anaesthetics Volatile anesthetics attenuate or abolish the auto regulation of cerebral blood flow in a dose dependent manner in the following order : halothane > enflurane > isoflurane. (HEI) Vasodilators
  • 2. CORONARY CIRCULATION Coronary blood flow is dependent upon the aortic diastolic blood pressure and the coronary vascular resistance. RENAL BLOOD FLOW Renal blood flow is controlled in two ways : Extrinsic autonomic and Hormonal mechanisms and Intrinsic auto regulation. BLOOD PRESSURE GOAL The aim of Hypotensive anaesthesia is to reduce blood loss and provide a dry operating field. Hence, the degree of hypotension should be individualized. The hypotension should be considered satisfactory when bleeding appears to be minimal and organ perfusion adequate. Inducing hypotension to a MAP of 30% below a patients usual MAP, with a minimum of 50mmHg in young patients and 80mmHg in the elderly is clinically acceptable. PATIENT LIMITATIONS Cardiac disease Diabetes mellitus Anaemia, haemoglobinopathies, polycythaemia Hepatic disease Ischaemic cerebrovascular disease Renal disease Respiratory insufficiency Severe systemic hypertension Intolerance to drugs available to produce hypotension ANAESTHETIST LIMITATIONS Lack of understanding of the technique. Lack of technical experience. Inability to monitor the patient adequately. TECHNIQUE : MAP = CARDIAC OUTPUT X SYSTEMIC VASCULAR RESISTANCE = (Stroke volume x Heart rate) x SVR Arterial bleed directly prop to MAP beta blockers reduce Stroke volume and Alpha blockers reduce Peripheral vascular resistance Capillary bleed by local adrenaline and hyperventilation to reduce arterial and venous pCO2 Venous Tone reduced by intravenous nitrates, positioning