Hypotensive anaesthesia pros and cons.pptx

How to provide hypotensive anesthesia

1. Hypotensive anaesthesia

2. Prepared by, Dr. Muhammad nahidul Islam Resident phase B Anaesthesiology Guided by, Pro ffesor Dr. Satyajit Dhar

3. Outlines Introduction and history Definitions Principle of hypotension Technique Anaesthetic management

4. Deliberate hypotension was first introduced in 1917 in order to provide a bloodless field for neurosurgery. In 1946, the concept of induced hypotension using arteriotomy to produce a bloodless field was introduced. In 1948, high spinal anaesthesia was use to induce hypotension and create a dry field. in 1951 the high epidural block was introduced. In 1962, sodium nitroprusside was first used to induce hypotension during anaesthesia . Introduction & history

5. Definition Hypotensive anaesthesia is the elective lowering of arterial blood pressure. The primary advantages of this technique are minimization of surgical blood loss and better surgical visualization. Also known as deliberate hypotension/ controlled hypotension .

6. Safe level of hypotension Depends on the patients Healthy young individuals may tolerate mean arterial pressure (MAP) to 50-60 mmHg without complications. On the other hand chronically hypertensive patients have altered autoregulation of cerebral blood flow and may tolerate a mean arterial pressure of no more than 20% to 30% lower than baseline.

7. Patient’s with a history of transient ischemic attacks may not tolerate any decline in cerebral perfusion. The risk and benefits of controlled hypotension should be discussed with the patient and the risk should be reviewed with the surgeon when this technique is requested. Safe level of hypotension cont.

8. Advantages REDUCTION IN BLOOD LOSS hemodynamic and metabolic stability less transfusion requirements/complications related to transfusion IMPROVEMENT OF SURGICAL FIELD improved visualization → better and faster surgery FACILITATION OF SURGERY prevention of progressive stretching of thin walls of vessels →easier suturing and clipping (aortic surgery, AVM , intracranial aneurysm clipping) Decrease use of cautery and hematoma formation leads to better wound healing

9. Indication N eurosurgery (AVM , intracranial aneurysm, brain tumor resection ) Major orthopaedic surgery surgery (spinal surgery, shoulder/hip arthroplasty) ENT surgery (middle ear surgery) Head and neck ( faciomaxillary tumours , radical neck dissection ) Pelvic (Major gynaecological or rectal surgery) Other surgery associated with significant blood loss.

10. Relative Contraindications Some patients have predisposing illness that decrease the margin of safety for adequate organ perfusion: Severe anemia Hypovolemia Atherosclerotic cardiovascular disease Renal and hepatic insufficiency Cerebrovascular disease or Uncontrolled glaucoma

11. Some possible complications include: Cerebral thrombosis Hemiplegia( due to decreased spinal cord perfusion) Acute tubular necrosis Massive hepatic necrosis MI Cardiac arrest Blindness( retinal artery thrombosis) These complications are more likely in Patient’s with coexisting anaemia. Complications

12. Principle of hypotension Profuse bleeding Decrease BP Natural survival mechanism Reduction or cessation of bleeding Same principle is applied to surgery

13. Hypoperfusion Brain Renal Heart Mainly to 3 organs

14. Cerebral blood flow Autoregulation Normal CBF is maintained at 45-50 ml/100g/min MAP = 50 - 150 mmHg

15. Factors influencing CBF 1) Volatile anesthetics Attenuates/ abolishes autoregulation Dose dependent: halothane > enflurane > isoflurane

16. Factors influencing CBF 2) PaCO2 Decreased – vasoconstriction For every mm in PaCO2 - CBF by 2% in normotensive subjects or for every mmHg in PaCO2 - CBF in the order of 1ml/100g/ml

17. 3) PaO2 Administration of 100% O2 during induced hypotension not beneficial Hyperoxia may be associated with only minimal decrease in CBF Whereas severe hypoxemia (PO2 <50 mmHg) greatly increase CBF Factors influencing CBF

18. 4 ) Position For every 2.5 cm head raised - CPP by 2 mmHg Head elevation in hypotensive anesthesia aggravates CBF Factors influencing CBF

19. Techniques MAP = CO x SVR Key equation in providing hypotension anesthesia MAP can be manipulated by increasing or decreasing CO or SVR or both

20. Techniques Non- pharmacological Ph armacological

21. Commonly used drugs Beta adrenergic antagonist Used alone or adjunct Advantages Rapid onset No increased in ICP No pulmonary shunt Disadvantages Decreased CO Heart block Bronchospasm - asthma pt Limited efficacy when used alone 7/4/2024 22

22. Commonly used drugs Propofol Vasodilator Advantages Rapid onset/offset Anti-emetic Disadvantages PRIS Pain at injection site Increased pulmonary shunt

23. Commonly used drugs Opioids Alfentanil Sufentanil Remifentanil Rapid action Fast recovery

24. Commonly used drugs Inhalation Negative inotropic effect vasodilator Advantages Provide surgical anesthesia Rapid onset/offset Easy to titrate Cerebral protection Disadvantages Need high conc. When used alone Decrease CO cerebral vasodialation Shivering

25. Commonly used drugs Neuromascular blocking agents Vecuronium Pancuronium – produces tachycardia

26. Commonly used drugs Dexmedotomidine (𝜶2 agonist) Site of action: Brain(locus cereleus ) Spinal cord Autonomic nerve CNS effect: sedatives/hypnosis Anxiolysis Analgesia Autonomic activity decrease sympa thetic activity decrease BP & HR Disadvantages Prolong duration of action Increased ICP Increased pulmonary shunt

27. Commonly used drugs Sodium Nitroprusside Direct vasodilator(Nitric oxide release) Dose - 0.5 -10 mcg/kg/min Advantages Rapid onset(~1 min) Easy to titrate Increases CO Disadvantages Cyanide/Thiocyanate toxicity Increased ICP Increased Pulmonary shunt Sympathetic stimulation Rebound hypertension Steal phenomenon Tachyphylaxis

28. Non-Pharmacological techniques Positional Elevation of site of operation- venous drainage Inclining 15-20 o For each 2.5cm elevation above heart, BP drops 2 mmHg

29. Non-Pharmacological techniques Acute Normovol emic Hemodilutional (ANH) 1 or 2 units of pts blood drawn immediately before or shortly after induction of anesthesia Bleeds diluted blood After completion of surgery – retransfused autologous blood Prerequisite – Hb >= 12g/dL

30. Non-Pharmacological techniques Positive airway pressure Decreases venous return Can be enhanced by: Increasing tidal volume prolonging inspiratory time raising PEEP Drawbacks : Deleterious effect on heart Increased dead space Increased CBF & ICP

31. An a esthetic management Preoperative evaluation Postop care Monitoring Intra-op Mx Fluid therapy

32. Preoperative Thorough knowledge by anesthetist Proper patient evaluation & selection I nv - Hb , urea, S/E, ECG Hb of 10g/dL Baseline ABG Premedication: Anxiolysis Analgesia 𝜷 & 𝜶 blocker Antihypertensive Vagolytics avoided

33. Intraoperative Stress free induction NMB Pressure points avoid nasal intubation

34. Monitoring Meticulous monitoring IBP NIBP - short surgery ECG SpO2 EtCO2 Temperature CVP U rine output Blood loss Cerebral oxymetry

35. Fluid Therapy Proper fluid therapy is essential Optimize fluid & electrolytes before Surgery. Maintenance fluid Blood loss replacement if exceeds 20 -25% of blood volume

36. Postop Rebound hypertension Reactionary hemorrhage Airway Analgesia Fluid balance

37. Thank you