Intracranial pressure, anesthetics.pptx

ICP and Anesthetic agents

1. Intracranial pressure, effect of anaesthetic agents and techniques on CBF & CMR By: Biruk A September ,2021 9/30/2021 1

2. Outline 9/30/2021 2 Introduction ICP Effects of increased ICP Strategies to decrease an elevated ICP Effects of anaesthetic agents on CBF&CMR Principles of neuroanaesthesia

3. Introduction Alexander Monro (1733–1817) first described ICP in 1783. He described that brain tissue is nearly incompressible and surrounded by non-expandable cranium. he suggested that intracranial blood volume remains constant. George Kellie (1720–1779) stated that intracranial fluid could not be added or removed without simultaneous equivalent replacement or displacement. 9/30/2021 3

4. Introduction... 9/30/2021 4 Francois Magendie (1783–1855) first described the circulation of CSF flowing from the ventricles to the spinal cord by discovering a small foramen in the roof of the fourth ventricle (foramen Magendie ). The neurosurgeon Harvey Cushing (1869–1939) and his co-worker Lewis Weed endorsed the doctrine of Monro and Kellie by stating that: With an intact cranium, the net sum of all intracranial vault volumes (brain tissue, blood, CSF volume) remains constant and that an increase in one component should cause a reduction in one or both of the other two components.

5. Contents of the Intracranial Vault 9/30/2021 5 The skull is the brain’s bony (stiff) hull that has only one big outlet, the foramen magnum. It contains all relevant compartments, including the brain tissue, CSF, and arterial and venous blood.

6. Contents of intracranial vault... 9/30/2021 6 a) Brain Parenchyma : The brain parenchyma including the cranial nerves makes up about 85% of total intracranial volume (ICV). Volume expansion of the parenchyma might be caused by tumour, abscess, intracranial haemorrhage (ICH), or oedema. A natural atrophy of the brain can be observed during ageing, which provides more space for volume expansion in elderly people.

7. Contents of intracranial vault... 9/30/2021 7

8. Contents of intracranial vault... 9/30/2021 8 b) Cerebrospinal Fluid : The CSF space makes up 10% of the ICV, equalling a total of 120–200 ml. It is mainly produced by ultrafiltration from blood in the plexus choroideus at a rate of 250– 500 ml/24h. Its resorption sites are arachnoidal granulations close to the venous sinuses. Production and resorption are in a physiological balance.

9. Contents of intracranial vault... 9/30/2021 9 c) Blood: The cerebral blood volume makes up 5% of the ICV. Cerebral blood flow (CBF) and associated cerebral blood volume (CBV) are regulated by mechanisms influencing cerebral resistance (i.e., constriction or dilation of vessels) . The concept of the ‘optimal CPP’ should be followed, since values beyond the optimal CPP level are associated with fatal outcome or increased disability.

10. Contents of intracranial vault... 9/30/2021 10

11. Intracranial Compliance 9/30/2021 11 The pressure-volume relationship between ICP, ICV, and CPP is known as the Monro -Kellie doctrine , which states that: a) the brain is enclosed in the non-expandable cranium; b) brain parenchyma is nearly incompressible; c) the blood volume of the intracranial vault is nearly constant; and d) a continuous outflow of venous blood from the intracranial vault is required to make room for incoming arterial blood.

12. Intracranial compliance... 9/30/2021 12 The cranial vault is a rigid structure with fixed volume of brain (85%), blood( 5%) and CSF( 10 %). “ Any increase in one component must be offsetted by an equivalent decrease in another to prevent rise in ICP” Monro - kellie doctrine .

13. Intracranial compliance... 9/30/2021 13 “ Within the rigid skull the sum of volumes of brain, CSF,& IC blood is constant” An increase in one should cause a decrease in one or both of the remaining two if a rise in ICP is to be avoided. V IC= V blood + V CSF + V brain tissue

14. Intracranial compliance... 9/30/2021 14 Intracerebral compliance (CIC = ∆V/ ∆P) reflects the ability of the intracranial system to compensate for changes in volume (∆V) per unit change in pressure (∆P). Intracerebral elastance (EIC = ∆P/∆V) is the inverse of compliance. Intracranial elastance determined by measuring the change in ICP in response to change in intracranial volume.

15. Intracranial compliance... 9/30/2021 15

16. Cerebral perfusion pressure 9/30/2021 16 ICV, and thereby ICP, is predominantly influenced by arterial partial pressure of carbon dioxide (PaCO2). CBF is tightly coupled to cerebral metabolism. CPP = MAP–ICP. Normal CPP values range between 70 and 90 mmHg. Cerebral perfusion and autoregulation may be disturbed in acute brain injury, potentially causing an increase in CBV and ICP, thereby decreasing CPP and causing subsequent brain injury.

17. Intracranial pressure 9/30/2021 17 ICP is measured at the level of the  foramen of Monro . The normal value for ICP at rest is 10±5 mmHg for a supine adult. ICP elevation can be categorized as: 16–20  mmHg → mild 21–30 mmHg → moderate 31–40 mmHg → severe ICP elevation Initial increases in volume are well compensated until it reaches a point in which further increase can cause rise in ICP .

18. ICP… 9/30/2021 18 If ICP is not measured directly, we can estimate it and therefore, make changes in MAP to maintain CPP . GCS 9-13, ICP ∼20mmHg GCS ≤ 8, ICP ∼ 30mmHg

19. ICP…(P-V relationship) 9/30/2021 19

20. ICP…(P-V relationship) 9/30/2021 20 Stage 1/2=compensation phase: As one of the intracranial constituents increases in volume, the other two constituents decrease in volume in order to keep the intracranial pressure constant. Stage 3/4= decompensated phase: When compensatory mechanisms are exhausted, small increases in the volumes of intracranial constituents cause large increases in ICP. The slope of the curve is dependent on which intracranial constituent is increasing. If it is blood or CSF, both of which are poorly compressible , then the slope is steeper. If it is brain tissue, such as a tumour or oedema, the curve is less steep as the tissue is relatively compressible.

21. ICP… 9/30/2021 21 Major compensatory mechanisms include: Displacement of CSF from cranial to spinal compartment An increase in CSF resorption Decrease in CSF production Decrease in total cerebral blood volume

22. ICP... 9/30/2021 22 Pathophysiology of ICP

23. Conditions causing raised ICP 9/30/2021 23

24. Effects of raised ICP As ICP rises, CPP falls eventually to a point when there is no cerebral blood flow, no cerebral perfusion and brain death. Prior to this, brain structures begin to herniate (protrude through an opening). Herniation of brain tissue from one compartment to another (or into the surgical field) , with resultant mechanical injury to brain tissue. 9/30/2021 24

25. Brain Herniation The  tentorium :  is an extension of the dura mater that separates the Cerebellum  from the Cerebrum . There are two major classes of herniation : supratentorial and infratentorial. Supratentorial : refers to herniation of structures normally found above the  tentorial notch. Infratentorial : refers to structures normally found below the tent. 9/30/2021 25

26. Herniation … Supratentorial lesions: usually have raised ICP . Infratentorial lesions: cause problems related to pressure effects on vital brain stem structures and increased ICP . 9/30/2021 26

27. Herniation … Where does the displaced brain go? Side to side: subfalcine. Side to bottom : uncal (transtentorial) . Top to bottom: central tentorial . Bottom to top: “ upward” Bottom through the “hole”: tonsillar cerebellar . falx tentorium foramen magnum 9/30/2021 27

28. Herniation … 9/30/2021 28 1) Subfalcine herniation : the most common cerebral herniation  pattern . when the brain is pushed into the opposite half of the cranium under the falx cerebri . Anterior cerebral artery compression: contralateral leg paresis 2) Uncal herniation : the innermost part of the  temporal lobe, the  uncus , can be squeezed so much that it moves towards the  tentorium  and puts pressure on the  brainstem , most notably the midbrain. causes cranial nerve III palsy , dilatation of pupil on the ipsilateral , followed by movement of eye down and out.

29. Herniation … 9/30/2021 29 3) Tonsilar herniation . Herniation of cerebellum through the foramen magnum. Pressure on the brainstem causes the Cushing reflex – hypertension, bradycardia and problems in breathing. 4) Transcalvarial herniation : the brain squeezes through a fractured skull or a surgical site in the skull or any area with a defect in the skull.

30. Herniation pathways: 9/30/2021 30 Subfalcine Uncal / transtentorial tonsilar , and Transcalvarial

31. Identify potential site of herniation A: uncal B: central C: Subfalcine D: Tonsillar 9/30/2021 31

32. Herniation syndrome & its clinical manifestation 9/30/2021 32

33. Clinical signs of herniation … 9/30/2021 33

34. Symptoms and signs of raised ICP Early clinical signs of increased ICP: decreased level of consciousness, confusion, restlessness, lethargy, cerebral and pupillary dysfunction, deterioration of motor function, headache, personality changes, and decreasing GCS score. 9/30/2021 34

35. Symptoms and signs of raised ICP… 9/30/2021 35 Late clinical signs of increased ICP: continued decrease in level of consciousness (stupor, coma), dilated pupils, no reaction of pupils to light, vomiting, bradycardia , hyperthermia,and papilloedema .

36. Management principles in neurosurgery 9/30/2021 36 1. Preventing increases in ICP or Reducing an ICP that is already elevated. 2. Maintain CBF When the cranium is Closed & with raised ICP : the objective is to maintain adequate CPP and prevent the herniation of brain tissue between intracranial compartments or through the foramen magnum.

37. Mx principles in neurosurgery… 9/30/2021 37 When the cranium is open, the issue may be: Providing relaxation of the intracranial contents to facilitate surgical access or, In extreme circumstances, reverse the process of brain herniation through a craniotomy. The principles that apply are similar whether the cranium is open or closed .

38. Mx principles in neurosurgery… 9/30/2021 38 1. Avoid increasing cerebral blood flow : Avoid hypercarbia ,hypoxia ,hypertension, and hyperthermia Use IPPV, control PaCo2 and ensure good oxygenation ,adequate analgesia, and anesthetic depth. 2. Avoid increasing venous pressure : avoid coughing and straining ,the head down position , obstructing neck veins with ET tube ties. 3. Prevent further cerebral edema : fluid restriction, but important to maintain intravascular volume and CPP.

39. Mx principles in neurosurgery… 9/30/2021 39 Do not use hypotonic solutions : fluid flux across the BBB is determined by plasma osmolality . Maintenance of a high normal plasma osmolality is essential. 4. Maintain CPP : Avoid Hypotension(control blood pressure using fluids and vasopressors ) target to have above 70 mmHg of CPP. 5. Avoid anesthetic agents that increase ICP.

40. Specific measurements 9/30/2021 40 a) Diuretics : Reduce cerebral edema osmotic diuretics:mannitol:0.25g/kg -1g/kg over 15 minutes Loop diuretics : Furosemide 0.25-1mg/kg & Urinary catheterization is must . b) Modest hyperventilation : has transient effects in reducing ICP for 24 hrs c) Corticosteroids : Reduce edema surrounding tumors and abscess. they take several hours to work. Dexamethasone 4mg 6 hourly is often given for elective surgery preoperatively.

41. Specific measurements… 9/30/2021 41 d) Head up tilt : to reduce central venous pressure ,always ensure that MAP is not significantly reduced as the overall result could be a reduction in CPP. e) Anticonvulsants : For frontal and temporal surgery phenytoin can be given as a loading dose, 15mg/kg intravenously, but should be given slowly as it causes hypotension and can cause arrhythmias.

42. Strategies to reduce ICP 9/30/2021 42

43. Effects of anesthetic drugs on CBF and CMR Volatile anesthetics IV Induction agents Neuromuscular blocking agents 9/30/2021 43

44. Anaesthetic agents 9/30/2021 44 Most anaesthetic agents Reduce neuronal activity and so reduce the brain’s cerebral metabolic requirement for oxygen (CMR02 ). They provide a protective mechanism when oxygen demand may outweigh supply. Unfortunately, many anaesthetic agents also reduce the MAP by causing Systemic arterial vasodilatation with a potentially adverse effect on CPP.

45. Volatile anaesthetics 9/30/2021 45 All volatile anesthetics suppress cerebral metabolism in a dose-related fashion. Volatile anesthetics also possess intrinsic cerebral vasodilatory activity as a result of direct effects on vascular smooth muscle. The net effect of volatile anesthetics on CBF is therefore, a balance between a reduction in CBF caused by CMR suppression and an augmentation of CBF caused by the direct cerebral vasodilation .

46. Volatile anaesthetics… 9/30/2021 46 When administered at a dose of 0.5 MAC, CMR suppression–induced reduction in CBF predominates, and net CBF decreases in comparison with the awake state. At 1 MAC, concentrations of isoflurane , sevoflurane , or desflurane , CBF remains unchanged; at this concentration, CMR suppression and vasodilatory effects are in balance .

47. Volatile anaesthetics… 9/30/2021 47 Beyond 1 MAC, the vasodilatory activity predominates , and CBF significantly increases, even though the CMR is substantially reduced. Vasodilation with increasing doses of volatile agents lead to an attenuation of cerebral autoregulation . With large doses, autoregulation is abolished and cerebral perfusion becomes pressure passive.

48. Volatile anaesthetics… Halothane Has greatest effect on CBF Con.> 1% : abolishes auto regulation Generalized increase in CBF Maximally, CBF increases up to 200%. Isoflurane increases CBF Auto regulation maintained up to 1 MAC Maximally, CBF increases up to 20%. 9/30/2021 48

49. Volatile anaesthetics… 9/30/2021 49 Sevoflurane : CBF effects similar to Isoflurane Produce slightly less vasodilation Auto regulation maintained up to 1.5 MAC Desflurane : CBF similar to isoflurane Autoregulation progressively abolished as dose increases.

50. Volatile anaesthetics… 9/30/2021 50 Nitrous Oxide: When administered on its own - increases both CBF and metabolism . when added to a background of another anesthetic, it increases CBF without changing metabolism. It is a direct acting and potent cerebral vasodilator.

51. Volatile anaesthetics… 9/30/2021 51

52. Volatile agents… 9/30/2021 52

53. IV induction agents 9/30/2021 53 IV anesthetic agents all decrease cerebral metabolism, CBF and ICP with the exception of ketamine . All the reductions are in a dose dependent fashion. Once maximal suppression of metabolism occurs, no further reduction in CBF occurs . CO 2 reactivity and autoregulation of cerebral circulation are well maintained during propofol /thiopental anesthesia.

54. IV induction agents… 9/30/2021 54 Barbiturates /Thiopentone Barbiturates maximal 50% reduction in CBF and metabolism. CO2 reactivity is maintained but is quantitatively reduced compared to the awake response. Cerebral auto regulation maintained intact. Anticonvulsant properties are advantageous.

55. IV induction agents… 9/30/2021 55 Propofol Propofol produces a coupled dose dependent reduction in CMRO2 and CBF. At High doses of propofol , its vasodilator effect overcomes the coupling & CBF increases. Both CO2 responses and auto regulation are maintained intact in the normal brain.

56. IV induction agents… 9/30/2021 56 Ketamine Dilates the cerebral vasculature and increases CBF ( 50 – 60%) It is not routinely used for elective neurosurgical anaesthesia at present, but has gained acceptance as an appropriate agent for Emergency induction of anaesthesia and maintenance of sedation in head injured patients , particularly those with multiple injuries and haemodynamic compromization .

57. IV induction agents… 9/30/2021 57

58. Opioids 9/30/2021 58 Opioids at low doses produce very little effect on CBF if an increase in PaCo 2 is avoided. Auto regulation remains intact BP vasodilatation to maintain CBF. Fentanyl and morphine – these agents have little effect on intracranial pressure or blood flow which makes them suitable for titration to provide postoperative analgesia.

59. NMBD 9/30/2021 59 No direct effect on CBF Histamine releasing agents can cause hypotension , and decrease in CPP Suxamethonium causes a rise in ICP through muscle fasciculation increasing venous pressure. This effect is moderate and of little clinical relevance. Should be used when RSI is required in the presence of a potentially full stomach.

60. Luxury perfusion , cerebral steal,& Reverse steal phenomena 9/30/2021 60 Luxury perfusion ? Intracerebral steal ? Reverse steal phenomenon ? What is penumbra? Semi stable cells that can be saved for a full recovery with appropriate treatment including optimal anesthetic management.

61. Luxury perfusion The combination of a decrease in CMRO 2 and increase in CBF has been termed luxury perfusion. Metabolic Demand, but Metabolic Supply Seen in Acute cerebral infarction : Vessels – max. dilated Induced hypotension with isoflurane 9/30/2021 61

62. Intracerebral Steal phenomenon In a setting of focal ischemia , vasodilatation in a normal area would shunt blood away from the ischemic area. ischemic normal Seen in increase in PaCO 2 in cerebral ischemia and Volatile anesthetic agents. Results in vasodilatation in normal areas not in ischemic areas. 9/30/2021 62

63. Reverse Steal phenomena Diversion or redistribution of blood flow from normal to ischemic areas in the brain is termed Reverse Steal / Robin Hood phenomenon. ischemic normal 9/30/2021 63

64. 9/30/2021 64 Thank you !!!