Intracranial pressure methods of monitoring and effect of anesthetic agents and techniques

1. Intracranial pressuremethods of monitoringandeffect of anesthetic agents and techniques Dr. Nitishparmar University College of Medical Sciences & GTB Hospital, Delhi

2. Overview • introduction • Clinical importance of ICP measurement • Indications of ICP measurement • Ideal ICP monitor • Individual ICP monitors: merits and demerits • Complications of ICP monitoring • ICP waveforms and their interpretation • Effects of anaesthetic agents on ICP

3. Introduction Assessment of brain function in conscious patient relatively easy One of the most reliable tool of monitoring of deterioration of brain function in unconscious neurosurgical patient is the measurement of ICP Recent audit shows twofold reduction in mortality brain trauma patient in centers where ICP is monitored

4. Normal ICP Adults and young children =10-15mmHg Young children =3-7 mmHg Infants =1.5-6mmHg • Raised ICP 20-30 mmHg = mild risk of herniation 30-50mmHg =moderate >50mmHg =severe (herniation) Temporal mass lesion may herniate even at 20 mmHg

5. Monroe Kellie doctrine • skull is a rigid compartment that contains 3 component • Brain tissue • Blood • CSF • Balance in state of dynamic equilibrium

6. Intracranial P-V curve

7. Volume pressure response • Measure of compliance • Measures the change in ICP that occurs after adding or withdrawing 1ml of CSF • Normal< 2mmHg/ml • VPR> 5mmHg/ml suggests severe reduction in compliance

8. Pressure volume index • Pressure volume index (PVI): volume of fluid to be added to the CSF to raise the ICP 10 times the baseline. • Normal=26±4 ml • Used as a measure of compliance • Significant reduction in compliance when PVI< 13ml

9. Clinical importance of ICP measurement • Raised ICP may impede CBF and may result in cerebral ischemia • Raised ICP may lead to cerebral herniation. • Raised ICP is an important secondary insult in brain injured patient and a predictor of poor outcome • ICP is used to calculate CPP(MAP-ICP) which is used as therapeutic target in neuro ICU’s

10. Indications • Severe head injury (GCS 3-8) • Abnormal CT • Normal CT but age >40 or SBP <90 or abnormal motor posturing • Moderate head injury (GCS 9-12) • If anaesthetized or deeply sedated • Abnormal CT • SAH- associated with hydrocephalus • Spontaneous intracerebral hemorrhage • Brain tumor- in pt. deemed at high risk of swelling or obstructive hydrocephalus eg. Post. Fossa surgery • Benign intracranial hypertension • Reye’s syndrome

11. Before measuring….. • ICP is not evenly distributed in all pathological states– compartmentalization is very common. • ICP varies over time: averaging for at least 30 minutes is needed to calculate mean ICP • Patient supine and avoid movement and speaking during measurement • Overnight monitoring during natural sleep regarded as gold standard in conscious patient.

12. Choice of monitoring systems will depend on experience of the surgeon, the available equipment and the particular circumstances of each case • Pre procedure consent, image of brain and CSF space, coagulation studies and their correction

13. Ideal ICP monitor • Accurate over a large pressure range • Reliable over time- minimal drift • Minimal patient morbidity- infection, hemorrhage, trauma to the brain tissue • Allows waveform analysis • Easy to insert and read • Cost effective

14. methods • Invasive • Intraventricular • Intraparenchymal • Subdural / extradural • Subarachnoid • Non invasive • Clinical • CT • Transcranialdoppler • Tympanic membrane displacement • Scalp blood flow • ophthalmodynamometry

15. Invasive

16. Intraventricular catheters • AKA external ventricular drainage (EVD), connected to an external pressure transducer via fluid-filled tubing. • Gold standard • Requires placement of catheter into lateral ventricles. Usually the non dominant hemisphere is chosen. The reference point for external transducer is foramen of Monroe.(external auditory meatus) • Advantages • Accurate ICP measurement • Access to CSF for drainage • Access to CSF for instilling contrast media/medication • Reliable evaluation of intracranial compliance

17. Disadvantages • Inc. risk of infection • Requires frequent recalibration • Insertion difficult if ventricles are small compressed or displaced • Inc. risk of CSF leak

21. Intraparenchymal • Next most suitable alternative to intraventricular catheters • Two types • Fibre-optic (camino) : change in light intensity is interpreted in terms of pressure • Microchip transducer (codman) : solid state pressure transducer • Advantages • Requires zeroing only once • Less chances of infection • Less chances of CSF leak

22. Disadvantages • Provides no access to CSF • Cannot be recalibrated after placement • Requires periodic replacement d/t drift

25. Subarachnoid bolt or screw • Advantages • Associated with lower infection rates than ventriculostomy • Quickly and easily placed • Can be used in small and collapsed ventricles • Requires no penetration of brain tissue • Disadvantages • Potential for dampened waveform • Less accurate at high ICP levels • Frequent recaliberation is required • No CSF acccess

26. Subdural/epidural catheter • Usually used in the setting of elective craniotomy or for hepatic encephalopathy. • Advantages • Least invasive • Low risk of infection • Easily and quickly placed • Disadvantages • Inc. baseline drift • Accuracy of placement very crucial • Less accurate • No access to csf • expensive

27. Non-invasive • Clinical • Early findings • Dec level of consciousness • Changes in mental state • Confusion • Lethargy • seizures • Abnormal eye examination • Sluggish pupillary response • Papilloedema • Cranial nerve deficiet • Late findings • Continued dec in level of consciousness • Stupor • Coma • Headache-especially in the early morning

28. Hemiplegia • Vomiting without nausea • Decorticate(flexion)/decerebrate(extensor) posturing • Brain stem pressure signs • Loss of protective reflexes- gag, cough, corneal reflex • Cushing triad- hypertension bradycardia irregular respiration • Cheyne stokes respiration • In infants • Suturaldiastesis • Bulging fontanelle (especially lambdoid) • Poor feeding • Upgaze paresis

29. CT scan: • May reveal mass • Hydrocephalus • Cerebral edema: compressed ventricle and midline shift.

31. Transcranial doppler • Principle: a shift in frequency of a wave when either the transmitter or receiver of the wave is moving with respect to the wave propagating medium. • Sound emanating from or reflected by an object moving towards the observer will have a higher frequency and vice-versa • The recorded dimension is velocity and not flow per se but proportionality does exist b/w velocity and flow when the arterial diameter remains constant

32. Advantages • Bedside • Non-invasive • Continuous • Disadvantages • Changes in velocity may reflect low flow or arterial vasoconstriction

33. Tympanic membrane displacement • ICP transmitted to perilymphatic fluid via cochlear aqueduct and can be assessed indirectly by recording tympanic membrane displacement during stapedial reflex • High pressure- greater medial motion • Low pressure- lesser medial motion • Advantages • Non invasive • Easily measured on a sequential basis

34. Disadvantages • Doubtful patency of cochlear aqueduct in elderly • Requires skilled audiologist • Does not give actual value of ICP • Inaccurate

35. Scalp blood flow: bears inverse relationship with ICP • Ophthalmodynamometry: central vein pressure and ICP have good corelation • Useful tool in suspected raised ICP

36. Complications of ICP monitoring CSF infection(0.5-5%) Hemorrhage(1-2%) Cerebral injury(1%) Invalid reading(5-10%) siezures Removal after seven days Correct coagulation defects before placing and removing Correct landmarks. Depth<6 cm Re-zero, drift resistant strain gauges Use anticonvulsants for duration of monitor

37. Analysis of intracranial pressure wave ICP recordings have two component • baseline pressure • pressure waves • Synchronous with arterial pulse • Synchronous with respiration • As the ICP increases the amplitude of the cardiac pulse component increases whereas that of the respiratory component decreases • These changes reflect altered intracranial compliance long before changes in intracranial pressure

38. normal pressure waveform

39. The arterial pressure wave consists of further sub waves • Normally P1>P2 • Inc in P2 above P1 suggests decreasing intracranial compliance even before any actual rise in the intracranial pressure e.g. fulminant hepatic failure

41. Pathological waveforms • Lundberg identified three different types of ICP variations • A waves • Severe pathological waves seen d/t regional alteration in CBV • Rises above 40-50 mmhg and sustained for 5-20 min before coming to baseline • Progressively even the baseline gets elevated • Associated with clinical deterioration • Headache, vomiting, LOC, altered pupillary response may be seen during these episodes

42. B waves • Have an amplitude of 20 mmhg and occurs @ 1-2/min • Warning signs of decreased intracranial compliance and impending elevation of intracranial pressure • B waves most commonly occur synchronously with cheyne stokes respiration • C waves • Small rhythmic oscillations of 20mmhg occurring at a frequency of 4-8/min and is of doubtful significance

43. Lundberg waves

44. Effect of anesthetic agent on ICP • Important factors effecting ICP • Cerebral blood flow • Ph • Pco2 • Po2 • CSF dynamics • CBV and not CBF is the most important factor influencing ICP. • Generally parallel correlation between CBF and CBV except ischemia caused by hypotension or vessel occlusion. • Also no 1:1 relation • Practically very difficult to measure CBV.

45. Intravenous induction agents • Barbiturates • Dose dependent decrease in cmro2 and CBF leading to a decrease in CBV and thus ICP • High doses of thiopentone causes a decrease in CSF formation (Vf) and either no change or decrease in resistance to CSF absorption (Ra) with a predicted dec. in ICP • Auto regulation and co2 responsiveness is maintained • Propofol • Dose dependent decrease in cmro2 and CBF leading to a decrease in CBV and thus ICP • Propofol causes no change in CSF dynamics • Auto regulation and co2 responsiveness is maintained • Antinausea effect of propofol may also be beneficial

46. Etomidate • Dose dependent decrease in cmro2 and CBF leading to a decrease in CBV and thus ICP • High doses of etomidate causes a decrease in CSF formation (Vf) and either no change or decrease in resistance to CSF absorption (Ra) with a predicted dec. in ICP • Auto regulation and co2 responsiveness is maintained • Reduces ICP without decreasing CPP • Ketamine • Inc. in CBF and cmro2 leading to inc. in CBV and thus ICP • Inc. Ra and no change in Vf with predicted inc. in ICP • Auto regulation and co2 responsiveness is maintained

47. Narcotics • In clinically used dosage no effect on CBF/cmro2 in an un-stimulated nervous system • Higher dosage may cause reduction in both • Substantial reduction may be obtained in highly aroused patients suffering from pain • In cases where pt. is spontaneously breathing inc. in ICP d/t respiratory depression and co2 retention • Morphine in large doses may cause histamine release and inc. in CBV/ICP • At low doses fentanyl, alfentanyl, sufentanyl, remifentanyl no change in Vf and a dec in Ra with predicted dec in ICP.

48. At high doses sufentanyl causes no change in Vf and either no change or inc. in Ra predicting no change or inc. in ICP. • Some reports have also suggested dec. in MAP leading to cerebral vasodilation as a cause of sufentanyl induced rise in ICP

49. Benzodiazepines • Small dec. in CBF/cmro2 • Uncertain effects on CSF dynamics • ICP effects are small with either no change or slight reduction in ICP

50. Volatile anaesthetic agents • All volatile anaesthetic agents supress cerebral metabolism (cmro2 dec.) in dose related manner • All have intrinsic vasodilatory effect • Halothane>>enflurane>desflurane=isoflurane>sevoflurane • Net effect is the interplay of both factors • At 0.5 MAC---cmro2 induced dec in CBF predominates and ICP dec. • At 1.0 MAC---CBF remains unchanged so does ICP • At >1.0 MAC—vasodilatory effect predominates and ICP inc.