Cerebral oximetry brain protection

1. Cerebral Oximetry
A helmet for brain protection
Wesam Farid Mousa
Proffessor of Anesthesia & Surgical
ICU

2. No competing interests or
relationships
to disclose

3.  Complex and fragile system
 Weighs ± 1350 grams: “2% body weight”
 receives 15% of total cardiac output
 utilizes 20% of the oxygen
 Vulnerable to short times of desaturation
events
The brain:

4. The brain consumes adenosine triphosphate at
an incredible rate and holds little stores of this
critical metabolite
Hence, continuous delivery of oxygen and
glucose is essential to maintain adenosine
triphosphate synthesis

5. Under general Anesthesia, the
anesthesiologists are sometimes faced
with neuronal dysfunction/death

6. •Neurological complications vary in severity; some are
transient and some are permanent
•Adverse cerebral outcomes include focal injury, stupor, coma,
seizures, memory deficit or deterioration in intellectual function

7. NEURODETECTION & NEUROPROTECTION
• No “real time” bioassays to detect the onset of
brain injury
•CT, ECHO, EEG & MRI are late indicators of
brain injury

8. The need is

9. THE EVIDENCE
Approximately 465,000 cardiopulmonary` bypass
surgeries performed in the U.S. each year
∗Cerebral oxygen desaturation occurs in 17%-23%
∗ Adverse neurologic outcomes occurs in 6%

10. CEREBRAL OXIMETRY?
• NIRS cerebral oximetry is non-invasive
and continuous “real-time” detection of
cerebral oxygen saturation (SctO2) that
guides clinicians in their interventions

11. Scientific Basis For Cerebral Oximetry
 The Spectrum of Light
The NIRS “Window” From 650nm to 900nm
More Wavelengths = Greater Accuracy
 Chromophores In Cerebral Tissue
More Wavelengths = Greater Accuracy
 The Elliptical Photon Pathway In The Brain
Depth Of Penetration
 The Modified Beer-Lambert Law
absorbance of a material sample is directly proportional to path
length and concentration

12.  The Spectrum of Light
The NIRS “Window” From 650nm to 900nm
More Wavelengths = Greater Accuracy
Scientific Basis For Cerebral Oximetry

13. The Spectrum of Light
• The term “spectrum” for the
colors produced by a prism
• colors in sunlight can be
recombined to make white
light.
Sir Isaac Newton
1642-1727

14.  Microwave
 Infrared
 Near-infrared
 Visible
 Ultraviolet
 X-ray
 Gamma ray
Window for NIRS Between 600 and 900 Nanometers

15. This technology takes advantage of the optical window in which
skin, tissue, and bone are mostly transparent to NIR light in the
spectrum of 600–900 nm, while hemoglobin and deoxygenated-
hemoglobin are stronger absorbers of light.

16. Differences in the absorption spectra of deoxy-Hb and oxy-Hb
allow the measurement of relative changes in hemoglobin
concentration through the use of light attenuation at multiple
wavelengths.

17. Two or more wavelengths are selected, with one wavelength
above and one below the isosbestic point of 810 nm at which
deoxy-Hb and oxy-Hb have identical absorption coefficients

18. Thus, cerebral oximetry measures venous and arterial blood and
includes contributions from both of them in a 3:1 ratio

19. This provides real-time data about the balance of oxygen
supply and demand, thus reflecting venous oxygen reserve:
“the oxygen remaining after extraction by tissues”

20. Old Technology uses two wave lengths, with no
absolute normal values and their Algorithms are
only designated for adults

22. Absorption spectra for HbO2, Hb, Caa3, melanin,
and water (H2O) over wavelengths in NIR range

23. Accuracy
Old technology NIRS: Two channels 90.18%
Recent technology NIRS : Five channels 97%
| |Standard Finger Oxygen Sats =98% | |

24. Accurate Precise Accurate Imprecise Inaccurate Precise Inaccurate Imprecise
Precision and Accuracy
The true value of the quantity being measured
The two concepts are independent of each other,
so a particular set of data can be said to be either
accurate, or precise, or both, or neither.

25. Scientific Basis For Cerebral Oximetry
 The Spectrum of Light
The NIRS “Window” From 650nm to 900nm
More Wavelengths = Greater Accuracy
 Chromophores In Cerebral Tissue
Random Background Scattering Of Light
 The Elliptical Photon Pathway In The Brain
Depth Of Penetration
 The Modified Beer-Lambert Law
absorbance of a material sample is directly proportional to path
length and concentration

26.  Chromophores In Cerebral Tissue
Random Background Scattering Of Light
Scientific Basis For Cerebral Oximetry

27. Other Chromophores as melanin, water, Caaa3 can absorb light in
the same region as oxy-Hb and deoxy-Hb.
Interference caused by these chromophores must be detected and
accounted for to get accurate SctO2 measurements.

28. Also, light is forced to deviate from a straight trajectory due to
non-uniformities in the medium through which they pass or by
small particles.
This causes some optical phenomena such as rainbows, the color
of the sky.
Maxwell's equations are the basis of computational methods
describing light scattering

29. Light travels from the sensor’s light emitting diode to either a
proximal or distal detector, permitting separate data processing
of shallow and deep optical signals

30. Data from the scalp and surface tissue are subtracted
and suppressed, reflecting rSO2 in deeper tissues

31. Scientific Basis For Cerebral Oximetry
 The Spectrum of Light
The NIRS “Window” From 650nm to 900nm
More Wavelengths = Greater Accuracy
 Chromophores In Cerebral Tissue
Random Background Scattering Of Light
 The Elliptical Photon Pathway In The Brain
Depth Of Penetration
 The Modified Beer-Lambert Law
absorbance of a material sample is directly proportional to path
length and concentration

32.  The Elliptical Photon Pathway In The Brain
Depth Of Penetration
Scientific Basis For Cerebral Oximetry

33. Emitter-detector pairs showing the banana-
shaped paths of light.

34. Scientific Basis For Cerebral Oximetry
 The Spectrum of Light
The NIRS “Window” From 650nm to 900nm
More Wavelengths = Greater Accuracy
 Chromophores In Cerebral Tissue
Random Background Scattering Of Light
 The Elliptical Photon Pathway In The Brain
Depth Of Penetration
 The Modified Beer-Lambert Law
absorbance of a material sample is directly proportional to path
length and concentration

35.  The Modified Beer-Lambert Law
absorbance of a material sample is directly proportional to path
length and concentration
Scientific Basis For Cerebral Oximetry

36. Lambert's law: Absorbance of a material is directly proportional to its
thickness (path length).
Much later, August Beer discovered another attenuation relation in 1852
caused by the concentrations of the material.

37. From Pulse Oximetry to
Cerebral Oximetry

38. •Both are based on Beer-Lambert’s Law
• Pulse Oximetry: Only Two wavelengths! Using light loss (Systole – Diastole) to
calculate only signals due to pulsation of arterial blood to derive arterial O2 saturation.
• Cerebral Oximetry: Looking into entire nonpulsating field to derive tissue O2
saturation. It requires more wavelengths to account for light lost from other elements
-as melatonin- in addition to Oxy- and Deoxy-Hemoglobin.
From Pulse Oximetry to Cerebral Oximetry

39. Arterial Pulse Oximetry
• Tells how much oxygen blood is carrying in
arterial system (oxygenated Hb)
• Unable to determine how much oxygen is
used (venous system)
• Unable to determine how different organs use
oxygen (global vs regional) Accuracy about 2%
(not accurate below 85%)

41. VeinsArteries
Tissue (Arterioles, capillaries, venules)
Pulse Oximetry
SpO2 : Arterial
Oxygen Saturation
Normal range:
90-100%
Cerebral Oximetry
SctO2: Regional Tissue
Oxygen Saturation
Normal Range: 60-80%
SjvO2: Jugular Venous
Oxygen Saturation
Normal Range: 50-70%

43. Interpretation of Cerebral Oximetry
rSO2 of 50
20% decline from baseline
are causes for concern and intervention

44. • Coronary artery bypass grafting
• Valve replacement
• Aortic arch replacement with DHCA
• Ventricular assist device
• Liver transplantation
Clinical Applications Of Cerebral Oximetry

45. • ECMO
• Carotid endarterectomy
• “Beach Chair” positioning surgery
• Neonatal cyanotic heart defects
• High-frequency ventilation
• Bowel Ischemia (Neonates)

46. Does the use of this technology changes outcome

49. This article was featured in Anesthesiology2011 accompanied with an
editorial

50. Preoperative mannitol infusion maintains perioperative rSO2 during
laparoscopic cholecystectomy and shortens extubation time with earlier
resurgence of OAAS.

53. 2007 Dec;11(4):274-81

56. Goals in the past were limited to:-

58. LIMITATIONS: Brain Areas Accessible by NIRS
What Part of the Brain is Involved

59. LIMITATIONS: What Part of the Brain is Involved

60. LIMITATIONS: What is the cause
Know how Different Organs
Behave Under Different Conditons
Ischemia (Poor Flow)
Vs
Hypoxia (No Oxygen)
Vs
Venous Congestion

61. Future applications for oximetry