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BEDSIDE MONITORING OFTISSUE PERFUSION AND   OXYGENATION                  Dr.Tushar Patil                       MD
Oxygen transport  involves a series of convective and diffusive processes. Convective transport-bulk movement of oxygen ...
Capillary blood to individual                 cells      resting extraction ratio from capillary blood is      about 25%...
Tolerance to hypoxia of      various tissues Tissue    Survival time1.   Brain<3 min2.   Kidney and liver15-20 min3.   Sk...
Tissue Hypoxia in Critically Ill    disordered regional distribution of blood   Regional and microcirculatory distributi...
EFFECTS OF HYPOXIA   PaO2 level approaches 55mmHg-.short term    memory loss, euphoria and impaired judgment    PaO2 30-...
Clinical features of tissue                hypoxia   Dyspnoea   Altered mental state   Tachypnoea or hypoventilation  ...
Monitoring Tissue Perfusion and              Oxygenation1.   Clinical Evaluation2.   Hemodynamic Monitoring3.   Pulse Oxim...
Clinical Evaluation HISTORY-Dyspnoea-Cough-Fever-Rash-Discolouration of digits/limbs-Palpitations-Altered sensorium-Convu...
Clinical Evaluation Level of Consciousness Evaluation of Peripheral & Central Pulses Capillary Refill Time Cyanosis R...
Hemodynamic Monitoring Arterial Blood Pressure-Non Invasive-Invasive Central Venous Pressure Monitoring Pulmonary Arter...
Monitoring arterial pressure    Organ perfusion depends on the organ    metabolic demand ,perfusion pressure,local    vas...
Noninvasive measurements of           arterial pressure    can be determined either manually or by oscillometric    metho...
Arterial CatheterisationINDICATIONS ABSOLUTE- As a guide to synchronization of intra-aortic   balloon counter pulsation ...
Arterial CatheterisationUSEFUL APPLICATIONS Differentiating cardiac tamponade (pulsus paradoxus) from respiration-induced...
Arterial CatherisationCOMPLICATIONS- temporary occlusion- hematomas- Serious ischemic damage- sepsis- pseudoaneurysm
Central venous pressure monitoringPressure in the large central veins proximal  to the right atrium relative to atmosphere...
Factors affecting measured                 CVP1.Central venous blood volume Venous return/cardiac output Total blood vol...
Factors affecting measured                CVP4.Cardiac rhythm Junctional rhythm Atrial fibrillation (AF) Atrio ventricu...
Limitations of CVP Being  wrongly used as a parameter/ goal  for replacement of intravascular volume The validity as ind...
Pulmonary artery                   catheterization   Developed in the 1940s and later refined by Swan and Ganz in    1970...
PACCONTRAINDICATIONS Tricuspid or pulmonary valve mechanical  prosthesis Right heart mass (thrombus and/or tumor) Tricu...
PACMEASURED PARAMETERS1.  Central Venous Pressure2.  Pulmonary Capillary Wedge Pressure3.  Cardiac Index4.  Stroke Volume ...
Complications of PAC  Venous access complications - include arterial puncture - hemothorax - Pneumothorax Arrhythmias - ...
Measuring Cardiac Output1. Pulmonary Artery Catheter2. Pulse Contour Analysis   -Lithium dilution    -Transpulmonary Therm...
Pulse OximetryPRINCIPLE Displayed readings determined primarily by two   components:1. The different absorption spectra o...
Pulse OximetryAPPLICATIONS indicated in circumstance where hypoxaemia  May occur. should be included in the routine vita...
Pulse Oximetry Improving oximeter signals•   Warm and rub the skin•   Apply a topical vasodilator•   Try a different prob...
Pulse Oximetry    PITFALLS1.   Dyshemoglobinemias2.   Poor function wiyh poor performance3.   Difficulty in detecting hig...
Monitoring ventilation using end-          tidal carbon dioxide    provides information regarding alveolar ventilation. ...
End Tidal Carbon DioxideAPPLICATIONS Confirming endotracheal tube placement detecting endotracheal tube dislodgment det...
End Tidal CO2     sudden loss of the capnogram waveform    –ET obstruction     -extubation     - ventilator malfunction  ...
End Tidal CO2 Capnography    can be used to monitor  patients in whom hypercarbia may be  detrimental PetCO2 values grea...
Monitoring Tissue Hypoxia   Global markers of tissue hypoxia          - serum lactate          -central venous oxygen sat...
Serum Lactate   byproduct of anaerobic metabolism, resulting from the    inabilityof pyruvate to enter the Krebs cycle. ...
Central venous oxygen saturation Mixed venous oxygen saturation (SvO2) - a measure of tissue hypoxia.   o Obtained with ...
ScvO2  venous oxygen saturation near the junction of the  superior vena cava and right atrium. obtained from subclavian ...
Sublingual capnometry    studies perfusion of the splanchnic circulation.    sensor placed under the tongue    measures...
Gastric Tonometry   Offers an index of aerobic metabolism in gut    mucosa.   Based on increase in tissue CO2   A ballo...
Orthogonal polarization                 spectroscopy    uses polarized light to visualize the microcirculation directly....
Near-infrared spectroscopy  measures the concentrations of hemoglobin, oxygen saturation,and cytochrome aa3    Cytochrom...
Transcutaneous oxygen tension measure transcutaneous oxygen or carbon dioxide.   Use heated probes placed on the skin•ma...
Cerebral Perfusion and         Oxygenation monitoring1.   Jugular venous bulb oximetry2.   Direct brain tissue oxygen tens...
Jugular venous oxygen               saturation(SjvO2)   Retrograde placement of jugular venous catheter with oximeter   ...
SjvO2LIMITATIONS- changes in arterial oxygen content-   hemodilution-   prone position of catheter-   necessity for freque...
Brain tissue oxygen                 pressure(PBO2)   Small flexible microcatheter inserted into brain parenchyma.    mar...
Near infrared spectroscopy    monitoring of transmittance across the brain at two or    more wavelengths   optical atten...
NISAPPLICATIONS detection of changes during carotid cross-clamping  during carotid endarterectomy & cardiac surgery to d...
NISLIMITATIONS  limited and variable penetration of infrared light through   the skull (2–3 mm, limited to gray matter) ...
Cerebral Microdialysis   bedside monitor to provide on-line analysis of brain tissue    biochemistry during neurointensiv...
MD data displayBrain Tissue O2    monitorMD Bedside AnalyserJugular Venous  Saturation   Monitor
Applications of MD   Most clinical experience with TBI and SAH   Severe cerebral hypoxia /ischemia associated with    ma...
Cerebral Blood Flow Monitoring Kety-Schmidt  method Radioactive tracer techniques Continuous quantitative cerebral bloo...
Neuroimagong [18F]2-deoxy-D-glucose   PET oxygen-15 PET SPECT Xenon-enhanced CT scanning perfusion CT Perfusion weig...
THANKS
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
Bedside monitoring of tissue perfusion and oxygenation
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Bedside monitoring of tissue perfusion and oxygenation

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This presentation is about bedside monitoring of tissue oxygenation and ischemia, both clinically and with instruments

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  1. 1. BEDSIDE MONITORING OFTISSUE PERFUSION AND OXYGENATION Dr.Tushar Patil MD
  2. 2. Oxygen transport involves a series of convective and diffusive processes. Convective transport-bulk movement of oxygen in air or blood-active, energy consuming processes generating flow Diffusive transport- passive movement of oxygen down its concentration gradient across tissue barriers- across the extracellular matrix- depends on the oxygen tension gradient and the diffusion distance
  3. 3. Capillary blood to individual cells resting extraction ratio from capillary blood is about 25% may increase to 70­80% during exercise Factors affecting O2 extraction from cappilary blood1. Rate of O2 delivery to capillary2. O2-Hb dissociation relation3. Size of capillary to cellular PO2 relation4. Diffusion distance to cells5. Rate of use of O2 by cells
  4. 4. Tolerance to hypoxia of various tissues Tissue Survival time1. Brain<3 min2. Kidney and liver15-20 min3. Skeletal muscle60-90 min4. Vascular smooth muscle24-72 h5. Hair and nails -Several days
  5. 5. Tissue Hypoxia in Critically Ill disordered regional distribution of blood Regional and microcirculatory distribution of cardiac output endothelial, receptor, neural, metabolic, and pharmacological factors small resistance arterioles and precapillary sphincters shunting and tissue hypoxia despite high global oxygen delivery and mixed venous saturation. reduce regional distribution, particularly to the renal and splanchnic capillary beds
  6. 6. EFFECTS OF HYPOXIA PaO2 level approaches 55mmHg-.short term memory loss, euphoria and impaired judgment PaO2 30-50mmHg -Progressive loss of cognitive and motor functions, increasing tachycardia PaO2 below 30mmHg-loss of consciousness
  7. 7. Clinical features of tissue hypoxia Dyspnoea Altered mental state Tachypnoea or hypoventilation Arrhythmias Peripheral vasodilatation Systemic hypotension Coma Cyanosis (unreliable) Nausea, vomiting, and gastrointestinal disturbance
  8. 8. Monitoring Tissue Perfusion and Oxygenation1. Clinical Evaluation2. Hemodynamic Monitoring3. Pulse Oximetry4. End Tidal CO2 Monitoring5. Monitoring Tissue Hypoxia6. Cerebral Oxygenation Monitoring
  9. 9. Clinical Evaluation HISTORY-Dyspnoea-Cough-Fever-Rash-Discolouration of digits/limbs-Palpitations-Altered sensorium-Convulsions
  10. 10. Clinical Evaluation Level of Consciousness Evaluation of Peripheral & Central Pulses Capillary Refill Time Cyanosis Respiratory Rate & Pattern Blood Pressure Systemic Examination
  11. 11. Hemodynamic Monitoring Arterial Blood Pressure-Non Invasive-Invasive Central Venous Pressure Monitoring Pulmonary Artery Catheterisation Measuring Cardiac Output
  12. 12. Monitoring arterial pressure Organ perfusion depends on the organ metabolic demand ,perfusion pressure,local vasomotor tone and cardiac output tissue perfusion is maintained through ‘‘autoregulation’’ Organ perfusion pressure cannot be measured directly at the bedside As a surrogate for tissue perfusion pressure, arterial blood pressure is monitored.
  13. 13. Noninvasive measurements of arterial pressure can be determined either manually or by oscillometric method . Oscillometric devices, determine MAP and then provide readings for systolic and diastolic pressures. Oscillometric devices tend to underestimate systolic and overestimate diastolic blood pressure noninvasive measurements less reliable with marked hypovolemia or abnormal cardiac function. Oscillometric measurements also limited by cycling delay of the device.
  14. 14. Arterial CatheterisationINDICATIONS ABSOLUTE- As a guide to synchronization of intra-aortic balloon counter pulsation PROBABLE-1. Guide to management of potent vasodilator drug infusions2. Guide to management of potent vasopressor drug infusion3. As a port for the rapid and repetitive sampling4. As a monitor of cardiovascular deterioration in patients
  15. 15. Arterial CatheterisationUSEFUL APPLICATIONS Differentiating cardiac tamponade (pulsus paradoxus) from respiration-induced swings in systolic BP Differentiating hypovolemia from cardiac dysfunction as the cause of hemodynamic
  16. 16. Arterial CatherisationCOMPLICATIONS- temporary occlusion- hematomas- Serious ischemic damage- sepsis- pseudoaneurysm
  17. 17. Central venous pressure monitoringPressure in the large central veins proximal to the right atrium relative to atmosphere. METHODS- central venous line / Swan-Ganz catheter with distal tip connected to manometer/ pressure transducer- noninvasively as jugular venous pressure
  18. 18. Factors affecting measured CVP1.Central venous blood volume Venous return/cardiac output Total blood volume Regional vascular tone2.Compliance of central compartment Vascular tone RV compliance Myocardial disease Pericardial disease Tamponade3.Tricuspid valve disease Stenosis Regurgitation
  19. 19. Factors affecting measured CVP4.Cardiac rhythm Junctional rhythm Atrial fibrillation (AF) Atrio ventricular (A-V) dissociation5.Reference level of transducer Positioning of patient6.Intrathoracic pressure Respiration IPPV Positive end-expiratory pressure (PEEP) Tension pneumothorax
  20. 20. Limitations of CVP Being wrongly used as a parameter/ goal for replacement of intravascular volume The validity as index of RV preload nonexistent Poor correlation with cardiac index, stroke volume, left ventricular end-diastolic volume, and right ventricular end-diastolic volume
  21. 21. Pulmonary artery catheterization Developed in the 1940s and later refined by Swan and Ganz in 1970INDICATIONS Diagnostic – Diagnosis of shock states – high- versus low-pressure pulmonary edema – primary pulmonary hypertension (PPH) – valvular disease, intracardiac shunts, cardiac tamponade, and pulmonary embolus (PE) – Monitoring complicated AMI – hemodynamic instability after cardiac surgery Therapeutic - Aspiration of air emboli
  22. 22. PACCONTRAINDICATIONS Tricuspid or pulmonary valve mechanical prosthesis Right heart mass (thrombus and/or tumor) Tricuspid or pulmonary valve endocarditis
  23. 23. PACMEASURED PARAMETERS1. Central Venous Pressure2. Pulmonary Capillary Wedge Pressure3. Cardiac Index4. Stroke Volume Index5. LV Stroke Work Index6. RVSWI7. RV Ejection Fraction8. RV End Diastolic Volume9. Systemic Vascular Resistance Index10. Pulmonary Vascular Resistance Index11. Mixed Venous O2 Saturation12. O2 delivery13. O2 uptake14. O2 exraction Ratio
  24. 24. Complications of PAC Venous access complications - include arterial puncture - hemothorax - Pneumothorax Arrhythmias - PVCs or nonsustained VT - Significant VT or ventricular fibrillation Right bundle-branch block (RBBB) PA rupture PAC related infection Pulmonary infarction
  25. 25. Measuring Cardiac Output1. Pulmonary Artery Catheter2. Pulse Contour Analysis -Lithium dilution -Transpulmonary Thermodilution -Without diluion calibration3. CO2 Rebreathing4. Trans thoracic Electrial Bioimpedence5. Trans Thoracic Echo6. Esophageal Doppler Monitoring
  26. 26. Pulse OximetryPRINCIPLE Displayed readings determined primarily by two components:1. The different absorption spectra of oxyhemoglobin and deoxyhemoglobin at different wavelengths2. Pulsatile arterial blood Probe (finger, ear, or forehead) contains two light- emitting diodes that emit light at 660 nm and 940 nm. Photoreceptor receives light, and compares absorption two wavelengths,
  27. 27. Pulse OximetryAPPLICATIONS indicated in circumstance where hypoxaemia May occur. should be included in the routine vital signs. . continuous monitoring. pattern of oxygenation can be recorded. can replace arterial blood gas analysis in cases where assessment of oxygenation is indication. Regulation of oxygen therapy Testing adequecy of circulation
  28. 28. Pulse Oximetry Improving oximeter signals• Warm and rub the skin• Apply a topical vasodilator• Try a different probe site, especially the ear• Try a different probe• Avoid motion artefact• Use a different machine
  29. 29. Pulse Oximetry PITFALLS1. Dyshemoglobinemias2. Poor function wiyh poor performance3. Difficulty in detecting high oxygen partial pressures4. Delayed detection of hypoxic events5. Erratic performance with irregular rhythms6. Nail polish and coverings7. Loss of accuracy at low values8. Electrical interference9. Failure to detect hypoventilation
  30. 30. Monitoring ventilation using end- tidal carbon dioxide provides information regarding alveolar ventilation. PetCO2 - concentration of carbon dioxide at end expiration . measured in both mechanically ventilated and spontaneously breathing patients. displayed as either numerical value (capnometry) or as a graphic waveform plotted against time (capnography). PetCO2 underestimatesPaCO2 by 2 to 5 mm Hg because of the influence of dead space ventilation relationship between PetCO2 and PaCO2 is unreliable in critically ill patients.
  31. 31. End Tidal Carbon DioxideAPPLICATIONS Confirming endotracheal tube placement detecting endotracheal tube dislodgment detecting ventilator malfunction assessing the success of cardiopulmonary resuscitation evaluation of weaning from mechanical ventilation determining the optimal level of PEEP
  32. 32. End Tidal CO2 sudden loss of the capnogram waveform –ET obstruction -extubation - ventilator malfunction –cardiac arrest sudden drop of the waveform -partial obstruction of ET -an airway leak -hypotension
  33. 33. End Tidal CO2 Capnography can be used to monitor patients in whom hypercarbia may be detrimental PetCO2 values greater than 40 mm Hg correlate with equal or higher value of PaCO2 Elevated PetCo2 indicate sthe need for alterations in management
  34. 34. Monitoring Tissue Hypoxia Global markers of tissue hypoxia - serum lactate -central venous oxygen saturation (ScvO2) Monitoring regional hypoxia -Sublingual Capnometry –Gastric Tonometry - Orthogonal Polarization Spectroscopy (OPS) - Near Infra Red Spectroscopy (NIRS) -Trans cutaneous Oxygen Tension -Resonance Raman Spectroscopy
  35. 35. Serum Lactate byproduct of anaerobic metabolism, resulting from the inabilityof pyruvate to enter the Krebs cycle. The normal serum value - less than 2 mmol/L. lactate levels above 4mmol/L strongly associated with worse outcome. more important is the time to normalization of lactateLevels- ‘‘lactate clearance time.’’ Prolonged lactate clearance time(>48hrs)-significantly higher rates of infection, organ dysfunction, and death Better survival correlates with a lactate clearance time <24 hrs.
  36. 36. Central venous oxygen saturation Mixed venous oxygen saturation (SvO2) - a measure of tissue hypoxia. o Obtained with pulmonary artery catheter. FACTORS INFLUENCING SvO2- arterial oxygen saturation- hemoglobin concentration- cardiac output- tissue oxygen consumption.-NORMAL VALUES- 70% to 75%.- Values below 60% indicate cellular oxidative impairment- values below50% associated with anaerobic metabolismpulmonary artery catheters not placed routinely ScvO2 - surrogate For SvO2
  37. 37. ScvO2 venous oxygen saturation near the junction of the superior vena cava and right atrium. obtained from subclavian or internal jugular central venous catheter. Because ScvO2 neglects venous return from the lowerbody, values for ScvO2 typically are 3% to 5% less than SvO2 values < 65% -ongoing oxidative impairment. values > 80% - cellular dysfunction with impaired oxygen consumption. - seen in late stages of shock To be used in context with other markers of tissue perfusion (eg, lactate).
  38. 38. Sublingual capnometry studies perfusion of the splanchnic circulation. sensor placed under the tongue measures partial pressure of carbon dioxide in the sublingual tissue (PslCO2). Normal values for PslCO2 - 43 to 47 mmHg PslCO2 >70 mm Hg - correlates with elevated arterial lactate levels more important is the ‘‘PslCO2 gap.’’- difference between PslCO2 and PaCO2 A PslCO2 gap of> 25 mm Hg identifies patients at a high risk of mortality.
  39. 39. Gastric Tonometry Offers an index of aerobic metabolism in gut mucosa. Based on increase in tissue CO2 A balloon in stomach,measures intramucosal pCO2 Using this and arterial (HCO3), gastric intramucosal PH is calculated
  40. 40. Orthogonal polarization spectroscopy uses polarized light to visualize the microcirculation directly. hemoglobin absorbs polarized light real-time images reflected to videomicroscope functional capillary density measured. sensitive marker of tissue perfusion and an indirect measurement of oxygen delivery. Tissues evaluated- oral mucosa, sublingual mucosa, rectal mucosa,and vaginal mucosa. LIMITNG FACTORS- -movement artifacts -presence of saliva -observer related bias
  41. 41. Near-infrared spectroscopy measures the concentrations of hemoglobin, oxygen saturation,and cytochrome aa3 Cytochrome aa3- final receptor in the electron transport chain - responsible for 90% cellular O2 consumption - remains in a reduced state during hypoxia used primarily to evaluate the perfusion of skeletal muscles.PROBLEMS-signal contamination by light scatter-variable interpretations of the data-lack of a reference standard for comparison
  42. 42. Transcutaneous oxygen tension measure transcutaneous oxygen or carbon dioxide. Use heated probes placed on the skin•markers of regional tissue hypoperfusion increased mortality in patients with low transcutaneous oxygen orhigh CO2•LIMITATIONS-Tissue trauma from probe insertion,- thermal injury if probes are not moved every4 hours- lack of established critical values to guide resuscitation .
  43. 43. Cerebral Perfusion and Oxygenation monitoring1. Jugular venous bulb oximetry2. Direct brain tissue oxygen tension3. Near inrared spectroscopy4. Cerebral Microdialysis5. Cerebral Blood Flow Monitoring6. Oxygen-15 PET
  44. 44. Jugular venous oxygen saturation(SjvO2) Retrograde placement of jugular venous catheter with oximeter cannulate dominant IJV catheter tip positioned in jugular bulb compatible with MRI. SjvO2 - result of the difference between cerebral oxygen delivery (supply) and cerebral metabolic rate of oxygen (demand) Low SjvO2 (!50% for O10 minutes) -hypoperfusion / increased . cerebral metabolism.APPLICATIONS - comatose patients (GCS <8) -treatment of SAH- - neurosurgical procedures
  45. 45. SjvO2LIMITATIONS- changes in arterial oxygen content- hemodilution- prone position of catheter- necessity for frequent calibrations- infection- increase in ICP- thrombosis- arterial Puncture- pneumothorax- reflects global cerebral oxygenation and does not detect regional ischemia in smaller regions ipsilateral or in contralateral hemisphere
  46. 46. Brain tissue oxygen pressure(PBO2) Small flexible microcatheter inserted into brain parenchyma. marker of the balance between regional oxygen supply and use. ICP, brain temperature (Licox, Integra Neurosciences) or tissue partial pressure of carbon dioxide (PBCO2) and pH (Neurotrend, Johnson & Johnson) can be monitored Licox device uses polarographic technique by Clark electrode Neurotrend uses ‘‘optimal luminescence’’ catheter should pass through gray matter into white matter tunneled after craniotomy or placed through a double or triple lumen bolt measured tissue volume 17 mm3. PBO2 levels highest in dense population of neurons and lower in white matter PBO2 and amplitude of changes lower with Neurotrend than Licox compatible with MRI
  47. 47. Near infrared spectroscopy monitoring of transmittance across the brain at two or more wavelengths optical attenuation of the spectra converted into changes of cerebral oxygenation methods include time-resolved, spatially resolved, and phase-resolved spectroscopy INVOS system provides a numerical value for oxygen saturation using rSO2 normal range-60-80% NIRO oximeters present values for oxygenated and total Hb concentration, cytochrome aa3, and a tissue oxyge index
  48. 48. NISAPPLICATIONS detection of changes during carotid cross-clamping during carotid endarterectomy & cardiac surgery to detect cerebral vasospasm causing delayed cerebral ischemic deficit after SAH assessment of perfusion reductions in stroke Reconstruction of a three-dimensional image using optical tomography attractive because applied by attaching pads to the forehead or other regions of interest.
  49. 49. NISLIMITATIONS limited and variable penetration of infrared light through the skull (2–3 mm, limited to gray matter) contamination by extra- and intracranial sources (mixture of capillary, venous,and arterial blood), and uniform distribution of infrared light in the CSF layer. degree of scatter unpredictable inconsistent impact of monitoringof decreased oxygenation on neurologic outcome
  50. 50. Cerebral Microdialysis bedside monitor to provide on-line analysis of brain tissue biochemistry during neurointensive care. The principles and clinical double-lumen probe, lined at it tip with dialysis membrane. perfused by an inlet tube with fluid isotonic to the tissue interstitium perfusate passes along the membrane before exiting collecting chamber. catheter acts as an artificial blood capillary. Measures microdialysate concentrations of glucose, lactate, pyruvate, glycerol, and glutamateThe concentration of these substances in the microdialysate does not correspond to their true extracellular fluid concentration proportion of the extracellular fluid concentration the ‘‘relative recovery”
  51. 51. MD data displayBrain Tissue O2 monitorMD Bedside AnalyserJugular Venous Saturation Monitor
  52. 52. Applications of MD Most clinical experience with TBI and SAH Severe cerebral hypoxia /ischemia associated with marked increases in the lactate-pyruvate ratio Ratio greater than 20 to 25 associated with poor outcome Glycerol is a marker of ischemic cell damage Increased MD glycerol concentrations associated with poor outcome Increased excitatory amino acids and reduced brain ECF glucose associated with metabolic catastrophes after acute brain injury.
  53. 53. Cerebral Blood Flow Monitoring Kety-Schmidt method Radioactive tracer techniques Continuous quantitative cerebral blood flow monitoring-Laser Doppler flowmetry-Thermal diffusion flowmetry Double-indicator dilution technique Transcranial Doppler ultrasonography
  54. 54. Neuroimagong [18F]2-deoxy-D-glucose PET oxygen-15 PET SPECT Xenon-enhanced CT scanning perfusion CT Perfusion weighted imaging (PWI)
  55. 55. THANKS
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