Bedside monitoring of tissue perfusion and oxygenation

BEDSIDE MONITORING OF
TISSUE PERFUSION AND
OXYGENATION

Dr.Tushar Patil
MD

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

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
blood
1. Rate of O2 delivery to capillary
2. O2-Hb dissociation relation
3. Size of capillary to cellular PO2 relation
4. Diffusion distance to cells
5. Rate of use of O2 by cells

Tolerance to hypoxia of
various tissues Tissue
 Survival time
1. Brain<3 min
2. Kidney and liver15-20 min
3. Skeletal muscle60-90 min
4. Vascular smooth muscle24-72 h
5. Hair and nails -Several days

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

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

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

Monitoring Tissue Perfusion and
Oxygenation
1. Clinical Evaluation
2. Hemodynamic Monitoring
3. Pulse Oximetry
4. End Tidal CO2 Monitoring
5. Monitoring Tissue Hypoxia
6. Cerebral Oxygenation Monitoring

Clinical Evaluation
 HISTORY
-Dyspnoea
-Cough
-Fever
-Rash
-Discolouration of digits/limbs
-Palpitations
-Altered sensorium
-Convulsions

Clinical Evaluation
 Level of Consciousness
 Evaluation of Peripheral & Central Pulses
 Capillary Refill Time
 Cyanosis
 Respiratory Rate & Pattern
 Blood Pressure
 Systemic Examination

Hemodynamic Monitoring
 Arterial Blood Pressure

-Non Invasive
-Invasive
 Central Venous Pressure Monitoring
 Pulmonary Artery Catheterisation
 Measuring Cardiac Output

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.

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.

Arterial Catheterisation

INDICATIONS
 ABSOLUTE- As a guide to synchronization of intra-aortic
balloon counter pulsation
 PROBABLE-
1. Guide to management of potent vasodilator drug
infusions
2. Guide to management of potent vasopressor drug
infusion
3. As a port for the rapid and repetitive sampling
4. As a monitor of cardiovascular deterioration in patients

Arterial Catheterisation
USEFUL APPLICATIONS
 Differentiating cardiac tamponade (pulsus
paradoxus) from respiration-induced
swings in systolic BP
 Differentiating hypovolemia from cardiac
dysfunction as the cause of hemodynamic

Arterial Catherisation
COMPLICATIONS
- temporary occlusion
- hematomas
- Serious ischemic damage
- sepsis
- pseudoaneurysm

Central venous pressure monitoring
Pressure 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

Factors affecting measured
CVP
1.Central venous blood volume
 Venous return/cardiac output
 Total blood volume
 Regional vascular tone
2.Compliance of central compartment
 Vascular tone
 RV compliance
 Myocardial disease
 Pericardial disease
 Tamponade
3.Tricuspid valve disease
 Stenosis
 Regurgitation

Factors affecting measured
CVP
4.Cardiac rhythm
 Junctional rhythm
 Atrial fibrillation (AF)
 Atrio ventricular (A-V) dissociation
5.Reference level of transducer
 Positioning of patient
6.Intrathoracic pressure
 Respiration
 IPPV
 Positive end-expiratory pressure (PEEP)
 Tension pneumothorax

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

Pulmonary artery
catheterization
 Developed in the 1940s and later refined by Swan and Ganz in
1970

INDICATIONS
 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

PAC

CONTRAINDICATIONS
 Tricuspid or pulmonary valve mechanical
prosthesis
 Right heart mass (thrombus and/or tumor)
 Tricuspid or pulmonary valve endocarditis

PAC
MEASURED PARAMETERS
1. Central Venous Pressure
2. Pulmonary Capillary Wedge Pressure
3. Cardiac Index
4. Stroke Volume Index
5. LV Stroke Work Index
6. RVSWI
7. RV Ejection Fraction
8. RV End Diastolic Volume
9. Systemic Vascular Resistance Index
10. Pulmonary Vascular Resistance Index
11. Mixed Venous O2 Saturation
12. O2 delivery
13. O2 uptake
14. O2 exraction Ratio

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

Measuring Cardiac Output
1. Pulmonary Artery Catheter
2. Pulse Contour Analysis
-Lithium dilution
-Transpulmonary Thermodilution
-Without diluion calibration
3. CO2 Rebreathing
4. Trans thoracic Electrial Bioimpedence
5. Trans Thoracic Echo
6. Esophageal Doppler Monitoring

Pulse Oximetry

PRINCIPLE
 Displayed readings determined primarily by two
components:
1. The different absorption spectra of oxyhemoglobin and
deoxyhemoglobin at different wavelengths
2. 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,

Pulse Oximetry
APPLICATIONS
 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

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

Pulse Oximetry
 PITFALLS
1. Dyshemoglobinemias
2. Poor function wiyh poor performance
3. Difficulty in detecting high oxygen partial
pressures
4. Delayed detection of hypoxic events
5. Erratic performance with irregular rhythms
6. Nail polish and coverings
7. Loss of accuracy at low values
8. Electrical interference
9. Failure to detect hypoventilation

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.

End Tidal Carbon Dioxide
APPLICATIONS
 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

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

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

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

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.

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 metabolism

pulmonary artery catheters not placed routinely
ScvO2 - surrogate For SvO2

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 lower
body, 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).

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.

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

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

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

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 or
high CO2

•LIMITATIONS
-Tissue trauma from probe insertion,
- thermal injury if probes are not moved every4 hours
- lack of established critical values to guide resuscitation .

Cerebral Perfusion and
Oxygenation monitoring

1. Jugular venous bulb oximetry
2. Direct brain tissue oxygen tension
3. Near inrared spectroscopy
4. Cerebral Microdialysis
5. Cerebral Blood Flow Monitoring
6. Oxygen-15 PET

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

SjvO2
LIMITATIONS
- 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

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

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

NIS

APPLICATIONS
 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.

NIS
LIMITATIONS

 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 monitoring
of decreased oxygenation on neurologic outcome

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”

MD data display

Brain Tissue O2
monitor

MD Bedside
Analyser

Jugular Venous
Saturation
Monitor

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.

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

Neuroimagong
 [18F]2-deoxy-D-glucose PET
 oxygen-15 PET
 SPECT
 Xenon-enhanced CT scanning
 perfusion CT
 Perfusion weighted imaging (PWI)

Bedside monitoring of tissue perfusion and oxygenation

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Bedside monitoring of tissue perfusion and oxygenation