3. 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
4.
5.
6. 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
7.
8. 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
9. 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
10.
11. 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
12. 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
13. 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
17. 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.
18.
19. 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.
20. 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
21.
22. 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
24. 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
25. 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
27. 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
28. 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
29.
30. PAC
CONTRAINDICATIONS
Tricuspid or pulmonary valve mechanical
prosthesis
Right heart mass (thrombus and/or tumor)
Tricuspid or pulmonary valve endocarditis
31. 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
32. 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
34. 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,
35.
36. 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
37. 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
38.
39. 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
40. 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.
41.
42. 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
43. 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
44. 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
45. 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
46. 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.
47. 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
48.
49. 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).
50. 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.
51. 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
52.
53. 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
54.
55.
56. 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
57.
58.
59. 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 .
60.
61. 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
62. 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
63.
64. 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
65. 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
66.
67.
68.
69. 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
70.
71. 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.
72.
73. 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
74.
75. 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”
78. 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.