Oxygen Transport:

1
Oxygen Transport

• A Clinical Review
• Burn-Trauma-ICU
• Adults Pediatrics
• Bradley J. Phillips, M.D.

2
The First Concern

• the first concern in any life-threatening
  illness
• is to maintain
• an adequate supply of oxygen
• to sustain oxidative metabolism
• Marino 2nd ed.

3
Context

• The human adult has a vascular network that
  stretches over 60,000 miles
• More than twice the circumference of the earth
• 8,000 liters of blood pumped per day
• Principle of Continuity
• Conservation of mass in a closed hydraulic system
• the volume flow of blood is and must be the same
  at all points throughout the circuit

4
Flow Velocity Cross-sectional Area
5
Respiratory Gas Transport

• Respiratory function of blood
• Dual system
• Transport delivery of oxygen TO the tissues
• Transport delivery of carbon dioxide FROM the
  tissues
• Oxygen is the most abundant element on the
  surface of this planetyet it is completely
  unavailable to the cells on the interior of the
  human system
• the body, itself, acts as its own natural
  barrier
• Why ? (rememberoxygen-metabolites are toxic)

6
Oxygen Radicals
The metabolism of oxygen occurs at the very end
of the electron transport pathway i.e.
oxidative phosphorylation within the
mitochondrial body
7
Antioxidant Therapy
Selenium (glu. Peroxidase) Glutathione (acts via
reduction) N-acetylcysteine (a glutahione
analog) Vit. E (blocks lipid peroxidation) Vit.
C (pro-oxidant to maintain iron as
Fe(II) Aminosteroids (? lipid peroxidation)
8
the transport system for oxygen is separated into
4 componentstaken together, these form the
oxygen transport variables
9
The Oxygen Transport Variables

• Oxygen Content CaO2
• Oxygen Delivery DO2
• Oxygen Uptake VO2
• Extraction Ratio ER

10
Oxygen Content (1)

• the oxygen in the blood is either bound to
  hemoglobin
• or dissolved in plasma
• the Sum of these two fractions is called the
  Oxygen Content
• CaO2 the Content of Oxygen in Arterial Blood
• Hb Hemoglobin (14 g/dl)
• SaO2 Arterial Saturation (98 )
• PaO2 Arterial PO2 (100 mmHg)

11
Oxygen Content (2)

• CaO 2 (1.34 x Hb x SaO2) (0.003 x PaO2)
• amount carried by Hb
  amount dissolved in plasma
• CaO2 (1.34 x 14 x 0.98) (0.003 x 100)
• CaO2 18.6 ml/dl (ml/dl vol 18.6 vol )
• at 100 Saturation, 1 g of Hb binds 1.34 ml of
  Oxygen !

12
Oxygen Content (3)

• Note that the PaO2 contributes little to the
  Oxygen Content !
• Despite its popularity, the PaO2 is NOT an
  important measure of arterial oxygenation !
• The SaO2 is the more important blood gas variable
  for assessing the oxygenation of arterial blood !
• the PaO2 should be reserved for evaluating the
  efficiency of pulmonary gas exchange

13
Hemoglobin vs. PaO2 CaO2

• the trifecta
• Arterial oxygenation is based on 3 (and ONLY 3)
  things
• Hb
• SaO2
• PaO2
• A 50 reduction in Hb leads to a direct 50
  reduction in CaO2
• A 50 reduction in PaO2 leads to a 20 reduction
  in CaO2

14
CaO2 why do we so often forget ?

• PaO2 influences oxygen content only to the
• extent that it influences
• the saturation of hemoglobin
• Hypoxemia (i.e. a decrease in PaO2) has a
• relatively SMALL impact
• on arterial oxygenation if the accompanying
  change
• in SaO2 is small !

15
Oxygen Content (4)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• Hb 12
• Hct 36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• Question What is this
• Patients Oxygen Content ?

16
Oxygen Content (5)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• Hb 12
• Hct 36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• Oxygen Content
• CaO2 (1.34 x Hb x SaO2)
• CaO2 ..

17
Oxygen Delivery (1)

• DO2 the Rate of Oxygen Transport in the Arterial
  Blood
• it is the product of Cardiac Output Arterial
  Oxygen Content
• DO2 Q x CaO2
• Cardiac Output, Q, can be indexed to body
  surface area
• Normal C.I. 2.5 - 3.5 L/min-m2
• Bu using a factor of 10, we can convert vol to
  ml/min

18
Oxygen Delivery (2)

• DO2 Q x CaO2
• DO2 3 x (1.34 x Hb x SaO2) x 10
• DO2 3 x (1.34 x 14 x .98) x 10
• DO2 551 ml/min
• Normal Range (CO) 800 1000 ml/min
• Normal Range (CI) 520 - 720 ml/min/m2

19
Oxygen Delivery (3)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• H/H 12/36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• CO 4.8 CI 2.1
• Question What is this
• Patients Oxygen Delivery ?

20
Oxygen Delivery (4)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• H/H 12/36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• CO 4.8 (CI 2.1)
• Oxygen Delivery
• DO2 Q x CaO2 x 10
• DO2

21
Oxygen Uptake (1)

• oxygen uptake is the final step
• in the oxygen transport pathway and it represents
  the oxygen supply
• for tissue metabolism
• The Fick Equation
• Oxygen Uptake is the Product of Cardiac Output
• and
• the Arteriovenous Difference in Oxygen Content
• VO2 Q x (CaO2 - CvO2)

22
Oxygen Uptake (2)
23
Oxygen Uptake (3)

• The Fick Equation
• VO2 Q x (CaO2 - CvO2)
• VO2 Q x (1.34 x Hb) x (SaO2 - SvO2) x 10
• VO2 3 x (1.34 x 14) x (.98 - .73) x 10
  
• VO2 3 x 46
• VO2 140 ml/min/m2
• Normal VO2 110 - 160 ml/min/m2

24
Oxygen Uptake (4)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• Hb/Hct 12/36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• CO 4.8
• SvO2 56
• Question What is this
• Patients Oxygen Uptake ?

25
Oxygen Uptake (4)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• Hb/Hct 12/36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• CO 4.8 (CI 2.1)
• SvO2 56
• Oxygen Uptake
• VO2 Q x (CaO2 - CvO2)
• VO2 Q x (1.34 x Hb) x (SaO2 - SvO2) x
  10
• VO2 .

26
Extraction Ratio (1)

• the fractional uptake of oxygen
• from the capillary bed
• O2ER derived as the Ratio of Oxygen Uptake to
  Oxygen Delivery
• O2ER VO2 / DO2 x 100
• O2ER 130 / 540 x 100 Normal
  Extraction
• O2ER 24 22 - 32

27
Extraction Ratio (2)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• H/H 36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• C0 4.8
• SvO2 71
• Question What is this
• Patients Extraction Ratio ?

28
Extraction Ratio (3)

• 35 yr old male s/p GSW to Chest
• Pulse 126 BP 164 / 72 RR 26
• H/H 36
• ABGs pH 7.38 / PaO2 100 / PaCO2 32 / 96
  Sat
• C0 4.8
• SvO2 71
• Extraction Ratio
• O2ER VO2 / DO2 x 100
• O2ER ..

29
Extraction Ratio (3)

• Questions
• 1. ER 16 , what does this imply ?
• 2. ER 42 , what does this imply ?

30
Control of Oxygen Uptake

• the uptake of oxygen from the microcirculation is
  a
• set point that is maintained by adjusting the
• Extraction Ratio
• to match changes in oxygen delivery
• the ability to adjust
• O2 Extraction
• can be impaired in serious illness

31
The Normal Response O2ER (1)

• The Normal Response to a
• Decrease in Blood Flow is an Increase in O2
  Extraction
• sufficient enough to keep VO2 in the normal range
• VO2 Q x Hb x 13.4 x (SaO2 - SvO2)
• Q 3 VO2 3 x 14 x 13.4 x (.97 - .73)
  110 ml/min
• Q 1 VO2 1 x 14 x 13.4 x (.97 - .37)
  109 ml/min

32
The Normal Response O2ER (2)

• The Drop in Cardiac Index is BALANCED by an
• Increased (SaO2 - SvO2) Differenceand VO2
  remains Unchanged
• Note the drop in SvO2 from 97 to 37 !!
• This association between SvO2 O2ER is the Basis
  for SvO2 Monitoring
• The Ability to Adjust Extraction is a feature of
  all vascular beds
• except the Coronary Circulation the Diaphragm !

33
The DO2 - VO2 Curve (1)
34
The DO2 - VO2 Curve (2)

• As O2 delivery decreases below normal, the ER
  increases proportionally to keep VO2 constant
• When ER reaches its maximum level (50 60),
  further decreases in DO2 are accompanied by
  proportional decreases in VO2
• Critical DO2
• The DO2 at which consumption becomes
  supply-dependent
• The point at which energy production within the
  cell becomes oxygen-limited

35
The DO2 - VO2 Curve (3)

• Flat Portion of the Curve
• VO2 Flow - Independent
• O2 Extraction varies in response to Blood Flow
  (VO2 Constant)
• Linear Portion of the Curve
• VO2 Flow - Dependent
• Indicates a defect in oxygen extraction from the
  microcirculation
• Extraction is fixed and VO2 becomes directly
  dependent on Delivery
• Critical Level of Oxygen Delivery
• The Threshold DO2 needed for Adequate Tissue
  Oxygenation
• If DO2 falls below this level, oxygen supply will
  be sub-normal

36
The DO2 - VO2 Curve (2)
37
In the ICU

• The critical DO2 in anesthesized patients is
  around 300 ml/min.
• However, in critically-ill patients, the Critical
  DO2 varies widely from 150 1000 ml/min
• Leach et al. Dis Mon. 199430301-368

38
Mixed Venous Oxygen

• By rearranging the Fick Equation, the
  determinants of Venous Oxygen are
• VO2 Q x Hb x 13 x (SaO2 - SvO2)
• SvO2 SaO2 - (VO2/Q x Hb x 13)
• the most prominent factor in determining SvO2
  is VO2/Q
• Causes of a Low SvO2 Hypoxemia
• Increased Metabolic Rate
• Low Cardiac Output
• Anemia

39
Remember Mixed Venous

• In Critically-Ill Patients, augmenting the
  extraction ratio
• (in response to a change in oxygen delivery)
• may not be possible !
• In these patients, the Venous Oxygen Levels may
  change
• little in response to changes in Cardiac Output !
• thus, the Relationship
• between CO (Q) and Mixed Venous Oxygen must be
• determined before using SvO2 or PvO2 to monitor
• changes in DO2 or VO2

40
Oximetry

• Arterial Oxygen Saturation can be estimated but
• Venous Oxygen Saturation
• MUST be Measured !
• Due to the shape of the Oxyhemoglobin Curve
• The arterial Sat falls on the flat portion can
  be safely estimated
• The venous Sat (68 - 77 ) falls on the Steep
  Portion and can vary significantly even with
  small errors in estimation !

41
OxyHb Curve (1)

• Rule-of-Dennis-Betting
• 50 SatPO2 25
• Mixed Ven. Sat 75PO2 40

42
OxyHb Curve (2)

• Right-shift off-loading
• Acidosis
• Elevated temperature
• Elevated CO2
• Increased 2,3-DPG

43
Carbon Dioxide (1)

• An increase in PCO2 of 5 mmHg can result in a
• twofold increase in minute ventilation
• to produce the same increment in ventilation,
• the PaO2 must drop to 55 mmHg
• The ventilatory control system keeps a close eye
  on
• CO2 but pays little attention to PaO2while
  clinicians keep a close eye on PaO2
• and pay little attention to PCO2

I just dont understand.
44
Carbon Dioxide (2)

• The CO2 Sink
• Ready source of ions (H HCO3-)
• Buffering capacity of Hb
• (6x that of all the plasma
• proteins combined)

45
CO2 Extraction
46
The Respiratory Quotient

• RQ VCO2 / VO2
• VCO2 normally 10 mEq/min (14,400 mEq/24 hrs)
• Exercise lung excretion can reach 40,000 mEq/24
  hrs.
• The kidneys normally excrete 40 80 mEq acid /24
  hrs

47
Tissue O2-Balance

• Oxygen supply to the tissues is the rate of O2
  uptake from the microcirculation
• VO2 ER
• The metabolic requirement for oxygen is the rate
  at which oxygen is metabolized to water within
  the mitochondria
• MRO2
• Because oxygen is NOT stored in the tissues, VO2
  must match MRO2 if aerobic metabolism is to
  continue
• when matching occurs, glucose is completely
  oxidized to
• yield 36 moles of ATP

48
Oxygen Balance

• when matching occurs, glucose is completely
• oxidized to yield 36 moles of ATP
• When matching is not equal (VO2 is less than
  MRO2), a portion of the glucose is diverted to
  the production of lactate in an attempt to
  salvage energy
• Per mole of glucose converted through anaerobic
  metabolism, 2 moles of ATP are gained (47 kcal)

49
Dysoxia

• the condition in which the production of ATP
• is limited by the supply of oxygen
• when cell dysoxia leads to a measurable
• change in organ function.SHOCK

50
VO2 MRO2
51
VO2 Deficit

• In ICU patients, a VO2 that falls below the
  normal range (i.e. below 100 ml/min), can be used
  as evidence of impaired tissue oxygenation
• Studies have shown a direct relationship between
  the magnitude of the VO2 deficit and the risk of
  multiorgan failure
• Dunham et al. CCM 199119231-243
• Shoemaker et al. Chest 1992102208-215

52
Oxygen Debt
The cumulative VO2 deficit is referred to as the
oxygen debt In ICU patients, there may be a
progressive and linear relationship between VO2
DO2
53
Monitoring of O2 Transport

• The transport variables provide
• no information
• about the ADEQUACY of
• tissue (cellular) oxygenation
• because that requires a measurement of
• metabolic rate.

54
Interpreting the Transport Variables

• Low VO2
• Indicates a tissue oxygen deficit
• Oxygen Debt
• The total VO2 deficit over time
• Remember the direct relationship exists between
  magnitude of the oxygen debt and subsequent risk
  of multiorgan failure
• Normal VO2
• Requires a blood lactate level to determine the
  adequacy of global tissue oxygenation

55
Correcting a VO2 Deficit (1)

• Step 1 CVP or PWP
• If low, infuse volume to normalize filling
  pressure
• If normal or high, go to step 2
• Step 2 CO
• If low filling pressures not optimalinfuse
  volume
• If low filling pressures high, start DOBUTAMINE
  titrate keep CI gt 3 L/min/m2 (some believe 5)
• If blood pressure is also low, start DOPAMINE or
  LEVOPHED
• If CI gt 3, proceed to Step 3.

56
Correcting a VO2 Deficit (2)

• Step 3 VO2 (Oxygen Uptake)
• If VO2 is less than 100 ml/min/m2, use VOLUME
• to goal of CVP 8 12 PWP 18 20
• inotropic therapy to achieve a CI gt 4.5 L/min/m2
• Correct Hb if less than 8 g/dl (some say 10 g/dl)
• If VO2 is greater than 100 ml/min/m2, proceed to
  Step 4.
• Step 4 Blood Lactate
• Lactate gt 4 with other signs of shock (i.e. organ
  failure, low BP), decrease METABOLIC RATE via
  sedation or paralysis (? Pentobarbital coma)
• Lactate 2 4...controversial !
• Lactate lt 2observe

57
VO2 DO2 vs. Time
58
Role of Serum Lactate (1)

• An elevated lactate indicates that VO2 is less
  than the metabolic rate
• The approach must then be to either decrease the
  metabolic rate or increase the VO2
• achieving a supranormal level of VO2 may be
  difficult
• and carries risks

59
Serum Lactate (2)
Aduen, et al. JAMA 19942721678-1685
60
Serum Lactate Cardiac Index
61
Serum Lactate Cardiac Index
62
Optimizing Oxygen Transport The Steps
Filling Pressures Cardiac Output VO2 Serum
Lactate
63
Oxygen Transport Variables

• Parameter Normal Range
• Delivery (DO2) 500 - 800 ml/min
• Uptake (VO2) 110 - 160 ml/min
• Extraction Ratio (ER) 22 - 32
• Mixed Venous PO2 33 - 53 mmHg
• Mixed Venous SO2 68 - 77
• DO2 VO2 can be indexed to body surface area

64
Oxygen Transport

• it would be a most
• difficult task
• to
• explain
• Any Questions Yet ?

65
Oxygen Transport Case 1 (1)
32 yr old male 6 hrs s/p GSW to the
Abdomen Hypotensive nearly coded on the
table Liver shattered packed Multiple holes
in the Small Bowel, Stomach, and Right
Chest Packed and whip-stitched closed the
fascia Now hypotensive and dropping her sats
what do you want to do ?
66
Oxygen Transport Case 1 (2)
Remember the Steps Filling Pressures Cardi
ac Output VO2 Serum Lactate
67
Questions? The Oxygen Transport Variables

• Oxygen Content CaO2
• Oxygen Delivery DO2
• Oxygen Uptake VO2
• Extraction Ratio ER