oxygen transport: a clinical review burn-trauma-icu adults & pediatrics bradley j. phillips, m.d
TRANSCRIPT
![Page 1: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/1.jpg)
Oxygen Transport:A Clinical Review
Burn-Trauma-ICUAdults & Pediatrics
Bradley J. Phillips, M.D.
![Page 2: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/2.jpg)
“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.]
![Page 3: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/3.jpg)
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”
![Page 4: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/4.jpg)
Flow Velocity & Cross-sectional Area
![Page 5: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/5.jpg)
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 planet…yet it is completely unavailable to the cells on the interior of the human system– the body, itself, acts as its own natural barrier…
– Why ? (remember…oxygen-metabolites are toxic)
![Page 6: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/6.jpg)
Oxygen Radicals
The metabolism of oxygen occurs at
the very end of the
electron transport pathway
i.e. oxidative phosphorylation within
the mitochondrial body
![Page 7: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/7.jpg)
Antioxidant TherapySelenium(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)
![Page 8: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/8.jpg)
the transport system for oxygen is separated into 4 components:
taken together, these
form the “oxygen transport variables”
![Page 9: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/9.jpg)
The Oxygen Transport Variables
• Oxygen Content [CaO2]
• Oxygen Delivery [DO2]
• Oxygen Uptake [VO2]
• Extraction Ratio [ER]
![Page 10: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/10.jpg)
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)
![Page 11: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/11.jpg)
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 !
![Page 12: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/12.jpg)
Oxygen Content (3)
• Note that the PaO2 contributes little to the Oxygen Content !
• Despite it’s 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
![Page 13: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/13.jpg)
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
![Page 14: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/14.jpg)
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 !
![Page 15: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/15.jpg)
Oxygen Content (4)
35 yr old male s/p GSW to Chest
Pulse 126 BP 164 / 72 RR 26
Hb = 12
Hct = 36
ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % Sat
Question: What is this
Patient’s Oxygen Content ?
![Page 16: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/16.jpg)
Oxygen Content (5)
35 yr old male s/p GSW to Chest
Pulse 126 BP 164 / 72 RR 26Hb = 12Hct = 36
ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % Sat
Oxygen Content:
CaO2 = (1.34 x Hb x SaO2)
CaO2 = ……..
![Page 17: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/17.jpg)
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
![Page 18: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/18.jpg)
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
![Page 19: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/19.jpg)
Oxygen Delivery (3)
35 yr old male s/p GSW to Chest
Pulse 126 BP 164 / 72 RR 26
H/H = 12/36
ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % Sat
CO = 4.8 CI = 2.1
Question: What is this
Patient’s Oxygen Delivery ?
![Page 20: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/20.jpg)
Oxygen Delivery (4)
35 yr old male s/p GSW to Chest
Pulse 126 BP 164 / 72 RR 26H/H = 12/36ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % SatCO = 4.8 (CI = 2.1)
Oxygen Delivery:DO2 = Q x CaO2 x 10DO2 = ……
![Page 21: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/21.jpg)
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)]
![Page 22: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/22.jpg)
Oxygen Uptake (2)
![Page 23: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/23.jpg)
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
![Page 24: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/24.jpg)
Oxygen Uptake (4)
35 yr old male s/p GSW to ChestPulse 126 BP 164 / 72 RR
26Hb/Hct = 12/36
ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % Sat
CO 4.8
SvO2 56 %
Question: What is this Patient’s Oxygen Uptake ?
![Page 25: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/25.jpg)
Oxygen Uptake (4)
35 yr old male s/p GSW to Chest
Pulse 126 BP 164 / 72 RR 26Hb/Hct = 12/36ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % SatCO 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 = …….
![Page 26: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/26.jpg)
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 %
![Page 27: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/27.jpg)
Extraction Ratio (2)
35 yr old male s/p GSW to ChestPulse 126 BP 164 / 72 RR
26H/H= 36
ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % Sat
C0 4.8
SvO2 71 %
Question: What is this Patient’s Extraction Ratio ?
![Page 28: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/28.jpg)
Extraction Ratio (3)
35 yr old male s/p GSW to Chest
Pulse 126 BP 164 / 72 RR 26H/H= 36ABG’s: pH 7.38 / PaO2 100 / PaCO2 32 / 96 % SatC0 4.8SvO2 71 %
Extraction Ratio:O2ER = VO2 / DO2 x 100O2ER = …..
![Page 29: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/29.jpg)
Extraction Ratio (3)
Questions:
1. ER = 16 %, what does this imply ?
2. ER = 42 %, what does this imply ?
![Page 30: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/30.jpg)
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
![Page 31: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/31.jpg)
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
![Page 32: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/32.jpg)
The Normal Response: O2ER (2)
• The Drop in Cardiac Index is BALANCED by an
Increased (SaO2 - SvO2) Difference…and 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 !
![Page 33: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/33.jpg)
The DO2 - VO2 Curve (1)
![Page 34: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/34.jpg)
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
![Page 35: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/35.jpg)
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
![Page 36: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/36.jpg)
The DO2 - VO2 Curve (2)
![Page 37: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/37.jpg)
“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. 1994;30:301-368]
![Page 38: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/38.jpg)
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
![Page 39: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/39.jpg)
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
![Page 40: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/40.jpg)
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 !
![Page 41: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/41.jpg)
OxyHb Curve (1)
•“Rule-of-Dennis-Betting”
• 50 % Sat…PO2 25
•Mixed Ven. Sat 75…PO2 40
![Page 42: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/42.jpg)
OxyHb Curve (2)
“Right-shift: off-loading”
• Acidosis
• Elevated temperature
• Elevated CO2
• Increased 2,3-DPG
![Page 43: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/43.jpg)
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 PaO2…while clinicians keep a close eye on PaO2
and pay little attention to PCO2
“I just don’t understand….”
![Page 44: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/44.jpg)
Carbon Dioxide (2)
• The CO2 “Sink”
• Ready source of ions (H+ & HCO3
-)
Buffering capacity of Hb
(6x that of all the plasma
proteins combined)
![Page 45: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/45.jpg)
CO2 Extraction
![Page 46: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/46.jpg)
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
![Page 47: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/47.jpg)
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
![Page 48: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/48.jpg)
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)
![Page 49: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/49.jpg)
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
![Page 50: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/50.jpg)
VO2 & MRO2
![Page 51: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/51.jpg)
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 1991;19:231-243][Shoemaker et al. Chest 1992;102:208-215]
![Page 52: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/52.jpg)
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
![Page 53: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/53.jpg)
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.
![Page 54: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/54.jpg)
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
![Page 55: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/55.jpg)
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 optimal…infuse volume
– If low & filling pressures high, start DOBUTAMINE & titrate keep CI > 3 L/min/m2 (some believe 5)
• If blood pressure is also low, start DOPAMINE or LEVOPHED
– If CI > 3, proceed to Step 3.
![Page 56: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/56.jpg)
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 > 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 > 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 < 2…observe
![Page 57: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/57.jpg)
VO2 & DO2 vs. Time
0
200
400
600
800
1000
1200
1400
1600
Admit 2 Hrs 12 Hrs 16 Hrs 18 Hrs 24 Hrs
VO2
DO2
![Page 58: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/58.jpg)
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
![Page 59: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/59.jpg)
Serum Lactate (2)
Aduen, et al. JAMA 1994;272:1678-1685
![Page 60: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/60.jpg)
Serum Lactate & Cardiac Index
0
1
2
3
4
5
6
7
8
Admit 12 hrs 24 hrs 72 hrs
LactateC.I.
![Page 61: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/61.jpg)
Serum Lactate & Cardiac Index
0
1
2
3
4
5
6
7
Admission 6 12 18 24
Lactate
C.I.
![Page 62: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/62.jpg)
Optimizing Oxygen Transport: The Steps
Filling Pressures
Cardiac Output
VO2
Serum Lactate
![Page 63: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/63.jpg)
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
![Page 64: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/64.jpg)
Oxygen Transport
“it would be a mostdifficult task
to explain”
Any Questions Yet ?
![Page 65: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/65.jpg)
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 ?”
![Page 66: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/66.jpg)
Oxygen Transport: Case 1 (2)
Remember the Steps:
Filling Pressures…
Cardiac Output…
VO2…
Serum Lactate…
![Page 67: Oxygen Transport: A Clinical Review Burn-Trauma-ICU Adults & Pediatrics Bradley J. Phillips, M.D](https://reader036.vdocuments.us/reader036/viewer/2022062518/56649d085503460f949d97c0/html5/thumbnails/67.jpg)
Questions…? The Oxygen Transport Variables
• Oxygen Content [CaO2]
• Oxygen Delivery [DO2]
• Oxygen Uptake [VO2]
• Extraction Ratio [ER]