Oxygen Transport & Oxygen Transport & DeliveryDelivery

Dr Prashant S AgarwalDr Prashant S Agarwal

Dr Ashok JadonDr Ashok Jadon

Deptt of AnaesthesiaDeptt of Anaesthesia

Learning ObjectivesLearning Objectives

To understand the basic physiology of oxygen To understand the basic physiology of oxygen transport.transport.

Oxygen FluxOxygen Flux Oxygen delivery to tissuesOxygen delivery to tissues Extraction ratioExtraction ratio Oxygen debtOxygen debt How O2 therapy worksHow O2 therapy works

Anaerobic? So What?Anaerobic? So What?Inadequate

CellularOxygenation

InadequateCellular

Oxygenation

AnaerobicMetabolismAnaerobic

Metabolism

MetabolicFailure

MetabolicFailure

MetabolicAcidosis

MetabolicAcidosis

InadequateEnergy

Production

InadequateEnergy

Production

Lactic AcidProduction

Lactic AcidProduction

Cell Death!Cell Death!

Tourniquet application Vs Tourniquet application Vs Carotid Clamping…..Carotid Clamping…..

Tourniquet is well tolerated for certain Tourniquet is well tolerated for certain period but not carotid clamping period but not carotid clamping

In muscles these ions easily diffuse out In muscles these ions easily diffuse out causing metabolic acidosis.causing metabolic acidosis.

In brain the BBB prevents this diffusion In brain the BBB prevents this diffusion leading to intracellular acidosis and leading to intracellular acidosis and structural damage.structural damage.

Fate of OxygenFate of Oxygen

1. 1. From atmosphere to lung From atmosphere to lung capillariescapillaries..

2. Oxygen in blood.2. Oxygen in blood.

3 Cellular Function.3 Cellular Function.

PiO2 Nose : PB-47)x FiO2PiO2 Nose : PB-47)x FiO2 PiO2 Alveoli: (PB-47)x FiO2- PaCO2/RPiO2 Alveoli: (PB-47)x FiO2- PaCO2/R

: Arterial pressure: PaO2: Arterial pressure: PaO2

Alveolar-arterial Dissociation:=Alv-artAlveolar-arterial Dissociation:=Alv-art

Sea Level Pao2: 760 x0.21=159 mmhg.Sea Level Pao2: 760 x0.21=159 mmhg. Nose: ( 760-47)x .21=149 mmhg.( water Vapor)Nose: ( 760-47)x .21=149 mmhg.( water Vapor) At Alveoli: 149- 40/0.8=100 mmhg.( C02).At Alveoli: 149- 40/0.8=100 mmhg.( C02). At Arterial level:90 mmhg ( gradiant 5-10mmhg)At Arterial level:90 mmhg ( gradiant 5-10mmhg) At venous : 47 mmhgAt venous : 47 mmhg Mitrochondria: 35-40 mmhgMitrochondria: 35-40 mmhg

Interference to the delivery of oxygen at any point in the Interference to the delivery of oxygen at any point in the cascade, significant injury can occur downstreamcascade, significant injury can occur downstream

Lung to BloodLung to Blood

Four factors influence transmission of Four factors influence transmission of oxygen from the alveoli to the capillaries oxygen from the alveoli to the capillaries

1. Ventilation perfusion (V/Q) mismatch, 1. Ventilation perfusion (V/Q) mismatch, 2. Right to left shunt, 2. Right to left shunt, 3. Diffusion defects,3. Diffusion defects, 4. Cardiac output.4. Cardiac output.

Essentials of Gas Essentials of Gas ExchangeExchange

PiO2 =150 mmHg

PALV O2= 100 mmHgDue to CO2 added

PAPa Pv

Zone 1PA>Pa>Pv

Low Flow

PA

Pa Pv

PA

Pa Pv

Zone 2Pa>PA>Pv

Waterfall

Zone 3Pa>Pv>PA

Hi Flow

O2

CO2

venous arterial

PB=0

PA<0

Flow=P/R

V/Q mismatchV/Q mismatch

PO2 = 40PCO2 = 45

Normal VA/QLow VA/Q High VA/Q

CO2 = 45

PO2 = 150PCO2 = 0

PO2 = 100PCO2 = 40

PO2 = 150PCO2 = 0

. . .

Ventilation Perfusion Ratios

No flow

PO2 = 40PCO2 = 45

Low VA/Q.

Normal VA/Q.

PO2 = 100PCO2 = 40

High VA/Q.

PO2 = 150PCO2 = 0

PO2 (mm Hg)

PC

O2 (

mm

Hg)

50 100 150

50

Base

Apex

ShuntsShunts

Shunt- Why O2 dose not Shunt- Why O2 dose not workwork

Oxygen ContentOxygen Content

Amount of O2 carried by Amount of O2 carried by 100 ml of 100 ml of bloodblood

In two forms –In two forms – Bound to Bound to Hb 98%Hb 98% Dissolved in Dissolved in plasma 2%plasma 2%

N = N = 20 ml 20 ml of O2 in 100 ml bloodof O2 in 100 ml blood

98% O2 is bound to Hb.( Hb 1.34 SaO2 )

Oxygen contentCaO2 =

2% Dissolved O2( PaO2 0.003 ml )

Oxygen transportOxygen transport

Look at the graphLook at the graph Hb becomes almost fully Hb becomes almost fully

saturated with oxygen at saturated with oxygen at high partial pressures high partial pressures such as is found in the such as is found in the lungslungs

Oxyhaemoglobin Oxyhaemoglobin dissociates under low dissociates under low partia pressures such as partia pressures such as found in respiring tissue. found in respiring tissue.

Oxygen transportOxygen transport

Why is the curve S shaped?Why is the curve S shaped? Each molecule of Hb has four haem Each molecule of Hb has four haem

groupsgroups When the first oxygen combines with the When the first oxygen combines with the

first haem group the shape of the Hb first haem group the shape of the Hb molecule becomes distortedmolecule becomes distorted

This makes it easier for the other three This makes it easier for the other three oxygen molecules to bind to the other oxygen molecules to bind to the other haem groupshaem groups

Hb O2 Content by 70 folds but in PO2 …..

Oxygen dissociation Oxygen dissociation curve.curve.

HB% 12SAT 100%

HB% 12SAT 50%

HB 6 SAT 100%

HB 13 SAT 90%

PaO2 SATURATION O2 content

Normal

↓

↓

↓or N

PaO2

SaO2OXY (Sat) 98%

HAEMOGLOBIN

2 % DissolvedOxygen

O.

D.

C.

PAO2

A.C.I.

CaO2CaO2Content of oxygenMl/100 of blood

DeliveryOf

OxygenTo

Tissues

DaO2O2

Cardiac output

A.C.I.( Alveolar capillary interface)

O2 Flux (delivery)O2 Flux (delivery)

Amount of O2 leaving the left ventrical per Amount of O2 leaving the left ventrical per minuteminute

Overall oxygen delivery = arterial oxygen Overall oxygen delivery = arterial oxygen content x cardiac outputcontent x cardiac output

DO2 = CO x CaO2DO2 = CO x CaO2 DO2 = C.O. xDO2 = C.O. xHb saturationHb saturation x xxxb concb conc

100100 100 100= 5500 x= 5500 xxxx x

DO2 = DO2 = 800 – 1200 ml/min800 – 1200 ml/min

If Hb 7.5 gm%If Hb 7.5 gm%

O2 flux = 513 ml/minO2 flux = 513 ml/min

If C.O. is also to 3000 ml

O2 flux = 580 ml/min

If both are then O2 flux = 280ml/min

O2 UptakeO2 Uptake

Oxygen Uptake VO2 : Is a function of Oxygen Uptake VO2 : Is a function of Cardiac outputCardiac output

Difference in oxygen content b/w arterial Difference in oxygen content b/w arterial and venous bloodand venous blood

VO2 = CO x 1.34 x Hb (SaO2 – SvO2) 10VO2 = CO x 1.34 x Hb (SaO2 – SvO2) 10

VO2 = 200 – 300 ml/minVO2 = 200 – 300 ml/min

More unloaded with more More unloaded with more needneed

Resting cell PO2Resting cell PO240 mmHg40 mmHg

Working cell PO2 Working cell PO2 20 mmHg20 mmHg

Oxygen Extraction Ratio Oxygen Extraction Ratio (O2 ER)(O2 ER)

Is the ratio of oxygen uptake to delivery. Usually 20-30%Is the ratio of oxygen uptake to delivery. Usually 20-30% O2 ER = VO2/DO2O2 ER = VO2/DO2 Uptake is kept Uptake is kept constant constant by increasing extraction when by increasing extraction when

delivery dropsdelivery drops Critical Oxygen Delivery (DO2crit)Critical Oxygen Delivery (DO2crit)

Maximal extraction ~ 50-60%Maximal extraction ~ 50-60% Once this is reached a decrease in delivery = decrease Once this is reached a decrease in delivery = decrease

in uptakein uptake Known as ‘Known as ‘critical oxygen delivery’critical oxygen delivery’ O2 uptake and aerobic energy production is now supply O2 uptake and aerobic energy production is now supply

dependentdependent

Can you rememberwhy it is importantto warm down afterexercise?

OXYGEN DEBT‘The extra amount of oxygen needed

to recover from anaerobic activity

You will develop oxygen debt after about 5 minutes or more of constant exercise.

This is the point when the exercise becomes ANAEROBIC (without the use of oxygen) and which has to be paid back later- hence OXYGEN DEBT.

If the exercise is just AEROBIC (with oxygen) there will be no oxygen debt.

Estimates of anaerobic effortEstimates of anaerobic effort

1.1. Post-exercise oxygen consumptionPost-exercise oxygen consumption Oxygen debt – excessive post-exercise oxygen consumption - EPOC Oxygen debt – excessive post-exercise oxygen consumption - EPOC

Estimates of anaerobic effortEstimates of anaerobic effort

1.1. Post-exercise oxygen consumptionPost-exercise oxygen consumption Oxygen debt – excessive post-exercise oxygen consumption - EPOC Oxygen debt – excessive post-exercise oxygen consumption - EPOC

2.2. The lactic threshold The lactic threshold The point at which blood lactate begins accumulate above resting values during exercise of increasing intensity. The onset of blood lactate The point at which blood lactate begins accumulate above resting values during exercise of increasing intensity. The onset of blood lactate

accumulation (OBLA) is a standard value set at either 2.0 or 4.0 mmol lactate.Laccumulation (OBLA) is a standard value set at either 2.0 or 4.0 mmol lactate.L-1-1 O O22 and is used as a common reference point. Expressed as percentage of and is used as a common reference point. Expressed as percentage of

VoVo2 max2 max – best determinant of athletes pace in endurance events. Untrained people – lactate threshold at 50-60% of Vo – best determinant of athletes pace in endurance events. Untrained people – lactate threshold at 50-60% of Vo2-max2-max, in elite runners at 70-80%, lactate formation contributes to fatigue, in elite runners at 70-80%, lactate formation contributes to fatigue

2.2. The lactic threshold The lactic threshold The point at which blood lactate begins accumulate above resting values during exercise of increasing intensity. The onset of blood lactate The point at which blood lactate begins accumulate above resting values during exercise of increasing intensity. The onset of blood lactate

accumulation (OBLA) is a standard value set at either 2.0 or 4.0 mmol lactate.Laccumulation (OBLA) is a standard value set at either 2.0 or 4.0 mmol lactate.L-1-1 O O22 and is used as a common reference point. Expressed as percentage of and is used as a common reference point. Expressed as percentage of

VoVo2 max2 max – best determinant of athletes pace in endurance events. Untrained people – lactate threshold at 50-60% of Vo – best determinant of athletes pace in endurance events. Untrained people – lactate threshold at 50-60% of Vo2-max2-max, in elite runners at 70-80%, lactate formation contributes to fatigue, in elite runners at 70-80%, lactate formation contributes to fatigue

Partial pressurePartial pressure

The partial pressure gradients for O2 & The partial pressure gradients for O2 & CO2 are the key to gas movement.CO2 are the key to gas movement.

However, the amount of both of these However, the amount of both of these gases would be grossly inadequate if Hb gases would be grossly inadequate if Hb is not there. is not there.

(Ganong 20th ed)(Ganong 20th ed)

Dalton’s LawDalton’s Law

In a mixture of ideal gases, each gas has a In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the partial pressure which is the pressure which the gas would have if it alone occupied the volume. gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the partial pressures of each individual gas in the mixture.the mixture.

Thus, if the normal pressure of atmospheric Thus, if the normal pressure of atmospheric gases is 760 mmHg and there is gases is 760 mmHg and there is 21% oxygen21% oxygen, , the partial pressure of oxygen is 760 × 0.21 = the partial pressure of oxygen is 760 × 0.21 = 160 mmHg.160 mmHg.

160 mmHg O2160 mmHg O2

What we breath..?

H2OCO2

Shunts

35-40mmHg

47mmHg

160 mmHg

Pasture Point….Pasture Point…. Critical PO2 (1-2mmHg) Critical PO2 (1-2mmHg) during hypoxia during hypoxia

where aerobic metabolism failswhere aerobic metabolism fails in in mitocondria.mitocondria.

O2 therapyO2 therapy

To increase the FiO2 & PaO2To increase the FiO2 & PaO2 If breathing If breathing 100% O2100% O2 Then FiO2 is 1 & Then FiO2 is 1 & PaO2 610 mmHgPaO2 610 mmHg

35-40mmHg

47mmHg

160 mmHg

1. The oxygen cascade describes the process of declining oxygen tension 1. The oxygen cascade describes the process of declining oxygen tension from atmosphere to mitochondria. from atmosphere to mitochondria.

2. The amount of oxygen in the blood is calculated using the formula: 2. The amount of oxygen in the blood is calculated using the formula: [1.34 x Hb x (SaO2/100)] + 0.003 x PO2 = 20.8ml [1.34 x Hb x (SaO2/100)] + 0.003 x PO2 = 20.8ml

3. The delivery of oxygen to the tissues per minute is calculated from: 3. The delivery of oxygen to the tissues per minute is calculated from: DO2 = [1.39 x Hb x SaO2 + (0.003 x PaO2)] x Q DO2 = [1.39 x Hb x SaO2 + (0.003 x PaO2)] x Q

4. Tissue oxygen extraction is calculated by subtracting mixed venous 4. Tissue oxygen extraction is calculated by subtracting mixed venous oxygen content from arterial oxygen content. oxygen content from arterial oxygen content.

5. The Oxyhemoglobin dissociation curve describes the non-linear 5. The Oxyhemoglobin dissociation curve describes the non-linear tendency for oxygen to bind to hemoglobin: below a SaO2 of 90%, small tendency for oxygen to bind to hemoglobin: below a SaO2 of 90%, small differences in hemoglobin saturation reflect large changes in PaO2 Right differences in hemoglobin saturation reflect large changes in PaO2 Right to left shunting causes hypoxemia resistant to oxygen therapy. . to left shunting causes hypoxemia resistant to oxygen therapy. .

6. Right to left shunt causes hypoxemia unresponsive to 6. Right to left shunt causes hypoxemia unresponsive to oxygen therapy Diffusion defects and ventilation oxygen therapy Diffusion defects and ventilation perfusion mismatches cause hypoxemia, responsive to perfusion mismatches cause hypoxemia, responsive to exogenous oxygen and positive pressure ventilation. exogenous oxygen and positive pressure ventilation.

7. The objective of oxygen therapy is to give the patient 7. The objective of oxygen therapy is to give the patient as much oxygen as is required to return the PaO2 to as much oxygen as is required to return the PaO2 to what is normal for the particular patient. what is normal for the particular patient.

8. Oxygen is given thru fixed and variable performance 8. Oxygen is given thru fixed and variable performance devices.devices.