1 mosby items and derived items © 2011, 2006 by mosby, inc., an affiliate of elsevier inc. chapter...

1Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.

Chapter 5Chapter 5

Oxygenation AssessmentsOxygenation Assessments


Oxygen Transport ReviewOxygen Transport Review

Oxygen is carried in the blood in two ways:Oxygen is carried in the blood in two ways:1.1. As dissolved oxygen in the blood plasmaAs dissolved oxygen in the blood plasma2.2. Bound to the hemoglobin (Hb)Bound to the hemoglobin (Hb)

Most oxygen is carried to the tissue cell bound to Most oxygen is carried to the tissue cell bound to the hemoglobin.the hemoglobin.


Oxygen Dissolved in the Blood Oxygen Dissolved in the Blood PlasmaPlasma

At normal body temperature, about 0.003 mLAt normal body temperature, about 0.003 mLof oxygen (Oof oxygen (O22) will dissolve in each 100 mL of ) will dissolve in each 100 mL of

blood for every 1 mm Hg of POblood for every 1 mm Hg of PO22.. Thus when the PaOThus when the PaO22 is 100 mm Hg, about is 100 mm Hg, about

0.3 mL of dissolved O0.3 mL of dissolved O22 exists in every 100 mL exists in every 100 mL

of plasma: 0.003 × 100 mm Hg = 0.3 mLof plasma: 0.003 × 100 mm Hg = 0.3 mL Clinically, written as 0.3 volume percent (volClinically, written as 0.3 volume percent (vol

%)%) 0.3 vol% O0.3 vol% O22


Hb value in normal man: 14 to 16 g/100 mLHb value in normal man: 14 to 16 g/100 mL Hb value in normal woman: 12 to 15 g/100 Hb value in normal woman: 12 to 15 g/100

mLmL Clinically, the weight measurement of Clinically, the weight measurement of

hemoglobin, in reference to 100 mL of blood, hemoglobin, in reference to 100 mL of blood, is known as the is known as the grams percent hemoglobin grams percent hemoglobin (g(g% Hb)% Hb)

Oxygen Bound to HemoglobinOxygen Bound to Hemoglobin


Each g% Hb can carry 1.34 mL of OEach g% Hb can carry 1.34 mL of O22

Thus if the Hb level is 12 g% and if the Hb is Thus if the Hb level is 12 g% and if the Hb is fully saturated, about 15.72 vol% of Ofully saturated, about 15.72 vol% of O22 will be will be

bound to the Hb:bound to the Hb:

OO22 bound to Hb = 1.34 mL O bound to Hb = 1.34 mL O22 × 12 g% Hb × 12 g% Hb

= 15.72 vol% O= 15.72 vol% O22

Oxygen Bound to Hemoglobin Oxygen Bound to Hemoglobin (Cont’d)(Cont’d)


At a normal PaOAt a normal PaO22 of 100 mm Hg, however, of 100 mm Hg, however,

the Hb saturation (SaOthe Hb saturation (SaO22) is only about 97% ) is only about 97%

because of these normal physiologic shunts:because of these normal physiologic shunts: Thebesian venous drainage into the left atriumThebesian venous drainage into the left atrium Bronchial venous drainage into the pulmonary Bronchial venous drainage into the pulmonary

veinsveins



Thus the amount of arterial oxygen in the Thus the amount of arterial oxygen in the calculation must be adjusted to 97%:calculation must be adjusted to 97%:

15.72 vol% O15.72 vol% O22

× .97× .97 15.24 vol% O15.24 vol% O22



To calculate the total amount of oxygen in To calculate the total amount of oxygen in 100 mL of blood, the following must be added 100 mL of blood, the following must be added together:together: Dissolved oxygen Dissolved oxygen Oxygen bound to hemoglobin Oxygen bound to hemoglobin

Total Oxygen ContentTotal Oxygen Content


A 44-year-old woman with a long history of A 44-year-old woman with a long history of asthma arrives in the emergency room in asthma arrives in the emergency room in severe respiratory distress. Her vital signssevere respiratory distress. Her vital signsare respiratory rate 36 breaths/min, heart rate are respiratory rate 36 breaths/min, heart rate 130 bpm, and blood pressure 160/95 mm Hg. 130 bpm, and blood pressure 160/95 mm Hg. Her hemoglobin concentration is 10 g%, and Her hemoglobin concentration is 10 g%, and her PaOher PaO22 is 55 mm Hg (SaO is 55 mm Hg (SaO2 2 85%). Based on 85%). Based on

these data, the patient’s total oxygen content is these data, the patient’s total oxygen content is determined on the next slide:determined on the next slide:

Case ExampleCase Example


55 PaO55 PaO22

× 0.003× 0.003 (dissolved O (dissolved O22 factor) factor)

0.165 vol% O0.165 vol% O22

1. Dissolved O1. Dissolved O22


2. Oxygen Bound to Hemoglobin2. Oxygen Bound to Hemoglobin

10 g% Hb10 g% Hb × 1.34× 1.34 (O (O22 bound to Hb factor) bound to Hb factor)

13.4 vol% O13.4 vol% O22 (at SaO (at SaO22 of 100%) of 100%)

Above answer is then followed by the SaOAbove answer is then followed by the SaO2 2

factor:factor: 13.4 vol% O13.4 vol% O22

× .85 SaO× .85 SaO22

11.39 vol% O11.39 vol% O22 (at SaO(at SaO22 of 85%) of 85%)


11.39 vol% O11.39 vol% O22 (bound to hemoglobin)(bound to hemoglobin)

+ 0.165 vol% O+ 0.165 vol% O22 (dissolved O(dissolved O22))

11.555 vol% O11.555 vol% O22 (total amount of O(total amount of O22/100 mL of blood)/100 mL of blood)

3. Total Oxygen Content3. Total Oxygen Content..


The total oxygen content can be calculated inThe total oxygen content can be calculated inthe patient’s:the patient’s: Arterial blood (CaOArterial blood (CaO22)) Venous blood (CvOVenous blood (CvO22) ) Pulmonary capillary blood (CcOPulmonary capillary blood (CcO22))

Total Oxygen Content (Cont’d)Total Oxygen Content (Cont’d)


CaOCaO22 = Oxygen content of arterial blood = Oxygen content of arterial blood

(Hb × 1.34 × SaO(Hb × 1.34 × SaO22) + (PaO) + (PaO22 × 0.003) × 0.003)

CvOCvO22 = Oxygen content of mixed venous blood = Oxygen content of mixed venous blood

(Hb × 1.34 × Sv(Hb × 1.34 × SvOO22) + (Pv) + (PvOO22 × 0.003) × 0.003)

CcOCcO22 = Oxygen content of pulmonary capillary = Oxygen content of pulmonary capillary

bloodblood (Hb × 1.34) + (PAO(Hb × 1.34) + (PAO22 × 0.003) × 0.003)

Total Oxygen Content (Cont’d)Total Oxygen Content (Cont’d)


Oxygenation IndicesOxygenation Indices

Oxygen tension–based indicesOxygen tension–based indices Oxygen saturation and content indicesOxygen saturation and content indices


Oxygen Tension–Based IndicesOxygen Tension–Based Indices

Arterial oxygen tension (PaOArterial oxygen tension (PaO22)) Alveolar-arterial oxygen tension difference Alveolar-arterial oxygen tension difference

(P[A-a]O(P[A-a]O22))


Arterial Oxygen Tension (PaOArterial Oxygen Tension (PaO22))

Good indicator of the patient’s oxygenation Good indicator of the patient’s oxygenation statusstatus

The PaOThe PaO22, however, may be misleading in , however, may be misleading in

these clinical situations:these clinical situations: Low HbLow Hb Decreased cardiac outputDecreased cardiac output Peripheral shuntingPeripheral shunting Carbon monoxide and cyanide exposureCarbon monoxide and cyanide exposure


Alveolar-Arterial Oxygen Tension Alveolar-Arterial Oxygen Tension Difference (P[A-a]ODifference (P[A-a]O22))

The P(A-a)OThe P(A-a)O2 2 is the oxygen tension difference is the oxygen tension difference

between the alveoli and arterial blood.between the alveoli and arterial blood.


Alveolar-Arterial Oxygen Tension Alveolar-Arterial Oxygen Tension Difference (P[A-a]ODifference (P[A-a]O22) (Cont’d)) (Cont’d)

PAOPAO22 = FIO = FIO2 2 (P(PBB − PH − PH22OO) − PaCO) − PaCO22 (1.25) (1.25)


Case Study ExampleCase Study Example

If a patient is receiving an FIOIf a patient is receiving an FIO22 of 0.30 on a day of 0.30 on a day

when the barometric pressure is 750 mm Hg, when the barometric pressure is 750 mm Hg, and if the patient’s PaCOand if the patient’s PaCO22 is 70 mm Hg and is 70 mm Hg and

PaOPaO22 is 60 mm Hg, the P(A-a)O is 60 mm Hg, the P(A-a)O22 can be can be

calculated as shown on the next slide:calculated as shown on the next slide:


Case Study Example (Cont’d)Case Study Example (Cont’d)

PAOPAO22 = = FIOFIO2 2 (P(PBB − P − PHH22OO) − PaCO) − PaCO22 (1.25) (1.25)

= 0.30 (750 − 47) − 70 (1.25)= 0.30 (750 − 47) − 70 (1.25)= (703) 0.30 − 87.5= (703) 0.30 − 87.5= (210.9) − 87.5= (210.9) − 87.5= 123.4 mm Hg= 123.4 mm Hg


Case Study Example (Cont’d)Case Study Example (Cont’d)

Using the PaOUsing the PaO22 obtained from the ABG: obtained from the ABG:

123.4 (PAO123.4 (PAO22))

− − 60.0 (PaO60.0 (PaO22))

63.4 mm Hg [P(A-a)O63.4 mm Hg [P(A-a)O22]]

The normal P(A-a)O2 ranges from 7 to 15 mm Hg and should not exceed 30 mm Hg.


P(A-a)OP(A-a)O22 Increases Increases

Oxygen diffusion disorders Oxygen diffusion disorders Decreased V/Q ratiosDecreased V/Q ratios Right-to-left cardiac shuntingRight-to-left cardiac shunting AgeAge


Note: The P(A-a)ONote: The P(A-a)O22

Loses sensitivity in patients breathing high FIOLoses sensitivity in patients breathing high FIO22


Oxygen Saturation– and Oxygen Saturation– and Content–Based IndicesContent–Based Indices


Oxygen Saturation– and Content–Based Oxygen Saturation– and Content–Based IndicesIndices

CaOCaO22 = (Hb × 1.34 × SaO = (Hb × 1.34 × SaO22) + (PaO) + (PaO22 × 0.003) × 0.003)

CvOCvO22 = (Hb × 1.34 × SvO = (Hb × 1.34 × SvO22) + (PvO) + (PvO22 × 0.003) × 0.003)

CcOCcO22 = (Hb × 1.34) + (PAO = (Hb × 1.34) + (PAO22 × 0.003) × 0.003)


Most Common Oxygen Saturation–and Most Common Oxygen Saturation–and Content–Based IndicesContent–Based Indices

Total oxygen deliveryTotal oxygen delivery Arterial-venous oxygen content differenceArterial-venous oxygen content difference Oxygen consumptionOxygen consumption Oxygen extraction ratioOxygen extraction ratio Mixed venous oxygen saturationMixed venous oxygen saturation Pulmonary shunting Pulmonary shunting


Total Oxygen DeliveryTotal Oxygen DeliveryDODO22 = Q = QTT × (CaO × (CaO22 × 10) × 10)

The total oxygen delivery is the amount of The total oxygen delivery is the amount of oxygen delivered to the peripheral tissue cells.oxygen delivered to the peripheral tissue cells.


Total Oxygen DeliveryTotal Oxygen Delivery DO DO22 = Q = QTT × (CaO × (CaO22 × 10) (Cont’d) × 10) (Cont’d)

For example, if a patient has a cardiac output of For example, if a patient has a cardiac output of 4 L/min and a CaO4 L/min and a CaO22 of 15 vol%, the DO of 15 vol%, the DO2 2 is 600 is 600

mL of oxygen per minute—as calculated on the mL of oxygen per minute—as calculated on the next slide:next slide:


Total Oxygen DeliveryTotal Oxygen Delivery

DODO22 = Q = QTT × (CaO × (CaO22 × 10) × 10)

= 4 L/min × (15 vol% × 10)= 4 L/min × (15 vol% × 10)= 600 mL O= 600 mL O22 per minute per minute

Normally, about 1000 mL/minNormally, about 1000 mL/min


Total Oxygen Delivery (Cont’d)Total Oxygen Delivery (Cont’d)

Decreases:Decreases: Low PaOLow PaO22 Low SaOLow SaO22

Low HbLow Hb Low cardiac outputLow cardiac output


Total Oxygen Delivery (Cont’d)Total Oxygen Delivery (Cont’d)

Increases:Increases: Increased PaOIncreased PaO22 Increased SaOIncreased SaO22

Increased HbIncreased Hb Increased cardiac outputIncreased cardiac output


Arterial-Venous Oxygen Content Arterial-Venous Oxygen Content DifferenceDifference

C(a-v)OC(a-v)O22 = CaO = CaO22 − CvO − CvO22

The arterial-venous oxygen content difference The arterial-venous oxygen content difference (C[a-v]O(C[a-v]O22) is the difference between the CaO) is the difference between the CaO22

and the CvOand the CvO22—that is, CaO—that is, CaO22 − CvO − CvO22..


Arterial-Venous Oxygen Content Arterial-Venous Oxygen Content DifferenceDifference

C(a-v)OC(a-v)O22 = CaO = CaO22 − CvO − CvO2 2 (Cont’d)(Cont’d)

For example, if a patient’s CaOFor example, if a patient’s CaO22 is 15 vol% and is 15 vol% and

the CvOthe CvO22 is 8 vol%, the C(a-v)O is 8 vol%, the C(a-v)O22 is 7 vol%—as is 7 vol%—as

calculated on the next slide:calculated on the next slide:


Arterial-Venous Oxygen Arterial-Venous Oxygen Content DifferenceContent Difference

C(a-v)OC(a-v)O22 = CaO = CaO22 − CvO − CvO22

= 15 vol% − 8 vol%= 15 vol% − 8 vol%= 7 vol%= 7 vol%

Normally, 5 vol% Normally, 5 vol%


Arterial-Venous Oxygen Arterial-Venous Oxygen Content Difference (Cont’d)Content Difference (Cont’d)

Increases:Increases: Decreased cardiac outputDecreased cardiac output ExerciseExercise SeizuresSeizures HyperthermiaHyperthermia


Arterial-Venous Oxygen Arterial-Venous Oxygen Content Difference (Cont’d)Content Difference (Cont’d)

Decreases:Decreases: Increased cardiac outputIncreased cardiac output Skeletal relaxationSkeletal relaxation Peripheral shuntingPeripheral shunting CyanideCyanide HypothermiaHypothermia


Oxygen ConsumptionOxygen ConsumptionVVOO22 = Q = QTT [C(a-v)O [C(a-v)O22] × 10] × 10

Oxygen (VOOxygen (VO22) consumption is the amount of ) consumption is the amount of

oxygen consumed by the peripheral tissue cells oxygen consumed by the peripheral tissue cells during a 1-minute period. during a 1-minute period.


Oxygen ConsumptionOxygen ConsumptionVOVO22 = Q = QTT [C(a-v)O [C(a-v)O22] × 10 (Cont’d)] × 10 (Cont’d)

For example, if a patient has a cardiac output of For example, if a patient has a cardiac output of 4 L/min and a C(a-v)O4 L/min and a C(a-v)O22 of 6 vol%, the total of 6 vol%, the total

amount of oxygen consumed by the tissue cells amount of oxygen consumed by the tissue cells in 1 minute would be 240 mL—as calculated on in 1 minute would be 240 mL—as calculated on the next slide:the next slide:


Oxygen ConsumptionOxygen Consumption

VOVO22 = Q = QTT [C(a-v)O [C(a-v)O22] × 10] × 10

= 4 L/min × 6 vol% × 10= 4 L/min × 6 vol% × 10= 240 mL O= 240 mL O22/min/min

Normal is 250 mL ONormal is 250 mL O22/min/min


Oxygen Consumption (Cont’d)Oxygen Consumption (Cont’d)

Increases:Increases: SeizuresSeizures ExerciseExercise HyperthermiaHyperthermia Body sizeBody size


Oxygen Consumption (Cont’d)Oxygen Consumption (Cont’d)

Decreases:Decreases: Skeletal muscle relaxationSkeletal muscle relaxation Peripheral shuntingPeripheral shunting Certain poisons (e.g., cyanide)Certain poisons (e.g., cyanide) HypothermiaHypothermia


Oxygen Extraction RatioOxygen Extraction RatioOO22ER = ER = CaOCaO22 − CvO − CvO22

CaOCaO22The OThe O22ER is the amount of oxygen consumed ER is the amount of oxygen consumed

by the tissue cells divided by the total amount of by the tissue cells divided by the total amount of oxygen delivered.oxygen delivered.


Oxygen Extraction RatioOxygen Extraction RatioOO22ER = ER = CaOCaO22 − CvO − CvO22

CaO CaO2 2 (Cont’d)(Cont’d)

For example, if a patient’s CaOFor example, if a patient’s CaO22 is 15 vol% and is 15 vol% and

the CvOthe CvO22 is 10 vol%, the O is 10 vol%, the O22ER would be 33%—ER would be 33%—

as calculated on the next slide:as calculated on the next slide:


Oxygen Extraction RatioOxygen Extraction Ratio

OO22ER = ER = CaOCaO22 − CvO − CvO22

CaOCaO22= = 15 vol% − 10 vol%15 vol% − 10 vol%

15 vol%15 vol%= = 5 vol% 5 vol% 15 vol%15 vol%= 0.33= 0.33

Normal is 0.25% Normal is 0.25%


Oxygen Extraction Ratio (Cont’d)Oxygen Extraction Ratio (Cont’d)

Increases:Increases: Decreased cardiac outputDecreased cardiac output Periods of increased OPeriods of increased O22 consumption consumption

Exercise, seizures, hyperthermiaExercise, seizures, hyperthermia AnemiaAnemia Decreased arterial oxygenation Decreased arterial oxygenation

↓ ↓ Hb, ↓ PaOHb, ↓ PaO22


Oxygen Extraction Ratio (Cont’d)Oxygen Extraction Ratio (Cont’d)

Decreases:Decreases: Increased cardiac outputIncreased cardiac output Skeletal muscle relaxationSkeletal muscle relaxation Peripheral shuntingPeripheral shunting Certain poisons (e.g., cyanide)Certain poisons (e.g., cyanide) HypothermiaHypothermia Increased arterial oxygenation Increased arterial oxygenation

↑ ↑ Hb, ↑ PaOHb, ↑ PaO22


Mixed Venous Oxygen SaturationMixed Venous Oxygen Saturation SvO SvO22

Signals changes in the:Signals changes in the: C(a-v)OC(a-v)O22

VOVO22

OO22ERER

Normally about 75%Normally about 75%


Mixed Venous Oxygen SaturationMixed Venous Oxygen Saturation SvO SvO2 2 (Cont’d)(Cont’d)

Decreases:Decreases: Decreased cardiac outputDecreased cardiac output ExerciseExercise SeizuresSeizures HyperthermiaHyperthermia


Mixed Venous Oxygen SaturationMixed Venous Oxygen Saturation SvO SvO2 2 (Cont’d)(Cont’d)

Increases:Increases: Increased cardiac outputIncreased cardiac output Skeletal muscle relaxationSkeletal muscle relaxation Peripheral shuntingPeripheral shunting Certain poisons (e.g., cyanide)Certain poisons (e.g., cyanide) HypothermiaHypothermia


Pulmonary Shunt FactionPulmonary Shunt Faction

QQss = = CcOCcO22 − CaO − CaO22

QQTT CcOCcO22 − CvO − CvO22


Ventilated Alveolus

Ventilated Alveolus

AlveolusAlveolus

Pulmonary capillaryPulmonary capillaryOxygenated

bloodOxygenated

blood

Nonoxygenated blood

Nonoxygenated blood

Normal alveolar-capillary unit.Normal alveolar-capillary unit.


Ventilated Alveolus

Ventilated Alveolus

AlveolusAlveolus

Pulmonary capillaryPulmonary capillaryOxygenated

bloodOxygenated

blood

Nonoxygenated blood

Nonoxygenated blood

Anatomic shunt.Anatomic shunt.

Anatomic shunt

Anatomic shunt


AlveolusAlveolus

Pulmonary capillaryPulmonary capillaryNonoxygenated

bloodNonoxygenated

blood

Nonoxygenated blood

Collapsed Alveolus

or

Consolidated or Fluid-Filled

Alveolus

Collapsed Alveolus

or

Consolidated or Fluid-Filled

Alveolus

Types of capillary shunts.Types of capillary shunts.


AlveolusAlveolus

Pulmonary capillaryPulmonary capillaryNonoxygenated

bloodNonoxygenated

blood

Nonoxygenated blood

Alveolus with Decreased Ventilation

or

Alveolus with a Diffusion Defect

Alveolus with Decreased Ventilation

or

Alveolus with a Diffusion Defect

Types of relative or shuntlike effects.Types of relative or shuntlike effects.


Pulmonary ShuntingPulmonary Shunting

Need following information:Need following information: Barometric pressure Barometric pressure PaOPaO2 2

PaCOPaCO2 2

PvOPvO22

Hb concentrationHb concentration PAOPAO22 (partial pressure of alveolar oxygen)(partial pressure of alveolar oxygen) FIOFIO22


Case Example:Case Example:Automobile Accident VictimAutomobile Accident Victim

A 22-year-old man is on a volume-cycled A 22-year-old man is on a volume-cycled mechanical ventilator on a day when the mechanical ventilator on a day when the barometric pressure is 755 mm Hg. The patient barometric pressure is 755 mm Hg. The patient is receiving an FIOis receiving an FIO22 of 0.60. The following of 0.60. The following

clinical data are obtained:clinical data are obtained: Hb: 15 g/dLHb: 15 g/dL PaOPaO22: 65 mm Hg (SaO: 65 mm Hg (SaO22 = 90%) = 90%) PaCOPaCO22: 56 mm Hg: 56 mm Hg PvOPvO22: 35 mm Hg (SvO: 35 mm Hg (SvO22 = 65%) = 65%)


Case Example:Case Example:Automobile Accident Victim (Cont’d)Automobile Accident Victim (Cont’d)

With this information the followingWith this information the followingcan now be calculated:can now be calculated: PAOPAO22

CcOCcO2 2

CaOCaO2 2

CvOCvO22



PAOPAO22 = (P= (PBB − PH − PH22O) FIOO) FIO22 − PaCO − PaCO22 (1.25) (1.25)

= (755 − 47) 0.60 − 56 (1.25) = (755 − 47) 0.60 − 56 (1.25) = (708) 0.60 − 70= (708) 0.60 − 70= 424.8 = 424.8 − 70− 70= 354.8 = 354.8



CcOCcO22 = (Hb × 1.34) + (PAO = (Hb × 1.34) + (PAO22 × 0.003) × 0.003)

= (15 × 1.34) + (354.8 × 0.003)= (15 × 1.34) + (354.8 × 0.003)= 20.1 + 1.064= 20.1 + 1.064= 21.164 (vol% = 21.164 (vol% OO22))



CaOCaO22 = (Hb × 1.34 × SaO = (Hb × 1.34 × SaO22) + (PaO) + (PaO22 × 0.003) × 0.003)

= (15 × 1.34 × 0.90) + (65 × 0.003)= (15 × 1.34 × 0.90) + (65 × 0.003)= 18.09 + 0.195= 18.09 + 0.195= 18.285 (vol% O= 18.285 (vol% O22))


Case Example:Case Example:Automobile Accident Victim (Cont’d)Automobile Accident Victim (Cont’d) CvOCvO22 = (Hb × 1.34 × SvO= (Hb × 1.34 × SvO22) + (PvO) + (PvO22 × 0.003) × 0.003)

= (15 × 1.34 × 0.65) + (35 × 0.003)= (15 × 1.34 × 0.65) + (35 × 0.003) = 13.065 + 0.105= 13.065 + 0.105 = 13.17 (vol% O= 13.17 (vol% O22))



QQSS == CcOCcO22 − CaO − CaO

QQTT CcO CcO22 − CvO − CvO22

== 21.164 − 18.28521.164 − 18.28521.164 − 13.1721.164 − 13.17

== 2.8792.879 7.9947.994

== 0.360.36


Table 5-2. Clinical Significance of Pulmonary Shunting Table 5-2. Clinical Significance of Pulmonary Shunting


Table 5-3. Oxygenation Index Changes Commonly Seen in Respiratory Diseases Table 5-3. Oxygenation Index Changes Commonly Seen in Respiratory Diseases


HypoxemiaHypoxemia

HypoxemiaHypoxemia refers to an abnormally low refers to an abnormally low arterial oxygen tension (PaOarterial oxygen tension (PaO22) and is ) and is

frequently associated with hypoxia. frequently associated with hypoxia. Although hypoxemia may suggest tissue Although hypoxemia may suggest tissue

hypoxia, it does not necessary mean the hypoxia, it does not necessary mean the absolute existence of tissue hypoxia.absolute existence of tissue hypoxia. For example, a low arterial oxygen level may be For example, a low arterial oxygen level may be

offset by an increased cardiac output.offset by an increased cardiac output.


Table 5-4. Hypoxemia Classifications* Table 5-4. Hypoxemia Classifications*


HypoxiaHypoxia

HypoxiaHypoxia refers to low or inadequate oxygen refers to low or inadequate oxygen for aerobic cellular metabolism.for aerobic cellular metabolism.


Table 5-5. Types of Hypoxia Table 5-5. Types of Hypoxia


Cor PulmonaleCor Pulmonale

The term used to denote:The term used to denote: Pulmonary arterial hypertensionPulmonary arterial hypertension Right hypertrophyRight hypertrophy Increased right ventricular workIncreased right ventricular work Right ventricular failureRight ventricular failure


Cor Pulmonale (Cont’d)Cor Pulmonale (Cont’d)

Three major causes:Three major causes: Increased viscosity of blood (polycythemia)Increased viscosity of blood (polycythemia) Increased vascular resistanceIncreased vascular resistance

• Caused by hypoxic vasoconstrictionCaused by hypoxic vasoconstriction Obliteration of the pulmonary capillary bedObliteration of the pulmonary capillary bed


PolycythemiaPolycythemia

Increased red blood cell levelIncreased red blood cell level


Hypoxic Vasoconstriction Hypoxic Vasoconstriction of the Lungsof the Lungs

Caused by decreased Caused by decreased PAOPAO22

Generalized pulmonary vasoconstriction Generalized pulmonary vasoconstriction combined with polycythemia leads to:combined with polycythemia leads to: Cor pulmonaleCor pulmonale Distended neck veinsDistended neck veins Peripheral edema and pitting edemaPeripheral edema and pitting edema


Pitting edema. (From Bloom A, Ireland J: Pitting edema. (From Bloom A, Ireland J: Color atlas of diabetesColor atlas of diabetes, ed 2,, ed 2,London, 1992, Mosby-Wolfe.)London, 1992, Mosby-Wolfe.)


DistendedDistendedNeck VeinsNeck Veins

Distended neck veins (Distended neck veins (arrowsarrows).).

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