Determinants and assesssmet of oxygen delivery and oxygen consumption

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Oxygenation

involves the integration and coordination of the pulmonary, cardiovascular, neurologic, hematologic and metabolic processes.

Ventilation

the process in which oxygen is being brought into the internal enviroment via the respiratory system

Oxygenation- 3 compenents

Pulmonary gas exchange, Oxygen delivery, oxygen consumption

Pulmonary gas exchange

the intake of oxygen from the externa envroment into the internal enviiroment and is carried out by the processes of ventilation, diffusion, and perfusion

Oxygen delivery

"DO2"
process of transportation of oxygen to cells and is dependant on Cardiac output, hemoglobin saturation with oxygen, and the partial pressure of oxygen in arterial blood

Oxygen consumption

"VO2"
the use of oxygen at the cellular level to generate energy for cells to use to perform their specific functions.

Pulmonary Gas Exhange- 3 components

Ventilation, diffusion, perfusion

Ventilation

movement of air to and from the atmosphere and the alveoli, requires breathing and ventilatory muscles thorax, lungs, conducting airways, and nervous system

Diffusion

the movement of gas across a pressure gradient from an area of high concentration to low concentration
mechanism- which oxygen moves across the alveoli and into the pulmonary capillar

Diffusion- 3 factors that affect D.

pressure gradiant, surface area, thickness

Perfusion- 3 factors that affect P.

hemoglobin concentration, affinity of oxygen to Hb, blood flow

Conditions that impair Pulmonary gas exchange- Ventilation Impairment

inspiratory muscle weakess or trauma (Guillian Barre, spinal cord injury)
Decreased level of consciousness
Obstruction or trauma to airways, lung, thorax (flail chest, mucous plug)
Restrictive Pulmonary disorders

Conditions that impair Pulmonary gas exchange-- Diffusion impairment

decrease in aveolar- capillary membrane surface area
ex. atlectasis, lung tumors, pneumonia
increase in alveolar-capillary embrane thickness
ex. acute respiratory distress syndome, pulmonary edema, pneumoni
decreased pressure gradiant for oxygen Ex. decreased FiO2

Conditions that impair Pulmonary gas exchange-
Perfusion impairment

decreased Hb (anemia, carbon monoxide poisoning)
decreased perfusion (decreased cardiac output, hemorrhage, pulmonary emboli)
pulm. vasoconstriction (pulm. hypertension, hypoxemia)

Oxygen delivery

process of transporting oxygen to cells
include cardiac ouput, autoregulation, oxygen content of arterial blood (CaO2), autonomic nervous system

Cardiac Output

the amount of blood pumped by the heart each minute
Ex. when tissue require more oxygen, heart rate will increase in an attempt to augment cardiac output in the delivery of more oxygenated blood

Autoregulation

tissues have the ability to regulate their own blood supply by dilating or constricting local blood vessels

CaO2

content of oxygen in arterial blood
Normal: 20ml/100ml

Pa02

the amount of oxygen carried in the blood in the nondissolved from

SaO2

the saturation of hemoglobin with oxygen
Measurement of Sa02 by arterial bood gas analysis is a measure of the ratio of oxygenated hemoglobin to total hemoglobin
Ex. If SaO2 is 95 percent, it can be interpreted that 95 percent of the available seats on the hemoglobin seats are occcupied by oxygen

Oxyhemoglobin

hemoglobin is fuly saturate with oxygen

Oxygen consumption

the process by which cells use oxygen to generate energy

oxygen extraction

the process by which cells take oxygen from the blood

Hypoxemia

condition characterized by an inadequte amount of oxygen in the blood as a result of impaired gas exchange
PaO2 less than 60
can result in Hypoxia

Hypoxia

inadequate amount of oxygen available at the ceullar level such that cells experience anaerobic metabolism

Dysoxia

characterized by an inability of the cells to use oxygen properly despite adequate levels of oxygen delivery

Dysoxia and Hypoxia can lead to....

Shock states and MODS

Shock

characterized by an imbalance of oxygen supply and demand

MODS

characterized by a continouing impairment of oxygenation, mediated by the inflammatory process

Two goals in the assessment of oxygenation

to determine overral adequacy of oxygenation
to determine which component of oxygenation dysfunction should be manipulated

Assessment of pulmonary gas exchange

ABG (PaO2, PaCO2)
Auscultation
End tidal CO2
Pulmonary functon test
QS/QT
PaO2/FiO2 ratio

Discontinous sound

Crackles

Continous sound

wheezes

Ventilatory Failure

PaCo2 greater than 50mm Hg

End tidal CO2

measure by placing a sensor at the end of the endotracheal tube to measure the amount of exhaled CO2

Tidal Volume

Vt

Minute ventilation

MV

Alveolar ventilation

AV

Vital Capacity

VC

rapid shallow breathing index

accurate predctor of how well a patient is tolerating weaning form mechanical ventilation
- the ratio is expressed as the frequency of respiration divided by the tidal volume as measured during spontanous unsupported respiration
Weaning failure- greater than 105

Intrapulmonary shunt

Qs/Qt
porportion of blood that flows past alveoli without participating in gas exchange
PaO2/FiO2
normal value is more than 286
less than 200 suggesting a large intrapulmonary shunt

Assessment of Oxygen delivery inlcludes..

cardaic output, Hb, Sa02, PaO2

Physical assessment of oxygen delivery

skin color, temperature, capillary refill

Cyanosis

a term used to describe bluish skin discoloration

Cool extremities indicate..

poor perfusion

Inadequate Oxygen delivery symptoms

restlessness, confusion, rapid heart rate, tachypnea

Sa02

th ratio of oxygenated hemoglobin to total hemoglobin

normal serum levels of lactate

less than 2mMol/L
cause: inadequate oxygen delivery to meet cellular oxygen needs
Measured using serial measurements for example four to eight hours can be used as an indicator of imporivng or worsening oxygen delivery in relation to to oxygen consumptoin

"Mixed" venous blood

when it has reached pulmonary artery
The saturation os this mixed venous blood SvO2 represents an average of the venous saturation of blood form all parts of thebody
Normal= 60 to 80 percent
below= oxygen delivery is inadequate

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