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49 terms

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