Flashcards in Session 14 _ Arterial blood gases & Obstructive/ Restrictive lung disease Deck (56)
PaO2 (PO2) =
• Partial pressure of arterial oxygen
• amount of O2 in blood (both attached to Hgb and dissolved in plasma)
• amount of O2 bound to Hgb is related to PaO2
• If Hgb is low, SaO2 will be fine but PaO2 decreases
Alveolar ventilation is represented by PCO2, what is the normal range?
retains CO2 (CO2 >40)
blow off CO2 (CO2
In normal individuals without lung pathology, what happens if they hypoventilate? If they hyperventilate?
Hypoventilate - CO2 eventually causes respiratory center to stimulate increased ventilation
Hyperventilate - CO2 signals respiratory center to decrease ventilation
What is the normal value for PO2, PCO2 and pH?
PCO2 = 40
pH = 7.4
what is the normal range for pH? PO2? PCO2?
ph = 7.35-7.45
PO2 = 80-100 mmHg
PCO2 = 35-45 mmHg
mild Hypoxemia =
moderate Hypoxemia =
severe Hypoxemia =
When matching ventilation with the needs of the body, the goal is to maintain appropriate O2, CO2 and H+. What molecules are control mechanisms responsive to?
• CO2 and H+
Central control of ventilation is known as the central chemoreceptors (medulla). What do they respond to?
increase PCO2, pH and CSF
Peripheral control of ventilation is known as the peripheral chemoreceptors. What do they respond to?
• Carotid bodies (cranial n. IX)
--> respond to decrease in PO2 or decreased pH
• Aortic bodies (cranial n. X)
--> respond to decreased PO2 or decreased pH
In the regulation of respiration, a decrease in PO2 causes:
• little effect until drops 40% or below 60 mmHg
• if drops to 40 mmHg, then respiration increases only 50-60%
In the regulation of respiration, a increase in PCO2 causes:
• if increases 10%
• respiration increases by 2x
• even if PO2 is normal
• CO2 regulates respiratory activity under normal conditions
• subject to adaptation
What are the affects of pulmonary disease on respiration?
• Retention of CO2 can occur (making it difficult to exhale; get pockets of air retained in alveoli)
• Example: Emphysema
• PCO2 chronically elevated (system adapts to elevated PCO2)
*** Therefore, reduced PO2 acts on peripheral chemoreceptors and provides main stimulus for respiration = hypoxic drive
Blood gas analysis provides information on:
•Blood O2 levels through gas exchange
• blood CO2 levels
•pH- acid base balance or imbalance (*noted in extra-celluar fluid)
Blood gas analysis reflects oxygen status and acid-base balance needed to sustain life. pH
pH 7.8 is lethal
Acidic blood = force of cardiac contraction LESSENS
Alkaline blood = impaired neuromuscular function
What are the 3 processes in the body that regulate acid-base?
1. chemical buffers
•substances combining with acid or bases
2. respiratory system
• regulates CO2 in the blood
• central chemoreceptors note change in pH - regulate rate and depth of breathing
3. renal system
• slower system
• retain or excrete acids and bases to maintain equilibrium
Respiratory vs metabolic cause of acid base change=
respiratory = lung dysfunction does not allowing to correct amount of CO2 to be exhaled
metabolic = something else going on in the body that is causing a build up of H+ --> allow pH drop
How do you interpret blood gases?
• Look at PCO2 to determine alveolar ventilation
• Look at pH to see if normal acid-base balance and whether acute or chronic
• Look at PO2 to determine oxygenation or hypoxemia and to what degree
To determine if acidosis or alkalosis and if cause is respiratory or metabolic
Is the patient on oxygen or mechanical ventilation with these values?
this is the question to ask yourself
If pH is 7.4 =
potential for acidosis
potential for alkalosis (more basic EN)
Elevators and see-saws: help to remember how pH and CO2 move in relation to each other. What is the see saw in metabolic dysfunction?
metabolic dysfunction - pH decrease, CO2 (biocarbonate) goes down
See-saw; if pH is going down --> CO2 increase =
In a metabolic elevator:
• check pH
• examine HCO3-
• if metabolic, HCO3 will go in same direction as pH
• Low pH and low HCO3- = METABOLIC acidosis
What is an example of metabolic acidosis?
In a respiratory see-saw:
• check pH
• CO2 will go in opposite direction as pH is respiratory imbalance
• RESPIRATORY acidosis low pH and high CO2
Explain what occurs during respiratory failure:
• Inability to meet needs to body ( "the arterial oxygen, carbon dioxide or both cannot be kept at normal levels. A drop in the oxygen carried in blood is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercampia"
• pH below 7.30
• PCO2 above 50; usually also have hypoxemia
• Treatment includes: oxygen therapy and positive airway pressure
** Respiratory ventilation - airflow to help keep airways open (used with sleep apnea and with critically ill patients (ex. with end-stage COPD)
What disease pathology causes patients to have respiratory failure?