Arterial Blood Gases and Improving Gas Exchange Flashcards
PaO2 (PO2) definition
partial pressure of arterial oxygen
amount of O2 in blood (both attached to Hgb and dissolved in plasma)
SaO2 definition
amount of O2 bound to Hgb
related to PaO2
if Hgb is low, SaO2 will be fine but PaO2 decreases
alveolar ventilation
- represented by…
- normal range
- hypoventilation
- hyperventilation
represented by PCO2
normal range 35-45 mmHg
hypoventilation - retains CO2 (CO2 > 40)
hyperventilation - blow off CO2 (CO2 < 40)
ventilation in normal individuals without lung pathology
in hypoventilate, CO2 eventually causes respiratory center to stimulate increased ventilation
if hyperventilate, CO2 signals respiratory center to decrease ventilation
normal values
- PO2
- PCO2
- pH
PO2 -80 PCO2 -40 pH -7.4
ranges
- pH
- PCO2
- PO2
pH -7.35-7.45 PCO2 -35-45 mmHg PO2 -80-100 mmHg
PO2 values for…
- hypoxemia
- mild hypoxemia
- moderate hypoxemia
- severe hypoxemia
<80
60-80
40-60
<40
goal of ventilation
maintain appropriate [O2], [CO2], and [H+]
control mechanisms are responsive to concentrations of these molecules
-[CO2] and [H+]
-[O2]
central control of ventilation
-respond to…
central chemoreceptors (medulla) -respond to increased PCO2 and pH of CSF
peripheral chemoreceptors
-respond to…
carotid bodies (CN IX)
-respond to decreased PO2 or decreased pH
aortic bodies (CN X)
-respond to decreased PO2 or decreased pH
effect of decreased PO2 on respiration
little effect until drops 40% or below 60 mmHg
if drops to 40 mmHg, then respiration increases only 50-60%
effect of increased PCO2 on respiration
if increases 10j% -respiration increases by 2x -even if PO2 is normal CO2 regulates respiratory activity under normal conditions subject to adaptation
pulmonary disease effect on ventilation
retention CO2 can occur
-difficult to exhale; get pockets of air retained in alveoli
-ex. emphysema
PCO2 chronically elevated
-system adpats to elevated PCO2
therefore, reduced PO2 acts on peripheral chemoreceptors and provided main stimulus for respiration = hypoxic drive
blood gas analysis
- provides info on…
- reflects…
information -blood O2 levels through gas exchange -blood CO2 levels -pH - acid-base balance or imbalance --noted in extra-cellular fluid reflects oxygen status and acid-base balance needed to sustain life
lethal pH levels
-why?
<6.8
-force of cardiac contraction lessens
>7.8
-impaired neuromuscular function
3 processes in body to regulate acid-base
chemical buffers
-substances combining with acids or bases
respiratory system
-regulates CO2 in the blood
-central chemoreceptors note change in pH - regulate rate and depth of breathing
renal system
-slower system
-retain or excrete acids and bases to maintain equilibrium
blood gas interpretation
- PCO
- pH
- PO2
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
pH values for acidosis vs. alkalosis
acidosis: below 7.4
alkalosis; above 7.4
respiratory vs. metabolic acidosis/alkalosis causes
respiratory
-abnormal respiratory function
metabolic
-non-respiratory cause
metabolic elevator
check pH
examine HCO3-
if metabolic, HCO3- will go in same direction as pH
low pH and low HCO3- = metabolic acidosis
respiratory see-saw
check pH
CO2 will go in opposite direction as pH if respiratory imbalance
respiratory acidosis low pH and high CO2
respiratory failure
-define
inability to meet needs of body
-“the arterial oxygen, CO2 or both cannot be kept at normal levels. a drop in the oxygen carried in blood is known as hypoxemia; a rise in arterial CO2 levels is called hypercapnia
respiratory failure important levels
pH below 7.3
PCO2 above 50; usually also have hypoxemia
respiratory failure
-Tx includes
O2 therapy
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)
