Blood Gas and pH measurements Flashcards
What will diagnostic tests identify?
(and evaluate) dysfunction if patient’s history and physical examination reveal evidence of respiratory dysfunction
one of the first test ordered to assess respiratory status because it helps evaluate gas exchange in lungs
Arterial blood gas
*measures how well the person’s lung and kidneys are working and how well the body is using energy
Any substance that can yield hydrogen (H+) or hydronium ion (H3O+) when dissolved in water
Acid
release of proton or H+
Substance that can yield hydroxyl ions (OH-)
Base
ACCEPT proton or H+
negative logarithm of the ionziation constant of an acid
pK or pKa
pKa value of strong acids
<3
pKa value of strong bases
> 9
^pKa ^pH
It is the affinity of the acid whether or not to give out its H+
pKa
negative logarithm of H+ concentration
pH
represents hydrogen concentration
*pH= pKa + log [base]/[acid]
combination of a weak acid and/or weak base and its salt
buffer
*able to resist changes in pH
Effectiveness of buffer depends on
pK of buffering system
pH of environment in which it is placed
Normal pH range, acidosis and alkalosis
Normal: 7.35-7.45
Acidosis: < 7.35
Alkalosis > 7.45
diagnostic procedure in which blood is obtained from an artery directly by an arterial puncture or accessed by a way of indwelling arterial catheter
Arterial Blood Gas
Arterial blood gas is only taken for (indications):
- To obtain information about patient ventilation (pCO2), oxygenation (pO2), and acid-base balance
- To monitor gas exchange and acid-base abnormalities for patient on mechanical ventilator or not
- To evaluate response to clinical intervention and diagnostic evaluation (oxygen therapy)
When is arterial blood gas most useful?
when a person’s breathing rate is increased or decreased
when person has very high blood sugar levels, sever infection or heart failure
Components of ABG
pH
pCO2
pO2
HCO3-
[Components of ABG]
Measures hydrogen ion concentration in the blood, it shows blood acidity or alkalinity
pH
normal value: 7.35-7.45
[Components of ABG]
carried by the blood for excretion by the lungs, known as respiratory parameter
pCO2
It is the partial pressure of CO2
normal value: 35-45 mmHg
[Components of ABG]
dissolved in the blood; reflects body’s ability to pick up oxygen from the lungs
pO2
(partial pressure of O2)
normal value: 80-100 mmHg
[Components of ABG]
metabolic parameter;; reflects kidneys ability to retain and excrete bicarbonate
HCO3-
normal value: 22-28 mEq/L
T or F: The body constantly works to maintain a balance (homeostasis) between acids and bases
True
These are byproducts formed as cells use nutrients to produce energy
H+ and CO2
Where does Acid-base balance depend on?
regulation of free H+
*slight imbalances affect emtabolism and essential body functions
What conditions affect acid-base balance?
infection or trauma
Disorder trend for respiratory acidosis
Respiratory
Acidosis ↓pH ↑pCO2
uncompensated HCO3-
Disorder trend for respiratory ALKALOSIS
MATAAS NA PH
MABABANG PCO2
UNCOMPENSATED HCO3-
Disorder trend for METABOLIC ACIDOSIS
LOW PH
UNCOMPENSATED PCO2
LOW HCO3-
Disorder trend for METABOLIC ALKALOSIS
HIGH PH AND HCO3-
Uncompensated pCO2
T or F: The circulatory and metabolic system works together to keep the body’s acid-base balance within normal limits (compensation)
respiratory and metabolic
Compensation mechanism for respiratory acidosis and respiratory alkalosis
Metabolic system
r. acid: high hco3- reabsorption
r. alkal: low hco3- reabsorption
Compensation mechanism for metabolic acidosis and alkalosis
Respiratory rate
m. acid: increase in rate and depth (low pCO2)
m. alkal: decrease in rate and depth (high pCO2)
Why is pH decreased and pCO2 increased in uncompensated phase of respiratory acidosis?
no response from kidneys yet to the acidosis, so the HCO3- will remain normal
What happens during the partially compensated phase of respiratory acidosis?
The kidneys start to respond to the acidosis by increasing the amount of circulating HCO3–
↓ pH ↑ pCO2 ↑HCO3-
Stage in respiratory acidosis where pH returns to normal pCO2 and HCO3- levels are still high to correct acidosis
Fully compensated
N ↑ ↑
*results are opposite in respiratory alkalosis (see trans)
Why are both pH and HCO3- decreased in uncompensated phase of metabolic acidosis?
there is no response from the lungs yet to acidosis the PaCO2 will remain normal
T or F: all are decreased in partially compensated phase of metabolic acidosis
True
*lungs start to respond to the acidosis by decreasing the amount of circulating pCO2
T or F: pH, pCO2 and HCO3- are the same in fully compensated phase of metabolic acidosis and respiratory alkalsosi
true (NpH ↓pCO2 ↓HCO3-)
*pH returns to normal; pCO2 and HCO3– levels are still low to correct acidosis
What are increased in uncompensated phase of metabolic alkalosis?
pH and HCO3-
no response from lungs yet to alkalosis so the pcO2 remains normal
In partially compensated phase of metabolic alkalosis, lungs start to respond to alkalosis by increasing the amount of circulating PaCO2 so what is the trend?
↑ ↑ ↑
What are high during the fully compensated phase of metabolic alkalosis?
pCO2 and HCO3- to correct alkalosis
ph = normal
pCO2 and HCO3- for respiratory ACIDOSIS and metabolic ALKALOSIS
↑ ↑
*pco2 is compensated in respi, HCo3- in metabolic
pCO2 and HCO3- for RESPIRATORY ALKALOSIS and metabolic ACIDOSIS
↓ ↓