Blood Gas Flashcards
What is the pH range in the human body?
7.35-7.45
What is Ka
The dissociation constant
Define pKa
The negative log of the dissociation constant
When is the body in acid-base balance?
PH = pKa
What does a buffer consist of?
A weak acid and a salt of its conjugate base
What is the function of a buffer?
To allow a solution to resist changed in pH upon adding acid or base
What is the most important buffering system in the body?
H2CO3 (bicarbonate)
What organ in the body changes HCO3 concentration?
Kidneys
What organs regulate the acid base balance (transport of CO2)?
Lungs and Kidneys
_____ is the end product of most aerobic metabolic processes.
CO2
Dissociation of __a__ causes the development of a concentration gradient due to the increase in __b__ concentration within the RBC.
A) H2CO3
B) HCO 3-
How do the kidneys regulate pH?
- excreting acid (primarily in the ammonium ion)
- reclaiming HCO3- from glomerular filtrate
The dissolved carbon dioxide (dCO2) that is expelled by the lungs is known as the ___
Respiratory component
How the kidneys control the bicarbonate concentration by reabsorption or excretion is known as the ___
Metabolic component
Acidemia/Acidosis
When the blood pH is less than the reference range
Causes of acidosis include
1) primary metabolic imbalance: the amount of acid exceeds the capacity of the buffer systems and there is a decrease in bicarbonate
2) primary respiratory imbalance
How does the body compensate for metabolic acidosis?
Hyperventilation
Alkalemia/alkalosis
When blood pH is greater than the reference range
Cause of primary respiratory alkalosis
Increased rate of alveolar ventilation which causes an excessive elimination of CO2 by the lungs
How do the kidneys compensate for primary respiratory alkalosis?
By excreting HCO3- in the urine and reclaiming H+ to the blood through decreased activity of Na+ and H+ exchange
-osis
Refers to a process in the body
-emia
Refers to the corresponding state in blood
Acidemia
Will result if the hydrogen ion concentration increased through pCO2 concentration or decreases in the bicarbonate concentration
Alkalemia
Will result if the H+ concentration decreases, either from decreased PCO2 or increased concentration of bicarbonate
Primary Respiratory Acidosis or Alkalosis
A disorder caused by respiratory dysfunction — a change in the pCO2
Metabolic acidosis or alkalosis
A disorder resulting from a change in the bicarbonate level — a consequence of renal or metabolic dysfunction
Compensation
The response to maintain acid-base homeostasis and is accomplished by the organ not associated with the primary process
Fully compensated
Implies that the pH has retuned to the normal range and ratio has returned to 20:1 (normal)
Partially compensated
Implies that the pH is approaching normal
Uncompensated
Implied that the pH is abnormal and the body has not started compensating for the acid-base imbalance
Carbonic acid is a ___ acid
weak
What does the HH equation do?
It expresses the acid base relationship in a mathematical equation
What is CO2 in the acid base balance of lungs and kidney?
End product of metabolic processes
What is the relationship between the bicarbonate and hgb buffering systems?
CO2 has an acid/base effect despite not being one
What is the most acidic pH your urine can be?
pH = 4.6
What happens to HCO3 re absorption when there is increased plasma pH
There is decreased Na-H exchange and HCO3 re absorption is decreased
What happens to HCO3 re absorption when there is decreased plasma pH
There is increased Na-H exchange and HCO3 reabsorption is increased
What is in equilibrium in the bicarbonate buffering system?
The dissolved CO2 (dCO2) is in equilibrium with CO2 gas in the lungs, which can be expelled.
What is the respiratory component of the bicarbonate system?
The dissolved carbon dioxide (dCO2) that is expelled by the lungs
What is the metabolic component of the bicarbonate system?
How the kidneys control the bicarbonate concentration by reabsorption or excretion
What is acidosis?
When blood pH is less than 7.35
How is metabolic acidosis compensated for?
Increased rate or depth of breathing (hyperventilation)
What is alkalosis?
When blood pH is greater than 7.45
How does the body compensate for metabolic alkalosis?
The kidneys compensate by excreting HCO3− in the urine and reclaiming H+ to the blood through decreased activity of the Na+-H+ exchange.
What is respiratory acidosis?
Decreased alveolar ventilation causes a decreased elimination of Co2
What is respiratory alkalosis?
Caused by an increased rate of alveolar ventilation which is causing an excessive elimination fo Co2 by the lungs
What are the characteristics of acid base disorders?
What is the percentage of oxygen and nitrogen in blood gas exchange?
20% O2
78% Nitrogen
What factors influence the amount of O2 that moves into the alveoli?
Destruction of the alveoli
Pulmonary edema
Airway blockage
What factors infleunce the amount of O2 delivered to the tissues
Inadequate blood supplt
Diffusion of CO2 and O2
Intrapulmonary shunting
Anemia
What are the four forms in which Hgb exists?
Oxyhemoglobin (O2Hb)
Deoxyhemoglobin (HHb)
Carboxyhemoglobin (COHb)
Methemoglobin (MetHb)
What is Oxyhemoglobin (O2Hb)
hgb with ferrous iron in the heme group that is reversibly bound to O2
What is Deoxyhemoglobin (HHb)
Reduced hgb-hgb without O2
What is
Carboxyhemoglobin (COHb)
hgb bound to CO
What is Methemoglobin (MetHb)
Hgb unable to bind to O2 because Iron is in an oxidized state
What are the four parameters commonly used to assess a patient’s oxygen status
1) O2 saturation
2) fraction % of oxyhemoglobin which is the ratio of oxyhgb to toal hgb
3) Trens in O2 sat asses by transcutaneous and pulse ox
4) amount of O2 dissolved in plasma
T/F:
Hgb acts as both an acid base buffer and an O2 buffer
TRUE
What do blood gas analyzers use to measure pO2, pCO2, and pH?
Electrodes and glass membranes as sensing devices
What is a calulated parameter for blood gas analyzers?
HCO3 using HH equation
Positive = base excess, indicates a excess of bicarbonate, positive alkalosis
Negative = base deficit = deficit of bicarbonate = Metabolic acidosis
What levels are surrogate liquid control levels at for QC?
usually 3 levels, low, normal, high—significantly different matrix than fresh whole blood.
