Respiratory P2 Flashcards
O2 content in the blood depends on 3 things
PO2
RBC #
Hemoglobin
Normal Hb ranges
Males: 13-18 g/dl
Female: 12-16 g/dl
Each Hb carries
1.34 ml O2 if fully saturated
4 binding sites for O2
A normal person will carry…
20 ml O2
a person with anemia
has a decrease in RBC mass or amount of Hb
will only have 13.4 ml O2
O2 dissolved in plasma .2 ml/dl
S/S of Anemia
decreased endurance
tachycardia
pallor
shortness of breath
dizziness
cold hands/feet
At rest, what can we expect the SPO2 of a pt who has anemia to be?
likely normal
not measuring absolute hemoglobin, but a ratio
remember that SPO2 is not a complete measure of circulatory sufficiency or O2 content in blood
Why is less than 90% PO2 a critical clinical point with regards to SaO2?
- it is when the slope begins to drastically change
- clinical signs of hypoxemia
- cut-off point for safe mobility or exercise
- supplemental O2
RV/LV output in an adult
5.5L
rate of blood flow through the pulmonary circulation is equal to the rate of blood flow through systemic circulation
Driving pressure in pulmonary circulation
-10 mmHG
-it HAS to be low for pulmonary circulation to equal systemic circulation. lungs would fill with fluid if it was higher
-low pressure and low resistance produces less filtration then systemic capillaries
V/Q
ratio of the amount of air getting to the alveoli (alveolar ventilation) and the amount of blood being sent to the lungs (cardiac output)
Why is VQ ratio is important ?
it is one of the major factors affecting alveolar (arterial) levels of O2 and CO2
upright lung V/Q
Physiological dead space: V>Q
Mid: V/Q = 1
shunt: V<Q
What is the average V/Q ratio across the lungs?
.8
this means that there is more perfusion vs ventilation
autoregulation causes the lungs to try to match V & Q by altering the size of pulmonary arterioles
V/Q mismatch
contributes to the 5 mmHg difference between PO2 in alveolar air and PO2 in arterial blood
Which lung are you more likely to aspirate?
right
High V/Q ratio
pulmonary embolism
Q is the pathology
Low V/Q ratio
pneumonia
ventilation is the pathology
Goal of turning schedule
allow for drainage of different areas of the lungs via gravity to ensure better ventilation/perfusion ratio
CO2 Transport
CO2 must be removed from living tissues via diffusion out of cells, movement into blood, excretion by lungs
Transported in blood via
1. dissolved CO2
2. carbamino compounds
3. HCO3
What happens to CO2 within RBCs in systemic capillaries?
- reaction is catalzyed by carbonic anhydrase in RBCs
- CO2 combines with water to make carbonic acid
- build up of carbonic acid dissociates and becomes bicarbonate
- release of bicarbonate is buffered by Hb
What happens to CO2 in lung capillaries?
- Deoxy-Hb is converted into oxy-Hb
- oxy-Hb has weak affinity for H+, H+ is released within the RBCs
- Eventually forms carbonic acid, which becomes O2 and CO2
Blood pH norm
7.35 to 7.45
Blood pH is maintenance
Lungs, maintains PaCO2
Kidneys, maintains bicarbonate (base) and hydrogen (acid) levels
Types of acids in body
Volatile acids
Nonvolatile acids
Volatile acids
can leave solution and enter atmosphere as a gas
carbonic acid
carbonic acid is controlled by lungs
Nonvolatile
do not leave solution, we can’t breathe these off
- sulfuric and phosphoric acids
- by products of aerobic and anaerobic metabolism during starvation
must be buffered in body fluids before excretion by kidneys
Buffer systems
provide or remove hydrogen to stabilize pH
bicarbonate is the most important extracellular fluid buffer
kidneys excrete excessive H and produce bicarbonate
PO2 ranges of arterial blood gases
80 mmHg to 100 mmHg
PCO2 range of arterial blood gases
35-45 mmHg
Bicarbonate range of arterial blood gases
22-26 mEq/L
Acceptable ranges of ABGs are generally reported in following format
PO2
PCO2
pH
HCO3
Why and when would ABGs be performed?
lung disease with poor gas exchange, kidney disease, electrolyte problems
Acute disorders of acid-base
Respiratory Acidosis
Respiratory alkalosis
Metabolic Acidosis
Metabolic Alkalosis
Respiratory Acidosis
1.reduction in pH due to primary increase in PCO2 (hypercapnia)
2. features include low pH, high PCO2, normal HCO3
3. Causes include hypoventilation, obstructive lung disorders, CNS depression
Hypoventilation
can be caused by oversedation (opioids), chest wall deformities
Respiratory alkalosis
- increase in pH due to primary decrease in PCO2 (hypocapnia)
- features include high pH, low PCO2, normal bicarbonate
- causes include hyperventilation, hypoxemia, pulmonary embolus
Hyperventilation
caused by anxiety, pain, shock, manual ventilation
Left shift of oxy-Hb curve
Hb has increased affinity for O2, making unloading of O2 into tissues harder
alkalosis (increased pH) can be caused by hyperventilation, vomiting, pancreatic diseases
Pulmonary Embolism
- Blood flow to lung tissue is blocked by embolus
- decreased perfusion, increased V/Q ratio
- hypoxemia triggers increased RR, leads to alkalosis
Metabolic Acidosis
- decrease in pH due to primary decrease in bicarbonate
- features include low pH, normal PCO2, low HCO3
- Causes include ketoacidosis, posisonings, renal failure, prolonged diarrhea
Ketoacidosis
caused by starvation
Prolonged diarrhea…
is losing base
Metabolic Alkalosis
- increase in pH due to primary increase in bicarbonate
- features include high pH, normal PCO2, high bicarbonate
Causes include vomiting, diuretic therapy, severe potassium depletion, excessive ingestion of black licorice
Prolonged vomiting
losing acid
Diuretic therapy
loss of H+, causes increase pH
Severe potassium depletion
leads to loss or excessive excretion of H+
Excessive ingestion of black licorice
loss of hydrogen and potassium in urine is increased
What does PCO2 tell us?
alveolar ventilation
What does PO2 tell us?
oxygenation status, can also estimate with pulse oximetry
What does HCO3 tell us?
buffering capacity
base excess/base deficit
Your patient in the hospital has had ABGs drawn. The chart is as follows = 92/49/7.31/25
- Pt is slightly acidic
- PCO2 is high, HCO3 is normal. Primary respiratory problem.
- Condition is described as respiratory acidosis
Your patient in the hospital has had ABGs drawn. The chart is as follows: 92/40/7.32/20
- pt is acidic
- PCO2 is normal, HCO3 is low. Metabolic problem.
- Condition is described as acute metabolic acidosis, can be caused by type 1 diabetes
Your patient in hospital has had ABGs drawn. They are listed in the chart 92/47/7.35/28
- pt is in acid/base balance
- PCO2 and HCO3 are both high, respiratory acidosis and metabolic alkalosis
- Can be either respiratory acidosis w/compensation of metabolic alkalosis (COPD) or metabolic alkalosis w/compensation of respiratory acidosis (vomiting w/hypoventilation)
Your patient in the hospital has had ABGs drawn. They are in the chart as 92/33/7.35/21
- pt is in acid-base balance
- Low PCO2 and low HCO3, have both respiratory alkalosis and metabolic acidosis
- respiratory alkalosis comp for metabolic acidosis (hyperventilation w/diabetes ketoacidosis) OR metabolic acidosis comp w/respiratory alkalosis (hyperventilation, kidneys produce less bicarbonate)
Kussmaul Respirations
hyperventilation associated with diabetic ketoacidosis
Roles of dissolved O2 in plasma
- Establishes PO2 of blood and tissue fluids
- only dissolved O2 in plasma can be utilized by cells
- partial pressure of O2 plays role in determining loading of O2 onto Hb in lungs and unloading of O2 into cells
- plays role in regulation of breathing by stimulating chemoreceptors
Regulation of breathing occurs via
Medulla Oblongata
Pons
Medulla Oblongata
loose collection of neurons in the reticular formation called rhythmicity center. Control autonomic breathing.
has both ventral and dorsal respiratory group
Pons
controls rhythmicity center in medulla
apneustic center (excitatory) and pneumotaxic center (inhibitory)
3 ways to stop breathing
stroke
spinal cord injury
paralyze diaphragm
Dorsal respiratory group
- contains inspiratory neurons that innervate both diaphragm and ventral respiratory group
- receives input from CN IX, X, VRG
- most likely integrate regulation of respiration rate and depth
a part of medulla
Ventral respiratory group
contains both expiratory and inspiratory neurons
controls motor neurons to internal intercostal muscles
part of medulla
Apneustic center
- promotes inspiration by stimulating inspiratory neurons in medulla
- provides constant stimulus for inspiration
- if no input received from the pneumotaxic center, prolonged inspiratory gasps occur
Pneumotaxic center
- may inhibit apneustic center, inhibiting inspiration
- modulates output of medullary centers
- function still incompletely understood, likely maintains normal respiration
Rhythmicity Center
from the medulla
made up of dorsal respiratory and ventral respiratory groups
controls autonomic breathing
What regulates breathing?
voluntary control
automatic control–> chemoreceptors that monitor changes in blood PCO2, PO2, pH
Peripheral chemoreceptors
carotid and aortic bodies
control breathing indirectly via sensory nerve fibers to medulla
Chemoreceptor control
input for chemoreceptors modify rate and depth of breathing
-O2 content of blood decreases slowly because we have a reservoir
-PCO2 is more immediately affected by changes in ventilation, rate and depth is adjusted to maintain
Chemoreceptors are more sensitive to changes in
PCO2
Peripheral chemoreceptors
cartoid bodies are more important than aortic bodies in meditating respiratory changes in response to chemical changes in plasma
only chemoreceptors that increase ventilation in response to hypoxemia
Firing rate of carotid bodies increases when
arterial PCO2 increases
pH decreases
PO2 decreases below 60 mmHg (or lower than 89% in pulsoximeter)
Chemoreceptors and pH
cerebral cortex has a slower reaction to pH
brainstem has the 1st response to pH
Central Chemoreceptors
within the medulla
fall in CSF pH stimulates these
responsible for 70-80% of increased ventilation that occurs in response to sustained rise in arterial PCO2
takes several minutes to respond after peripheral
Acclimatization to high altitude
high altitude = cause of hypoxemia
-PaO2 decreases, carotid bodies increase RR/TV
-hypoxic ventilatory produces hyperventilation, produces initial respiratory alkalosis
-kidneys excrete bicarbonate to alter pH
-kidneys secrete EPO to trigger more RBC and increase Hb
Altitude Training
increases RBC number
increases Hb concentration
angiogenesis
altered glucose transport, glycolysis, pH regulation
