WK 12- Acid Base and Chest X-ray Flashcards
What is the normal pH value
7.35 – 7.45
What is the normal CO2 value
35-45
What is the normal HC03 value
24-28
What is the base excess
- The base excess is defined as the amount of H+ ions that would be required to return the pH of the blood to 7.35 if the pCO2 were adjusted to normal.
- the excess is positive (above 3) in alkalosis
- the excess is negative (-3) in acidosis
- 3 +3
- bigger the number- more acid:base imbalance
- only tells you about metabolic component (not respiratory)
If you have a low pH and a high PCO2, what is it
respiratory acidosis
What causes the O2 curve to shift to the right
- Right shift, lower SpO2 for a given PaO2
- Increased temperature
- Increased Hydrogen
- Increased CO2
- Increased 2-3-DPG
- Improve oxygen delivery in tissues
What are the 2 ways to acquire acidosis
-2 ways to acquire acidosis
→ too much CO2= lungs are not functioning= respiratory acidosis
→ added to much acid (accumulate H+) to blood/lost bicarb (low HC03)= metabolic acidosis
What are the two ways to acquire alkalosis
→ loss of CO2= respiratory alkalosis
→ accumulate bicarb or loss of H+ (acid)= metabolic alkalosis
- pH= 7.2
- PO2= 80mmg
- PCO2= 60mmHg
- HCO3= 30 mmol/L (low)
-low pH, high PCO2, High HCO2
→ high PCO2 triggers high bicarb to try and neutralise→ therefore has primary resp acidosis with compensatory metabolic alkalosis
-never fully compensate→ pH is still low
→ primary process must be the one in the direction of the pH
What is the anion gap
-represents the difference between the cations (pos) and anions (neg) in blood
-major cations= Na and K
-major anions= Cl and HCO3
=Cations – Anions
→ Na + K – ( HCO3+Cl)
What is the normal anion gap
-normal anion gap should be less than 16
-if above 16= acid is coming from something not normally present in body→ another anion floating around
-if below 16→ acidosis is due to the accumulation of HCL/loss of bicarb
→RAISED ANION GAP INDICATES METABOLIC ACIDOSIS
What causes a raised AG (HAGMA)
Raised AG with 1:1 change in bicarb and AG→ cause by ketoacidosis, lactic acids, urea, salycilate- also the causes of metabolic acidosis
What is a NAGMA
NAGMA: non-anion gap metabolic acidosis
- Bicarb loss/consumption→ diarrhoea
- Acid production
- Endocrinopathies
What causes metabolic acidosis
due to accumulation of H+ or loss of HC03
- H+ is an acid, so will bind to base HC03-> causing loss of HC03
- HCO3 can also be lost in diarrhoea without addition of H+ occuring
- compensated for by resp alklaosis (hypoventilation)
What causes metabolic alkalosis
loss of H+ (ie. in vomit)
-compensation by resp acidosis (increased CO2)= hyperventilation
What causes respiratory alkalosis
- drop in CO2
- hyperventilation, hypoxia at altitidue
- can be compensated by metabolic acidosis (increasing H+)
What causes respiratory acidosis
- Increased CO2
- hypoventilation/resp insufficiency= COPD
What is the alveolar arterial oxygen gradient
- refers to tension of oxygen in the alveolar sac compared to blood running past it
- measured by blood gas and can approximate alveolar concentration
How do you calculate the A-a gradient
do alveolar pressure- arterial pressure (PO2)
How do you calculate the alveolar pressure
0.21 x (760mmHg- 47mmHg) – 5/4 x PaC02
What does it mean if the Aa gradient is raised
ventilation perfusion mismatch→ due to pathologies in the lung
How do you calculate the respiratory compensation (winters formula)
- used to calculate the expected PCO2 in someone with metabolic acidosis
- pCO2= 1.5 x HCO3 + 8 +/- 2
- if CO2 is higher than calculated compensation= resp insufficiency
What is the acronym used for analysing CXR
D= details
R= RIPE
R- rotation-> are the clavicles equidistant from the spinous process, do the clavicles and sternum line up
I- inspiration= should be 5-7 ribs seen-> anymore= hyperinflation= COPD
P- projection= PA posterior-anterior view
E- exposure= should be able to see the spinous processes going all the way down the spine
S= soft tissues and bone-> lung tissue (check for consolidation), look at scapula and ribs (check for breaks)
A= airway-> check trachea and bronchus- are they deviated- pneumothorax
B= breathing-> compare lung fields-> divide into middle, upper and lower
C= cardiac-> clear cardiac margins? (lost in pneumonia due to silhouette sign), also check the size of the heart (length of the heart should be 1/3 the size of the thoracic cage)
D= diaphragm= check costophrenic angles (angle between the ribs and diaphragm-> meniscus sign), also check height of the diaphragm->make sure they are equal
E= extras-> ECG lines
What structures are found on the right side of the chest in an X-RAY
SVC, IVC, RA, hilar structures (right bronchus, pulmonary artery)
What structures are found on the left side of the chest in an X-RAY
Aortic arch, left atrium, left ventricle, hilar structure (left bronchus, pulm trunk)
What is the silhouette sign
-when two objects of the same density touch eachother, the edge between them disappear
→ if there is pneumonia (lung filled with pus), then the line between the lung and heart will disappear as they will be same density
What is the meniscus sign
-loss of costodiaphragm angle→ effusion cause by heart failure and pneumonia
What sign is seen in pulmonary oedema
-Batwing sing→ fluid in the alveolar tissue
What X-ray changes are seen in heart failure
- upper lobe diversion
- Kerley B lines→ fluid in the interstitial tissue in the peripheral lungs
- cardiomegaly
- batwing appearance with severe heart failure
- pleural effusion
What CXR changes are seen in COPD
- Large lung field
- high number of ribs present due to hyper-inspiration
- flat diaphragm
