Respiratory Acidosis & Alkalosis

Question 1

What is the Pa of HCO3-, CO2 and O2?

Answer 1

paHCO3- = 24mmHg, 22-28mmol
paCO2 = 40mmHg, 5.1-5.6kPa
paO2 = 95mmHg, 10.5-13.5kPa

Question 2

What is the normal PA of CO2 and O2?

Answer 2

pACO2 = 36mmHg
pAO2= 105mmHg

Question 3

What is respiratory acidosis?

Answer 3

conditions where there is build up of CO2 in the blood so blood becomes more acidic, breathing difficulty, lungs do not adequately dispel CO2 (alveolar hypoventilation) through alveolar ventilation so accumulates, PaCO2 increased (hypercapnia), blood ph <7.35

Question 4

What are the main causes of respiratory acidosis?

Answer 4

• hypoventilation due to drugs supressing breathing (narcotics)
• disease of airways (asthma, COPD)
• disease of chest (scoliosis lungs less efficient)
• diseases affecting nerves and muscles (lungs inflate or deflate)
• severe obesity (restricts lung expansion)

Question 5

What is the equilibrium state?

Answer 5

Unchanging concentrations of all reactants, rate of forward reaction = rate of backward reaction

Question 6

What does the law of mass action state?

Answer 6

If we add excess of one reactant to an equilibrium you get more of the products on the other side of the reaction so equilibrium is pushed to the other side

Question 7

What is the equilibrium constant?

Answer 7

K = [C]x[D]/[A]x[B]

Question 8

What does the Henderson-Hasselbalch equation tell us?

Answer 8

pH is controlled by ratio of [HCO3-]/pCO2

[HCO3-]/0.03pCO2

Question 9

In respiratory acidosis what is the ratio of [HCO3-]/pCO2 and why?

Answer 9

high paCO2 and slightly raised HCO3- so ratio decreases and so does pH

Question 10

Why does elevated pCO2 cause a fast pH change?

Answer 10

CO2 is lipid soluble so rapidly diffuses across BBB, CSF also has less protein so less buffering

Question 11

What are the symptoms of respiratory acidosis?

Answer 11

As a result of low CNS pH -> increased brain blood flow but decrease to some areas:
headache, drowsiness, lethargy, anxiety, sleepiness, fatigue, memory loss, restlessness, muscle weakness

Question 12

What are the signs of respiratory acidosis?

Answer 12

slowed breathing, gait disturbance, blunted deep tendon reflexes, disorientation, tremor, papilledema, tachycardia, bp drop, blood vessels swell

Question 13

How is respiratory acidosis diagnosed?

Answer 13

ABG with pH <7.35, high pCO2 over 45mmHg

Question 14

How is respiratory acidosis treated?

Answer 14

aimed at underlying lung disease:

bronchodilators, non invasive positive pressure ventilation, oxygen, treatment to stop smoking

Question 15

How does acute respiratory acidosis present?

Answer 15

PaCo2 elevated above 6.3kPa (47mmHg) and acidemia
abrupt failure of ventilation - caused by depression of central respiratory centre due to cerebral disease or drugs/neuromuscular disease so cannot ventilate adequately, airway obstruction

Question 16

How does chronic respiratory acidosis present?

Answer 16

PaCO2 elevated above 6.3kPa (47mmHg)
blood is normal or near normal pH
renal compensation = highly elevated serum bicarb
secondary to many disorders - COPD hypoventilation, obesity hypoventilation syndrome, neuromuscular disorders, restrictive ventilatory defects

Question 17

How can COPD cause hypoventilation?

Answer 17

• decreased hypoxia and hypercapnia responsiveness
• increased ventilation perfusion mismatch = increased dead space ventilation
• decreased diaphragm function secondary to fatigue and hyperinflation

Question 18

How is there metabolic compensation for respiratory acidosis?

Answer 18

high blood H+ concentration stimulates kidney to generate and retain bicarb so ratio of bicarb to pCO2 is back near to normal raising pH = compensating metabolic alkalosis

Question 19

What is the maximum level of plasma HCO3- that can be reached via compensating metabolic alkalosis?

Answer 19

45mmol/L

Question 20

What is respiratory alkalosis?

Answer 20

condition where the amount of carbon dioxide found in the blood drops to level below normal, causes body’s system to make more alkaline
usually when a person hyperventilates, increased alveolar respiration, expels CO2 from circulation
H+ an HCO3- in plasma react via carbonic anhydrase so more CO2, decreased circulating H+ so increased pH

Question 21

What are the effects of respiratory alkalosis?

Answer 21

• cerebral blood vessel constriction
• impaired O2 delivery to tissue as haemoglobin O2 dissociation curve is shift to the left
• increase in neuromuscular excitability as blood calcium levels change
• hypokalaemia: decreased hydrogen ion excretion by kidney means other cations have to take its place so increased K+ excretion

Question 22

What are the symptoms of respiratory alkalosis?

Answer 22

hyperventilation - also primary cause, accompanied by dizziness, light headedness, agitation, confusion, cramps, tingling or numbing around mouth/fingers/hands
muscle twistiching, hyperpnea, chest pain, blurred vision, spasms, weakness, seizures, irregular heart beats, tetany

Question 23

What CNS symptoms are seen with respiratory acidosis and alkalosis?

Answer 23

Acidosis: drowsiness, lethargy, anxiety, fatigue
Alkalosis: gait disturbance, altered deep tendon reflexes, disorientation, tremor, seizures, myoclonic jerks

Question 24

What are the main causes of respiratory alkalosis?

Answer 24

• intracerebral haemorrhage, meningitis, stroke
• salicylate and progesterone usage
• Anxiety, hysteria, stress and pain
• Cirrhosis of the liver
• Sepsis
• Elevated body temperature
• Hypoxia

Question 25

What are the types of respiratory alkalosis?

Answer 25

acute: rapidly occurs, person loses consciousness, rate of ventilation resumes to normal chronic: symptomless due to metabolic compensation, kidney excretes increased bicarbonate so get metabolic acidosis compensation for alkalosis, compensation compensation complete in 7-10 days

Question 26

What is the diagnosis of respiratory alkalosis?

Answer 26

ABG - pH > 7.44 | paCO2 in blood will be low, under 35mmHg

Question 27

How is respiratory alkalosis treated?

Answer 27

focuses on correctly underlying condition: - relieve hyperventilation syndrome due to anxiety by breathing into paper bag, rebreathe air that is exhaled so higher amount of CO2 is inhaled than normal - antimicrobials to treat pneumonia/other infections, treat fever/seizures/arrhythmias with other meds

Question 28

What are the 2 types of respiratory failure?

Answer 28

- type 1 hypoxic (PaO2<60mmHg and normal/low PCo2) | - type 2 hypercapnia (PaCo2>50mmHg)

Question 29

What are some common causes of type 1 respiratory failure?

Answer 29

Ventilation/Perfusion (V/Q) mismatch Shunting of blood across lungs Poor gas exchange (alveoli filled with fluid eg in pneumonia) Decreased minute ventilation (MV) relative to demand Increased dead space ventilation (less gas to alveoli)

Question 30

How does type 1 respiratory failure occur?

Answer 30

Co2 diffuses out of lungs more easily than O2 diffuses in, most common form of resp failure, is a resp pathology that can occur with or without pH alteration

Question 31

What happens to perfusion if a lobe is poorly ventilated?

Answer 31

capillaries and arterioles constrict so blood flow is reduced, adaptive mechanism to redirect blood away from poorly ventilated regions to better ventilated ones

Question 32

How does V/Q mismatch cause type 1 respiratory failure?

Answer 32

If all bronchioles constricted due to asthma downstream alveoli will be hypoxic, all local capillaries constrict, even less oxygen uptake occurs in affected region, vasoconstriction occurs to reduce perfusion to that area so even less oxygen = hypoxia

Question 33

What is the anion gap?

Answer 33

the difference between the concentrations of the main cation sodium* and the main anions chloride and bicarbonate in the plasma Normally [Na+] - ([Cl-] + [HCO3-]) < 11 mEq/ - thus the amount of unmeasured anions in plasma

Question 34

What does a high anion gap mean?

Answer 34

Loss of plasma bicarbononate, due to elevated levels of anions like lactate, beta-hydroxybutyrate and acetoacetate usually indicates metabolic acidosis

Question 35

How do you convert mmHg to kPa?

Answer 35

multiply by 0.133