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CR2 > Respiratory Acidosis & Alkalosis > Flashcards

Respiratory Acidosis & Alkalosis Flashcards

1
Q

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

A 
paHCO3- = 24mmHg, 22-28mmol
paCO2 = 40mmHg, 5.1-5.6kPa
paO2 = 95mmHg, 10.5-13.5kPa
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2
Q

What is the normal PA of CO2 and O2?

A 
pACO2 = 36mmHg
pAO2= 105mmHg
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3
Q

What is respiratory acidosis?

A

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

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4
Q

What are the main causes of respiratory acidosis?

A
  • 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)
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5
Q

What is the equilibrium state?

A

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

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6
Q

What does the law of mass action state?

A

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

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7
Q

What is the equilibrium constant?

A

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

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8
Q

What does the Henderson-Hasselbalch equation tell us?

A

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

[HCO3-]/0.03pCO2

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9
Q

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

A

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

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10
Q

Why does elevated pCO2 cause a fast pH change?

A

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

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11
Q

What are the symptoms of respiratory acidosis?

A

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

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12
Q

What are the signs of respiratory acidosis?

A

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

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13
Q

How is respiratory acidosis diagnosed?

A

ABG with pH <7.35, high pCO2 over 45mmHg

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14
Q

How is respiratory acidosis treated?

A

aimed at underlying lung disease:

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

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15
Q

How does acute respiratory acidosis present?

A

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

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16
Q

How does chronic respiratory acidosis present?

A

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

17
Q

How can COPD cause hypoventilation?

A
  • decreased hypoxia and hypercapnia responsiveness
  • increased ventilation perfusion mismatch = increased dead space ventilation
  • decreased diaphragm function secondary to fatigue and hyperinflation
18
Q

How is there metabolic compensation for respiratory acidosis?

A

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

19
Q

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

A

45mmol/L

20
Q

What is respiratory alkalosis?

A

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

21
Q

What are the effects of respiratory alkalosis?

A
  • 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
22
Q

What are the symptoms of respiratory alkalosis?

A

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

23
Q

What CNS symptoms are seen with respiratory acidosis and alkalosis?

A

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

24
Q

What are the main causes of respiratory alkalosis?

A
  • intracerebral haemorrhage, meningitis, stroke
  • salicylate and progesterone usage
  • Anxiety, hysteria, stress and pain
  • Cirrhosis of the liver
  • Sepsis
  • Elevated body temperature
  • Hypoxia
25
Q

What are the types of respiratory alkalosis?

A

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

26
Q

What is the diagnosis of respiratory alkalosis?

A

ABG - pH > 7.44

paCO2 in blood will be low, under 35mmHg

27
Q

How is respiratory alkalosis treated?

A

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
28
Q

What are the 2 types of respiratory failure?

A
  • type 1 hypoxic (PaO2<60mmHg and normal/low PCo2)

- type 2 hypercapnia (PaCo2>50mmHg)

29
Q

What are some common causes of type 1 respiratory failure?

A

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)

30
Q

How does type 1 respiratory failure occur?

A

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

31
Q

What happens to perfusion if a lobe is poorly ventilated?

A

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

32
Q

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

A

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

33
Q

What is the anion gap?

A

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

34
Q

What does a high anion gap mean?

A

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

35
Q

How do you convert mmHg to kPa?

A

multiply by 0.133

CR2 (35 decks)

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