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respiratory acidosis Flashcards

1
Q

what is the normal range of PaO2 in arterial blood?

A

10-13.5kPa

80-100mmHg

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2
Q

what is the normal range PaCO2 in arterial blood?

A

4.7-6.0kPa

35-45mmHg

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3
Q

what is the normal PaO2 in alveolar blood?

A

14kPa

105mmHg

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4
Q

what is the normal PaCO2 in alveolar blood?

A

4.8kPa

36mmHg

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5
Q

define respiratory acidosis

A

condition where build-up of CO2 in the blood shift’s pH balance and causes blood to be more acidic (pH<7.35)

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6
Q

what is the mechanism of respiratory acidosis?

A

Alveolar hypoventilation –> increased PaCO2 (hypercapnia) –> decrease in blood pH

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7
Q

what are the main causes of respirtory acidosis?

A
  • Hypoventilation bc of drugs that suppress breathing (inc powerful pain meds e.g. narcotics and ‘downers’ e.g. benzodiazepines) esp when combined with alcohol
  • Diseases of the airway e.g. asthma, chronic obstructive lung disease
  • Diseases of the chest e.g. scoliosis which makes the lungs less efficient at filling and emptying
  • Diseases affecting the nerves and muscles that drive the lungs to inflate/deflate
  • Severe obesity – restricts how much the lungs can expand
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8
Q

what is the ratio that controls pH?

A

[HCO3-]/pCO2

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9
Q

explain how alkalosis occurs in terms of the henderson-hasselbach equation?

A

If HCO3- higher than ref and/or CO2 is lower than ref then pH = high –> alkalosis

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10
Q

explain how acidosis occurs in terms of the henderson-hasselbach equation?

A

If HCO3- lower than ref and/or CO2 is higher than ref then pH = low  acidosis

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11
Q

why does CO2 rapidly diffuse across the BBB?

A

it’s lipid-soluble gas

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12
Q

why does the pH of the CSF change more rapidly?

A

no proteins to buffer it

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13
Q

why may areas of the brain become relatively hypoxaemic or hyperoxic?

A

Normally brain can regulate its own local pH. Global acidity of the blood disrupts the local control so areas of the brain may become relatively hypoxaemic or hyperoxic

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14
Q

what is the main cause of the signs and symptoms of respiratory acidosis?

A

primarily a result of low CSF pH

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15
Q

what are the symptoms of respiratory acidosis?

A

Headache, drowsiness, lethargy, anxiety, sleepiness, fatigue, memory loss, restlessness, and muscle weakness

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16
Q

what are the signs of respiratory acidosis?

A

Slowed breathing, gait disturbance, blunted deep tendon reflexes, disorientation, tremor, myoclonic jerks, papilledema, tachycardia, drop in blood pressure, and swelling of blood vessels in the eyes may also be present

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17
Q

how do you diagnose respiratory acidosis and what is the key finding?

A
  • Provisionally diagnosed based on signs and symptoms
  • Blood sample to test for pH and ABG will confirm the diagnosis
  • Key finding: The pCO2 in the blood will be high, usually over 5.9 kPa (45 mm Hg).
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18
Q

how do you treat respiratory acidosis?

A

wAimed at the underlying lung disease. May include;
• Bronchodilator drugs to reverse some types of airway obstruction
• Noninvasive positive-pressure ventilation (sometimes called CPAP or BiPAP) or mechanical ventilation if needed
• Oxygen if the blood oxygen level is low
• Treatment to stop smoking

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19
Q

what is acute respiratory acidosis?

A

PaCo2 is elevated above 6.3kPa (47mmHg) with an accompanying acidemia (blood pH <7.35)

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20
Q

what causes acute respiratory acidosis?

A

• Occurs when an abrupt failure of ventilation occurs – may be caused by;
o depression of central respiratory centre by cerebral disease or drug
o Inability to ventilate normally bc of neuromuscular disease e.g. myasthenia gravis, amyotrophic lateral sclerosis, Guillain-Barré syndrome, muscular dystrophy
o Airway obstruction related to asthma or chronic obstructive pulmonary disease (COPD) exacerbation

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21
Q

what is chronic respiratory acidosis?

A

• PaCO2 is elevated above 6.3 kPa (47 mm Hg) but the blood pH is normal or near normal.

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22
Q

what causes chronic respiratory acidosis?

A
  • This is bc renal (metabolic) compensation is occurring and has produced a highly elevated serum bicarbonate (HCO3− >30 mm Hg) – restores pH to near normal
  • Chronic RA may be secondary to disorders like COPD
23
Q

what are the multiple mechanisms of hypoventilation in COPD?

A

o Decreased responsiveness to hypoxia and hypercapnia
o Increased ventilation-perfusion mismatch leading to increased dead space ventilation
o Decreased diaphragm function secondary to fatigue and hyperinflation

24
Q

what is chronic respiratory acidosis secondary to?

A

COPD
o Obesity hypoventilation syndrome
o Neuromuscular disorders e.g. amyotrophic lateral sclerosis
o Severe restrictive ventilatory defects as seen in interstitial fibrosis and thoracic deformities.

25
Q

what is compensating metabolic alkalosis?

A

increased bicarbonate retention

26
Q

what is the max level of plasma HCO3 that can be reached?

A

45mmol/L

27
Q

how does metabolic compensation for respiratory acidosis occur?

A
  • After a few days of respiratory acidosis, high blood H+ stimulates kidney to retain bicarbonate
  • High plasma bicarbonate compensates for the high PaCO2 – brings bicarbonate/PaCO2 ration back to near normal  raises pH to normal
28
Q

define respiratory alkalosis?

A

condition where the amount of CO2 found in the blood drops to levels below the normal range. Body system becomes more alkaline

29
Q

how does respiratory alkalosis occur?

A

Occurs when a person hyperventilates – produces increased alveolar respiration and expels more CO2 from circulation
• H+ and bicarbonate in the plasma react via carbonic anhydrase to make more CO2  decreased circulating H+  increased pH (alkaline)

30
Q

what is the primary cause and symptom of respiratory alkalosis?

A

hyperventilation

31
Q

what are the signs and symptoms of respiratory alkalosis in acute cases?

A

accompanied by dizziness, light headedness, agitation, confusions, cramps and tingling or numbing around the mouth and in the fingers and hands.

32
Q

what are other signs and symptoms of respiratory alkalosis?

A

Muscle twitching, hyperpnea, chest pain, blurred vision, spasms, and weakness

33
Q

what are signs and symptoms of extreme cases of respiratory alkalosis?

A

seizures, irregular heartbeats, and tetany

34
Q

what are acidosis CNS symptoms?

A

mainly associated with fatigue e.g. drowsiness, lethargy, anxiety, fatigue, etc

35
Q

what are alkalosis CNS symptoms?

A

mainly associated with overactivity: gait disturbance, altered deep tendon reflexes, disorientation, tremor, seizures, myoclonic jerks, etc

36
Q

what are the metabolic effects of respiratory alkalosis?

A
  • Decrease in blood CO2 causes constriction of cerebral blood vessels
  • Alkalaemia shifts the haemoglobin O2 dissociation curve to the left, impairing O2 delivery to the tissue.
  • pH related changes in blood Ca2+ levels  increase in neuromuscular excitability
  • Resp alkalosis causes reduced H+ excretion by the kidney. Some other cation must take its place – normally K+  increased K+ excretion and hypokalaemia
37
Q

what happens during acute respiratory alkalosis?

A

• Person may lose consciousness where the ventilation rate will resume to normal

38
Q

why is chronic respiratory alkalosis symptomless?

A

bc of metabolic compensation

• Kidney excretes increased bicarbonate to give a metabolic acidosis that compensates for the respiratory alkalosis

39
Q

when does full compensation occur in chronic respiratory alkalosis?

A

• If the condition has been present for 7 days or more full compensation may occur

40
Q

what is the minimum achievable plasma HCO3-?

A

12 mmol/L

41
Q

what are common causes of respiratory alkalosis?

A
  • Intracerebral hemorrhage, meningitis, stroke (altered respiratory drive)
  • Salicylate and Progesterone drug usage
  • Anxiety, hysteria, stress and pain
  • Cirrhosis of the liver
  • Sepsis
  • Elevated body temperature
  • Hypoxia
42
Q

how is respiratory alkalosis diagnosed?

A

• May be suspected based on symptoms
• Blood sample to test for pH and ABGs to confirm the diagnosis
o pH will be elevated above 7.44. paCO2 in the blood will be low, usually under 35 mmHg.

43
Q

how is respiratory alkalosis treated? give examples

A

correcting the condition causing the alkalosis
• Hyperventilation syndrome bc of anxiety - get patient to breathe into a paper bag
o By rebreathing breathed air, patient inhales more CO2 than normal
• Antimicrobials to treat pneumonia or other infections
• Other medications to treat fever, seizures, or irregular heart beats
• Treatment for poisoning if alkalosis related to drug overdose
• Use of mechanical ventilation may be necessary

44
Q

what is type 1 respiratory failure?

A

Hypoxic (Pa O2 <60 mm Hg) with normal or low PCO2

45
Q

what is type 2 respiratory failure?

A

Hypercapnic (PaCO2 >50 mm Hg) with or without hypoxia

46
Q

what are 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)
  • Can occur with all disease of the lungs which involve fluid filling or collapse of alveoli. E.g. pulmonary edema, pneumonia, and pulmonary hemorrhage
47
Q

what is the most common type of respiratory failure?

A

type 1

48
Q

why does a patient become hypercapnic when they become hypoxic?

A

This is bc CO2 diffuses out more easily than O2 diffuses in – steeper concentration gradient between the blood and the alveoli

49
Q

what is the ventilation perfusion ratio?

A

match between ventilation of a lobe and blood flow through it

50
Q

what is the healthy mechanism for a poorly ventilated lobe?

A

capillaries and arterioles constrict = reduced blood flow

o Healthy adaptive mechanism bc it redirects blood away from poorly ventilated regions to better ventilated ones

51
Q

define anion gap

A

difference between the concentrations of the main cation sodium* and the main anions chloride and bicarbonate in the plasma

52
Q

why are there less anions than cations?

A

Less anions than cations bc some anions aren’t measured e.g. lactate

53
Q

what causes a high anion gap?

A

loss of plasma bicarbonate – usually due to elevated levels of anions like lactate, beta-hydroxybutyrate and acetoacetate
• A high anion gap normally indicates metabolic acidosis

54
Q

what happens if a patient’s bicarbonate is low but the cholride levels are high? when does this occur?

A

patient may have a normal anion gap but still be unwell

- Occurs in GI loss of bicarbonate bc of vomiting/diarrhoea or renal loss of bicarbonate bc of renal damage

c2 (37 decks)

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