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CI1 > Respiratory Physiology & Impaired Gas Exchange > Flashcards

Respiratory Physiology & Impaired Gas Exchange Flashcards

1
Q

What is dead space?

A

Where gas exchange is not being undertaken

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2
Q

What are the two types of dead space?

A

Anatomical: In conducting airways, e.g. trachea
Alveolar: Alveoli that aren’t being exposed to blood flow so don’t contribute to gas exchange

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3
Q

What makes up the majority of dead space?

A

Anatomical, only very small amount of alveolar dead space

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4
Q

What is reduced alveolar ventilation associated with?

A
  • Rapid shallow breathing

- Increased physiological dead space

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5
Q

True or false: The distribution of air in the lungs is not equal

A

True

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6
Q

Why is the distribution of ventilation uneven within the lung?

A
  • Varying pleural pressures from the bases to the apices (interaction with lung compliance)
  • Patterns of respiratory activation
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7
Q

When you take a breath in, where does most of the air go?

A

The base of the lungs, i.e. it is not evenly distributed

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8
Q

Why is the intrapleural pressure less negative at the base than the apex?

A

Because of the weight of the lungs

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9
Q

In what area of the lungs do the alveoli expand the most?

A

At the apex, because of the differences in pleural pressure

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10
Q

What is the relationship between volume and lung compliance?

A

At higher volumes the lung becomes stiffer

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11
Q

How is blood flow distributed across the lungs?

A

More blood flow at the base, decreases as it gets higher due to gravity and pressures from the surrounding alveoli

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12
Q

What is the relationship between ventilation and perfusion and what does it mean?

A
  • Ratio of air reaching the alveoli to blood reaching the alveoli via capillaries
  • Greater at the apex
  • Blood coming from different parts of the lungs have different levels of oxygenation
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13
Q

What 3 main respiratory problems can physio treat?

A
  • Shortness of breath (dyspnoea)
  • Difficulty clearing sputum
  • Lung collapse (atelectasis)
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14
Q

What two factors determine oxygen delivery to the tissues?

A
  • Content of oxygen in arterial blood (CaO2)
  • Cardiac output (CO)

Delivered O2 = CO x CaO2

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15
Q

What are the two ways oxygen is delivered to tissues?

A
  • Bound to haemoglobin (Hb) in red blood cells

- Dissolved in plasma

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16
Q

What is hypoxia?

A

Inadequate oxygen delivery to tissues

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17
Q

What are the signs of severe generalised hypoxia?

A
  • Reduced level of consciousness (LOC)
  • Seizures
  • Coma
  • Death
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18
Q

What are the signs of hypoxia?

A
  • Cyanosis (blueish discolouration)
  • Tachycardia & hypertension
  • Shortness of breath & tachypnea
  • Restlessness & confusion
  • Sweating
  • Pallor
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19
Q

What are the causes of hypoxia?

A
  • Reduced CO or perfusion
  • Dysoxia (disruption of cell enzymes)
  • Haemoglobin deficiency
  • Hypoxaemia (decreased partial pressure of oxygen in arterial blood, PaO2)
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20
Q

What are the normal haemoglobin ranges?

A

Females: 11.5-16 g/100mLs
Males: 13-18 g/100mLs

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21
Q

How is hypoxaemia defined?

A

Decreased partial pressure of oxygen in arterial blood PaO2 < 80mmHg

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22
Q

What is hypoxaemic respiratory failure?

A

PaO2 < 60mmHg

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23
Q

What is the normal PaO2 in arterial blood?

A

80-100mmHg

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24
Q

What is the effect of ageing on PaO2?

A

PaO2 decreases as a normal function of age

25
Q

How does PaO2 and PaCO2 change at gas exchange?

A

Venous PaO2: 40mmHg
Arterial PaO2: 100mmHg

Venous PaCO2: 46mmHg
Arterial PaCO2: 40mmHg

26
Q

During inspiration, why does PaO2 decrease between the atmosphere and the alveoli?

A

Due to moisture in the airways

27
Q

What is the normal arterial percent O2 saturation (SaO2)?

A

95-100%

28
Q

What happens at PaO2 of 60mmHg?

A 
SaO2 is approx 90%
Oxygen content (CaO2) falls rapidly below SaO2 of 90%
29
Q

What happens with decreased affinity of O2 for Hb?

A
  • Right shifted curve
  • Favours O2 unloading
  • Acute acidosis
  • High CO2
  • Increased temp
  • Abnormal Hb
30
Q

What happens with increased affinity of O2 for Hb?

A
  • Left shifted curve
  • Favours O2 loading
  • Acute alkalosis
  • Decreased PCO2
  • Decreased temp
31
Q

What is FiO2?

A

Fraction of inspired oxygen, normal level is 0.21 (21% or room air)

32
Q

How is oxygenation assessed in clinical practice?

A
  • Clinical examination
  • Arterial blood gases
  • Pulse oximetry
33
Q

What are pulse oximeters?

A

Non-invasive measure of oxyhaemoglobin saturation (SpO2) and heart rate
Normal values same as SaO2

34
Q

What can give a pulse oximeter a false high?

A
  • HbCO
  • Nail polish
  • Dark skin pigmentation
35
Q

What are arterial blood gases (ABGs)?

A

Gold standard measure of the integrity of the respiratory system

36
Q

What do ABGs measure?

A
  • pH
  • PaCO2
  • PaO2
  • HCO3 (bicarbonate)
  • BE (base excess)
  • SaO2 (O2 haemoglobin saturation)
37
Q

What are the normal ABG values?

A
  • pH 7.35-7.45
  • PaCO2 35-45mmHg
  • PaO2 80-100mmHg
  • HCO3 22-28mmol/L
  • BE -3 to +3
  • SaO2 95-100%
38
Q

What does enzymatic activity rely on?

A

Closely regulated hydrogen ion activity

39
Q

What is the role of the kidneys in acid elimination?

A
  • Excrete the non carbonic acid that is produced by metabolism
  • Reabsorb bicarbonate to maintain acid-base balance
  • Regulate pH by changing HCO3 levels
40
Q

What is respiratory acidosis and when can it occur?

A

Hypoventilation (shallow breaths)

  • Overdose of sedative
  • Depression of respiratory drive during sleep
  • Respiratory fatigue
41
Q

What is respiratory alkalosis and when can it occur?

A

Hyperventilation

  • Emotional stress/anxiety
  • Fever
  • Pain
  • Hypoxia at altitude
  • Asthma
42
Q

What is metabolic acidosis and when can it occur?

A

Accumulation of fixed acids

  • Renal failure
  • Ingestion of toxins
  • Uncontrolled diabetes
  • Severe diarrhea
43
Q

What is metabolic alkalosis and when can it occur?

A

Accumulation of bicarbonate

  • Vomiting
  • Nasogastric drainage
  • Diuretics
44
Q

What are the physiological causes of hypoxaemia?

A
  • Ventilation/perfusion mismatch
  • Hypoventilation
  • Diffusion impairment
45
Q

What is an anatomical shunt?

A

When blood passes into the arterial system without going through the ventilated areas of the lung (V/Q = 0)

46
Q

What is V/Q mismatch the most common cause of?

A

Hypoxaemia

47
Q

What conditions cause V/Q mismatch?

A
  • COPD
  • Pneumonia
  • Asthma
  • Ageing
  • Pulmonary oedema
48
Q

What are examples of when a shunt occurs?

A
  • Atelectasis (collapse)
  • Pulmonary oedema
  • Pneumonia
49
Q

When does hypercapnic respiratory failure occur?

A

PaCO2 > 50mmHg

50
Q

How is CO2 transported?

A
  • Dissolved in physical solution (8%)
  • Chemically combined with protein (12%)
  • Ionised as bicarbonate (80%)
51
Q

What is hypercapnia?

A

Elevated CO2

52
Q

What are the physiological causes of hypercapnia?

A
  • Decreased minute ventilation (MV)
  • Ventilation/perfusion mismatch
  • Increase CO2 production in the setting of fixed ventilation
53
Q

What are the clinical signs of hypercapnia?

A
  • Altered mental state (lethargy, drowsiness)
  • Headache
  • Tachycardia
  • Hypertension
  • Sweating
  • Vasodilation
  • Dyspnea
  • Muscle tremor
54
Q

Where does equilibration not occur?

A

Between the PO2 in the alveolar gas and the pulmonary capillary blood

55
Q

What are examples of diffusion impairment?

A
  • Diffuse interstitial fibrosis
  • Asbestosis
  • Sarcoidosis
56
Q

How is impaired gas exchange managed?

A
  • Treat underlying cause
  • Manage complications
  • Correct acid/base balance
  • Provide O2
57
Q

What are the indications for home O2?

A
  • Nocturnal O2 (SpO2 <88%)
  • Terminally ill
  • Role in exercises as supplement
  • Arterial PaO2 < 55mmHg on room air, rest & awake
  • Daytime PzO2 55-59mmHg, hypoxic organ damage/heart failure
58
Q

What are the adverse effects of O2?

A
  • O2 toxicity (high levels of O2 for long periods)
  • Depression hypoxic drive
  • Absorption atelectasis
  • Impaired mucus clearance (drying of mucus)
  • Retrolental fibroplasia (blindness)
  • Fire

CI1 (21 decks)

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