hypercapnia and hypoxia

Question 1

causes of hypoxia

Answer 1

reduced oxygen inspired
- BOAS
- altitude = lower atmospheric pressure = decreased partial pressure of O2 = PAO2 lower)
- hypoventilation (as PACO2 increases PA O2 decreases)

cannot get O2 to lungs
- can be due to equipment failure in anaesthesia)
- URT obstruction
- pneumothorax (air reaches lungs but escapes into pleural space and cant participate in gas exchange

Reduced systemic O2
- anemia
- heart disease
- hypovolemia
- extreme vasoconstriction
- sepsis

O2 cannot bind to Hb and/or O2 cannot get off Hb
- smoke inhalation

cannot get O2 into blood
- VQ mismatch
- intramulmonary shunts
- diffuse intersitial disease

Question 1

causes of hypercapnia

Answer 1

• hypoventilation
• hyperthermia
• respiratory depression
• lung pathology
• increase in metabolic CO2 production (rare)

Question 2

responses to and signs of hypoxia/hypoxaemia

Answer 2

normal physiological:
- normal drive to ventilation is increased CO2
- at 10% increase in CO2 doubles ventilation even ifoxygen levels are normal
- oxygen levels must drop by 40% before respiratory rate increases
- mild hypoxia without hypercapnia has little effect on breathing

why is it bad:
- decreases brain function including ventilation
- decreases cardiac function including output
- masde worse where there is concurrent hypercapnia
- cardiac dysrhythmia
- cardiac arrest

signs
- tachypenea
- increased resp effore
- tachycardia
- patients unable to compensate for hypoxaemia may not show outward evidence of resp distress due to resp muslce weakenss
- cyanosis may be detected by the human eye is hypoxia is particularly bad
- obtundation or coma may occur in patients with prolonged uncompensated hypoxaemia
- death

Question 3

effects of hypercapnia

Answer 3

• shortness or breath
• muscle tremors
• tachycardia
• high BP
• sweating
• unconsciousness

Question 4

management of hypoxia and hypercapnia

Answer 4

• clinical assessment (unreliable as signs coincide with numerous conditions)
• capnography (tells us about hypoventilation, approximate PAO2 and PACO2)
• blood gas analysis to measure Pa CO2, PaO2, pH, electrolytes, lactate, etc
• pulse oximetry
• increase O2 supply (careful with O2 boxes as can overheat)
• manage underlying disease (heart failure, IV fluid for hypovolaemia, ventilate)
• DO NOT use respiratory stimulants

Question 5

define cyanosis

Answer 5

the blueish/purplish discolouration of the skin or mucous membranes due to the tissues near the skin surface having low O2 saturation
- indicates severe hypoxaemia
- an emergency

Question 6

what is the difference between hypoxia and hypoxaemia

Answer 6

hypoxia: reduced oxygen in tissues
Hypoxaemia: reduced oxygen in the blood

Question 7

what is hypoxic pulmonary vasoconstriction

Answer 7

a physiological phenomenon in which small pulmonary arteries constrict in the presence of alveolar hypoxia. by redirecting blood flow from poorly ventilated lung regions to well ventilated lung regions, HPV is though to be the primary mechanism underlying ventilation/perfusion matching

Question 8

how does the respiratory system regulate pH

Answer 8

Question 9

what is hypercapnia

Answer 9

an elevation in CO2 in arterial blood above the normal range (35-45 mmHG)

Question 10

why is hypercapnia bad

Answer 10