Flashcards in Hypoxia And Respiratory Failure Deck (30)
What is hypoxia?
Oxygen deficiency at tissue level
Name the different types of hypoxia
Describe hypoxaemic hypoxia
Caused by respiratory failure
Poor oxygenation in the lungs
Describe anaemic hypoxia
Insufficient oxygen bound to Hb
Describe stagnant/circulatory hypoxia
Poor perfusion to regional arteries
Reduced oxygen delivery
Can be global or local
Describe cytotoxic hypoxia
Problem getting oxygen into tissues and using it in these cells
Eg. Cyanide poisoning
Normal partial pressure of oxygen but insufficient haemoglobin
What is the normal range for oxygen saturation?
94 - 98%
What is the normal range for partial pressure of oxygen?
11.1 - 14.4 kPa
Tissue damage is most likely to occur when oxygen sats or partial pressure oxygen falls below ...
Oxygen sats < 90%
Partial pressure O2 < 8kPa
Describe a type 1 respiratory failure
Partial pressure of oxygen arterial blood low (<8)
Oxygen sats <90%
But carbon dioxide levels are normal or low
(Type 1 affects 1 - oxygen)
Describe a type 2 respiratory failure
Partial pressure of oxygen in arterial blood <8
Oxygen sats <90%
And partial pressure of CO2 is high
What is the normal partial pressure range for CO2 in plasma?
4.3 - 6.4 kPa
What are the 3 general mechanisms of respiratory failure?
Ventilatory failure - unable to move sufficient air in and out
Poor diffusion across alveoli
(More than one mechanism may be operating in a given disease)
Give examples of things that cause hypoventilation
Give some causes of chronic type 2 respiratory failure
Late stages COPD
What is a flail segment?
Segment of the chest wall where multiple ribs are fractured in 2 places
During inspiration the segment gets sucked inwards
Preventing adequate lung expansion
What are the acute effects of type 2 respiratory failure?
Partial pressure CO2 rises, oxygen falls
Central chemoreceptors stimulated - increase in ventilation
Unable to completely correct due to disease causing
Assisted ventilation needed
What is the commonest cause of Type 2 resp failure?
Acute exacerbation of COPD
Give some examples of how diffusion is compromised in certain resp diseases
Lung fibrosis - increased thickness of membrane
Emphysema - surface area decreased
How do we work out AVR?
(Tidal volume - dead space) x resp rate
What happens to resp system in a PE?
Reduced blood flow to an area (V/Q > 1)
Blood diverted to other parts of the lungs
More blood available than can be used (V/Q <1)
Other than respiratory failure, name some consequence of a massive PE
Acute right heart failure (increased resistance in pulmonary circulation)
Reduce cardiac output - circulatory collapse
How do we manage respiratory failure?
Treat cause of the failure
Oxygen therapy - improve hypoxia
In type 2, problem of hypercapnia often requires assisted ventilation
Give some clinical features of hypoxia
What is cyanosis?
Bluish discolouration of skin and mucous membranes due to the colour of desaturated Hb
Present if >50gm/L desaturated Hb in blood
What are the effects of chronic hypoxia?
Increased EPO causing elevated Hb levels
Increased 2,3 - BPG in RBCs
Hypoxia vasoconstriction of pulmonary arterioles
(Pulmonary hypertension, RH failure, cor pulmonale)
Give 2 clinical signs of chronic hypercapnia
What happens to the chemoreceptors in chronic hypercapnia?
CSF acidity corrected by addition of bicarbonate by the choroid plexus cells
Now reset to a higher partial pressure of CO2
Peripheral chemoreceptors remain sensitive to hypoxia
Respiration is now driven by hypoxia