Hypoxia and respiratory failure Flashcards
basic concepts to refresh memeory
Define hypoxia
reduced oxygen as tissue level.
Abnormalities occurring at any point on the oxygen supply chain can result in hypoxia
Hypoxaemia
decrease in the pO2 in the blood.
what is Respiratory failure ?
is considered to exist when the arterial pO2 falls below 8kPa (60 mmHg) when breathing air at sea level.
Types of resipiratory failure and conditions what leads to each
Type 1 respiratory failure is characterised by a low pO2 (< 8kPa) with a normal or low PCO2.
Type 2 respiratory failure is characterised by a low pO2 (< 8kPa) and a high pCO2 of > 6.7 kPa (50 mmHg)
what happens to BV in response to hypoxia? hypercapnia?
hypoxic vasoconstriction
hypercapnia> peripheral vasodilation> bounding pulse
Effects of Hypoxia
- Impaired CNS function
- Central cyanosis (bluish discolouration of the mucous membranes due to low Hb)
- Cardiac arrhythmias
- Hypoxic vasoconstriction of pulmonary vessels
Effects of Hypercapnia
- Respiratory acidosis
- Impaired CNS function: drowsiness, confusion, coma, flapping tremors
- Peripheral vasodilatation –warm hands, bounding pulse
- Cerebral vasodilation - headache
Cyanosis
types
is defined as the bluish or purplish discolouration of the skin or mucous membranes due to the tissues near the skin surface having low oxygen saturation.
which factors are needed to maintain arterial pO2 in the normal range?
- Normal inspired pO2
- Normal alveolar ventilation
- Ventilation Perfusion matching
- Normal alveolar capillary membrane
- Cardiac output from the right heart needs to pass through gas exchanging alveoli (i.e. there should be no right to left shunts)
how much is the amount of air we move in and out in one second?
alveolar ventilation: approz 5L
causes of Low inspired O2?
high altitudes where the atm p. is less than 101 kPa
(e.g. acute mountain sickness) develop hypoxaemia > due a low inspired pO2 level.
The resulting stimulation of the peripheral chemoreceptors causes hyperventilation with an increase in CO2 washout.
The end result is a low pO2 and a low pCO2.
Type 1
People who live at high altitudes have numerous physiological adaptations to survive in low O2 conditions, name them.
polycythaemia,
increased red cell 2-3 BPG
increased capillary density in tissues
Causes of hypoventilation
whcih type of respiratory failure will it cause?
- Respiratory centre depression e.g. Head injury, drug overdose
- Respiratory muscle weakness > due to damage/disease of any part of nerve pathways from the respiratory centre to the muscles of respiration – ( e.g. Brain stem /spinal cord / intercostal nerves /phrenic nerve/NMJ /Muscle disease)
- Chest wall problems (mechanical problems) e.g. Scoliosis/ kyphosis, morbid obesity, rib fractures
- Hard to ventilate lungs due to severe lung fibrosis, or widespread severe airway obstruction (life threatening asthma, late stages of COPD),
ALWAYS TYPE 2
Most common cause of CHRONIC type 2 respiratory failure
SEVERE COPD
difference btw acute and chronic hypoventilation
acute: needs urgent treatment
Chronic: body ahs time to compensate! YAAY> therefore better tolerated!
how does chronic hypoxia effect arterioles? what will it eventually lead to?
Hypoxia induced vasoconstriction of pulmonary arterioles which eventually leads to pulmonary hypertension >
Right heart failure (Cor pulmonale) due to pulmonary hypertension.
4 Effects of chronic hypoxia
- Polycythaemia (↑Hb level) due to increased EPO secretion by the kidney, increases O2 carrying capacity of blood,
- Increase in red cell 2,3, BPG levels which allows better unloading of O2.
- Hypoxia induced vasoconstriction of pulmonary arterioles which> eventually leads to pulmonary hypertension
- Right heart failure (Cor pulmonale) due to pulmonary hypertension.
how does chronic hypercapnia effect on central chemoreceptors:
CO2 diffuses in to CSF> CSF pH drops > stimulates central chemoreceptors> choroid plexus imports HCO3- into the CSF.
This restores the CSF pH to normal and results in the central chemoreceptors being ‘reset’ (adapted) to the higher CO2 level
it what ways can treatment of hypoxia in patients with chronic type 2 respiratory failure worsen hypercapnia?
(2 reasons)
so how is it treated?
- giving O2 would eliminate the hypoxemia> which was driving the respiratory centers to work!> alveolar ventilation can drop this way causing hypercapnia to get worse!
- Correction of hypoxia removes pulmonary hypoxic vasoconstriction leads to increased perfusion of poorly ventilated alveoli, diverting blood away from better ventilated alveoli.
although oxygen is life saving!>> it must be given > bs CO2 has to be monitered ya alaaa
what is the is the most common cause of hypoxaemia ?
V/Q mismatch
Gas exchange is optimal when alveolar ventilation and perfusion are matched, with V/Q ratio ≈ ?
1
Ventilation-perfusion mismatch can occur in 2 ways :
(a) Ventilation is reduced (while perfusion of the affected area is normal)
(b) Perfusion is reduced (while ventilation of the affected area is normal).
conditions where Ventilation is reduced
These alveoli have a low V/Q ratio, which result in a low pO2. Common causes of reduced ventilation include
- asthma (early stages),
- COPD (early stages),
- pneumonia,
- respiratory distress syndrome of new-born (some alveoli are not expanded due to lack of surfactant).
conditions where Perfusion is reduced ?
This is usually due to pulmonary embolism. The affected alveoli are poorly perfused due to obstruction, and the blood is diverted to unaffected parts of the pulmonary circulation. If this extra blood flow (increased perfusion Q) cannot be not matched by the ventilation (V) of these alveoli, the reduced V/Q ratio causes a drop in paO2.
what is the outcome of a V/P mismatch
causes a drop in pO2 (and an initial rise in pCO2) which stimulates hyperventilation. This results in increased CO2 removal from unaffected alveolar units. The end result is a pCO2 which is normal or low.
However hyperventilation of unaffected areas cannot compensate for the hypoxaemia. bc normally O2 is loaded up w/ 100% saturation! so extra amount of P02 CANNOT LOAD THE O2 FURTHER! bs khala9, o2 has a certain limit ya jima3a!
explain V/P mismatcn in PE
and what the end result is
how can u get diffusion imparment? name condisiton that lead to diffuision impairment!
if the barrier is thicker>> lung fibrosis
diffusion pathway lengthens>> pulmonary oedema (where the extra layer fluid increase the distance across which gases have to diffuse. )
total area available for diffusion is reduced> emphysema,
what is affected more by any change to the diffusion barrier. ? O2 or Co2? why?
O2 diffuses much less than CO2,
and so O2 is always affected more by any change to the diffusion barrier.
Therefore diffusion impairment causes
Type 1 Respiratory failure with hypoxia with a normal or low PCO2.
Type 1 respiratory failure may eventually progress to type 2 failure as the disease progresses.
give exmaple
Asthma!
starts o as type 1, cuz u still have healthy bits oflung left to allow compensation, but as the disease progresess……
ur lungs cant compensate and evetually u’;; get TYPE 2
with Low Po2 and high CO2
Guillain–Barre syndrome.
Guillain–Barre syndrome.
symptoms
