Lecture 1 - Respiratory Pathophysiology 1 Flashcards
Respiratory failure definition?
when the lungs fail to adequately oxygenate the arterial blood and/or fail to prevent undue CO2 retention
Hypoxia?
PaO2 < 8kPa (60mmHg) - type I respiratory failure
Hypercapnia?
PaCO2 > 6.6kPa (50mmHg) - type II respiratory failure
Causes of hypoxaemia?
reduced PiO2 (e.g. altitude), hypoventilation, V/Q mismatch, R-L shunt, diffusion
Oxygen cascade?
atmospheric -> upper airway -> alveoli (influenced by pleural pressure and aCO2) -> capillaries (gas exchanged w influences) -> arteries -> tissues (big drop)
Partial pressure of oxygen (PaO2)?
pressure that is exerted by oxygen when you have a mixture of gases
Oxygen content (CaO2)
Amount of O2 bound to Hb + amount of O2 dissolved in blood (mL/dL)
Oxygen saturation?
Fraction of oxygen saturated Hb relative to total Hb (saturated & unsaturated)
Alveolar hypotension sign and causes?
PaCo2 rise; decreased brainstem respiratory drive (drugs), neuro-muscular incompetance (polio, mayasthenia gravis), abnormal load (related to work of respiratory muscles e.g. obesity, kyphosis
Causes of hypercapnia?
alveolar hypotension or V/Q mismatch
Alveolar ventilation?
inversely proportional to Pa CO2, minute ventilation = alveolar ventilation + dead space ventilation; pathology involves increase in minute but decrease in alveolar due to increase in ded space
Influences on PAO2?
Patm, FiO2, PH2O, PACO2`
Respiratory quotient?
R/RQ, ratio of CO2 produced by the body to oxygen consumed by the body, approx. 0.8
A-a gradient calculation?
20 - (PaCO2/0/8) - PaO2 = 1-2kPa; young healthy can be less than 1, range widens through age due to V/Q mismatch
Diffusion depends on?
area, thickness, driving pressure (capillary volume) and solubility and molecular weight of gas (Hb)
Why use CO?
diffusion (and not perfusion limited), soluble, avidly binds Hb therefore no back pressure
Diffusion equation?
Vgas = (solubility/sqrtMW) x (area/thickness) x (PA - Pc)
Abnormal diffusion - alveolar capillary block?
interstitial/diffuse lung disease
Abnormal diffusion - loss of diffusing surface area?
alveolar surface area issues e.g. emphysema
Abnormal diffusion - capillary volume/Hb?
affected pulmonary vasculature e.g. pulmonary hypertenion, anaemia, pulmonary embolism
