oxygen, respiratory failure and oxygen therapy Flashcards
what is PiO2?
partial pressure of inspired oxygen
what is PaO2?
partial pressure of oxygen in arterial blood
what is PAO2?
partial pressure of alveolar oxygen
what is FiO2?
fraction of inspired oxygen
what is ViO2?
volume of oxygen
what is R?
respiratory quotient
what is PaCO2?
partial pressure of CO2
what is VA?
alveolar ventilation
what is SVP?
saturated vapour pressure - measurement of amount of moisture in the air
what is the oxygen cascade?
the decrease in oxygen as it passes from the atmosphere into the body and into the arterial circulation.
what is the concentration of O2 in the air?
20.94%
what is tracheal gas?
PO2 after humidification
how do you calculate tracheal gas?
fractional concentration of oxygen in the dry gas phase x (barometric pressure – saturated vapor pressure)
what factors affect alveolar gas?
- Hypo or ventilation
- Oxygen consumption
- CO2 production
what is the equation for alveolar gas?
PAO2 = dry barometric pressure x (FiO2 – VO2/ VA).
what is the normal PaO2?
13.6kPa
what determines the alveolar to arterial PO2 difference?
shunting
what is shunting?
an area of the lung that is perfused but not ventilated
what happens to shunting in disease?
in disease, the amount of shunting increases
what is the equation that shows the amount of oxygen delivered to the body in one minute?
(Hb) x Oxygen Saturation of Hb x 1.34 x CO.
1.34 is the oxygen binding capacity of Hb
what is respiratory failure?
= Inadequate gas exchange, meaning that either PaO2 or PAO2 is not maintained at normal levels.
why does oxygen decrease first in respiratory problems?
CO2 is easier to exchange than O2
what are signs of respiratory failure?
- signs of respiratory compensation
- increased sympathetic tone
- end-organ hypoxia
- haemoglobin desaturation
- CO2 retention
what are signs of respiratory compensation?
tachypnoea, use of accessory muscles, nasal flaring, intercostal or suprasternal recession
what are signs of increased sympathetic tone?
tachycardia, hypertension, sweating
what are signs of end organ hypoxia?
altered mental status, bradycardia and hypotension (late)
what are signs of haemoglobin desaturation?
cyanosis
what are signs of CO2 retention?
flap
bounding pulse
what is type 1 respiratory failure?
hypoxia only
why does type 1 respiratory failure occur?
Occurs because of damage to lung tissues. Damage prevents adequate oxygenation of the blood but the normal lung is still sufficient to excrete CO2 made by tissue metabolism.
name examples of type 1 respiratory failure
- Pulmonary oedema
- Pulmonary fibrosis
- Asthma
- Pneumothorax
- Pneumonia
- Obesity
what is type 2 respiratory failure
type 1 with fatigue; hypoxaemia and hypercapnia (PaO2 < 8 and PaCO2 > 6.5).
name types of type 2 respiratory failure
- Drug overdose most common cause
- Severe asthma (fish diagram)
- Poisonings
- Head/cervical cord injury.
what are causes of hypoventilation?
brainstem, metabolic encephalopathy, depressant drugs, spinal cord, nerve root injury, nerve trauma, neuropathy, neuromuscular junction, respiratory muscles, airway obstruction, decreased lung or chest wall compliance
what is the first line of treatment of respiratory failure?
oxygen
what are indications of O2 therapy?
- Respiratory failure
- Cardiac arrest
- Tachypnoea
- Cyanosis
- Hypotension
- Metabolic acidosis
what patients are given oxygen masks with nasal cannula?
patients with normal vital signs
what patients are given face masks with reservoir bags and why?
patients in an emergency - higher O2 concentration
when are venturi masks used?
controlled treatment in long term respiratory failure
what are low flow masks?
nasal cannulase, face mask, mask with reservoir bag
what are high flow masks?
Venturi masks: deliver O2 at a rate above peak IFR, deliver fixed concentration
when should pulse oximetry be started?
should be started immediatel
what is the critical threshold for pulse oximetry?
94%
what is the purpose of arterial blood gases?
Used to keep the FiO2 (fraction of inspired O2) at a minimum required to achieve adequate O2
why is oxygen toxic?
produces free radicals that can damage the body
in how many COPD patients will the CO2 go up if given O2?
10%
what treatment do you give if the CO2 retention isnt known?
o Start high flow of oxygen.
o Monitor for drowsiness.
o Check ABG after 30 minutes.
what treatment is given if CO2 retention is known?
o Set up a controlled mask.
o Titrate for lowest possible O2.
o Measure ABG as soon as possible.
o Repeat ABG 30 minutes later.
what is ventilation used for?
- Not for hypoxia
* Used for hypercapnia (due to hypoventilation).
