Hypercarbia Flashcards
(21 cards)
Normal PaCO2 levels
36-44mmHg
Hypoxemia
abnormally low PaO2 (low oxygen content in the blood)
Hypoxia
tissue oxygenation inadequate to meet metabolic needs
Factors contributing to hypoxia:
- low FiO2
- hypoventilation
- diffusion abnormalities
- dead space ventilation
- shunting
Dead space vs shunting
- Dead space ventilation = ventilation without perfusion
- Shunting = perfusion without ventilation
hypercarbia
Hypercarbia reflects inadequate ventilation and / or increased CO2 production
How hypercapnia causes marked physiological effects:
- CO2 crosses lipid barriers
- Acidosis
- Enzyme functions imparied
Sensors, controllers, effectors of hypercarbia
Sensors
- chemical chemo-R
- peripheral chemo-R
- other
Controllers
- higher CNS
- Pain
- Voluntary control
- Temp
Effectors
- muscles of insp and exp
- accessory mm
- abdominal mm
Centrol sensors of hypercarbia
Medulla = respond to changes in [H+] in the adjacent brain ECF
CO2 can cross the BBB leading to immediate changes in the [H+]\
The pH changes will stimulate the respiratory centre to inc minute vol
Peripheral sensors of hypercarbia
- Aortic- and carotid bodies
- Respond to changes in PaO2
- Also responds to PaCO2 and pH
Other sensors
- Stretch receptors in lungs!
- Irritant receptors
- J receptors
- Muscle- and joint receptors
PaCO2 vs PACO2
- PACO2 = partial pressure of CO2 in the alveoli
- PaCO2 = partial pressure of CO2 in arterial blood
PEtCO2
- PEtCO2 = partial pressure of CO2 at the end of expiration
Causes of increased carbon dioxide production (VCO2):
- Sepsis
- Fever
- Malignant hyperthermia
- Thyrotoxicosis
- Shivering
- Convulsions
Neurogenic causes ofo hypoventilation
o CVA
o Encephalopathy
o Hypothermia
o Prematurity
CNS effects of hypercarbia
- Cerebral vasodilatation
- Increased CBF … NB to control this in head injury patients as they can’t afford a further increase in CO2 (every 1 mmHg increase in CO2 = 4% increase in CBF)
- Increased ICP
- Trigger chemoreceptor stimulation of ventilation
- Sympathetic stimulation
- Hypoxia also affect CNS
- Central depression at very high levels
- During recovery they must CO2 to get the patient to have a respiratory drive but >60mmHg = CO2 narcosis thus there is a fine balance
Sx of hypercarbia
- Disorientation / confusion
- Headache
- Mentally obtund blunted
- Focal neurological signs
- Coma
CVS effects of hypercarbia
o Increased CBF
o General peripheral vasodilatation
o Depressed myocardial contractility
o Increased risk of arrhythmias
o Sympathetic stimulation
- Warm & flushed
- Sweaty
- Tachycardia with bounding pulses
Hypercarbia under anaesthesia sx
- Hypertension
- Hypotension
- Tachypnoea (in absence of muscle relaxant)
- Tachycardia
- Dysrhythmias
Sx of HYPOcarbia
- Hyperventilation
- Intracellular alkalosis (decr H+ ions)
- decr cardiac output
- decr cerebral blood flow
- Respiratory depression
- left shift of oxyhaemoglobin curve
