Pharmacokinetics of inhaled drugs
[Ref: SH4:p23]
Important phases
- Absorption from alveoli into blood
- Distribution in body
- Metabolism
- Elimination (principally via lung)
Age-related changes
In elderly:
- Vd is increased
* Decreases in lean body mass
* Increases in body fat
- Clearance is decreased
* Decreased hepatic function
* Decreased pulmonary gas exchange (secondary to lower metabolic rate)
- Tissue perfusion decreasd and regional blood flow altered
* Decreased cardiac output
Delivery of anaesthetics to brain
Brain is the target organ
PA <=> Pa <=> Pbr
NB:
- PA = alveolar partial pressure
- Pa = arterial partial pressure
- Pbr = partial pressure at brain
