College Answer

Consideration  should  be  given  to  pharmacodynamics  (dose  requirements,  side  effect  profile, effectiveness),  as  well  as  cost  and  other  interrelated  effects.     Methods  of  delivery  include intravenous, sub-cutaneous, via metered dose inhaler and via nebuliser.

Intravenous: excellent systemic delivery assured, but to areas that are perfused.  Systemic effects maximal so side effects are more pronounced.

Sub-cutaneous: easy to administer, but less predictable effects as delayed peak effect and lower bioavailability.  Systemic side effects still prominent.

Metered dose inhaler: easy to administer via adapter; many multiples of non-

intubated dose are required [eg. 10 puffs per treatment]; does not require breaking of ventilatory circuit; very low bioavailability, optimal via inline spacer (but adds cost, breaks circuit at least once, may become reservoir for infection); minimal systemic side effects.

Nebuliser:  can  be  given  continuously;   maximises  local  delivery  while  minimising  systemic absorption; easy to administer but requires specific equipment; requires break in circuit for each treatment; variable interaction with ventilator [some cannot compensate for flow].

Discussion

Prior to reading this question, I was not aware that beta-2 agonists could be given subcutaneously.Turns out, people have done this to infants, and "no local or general adverse reactions were observed".