This has appeared in the ancient Question 12 from the second paper of 2002. The candidates were asked to "compare and contrast the methods of delivery of beta-2 agonists in intubated patients". The college does not limit themselves to nebulisation; however this is the most common method, and will be the focus of this chapter.

LITFL has a good page about it, which does into some detail regarding the various types of nebuliser, and their relative merits.

Advantages of nebulized drug delivery

  • Smaller dose than systemic administration
  • Fewer systemic side effects due to decreased dose.
  • Immediately available to the bronchial suface (an advantage for bronchodilators)
  • Immediate onset of activity
  • Bypasses first-pass metabolism

Problems with nebulising drugs in the ICU

  • Some residual volume may remain in the delivery device
  • The delivery to the lower airways is variable
  • Manual bagging may be required to really "get it in there"
  • Impossible with a HME: saturates the filter
  • Delivery devices can add dead space and resistance
  • Loss of PEEP can occur when circuits are broken to insert devices
  • Amount of drug delivered to the site of maximum activity may be very small, due to the deposition of droplets on the plastic surfaces of artifical airways
  • The pooling of droplets inside airway equipment may result in highly concentrated droplets, which - when they fall and are absorbed though the mucosa - make the dose rate erratic and unpredictable.
  • Gas density affects the efficiency of drug delivery by aerosol particles. Lower viscosity gas mixtures, eg. 30/70 Heliox, are known to improve drug delivery to the alveoli and distal airways.

Available equipment

  • Metered-dose inhalers
  • Spacer devices
  • Swivel tubing
  • In-line ultrasonic nebulisers
  • In-line jet nebulisers

Optimal technique

  • Suction airway secretions
  • Use warmed MDIs (not refrigerated)
  • Coordinate MDI actuation with beginning of inspiration
    • Manual inspiratory bagging may be required
  • Wait at least 15 s between doses

Other methods of administering bronchodilators

Prior to reading Question 12 from the second paper of 2002, 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".

A table of comparison is offered, as it is essentially the tabulated form of the college's own model answer.

Features

Metered dose inhaler

Nebuliser

Intravenous

Advantages

Cheap

Easy to set up

Lowest toxicity

Does not break the circuit

Cheap

Low toxicity

Certainty regarding dose delivery

No need to break the circuit

Disadvantages

Spacer adds dead space into the circuit

Drug precipitation occurs in the upper airways and the tubing

Needs to be timed with ventilator breaths

Unreliable drug delivery to the site of action

Drug precipitation occurs in the upper airways and the tubing

Unreliable drug delivery to the site of action

Greatest toxicity


Undesirable systemic effects, including hemodynamic effects and lactic acidosis

References

Thomas, S. H., et al. "Pulmonary deposition of a nebulised aerosol during mechanical ventilation." Thorax 48.2 (1993): 154-159.

Dhand, Rajiv. "Basic techniques for aerosol delivery during mechanical ventilation." Respiratory care 49.6 (2004): 611-622.