Walsh: Perinatal and Pediatric Respiratory Care, 3rd Edition

Chapter 13: Aerosols and Administration of Medication

Answers to Assessment Questions and Clinical Scenarios

1.	C
Rationale: Reduction in efficiency may result in infants receiving weight-appropriate dosing compared with adults. For example, a deposition efficiency of 0.5% of a standard dose of albuterol sulfate (2500 µg) would result in a lung dose of 12.5 µg, or 6.25 µg/kg for a 2-kg infant, whereas a 70-kg adult with 10% deposition has a lung dose of 250 µg, equivalent to 3.6 µg/kg.
2.	D
Rationale: Fok and colleagues measured radioaerosol deposition of salbutamol by jet nebulizer and pressurized metered dose inhaler (pMDI) in ventilated and nonventilated infants with bronchopulmonary dysplasia, finding less than 1% of dose delivered to the lung in all cases (see Figure 13-3). Delivery of aerosol was low for all delivery systems, and similar whether or not subjects were intubated, with considerable variability across patients. Lung deposition in the ventilated infants was similar to those obtained from previous in vitro, in vivo animal, and indirect human studies.
3.	B
Rationale: Gas density affects both aerosol generation and delivery of aerosol to the lungs, especially with low-density helium–oxygen mixtures. The lower the density of a carrier gas, the less turbulent the flow, which theoretically decreases aerosol impaction, allowing more aerosol to pass beyond an obstructed airway. This is true with virtually any aerosol, with high-concentration heliox increasing aerosol delivery by as much as 50%. Heliox concentrations as low as 40% can improve aerosol delivery. When using heliox to drive a jet nebulizer, the aerosol output is much less than with air or oxygen, requiring double the flow to produce a comparable output of respirable aerosol per minute. Thus, although helium can increase the amount of aerosol reaching the lungs, it impairs the production of aerosol from jet nebulizers.
4.	E
Rationale: The small-particle aerosol generator (SPAG) (Valeant Pharmaceuticals International) is a jet aerosol generator used to nebulize the antiviral agent ribavirin (see Figure 13-6). The SPAG incorporates a secondary drying chamber that reduces the mass median aerodynamic diameter (MMAD) to 1.2 µm, with a geometric standard deviation (GSD) of 1.4 and relatively high output. The SPAG reduces the 50 psi of line pressure medical gas to 26 psi, which is connected to two flowmeters controlling flow to the nebulizer and the drying chamber. As the aerosol leaves the medication reservoir, it enters the long cylindrical drying chamber, where additional flow of dry gas reduces the size of the aerosol particles through evaporation.
5.	B
Rationale: The suggestion that pMDIs can be tested for drug remaining by floating the canister in water has proven not to be accurate and to compromise performance for the pMDI. It is more accurate for the patient or parent to note when the medication was started, the number of doses to be taken each day, and the number of doses in the canister, and from this information to calculate a discard date.
6.	A
Rationale: The peak inspiratory flow rate of children is limited and associated with age, making it unlikely that a child less than 6 years old could reliably empty a DPI requiring greater than 50 L/minute (see Figure 13-12).
7.	E
Rationale: Because of this fact, patients should use only one type of aerosol-generating device for inhalation therapy to simplify things. The technique of using each device is different, and repeated instruction is necessary to ensure that the patient uses the device appropriately. The use of different devices for inhalation can be confusing for patients and may decrease their compliance with therapy. This has been referred to as “device dementia.”
8.	E
Rationale: See Emergency Bronchodilator Resuscitation in text.
9.	A
Rationale: In mechanically ventilated patients the ventilator circuit and endotracheal tube (ETT) act as baffles that trap particles with larger diameter en route to the bronchi, and hygroscopic particles might increase further in size in the ventilator circuit. Wide variability exists in the MMAD of aerosols produced by different brands of nebulizers. Nebulizers producing aerosols smaller than 2 µm MMAD are likely to produce greater deposition in the lower respiratory tract of ventilator-supported patients.
10.	E
Rationale: Insulin was one of the first medications to be administered by aerosol. Because of the nebulizer and insulin formulation available at that time, absorption and efficacy were highly unpredictable. This has changed dramatically with the development of ultrafine particles and aerosol devices that can efficiently and reliably target the alveolar space.