Aerosol Therapy in Mechanically Ventilated Patients: Recent Advances and New Techniques

Abstract

Therapeutic aerosols are commonly used in mechanically ventilated patients, yet information regarding their efficacy and optimal technique of administration has been limited. The advantages of aerosol therapy include a smaller dose, efficacy comparable with that observed with systemic administration of the drug, and a rapid onset of action. Inhaled drugs are delivered directly to the respiratory tract, their systemic absorption is limited, and systemic side effects are minimized. Inhaled bronchodilators are routinely used with mechanically ventilated patients in the intensive care unit, but a variety of drugs ranging from antibiotics to surfactants has been administered. Nebulizers and metered-dose inhalers (MDIs) are commonly used aerosol generators because they produce respirable particles with a mass median aerodynamic diameter (MMAD) between 1 and 5 mum. Due to the limitation of available formulations, MDIs are chiefly used to deliver bronchodilators and steroids, whereas nebulizers have greater versatility and can be used to administer bronchodilators, antibiotics, surfactant, mucokinetic agents, and other drugs. The delivery of inhaled drugs in mechanically ventilated patients differs from that in ambulatory patients in several respects. Until recently, the consensus of opinion was that the efficiency of aerosol delivery to the lower respiratory tract in mechanically ventilated patients was much lower that that in ambulatory patients. Data suggest that this might be overly pessimistic and that the endotracheal tube may actually facilitate greater aerosol delivery compared with the normal airway when a variety of variables effecting aerosol delivery during mechanical ventilation are optimized.

Placement of the nebulizer before the humidifier during mechanical ventilation: Effect on aerosol delivery

“…Therefore, some investigators have suggested that the humidifier should be bypassed during aerosol administration, 8 although administration of dry gas for the period of nebulization may be detrimental to the airway mucosa. 9 Fink et al 10 studied the effects of 4 different positions of nebulizer in the inspiratory limb of a ventilator circuit on the delivery of albuterol in a tracheobronchial lung model. Measurements were taken under both dry and humidified conditions.…”

Stability of commonly nebulized drugs in heated and humid condition

“…Heated humidification is common method to increase temperature and water content of inhaled gas to Body Pressure Temperature Saturated (BPTS) conditions and helps prevent damage to airway mucosa from exposure to cold dry gas [1,20].…”

“…Heated humidification is used to condition anhydrous gas mixtures and minimize adverse effects of by-passing upper airway in intubated patients [1]. Many drugs are administered as aerosol [2] using nebulizers for treatment of intubated mechanically ventilated patients [3].…”

Using an evidence-based protocol to guide rehabilitation and weaning of ventilator-dependent cervical spinal cord injury patients

“…Reducing airway resistance is paramount in patients with limited ventilatory reserve and increased work of breathing associated with training. Although a number of studies have reported that metered-dose inhalers (MDIs) are equally effective as small volume nebulizers (SVNs) in mechanically ventilated patients [17,18], it is not known whether this also applies to ventilator-dependent cervical SCI patients.…”

“…Furthermore, in combination therapy, tolerance to a ß agonist is far less likely, and overall clinical efficacy is improved [21]. Bronchodilators were aerosolized via an SVN [17] placed proximal to the outlet filter on the ventilator to improve delivery of aerosol to the lungs [22].…”