Mathews, Paul J. RRT, PhD, FAARC, FCCM, FCCP
Here’s what’s in the air for drug delivery and treatment for ARDS.
WE’RE ALL FAMILIAR with the use of aerosolized inhaled bronchodilators to treat pulmonary disease. But aerosol drug delivery isn’t just for pulmonary disease anymore: Cancer chemotherapy and gene therapy are just two of the newer uses for this route. And morphine is now being given as an aerosol; delivering the drug directly to the lungs means faster absorption, faster pain relief, and faster relief of dyspnea. This route is especially useful if the patient doesn’t have intravenous access (for example, in home or hospice settings).
As they explore the pros and cons of aerosol delivery, researchers are also comparing the effectiveness of various delivery devices, such as spacers on metered-dose inhalers (MDIs). Here, we’ll describe what’s new in the field of aerosol drug delivery, plus some interesting new information on positional therapies under investigation for acute respiratory distress syndrome (ARDS).
A twist on medication delivery
Aerosol therapy is the second most common route of delivery for prescription medication in the United States, following the oral route.
As you know, an aerosol is a suspension of liquid or solid particles in a gas. To be effective, medication particles must be small enough to penetrate into the lungs. The medication must also be available in a formulation that can be delivered by MDI, dry powder inhaler, or nebulizer. At present, more aerosol medication is available in liquid form for nebulization than through MDIs, although MDIs are catching up rapidly.
Inhaled antibiotics have been used for several decades to treat cystic fibrosis. Antiviral aerosol therapy includes ribavirin for respiratory syncytial virus, pentamidine for Pneumocystis carinii pneumonia, and zanamivir for influenzas A and B. Inhaled interferon alpha, a cytokine, is being tested for its antimicrobial effects against tuberculosis.
Gene therapy delivered by aerosol has generated much interest. For example, to treat a patient with cystic fibrosis, researchers believe they can use the aerosol route to deliver a vector carrying a functional copy of the gene to the lungs.
Gene therapy using aerosolized brimonidine is being tested for patients with alpha1-antitrypsin deficiency. Researchers also are testing aerosolized gene therapy for hemophilia and aerosolized chemotherapy for lung cancer. Because inhaled medication generally has a quick onset of action with fewer systemic effects, aerosolized cancer chemotherapy may offer effective treatment while causing fewer adverse reactions.
In infants with chronic lung disease, aerosolized diuretics have improved pulmonary mechanics. Insulin administered by aerosol continues to show promise as an alternative dosing format for patients with diabetes and in the future may reduce or eliminate the need for injections.
—Shirley Wilcoxon, RRT, BS
Are MDI spacers a waste of time?
Spacers for MDIs can increase aerosol medication delivery—if patients use them correctly.
Spacers are used for two main reasons:
* to help overcome problems associated with poor technique and coordination for patients using a pressurized MDI
* to improve drug delivery to the lungs.
Patients using MDIs without spacers need to inhale as they activate their MDI so that medication gets into the lungs. With a spacer attached to the MDI, the patient no longer has to coordinate inhalation and MDI activation; the spacer acts as a holding chamber from which the patient can inhale the medication.
A study comparing salbutamol MDIs with and without spacers found that MDIs with spacers increased medication delivery to the lungs by 23%. Washing the spacer before treatment sessions (to prevent medicine from adhering to the inside of the spacer via static electricity, not as an infection control measure) increased the amount of medication delivered even more, to 50% more than with the MDI alone.
Figure. With a spac...Image Tools
Figure. MDIs with s...Image Tools
However, many patients with asthma use their MDIs incorrectly. Comprehensive instruction on MDI use should be provided at the time inhaled drugs are prescribed, and patients’ technique should be checked at follow-up appointments.
—Andrew Chung, CRT, BS; Bryce Younger, CRT, BS; and Paul J. Mathews, RRT, PhD, FAARC, FCCM, FCCP
Treating ARDS with prone positioning and rotational therapy
Despite extensive research, the mortality rate for ARDS is virtually unchanged from when the syndrome was first described in the 1960s. Most patients die of severe lung impairment or secondary complications. Prone position ventilation (PPV), which has been used since the 1970s, is getting another look as a therapy for ARDS. Preliminary results of PPV studies being done in China have been encouraging.
The main effect of PPV is to improve oxygenation. Placing the patient prone—either with pillows under the pelvis and upper chest or by using a proning bed—apparently frees the abdomen to move, redistributing pulmonary infiltrates, increasing pulmonary perfusion, and reducing intrapulmonary shunting. Researchers believe that the gravitational force helps to ventilate atelectatic areas, thereby improving the patient’s ventilation/perfusion (V̇/Q̇) ratio.
Figure. Rotational ...Image Tools
When PPV works, results can be dramatic. But the mortality rate from ARDS remains high, and PPV has several drawbacks, including the risk of peripheral nerve injuries, corneal ulcerations, abdominal wound dehiscence, and facial edema. Putting a patient in prone position is cumbersome, makes nursing care difficult, and increases the risk of vascular decannulation and inadvertent tracheal extubation. As a result, PPV is usually considered a last resort treatment method in severe cases of ARDS.
Rotational therapy, in which a special bed turns the patient’s body from side to side a specified number of degrees, has been shown to be the most effective positioning strategy and is generally tried first. Rotational therapy can dramatically enhance the V̇/Q̇ ratio, reduce work of breathing, and improve respiratory secretion control.
—Cristie Banks, RRT, BS; Tamika Cranford, RRT, BS; and Paul J. Mathews, RRT, PhD, FAARC, FCCM, FCCP
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© 2003 Lippincott Williams & Wilkins, Inc.