Bacterial/viral filtration: let the breather beware!

Most clinicians believe that any device that is marketed as a "bacterial/viral filter" must necessarily be capable of capturing any individual bacteria or viruses that might be suspended within inhaled or exhaled gases. We were surprised to discover that this is, by no means, a justifiable assumption. This article describes testing methods that manufacturers employ to generate the often-misleading efficiency specifications that are claimed for some of these devices. We discuss articles that have documented the presence of airborne pathogens in the effluent of a ventilator circuit, and characterize the attributes that a competent filter must exhibit if it is to succeed in protecting patients and caregivers from incidental exposure to bacteria, viruses, aerosolized drugs, and endotoxins. This article continues with a discussion of the numbers of particles that are commonly produced with commercially available pneumatic nebulizers, the comparative performance characteristics of filters and heat/moisture exchanging filters (HMEFs), and the success or failure of various brands of HMEFs to comply with the guidelines recently developed by the Centers for Disease Control and Prevention for the management of patients who are harboring active tuberculosis. The presentation concludes with a description of the standards that apply to any filter that classifies as a high-efficiency particulate aerosol (HEPA) device, and demonstrates that the performance of filters/HMEFs in common clinical use can range from approximately 1/50th to > 30-fold the efficiency of a HEPA-grade device. Those who frequent the bedside of patients receiving ventilation might unwittingly be placing themselves at considerable risk of exposure to infectious microaerosols, but methods are available to dramatically decrease those risks.

A technique for the administration of ribavirin to mechanically ventilated infants with severe respiratory syncytial virus infection.

Fifteen infants with respiratory syncytial virus pulmonary infection admitted to our pediatric ICU from December 1, 1985 through April 30, 1986, required mechanical ventilation. These patients were placed on an open trial of ribavirin therapy. We describe a technique for the safe delivery of aerosolized ribavirin to these infants while on the ventilator. The agent was delivered for 16 h/day for 7 days. Modifications of the ventilator circuit were needed to prevent the condensation of the drug in the ventilator tubing and to allow for the safe and effective operation of the ventilator. A common ventilator strategy was used for all patients. The highest positive inspiratory pressure generated was 42 +/- 9.5 (SD) cm H2O, the highest PEEP was 5.9 +/- 3.2 cm H2O, the duration of ventilation was 10.7 +/- 8.5 days, and exposure to fraction of inspired oxygen was greater than or equal to 0.6 for 55.3 h. Ribavirin levels were measurable in two patients, thereby demonstrating that the drug was in fact delivered and absorbed. Our preliminary results demonstrate that ribavirin can be delivered to the patients with respiratory syncytial viral infections who require mechanical ventilation; however, further studies are indicated to evaluate the efficacy and dose responsiveness, alterations in pulmonary dynamics, and safety of ribavirin in delivery to infants requiring ventilation.

Administration of ribavirin to neonatal and pediatric patients during mechanical ventilation.

We have modified the circuits of pressure-preset and volume-preset ventilators to permit the administration of ribavirin to mechanically ventilated infants suffering from respiratory syncytial virus. The modifications isolate the ventilator itself and permit continuous aerosolization for as long as seven days without ventilator malfunction from the effects of crystallized medication. Excessive spilling of ribavirin into the environment is also avoided. Each institution must devise its own experimental protocols and gain permission from its own committee on human experimentation and from the parent/guardian of the patient before administering such treatment.

Some potential pitfalls associated with the use of computers and microprocessors.

Although digital computers and microprocessors are marvelously sophisticated devices, users are well advised to be aware of certain possible drawbacks associated with their use in the clinical environment. One relates to flawed software, the use of which can generate spurious data upon which subsequent treatment decisions might be based. Another drawback may arise when the computational power of a computer is tapped to generate data that, though mathematically correct, are interpreted in the context of physiologic assumptions that may themselves be faulty. Finally, one must resist the temptation to use computers solely "because they are there." Certain tasks are better left undone, and one must exercise restraint and not plunge into a task simply because a computer is very well suited for that task.

Evaluation of methylene blue and squamous epithelial cells as oropharyngeal markers: a means of identifying oropharyngeal contamination during transtracheal aspiration.

The usefulness of 1% methylene blue (MB) and squamous epithelial cells as oropharyngeal markers in transtracheal aspiration was prospectively evaluated. In vitro studies showed that failure to detect MB by spectrophotometry ruled out contamination by greater than 0.05 microliters of oropharyngeal secretions and that visual inspection was almost as sensitive as spectrophotometry. Even minute contamination could be ruled out if greater than 5 x 10(4) organisms were found by culture of Gram-stained smear in a specimen that was MB-negative by spectrophotometry. In specimens of transtracheal aspirate obtained from 10 bronchitic patients, quantitative bacteriology ruled out even minute contamination in nine. Cytologic-morphometric examination revealed that 70% of both sterile and colonized specimens of transtracheal aspirate contained squamous epithelial cells that were indistinguishable, except by electron microscopy, from buccal mucosal cells. MB is a useful marker for identification of oropharyngeal contamination during transtracheal aspiration, and traditional cytologic screening is misleading in conditions associated with tracheobronchial squamous metaplasia.

An outbreak of acinetobacter infection associated with the use of a ventilator spirometer.

Although respiratory therapy equipment is a well-known source of nosocomial infection, ventilator spirometers have not been previously implicated. We report 17 Acinetobacter calcoaceticus variety anitratus infections traced to contaminated spirometers. Isolates from infected patients were recovered from urine, sputum, wounds, and blood. A review of attack rates for Acinetobacter was prompted by a dramatic increase in blood culture isolates. Prospective surveillance of intensive care environment, personnel, and patients established that Bennett MA-1 spirometers constituted the major reservoir of infecting organisms. Despite daily sterilization, 30% of spirometers in use were found to be contaminated. The hands of 12% of intensive care nurses and 10% of respiratory therapists cultured were found to be colonized. In addition to the infected patients, 28 other patients on spirometer-equipped ventilators were judged to be colonized by Acinetobacter following examination of sputa and/or mouthwashings. Following discontinuation of spirometer use and following increased emphasis on proper handwashing, the incidence of Acinetobacter infections dropped dramatically. Antibiosis in the intensive care environment and a deterioration in aseptic awareness serve to make Acinetobacter an environmental opportunist of increasing importance.