INFLUENCE OF TYPE, POSITION AND BIAS FLOW ON AEROSOL DRUG DELIVERY IN SIMULATED PEDIATRIC AND ADULT LUNG MODELS DURING MECHANICAL VENTILATION
Aru Ari Phd RRT PT CPFT, Orcin Telley Ataley Phd PT, Robert Harwood MSA etal
Respir Care 2010;55(7):845-851
The above study should be scrutinized concerning several key assumptions regarding the use of bronchodilators on ventilators and Bipaps for the adult clientele.
ALL TESTS IN THE STUDY WERE PERFORMED ON CLOSED CIRCUIT VENTILATOR CIRCUITS HEATED TO THIRTY FIVE DEGREES CENTIGRADE
DEVIATION FROM CLINICAL PRACTICE
NO INFORMATION IN THIS STUDY CAN BE APPLIED TO BIPAPS SINCE THEY ARE NEITHER TOTALLY CLOSED SYSTEMS, HAVING BOTH ORAL LEAKS AND MECHANICAL CIRCUIT LEAKS, NOR ARE THEY USUALLY HEATED TO 35C AT ANY TIME EXCEPT FOR TRACHEOSTOMY.
RATIONALE FOR ARGUMENT
Bipaps are used dry at first in their administration. Some facilities deem that the first four hours of Bipap use is a temporary use and therefore the expense of humidification is unwarranted. Once a chronic need for ventilation is deemed appropriate, room air temperature passover humidification is used to partially bring the dry gas towards the moisture content of the room. In many institutions, such as at LUNGLORD’s facility, Bipaps are never heated regardless of length of patient stay, a point for discussion at another venue. What is gained in humidity is lost in patient compliance. Obtunded people reject our ventilatory lung sauna, though LUNGLORD does try to sell the idea as a lung spa to those that are dioxide narcotic.
Reflect on this idea. Relative humidity in most hospitals is regulated to very low levels to retard bacteria growth. Therefore, it is a reasonable conclusion that, a mix of bone dry source oxygen and relatively dry entrained gas passing momentarily through a cold chamber will achieve only minimal amounts of humidity.
A fair question concerning an RCP’s goal of highest possible reason and best practice should be asked here.
Consider. When we’ re giving a conventional nebulizer treatment, the mist disappears once it has traveled four to eight inches from the cup. Why? The very dry air robs the mist of moisture by evaporation, reducing particle size until the medicine is far below optimal size, in fact has an infinitesimal particle size.
How much of this medication would be at optimal particle size after traveling seventy two inches through a corregated ( thus turbulent) BIPAP circuit or a ventilator circuit where it is well tumbled in dry gas?
Is any of the medicine at proper size for absorption?
LUNGLORD believes it is exceptionally imprudent and unreasonable that these questions weren’t asked by these Phds.
How much of the medicine gets past the pilot hole built into the circuit?
How much is lost in the passover or heated humidifier?
We know that particle sizes that are too small are exhaled and not absorbed at all because they lack enough mass for inertial impaction.
CONCLUSION: NONE OF THIS INFORMATION AS PRESENTED BY THE AUTHORS APPLIES TO THE EFFFICACY OF UNHEATED VENTILATORS AND BIPAPS.
THE FILTER USED TO COLLECT THE BRONCHODILATOR IS AN ABSOLUTE FILTER, THAT IS, 100% EFFICIENT AT CAPTURE OF ALL PARTICLES COMING TOWARDS IT.
LOGIC ERROR: STUDY DEVIATES FROM THE PHYSIOLOGICAL REALITY COMMON TO ALL HUMAN ANATOMY
NO BIOLOGICAL SYSTEM OF THE BODY IS 100% EFFICIENT. ONLY PARTICLES LESS THAN A CERTAIN SIZE CAN GET INTO THE LUNG. FURTHER, THE LUNG ONLY RETAINS PARTICLES IN A CERTAIN MICRON RANGE. THIS STUDY IS OF LIMITED VALUE IN THAT IT DOES NOT SPECIFY WHICH SIZE PARTICLES AND THEIR PERCENT OF THE WHOLE ARE ARRIVING AT THE FILTER.
RATIONALE FOR ARGUMENT
Obviously, cigarette smokers exhale smoke, these particles too small and of insufficient mass to impact on the bronchial or alveolar walls. Larger particles rain out in the upper airway resulting in stained teeth. Likewise with these aerosols, particle size must be right sized to impact and to prevent exhalation. The study used HCL to remove and sluice all albuterol from the filter. It was then weighed without regard to particle size. Only the crude amount was considered.
This lack of specificity results in a lack of utility.
Had the authors used absolute filters that would send the gas first through a 5 micron, then 4, then 3, 2, 1, .5, .25, .15 and <.15 particle sizes in successive filter traps, the whole premise of the study might have illuminated the elephant in the room.
The elephant here is that aerosol particles robbed of their liquid suspension have an unspecified mass and their particle size is far out of the specified range.
True the meds are captured in the 100% filter, but this is sleight of hand. This is a huge confidence distractor and reflects sloppiness on the part of the researchers who would have certainly known that the useable particle size would be an important consideration since is represents efficacy of retention of the lung in the lung, especially in any environment less than 37c.
An argument can be made that MDIs also aerosolize anhydrous albuterol, therefore what is the difference. Simply, these MDI meds are formulated with HFAs and CFCs previously to a high degree of precision to achieve proper particle size. No description of particle size is being offered by this study.
Colleagues, is it not reasonable that the more proximal the HHN is to the patient, the more medication they will receive both in volume and in proper particle size, having avoided all these losses?
LUNGLORD would humbly recommend that in the future all nebs be inserted in the circuit with a spring loaded T piece, that is, between the Bipap mask and the pressure sensor/pilot hole, as a matter of policy and practice. The spring loaded T piece is essential for safety, for should the neb disconnect, no pressure would be generated in the circuit.
Let us abandon the both convenient and highly inefficient practice of placing the HHN on the main flow filter where it comes out of the ventilator or Bipap, this some six feet from the patient.
The medicine our patient’s need to reduce their WOB should be placed as proximal and as close to an ideal particle size as possible. This improvement in practice might well be the difference between intubating our COPD, CB, and asthmatic clients. Consider the cost and morbidity such a change in your methodology might make to your clients and their LOS.
What is factual and correct in the study is that the inspiratory limb can serve as a spacer, a plenum for the neb during exhalation, the mist building in volume and moving closer to the Y during this time, that is if the neb is backed away from the Y a foot or so and the circuit is heated. For this information, LUNGLORD is grateful to the researchers.