1 Laboratoire Universitaire de Recherche en Immuno-Allergologie (LURIA), Centre d'Allergologie, Hôpital Tenon (AP-HP), 4 rue de la Chine, F-75970 Paris Cedex 20, France. 2 Laboratoire de Physiopathologie Respiratoire, Université Paris V, UFR Biomédicale, 45 rue des Saints-Pères, F-75270 Paris Cedex 06, France
* Corresponding author. E-mail: francisque.leynadier{at}tnn.ap-hop-paris.fr
Accepted for publication April 29, 2005.
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Abstract |
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Methods. Guinea pigs (n=810 in each group) were exposed to aerosolized NRL-contaminated cornstarch powder or to NRL in saline for 1 h every day for 2 weeks. The experiments were repeated with a PallTM BB25 filter placed over the aerosol system. Control groups were exposed to non-contaminated cornstarch or to saline alone. Three weeks after the last exposure, specific bronchial challenge was performed and thromboxane (Tx) B2 levels in bronchoalveolar lavage fluid were measured.
Results. After bronchial challenge, the animals exposed to NRL or NRL-contaminated cornstarch with the BB25 filter in place showed a level of bronchoconstriction (i.e. the variation of pulmonary insufflation pressure) not different from controls. Conversely, those exposed to NRL or NRL-contaminated cornstarch without the filter showed a higher level of bronchoconstriction (respectively, P<0.02 and P<0.001) than control. Elevated TxB2 levels were found in the lungs of the guinea pigs, which inhaled NRL or NRL-contaminated cornstarch in the absence of a filter. Animals treated with the filter showed comparable TxB2 levels with those of control.
Conclusion. The PallTM BB25 filter efficiently protected the guinea pigs from sensitization to NRL. This filter can be used as a complementary measure for avoidance of NRL contact during surgical procedures particularly if the mechanical ventilator apparatus contain NRL devices.
Keywords: airway ; complications, latex allergy ; equipment, filters ; model, guinea pigs
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Introduction |
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We reported recently a bacterial/viral filter used in anaesthesia (PallTM BB25) that efficiently retained the NRL proteins.10 In the present study, we tested the relevance of the PallTM BB25 filter in prevention of NRL sensitization in guinea pigs. For this purpose the animals were placed in similar conditions of airway exposure as a patient connected to an artificial breathing system during surgical procedures. A BB25 filter was inserted at the top of the NRL-nebulizing system in order to retain NRL-contaminated cornstarch particles or NRL solubilized in saline solution. In addition, a model of sensitization to ovalbumin was also used for comparison to a well-known antigen.
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Materials and methods |
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Antigen sources
All the NRL sources used in this study were the same as utilized previously.8 9
The latex solution was prepared with a lyophilized non-ammoniated latex extract (C-serum) from a Hevea brasiliensis tree in Thailand. The lyophilized C-serum contained 57.2 µg latex antigenic proteins g1 of lyophilizate determined with the Competitive Immunoassay for Antigenic Latex Proteins (CIALP), an ELISA method for the assessment of antigenic NRL proteins described elsewhere.11 For the preparation of NRL in saline, C-serum was reconstituted in saline solution and diluted to 0.5 µg NRL antigenic proteins ml1.
Latex-contaminated cornstarch (NRL-cornstarch) was collected in the slurry tank on the glove production line of a latex glove manufacturer in Thailand. Its antigenic NRL protein content was 0.85 µg g1 of dry powder (CIALP).
Virgin or non-contaminated cornstarch (Agenasorb 9020, Agrana Stärke GMBH, Wien, Austria) habitually used for powdering latex gloves that had never been in contact with NRL sources was utilized as a control for NRL-cornstarch.
Ovalbumin used for sensitization and challenge was a commercial reagent from Serlabo, France.
Sensitization protocol
The sensitization protocol was conducted exactly in the same manner as described previously.9 Guinea pigs, separated in six groups (n=810 in each), were exposed to aerosolized NRL solubilized in saline or to NRL-cornstarch (10 µg of antigenic NRL proteins) once a day for 1 h for 2 weeks (2x5 days). The exposure was performed with or without a BB25 filter placed at the top side of the nebulizer. Control groups were exposed to saline alone or to non-contaminated cornstarch. All animals were challenged with NRL between days 31 and 33 of the sensitization protocol. Thirty minutes after bronchial challenge, the animals were bled and bronchoalveolar lavage (BAL) was performed.
Two additional groups were exposed to 10 µg ovalbumin every day as described above with (ovalbumin+filter group, n=10) or without a BB25 filter (ovalbumin group, n=8) inserted in the aerosol system. The ovalbumin bronchial challenge and BAL were performed according to the NRL sensitization schedule described above.
Specific bronchial provocation
The degree of bronchoconstriction after NRL or ovalbumin challenge was evaluated by the Konzett and Rössler method,12 modified as described previously.8 Guinea pigs were anaesthetized with urethane intraperitoneally (1.5 g kg1), the right carotid artery was catheterized and connected to an arterial pressure transducer (DPT 700-500, NARCO Biosystems, Houston, TX, USA). The animals were tracheotomized and connected to an artificial respiration pump (Braun, Melsungen, Germany) and a differential pressure transducer (PM5, Statham, LA, CA, USA). The ventilation parameters (volume and frequency) for each animal were calculated according to the table of Kleinman and Radford.13 Anaesthetized animals were pre-treated with propranolol (2 mg kg1) (Sigma, St Louis, MO, USA) at least 10 min before challenge to prevent possible bronchodilatation induced by catecholamines.14 Challenge was then performed by instillation of 1 mg NRL or ovalbumin in 20 µl of saline solution directly into the lungs via the trachea. Pulmonary insufflation pressure variation and arterial pressure were recorded over 15 min with the differential pressure captor connected to a Physiograph E&M (NARCO Biosystems). The level of bronchoconstriction was determined after calculation of the area under the curve using the KaleidaGraphTM 3.09 software (Synergy Software, Reading, PA, USA).
Thromboxane B2 determination in BAL fluid
Thirty minutes after NRL or ovalbumin challenge, BAL was performed as described below. Five millilitres of cold saline was instilled through the tracheal cannula then removed and re-injected five times with a 5 ml-syringe. The operation was repeated three times and the total volume of BAL fluid (BALF) was measured. BALF was centrifuged (15 min at 1000 g) and the supernatant stored at 20°C until assayed.
Thromboxane (Tx) B2 was determined in BALF with a commercial kit supplied by Cayman Chemical Company (TxB2 EIA kit, Ann Arbor, MI, USA). The assay was performed according to the supplier's recommendations with a detection limit of 13 pg ml1.
Statistical analysis
Results were expressed as median (SEM) unless noticed otherwise. The MannWhitney U-test was used for comparisons between groups. A P<0.05 was considered as statistically significant.
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Results |
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Discussion |
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The present study corroborates these findings as exposure to NRL in the presence of the BB25 filter significantly decreased bronchoconstriction and TxB2 production in lungs after bronchial challenge. The inflammatory mediator TxA2 and its more stable metabolite TxB2 are not allergen-specific but they are known to be the most potent bronchoconstrictors in guinea pig airways.15 Arakida and colleagues16 also reported that TxA2 was the mediator predominantly found in the lungs of passively sensitized guinea pigs exhibiting asthmatic reactions.
The capacity for retention of cornstarch and NRL-cornstarch particles by the BB25 filter has already been tested.10 In the present experiments, we confirmed in vivo that the BB25 filter is able to protect guinea pigs from NRL sensitization during exposure to airborne NRL-cornstarch particles or NRL solubilized proteins. Animals exposed to NRL with the BB25 filter exhibited airway responses similar to those of the controls. Exposure to the well-known antigen ovalbumin supported these findings. The high variability in pulmonary insufflation pressure observed may be the result of a variation of the dose of allergen effectively received. Guinea pigs were allowed to breathe spontaneously during the sensitization protocol, thus the dose of the NRL inhaled was not controlled. This variability was also observed in animals sensitized to ovalbumin.
NRL is known to be responsible for anaphylactic reactions in patients during surgical procedures in 16.6% of the cases. The severity of these reactions underlines that pre-anaesthetic detection of the triggering parameters is very important and the implementation of preventative measures is essential. Recent reports re-inforced the need to take measures to efficiently protect patients and/or HCW against NRL exposure.17 18 The key elements are the establishment of an as close as possible latex-free environment and minimizing the exposure to latex either in primary or secondary prophylaxis.19 20 For example, in a 5-yr prospective study on 100 children mostly with spina bifida, the anti-latex IgE was reduced in 64% of the patients by applying these procedures.21 A notable efficiency in the HCW population was also observed.22 23
As a result of the latex risk, NRL-made devices have been discarded from the operating theatre. However, in many hospitals, mechanical ventilation is still provided by older equipment with components containing NRL. The wear of such apparatus can lead to latex scatter within the piping, which can be inhaled by the patient. Nevertheless, the recommendations mentioned above are strengthened when a patient at risk is anaesthetized even when using a newer breathing system. Hence, some anaesthetists require that the viral and bacterial filter be inserted between the Y-piece and the patient to efficiently retain latex particles.
The BB25 filter has been developed for anaesthesia, it retains small airborne bacterial and viral contaminants with a retention efficiency of more than 99.999% (Brevundimonas diminuta, Bacteriophage MS2) and larger particles (Bacillus subtilis, Serratia marcescens) with a retention efficiency of more than 99.9999%. Its hydrophobic membrane prevents the passage of aqueous suspension of Mycobacterium bovis, Mycobacterium tuberculosis, HCV and HIV. The present study demonstrated that the use of this filter should contribute efficiently to the patient protection during surgery or any procedure necessitating mechanical ventilation. However, all other measures intended to avoid contact between the patient and NRL devices must be taken. Nakamura and colleagues24 reported a high incidence of latex allergy in children requiring home mechanical ventilation.
Mitakakis and colleagues25 have tested the efficiency of a particulate mask to protect HCW from airborne latex allergens. But to our knowledge, this is the first study of a device used to prevent latex-allergy reactions in patients.
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Acknowledgments |
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Footnotes |
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References |
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