- Email: [email protected]
This letter was shown to Dr Koerner whose reply follows
234
Letters
to the Editor
Sir, Drs van Saene, Damjanovic, Williets et al. question the significance of infective particles dislodged from endotracheal tubes (ET-tubes) to the contribution of ventilator-associated pneumonia (VAP) in comparison with micro-aspiration. They base their reasoning on the fact that micro-aspiration requires an inoculum lOOO-fold lower than that needed with inhaled aerosols.’ The application of these data in this context is incorrect, They are based on a model in which the animals inhaled infective particles via the upper airway.’ In contrast infective particles dislodged from ET-tubes bypass the protective upper airway mechanisms3 which if not bypassed lead to the requirement for higher infective doses as mentioned by van both experimentally and theoretically Saene et al. Inglis et al. demonstrated that these particles are sufficiently small to reach the lower airways.4*5 Without repeating what has been discussed already in my review I would like to comment as follows: (1) The pathogenesis of community-acquired pneumonia was not the subject of this review. (2) ET-tubes are colonized by endogenous bacterial flora, hence they contribute to the pathogenesis of endogenous VAP. (3) A variety of factors contributing to the development of intraluminal accretion in tracheal tubes have not been investigated or even identified, hence an unifying concept cannot be developed at this stage. (4) It was not the intention of the review to discuss the mechanisms of bacterial adhesion and formation of microbial biofilm. They have been considered in detail by other authors.6-9 (5) The discussion of disadvantages, benefits and indications for selective decontamination of the digestive tract (SDD) was not subject of this review and it is difficult to comment on only partially published data. However the limitations of meta-analyses have recently been well-demonstrated.” In an accompanying editorial Bailar warns the medical profession that the reduction of the results of disparate studies to a single value with confidence bounds in a meta-analysis may lead to incorrect conclusions.” The importance of infective particles dislodged from ET-tubes as a contributory factor to VAP has been investigated by different groups of clinicians, medical microbiologists and scientists. It would be imprudent to ignore the results of these very thoroughly performed studies. Furthermore the impact of dissimination of bacterial antigens and host-derived inflammatory mediators into the lungs on the host response and subsequent induction of inflammatory pulmonary changes may be one of many aspects explaining culture-negative VAP warranting further investigation as has been already suggested by Inglis.” R. J. Koerner
Department of Microbiology, Freeman Hospital, High Heaton, Newcastle-upon- Tyne NE 7 7DN, UK
Letters
to the Editor
235
References 1. Berendt
RF.
Relationship of method of administration to respiratory virulence of Klebsiellapneumoniae for mice and squirrel monkeys. Infect Immunity 1978; 20: 581-583. 2. Berendt RF, Long GG, Walker JS. Treatment of respiratory Klebsiella pneumoniae infection in mice with aerosols of kanamycin. Antimicrob Agents Chemother 1975; 8:
585-590. J. Lung defence mechanisms Part I. New Engl 3. Newhouse M, Sanghis J, Bienenstock J Med 1976; 295: 990-998. 4. Inglis TJJ, Millar MR, Jones G, Robinson DA. Tracheal tube biofilm as a source of bacterial colonisation of the lung. J Clin Microbial 1989; 18: 2014-2018. 5. Inglis TJJ, Jones JG, Paxton S. Penetration of an aerosol, produced by film atomization, through the carinal bifurcation. Br J Anaesth 1993; 70: 527-531. Loeb GI, Neihof RA. Marine conditioning films. Adv Chem 1975; 145: 319-335. ;: Costerton JW, Cheng KJ, Geesey GG, Ladd TI, Nickel JC, Dasgupta M, Marrie ThJ. Bacterial biofilms in nature and disease. Ann Rev Microbial 1987; 41: 435-464. 8. Cooksey KE, Wigglesworth-Cooksey B. Adhesion of bacteria to surfaces in the sea: a review. Aquatic Microbial Ecol 1995; 9: 87-96. Z, Caldwell DE, Korber DR, Lappin-Scott HM. Microbial 9. Costerton JW, Lewandowski biofilms. Ann Rev Microbial 1995; 49: 711-745. 10. LeLorier J, Grtgoire G, Benhaddad A, Lapierre J, Derderian F. Discrepancies between meta-analyses and subsequent large randomized, controlled trials. New Engl J Med 1997; 337: 536-542. 11. Bailar III JC. The promise and problems of meta-analysis. New EngZJMed 1997; 337: 559-561. 12. Inglis TJJ. New insights into the pathogenesis of ventilator-associated pneumonia. J Hosp Infect 1995; 30 (Suppl.): 409413.
Sir, Lancets
as a source
of sharps injuries
Patient monitoring with devices which utilize capillary blood samples is common practice, and set to increase. The advantages of such systems are at least twofold: first, the simplicity of capillary blood sampling means that samples may be obtained by relatively unskilled staff or patients, and second, the equipment used is often portable enabling near-patient testirlg either within the healthcare setting, at home or even in the high street. Capillary blood samples may be obtained either by pricking the finger (or heel) directly with a lancet or by using it in conjunction with a spring loaded device. The cross-infection risk from spring loaded devices was unrecognized until at least three outbreaks of hepatitis B occurred.’ Their cause was traced to a failure to change the platform as well as the lancet between patients. Whilst used lancets are a potential source of sharps injury we were surprised to discover how often they are implicated. In 1992, a sharps audit programme was introduced within our trust. Staff attending Accident and Emergency or Occupational Health following an injury are requested to fill in a questionnaire detailing the circumstances of the injury including the implement involved. Completed forms are analysed on an individual basis shortly after receipt, and then again as part of an annual review of all
Letters
to the Editor
Sir, Drs van Saene, Damjanovic, Williets et al. question the significance of infective particles dislodged from endotracheal tubes (ET-tubes) to the contribution of ventilator-associated pneumonia (VAP) in comparison with micro-aspiration. They base their reasoning on the fact that micro-aspiration requires an inoculum lOOO-fold lower than that needed with inhaled aerosols.’ The application of these data in this context is incorrect, They are based on a model in which the animals inhaled infective particles via the upper airway.’ In contrast infective particles dislodged from ET-tubes bypass the protective upper airway mechanisms3 which if not bypassed lead to the requirement for higher infective doses as mentioned by van both experimentally and theoretically Saene et al. Inglis et al. demonstrated that these particles are sufficiently small to reach the lower airways.4*5 Without repeating what has been discussed already in my review I would like to comment as follows: (1) The pathogenesis of community-acquired pneumonia was not the subject of this review. (2) ET-tubes are colonized by endogenous bacterial flora, hence they contribute to the pathogenesis of endogenous VAP. (3) A variety of factors contributing to the development of intraluminal accretion in tracheal tubes have not been investigated or even identified, hence an unifying concept cannot be developed at this stage. (4) It was not the intention of the review to discuss the mechanisms of bacterial adhesion and formation of microbial biofilm. They have been considered in detail by other authors.6-9 (5) The discussion of disadvantages, benefits and indications for selective decontamination of the digestive tract (SDD) was not subject of this review and it is difficult to comment on only partially published data. However the limitations of meta-analyses have recently been well-demonstrated.” In an accompanying editorial Bailar warns the medical profession that the reduction of the results of disparate studies to a single value with confidence bounds in a meta-analysis may lead to incorrect conclusions.” The importance of infective particles dislodged from ET-tubes as a contributory factor to VAP has been investigated by different groups of clinicians, medical microbiologists and scientists. It would be imprudent to ignore the results of these very thoroughly performed studies. Furthermore the impact of dissimination of bacterial antigens and host-derived inflammatory mediators into the lungs on the host response and subsequent induction of inflammatory pulmonary changes may be one of many aspects explaining culture-negative VAP warranting further investigation as has been already suggested by Inglis.” R. J. Koerner
Department of Microbiology, Freeman Hospital, High Heaton, Newcastle-upon- Tyne NE 7 7DN, UK
Letters
to the Editor
235
References 1. Berendt
RF.
Relationship of method of administration to respiratory virulence of Klebsiellapneumoniae for mice and squirrel monkeys. Infect Immunity 1978; 20: 581-583. 2. Berendt RF, Long GG, Walker JS. Treatment of respiratory Klebsiella pneumoniae infection in mice with aerosols of kanamycin. Antimicrob Agents Chemother 1975; 8:
585-590. J. Lung defence mechanisms Part I. New Engl 3. Newhouse M, Sanghis J, Bienenstock J Med 1976; 295: 990-998. 4. Inglis TJJ, Millar MR, Jones G, Robinson DA. Tracheal tube biofilm as a source of bacterial colonisation of the lung. J Clin Microbial 1989; 18: 2014-2018. 5. Inglis TJJ, Jones JG, Paxton S. Penetration of an aerosol, produced by film atomization, through the carinal bifurcation. Br J Anaesth 1993; 70: 527-531. Loeb GI, Neihof RA. Marine conditioning films. Adv Chem 1975; 145: 319-335. ;: Costerton JW, Cheng KJ, Geesey GG, Ladd TI, Nickel JC, Dasgupta M, Marrie ThJ. Bacterial biofilms in nature and disease. Ann Rev Microbial 1987; 41: 435-464. 8. Cooksey KE, Wigglesworth-Cooksey B. Adhesion of bacteria to surfaces in the sea: a review. Aquatic Microbial Ecol 1995; 9: 87-96. Z, Caldwell DE, Korber DR, Lappin-Scott HM. Microbial 9. Costerton JW, Lewandowski biofilms. Ann Rev Microbial 1995; 49: 711-745. 10. LeLorier J, Grtgoire G, Benhaddad A, Lapierre J, Derderian F. Discrepancies between meta-analyses and subsequent large randomized, controlled trials. New Engl J Med 1997; 337: 536-542. 11. Bailar III JC. The promise and problems of meta-analysis. New EngZJMed 1997; 337: 559-561. 12. Inglis TJJ. New insights into the pathogenesis of ventilator-associated pneumonia. J Hosp Infect 1995; 30 (Suppl.): 409413.
Sir, Lancets
as a source
of sharps injuries
Patient monitoring with devices which utilize capillary blood samples is common practice, and set to increase. The advantages of such systems are at least twofold: first, the simplicity of capillary blood sampling means that samples may be obtained by relatively unskilled staff or patients, and second, the equipment used is often portable enabling near-patient testirlg either within the healthcare setting, at home or even in the high street. Capillary blood samples may be obtained either by pricking the finger (or heel) directly with a lancet or by using it in conjunction with a spring loaded device. The cross-infection risk from spring loaded devices was unrecognized until at least three outbreaks of hepatitis B occurred.’ Their cause was traced to a failure to change the platform as well as the lancet between patients. Whilst used lancets are a potential source of sharps injury we were surprised to discover how often they are implicated. In 1992, a sharps audit programme was introduced within our trust. Staff attending Accident and Emergency or Occupational Health following an injury are requested to fill in a questionnaire detailing the circumstances of the injury including the implement involved. Completed forms are analysed on an individual basis shortly after receipt, and then again as part of an annual review of all