Nosocomial Pneumonia and Patient Ventilation

Clinical Problem

Nosocomial infection continues to be an important clinical problem.

Hospital acquired (nosocomial) pneumonia represents the third most-common diagnosed nosocomial infection in the intensive-care environment,¹ utilizing approximately 39% of all funds allocated for the treatment.

Up to half of all nosocomial infections in ICU are pneumonias.

Two and one-half billion dollars were spent in the treatment of nosocomial pneumonia in 1991 (this translates into a $3.65 billion projected expenditure based on 1996 dollars). Patients with nosocomial pneumonia are reported to have an increased average length of stay (LOS) of 5.9 days,^2,3Nosocomial lung infections are costly and, if not treated promptly, carry up to 60% mortality rate.³

Nosocomial pneumonia can be exogenous and endogenous in origin.

Although nosocomial pneumonia is often endogenous in origin, the contribution of exogenous micro-organisms, and of external transfer of endogenous organisms from other sites, may have been underestimated.³ Infection can arise from micro-organisms in the ventilator circuit. It has been shown that the breakdown of a single step in the procedure for decontaminating ventilation equipment can be responsible for infectious episodes.^4-8

Author, Year Incident/problem identified

Conly et al., 1985 Contamination of circuit by temperature probes

Harstein et al., 1988 Inadequate handwashing by staff handling circuits

Cefai et al., 1990 Insufficient decontamination of circuits

Berthelot et al., 1992 Contamination of circuit by temperature probes

Wendt et al., 1993 Inadequate decontamination of humidifier and temperature probes

Nosocomial pneumonia of exogenous origin is therefore a problem in clinical practice.

Johanson et al., established that there is a link between the colonization of the patients’ airways, and the development of nosocomial pneumonia. Langer et al., showed that the colonization of the airway is connected to the contamination of the breathing circuit.^10,11

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Patient Protection

Infection control measures are required.

Various general recommendations have been given and patient care protocols have been suggested in order to reduce nosocomial pneumonia. These include guidelines on handwashing prior to each procedure on the patient's airway, attention to tracheal lavage procedures, and disinfection of ventilation bags between patients. In recent years, attention has been focused on selective decontamination of the digestive tract, but results have been disappointing.

Contamination of the ventilator circuit must be considered.

Some authors recommend that ventilator circuits be changed at regular intervals. This solution does not resolve problems with inadequate decontamination of ventilation equipment or those associated with reinfection from the patient's own organisms during long-term ventilation.

For many years evidence has accumulated on the potential role of heat and moisture exchanging filters (HMEF) in the control of contamination in the respiratory-therapy system.

Researchers have studied methods of curbing the rise in the nosocomial pneumonia rate. The Centers for Disease Control and Prevention and The American Association of Nurse Anesthetists have placed into their respective infection-control guidelines the use of filters to reduce the contamination of breathing circuits. ^6,7

Heat and moisture exchanging filters can be an effective hygienic measure for protection of ventilated patients.

These devices have a dual function, both as a means of warming and humidifying the cold, dry inspired gas/air mixtures, and providing a barrier to the passage of micro-organisms.

The level of humidification provided closely matches the physiological level provided in normal nasal breathing.

Not all HMEFs are the same.

There are two types of HMEFs. Composite devices combine a hygroscopic HME element with a filter medium of electrostatically charged felt. These devices act as filters under dry conditions, but have been shown to be ineffective as a liquid barrier; thus, liquid-borne contamination is not reliably retained.¹³

Hydrophobic membrane filter media consist of bonded ceramic filaments. A large surface area of media is provided by pleating it within the filter housing. The medium act not only as an effective filter under dry conditions, but also provides a barrier to the passage of liquids, while maintaining gas flow at low resistance.¹⁴ Therefore with such devices there is a fully effective barrier, which isolates the patient from the ventilator with respect to potential microbial contamination.^13-16

The difference between the two types of HMEFs has been demonstrated in a comparative study, in which a hygroscopic device allowed a contaminated solution to pass through, while the hydrophobic membrane completely retained it.¹⁷

Retention of liquid borne contamination is particularly important in mechanical ventilation.

Potentially contaminated patient fluids, such as tracheal secretions, saliva, and blood can be present in the expired air and can provide a source of contamination into the breathing system. Hygroscopic devices are unable to provide protection against this.^18-21

Author, Year HMEF Contamination rate Details

Bygdeman et al., 1994 Hygroscopic 8/33 patients Breakthrough of bacteria from trachea to humidifier

H'Mouda et al., 1990 Hygroscopic circuits 11/29 ventilator In 1 case same organism isolated from circuit and patient

Brun-Buisson et al., 1990 Hygroscopic 13/50 filters contaminated In 2 cases same organism isolated from patient and machine side of HMEF

Dreyfuss et al., 1995 Hygroscopic Contamination of Y-piece up to 10⁶ CFU/mL Enterobacteriacea and Gram positive bacteria isolated

Pall pleated hydrophobic membrane HMEFs prevent liquid passing into the ventilator circuit and microbiologically isolate the patient from the breathing circuit and the ventilator.

This lowers the risk of patient re-contamination with their own bacteria and protects the environment from potential contamination. It has been demonstrated that the use of a Pall pleated hydrophobic membrane HMEF, positioned between endotracheal tube adapter and Y-piece, prevented the passage of pathogenic organisms originating from patients undergoing long term ventilation.²² In a comparative study of three conditionally hydrophobic devices and a Pall pleated hydrophobic filter, using a pig model, identical bacteria were found both on the machine and patient side of all the hygroscopic devices. However, the Pall pleated hydrophobic filter showed no contamination on the machine side, thus demonstrating that bacteria were prevented from passing from the subject into the ventilator circuit. ²³

The use of an appropriate HMEF can have an impact on the incidence of nosocomial pneumonia.

Three studies have shown that the incidence of nosocomial pneumonia is not reduced by the use of hygroscopic HMEFs^21,24,25 a possible reflection of their inability to prevent the passage of liquid-borne contamination. However, a recent prospective randomised trial of 240 patients in a trauma ICU compared a heated wire humidifier with Pall Medical’s hydrophobic membrane HMEF. Pneumonia was classified according to US CDC criteria.

Heated wire humidifier Pall pleated hydrophobic HMEF Significance

Number of patients 140 140 ns

Community acquired pneumonia 24 26 ns

Ventilated associated pneumonia 22 9 <0. 005

Circuit costs (group) $3893 $2444 <0. 005

Median circuit cost per patient $27.80 $17.46

Antibiotic costs (group) $22600 $4700

Ventilator-associated pneumonia can be reduced by the use of a Pall pleated hydrophobic membrane HMEF.

The authors found that the rate of ventilator-associated pneumonia in the HMEF group was half that of the heated wire humidifier group, while ventilator circuit costs were reduced by 63% and ICU stay was significantly reduced.26 The cost of antibiotic treatments was reduced by 80% in the filter group.²⁷

Based on DeHaven and Kirton’s study, and the current costs of treating nosocomial pneumonia, significant savings can be realized when using a Pall pleated hydrophobic membrane HMEF.²⁷

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Summary

Heat and moisture exchanging filters can be an effective hygienic measure for protection against nosocomial infections; however, not all HMEFs are the same. Pleated, hydrophobic membrane HMEFs prevent liquid from passing into the ventilator circuit and effectively isolate the patient from microbiological contaminants.

Ultimately, the use of an appropriate HMEF can realize significant cost savings and a reduction in overall VAP rates.

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References

Anonymous: National Nosocomial Infection Surveillance (NNIS) Semiannual Report. Am J Infect Control. 1995; 23:377-85.
Haley R.W.: Managing hospital infection control for cost effectiveness. American Hospital Publ., Inc. Chicago, IL 1986.
Bonten MJM, Gaillard CA, de Leeuw PW, Stobberingh EE, Role of colonization of the upper intestinal tract in the pathogenesis of ventilator-associated pneumonia. Clin Infect Dis 1997; 24:309-319.
Conly JM, Klass L, Larson L, Kennedy J, Low DE, Harding GDM. Pseudomonas cepacia colonization and infection in intensive care units. Can Med Assoc J. 1986; 134 :363-366
Harstein AI, Rashad AL, Liebler JM, Actis LA, Freeman J, Rourke JW, Stibolt TB, Tolmasky ME, Ellis GR, Crosa JH. Multiple intensive care unit outbreak of Acinetobacter calcoaceticus subspecies anitratus respiratory infection and colonisation associated with contaminated, reusable ventilator circuits and resuscitation bags. Am J Med. 1988; 85:624-631
Cefai C, Richards J, Gould FK, Mc Peake P. An outbreak of Acinetobacter respiratory tract infection resulting from incomplete disinfection of ventilatory equipment. J Hosp Infect. 1990; 15:177-182
Berthelot P, Grattard F, Mahul P, Jospe R, Pozzetto B, Ros A, Gaudin OG, Auboyer C. Ventilator temperature sensors: an unusual source of Pseudomonas cepacia in nosocomial infection. J Hosp Infect. 1993; 25:33-43.
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Johanson WG: Nosocomial respiratory infections with gram-negative bacilli. The significance of the respiratory tract. Ann Intern Med. 1972; 77:701-6.
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Anonymous. Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care facilities. MMWR. 1994; 43(RR-13):J-132.
Anonymous. Infection control guide for certified nurse anesthetists, 1993. (Second Ed.): 1-28.
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Speight S, Bennett A.M, Lever M.R, Benbough J. Efficacy of a pleated hydrophobic filter as a barrier to Mycobacterium tuberculosis transmission within breathing systems. Centre for Applied Microbiology and Research. Porton Down, Salisbury, Wiltshire, UK
Wille B. Hygienemassnahmen füer narkose-und Beatmungszubehoer. Krh-Hyg & Inf Verh. 1989; 11:148-150
Bygdeman S, Von Euler C, Nystöm B. Moisture exchangers do not prevent patient contamination of ventilators: a microbiological study. Acta Anaesthesiol Scand. 1984; 28:591-594
H'Mouda H, Tenaillon A, Gauthier M, Geib I, Boiteau R, Perrin-Gachodoat D. P06. XIX Congres de la Société de Réanimation de Langue Francaise, Paris, 22-25 Novembre 19901.
Brun Buisson C, Legrand P, Tassin P. Efficacité de la protection microbiologique des circuits de ventilation par les filtres. Workshop Péters et DAR XVIII Congräs de la Société de Réanimation de Langue Francaise. Paris. 23-26 Novembre 1989.
Dreyfuss D, Djedaini K, Gros I, Mier L, Le Bourdellés G, Cohen Y, Estagnasié P, Coste F, Boussougant Y. Mechanical ventilation with heated humidifiers or heat and moisture exchangers: effects on patient colonization and incidence of nosocomial pneumonia. Am J Crit Care Med. 1995; 151:986-992
Gallagher J, Strangeways JE, Allt-Graham J. Contamination control of long term respiratory therapy circuits using a hydrophobic HMEF. anesthesia: 1987; 42: 476-481
Preis I, Kobelt F, Joachim S, Preis C. Heat and moisture exchange filters for bacterial retention in intubated pigs during intensive care. Intensive Care Med. 1995; 21: S38
Blin F, Fraisse F, Chauveau P, Lahilaire P, Boulet E, Bouhaddi R, Sadourny F, Shalatter J, Trouillet G, Hermitte M, Kleinknecht D. Incidence of nosocomial pneumonias among 1788 ventilated patients in 6 ICUs according to the type of humidification used. Intensive Care Med. 1996; 22:S 218
Boots R.J, Clinical utility of hygroscopic heat and moisture exchangers in intensive care patients. Crit Care Med. 1997; 25: 1707-1712
Kirton O.C, DeHaven B, Morgan J, Morejon O, Civetta J. A prospective randomised comparison of an in-line heat and moisture exchange filter and heated wire humidifiers. Chest 1997; 112:1055-1059
DeHaven B, Kirton O.C. How and why to prevent respiratory infections in ICU. Anaesthesia Pain Intensive Care Medicine 1997.

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