Curbing the Incidence of Ventilator-Associated Pneumonia
Curbing the Incidence of Ventilator-Associated Pneumonia
By Francie Scott
A respiratory therapist making rounds notes the ventilator patient in the neuro ICU has a higher fever and purulent secretions. These symptoms could point to ventilator-associated pneumonia (VAP), a dangerous pathogen that plagues intubated patients. This is where the controversy begins. What should the care team do next to keep the patient alive?
According to one school of thought, a course of antibiotics should be initiated if patients present with two or more clinical symptoms of VAP. These include temperatures greater than 38o C or lower than 36o C, leukopenia, leukocytosis, purulent tracheal secretions and decreased PaO2. Many clinicians also culture endotracheal tube aspirates.
Another clinical strategy, one advocated particularly by European physicians, contends the presence of bacteria should be confirmed by an invasive test such as bronchoscopy or protected specimen brush sampling before antibiotics are administered.
That way, clinicians can target the actual pathogens attacking the patient rather than trying to hit it with a broad spectrum antimicrobial. Advocates of this school blame the emergence of drug-resistant pathogens on the overuse of antibiotics and suggest clinicians may be missing other clinical problems by blaming VAP for the non-specific symptoms if they skip the invasive testing.
The American College of Chest Physicians hoped to put the controversy to rest by appointing a panel of doctors to examine the current literature and prepare guidelines for the diagnosis and management of VAP. Members of the panal conscientiously examined 155 references but found no conclusive answer to their question.
“We couldn’t determine which approach is best, based on our understanding of the literature,” said panel chair Ronald F. Grossman, MD, a professor of medicine at the University of Toronto and a pulmonologist at Toronto’s Mt. Sinai Hospital.
Panel findings are published in a supplement included with the April edition of Chest1. Although Grossman said some people would be disappointed with the results, panel members suggested hospitals continue their current practice until more randomized controlled trials are conducted to clarify the issue.
Two such trials recently published did not favor one approach or the other in the final statistical analysis. One study, described by Grossman as a “small pilot trial,” found no difference in outcomes but slightly favored the least invasive approach. The second study also reported no difference in long-term outcomes, but the Paris-based investigators noted the invasive approach used fewer antibiotics.
While the debate continues, RTs at the bedside should look for early-warning signs of VAP and maintain stringent universal precautions to keep mortality and morbidity from VAP at a minimum. Grossman recommends keeping ventilator patients in a semi-upright position and carefully washing hands before approaching patients as “the two most effective ways” of preventing VAP.
Richard G. Wunderink, MD, director of the research department at Methodist Healthcare in Memphis, Tenn., offered similar advice. He also urged RTs to look for increased secretions and high minute ventilation in patients with healthy lungs.
Therapists must pay scrupulous attention to cleaning respiratory equipment, but both doctors said tubing and circuits should be changed as infrequently as possible since studies show that frequent changes increase the risk of VAP.
“It makes good sense when you think about it in terms of handling the airway,” Wunderink said.
Writing in Chest2, Wunderink suggested continuous aspiration of subglotic secretions can reduce the incidence of VAP, especially in surgical patients. In the same edition of Chest3, Marin Kollef, MD, of Barnes-Jewish Hospital in St. Louis, Mo., described how clinicians employed that method to “significantly” delay the occurrence of VAP in patients undergoing cardiac surgery.
The study involved 343 patients who required mechanical ventilation. Of that group, 160 patients received continuous aspiration and 183 received routine post-operative care. Clinicians identified VAP in 8 patients in the study group and 15 in the control group.
“A lot of people have this false impression that a cuffed tube prevents aspiration,” Wunderink told ADVANCE, but the cuffed tube prevents only “macro aspiration,” not small leaks every time patients turn their heads. “Millions of bugs just got down to the lower respiratory tract,” when that happened, he said.
Wunderink advocates placing patients in a semi-upright position to reduce the risk of such leaks.
Kollef discussed prevention of VAP in detail in the New England Journal of Medicine4 including a description of the pathogenesis plus pharmacologic and non-pharmacologic strategies. He included continuous subglottic suctioning, humidification with heat and moisture exchangers to minimize condensate within ventilator circuits and postural changes among the non-pharmacologic strategies. On the pharmacologic side, Kollef noted stress ulcer prophylaxis could be administered because ventilator patients are at risk for gastrointestinal bleeding from stress ulcers. He also suggested the role of gastric pH in the pathogenesis of VAP is controversial.
On the cutting edge, Kollef reported some clinicians have tried immunoglobulin, which reduced the overall incidence of VAP but proved expensive and fraught with side effects. Others have tried vaccines against specific pathogens such as H. influenzae and S. pneumoniae. Prophylactic treatment of neutropenia has also been tried since the presence of the condition has been linked to increased risk for both community-acquired and nosocomial infections.
In the big picture, nosocomial pneumonia is a killer at large in the nation’s hospitals, accounting for approximately 30 percent of deaths from hospital-acquired infections. Much of the pneumonia occurs in the ICU, and critical care clinicians view it as a particularly nasty enemy they find difficult to tame.
“Dreaded,” is the adjective Kollef chooses.
Ventilator-associated pneumonia stands in a class by itself and is associated with higher mortality rates, prolonged hospital stays and higher medical costs. It appears to follow two paths: First is early onset VAP, that occurs within 2-4 days of intubation and is often due to antibiotic-sensitive bacteria such as S. aureus, according to Kollef’s NEJM article. Second is late-onset VAP, which may be associated with antibiotic-resistant pathogens such as P. aeruginosa, acinetobactor species and enterobacter species.
Depending on the population studied, the prevalence of VAP may range from as low as 6 patients per 100 to as high as 52 patients per 100, according to Grossman and his team. They noted the crude rate of VAP increases from 1 to 3 percent for every day a patient receives mechanical ventilation; the death rate increases from two-fold to 10-fold during the same time period.
These statistics paint a sobering picture for ICU clinicians as they strive to reduce the incidence of VAP infection.
Invasive medical devices are considered important contributors to the pathogenesis and development of VAP, Kollef suggested. These culprits include nasogastric tubes that predispose patients to gastric reflux and aspiration, endotracheal tubes that fall prey to bacterial colonization, pools of contaminated secretions generated by a mucosal above the endotracheal tube-cuff and ventilator circuits and respiratory therapy equipment.
Wunderink favors two high doses of one antibiotic to treat early-onset VAP because it is usually associated with bacteria from aspirating gastric contents or leaking from secretions above the cuff. At this early stage, the pathogens are sensitive to antibiotics and the patient recovers from the pneumonia.
“Frankly, early onset pneumonia doesn’t often kill patients,” he said.
When late-onset VAP invades the body, clinicians must consider several sites of infection, including sites of indwelling catheters and central lines, and the sinuses. Late-onset VAP often involves drug-resistant pathogens so heavy-hitting and expensive antibiotics may be necessary to reverse the disease process.
Clinicians have no successful strategies for preventing late-onset VAP, except, as Wunderink wrote, “an accurate diagnosis of early-onset VAP and avoidance of antibiotics as much as possible.”
Grossman said some clinicians have tried rotating beds but he considers this “a very expensive option.”
Ideally, rapid extubation is the goal for all ventilator patients. The longer the tube is in place, the more vulnerable patients are to VAP and other complications. *
1. Grossman RF, et al. Evidence-based assessment of diagnostic tests for ventilator-associated pneumonia. Chest (April 2000; 117,4: supp 2.).
2. Wunderink RG. Prevention of ventilator-associated pneumonia: Does one size fit all? Chest (Nov. 1999; 116:1155-1156).
3. Kollef MH, et al. A randomized clinical trial of continous aspiration of subglottic secretions in cardiac surgery patients. Chest (Nov, 1999; 116:1339-1346).
4. Kollef MH. The prevention of ventilator-associated pneumonia. New England J. Medicine (Feb. 25, 1999; 8: 340: 627-634).
Francie Scott is an ADVANCE senior editor.
Some Infection Rates Moving Downward
Good news emerged last year from the 285 hospitals in 42 states that reported their data to the National Nosocomial Infections Surveillance (NNIS) program. During the past decade, risk-adjusted infection rates had decreased for three body sites: the respiratory tract, the urinary tract and the bloodstream.
Statisticians, using data collected between 1997 and 1999 as a benchmark, reported their findings in the Morbidity and Mortality Weekly Report 1 recently.
Bloodstream infection dropped the most dramatically (44 percent) in medical ICUs, and coronary ICUs (43 percent). A 32 percent drop was logged in pediatric ICUs.
Ventilator-associated pneumonia (VAP) rates were highest in surgical ICUs (13.0 cases of pneumonia for every 1,000 days a ventilator was in use). The lowest rates of VAP were reported from pediatric ICUs, at 5.0 cases per 1,000 ventilator days. Sick children were not always so fortunate. The NNIS figures showed pediatric ICUs reported the highest rate of bloodstream infection associated with a central line, at 4.3 bloodstream infections per 1,000 days a central line was used.
Not surprisingly, a compilation of the data showed ICU patients are at highest risk for contracting a nosocomial infection.
The voluntary hospital reporting system, NNIS, was established in 1970 to monitor hospital-acquired infection and to guide prevention efforts. At that time, 62 hospitals in 31 states contributed data to the system. All NNIS hospitals operate more than 100 beds and most are licensed for more. The median size of an NNIS hospital is 360 beds.
Infection control practitioners who are trained at the Centers for Disease Control in Atlanta drive the program.
–By Francie Scott
Monitoring hospital-acquired infections to promote patient safety–United States, 1990-1999. Morbidity and Mortality Weekly Report (1999; 49 (8): 149-153).