Page 702 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 59: Ventilator-Associated Pneumonia 521

■ INCIDENCE

examination of pulmonary secretions, intrinsic antibacterial activities The exact incidence varies widely depending on the case definition
of antimicrobial agents, and their pharmacokinetic characteristics. of pneumonia and the population being evaluated. 22-27 All studies,
• Once the microbiologic data become available, antimicrobial ther- however, have confirmed that nosocomial pneumonia is considerably
apy should be reevaluated in order to avoid prolonged use of a more frequent in ventilated patients than in other ICU patients, with
broader spectrum of antibiotic therapy than is justified by the avail- an incidence increasing by as much as 6- to 20-fold in this subset of
able information. For many patients, including those with late-onset patients. VAP occurs in 9% to 27% of all intubated patients and its
6,28
infection, the culture data will not show the presence of highly resis- incidence increases with duration of ventilation. 26,29 The risk of VAP is
tant pathogens, and in these individuals, therapy can be narrowed highest early in the course of hospital stay, and is estimated to be 3% per
or even reduced to a single agent in light of the susceptibility pattern day during the first 5 days of ventilation, 2% per day during days 5 to
of the causative pathogens without risking inappropriate treatment. 10 of ventilation, and 1% per day after this. Because most mechanical
29
• Some very simple, no-cost measures, such as avoiding nasal inser- ventilation is short term, approximately half of all episodes of VAP occur
tion of endotracheal and gastric tubes, maintaining the endotra- within the first 4 days of mechanical ventilation.
cheal tube cuff pressure above 20 cm H O to prevent leakage of In a large epidemiological study, independent predictors of VAP
2
bacteria around the cuff into the lower respiratory tract, removal of retained by multivariable analysis were a primary admitting diagnosis
ventilator tubing condensates with minimal exposure to patients, of burns, trauma, central nervous system disease, respiratory disease,
placement of ventilated patients in a semirecumbent position cardiac disease, mechanical ventilation during the preceding 24 hours,
when enteral nutrition is used, providing adequate oral hygiene witnessed aspiration, and use of paralytic agents. Exposure to antibiotics
with an antiseptic such as chlorhexidine, as well as avoiding unnec- conferred protection, but this effect was attenuated over time. 29
essary sedation, may have an impact on the frequency of VAP. According to four studies, the VAP rate was higher in patients with
ARDS than other ventilated patients, affecting between 34% and >70%
of patients with ARDS and often leading to the development of sepsis,
multiple organ failure and death. 10,30-32
Ventilator-associated pneumonia (VAP) remains a major cause of
spectrum antimicrobial agents, major advances in the management of ■ MORTALITY, MORBIDITY, AND COST
mortality and morbidity despite the introduction of potent broad-
ventilator-dependent patients admitted to ICUs, and the use of pre- Mechanically ventilated patients in the ICU with VAP appear to have a
ventive measures, including the routine use of effective procedures to two- to tenfold higher risk of death as compared with patients without
disinfect respiratory equipment. Rates of pneumonia are considerably pneumonia. Although these statistics indicate that VAP can be lethal,
higher among patients hospitalized in ICUs compared with those in previous studies have not demonstrated clearly that pneumonia is
33
hospital wards, and the risk of pneumonia is increased three- to tenfold responsible for the higher mortality rate of these patients. It is often
for the intubated patient on mechanical ventilation (MV). In contrast difficult to determine whether ICU patients with severe underlying ill-
1-8
to infections of more frequently involved organs (eg, urinary tract and ness would have survived if VAP had not occurred. VAP, however, has
skin), for which mortality is low, ranging from 1% to 4%, the mortality been recognized in several case-controlled studies or studies using mul-
rate for VAP, defined as pneumonia occurring more than 48 hours after tivariate analysis as an important prognostic factor for different groups
endotracheal intubation and initiation of MV, ranges from 20% to 50% of critically ill patients. 8,33-37
and can reach >70% in some specific settings or when lung infection is Other factors beyond the simple development of VAP, such as the
caused by high-risk pathogens. 2,9-14 Because several studies have shown severity of the disease, the responsible pathogens or the appropriateness
that appropriate antimicrobial treatment of patients with VAP signifi- of initial treatment, may be more important determinants of outcome
cantly improves outcome, more rapid identification of infected patients for patients in whom pneumonia develops. Indeed, it may be that VAP
38
and accurate selection of antimicrobial agents represent important clini- increases mortality only in the subset of patients with intermediate sever-
37
cal goals. 2,9-16 However, consensus on appropriate diagnostic, therapeu- ity of illness, when initial treatment is inappropriate, 13,15,39-44 and/or in
tic, and preventive strategies for VAP has yet to be reached. patients with VAP caused by high-risk pathogens, such as P. aeruginosa. 38,45
Patients with very low severity and early-onset pneumonia caused by
EPIDEMIOLOGY organisms such as Haemophilus influenzae or Streptococcus pneumoniae
have excellent prognoses with or without VAP, whereas very ill patients
Accurate data on the epidemiology of VAP are limited by the lack of with late-onset VAP occurring while they are in a quasi-terminal state
standardized criteria for its diagnosis. Conceptually, VAP is defined as would be unlikely to survive. Using a multistate progressive disability
an inflammation of the lung parenchyma caused by infectious agents not model that appropriately handled VAP as a time-dependent event
present or incubating at the time MV was started. Despite the clarity of in a high-quality database of 2873 mechanically ventilated patients,
this conception, the past three decades have witnessed the appearance of Nguile-Makao et al recently showed that VAP attributable mortality was
numerous operational definitions, none of which is universally accepted. 8.1% overall, varying widely with case-mix, severity at admission, time
Even definitions based on histopathologic findings at autopsy may fail to VAP onset, and severity of organ dysfunction at VAP onset. These
38
to find consensus or provide certainty. Pneumonia in focal areas of a results are consistent with the 10.6% value obtained in five German
lobe may be missed, microbiologic studies may be negative despite the ICUs using also a multistate progressive disability model and other
presence of inflammation in the lung, and pathologists may disagree on studies having used similar methodology for determining attributable
the findings. 17-20 The absence of a “gold standard” continues to fuel con- mortality. 46,47
troversy about the adequacy and relevance of many studies in this field. It is impossible to evaluate precisely the morbidity and excess costs
Prolonged (>48 hours) MV is the most important factor associated associated with VAP. All studies, however, have shown clearly that
with nosocomial pneumonia. However, VAP may occur within the first patients with VAP have prolonged duration of mechanical ventilation
48 hours following intubation. Since the seminal study by Langer and and lengthened ICU and hospital stay as compared with patients who
colleagues, it is usual to distinguish early-onset VAP, which occurs dur- do not have VAP. 1,3,48,49 Summarizing available data, VAP appears to
ing the first 4 days of MV, from late-onset VAP, which develops 5 days extend the ICU stay by at least 4 to 6 days, with the attributable ICU
or more after initiation of MV. Not only are the causative pathogens length of stay being longer for medical than surgical patients and for
21
commonly different, but the disease also is usually less severe and the patients infected with “high-risk” as opposed to “low-risk” organisms.
50
prognosis better in early-onset than late-onset VAP. 1,3 The prolonged hospitalization of patients with VAP underscores the

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