Page 705 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

524 PART 4: Pulmonary Disorders

low-pressure cuffs further lowered it to 20%. Leakage around the cuff inconsistency in the efficacy of the semirecumbent position on VAP
107
allows secretions pooled above the cuff to enter the trachea; this mecha- prevention was confirmed by a recent meta-analysis that pooled data
nism, recently confirmed, underlines the importance of maintaining from all randomized trials and did not find a significant reduction of
adequate intracuff pressure for preventing VAP. 108 clinically or microbiologically diagnosed VAP. 126
In addition to the presence of endotracheal tubes, reintubation is, ■
per se, a risk factor for VAP. This finding probably reflects an RESPIRATORY EQUIPMENT
109
increased risk of aspiration of colonized oropharyngeal secretions into Ventilators with humidifying cascades often have high levels of tubing
the lower airways by patients with subglottic dysfunction or impaired colonization and condensate formation that may also be risk factors for
consciousness after several days of intubation. Another explanation is pneumonia. The rate of condensate formation in the ventilator circuit is
direct aspiration of gastric contents into the lower airways, particularly linked to the temperature difference between the inspiratory-phase gas
when a nasogastric tube is kept in place after extubation. and the ambient temperature, and may be as high as 20 to 40 mL/h. 127,128
Some investigators postulated that early tracheotomy could lower Examination of condensate colonization in 20 circuits detected a median
VAP rate because it can permit easier oral hygiene and bronchopulmo- level of 2.0 × 10 organisms/mL, and 73% of the 52 gram-negative
5
nary toilet or less time spent deeply sedated. Such benefit, however, isolates present in the patients’ sputum samples were subsequently
110
was not confirmed in other studies, including two large recent random- isolated from condensates. Because most of the tubing colonization
128
ized trials having systematically evaluated this issue. 111-114 was derived from the patients’ secretions, the highest bacterial counts
■ NASOGASTRIC TUBE, ENTERAL FEEDING, AND PATIENT POSITION were present near the endotracheal tube. Simple procedures, such as
turning the patient or raising the bed rail, may accidentally spill con-
129
Almost all ventilated patients have a nasogastric tube inserted to taminated condensate directly into the patient’s tracheobronchial tree.
evacuate gastric and enteral secretions, prevent gastric distention, and/ Inoculation of large amounts of fluid with high bacterial concentrations
or provide nutritional support. The nasogastric tube is not generally is an excellent way to overwhelm pulmonary defense mechanisms and
considered to be a potential risk factor for VAP, but it may increase oro- cause pneumonia. Heating ventilator tubing markedly lowers the rate of
pharyngeal colonization, cause stagnation of oropharyngeal secretions, condensate formation, but heated circuits are often nondisposable and
and increase reflux and the risk of aspiration. A multivariate analysis are expensive. In-line devices with one-way valves to collect the con-
retained the presence of a nasogastric tube as one of the three indepen- densate are probably the easiest way to handle this problem; they must
dent risk factors for nosocomial pneumonia based on a series of 203 be correctly positioned into disposable circuits and emptied regularly.
patients admitted to the ICU for 72 hours or more. 80 To decrease condensation and moisture accumulation in ventila-
Early initiation of enteral feeding is generally regarded as beneficial in tor circuits, several studies have investigated the use of heat-moisture
critically ill patients, but it may increase the risk of gastric colonization, exchangers (HME) in place of conventional heated-water humidifica-
gastroesophageal reflux, aspiration and pneumonia. 115,116 The aspiration tion systems. Slightly lower VAP rates were observed in four studies
rate generally varies as a function of differences in the patient popula- and a significant difference in a fifth study, suggesting that HME are
tion, neurological function, type of feeding tube, location of the feed- at least comparable to heated humidifiers and may be associated with
ing port and method of evaluating aspiration. Clinical impressions and lower VAP rates than heated humidifiers. 130-134 Changing the HME every
preliminary data suggest that postpyloric or jejunal feeding entails less 48 hours did not affect ventilator-circuit colonization and the authors
risk of aspiration and may therefore be associated with fewer infectious concluded that the cost of mechanical ventilation might be substantially
complications than gastric feeding, although this point remains contro- reduced without any detriment to the patient by prolonging the time
135
versial. 117,118 Nonetheless, aspiration can easily occur should the feeding between HME changes from 24 to 48 hours. Furthermore, using
tube be inadvertently dislodged. A retrospective study of noncritically ill HME may decrease the nurses’ workload (no need to refill cascades, to
adult patients showed a 40% rate of accidental feeding-tube dislodgment, void water traps on circuits, and so on), decrease the number of septic
but all the patients whose tube was dislodged were confused, disoriented procedures (it was clearly shown that respiratory tubing condensates
or had altered awareness, as is frequently observed in ICU patients. 119 must be handled as an infectious waste), and reduce the cost of mechani-
Maintaining ventilated patients with a nasogastric tube in place in a cal ventilation, especially when used for prolonged periods without
supine position is also a risk factor for aspiration of gastric contents into change. Because some observational studies, however, have documented
the lower airways. When radioactive material was injected through a an increased resistive load and a larger dead space associated with
nasogastric tube directly into the stomach of 19 ventilated patients, the exchangers, 136,137 their use should be discouraged in patients with ARDS
mean radioactive counts in endobronchial secretions were higher in a ventilated with a low tidal volume and in patients with COPD during
time-dependent fashion in samples obtained from patients in a supine the weaning period, if pressure support, and not T-piece trials, are used.
position than in those obtained from patients in a semirecumbent posi- There is no apparent advantage to changing ventilator circuits
tion. The same microorganisms were isolated from the stomach, phar- frequently for VAP prevention. This holds true whether circuits are
120
ynx and endobronchial samples of 32% of the specimens taken while changed every 2 days or every 7 days compared with no change at all, and
patients were lying supine. The same investigators conducted a random- whether they are changed weekly as opposed to 3 times per week. 138-140
ized trial comparing semirecumbent and supine positions. The trial, A policy of no circuit changes or infrequent circuit changes is simple to
121
which included 86 intubated and ventilated patients, was stopped after implement and the costs are likely lower than those generated by regular,
the planned interim analysis because the frequency and the risk of VAP frequent circuit changes; thus, such a policy is strongly recommended by
were significantly lower for the semirecumbent group. These findings the 1997 CDC guidelines and other guidelines. 141-143
of the supine patient during the first 24 hours of mechanical ventila- ■ SINUSITIS
were indirectly confirmed by the demonstration that the head position
tion was an independent risk factor for acquiring VAP. However, to While many studies have compared the risk of nosocomial sinusitis as a
36
what degree of elevation the head of bed should be targeted remains function of the intubation method used and the associated risk of VAP,
controversial. 122-125 Van Nieuwenhoven and colleagues randomized 221 only a few were adequately powered to give a clear answer. In one study of
patients to be placed either in the semirecumbent position or supine, 300 patients who required mechanical ventilation for at least 7 days and
but not completely flat. In that study, microbiologically confirmed as were randomly assigned to undergo nasotracheal or orotracheal intuba-
well as clinically diagnosed VAP were not different between the groups. tion, computed tomographic evidence of sinusitis was observed slightly
Importantly, the feasibility of the 45° elevation of the head was also more frequently in the nasal than oral endotracheal group (p = 0.08),
challenged by the authors, who were unable to maintain this position but this difference disappeared when only bacteriologically confirmed
in their patients despite constant monitoring of bed position. The sinusitis was considered. 144
125

section04.indd 524 1/23/2015 2:20:33 PM