diagnosis of ventilator-associated pneumonia by ......diagnosis of ventilator-associatedpneumonia by...
TRANSCRIPT
Diagnosis of Ventilator-associated Pneumonia by BacteriologicAnalysis of Bronchoscopic and Nonbronchoscopic "Blind"Bronchoalveolar Lavage Fluid1
,2
JEROME PUGIN, RAYMOND AUCKENTHALER, NABIL Mill, JEAN-PAUL JANSSENS,~ DANIEL LEW, and PETER M. SUTER
SUMMARY Substantial efforts have been devoted to improving the means for early and accuratediagnosis of ventilator-associated (VA)pneumonia in intensive care unit (leU) patients because ofIts high incidence and mortality. A good diagnostic yield has been reported from quantitative cultures of bronchoalveolar lavage (BAL) fluid or aprotected specimen brush, both obtained by flberoptic bronchoscopy. As bronchoscopy requires specific skills and is costly, we evaluated a simplermethod to obtain BAL fluid, that Is, by a catheter Introduced blindly into the bronchial tree. Quantitative cultures from bronchoscoplcally sampled BAL (B-BAL) and blindly nonbronchoscopically collected BAL (NB-BAL) were assessed for sensitivity, specificity, and predictive value for the diagnosisof VApneumonia. A total of 40 pairs of samples were examined in 28 patients requiring prolongedmechanical ventilation and presenting a high risk of developing pneumonia. For comparison withbacteriologic data we defined a clinical score for pneumonia ranging from zero to 12 using the following variables: body temperature, leukocyte count, volume and character of tracheal seerettens,arterial oxygenation, chest X-ray,Gram stain, and culture of tracheal aspirate. Toquantify the bacteria In BAL the bacterial Index (BI) was used, defined as the sum of the logarithm of the numberof bacteria cultured per milliliter of BAL fluid. A good correlation between clinical score and quantitative bacteriology was observed (r = 0.84 for B-BAL and 0.76 for NB-BAL; p < 0.0001). Similarto studies in baboons, patients with pulmonary infection could be distinguished by a BI ~ 5 witha sensitivity of 93% and a specificity of 100% (B-BAL). Quantitative culture of blind sampling ofBAL resulted in a slightly lower sensitivity (73%) and a specificity of 96% for the diagnosis of pneumonia. When analyzing pairs of B-BAL and NB-BAL samples we found similar results for both qualitative and quantitative bacteriology even if BAL fluids came from different lobes or the contralaterallung. These results suggest that "blind" sampling of BAL can be of value In clinical practice. Microscopic examination of BAL provided rapid (the day of BAL), sensitive (100%), and specific (88%)results, allOWing us to Introduce early and specific antibiotic therapy.
AM REV RESPIR DIS 1991; 143:1121-1129
IntroductionBacterial pneumonia is a frequent complication in patients requiring mechanical ventilation in an intensive care unit(lCU) and carries a significant mortality. Craven and colleagues reported a 20%incidence of nosocomial pneumonia ina general ICU (1),but this figure is higher in certain conditions, such as the adultrespiratory distress syndrome (ARDS)(2). The risk of developing ventilatorassociated (VA)pneumonia rises linearly by about 1%/day, with most of thepneumonias occurring in the first 8 daysafter intubation (3, 4). The mortality rateof VA pneumonia reaches 50 to 70070(1, 3-6).
This condition presents a major diagnostic challenge because of the low yieldof clinical criteria, such as fever, leukocytosis, or radiology (2, 3, 7). When theseparameters are combined the predictivevalue is higher, but still less than 100%,particularly in ARDS (7). The distinction between tracheobronchial colonization and pulmonary infection is also difficult if the standard semiquantitativemethod is used for culture of trachealaspirates (8). Using quantitative cultureswith a threshold of 107 bacteria/ml allows one to exclude false positive resultsdue to contamination or colonization (9).Salata and coworkers report a significantdifference between infected and colonized patients with this method (106 versus 104 bacteria/ml), but a large overlapbetween the two groups results in a lowspecificity of this costly technique (5).The same authors showed that the finding of 3+ bacteria on a Gram stain ofbronchial secretions together with thepresence of elastin fibers on a KOH stainwas associated with a high probabilityof nosocomial pneumonia.
A more invasive approach has beenproposed by Chastre and colleagues (10),that is, bronchoscopy and quantitative
culture of a protected specimen brush(PSB). By using 103 bacteria/ml as athreshold the sensitivity was almost 90070and the positive predictive value above75% for the detection of VApneumonia(3, 11). The disadvantages of a PSB technique are (1) high cost, (2) significantmorbidity (1 to 25070 incidence of pneumothorax or bleeding) (7, 11-13), (3) falsenegative results (14, 15), and (4) the 24to 48-h delay in obtaining the results ofbacterial cultures (14). To overcome theproblem of delay Chastre and coworkers combined PSB with counting polymorphonuclear leukocytes (PMN) containing intracellular bacteria in bronchoalveolar lavage (BAL) fluid (14). VApneumonia was associated with the presence of more than 15% of infected PMN.
Johanson and colleagues evaluatedquantification of bacteria in BAL fluid
for the diagnosis of pneumonia in a baboon model (15). In this study the correlation was good between the quantitative culture of bacteria in BAL fluid andboth the quantitative cultures of the pulmonary lobe sampled as wellas the mostinfected lobe at the time of sacrifice.These results suggest that there are no
(Received in original form February 26, 1990 andin revised form November 28, 1990)
1 From the Division of Surgical Intensive Care,Department of Anesthesiology, the Divisions of Infectious Diseases and Pneumology, Department ofMedicine, University Hospital of Geneva, Geneva,Switzerland.
2 Correspondence and requests for reprintsshould be addressed to Dr. Jerome Pugin or Dr.Peter M. Suter, Division of Surgical Intensive Care,University Hospital of Geneva, 24, rue Micheli-duCrest, CH-1211 Geneva 4, Switzerland.
1121
1122 PUGIN, AUCKENTHALER, Mill, JANSSENS, LEW, AND SUTER
* Total points = CPIS (varies from 0 to 12 points).
TABLE 1
CPIS USED FOR THE DIAGNOSIS OF VA PNEUMONIA*
1. Temperature °C~ 36.5 and ~ 38.4 = 0 point~ 38.5 and ~ 38.9 = 1 point~ 39 or ~ 36.0 = 2 points
2. Blood leukocytes, rnrn?~ 4,000 and ~ 11,000 = 0 point< 4,000 or > 11,000 = 1 point + band forms ~ 500 = + 1 point
3. Tracheal secretions< 14 + of tracheal secretions = 0 point~ 14 + of tracheal secretions = 1 point + purulent secretion = + 1 point
4. Oxygenation: Pao/Flo2' mm Hg> 240 or ARDS = 0 point~ 240 and no evidence of ARDS = 2 points
5. Pulmonary radiographyNo infiltrate = 0 pointDiffused (or patchy) infiltrate = 1 pointLocalized infiltrate = 2 points
6. Culture of tracheal aspirate (semiquantitative: 0-1-2 or 3+)Pathogenic bacteria cultured ~ 1+ or no growth = 0 pointPathogenic bacteria cultured> 1+ = 1 point + same pathogenic bacteria seen
on the Gram stain> 1 + = + 1 point
significant differences in the bacteriologic findings when sampling is done indifferent sites. This important point remains to be demonstrated in ventilatedpatients with a radiologically localizedinfiltrate. Johanson's group also observed a comparable specificity for theresults of BAL and PSB in the baboonmodel, but the sensitivity was clearly superior for BAL (100 versus 62070) (15).Torres and coworkers found an equivalent diagnostic yield with both techniquesin mechanically ventilated patients (11).Quantitative culture of bronchoscopicBAL (B-BAL) was used recently in immunocompromised patients. Growth ofmore than 105 bacteria/ml in BAL fluidwas associated with a pneumonia (16, 17).
B-BAL needs expertise and training.Nonbronchoscopic, that is, "blind" BAL(NB-BAL) sampling is much simpler andwas first used in the acquired immunodeficiency syndrome (18, 19) and then inintubated patients in the leu (20, 21).Qualitative bacteriologic results fromNB"BAL gave results similar to those obtained by PSB or postmortem culture (20,21). However, no attempt was made todifferentiate between colonized and infected patients.
The aims of the present study were firstto validate a new, blind sampling method that is less costly and simpler to perform by comparing quantitative bacteriology obtained by BAL with a fiberoptic bronchoscope with BAL sampledblindly with a new catheter. Second, weattempted to determine early criteria forthe diagnosis of pulmonary infection bymicroscopic examination of BAL. Ourfindings suggest that blind BAL samplingcombined with quantitative bacteriology gives an accurate diagnosis of pneumonia. Rapid diagnosis is possible usingthe Gram stain together with a stainingtechnique for elastin fibers in BAL fluid.
Methods
PatientsOver a 6-month period from January 1 toJune 30, 1989,28 ventilated patients at highrisk for developing a nosocomial pneumoniawere studied in the division of surgical intensive care at the University Hospital, Geneva,Switzerland. This is a 20-bed unit with 1,300admissions/yr. Patients were included in thestudy if they had been intubated and mechanically ventilated for more than 72 h and hada recognized predisposing pathology, such asmultiple trauma, cerebraltrauma, major emergency surgery, esophagectomy, or postoperative complications of cardiovascular surgery.Of these 28 patients 19 were studied once(680/0), 6 werestudied twice several days apart
(21 %), and 3 were investigated three times(11%). A total of 40 episodes were studied.
The APACHE II score was used to assessthe severity of the clinical condition at thetime of admission to the ICU (22). The percentage of patients with ARDS and the number of days ofprior and total mechanical ventilation were noted. The l-month mortalitywas recorded. Postmortem findings (if autopsy was performed) were noted.
The study was approved by the committeefor ethics in human research of our institution. Informed consent was obtained fromthe patient or, if this wasnot possible becauseof the clinical condition, by a member of thefamily or the treating physician.
Clinical VariablesThe following variables were recorded for the2 days before the study and on the day of investigation: (1) body temperature; (2) bloodleukocyte count and number of band forms;(3) character of tracheal secretions (purulentor not) and quantity of tracheal aspirates (foreach endotracheal aspiration the nurses estimated the quantity of secretions from 0 to4+s; estimation of the volume of total secretions per day was calculated by adding all the+ values recorded over 24 h together; to ensure a certain uniformity of this estimationonly nurses having at least 2 yr of continuoustraining in our ICU participated in this investigation; the total number of tracheal aspirations also was recorded); (4) microscopicexamination (Gram stain) and semiquantitative culture of the bronchial secretions; (5)arterial oxygen tension/inspiratory fractionof oxygen (Pac/PI02); and (6) chest X-ray.The presence of bacteremia or positive culture of the pleural fluid in the 5 days preceding and the 5 days following BAL were compared with bacteria cultured from sputum andin BAL fluids.
A clinicalpulmonary infection score (CPIS)
with a range of 0 to 12 was obtained fromthese clinical parameters (table 1).The rangeand weighting for temperature, leukocytes,sputum culture, and character as wellas chestX-rayweredetermined from published studies(2, 22-25). The range and weight for thePa02/Fl02 ratio and the sputum volume weredetermined by retrospective analysis of thefrequency of distribution.
Bronchoalveolar Lavage (BAL)The two BAL techniques were performed ina sequential manner in all patients, startingwith bronchoscopic BAL. The heart rate, systemic arterial pressure, and arterial oxygensaturation (Sa02) weremonitored throughoutthe procedure. The study was stopped if Sa02fell below 900/0 or if the patient becamehypotensive (mean systemic arterial pressurebelow 60 mm Hg). The majority of the central nervous system trauma patients had intracranial pressure monitoring. The study wasstopped if the cerebral perfusion pressure (thatis, mean systemic arterial pressure minus intracranial pressure) fell below 60 mm Hg.
Before starting BAL all patients were ventilated with 100% oxygen and sedated withmidazolam and morphine intravenously;head-injured patients weregivensodium pentothal. All patients received ventilatory support during the study with a 20070 increasein tidal volume. The site for B-BAL was chosen according to chest X-ray appearance.B-BAL was performed in an area of localized pulmonary infiltration if present. Whena diffuse infiltrate or no infiltrate was seenon X-ray B-BAL was performed in the mostinflamed or purulent pulmonary segment determined by visual inspection. If no inflammation or purulent secretions were seenB-BAL was performed in the right lower ormiddle lobe. B-BAL was performed via theendotracheal tube using a swivel adaptor(Bodai Suction-Safe", SwivelY,Sontek Med-
ACCURATE DIAGNOSIS OF VENTILATOR-ASSOCIATED PNEUMONIA 1123
Fig. 1. Chest X-ray showing position of catheter introduced "blindly" and territory sampled by SAL. Films are takenafter injection of 5 ml contrast liquid. (Left) Antero-posterior view; (right), right oblique posterior view.
ical, Hingham, MA). Under visual control thebronchoscope was advanced in the directionof the chosen pulmonary segment until awedged position was achieved. Lavage wascarried out using two aliquots of 50 ml sterileisotonic saline. The bronchoscope was removed and ventilation with an FI02 of 100%continued for a further 10 min (26).
NB-BAL was then performed using a flexible, single-lumen, 14French polyvinyl catheter with a proximal Luer adaptor, stiffenedwith a metallic Teflonv-coated, guide wire(catheter for duodenography no. PVI4.0-75P-NS-BBD; Cook A.G., Sempach-Station,Switzerland). The catheter was introduced ina blind manner through the same swivel adaptor used for the B-BAL. It was advanced until a resistance (generally at a distance of 50to 60 em from the adaptor) was felt and maintained in a wedged position. The guide wirewas then removed and the lavage performedwith two aliquots of 50 ml sterile isotonic saline. For NB-BAL as well as for B-BAL lavage with a third aliquot of 40 to 50 ml wasperformed if there was a poor yield from thefirst 100ml. In severe pulmonary failure, thatis, ARDS patients, BAL was done with a total of 60 to 75 ml. After NB-BAL the catheter was maintained in the wedged position and5 ml contrast liquid (Omnipaques-Sou; Schering A.G. Pharma, Berlin, Germany) was injected to determine the site of BAL. An anteroposterior and oblique chest film were taken (figure 1). The site of NB-BAL was thenassessed in a blind manner by a radiologistwho had no knowledge of the patient's condition. BAL samples were sent to the bacteriology laboratory within 5 min and processedimmediately. The sequence B-BAL followedby NB-BAL was maintained for the wholestudy because the contrast liquid has bacteriostatic properties and could thereby producefalse negative results for the followingexamination.
BacteriologyThe 40 pairs of BAL samples were treated in
a similar manner. To a first part of BAL fluid2 ml of dithiothreitol (Dl'T) (Sputolysin'" StatPak; Behring Diagnostics, San Diego, CA)was added, vortexed until homogenization,and then centrifuged. Supernatant (50 ul) wasplated on solid media using Spiral Plater" volume deposition (Spiral System Instruments,Inc., Bethesda, MD). Sheep blood agar,colistin nalidixic acid (CNA) agar, chocolateagar, and McConkey's agar were incubatedin 5010 CO 2 for 72 h. Legionella, mycobacteria, mycoplasma, or viruses were not cultured.Colonies were quantified and identified conventionally and sensitivity tests performed.A bacterial index (BI) was calculated for eachsample according to Johanson's formula: BI= sum of log quantity of different bacteriacultured (15).
A manual microscopic count of cells wasdone on BAL fluid using standard techniques.BAL fluid was then cytocentrifuged at 1,200rpm for 5 min (Cytospin'" 2; Shandon Southern Products, Cheshire, UK) and stained witha May-Griinwald-Giemsa for cell identification and differential count. On a Gram stainof cytocentrifuged material the quantity ofbacteria was determined with a standard scaleof 0 to 3+ according to the number of bacteria seen per oil-power field (5). Gram-negativeand gram-positive bacilli and cocci, yeasts,and the percentage of PMN containing intracellular bacteria weredetermined. The presence or absence of elastin fibers was assessedwith an elastin stain followed by microscopicexamination.
Statistical AnalysisData are expressed as means ± standard deviation (SD). An unpaired Student's t test wasused to compare the mean of two groups, theMann-Whitney U test to compare groups withvariables not normally distributed, and apaired t test for paired values. Frequenciesand categories were compared with a X2 testwith the Yates correction. Linear regressionwas calculated using the method of leastsquares. Sensitivity, specificity, and predic-
tive values were calculated according to standard formulas.
ResultsPatients and BAL Procedures
There was no significant difference inage, sex,diagnostic categories, APACHEII score, percentage of ARDS, or mortality between infected and noninfectedpatients (table 2).
No serious complications were notedduring or after the BAL procedures. Asignificant decrease in the Pao2/PIo2 ratio was observed in 40070 of patients,necessitating a temporary increase inPIo2. All patients recovered baselinevalues of oxygenation within 12 h. Noprocedure had to be stopped because ofhypoxemia, hypotension, or othercomplications.
Bacteriologic Analysis of BALA significant correlation was found between the CPIS and the BI calculatedfrom Johanson's formula (r = 0.84,p < 0.0001 for B-BAL and r = 0.76,p < 0.0001 for NB-BAL; figures 2 and3) (15). When analyzing B-BAL sampleson the plot of CPIS versus BI (figure 2),two groups of results can be identified:one group with a CPIS >6, in whom 93070of the corresponding fluids had a culture with a BI ~ 5 (defined as pulmonary infection) and a second group inwhom the CPIS was ~ 6 and all corresponding BI were < 5, patients withoutpulmonary infection. Using a CPIS > 6as clinical definition of pulmonary infection in ventilated patients, the sensitivityof the quantitative culture ofB-BALfluid assessed by the calculation of J0
hanson's BI was 93070; the specificity andpositive predictive value were 100070. TheBI calculated on NB-BAL samples gaveslightly lower sensitivity (73%), specificity (96070), and positive predictive value(92%).
Comparison of paired BI calculatedfrom B-BALand NB-BAL fluids showedno statistical difference. This was unaffected by the site of BAL sampling. Thedifference of means of the BI of samplesobtained from the same lobe was 1.6 (p= 0.23), from a different lobe 0.5 (p =0.39), from the same lung 0.2 (p = 0.77),and from the contralateral lung 0.02 (p= 0.98). Also in those cases in whomB-BAL was performed at the site of aradiologically localized pulmonary infiltrate and NB-BAL was sampled fromanother radiologically healthy site, theBI obtained by the two methods werenotsignificantly different (n = 12, mean BI
1124 PUGIN, AUCKENTHALER, MILl, JANSSENS, LEW, AND SUTER
TABLE 2
CLINICAL DATA AND DIAGNOSIS OF THE 28 PATIENTS STUDIED
No Pulmonary PulmonaryInfection Infection Total
(N = 15 Patients, (N = 13 Patients, Patientsmean ± SO) mean ± SO) p Value (N = 28)
Age, yr 51 ± 18 44 ± 21 NSAPACHE II score 12 ± 5 14 ± 6 NSSex, M:F 10:5 11:2 NS
(X2 = 0.43)
Duration of prior ventilation, days 5.3 ± 3.1 6.3 ± 4.7 NSDuration of total ventilation, days 8.7 ± 4.9 10.8 ± 6.8 NSDiagnosis
Polytrauma 3 8 11Cerebral trauma 2 2 4Complications after cardiovascular surgery 3 1 4Septic shock 1 1 2Esophagectomy 1 1 2Pancreatitis 2 0 2Peritonitis 3 0 3ARDS (%) 4 (26) 1 (7) NS 5 (18)
(X2 = 0.66)
Mortality rate, % 33 54 NS 42(X2 = 0.51)
18 ~
16
14 0c::0011I 12 No
~ G.l
~-a 10pulmonary Q)
.s~ - infection - d> 0
calli 8 0.;::~ :0
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~= 4 0 0 0 0 BI=5
= 00 ~
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0 0 am an O'W0 2 4 6 8 10 12
from B-BAL - mean BI from NB-BAL= 0.5, p = 0.44). The paired comparison of cellularity was also not significantlydifferent if samples wereobtained fromthe same site or a different site.
Patients with pneumonia receivingprophylactic intravenous antibiotic therapy (n = 8) after contaminated surgeryor open fractures had a lower BI in BAL(6.8 ± 2.1)than those (n = 7) not receiving antibiotics (9.6 ± 2.9, p < 0.05). Allbut one value was above the thresholdvalue of 5 (figure 4). Blood cultures werepositive in 2 of the 15patients with pneumonia, with bacteria identical to thoseisolated from B-BAL and NB-BAL (Patients 5 and 10). In 1 patient with pneumonia culture from pleural fluid yieldedthe same microorganism as BAL fluids(Patient 8). Of the 7 patients who diedin the group of pulmonary infections, 3patients had an autopsy within 8 days after the BAL procedures. The lungs ofthese 3 patients showed macroscopic andhistologic signs of moderate to severeconfluent bronchopneumonia. One ofthese patients also had positive blood cultures with the same organism (Pseudomonas aeruginosa) present in sputumand BAL fluids. Of the 5 patients whodied in the noninfected group of patients,3 had an autopsy: 2 of them did not showany sign of pneumonia and the third, whodied 12days after BAL, had signs of mildbronchopneumonia.
The bacteria responsible for pulmonary infection in the group of patientswith pneumonia are summarized in table 3. Of the infections 87010 were polymicrobial and the predominant bacteriacultured quantitatively were the same inB-BAL and NB-BAL in 14of 15samples(93010). In the pneumonia group one identical microorganism was cultured in bothBAL fluid and tracheobronchial secretions in 13of 15 patients (87%), but thepredominant bacteria of B-BAL fluidwere found in only 11 of 15tracheobronchial aspirates, resulting in a sensitivityof 73%. Culture of tracheal aspirateresulted in a specificity of only 48010 (13samples with bacterial growth of the 25from patients without clinical pulmonaryinfection).
Extracellular bacteria wereseen in 93%of samples from patients with pulmonaryinfection but in only 12010 of samples inthe control group. Using semiquantitative determination on a Gram stain ofBAL, gram-negative bacilli and grampositive cocci werefound more frequentlyin both B-BAL (p <0.0001) and NB-BAL(p < 0.0002) from patients with a pul-
Fig. 2. Relationship between bacterialindex, that is, the sum of log quantity ofbacteria (15)cultured from SAL obtainedby bronchoscopy and the clinical pulmonary infection score determined from 40investigations in 28 patients.
Fig. 3. Relationship between bacterialindex obtained by quantitative culturefrom nonbronchoscopic blind BAL andthe clinical pulmonary infection scoredetermined from 40 investigations in 28patients.
Fig. 4. Bacterial index (BI) in patientswith pulmonary infection depending onconcomitant antibiotic therapy for surgical prophylaxis or not. Open circles =individual values; closed circles with barindicate mean ± SD. Asterisk indicatesp < 0.05.
o '·11'" threshold:BI=5
No antibiotics(N=7)
o
I.V. antibiotics(N=8)
Clinical Pulmonary Infection Score
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1126 PUGIN, AUCKENTHALER, MILl, JANSSENS, LEW, AND SUTER
TABLE 4
B-BAL AND NB-BAL·
Bronchoscopic BAL Nonbronchoscopic BAL(N = 40) (N = 40)
No Pneumonia Pneumonia No Pneumonia Pneumonia(N = 25, Mean ± SO) (N = 15, Mean ± SO) p Value (N = 25, Mean ± SO) (N = 15, Mean ± SO) p Value
Cellularity, rnm- 1,200 ± 1,500 3,100 ± 3,400 0.02 1,500 ± 1,500 2,900 ± 2,300 0.08PMN cells, mrn- 650 ± 900 2,400 ± 2,700 0.006 650 ± 900 2,400 ± 2,200 0.001Macrophages, rnrn- 290 ± 380 340 ± 270 > 0.05 260 ± 210 240 ± 220 > 0.05Lymphocytes, rnrn- 260 ± 550 440 ± 520 > 0.05 540 ± 1,470 241 ± 240 > 0.05Gram stain"
Gram positive cocci 0.08 ± 0.28 0.6 ± 0.5 0.0002 0.08 ± 0.28 0.87 ± 0.9 0.0003Gram negative bacilli 0.04 ± 0.2 1.1 ± 0.9 < 0.0001 0.12 ± 0.28 1.1 ± 1 < 0.0001Yeasts 0.08 ± 0.28 0.2 ± 0.5 > 0.05 0.08 ± 0.27 0.13 ± 0.35 > 0.05
% PMN with intracellularbacteria 0 8.3 ± 11.5 0.0008 0 11.7 ± 14 0.0001
Presence of PMN withintracellular bacteria (%) 0/25 (0) 11/15 (73) < 0.0001 0/25 (0) 9/15 (60) < 0.0001
(X2 = 21.4) (x2 = 16.1)
Presence of elastinfibers (%) 2/25 (8) 7/15 (47) < 0.01 3/25 (12) 8/15 (53) < 0.01
(X2 = 5.9) (X2 = 6.1)
Brl: 1.7 ± 1.6 8.1 ± 2.8 < 0.0001 1.6 ± 1.8 8.4 ± 4.2 < 0.000195% Confidence interval 0.9-2.1 6.6-9.7 0.85-2.3 6.1-10.7Range 0-4.2 4.3-13.6 0-5.2 2.6-17
• Analysis of cellularity, Gram stain, and culture of the SAL fluid (40 investigations in 28 patients).t Semiquantitative: 0-1-2 or 3 + .:j: L log of cultured bacteria.
monary infection than from noninfected patients (table 4).
PMN with intracellular bacteria werefound in 73% in B-BAL and 60070 in NBBAL fluids from infected patients. Nosamples in the control group had PMNwith intracellular bacteria (p < 0.0001).The percentage of PMN containing bacteria in B-BAL fluid was 8.3 ± 11.5070and in NB-BAL 11.7 ± 14070 of all cellsin patients with pulmonary infection.
Elastin fibers were found in 47070 ofpulmonary infections compared with 8070in controls in B-BAL fluid (p < 0.01). InNB-BAL samples they were found in53070 of infected patients versus 12070 ofcontrol subjects (p < 0.01). In infectedpatients, elastin fibers were associatedwith gram-negative bacilli and radiologically localized pulmonary infiltrates (table 3). The false positive results, that is,elastin fibers seen in patients without pulmonary infection, were sampled fromtwo patients with severeARDS.
Extracellular or intracellular bacteriaor elastin fibers were seen in 100% ofsamples taken from patients with pulmonary infection but in only 12070 of thesamples of the group without infection.
There was a significant difference between the total cellularity (p <0.05) andquantity ofPMN (p <0.01) recovered inBAL fluid from infected and noninfected patients, but not in the number ofmacrophages and lymphocytes (table 4).
Clinical VariablesOf the clinical variables recorded on theday of BAL and included in the clinicalpulmonary infection score (tables 5 and6), four show a significant differencewhen comparing infected with noninfected patients: temperature, number ofbronchial aspirations that had to be performed per day, quantity of trachealsecretions, and Paa/FIa2 ratio, but notradiology, percentage of patients withpurulent tracheal secretions, blood leukocyte count, or band forms.
An analysis of the change in clinicalparameters between 2 days before BALand the day of BAL showed that patientswith pulmonary infection had an increasein the volume of secretions (p < 0.005),a decrease in the Paa/FIa2 ratio (p <0.05), a nonsignificant rise in body temperature, and no change in blood leukocyte count or band forms (table 6).
DiscussionThe management of VA pneumonia requires a rapid and accurate diagnosis.The gold standard for the diagnosis ishistology, but this is rarely available inICU patients. Most investigations of VApneumonia have therefore defined pulmonary infection using a number of clinical variables. If taken separately thesevariables do not permit one to distinguishpatients with colonization from those
with pneumonia. This is particularly truefor patients presenting with ARDS andthose requiring long-term ventilatorysupport for acute exacerbation of chronicobstructive pulmonary disease (COPD)(2, 10). Fever, leukocytosis, or X-ray abnormalities are often due to a noninfectious cause in ICU patients, explainingtheir poor sensitivity and specificity (4,7, 10).The diagnostic yield of these variables increases, however, when they arecombined.
In this report wedescribed a CPIS thatuses six easily obtained variables. Thisscore expands clinical judgment by including elements of chest X-ray and bacteriology and permits us to quantify signsof pneumonia. A good correlation wasobserved between this score and the BIof quantitative culture of BAL fluid calculated according to Johanson's method in VA pneumonia in baboons (15).Two groups of patients can be distinguished by drawing a line between theCPIS values of 6 and 7. We suggest thatpatients with a CPIS > 6 have a pneumonia, and all their bronchoscopicallyobtained BAL samples except one hada BI ~ 5. The sensitivity of detecting pulmonary infection by quantitative cultureof B-BAL was therefore 93070. The onlyfalse negative result was obtained in a patient treated for sinusitis with antibiotics active against bacteria found in hislower respiratory tract and presenting
ACCURATE DIAGNOSIS OF VENTILATOR-ASSOCIATED PNEUMONIA
TABLE 5
CLINICAL VARIABLES OBTAINED ON THE DAY OF STUDY"
1127
Temperature, 0 CBlood leukocytes/rnmBand forms, %Band forrns/mm!Number of aspirations/dayNumber of + tracheal secretions/dayPurulent tracheal secretions (%)
Pao/FI02' mm HgtPulmonary radiography (%)
No infiltrateLocalized infiltrateDiffuse infiltrate
Bacteriologic examination of tracheal secretionsGram stain§
Polymorphonuclear cellsGram-positive cocciGram-negative bacilliTotal bacteria seenll
Culture§Total bacteria cultured II
• Forty investigations in 28 patients.t ARDS not included.:t: Between no and !ocalized infiltrate.§ Semiquantitative: 0-1-2 or 3 + .IIGram-positive + gram-negative rods and cocci + yeasts.
No PulmonaryInfection
(N = 25, Mean ± SO)
38.1 ± 0.813,500 ± 5,500
10 ± 121,400 ± 2,100
4.7 ± 2.410 ± 7.5
11/25 (44)
270 ± 100
8 (32)5 (20)
12 (48)
1.7 ± 0.70.2 ± 0.4
0.08 ± 0.20.5 ± 0.9
0.7 ± 1
PulmonaryInfection
(N = 15, Mean ± SO)
38.8 ± 0.814,300 ± 5,500
12 ± 141,700 ± 2,000
7.2 ± 2.519 ± 4.5
12/15 (80)
190 ± 45
3 (20)12 (80)
o
2.4 ± 0.70.8 ± 11.7 ± 1.23.1 ± 2
3.7 ± 1.7
p Value
< 0.01NSNSNS
< 0.005< 0.001
0.057(x2 = 3.6)
< 0.01
0.063+(X2 = 3.45)
< 0.005< 0.01< 0.05< 0.0001
< 0.0001
TABLE 6
CHANGES IN CLINICAL VARIABLES BETWEEN 2 DAYS BEFORE BAL AND THE DAY OF BAL"
ity of 100070 in the detection of bacterialpneumonia.
As in Johanson's study, we observeda high incidence (87070) of polymicrobialcultures in VA pneumonia. The use ofthe BI, taking into account more thanone microorganism in BAL, seems to beimportant when comparing differentsamples. The reported incidence of polybacterial VA pneumonia seems lowerwhen the diagnosis is made by PSB (3).PSB probably recovers only a small 10cal sample, which is less representativeof the whole infected region, whereasBAL allows collection of the microfloraof an entire lung segment (27). Chastreand colleagues observed false negativeresults using PSB with a threshold valueof 103 bacteria/mI, both positive or negative results being obtained in clinicallyinfected patients (14). This group did not
with clear-cut clinical and radiologicsigns of pneumonia resulting in a CPISof 11. In patients with a CPIS ~ 6 theBI was consistently < 5, correspondingto a specificity and a positive predictivevalue of 100070 for the B-BAL. Sensitivity, specificity, and predictive values areslightly lower for NB-BAL but still seemvalid for clinical use.
Our threshold value for BI = 5 is closeto that found by Johanson's group (15).In their study on ventilated baboons aBI ~ 6 was alwaysassociated with moderate to severepneumonia on histology, butno or only mild signs ofpneumonia wereobserved when the BI was < 6. Our index of 5 is also similar to the thresholdvalue of 105 bacteria/ml cultured fromB-BAL fluid reported in immunocompromised patients (16, 17), resulting ina sensitivity of 85 to 89070 and a specific-
Body temperature, 0 CBlood leukocyte count, rnrn"Band forms, rnm-Volume of tracheal secretions, NB of +Pao/Flo2 mm Hg
Definition of abbreviation: NB '" number .• Forty investigations in 28 patients.
No PulmonaryInfection
(Mean ± SO, N = 25)
0.37 ± 0.61450 ± 6,000
-200 ± 3,000-0.3 ± 6.7
-8 ± 57
Episodes ofPulmonary Infection
(Mean ± SO, N = 15)
0.89 ± 0.95- 1,400 ± 9,000
-90 ± 1,0006.8 ± 5.6
- 57 ± 83
p Value
0.0720.460.89
< 0.005< 0.05
find a clear threshold value using Johanson's BI on BAL samples to differentiate colonization from pneumonia. Themean BI was 11.7 ± 6.2 in the 5 patientswith proven pulmonary infection, withall five values above our threshold valueof 5. However, the specificity of the BIwas low,with a high rate of false positiveresults (14). These different results areprobably due to other criteria used forthe diagnosis of pneumonia, resulting ina different classification of other typesof lower respiratory tract infection, suchas tracheobronchitis, possibly recordedas bronchial colonization (17,27-29). Inour study 3 of the 15episodes of pulmonary infection were not associated withinfiltrates on chest X-ray but with clearclinical signs of infection (CPIS of 8, 9,and 10)and BI of 5.9, 9.6, and 9.6, respectively, consistent with purulent tracheobronchitis (30). The second reason forthe discrepancy between our results ofBAL cultures and those of Chastre'sgroup (14) is a difference in the populations studied. Our population consistedmainly of young multiple trauma patients, whereas Chastre's group studiedmostly patients with COPD in whomheavy bronchial colonization is commonand could explain the high false positiverate found using the BI of BAL samplesin their study.
As in all studies of nosocomial pneu-
1128 PUGIN, AUCKENTHALER, MILl, JANSSENS, LEW, AND SUTER
monia we found a clear predominanceof aerobic gram-negativebacilli as causative bacteria. Haemophilus influenzaewas detected in 53070 of patients in ourstudy, a well-recognized miroorganism in"early-onset nosocomial pneumonia" asa primary endogenous infection, originating from oropharyngeal flora. Pollockand coworkers found H. influenzae in65070 of nosocomial pneumonia patients(30), Reusser and colleagues in 53% ofhead trauma patients (31), and Fagon andcoworkers in 33% of VApneumonia patients (3). Chastre and colleagues reported a lower incidence of early-onset pneumonia, probably because their patientshad a longer period of respiratory support before BAL (15 ± 11 versus 6.3 ±4.7 days in our study).
Weobserved a good agreement for thetype of microorganism between B-BALand NB-BAL. The predominant bacteria cultured were identical in 93%, andno significant differences were found forthe BI or the cellularity in the two samples. This wasalso true when B-BALwasperformed at the site of a localized pulmonary infiltrate and NB-BAL in adifferent lobe or the contralateral andradiologically healthy lung. This is inagreement with the data of Johanson'sgroup obtained in baboons, demonstrating that BI calculated on B-BAL samples correlated with both the culture fromthe lavaged lung lobe and the most infected lobe, that is, the greatest BI (15).This suggests that in ventilated patientsbacteriology and cellularity are similarin all pulmonary lobes and both lungseven when a localized infiltrate is present on chest X-ray. This is interesting andmay explain the good sensitivity andspecificity of a "blind" sampling technique like BAL.
Results from quantitative cultures ofBAL can only be obtained after 24 to48 h, but the proportion of PMN withintracellular bacteria seen on a Gramstain provides a more rapid diagnosis. Inpneumonia more than 15% ofPMN contain intracellular bacteria, but this wasseen in only 1 of 13BAL samples ofpatients without pneumonia (14). In ourstudy no intracellularbacteria werefoundin patients without pneumonia but in730/0 of samples from patients with pneumonia. The presence of bacteria withinPMN in BAL fluid seemsspecific (100%)but lacks sensitivity (73%). Adding extracellular and/or intracellular bacteriaand/or presence of elastin fibers improved the sensitivity in the detection ofpulmonary infection to 100070, but the
specificity fell to 88%. Elastin fibers inBAL fluid were associated with gramnegative pulmonary infection and infiltrates on chest X-ray. False positiveresults were obtained in two cases of severe ARDS in whom damage to pulmonary parenchyma is common. Our findings on elastin fibers in BAL fluid aresimilar to those reported by Salata andcoworkers (5) in sputum of ventilatedpatients.
Analysis of clinical criteria takenseparately resulted in significant differences in the mean value for several variables between the patients with and without pneumonia, with marked overlaps asreported previously (14). In our study,however, the association of clinical variables in a score (CPIS) allowed us to discriminate patients with a high concentration of bacteria in BAL from thosewith low amounts of bacteria.
Standard cultures of tracheal aspirateswere of poor value to separate infectedfrom noninfected patients (positive predictive value and specificity were 48%),confirming the results of earlier studies(8, 11).
In summary, this study describes avaluable clinical pulmonary infectionscore calculated from six easily obtainedvariables. This score correlated with thequantitative culture of BAL obtained byboth bronchoscopy and a catheter introduced blindly into the bronchial tree. Theclinical score allowed us to differentiatebetween infected and colonized patients.As previously suggested in a study onventilated baboons, we confirmed thatthe site of BAL sampling is not important for making a correct diagnosis.Quantitative bacteriology on BAL samples gave identical results irrespective ofthe pulmonary segment sampled, evenin the presence of a localized infiltrateon the chest X-ray.Quantification of extracellular and intracellular bacteria observed on the Gram stain and the searchof elastin fibers in the BAL fluid allowedrapid and accurate diagnosis, availablewithin 1 h after BAL. Further studiesshould now be done to evaluate if earlyand accurate diagnoses of VApneumonia will affect the outcome of thesepatients.
AcknowledgmentThe writers thank Mrs. Olga Delaspre andthe staff of the laboratory of bacteriology andof the surgical intensive care unit (UniversityHospital of Geneva) for their technical assistance and Dr. Kevin Gunning for his helpin the preparation of the manuscript.
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