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811

Effect of Mechanical Ventilation and Positive End-Expiratory Pressure (PEEP) on Chest Radiograph

Jack Lawrence Mohammad

The effect of differing ventilator settings and positive end-expiratory pressure (PEEP) on the chest radiograph was studied in I 2 patients with acute respiratory failure. Chan9ing ventilator settings produced dramatic variations in the appearance of pulmonary infiltrates in technically identical radiographs exposed over a 10-15 mm period. PEEP had the greatest effect on radiographic appearance. In seven patients, the diagnosis or estimation of severity of pulmonary infiltrates would have been altered if only the film during PEEP had been available. Knowledge of ventilator settings is vital in evaluating the severity of infiltration and radiographic diagnosis in patients with acute respiratory failure.

E. Zimmerman1 R. Goodman2 B. G. Shahvari1

Positive

end-expiratory

oxygenation

pressure

in the patient

with

(PEEP)

acute

is an important

respiratory

failure.

means

PEEP

of improving

is usually

gener-

ated by a pressure-sensitive valve that elevates intrapulmonary pressure at end expiration, thus increasing end-expiratory lung volume (functional residual capacity). This increased lung volume opens collapsed airways and previously unventilated alveoli and diminishes intrapulmonary shunting [1 ]. The improvement in oxygenation

levels. airways

(ARDS),

pulmonary

In the radiograph vagaries

March 2, 1979.

Presented can Roentgen ada, March

26,

1979;

at the annual Ray Society, 1979.

Division

of Critical

of Anesthesiology,

dare

George

accepted

meeting Toronto,

after

re-

of the AmeriOntario, can-

Medicine,

Department

Washington

University

Medical Center, 901 23d St., NW., Washington, D.C. 20037. Address reprint requests to J. E.

the

inspired

PEEP is most in conditions edema,

day-to-day

and

evaluation

and

in every

date, there mechanical designed pulmonary

graphic

concentration

PEEP.

Lung

patient

and

has been ventilation

hyperinflation

the

hyperinflation

degree

with

most

to

failure,

the

and physiologic evaluation. by the use of positive-pressure

The

and

of change

frequency and

decreased

with unstable, coldistress syndrome

acute

respiratory

apparent

diminution

reported with both mechanical 3]. However, alteration of the

no systematic study used and alterations

to determine

parameters

the

to be

atelectasis.

of patients

pulmonary infiltrates have been PEEP in children and adults [2, seen

oxygen

effective in treating patients such as adult respiratory

is an important addition to clinical of portable radiography are compounded

ventilation Received vision July

permits

nontoxic lapsible

the

and least

and use

likely

is somewhat

and is not

unpredictable.

To

of the relationship in the radiograph. degree

of PEEP

of change and

to be altered

in visible

ventilation radiograph

between type of Our study was caused

to determine

by simple those

radio-

by the respirator.

Zimmerman. 2

Department

mann Medical PA 19102. AJR

of College

133:811-815,

Diagostic and

Radiology, Hospital,

November

1979

0361 -803X/79/l335-08l 1 $00.00 © American Roentgen Ray Society

Hahne-

Philadelphia,

Subjects Adult following etiology

and

Methods

patients with acute respiratory failure were selected for study when they met the criteria: (1) clinically stable, but requiring ventilatory support with PEEP; (2) of respiratory failure well established; and (3) infiltrative density visible on previous

ZIMMERMAN

812

chest radiograph. Twelve adult patients with acute respiratory failure of varying etiology were studied. A clinical diagnosis was made in all patients by means of clinical data and laboratory findings and was confirmed by fiberoptic bronchoscopy, measurement of pulmonary capillary wedge pressure, lung biopsy, or autopsy exami-

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nation.

Each patient was receiving assisted or controlled mechanical ventilation with a volume-cycled ventilator (Bennett MA-i ). Tidal volume, determined by body weight and pulmonary compliance in each patient, was 1 0-1 5 mI/kg [4]. The amount of PEEP used during radiographic exposure represented that level that produced the best total static compliance and an arterial oxygen tension of 80-100 mm Hg on 40%-50% oxygen [5]. Four technically identical anteroposterior chest radiographs were exposed within a 1 0-1 5 mm period at end inspiration in the following sequence: (1) tidal volume without PEEP (TV-i); (2) “sigh” setting of 1 i/2_2 times tidal volume (S); (3) tidal volume plus PEEP (PEEP); and (4) tidal volume after removal of PEEP (TV-2). All films were exposed at about a 1 00 cm target-film distance with the patient semierect or erect. A brief interval between exposures was allotted in order to stabilize the patient when ventilator settings were changed. Exhaled tidal volume was monitored carefully after addition of PEEP, and it was assumed that air trapping had reached a steady state when the inspired and expired tidal volumes were equal. Films were interpreted by one of us (L. G.), who had no knowledge of the clinical diagnosis or ventilator settings at the time of exposure. Each patient’s films were subjectively classified into . ‘best’ ‘ film (least apparent disease), ‘ ‘worst’ ‘ film (most apparent disease), and intermediate categories. After classification, the ‘ ‘ best’ ‘ and ‘ ‘worst’ ‘ film of each patient were compared to determine whether the radiographic diagnosis would have been altered if only the ‘ ‘best’ ‘ film had been available. Specific factors were then evaluated including height of the diaphragm; severity of perceived infiltrate; presence of the silhouette sign; and the size of the heart, mediastinum, and pulmonary vessels.

ET AL.

AJR:133,

Clinical information describing the patients studied and conditions of film exposure are presented in table 1 . Pulmonary infiltrates were caused by congestive heart failure in four patients, aspiration pneumonitis in three patients, bacterial sepsis

pneumonitis in two patients, in three patients. Lung inflation

1 ,000

ml during

without

PEEP,

ered

‘

‘sighs.

H2O. Table graphs

‘ ‘

and peritonitis volume was

and 550-

exposure at usual tidal volume with and and 900-1 ,800 ml during respirator-delivLevels of PEEP ranged from 1 0 to 20 cm

.

Eliology Failure

2 lists the

the

subjective

changes

classification

in interpretation

of

the

caused

radio-

‘

‘best’

‘ film and the tidal 1 ). Films taken during

apparent infiltrate and ranked ‘ ‘ best’

volume film was the “worst” ‘ ‘sigh’ ‘ demonstrated less

a

than tidal volume films in seven patients, ‘ in one patient and ‘ ‘worst’ ‘ in one patient.

Marked alterations in radiographic diagnosis were apparent when the ‘ ‘ best’ ‘ or PEEP films and ‘ ‘worst’ ‘ or tidal volume films were comparatively assessed. In four of 12 patients,

the

interpreter

believed

a different

diagnosis

TV-i

During

Exposu

S

re

PEEP

TV-2

pneu-

monia:

1 2 3 Congestive

800 900 1,000

1,200 1,800 1,600

800 900 1,000

+

12

+

15

800 900

+

20

1,000

4 5 6

700 800 900

1,200 1,200 1,450

700 800 900

+ +

10 15 12

700 800 900

7

800

1,200

800

+

12

800

800

1,200

800

+

15

800

900

1,800

900

+

12

900

550 800 1,000

900 1,200 1,500

550 800 800

+ +

12 12

+

15

550 800 1,000

heart

failure:

Pneumocystis monia, Pseudomonas monia,

ARDS,

+

pneu8 pneu9

peritonitis:

10 11 12 Note-In

addition,

fluid overload;

cases

pressure = 1 8 mm . TV-i = inilial and level of positive removal of PEEP.

case 3 had interstitial fibrosis and pulmonary edema; case 1 1 and 1 2 had septic shock (patient 1 1 . pulmonary capillary Hg). ARDS = adult respiralory distress syndrome

tidal volume

(ml); S

end-expiralory

sigh

=

pressure

volume

(cm

H20);

1 0 had

wedge

(ml); PEEP = tidal volume (ml) = fidal volume (ml) afler

TV-2

TABLE 2: Effects of Respiratory Support on Perception of Radiographic Abnormalities and Diagnostic Interpretation Class ification Case No.

Worst

Film

Effeci

of Chan ges Film

on Interpretation

Changed

Inlermediale

Changed

Se-

verity

1

PEEP

TV-i

TV-.2

-

2 3

PEEP PEEP

TV-i TV-i

S S

+

+

+

+

4 5 6 7 8

5 PEEP PEEP PEEP PEEP

TV-2 TV-2 S TV-i TV-2

TV-i S TV-i S S

-

-

+ + +

-

+

-

9 10 ii 12

level

removal

I

I

I

-

-

TV-2 TV-i TV-i

TV-i S S

+

+

-

-

initial

tidal volume end-expiratory

-

+

PEEP PEEP PEEP

of positive

TV-i

.

of PEEP;

I

-

(ml); S

sigh

=

pressure

(cm

-

volume

(ml);

H20);

TV-2

PEEP =

Di-

agnosis

tidal

=

tidal volume volume

(ml)

(ml) after

all films identical

by venti-

lator manipulation. The type of mechanical ventilatory support received influenced the subjective classification in 10 of the 1 2 patients studied. In 1 0 patients, the PEEP film was the (fig.

Condition

of Respiratory and CaseNo

Aspiration

and

and

1979

TABLE 1 : Effect of Respiratory Support on Chest Radiograph: Clinical Diagnosis and Conditions During Radiographic Exposure

Best

Results

November

would

have been entertained or an infiltrate overlooked if only the ‘ ‘ best’ ‘ film had been available (fig. cases,

the

ity of the regressing.

interpreter

believed

infiltrate so greatly In the other five

that

PEEP

completely 2). In three

altered

ences were visible, they would not have significantly interpretation of the radiograph. Films exposed during ‘ ‘sigh’ ‘ were not uniformly than the

the ‘

‘sigh’

tidal ‘

film

volume show

films. less

the sever-

to be

that infiltrates appeared cases, although minor

In only infiltrate

differaltered better

seven

of 1 2 patients

when

directly

compared

did

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AJR:133,

November

PEEP

1979

AND

CHEST

RADIOGRAPHY

813

D Fig.

1 -Case

3. Aspiration

pneumonitis

after

and exposed within 1 5 mm). A, Tidal volume = hemidiaphragm and aorta silhouetted. B, “Sigh” ml + 20 cm PEEP. Minimal patchy densities visible descending volume

with

=

the

pearance

aorta, and left hemidiaphragm 1 000 ml after removal of PEEP.

tidal

volume

on the TV-2

Previous use of “sigh” utes caused the TV-2

films.

The

radiograph

heroin =

overdose.

Changes

visible for Radiograph

first

time. returns

Only diagnosis to baseline.

to “baseline” apwas relatively complete. settings for several min-

return

and PEEP film to demonstrate

induced

by mechanical

ventilation

and

PEEP.

(All

films

1 .000 ml. Diftuse interstitial edema throughout both lungs and alveolar infiltrate 1 .600 ml. Slightly improved with increased inflation. Basic diagnosis not altered. at right base. Edema not visible and diaphragm has descended 1 interspace. Upper

less

disease

than

of minimal bilateral Still some improvement

the TV-i were ations The

lower lobe infiltrates is possible visible at left base.

film in three

minor

and

would

in interpretation. specific factors

of 12 patients. not

have

that

changed

from

using

identical

in right lower C, Tidal volume lobe pulmonary this

radiograph.

All of these

resulted

lung.

Left 1 .000 vessels,

=

0,

Tidal

differences

in important

radiographic

technique

alterinterpre-

ZIMMERMAN

814

ET AL.

AJR:133,

November

1979

Fig. 2.-Case 7. Congestive heart failure. Composite of changes in right lung caused by mechanical ventilation and PEEP (All films using identical technique and exposed within 10 mm). A, Tidal volume = 800 ml. Pulmonary

edema

due to congestive

heart failure.

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B,

“Sigh’ = 1 .200 ml. Infiltrate ished: diaphragm is interspace pulmonary vessels smaller and

Diagnosis of mild pulmonary

800 improvement

Further

radiograph. Diagnosis heart failure not possible mal’ radiograph.

A

B

tation

when

PEEP

was added

are listed

descent (eight or sharpness

silhouette

and

the

The

initial

less

sign,

frequently.

size

in table

3. The most

of 1 2 patients). of pulmonary of the

tidal

heart

volume

‘sigh, ‘ ‘ and level of PEEP did not ence in determining which patients improvement with PEEP. However,

TABLE

3: Radiographic

PEEP vessels,

or

Radiographic

influthe

mediastinum

setting,

volume

of

appear to have an infludeveloped radiographic patients with clinically

‘

diagnosed clearing

lung edema did appear of infiltrates with PEEP.

to have

more

demonstrated dramatic

pearance of pulmonary appear within minutes. a remarkable

that variations

degree

‘).

their tidal This

changes in the

infiltrates that The radiographic the

ventilation on lung volume Adult patients with acute

Decreased Increased Decreased Decreased

physiologic

in ventilator radiographic

may occur and dischanges parallel to effects

of mechanical

and alveolar gas respiratory failure

lungs with small volumes without type of ventilatory

setap-

Induced

by PEEP

Change

No.

Patients

10 8

4 4

of silhouette

4

sign

3 i

heart size width of mediastinum

exchange. spontaneously

(250-400 intermittent pattern

ml), relatively hyperinflation has been shown

spontaneous

(10-15

to reverse

of PEEP during in end-expiratory

with

of this

and

periodic

atelectasis

mechanical ventilation lung volume which

effect in reducing in arterial oxygen

of mechanical

mI/kg)

some

alveolar tension

and airway (Pa02) that

ventilation maximal

or addition elevations

hyperinflation [7].

produces has an closure. results

of PEEP occurring

The

addition

an increase even greater The after

increase initiation

occurs

within

in 20-30

mm

[8]. improvement

mechanical

in the chest ventilation

radiograph

parallels

these

after

initiation

physiologic

In some

when a ‘ ‘sigh’ the usual tidal

of our

further volume.

‘

patients,

a similar

hyperinflated The dramatic

the lung radio-

graphic improvement that follows PEEP can be explained by a further marked increase in lung volume. When PEEP is added during ventilatory management, the first few expired tidal volumes are invariably smaller than the inspired volume because gas is trapped in the lungs at end exhalation. The cumulative sum of these volume decrements approximates the increase in functional residual

Whyte

volumes

ventilation.

effect occurred to 1 1/2_2 times

tidal

The

Changes

size of pulmonary vessels sharpness of pulmonary vessels

Disappearance

capacity

of

congestive this “nor-

Diminished infiltrate Lowered diaphragm

to lead to progressive alveolar collapse and airway closure (atelectasis) with nonventilation of perfused alveoli and consequent hypoxemia [6]. Mechanical ventilation using large

minutes

on

± of

changes. The large tidal volumes that tend to reverse alveolar collapse and hypoxemia often represent an end-inspiratory lung volume 2-3 times that of films taken during

Our study tings produce

tends

of

from ml

dramatic

Discussion

ventilate constant (‘ ‘sighs’

=

C

frequent changes induced by adding PEEP were diminution in pulmonary infiltrate (1 0 of 1 2 patients) and greater degree of diaphragmatic enced the size

edema

C, PEEP

this radiograph. 12 cm PEEP.

diminlower; sharper.

crease depends

and

of PEEP. with

radiographs atory lung at usual Abrupt

volume

PEEP

this

in several

during volume

tidal

by

PEEP 1 ,200-i

PEEP

capacity produced lung compliance, value

Measurements of our

The

ml/5

increase

patients

in-

by PEEP but Hedley-

to be 400

of the

were 400

[8].

cm

in lung

revealed

that

exposed at an end-inspirml greater than exposure

volume.

removal

of PEEP

trapped gas is immediately in transpulmonary pressure removing oxygen

induced

et al. [9] approximated

increment volume

lung

in functional residual on total and regional

PEEP tension

produces

an opposite

effect,

and

exhaled. The sudden decrease and lung volume caused by

is accompanied within i mm

by a dramatic fall in arterial [8]. The deterioration in the

AJR:133,

November

appearance

of the

parallels

these

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oxygenation. radiographic by changes

PEEP

1979

chest

abrupt

radiograph

decreases

after in lung

AND

removal volume

CHEST

of PEEP and

i

We believe that the mechanism of the dramatic changes induced by PEEP is explained solely in lung volume.

our

cases

(elevated show the

reveals

that

initiation of PEEP. would have resulted monary

patients

with

pulmonary capillary wedge most dramatic radiographic

edema

not have significantly

present.

In

two

other

the severity appeared who clinically and

pulmonary edema, the with the use of PEEP.

radiographs This confirms

to justify

using

response

to PEEP

patients

with Howdid

did improve the opinion responsive to is not specific

diagnostically

alter with posed

the patient’s the settings [10].

on serial

radiographs,

it may be necessary

respirator settings temporarily at the time the comparison

5.

6.

. Ashbaugh physiology,

DG, Petty TL: Positive end-expiratory pressure: indications and contraindications. J Thorac Cardiovasc Surg 65:165-170, 1973 Oh KS, Stitik FP, Galvis AG, Bearman SB, Heller RM, Dorst JP: Radiological manifestations in patients on continuous positive-pressure breathing. Radiology i 1 0 : 627-630, 1974 McLoud TC, Barash PG, Ravin CE: PEEP: radiographic features and associated complications. AJR 1 29 : 209-21 3, 1977 Suter PM, Fairley HB, Isenberg MD: Effect of tidal volume and positive end-expiratory pressure on compliance during mechanical ventilation. Chest 73:158-162, i978 Suter PM, Fairley HB, Isenberg MD: Optimum end-expiratory airway pressure in patients with acute pulmonary failure. N Engi J Med 292 :284-289, 1975 Bendixen HH, Hedley-Whyte J, Layer MB: Impaired oxygenation in surgical patients during general anesthesia with controlled ventilation: a concept of atelectasis. N EngI J Med 269: 991-996,

as

a means of separating edema from nonedema patients. Because the response to PEEP is not uniformly predictable, it is difficult to estimate how much improvement can be expected when PEEP is initiated or deterioration when PEEP is discontinued. Therefore, in following the progress

of an infiltrate

3. 4,

PEEP pul-

to diminish. radiographically

of Oh et al. [2] that pulmonary edema is more PEEP; however, change or absence of change enough

edema

2.

tend to with the

In three of the four cases where in a missed or altered diagnosis,

was

pulmonary edema, ever, in two patients

pulmonary pressures) changes

REFERENCES

arterial

Our observations confirm the impressions of others [2, 3] that PEEP may markedly alter the appearance of the radiograph. Both the apparent improvement with initiation and worsening with discontinuance of PEEP are rapid. A review of

815

RADIOGRAPHY

to

to coincide film was ex-

1963

7. Pontoppidan H, Geffin B, Lowenstein E: Acute respiratory failure in the adult. N Eng! J Med 287:690-697, 743-752, 799-806, 1972 8. Kumar A, Falke KJ, Geffin B, Aldredge CF, Layer MB, Lowenstein E, Pontoppidan H: Continuous positive-pressure ventilation in acute respiratory failure. N EngI J Med 283:14301436, 1970 9. Hedley-Whyte J, Burgess GE, Feeley TW, Miller MG: Applied Physiology of Respiratory Care, 1st ed., Boston, Little, Brown, 1976

10.

Zimmerman JE: Life support techniques, in Intensive Care Radiology: Imaging of the CriticallyIll,edited by Goodman LR, Putman CE, St. Louis, Mosby, 1978, pp 1-28