TO

me

eonx

Communications for thLs section will be publLshed as space and priorities permit. The comments should not exceed 500 words in length, with a maximum of jive references; one figure or table can be printed. Exceptions may occur under particular circumetances. Contributions may include comments on articles published in this penodical, or they may be reports of unique educational character. Specific permission to publish should be cited in a covering letter on appended as a postscript.

development of mediastinal emphysema was first deseribed by Sauerbruch and was later confirmed by other authors.6’7 The mechanism is valid for subjects breathing spontaneously, as well as for patients receiving mechanical ventilation; and it may be set in action not only by fractured ribs but also by penetrating thoracie injuries

from

the

exterior,4

especially

in

case

of

preexist-

ing pneumothorax. When sufficient pressure develops, air always escapes from the mediastinum following one of three paths,8 one of which leads through the diaphragm, about the aorta and the esophagus, to the retroperitoneal tissues, with the consequence of pneumoretroperitoneum. DIScussIoN

Retroperitoneal

Air

and

Ventilation

Mechanical

Overexpansion of the lung during artificial ventilation long been an interesting subject in critical care medicine; however, in one of the cases presented by

Dissection

has

Powner

To the Editor: I read

great

with

associates

on

with 1976),

Mechanical in which

veloped

interest

the article by Powner and Air Dissection Associated Ventilation” (Chest 69:739-742, they described three patients who de-

“Retroperitoneal

pneumoretroperitoneum

ventilation.

This

article

during requires

some

mechanical additional

com-

concerning the pathogenic mechanisms of the disorder reported. It must be emphasized ( 1 ) that retroperitoneal air dissection as an adverse effect of medianical ventilation cannot be imagined without antecedent mediastinal emphysema and (2) that, under certain circumstances, production of mediastinal emphysema in a subject receiving mechanical ventilation may be the result of a mechanism other than “expansion rupture” of the lung, as will be outlined herein.

ment

PAmoPin SIoLocIc

CONSIDERATIONS

Introduction of air into the mediastinum during mechanical ventilation is a phenomenon commonly attributed and

to “barotrauma” “expansion

brought

rupture”

of

about

the

lung

by by

overinfiation a

mechanism

elaborately investigated and Mackin3 decades ence to which Powner amply

by Mackli&’2 and by Macklin ago. This mechanism, with referet al explain their observations, is in the original report and need not be

discussed

reexplicated

here.

Nevertheless,

in subjects

causative

physema. case 1.

receiving

of

into

the mediastinum

ventilation

may

air

mechanical

be

al,

one

should

be

lung

may

above

be lacerated.

zero,

positive

end-expiratory

pressure

to an important,

complex

field

but

Whenever

CHEST, 71: 3, MARCH,

will

pass

pressure

1977

from

the

in the

(PEEP)

less

of “pulmonary

accepting

the

was

instituted.

appreciated,

aspect

in the

barotrauma.”

due

Klawc D. Siemoneit, M.D. Division of Anesthesiology Department of Thoracic Surgery Lungenklinik Heckeshorn West Berlin, West Germany

airway

lung into subcutaneously lacerated soft tissues via the pleural space, with or without radiographically apparent pneumothorax,4 and may, after distending the soft tissues of the chest and the neck, spread along fascial planes to enter the mediastinum at the neck. This mechanism of air

in

Thereafter, four hours later, subcutaneous emphysema in the supraclavicular region was noted. Did the change from zero end-expiratory pressure to PEEP, together with poor pulmonary compliance, open a bronchopleural fistula in the damaged region of the thoracic cage and cause egress of air into the overlying subcutaneous tissues? I should think so. The close anatomic relationship between the supraclavicular soft tissues and the damaged part of the thoracic cage easily explains why the first traces of air escaping from the pleural space appeared in the supraclavicular region. Unfortunately, the report on case 1 by Powner et al is not detailed enough to answer all questions. But it may, anyhow, invite the attention of those practicing mechanical venti-

to a second mechanism quite different from the one mentioned previously. With fractures of the ribs, the parietal pleura, the visceral pleura, and the underlying rises

careful

offered in their article. I hesitate to bein each of the patients reported, a so-called rupture” of alveoli or small airways was the event for the production of mediastinal emThis may be true for cases 2 and 3 but not for

Case 1 represents a patient with fractures of the second through fourth ribs posteriorly on the right. He was intubated to receive mechanical ventilation because of increasing hypoxemia. During the first 32 hours of ventilation, the peak inspiratory airway pressure rose from 28 to 45 cm H20, presumably as a consequence of decreasing pulmonary compliance. Then therapy with

lation introduction

et

interpretation lieve that “expansion

injured

REFERENCES 1 Macklin

CC : Pneumothorax

experimental

Med Assoc J 2

Maeklin

CC

local

with

over-inflation

36:414-420, : Transport

of

massive

collapse

the lung substance.

from Can

1937 of

air

along

sheaths

of

pulmonie

COMMUNICATIONS TO THE EDITOR

431

3

4 5

6

blood vessels from alveoli to mediastinum. Arch Intern Med 64:913-926, 1939 MackIln NIT, Macklin CC: Malignant interstitial emphysema of the lungs and mediastinum as an important occult complication in many respiratory diseases and other conditions: An interpretation of the clinical literature in the light of laboratory experiment. Medicine 23:281-357, 1944 Sheinfeld W: Subcutaneous emphysema following chest trauma. Surgery 23:278-288, 1948 Sauerhruch F: Die Bedeutung des Mediastinalemphysems in der Pathologie des Spannungspneumothorax. Beitr Klin Chir 6O: 5O-478, 1908 Jessup PM: Mediastinal emphysema. Arch Surg 23:760-

complex

782,

annulus.

1931

7 Liebig S, Siemoneit gleitpneumothorax:

28: 1 133-1 138, L: Mediastinal

Pneumol

8 Hamman

To the

KD: Mediastinalemphysem Entstehung und Behandlung. 1974 emphysema.

JAMA

und

128: 1-6,

BePrax

(Chest

our

Associated

publication with

69:739-742,

1976),

teresting

viewpoints

standing

of

various

Dr.

Siemoneit

importance

forms

of

for

interstitial

has

added

further

ina

of our

patient

1 ; however,

the

appearance

cavities

without

brought to our attention the cause of mediastinal versa, which is another grateful to him for these

Director, University

Late

Thrombosis

Bjork..Shiley

position,

cient

for flow

in stasis happen nulus

the

smaller

adhesions.

Dr.

and,

serted

in a slightly To

tilting

disk,

tilted

allow

has

sufficient

of size after

using

the

patients

25

and

cardiac

Bjork-Shiley drugs.

July

1976

mechanism

issue

even

Bjork-Shiley

prosthesis,

reports

both

been

in-

aortic

sides

of

the

to insert

is practically

complete

a

always

decalcification

we

of the

seen not

only

taking

two anti-

therapy

hemodynamically

had the

have

both anticoagulative

the

is

excellent

been

advocated

experience

with

already this

in

of

type

J. Messmer,

M.D., F.C.C.P. Professor of Surgery der Rheinisch-Westfalischen Techntschen Hochschule of Cardiovascular Surgery Aachen, West Germany

Department

REFERENCES

1 Fernandez J, Samuel A, Yang SS, et al: Late thrombosis of the aortie Bjork-Shiley prosthesis: Its clinical recognition and management. Chest 70: 12-16, 1976 2 Messmer BJ: Experience with the Bjork-Shiley aortic prosthesis. In discussion of Bj#{246}rIC VO: A new central-flow tilting disc prosthesis. J Thorac Cardiovasc Surg 60:372,

It

COMMUNICATIONS TO THE EDITOR

to the

This

careful

with

about

has

Okies JE, Hailman CL, et al: Aortie valve Two years’ experience with the Bjork-Shiley prosthesis. Surgery 72:772-779, 1972

been

well

is

a factor

coagulation

of a valve

in regard

To the Editor:

has

remained

of Chest.

of thrombosis

subaortic has

possible,

prosthesis,

That

mandatory,

tilting-disc

a serious hazard ever since artificial valves have been used. Despite the excellent hemodynamic performances of the Bj#{246}rk-Shiley prosthesis in the aortic position, this prosthetic valve has not been proved free of clotting problems, as demonstrated by the article of Fernandez et all in the

severe

prosthesis on

prosthesis,

a clotted

3 Messmer BJ, replacement:

Aortic

valves

ineffiresulting

This can especially of the aortic an-

whenever

or more.

careful

with

coagulant

the of prosthetic

flow

is

et the

1970

Ake Grenvik, M.D., F.C.C.P. Professor of Anesthesiology Division of Critical Care Medicine of Pittsburgh School of Medicine

Prosthesis

Thrombosis

position

it is important,

prosthesis

become valves,

with

the

Klinikum

that subcutaneous air can be emphysema, rather than owe interesting possibility. We are comments.

of the

may

in patients or when

It

by Fernandez Especially in

Bjork-Shiley

furthermore, hypertrophy

of sub-

Siemoneit

aperture

in small-sized

to ther-

prostheses.

reported or less.

at this part of the prosthesis. after insufficient decalcification

muscular

contribute

of small-sized

Bruno

To the Editor:

432

implantation

aortic

factors

anticoagulative

that five of the patients a prosthesis of size 23

air

pleural

The

(2)

major

of adequate

23

without simultaneous pneumothorax in patients with chest trauma due to fractured ribs particularly occurs in elderly patients with pleural adhesions. Our patient 1 was a 22-year-old man without previous pulmonary disease whom we expected would have intact cutaneous

and

evident al’ had

early

condition which has become a quite common occurrence in intensive care units. We did indeed consider the explanation that Siemoneit discusses for the dissection of air in interstitial tissues

apy,

two

lack

annulus and the subvalvular area. If necessary, the annulus can be split in front of the commissure between the left and right coronary cusps. Among some 300 isolated aortic valvular replacements

under-

emphysema,

however,

(1)

aortic aortic

on “Retropentoneal Air Mechanical Ventilation”

of

one;

problem:

feasible

1945

Editor:

Regarding Dissection

the

is certainly

a

aortie

deposits

critical

factor

the

that

Bjork-Shiley

calcific tioning

established

of the smaller

prosthesis.

may

that

that

also

has

our

this

of

removal

In our

is the the

tilting-disk

of

experience

emphasized opinion,

anti-

thrombosis

Inadequate

been In

of

to

be a factor.

not

prosthesis. aperture

inadequate

contributes

a

posi-

relation

valve

of

to

the

surrounding structures is of crucial importance. In all of our seven cases of thrombosed aortic Bjork-Shiley prostheses, the valve was positioned with the smaller aperture toward the septum ( 1970 to October 1973). Since

that

date,

the

prosthesis

has

been

positioned

CHEST, 71: 3, MARCH,

1977