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THE LANCET
Turning to the past
J Dean Sandham
The stock-in-trade of critical care is the physiological
currently being assessed in clinical trials (Kelly). Due to
support of patients with failing organs. The critical-care
their greater density, PFC accumulate in dependent lung
literature reflects thiswith a prominent focus on support
where they may physically expand atelectatic lung (acting
of the injured lung. Two interesting areas of developing
like liquid positive end-expiratory pressure), provide
understanding are use of the prone position for ventilation
surface-tension reducing properties, or displace blood
flow to less dependent lung areas. By floating
and use of partial liquid ventilation (PLV).
Dramatic improvement in
aqueous substances and
lung oxygenation in patients
inflammatory debris to the
with adult respiratory distress
surface for removal, the
syndrome (ARDS) who were
inflammatory process may be
cared for in the prone
decreased.
position was first observed in
Because
improved
the 1970s. General use of the
physiological
support
technique has not been
has
prolonged patients'
intensive-care-unit (ICU)
adopted (Webster). In the
survival, we
face
the
largest single series of cases
reported to date (Chatte), a
overwhelming
"mediator
storm" precipitated by injury
positive response (defined as
or infection. This systemic
increases in the PaO2/FiO 2
inflammatory
response
ratio by >20 mm Hg within
syndrome, mediated by
1 h of turning) was found in
macrophage-derived
78%
of
30
optimally
ventilated patients. In 57% of
cytokines that target endresponders, the improvement
organ receptors in response
to injury or infection, causes
in gas exchange persisted for
further dysfunction or failure
the study duration (4 h). This
of vital organ systems.
improvement may be due to
Attempts
to
modulate
modification of the wellthis
response
with
known
mismatch
of
ventilation and perfusion that
non-glucocorticoid
antiinflammatory agents (such as
occurs in ARDS associated
monoclonal antibody to
with dependent water in the
Chest radiograph of a patient being ventilated with PFC
tumour necrosis factor) have
lung, caudal movement of the
been the object of intense
dorsal diaphragm (much less
interest. A systematic review (Zeni) of 18 clinical trials of
mobile in the supine position), or a more homogeneous
six of these agents and nine clinical trials of
distribution of ventilation in the prone position. At least
glucocorticoids in management of sepsis and septic shock
three experienced staff members are required to perform
assessed 6429 patients. When pooled, the patient data
prone-positioning turns safely while protecting the airway
showed a small beneficial treatment effect that was not
and intravenous catheters. Studies are small and
statistically significant (OR 1:11; CI 0.99-1.23; p=0.07).
physiological endpoints (changes in blood oxygenation)
Given the complexity and multiplicity of the mediators of
are used as surrogates for more important outcomes
systemic inflammatory response, the development of the
(changes in morbidity or mortality).
potential of this therapy is an exciting challenge.
Perfluorocarbons (PFC) are clear liquids more dense
than water with a much greater solubility for oxygen and
carbon dioxide. They have been shown to allow liquid
Key references for 1997
ventilation of the lungs of both mechanically ventilated
Bartlett R, C r e t e M, H c r s c h l R, et al. A phase II r a n d o m i z e d
and spontaneously breathing animals. Total liquid
controlled trial o f partial liquid ventilation (PLV) i n adult
ventilation requires complex ventilators. The concept of
patients w i t h a c u t e h y p o x e m i c respiratory failure ( A H R F ) . Crit
partially fillings lungs with PFC to functional residual
Care M e d 1997; 25: No 2 (suppl).
capacity and then ventilating with a standard gas operated
Chatte G, S a b J, D n b o i s J, et al. P r o n e position in m e c h a n i c a l l y
ventilated patients w i t h severe a c u t e respiratory f a i l u r e . . 4 m J
ventilator (partial liquid ventilation [PLV]) has allowed
Respir Crit Care M e d 1997; 155: 473-78.
early clinical application in a small series of paediatric
Kelly K. P a r t i a l H q u i d v e n t i l a t i o n - - t u r n i n g b a c k a P A G E on
(N Engl J Med 1996; 335: 761) and adult patients
evolution. B r J A n a e s t h 1997; 78: 1-2.
(Bartlett). One of these substances, Perflubron, is
Webster N. Ventilation in the prone p o s i t i o n . L a n c e t 1997; 349:
Lancet 1997; 350 (suppl III): 3
Foothills Hospital, Calgary, AB T2N 2T9, Canada (J D Sandham MD)
End O f Year Review ° 1997
1638-39.
Z e n i F, F r e e m a n B , N a t a n s o n C. A n t i - i n f l a m m a t o r y therapies to
treat sepsis and septic shock: a r e a s s e s s m e n t . Crit Care M e d
1997; 25: 1095-100.
SIII3

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