J Trauma, J Intensive Care Med, J Appl Physiol, A&A
|Abstracted by: Dr A Kovacic (Registrar, University of the
Summary of abstract
Controversy continues about the value of prone ventilation in Acute Respiratory
Distress Syndrome and related disorders. But this is nothing compared to
the controversy about recruitment maneuvers. You decide!
(You may wish to briefly browse our editorial comment
1. The Effects of Prone Positioning
The study population group consisted of 16 patients that were mechanically ventilated and turned prone without
minimizing the restriction of the abdomen.
Measurements were performed after 180 minutes duration of supine and prone positioning.
A period of 60 minutes was allowed for equilibration in each position.
Measurements included intra-abdominal pressure, PaO 2 /FiO 2 ratio, cardiac index, mean
arterial pressure, oxygen delivery index, renal fraction of cardiac output, renal vascular
resistance, renal blood flow, glomerular filtration rate, filtration fraction and urine
volume. Cardiac output monitoring as well as complex measurement and calculations of
renal function were performed.
Conclusion of the study:
contributes to improved arterial oxygenation and systemic blood flow without affecting
renal perfusion and function.
Such positioning doesn't substantially restrict abdominal excursion,
although it is associated with a small increase in intra-abdominal pressure.
- Small study group
- Very complex measurements
- Numerous calculations and data
- No standard ventilatory data were given, ventilatory settings were determined by
the physician responsible for the care of the patient.
- What would the results have been had pillows been carefully positioned
under chest and pelvis to permit more free abdominal excursion?
THE EFFECTS OF PRONE POSITIONING ON INTRAABDOMINAL
PRESSURE AND CARDIOVASCULAR AND RENAL FUNCTION IN PATIENTS
WITH ACUTE LUNG INJURY
Anesthesia and Analgesia 2001; 92:1226-31 |
Clinical Study |
Adolf Hering, MD, department of Anesthesiology and Intensive Care Medicine and
Rheinische Friederich-Wilhelms University, Bonn, Germany |
2. A rapid improvement in oxygenation with recruitment!
A retrospective study of 19 patients with secondary ARDS.
Accent is placed on prevention of derecruitment on returning to supine position.
- patient is placed on pressure control ventilation with PEEP 8-12 cm 2 O, and a
PIP not higher than 35 cmH 2 O, pH is maintained> 7,25
- patient is then sedated and paralyzed, and turned prone
- observations are done -- oxygenation index, PaO 2 /FiO 2 ratio and A-a DO 2
- FiO 2 is then increased to 1,0, ventilatory rate turned to zero, and PEEP increased
to 40cmH 2 O for 90 seconds
- PEEP is then decreased to 15 cmH 2 O, PIP maintained below 35 cmH 2 O
- 5 minutes later another set of observations is done
- observations after 24 hours
Prone positioning does improve the oxygenation index and decrease
A-aDO 2 in ARDS patients without significant effect on mean arterial pressure. PEEP of
15 cmH 2 O post recruitment maneuver is most important for prevention of derecruitment
after returning to supine position.
- Recruiting maneuver is well defined and includes precise ventilatory parameters
- All steps of the study are equally applied to each patient.
- There are no complex measurements and calculations
- This study looks into the more prolonged beneficial effects of the recruiting maneuver
- Study is very clear and comprehensible
- A criticism - indices were not corrected for altitude!
RAPID REDUCTION OF OXYGENATION INDEX BY EMPLOYMENT OF A
RECRUITMENT TECHNIQUE IN PATIENTS WITH SEVERE ARDS
J Intensive Care Med 2001; 16: 193-199 |
Clinical Study |
Division of Critical Care and pulmonary medicine, Department of Medicine, University
of Witwatersrand, Johannesburg, South Africa |
3. Prone with NO!
Population group is small with 16 ARDS patients.
Patients received mechanical ventilation in supine position, mechanical ventilation with
inhaled nitric oxide (INO) in supine position, than turned prone and received mechanical
ventilation without and with INO.
Measurements were done after every change of treatment and position, and involved
numerous measured and calculated variables that required invasive cardiac output
An interesting point: pulmonary vascular resistance decreases more in prone than in supine
position when INO is given which raises the question of what exactly is the mechanism
of improvement in PaO 2 with prone positioning? Study also showed the synergistic
beneficial effect of prone positioning together with INO on ARDS, that could be
explained by recruitment of lung volume allowing INO to alter V/Q ratios in these areas.
- Short duration of study (6,3+/- 1 hours)
- No long term benefit of this treatment is shown
- No proof of effect on outcome
- Cost is a large issue (INO)
- All patients are trauma patients, therefore there is no indication of effect on ARDS of
- Duration of ventilation before attempting the study is not indicated
- There is no standardized type of ventilation
PRONE POSITIONING AND INHALED NITRIC OXIDE: SYNERGISTIC
THERAPIES FOR ACUTE RESPIRATORY DISTRESS SYNDROME
J Trauma, 2001: 5: 589-596 |
Clinical Study |
Jay A. Johannigman, MD
University of Cincinati, Department of surgery |
4. Blood distribution - supine and prone
Electron-beam CT was used to study the effects of prone positioning on regional
pulmonary perfusion in 6 healthy subjects.
Patients were scanned when supine and ventilated, and then turned prone. After a 15
minutes stabilization period scanning was repeated.
- Gravitational gradient of pulmonary perfusion existed in both supine and prone
- The distribution of perfusion between the supine or prone positions did not differ.
- Distribution of lung parenchyma was more uniform in the prone position
- Factors other than gravity may be at least as important in determining the distribution
of pulmonary perfusion in humans.
- Very short stabilization period was allowed after changing of positions (15minutes)
- Population group was very small (6 patients)
- Patients were healthy -- can these findings be applied to diseased lungs in ARDS
PULMONARY PERFUSION IN SUPINE AND PRONE POSITIONS: AN
ELECTRON-BEAM COMPUTED TOMOGRAPHY STUDY
J Applied Physiol 90: 1342-1348, 2001 |
Clinical Study |
Andrew T. Jones, David M. Hansell, and Timothy W. Evans
Unit of Critical Care and department of imaging, National Heart and Lung Institute,
imperial Cellege School of Medicine, Royal Brompton Hospital, London |
Editorial - The Big Wheel turns!
Several decades ago, ventilators were built with a sigh mode (Our venerable
900Cs in ICU still have one). Giving large volumes to 'recruit' collapsed
alveoli then fell into disfavour, but recent evidence (such as that of Richards et al.) suggests that in certain patients
recruitment is indeed a good thing ! Why the change?
One factor that was not fully appreciated thirty years ago was that in
the diseased lung, some alveolar units have very long time constants.
Markstaller and colleagues [Br J Anaesth 2001 Sep 87(3) 459-68] found
in the saline lavage model of ARDS in pigs, that a proportion of lung units
had time constants in the range of 8 to 17 seconds. Despite the limitations
of this model, extrapolation to humans with ARDS suggests that a brief
period of inflation is unlikely to fully recruit the lung.
In the past too, some authorities have paid great attention to the lower
inflection point of the (quasi-)static pressure-volume curve (QSPVC), especially
in determining "best" positive end expiratory pressure (PEEP). We now realise
that such obsession with a single number is probably incorrect. There are
many problems associated with a religious attitude to the QSPVC, including
differing inspiratory and expiratory curves (which should one use?), the
influence of a non-unitary respiratory quotient, and the absence of an inflection
point on many curves. But now, and this is the killer, we have come to
realise that recruitment may well occur across the entire range of total
lung capacity [Crotti et al, Am J Respir Crit Care Med 2001 Jul 164(1) 131-40;
Pelosi et al. ibid , 122-30]!
Another point that was not previously appreciated is how rapidly de-recruitment
occurs. Even in anaesthetised normal individuals, de-recruitment occurs
immediately upon removal of small amounts of PEEP [Sigurdsson et al, Acta Anaesthesiol Scand
2000 Sep 44(8) 980-4]. This underlines the recommendations of Richards et al.
that PEEP should be maintained at high levels after recruitment, although
again, we should perhaps beware of religious adherence to a particular number!
We should also be concerned that even brief removal of PEEP, during entotracheal
tube disconnection in ICU, might markedly compromise patients with
substantial lung injury (A justification for closed suctioning systems?). Fortunately
for us, repeated recruitment maneuvers may be effective. [Foti et al,
Intensive Care Med 2000 May 26(5) 501-7]. A fascinating article by Mutch
et al. [Am J Respir Crit Care Med 2000 Jul 162(1) 319-23] suggests that
normal 'biological noise' - natural variation in ventilation - is far
more effective in recruiting collapsed lung tissue that conventional
"monotonously regular" ventilation! (The big wheel really does turn, doesn't
Finally, what is the role of prone position in lung recruitment?
An attractive feature of the study by Richards et al is that all patients
were placed in the prone position prior to recruitment. It would seem
logical that in the supine position, surfactant-depleted but already well-inflated
lung regions (especially in the lung apices) might preferentially receive
large volumes delivered during a recruitment maneuver. (Consider Laplace's law)!
It makes sense that preventing excursion of these regions of the lungs by prone
positioning might preferentially recruit collapsed dependent areas.
We await meticulous experimental confirmation, or disproof, of this concept.