"Prone & Recruit"

Journals Reviewed: J Trauma, J Intensive Care Med, J Appl Physiol, A&A
Abstracted by: Dr A Kovacic (Registrar, University of the Witwatersrand)

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:

Prone positioning 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?
Anesthesia and Analgesia 2001; 92:1226-31
Article type: Clinical Study
Authors: Adolf Hering, MD, department of Anesthesiology and Intensive Care Medicine and Internal Medicine, 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. Recruiting maneuver:

  1. 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
  2. patient is then sedated and paralyzed, and turned prone
  3. observations are done -- oxygenation index, PaO 2 /FiO 2 ratio and A-a DO 2
  4. FiO 2 is then increased to 1,0, ventilatory rate turned to zero, and PEEP increased to 40cmH 2 O for 90 seconds
  5. PEEP is then decreased to 15 cmH 2 O, PIP maintained below 35 cmH 2 O
  6. 5 minutes later another set of observations is done
  7. 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!
J Intensive Care Med 2001; 16: 193-199
Article type: Clinical Study
Authors: G.Richards, PhD H.White, FCP(SA) M.Hopley, FCP(SA) 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 monitoring. 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 other etiologies
  • Duration of ventilation before attempting the study is not indicated
  • There is no standardized type of ventilation
J Trauma, 2001: 5: 589-596
Article type: Clinical Study
Authors: 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 positions.
  • 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 patients?
J Applied Physiol 90: 1342-1348, 2001
Article type: Clinical Study
Authors: 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 it?)

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.


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