Ventilator hyperinflation and Recruitment maneuvers. whats the difference?

[VenPTs]

Hello, im conducting a literature review for a survey on current usage of vetilator hyperinflation in uk ICUs. Im hoping someone may help in clafiying the difference between a recruitment maneuver (RM) (sometimes referred to as lung/pulmonary recruitment maneuver) and ventilator hyperinflation (VHI). The reason being, i am uncertain as to whether i need to include the term 'recruitment maneuver' in the search strategy.

my current understanding based on what ive read is:

the recruitment maneuvers (RM/LRM/PRM) documented in the literature appear to have the sole aim of recruiting collapsed/de-recruited alveoli. They are characterised by increasing PEEP to maintain alveolar recruitment and keeping tidal volumes low to prevent trauma.

vhi may be classed as a type of recruitment maneuver, as some alveolar recruitment does occur during vhi. However with vhi the tidal volumes are deliberately increased and peep is maintained, not increased, in order to facilitate a high peak expiratory flow rate which will aid sputum clearance.

so in my head at the moment, im classing RM's and VHI as two completely different techniques, VHI which i want to research and RM which i dont as its mechanisms/technique/implementation are different to vhi .... so therfore i shouldn't include it in a search strategy when the aim is to investigate ventilator hyperinflation.

my question is....... is this at all correct?

... im hoping that someone with more knowledge here than myself might be able to spare a second and give their views on the matter, any help would be greatly appreciated.

Thank you very much in advance,

Pete

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[thomas bibu]

dear VenPT,

at the outset let me wish you & all physioforum pals an exciting new year.

well, recruitment is a strategy aimed at re-expanding collapsed lung tissue, and then maintaining high PEEP to prevent subsequent 'de-recruitment'. in order to recruit collapsed lung tissue, sufficient pressure must be imposed to exceed the critical opening pressure of the affected lung. in dependent areas of the lung, the pressures required may exceed 50cm H2O. such pressures are far in excess of pressures needed to recruit areas in the upper lobes, and in fact may over-distend and even injure the upper lobe alveoli. a strategy is needed to limit trans-alveolar pressures in the upper lobes and provide sustained high pressures in the lower areas of the lungs sufficient to cause recruitment of collapsed tissue. various ventilatory modes such as inverse ratio pressure-controlled ventilation, airway-pressure release ventilation, and even high-frequency oscillatory ventilation have been used to promote recruitment.

an effective recruitment strategy depends on the following;

1. Select an appropriate patient
ideal patients for recruitment maneuvers are patients with putative ARDS in the early phase of the disease (before the onset of fibro-proliferation). patients should be poorly oxygenated on a high FiO2. pre-existing focal lung disease that may predispose to barotrauma should be regarded as a relative contra-indication to the maneuver (for example extensive apical bullous lung disease). patients with 'secondary' ARDS (following on, for example, abdominal sepsis) are thought to be more likely to respond favourably to the maneuver than patients with 'primary' lung disease and acute lung injury.

2. Position the patient prone
this is easily done (after some initial resistance from nursing staff)! an important component of prone positioning for recruitment is to have a pillow under the upper chest, and another beneath the pelvic area, so the abdomen hangs down somewhat in between the two pillows. continue appropriate mechanical ventilation.

3. The patient must be fully monitored
monitoring should include (at least) invasive arterial blood pressure monitoring, pulse oximetry and ECG. the patient must also be completely paralysed with non-depolarising neuromuscular blockade, to prevent attempts at respiration during the maneuver. a baseline arterial blood gas analysis (ABG) should be obtained after the FiO2 has been increased to 100%.

4. Administer 40cm H2O of PEEP for 90s
set the ventilator to an effective rate of zero (with no machine breaths) and then immediately raise the PEEP to 40cm H2O for a carefully timed period of one and a half minutes. then re-institute ventilation as before.

5. Wait and recheck the ABG
wait for a period of five minutes, leaving the patient in the prone position, and obtain a blood gas analysis. if the PaO2 is under 300mmHg, then consider repeating the maneuver at PEEPs of 45mmHg and (if this fails) 50mmHg, also for ninety seconds.

6. Prevent 'de-recruitment'
the patient should now be maintained on a PEEP of 15 cmH2O. often, the patient can be turned back to a supine position without substantial worsening of oxygenation. ventilation should continue with a strategy that minimizes additional alveolar trauma (for example, inverse ratio pressure-control ventilation, with every attempt to keep trans-alveolar pressure to under 35cm H2O). ventilator tidal volumes should perhaps be limited to approximately 6 ml/kg.

going thru the above I am sure you are curious to know why use the prone position well, the rationale behind the above maneuver is that prone ventilation splints the thoracic cage, especially the anterior portion and the area around the upper lobes. if diaphragmatic excursion is promoted (by freeing up the abdomen) then preferential ventilation of the lower lobes is encouraged, and overdistension of the upper lobes is prevented.

sustained pressures of 40 to 50 cm H2O are applied to the airway for a sufficient time to distribute pressure to collapsed lung areas, and promote recruitment.

once adequate recruitment has been achieved, high PEEP is used to prevent recurrent airway collapse.

although prone positioning is highly desirable, it is not essential. however, if you don't position the patient prone, you have to limit expansion of the upper regions of the lung using other maneuvers. one way is simply to press forcefully on the upper chest during the maneuver (with about 20kg of force), or to apply 20kg sandbags. (Gattinoni has even used an inflatable device that intermittently compresses the upper chest with each breath)!

to add on, manual hyperinflation (MHI) and ventilator hyperinflation (VHI) are two methods of recruitment maneuvers used in ventilated patients to improve lung compliance and secretion mobilization. the use of VHI may minimize the adverse effects of disconnection from the ventilator, but it is uncertain whether high levels of positive end-expiratory pressure (PEEP) would decrease the peak expiratory flow rate (PEFR) and consequently affect secretion clearance. however, comparative studies have proved that the VHI technique seems to promote greater improvements in respiratory mechanics with less metabolic disturbance compared with MHI. other variables such as sputum production, hemodynamics, and oxygenation were affected similarly by both techniques.

hope your confusion is clear.

cheers,

thomas