Recruitment manoeuvres

Recruitment manoeuvres have come up at least once in the CICM Part II exam, as a "critically evaluate" question (Question 8 from the first paper of 2018). Though the college question and model answer asks about "maneuvers", the discussion will refer to them as "manoeuvres" as does the majority of the English-speaking world. This question breaks the trend of the normal 18-month lag between something happening in the literature and it being asked about in the Fellowship paper; though recruitment manoeuvres have existed since time immemorial, the ART (Alveolar Recruitment Trial) study was only published in October 2017, a mere five months prior to the written paper. The PHARLAP trial was also mentioned, which had ceased recruitment in view of ART results.

The official college stance on this matter is that recruitment manoeuvres are harmful. If the candidate advocated a routine use of this strategy in their answer, "they were should be marked down" by the examiners. This position is largely due to the findings by ART investigators, that mortality in ARDS is increased by recruitment manoeuvres. Excellent reviews and discussions of this reaction are carried out by Villar et al (2017) and Calvalcanti et al (2018). For the trainee short on time, these articles cover the topic to a satisfactory extent. Rocco et al (2010) go into some detail regarding the effects of recruitment manoeuvres and their pros and cons. 

Definition of recruitment manoeuvres

There should probably be some sort of definition for this term, and when anybody hears "recruitment manoeuvre" they usually have some image of what to expect, but nobody is able to pin down exactly what it means. Without a strict definition apart from the literal meaning of the words, one might describe prone position ventilation as a recruitment manoeuvre because it is "a cleverly planned action that is intended to get an advantage" which achieves the opening of collapsed alveoli. The Medical Dictionary defines a recruitment manoeuvre as "any technique in which sustained high airway pressures are applied to the patent airway in order to diminish collapse of alveoli during mechanical ventilation", which is also somewhat vague and could describe just abount anything that happens during positive pressure ventilation. The definition in the official college answer is even worse ("ventilator manipulations to improve oxygenation in moderate to severe ARDS").

In order to be able to write an introductory statement for a "critically evaluate" question, there needs to a satisfactory definition. A good option is the definition accepted by Hodgson et al (2016) for their Cochrane review of recruitment manoeuvres:

"We defined a recruitment manoeuvre as any technique that transiently increased alveolar pressure above normal tidal ventilation (which may have included an increase in any pressure, such as plateau, peak or end-expiratory pressure) and sustained that pressure beyond the normal time."

This definition has the added credibility of coming from the same group of authors who subsequently tried running the  PHARLAP trial (though recruitment was stopped in November, some pun intended).

Rationale for the use of recruitment manoeuvres

In summary,

• ARDS is characterised by heterogeneity of lung disease (Gattinoni & Pesenti, 2006)
• Some areas of lungs may be collapsed/atelectatic and not be participating in gas exchange
• These regions may be reinflated by the application of enough positive transpulmonary pressure
• If these regions can subsequently be kept inflated by an open-lung (high PEEP) strategy, an improvement in gas exchange should result
• An improvement in gas exchange should decrease hypoxia, produce a decrease in the required FiO₂, and therefore decrease oxygen toxicity and organ dysfunction due to hypoxia and hypercapnea.  

The following techniques have been suggested (this is plagiarised directly and shamelessly from Table 1 in the 2016 Hodgson review):

Advantages of recruitment manoeuvres

In summary:

• They are easy to perform (all you need is a ventilator)
• Compared to other techniques of improving oxygenation, this is the cheapest (followed by prone position). Other techniques either require expensive consumables (inhaled nitric oxide, prostacycline) or equipment (high frequency oscillation, ECMO).
• There is a range of different manoeuvres in the literature, which means one is not restricted to one technique. It is possible to tailor the therapy to the patient and vary the technique depending on the degree of atelectasis, haemodynamic performance and expected friability of the lungs.
• Oxygenation may improve. This is the one thing which is consistently demonstrated by all the studies, including those which did not find any beneficial effect on mortality.
• The patient with ARDS will usually already be paralysed and sedated, i.e. it is not inconvenient to sedate and paralyse them just for this procedure
• In the prone position, recruitment manoeuvres are more effective.

Disadvantages of recruitment manoeuvres

• Nobody can agree on how much pressure to use, or for how long (i.e. the fact that there is a range of techniques is a mixed blessing)
• They may not be appropriate in all conditions, eg. the classically fragile lung in PJP pneumonia
• If the patient has already had a pneumothorax, obviously it will get worse 

Complications arising from recruitment manoeuvres​​​

Depending on how much pressure you use and for how long, some, all or none of these complications may manifest

• Barotrauma and ventilator-induced lung injury
  • Pneumothorax
  • Subcutaneous emphysema
  • Pneumomediastinum
  • ​​​​​​Cyclic atelectasis (i.e. with repeated recruitment manoeuvres, after each the reinflated lung may just collapse again)
  • The pressure will first be selectively distributed to well-aerated lung, potentially damaging those alveoli which were previously performing well as gas exchange units. After such an assault, these lung units may have impaired gas exchange. 
• Poor or unexpectedly opposite effect on oxygenation:
  • The recruitment manoeuvre may be ineffective because the pressure used may be insufficient, and a sufficient pressure may be comically excessive. 
  • The effect on oxygenation is only transient: 
  • The effect of increasing pressure may produce worsening shunt (i.e. instead of recruiting the collapsed lung regions, you push more blood flow into them, increasing the shunt fraction and therefore degrading oxygenation).
• Haemodynamic effects
  • Because of increased intrathoracic pressure, RV afterload increases and RV preload decreases. The consequence of this is a decrease in cardiac output. In the critically ill patient, this will manifest as a marked fall in blood pressure
  • A cytokine/endotoxin shower may be produced by the shunt. The blood shunted through diseased lung will incrrease the systemic delivery of bacterial toxin and cytokines, contributing to haemodynamic instability which may be sustained even after the manoeuvre is completed.

Evidence for and against recruitment manoeuvres

• Experimental animal models have demonstrated improved lung mechanics and gas exchange (summarised by Moran et al, 2003), which encouraged human studies
• Small-scale trials have demonstrated benefits in specific patient categories and scenarios, but this evidence has been inconsistent and patchy. For example, post-suctioning recruitment manoeuvres work really well in pigs (Kasim et al, 2009) but not in human children (Morrow et al, 2007)
• The 2016 Cochrane review by Hodgson et al found that only low-quality evidence supported the use of recruitment manoeuvres, in terms of improved ICU mortality (but not hospital mortality). In total, data from 1658 trial participants were compiled.
• The ART trial (Cavalcanti et al, 2017) enrolled 1010 patients and found an increased 28-day all-cause mortality associated with recruitment manoeuvres to 50-60 cmH₂O. ​​​​​​​​​​​​​​
• The PHARLAP trial (Hodson et al, 2019) was stopped early because the steering committee lost equipoise following the publication of ART. What data they managed to collect did not suggest any improvement in patient-centred outcomes.