The Role of Nutritional Support in the Physical and Functional Recovery of Critically Ill Patients

A Narrative Review

Danielle E. Bear; Liesl Wandrag; Judith L. Merriweather; Bronwen Connolly; Nicholas Hart; Michael P. W. Grocott


Crit Care. 2017;21(226) 

In This Article

Methodological Challenges

Patient Selection

One of the major challenges in demonstrating benefit from nutrition in critically ill patients is the heterogeneous nature of the clinical population. In this regard it is unlikely that all patients will benefit from the same treatment at the same time point. Whilst feeding protocols are recommended as a means of encouraging early enteral feeding, a 'one size fits all' approach to the treatment of critically ill patients is no longer considered appropriate. However, defining patients who are likely to benefit from a nutritional intervention will be challenging and will require rigorous investigation. One method currently suggested to distinguish those patients who may benefit from a targeted nutrition intervention from those who may not is the determination of nutrition risk. The most popular nutritional risk scoring systems for critically ill patients are the Nutrition Risk Score 2002 (NRS 2002)[56] and the Nutrition Risk in the Critically Ill (NUTRIC) score.[57,58] Although recent clinical trials have used the NRS 2002 in their inclusion criteria, this score may lack the specificity to determine the true nutrition risk of critically ill patients as an APACHE II score > 10 automatically gives the highest risk score. Although the NUTRIC score was developed specifically for critically ill patients, it is yet to be validated prospectively. However, post-hoc analyses from the PermiT (The Permissive Underfeeding versus target Enteral Feeding in Adult Critically Ill Patients) trial did not show a mortality improvement when stratifying by this score.[59] In addition, these scoring systems do not include variables relating to muscle mass or baseline physical function therefore more work is required in the area of nutrition risk before it can be used as a criterion in future nutrition studies.

Potential tools for patient selection in clinical trials include those to determine both baseline skeletal muscle quantity and quality and change over time. Such tools include muscle ultrasound and CT. However, there are limitations with the use of these tools outside the research setting. First, there is currently no standardised, universal technique to perform muscle ultrasound;[60] and second, only patients who have required a CT scan for clinical purposes have been investigated, meaning that a selection bias may be present.[61] Nonetheless, with further work to standardise techniques, these measures may prove useful in the future either on their own or as an adjunct to existing nutrition risk tools. Lastly, if physical or functional outcomes are to be included as important clinical outcomes, then the limitations surrounding obtaining baseline measurements for non-elective ICU admissions will be equally as important and further work needs to be undertaken to understand this in detail.

Delivery of the Intervention

Ensuring adequate delivery of the intervention is an essential factor in being able to interpret the outcome of such studies. Several studies in critical care nutrition have not been successful in reaching either target energy or protein delivery (Table 1).[2,3,4,7,40,41,42] Notwithstanding that there may be physiological differences in the utilisation of substrates depending on the route and timing of nutrition delivery, strategies to enhance nutrition delivery[62,63] should be factored into clinical trials where the outcome is dependent upon meeting a target.

Duration of the Intervention

Biological plausibility is fundamental to any nutrition research. This includes the likelihood that an outcome will be observed at a particular time point as a result of the specified duration of an intervention. Effects from nutrition dosing are unlikely to be observed immediately and any effect will be reliant on the consistency of delivery of the intervention. For example, the EDEN trial reported no difference in physical outcomes at 1 year when trophic or full feeding was given for 6 days.[37] Given that current data suggest that oral intake is inadequate post extubation[64,65] and in the post-ICU recovery phase,[66] it may be unlikely that an effect would be observed 1 year after such a short intervention. Observational studies tend to include patients fed over a longer period of time and exclude those patients fed over shorter durations. Because of the risk of bias associated with the short duration of trials, we propose that critical care nutrition studies should continue for longer than the first week of critical illness and should consider post-ICU nutritional intake.