NHD clinical - nutrition in critical care by Rowan Sutherill Specialist Dietitian for Neurosciences Sheffield Teaching Hospitals (Royal Hallamshire Hospital)
Rowan Sutherill trained and worked in Sheffield for ten years. She has spent the past six years working at the Royal Hallamshire Hospital, specialising in neuromedicine (in-patients and out patient MND clinic) and neurosurgery (in-patients).
Nutrition Support on the Neuro Critical Care Unit Adequate provision of nutrition is associated with improved outcomes in neuro-critical illness. Complications and management of the trauma or illness in addition to significantly increased nutritional requirements, all contribute towards making this a difficult aim to achieve. Working as part of a multidisciplinary team on a neuro-critical care unit, there many obstacles to overcome in order to successfully meet our patients’ nutritional needs as early as possible. Road traffic accidents, falls, assaults and accidents occurring at home or work cause most incidents of brain injury seen on neurocritical care units. The primary brain injury is sustained at the time of the incident and, dependent on the type of incident, can induce prolonged coma or severe focal damage. A second brain injury may follow at any time due to several reversible or potentially preventable causes such as intracranial haemorrhage, impaired respiration, hypercapnia, decreased cerebral perfusion pressure due to hypotension and hypoxia (1). The essence of brain injury management is to continuously monitor patients in order to recognise signs of deterioration and prevent secondary insults by aiming to maintain optimal pressures in the brain. The Glasgow Coma Scale is a universally recognised tool to assess patient levels of consciousness and can help to predict prognosis. With the minimum possible score at three and the maximum at 15, patients scoring 3-8 will tend to necessitate management on an intensive care unit (ITU) (2). This article focuses on patients with severe brain injury, due to the extremity of metabolic and nutritional consequences.
Metabolic and nutritional consequences of severe brain injury
Within 72 hours of suffering a brain injury, patients become hypermetabolic and hypercatabolic, resulting in energy and protein requirements which are unachievable in practice (3,4). The cause of the hypermetabolic response is thought to be associated with high levels of counter regulatory hormones such as cortisol, glucagon, norepinephrine and epinephrine, which are found specifically in patients with brain injury. Other proteins and hormones are implicated in this process such as cytokines and corticosteroids, but their exact role in increasing metabolism is not fully understood (7-9). 18
Energy requirements have been measured at 130-135 percent above BMR (3). In practice these requirements are calculated using the Schofield equation with stress and activity factors added on at around 20-30 percent (10). They are then reviewed and adjusted accordingly, in direct relation to the patient’s clinical state. Hypercatabolism (also considered to be caused by counter regulatory hormones) is characterised by a significant increase in protein turnover. Irrespective of protein intakes, brain injured patients often remain in negative nitrogen balance for several weeks post injury (11). Nitrogen requirements calculated as a response to urinary nitrogen excretion in these patients can be as high as 0.35g/ kg/day (28), which is generally considered unachievable in practice. Although still to be definitively proven, there appears to be little benefit from feeding nitrogen levels in excess of 0.2g/kg/d in critically ill patients (12). Consequently, whilst these patients remain catabolic it is realistic to aim to minimise rather than prevent nitrogen losses. Classically, patients display signs of muscle wasting which can be distressing for relatives to witness, but should be viewed as reversible once patients become less hypercatabolic and hypermetabolic and enter the rehabilitation phase of their recovery. In reality, this is estimated to take from two weeks to one year, depending on the type and severity of the injury and any complications experienced (3,13).
Providing nutrition support
As with most clinical conditions, early feeding of brain-injured patients is associated with improved outcomes (14-16). Although there is no agreed time limit in which to initiate feeding, evidence suggests nutritional support should be commenced within 72 hours post brain injury (17). Further evidence suggested that patients not fed within 5 to 7 days after brain injury have been found to have a two and four fold increased likelihood of death respectively (18). Enteral feeding is considered to be the preferred method of providing nutritional support, assuming the gut is accessible and functioning (19). Naso-gastric (NG) feeding
is most commonly used, however, depending on the type of injury sustained, it may be necessary to pass an oral gastric (OG) tube. OG feeding can be problematic as less sedated patients may bite through the feeding tube, risking aspiration.
Factors affecting administration of feeds It has been well documented from several studies that only 55-75 percent of feeds are delivered to patients on neuro ITU settings (20-23). A deficit in energy provided compared to that prescribed within the first five days has been shown to be associated with increased mortality rates (18). There are many factors, however, that can affect or stop the delivery of feed in neuro-critically ill patients. Delayed gastric emptying and increased susceptibility to gastric reflux, appear to be more problematic and prolonged in brain injured patients, although the exact cause is not known. Delayed gastric emptying is defined as aspirates of 200-250ml (depending on individual ITU protocols). First line management generally involves slowing the rate of the enteral feed and prescribing prokinetic agents (Erythromycin and/or Metoclopramide) (24). Should this approach fail to improve absorption within 24 to 48 hours, the options are to pass a jejunal tube to allow for post pyloric feeding or consider parenteral nutrition (19). Once considered to increase intracranial pressure and cerebral oedema in head injury patients, parenteral nutrition is now considered safe. Despite this, enteral feeding remains the preferred choice of feeding route (19). See table 1 for comparisons of enteral and parenteral feeding. Feeding is regularly interrupted within any 24-hour period due to treatment plans which demand radiological scanning, surgery, intubation, extubation, tracheostomy insertion and chest physiotherapy. For these to be safely carried out, feeds are stopped for varying lengths of time. Patients who are awake and cognitively impaired may remove NG feeding tubes several times a day. This interrupts feeding, increases risk of aspiration if continuNHDmag.com Dec ‘09/Jan '10 - issue 50
