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Gastrointestinal, Liver and Nutritional Alterations 511

● Analysis of the pH of gastric secretions is not reliable.
A pH of 0–5 may be used to indicate gastric placement TABLE 19.4 Methods of feed delivery
of enteral feeding tubes, although this technique may
be problematic for patients receiving histamine-2- Method Description
receptor antagonists or proton pump inhibitors. If the
aspirated fluid has a low pH, it may be assumed that Bolus ● Delivery of a large volume of tube feed into the
stomach over a short period of time (>100 mL)
the fluid originated in the stomach but the pH of fluid ● Associated with complications, such as
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from an infected pleural space can also be acidic, aspiration and vomiting 127,128
therefore pH testing as a sole method to determine
tube placement is not recommended. 116 Intermittent ● A several-hour infusion a few times a day (e.g.
150 mL/h for 3 hours, three times per day), or
● End-tidal CO 2 (ETCO 2 ) detectors: capnometry and delivered over a longer period (12–16 hours)
capnography. Capnometry and capnography use with an 8–12-hour rest period 127
ETCO 2 CO 2 detectors to evaluate enteral tube place- ● Allows gastric acidity and therefore limits
ment but they are not used in routine clinical bacterial overgrowth
practice. 107,117-122 Differentiating between oesophageal, ● Requires a higher hourly rate to meet caloric
stomach or intestinal placement is not possible. 116 requirements
● Pepsin/trypsin. Measuring the concentrations of Continuous ● The delivery of small amounts of formula per
pepsin and trypsin in feeding tube aspirates can be hour over a 24-hour period 129
used as a method of predicting tube placement ● May make caloric requirements more
however methods to measure pepsin and trypsin at achievable
the bedside are currently unavailable. 123 ● Continuous dilution of gastric acid may
contribute to bacterial overgrowth
Ongoing assessment of feeding tube placement is essen-
tial, as feeding tubes may migrate after initial placement. their daily caloric requirements should be employed.
Marking the feeding tube at the point where it exits the When a patient has experienced a prolonged period of
nose and measurement of tube length protruding from starvation or total parenteral nutrition, the approach
the anterior nares will facilitate detection of migration of to enteral feeding is somewhat more reserved, as the risk
the enteral tube. Radio-opaque tubes have markers to of refeeding syndrome is increased. 130-132 Although not
enable accurate measurement and documentation of common, this syndrome is associated with severe derange-
tube position. It should be used with the methods previ- ment in fluid and electrolyte levels (particularly hypo-
ously described for ongoing assessment. phosphataemia, hypomagnesaemia and hypokalaemia),
and may result in significant morbidity and mortality.
In the absence of X-ray, several approaches should be
used in combination to verify tube position. Metheny Managing complications of enteral feeding
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and colleagues found measuring: (a) length of tubing Once enteral feeding is established, it is important to
extending from the insertion site, (b) volume of aspirate assess for such complications as:
from the feeding tube, (c) appearance of the aspirate, and
(d) pH of the aspirate were able to correctly differentiate ● feeding intolerance
between gastric and bowel tube placement during con- ● gastric distension
tinuous feedings in 81% of the predictions. Ongoing ● vomiting
assessment of feeding tube placement is also essential, as ● diarrhoea
feeding tubes may migrate after initial placement. ● pulmonary aspiration
● hyperglycaemia
Feeding regimens ● hypercarbia
● electrolyte imbalances
Once the enteral feeding tube is successfully placed, ● feed contamination.
administration of the feeding solution can begin using a
variety of methods, including bolus, intermittent and This intolerance to enteral feeding can result in gastric
continuous enteral feeding (see Table 19.4). Bolus enteral distension, diarrhoea and increased GRV. 87,133,134
feeding is rarely used in the critically ill, but it is less clear
whether intermittent or continuous feeding is more
beneficial. 124-126 Because of inconclusive evidence regard- Practice tip
ing feeding regimens, decisions are best based on indi-
vidual patient assessment and the clinician’s clinical When evaluating gastric residual volume in relation to the rate
judgement. of enteral feeding, remember to take into account the produc-
tion of gastric secretion, which can be as much as 2500 mL/day.
Commencing enteral feeding
The starting rate for enteral feeding is controversial, with Critically ill patients exhibit elevated gastric residual
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suggestions in the range of 10–100 mL/h, and the com- volume for a variety of reasons including feeding
monest starting rate being 30 mL/h, despite there being intolerance 135-139 and reduced gastric motility. 135,136,140
no empirical data on which to base this recommenda- Monitoring tolerance to enteral feeding through the mea-
tion. Increasing the rate of enteral feeding is equally vari- surement of gastric residual volume has always been
able, but strategies to progress patients towards meeting viewed as an important aspect of nursing management,