Improved design of nasogastric feeding tubes

Improved Design of Nasogastric Feeding Tubes R. G. Rees, I-I. Attrill, D. Quinn and D. B. A. Silk Department of Gastroenterology Reprint requests fo D.B.A.S.)

&Nutrition,

Central Middlesex Hospital, Acton Lane, London NW10 7NS, U.K.

Disappointed with the overall performance of weighted and unweighted nasogastric feeding tubes, a design programme was initiated which resulted in the development of two new nasogastric tubes, one weighted and one unweighted. The tubes were manufactured with polyurethane rather than polyvinylchloride (PVC) which permitted an increase in diameter of the internal lumen which in turn was coated with water activated lubricant to ease removal of the introducer wire. A specially modelled outflow port was incorporated into the tips of both tubes. The performance of the two new polyurethane nasogastric feeding tubes was assessed under controlled trial conditions using as a reference a widely used PVC unweighted open ended tube. While intubation times were similar in patients without concurrent endotracheal intubation, it took a significantly shorter time to intubate patients with concurrent endotracheal intubation with the new weighted tube. Following tube intubation, it was possible to aspirate gastric contents significantly more often through the new polyurethane tubes (p < 0.001) than through the PVC tube, and the unweighted polyurethane tube stayed in situ longer (p < 0.05) than the PVC tube. The newly designed polyurethane nasogastric feeding tubes are the first tubes that have been shown to have advantages over the simpler type of open ended, unweighted PVC nasogastric feeding tubes.

ABSTRACT

were removed inadvertently during enteral feeding, with 2.5 f SE0.8 tubes being required per course of enteral nutrition [7]. Subsequent delays in reintubation, which most commonly occur at night, result in an inadequate intake of diet. The incorporation of 3-5 g weights into the tip of fine bore nasogastric tubes did not appear to lengthen tube usage [7]. Other problems that have been identified with the unweighted open ended nasogastric feeding tubes have included occasional difficulties in withdrawing the introducer wire after tube insertion, the frequent failure to aspirate gastric contents, particularly when checking the position of the tubes, and resistance to inflow of the more viscous energy dense and fibre containing enteral diets [8,9]. These experiences suggested the need for further research into the area of entera! feeding tube technology [7] and we initiated such a programme in our unit 3 years ago. A series of new tubes were designed and their clinical performance assessed in pilot studies based on a protocol previously described [7]. According to results, designs were altered, and these experiences have led to the development of two new polyurethane nasogastric feeding tubes. We report here the results of a prospective controlled clinical trial undertaken to compare the performance of these with that of an unweighted open ended nasogastric tube exactly similar in design to those previously used in our Unit [7].

INTRODUCTION Enteral nutrition has been an accepted method of providing nutritional support to patients with normal or near normal gastrointestinal function. The most widely used administration technique usually comprises a 24 h infusion of a formulated enteric diet, with or without the use of a peristaltic pump [ 11, via pernasal fine bore feeding tubes positioned in the stomach or small intestine [2]. Results of recent controlled studies show that positive nitrogen balance is often difficult to achieve consistently over a 2-3 week period of enteral nutrition 12-41. In traumatised hypermetabolic patients, even an adequate intake ui nitrogen and calories may not overcome the primary neuroendocrinological responses and at least in the early phases patients will remain in overall negative nitrogen balance. In other patients, however, negative nitrogen balance is more likely to persist on account of inadequate intake. Reasons for this have been shown to be related to use of starter regimes [5], use of small volume containers [6] and slowing of infusion rates to counteract gastrointestinal side effects [ 11. In addition we and others have now documented a further and more important technical problem, namely the poor performance of fine bore feeding tubes [7]. In this recent study, it was found that 62”,, of 419 open ended, unweighted fine bore nasogastric feeding tubes 203

204

IMPROVED

DESIGN

OF NASOGASTRIC

FEEDING

TUBES

Fig. 1 Distal ends of the three feeding tubes used in the trial. The top tube is the open ended unweighted PVC Prima nasogastric feeding tube (Portex Ltd, Hythe, Kent, England; length 85 cm; OD 2.1 mm; ID 1.1 mm). The middle tube is the unweighted occluded tipped Corpak bullet polyurethane nasogastric feeding tube (Corpak Co., Wheeling IL, USA; length91.4cm; OD 2.1 mm; ID 1.37mm). The bottom tube is the weighted polyurethane Corpak nasogastric feeding tube (Corpak Co., Wheeling IL, USA; length 91.4 cm, OD2.lmm;ID 1.37mm).

Fig. 2 Higher power view of the distal end of the unweighted occluded tipped Corpak Bullet polyurethane nasogastric feeding tube, showing the long singie wide necked smooth and curved edge outflow port.

MATERIALS Nasogastric

AND METHODS

feeding

ducer beyond the outflow orifice of the tube is prevented by the incorporation of a plastic hub at its proximal end. The two new nasogastric feeding tubes (Corpak Co., Wheeling, IL, USA) are constructed with a 91.4cm length of Polyurethane. The tip of one tube is weighted (1.5 g) with cylindrical shapes of tungsten, the other has an unweighted occluded tip (Bullet tube, Fig. 1). Polyurethane was preferred to PVC, silicone or latex because our clinical experience showed that ‘kink resistance’ could be maintained despite using thinner thickness tubing. Thus while the OD of the new two tubes (2.10 mm, 6 F) is exactly that of the PVC Prima tube, the ID (137mm) is 24.5”,, larger with a 54”,, increase in flow area, providing therefore less resistance to infusion of the relatively more viscous energy dense feeds. The interior wall as well as the outside of the tip of the feeding tube is impregnated with a water activated lubricant the aim of which is to ease tube insertion through the nasopharynx and facilitate the removal of the introducer wire. In our previous experience difficulties have arisen on occasions when withdrawing the introducer wire from the Prima PVC tube [9]. In the early phase of our tube development programme, difficulties arose when attempting to aspirate from side ports, particularly when multiple ports were employed. Moreover, difficulties with diet infusion also arose when mucus and/or curdled diet accumulated in tube distal to the side port or ports. In retrospect we realised that resistance to outflow could occur when too smalt a side port was employed, and that the shape was important, outflow seeming to be restricted if the edges of the port were rightangled. In the final design of the outflow posts of the new tubes, therefore, attempts were made to mimic as far as possible the flow characteristics of the open ended Prima PVC tube. Thus the tubes contain, as shown in Figure 2, a long, single, wide-necked, smooth and curved edged outflow port. There is no ‘dead space’ distal to outflow port to trap mucus or curdled diet. The tubes are introduced with the aid of a braided steel introducer wire, looped at this distal end. This is ‘softer’ in texture than the introducer wire of the PVC tube. A hub is incorporated into the proximal end of the introducer wire to ensure that the accidental protrusion through the outflow port cannot occur.

tubes

The open ended unweighted polyvinylchloride (PVC) Prima nasogastric feeding tube (Portex Ltd, Hythe, England) is similar in design to other brands of tubes used extensively by the investigators themselves [7] and clinicians throughout the United Kingdom and Europe. The tube (Fig. 1) is 85cm in length, has an outside diameter (OD) of 2.1 mm and internal diameter (ID) of 1.1 mm. The passage of the stainless steel intro-

Trial design

Sixty-nine patients who in the opinion of the Nutritional Support Team required nasogastric enteral nutritional support, were included in the study. On entry, patients were randomised to be intubated with one of the three nasogastric tubes. In the event of nonelective extubation patients were re-randomised. The

CLINICAL

Table 1

Intubation

NUTRITION

205

RESULTS

times Without concurrent endotracheal intubation

With concurrent endotracheal intubation

115.5 * 65.9 (n = 32)

205.2 f 87.7t (n = 5)

114.1 k 69.9 (n = 28) 116.0 + 62.0 [n = 28)

113.3 (n 85.6 (n

Nasogastric feeding tube Prima unweighted open ended Polyurethane unweighted ‘bullet’ Polyurethane weighted

Values arc mean f SD seconds.

tp

* = f =

41.9 12j 30.4-t 8)

< 0.05

open ended unweighted PVC Prima nasogastric tubes were connected to the giving sets (Vx 536, Viomedex Ltd). The two polyurethane tubes were connected to this same giving set via a double male luer connection (Vygon 874.10). The patients were also randomised to receive one of three aseptically prepared polymeric enteral diets from 1 L plastic containers (Vx 534, Viomedex Ltd): a) Forrison” Standard 1 .O Kcal/ml, 12.6 g Nitrogen ‘L, Cow & Gate (n = 27); b) Forrison” Plus 1.5 Kcal,‘ml 15.6 g Nitrogen/L, Cow & Gate (n = 22); c) Nutrison” 1 .S Kcal*ml 18.8g NitrogerPL, Nutricia in = 20).

The aim was to infuse 21 of each diet continuously over 24 h. Enteral feeding pumps were not used routinely during the study, but when used they did not influence the performance of the feeding tubes. The time taken between inserting each tube into the nostril and completion of gastric aspiration was recorded on each occasion (intubation time). Note was made throughout of whether gastric contents could be aspirated (presence of bile stained fluid, or clear fluid that was acid on litmus paper testing). The duration of rnteral feeding per intubation was recorded, as well as elective and non elective reasons for extubation. In the light of our previous observations that there could be advantages to using weighted nasogastric feeding tubes if patients are already intubated with a cuffed endotracheal tube [lo], intubation times were analysed separately for those patients with and without concurrent endotracheal intubation. The statistical significances of differences in intubation times, and duration of enteral feeding for intubation were assessed using the students ‘T’ test. The statistical significances of differences in the incidence of non elective extubation and the ability to aspirate gastric contents following intubation were assessed using the chi square test.

On completion of the trial all but four (Prima unweighted open ended, 1; Polyurethane unweighted Bullet, 1; Polyurethane weighted, 2) of 117 nasogastric feeding tubes were successfully inserted. Sixty-nine patients had been intubated on 113 occasions with either the Prima PVC open ended tube in -= 37), the polyurethane unweighted bullet tube (n = 40) or the polyurethane weighted tube (n = 36). The intubation times are shown in Table 1. No differences were found in the times taken to concurrent intubation with the three different tubes. With regard to the patients with concurrent endotracheal intubation, intubation took the longest when the Prima PVC open ended tubes were used (mean 205 f SD 87.7 s). Although intubation times were shorter when the two new polyurethane tubes were used, the differences were only significant for the weighted tube (p < 0.05). Gastric contents could only be aspirated after insertion of 4 of 37 (10.8”,,) Prima PVC open ended tubes. In contrast it was possible to aspirate gastric contents significantly more often after insertion of the polyurethane ‘bullet’ tube (241’40, 60”,,, p < 0.001) and the polyurethane weighted tube 122:36, hl.l”, , p < 0.001). As can be seen from Table 2, it was commoner for all three tubes to be removed non electively than electively. There was no significant difference between the incidences of non elective tube removal I Prima unweighted open ended 68.3”,,; polyurethane ‘bullet’ weighted 57.8”,, ). ‘l‘he three 60.X”,,; polyurethane tubes were usually either pulled out by the patient or no specific cause was identified. Elective tube removal was performed most commonly following return to oral nutrition or due to the death of the patient. Although overall there were no significant differences in the incidence of non elective removal of the three tubes, the data summarised in Table 2 provides no information about the timing of non elective tube removal. Further analysis of the data (Table 3) showed that on average both the polyurethane tubes remained in situ longer than the Prima unweighted open ended tubes. The difference was only significant for the polyurethane unweightcd ‘bullet’ tube (p ‘c 0.05).

DISCUSSION In the present trial we chose as our references the simple PVC Prima open ended unweighted tube, not because we believed that its performance would necessarily bias the results in favour of the newly designed polyurethane tube, but because we have a wide experience of this type of tube and two previous studies one retrospective [7] and the other prospective [ 111, did not

206

IMPROVED

DESIGN

Table 2

OF NASOGASTRIC

Extubation

FEEDING

TUBES

of nasogastric feeding tubes

(n) Non elective Pulled out by patient Unknown cause Accidental removal by staff Tube blockage Vomited Total Elective Death Return to oral nutrition Return to parenteral nutrition Discomfort Total

Table 3 days)

Prima unweighted open ended 37

Polyurethane unweighted ‘bullet’ 40

9 (24.3”,,) 12 (32.4”.,,) 1 (2.7”,,) 3 (8.1<‘,,) 1 (2.7O,,,) 26 (70.2L’,,)

12 (30.0”,,) 8 (20.0”,,) 1 (2.5<‘,,) 2 (5.0”,,) 2 (5.0”,,) 25 (62.5<‘,,)

7 (18.9’,,,,) 4 (10.8”,,)

4 (lO.OO<,) 10 (25.0”,,) 1 (2.50,))

11 (29.7”,)

Duration of feeding per intubation (all values in

(n) mean f SD median range

Prima unweighted open ended 37

Polyurethane unweighted ‘bullet’ 40

2.8 * 2.5* 2 0.5-l 1

5.2 * 7.4* 3 0.5-25

Polyurethane weighted 36 4.4 f 4.2 3 0.5-16

lp CO.05. suggest that the performance of nasogastric feeding tubes could be improved by weighting the tip and employing side aspiration ports. It was not possible to assess prospectively whether the water activated lubricant on the tips of the new polyurethane tubes lessened discomfort during tube insertion as we felt it was unethical to submit patients to double intubation at the outset of enteral feeding. Nevertheless, the unblinded opinion of the two clinicians who intubated the patients (RGR and HAA) was that less discomfort occurred during insertion of the lubricated than unlubricated tubes to the region of the oropharynx. We do confirm, however, the observations of others [12] that the water activated lubricant lining the internal lumen of the polyurethane tubes allowed considerably easier removal of the introducer wire than was experienced when handling the PVC Prima open ended unlubricated tubes. One important aspect of the results is that the design of the outflow ports of the new tubes had a significantly beneficial effect on the ability to aspirate gastric contents after tube insertion. The problems arising when checking the position of nasogastric feeding tubes have been reviewed [ 131, and although insufflating air down

15 (37.5”,,)

Polyurethane weighred 36

13 (36.1”,,) 7 (19.4”,,) 1 (2.8”,,) 1 (2.8”,,) 22 (16.1”,,) 4(11.1”,,) 9 (25.0”,,) 1 (2.8”,,) 14 (38.9”,,)

the tube and auscultating over the epigastrium is a recommended method [14], problems can arise in the case of tubes positioned in the bronchial tree in the presence of copious bronchial secretions [13]. An improved ability to aspirate gastric contents as demonstrated in this study would, therefore, lessen the need for X-ray confirmation of tube positioning. In turn this would be expected to reduce radiation exposure particularly in patients requiring frequent reintubation. As mentioned in the methods section, the use of polyurethane rather than PVC allows a 54O,, increase in flow area for a 6 F (1.1 mm) tube. In the present study, no problems of diet inflow through the three tubes were encountered even during infusion of the two relatively viscous energy dense (1.5 Kcal/ml) diets. In the past, however, [8] we have encountered such difficulties in infusing a fibre containing diet through the Prima PVC open ended unweighted tubes that a larger internal and outside diameter feeding tube had to be used. Despite claims to the contrary [8], the use of fibre containing enteral diets for some patients, particularly on long term feeding, is proposed [I5], and in these it would seem sensible to use a feeding tube, similar in design to the present polyurethane tubes, that minimise resistance outside

to inflow

at the same time

as preserving

a small

diameter.

Two further aspects of the outflow post design are worthy of comment. Firstly, in contrast to earlier designs that incorporated side ports, clogging with mucus or curdled diet did not occur, and secondly ir is not possible for the introducer wire to exit from the outflow port, a problem that has been commented upon when side ports are employed [ 121. In patients without concurrent endotracheal intubation, time for the three nasogastric feeding tubes were similar, so that in this respect neither of the poly-

CLINICAL

urethane tubes would appear to offer an advantage over the simpler PVC open ended unweighted tubes. The results do confirm previous observations [lo], that it is easier to intubate patients already intubated with a cuffed endotracheal tube if a weighted tube is used. The reason for this was probably that following pernasal insertion into the oropharynx, the 9 1.4 cm long tungsten weighted end then lay on the posterior oropharynx pointing towards the oesophagus, this position making oesophageal entry more likely. Additionally, the weighted end of the tube is probably more rigid than the ends of the two unweighted tubes, making it more unlikely to kink and coil, thereby allowing it to more easily traverse the section of the oesophagus compressed by endotracheal tube and cuff. At first sight, the high incidence of non elective extubation of the two new polyurethane tubes is disappointing, and it might be concluded that this is one aspect of tube performance that has not been improved. However, one very important aspect of the results was that both the new polyurethane tubes remained in situ on average longer than the Prima unweighted open ended tube and the difference was statistically significant for the ‘bullet’ unweighted tube. Since one of the most common causes of non elective extubation was that the tubes were pulled out by the patients themselves, it seems likely that the polyurethane tubes were tolerated better than the PVC tube. In conclusion the findings of the present controlled trial show that compared to an open ended tip, the newly designed outflow ports facilitate aspiration of gastric contents through nasogastric feeding tubes. The relatively larger internal lumen diameter unweighted ‘bullet’ polyurethane nasogastric feeding tube stayed in position longer and was therefore probably better tolerated than the Prima PVC open ended tube, and the advantage of using a weighted tube in patients with concurrent endotracheal intubation was confirmed. The two new polyurethane nasogastric feeding tubes are to date the only nasogastric feeding tubes that have been shown, under controlled trial conditions, to have any advantages over the simpler type of open ended unweighted PVC tube still used extensively in the United Kingdom and Europe. .Srrht~&l~lrr &I<: 5 December

1985. Acceptedujter

revision:

NUTRITION

207

REFERENCES

[II Jones B J M, Payne S, Lees R et al 1980 Indications for pump-assisted enteral feeding. Lancer i: 1057-1058

121Silk D B A 1982 Enteral Nutrition. [31

[41

[51

[61

[71

PI

[91 (101

[Ill

[I21

[I31 [I41

[I51

Medicine International 15: 668-673 Jones B J M, Lees R, Andrews J et al 1983 Comparison of an elemental and polymeric enteral diet in patients with normal gastro-intestinal function. Gut 24: 78-84 Jones D C, Rich A J, Wright P D et al 1980 Comparison of proprietary elemental and whole protein diets in unconscious patients with head injury. British Medical Journal I: 1493-1495 Keohane PI’, Attrill H, Love M et al 1984 Relations between osmolality of diet and gastrointestinal side effects in enteral nutrition. British Medical Journal 288: 674-68 1 Keohane I’ I’, Attrill H, Love M, Frost I’, Silk D B A 1983 A controlled trial of aseptic enteral diet preparation-significant effects on bacterial contamination and nitrogen balance. Clinical Nutrition 2: 119-122 Keohane I’ I’, Attrill H, Jones B J M, Silk D B A 1983 Limitations and drawbacks of ‘fine bore’ nasogastrir feeding tubes. Clinical Nutrition 2: 85-86 Patil D H, Grimble G K, Keohane P Pet al 1985 Do fibre containing enteral diets have advantages over existing low residue diets? Clinical Nutrition 4: 67-72 Silk D B A Enteral Nutrition-The Future. Gut /In Press) Keohane PI’, Attrill H, Silk D B A 1983 Climcal indications for weighted enteral feeding tubes. Clinical Nutrition 2: 85-86 Keohane I’ I’, Attrill H, Silk D B A Critical appraisal of capabilities and deficiencies of enteral feeding tubes~-A controlled trial (in preparation) Croker K, Krey S, Steffee W 1981 Performance evaluation of a new nasogastric feeding tube. Journal of Parenteral and Enteral Nutrition 1: 80-82 Bastow M D The complications of enteral nutrition. Gut (In Press) Allison S P, Walford S, Todrovic V et al 1979 Practical aspects of nutritional support. In: Johnston I D A, Lee H A (eds). Developments in clinical nutrition. Research and Clinical Forums 1: 48-57 Slavin J L, Nelson N L, McNamara E A et al 1985 Bowel function of healthy men commencing liquid diets with and without dietary fibre. Journal of Parenteral and Enteral Nutrition 9: 3 17-32 1

14 July 1986.