Assessment of hindgut function in premature newborns

Assessment of Hindgut Function in Premature Newborns By W.I.H. Garstin and V.E. Boston Belfast, N o r t h e r n Ireland 9 Anorectal m a n o m e t r y was performed on 32 small for dates and or preterm infants, using a micro-tip pressure transducer. A normal rectoanal reflex was observed in otherwise normal infants on the first day of life. During the neonatal period, hindgut function in these infants was studied Iongitidunally using the minimum excitation energy (MER) to elicit a rectoanal reflex. Data suggest that hindgut dysfunction (indicated by a significant increase in MER) develops prior to the onset of abdominal distension or necrotizing enterocolitis (NEC), rather than being present from birth. Consequently, this abnormality of function probably does not initiate the process that leads to NEC. This increase in M E n may be a warning that the infant is about to develop abdominal distension or NEC. 9 1987 by Grune & Stratton. Inc. INDEX W O R D S : Anorectal manometry; necrotizing enterocolitis.

N O R E C T A L M A N O M E T R Y is an established diagnostic method but some reports have cast doubt about its reliability in premature and newborn infants. TM It is not clear whether these findings are related to technical problems or whether syndromes such as ganglionic immaturity 5 are responsible for the temporary manometric abnormality in these children. If hindgut dysfunction does occur in this age group then this could lead to a degree of intestinal obstruction, the affects of which would be primarily upon the proximal colon. In a susceptible infant this could then predispose to the pathologic changes that culminate in necrotizing enterocolitis (NEC) (cf, the enterocolitis of Hirschsprung's disease). This mechanism may explain the distribution of the affected gut in NEC and its preponderance in preterm infants, facts which have not yet been adequately explained. Physiologically, colonic evacuation depends upon a neural reflex whose afferents lie in the intramural plexus of the rectum. 6 These afferents are shared by the rectoanal reflex, which causes the internal anal sphincter to relax following rectal stimulation] The two reflexes are thought to be interrelated since observed insensitivity of the rectoanal reflex coexists with impaired colonic evacuation. 8 Hindgut function can therefore be quantified by measuring the minimum excitation energy (MER) necessary to elicit a normal rectoanal reflex. 9 An increase in M E R indicates a reduction in the efficiency of colonic evacuation. The development of the micro-tip pressure transducer may reduce the technical problems inherent in

A

Journal of Pediatric Surgery, Vo122, No 4 (April), 1987: pp 353-355

the perfusion or balloon catheter systems used for rectoanal manometry, g~ Such systems tend to cause spontaneous inhibition of the internal sphincter and are relatively insensitive to the low pressures often present in the anal canal of preterm infants. ~ The micro-tip transducer accurately measures low pressure and is less likely to stimulate the anorectum significantly because it is small and perfusion fluids are not required, g~ Rectoanal manometry was performed on neonates at risk of developing NEC. Studies were performed on the first day of life and at approximately 48-hour intervals thereafter to determine whether those infants who developed NEC have abnormally high M E R results (which might indicate hindgut dysfunction) from birth. MATERIALS A N D METHODS Rectoanal manometry was performed using the catheter system illustrated in Fig 1 (Gaeltec LTD, Dunvegan, Isle of Skye). Pressures within the balloon and within the internal sphincter were measured by microtransducers mounted on the catheter. The distal transducer was positioned so that maximal internal sphincteric activity was recorded. Care was taken to minimize distal displacement during balloon inflation as this could produce a false-normal result. It was necessary to wait until the infant was completely relaxed before accurate results could be recorded. Studies were performed on small for dates (SFD) and/or preterm infants <2.5 kg as soon as possible after birth and repeated at approximately 48-hour intervals throughout the neonatal period until the infant was thriving and stooling normally or until some complication such as abdominal distension or N E C developed. Rhythmic internal sphincter contraction activity was recorded. A normal response was judged to have occurred when there was a drop in the anal canal pressure and/or cessation of normal rhythmic activity after rectal stimulation, u The method described by Boston et al 9 to quantify the m i n i m u m stimulus required to elicit an rectoanal reflex ( M E R ) was used as an indicator of hindgut function. The manometric results were plotted against age for normal infants and a normal distribution curve obtained (Fig 2). It was then possible to use this curve to compare M E R results of infants who developed abdominal distension or N E C at that time.

From the Department of Surgery, The Queen's University of Belfast, and the Royal Belfast Hospital for Sick Children, Belfast. Address reprint requests to W.LH. Garstin, Registrar in General Surgery, Department of Surgery, The Queen's University of Belfast, Institute of Clinical Sciences, Grosvenor Rd, Belfast BTI2 6BJ Northern Ireland. 9 1987 by Grune & Stratton, Inc. 0022-3468/87/2204-0012503.00/0

353

354

GARSTIN AND BOSTON

Table 1. Clinical Details of 32 Infants Studied Mean Gestational age (wk) Birth weight (g) Delivery Normal vaginal Forceps Cesarian sections

I

I

1

2

I

3

I

4

I

5

I

I

6

Apgar score At 1 minute At 5 minutes

SD

32.08

2.65

1582.18

366.10

12 3 25 5.45 7.90

2.00 1.60

7

Fig 1. (Top) Catheter system with t w o micropressure transducers mounted at tip and 6 cm distally, (Bottom) Catheter system with balloon attached.

subsequently thrived normally and were assumed to have regained normal hindgut function. There were no known complications attributed to this investigation.

RESULTS

DISCUSSION

The clinical details of the 32 infants examined are presented in Table 1. The mean time of investigation on the first day of life was 4.53 (SD 4.87) hours and the mean number of manometric investigations performed on each infant was 5.53 (SD 1.5). Rhythmic activity in the anal canal was demonstrated in all infants, though in some, pressures were not recorded for periods of up to five minutes after catheter insertion. All infants demonstrated a normal rectoanal reflex on the first day of life. Seventeen infants developed abdominal distension and eight of these developed NEC. Fifteen infants showed no signs of abdominal distension and were used as controls. There was no significant difference in M E R results on day 1 between infants with N E C (1.99 m J, SD 1.26 m J) or abdominal distension alone (1.68 m J, SD 0.91 mJ) and controls (1.32 mJ, SD 0.63 mJ; P = .063 and .025, respectively, binomial test). M E R results observed in the 48-hour period prior to the onset of N E C (4.07 m J, SD 0.83 m J) were significantly higher than controls (2.1 m J, SD 0.29 m J; P = .008, binomial test). There were no significant differences in M E R results between infants with abdominal distension alone (3.59 mJ, SD 1.61 mJ) and infants with N E C during this time (P = .65, Mann Whitney U test). Further studies on infants with abdominal distension alone showed a return of normal hindgut function. There was one death in the series attributed to NEC. The seven remaining neonates who had N E C

Since rectoanal manometry has been employed as a diagnostic method there has been debate as to its value in preterm infants and in the neonatal period. 14 Some have argued that a real disorder of function from whatever cause occurs in these infants, whereas others have emphasized the technical problems and the subjectivity of the technique as the main cause of apparently inappropriate results. 1~ Our impression of the micro-tip transducer mounted catheter system is that many of these problems, in particular subjectivity, are reduced. Like Arhan et al ~3 we observed high excitation thresholds in some infants, particularly those who developed abdominal distension or N E C . In such cases insufficient balloon inflation might be mistaken for a response indistinguishable from Hirschsprung's disease. In addition, the artefact caused by catheter displacement can be confused with a normal manometric response and repeated observations are therefore imperative if this important problem is to be avoided. These data confirm our previous impression that normal preterm and/or SFD infants display normal rhythmic internal sphincter activity and normal rectoanal reflexes on the first day of life. Contrary to our expectations, however, there is no evidence that hindgut dysfunction predisposes preterm and/or SFD infants to N E C in as much as there is no significant difference in M E R results between index and control cases on the first day of life. The observed increase in M E R that occurs may be a warning that the baby is about to develop abdominal distension or N E C rather than being the cause of these problems. There were no complications obviously attributed to manometry in the cases reported. We feel that this technique using the micro-tip pressure transducer in SFD and/or preterm infants is safe and potentially useful in assessing hindgut function in this group of patients.

34

t kJ J

J DAYS

Fig 2.

MER values from birth for normal neonates.

HINDGUT FUNCTION IN NEONATES

355

REFERENCES

1. Howard ER, Nixon HH: Internal anal sphincter. Arch Dis Child 43:568-578, 1968 2. Ito Y, Donahoe PK, Hendren WH: Maturation of the rectoanal response in premature and perinatal infants. J Pediatr Surg 12:477-482, 1977 3. Holschneider AM, Kellner E, Streibl P, et al: The development of anorectal continence and the significance in the diagnosis of Hirschsprung's disease. J Pediatr Surg 11:151-156, 1976 4. Meunier P, Marechal P, Mollard P: Accuracy of the manometric diagnosis of Hirschsprung's. J Pediatr Surg 13:411-415, 1978 5. Smith B: Prenatal and postnatal development of the ganglion cells of the rectum and its surgical implications. J Pediatr Surg 3:386-394, 1968 6. Holschneider AM: The problem of anorectal continence. Prog Pediatr Surg 9:85-97, 1976 7. Gowers WR: The automatic action of the sphincter ani. Proc R Soc Lond 26:77, 1878

8. Boston VE: The diagnosis of Hirschsprung's disease with reference to anorectal manometry and quantitative assay of acetylcholinisterase. MD Thesis, Part 1, pp 35-44, 1980 9. Boston VE, Cywes S, Davies MRQ: Qualitative and quantitative evaluation of internal and sphincter function in the newborn. Gut 18:1036-1044, 1977 10. Rosenberg AJ, Vela AR: A new simplified technique for paediatric anorectal manometry. Pediatr 71:240-244, 1983 11. Boston VE, Scott JES: Anorectal manometry as a diagnostic method in the neonatal period. J Pediatr Surg 11:9-16, 1976 12. Aaronson I, Nixon HH: A clinical evaluation of anorectal pressure studies in the diagnosis of Hirschsprung's disease. Gut 13:138-146, 1972

13. Arhan P, Faverdin C, Thouvenot J: Ano-rectal motility in sick children. Scand J Gastroenterol 7:309-312, 1972