Chronic cannulation of an abdominal viscus or pouch is aided by the use of a cannula which does not leak or kink. Existing cannulae have been modified to achieve this. An unusual complication was encountered in jejunal cannulae after 1 - 3 months; large concretions of dicalcium orthophosphate precipitated on the inner cannula flange, completely blocking the lumen. Concretions were derived from the food, precipitation being aided by physicochemical factors in the jejunum.S. Afr. Med. J., 48, 1879 (1974)

Arnot, RS

Barbezat, GO

Terblanche, J

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11 September 1974 S.-A. MEDIESE TYDSKRIF(Byvoegsel-Sllid-Afrika{/nse Tydskrif vir LaborCIlOrillm- en Klinieklt"erk)1879LKW 109A Flexible Unkinkable Cannula and itsObstruction by Dicalcium OrthophosphateConcretionsG. O. BARBEZAT, R. S. ARNOT, J. TERBLANCHESUMMARYChronic cannulation of an abdominal viscus or pouch isaided by the use of a cannula which does not leak orkink. Existing cannulae have been modified to achievethis. An unusual complication was encountered in jejunalcannulae after 1 - 3 months; large concretions of dicalciumorthophosphate precipitated on the inner cannula flange,completely blocking the lumen. Concretions were derivedfrom the food, precipitation being aided by physico-chemical factors in the jejunum.S. Afr. Med. J., 48, 1879 (1974).Experimental cannulation of the small bowel mav becomplicated by leakage or obstruction. The former pro'blemshould be prevented by adequate surgical technique andthe use of suitable cannulae, and the latter is relativelyrare. In this paper, modifications of existing cannulaewhich help to prevent leakage and obstruction aredescribed. Blockage of these cannulae by dicalcium ortho-phosphate concretions 'occurred in a particular experimentalmodel, a complication which, to the best of our knowledge,has not been recorded previously.MODIFICATIONS IN CANNULA DESIGNThe Gregory cannula has been used successfully for manyyears to obtain secretions from experimental animals.'An important principle is that the cannula does notrotate and permits sealing around the internal end.Leakage, however, does sometimes occur, and attemptshave been made to modify the Gregory cannula to avoidthis frustrating complication. Condon and Harkins' de-signed a cannula to prevent pressure necrosis of gastricpouches after having found that about 20% of previouscannulae leaked. This cannula transferred the weight ofcollected secretions from the sensitive gastric mucosa tothe tough anterior abdominal wall. Hoh, Shinohara andDepartments of Medicine and Surgery, University of CapeTown, and Gastro-intestinal Clinic, Groote Schuur Hospital,Cape TownG. O. BARBEZAT, M.D., F.C.P. (S.A.)R. S. ARNOT, CH.M., F.R.C.S.J. TERBLANCHE, CH.M., F.C.S. (S.A.), F.R.C.S.Date received: 11 April 1974.Reprint requests to: Dr G. O. Barbezat, Gastro-intestinal Clinic, GrooleSehuur Hospital. Observatory. Cape.Honda3 modified the traditional Gregory cannula byintroducing a flexible silicone rubber segment to themiddle of the cannula. In this way they avoided disturbingthe internal end of the cannula when the long exteriorisedend was moved as a lever. The natural reaction of thetissues around the cannula was thus undisturbed. We haveintroduced a further modification when kin king of thesilicone rubber tube poses a problem.The cannula has features of all three types already des-cribed. The basic unit is a Gregory-type cannula with theinternal part made of synthetic nylon (Polypenco Nylotron66; Fluorocarbon Resins (Pty) Ltd, Cape Town), and theexternal part of stainless steel (Figs I and 2). A perforatedwasher is inserted between these two materials (equivalentto the Condon and Harkins modification); the perforationsenable the washer to be sutured to the abdominal wall ifdesired. The acrylic resin shaft is interrupted by a flexiblesiliconised rubber segment. A single thickness of siliconisedrubber was found to kink very easily and obstruct thecannula (Fig. 3). This difficulty was overcome by intro-ducing a smaller segment of siliconised rubber inside theouter tube. The cannula was therefore still flexible, butdid not kink and maintained a patent lumen. The lengthof the flexible segment was varied according to need, andthe outer larger rubber segment tied over the syntheticnylon with non-absorbable suture material. This flexiblesegment can be introduced into an existing Gregorycannula by dividing the shaft near its internal end.A bite block is fixed to the exterior of the cannula forthe first postoperative week. A thread can be turned inthe exterior end of the steel shaft so that the cannulacan be sealed with a screw cap if necessary (e.g. forchronic fistulae of the small bowel).PRESENTATION OF CONCRETIONSMongrel dogs were surgically prepared with 3 cannulaeinserted into the jejunum (10, 20, and 50 cm distal to theduodenojejunal flexure) and 1 into the ileum (10 cmproximal to. the ileocaecal valve). The dogs were givensubcutaneous fluids for 3 days postoperatively, and thenfed proprietary dog cubes containing protein (minimum)20%; fat (minimum) 4%; fibre (maximum) 5%; calcium(maximum) 1,55%; phosphate (maximum) 1,3% (calcium:phosphate ratio 1: 1); methionine 0,34%; sulphaminoacids0.64"b; lysine 1,Q"b; tryptophan 0,18°(,; arginine 1,2%'and salt 1,Q~~, with added fat and water-soluble vitamins1880LCM 110S.A. MEDICAL JOURNAL(S//pplemefll-Sotl/h African Jo//rnal of Laboratory and Clinical Medicine)11 September 1974Fig. 3. Left: Flexible part of cannula bent to show kinkingfound with singte section siliconised rubber. Right: Flexi~ble part of cannula bent but no kinking produced withdouble silicone rubber segment.HGFEoScale .!£n~~ ~. _:=:::W n IlIIfJ,,-,--,-,--,====c--C-"• .=0- C±:==JlI!fI! ~ aL_-=_=:i!iii:il U IIBL1t- J l~ @,:~ UO~~AFig. 1. Component parts of cannula: A - acrylic resininternal end; B - outer silicone rubber tube; C - innersilicone rubber tube; D - acrylic resin portion of shaft;E - perforated washer; F - stainless steel shaft; G -washer (acrylic resin); H - end screw; I - bite block.Fig. 2. Assembled cannula. Constituent parts of flexiblesegment are shown below cannula.and trace elements. Water was given ad libitum. Experi-ments began at least 2 weeks after surgery and consistedof perfusing an electrolyte solution isotonic to plasma(Na 140, K 5, Cl 110, and HCO, 35 rnEqjlitre, and polye-thylene glycol, molecular weight 4000, 50 gjlitre) into themost proximal cannula at 7 mljmin and withdrawingaliquots of secretions plus perfusate from the more distalcannulae. Each experiment lasted a maximum of 4 hours.Animals were fasted for 18 hours before each of thestUdies, which were not performed more frequently thanonce in 72 hours.Between 4 and 12 weeks after surgery, difficulty was ex-perienced in maintaining the patency of the 3 proximalcannulae in 2 dogs. Initially the lumen could be clearedby blowing water through the cannulae with a syringe,and later a soft plastic probe was sometimes successfulin restoring patency. A gritty, granular material wasusually recovered from the lumen. The ileal cannula wasFig. 4. Cannulae removed from experimental animalshowing concretions obstructing opening into lumen. Partof the gut wall has been left around the cannula on theleft.11 September 1974 S.-A. MEDIESE TYDSKRIF 1881(BYI'oegsel-Sllid-Afrikaall5e Tydskrif vir Laboratorillm- en Kliniekwerk) LKW 1]1TABLE I. COMPOSITION OF CONCRETIONSANALYSIS OF CONCRETIONSCalclIlated Found% %Ca 23,28 2331P 18,02 18,54Ash 73,84 72,72It was therefore apparent that the concretions wereessentially dicaIcium orthophosphate with a small amountof proteinaceous matter and free moisture. This compoundwas present in the feed and was found to be soluble inacidic solution, to have a very low solubility in neutralsolution, and to be almost insoluble in alkaline solution.We wish to thank Mr D. Stewart, of the Department of Bio-engineering, Groote Schuur Hospital, who constructed thecannulae, and Mr . Greenblau, of Consulting Testing Labora-tories, Cape Town, who analysed the concretions. Financialassistance was provided by the South African Medical ResearchCouncil and by a grant from the University of Cape TownStaff Research.However, in the particular model described above, preci-pitation of dicalcium orthophosphate on the inner flangeof the cannula led to intractable blocking.It is suggested that if the jejunal pH were greater than7,0, any dicalcium orthophosphate present in that part ofthe bowel would be precipitated, and that any foreignmaterial would be a possible site for collection of theseeded precipitate. Although the synthetic nylon of thetype used in this cannula is virtually inert, the very smallcharge present' and its action as a foreign body wouldact as a focus for the deposition of the concretion.We have noticed a fine precipitate on the steel cannulaepreviously used in our laboratory; this, together with therarity of the complication, would suggest that compositionof the cannula is not the most important factor in thedeposition of this material.Other variables that predispose to concretion formationcould be: (a) food composition-an excess of calciumphosphate in the diet might raise the salt concentrationabove the critical level for solubility; (b) dehydration-ifthe animals have insufficient oral fluid intake, similarresults may occur; (c) jejul1al pH-this is usually between6 and 7;" but in conditions where acid is continuouslydiverted to the exterior (e.g. chronic gastric fistula stUdies),the small bowel pH may rise and render the dicalciumorthophosphate insoluble. Similarly, perfusion of alkalinesolutions into the upper small bowel for prolongedperiods may have the same result. It is not known whichfactor was applicable to our 2 dogs.The total absence of concretions in the ileum is ofinterest, since this would appear to be a likely site ofoccurrence due to the alkaline pH of 7 - 8 normallypresent at this site.··· It is likely that most of the salt hadbeen absorbed or precipitated in the proximal bowel,leaving little or none for precipitation on the ilealcannula.Similarly, concretions have never occurred in Thiry-Vella loops of small bowel (jejunum and ileum) or ingastric pouches, and the continued use of these cannulaein these sites is fully justified. It is concluded that thedeposition of dicaIcium orthophosphate is determined bydietary constituents and the particular physicochemicalfactors present in the proximal small bowel.(51,58% as P04)(31,34% as CaO)(equivalent to1,84% protein)(mass/mass)The concretions were analysed and their composition isgiven in Table I. Correcting for the presence of freemoisture and proteinaceous matter, the results calculatedin respect of the phosphate of calcium, which was themost significant inorganic component, were calcium 23,31 %.ash 72,72% and phosphorus 18,54%. The molar proportionCa : P or Ca : PO, was approximately 1,0. Theoreticallyconsidering dicaIcium orthophosphate (CaHPO,.2H,O)which changes to calcium pyrophosphate upon ashing(2CaHPO,.2H,0----7Ca,P,O, +5H,O), the analysis of thedicalcium orthophosphate was as follows:not affected in either dog. Eventually all 3 jejunal cannu-lae became completely obstructed and the dogs weresacrificed.At autopsy, large stony-hard, greeny-brown concretionswere found firmly adherent to the synthetic nylon baseof each jejunal cannula (Fig. 4). The concretions were2 - 3 cm in diameter and 0,7-1 cm thick. Some wererounded and some slightly elliptical along the length ofthe bowel. The larger concretions almost obstructed thebowel lumen.Moisture content 2,06%Ash content 69,90%Phosphorus content 17,82%Calcium content 22,40%Nitrogen content 0,24%DISCUSSIONModification of the existing forms of cannulae haveminimised a previously high incidence of leaks at the siteof entry into a viscus or pouch. Obstruction as a resultof kinking of the flexible segment has been eliminated.REFERENCES1. Gregory. R. A. (1950): J. Physiol. (Lond.). 111. Il9.2. Condon. R. E. and Harkins. H. N. (962): Surgery. 52, 363.3. Hoh. Z., Shinohara. H. and Honda. R. (1972): J. Surg. Res .. 2, 77.4. Bloch. B. (972): Bio-me<!. Engng .. 7. 426.5. f~rdlran. J. S. and Locklear. T. W. (1966): Amer. J. Dig. Dis .. 2,~O>.6. Meldrum. S. J .. Walson, B. W .. Riddle. H. C .. Brown. R. L. andSladen, G. E. (1972): Brit. Med. J .• 2. 104.

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A flexible unkinkable cannula and its obstruction by dicalcium orthophosphate concretions

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A flexible unkinkable cannula and its obstruction by dicalcium orthophosphate concretions

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