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Parenteral nutrition: practical considerations
1Serials
Nutrition
(
Parenteral nutrition: practical considerations
J. W. L. Puntis Introduction
Table 1
Providing an effective parenteral nutrition support service requires knowledge of how to deal with a number of practical problems. This article briefly reviews some of those most commonly encountered. Prevention of sepsis is an important issue for any unit using central venous lines whilst management of this complication may vary according to the patient’s dependence upon central venous access. Serious mechanical catheter related complications are not uncommon’ and occlusion or fracture may be a potential disaster in patients receiving long term intravenous nutrition, when the catheter is literally a life-line. The risk of many types of complication becomes less with an experienced multi-disciplinary team approach to nutritional support. Indications for parenteral nutrition are shown in Table 1.
Indications for parenteral nutrition
Neonates (a) Absolute
(b)
1 indications
Relative indications
Older infants and children (a) Intestinal failure
(b)
Venous access Once a decision to initiate parenteral feeding has been reached, venous access must be established.
(c)
Exclusion of luminal nutrients Organ failure
(d)
Hyper-catabolism
?? intestinal failure (short
gut, functional immaturity, pseudoobstruction) 0 necrotising enterocolitis ?? hyaline membrane disease ??promotion of growth in preterm infants ?? possible prevention of necrotising enterocolitis ??short gut ??protracted diarrhoea ??chronic intestinal
pseudo-obstruction 0 post-operative abdominal or cardio-thoracic surgery ??radiation/cytotoxic therapy ?? Crohn’s disease 0 pancreatitis 0 acute renal failure 0 acute liver failure ??extensive burns 0 severe trauma
Peripheral venous infusion
ing of drips can be ameliorated by using topical anaesthetic cream. Additional problems with the use of peripheral cannulae include the danger of destructive extravasation injury (particularly in small infants), infection and phlebitis. The risk of phlebitis can be reduced by filtering the glucose and electrolyte mixture through a 0.22 micron pore filter to remove particulate matter; in adults, transdermal application of glyceryl trinitrate over the infusion site has also been shown to be helpful. A 0.6 mm diameter neonatal silastic central venous catheter cut short and used as a peripheral drip appears much less likely to cause phlebitis than a teflon cannula.2
Peripheral access using a standard intravenous cannula has the merit of simplicity but is difficult to maintain as the hypertonic nature of feeding solutions result in veins becoming thrombosed, so that the overall dextrose concentration should not usually exceed 12.5%. Difficulty resiting drips or the need for fluid restriction may result in a sub-optimal calorie intake. The pain and discomfort from repeated resit-
John W. L. Puntis, MRCP, Consultant Paediatrician, Department of Paediatrics and Child Health, University of Leeds, D Floor, Clarendon Wing, The General Infirmary at Leeds, Belmont Grove, Leeds LS2 9NS. Correspondence and requests for offprints to JWL. Currenr Paediatrics X3 1992 Longman
(1992) 2, 175-177
GroupUK Ltd
175
176
CURRENT
PAEDIATRICS
Central venous catheterisation
Central venous catheterisation offers convenient and reliable venous access and should be used when it is anticipated that parenteral nutrition will be required for more than a week. The central vein may be entered directly, either surgically or percutaneously, or indirectly via a peripheral vein. The use of fine (0.6 mm external diameter) silastic catheters such as the Vygon Epicutaneo-cava-catheter has found wide application in premature and older infants.3 Insertion is performed at the bedside and the technique can be learned easily by anyone used to peripheral venous cannulatiom4 ante-cubital and temporal veins are the sites of choice. Insertion complications are extremely uncommon but position of the catheter tip within the superior vena cava or upper right atrium must be confirmed radiologically as complications of malposition may occur. Care and attention should be given to taping the catheter in place making sure that it cannot be pulled out accidentally. When it is impossible to introduce a fine silastic catheter from a peripheral vein, a tunnelled, silicone rubber catheter of the type first described by Broviac should be surgically inserted under general anaesthesia. These catheters are inert, non-thrombogenic and flexible being made of silicone rubber, and have a sub-cutaneous Dacron cuff which helps to fix them in place and obliterate part of the skin tunnel; bore sizes range from OS-l.0 mm. The catheter was later modified by Hickman and colleagues, creating a larger lumen with a selection of diameters from 1.6-2.6 mm. There is now a range of polymeric silicone catheters of this type available, impregnated with barium to make them radiopaque. Insertion is usually from the internal jugular vein but other sites including the femoral vein may be used.’ The catheter tip should be in the superior vena cava or right atrium, but not close to the tricuspid valve. Skin tunnelling does not appear to reduce the risk of catheter sepsis, but helps prevent dislodgement and allows the catheter to exit at a convenient point. In a female infant this should be away from the area of future breast development; an inter-scapula exit may decrease the risk of catheter removal in the mobile and inquisitive toddler. Percutaneous placement via the subclavian vein is possible using a Seldinger technique but must be performed by an expert as serious complications such as those listed in Table 2 are more likely to occur than when a direct surgical approach is employed. Silicone rubber catheters are still those most widely
Table 2
Complications
following
insertion of central lines
used for parenteral nutrition,6 but a range of polyurethane catheters are also available and may be associated with a lower incidence of complications. Double and triple lumen catheters are not usually necessary unless there are additional intravenous therapies being given. Totally implantable venous access devices with subcutaneous reservoir (e.g. Portacath, Mediport) are commonly used in oncology patients, but there is less experience with them in parenteral nutrition. They are expensive for short term use, and in the long term, repeated needle access may lead to skin ulceration, If a catheter blockage occurs they are more difficult to flush than an external device.
Catheter complications Infection
Sepsis remains the most common and serious problem related to use of central venous catheters.7 Catheter sepsis should be suspected in a child with evidence of infection but with no obvious focus. Catheter sepsis may be associated with non-specific features such as fever, unstable blood glucose, low platelet count, vomiting or diarrhoea, but other infections such as meningitis or urinary tract must be excluded. Peripheral blood cultures are nearly always positive and coagulase negative staphylococci the most common infecting agent. If the microbiology laboratory offer quantitative techniques, blood should be taken from both the catheter and a peripheral vein at the same time. The colony count from identical volumes of blood is compared, and a lo-fold excess in the through-line culture indicates catheter infection, rather than contamination or non-catheter related bacteraemia. When a patient with a central line becomes acutely unwell with hypotension, shock or evidence of septic emboli, treatment should include antibiotics and prompt removal of the catheter. If the illness is less severe, a decision whether or not to remove the catheter must take into account how necessary it is to maintain central venous access. For example, in a preterm infant on short term parenteral feeding it may be prudent to remove the catheter at the first suspicion of sepsis, rather than await bacterial confirmation. In a child with short bowel syndrome requiring prolonged parenteral nutrition however, it is justified to make every attempt to save the catheter. Following blood cultures, parenteral feeding can be given peripherally and treatment with vancomycin and gentamicin commenced until sensitivities are known. The first dose of antibiotics is given into the central line together with 2500 units of urokinase and left there for 24 h (an antibiotic lock). Antibiotic treatment may be continued for a fortnight, given via the catheter itself during interruption of fluid administration. The catheter should be removed if, despite giving appropriate antibiotics, blood cultures remain
PARENTERAL
positive after 72 h, or there is a deterioration in clinical condition.8 Although there is some risk of re-infection, it may be possible to use the existing catheter track to insert a new central line at the time the infected one is withdrawn. This is sometimes appropriate in children in whom very long term central venous access is envisaged and there is a need to conserve suitable venous insertion sites. Factors which may contribute to a decreased risk of catheter sepsis are shown in Table 3. Catheter occlusion
Catheters sometimes block partially or completely with blood or fibrin,’ fat, mineral precipitates, or a combination of all of these. A solution of urokinase 2500 units, with 0.5 ml of 0.1 N hydrochloric acid or 0.5 ml of 70% ethanol is inserted into the line and aspirated after 1 h. An attempt should then be made to flush the line with saline. When saving the catheter is paramount, it may be justified to clear the blockage using a guide wire. Sometimes catheters block close to the hub (or metal cylinder in the Vygon catheter) and replacing the hub may salvage the line. Broken or tethered catheters
Leaks from the proximal catheter are dealt with by removing the damaged segment and using a repair kit supplied by the catheter manufacturer. In the case of a neonatal 0.6 mm catheter a new hub can be attached by feeding a 25 gauge Butterfly needle into the line. Rarely, a complete fracture of the catheter occurs during insertion or removal, or when the line is in use. If the distal portion of the catheter is lost, a chest X-ray should be taken. Radio-opaque skin markers applied before X-ray help to localise accurately the retained segment prior to exploration under general anaesthesia. Alternatively, invite a paediatric cardiologist to attempt transluminal retrieval of the fragment using a myocardial biopsy catheter (loop snare or helical basket). Tethering of very fine percutaneous neonatal catheters has been reported in association with catheter sepsis. Gentle, sustained traction on the catheter maintained by stretching and taping the proximal Table 3
Factors which may reduce the risk of catheter sepsis
scrupulous aseptic technique dedicating line solely for parenteral nutrition mmlmum number of hne connectlons cleaning hub with isopropyl alcohol
NUTRITION:
PRACTICAL CONSIDERATIONS
I77
end to a splint for up to 36 h can result in the catheter pulling free without breakage.
Infusion pumps A volumetric pump should be used in conjunction with parenteral nutrition fluids for children.” These pumps are calibrated in ml/h and most use a peristaltic pumping mechanism which enables a fairly standard (but dedicated) administration set to be accomodated. Accuracy of delivery is usually well within f 5% if flow rates are above 5 ml/h. Below this flow rate (e.g. neonatal lipid infusions) syringe pumps should be used unless a specifically designed neonatal volumetric pump is available which will accurately deliver rates as low as 1 ml/h. Most volumetric pumps have features which include rate control, the facility to select volume to be infused and a display of volume infused. Pumping pressure maintains the set rate in spite of variable resistance. Protection against air embolism and comprehensive alarm systems are usually provided. Some pumps measure the pressure in the administration line independently of the pumping and drive mechanisms allowing the manufacturer and, with some pumps, the user to choose the level of the occlusion alarm pressure setting. In the case of neonatal infusions through a peripheral drip the alarm pressure can be set very low to give early warning of impending trouble.
References 1. Goutail-Flaud MF, Sfez M, Berg A, Laguenie G, Couturier C, Barbotin-Larrieu F, Saint-Maurice C. Central venous catheter-related complications in newborns and infants: a 587-case survey. J Ped Surg 1991; 26: 645-650. 2. Madan M, Alexander DJ, McMahom MJ. Influence of catheter type on occurrence of thrombophlebitis during peripheral intravenous nutrition. Lancet 1992; 339: 101-103. 3. Puntis JWL. Percutaneous insertion of central venous feeding catheters - the first choice in paediatric parenteral nutrition. Intensive Therapy and Clinical Monitoring 1987; 8: 7-10. 4. Puntis JWL. Percutaneous insertion of central venous feeding catheters. Arch Dis Child 1986; 61: 1138-I 140. 5. Jewett TC. Techniques with catheters and complications of total parenteral nutrition. In: Lebenthal E, ed. Total parenteral nutrition. New York; Raven Press, 1986; 185-206. 6. Editorial. Central venous access in children. Lancet 1991; 338: 1301-1302. 7. Decker DM. Central venous catheter infections. Pediat Clin North Am 1988; 35: 579-612. 8. Flynn PM, Shenep JL, Stokes DC, Barrett FF. In situ management of confirmed central venous catheter-related bacteraemia. Pediatr Infect Dis J 1987; 6: 729-734. 9. Winthrop AL, Wesson DE. Urokinase in the treatment of occluded central venous catheters in children. J Pediat Surg 1984; 19: 536-538. IO. Auty B. Choice of instrumentation for controlled IV infusion. Intensive Therapy and Clinical Monitoring 1989; 10: 117-122.
Nutrition
(
Parenteral nutrition: practical considerations
J. W. L. Puntis Introduction
Table 1
Providing an effective parenteral nutrition support service requires knowledge of how to deal with a number of practical problems. This article briefly reviews some of those most commonly encountered. Prevention of sepsis is an important issue for any unit using central venous lines whilst management of this complication may vary according to the patient’s dependence upon central venous access. Serious mechanical catheter related complications are not uncommon’ and occlusion or fracture may be a potential disaster in patients receiving long term intravenous nutrition, when the catheter is literally a life-line. The risk of many types of complication becomes less with an experienced multi-disciplinary team approach to nutritional support. Indications for parenteral nutrition are shown in Table 1.
Indications for parenteral nutrition
Neonates (a) Absolute
(b)
1 indications
Relative indications
Older infants and children (a) Intestinal failure
(b)
Venous access Once a decision to initiate parenteral feeding has been reached, venous access must be established.
(c)
Exclusion of luminal nutrients Organ failure
(d)
Hyper-catabolism
?? intestinal failure (short
gut, functional immaturity, pseudoobstruction) 0 necrotising enterocolitis ?? hyaline membrane disease ??promotion of growth in preterm infants ?? possible prevention of necrotising enterocolitis ??short gut ??protracted diarrhoea ??chronic intestinal
pseudo-obstruction 0 post-operative abdominal or cardio-thoracic surgery ??radiation/cytotoxic therapy ?? Crohn’s disease 0 pancreatitis 0 acute renal failure 0 acute liver failure ??extensive burns 0 severe trauma
Peripheral venous infusion
ing of drips can be ameliorated by using topical anaesthetic cream. Additional problems with the use of peripheral cannulae include the danger of destructive extravasation injury (particularly in small infants), infection and phlebitis. The risk of phlebitis can be reduced by filtering the glucose and electrolyte mixture through a 0.22 micron pore filter to remove particulate matter; in adults, transdermal application of glyceryl trinitrate over the infusion site has also been shown to be helpful. A 0.6 mm diameter neonatal silastic central venous catheter cut short and used as a peripheral drip appears much less likely to cause phlebitis than a teflon cannula.2
Peripheral access using a standard intravenous cannula has the merit of simplicity but is difficult to maintain as the hypertonic nature of feeding solutions result in veins becoming thrombosed, so that the overall dextrose concentration should not usually exceed 12.5%. Difficulty resiting drips or the need for fluid restriction may result in a sub-optimal calorie intake. The pain and discomfort from repeated resit-
John W. L. Puntis, MRCP, Consultant Paediatrician, Department of Paediatrics and Child Health, University of Leeds, D Floor, Clarendon Wing, The General Infirmary at Leeds, Belmont Grove, Leeds LS2 9NS. Correspondence and requests for offprints to JWL. Currenr Paediatrics X3 1992 Longman
(1992) 2, 175-177
GroupUK Ltd
175
176
CURRENT
PAEDIATRICS
Central venous catheterisation
Central venous catheterisation offers convenient and reliable venous access and should be used when it is anticipated that parenteral nutrition will be required for more than a week. The central vein may be entered directly, either surgically or percutaneously, or indirectly via a peripheral vein. The use of fine (0.6 mm external diameter) silastic catheters such as the Vygon Epicutaneo-cava-catheter has found wide application in premature and older infants.3 Insertion is performed at the bedside and the technique can be learned easily by anyone used to peripheral venous cannulatiom4 ante-cubital and temporal veins are the sites of choice. Insertion complications are extremely uncommon but position of the catheter tip within the superior vena cava or upper right atrium must be confirmed radiologically as complications of malposition may occur. Care and attention should be given to taping the catheter in place making sure that it cannot be pulled out accidentally. When it is impossible to introduce a fine silastic catheter from a peripheral vein, a tunnelled, silicone rubber catheter of the type first described by Broviac should be surgically inserted under general anaesthesia. These catheters are inert, non-thrombogenic and flexible being made of silicone rubber, and have a sub-cutaneous Dacron cuff which helps to fix them in place and obliterate part of the skin tunnel; bore sizes range from OS-l.0 mm. The catheter was later modified by Hickman and colleagues, creating a larger lumen with a selection of diameters from 1.6-2.6 mm. There is now a range of polymeric silicone catheters of this type available, impregnated with barium to make them radiopaque. Insertion is usually from the internal jugular vein but other sites including the femoral vein may be used.’ The catheter tip should be in the superior vena cava or right atrium, but not close to the tricuspid valve. Skin tunnelling does not appear to reduce the risk of catheter sepsis, but helps prevent dislodgement and allows the catheter to exit at a convenient point. In a female infant this should be away from the area of future breast development; an inter-scapula exit may decrease the risk of catheter removal in the mobile and inquisitive toddler. Percutaneous placement via the subclavian vein is possible using a Seldinger technique but must be performed by an expert as serious complications such as those listed in Table 2 are more likely to occur than when a direct surgical approach is employed. Silicone rubber catheters are still those most widely
Table 2
Complications
following
insertion of central lines
used for parenteral nutrition,6 but a range of polyurethane catheters are also available and may be associated with a lower incidence of complications. Double and triple lumen catheters are not usually necessary unless there are additional intravenous therapies being given. Totally implantable venous access devices with subcutaneous reservoir (e.g. Portacath, Mediport) are commonly used in oncology patients, but there is less experience with them in parenteral nutrition. They are expensive for short term use, and in the long term, repeated needle access may lead to skin ulceration, If a catheter blockage occurs they are more difficult to flush than an external device.
Catheter complications Infection
Sepsis remains the most common and serious problem related to use of central venous catheters.7 Catheter sepsis should be suspected in a child with evidence of infection but with no obvious focus. Catheter sepsis may be associated with non-specific features such as fever, unstable blood glucose, low platelet count, vomiting or diarrhoea, but other infections such as meningitis or urinary tract must be excluded. Peripheral blood cultures are nearly always positive and coagulase negative staphylococci the most common infecting agent. If the microbiology laboratory offer quantitative techniques, blood should be taken from both the catheter and a peripheral vein at the same time. The colony count from identical volumes of blood is compared, and a lo-fold excess in the through-line culture indicates catheter infection, rather than contamination or non-catheter related bacteraemia. When a patient with a central line becomes acutely unwell with hypotension, shock or evidence of septic emboli, treatment should include antibiotics and prompt removal of the catheter. If the illness is less severe, a decision whether or not to remove the catheter must take into account how necessary it is to maintain central venous access. For example, in a preterm infant on short term parenteral feeding it may be prudent to remove the catheter at the first suspicion of sepsis, rather than await bacterial confirmation. In a child with short bowel syndrome requiring prolonged parenteral nutrition however, it is justified to make every attempt to save the catheter. Following blood cultures, parenteral feeding can be given peripherally and treatment with vancomycin and gentamicin commenced until sensitivities are known. The first dose of antibiotics is given into the central line together with 2500 units of urokinase and left there for 24 h (an antibiotic lock). Antibiotic treatment may be continued for a fortnight, given via the catheter itself during interruption of fluid administration. The catheter should be removed if, despite giving appropriate antibiotics, blood cultures remain
PARENTERAL
positive after 72 h, or there is a deterioration in clinical condition.8 Although there is some risk of re-infection, it may be possible to use the existing catheter track to insert a new central line at the time the infected one is withdrawn. This is sometimes appropriate in children in whom very long term central venous access is envisaged and there is a need to conserve suitable venous insertion sites. Factors which may contribute to a decreased risk of catheter sepsis are shown in Table 3. Catheter occlusion
Catheters sometimes block partially or completely with blood or fibrin,’ fat, mineral precipitates, or a combination of all of these. A solution of urokinase 2500 units, with 0.5 ml of 0.1 N hydrochloric acid or 0.5 ml of 70% ethanol is inserted into the line and aspirated after 1 h. An attempt should then be made to flush the line with saline. When saving the catheter is paramount, it may be justified to clear the blockage using a guide wire. Sometimes catheters block close to the hub (or metal cylinder in the Vygon catheter) and replacing the hub may salvage the line. Broken or tethered catheters
Leaks from the proximal catheter are dealt with by removing the damaged segment and using a repair kit supplied by the catheter manufacturer. In the case of a neonatal 0.6 mm catheter a new hub can be attached by feeding a 25 gauge Butterfly needle into the line. Rarely, a complete fracture of the catheter occurs during insertion or removal, or when the line is in use. If the distal portion of the catheter is lost, a chest X-ray should be taken. Radio-opaque skin markers applied before X-ray help to localise accurately the retained segment prior to exploration under general anaesthesia. Alternatively, invite a paediatric cardiologist to attempt transluminal retrieval of the fragment using a myocardial biopsy catheter (loop snare or helical basket). Tethering of very fine percutaneous neonatal catheters has been reported in association with catheter sepsis. Gentle, sustained traction on the catheter maintained by stretching and taping the proximal Table 3
Factors which may reduce the risk of catheter sepsis
scrupulous aseptic technique dedicating line solely for parenteral nutrition mmlmum number of hne connectlons cleaning hub with isopropyl alcohol
NUTRITION:
PRACTICAL CONSIDERATIONS
I77
end to a splint for up to 36 h can result in the catheter pulling free without breakage.
Infusion pumps A volumetric pump should be used in conjunction with parenteral nutrition fluids for children.” These pumps are calibrated in ml/h and most use a peristaltic pumping mechanism which enables a fairly standard (but dedicated) administration set to be accomodated. Accuracy of delivery is usually well within f 5% if flow rates are above 5 ml/h. Below this flow rate (e.g. neonatal lipid infusions) syringe pumps should be used unless a specifically designed neonatal volumetric pump is available which will accurately deliver rates as low as 1 ml/h. Most volumetric pumps have features which include rate control, the facility to select volume to be infused and a display of volume infused. Pumping pressure maintains the set rate in spite of variable resistance. Protection against air embolism and comprehensive alarm systems are usually provided. Some pumps measure the pressure in the administration line independently of the pumping and drive mechanisms allowing the manufacturer and, with some pumps, the user to choose the level of the occlusion alarm pressure setting. In the case of neonatal infusions through a peripheral drip the alarm pressure can be set very low to give early warning of impending trouble.
References 1. Goutail-Flaud MF, Sfez M, Berg A, Laguenie G, Couturier C, Barbotin-Larrieu F, Saint-Maurice C. Central venous catheter-related complications in newborns and infants: a 587-case survey. J Ped Surg 1991; 26: 645-650. 2. Madan M, Alexander DJ, McMahom MJ. Influence of catheter type on occurrence of thrombophlebitis during peripheral intravenous nutrition. Lancet 1992; 339: 101-103. 3. Puntis JWL. Percutaneous insertion of central venous feeding catheters - the first choice in paediatric parenteral nutrition. Intensive Therapy and Clinical Monitoring 1987; 8: 7-10. 4. Puntis JWL. Percutaneous insertion of central venous feeding catheters. Arch Dis Child 1986; 61: 1138-I 140. 5. Jewett TC. Techniques with catheters and complications of total parenteral nutrition. In: Lebenthal E, ed. Total parenteral nutrition. New York; Raven Press, 1986; 185-206. 6. Editorial. Central venous access in children. Lancet 1991; 338: 1301-1302. 7. Decker DM. Central venous catheter infections. Pediat Clin North Am 1988; 35: 579-612. 8. Flynn PM, Shenep JL, Stokes DC, Barrett FF. In situ management of confirmed central venous catheter-related bacteraemia. Pediatr Infect Dis J 1987; 6: 729-734. 9. Winthrop AL, Wesson DE. Urokinase in the treatment of occluded central venous catheters in children. J Pediat Surg 1984; 19: 536-538. IO. Auty B. Choice of instrumentation for controlled IV infusion. Intensive Therapy and Clinical Monitoring 1989; 10: 117-122.