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Gastroschisis is a congenital defect of the anterior abdominal wall located to the right of the umbilicus leading to evisceration of the small and large intestines and in some cases other organs.(1) The condition is diagnosed during pregnancy and thus facilitates planning for the requisite surgery and counselling for parents. The prognosis for most infants affected by gastroschisis is quite good and in 90% of cases they make a full recovery with few long term problems.(2)
Figure 1 Gastroschisis defect.(3)
The prevalence rates for gastroschisis vary across regions within the UK from a high of 6.2 per 10,000 births in Wales to a low of 1.6 per 10,000 births in North West Thames. The figure for the Glasgow area is 4.9 per 10,000 births. These figures may differ as a result of the manner in which the data is collected. In Glasgow for instance all data is included, including those cases which led to induced abortions following prenatal diagnosis. This may help to explain the apparent South to North increase in prevalence rates.(4) The average figure has increased significantly over the last ten years from 2.5 to 4.4 per 10,000 births.(5)
Understanding the pathogenesis of gastroschisis requires a tacit understanding of the normal development of the embryo following conception through to the final stages of gestation leading to birth. At between 3 to 4 weeks of development the gut and the yolk sac become distinct from one another. Following further development at week 6, the midgut elongates a rate which is in excess of that of the embryonic body which leads to the formation of an umbilical hernia. Following on from this at the 10th week of development the herniation is closed after retreat of the midgut to rejoin the embryonic abdominal cavity. It is the failure of this normal physiological development role that is central to gastroschisis, though why it fails to happen is not clear.(6)
The sporadic occurrence of gastroschisis as an isolated defect suggests that it most likely has multifaceted aetiology. However the occurrence in twins and familial clusters suggest some hereditary involvement and there have been other case reports of possible genetic aetiology in the incidence of the condition.(7, 8) As discussed earlier the increasing prevalence of gastroschisis in births across wide geographical areas and amongst different population sub-types suggest an environmental role in defect occurrence possibly through exposure to teratogens. Medication which acts on the vasculature has been implicated including some herbal and over the counter medications such as pseudoephedrine, paracetamol and aspirin amongst others.(9, 10) Some reports have suggested a link with maternal smoking and gastroschisis with an increase in prevalence reported as well as poorer outcomes for those mothers who smoked.(11) Drinking alcohol, smoking and taking ibuprofen were also implicated in a moderate increase in the likelihood of gastroschisis in another study.(12)
Treatment of Gastroschisis
The management of gastroschisis falls into a number of categories mainly based on the stages of treatment and includes (although is not limited to); pre-surgical management, surgical management/techniques, parenteral nutrition and pain and infection control.(3)
1. Pre-surgical management
Assuming detection at the 20 week scan, management of both the mother and foetus begins almost immediately and will usually begin with a decision on the plan for the mode of delivery. Whilst intuitively one might suspect that an elective Caesarean section is the preferred option for delivery to remove the possibility of trauma to the exposed organs, the clinical data does not suggest a significant difference exists with vaginal delivery.(13)
There are a significant number of considerations that must be made in the management of a newborn with gastroschisis. These include amongst others thermoregulation, fluid volume status, gastric distention and intestinal compromise, infection control, respiratory status, and preparation for surgery. Investigation to determine the existence of other anomalies should also be carried out as some patients with gastroschisis may also have other anomalies although their occurrence is less than with other abdominal wall defects such as omphalocele.(14)
The outcome for the infant is best when these considerations have been stabilised before surgery takes place. Following delivery a "bowel bag" is used to protect the infant's trunk and lower extremities and the infant is placed in a warmer to maintain body temperature. The use of a bowel bag also facilitates the reduction in heat loss through the large area of exposed tissues and also provides some protection against infection. The pooling of fluid lost through the exposed tissue also allows for more accurate calculation of the total volume of lost fluid. The loss of large volumes of fluid may mean that the infant displays symptoms of shock and management with isotonic solutions may be required. Once normalisation of urine output occurs or the acid/base balance equilibrates fluid resuscitation may be ceased. The increase loss of fluid volumes through the exposed tissue will mean that the maintenance volumes of fluid required for an infant with gastroschisis will be 2 or 3 times that required for a normal infant. Therefore it is important to monitor the infant's glucose load; multiple infusions with dextrose solutions can lead to hyperglycaemia.(3)
In order to prevent gastric distension it is also important to ensure that a naso/orogastric tube is in place. The stomach and the bowel should be kept decompressed this is achieved by intermittently placing the tube under suction. Oxygenation of the bowel is maintained since this prevents a total or indeed partial blocking of blood flow. To neglect this requirement may lead to an increased risk of necrosis of the bowel. The risk of emesis and consequently aspiration is also decreased by decompression.(15) Positioning of the infant is also important and can help to reduce the risk of bowel compromise. Therefore as a means of increase venous blood return from the gut, infants should be placed on their side (right) in a lateral decubitus position.
One of the final and perhaps most important considerations needed before surgery is prophylactic antibiotic therapy. Due to the nature of the condition and the fact of surgery by itself infants are broad spectrum antibiotics are administered to reduce the possible risk of infection from the exposed bowel. Typically biochemical and haematological tests are also carried out before surgery.
2. Surgical management/techniques
Some controversy surrounds the different approaches to surgical treatment of gastroschisis.
The approach which is most preferred is to carry out a primary closure of the defect however this may not always be an option and in these cases a staged closure using a Silo may be employed. The size of the gastroschisis will usually determine the approach with small and medium sized gastroschisis permitting a primary closure in most cases while a larger gastroschisis will necessitate a staged closure, usually over 7-10 days. This procedure involves tucking the exposed bowel into a silastic sheet or silo which is affixed perpendicular to the torso. Periodically the silo is shortened to force the bowel back into the abdominal cavity. Once the entire bowel has been returned to the abdominal cavity the infant's abdomen is then surgically closed Figure 2.(15)
3. Parenteral nutrition, pain control and infection control
These three concerns play a dominant role in the function of the clinical pharmacist. Infection is a primary concern for infants with gastroschisis. Obviously, the breech in the skin which normally functions as a barrier to infection causes an increase risk to infants with gastroschisis. Those patients who undergo a stage repair may spend a number of days with this continuing risk.
Research has shown that sepsis is the primary cause of mortality in patients with gastroschisis although delay in the closure of the abdominal wall defect showed no significant affect on outcome.(16) There are also other factors which need to be considered in terms of the increased risk for gastroschisis patients. These include the prolonged need and use of a central venous line, long-standing need for TPN and the general immaturity of the patient's immune system.
Following surgical treatment the continuation of the use of broad spectrum antibiotics for a period of 3-7 days is advised. All health care staff are encouraged to be vigilant for any physical signs of infection peripheral to the wound site.
Following initial stabilisation the primary objective is to give sufficient nutrition to the infant and to manage any analgesic requirements. Since intestinal dysmotility caused by exposure of the intestine to inuterine amniotic fluid is a factor for all patients total parenteral nutrition (TPN) is required. Due to the fact that TPN will be needed for a number of weeks it usually requires a central line to be administered and is normally started 24 -48 hours post operatively. The TPN requirements post operatively are as a minimum 90 to 100kCal/kg/day, 3-4 g/kg/day of intravenous lipids and dextrose (this is needed to maintain euglycaemia) and 3g/kg/day of protein. However, due to the surgical stress additional protein in the TPN may be needed. Enteral feeds should be commenced as soon as possible following the return of gut motility since there is a positive correlation between time of introduction of enteral feeds and hospital discharge. A number of different feed types have been indicated including expressed human milk, pre-term formula and elemental formula as they are easily digested. Usually at the initiation of feeds the volumes are low around 10-20 ml/kg/day. The control of pain is of crucial importance in dealing with infants with gastroschisis and they should be assessed for pain. The assessment should be carried out following established and validated pain assessment tool and guidelines for pain management should be adhered to in terms of the administration of analgesia.
Treatment of Baby L
Early onset sepsis (EOS) is an infection in infants usually caused by vertical transmission before or during labour from the maternal genital tract(17) The infection is most often caused by group B streptococcus which commonly colonise pregnant mothers although other gram negative bacteria can also be involved including Escherichia coli. Those mothers that experience a long duration of membrane rupture or have other risk factors can be at a particularly high risk of transmitting the bacteria to their infants.
Treatment initially usually includes a narrow spectrum antibiotic active against gram negative bacteria such as Gentamicin as well as benzylpenicillin.(18) In this case Baby L was treated with Benzylpenicillin 66mg twice daily which is consistent with the dose recommendation in the BNFc of 25mg/kg every 12 hours.(19) Baby L was also treated with Gentamicin 13mg daily initially. Similarly, this is in agreement with the dose in the BNFc which is 4-5mg/kg every 24hours.(20) This procedure is also in agreement with the local NHS guideline.(21) The monitoring of serum Gentamicin concentrations and renal function was carried out according to the Greater Glasgow & Clyde Neonatal IV Drug Monograph.(22)
Following treatment for EOS Baby L's CRP level began to increase on day 4. This may have been indicative of late onset sepsis (LOS). Although no positive culture test had been carried out the fluctuation in the CRP was sufficient to warrant treatment for possible LOS.
LOS can be caused by gram positive and gram negative bacteria as well as by fungal infection.(23) Consequently, treatment will usually consist of antibiotics to tackle the gram positive and gram negative bacteria as well as an antifungal. In this case Baby L was treated initially with Vancomycin 26mg every 12 hours. According to the Vancomycin Dosing and Monitoring guideline the initial dose should be 10mg/kg 12 hourly when the Serum creatinine concentration is 65-100.1 Î¼mol/L. Since Baby L's serum creatinine concentration was 69 Î¼mol/L the dose of 26mg initially was suitable.(24) Baby L was also given Fluconazole 31mg every 72 hours to combat any possible fungal infection. This dose is in agreement with that which is recommended in the children's BNF of 6-12mg/kg every 72 hours.(25) Baby L was also given metronidazole 20 mg twice daily as prophylaxis before the final closure operation.
There has been some acknowledgement recently that neonates can indeed feel pain and gastroschisis specifically has been identified as a condition that can cause it.(26) The management of Baby L's pain was achieved using morphine. Post-operative analgesia is often achieved using fentanyl or morphine infusions.(27) The dose of Morphine used was changed over the course of her stay but began with an infusion of 10Î¼g/kg/hour. The recommended dose in the BNF for children is 5-40 Î¼g/kg/hour for an intravenous infusion of morphine.(28)
The nutritional needs of Baby L were monitored on a continual basis. She was initially started on a "neonatal standard bag" containing; Protein 6.25g, Glucose 30g, Sodium 6mmol, Potassium 3mmol, Phosphate 3mmol, Calcium 3mmol, Magnesium 0.41mmol and Chloride 3mmol at a flow rate of 90ml/kg/day. This was in agreement with the guidelines as laid out in the Parenteral Nutrition Guidelines.(29) Following monitoring of her biochemical data the flow rate of her TPN was increased as required. Her parenteral lipids were started on day 2 at a rate of 0.7g/kg and increased to over the following few days. As outlined earlier the addition of enteral feeds as soon as possible helps to increase the prognosis for patients. Therefore on day 14 she was given previously expressed breast milk (PEBM) 1ml/hour. It should also be noted that as her TPN requirements changed based on the biochemical data her TPN bag was switched from a standard bag to a Non-standard bag to ensure she received the nutrients she required. This is also in agreement with the clinical guidelines.