Author Sathyaseelan Subramaniam, MD, FAAP Chief Fellow in Pediatric Emergency Medicine, Kings County Hospital, State University of New York Downstate Medical Center Sathyaseelan Subramaniam, MD, FAAP is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Pediatrics, American Institute of Ultrasound in Medicine Disclosure: Nothing to disclose. Coauthor(s) Jennifer H Chao, MD, FAAP Clinical Associate Professor of Pediatric Emergency Medicine, State University of New York Downstate College of Medicine; Attending Physician, Pediatric Emergency Department, Kings County Hospital and University Hospital Brooklyn Jennifer H Chao, MD, FAAP is a member of the following medical societies: American Academy of Pediatrics, American College of Emergency Physicians Disclosure: Nothing to disclose. Richard H Sinert, DO Professor of Emergency Medicine, Clinical Assistant Professor of Medicine, Research Director, State University of New York College of Medicine; Consulting Staff, Vice-Chair in Charge of Research, Department of Emergency Medicine, Kings County Hospital Center Richard H Sinert, DO is a member of the following medical societies: American College of Physicians, Society for Academic Emergency Medicine Disclosure: Nothing to disclose. Specialty Editor Board Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference Disclosure: Nothing to disclose. Grace M Young, MD Associate Professor, Department of Pediatrics, University of Maryland Medical Center Grace M Young, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Emergency Physicians Disclosure: Nothing to disclose. Chief Editor Kirsten A Bechtel, MD Associate Professor of Pediatrics, Section of Pediatric Emergency Medicine, Yale University School of Medicine; Co-Director, Injury Free Coalition for Kids, Yale-New Haven Children's Hospital Kirsten A Bechtel, MD is a member of the following medical societies: American Academy of Pediatrics Disclosure: Nothing to disclose. Additional Contributors Garry Wilkes, MBBS, FACEM Associate Director, Emergency Medicine, Goulburn Valley Health, Victoria, Australia; Clinical Associate Professor, University of Western Australia; Adjunct Associate Professor, Edith Cowan University, Western Australia Disclosure: Nothing to disclose. Jagvir Singh, MD Director, Division of Pediatric Emergency Medicine, Lutheran General Hospital of Park Ridge Jagvir Singh, MD is a member of the following medical societies: American Academy of Pediatrics Disclosure: Nothing to disclose. Acknowledgements Dara A Kass, MD Clinical Assistant Instructor, Department of Emergency Medicine, State University of New York Downstate Medical Center, Kings County Hospital Dara A Kass, MD is a member of the following medical societies: American College of Emergency Physicians, Emergency Medicine Residents Association, and Society for Academic Emergency Medicine Disclosure: Nothing to disclose.
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Key points
Pyloric stenosis is the result of hypertrophy of the smooth muscle of the pylorus, which forms the gastric outlet. Its aetiology is uncertain, although a number of environmental and hereditary contributory factors have been identified. The reported incidence varies between 0.9 and 5.1 per 1000 live births.1 In England and Wales it is 1.5 per 1000 live births and has remained static in recent years.2 The risk of the disease is four to five times higher in boys than girls.3 There is a decline in risk with increasing birth order with an odds ratio of 1.9 for first-born children.3 The genetic element is evidenced with higher rates of concordance in monozygotic than dizygotic twins and a number of susceptibility loci have been identified. Babies with infantile hypertrophic pyloric stenosis present most commonly in the 2nd and 3rd months of life.2 However, a recent review of surgical outcomes for 9686 infants who underwent pyloromyotomy in England over a 10-year period, found that 30% of patients were aged 7–28 days at the time of surgery.2 The classic presentation is projectile vomiting of non-bilious stomach contents, loss of weight or failure to gain weight (crossing centiles on the growth chart), and dehydration. Abdominal examination may reveal a palpable ‘olive’; however, modern developments mean that the majority of patients are being diagnosed earlier with ultrasound and this physical finding is becoming less common. Vomiting is the principal symptom of pyloric stenosis, classically described as being projectile in nature. The vomitus in pyloric stenosis consists of gastric secretions. These secretions are high in hydrogen and chloride ions with some sodium and potassium, all of which are lost along with water. The electrolyte losses result in a hypokalaemic, hypochloraemic metabolic alkalosis. The water loss causes dehydration and a reduction in plasma volume; this results in the secretion of aldosterone. Aldosterone causes sodium and water retention by the kidneys in an attempt to restore blood volume. It has effects on the Na+/K+ exchange mechanism causing further potassium loss in the urine, in addition to that lost in gastric secretions, worsening the hypokalaemia. Initially, bicarbonate is excreted in the urine to compensate for the alkalosis caused by hydrogen ion loss from the stomach; this produces alkaline urine. Eventually maintenance of plasma volume becomes the priority and the kidneys excrete hydrogen ions in exchange for sodium and water, resulting in the paradoxical production of acidic urine despite the metabolic alkalosis. Medullary chemoreceptors in the brain stem respond to changes in the hydrogen ion (H+) concentration in the cerebrospinal fluid (CSF), with an increase in the H+ ion concentration stimulating ventilation. An increase in the arterial partial pressure of carbon dioxide results in an increased CSF H+ concentration as the carbon dioxide readily penetrates the CSF where it is promptly hydrated to form carbonic acid. Conversely, metabolic alkalosis can cause respiratory depression and apnoea. This will be aggravated by the CNS depressant effect of general anaesthesia. Preterm infants of <60 weeks postmenstrual age are known to be at risk of postoperative apnoea. This complication has also been reported in term infants after pyloromyotomy.4 Therefore, to minimise the risk of postoperative apnoea, the alkalosis must be corrected before surgery. Furthermore, equilibration of CSF pH with plasma pH takes several hours.1 It is possible that plasma pH may have returned to normal whilst the CSF pH remains increased, thereby exerting a respiratory depressant effect; hence all infants should be monitored for apnoea after pyloromyotomy. The degree of dehydration must be calculated and corrected slowly unless there is cardiovascular instability with hypovolaemic shock; in this case the child should receive an initial bolus of isotonic crystalloid 20 ml kg−1 followed by frequent reassessment and further fluid resuscitation if required. The patient is kept nil by mouth and maintenance fluid in the form of 0.45% saline with glucose 5% and 10 mmol potassium chloride per 500 ml bag is given at a rate of 150 ml kg−1 day−1; this will correct the deficiencies in sodium, potassium, and chloride.5 Once the alkalosis has been corrected, the fluid input is reduced to 100 ml kg−1 day−1. Biochemical findings once the alkalosis has been corrected should be within the following range: pH 7.3–7.45; Cl– 95–112 mmol litre−1; base excess –4 to 2.5 mmol litre−1; K+ 3.5–5.5 mmol litre−1. Pyloric stenosis is a medical, not a surgical, emergency. Patients can safely wait for surgery while they are rehydrated and their electrolyte abnormalities and alkalosis are corrected. Ramstedt described a surgical approach to the management of pyloric stenosis in 1912. This involved a horizontal incision through the abdominal wall in the right upper quadrant, and a longitudinal incision through the muscle of the pylorus, through to, but not perforating, the mucosa. Surgical advances have altered the skin incision for better cosmetic appearance. A curved circum-umbilical skin incision is now commonplace. However, the incision of the pylorus remains much the same. A laparoscopic approach was described by Alain and colleagues in 1991.6 In England, 23.7% of pyloromyotomies were performed laparoscopically in 2011.2 In the USA, the proportion of pyloromyotomies performed laparoscopically in 2015 was 65.5%.7 A review of 9686 infants who underwent pyloromyotomy in England between 2002 and 2011 found that laparoscopic pyloromyotomy may be associated with an increased risk of inadequate myotomy requiring reoperation (odds ratio 2.28; 95% confidence interval 1.14–4.57).2 However, a review of 4847 infants who underwent pyloromyotomy in the USA between 2013 and 2015 found no difference between open and laparoscopic pyloromyotomy re-operation rates.7 The English report found no difference between laparoscopic and open pyloromyotomy in postoperative length of stay, whilst the US report described a reduced length of stay after laparoscopic pyloromyotomy (1.5 days vs 1.9 days).2, 7 Laparoscopic pyloromyotomy may be associated with less postoperative pain and a slightly shorter time to full feeds.1, 8 The duration of surgery and anaesthesia is similar for laparoscopic and open pyloromyotomy.7 The gastric outlet obstruction associated with pyloric stenosis prevents stomach emptying and poses a risk of pulmonary aspiration of gastric secretions under general anaesthesia. The stomach may contain significant volumes of acidic gastric secretions; these need to be removed before induction of anaesthesia and consequent suppression of the protective airway reflexes. Previously, nasogastric (NG) tubes were inserted routinely as part of the medical management some time before arrival in the operating room. It has been proposed that constant drainage of gastric secretions worsens the electrolyte imbalance and, in the absence of milk feeds, is unnecessary in the preoperative period.9 Consequently, depending on institutional practice, a patient may arrive in the operating room without an NG tube; these patients still require insertion of a NG or orogastric tube to empty the stomach before induction of anaesthesia. In a small prospective randomised trial of the effects of preoperative NG tubes on emesis rates, patients were randomised to receive a gastric tube at diagnosis or only immediately before anaesthesia.10 None of the 25 patients who had an NG tube inserted early vomited on induction. Two of the 25 patients in whom an NG tube was inserted in theatre, vomited on induction of anaesthesia, risking aspiration of acidic stomach contents. For those patients who arrive in theatre with an NG tube in place, maintain an index of suspicion that the NG tube may be blocked or malpositioned. Check the depth of insertion: it should be >20 cm. Check the fluid balance chart: a fluid balance chart documenting regular aspirates suggests a well-placed NG tube. If suctioning the NG tube yields absolutely no gastric fluid, consider that it may be blocked. Insufflate a small amount of air to exclude a blocked NG tube. If in doubt, remove the NG tube and replace it with a 14 French orogastric tube. Emptying the stomach may be performed by rotating the infant from the supine, to left lateral decubitus, to prone, to right lateral decubitus—aspirating the NG tube in each position. Ultrasound assessment of gastric contents has been studied in infants with pyloric stenosis demonstrating that a qualitative assessment of stomach contents can be made quickly and easily before induction of anaesthesia (Table 1; Fig. 1).11 This non-invasive bedside test may be a way of confirming an empty stomach. Gastric ultrasound before induction of anaesthesia for pyloromyotomy
To reduce the risk of pulmonary aspiration of gastric contents, smooth induction of anaesthesia, avoidance of hypoxaemia, and airway instrumentation with complete neuromuscular block are paramount.12 The risk of vomiting or regurgitation is highest during laryngoscopy when airway stimulation is at its greatest.12 Ensure an adequate depth of anaesthesia and complete neuromuscular block before laryngoscopy to prevent the patient coughing and gagging. Classic rapid-sequence induction and intubation, as performed in adult patients, with pre-oxygenation, cricoid pressure and no bag-mask ventilation, should not be applied without modification when anaesthetising neonates and infants.12 The infant airway is compressible and easily deformed by external pressure. The application of cricoid pressure may make intubation difficult; if not impossible.13 Identification of the cricoid ring is also more difficult than in adults. Cricoid pressure is, therefore, best avoided. Functional residual capacity is reduced in infants compared with older children and adults as a result of increased chest wall elasticity and splinting of the diaphragm by their comparatively large abdomens. They also have a much greater oxygen consumption, which makes the onset of hypoxaemia much more rapid in infants than adults. This means that gentle bag-mask ventilation is required after induction of anaesthesia and before tracheal intubation to prevent hypoxaemia and bradycardia. Choice of anaesthetic induction technique remains controversial. In the authors' institution, 17 out of 25 consultant paediatric anaesthetists choose to perform an inhalation induction whilst the remaining eight choose an i.v. induction. The use of inhalation induction for pyloromyotomy has been described in a retrospective case series of 269 cases including 252 inhalation inductions.14 None of the patients in this case series suffered pulmonary aspiration of gastric contents. All but one patient had a working peripheral i.v. cannula in place before induction. The following description of the technique represents local practice in the authors' institution. Induction takes place in the operating room, after evacuation of gastric contents and gastric ultrasound examination, with active warming and standard monitoring established. The i.v. cannula is flushed with 0.9% saline to check that it is working. Sevoflurane (4–6%) in oxygen at 6 litre min−1 is administered via face-mask with a Jackson Rees T-piece Intersurgical Mapleson F infant T-piece breathing system, Intersurgical Ltd. Wokingham, Berkshire, UK. Gentle continuous positive airway pressure is applied by partially occluding the reservoir bag of the breathing system. A good face-mask seal and a patent upper airway are confirmed by movement of the reservoir bag as the infant breathes spontaneously. Attention to patient positioning, avoiding excessive neck flexion caused by the relatively large occiput, and skill in holding the face-mask, are required to avoid inadvertently occluding the airway. Once the infant has lost consciousness, atracurium 0.5 mg kg−1 is administered. As the baby becomes apnoeic, gentle bag-mask ventilation replaces spontaneous ventilation. Care is taken to avoid vigorous bag-mask ventilation and bag-mask ventilation with an occluded upper airway; both are likely to inflate the stomach and increase the risk of aspiration. Time is allowed for neuromuscular block to take effect before laryngoscopy. The onset time [injection to 95% depression of the first twitch of the train-of-four represented as the mean and standard error of the mean (sem)] of atracurium 0.5 mg kg−1 in neonates and infants is 0.9 (0.1) min.15 Laryngoscopy is performed and the infant's trachea is intubated with a size 3.0 Microcuff endotracheal tube (Halyard Health Inc. Alpharetta. Georgia. USA). I.V. induction of anaesthesia can be performed with either propofol 3 mg kg−1 or ketamine 2 mg kg−1.1 Neuromuscular block can be achieved with succinylcholine 2 mg kg−1, atracurium 0.5 mg kg−1, or rocuronium 0.3–0.7 mg kg−1. Recovery after atracurium 0.5 mg kg−1 is more rapid in neonates than infants or older children. The time from injection until the first twitch of the train-of-four has recovered to 25% of the control twitch height, represented as the mean (sem), is 28.7 (1.9) min in neonates compared with 33.7 (1.2) min in older children.15 Recovery from atracurium does not rely on hepatic microsomal enzyme systems, which are immature in neonates and infants. The mean [standard deviation (sd)] onset time of rocuronium 0.3 mg kg−1 was reported as 47 (12) s in children aged <6 months, producing 100% block in 18 out of 19 children.16 The time for recovery of the first twitch of the train-of-four to 25% of the control twitch height after rocuronium 0.3 mg kg−1 in this age group is 26.1 (sd 11.1) min, compared with 41.9 (3.2) min in infants aged 2–11 months who received rocuronium 0.6 mg kg−1.16, 17 The effect of rocuronium is prolonged in neonates compared with other age groups.1 Historically, awake intubation was a popular airway management strategy for infants undergoing pyloromyotomy. The perceived advantage was the preservation of protective airway reflexes and avoidance of hypoxaemia after induction of anaesthesia. In 1998, Cook-Sather and colleagues18 showed that the successful first attempt intubation rate is greater, and time to intubation shorter, in patients receiving general anaesthesia and a neuromuscular blocking agent than patients having awake intubation, with no difference in complication rates. Awake intubation is no longer recommended. The use of a Microcuff tracheal tube may be advantageous. They are currently available for children weighing >3 kg and reduce the time to isolation of the lower respiratory tract by reducing the need for tracheal tube changes to establish the best fit. Anaesthesia is maintained with sevoflurane or desflurane in a mixture of oxygen and air. Nitrous oxide is usually avoided because it causes expansion of bowel gas. Isoflurane is associated with more episodes of postoperative apnoea and longer recovery times when compared with desflurane in infants undergoing pyloromyotomy.19 Analgesia may be provided by ultrasound guided rectus sheath block, transversus abdominis plane (TAP) block, or local anaesthetic infiltration by the surgeon. Rectus sheath block is an appropriate choice for open pyloromyotomy with a circum-umbilical skin incision. TAP block may be useful for open or laparoscopic pyloromyotomy. There is no evidence that a regional technique is more effective than local infiltration but it has been suggested that bilateral rectus sheath blocks reduce the intraoperative end-tidal vapour concentration required to maintain adequate anaesthesia during open pyloromyotomy.20 Paracetamol is the only systemic analgesic required. I.V. paracetamol is licensed for use in neonates of >32 weeks postmenstrual age but great care must be taken to ensure the correct dose is given. Suitable doses for small babies are: 7.5 mg kg−1 every 8 h for preterm infants between 32 and 36 weeks postmenstrual age; 7.5 mg kg−1 every 6 h for infants between 36 and 44 weeks postmenstrual age; 15 mg kg−1 every 6 h from 44 weeks postmenstrual age (7.5 mg kg−1 in a 3 kg child is 22.5 mg or 2.25 ml of the standard 10 mg ml−1 i.v. preparation). The rectal paracetamol 40 mg kg−1 is an alternative. There is rarely any need for opioid analgesics. Regular paracetamol is usually sufficient for postoperative analgesia. During a laparoscopic approach, be especially vigilant during abdominal insufflation. The procedure is usually well tolerated but intra-abdominal pressure should be kept less than or equal to 10 mmHg.1 Ventilator adjustments are likely to be required to maintain an adequate minute ventilation and the absorption of CO2 across the peritoneum may lead to hypercapnia. Towards the end of the operation the surgeon may ask the anaesthetist to insufflate a volume of air into the stomach through the NG tube. The absence of air escaping through the mucosa suggests that it has remained intact. Visualisation of air passing into the duodenum suggests that the division of the pylorus has been satisfactory. Great care must be taken to ensure that air is introduced into the NG tube and not an i.v. line. However, the introduction of NG tubes with connections that are not compatible with i.v. Luer syringes and purple coloured enteral syringes should mitigate this risk. The NG tube should be aspirated again and can then be removed. The infant is extubated in the left lateral position once fully awake. There should be adequate spontaneous ventilation and the child should be obviously awake and moving vigorously. 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