© Springer International Publishing AG 2017
Linda S. Aglio and Richard D. Urman (eds.)Anesthesiologyhttps://doi.org/10.1007/978-3-319-50141-3_5555. Pyloric Stenosis
(1)
Division of Pediatric Anesthesia, Department of Anesthesiology and Perioperative Medicine, University of Massachusetts Medical School, University Campus, 55 Lake Avenue North, Worcester, MA 01655, USA
Keywords
Pyloric stenosisProjectile vomitingPyloric oliveMetabolic alkalosisString signPyloromyotomyNeonatal anesthesiaRapid sequenceAwake intubationMask inductionPostoperative apneaIntroduction
Pyloromyotomy for PS is a common surgical procedure performed routinely at pediatric hospitals. It is the most common condition requiring surgery in the first few months of life [1]. Because of modern medical, surgical and anesthetic care, these patients do extremely well, with little morbidity and mortality [2]. A typical hospital course can consist of admission and diagnosis on hospital day one, medical treatment and stabilization overnight, surgery on hospital day two, and hospital discharged the next day. Pyloromyotomy is one of the most satisfying and rewarding cases for pediatric caregivers not only because the treatment is quickly successful, but also the patient swiftly recovers and is returned to a normal diet and activity within days [3]. The pediatric anesthesiologist plays a vital role in ensuring that these neonates safely undergo surgery with their perioperative risks minimized. This chapter will review the medical and surgical management of PS, and examine current anesthetic management techniques. Areas of controversy regarding induction and intubating methods and the use of regional anesthesia will also be discussed.
Incidence
PS is a relatively common condition. Rates of approximately 2–4 per 1000 live births in western countries have been reported [4–6]. The incidence is correlated with geographic location, season, and ethnic origin [7]. There is some evidence that in recent years the incidence in boys has increased in some parts of the United Kingdom [8–10]. The incidence has been reported to be four times lower in Southeast Asian and Chinese populations [4, 5, 7]. In fact, PS is considered relatively rare in patients of African, Chinese, and Indian extraction [11, 12].
Inheritance
Gender and genetics influence the incidence of PS. Males are affected four times more often than females [13]. Firstborn males are most commonly affected. Siblings of patients with PS are 15 times more likely to suffer the condition than those without a family history [14]. There is a higher incidence in the offspring of affected parents. Children of affected men are only affected 3 and 5% of the time, whereas children of affected women are affected between 7 and 20% of the time [15].
Pathogenesis
Though the etiology of PS is not fully understood, recent progress has been made in characterizing the condition. It is proposed that PS is inherited via a multifactorial threshold model. This model assumes that the ability to develop PS is affected by the additive effects of numerous genetic and environmental factors [16]. Although no specific gene has been linked to the pathogenesis of PS, genetic syndromes such as Smith–Lemli–Opitz, Cornelia de Lange, and other chromosomal abnormalities have been associated with it [17].
Recent studies suggest that, in pyloric stenosis, the smooth muscle cells of the pylorus are improperly innervated. Non-adrenergic, non-cholinergic nerves that mediate smooth-muscle relaxation are likely absent causing excessive contraction and hypertrophy of the pyloric muscle. The increased expression of certain growth factors and their receptors in the hypertrophied pyloric muscle suggests that the increased local synthesis of these factors play an important role in smooth-muscle hypertrophy. The circular smooth muscle cells are actively synthesizing collagen, and this may be responsible for the characteristic “firm” nature of the pyloric tumor. Particular attention has been paid to the role of gastrin in the pathogenesis of PS. It has been suggested that repeated hyperacid stimulation of the duodenum induced by gastrin evokes repeated pyloric sphincter contractions causing hypertrophy of the pylorus [2].
Clinical Presentation and Evaluation
Feeding intolerance and gastroesophageal reflux are conditions considered in the early differential diagnosis of PS. When typical treatments for these conditions fail, and the patient’s feeding intolerance worsens, PS should be considered. The typical PS patient is a full term, previously healthy infant 2–4 weeks old. The cardinal sign is a history of nonbloody, nonbilious emesis, often described as projectile in nature. 8% of patient may present with a temporary jaundice, but this reverses once feeding is resumed [11, 18]. The clinical presentation of patients with PS may vary widely, from a toxic infant who is severely dehydrated and malnourished, to a relatively healthy appearing infant. In recent years, due to earlier diagnosis, fewer patients present with severe symptoms [19]. A typical patient may be non-vigorous, mildly dehydrated, and have had a small amount of weight loss. Volume status is evaluated by assessing the fontanels, mucous membranes, skin turgor, and the absence of tears. Obtaining a history about the amount of wet diapers produced in a day (at least 5–6) is important in assessing the degree of dehydration. On the abdominal physical exam, one may palpate the classic “olive” between the midline and right upper quadrant, Gastric peristalsis may be observed. Blood chemistries are obtained when establishing intravenous (IV) access. Abnormally low chloride and high bicarbonate is characteristic of patients with PS. Arterial blood gas analysis is also obtained in the severely dehydrated patient to further assess the acid-base status. The finding of acidosis on arterial blood gas analysis is a sign of severe dehydration and organ hypoperfusion. The diagnosis of PS can be made with history and physical exam alone 90% of the time. However, in contemporary practice, patients almost always undergo radiolographic studies to confirm the diagnosis.
Radiolographic Studies
Ultrasound is the diagnostic modality of choice for evaluating suspected PS. A pyloric muscle thickness greater than 3 mm and a pyloric channel length of greater than 15 mm is considered diagnostic for PS [20, 21]. When ultrasound is inconclusive or unavailable, the upper gastrointestinal study is a reliable alternative. Poor gastric emptying in the presence of the classic string sign caused by the hypertrophied pyloric muscle is diagnostic for PS. If a contrast upper GI study has been performed, this must be taken into account during induction of general anesthesia.
Preoperative Medical Treatment
Careful preoperative management is likely the major factor in reducing the mortality related to PS to less than 0.5% [11, 19, 22–24]. PS is a medical emergency first. It is mandatory that the patient’s volume status, acid-base balance, and electrolyte abnormalities are corrected prior to anesthesia and surgery to minimize the potential for intraoperative and postoperative complications. The hypochloremic, hypokalemic, metabolic alkalosis is a chloride-responsive alkalosis. The goals are to replenish the extracellular fluid volume, and to replace Na+ and Cl− to enable the kidney to excrete HCO3 − and correct the alkalosis. The fluid deficit should initially be replaced with boluses of isotonic fluids. Maintenance fluids should be started using D5 0.45% NS or D5 0.2% NS. Once urine output is established, potassium is added to the maintenance fluid [25]. Once the fluid deficit is corrected, maintenance fluids of D5 0.45% NS or D5 0.2% NS with potassium may be given at a rate of 4 ml/kg/hr [26]. The plasma chloride concentration is used as a guide in the assessment and correction of the acid-base status of the patient. When the hypochloremia has been corrected, the correction of the alkalemia usually follows [27]. In infants, a chloride concentration of 95–105 mEq/L is considered normal [28]. Repeat laboratory studies prior to surgery must document the correction of the patient’s metabolic status.
Pyloromyotomy
Fredet in 1908 was the first to suggest a full-thickness incision of the pylorus followed by a transverse closure. Ramstedt modified the technique and later described the sutureless, extramucosal longitudinal splitting of the pyloric muscle, which left the mucosa intact [29]. This technique is the guiding principal of the current surgical approaches for PS today [3]. There are three methods of operative treatment for PS: open (right upper quadrant incision), transumbilical, and laparoscopic. The laparoscopic technique is rapidly being acknowledged as the standard of care [30]. Advantages of the laparoscopic approach include a lower incidence of wound infection, shorter length of hospital stay, and decreased time to feeding. The complication rate for laparoscopic pyloromyotomy is similar to that of open procedures [31]. Surgical pyloromyotomy is considered the treatment of choice for PS [11].
Conservative Treatment
Atropine has been historically used as a non-surgical treatment for PS. The antispasmodic properties of atropine act to reduce pyloric muscle spasm. This modality has largely been abandoned over the past 40 years due to the excellent results with surgery. Recently, atropine’s effectiveness as a nonsurgical alternative in the treatment of PS has been revisited. Studies of atropine treatment in PS have demonstrated success rates of 75–87% [32–34]. There may be a role for atropine treatment for PS but this must be further investigated [32]. Until then, surgical treatment remains the gold standard treatment.
Anesthesia
General Considerations
The relevant anesthetic issues for pyloromyotomy surgery for an infant are
- 1.
General considerations of neonatal anesthesia including differences in physiology and pharmacology of infants.
- 2.
Ensuring the restoration of intravascular volume preoperatively.
- 3.
Correction of electrolyte abnormalities preoperatively.
- 4.
Airway management of an infant while minimizing the risk of pulmonary aspiration in a patient with a full stomach.
- 5.
Pain management, especially considerations of opioids in infants and the risk of postoperative respiratory depression.
- 6.
Surgical approach—open versus laparoscopic.
It should be noted that only anesthesia providers experienced with pediatric care should perform anesthetics for neonates. This will often mean a pediatric anesthesiologist. If pyloromyotomy is not considered a routine case for the anesthesiologist, surgeon, or hospital, the patient should be transferred to an institution where appropriate personnel and resources are available. PS is not a surgical emergency, and therefore after medical stabilization is achieved, arrangements can be made for the safe transport of the patient to an appropriate facility.
Regional Anesthesia
Concerns regarding the possible adverse neurobehavioral effects of anesthetics on young children have prompted reevaluations and new investigations into regional anesthesia alternatives for surgery [35]. Currently general endotracheal anesthesia remains the standard technique.
Pyloromyotomy has been performed utilizing many regional anesthetic techniques. Historically, local anesthesia has been utilized, but with higher surgical complication rates [24]. Caudal block remains the standard anesthetic technique practice at the Hospital Infantil de México [36]. Willschke et al. [37] demonstrated the ability to provide anesthesia with an ultrasound guided single shot thoracic epidural injection for open pyloromyotomy. Spinal anesthetics for open and laparoscopic pyloromyotomy are possible [38, 39]. Spinal anesthetics have been considered in order to avoid (1) the issues of postoperative apnea and respiratory depression, (2) possible aspiration with induction, and (3) the stress of awake intubations. With the shift from open towards laparoscopic approaches, the only regional technique that may have potential application is the spinal. Currently the use of spinals for laparoscopic pyloromyotomy is not routinely recommended.
Regional blocks for postoperative pain control have also been investigated. Among them, the ultrasound guided rectus sheath block seems to be the simplest method for providing intra and postoperative analgesia for the open pyloromyotomy [40].
Preoperative Evaluation
Prematurity and postconceptional age (PCA, gestational age + chronological age) should be noted, as anesthetizing premature infants will require additional precautions. Premature infants less than 60 weeks PCA are at risk for apnea after general anesthesia and may require pediatric intensive care unit (PICU) admission postoperatively [41]. The fontanels, mucous membranes, skin turgor, and evidence of tearing should be examined to ensure that there has been adequate fluid resuscitation. The laboratory chemistries should be reviewed to ensure that metabolic disturbances have been corrected. Adequate IV access should be confirmed as well. Finally, informed consent for the anesthetic should be obtained from the parents. Parents should be reassured that their child will have adequate postoperative pain control, and that special precautions will be taken to avoid aspiration. As with any neonatal surgery, parents should be informed that their child may require postoperative intubation/ventilation and care in the ICU, but for an uncomplicated pyloromyotomy, this would be rare.
Preparation and Monitoring
The room, anesthesia machine, and all equipment should be appropriate for a neonate. An appropriately sized anesthesia circuit, reservoir bag, and mask should be utilized. Suction should be set up with an appropriately sized suction tip. Monitors should be of the appropriate size, and alarms should be set to a neonatal mode. Standard monitoring for neonates includes three lead EKG, noninvasive blood pressure cuff, pulse oximetry, end-tidal gas monitoring, and temperature probe. Airway set up includes appropriately sized masks, oral airways, endotracheal tubes, and laryngoscope blades. For the neonate, a 3.0 or 3.5 cuffed or uncuffed endotracheal tube are often appropriate. If a cuffed tube is used, meticulous management of cuff pressures is critical in this patient population. This can be done using a manometer or checking a tube/cuff leak using auscultation at the neck. A Miller 0 or 1 blade should be appropriate for laryngoscopy. A pediatric stylet should be loaded into the endotracheal tube in preparation for a rapid sequence induction. IV maintenance fluids of D5 0.45% NS with 20 mEq KCl should be administered at 4 ml/kg/hr via an infusion pump. 0.9% NS should be available for 10 mg/kg fluid boluses if needed. Angiocaths for intravenous access should be ready in case IV access is lost. All medications should be drawn up and ready for use. Many practitioners will have unit doses of medications available to decrease the chance of inappropriate dosing in infants. Atropine and succinylcholine should be ready with intramuscular needles in case IV access is lost. Propofol 2–3 mg/kg is a commonly used induction agent. Epinephrine should be immediately ready to administer in the event of cardiovascular collapse, which fortunately is an uncommon occurrence. Acetaminophen (IV or PR) is commonly administered intraoperatively for postoperative analgesia. The room should be warmed and a circulating air warming blanket should be turned on to warm the operating room table prior to the patient’s arrival.
Preinduction
Once in the operating room, the patient’s gown is removed and a warmed blanket is placed over the patient. All monitors are applied (except the temperature probe). IV Atropine is administered at a dose of 10–20 mcg/kg with a minimum dose of 100 mcg. Atropine premedication is used to prevent a vagal reflex when suctioning the stomach, and to prolong the time from oxygen desaturation to bradycardia if intubation is prolonged. A large-sized endotracheal suction catheter (12 french) is typically used to suction the stomach in an attempt to reduce the gastric volume and thereby reduce the aspiration risk. It must be clear that suctioning the stomach does not ensure an empty stomach, but it is recommended to reduce the gastric volume [42]. Orogastric suction is employed, and the patient is turned side to side with the catheter in place. Suction is intermittently applied. The catheter is removed, and the process is repeated once or twice until no fluid can be aspirated.
Orogastric tubes are replaced after intubation to decompress the stomach to ensure adequate surgical exposure. A decompressed stomach is required for safely accessing the abdominal cavity in laparoscopic surgery. Surgeons typically request the insufflation of air into the stomach after the pyloromyotomy is complete to ensure that the pyloric mucosa has not been perforated.
Induction and Intubation
Controversy still exists concerning induction techniques for pyloromyotomy. Mask inductions recommended by Stevens et al. [43] have gone out of favor, but the technique is still occasionally practiced. Recently Scrimgeour et al. [44] has suggested that inhalational induction it is no more risky than RSI and may confer some advantages. The proposed advantage was avoiding the RSI technique altogether. RSI may not decrease the risk of aspiration in PS patients while actually increasing the incidence of failed intubations. Controversy also exists concerning the method of intubation, awake versus asleep. Cook-Sather et al. [42] compared awake, RSI, and modified RSI intubating methods for PS. They concluded that intubations performed in unanesthetized and awake patients were not superior to intubations performed in anesthetized and paralyzed patients. Outcomes evaluated were maintenance of stable vital signs. Thus, they concluded that the practice of awake intubations should be abandoned in otherwise healthy infants. Of note, it was also determined that the modified RSI method, providing mask ventilation with cricoid pressure (CP), conferred no advantage over immediate tracheal intubations in preserving oxygen saturation [45].
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