C Anesthetic considerations for selected cases
Pyloric stenosis
Pyloric stenosis is an obstructive lesion, characterized by the “olive-shaped” enlargement of the pylorus muscle. It is a common gastrointestinal anomaly, particularly in boys. It is usually diagnosed between 2 and 12 weeks of life. Clinical symptoms include nonbilious postprandial emesis, becoming more projectile with time; a palpable pylorus; and visible peristaltic waves. The procedure to correct the problem is a pyloromyotomy.
Historically, pyloric stenosis was considered a surgical emergency; however, as with medical progress on many fronts, the procedure is now treated as a medical emergency with the patient being optimized before elective surgery. Fluid, electrolyte, and acid-base balance should be corrected before anesthesia. Hypokalemia, hypochloremia, and metabolic alkalosis are the most common electrolyte abnormalities.
2. Anesthetic technique
a) Before induction, the neonate’s stomach must be emptied via orogastric tube. Some anesthesia providers irrigate the stomach via the orogastric tube with warm normal saline until the aspirate is clear and minimal. Others tilt the baby in various directions to evacuate the remaining contents.
b) After preoxygenation, the induction should be a modified rapid sequence with properly applied cricoid pressure and gentle positive-pressure ventilation via mask. (Many practitioners still perform an awake oral or a true rapid sequence.)
c) Oral endotracheal intubation is mandated to protect the airway from any gastric contents that may be residual.
Inguinal hernia
Inguinal hernias are particularly prevalent in preterm infants. The surgical problem presents the possibility of incarceration of the small bowel in the hernia defect, resulting in ischemia and tissue death. Also of concern is the potential injury to the ipsilateral testicle. These babies routinely have their hernia repair before discharge from the NICU, and the anesthesia provider is faced with all the usual problems of prematurity, such as BPD. The surgical approach can be the standard abdominal incision; in some centers, laparoscopy is the preferred technology. In most situations, the contralateral side is explored to rule out the presence of another defect because of the high incidence of bilateral involvement. When this procedure is performed by a urologist, the contralateral side is most often not explored.
Congenital diaphragmatic hernia
A congenital diaphragmatic hernia (CDH) is a defect of the diaphragm that allows extrusion of the abdominal contents into the thoracic cavity. This disorder has an incidence of one in 2500 live births. The herniated abdominal contents act as a space-occupying lesion and prevent normal lung growth and development. Most of these defects are left sided via the foramen of Bochdalek, and the lung affected to the greatest extent is on the ipsilateral side. However, the other lung can be affected as well. The lungs have reduced sized bronchi, less bronchial branching, decreased alveolar surface area, and abnormal pulmonary vasculature. There is a thickening of the arteriolar smooth muscle extending to the capillary level of the alveoli. This results in increased pulmonary artery pressure and causes right-to-left intrapulmonary shunting.
Neonates with CDH present immediately after birth with a classic triad that includes cyanosis, dyspnea, and dextrocardia. Other symptoms include tachypnea, absence of breath sounds on the affected side, and severe retractions. Their physical appearance is a scaphoid abdomen and a barrel chest. Diagnosis is confirmed by chest radiographs documenting bowel in the thoracic cavity and a gasless abdominal cavity. Between 44% and 66% of neonates with CDH have other anomalies, particularly heart lesions.
The emergent nature of the repair has been recently reexamined, and more emphasis is now placed on the stabilization of the pulmonary hypertension and other medical issues. Extracorporeal membrane oxygenation (ECMO) is one method of bridging the gap between birth and surgical repair; however, it is not the mode of treatment for all patients.
3. Anesthetic technique
a) A thorough assessment of the baby, including laboratory, radiographic, and physical symptoms, is mandatory.
b) Listening to breath sounds will assist in evaluating the degree of ventilation on each side of the chest after intubation.
c) Because of the respiratory manifestations of the problem, the patient will be already intubated and have IV access and arterial lines in place when arriving in the operating room.
d) If the patient is not intubated, an ETT should be placed after a rapid-sequence induction. If a difficult airway is suspected, an awake intubation should be done.
e) It is important in these patients to administer an anticholinergic (atropine 0.02 mg/kg) IV just before induction to prevent the bradycardia during induction.
f) If an awake intubation is planned, some type of analgesia should be used to decrease the stress response of airway instrumentation.
g) Ventilation should be delivered gently to avoid inflating the stomach with air, further compromising the pressure in the chest. Volutrauma can be avoided by delivering small tidal volume and PEEP if necessary.
h) The patient’s hemodynamic stability should determine the anesthetic drugs used. A high-dose narcotic technique is commonly used (fentanyl, 15-25 mcg/kg) if tolerated.
i) The use of inhalation agents must be judicious because they pose significant risk to the baby’s cardiovascular stability.
j) Nitrous oxide should be avoided because it will increase the volume of gastrointestinal tissue and further impair ventilation.
k) Monitoring must include blood pressure, ECG, pulse oximetry, capnography, temperature, and heart rate.
l) To monitor for right-to-left cardiac shunting, oximeter probes should be placed preductal (right upper extremity) and postductal (lower extremity).
m) The use of arterial blood pressure monitoring not only allows beat-to-beat assessment of blood pressure but also provides an outlet for easier blood sampling.
n) All conditions that can increase pulmonary vascular resistance (hypoxia, hypothermia, or acidosis) should be avoided.
o) Carbon dioxide should be kept at normal or slightly elevated levels, and oxygen saturation should be maintained above 80 mmHg.
p) Any derangement of electrolytes should be corrected quickly, and any significant blood loss should be replaced.
q) In the event that cardiorespiratory instability prevents the neonate from being transported to the operating room, the anesthesia provider might be required to administer anesthesia in the NICU while the baby is still on ECMO.
r) Under these circumstances, the recommended anesthetic choice is an opioid and nondepolarizing muscle relaxant technique instead of an inhalation agent.
Omphalocele and gastroschisis
Omphalocele and gastroschisis present with similar physical findings, but they originate from distinct abnormalities that occur in utero. An omphalocele occurs from failure of portions of or the entire contents of the intestine to return to the abdominal cavity. In gastroschisis, the abdominal contents have already returned to the abdominal cavity, but ischemia from insufficient blood supply by the omphalomesenteric artery causes a defect at the base of the abdominal wall and thus extrusion of abdominal contents. It is more common to encounter omphalocele in term newborns and gastroschisis in preterm newborns. The primary difference in the two defects is the presence of a membrane (the peritoneum) covering the extruded abdominal contents in the baby with omphalocele and the lack of membrane in the baby with gastroschisis. They are often associated with other anomalies. These anomalies might be cardiac, genitourinary (bladder exstrophy), metabolic (e.g., Beckwith-Wiedemann syndrome, macroglossia, hypoglycemia, organomegaly, gigantism), malrotation, Meckel diverticulum, and intestinal atresia. When the omphalocele is in the epigastric region, cardiac and thoracic anomalies are more prevalent. If the omphalocele is located in the hypogastric area, cloacal anomalies and exstrophy of the bladder are seen more often. Both gastrointestinal anomalies, although very different in presentation, are almost identical in anesthetic management.
2. Anesthetic technique
a) A newborn with an omphalocele or gastroschisis is usually brought to the operating room very soon after birth to minimize the possibility of infection, the loss of fluid and heat, and the possible death of bowel tissue.
b) A thorough preoperative evaluation must be done to identify the presence of any of the previously mentioned associated anomalies.
c) Historically, the surgical approach was to immediately attempt primary closure of the defect. This entailed placing a large amount of abdominal contents into a cavity that was not usually large enough, and the result was a significant increase in intraabdominal pressure that impeded ventilation and profound hypotension secondary to aortocaval compression.
d) Over the past decade, surgeons have opted for a staged closure using a Silastic silo as a temporary housing for the bowel. This silo is sutured to the defect, and the silo is reduced over the next 3 to 7 days to allow for accommodation of the gastric contents and abdominal wall stretching. Then the neonate is usually brought for complete closure.
e) In the event primary closure is attempted, it should be noted that excessive intraabdominal pressure can increase the possibility of unsuccessful completion of the closure, as shown in the following box.
