Peads Yao

Question 1

What differential diagnoses are compatible with these signs and symptoms?

Answer 1

The differential diagnosis of cyanosis and respiratory distress in the newborn is broad and includes respiratory distress syndrome, meconium aspiration, diaphragmatic hernia, persistent pulmonary hypertension (PPH) of the newborn, cyanotic congenital heart disease, choanal atresia, airway abnormalities, and bronchopulmonary sequestration. However, CDH should be suspected in any infant with respiratory distress, shift of cardiac sounds to the right, decreased breath sounds ipsilateral to the side of the hernia, bowel sounds heard in the chest and a concave/scaphoid abdomen. Confirmation of diagnosis includes a chest x-ray demonstrating herniation of abdominal contents into the hemithorax, little or no visible aerated lung on affected side and mediastinal shift (Fig. 37.1). If in doubt, a radiopaque dye may be injected through a nasogastric tube to delineate the stomach and intestine in the chest cavity. If the CDH is right sided, the liver may be the only herniated organ and appear as a thoracic soft tissue ma

Question 2

Describe the incidence and classification of congenital diaphragmatic hernia (CDH).

Answer 2

○ The incidence of CDH is between 1 per 2,000 and 1 per 3,000 births.
○ Eighty-five percent of defects are left sided and <5% are bilateral.
○ Ninety percent of defects are posterolateral (Bochdalek hernia).
○ Anteromedial and paraesophageal hernias and eventrations make up the remainders (Fig. 37.3).
○ There is no difference in mortality between left- and right-sided herniations, although right sided may have a higher incidence of pulmonary complications.
○ Associated anomalies can include central nervous system (CNS) lesions, esophageal atresia, omphalocele, and cardiovascular lesions. ○ In addition, trisomy 21, trisomy 13, trisomy 18, and tetrasomy 12p are examples of syndromes associated with CDH.

Question 3

What are the causes of hypoxemia in patients with CDH?

Answer 3

○ Infants with CDH have deficient bilateral major airway and vessel branching not explained by simple compression of the ipsilateral and contralateral lungs.
○ The severity of pulmonary vascular hypoplasia correlates with mortality in CDH.
○ Airway maldevelopment leads to reduced total number of bronchi and alveoli at birth with resulting decreased lung compliance and decreases in both ventilation and surface area for gas exchange.Oxygenation is thus impaired. ○ Pulmonary vascular hypoplasia results in pulmonary hypertension, causing right-to-left shunting through the patent ductus arteriosus, with resultant hypoxemia.

Question 4

How do you make a diagnosis of right-to-left shunting through the patent ductus arteriosus?

Answer 4

○ Clinical signs of ductal patency include murmur, tachycardia, bounding peripheral pulses with wide pulse pressure, congestive heart failure, and unexplained metabolic acidosis.
○ Preductal (upper extremity) and postductal (lower/umbilical arteries) oxygen saturation measurements by pulse oximetry demonstrate a 10% or higher gradient difference (with preductal saturation being higher).
○ The gold standard for diagnosis is with Doppler echocardiogram to demonstrate the size of the ductal opening and the shunt and allow estimation of mean pulmonary pressure.

Question 5

What other congenital anomalies are usually associated with CDH?

Answer 5

○ About one-third of patients born with CDH have major congenital abnormalities.
○ 10% having a chromosome abnormality, most commonly trisomy 18 and isochromosome 12p
○ 25% having cardiovascular malformations including ventricular septal defect (VSD), autism spectrum disorder (ASD), tetralogy of Fallot (TOF), and hypoplastic left heart syndrome
○ 28% having CNS abnormalities including neural tube defects, hydrocephalus, agenesis of corpus callous, and sensorineural hearing loss 15% having genitourinary abnormalities including undescended testis and hypospadias
○ 20% having gastrointestinal malformations including malrotation, atresia, omphalocele, and gastroesophageal reflux

Question 6

How would you interpret the following arterial blood gas analyses: pH, 7.20; PaCO2, 55 mmHg; PaO2, 35 mmHg; and CO2 content, 19 mEq per L? How would you correct them?

Answer 6

○ The blood gas analyses demonstrate a mixed respiratory and metabolic acidosis with severe hypoxemia.
○ In this patient, the severe hypoxemia is due to the pulmonary pathology and PPH.
° As alveolar PO2 decreases below a threshold of 50 mmHg at normal PCO2, ventilation increases initially and respiratory alkalosis followers.
°However, if hypoxemia is not corrected, patient fatigue results in CO2 retention and a respiratory acidosis.
° In addition, the hypoxemia results in anaerobic metabolism and a concomitant lactic acidosis.
○ Treatment includes mechanical ventilation with control of oxygenation and ventilation.
°Metabolic acidosis should be corrected by administration of sodium bicarbonate and improvement of circulation/perfusion with fluid therapy.

Question 7

What immediate treatment should be given to improve the newborn’s respiratory status preoperatively?

Answer 7

○ Immediate treatment should include intubation and ventilation and decompression of the intrathoracic bowel with a nasogastric tube.
○ Barotrauma and further pulmonary damage must be avoided by maintaining peak inspiratory pressures under 25 cm H2O and fraction of inspired oxygen (FIO2) adjusted to preductal arterial saturations >85%.
○ Institution of pressure support ventilation, use of high-frequency oscillatory ventilation, permissive hypercarbia, and even ECMO are modes to optimize the oxygenation status.

Question 8

Should CDH be repaired urgently once the diagnosis is made and confirmed?

Answer 8

○ Surgical repair of CDH was treated as a surgical emergency.
°However, improvement in gas exchange, thoracic compliance, or PaCO2 was not proven from immediate surgery. ° This has resulted in delay for clinical stabilization of the neonate’s respiratory and cardiovascular status and ensuring adequate endorgan perfusion, as evidenced by improved oxygenation, decreasing pulmonary vascular hypertension, and correction of metabolic acidosis.

Question 9

What are the effects of nitric oxide (NO) on pulmonary and systemic circulation?

Answer 9

○ In vivo, NO is an endothelium-derived relaxing factor, which causes smooth muscle relaxation and vasodilation. °Inhaled NO (iNO) is unique in that it is a selective pulmonary vasodilator and has no effect on systemic circulation. °In low concentrations, iNO diffuses into pulmonary smooth muscle, raises the concentration of current good manufacturing practice (cGMP), which induces selective vasodilation and decreased vascular tone.
° Unfortunately, most neonates with CDH with pulmonary hypertension plus lung hypoplasia do not have a dramatic response to iNO.
°A Cochrane review concluded that iNO does not improve outcomes in neonates with CDH and may, in fact, worsen outcomes.

Question 10

What is the current role of extracorporeal membraneoxygenation (ECMO) in the management of CDH?

Answer 10

○ Despite wide use over many decades, survival of patients with CDH treated with ECMO remains unchanged at 50%.
○ A recent United Kingdom study showed infants who received ECMO for CDH had significant mortality in the first year of life and there was long-term physical and neurodevelopmental morbidity in the majority of survivors.
○ Consensus of significant risks associated with ECMO, such as bleeding, intracranial hemorrhage, and sepsis, have shifted the implementation of ECMO, as a rescue therapy for infants with persistent preductal hypoxemia and acidosis despite inotropic and ventilator support.

Question 11

What monitors would you use for this neonate during surgery? CDH

Answer 11

Respiratory
° Two pulse oximeters, for preductal and postductal oxygen saturation
° Capnometry
° Inspiratory pressure measurement ° Inspiratory oxygen concentration ° Intraoperative arterial blood gas analysis
Cardiovascular
° Five-lead electrocardiogram
° Blood pressure cuff
° Arterial line: right radial artery for preductal PaO2
° Central venous pressure (CVP) line for evaluating volume status and right ventricular performance Thermoregulatory
° Esophageal or rectal temperature probe

Question 12

How would you induce and maintain anesthesia?

Answer 12

○ In general, the preoperative care of the neonate is continued into the operating room with the addition of high-dose opioids and nondepolarizing muscle relaxant.
○ Ventilation strategies focus on permissive hypercarbia (60 to 65 mmHg), preductal oxygen saturation of 90% to 95%, and peak pressures <25 cm H2O. ○ Volatile agents may be instituted with precaution because systemic vascular resistance may decrease more than pulmonary vascular resistance (PVR) resulting in worsening of right-to-left shunt.
○ Frequent blood gas sampling will guide changes in respiratory management and assessment of acid–base status.
○ Availability of agents to maintain blood pressure support should be readily available and include isotonic fluids and inotropes such as dopamine and/or dobutamine and hydrocortisone.
○ Meticulous attention to temperature is essential because hypothermia can increase PVR and thus increase right-to-left shunting.

Question 13

Would you use nitrous oxide for anesthesia? Why?

Answer 13

○ Nitrous oxide is avoided because it will expand air-filled cavities (such as bowel) and potentially further compress functioning lung tissue and because it limits the inspired oxygen concentration, which can be provided to a compromised neonate.

Question 14

How would you ventilate the patient?

Answer 14

○ The goals of ventilation and oxygenation in the operating room are the same as preoperative:
° Avoid volutrauma by using small tidal volumes and low-peak inspiratory pressures, adequate oxygenation with the goal of saturations in the low to mid 90s, and permissive hypercapnia with maintenance of pH >7.25.

Question 15

Is the infant with CDH more at risk from hypothermia?

Answer 15

○ All neonates are susceptible to heat loss because of a high ratio of surface area to body weight, reduced subcutaneous fat, and an underdeveloped ability to shiver (thermogenesis) in response to cold.
○ However, infants with CDH have increased morbidity and mortality secondary to hypothermia because the resulting increased PVR can cause decreased oxygen delivery, worsening acidosis, shunting, and continued increases in PVR.
○ Concentrated efforts to maintain normothermia are mandatory and include maintaining ambient operating room temperature >23°C, use of warmed intravenous fluids, passive insulation with drapes and blankets, forced-air warming, and passive humidification of inspired anesthetic gases.

Question 16

The surgeon returned the intrathoracic stomach and intestine to the peritoneal cavity and the ipsilateral lung was found to be hypoplastic and collapsed. The resident anesthesiologist tried to expand the collapsed lung manually with positive airway pressure. Five minutes after the abdomen was closed, the blood pressure suddenly dropped from 70/40 to 30/20 mmHg, the heart rate from 150 to 80 beats per minute, and the pulse oximeter from 95% down to 60% saturation. What would you immediately do?

Answer 16

○ Any sudden deterioration in blood pressure, heart rate, oxygen saturation, or pulmonary compliance is suggestive of tension pneumothorax.
○ Auscultation of the chest, particularly the contralateral side, should be done immediately.
° If absent or diminished breath sounds confirm the diagnosis, a chest tube should be inserted immediately.
° A large-bore intravenous catheter with needle may be inserted to release the tension pneumothorax if a chest tube is not immediately available.
° The tension pneumothorax is usually on the contralateral side because the high airway pressure required to inflate the hypoplastic lung may rupture the normal alveoli on the contralateral side, resulting in pneumothorax.
° Moreover, the ipsilateral chest usually already has a chest tube after surgery. ° If there is no pneumothorax, or if deterioration is not improved after insertion of a chest tube, inferior vena cava compression (resulting in decreased venous return and decreased cardiac output) should be considered.
° The abdominal cavity is often underdeveloped and unable to fully accommodate the returned abdominal organs, which increases the intra-abdominal pressure, displaces the diaphragm cephalad, and ultimately decreases pulmonary compliance (in the healthy lung).
° The net result clinically is desaturation, hypercarbia, and overall instability.
° In this circumstance, the abdominal wound should be reopened to relieve the compression on the great vessels and displacement of the diaphragm.
° A patch closure of the abdomen can be attempted or a Silo pouch is placed until growth allows safe return to the abdominal cavity.

Question 17

Discuss fluid therapy in this patient. CHD

Answer 17

○ Fluid and electrolyte management in newborns should be focused on maintaining homeostasis while recognizing the impact of gestational age, physiologic changes in renal function, redistribution of total body water, water loss secondary to environmental factors, underlying medical condition of neonate, and surgical stress on fluid requirements.
○ Neonates are obligate sodium losers, and therefore, exogenous sodium should be supplied.
° In addition, urine concentrating ability is limited in the newborn and as a result, the risk of volume depletion is increased due to the inability to maximally concentrate urine, decreased response to antidiuretic hormone (ADH), limited sodium reabsorption due to tubular immaturity, and reduced responsiveness to aldosterone.
○ The preoperative fluid deficit may be evaluated by careful history taking, signs and symptoms of dehydration, urine output, and CVP monitoring.
○ Maintenance fluids consisting of 5%dextrose in one-fourth to one-half strength saline are given at 4 mL/kg/hr.
○ Intraoperative evaporative and third-space losses are replaced with lactated Ringer’s, Plasma-Lyte, or saline at approximately 6 to 8 mL/kg/hr.
○ Each milliliter of blood loss is replaced with 3 mL of lactated Ringer’s or 1 mL of 5% albumin.
○ Blood pressure, heart rate, urine output, CVP, hematocrit, and electrolytes should guide fluid therapy.

Question 18

At the conclusion of surgery, would you extubate the patient in the operating room? CDH

Answer 18

No, the patient should remain intubated at the conclusion of surgery. Varying degrees of pulmonary dysfunction, fluid shifts, and changes in abdominal compliance must be anticipated, and the need for postoperative mechanical ventilation and stabilization is mandatory.

Question 19

What is the mortality rate in patients with CDH? What postoperative problems would you expect in this patient? CDH

Answer 19

○ Despite advances in medical and surgical treatment, the mortality rate in patients with CDH has remained at approximately 20% to 30% over the past two decades.
○ Pulmonary hypoplasia and PPH are the two main prognosticators.
○ Survival is complicated by both restrictive and obstructive lung disease patterns and BPD is often documented radiographically.
○ Curiously, by childhood or adolescence, survivors of CDH seem to recover and remodel achieving nearnormal lung volumes and mechanics.
○ Gastroesophageal reflux disease, intestinal obstruction, delayed growth, neurocognitive defects, sensorineural hearing loss, and musculoskeletal abnormalities (mainly scoliosis and pectus excavatum) also complicate long term survival.

Question 20

A 12-hour-old full-term infant weighing 2.5 kg presents with choking and cyanosis during his first feed. Neonatal intensive care unit (NICU) staff is unable to pass a feeding tube into the stomach. The baby also has copious oral secretions. Before birth, polyhydramnios was noticed.
What is the diagnosis?
What are the clinical featuresof this disease?

Answer 20

○ This patient has EA with a TEF.
○ This occurs in 1 per 3,000 live births. ○ The diagnosis is suspected prenatally by the presence of polyhydramnios, which is caused by the failure of the fetus to swallow amniotic fluid (secondary to EA).
○ Polyhydramnios is a nonspecific prenatal finding.
○ The combination of polyhydramnios and absent stomach bubble on prenatal ultrasound gives a 44% to 56% likelihood of EA/TEF.
○ After birth, the neonate will have copious drooling from inability to swallow secretions.
° Attempts to feed the baby will result in coughing and cyanosis.
° An orogastric tube (OGT) will coil up in the upper esophageal pouch rather than pass into the stomach.

Question 21

What is the pathophysiology of this disease? TOF

Answer 21

○ In this abnormality, there are two distinct problems: TEF and EA.
° In TEF, the trachea is connected to the esophagus through a fistula.
° This causes two problems. First, inhaled air can bypass the lungs through the fistula into the stomach and cause hypoventilation and gastric distension.
° If the lungs are especially noncompliant or the fistula is large, attempts to institute positive pressure ventilation (PPV) can lead to severely compromised ventilation due to gastric expansion or even rupture.
° Second, there is the continual risk of acidic stomach contents refluxing via the fistula back into the trachea causing aspiration pneumonitis.
° With EA, the esophagus is divided into a proximal and distal portion. The proximal portion ends in a blind pouch. Secretions from the hypopharynx pool here and cause drooling,coughing, and choking with feeds.
° The child is unable to feed orally.

Question 22

Describe the normal development of the trachea and esophagus.

Answer 22

○ The foregut arises first from primitive endoderm.
○ This structure will eventually differentiate into trachea and esophagus. ○ Lung buds form anteriorly at pharyngeal arch 6.
○ Differential expression of various growth factors results in the anterior foregut developing into trachea and lung tissue, whereas the posterior portion develops into esophagus.
○ The actual septation process is believed to arise at the level of the lung bud and proceed toward the pharynx.
○ This process requires multiple gene signals, including Sonic hedgehog, Sox2, and NKX2.1.
○ Errors in this process of separation of the trachea from the foregut results in a residual fistula between the esophagus and trachea.

Question 23

How are tracheoesophageal fistula (TEF) and esophageal atresia (EA) inherited?

Answer 23

○ TEF/EA is believed to be multifactorial in etiology and sporadic.
° Rarely, it is associated with a specific genetic mutation or syndrome.
° These include trisomy 18, Hall-Hittner syndrome, anophthalmia-esophageal-genital (AEG) syndrome, Feingold syndrome, and 16q24.1 deletion syndrome. Most of the cases, however, are nonfamilial.
○ There is a 1% chance of recurrence in each sibling of someone with EA.
○ EA is twice as common in twins.

Question 24

How are the different types of TEF/EA classified?

Answer 24

○ There are five types of TEF according to the classic Gross classification (Fig. 36.1). • Type A is pure EA with no involvement of the respiratory tree; this occurs in 8% of cases.
• Gross type B has EA and a fistula connecting the proximal esophageal pouch to the trachea; this occurs in less than 1%.
• The most common is type C, with EA and fistula linking the distal esophagus to the trachea; this occurs in 75% to 80% of cases.
• Rarely, type D occurs with two fistula connecting both proximal and distal esophagus to the trachea (2%).
• Type E, known as an H-type fistula, has no atresia. Instead, an intact esophagus has a linkage with trachea through a fistula, and it occurs in 4%.

Question 25

What other problems may this child have, and when should these be investigated?

Answer 25

○ Fifty percent of children with EA/TEF will have additional anomalies.
○ Most often, they occur in the spectrum known as VACTERL (formerly known as VATER):
• V = vertebral anomalies (10%)
• A = anal canal defect (anal atresia) (14%)
• C = cardiac malformations (29%), including ventricular septal defect, atrial septal defect, tetralogy of Fallot, right-sided arch, patent ductus arteriosus • TE = tracheoesophageal fistula
• R = renal dysplasia
• L = limb defect (radial aplasia)
○ A patient is considered to have VACTERL association with the presence of three or more of these lesions. Nearly one-third of TEF patients will have an additional VACTERL lesion, and an additional one-fifth will have two.
○ Other possible gastrointestinal problems include malrotation of the midgut and duodenal atresia.
○ Renal problems can include malposition, hydronephrosis, and ureteral abnormalities.
○ Because the existence of these associated defects may alter the surgical or anesthetic plan, and because the TEF is an urgent but not emergent procedure, these other possible defects should be assessed prior to TEF repair.

Question 26

What should the parents be told regarding perioperative risk? Risk of recurrence?

Answer 26

○ The survival of TEF babies has improved over the years because of the improvements in intensive care unit care, anesthesia, and surgical technique.
○ Risk of perioperative mortality remains well stratified by the Spitz Classification in a recent series of 248 neonates over a 20-year period.
• Spitz group I: birth weight more than 1.5 kg, no major cardiac disease, survival 96%
• Spitz group II: birth weight less than 1.5 kg, or major cardiac disease, survival 79% • Spitz group III: birth weight less than 1.5 kg and major cardiac disease, survival 38%

Question 27

What laboratory workup should be obtained before surgery?

Answer 27

○ First, a plain chest x-ray is used to assess the presence and severity of pulmonary disease, especially looking for aspiration pneumonia and respiratory distress associated with prematurity.
° It may also show the presence of congestive heart failure in the setting of associated cardiac disease, which may be optimized by administering a diuretic.
° A radiopaque OGT will be seen coiled in the proximal esophageal pouch, whereas an abdominal x-ray may show air in the bowels entering through the fistula.
° Because of the risk of aspiration, the use of contrast dye to delineate the fistula should be used only when there is diagnostic uncertainty.
° Of note, an OGT that appears to enter the stomach may in fact have passed through an esophageal perforation caused by repeated traumatic insertion attempts.
○ Second, an echocardiogram is mandatory because major cardiac defects strongly influence survival and may have an impact on anesthetic management.
° If the child has severe tetralogy of Fallot, he may require placement of a temporary shunt between the systemic arterial and pulmonary circulation prior to repair of the TEF.
° In addition, one wants to look for presence of a right-sided aortic arch because this will require positioning the infant with the opposite side down from usual.
○ Spinal plain films should be done to exclude vertebral anomalies, especially if epidural pain management is being considered.
○ Renal ultrasound should be done to rule out abnormalities, especially hydronephrosis.
○ In addition, complete blood count (CBC), arterial blood gas, and electrolytes should be drawn, and at least 1 unit of packed red blood cells should be type and crossed.

Question 28

Describe management in the NICU before surgery.

Answer 28

○ After the diagnosis of TEF is established, the baby should not be fed, and intravenous (IV) replacement of fluid and glucose provided.
○ A drainage tube should be placed in the proximal esophageal pouch and kept on intermittent suction to minimize aspiration of oral secretions.
○ He should be positioned either prone or supine with the head up 30 degrees to minimize reflux of gastric fluids into the lungs via the fistula.
○ Antibiotics to treat aspiration pneumonia should be given when appropriate.
○ Ensure that blood is available from the blood bank.
○ Because the patient will require a thoracotomy with lung retraction and intermittent compression of the trachea and great vessels, an arterial catheter is mandatory for the case.
° This should ideally be placed in the NICU.
° An umbilical artery catheter may be conveniently placed by a qualified neonatologist.
○ Two additional IV catheters should also be placed.
○ A central venous catheter is not necessary.
○ Avoid placing IV access in the right arm because this arm will most likely be elevated during right thoracotomy and access to it may be limited

Question 29

How is severe lung disease managed before repair?

Answer 29

○ Very early primary repair is considered standard of care.
° However, there remains a subset of neonates with either severe pneumonia or respiratory distress syndrome (from prematurity), who are poor anesthetic and surgical risks (Waterston type C) and who need to be intubated because of respiratory disease.
° The baby can be intubated conventionally while a simple gastrostomy is simultaneously placed to relieve gastric distension that can occur with PPV in the setting of a type C TEF.
° This procedure can be performed under local anesthesia. The problem with this approach is that by decompressing the stomach, gas from the trachea can now bypass the lungs and exit through the stomach. This is especially a concern if the baby’s lungs are noncompliant from pneumonia or respiratory distress syndrome. This can make it difficult or impossible to ventilate the baby adequately.
○ Alternately, the baby can be ventilated using a high-frequency oscillator, which has the advantage of providing oxygenation and carbon dioxide (CO2) removal while minimizing the peak inspiratory pressure and therefore gastric distension.

Question 30

Should this patient be intubated preoperatively for airway protection? TOF

Answer 30

○ Unless mandated by severe pulmonary disease, the child is not intubated preoperatively to minimize the possibility of gastric distension from PPV through the fistula.
○ Intubation does not protect the child from aspiration of gastric contents through the fistula.

Question 31

What invasive lines and monitoring are appropriate before induction? After induction?

Answer 31

○ At least one peripheral IV should be in place before induction.
○ A second may be placed after the patient is anesthetized.
○ If the surgeon intends to give the child total parenteral nutrition postoperatively, a central line may be placed.
○ An arterial catheter for blood gas and hemodynamic monitoring should be in place before incision.
° It is especially useful if thoracoscopy is planned. If a peripheral arterial is not feasible, an umbilical arterial line may be placed by a skilled NICU practitioner.
○ Electrocardiogram, oxygen saturation, end-tidal CO2, and rectal temperature should also be monitored.
○ A precordial stethoscope should be placed over the left axilla to assess breath sounds in case of inadvertent movement of the endotracheal tube (ETT) during surgical retraction or positioning.
° A second stethoscope placed over the stomach may be useful to assess if the fistula is being ventilated.

Question 32

Discuss fluid and temperature management for this baby.

Answer 32

○ As with all neonates undergoing surgery, meticulous attention to fluid management and temperature is essential. ○ Limited subcutaneous fat renders the neonate prone to hypothermia.
○ Hypothermia is dangerous because it will increase pulmonary vascular resistance and may result in a reversion to transitionalcirculation, greatly complicating intraoperative care.
○ The child should be transported to the operating room (OR) in a warmed isolette, with a stocking cap on his head to minimize heat loss.
○ The OR should be prewarmed to at least 30°C.
○ Surgical irrigation and RBCs should be warmed.
○ Using a forced-air convective warming system is strongly recommended.
○ The baby will require intraoperative glucose infusion.
° One must remember that once infused, the glucose will be rapidly metabolized, leaving behind a potentially hypotonic solution.
° In the past, free water was routinely infused in the form of a hypotonic glucose solution such as D10/0.2 normal saline (NS) administered at a rate of 4 mL/kg/hr.
° This was sufficient to prevent hypoglycemia.
° Recent studies have focused on the role of increased antidiuretic hormone (ADH) secretion, which occurs during surgery. ° This ADH secretion renders the infant at a fivefold increased risk of severe hyponatremia when given free water. ° Current recommendations including infusing isotonic glucose solution for maintenance.
○ Insensible losses should be estimated at 3 to 4 mL/kg/hr and replaced with an isotonic (nonglucose-containing) solution. ○ Urine output (ideally 1 mL/kg/hr) may be difficult to assess accurately in a low birth weight baby.

Question 33

What are the options regarding induction and intubation?

Answer 33

○ The goal is to intubate the baby to allow adequate gas exchange with the lowest possible inspiratory pressure needed to inflate the lungs, avoid atelectasis, and minimize gas flow through thefistula. ○ One-lung ventilation is generally not required.
○ The most important aspect of the intubation is the correct positioning of the ETT.
○ The goal is to have the tip of the ETT distal to the fistula yet proximal to the carina.
○ If the tube is deliberately placed deep (into the right mainstem) with the bevel facing forward, then slowly pulled back just until breath sounds occur on the left equal to the right, the tube is likely to be in good position.
○ Keep in mind the following options: 1. Avoidance of PPV until the fistula is ligated will decrease the risk of gastric distension.
• One can intubate awake or after inhalation induction while maintaining spontaneous ventilation.
• Awake intubation can be associated with the risk of increased intracranial pressure or intraventricular hemorrhage in the premature infant and discomfort to the child.
• If one chooses to intubate after induction, this will require deep anesthesia with spontaneous ventilation using an inhalation anesthetic.
• The lowest inspiratory pressure assistance is used to prevent atelectasis while minimizing distension of the stomach.
• If the lungs are suspected of being poorly compliant due to pneumonia or prematurity, then mask ventilation should be avoided.
• Good intubating conditions can be achieved with a volatile agent, but maintaining adequate ventilation and surgical conditions during a thoracotomy without muscle relaxant may be challenging.
2. Rapid sequence IV induction and placement of the ETT below the fistula is another option.
• If the ETT is in good position, then muscle relaxants can be given and normal PPV maintained.
• The difficulty lies in maintaining good position of the ETT during surgical manipulation and turning the patient lateral.
• Alabbad et al. describe a disastrous scenario in which a neonate with TEF was intubated and ETT position confirmed by breath sounds; yet after turning the patient, the ETT migrated into the fistula without being recognized.
° This resulted in failure to ventilate the baby and eventual cardiac arrest.
3. Another option, to avoid the risk of ETT malposition, is to deliberately keep the tip of the tube above the fistula (if it is shown by bronchoscopy to be small) and keep ventilation pressures low until the fistula is ligated.
• This comes with a high risk of gastric distension.
4. In cases where the lung compliance is poor, or the fistula is located near the carina, high-frequency oscillating ventilation (HFOV) can be used because it provides gas exchange with a much lower inspiratory pressure.
• This technique is technically cumbersome and requires utilization of a total IV anesthetic technique.

Question 34

What is the role of rigid and fiberoptic bronchoscopy in this patient prior to incision? TOF

Answer 34

○ Perioperative bronchoscopy before commencing TEF repair allows assessment of the size and location of the fistula.
○ A cervical level fistula does not require a thoracotomy to repair.
○ A low-lying or subcarinal fistula will predict difficult in placing an ETT that does not ventilate the fistula.
○ The presence of a second fistula can be ruled out.
○ If deemed appropriate, the fistula can be occluded using a no. 3 French Fogarty occlusion catheter, thereby allowing normal PPV without distending the abdomen.
○ Following placement of the balloon, the rigid bronchoscope is removed and the child intubated with a microcuff ETT alongside the catheter.
○ There is a real possibility that during positioning or surgical manipulation, the Fogarty balloon may slide back into the trachea.
° This could precipitate immediate complete airway obstruction if not promptly recognized and treated

Question 35

Describe the steps of an open repair of EA/TEF.

Answer 35

○ First, the patient is positioned in the lateral position, left side down.
○ If the patient has a right-sided aortic arch (rare), the surgeon will position the patient with right side down.
○ A retropleural approach is used, which minimizes the danger from an anastomotic leak.
○ The azygos vein is ligated to better visualize the fistula.
○ The fistula is exposed and ligated, leaving a little stump; this usually occurs within 45 minutes.
○ It is important to remember that a fistula stump remains after repair, at least initially.
○ When the patient returns for follow-up surgery (e.g., esophageal dilations), during intubation, the ETT may be observed to pass through the vocal cords yet the tip end up in the stump, precluding effective ventilation.
○ An anterior posterior chest x-ray (AP CXR) will not show this, but a lateral film will.
° This possibility should always be entertained if unable to ventilate one of these patients despite apparent successfulintubation.
○ If the patient is stable, then normal PPV can commence while the repair of the esophagus begins.
○ The upper esophagus is mobilized, then the distal esophagus.
○ The esophagus is joined together.
○ Following this, a feeding tube is placed across the anastomosis to allow feeding (if the patient does not have a gastrostomy). ○ The lung should be carefully reexpanded to eliminate atelectasis before closure.
○ Chest tubes are not routinely placed following repair.

Question 36

What are common intraoperative problems, and how can they be managed? TOF

Answer 36

○ Interference with ventilation is the most common problem and can have many causes.
○ Lung retraction with resulting atelectasis leads to frequent desaturation. ○ It may be difficult if not impossible to maintain normocarbia.
○ The partial pressure of arterial carbon dioxide (PaCO2) may rise to 70 to 80 mmHg despite all attempts to optimize ventilation.
○ If the patient has a Fogarty catheter in the fistula, it may be displaced into the trachea causing total airway obstruction. ○ Surgical manipulation of the soft trachea makes the ETT vulnerable to kinking or displacement distally into right mainstem or proximally above the fistula.
○ Frequent compression of vital structures in the mediastinum can lead to profound hemodynamic compromise. ○ Blood and secretions are a constant problem, which risk obstructing the tube. ○ The ETT should be suctioned frequently, more so if blood is seen.
○ The retracted lung may need to be intermittently re-expanded to avoid severe hypoxia.
○ Severe gastric distension before ligation of the TEF may requireemergent gastric needle decompression.
○ It is crucial to maintain close communication with the surgeon.
○ Avoid hypothermia.

Question 37

If the surgeon decides to proceed thoracoscopically, how will you perform your anesthetic? Is one-lung ventilation required? What are some complications unique to thoracoscopy in the newborn?

Answer 37

○ Thoracoscopy to repair TEF/EA has gained increasing popularity over the past decade.
○ Three major advantages are described. ° First, the approach provides excellent visualization of the fistula, which allows rapid ligation and stabilization of ventilation.
° Second, avoidance of thoracotomy results in less pain.
° Third, avoiding posterolateral thoracotomy results in better chest wall symmetry and less long-term scoliosis.
○ A metaanalysis by Borruto et al. showed that the anastomosis leak rate was not increased in the thoracoscopic group.
○ To perform this anesthetic, an arterial line is mandatory due to the significant gradient between end-tidal and arterial CO2.
○ Concerns regarding intubation, PPV, paralysis, fluid, and temperature management are identical to that for an open repair.
○ Opioid requirements may be reduced. ○ Isolating the right lung is not required for a successful thoracoscopy.
○ One lung ventilation is helpful but not necessary and may not be tolerated well in the neonate.
○ Deliberate left mainstem ETT intubation to collapse the right lung may result in prolonged left upper lobe lung collapse.
○ Exposure of the fistula is attained by insufflation of the right chest cavity with CO2 to a pressure of 5 mmHg.
° Hypercapnia and acidosis are expected with both open repair and thoracoscopic repair, but the degree of hypercapnia and acidosis is worse with thoracoscopy (PaCO2 59 mmHg vs. 51 mmHg in one study).
○ The potentially impact of the raised intrathoracic pressure and hypercapnia associated with thoracoscopy on neonatal brain oxygenation has been explored.
° One single-center study found no significant effect on brain cerebral oximetry measurement in infants having repair thoracoscopically compared to open repair, provided mean arterial pressure was maintained with a combination of fluid and inotropic support.

Question 38

When should the baby be extubated?

Answer 38

○ Although some surgeons prefer to have the baby extubated immediately in the OR to minimize tension on the suture line, this can be risky.
° Many infants with TEF have a deficiency of tracheal cartilage at the level of the fistula predisposing totracheomalacia. This can result in airway obstruction requiring immediate reintubation.
° Many of the children have significant lung disease from prematurity or aspiration pneumonia; they should stay intubated.
° If opioid-based postoperative analgesia is planned, mechanical ventilation is preferred due to the risk of hypoventilation.
○ If early extubation is planned, an epidural technique might be helpful. ° However, if the child is to remain intubated, care should be made to limit inspiratory pressure to protect the repair from disruption.

Question 39

What options are available for postoperative analgesia?

Answer 39

○ For patients who are to remain intubated postoperatively, a narcotic anesthetic technique with fentanyl at 10 to 20 μg per kg with muscle relaxant will give hemodynamic stability and allow analgesia to be continued in the postoperative period.
○ For experienced practitioners, an epidural catheter can also be placed.
° An epidural catheter threaded through the caudal space can be easily threaded up to the thoracic dermatomes.
° The position of the catheter placed in this way should be confirmed with fluoroscopy or ultrasound prior to use.
° This technique should only be undertaken by one who is experienced in regional anesthesia for children.

Question 40

What are early and late complications of TEF repair?

Answer 40

○ Early anastomosis leakage occurs in up to 15% of patients.
° This may require immediate exploration or may be managed expectantly.
○ Esophageal dysmotility and gastroesophageal reflux disease (GERD) are common.
° The dysmotility may be from abnormal innervation of the distal esophagus or may be related to vagal nerve injury during the repair.
○ Stricture of the esophageal anastomosis may require repeated dilatations. ○ Tracheomalacia may be evident postoperatively, and vocal cord paresis has been reported.

Question 41

A 3-week-old first-born male infant had projectile vomiting, which contained the ingested formula but no bile. His body weight was 2.5 kg; serum electrolytes: K+, 2.2 mEq per L; Cl−, 86 mEq per L; and blood pH, 7.68. This infant was also noted to have a systolic murmur heard best at the second intercostal space along the left sternal border, which was assessed by a cardiologist and diagnosed as a ventricular septal defect (VSD
What is the diagnosis in this patient?

Answer 41

The most likely diagnosis in this patient is pyloric stenosis. The factors that favor the diagnosis are as follows: Age—3 weeks (average age at onset; range 5 days to 5 months) Boy child (boy-to-girl ratio = 4:1) Projectile vomiting (characteristic) Contents—ingested formula, no bile The resultant biochemical abnormality in this patient is a hypokalemic, hypochloremic, metabolic alkalosis. Pyloric stenosis occurs in 3 of 1,000 infants born in the United States; its incidence may be increasing. It is more common in Whites of Northern European ancestry, less common in Blacks, and rare in Asians. Reduced nitric oxide in pyloric tissue may contribute to the pathogenesis of pyloric stenosis.

Question 42

What is the differential diagnosis of pyloric stenosis?

Answer 42

Pyloric stenosis can be distinguished from other congenital anomalies that cause obstruction of the alimentary tract in the newborn. These other anomalies include chalasia of the esophagus, hiatus hernia, duodenal atresia, jejunal atresia, ileal atresia, pancreatic annulus, malrotation of the gut, intraabdominal hernias, and Meckel diverticulum. Pathognomonic features of pyloric stenosis include absence of bile staining of the vomitus and visible gastric peristaltic waves on abdominal examination along with the palpable pyloric mass. The diagnosis is commonly made clinically. An “olive” is sometimes palpated in the epigastrium just to the right of the midline. The diagnosis can be confirmed by abdominal ultrasound. Occasionally, an upper gastrointestinal (GI) series with barium is necessary.

Question 43

What are the metabolic problems in this newborn secondary to his disease?

Answer 43

Metabolic changes occur secondary to protracted vomiting and characteristically include a hypokalemic, hypochloremic alkalosis, as evident in this infant. Hyponatremia, although present, may not be manifested in serum value determinations because of severe dehydration. Compensatory respiratory acidosis is a frequent finding; it results from hypoventilation that may be marked and associated with periods of apnea. In severe dehydration leading to circulatory shock, the lack of adequate perfusion coupled with impaired renal and hepatic function may produce an entirely different picture of metabolic acidosis with hyperventilation, resulting in respiratory alkalosis. Therefore, depending on the severity and duration of vomiting and the type of fluid replenishment, one can encounter wide variations in arterial blood gas and electrolyte determinations. However, the most frequent findings are hypokalemia, hyponatremia, hypochloremia, and primary metabolic alkalosis with secondary respiratory acidosis. The renal response to vomiting is twofold. Initially, serum pH is maintained by the excretion of alkaline urine with sodium and potassium loss. Then, after the depletion of these electrolytes, the kidneys secrete acidic urine (paradoxic acidosis), which exacerbates the metabolic alkalosis. These findings are summarized in Table 40.1.

Question 44

What are the adverse effects of metabolic alkalosis?

Answer 44

An increase in pH results in shifting of the oxygendissociation curve to the left, thereby binding more oxygen to the hemoglobin and unloading less oxygen at the tissue level. This phenomenon assumes even more importance in newborns because at 3 weeks, they still have up to 70% fetal hemoglobin with an already low value of P50 (i.e., 20 to 22 mmHg). Respiratory compensation is affected by hypoventilation with increased potential for atelectasis as well as periods of apnea. Decrease in ionized calcium Increased potential for seizures

Question 45

How would you treat this infant?

Answer 45

Medical management of this infant with pyloric stenosis is acutely urgent. The principles of management can be grouped under the following three categories: supportive therapy to stabilize the patient, diagnostic tests to confirm the diagnosis and monitor therapy, and surgery as the corrective therapy. Supportive Therapy Circulatory support Correction of electrolyte imbalance Prevention of aspiration Fluids The infant with pyloric stenosis is hypovolemic and dehydrated secondary to persistent vomiting. Dehydration severity can varyfrom mild hypovolemia to circulatory shock. The following parameters are good indicators of dehydration severity: Physical appearance—skin turgor, parched mucous membranes, sunken fontanels, sunken eyeballs Blood pressure—decreased Pulse—increased Urine output—decreased Weight (birth and present) and weight loss Quantitative assessment of these parameters gives a fair estimate of the amount of total body fluid depletion. A widebore intravenous (IV) cannula should be placed and an infusion started immediately to correct the deficits and provide maintenance fluids. Electrolytes The patient is alkalotic, hypokalemic, hypochloremic, and hyponatremic and must be provided with necessary ions to replenish the deficit. Albumin or Ringer’s lactate may be used to treat the shock first. Next, the deficit should be corrected, 0.45% to 0.9% saline in 5% to 10% dextrose. Potassium (usually 40 mEq per L) must be added to this to correct hypokalemia and aid in the correction of alkalosis. However, potassium infusion should be withheld until satisfactory renal function is established. Fluid therapy should be continued until the infant is rehydrated and serum bicarbonate concentration is less than 30 mEq per dL, which implies that the alkalosis has been corrected. Prevention of Aspiration A nasogastric tube should be inserted to thoroughly empty the stomach, and the upper airway reflexes should be preserved. Diagnostic Tests To assess the severity of fluid and electrolyte derangement and to monitor therapy, the following should be evaluated:complete blood count, serum electrolytes, blood gases, blood urea nitrogen (BUN), electrocardiogram (ECG) (for marked hypokalemia). To confirm the diagnosis: barium swallow, ultrasound imaging Surgery Pyloromyotomy is the definitive treatment for these infants. Ramstedt pyloromyotomy through a right upper quadrant transverse incision has been the traditional treatment for hypertrophic pyloric stenosis. Recently, laparoscopic and circumumbilical approaches have been introduced as alternative methods to improve cosmesis, but concerns about greater operative times, costs, and complications remain. Surgery should be carried out early but only after the patient has been stabilized satisfactorily.

Question 46

How would you determine fluid replacement in a newborn, and what fluids would you use?

Answer 46

The general principles of fluid therapy are based on fluid maintenance, correction of deficits, and replacement of losses. Maintenance Fluids In the newborn, maintenance fluids are as follows: First 48 hours of life—75 mL/kg/day or 3 mL/kg/hr 2 days to 1 month—150 mL/kg/day or 6 mL/kg/hr 1 month onward (up to 10 kg)—100 mL/kg/day or 4 mL/kg/hr Estimation of the degree of dehydration in a newborn is shown in Table 40.2.The maintenance fluids take into account the fluid losses occurring normally through the kidney, bowel, skin, and lungs. At birth, the kidney is still undergoing maturation, and what may be called “a glomerular imbalance” exists. What it implies is that some mature glomeruli may be connected to the immature tubules and vice versa. Hence, the kidney is functionally limited at birth but undergoes rapid maturation during the first week of life. Electrolytes The newborn is an obligate sodium loser as well as a poor tolerator of excessive sodium overload. The maintenance electrolytes are as follows: Sodium—3 to 5 mEq/kg/day Potassium—2 to 3 mEq/kg/day Chloride—1 to 3 mEq/kg/day Correction of Deficits Deficits take into account the previous unreplaced losses because of a period of no intake by mouth and dehydration resulting from increased losses (e.g., from vomiting, diarrhea, and increased body temperature). The amount of deficit can be assessed by physical examination (Table 40.2), body weight loss, and hematocrit.

Answer 47

Electrolytes The newborn is an obligate sodium loser as well as a poor tolerator of excessive sodium overload. The maintenance electrolytes are as follows: Sodium—3 to 5 mEq/kg/day Potassium—2 to 3 mEq/kg/day Chloride—1 to 3 mEq/kg/day Correction of Deficits Deficits take into account the previous unreplaced losses because of a period of no intake by mouth and dehydration resulting from increased losses (e.g., from vomiting, diarrhea, and increased body temperature). The amount of deficit can be assessed by physical examination (Table 40.2), body weight loss, and hematocrit.

Question 48

How would you correct the metabolic alkalosis in this patient?

Answer 48

To correct the metabolic alkalosis in this patient, the underlying electrolyte derangements (hyponatremia, hypokalemia, and hypochloremia) must be corrected. We correct the deficits by using calculated volumes of 5% dextrose in normal saline or Ringer’s lactate solution, which helps to restore sodium and chloride mainly. Dextrose, 5%, with one-fourth strength normal saline may be used to provide maintenance fluids. Once renal function is established, potassium supplements are added to the infusion. Depending on the deficit, this therapy can requireanywhere from 12 to 72 hours. In severely alkalotic patients, HCl (hydrochloric acid) and NH4Cl (ammonium chloride) have been used to correct the derangement. However, we have rarely found it necessary.

Question 49

What causes a cardiac murmur?

Answer 49

Cardiac murmurs are caused by turbulent blood flow across cardiac valves or septal defects and are audible sound waves in the range of 20 to 2,000 Hz. Most murmurs in pediatric patients are normal or innocent, occurring in almost 50% of all schoolaged children but must be distinguished from those murmurs associated with significant structural heart disease. Auscultation is critically important in diagnosing these murmurs; however, echocardiography remains the gold standard.

Question 50

. How would you evaluate this patient preoperatively?

Answer 50

The following information is necessary in evaluating this patient: History Onset of illness, frequency and amount of vomiting, last feeding, diarrhea, urine output, activity of the newborn (active or lethargic), and birth weight Physical Examination Present body weight (to determine the weight loss), temperature, signs of dehydration (skin turgor, mucous membranes, fontanels,eyeballs, blood pressure, pulse, color, and volume of urine), muscle tone, and level of consciousness Laboratory Findings Complete blood count, electrolytes, BUN and blood sugar, urinalysis, and arterial blood gases Based on the data available, we can determine the fluid and electrolyte status of the patient and correct these accordingly to stabilize the patient for surgery and anesthesia.

Question 51

How would you evaluate a heart murmur?

Answer 51

Heart murmurs can be innocent or organic. By definition, innocent murmurs occur in the absence of structural or physiologic cardiac disease. The clinical diagnosis of a normal or innocent murmur should occur in the setting of an otherwise normal history, physical examination, and appearance. The presence of a family history of hypertrophic cardiomyopathy; congenital cardiac disease; or unexplained infant, childhood, or early adult death is particularly worrisome. The perinatal history of prematurity, maternal diabetes, drug or toxin ingestion, fetal distress, or clearly definable chromosomal disorders has particular cardiorespiratory relevance. The initial approach to the evaluation of the cardiovascular system should include an assessment of the cardiorespiratory system functionality as a pump and delivery system. An index of exercise or play capacity should be sought as a component of assessing growth and development. We would ask about exercise tolerance, shortness of breath, cyanotic episodes, growth (because congestive heart failure may manifest as failure to thrive), and symptoms of congestive heart failure.

Question 52

How would you differentiate between functional versus organic murmur?

Answer 52

Normal murmurs of childhood are composed of five systolic and two continuous types but never solely diastolic (Table 40.4). A functional murmur is usually soft, 1/6 or 2/6, and never associated with palpable thrill. Pathologic murmurs are usually louder, 3/6 or greater, and are associated with other cardiovascular pathologic features.

Question 53

What are the types of VSD? What type of shunt do they cause?

Answer 53

One common classification of VSD is based on anatomic location. Type I defects, or supracristal defects (5% of all VSDs), are outflow defects located above the crista supraventricularis just under the annulus of aorta. Type II defects, or infracristal defects (80% of all VSDs), are lower in membranous septum beneath the crista supraventricularis. Type III defects, or canal type (11% incidence), are inlet VSDs that accompany complete atrioventricular (AV) canal defects. They result from failure of the endocardial cushions to fuse.One common classification of VSD is based on anatomic location. Type I defects, or supracristal defects (5% of all VSDs), are outflow defects located above the crista supraventricularis just under the annulus of aorta. Type II defects, or infracristal defects (80% of all VSDs), are lower in membranous septum beneath the crista supraventricularis. Type III defects, or canal type (11% incidence), are inlet VSDs that accompany complete atrioventricular (AV) canal defects. They result from failure of the endocardial cushions to fuse.One common classification of VSD is based on anatomic location. Type I defects, or supracristal defects (5% of all VSDs), are outflow defects located above the crista supraventricularis just under the annulus of aorta. Type II defects, or infracristal defects (80% of all VSDs), are lower in membranous septum beneath the crista supraventricularis. Type III defects, or canal type (11% incidence), are inlet VSDs that accompany complete atrioventricular (AV) canal defects. They result from failure of the endocardial cushions to fuse.

Question 54

B.5. What are the risks of surgery and anesthesia in a patient with VSD? I

Answer 54

Infective endocarditis is a complication of most congenital cardiac anomalies, so the patient requires antibiotic prophylaxis. There is also risk of increasing the flow in the shunt or reversing the flow in the shunt, resulting from decreases in pulmonary vascular resistance causing hypoxemia and congestive heart failure or acute and persistent increases in systemic vascular resistance. Right ventricular infundibular hypertrophy may be present in the patients with a VSD. Normally, this is a beneficial change because it increases the resistance to right ventricular ejection, leading to decrease in magnitude of the left-to-right shunt. Nevertheless, perioperative events that exaggerate this obstruction to right ventricular outflow, such as increased myocardial contractility or hypovolemia, must be minimized. Therefore, these patients are often anesthetized with a volatile anesthetic. In addition, intravascular fluid volume should be maintained by prompt replacement of blood loss. During the anesthetic, a normal end-tidal carbon dioxide (CO2) should be maintained and routine air bubble precautions should be taken.

Question 55

How would you prepare this patient rapidly for emergency surgery? Is surgical intervention an acute emergency in this case?

Answer 55

Hypertrophic pyloric stenosis is a medical emergency and not a surgical emergency. Therefore, no newborn should be subjected to the additional hazards of anesthesia and surgery until stabilized medically.

Question 56

How would you prepare this patient for anesthesia?

Answer 56

Fluid and electrolyte replacement should be accomplished satisfactorily—this may take anywhere from 12 to 72 hours depending on the patient’s status. The next step is to empty the stomach through a wide-bore nasogastric tube, lavaging out the gastric contents and any leftover barium. Alternatively, an oralgastric approach allows for passage of a tube with wider lumen that ensures better stomach emptying. Premedication is usually atropine (0.01 to 0.02 mg per kg) IV or intramuscular if the patient does not have IV line.

Question 57

What induction–intubation sequence would you use?

Answer 57

These children should arrive to the operating room with an IV access. Standard monitors are placed. The stomach is emptied by inserting an orogastric tube (atropine may be used as premedication) to reduce the chance of regurgitation duringinduction. Because the stomach may not be completely emptied, a rapid sequence induction and intubation with cricoid pressure is highly recommended to minimize the risk of aspiration. Awake intubation may be accomplished in skillful hands in a lethargic neonate or in a critically sick infant. In most cases, however, neonates presenting for this procedure are fit and do not require awake intubation, which can be more traumatic.

Question 58

What are the anatomic characteristics of the airway in the newborn and how do they differ from those in the adult?

Answer 58

The special characteristics of the upper airway in the newborn are as follows: Nasopharynx—narrow nasal passages, obligate nasal breathers Oropharynx—large tongue, long and pendulous epiglottis Larynx—the distinctive features shown in Table 40.5
respiratory reserve can develop airway obstruction easily. The infant may present problems during intubation and tolerate airway trauma poorly. Comparative anatomy of the larynx and trachea in the newborn and the adult is shown in Table 40.5.

Question 59

How do you determine the size of an endotracheal tube in a pediatric patient?

Answer 59

The two parameters of endotracheal tube sizes are the tube length and diameter, depending on the age of the child, as shown in Table 40.6. However, these are approximate sizes and one must have one size bigger and one size smaller tube available when selecting any size tube. A simple way to remember these numbers is to know the sizes at newborn, 6 months, and 1 year. Between 2 and 12 years, the following guide may be used: Tube length from tip to incisor teeth (cm) = 11 + age in years Tube internal diameter (mm) = 4 + age / 4 French size (French) = 18 + age External circumference (French) = ID (mm) × 4 + 2
(French size means external circumference in millimeters, which equals π times external diameter; π = 3.1416.)

Question 60

What anesthesia system would you use and why?

Answer 60

We employ the circle system with a light circuit. The circle system is more advantageous because it maintains heat and humidification better and offers the freedom of choosing varying gas flows. The controversy about the increased resistance in the adult system is discounted by the fact that the respiration is assisted or controlled intraoperatively. Newer anesthesia machines use valves with much less resistance than older models. Dead space in these systems is no more than that of the Mapleson circuits.

Question 61

What are the advantages and the disadvantages of commonly employed nonrebreathing systems?

Answer 61

Commonly used nonrebreathing systems include Bain Breathing circuit (Mapleson D system) and Jackson-Rees modification of Ayre T-piece. They offer the following advantages and disadvantages: Advantages Minimal dead space No valves, low resistance Lightweight Reservoir bag to assist ventilation Good appreciation of patient’s respiratory exchange Disadvantages High flow of fresh gases required Low flows may allow rebreathing of gases without CO2absorption. Loss of heat and humidity because of high flow of cold, dry gases (Bain circuit allows some heating of inspired gases by surrounding fresh gas flow tubing with expired gas tubing.) Scavenging problems of waste gases

Question 62

How would you monitor this patient intraoperatively?

Answer 62

Monitoring should include blood pressure, ECG, rectal temperature, precordial stethoscope, pulse oximeter, and an endtidal CO2 monitor.

Question 63

How does the pulse oximeter function?

Answer 63

Commonly used pulse oximeters combine the scientific principles of spectrophotometric oximetry and plethysmography. Light of two wavelengths, 660 nm (red) and 920 nm (infrared), is emitted by a pair of light-emitting diodes (LED) and is passed through the tissue being measured to a photodetector. Because the saturated hemoglobin absorbs more blue light than unsaturated hemoglobin, the absorption of light for each color is an indication of the ratio of oxygen saturated blood to unsaturated blood. The pulsating vascular bed, by expanding and relaxing, creates a change in light-path length that modifies the amount of light detected. The microprocessor-controlled circuitry in the unit senses the pulsatile waveform, which is solely produced by the arterial blood, thereby allowing measurement of pulse rate and arterial saturation. The oximeter is reliably accurate in 60% to 100% saturation range.

Question 64

What factors affect the measurement of oxygen saturation by the pulse oximeter?

Answer 64

Dysfunctional hemoglobin, such as carboxyhemoglobin, sulfhemoglobin, and methemoglobin, can affect the accuracy of the oximeter. Intravascular dyes, such as indocyanine green and methylene blue, can also interfere with the accuracy of the instrument. Skin color, tissue thickness, venous blood, light intensity, and ambient light do not affect the accuracy of the instrument because they do not pulse.

Question 65

What are the complications that can occur in the postanesthesia recovery period?

Answer 65

The patient should be carefully observed for signs of respiratory depression and periods of apnea secondary to the combination of metabolic alkalosis, general anesthesia, and decreased body temperature. However, these infants do not appear to be at increased risk of postoperative apnea. Hypoventilation predisposes to atelectasis. These patients should be awake and responsive to avoid aspiration. Severe hypoglycemia resulting from depletion of liver glycogen stores has been reported 2 to 3 hours after surgery. Postextubation “croup” is a potentially dangerous complication in this age group.

Question 66

How would you treat postextubation “croup” in this infant?

Answer 66

Treatment of the potentially catastrophic postextubation laryngeal edema should be immediate, vigorous, and carried out under direct observation of the anesthesiologists. It consists of the following: Increasing inspired oxygen concentration (50% to 60%) Humidification of inspired gases Adequate hydration using parenteral fluids Light sedation to calm the patient and allow for cooperation in therapy Avoidance of any significant respiratory depression Epinephrine through handheld nebulizer and mask, 50 μg/kg/min of active isomer Racemic epinephrine (2.25%) 0.05 mL per kg diluted in 5mL saline solution delivered in 10 minutes Treatment should be given over 10 minutes and may be repeated every 30 minutes, as necessary. Rebound phenomenon may be expected approximately 2 hours after cessation of this therapy. Steroids—dexamethasone, 0.5 to 1 mg per kg IV Reintubation—if signs of deterioration or hypoxia appear Tracheostomy, if necessary—rarely, subglottic edema may be so rapid and so severe that tracheostomy is the only choice The age group most likely to manifest this complication is 1 to 4 years. Infants younger than 1 year are at most risk, mainly because of the size of their airway. Fortunately, an infant of this age is most amenable to early and vigorous intervention and should always be treated as an emergency requiring the continued presence of and evaluation by a physician who is adept at securing an airway for the child.