1. Fetal circulation is characterized by the presence of the following three main shunts:

The pulmonary bed has a high vascular resistance, partly from external compression (the alveoli are relatively closed and filled with fluid and the blood vessels are compressed). Therefore, only 10% of cardiac output (CO) circulates through the lungs from the right ventricle, which encourages growth and development of the pulmonary system and surfactant. The ductus arteriosus represents a low-resistance system because it is dilated secondary to a low PaO₂.

3. The ductus arteriosus initially constricts secondary to oxygenation, which functionally closes the foramen ovale. It will usually close permanently over the first few months; however, 30% will remain patent until age 30, and 20% remain patent thereafter.

4. Persistent pulmonary hypertension may be caused by hypoxia and acidosis, along with unknown factors. Persistence of pulmonary hypertension occurs mainly in the following three situations:

Persistent pulmonary hypertension will result in a Right → Left shunt through the foramen ovale and the ductus arteriosus. Treatment is dictated by the degree of respiratory compromise and underlying disease process, and may vary from permissive hypercapnia to conventional ventilator management and pressor support. Some argue that the risks for conventional ventilator management include barotraumas or volutrauma with increased chance of residual lung disease. Extracorporeal membrane oxygenation (ECMO) will theoretically allow the lung to rest and heal; however, it is associated with risks of bleeding secondary to heparin administration. Nitric oxide is being used experimentally to selectively vasodilate the pulmonary circulation, with promising results.

1. Signs/symptoms of chronic fetal hypoxia include the following:

Swallowed meconium ends up in the pulmonary system. This syndrome is to be differentiated from the passage of meconium due to fetal hypoxia during birth, which is quite thick and tenacious and mechanically obstructs the tracheobronchial system.

2. For newborn resuscitation for acute meconium aspiration during birth, routine oropharyngeal suctioning is recommended immediately at the time of delivery, but tracheal intubation and suctioning should be performed selectively, depending on the condition of the infant.

3. The four major reasons for the low renal blood flow (RBF) and glomerular filtration rate (GFR) seen in the neonates include the following:

The low pressure and high resistance result in a low RBF → low GFR. This leads to a limited ability to concentrate or dilute urine at birth.

4. By the time the normal full-term infant is 1 month old, the kidneys are approximately 70% mature.

5. Neonates are considered “obligate sodium losers” because immature tubular cells cannot completely reabsorb sodium under the stimulus of aldosterone. They will continue to excrete sodium in the urine even in the presence of a severe sodium deficit.

6. Neonates need a higher hematocrit (HCT)—approximately 35%—because of a high oxygen (O₂) demand and relatively limited ability to increase CO. A 3-month-old can easily tolerate an HCT of 25%.

7. Premature infants have problems with hypoglycemia, anemia, and sodium loss. Premature infants and neonates must receive full-strength, balanced salt solution for the replacement of third-space and blood losses during the perioperative period. Premature infants and those with bronchopulmonary dysplasia also have problems with increased lung water.

1. Anatomic differences of the neonatal head and airway, compared with those of the adult are as follows:

These differences make intubation altogether more difficult because of the problems with visualization and positioning.

Physiologic differences include the following:

These differences contribute to rapid desaturation during laryngospasm, breath-holding, or coughing on the endotracheal tube (ETT).

2. Choanal atresia is a life-threatening surgical emergency for infants because they are obligate nose-breathers. They are unable to coordinate the usual swallowing and breathing mechanics. Therefore, anything that obstructs the nares will compromise neonatal ability to breathe.

3. Level of glottis location:

4. An infant’s larynx appears anterior because it is more difficult to establish a line of vision between the mouth and larynx on laryngoscopic examination. When combined with the anterior-slanting vocal cords, the result is a more difficult laryngoscopic examination and intubation. Application of cricoid pressure will help visualize the neonatal larynx. Oftentimes this is more easily and accurately accomplished by the anesthesiologist utilizing the fifth finger of the intubating hand, than with the help of an assistant.

6. Closing volumes are the lung volumes at which alveoli close, resulting in the shunting of blood by a closed alveolus.

3. In neonates, O₂ consumption is three times greater than in adults. Therefore, respiratory rate must be three times greater, resulting in alveolar ventilation that is three times greater.

4. The clinical implication of a high ratio of minute ventilation to FRC is that there is a much more rapid induction of inhalation anesthesia, as well as more rapid awakening from inhalation anesthesia. More rapid induction of anesthesia also results from a higher percentage of neonatal body weight consisting of vessel-rich tissues.

5. Pliable ribs result in less efficient ventilation and a high energy price for the effort involved. This is one of the reasons for neonates to be susceptible to fatigue with airway obstruction.

6. The ability of the immature neonatal cardiovascular system to respond to stress is limited by the relatively low contractile mass per gram of cardiac tissue, resulting in a limited ability to increase myocardial contractility and a reduction in ventricular compliance. Any increase in CO must be accomplished by an increase in heart rate (HR).

7. The major cause of bradycardia in infants is hypoxia. The second major cause is vagal stimulation.

8. Limitations of the neonatal heart:

As the resting CO is normally near maximum, this leaves little reserve to access under periods of stress, or to provide flexibility during a pressure or volume change. The adult may have increased CO up to 300%, whereas the neonate can only increase about 30 to 40%. The neonates have immature baroreceptors that limit the ability to respond to hypotension. The baroreceptors would normally respond to hypotension with reflex tachycardia; this baroresponse is even more pronounced under anesthesia.

2. Ventilation should be controlled in infants under the following circumstances:

3. Awake tracheal intubation is the technique of choice in neonates under the following circumstances: