PEDIATRICS FOR THE ANESTHESIOLOGIST

Apnea of Prematurity

Periodic breathing or frank apnea, defined as cessation ofrespiratory airflow, is common in premature infants before 36 weeks post conceptual age. For a variety of reasons, infants that undergo surgery and anesthesia are at increased risk. Apnea associated with desaturation and/or bradycardia may be life threatening to these infants.

Risk factors for apnea include hypothermia, use of narcotics, airway obstruction and hypoxemia. Anemia, GE reflux and hypoglycemia have also been associated with an increased incidence. Chronically ill infants may be treated with theophylline or caffeine to prevent apnea. Many of these babies are monitored while they are at home.

The anesthetic for a premature infant should, ideally, be designed around their immature respiratory center and the probability of postoperative apnea. Short acting inhalational anesthetic agents, regional anesthesia rather than narcotics and increased attention to maintenance of normothermia, normoglycemia and a normal hematocrit reduce the probability of apnea. Treatment of at risk infants with methyl-xanthines such as caffeine or theophylline is extremely effective in reducing the incidence of apnea. Caffeine is available as a sodium benzoate derivative. Administration of 20 mg/kg as a slow bolus will provide several days of protection against apnea.

The infant that has a history of severe apnea and has undergone a substantial operative procedure requiring blood replacement should probably remain ventilated postoperatively until homeostasis is attained. Likewise, neonates less than 2500 grams that are cold or metabolically unstable should remain intubated after the surgical procedure.

Infants less than 52 weeks post conceptual age should be monitored after general anesthesia for at least 12 hours.

Asthma

Fifteen percent of children in the US will wheeze at some pointduring their development. Children from families that smoke and children that have been infected with the respiratory syncytial virus as infants are at increased risk. Usually mild and treatable with beta-adrenergic inhalers asthma may be significant, especially if the family fails to reduce the load of bronchial irritants in the home. Children from homes in which cigarettes or other tobacco products are used are at an especially high risk. Inhaled steroids and combination therapy – inhaled bronchodilators and steroids - for children with chronic rather than episodic disease is considered a standard. Systemic steroids are contraindicated unless bronchospasm is very severe because of the impact on bone growth.

The child with significant asthma represents a problem for the anesthesiologist because of the irritability of their airways and the dramatic bronchospastic response to foreign body placement or the useof irritating gases such as desflurane. Sevoflurane has profound bronchodilatory properties and is the mainstay for maintenance of anesthesia. For children that are unresponsive to more conservative measures aminophylline is still available as is epinephrine.

Obstructive sleep apnea

OSA presents in obese children and may be ameliorated by airway surgery, including tonsillectomy. Many of these children are hypoxemic at night and the worst will have elevated pulmonary artery pressures leading to right heart failure. These children are very sensitive to narcotics after surgical procedures often having twice the sensitivity to narcotics as a normal child. It is important to note that, given the widespread obesity that is now seen in the pediatric population, the number of children that have OSA greatly exceeds the number that have been diagnosed. Children with a BMI over 35 are at high risk. If the same child has hypertension it really clinches the diagnosis.

Obstructive sleep apnea is a problem because of the sensitivity of these patients to narcotics and other sedatives. A common, and sometimes lethal, combination of a fentanyl patch for postoperative pain control and promethazine to control nausea will produce excessive somnolence. For this reason, the ambulatory treatment of these patients must be reserved for patients with home support that is impeccable. The sensitivity of the central nervous system to the inevitable change in hydrogen ion concentration is not resolved immediately by reducing the airway obstruction. This requires continued vigilance in the postoperative period.

Retrolental Fibroplasia

RLF continues to be a common clinical entity despite ouknowledge of the pathophysiology, because of the large number of very premature infants that are resuscitated. It is a response of the native vasculature of the retina to extreme changes in arterial oxygen levels.

Hypoxia followed by relative hyperoxia produces neovascularization of the retina and may produce subsequent blindness. Untreated neovascularization will produce retinal detachment if untreated. This entity can be treated with cold probe and laser. The utilization of high levels of oxygen during anesthetics and surgical procedures in the premature is contraindicated if it can be avoided.

Bronchopulmonary Dysplasia 

The resuscitation of infants less than 25 weeks of gestation, despite the use of prenatal steroid compounds to mature the lungs of the fetus and exogenous surfactant for postnatal use, has produced a whole new generation of infants with chronic lung disease. Because the final development of alveoli off of terminal bronchioles doesn’t begin until after thirty weeks, the effect of chronic ventilation and high levels of inhaled oxygen used in the treatment of respiratory distress syndrome is a serious inflammatory response, which resolves with fibrosis – Bronchopulmonary Dysplasia (BPD).

Many of these infants have well-established pulmonary hypertension that is exacerbated by events that surround a surgical procedure. Pain, hypoxemia, cold stress, or acidosis will aggravate the already increased pulmonary artery pressures and escalate V/Q mismatch producing profound hypoxemia. Because the right heart is under continuous stress, situations such as this with low levels of arterial oxygen and high PA pressures, produce right heart failure, which is, of course, the most common cause of left heart failure.

Infants with BPD vary in the amount of support that they require after the acute insult. Some go home on nasal cannula oxygen and diuretics. Many will leave the hospital accommodated to arterial carbondioxide levels significantly above the norm; some greater than 60. For these infants, the balance of intravascular volume sufficient to support the cardiac output and grow but not so much that pulmonary interstitial water is increased is critical. For some the balance is so tenuous that postoperative ventilation is the only appropriate method of management for any surgical procedure more extensive that PE tubes.

Seizure disorders

Children that have chronic seizure disorders are routinely placed onanticonvulsants and most are monitored for the therapeutic level of the drug. Efficacy of the regimen can be assessed by asking about the most recent level and the last time that the child had a seizure. For children that have seizures, which are particularly difficult to control, some provision for assuring the administration of the drug during the NPO period must be made.

Most of the anticonvulsants have an impact on the metabolism of anesthetic drugs. Many will accelerate metabolism via cytochrome P450 reducing the beta half-life of action. Muscle relaxants are especially prone to this activity.

Valproic acid is commonly used for control of complex partial seizures. Massive bleeding associated with the inhibition of platelet function has been reported.

Sickle Cell Anemia

Sickle cell anemia is still common in the United States.Predominately present in African Americans, it is also seen in Asians, Hispanics and people from the Indian subcontinent. It is the most commoninherited genetic disorder in African Americans and the prevalence is about 1 in 400 live births in that population. An understanding of the pathophysiology over the last twenty years has reduced the number of children that present with severe sequelae such as stroke, pulmonary infarction and septic shock. The use of hydroxurea to produce myelosuppression and increase the production of Hgb F has been effective in cutting the number of painful crises in most children by one- half.

Red blood cells sickle in affected children when they are subjected to acidosis, hypoxia, or cold stress. Even the placement of a tourniquet for the surgical procedure can put the child at risk. Red blood cells that have an abnormal configuration do not carry oxygen efficiently and will be rapidly eliminated from the circulation by the microvasculature, or the spleen. Most children that are homozygous for S hemoglobin will have infarcted their spleen by the time that they are four years old. After this they are at increased risk for bacteremia and septic shock. Currently children that have good pediatric care receive pneumococcal vaccine early in their lives. Many of these children are also on prophylactic antibiotics.

Children with sickle cell disease may present with a history of stroke or multiple episodes of lung infarction. These children may be on a hypertransfusion protocol in order to reduce their risk of a crisis. Those children that have not had any of these events and have been followed closely by knowledgeable clinicians have been shown to tolerate surgical procedures that are of short or intermediate duration, without tourniquets, with simple transfusion to a hematocrit of ten. For complicated patients, in addition to making every effort to avoid a sickle crisis, the level of Hgb S should be reduced to a level below 20% by exchange transfusion.

Sickle cell disease and the other hemoglobinopathies that afflict children and adolescents produce acute and chronic pain and represent a management dilemma for pediatricians and hematologists. Issues related to narcotic addiction, pseudo-addiction and tolerance are often encountered. Acute, severe pain, the presence of chronic disease, inevitable disagreements about the need for narcotics between patient and practitioners, and the lack of available resources for psychological and social support interact to reduce the possibility of successful long- term management.

Painful crises in patients with SS disease begin early in life, sometimes in infancy. The inability of a preverbal infant or child to communicate pain should not be taken as evidence that pain is not present. On the other hand, the natural history of painful crisis in children with sickle cell is variable. A substantial number of patients will have few hospitalizations for painful crisis while a few will require intensive medical therapy to prevent painful crisis and remain functional. Frequently, patients with sickle cell refer themselves to an emergency room for treatment of a painful crisis. Because these healthcare providers do not know them, they may question the need for aggressive treatment. The anxiety that surrounds the possibility of lack of treatment accelerates the desire to be treated. In adolescents, faced with the possibility of not being treated at some point in the future, drug- seeking behavior – pseudo addiction - becomes a part of their life. In part because of this circumstance, ER treatment of painful crisis should be discouraged or an accepted method for tracking the patient (database demonstrating history of past hospitalizations) should be established. Many states now track narcotic compounds that are prescribed. This too will assist as it provides some reassurance to the health care provider. A comprehensive program to provide psychological and social support for these patients and their families will provide them a measure of confidence that they are being heard.

Commonly, when care is not coordinated, or when the patient doesn’t avail themselves of comprehensive services, no health care provider can feel that they understand the patterns of illness for a given patient. When this happens, and the patient presents with painful crisis, physicians may believe that the patient falls within a group of chronic drug seeking individuals that may divert narcotics. Subsequently, the desire for narcotics increases and the cycle of pseudo addiction begins. If the patterns of pain are known and if there is ongoing support, there is the opportunity to reduce drug-seeking behavior and decrease or shorten hospitalizations for painful crises. This should be one goal of a comprehensive program and, to some extent, the ongoing treatment of the patient may need to be contingent on close follow up and involvement with all of the resources that are available for support.

Cystic Fibrosis

CF is the most common heritable disease in the Caucasian population with an incidence of 1: 3500 live births. It is an autosomal recessive trait that produces abnormalities in the CFTR gene. Though there are many permutations of this abnormality, in patients with the classic form of the disease, the abnormality affects the protein that acts as a chloride channel at mucosal surfaces. Under normal conditions, as chloride exits a mucosal cell, water follows and mucous is thinned. In the patient with CF, mucous is thick and reduces mucociliary transport – a primary method for carrying debris out of the lungs. In addition, though it is thought of as primarily a pulmonary disease, evidence of the disorder can be found in the gut, liver, the exocrine pancreas and the skin. For the anesthesiologist, however, it is the pulmonary complications that are most problematic. Current therapy for pulmonary CF includes bronchodilators, inhaled antibiotics and adjuvants used to break up the tenacious secretions that inhabit the airway. Of note, many adolescents with CF are substantially underweight and this affects their ability to mount a substantial stress response.

Patients with cystic fibrosis may have pulmonary hypertension and heart failure, diabetes, anemia, GE reflux, malabsorption as well as abnormalities of the sweat glands. It is important to determine the severity of these secondary processes, as they will play a large role in morbidity and mortality associated with a surgical procedure.

Diabetes Mellitus

The incidence of diabetes has risen in the past ten years as a consequence of increasing obesity in children and adolescents. Most of these patients have Type 2 diabetes and only a few require insulin. For those patients, mostly adolescents, with brittle autoimmune Type 1 a preoperative plan for diet, insulin, and glucose control is important. 

Patients that are facing complex procedures such as scoliosis repair and cardiac surgery should be monitored closely during the entire perioperative period to attenuate hyperglycemia but more important to prevent hypoglycemia. Blood glucose levels below 100 that are produced by tight control with bolus or infusion insulin have not been shown to be effective in reducing postoperative complications and profound hypoglycemia has been shown to increase the risk of stoke and death dramatically. 

Patients with concurrent infection and diabetic ketoacidosis that come to the operating room for surgical drainage are at risk for cerebral edema. Patients that have rapid resuscitation and reduction in glucose levels have an increased risk for this complication.

Elderly patients with type 2 diabetes occasionally present with hyperosmolar, nonketotic coma. This is very rare in children and adolescents.

The Child with a Runny Nose

Children come to the operating room for procedures and often have a concurrent upper respiratory tract infection. Many of these children are below the age of five and require these procedures because of preexisting pathology in the pharynx and larynx. It has been assumed in the past that all of these patients should be canceled and rescheduled for a later time. The problem with that philosophy is that any five year old will have 2 – 4 discrete episodes of URI in any given year. Because of this any surgical procedure scheduled at any particular time during the high-risk period will cross paths with a URI. Because of this pediatric anesthesiologists have rethought the philosophy of treatment of these children to allow children that have mild symptoms to have the procedure. 

Each child should be considered independently, and parents should be informed about the risks of anesthetizing a wet airway, but, in general, if a child has clear rhinorrhea, is afebrile, and does not appear to be toxic, the procedure should be able to go forward. Patients that appear ill, are febrile, have green mucoid airway secretions, or have airway symptoms such as croup or wheezing should be further evaluated and probably should come back another day.

Malignant Hyperthermia

MH is a pharmacogenetic disease process that is characterized by a profound increase in cellular metabolism produced by release of intracellular calcium in striated muscle. This condition is related to an aberration in a ryanodine receptor in the muscle cell wall and is usually related to the administration of triggering agents such as volatile anesthetic agents and the depolarizing muscle relaxant succinylcholine. MH has also been associated with heat stress in experimental models and similar clinical circumstances have been seen in humans.

The initial treatment of MH is with dantrolene, a muscle relaxant related to diphenylhydantoin.  Patients with a family history of MH should be managed with TIVA rather than inhalational anesthetics. Children below the age of ten are not considered appropriate for definitive muscle biopsy.

Perioperative Apnea in Post Premature infants

Infants born before 37 weeks are considered to be premature. One important part of their immaturity is the ability to modulate control of respiration and respond appropriately to levels of arterial oxygen and carbon dioxide. Breathing patterns of these infants are variable and it is common to observe pauses in ventilation in an otherwise normal child that is not related to administration of narcotics, anesthetic agents, or obstruction of the airway. Respiratory pauses up to 20 seconds in length are common. 

In patients that have been anesthetized, or have been exposed to respiratory depressants such as narcotics, frank apnea with bradycardia and coincident hypoxemia is a common finding. Characteristics that predispose include anemia, hypothermia, hypocalcemia, hypoxia, and hypercarbia, but the most important aspect of the patient’s history that predisposes is post conceptual age.