Pediatric Anesthesia The Practical and the Practicable
Anesthesia clinicians who work with children are at an interesting point in history-the junction of the practical and the practicable. Practices that are realistically based in our experience have to be blended with our current knowledge of the biological responses of children to surgery and an evolving body of research.
Pediatric cases can be the most fun and the most frightening for an anesthesia caregiver. The rewards for a case well done are great-personal satisfaction, a good outcome for a child, and relieved and thankful parents. The narrower margin for error due to great differences in oxygen consumption, carbon dioxide production, fluid requirements, as well as risks of hypothermia, laryngospasm, and rapid desaturation combine to demand a heightened awareness on the part of the anesthesia clinicians “telescoping” of vigilance-in an effort to prevent anesthesia accidents.
Ever since the first recorded anesthetic death, a healthy 15-year-old girl named Hannah Greener undergoing toenail excision under chloroform anesthesia in 1848, there has been consistent recognition of age-related risks in anesthesia. Studies in pediatric anesthetic mortality over a 30 year period from 1948 to 1979 reveal a mortality range of 3.3: 10,000 to 0 in 35,000 in a variety of surgical populations. Most studies consistently reflect a greater mortality for children. Keenan and Boynan in 1985 reported a threefold greater risk of cardiac arrest due to anesthesia (4.7: 1 0,000) in children less than 12 years old. Despite these studies, there is nevertheless a paucity of data on the “near-misses,” the close calls that clinicians have in daily practice when working with children. Beginning in 1954 at The Children’s Hospital of Boston, statistics reflecting more than 150,000 patients from 0-20 years of age reveals an anesthetic mortality of 1.8:10,000 in the 0-10-year-old group from 1954-1966, decreasing to 0.8: 10,000 in this same group from 1966-1978, and 0. 6: 1 0,000 in the 10-20-year-old group.
Through the 1960s, aspiration was a leading cause of morbidity and mortality. Changing attitudes toward routine tracheal intubation and respiratory care of children contributed to decreasing this risk. Hemorrhage was revealed as a major source of morbidity over the following decade, and again, changing attitudes in favor of more aggressive fluid therapy for children affected this statistic. Over the last decade, there has been a steady growth in the number and complexity of pediatric surgical patients, and our attention is focused more than ever on fundamental concepts of pediatric anesthesia, critical care, and specific monitoring needs, concepts which inevitably impact on quality, outcome, and safety.
Heat Loss Threat
It has been long-recognized that infants and children are at two distinct disadvantages when it comes to defense against heat loss. First, they cannot sustain body temperatures as well as adults can in cold environments, and second, their high ratio of surface area to body weight results in greater heat loss through the skin. Premature infants are even more vulnerable, requiring higher environmental temperatures to maintain normothermia. “Core” temperature monitoring (esophageal, rectal) may be lm sensitive to hypothermia than axillary or skin temperature, where a temperature change will register earliest. Early detection provides the opportunity to make a therapeutic intervention, preventing further heat loss.
For procedures involving limited surgical exposure, such as plastic surgery of the face and neck or single extremity procedures, conservative means of addressing heat loss may be employed-a warming blanket, wrapping of extremities, and increasing the room temperature to a tolerable limit. For major procedures involving body cavity exposure for long periods of time, heated humidification systems supply both humidity and heat to the breathing circuit, and to the blood traversing the pulmonary circulation. Low flows in a semi-closed circle absorption system (I liter or less total fresh gas flaw) or closed circuit techniques achieve a higher temperature in the airway and minimize the amount of cold dry gas delivered to the humidifier. Confidence with low-flow anesthesia is bolstered by the routine use of a mass spectrometer as well as an oxygen analyzer.
As younger babies and veterans of the Newborn Intensive Care Unit are presenting themselves for anesthesia and surgery, maturation of ventilatory control has become a very important issue. Consensus is that abnormal postoperative ventilatory control in conception should be anticipated following anesthesia. Such patients are not good candidates for day-surgery. Alternative anesthetic techniques such as regional anesthesia exist, and investigations in several centers are underway in follow-up initial reports of a dramatic decrease in postoperative mechanical ventilation following the use of spinal anesthesia in ex-premature-s.
A better understanding of the dynamics of the pulmonary circulation has evolved over the last decade. In addition to knowledge of the transitional circulation in the term newborn, an understanding of the pulmonary circulation is particularly important when caring for the critically ill baby who may revert to a few circulatory pattern when pulmonary vascular resistance increases, in the setting of acidosis, hypercarbia, and hypoxemia. Anesthesiologists play a vital role in influencing the adequacy of pulmonary blood flow through their intraoperative choice of anesthetic agents, regulation of the depth of anesthesia, fluid management, and ventilatory volume, rate, and pattern.
Depth of anesthesia, choice of agents, and the role of stress attenuation is receiving increased attention. The well-known inverse relation between MAC and age has been expanded to include additional pharmacologic considerations such as significantly reduced MAC requirements in the premature and age-dependent differences in blood and tissue solubility of potent inhalation agents. Very recent studies examining hormonal, metabolic, and hemodynamic aspects of newborn surgical stress suggest a relationship between intraoperative anesthetic management and perioperative outcome. Clinical studies over the last several years examining the pharmacodynamics of fentanyl and sufentanyl in children form the basis for rational alternatives to pure inhalation techniques, for both cardiac as well as routine surgical procedures. The attenuation of postoperative pain in children following the intraoperative use of methadone has been enthusiastically accepted by patients and parents.
More than half of anesthetic deaths are attributed to airway related mishaps such as failure to ventilate, esophageal intubation, ventilator disconnects, or accidental extubations. In several studies, perhaps 75% of such accidents are avoidable. There are few routine airway considerations in the care of children, because care needs to be directed to age-specific concerns. First, the tongue is relatively large, and occupies the majority of the mouth and oropharynx. The large head of the infant and small child eliminates the desirability of a pillow or blanket to bring the head and neck into a I ‘sniffing” position, but this often makes manipulation more difficult. The larynx of the infant and small child is high and anterior, with the narrowest portion of the airway in the cricoid region, which is non-expansile. Lastly, the distance between the bifurcation of the trachea and the vocal cords in the infant is no more than 4-5 cm. Confirmation of tracheal tube placement needs to be accomplished not only by auscultation (breath sounds can be heard in the head of a newborn) but by direct examination of chest expansion, a persistent humidified “flash” in the tracheal tube, an “anesthesia” vital capacity maneuver (chest wall compression and simultaneous auscultation of breath sounds through the tracheal tube) and capnography when in doubt.
Mask ventilation in children needs to be accomplished with minimal encroachment of the fingers on the soft tissue of the submental area; pressure here only displaces the soft tissues of the oral cavity closer to the palate, worsening intra-oral obstruction.
Straight blade laryngoscopes are preferable in children up to school age because of the relatively large head size and the higher and more anterior position of the larynx. In school age children, curved blade-s can be employed as effectively as in adults. Once passed through the vocal cords, the tracheal tube may “hang up” at the cricoid or may impact on the anterior tracheal wall, requiring release of exposure by the laryn8oscope in order to allow the tube to advance. Finally, again, once the tube is passed, care should be taken to confirm the position of the tube in mid-trachea, as moderate amounts of flexion or extension may result in endobronchial or supraglottic placement of the tube with surgical positioning. Flex and then extend the patient’s head while listening to breath sounds, then tape the tube to the most immobile portion of the face (the maxilla and zygoma) unless other considerations are present.
Very Rapid Changes
All anesthesiologists during training and in practice develop a feeling for the different tempo that characterizes care for children. The rapidity of changes in oxygenation, adequacy of the airway and heart rate are traditionally monitored in real-time by “the experienced eye, ear, and hand” through stethoscopy and palpation, in addition to the usual non-invasive monitors. Direct observation through the senses of the clinician has, in the past, often been faster that available monitors, allowing rapid correction of recognized problems. Pulse oximetry and capnography now allow confirmation and quantification of real-time clinical senses, and augment the anesthesiologist’s ability to make fine adjustments or potentially life-saving interventions. Routine use of capnography has enabled early detection and intervention for malignant hyperthermia crises and venous air embolism. invasive vascular monitoring, particularly in the sick newborn, provides guidance on volume and metabolic status, and is part of the increasingly aggressive attitude toward early diagnosis and intervention in pediatric anesthesia and critical care.
The nature of pediatric practice is changing in very fundamental ways due to economic influences. Particularly in pediatrics, this impacts on the amount of time available to establish rapport with the child and family in the face of 60% day-surgery or day-admissions in many institutions. The patient and family have often been seen by another member of the department, on a different day in the Pre-Op Clinic, or may not have been seen at all until the day of surgery. When anesthesia care can be so de-centralized and out of control of the clinician with primary responsibility, a great deal of reliance is placed upon consistency and completeness of a colleague’s preoperative evaluation. Clear communication is essential under such circumstances, in addition to a investment of time for the sake of rapport with the parents and patient, lest we slip back to the image of the “faceless” practice of anesthesia.
Pediatric surgeons and pediatric anesthesiologists in tertiary care institutions are continuing to accept the challenges of caring for ever-younger, increasingly fragile patients, as well as & survivors of early medical and surgical interventions who present with subsequent “routine” surgical problems. With the combination of the “practical” approaches developed through experience and the “practicable” approaches based on current research and technical advances, and increased awareness of causes of anesthesia accidents, we hope to continue to tailor care to each patient’s needs, establishing parity with all of the other anesthesia subspecialties, against the backdrop of in increasing ability to provide for quality and safety when anesthetizing children.
Dr. Holzman is Clinical Director, Department of Anesthesiology, Children’s Hospital, Boston.