Respiratory Monitoring During Pediatric Sedation: Pulse Oximetry and Capnography Jay A
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PEDIATRICDENTISTRY/Copyright © 1988 by The AmericanAcademy of Pediatric Dentistry Volume10, Number2 Respiratory monitoring during pediatric sedation: pulse oximetry and capnography Jay A. Anderson, DDS, MDWilliam F. Vann, Jr., DMD,MS, PhD Abstract Routine Respiratory Monitoring: A major concernin pediatric dentistry is maximizingrisk The Problem managementthrough optimal monitoring of respiratory What should constitute routine respiratory monitor- function during sedation techniques. This article examines ing for all pediatric patients undergoing conscious or the problemsinherent in respiratory monitoring in sedated deep sedation long has been a topic of debate. In 1985 the pediatric dental patients, the traditional methodsof respira- American Academy of Pediatrics and the American tory monitoring, and new technologies which are useful in Academyof Pediatric Dentistry jointly adopted the optimizing respira tory monitoring. The authors discuss tran- Guidelines for the Elective Use of ConsciousSedation, Deep scutaneous oximetry and pulse oximetry as possible monitors Sedation, and General Anesthesia in Pediatric Patients of oxygenation, and capnographyas a possible monitor for (1985). These guidelines require the use of a precordial apnea, airway obstruction, and developing hypoventilation. stethoscope, visual assessment of the child’s color, continuous monitoring of heart and respiratory rate, Risk management involves striving for maximum and the frequent assessment of head position to ensure patient safety and should be a primary concern to all a patent airway. Visual assessment of chest and abdomi- dentists and physicians practicing conscious or deep nal movementto monitor for effective respiratory ex- sedation. A major component of risk management for cursions is implied in the guidelines. These standard sedation or anesthesia involves physiologic monitor- methods should be used routinely to assess the rate, ing. Monitoring may be defined as continuous observa- depth, and adaquacy of respiration. tion of data from specific organ systems to evaluate the While these time-tested methods are essential, each status of physiologic function. The purpose of monitor- has serious practical limitations. Visual assessment of ing is to permit prompt recognition of any deviation patients’ respiratory excursions, color, and general from normal, so corrective therapy can be instituted appearance requires close and continuous attention. For before morbidity ensues. Ideal monitors should be pediatric dental sedation, the sedationist is usually also continuous or "real time", rapidly responsive, noninva- the operator. Airway assessment is very difficult be- sive, accurate, dependable, convenient, and affordable. cause attention must be given to performance of de- The principal systems monitored during pediatric seda- tailed and sophisticated dental procedures. Even with tion are the central nervous, cardiovascular, and respi- constant attention, shallow respirations of a sedated ratory systems. child can be difficult to assess because of clothing, This discussion reviews monitoring of the respira- drapes, and restraining devices. Breath sounds may be tory system. There is compelling evidence that this is the difficult to hear with the precordial stethoscope, espe- most important system to monitor for pediatric pa- cially with the noise of the dental equipment. One is tients. Furthermore, major scientific advances are being often left to assess respiratory function by the patient’s made in this area which should be understood by all color and vital signs. In children this is a physiologically who use sedation and/or anesthesia, especially those dangerous method for respiratory monitoring, because whotreat pediatric patients. these changes do not occur until late in the process of 94 RESPIRATORY MONITORING FOR PEDIATRIC SEDATION: Anderson and Vann respiratory compromise when it may be too late to In summary, hypoxemia is a serious problem in the prevent an emergency situation leading to morbidity. sedation of pediatric dental patients and none of the time-honored methods of monitoring these patients is Hypoxemia reliable as a warning of hypoxemia. We conclude that Hypoxemia has been shown to be the leading cause there is a critical need for moreprecise monitoringof the of morbidity and mortality during anesthesia (Bendixin respiratory system during pediatric sedation. Specifi- and Laver 1965). Hypoxemiais defined as a low partial cally, monitoring should detect respiratory depression pressure of oxygen in the blood and may be caused by early, to prevent hypoxemiafrom occurring, rather than such conditions as a failure of oxygen supply, pulmo- detecting physiologic changes that occur as a result of nary disease, cardiovascular collapse, hypoventilation, hypoxemia. apnea (cessation of breathing), or airway obstruction. Hypoxemia develops readily during deep sedation Respiratory Monitoring: The Questions techniques used for dentistry in young adults (Dionne et al. 1981). It also has been shownto be the leading cause There are two principal questions to be answered by of death in two studies that focused specifically on respiratory monitoring: (1) Is the patient breathing? dental sedation and anesthesia in adults (Tomlin 1974; (i.e., Is apnea or airway obstruction present?); and (2) A1-Kishaliet alo 1978). ventilatory exchange adaquate? (i.e., Are oxygen and Evidence is overwhelming that hypoxemia is also carbon dioxide being exchanged adaquately?). For the major complication in the sedation of pediatric continuous intraoperative monitoring during sedation, dental patients. Goodson and Moore (1983) reported these two questions should be addressed separately. several cases of life-threatening reactions after sedation for pediatric dental procedures. Although morbidity Monitoring Apnea or Airway Obstruction and mortality were induced by drug overdosage, close Several monitoring devices have been suggested to scrutiny of the cases reveals that the commonfactor that assess whether or not the patient is breathing (exchang- led to death or severe morbidity was respiratory failure ing air). These include capnography, rib cage/abdomi- leading to hypoxemia. nal wall plethysmography, and nasal thermisters. Each The development of hypoxemia in pediatric dental will detect the presence or absence of normal air ex- patients is almost certainly more subtle and insidious change more precisely than observation or auscultation than most practitioners realize. Mooreet al. (1984) re- alone. In studies on the detection of sleep apnea, Keener ported that 25% of children sedated with 60 mg/kg and Phillips (1985) found the use of capnography to chloral hydrate and 50% nitrous oxide/oxygen could more reliable than the nasal thermister. Rib cage/ab- not maintain a patent airway. Houpt et al. (1985) re- dominal respiratory inductive plethysmography meas- ported partial airway obstruction and transitory reduc- ures a difference in electrical impedance between sur- tions in respiration in a study that compared several face electrodes placed on the chest or abdominal wall sedation regimens, including one with as little as 50 during respiratory movements, generating a respira- mg/kg chloral hydrate and 50% nitrous oxide/oxygen. tory waveform. Because chest and abdominal wall Recently, Mueller et al. (1985) evaluated oxygenation movements continue and often become exaggerated in sedated pediatric dental patients. Oxyhemoglobin during airway obstruction, this technique will not de- saturations below physiologically acceptable levels tect early obstruction reliably (Peabodyet al. 1979). were reported for a high percentage of children sedated The most promising technology for detection of with alphaprodine or with chloral hydrate plus 50% these respiratory problems appears to be capnography nitrous oxide/oxygen. This finding was significant which is the continuous analysis of the carbon dioxide because it demonstrated positively that children be- content of respired gases. Capnography recently has come hypoxemic even when supplemented with an risen to the forefront as a means of detecting apnea and enriched oxygen mixture. Furthermore, despite epi- airway obstruction. The simplest capnographs merely sodes of hypoxemia, there were no detectable changes detect the presence of carbon dioxide as CO2 is exhaled in vital signs or mucosalcolor (Mueller et al. 1985). This and therefore will indicate whether or not the patient is finding is not surprising because the signs and symp- breathing. This type of unit is the least expensive, but toms of hypoxemia often do not become evident clini- provides the least information. The more commonly cally until very low and dangerous levels of oxygen used capnographs are more sophisticated in that the tension develop (Manninen and Knill 1979). Expert carbon dioxide detected is also quantified. This proves observers are unable to recognize hypoxemia consis- to be a valuable source of additional data regarding tently until the arterial oxygen tension (PaO2) falls ventilatory adaquacy. below 40 mm Hg (Comroe and Bethelho 1947). The In capnography gas is suctioned continuously from normal value for PaO2 when breathing room air is 90- the airway for analysis. A waveform(Fig I -- next page) 100 mmHg. is produced that maybe analyzed to detect the presence Pediatric Dentistry: June, 1988 - Volume10, Number2 95 tube was inserted through a small needle puncture in NORMAL CAPNOGRAM the nasal cannula and threaded up the nasal prong so that the sampling