Monitoring the Procedural Sedation Patient: Optimal Constructs for Patient Safety

Abstract: Although emergency department procedural sedation in children is widely practiced, it is not without risk. Appropriate vital sign monitoring has been identified as an essential mechanism to reduce risk associated with procedural sedation. We describe the evolution of guidelines for procedural sedation monitoring in children and review monitoring principles, common adverse events, current monitoring modalities, future directions, and emerging monitoring technologies.

Keywords: procedural sedation; monitoring; children; adverse events; capnography; oximetry; bispectral index

Monitoring the Procedural Sedation Patient: Optimal Constructs for Patient Safety Joshua Nagler, MD, Baruch Krauss, MD, EdM

P Division of Emergency Medicine, Children’s Hospital Boston and the Department of Pediatrics, Harvard Medical School, Boston, MA. Reprint requests and correspondence: Joshua Nagler, MD, Division of Emergency Medicine, Children's Hospital Boston, 300 Longwood Ave, Boston, MA 02115. [email protected]

1522-8401/$ - see front matter © 2010 Elsevier Inc. All rights reserved.

rocedural sedation and analgesia (PSA) are essential parts of pediatric emergency medicine practice and the standard of care for relieving anxiety and pain associated with diagnostic and therapeutic procedures in children.1,2 Over the past 25 years, a robust body of literature supports the safety and efficacy of emergency department (ED) PSA in children. However, such pharmacologic interventions are not without risk. Monitoring modalities, both interactive and mechanical, are an integral part of procedural sedation and are the foundation for safe practice. In this article, we discuss the current state and future directions in PSA monitoring in children.

HISTORICAL BACKGROUND In the mid-1980s, reports of adverse outcomes and even fatalities associated with the practice of pediatric PSA in the outpatient setting began to emerge. In response, the American Academy of Pediatrics (AAP) published in 1985 the first set of guidelines for procedural sedation in children, with the aim of minimizing risk associated with this practice.3 Continued reports of unfavorable outcomes led to revisions of the AAP recommendations, as well as the development of similar guidelines in multiple

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other specialties practicing PSA.4-7 In addition, investigations into risk factors and root causes of these incidents were performed.8,9 From these studies, inadequate and inconsistent physiologic monitoring was identified as a risk factor for adverse events, prompting standardization of practice. Recommendations regarding what constitutes appropriate monitoring during PSA have evolved. During the early years of pediatric PSA, the primary monitoring modality was direct clinical observation. The first AAP guidelines mandated “continuous monitoring of heart rate, respiratory rate, and blood pressure, and visual monitoring of the patient's color.”3 The AAP revision in 1992 added “continuous quantitative monitoring of oxygen saturation (e.g., pulse oximetry)” to the prior recommendations.10 The most recent iterations of published guidelines from pediatrics as well as anesthesia and emergency medicine have introduced ventilation monitoring with capnography in their recommendations.5,6,11 Table 1 summarizes the current guidelines from the American Society of Anesthesiologists (ASA), AAP, and American College of Emergency Physicians (ACEP). In each, varying levels of monitoring are recommended, depending on depth of sedation. For minimal/mild sedation (anxiolysis), monitoring is not routinely recommended. Because respiratory events are of greatest concern and can be appropriately detected, recommendations uniformly endorse continuous oximetry for moderate and deep sedation. Ventilation monitoring with capnography is suggested by all organizations, with an emphasis on its use during deep sedation and as an adjunct when direct visualization of respiratory

pattern is not feasible. Finally, hemodynamic monitoring with electrocardiography (ECG) and blood pressure is less strongly advocated, largely because there is a paucity of evidence supporting the benefit of this practice.

MONITORING PRINCIPLES The implementation of guidelines has been demonstrated to reduce the risk of adverse events related to PSA. 12 Effective sedation protocols include the following elements: presedation assessment, trained personnel, appropriate equipment, continuous patient monitoring, documentation, and discharge criteria. Focusing specifically on monitoring, several general principles can be abstracted from the various procedural sedation guidelines and are discussed here.

Tailoring Monitoring to Pharmacopeia The rational approach to patient monitoring is based on the adverse event profile of the PSA agents. The overwhelming majority of adverse events associated with sedation are respiratory-related, including respiratory depression and hypoventilation, central and obstructive apnea, and hypoxia.13 Hemodynamic compromise is rare in children with routine doses of agents, with the exception of propofol in which transient hypotension is well described.14,15 Therefore, monitoring should focus on ventilation and oxygenation, with hemodynamic monitoring having the greatest importance when using propofol.

TABLE 1. Current guidelines for hemodynamic and respiratory monitoring during different levels of procedural sedation. Guidelines ASA

AAP

ACEP

Level of Sedation Mild Moderate Deep Mild Moderate Deep Mild Moderate Deep

Continuous ECG

BP

– Should be used if comorbidity Should be used – Should be used Should be used No evidence of benefit if no cardiopulmonary disease

– Q 5 min Q 5 min – Intermittent Q 5 min

Continuous Oximetry – Should be used Should be used – Should be used Should be used May not be necessary Should be used Should be used

Capnography – Consider, if separateda Consider – Encouraged, especially if difficult to observe a – Consider Consider

BP indicates blood pressure; AAP indicates American Academy of Pediatrics; ACEP indicates American College of Emergency Physicians; ASA indicates American Society of Anesthesiologists; ECG indicates electrocardiogram. a

For example, in computed tomography/magnetic resonance imaging scanner, or in darkened room.

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Depth of Sedation Physiologic monitoring should vary, commensurate with the anticipated level of sedation. By definition, minimal sedation (anxiolysis) leaves ventilatory and cardiovascular functions unaffected, suggesting little need for cardiorespiratory monitoring. In contrast, during deep sedation where spontaneous ventilation “may be inadequate” and cardiovascular function is not always maintained, more extensive monitoring is required.6 The challenge, however, is that depth of sedation reflects a continuum, rather than discrete categories with clearly discernible boundaries. As a result, children may pass into deeper levels of sedation than originally targeted. 16,17 To accommodate this potential “sedation drift,” monitoring recommendations tend to be uniformly conservative to capture potential risks associated with deeper levels of sedation than planned.

Preoxygenation Although recommendations regarding preoxygenation with PSA vary, pediatric patients are likely to benefit from this practice. Children, particularly infants and toddlers, are more susceptible to rapid desaturation than their adult counterparts. Smaller functional residual capacity relative to total lung volume results in a decreased oxygen reservoir, whereas increased metabolic rate produces higher oxygen consumption. 18 The result is a more precipitous decline in oxygen saturation during hypoventilatory or apneic periods. Preoxygenation can maximize intrapulmonary oxygen stores and help offset this risk.19 However, recent studies in sedated adults did not demonstrate a clear reduction in episodes of desaturation.20,21 In addition, concern has been raised that supplemental oxygen delivery may delay the onset of hypoxemia in patients with respiratory compromise. As a result, based solely on oximetry, the detection of hypoventilation and subsequent response may be delayed. To accommodate this limitation, direct observation and the use of capnography can be used to concomitantly detect ventilatory changes when supplemental oxygen is being administered. With this qualification, ASA and ACEP guidelines currently support the use of supplemental oxygen administration for patients undergoing moderate and deep sedation.5,6

When to Initiate Monitoring Baseline determination of vital signs should be documented before the administration of medications. Depending on the agent(s) being used, as well

as the rate and dose of administration, cardiorespiratory events can occur almost immediately. In addition, recognizing changes from baseline vitals can be valuable in alerting the provider to potential events. Standard cardiopulmonary leads are generally well tolerated by children. Challenges may occur in obtaining a blood pressure or placing a nasal cannula for oxygen delivery or end-tidal CO2 monitoring, or even placing an oximetry sensor on the finger or toe in some noncooperative children. Pediatric and anesthesia guidelines recognize that inability to obtain presedation vitals may be “technically precluded” in some cases. When necessary, these additional vitals can be obtained as soon as feasible after medication delivery.6,11

When to Remove Monitoring Patient-specific variables, as well as pharmacokinetics and dosage of the agent(s) used, will determine when a patient is at low risk for cardiorespiratory events. In a large prospective study of pediatric sedation, the length of time between medication administration and serious adverse events varied widely, although the vast majority of events occurred within 25 minutes of administration of the final drug dose. 22 Given this variability, the duration of observation and monitoring should be based on clinical criteria rather than a predetermined fixed length of time. In addition, nearly 10% of adverse events occur after a procedure is completed, emphasizing the importance of continued vigilant monitoring. Several sedation and recovery scales have been validated for use in determining when a patient is safe for discharge and when monitoring can be discontinued. 23,24 In addition, institution-specific discharge criteria are commonly available. Most criteria encompass some combination of: stable vital signs, a level of consciousness that is near baseline, and the ability to adequately maintain a patent airway. Monitoring should continue until these criteria are met.

ADVERSE EVENTS The frequency of adverse events related to PSA in children varies greatly, with reports ranging from 2% to 20% of cases.9,13,25 Differences in pharmacologic regimens, study design, and definition of adverse events contribute to this disparity.26 We will discuss those events for which monitoring may be beneficial, that is, respiratory and cardiac events. Other reported adverse outcomes including failure to achieve appropriate sedation, emergence and

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TABLE 2. Capnographic airway assessment for PSA.

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paradoxical reactions, myoclonus/seizure activity, and emesis will not be discussed here. Respiratory-related abnormalities in oxygenation and ventilation comprise the overwhelming majority of adverse events associated with PSA in children. These events can be categorized as hypoxemia, hypoventilation, partial airway obstruction, and apnea.

Hypoxemia Hypoxemia, manifest as oxygen desaturation, is the most common respiratory adverse event. The incidence across studies varies, depending on which medications were used and differing definitions of hypoxemia. Pena et al13 reported that 1% of patients desaturated to less than 90% (sea level) during PSA, Roback et al27 found that 7% to 8% of patients dropped to less than 90% (5280-ft elevation), and Pitetti et al25 noted that 15% of patients dropped to less than 93% (sea level). Drug regimens were also noted to influence the likelihood of hypoxemia, for example, fentanyl and midazolam being much more likely to result in hypoxemia than ketamine.25,27 Although there are no published supporting data, sound reasoning and expert consensus agree that early detection and response to hypoxemia during PSA should decrease the likelihood of a serious adverse outcome.6 Pulse oximetry has been demonstrated to be more effective than clinical observation in the detection of hypoxemia.28,29 In most circumstances, oxygen saturation will progressively decline, unless an acute airway event completely comprises oxygen delivery. Therefore, continuous oximetry provides a means to follow trends of declining oxygenation, allowing time for intervention before deleterious levels are reached. When detected or anticipated, the management of hypoxemia is to increase oxygen delivery and provide respiratory support as needed. In most circumstances, initiating or increasing supplemental oxygen delivery can be corrective. Reversal agents may also be useful when using opioids and/or benzodiazepines. When airway obstruction is a contributing factor, repositioning and, occasionally, an oral or nasal airway may be required. If these measures are ineffective, positive pressure ventilation with a bag and mask and, very rarely, via intubation can reverse profound hypoxemia (Table 2).

Hypoventilation Hypoventilation is a common adverse respiratory event that can occur during procedural sedation. Respiratory depression, with or without accompanying hypoxemia, can occur following administra-

tion of any PSA drug regimen. Slowed (bradypneic hypoventilation) or shallow (hypopneic hypoventilation) breathing can be subtle and difficult to detect by clinical observation alone. Continuous capnography provides a noninvasive and effective means for early detection of hypoventilation and respiratory depression. In addition, recognition of the characteristic waveform morphology for each type of hypoventilation provides insight into the underlying pathophysiology, which can guide subsequent interventions (Table 2). Bradypneic hypoventilation, with decreased respiratory rate and waveforms with tall and wide plateaus, suggests that a patient is heavily sedated. Caution should be exercised before administering additional sedatives in this situation, particularly if oxygenation has also been compromised. Positive pressure ventilation is not required, but should be readied if the condition were to progress to apnea or profound hypoxemia. Reversal agents can be helpful, when appropriate.

Partial Airway Obstruction Partial airway obstruction may also be seen during PSA. Many sedating medications lead to decreased upper airway muscle tone. As a result, the tongue or soft palate may fall into the posterior pharynx; or the epiglottis may drop forward in the supine child, leading to partial airway obstruction. Alternatively, partial laryngospasm may occur following the administration of some agents, particularly ketamine. Finally, secretions or gastric contents may occupy the hypopharynx or be aspirated, which can also partially occlude the upper airway or the vocal cords. Unlike hypoxemia and hypoventilation, partial airway obstruction is best detected clinically, with auditory cues from the patient indicating that the obstruction is partial and not complete. Changes in oxygenation or endtidal CO2 are unlikely to occur until there is nearcomplete obstruction. Treatment of partial upper airway obstruction will vary depending on the source of the obstruction. Supplemental oxygenation should be provided to increase intrapulmonary stores in case airway compromise progresses. Repositioning can help move soft tissue structures and maximize patency of the airway. If partial laryngospasm is suspected, pressure at the laryngospasm notch may also be helpful. The laryngospasm notch is posterior to the lobule of each ear, between the ascending ramus of the mandible, the mastoid process, and the base of the skull. Continuous pressure, using the thumbs at this point, over the styloid process may cause relaxation of the cords by a poorly defined mechanism,

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speculated to be via afferent input, a modified jaw thrust, or an increase in pharyngeal airway muscle tone secondary to the painful stimulus. Positive pressure breaths with a bag and mask can actually trigger progression to complete laryngospasm and therefore are not routinely recommended unless oxygenation or ventilation is compromised.

Apnea Apnea is a less frequent, though potentially more serious, respiratory event related to PSA. Central apnea most commonly results from oversedation, whereas obstructive apnea, including complete laryngospasm, may not correlate with a specific depth of sedation. Clinically, the 2 types of apnea can be distinguished by respiratory effort and airway patency. Patients with central apnea will have no respiratory effort (ie, no chest wall movement). Obstructive apnea is determined clinically by spontaneous respiratory effort with chest wall rise, but no effective air movement. Capnography has been shown to detect apnea more reliably than clinical observation or pulse oximetry, given that hypoxemia may lag behind corresponding ventilatory abnormalities, particularly when supplemental oxygen is being delivered. Either etiology of apnea will result in a flat capnogram. Importantly, with obstructive apnea, respiratory rate will still be registered if based on plethysmography (from impedance-sensitive ECG leads) because the chest wall continues to move, whereas airway-derived respiratory rate measured by capnography will be

zero given the absence of air movement (Table 2, Figure 1). When apnea is suspected, clinically correlate monitor findings by checking for a displaced or obstructed nasal-oral cannula or other equipment malfunction, which can result in a flat waveform in an otherwise spontaneously breathing patient. If equipment is properly functioning and central apnea is confirmed clinically, the patient should be stimulated. If there is no immediate response, reversal agents should be made available; and ventilation should be assisted with bag and mask using routine pressures. If obstructive apnea is determined, repositioning should be attempted. If there is no improvement with airway alignment maneuvers, positive pressure ventilation with bag and mask using constant high pressures should be initiated in an attempt to break the laryngospasm. Simultaneously, a neuromuscular blocking agent should be made immediately available in cases of complete laryngospasm.

MONITORING MODALITIES FOR PROCEDURAL SEDATION Given that the majority of PSA adverse events in children are respiratory related, careful and continuous evaluation of respiratory status is paramount. In addition to those aspects of respiratory status that can be detected through clinical observation, continuous mechanical monitoring of oxygenation and ventilation enhances safety by providing real-

Figure 1. Using the capnogram to determine airway-related adverse events.

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time objective data on the clinical status of the patient during PSA.

Clinical Observation Direct observation is the cornerstone of safe and effective PSA. Direct visualization of the patient allows for detection of changes in depth and rate of respirations, work of breathing, and skin color. In addition, patency of the airway and effectiveness of respiratory efforts can be quickly ascertained through auditory cues. However, to be effective, clinical observation needs to be continuous, which is not always feasible. Automated respiratory rate monitoring with adjustable limits and audible alarms can therefore help alert providers to concerning respiratory patterns.

Plethysmography Transthoracic impedance plethysmography has been the conventional means of monitoring respiratory activity. Respiratory leads, often integrated within ECG leads, are commonly available, well tolerated, and convenient. Chest wall expansion during inspiration increases the distance between the leads, resulting in recording of individual respirations. The main limitation to plethysmography is that this modality may fail to detect partial or complete airway obstruction. With obstruction, chest wall motion continues; and therefore, the monitor will continue to register perceived respirations. However, air movement is compromised.

Oxygenation Monitoring Pulse oximetry provides a noninvasive and reliable means for continuously monitoring oxygen saturation. Clinical detection of hypoxemia is unreliable until oxygen saturations have dropped to less than 80%.28 Oximetry, however, has been shown to allow more frequent and earlier detection of hypoxemic events than clinical assessment during general anethesia. 30 Similar data exist supporting the effective detection of oxygen desaturation during PSA as well.6 Oximeters use the relative absorption of specific wavelengths of light to determine oxygen saturation. Oximetry probes contain light-emitting diodes that produce 2 wavelengths of light that are differentially absorbed by oxygenated and deoxygenated hemoglobin. Measuring the amount of each wavelength that passes through a sample of blood can be used to calculate the concentration of the 2 forms of hemoglobin. Oxygen saturation is then derived by dividing the concentration of oxygenated hemoglo-

bin by the total amount of hemoglobin. To selectively determine the saturation of arterial samples, the amount of transmitted light is measured hundreds of times per second. Using these frequent measurements, the oximeter is able to detect the variable and pulsatile signal emanating from arterial flow. The static signal representing venous blood and other light-absorbing tissue can then be subtracted out, and arterial oxygen saturation can be derived (Figure 2).31 The finger is the most common probe site used for pulse oximetry. If the finger is inaccessible or unsuitable, other probe sites, such as the ear lobe or the bridge of the nose, may be used. In neonates and infants, the foot offers additional probe sites including the great toe, the heel, and the sole. There are several circumstances in which the accuracy of pulse oximetry is compromised. First, oximeters are not reliable at very low oxygen saturations. Microprocessors in oximeters use derived calibration curves that are based on measurements in healthy volunteers in whom hypoxemia was induced, but never less than 75% to 80%. Therefore, the shape of the calibration curves at lower saturations is extrapolated and not derived.31 Clinical studies have subsequently confirmed that pulse oximetry is less accurate at these lower saturations.10 Second, photodetectors can be affected by ambient light. Although devices are designed to subtract out such a static signal, oximeters can sometimes be affected by nontransmitted “noise.” Shielding the probe can be helpful in these circumstances. Third, oximeters can have difficulty distinguishing arterial signal if pulses in the measured tissue are weak, potentially secondary to hypovolemia, peripheral vasoconstriction, hypothermia, or hypotension. Warming the measured extremity and restoring effective circulating volume are required to correct this. Fourth, motion artifact can create an

Figure 2. Comparative light absorption of static and dynamic components by pulse oximetry. Reprinted with permission from The American Journal of Emergency Medicine, Sinex, J, Pulse oximetry: principles and limitations, 1999; 17.

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alternating signal that is interpreted as a valid pulsatile arterial signal. Myoclonus, shivering, or spontaneous movement during lighter levels of sedation can also contribute to this. However, recent advances in motion control technology have made pulse oximetry more reliable during patient movement. Finally, the presence of other forms of hemoglobin (eg, carboxyhemoglobin or methemoglobin) will affect the relative absorption of the 2 specific wavelengths of light used by oximeters, affecting the calculated oxygen saturation, although this is unlikely to be an issue during most PSAs.

Ventilation Monitoring Capnography provides an objective, noninvasive measure of ventilatory status. In addition to identifying the measured end-tidal CO2 value (ie, the maximum CO2 concentration for each breath), the capnograph adds a graphic display of a waveform (ie, capnogram) representing the concentration of expired CO2 as a function of time. Monitoring the waveform can provide important cues to actual or impending airway- or respiratory-related events during PSA. Capnography, like pulse oximetry, is based on the physics of infrared light absorption. A beam of filtered infrared radiation is sent through the sample of exhaled air to a photodetector. Based on the amount of radiation that is absorbed, a concentration of CO2 can be calculated. Capnographs are designed in a mainstream or sidestream configuration. Mainstream systems are configured for intubated patients, whereas sidestream systems can be used in either intubated or nonintubated patients. Mainstream devices measure CO2 directly from the airway, with the sensor located on the endotracheal tube. Sidestream devices measure CO2 by aspirating a small sample from the exhaled breath through tubing to a sensor located in the monitor. Nasal or nasal-oral cannula, which allow concomitant CO2 sampling and low-flow oxygen delivery, are used in spontaneously breathing patients. Controlled trials have demonstrated the superiority of capnography over clinical observation and pulse oximetry in detecting apnea and airway obstruction.20,32,33 As the majority of changes in oxygenation are preceded by changes in ventilation, capnography provides the earliest detection of respiratory compromise, allowing clinicians to recognize adverse airway and respiratory events and to intervene before they evolve into serious complications.34,35 Use of capnography, in conjunction with pulse oximetry, allows for preoxygenation before, and delivery of supplemental oxygen during,

the sedation. Furthermore, randomized controlled trials have shown that the use of capnography decreases the incidence of apnea and the number of hypoxic events during PSA. In one of these trials, the median time from detection of respiratory depression to hypoxia was 60 seconds, with a range of 5 to 240 seconds.21,36 There are several limitations to the use of capnography during PSA. First, partial obstruction of the cannula from nasal secretions, or displacement from the nares, can result in spuriously low end-tidal CO2 values. The cannula should be repositioned in the nares if partial obstruction or displacement is suspected. Complete obstruction of the cannula or the tubing will lead to the monitor displaying an obstruction warning. Second, some infants and young children will notice the sensation of the nasal cannula and may try to remove it.

Noninvasive Blood Pressure Monitoring Noninvasive blood pressure monitoring (NIBP), an automated method of repetitively determining blood pressure, has been widely used in anesthesia practice for more than 20 years. Automated devices allow for intermittent measurements to be obtained at a programmable frequency, allowing single measurements as well as trends. Noninvasive blood pressure monitoring provides a display of the heart rate and the systolic, diastolic, and mean blood pressures by electronically determining the pulse amplitude. Multiple studies have evaluated the accuracy of NIBP compared with intraarterial blood pressure measurement in both adults and children. Most suggest that comparative measurements are within 5 mm Hg; however, there is wide variability across manufacturers and devices. Current devices use oscillometric technology. An occluding cuff impedes blood flow in the selected extremity, most commonly using the brachial artery. As pressure in the cuff slowly decreases, pulsatile blood flow through the vessel resumes, creating vibrations in the arterial wall. When the cuff pressure falls below diastolic pressure, blood flow is completely unimpeded and vibrations cease. The magnitude of these vibrations follows a predictable pattern, peaking at mean arterial pressure.37 The oscillations are transferred through the air in the cuff into a transducer that converts the measurements to electrical signals. Microprocessors within the devices use empirically derived algorithms to calculate systolic and diastolic blood pressures from the pattern of vibrations. There are many potential factors that may affect the accuracy of NIBP readings. First, choosing an

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appropriate-sized cuff is particularly important, especially in children and obese patients. An undersized cuff will give falsely elevated readings, whereas a cuff that is too large will lead to falsely low values. Many cuffs have reference lines on them to provide guidance in choosing cuff size, or standardized references from the American Heart Association are available to help choose cuff size based on extremity circumference. 38 Second, irregular or rapid cardiac rhythms can intrinsically cause vibrations in arterial walls and therefore affect cuff-induced oscillations. Similarly, excessive patient movement or muscle stiffness can interfere with the detection of oscillations, leading to unobtainable or erroneous blood pressure measurements. Finally, it is important to remember that an inflated cuff will transiently compromise distal arterial flow, which can affect pulse oximetry readings if they are being recorded in the ipsilateral extremity.

Electrocardiographic Monitoring Continuous ECG monitoring can be used to detect alterations in cardiac rate or rhythm. Most commonly, 3 electrodes are used, allowing recognizable P waves and QRS complexes, with the option to change lead selection as needed to get the best tracing. In addition, the majority of current cardiac monitoring systems are interfaced with plethysmography to provide continuous impedance respiratory rate monitoring. Such devices are simple, inexpensive, and readily available in EDs. Characteristic pharmacodynamic changes occur following the administration of specific PSA agents, for example, increase in heart rate with ketamine or atropine, decreases in heart rate with propofol. In addition, heart rate can provide indirect information regarding a patient's level of comfort and whether he or she is experiencing pain. Bradycardia may develop as a direct result of some sedation medications or secondarily to physiologic alterations such as hypoxemia. Although extremely rare, reports of cardiac arrest have occurred in high-risk patients during PSA. Treatment of such events is determined by the underlying cardiac rhythm; and therefore, early recognition may be helpful. However, ECG monitoring is not mandatory nor standard of care for PSA in patients without underlying cardiovascular disease. There are few limitations to ECG monitoring. Perhaps the greatest is that tracings are easily affected by motion artifact. Calculated heart rate in particular can be spurious as a result of “spikes” in ECG tracings that are non–cardiac-based. In addi-

tion, inadequate contact between the electrodes and the patient can also lead to imprecise tracings that can be difficult to interpret. It is always important to interpret monitoring data in the clinical context to determine its reliability and usefulness.

FUTURE DIRECTIONS IN PROCEDURAL SEDATION MONITORING Processed Electroencephalographic Monitoring Processed electroencephalographic (EEG) monitoring has been proposed as an objective, quantitative means to measure the brain's response to anesthetic agents and to continuously monitor depth of sedation and awareness under anesthesia in the operating room. There are several versions of this technology that have been used in the operating room, with the bispectral index (BIS) being the most widely studied and the only one of these technologies to be used for ED PSA. Although these technologies have been used to monitor depth of sedation/anesthesia, in 2006, the ASA concluded that the clinical applicability in the operating room has not been established.39 The BIS technology uses a sensor placed across both sides of the forehead to record brain activity. The magnitude and distribution of EEG spikes are measured and processed to create a neurophysiologic variable with a unitless value from 0 to 100. Based on adult anesthesia data, an index was created to correlate depth of anesthesia with BIS values, with a BIS value of 100 considered to be complete alertness (ie, a fully awake patient), 40 to 60 consistent with general anesthesia, and zero depicting no cortical activity.40 Bispectral index monitoring has been studied in the ED in an attempt to objectify sedation end points by titrating to a target BIS score. Multiple pediatric and adult studies have evaluated the correlation between BIS values and depth of sedation as measured by validated sedation scales.41-45 However, these studies have found unacceptably wide ranges of BIS values at various depths of sedation that did not correlate with the Ramsey sedation scale. As a result, BIS monitoring may not be effective at discriminating between moderate and deep sedation, especially in children. 45,46 More importantly, the threshold above which ventilatory compromise will occur and the effectiveness of target BIS levels have not been determined, further limiting the usefulness of routine BIS monitoring for ED sedation.47,48 Miner et al48 found that the assignment of a preprocedural BIS target sedation

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level of moderate or deep sedation did not influence the level of sedation achieved, the rate of respiratory depression, the occurrence of complications, the time to return of baseline mental status, or the success of the procedure. Finally, BIS monitoring is less likely to correlate when using specific sedation agents, such as opioids, ketamine, and chloral hydrate.43,45,49 Ketamine leads to excitatory findings by EEG despite increasing level of dissociation. Conversely, sedation with opioids and chloral hydrate produces little change in the BIS despite increasing clinical effect of the medications. Newer depth of sedation technologies have recently been introduced into the operating room setting including entropy-based monitoring. Variability/irregularity in processed EEG signals and electromyography (EMG) signals from the forehead are used to gauge depth of sedation based on central nervous system response to anesthetic agents. At baseline in the normal nonsedated state (high levels of entropy activity), there is considerable variability in both EEG and EMG signals. With increasing depth of sedation, EEG cortical electrical activity becomes more regular with decreased variability; and EMG forehead muscle activity decreases and ultimately ceases (low levels of entropy activity). 50 This technology has not been studied outside of the operating room.

Cerebral Oximetry Respiratory, and less commonly cardiac, adverse events are not infrequent in PSA. With the exception of profound or prolonged compromise where clinical sequelae can be appreciated, the significance of transient changes in cardiorespiratory function is unclear. Cerebral oximetry (ie, regional as opposed to systemic oximetry) represents a new technology that provides a noninvasive measurement of oxygen delivery to the brain. As such, it may prove valuable in understanding which events detected by standard monitoring are most significant. Cerebral oximetry is based on the principles of near-infrared spectroscopy. Similar to pulse oximetry, sensors detect changes in light absorption. The use of 2 sensors allows measurements at different depths in nonpulsatile samples, thereby permitting tissue-level saturation recordings. Cerebral tissue oxygenation has been shown to correlate well with cerebral mixed venous oxygen saturation in pediatric cardiac surgery patients.51 Although determination of absolute values was judged to be unreliable, use of the device to follow trends was supported.

Initial investigation into the utility of cerebral oximetry during PSA in children shows promise.52 Cerebral oximetry was prospectively compared with traditional pulse oximetry and capnography during sedation in 100 children. The study demonstrated that cerebral oxygen saturation was well maintained throughout 98% of recordings. In only 23% of hypoxic events and 29% of hypercarbic events did cerebral oxygen saturation decrease. This suggests that transient cardiopulmonary events are probably of little clinical consequence. Conversely, other cerebral desaturation events were noted that did not correlate with changes in conventional monitoring. This initial study suggests that cerebral oximetry may provide additional insight into the significance and severity of conventionally detected events and may prove to be a more relevant measure of endorgan impact through direct measurement of oxygen delivery to brain tissue.

Noninvasive Hemodynamic Monitoring of Vascular Tone During PSA, blood pressure is typically measured using an oscillometric technique with an inflatable cuff around the upper arm or leg. However, these measurements may be inaccurate in some children, particularly when an inappropriate cuff size is used. In addition, such measurements provide intermittent but not continuous data. Emerging technologies may offer an alternative means of noninvasive evaluation of blood pressure. A newly developed finger cuff offers the possibility of continuous arterial pressure monitoring. The finger device contains an infrared photoplethysmograph that recognizes changes in blood volume in the finger through corresponding differences in light absorption. These data are translated into changes in the volume of air in the cuff. Finger arterial pressure is then measured indirectly by recording the cuff pressure. Pediatric-sized finger cuffs were developed and initially pilot tested in children between 0 and 4 years of age.53 More recently, these prototypes were compared with intra-arterially measured blood pressure in intubated, sedated pediatric intensive care unit patients.54 Finger-cuff arterial pressures were consistently lower than intra-arterial pressures, as would be expected physiologically because of increased resistance to peripheral flow. Using software algorithms, the measured finger pressures were reconstructed to represent brachial pressures; and these were compared with intra-arterial pressures and direct cuff measurements. The new finger cuff was found to provide nearly continuous

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readings that were more accurate than traditional, intermittent cuff measurements. The device was unsuccessful in obtaining measurements in less than 5% of cases, although more than one attempt was frequently needed to obtain a signal, particularly in the youngest children. It is not clear how well this device would be tolerated by noncritically ill children or how effective it is in recognizing abrupt changes in blood pressure.

Integrated Algorithms and Indices In addition to the development of technologies to monitor novel physiologic parameters during sedation, efforts have also been extended to create computer-generated software programs (ie, adaptive algorithms) that help integrate and interpret multiparameter data. Such programs offer distinct advantages over current monitoring strategies by their ability to filter large amounts of data, recognize complex data patterns, and provide an enhanced interpretation of data significance and trends. Audible monitor alarms provide a means to alert a clinician when a patient has reached a predetermined physiologic threshold (eg, bradycardia, tachycardia, hypotension, hypertension). Because the goal of monitoring during procedural sedation is to create an early detection system, recognition of trends toward such a value would be useful, especially if the designated value correlates with a physiologic danger zone. Such systems provide an opportunity to detect subtle or gradual changes and to put them in a context not always discernible to, or appreciated by, the sedation providers, while placing them in the context of previous data, prioritizing recent changes. The methodology uses prior data to predict future observations and then compares real-time recorded values to those that had been previously predicted. Discrepancies between the predicted and the observed values suggest a change in trend that may be a more sensitive early warning system. Early work with integrated algorithms in the operating room has shown that such systems are more accurate at identifying physiologic changes than the anesthesiologist.55 In a pediatric study using a similar tool, clinicians rated more than 60% of the detected changes as clinically significant, with less than 7% being attributed to artifact.56 In contrast, traditional alarms have been reported to indicate actual risk to the patient only 3% of the time.57 Further work is needed to determine how to best integrate these intuitive algorithms into practice, and to establish the impact on clinical outcome.

The concept of using context-sensitive physiologic monitoring as a novel early warning system and as an adjunctive tool to guide clinical decision making holds promise. An example where such an algorithm would be valuable is in patient-controlled analgesia (PCA). In the ED, PCA is primarily used for pain management in vasoocclusive crisis. Recently, continuous pulse oximetry and capnography monitoring have been integrated into PCA pumps. A study of 178 postoperative patients using PCA with integrated continuous pulse oximetry and capnography monitoring found that 12% had desaturations to less than 90% for 3 minutes or greater and 41% had respiratory depression (respiratory rate b10) for 3 minutes or greater.58-60 The integration of continuous oxygenation and ventilation monitoring into PCA delivery systems may allow for the future development of intuitive safety algorithms based on physiologic parameters rather than theoretical lockout times and absolute drug doses.

SUMMARY Patient monitoring during pediatric PSA has evolved over time. In addition to direct observation, cardiac and respiratory monitoring modalities can help rapidly identify physiologic changes and allow early intervention. In particular, data from oxygenation and ventilation monitoring provide important cues to the presence and etiology of airway or respiratory compromise. Novel application of available information and development of newer technologies continue to be investigated. Ongoing standardization of relevant definitions and collaborative research efforts offer the possibility of more precise outcome data to allow for continued improvement in the safety profile of ED procedural sedation in children.

ACKNOWLEDGMENTS Financial disclosure: Baruch Krauss is a consultant for Oridion Medical, a capnography company, and holds 2 patents in the area of capnography.

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