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From the Department of Anesthesiology, St. Louis Childrens Hospital, Washington University School of Medicine, St. Louis, Missouri.
Address correspondence and reprint requests to Priti G. Dalal, Department of Anesthesiology, St. Louis Childrens Hospital, Washington University School of Medicine, St. Louis, MO 63110. Address e-mail to pgdalal{at}hotmail.com.
| Abstract |
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| Introduction |
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Three sedatives and anesthetics commonly used in infants are oral chloral hydrate, IV pentobarbital, and IV propofol infusion. The sedation as well as recovery characteristics and safety profiles are variable depending on the sedative drug used and the underlying medical condition of the infant. In small infants, a single oral dose of chloral hydrate often serves as the sedation. Trained nurses, supervised by a physician, monitor the child according to a standardized protocol. For older infants or infants expected to need additional sedatives to achieve immobility, a protocol that uses intermittent boluses of IV pentobarbital is often used to achieve immobility. Infants and children who have underlying medical conditions or require prolonged studies often receive a continuous infusion of IV propofol titrated by pediatricians or anesthesiologists. Each approach has different advantages and disadvantages (79). The use and safety profile of various sedative regimens has been well described in the literature (1015). The ultimate safety of each sedation protocol depends on the experience and training of the nurse or physician who monitors the infant. A "safe" sedation program that meets the demand for sedation and anesthesia in infants should ideally match the abilities of the sedation provider with the appropriate sedative drugs.
The purpose of this study was to report our experience with a comprehensive program to meet the sedation and anesthesia needs of infants who require MRI studies. This observational study reports the efficacy of three sedation regimens in all infants who required sedation or anesthesia for an MRI procedure over a 24-mo period. The infants received either oral chloral hydrate or IV pentobarbital monitored by a nurse or received IV propofol infusion monitored by a physician.
| METHODS |
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Definition of Terms
The following definitions were used for the purpose of the study:
The Sedation Protocol
One of the nurses trained in sedation contacted parents and performed a preliminary health screen. On the basis of the history, ASA physical status, previous experience with anesthesia, and sedation, the patient was scheduled for sedation administered primarily by a sedation-trained nurse, a sedation-trained pediatrician, or an anesthesiologist. The selection process for sedation and anesthesia included ASA physical status, infant age, duration of procedure, the need for IV contrast for the MRI studies, and a history of previous sedation failure. The sedation-trained pediatricians were trained by pediatric anesthesiologists to use sedation in hospital settings. The training included a program of didactic training, one-on-one operating room experiences (4 wk) with a pediatric anesthesiologist, a simulation-based assessment, and observation by a pediatric anesthesiologist during the pediatricians first 20 propofol titrations in children. All the infants in our study were monitored in accordance with the standards recommended by American Academy of Pediatric, the American Society of Anesthesiologist task force, and the Joint Commission on Accreditation of Healthcare Organizations (79).
Pentobarbital With and Without Midazolam
In infants older than 6 mo, oral midazolam 0.5 mg/kg was used as premedicant 2030 min before placement of an IV catheter. After placement of the IV catheter, an initial 2.5 mg/kg IV bolus dose of pentobarbital was administered. If adequate sedation was not achieved with this dose, then additional doses of pentobarbital were repeated in increments of 1.25 mg/kg up to a total of 7.5 mg/kg or a maximum of 200 mg. IV midazolam in increments of 0.05 mg/kg could also be administered up to a maximum of 0.2 mg/kg if sedation was not accomplished with the use of pentobarbital. Advanced practice nurses working under physician supervision administered these drugs.
Chloral Hydrate
The initial oral chloral hydrate dose was 50100 mg/kg. If the patient was not adequately sedated within 30 min, additional chloral hydrate doses were administered orally in the dosage range of 25125 mg/kg up to a maximum of 2000 mg.
Propofol
The attending anesthesiologist or a sedation-trained pediatrician titrated propofol according to a standardized protocol. After induction of deep sedation with 12 mg/kg of an IV propofol bolus, deep sedation or anesthesia was maintained with an IV propofol infusion at the rate of 100200 µg/kg/min. The goal was to maintain the infants spontaneous ventilation throughout the procedure. An anesthesiologist was available for consultation and assistance in the sedation unit adjacent to the MRI suite.
Discharge Protocol
The discharge criteria included:
8 (each parameter from scale of 02 for activity, respiration, circulation, consciousness, color)
3 (crying, agitation, and pain complaints; scale 02)
1 (vomiting within the past 15 min, no vomiting within the past 15 min, none; scale 02)
Plan for Failed Sedation
Infants who failed sedation or did not achieve a sedative state after the administration of the primary sedative drug were referred to the supervising anesthesiologist for further management. In these infants, a decision to proceed or administer additional drug was at the discretion of the supervising anesthesiologist.
Statistical Analysis
The data were analyzed using SigmaStat Version 3.1© 2004 (Systat software, Point Richmond, CA). The results are expressed as mean and SD and percentages where appropriate. One-way analysis of variance (ANOVA) with multiple pairwise comparisons applying the Holm-Sidak method was used for significance testing for the weight data. The Kruskal-Wallis one-way ANOVA on Ranks with pairwise multiple comparisons applying the Dunns method was used for age and the sedation readiness (sedation-ready), procedure duration, and time to discharge. The
2 test was used for comparisons of the adverse events, rates of movement, and sedation failure rates. A P-value < 0.05 was considered statistically significant.
| RESULTS |
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The demographic data are as shown in Table 1. The mean values for age and weight were lowest in the chloral hydrate group (P < 0.001) compared to the pentobarbital and the propofol group. Infants in the chloral hydrate group were significantly younger, i.e., mean age of 147 days (mean 4.9 mo, range 16341 days) compared to 262 days (mean 8.7 mo, range 157364 days) in the pentobarbital group and 205 days (6.8 mo, range 57360 days) in the propofol group respectively; P < 0.05. The propofol group had the largest number of infants (11%) who belonged to ASA physical status >2. Thirty of 67 patients (44.7%) in the pentobarbital group and 18 of 68 patients (26.4%) in the propofol group received oral midazolam as premedication to facilitate insertion of an IV catheter. Twenty-five of 67 (37.3%) patients in the pentobarbital group received IV midazolam to reduce agitation and enhance sedation with pentobarbital.
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The mean values of times in minutes to readiness for the procedure, duration of procedure, and time to discharge are as shown in Table 2.
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Two patients were excluded from the analysis of sedation and recovery times because of failed sedation despite receiving the maximal dose of the sedative drug according to the protocol. One patient received pentobarbital while the other received chloral hydrate as the primary sedative drug. Both these infants were referred to an anesthesiologist who subsequently administered propofol infusion to complete the scanning procedure. These infants were considered sedation failures for chloral hydrate and pentobarbital, respectively.
The time in minutes from administration of sedation to readiness for procedure was longest in the chloral hydrate group (mean 23.5 min; P < 0.05 compared to propofol and pentobarbital) and shortest in the propofol group (mean 9.1 min, P < 0.05 compared to chloral hydrate and pentobarbital).
The mean duration of the procedure was found to be longest in the propofol group (58.5 min; P < 0.05 compared to chloral and pentobarbital) and similar in the pentobarbital (49.3 min) and chloral hydrate (48.1 min) groups. This finding may reflect the detailed scanning procedures in the propofol group. The mean values of time to discharge were longer in the pentobarbital group (80.3 min) compared to chloral hydrate (61.2 min, P < 0.05) and propofol groups (53.9 min, P < 0.05) with no significant difference for choral hydrate versus propofol. A number of additional studies followed the MRI scan, thereby, delaying discharge in one infant in the propofol group. The adverse events are as shown in Table 3.
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The incidence of respiratory events was least in the chloral hydrate group (2.9%) compared to the pentobarbital (12.1%) and propofol groups (13.6%). The respiratory events that occurred in the chloral hydrate group were minor (oxygen saturation >93% with stimulation or repositioning resolving the event) when compared to those that occurred in the propofol groups. In the nine infants in the propofol group who had respiratory events, two required bag-valve-mask ventilation and insertion of a laryngeal mask airway for inadequate ventilation and oxygen saturation <85%. An anesthesiologist assumed care for both of these infants. One patient in the pentobarbital group was noted to have bradycardia during and after MRI despite normal arterial blood pressure and oxygen saturation. Another patient in the pentobarbital group was noted to have hiccups. Two patients in the chloral hydrate group experienced vomiting. The MRI was aborted in one of the two infants. One infant who received pentobarbital experienced prolonged agitation that required transfer to a quiet room for recovery.
The side effects and complications related to the sedation as well as the infants who had excessive movement in the MRI scanner in the three groups are detailed in Table 3.
More infants in the chloral hydrate group (22.5%) aroused or moved during the MRI scanning compared to 12.2% in the pentobarbital group and 1.4% in the propofol group, respectively (P < 0.001). Twenty-three of 102 infants in the chloral hydrate group stirred during the scanning process. The MRI was aborted in 4 infants, completed with additional chloral hydrate in 18 infants, rescue propofol in 2 infants, and comfort maneuvers (repositioning, pacifier, swaddle) were used to complete the scan in the other 7 infants. In an infant who was receiving propofol, IV access was lost. A dose of chloral hydrate was successfully used as the rescue sedation in this infant. Of the eight patients in the pentobarbital group who moved during the scanning process, seven were able to complete the procedure. Six of the seven infants received additional doses of pentobarbital. In one child rescue propofol was administered by the anesthesiologist to complete the scan.
| DISCUSSION |
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In the 237 infants studied in this report, 20 infants (8.4%) experienced a respiratory event during sedation or anesthesia, an incidence similar to that reported by Malviya et al. (5,6) (overall 5.5% in children, 10% in infant age group) who used a similar definition of respiratory events in infants and children. We found that infants in the chloral hydrate group had fewer respiratory events (2.9%) compared to infants in the pentobarbital and propofol groups (12.1% and 13.6% respectively). These events were rapidly recognized and effectively treated by trained nursing personnel. The low incidence of adverse respiratory events and ease of administration supports the use of chloral hydrate as a first-line sedative drug (11). The safe and effective use of chloral hydrate in the majority of infants accomplished MRI studies without the need for continuous monitoring by a physician. However, a larger proportion (22.5%) in the chloral hydrate group moved or aroused during the scanning process compared to 12.2% in the pentobarbital group and 1.4% in the propofol group; P < 0.001. The imaging study was aborted in 3.9% of the patients in the chloral hydrate group, 1.4% of the patients in the pentobarbital group, and none in the propofol group. In addition, one patient who received chloral hydrate failed to sedate but was later successfully imaged using propofol sedation. The sedation failure rate (scanning process aborted completely) in the 237 infants was less than that reported in previous studies. Malviya et al. (6) reported a 7% failure rate in a similar study of infants and children. Our lower failure rate may be attributed to the selection process used to assign infants to the different sedative and anesthetic approaches available based on various patient and procedure factors. This assignment is evident in the more frequent use of chloral hydrate in the younger infants and also explains the use of either pentobarbital or propofol in older infants who are more likely to fail to sedate with the chloral hydrate doses used in this study. The higher ASA physical status and longer duration of procedures in infants who received propofol is also a function of the triage of children.
Propofol appears to uniformly provide the level of sedation or anesthesia necessary to obtain MRI studies in infants, especially because of its titrability and predictability. This ability to titrate to deeper levels of sedation and anesthesia is not without respiratory side effects and a need for airway management. In this study, a larger proportion of patients in the propofol group (13.6%) experienced a respiratory event compared to 12.1% in the pentobarbital group and 2.9% in the chloral hydrate group. Perhaps this may be attributed to the larger proportion of patients who belonged to a higher ASA class in the propofol group (8 of 68, 11.1%; respiratory events in 4 of 8), compared to 1.5% in the pentobarbital group and none in the chloral hydrate group. Although the incidence of adverse respiratory events was almost similar in the pentobarbital and propofol groups (12.1% vs 13.6% respectively), the severity of these events was greater in the propofol group. The management of these events in the propofol group included use of advanced airway maneuvers such as jaw thrust, use of oropharyngeal airway, laryngeal mask airway, and bag-valve-mask ventilation in contrast to simple maneuvers such as head tilt, chin lift, and use of a shoulder roll in the pentobarbital group, thereby reflecting the need for skillful management by an anesthesiologist during sedation with propofol.
The shorter time required for more intensive monitoring and more predictable recovery is an advantage of propofol. Indeed, the rapid readiness for procedure, quicker recovery times, low sedation failure rate, and its use as a final rescue drug make propofol ideal for procedural sedation in the pediatric population (15). The limiting factors for its use, however, include the establishment of an IV access, cost-effectiveness, and the need for trained personnel (1618). Although sedation-trained physicians who are nonanesthesiologists may administer propofol infusion for sedation in children, the nature and frequency of the airway events suggest that this approach to anesthesia for MRI studies requires careful monitoring and the availability of an anesthesiologist. This approach is consistent with a standard of care, scope of practice, resource management and reimbursement for sedation based on the depth of sedation achieved rather than the drug class, route of administration practitioner, or venue (19). This requirement is also reasonable based on the pharmacokinetics of this rapidly acting drug, with which it is possible to slip into increasing anesthesia depth based on minor changes in infusion rate and duration.
In summary, this report describes an approach to sedation and anesthesia for MRI studies in infants that uses sedatives and anesthetics monitored by appropriately trained nurses and physicians. Even though the titration of propofol, as expected, offered a shorter induction and more rapid recovery with a lower sedation failure rate when compared to pentobarbital or chloral hydrate in infants undergoing MRI, a relatively frequent incidence of respiratory events suggests that using propofol infusions by nonanesthesiology physicians, rather than anesthesiologists, requires additional study. The protocol described for chloral hydrate and pentobarbital indicates that these drugs are safe and effective. This study demonstrates that a tiered approach to the use of sedative and anesthetic drugs and monitoring personnel may be the most effective way to meet the increasing demand for MRI studies in infants.
| Footnotes |
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Partly presented as a poster at the Association of Anesthesiologist Annual Meeting, October 2005, Atlanta, Georgia and the Society for Pediatric Anesthesia, Winter Meeting, February 2006, Fort Myers, Florida.
Supported by The Clinical Research Division, Department of Anesthesiology, Washington University School of Medicine.
| REFERENCES |
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