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PEDIATRIC ANESTHESIA

Sedation and Anesthesia Protocols Used for Magnetic Resonance Imaging Studies in Infants: Provider and Pharmacologic Considerations

From the Department of Anesthesiology, St. Louis Children’s Hospital, Washington University School of Medicine, St. Louis, Missouri.

Address correspondence and reprint requests to Priti G. Dalal, Department of Anesthesiology, St. Louis Children’s Hospital, Washington University School of Medicine, St. Louis, MO 63110. Address e-mail to pgdalal{at}hotmail.com.

	Abstract

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 
Most studies report the efficacy of only a single drug to achieve sedation in a broad age range of children. In clinical practice, a variety of sedative and anesthetic regimes are monitored by nurses and physicians. In this study we report the efficacy of a tiered approach to monitoring and sedation in infants. Two-hundred-fifty-eight infants who required magnetic resonance imaging (MRI) studies received either oral chloral hydrate (n = 102) or bolus doses of IV pentobarbital (n = 67) monitored by nurses or IV propofol infusion (n = 68) titrated by physicians. Fewer cardiorespiratory events were observed in the chloral hydrate group (2.9%) compared to pentobarbital (13.4%) and propofol groups (13.6%); P < 0.05, propofol versus chloral hydrate. Infants who received propofol were ready to begin MRI scanning earlier (mean 9.1 ± 6.7 min) than infants who received oral chloral hydrate (mean 23.5 ± 13.4 min; P < 0.05). The time to discharge was longest in the pentobarbital (mean 80.3 ± 39.2 min) and shortest in the propofol group (mean 53.9 ± 30.1 min; P < 0.05). Infants in the chloral hydrate group moved more frequently (22.5%) during MRI scanning (with four sedation failures of 102) compared to 12.2% in the pentobarbital group and 1.4% in the propofol group (P < 0.001).

	Introduction

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 
The demand for comprehensive sedation and anesthesia program for infants and children often exceeds the availability of trained anesthesia personnel. For this reason, various sedative regimes, monitored by nurses, pediatricians, or anesthesiologists are often used in infants and children (1,2). Most sedation studies for magnetic resonance imaging (MRI) report the efficacy of a single pharmacologic regimen for a broad range of pediatric ages (3). Few studies report the efficacy of deep sedation and anesthesia regimes in infants <12 months of age (4–6). Infants are more likely to require deep sedation or anesthesia to keep them still during MRI studies, and they are also considered at higher risk for cardiorespiratory side effects of these drugs (5).

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 (7–9). The use and safety profile of various sedative regimens has been well described in the literature (10–15). 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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After obtaining approval of the IRB, we performed a retrospective review of the records of consecutive infants who required sedation or anesthesia services primarily for MRI during the 2-yr period from January 2003 to December 2004. The data were obtained from a number of sources from the patient’s record and included the demographic data, information regarding the type of sedation, use of premedication, adjunctive drugs to enhance or rescue sedation, time to readiness for the procedure after sedation administration, duration of procedure, and the time to discharge. Any sedation failures or occurrences of adverse events were noted.

Definition of Terms
The following definitions were used for the purpose of the study:

1. Time to readiness for the procedure (sedation-ready): The time in minutes from the administration of the primary sedative drug to the documented time of transfer to the MRI suite.
   
2. Duration of procedure: Time in minutes from the start of the procedure to the termination of the MRI procedure or the computed tomography (CT) scan, when the patients had CT scan in addition to the MRI.
   
3. Time to discharge: Time in minutes from the end of the procedure up to the time that the patient was discharged from the ambulatory procedure center.
   
4. Primary sedative drug: The first-administered sedative drug to achieve a sedative state so as to facilitate MRI.
   
5. Additional sedation: Administration of further doses of the primary sedative drug upon transfer to the MRI suite.
   
6. Rescue sedation: Administration of a sedative drug that is different from the primary sedative drug to achieve deeper sedation.
   
7. Failed sedation: Sedation deemed inadequate after the administration of the maximum dose of the primary sedative drug, resulting in an inability to perform the MRI studies.
   
8. Respiratory event: Documented wheezing, laryngeal spasm, apnea, desaturation (decrease in oxygen saturation more than 5% from the baseline) with need for maneuvers to improve patency of the airway, such as a shoulder roll, oropharyngeal, nasopharyngeal airway, laryngeal mask airway, or endotracheal intubation.
   
9. Cardiovascular event: Documented arrhythmias, hypotension (decrease in the mean arterial blood pressure >20% from the baseline).
   
10. Gastrointestinal side effects: Documentation of nausea, vomiting, and hiccups.
    
11. Paradoxical reaction or agitation: Documented irritability or combativeness after administration of the sedative drug.
    

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 pediatrician’s 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 (7–9).

Pentobarbital With and Without Midazolam
In infants older than 6 mo, oral midazolam 0.5 mg/kg was used as premedicant 20–30 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 50–100 mg/kg. If the patient was not adequately sedated within 30 min, additional chloral hydrate doses were administered orally in the dosage range of 25–125 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 1–2 mg/kg of an IV propofol bolus, deep sedation or anesthesia was maintained with an IV propofol infusion at the rate of 100–200 µg/kg/min. The goal was to maintain the infant’s 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:

1. Modified Aldrete score 8 (each parameter from scale of 0–2 for activity, respiration, circulation, consciousness, color)
   
2. Comfort score 3 (crying, agitation, and pain complaints; scale 0–2)
   
3. Emesis score 1 (vomiting within the past 15 min, no vomiting within the past 15 min, none; scale 0–2)
   
4. All infants were followed up by phone the following day and no adverse events were reported.
   

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 Dunn’s 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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Data were obtained from 258 infants who received sedation primarily for MRI during the study period. Out of these, five patients had general anesthesia with endotracheal intubation and propofol infusion for maintenance of anesthesia. In three patients the MRI scan was successfully performed without anesthesia and in two patients bottle feeding alone with natural sleep was sufficient to facilitate the scanning process. One patient had nine failed attempts at IV access before a decision was made to abandon the procedure. Data were incomplete in the remaining 10 cases. The remaining 237 infants were classified into three groups on the basis of the primary sedation received: chloral hydrate group (n = 102), pentobarbital group (n = 67), and the propofol group (n = 68). Sedation was administered primarily by trained nurses under physician supervision in the chloral hydrate and the pentobarbital group. Sedation was administered directly by physicians in 100% of the cases in the propofol group; an anesthesiologist administered sedation in 18 cases and sedation-trained pediatricians in the remaining 50 cases.

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 16–341 days) compared to 262 days (mean 8.7 mo, range 157–364 days) in the pentobarbital group and 205 days (6.8 mo, range 57–360 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.

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.

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.

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

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 
In a recent survey of pediatric sedation in North American children’s hospitals, propofol was used by nonanesthesiologists for 42% of the nonintubated patients and 63% of intubated patients (16). The authors found that a shortage of providers, particularly anesthesiologists, was the most common barrier to the development of pediatric sedation services. This study reports a program that uses three different approaches to achieving sedation or anesthesia. The goal of the program was to match a pharmacologic approach with appropriate trained personnel to monitor and, if necessary, intervene if the infant developed side effects from these drugs. Propofol was used to successfully obtain MRI studies, but was more frequently associated with a side effect that required intervention and an anesthesiologist’s assistance. This suggests that either the protocols that guide the use of propofol require revision or the training of the physicians should be reevaluated. The pharmacologic protocols that guide chloral hydrate and pentobarbital were designed to use doses that would be effective, yet not result in major respiratory side effects. The goal was to use doses that were often effective, but movement and sedation failure would be a more acceptable side effect than airway events associated with deep sedation and anesthesia. On the basis of our findings, the protocols for chloral hydrate and pentobarbital accomplish these goals. These findings would support the continued use of chloral hydrate and pentobarbital via protocol, but suggest that the safety profile of propofol titration by nonanesthesiologists requires further study.

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 (16–18). 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

 
Accepted for publication June 5, 2006.

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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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Dalal, P. G. Articles by Snider, R. Search for Related Content PubMed PubMed Citation Articles by Dalal, P. G. Articles by Snider, R. Related Collections Anesthetic Techniques Pediatrics Pharmacology