Radiology
Keira P. Mason, MD Pamela Sanborn, MS, CPNP David Zurakowski, PhD Victoria E. Karian, MSN, CPNP Linda Connor, RN Paulette J. Fontaine, BS Patricia E. Burrows, MD
Index terms: Anesthesia Computed tomography (CT), in infants and children Magnetic resonance (MR), in infants and children Published online before print 10.1148/radiol.2302030107 Radiology 2004; 230:537–542 1
From the Departments of Anesthesia (K.P.M.), Radiology (K.P.M., P.S., V.E.K., L.C., P.J.F., P.E.B.), Biostatistics (D.Z.), and Orthopaedic Surgery (D.Z.), Children’s Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA 02115. Received January 17, 2003; revision requested March 3; final revision received June 23; accepted July 31. Address correspondence to K.P.M. (e-mail:
[email protected]).
Superiority of Pentobarbital versus Chloral Hydrate for Sedation in Infants during Imaging1 PURPOSE: To compare the effectiveness and safety of oral pentobarbital and oral chloral hydrate for sedation in infants younger than 1 year during magnetic resonance (MR) imaging and computed tomography (CT). MATERIALS AND METHODS: A computerized database was used to collect information about all cases in which sedation was used. Outcomes of all infants who received oral pentobarbital or oral chloral hydrate for sedation between 1997 and 2002 were reviewed. Two study groups were compared for sedation and discharge times by using Student t test and for adverse events by using Fisher exact test and multiple logistic regression analysis. RESULTS: Infants (n ⫽ 1,316) received an oral medication for sedation. Mean doses were 50 mg/kg chloral hydrate and 4 mg/kg pentobarbital. Student t test demonstrated no difference in mean time to sedation and in time to discharge between groups. Overall adverse event rate during sedation was lower with pentobarbital (0.5%) than with chloral hydrate (2.7%) (P ⬍ .001). There were fewer episodes of oxygen desaturation with pentobarbital (0.2%) than with chloral hydrate (1.6%) (P ⬍ .01). Both medications were equally effective in providing successful sedation. CONCLUSION: Although oral pentobarbital and oral chloral hydrate are equally effective, the incidence of adverse events with pentobarbital was significantly reduced. ©
Author contributions: Guarantors of integrity of entire study, K.P.M., D.Z., P.S., V.E.K., L.C., P.E.B.; study concepts, K.P.M., P.E.B., D.Z.; study design, K.P.M., P.E.B.; literature research, P.E.B., K.P.M.; clinical studies, P.E.B., K.P.M., L.C.; data acquisition, K.P.M., P.J.F., D.Z.; data analysis/ interpretation, D.Z., K.P.M.; statistical analysis, D.Z.; manuscript preparation, V.E.K., D.Z., K.P.M., P.J.F., P.E.B., P.S.; manuscript definition of intellectual content, K.P.M., P.S., D.Z.; manuscript editing, all authors; manuscript revision/review and final version approval, K.P.M., P.E.B., D.Z. ©
RSNA, 2003
RSNA, 2003
Neonates and infants who undergo magnetic resonance (MR) imaging and computed tomographic (CT) studies often require sedation to minimize motion artifacts. Historically, chloral hydrate has been the drug of choice for the sedation of infants younger than 1 year of age (1– 4). Rates of successful sedation with this medication range from 85%–98% (5,6). Adverse events with chloral hydrate include oxygen desaturation, nausea, vomiting, hyperactivity, respiratory depression, and failure of adequate sedation (2,7). Until 1999, our radiology sedation protocol for infants younger than 1 year of age was limited to chloral hydrate. In an effort to decrease the rate of failed sedation, the time to discharge, and the adverse events at our institution, the radiology sedation committee explored oral pentobarbital as an alternative sedative. Findings of a pilot study (8) at our institution indicated that oral pentobarbital flavored with cherry syrup was more palatable and equally as effective as oral chloral hydrate. Subsequently, the radiology sedation committee and the hospital sedation task force approved an oral pentobarbital protocol for infants younger than 1 year. Since 1999, oral pentobarbital has replaced oral chloral hydrate as the primary sedative for infants who undergo MR imaging and CT studies. The purpose of our study was to compare the effectiveness and safety of oral pentobarbital (Nembutal; Abbott, North Chicago, Ill) and oral chloral hydrate (Major Pharmaceuticals, Rosemont, Ill) for sedation of infants younger than 1 year during MR imaging and CT studies. 537
MATERIALS AND METHODS
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Database In December 1993, the Children’s Hospital Radiology Sedation Committee was established to create sedation guidelines for the Department of Radiology and to monitor staff credentialing and quality assurance. The radiology nursing staff collects and records specific information related to each case of sedation. This information is transcribed to a computerized database (FileMakerPro, version 2.1; Claris, Cupertino, Calif) by one designated staff member (P.J.F.). The database contains information about patient demographics, medical diagnosis, body weight (in kilograms), time of examination, duration of fasting status, type of examination performed, date of the study, medications and doses (in milligram per kilogram of body weight) administered, patient’s American Society of Anesthesiologists physical status classification (9), adverse and paradoxical events both during and within 24 hours after discharge, time required to sedate, time to discharge, and cases of failed sedation. The information was documented by the radiology nurse or physician who was providing immediate care to the sedated patient. These data were transferred to the computerized database by a specialist trained in data input and retrieval. Within 24 hours of the sedation, a radiology nurse attempted to contact the parents of all patients who were sedated. Parental satisfaction and delayed adverse events were recorded at this time. All adverse events were reviewed at monthly meetings of the radiology sedation committee. Current protocols are routinely reviewed and modified, and new protocols were frequently started in an effort to improve practices regarding sedation.
Definition of Terms Definitions of adverse events recorded in the database (10) are listed as follows: A failed sedation.—Inadequate sedation subsequent to administration of the maximum allowable doses per the sedation protocol or inability to complete the planned procedure secondary to unacceptable motion artifacts. A paradoxical reaction.—Sustained irritability or combativeness of more than 30 minutes duration that occurs after administration of pentobarbital or chloral hydrate. A prolonged sedation.—Inability to meet discharge criteria 3 hours after ingestion 538
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of the sedative or failure to return to baseline mental and behavioral status within 24 hours of undergoing sedation. An abnormal oxygen saturation.—Sustained decrease in oxygen saturation of greater than 5% from baseline for more than 1 minute, despite oxygen delivery at 6 L/min through a face mask, head repositioning, suctioning, and physical stimulation. A need for resuscitation.—Decline in the patient’s respiratory rate and oxygen saturation that requires resuscitative efforts that include positive pressure ventilation, cardiopulmonary resuscitation, or the use of medications that reverse the sedation. A cardiovascular complication.—Sustained (⬎5-minute) decrease (⬎20%) in the patient’s mean arterial pressure with or without a decrease in heart rate below the lower limit of the normal range for the patient’s age. An unplanned admission.—An unexpected admission to the hospital overnight as a direct result of an adverse event directly related to the sedation. A gastrointestinal side effect.—Vomiting, aspiration, or diarrhea that occurs within 24 hours of the administration of sedation. An allergic reaction.—Unexplained rash or allergic symptoms that develop within 24 hours of undergoing sedation. The time to sedation.—Time in minutes from initial administration of a sedative to achievement of adequate sedation of the patient. The time to discharge.—Time in minutes from initial administration of a sedative to time at which the patient meets criteria for discharge from the recovery room.
Sedation Protocol All sedatives were administered by qualified individuals, according to strict sedation guidelines and protocols as established by the radiology sedation committee at our institution. All radiology nurses and supervising physicians must be credentialed to administer sedation in the Department of Radiology. The established requirements for credentialing include annual training in basic life support, biannual training in pediatric advanced life support, and an annual written examination on sedation designed by our institutional hospital sedation committee. The radiology nurses have extensive background in pediatric nursing that usually includes pediatric intensive care, neonatal intensive care, or pediatric emergency room care.
Prior to administration of sedatives, all sedation candidates are evaluated by a radiology nurse in order to determine whether the child has any medical conditions that would disqualify this patient from nurse-administered sedation. Specifically, in its sedation policies and guidelines, the radiology sedation committee established a list of medical conditions that would contraindicate nurse-administered sedation (Fig 1). The sedation policies and guidelines incorporate and expound on those recommended by the American Academy of Pediatrics (9). The nurse collects and documents data about the patient’s past medical, surgical, sedative, and anesthetic history. Results of physical examination, review of systems, and review of pertinent laboratory data are recorded, along with the current medications, allergies, and fasting status. After reviewing the information, the radiology nurse consults with the supervising radiologist for final approval of administration of sedatives. In the event that the radiologist needs additional information, consultations are arranged with appropriate specialty services (anesthesiology, otolaryngology, surgery, nephrology, endocrinology). After the radiologist orders the sedatives and discusses the plan with the nurse, the nurse then obtains signed informed consent from the parent of the patient. The chloral hydrate syrup (100 mg/ mL) was administered in doses of 20 –50 mg/kg to a maximum dose of 2,000 mg. Repeat doses of chloral hydrate may be administered every 30 minutes to a maximum of 100 mg/kg. Pentobarbital (50 mg/mL) is prepared with cherry syrup (Humco Cherry Syrup; Humco, Texarkana, Tex) and diluted to a 3:1 ratio. The initial dose is a standard 4 mg/kg that may be supplemented at aliquots of 2 mg/kg every 30 minutes to a maximum dose of 8 mg/kg. When diluted, the volume of pentobarbital usually fits into a 3-mL syringe. Chloral hydrate is administered in a 5- or 10-mL syringe, since the volume is greater. The oral medications are administered directly into the oral cavity with a syringe while the parent is holding the infant. All patients receive “blow by” oxygen (by means of either face mask or nasal prongs) throughout the sedation and during the procedure. Patients are monitored continuously by the radiology nurse, who records the oxygen saturation, respiratory rate, and heart rate at 5-minute intervals throughout the procedure. After the procedure, the patient is Mason et al
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in each adverse event outcome and failed sedation rate by using the two-tailed Fisher exact test and a significance level of .05 (nQuery Advisor, version 4.0; Statistical Solutions, Saugus, Mass). Analysis of the data was performed with a statistical package (SPSS, version 11.0; SPSS, Chicago, Ill). A two-tailed value with a difference with P ⬍ .05 was used to indicate statistical significance for all comparisons.
RESULTS
Figure 1. Medical conditions that contraindicate nurse-administered sedation.
transported to the radiology recovery room, where a nurse monitors and records the same vital signs every 15 minutes. A noninvasive blood pressure reading is documented prior to discharge from the recovery room. All patients are required to remain in the recovery room for a minimum of 2 hours after their final ingestion of sedative, regardless of whether they meet discharge criteria sooner.
Record Review After institutional review board approval to review the computerized database in the radiology department, we retrospectively reviewed the data to compare outcome variables for all infants younger than 1 year who received oral pentobarbital or oral chloral hydrate. The institutional review board at our institution did not require informed consent to perform this record review. Prospectively coded sedation records were abstracted by a data specialist. Patients in the oral chloral hydrate group underwent sedation from January 1, 1997, to December 31, 1999, and those in the oral pentobarbital group underwent sedation between January 1, 2000, and August 31, 2002. A total of 1,316 patients were included in this study. Outcome data were collected for statistical analysis as noted next.
Statistical Analysis Continuous variables were tested for normality by using the KolmogorovSmirnov goodness-of-fit test to deterVolume 230
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mine whether parametric or nonparametric statistical methods should be employed (11). Age, weight, and dose showed significant skewness and were therefore expressed in terms of the median and range, and the two groups were compared by using the Wilcoxon rank sum test (12). Time to sedation, sedation time, and time to discharge followed a normal distribution closely and were described with means and SDs, and groups were compared by using the two-sample Student t test. The Fisher exact test was used to compare proportions between the two groups for variables including sex, adverse events, and cases of failed sedation, whereas the Pearson 2 was used to compare American Society of Anesthesiologists level and type of procedure. A 95% CI was derived for the failed sedation rate in each group by using normal approximation (13). Multiple logistic regression analysis was applied to determine the odds of an adverse event and abnormal decrease in oxygen saturation between the two sedation groups in order to control for possible confounding effects of age, sex, weight, American Society of Anesthesiologists level, and type of procedure. The likelihood ratio test was used to assess the significance of the multivariate models (14). A power analysis was conducted a priori, and results indicated that the sample sizes of 1,024 cases of sedation with oral pentobarbital and 374 cases of sedation with oral chloral hydrate would provide 85% power to detect a 2% difference between the groups
There were a total of 1,398 cases of sedation. A total of 1,316 infants received either oral pentobarbital (985 patients, 1,024 cases of sedation) or oral chloral hydrate (331 patients, 374 cases of sedation). The two groups were comparable with respect to age, weight, sex (male-tofemale ratio nearly 1:1), American Society of Anesthesiologists level, and type of procedure (Table 1). The median dose was 4 mg/kg (range, 2– 8 mg/kg) for pentobarbital and 50 mg/kg (range, 20 –100 mg/kg) for chloral hydrate. In both groups, MR imaging accounted for 75% of the procedures. As shown in Table 2, there were no significant differences between the oral pentobarbital and chloral hydrate groups regarding mean time to sedation (18 minutes ⫾ 11 [SD] vs 17 minutes ⫾ 12, P ⫽ .47) or mean time to discharge (102 minutes ⫾ 34 vs 103 minutes ⫾ 36, P ⫽ .73). Patients in both groups had a mean approximate sedation time of 85 minutes ⫾ 35. Table 2 summarizes the adverse events during sedation and within 24 hours after discharge. During sedation, the proportion of adverse events was significantly lower in the oral pentobarbital group (0.5% vs 2.7%; P ⬍ .001, Fisher exact test). In the pentobarbital group, there were five adverse events (two cases of a decrease in oxygen saturation of ⬎5%, two cases of vomiting, and one case of prolonged sedation), whereas in the chloral hydrate group there were 10 adverse events (six cases of a decrease in oxygen saturation of ⬎5%, one case of vascular compromise, one case of vomiting, one case of a need for resuscitation, and one unplanned admission related to sedation). The unplanned admission was secondary to prolonged drowsiness in the recovery room. In this patient, discharge criteria were not met more than 3 hours after the last administration of sedation. No patients in the oral pentobarbital group required airway or cardiovas-
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cular resuscitation. There were no significant group differences observed with respect to drowsiness, hyperactivity, irritability, or vomiting within 24 hours after discharge. Figure 2 illustrates the percentage of patients in each sedation group according to specific types of adverse events. The rates were significantly different for the decrease in oxygen saturation (P ⬍ .01) and total adverse events (P ⬍ .001). There were no significant group differences in the rates of unplanned admissions (P ⫽ .27). Sedation failed in five patients in each group. While not statistically significant (P ⫽ .14), the failed sedation rate was lower with the oral pentobarbital protocol (0.5%; 95% CI: 0.2%, 1.0%) than with the oral chloral hydrate protocol (1.3%; 95% CI: 0.5%, 3.0%). Since variables potentially may have had an influence on adverse events in this study or may have led to confounding information, multiple logistic regression analysis was performed. After controlling for age, sex, weight, American Society of Anesthesiologists level, type of procedure, and sedative in the regression analysis, the only significant multivariate predictor of an adverse event was the sedative. The model indicated that age, sex, weight, American Society of Anesthesiologists level, and type of procedure were not associated with adverse events. Independent of these factors, patients who were sedated with oral chloral hydrate were estimated to be more than five times more likely to have an adverse event compared with those sedated with oral pentobarbital (adjusted odds ratio, 5.5; 95% CI: 2.3, 13.8; likelihood ratio test, 10.5; df ⫽ 1; P ⫽ .001). Given the significantly higher rate of abnormal oxygen saturation during sedation in the chloral hydrate group, we conducted the same kind of logistic regression analysis with decrease in oxygen saturation as the end point. The model revealed that age, sex, weight, American Society of Anesthesiologists level, and type of procedure were not significant predictors of a decrease in oxygen saturation (P ⬎ .20 for each variable); furthermore, after controlling for these other variables, the risk of an abnormally low oxygen saturation level during sedation was estimated to be more than seven times higher in patients sedated with oral chloral hydrate than it was in those sedated with pentobarbital (adjusted odds ratio, 7.3; 95% CI: 2.0, 36.5; likelihood ratio test, 8.1; df ⫽ 1; P ⫽ .004). 540
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TABLE 1 Demographic and Clinical Characteristics of Two Sedation Groups Group Characteristic
Oral Pentobarbital
Oral Chloral Hydrate
P Value
No. of patients Median age (d)* Median weight (kg)* Sex† M F ASA level† 1 2 3 No. of cases of sedation Median dose (mg/kg)* Type of procedure† MR imaging CT Both MR imaging and CT Nuclear medicine Interventional
985 212 (6–365) 7.7 (1.3–15.0)
331 185 (5–363) 7.3 (1.9–13.0)
.24 .27
498 (51) 487 (49)
169 (51) 162 (49)
.90
640 (65) 332 (34) 13 (1) 1,024 4 (2–8)
207 (63) 124 (37) 0 (0) 374 50 (20–100)
768 (75) 246 (24) 5 (0.5) 3 (0.3) 2 (0.2)
280 (75) 86 (23) 4 (1) 2 (0.5) 2 (0.5)
.14 NA .54
Note.—ASA ⫽ American Society of Anesthesiologists, NA ⫽ not applicable. * Data in parentheses are ranges. † Data in parentheses are percentages.
TABLE 2 Sedation and Adverse Event Data Cases of Sedation Datum Time to sedation (min)* Time to discharge (min)* Sedation time (min)* Adverse event† During sedation Abnormal oxygen saturation Allergy or paradoxical reaction Vascular compromise Vomiting Need for resuscitation Prolonged sedation Unplanned admission Total ⬍ 24 h after discharge Drowsiness Hyperactivity Irritability Vomiting Total Cases of failed sedation†
Oral Pentobarbital (n ⫽ 1,024)
Oral Chloral Hydrate (n ⫽ 374)
P Value
18 ⫾ 11 102 ⫾ 34 85 ⫾ 34
17 ⫾ 12 103 ⫾ 36 86 ⫾ 35
.47 .73 .60
2 (0.2) 0 (0) 0 (0) 2 (0.2) 0 (0) 1 (0.1) 0 (0) 5 (0.5)
6 (1.6) 0 (0) 1 (0.3) 1 (0.3) 1 (0.3) 0 (0) 1 (0.3)§ 10 (2.7)
⬍.01‡ ⬎.99 .27 ⬎.99 .27 ⬎.99 .27 ⬍.001‡
3 (0.3) 0 (0) 6 (0.6) 3 (0.3) 12 (1.2) 5 (0.5)
0 (0) 2 (0.5) 2 (0.5) 1 (0.3) 5 (1.3) 5 (1.3)
.57 .07 ⬎.99 ⬎.99 .79 .14
* Data are the mean ⫾ SD. † Data in parentheses are percentages. ‡ Statistically significant. § The unplanned admission was caused by oxygen desaturation during sedation that persisted in the recovery room.
DISCUSSION In 1993, the Department of Radiology established a computerized database for all cases of sedation. This database has enabled the radiology sedation committee to perform quality assurance, review
outcome data, and evaluate modifications of the sedation protocols. By conducting pilot studies with alternative sedation techniques (15) and analyzing the results efficiently with this database, we have been able to establish new protocols and improve existing ones (16). The seMason et al
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Figure 2. Bar graph shows comparison of oral pentobarbital and oral chloral hydrate with respect to cases of failed sedation, abnormal oxygen (O2) saturation, unplanned admissions, and adverse events. There was a statistically significant difference (ⴱ) between the two groups with respect to abnormal oxygen saturation and total adverse events. Percentage of cases of failed sedation was higher with oral chloral hydrate (1.3%) than with oral pentobarbital (0.5%), although this difference was not statistically significant (n.s.).
dation committee includes radiologists (P.E.B. among others), radiology nurses (L.C. among others), a clinical coordinator (L.C.), nurse practitioners (P.S., V.E.K.), and the director of Radiology Anesthesia (K.P.M.). In this way, the committee represents a collaboration between the Department of Anesthesia and the Department of Radiology, and this committee establishes guidelines, sets standards, and makes improvements to the sedation protocol. By using this computerized sedation database, we could review data about 1,316 infants younger than 1 year who underwent sedation with either oral chloral hydrate or oral pentobarbital over a span of almost 6 years. Chloral hydrate is used almost exclusively in the radiologic community as the oral sedative for infants (17). Chloral hydrate has a proved effectiveness and safety profile, especially for MR imaging and CT studies. With a peak gastric absorption at 60 minutes, chloral hydrate can produce prolonged sedation and respiratory and subsequent cardiovascular depression (18). The main difficulty in using this drug is related to its bad taste, which causes many infants to resist swallowing it or to regurgitate, making accurate dosing very difficult. Oral pentobarbital is more palatable than chloral hydrate (8). In adults, oral pentobarbital shows excellent absorption: Plasma levels of pentobarbital are the same following intramuscular and oral administration of equivalent Volume 230
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doses (19). Literature about oral pentobarbital as the sole sedative for infants is limited to that from our institution (8). Findings of a pilot study (8) with a small follow-up population suggested that oral pentobarbital was better tolerated and equally effective. In the larger population in the current study, we showed that oral pentobarbital has significantly fewer adverse events, including fewer episodes of oxygen desaturation. With failure rates ranging from 0.5% to 1.3%, both chloral hydrate and pentobarbital are equally successful in producing sedation. Findings reported in recently published literature (20) suggest that the rate of sedation-related adverse events (3.8% with conscious sedation, 9.2% with deep sedation) may be reduced by applying the guidelines established by the American Academy of Pediatrics/American Society of Anesthesiologists. Our adverse event rate is substantially less than that of others quoted in the literature (2,21,22). Our success, we believe, is multifactorial. It can be attributed in part to the close monitoring by the radiology sedation committee, availability of the sedation database, and our standards for credentialing both the radiologists and nurses. The skill of the radiology nurses, most of whom have extensive pediatric experience at the intensive care or emergency unit level, is an important component of a safe sedation program. This study had some limitations. We tried to design our study with good sta-
tistical power and sufficient numbers of patients in order to compare the two groups with respect to adverse events and cases of failed sedation. However, even with a good study design and a large number of patients, it is difficult to postulate the upper boundaries of what can be expected in the population, given that the actual numbers of adverse events are small. Specifically, there were five cases of failed sedation in each group, and on the basis of this small number, it is difficult to know how precise these rates are when applied to the larger pediatric population. We have tried to provide a reasonable idea of the precision of these rates by calculating 95% CIs. However, we acknowledge that the empiric adverse event and failed sedation rates observed in this study and the CIs that we have provided are limited in their application to the general pediatric population, given that our study groups were not random samples from the population and the numbers of actual adverse events were small. In conclusion, oral pentobarbital is a safe and effective agent for sedation of infants who undergo imaging procedures in the setting of an organized, appropriately staffed, and monitored sedation program. References 1. Ferrer-Brechner T, Winter J. Anesthetic considerations for cerebral computer tomography. Anesth Analg 1977; 56:344 – 347. 2. Greenberg SB, Faerber EN, Aspinall CL, Adams RC. High-dose chloral hydrate sedation for children undergoing MR imaging: safety and efficacy in relation to age. AJR Am J Roentgenol 1993; 161:639 – 641. 3. Greenberg SB, Faerber EN, Aspinall L. High dose chloral hydrate sedation for children undergoing CT. J Comput Assist Tomogr 1991; 15:467– 469. 4. American Academy of Pediatrics Committee on Drugs and Committee on Environmental Health. Use of chloral hydrate for sedation in children. Pediatrics 1993; 92:471– 473. 5. Thompson JR, Schneider S, Ashwal S, Holden BS, Hinshaw DB Jr, Hasso AN. The choice of sedation for computed tomography in children: a prospective evaluation. Radiology 1982; 143:475– 479. 6. Napoli KL, Ingall CG, Martin GR. Safety and efficacy of chloral hydrate sedation in children undergoing echocardiography. J Pediatr 1996; 129:287–291. 7. Ronchera-Oms CL, Casillas C, Marti-Bonmati L, et al. Oral chloral hydrate provides effective and safe sedation in paediatric magnetic resonance imaging. J Clin Pharm Ther 1994; 19:239 –243. 8. Chung T, Hoffer FA, Connor L, Zurakowski D, Burrows PE. The use of oral pentobarbital sodium (Nembutal) versus oral chloral hydrate in infants undergo-
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ing CT and MR imaging: a pilot study. Pediatr Radiol 2000; 30:332–335. American Academy of Pediatrics Committee on Drugs. Guidelines for monitoring and management of pediatric patients during and after sedation for diagnostic and therapeutic procedures. Pediatrics 1992; 89:1110 –1115. Mason KP, Zurakowski D, Karian VE, Connor L, Fontaine PJ, Burrows PE. Sedatives used in pediatric imaging: comparison of iv pentobarbital with iv pentobarbital with midazolam added. AJR Am J Roentgenol 2001; 177:427– 430. Armitage P, Berry G. Statistical methods in medical research. 3rd ed. Oxford, England: Blackwell Science, 1994; 394 – 403. Conover WJ. Practical nonparametric statistics. 3rd ed. New York, NY: Wiley, 1999; 271–286. Fleiss JL. Statistical methods for rates and proportions. 2nd ed. New York, NY: Wiley, 1981; 29 –38. Hosmer DW, Lemeshow S. Applied logis-
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tic regression. 2nd ed. New York, NY: Wiley, 2000; 47– 69. Mason KP, Michna E, DiNardo JA, et al. Evolution of a protocol for ketamine-induced sedation as an alternative to general anesthesia for interventional radiologic procedures in pediatric patients. Radiology 2002; 225:457– 465. Karian VE, Burrows PE, Zurakowski D, Connor L, Mason KP. Sedation for pediatric radiological procedures: analysis of potential causes of sedation failure and paradoxical reactions. Pediatr Radiol 1999; 29:869 – 873. Sury MR, Hatch DJ, Deeley T, Dicks-Mireaux C, Chong WK. Development of a nurse-led sedation service for paediatric magnetic resonance imaging. Lancet 1999; 353:1667–1671. Vade A, Sukhani R, Dolenga M, Habisohn-Schuck C. Chloral hydrate sedation of children undergoing CT and MR imaging: safety as judged by Ameri-
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can Academy of Pediatrics guidelines. AJR Am J Roentgenol 1995; 165:905–909. Nair SG, Dundee JW, Clarke RS, Howard PJ. Plasma pentobarbitone levels: influence of the preparation, route and method of administration. Anaesthesia 1976; 31:1037–1042. Hoffman GM, Nowakowski R, Troshynski TJ, Berens RJ, Weisman SJ. Risk reduction is pediatric procedural sedation by application of an American Academy of Pediatrics/American Society of Anesthesiologists process model. Pediatrics 2002; 109: 236 –243. Egelhoff JC, Ball WS Jr, Koch BL, Parks TD. Safety and efficacy of sedation in children using a structured sedation program. AJR Am J Roentgenol 1997; 168: 1259 –1262. Hubbard AM, Markowitz RI, Kimmel B, Kroger M, Bartko MB. Sedation for pediatric patients undergoing CT and MRI. J Comput Assist Tomogr 1992; 16:3– 6.
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