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Special Reports |
1 From the Department of Radiology, Johns Hopkins Hospital, 600 N Wolfe St, Baltimore, MD 21287. Received July 8, 1999; revision requested August 25; final revision received January 7, 2000; accepted January 12. Address correspondence to D.A.B.
ABSTRACT
PURPOSE: To measure the safety and effectiveness of conscious sedation in order to assess utilization and the effect on magnetic resonance (MR) imaging examinations.
MATERIALS AND METHODS: A database of conscious sedation records for MR imaging at the Johns Hopkins Hospital, Baltimore, Md, from 1991 to 1998 was searched. Safety data according to medication and procedure duration for each nurse were tabulated for 6,093 patient records. Data were analyzed by using quality control statistical measures to determine time utilization and effectiveness. Break-even costs for the procedure were determined.
RESULTS: Of 6,093 patients scheduled for examination, 4,761 patients (78.1%) received conscious sedation by the MR conscious sedation service. Complications were observed in 20 of the 4,761 patients (0.42%). No deaths occurred. The most common complication was oxygen desaturation (n = 8). Diagnostic and complete MR examinations were performed in 4,453 of the 4,761 patients (93.5%). The mean time to sedate the patient (± SD) was 23.6 minutes ± 15.2 for specialized MR sedation nurses and 26.8 minutes ± 20.1 for general radiology nurses (P < .001). For inpatient nurses from the inpatient hospital units, the sedation time was considerably longer (47.3 minutes ± 36.6, P < .001) and more variable. Break-even costs were 37% ($11 vs $8 for MR room time) more for general radiology nurses than for specialized MR sedation nurses performing the procedure.
CONCLUSION: Conscious sedation is safe and has a high effectiveness rate. A highly specialized nursing staff reduces procedure variability and cost.
Index terms: Anesthesia, **.121412 • Magnetic resonance (MR), in infants and children, **.12141 • Magnetic resonance (MR), quality assurance, **.12141 • Magnetic resonance (MR), safety, **.12141
Sedation is frequently necessary for certain patient groups undergoing magnetic resonance (MR) imaging examination. Pediatric patients may require sedation to reduce artifacts from motion. Adults who are claustrophobic represent an additional group of patients who may require sedation for successful completion of the MR examination. Sedation for MR imaging typically is described as "conscious sedation," in that the patient is able to be aroused and can maintain his or her airway and respiratory pattern. However, protective airway reflexes are lost. With high-field-strength MR, the high noise level of the imager frequently requires sedation at a deeper level and for a longer time than required for other diagnostic examinations, such as computed tomography (1).
The American Academy of Pediatrics (2) and the Joint Commission on the Accreditation of Health Care Organizations (3) recommend that the patients undergoing sedation be monitored by an independent observer whose sole responsibility is to observe the patient continuously and record vital signs at regular intervals. At our institution and others (4,5), radiologists work together with registered nurses who administer sedation medication and monitor the sedated patients.
MR sedation can be costly because of the time that must be allocated to the procedure. Sedated patients may interrupt the normal scheduling of examinations for other patients, since the MR suite must be available as soon as possible after the patient is sufficiently sedated. Failure to have the MR room available increases the likelihood of a nondiagnostic procedure due to the patient’s waking. The time requirement for sedation nurses and physicians is also very high. Brief physical examinations, medical histories, and reviews of systems are required. Intravenous catheters may be placed, and monitoring equipment must be placed on the patient. Sedation nurses have the exclusive duty of patient monitoring following medication administration and until the patient recovers. Thus, in addition to sedation safety and effectiveness, the "efficiency" of the sedation procedure depends on factors such as having the patient wake quickly after the MR examination and having the patient adequately sedated at a predictable time when the MR suite is available.
At the Johns Hopkins Hospital, Baltimore, Md, sedation procedures for MR imaging have been recorded in a database since 1991 for the purposes of adverse event, utilization rate, and quality assurance assessments. We performed this study to measure the safety and effectiveness of conscious sedation over an 8-year period in order to assess utilization and the effect on MR imaging examinations. In addition, we evaluated methods for assessing the efficiency of the sedation procedure for quality control purposes.
MATERIALS AND METHODS
Database
A sedation database was written (by S.N.B.) by using FILEMAKER PRO, version 2.1, software (Claris, Cupertino, Calif). Patient monitoring data were recorded on a conscious sedation flowchart by nurses; these data were later entered into the database by a single specified nurse who was familiar with the database and who entered data consistently. A total of 205 fields are present in the database. In addition to patient demographics, additional categories of information recorded include patient history, laboratory data, sedation medications, and MR imaging times. Representative fields recorded in the database are presented in Figure 1.
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Sedation Protocol
Sedation procedures were conducted according to our institutional and divisional policies for conscious sedation. During the MR examination, these policies necessitated continuous monitoring of the hemoglobin oxygen saturation (SpO2) and pulse rate. Noninvasive blood pressure measurement was performed at 5-minute intervals during induction and recovery and between MR pulse sequences. Visual patient monitoring with a closed-circuit camera of the MR bore or by nursing personnel in the MR imaging room was also required. All monitoring was performed by sedation nursing staff with physician oversight. Prior to sedation, a brief physical examination, determination of history of present illness, determination of past medical history, and review of systems were conducted by a physician radiologist (including D.A.B., S.N.B.) (an attending physician, fellow, or resident).
Contraindications to conscious sedation included known allergy to the sedation medication, less than 6 hours of fasting from solid food and less than 2 hours of fasting from liquids, abnormal electrocardiogram, any condition (including a cold or sinus infection) judged to result in airway compromise or that would interfere with intubation, known hemodynamic instability, and/or clinically important coexistent morbid conditions. Patients’ conditions were classified according to the American Society of Anesthesiologists system; class I (normally healthy) and II (mild systemic disorder) patients were eligible for conscious sedation.
The medication and dose used for sedation were based on patient age and weight and are shown in Table 1. For American Society of Anesthesiologists class I patients, benzodiazepines (oral or intravenous administration) were included in the sedation protocol for single medication equivalent doses greater than 10 mg of diazepam (0.2 mg per kilogram of body weight), as these were defined by hospital policy to induce sedation—deep sedation. If the patient had undergone a prior examination with sedation, the sedation database was consulted to determine whether adverse events or complications had previously occurred (eg, paradoxical reactions to sedation medication). If so, the sedation prescription was subsequently modified. The sedation regimen was selected by the sedation nurse staff and the physician staff.
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Complications and adverse events were recorded by nursing personnel. Follow-up telephone calls were made to determine patient outcome if complications were present during the examination. Oxygen desaturation was considered to be present if the SpO2 decreased by more than 5% relative to the baseline level.
Statistical Analysis
Database records were exported into STATVIEW, version 4.5 (Abacus Concepts, Berkeley, Calif). Control charts that display mean values (xbar charts) and the SDs of the mean values (sbar charts) were used. These are standard statistical constructs that show variation of a measured parameter over time. By convention, the "upper control limit" and the "lower control limit" for these displays are taken to be 3
. The variation of parameters, such as the time to sedate a patient, that are greater than the upper control limit or less than the lower control limit are said to be "out of control" or unpredictable. Variation that is greater than the lower control limit and less than the upper control limit is said to be "in control" or predictable.
Subanalysis was performed according to the type of sedation medication and according to the sedation nurse involved in the procedure. For comparison between groups, a two-tailed t test was used with unequal variance and with correction for repeated measures. Statistical measures were considered significant for a P value less than .05.
Cost Analysis
Examination charges and reimbursement rates for examinations were evaluated on the basis of hospital billing data from Current Procedural Terminology, or CPT, codes over a 6-month period. Sedation nursing costs (salary and benefits) were based on the number of full-time-equivalent staff available during the same period. The costs of medication and patient care items were estimated as $30 per examination over the entire study period on the basis of a review of supply costs.
RESULTS
Sedation Effectiveness and Safety
A total of 6,093 patients requiring sedation had examinations scheduled with the MR division sedation service over the interval of March 1991 to November 1998 (Fig 2, Table 2). The mean age of patients requiring conscious sedation nursing support was 12.6 years ± 18.6 (range, 0–97 years) (Table 3). Patients were typically scheduled by means of telephone conversation with the referring physician.
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Four thousand seven hundred sixty-one (78.1%) patients received at least one sedation medication. The administration of the medication initiated the formal conscious sedation flowcharts for monitoring and vital signs assessments. Of these 4,761 patients, 4,453 (93.5%) had successful sedation as defined with the criteria outlined in Materials and Methods. The distribution of medications used is shown in Table 4. The failure rates of sedation for chloral hydrate and pentobarbital sodium (4.8% and 4.9%, respectively) were lower than those for oral diazepam and alprazolam (13.1% and 9.4%, respectively) (P < .05).
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Adverse events associated with the sedation procedure occurred in 20 of the 4,761 patients (0.42%). The most frequent complication was hypoxemia (eight patients). Four patients had coughing and congestion that increased during the MR imaging. Associated motion in these patients prevented the completion of the examination. In three patients, bronchospasm and stridor were present during the sedation procedure. All patients were able to be discharged to home, and no long-term complications occurred. Table 5 lists complications and the associated medications.
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The duration of the MR examination was similar for all three nurse groups (group A, 50.7 minutes ± 23.2; group B, 48.0 minutes ± 23.4; hospital ward nurses, 45.5 minutes ± 20.0; P > .05 for all pairwise combinations, with correction for multiple comparisons). This indicates that the length of the MR examination was similar for all groups, so that examination complexity was not a factor in explaining shorter sedation times for group A compared with other nurses.
Medication doses were tracked to determine protocol compliance for ongoing safety review. Figure 6 is the quality control chart for the use of chloral hydrate, which shows consistency in the dosing patterns during the study period. Development of improved sedation protocols during the study period also contributed to decreased variability in the administered dose. Similar use patterns were noted for pentobarbital sodium (not shown).
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The charge for the sedation procedure is $292 at our hospital; the mean reimbursement is 88% of the charge ($256). Figure 7 shows cost versus reimbursement; the break-even point is the intersection of the cost line and the reimbursement line. By assuming a maximum of four sedation procedures per day per nurse, the break-even MR room cost per minute for group A nurses is $11/min. For group B nurses, MR room charges must be $8/min or less to break even.
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The success of sedation for MR has typically been measured by two factors: (a) the safety of the sedation procedure (lack of adverse events) and (b) the effectiveness of the procedure (successful completion of the diagnostic examination). Several authors (1,4,6) have reviewed their experience in this regard.
Shepherd et al (1) reported on a study of 375 patients, with successful examination completion in 85% of patients and with two adverse events (0.5%). Volle et al (6) described sedation procedures in 780 patients, with successful examinations in 91% and with two adverse events (0.3%). Similarly, Vade et al (4) examined 217 patients undergoing sedation for MR; the overall success rate was 97%, with an adverse event rate of 2.4% (moderate to severe hypoxemia, SpO2 < 90%, and/or emesis).
While these studies were composed primarily of pediatric patients, approximately 18% (857 of 4,702 patients) of our patient population were adults (older than 18 years of age). Our results of approximately a 0.5% complication rate over a very large and diverse patient population are nevertheless consistent with those in prior studies. We have also documented a success rate for sedation MR of 93.5%. In our study, we captured data on approximately seven times more patients than in other studies (1,4,6). On the basis of these results, sedation in MR should be considered to be both safe and effective for the protocols that we have used.
In our experience, sedation for MR can have a substantial effect on patient throughput. After administration of the sedation medication, an MR room is assigned to the patient for approximately 30 minutes later. If the patient is inadequately sedated, the MR examination is likely to be nondiagnostic because of motion. Inadequate sedation can also result in increased procedure time. Oversedation of the patient requires additional nursing staff time because of extended recovery periods, prevents others from undergoing their examinations because of nursing staff unavailability, and results in an increased rate of complications.
In addition to safety and effectiveness, the effect of sedation on MR examinations can be measured by assessing several time variables by using control limit charts. For personnel performing sedation procedures, we documented expertise in those nurses performing the most procedures. For example, nurses with a primary responsibility in MR performed better than nurses who performed duties for multiple imaging services. When a change in nursing staff occurred because of a retirement, the variation of procedure times markedly increased. MR room time is charged at approximately $7/min at our hospital, so that holding an MR suite open for a soon-to-be sedated patient is expensive. We observed 33% (20.1 vs 15.2 minutes [SDs]) more variation in the time for patients to be sedated when general radiology nurses were involved compared with the variation in time for dedicated MR sedation nurses. Compared with inpatient unit nurses, there was 2.4 times more variation (36.6 vs 15.2 min) with dedicated MR personnel.
In our hospital, only 78% (4,761 of 6,093) of scheduled sedation MR examinations were actually performed. Reasons for less than 100% utilization included patients who did not arrive for their appointments, physicians who canceled examinations, and patients who did not meet the criteria for conscious sedation. The number of sedation appointments available is determined by the number of sedation nurses multiplied by 8 hours and divided by the total procedure time (90 minutes ± 30). Conservatively, each sedation nurse could perform four procedures per day at 100% capacity. Since more than 20% of scheduled examina-tions are not performed, one option is to increase the number of sedation schedule appointments. Alternatively, additional nursing personnel time can be allotted to other duties within the MR section.
A limitation of this study was that data were collected by individuals performing the procedures, so that bias could be introduced. However, records were recorded on a standard medical record flow sheet contained as part of the patient’s medical record. Trends regarding time of examination were nevertheless present. We have also included data for both pediatric and adult sedation, since both populations are served by our MR sedation staff. Eighty percent of our study population were 18 years or younger, and the need for specialized nurses is much greater in the pediatric population. Pediatric versus adult groups receive different sedation medications (choral hydrate and pentobarbital sodium most commonly for pediatric patients). However, the principles of time monitoring and analysis of procedure variations apply to both groups, and both groups affect MR examinations in the same manner.
In conclusion, sedation for MR imaging according to the protocol outlined is safe and has a high effectiveness rate. Procedures are best performed by staff members whose primary responsibility is to perform these procedures. Sedation performed by other staff members leads to increased procedure time and increased variation in procedure time.
ACKNOWLEDGMENTS
The efforts of Jamie Flickinger, RN, in coordinating the database input and quality control monitoring are gratefully acknowledged. We thank Edward Smith, MBA, for helpful discussions, overall data review, and cost analysis. Paul Gurny, MBA, MS, graciously assisted in statistical method review and reviewed the study design.
FOOTNOTES
See also the editorial by Finn in this issue (pp 633–634 ).
Abbreviation: SpO2 = hemoglobin oxygen saturation,
Author contributions: Guarantor of integrity of entire study, D.A.B.; study concepts and design, D.A.B., S.N.B.; definition of intellectual content, D.A.B.; literature research, D.A.B.; data acquisition, D.A.B., S.N.B.; data analysis, D.A.B.; statistical analysis, D.A.B.; manuscript preparation, D.A.B.; manuscript editing and review, D.A.B., S.N.B.
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