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1 Department of Radiology, Children's Hospital, 300 Longwood Ave., Harvard
Medical School, Boston, MA 02115.
2 Departments of Biostatistics and Orthopaedic Surgery, Children's Hospital,
Harvard Medical School, Boston, MA 02115.
3 Department of Anesthesia, Children's Hospital, Harvard Medical School, Boston,
MA 02115.
Received March 21, 2003;
accepted after revision June 2, 2003.
Address correspondence to L. Connor.
Abstract
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SUBJECTS AND METHODS. One hundred sixty-five patients (70 girls, 95 boys) having a mean age of 3.4 years received IV pentobarbital sedation with or without fentanyl for undergoing MRI from January through March 2002. Each child was sedated with 2–6 mg/kg of body weight of IV pentobarbital and an additional 1–3 µg/kg of fentanyl if needed. After the administration of sedation, a 28-ft (8.5 m) nasal cannula with capnography capability was applied to each patient, and capnogram tracings and values were recorded every 5 min.
RESULTS. Mean values of end-tidal carbon dioxide were between 37 and 42 mm Hg during 60 min of sedation for both groups. When IV pentobarbital was used alone, no significant difference was seen between patients who received 3–5 mg of pentobarbital and those who received more than 5 mg (p = 0.97, F test).
CONCLUSION. End-tidal carbon dioxide levels remain within normal clinical range during sedation with IV pentobarbital with or without fentanyl. Our sedation protocol produced no significant deviations from normal respiratory parameters.
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Patients receiving sedation are graded according to levels of sedation as recommended by the American Society of Anesthesia, the American Academy of Pediatrics, and the Joint Commission on Accreditation of Healthcare Organizations [12-14]. After institutional review board approval and parental consent for sedation, all patients sedated with IV pentobarbital with or without IV fentanyl for MRI and tolerant of the nasal cannula from January 1, 2002 to March 31, 2002, were enrolled in this study. Patients who were intolerant of the nasal cannula and patients receiving oral sedation were excluded.
According to the radiology sedation guidelines of our institution, credentialed radiology nurses screen all sedation candidates before scheduling the MRI to determine if the patient meets nursing sedation criteria. The credentialing process for radiology nurses includes passing a written, on-line hospital sedation posttest, the pediatric advanced life support certification, and an annual competency demonstration of bag–valve–mask ventilation. On the day of the MRI, the radiology nurse reviews and updates the patient's medical history, current medications, allergies, fasting status, and vital signs and performs a physical assessment focused on the cardiovascular and respiratory systems. After reviewing the history and physical examination findings with the radiologist, the nurse obtains informed consent from the parent or guardian. Qualified and credentialed radiology nurses and radiologists administer all sedation in accordance with Joint Commission on Accreditation of Healthcare Organizations, American Academy of Pediatrics, and institution protocol [12–16].
Each child was sedated according to the Department of Radiology sedation guidelines with 2–6 mg/kg of body weight of IV pentobarbital. According to protocol, 2 mg is administered at 1-min intervals until the patient is adequately sedated. Adequate sedation is defined as a modified Ramsey sedation score of 4 or 5 [17]. If the patient was not adequately sedated with 6 mg/kg of IV pentobarbital, 1–3 µg/kg of IV fentanyl was added at doses of 1 µg/kg at 5-min intervals.
Once the child was sedated and positioned in the scanner, the nasal cannula was placed and oxygen was administered at 2 L/min. An MR monitor CE 0459 (Datascope, Paramus, NJ) was attached to the end-tidal carbon dioxide portion of the cannula and provided a capnogram tracing, end-tidal carbon dioxide values, and respiratory rate. Endtidal carbon dioxide was documented every 5 min throughout the procedure, as was oxygen saturation, heart rate, and respiratory rate. Additional predictor variables documented included age, weight, sex, reason for scan, current medications, pentobarbital dose, and American Society of Anesthesiologists status. Adverse events were recorded in accordance with sedation protocol. In 148 of our patients (90%), scanning lasted 15–60 min, and in 17 patients scanning required longer than 1 hr (65–90 min). Once scanning was completed, the nasal cannula was removed and the patient was taken to the recovery area.
End-tidal carbon dioxide measurements every 5 min were analyzed using regression analysis with a random-effects mixed model to account for the within-subject correlation and the different lengths of sedation time among patients [18].
Power analysis indicated that the sample size would provide 80% power using a paired t test to detect a variation of 5% in the end-tidal carbon dioxide values during the sedation period assuming an SD of 10% in each group. Patients receiving IV pentobarbital alone and those receiving IV pentobarbital plus IV fentanyl were compared throughout the sedation time using analysis of covariance with a group-by-time interaction F test to compare end-tidal carbon dioxide rates of change (slopes) between the two groups [19]. The same statistical approach was applied to assess time-related changes in end-tidal carbon dioxide among patients receiving different pentobarbital doses (3–5 mg/kg vs > 5 mg/kg) within the pentobarbitalalone group. Continuous variables following a normal distribution including age, weight, and dose were presented in terms of the mean and SD and were compared between groups using the Student's t test, whereas variables showing significant skewness (e.g., sedation time) were summarized by the median and interquartile range and compared using the Mann-Whitney U test [20]. Categorical data such as sex, scan type, and level of sedation immediately before scanning were compared between groups using Fisher's exact test for proportions. For all statistical tests, a two-tailed p value of less than 0.05 was considered statistically significant. Data analysis was performed using PROC GLM and PROC REG in the SAS statistical package (version 6.12, SAS Institute, Cary, NC). Sample size and power analysis calculations were determined using the nQuery Advisor software program (version 4.0, Statistical Solutions, Saugus, MA).
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Two patients had adverse events. One was dizzy and vomited after scanning was completed. Sedation failed in the other patient, who received 6 mg/kg of IV pentobarbital and 3 µg/kg of IV fentanyl; the patient was rescheduled to receive general anesthesia. Five patients were excluded because of mouth breathing that precluded our ability to achieve accurate capnography data. No patients in this study experienced an oxygen saturation rate of less than 95%.
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3 µg/kg), and does not alter the end-tidal carbon dioxide from
clinical norms. Although narcotics can increase endtidal carbon dioxide, our
study shows that small doses will not cause significant changes in ventilation
status. This is important for the sedation of patients who may have an
elevated intracranial pressure when increased end-tidal carbon dioxide is not
wanted. Although no significant adverse respiratory events occurred in this
study, published data for children undergoing sedation have indicated that
approximately 4% of patients with conscious sedation and 9% with deep sedation
experience decreased oxygen saturation and require resuscitation
[15]. End-tidal carbon dioxide
monitoring may alert the practitioner to impending oxygen desaturation and
significant respiratory depression
[21,
22]. The value of capnography is appreciated during anesthesia as an airway and ventilation monitor so much that it has become standard practice in the operating room [22]. Although our study does not show any clinically significant changes in respiratory parameters, the radiology sedation committee has approved end-tidal carbon dioxide monitoring for sedated patients undergoing MRI. Large-scale studies will determine whether end-tidal carbon dioxide monitoring can provide early detection of apnea and respiratory depression and subsequently allow early intervention before oxygen desaturation. A recent article suggests that applying the guidelines established by the American Academy of Pediatrics and the American Society of Anesthesiologists may reduce the rate of sedation-related adverse events [15]. Data from our institution have also shown that sedation may successfully and safely be administered by credentialed radiologists and nurses and available pediatric anesthesiologists with close monitoring by the radiology sedation committee [1]. The radiology nurses used in our sedation program have extensive pediatric experience at the intensive care or emergency unit level.
Our study had some limitations. The nasal cannulas are not reusable and cost $10 each. The cannula used in this study is not effective in mouth breathers. However, since our initial trial, we have found a company that manufactures a nasal–oral device, MAC-Line end-tidal carbon dioxide circuit (Oridian, Austin, TX). This device is similar to a nasal cannula but has an added midline extension that descends toward the mouth to collect exhaled carbon dioxide in mouth breathers. Because the nasal cannulas were removed at the end of scanning, we do not know how long it took for the end-tidal carbon dioxide levels to return to baseline. Our department is in the process of purchasing equipment to monitor end-tidal carbon dioxide in the radiology recovery area.
In conclusion, to our knowledge ours is the first study documenting end-tidal carbon dioxide levels in children during pentobarbital sedation for MRI. End-tidal carbon dioxide monitoring is known to be more sensitive than pulse oximetry for detecting potential respiratory events [4–6, 23, 24]. Studies at our institution have shown that the incidence of adverse respiratory events is less than 2% [1]. A larger prospective randomized study should be conducted to determine the sensitivity of end-tidal carbon dioxide monitoring for identifying impending oxygen desaturation and respiratory compromise. At our institution, end-tidal carbon dioxide monitoring is the standard of care for all patients receiving IV sedation for MRI. Our study is important because it confirms that pediatric sedation with IV pentobarbital and IV fentanyl within proper clinical guidelines does not elicit significant respiratory depression.
Acknowledgments
We thank Martha Curley for her collegial support.
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, n = 25). Curves illustrate significantly faster rate of
increase in end-tidal carbon dioxide for group who had fentanyl added, as
depicted by steeper slope (p = 0.004, F test).