Magnetic resonance imaging in children: Role of the anaesthesiologist:

Effect of ketamine pretreatment for anaesthesia in patients undergoing percutaneous transluminal balloon angioplasty with continuous remifentanil infusion

BACKGROUND

An appropriate level of sedation and pharmacological assist are essential during percutaneous transluminal balloon angioplasty (PTA). Ketamine provides good analgesia while preserving airway patency, ventilation, and cardiovascular stability with an opioid sparing effect suggesting that it would be ideal in combination with remifentanil and midazolam in spontaneously breathing patients. We evaluated the effect of a small dose of ketamine added to midazolam and remifentanil on analgesia/sedation for PTA procedures.

METHODS

Sixty-four patients receiving PTA were enrolled. The Control group received midazolam 1.0 mg i.v. and continuous infusion of remifentanil 0.05 µg/kg/min. The Ketamine group received, in addition, an intravenous bolus of 0.5 mg/kg ketamine. Patients' haemodynamic data were monitored before remifentanil infusion, 5 min after remifentanil infusion, at 1, 3, 5, 30 min after incision, and at admission to the recovery room. Verbal numerical rating scales (VNRS) and sedation [OAA/S (Observer's Assessment of Alertness/Sedation)] scores were also recorded.

RESULTS

The VNRS values at 1, 3, and 5 min after incision and OAA/S scores at 5 min after remifentanil infusion, and 1, 3, and 5 min after incision were lower in the Ketamine group than in the Control group. In the Control group, the VNRS value at 1 min after incision significantly increased and OAA/S values at 3, 5, and 30 min after incision significantly decreased compared to baseline values, while there were no significant changes in the ketamine group.

CONCLUSIONS

A small dose of ketamine as an adjunct sedative to the combination of midazolam and remifentanil produced a better quality of sedation and analgesia than without ketamine and provided stable respiration without cardiopulmonary deterioration.

Effect of distance and infusion rate on operation of Medfusion 2010 infusion pump during magnetic resonance imaging

STUDY OBJECTIVES

To determine the accuracy and reliability of intravenous infusion, as well as magnetic resonance image effect of the Medfusion 2010 infusion pump (Medex Medical Supplies, Inc., Duluth, GA) at distances of 2, 4, 8, 12, and 16 feet from a 1.5 Tesla MRI magnet over a four-week time interval, using infusion rates that would correspond to those of propofol administration.

DESIGN

Prospective, open-label study.

SETTING

Radiology department MRI in an American academic medical center.

INTERVENTIONS

Five infusion pumps, including one outside the MRI suite as control, were tested. Pumps were evaluated at distances of 2, 4, 8, 12, and 16 feet from a 1.5 Tesla magnet. One pump at distances of 2 and 16 feet was tested during 30 and 90 hours of operation, respectively. Three pumps at distances of 4, 8, and 12 feet were tested during 120 hours of operation. Pump batteries were recharged for 18 hours outside the MRI suite between the 6-hour test periods. Distilled, deionized water was infused from a 30-mL or 60-mL syringe via a 36-inch Medex small-bore extension set into a graduated collection cylinder at rates of 5, 10.5, 21, or 42 mL/hr. Each rate was increased to the next infusion rate level at 30-hour weekly intervals. The collection cylinder with infused water was weighed on an electronic scale accurate to within +/-0.001 g. Analysis of variance and regression analysis were used to analyze data. A p < 0.05 value was considered statistically significant.

MEASUREMENTS AND MAIN RESULTS

There was no significant difference comparing the grams weight of volume measured and the mL volume visualized within and between groups at varying distances from the magnet. Increasing infusion rates resulted in corresponding increases in volume delivered irrespective of the distance from the magnet.

CONCLUSIONS

The Medfusion 2010 infusion pumps were found to be reliable and accurate, without causing failure or any significant degradation of MRI images compared to control at infusion rate of 42 mL/hr at a distance of 2 feet for 30 hours; and a rate of 5.0, 10.5, 21, and 42 mL/hr at 16 feet for 90 hours; and at 4, 8, and 12 feet for 120 hours of operation.

Anaesthesia with midazolam and S-(+)-ketamine in spontaneously breathing paediatric patients during magnetic resonance imaging

We evaluated safety and efficacy of a sedation technique based on rectal and intravenous S-(+)-ketamine and midazolam to achieve immobilization during Magnetic Resonance Imaging (MRI). Thirty-four paediatric patients were randomly assigned to undergo either the sedation protocol (study group) or general anaesthesia (control group). Imaging was successfully completed in all children. Children in the study group received a rectal bolus (0.5 mg x kg(-1) midazolam and 5 mg x kg(-1) S-(+)-ketamine) and required additional i.v. supplementation (20+/-10 microg x kg(-1) x min(-1) S-(+)-ketamine and 4+/-2 microg x kg(-1) x min(-1) midazolam), spontaneous ventilation was maintained. Transient desaturation occurred once during sedation and four times in the control group (P=0.34). PECO2 was 5.3+/-0.5 kPa (40+/-4 mm Hg) in the study group and 4.1+/-0.6 kPa (31+/-5 mm Hg) in the control group (P<0.001). Induction and discharge times were shorter in the study group (P<0.001), recovery times did not differ significantly between the groups. Our study confirms that a combination of rectal and supplemental intravenous S-(+)-ketamine plus midazolam is a safe and useful alternative to general anaesthesia for MRI in selected paediatric patients.

Development of a nurse-led sedation service for paediatric magnetic resonance imaging

BACKGROUND

Children generally lie still enough for magnetic resonance imaging (MRI) only if they are asleep, either under sedation, which is deeper than conscious sedation, or under anaesthesia. Anaesthesia resources, however, are limited, and non-anaesthetists must use sedation frequently. Demand for MRI has increased and the failure of our sedation regimen led to an impractical demand for anaesthesia and unacceptable waiting times for scanning. We have therefore developed a nurse-led sedation service in a designated unit next to the scanner. This study assessed the safety and efficacy of this approach.

METHODS

Children who required MRI were sedated in the unit by designated sedationist nurses, who used an oral drug regimen (according to weight and age from conception: weight <5 kg, 50 mg/kg chloral hydrate; 5-10 kg, 100 mg/kg chloral hydrate; 10-20 kg, 1 mg/kg temazepam plus 0.25 mg/kg droperidol; >20 kg temazepam and droperidol as directed by radiologist, maximum doses 20 mg and 5 mg respectively). Nurses checked patients for their suitability, charted and administered the drugs according to a protocol, and monitored the children throughout the sedation. We prospectively audited failure and complications of sedation.

FINDINGS

During the 30 month study, there were 1155 sedations. 61 (5%) were unsuccessful, and there were no adverse events relating to the airway or breathing. After scanning had finished all children, in response to gently pinching the nose, could open their mouths to maintain their airway.

INTERPRETATION

This study suggests that it is possible to have a nurse-led sedation service for MRI of children that is both successful and safe.