There is an increased demand for pediatric anesthesiologists to travel outside the operating room to provide general anesthesia or monitored sedation for a variety of medical investigations or procedures in infants and children of all ages. The concept that treatment in a children’s hospital should be a pain-and stress-free experience is now well accepted, and this has placed additional responsibilities on the anesthesia service.
Equipment for the Remote Location
Each area should be fully equipped for the anesthesia care of the child and for any resuscitation that might be required; much of this may be provided by means of a travel cart. Each area should be provided with:
Primary and backup oxygen supply (checked O 2 tank), and means to provide intermittent positive-pressure ventilation (IPPV).
Facilities for gas scavenging if any inhalation anesthetics are used.
Functioning suction apparatus.
Electrical outlets (operating room standards).
Means of immediate communication to the operating room personnel.
Facilities and staff for the preparation and recovery of children according to published guidelines. *
* Guidelines for non-operating room anesthetizing locations. American Society of Anesthesiologists, Park Ridge Il, 2003.
Resuscitation cart and defibrillator (immediately available).
In addition, all drugs and equipment to manage the child during the procedure must be provided:
Monitoring for pulse oximetry, electrocardiography (ECG), end-tidal carbon dioxide, blood pressure, and body temperature.
Airway supplies; age and size appropriate facemasks, laryngoscope blades, endotracheal tubes, oropharyngeal airways, laryngeal mask airways, suction catheters, and breathing circuits.
Appropriate anesthesia equipment, infusion pumps, etc.
All necessary drugs for anesthesia and sedation, and, syringes, a variety of IV catheters, intravenous fluid and fluid administration sets.
Emergency resuscitation drugs.
Where indicated: equipment to maintain body temperature (e.g., forced air warmer for cardiac catheterization laboratory).
ADMINISTRATIVE PROCEDURE FOR REMOTE ANESTHESIA
For children anesthetized in remote locations, the following steps should be taken as in the OR setting:
A preanesthesia evaluation should be performed just before sedation.
Informed consent for anesthesia should be obtained or on file.
An anesthesia record should be completed.
The child should be recovered in an appropriately staffed and equipped recovery facility for children or go to the regular pediatric postanesthesia care unit (PACU).
A recovery record should be completed.
The child should be evaluated by the anesthesiologist when recovered and signed out of the unit (where appropriate this might be delegated using standard written criteria).
The technique chosen should result in minimal (if any) postanesthesia sequelae.
Use short-acting drugs that will not delay recovery and are not associated with postoperative nausea and vomiting. (Therefore, when possible, avoid opioids, barbiturates, and ketamine.) Propofol is ideal.
Most children can be managed with an oxygen mask or nasal prongs, and a support to extend the neck. Occasionally an oral or nasopharyngeal airway may be required. The laryngeal mask airway (LMA) may be a useful alternative. Finally, if all of the above maneuvers still result in an obstructed airway, tracheal intubation may be required. In general, tracheal intubation is avoided in remote locations to minimize postextubation airway problems and to abbreviate the recovery time.
When repeated anesthetics will be needed, a chronic intravenous line should be maintained: either a central line or a “Hep-Locked” peripheral line.
Monitor every child as you would in the operating room.
Diagnostic and Therapeutic Medical Procedures
CT scans require absolute immobility of the child throughout. However, modern CT scan times are exceedingly brief, most scans are complete (even when contrast is required) within 10 minutes. Hence many children can be managed without anesthesia and for the others, the anesthetic plan must be tailored accordingly. Small infants can be bundled and restrained during the procedure without sedation. Older children of normal intelligence can cooperate and do not require any form of sedation or anesthetic, they can be distracted and entertained for the short time necessary to complete a scan. It is sometimes necessary to sedate infants and children less than 3 years, and cognitively challenged children. Very rarely a general anesthetic is required; usually for a child with significant comorbid disease or injury.
Intravenous sedation alone is suitable for many children:
A propofol infusion is preferred.
Intravenous pentobarbital is an alternative; an initial dose of 3 mg/kg of pentobarbital may be given. After 3 minutes, further doses of 1 mg/kg may be titrated up to a maximum of 7 mg/kg. (This is a regimen that may be used by specially trained nurses under supervision of the radiologist.)
The child should be monitored with standard ASA monitors. All equipment required to establish an airway and ventilate the lungs should be immediately available.
If general anesthesia is required, use only plastic materials in the breathing circuit; metal components distort the image. Be aware that the metal spring in some LMA cuffs and tracheotomy tubes may also cause an artifact and need to be avoided or the spring needs to be taped away from the field.
Contrast media may be injected intravenously to enhance the images obtained; very rarely, reactions may occur (see later discussion); be aware to limit the dose in children with renal dysfunction.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) scans are commonly used to secure accurate anatomic diagnoses, but they may also provide valuable information on the physiologic changes associated with disease. The MRI is increasingly being used to define vascular anatomy (Magnetic resonance angiography (MRA)) especially in children with congenital heart disease, and this requires special considerations (see later discussion). The basic component of the MRI system is a powerful superconducting magnet into which the child must be placed. This presents some problems:
The space is very confined, which frightens children, may cause claustrophobia, and also limits access to the child should an emergency occur.
There may be a high noise level within the magnet (approximately 95 decibels), and the unit may vibrate and scare the child. Because of these considerations, deep sedation or general anesthesia is usually required for infants and children having MRI scans.
Ferrous metal objects are attracted to the magnet and become dangerous, life-threatening projectiles. Therefore all equipment including oxygen tanks, IV poles, etc., which are taken into the unit must be MRI compatible (nonferromagnetic).
It is essential that the child is screened for accompanied or implanted devices that might incorporate ferromagnetic material. These could be dangerously attracted to the magnet, their function could be affected by the magnetic field (e.g., cardiac pacemaker, transthoracic or transvenous pacing wires, vagal nerve stimulator) or they could seriously damage adjacent tissues (e.g., implanted prostheses, wires or vascular clips, cochlear implants, and metal foreign bodies).
N.B. For children with nonremovable ferromagnetic implanted material, an MRI is contraindicated.
The magnetic field may cause burns by inducing currents in wire leads (ECG or pulse oximeter cables) or temperature probes. These can produce heat and burn the child’s skin. Prevent direct contact between the cables and the child’s skin, avoid loops in the cables, and ensure that the cables are directed out of the center of the bore (not the sides) to minimize current induction. Most ECG cables today are carbon fiber lead electrodes. MRI compatible equipment and specifically, fiberoptic cables, are now available for ECG and pulse oximetry that precludes the risk of burns. Adolescents with tattoos may develop a burning sensation at the tattoo site if the dye contains ferromagnetic metals.
Implanted vagal nerve stimulators may contain wires that were coiled at the time of insertion so a screening x-ray may be indicated; the stimulator is generally shut off before entering the MR scanner. Cardiac pacemakers and implanted cardiac defibrillators are current not approved for use within any MRI scanner (although MRI compatible pacemakers have been patented).
The magnetic field may affect the performance of anesthesia delivery systems; syringe pumps may be unreliable, and vaporizers may become inaccurate (bimetallic strip is nonferromagnetic). Infusion pumps may be placed outside of the scanner room to avoid interference from the magnet. Extra long infusion tubing may be threaded through a conduit in the wall of the scanner room. Note that the long tubing may have significant resistance that could affect drug delivery by some infusion pumps; check proper function beforehand.
MRI is very motion sensitive; if the child moves at any stage, a whole scan sequence may need to be repeated.
The child may have a major life-threatening illness.
The child may have a difficult airway, in this case tracheal intubation should be performed in the operating room and the child transported to the MRI unit anesthetized, on a properly equipped gurney.
Resuscitation equipment cannot be brought into the MRI scan room should it be required. If resuscitation is required, the child must be rapidly moved from the MRI scan room to an adjacent room in which full resuscitation equipment is available.
Higher power magnets (3 Tesla) are now being installed and some equipment that was safe and reliable in the environment of a 1.5 Teslar shielded magnet may be unsafe and/or unreliable in a 3 Tesla unit. Currently units up to 8T are being studied. The shielding installed and the distance a piece of equipment is sited from the magnet are also vital safety concerns. The anesthesiologist should be very familiar with the safety concerns of the local unit.
Gadopentetate dimeglumine (gadolinium) is commonly used as a contrast agent to enhance the MRI image. This may cause minor side effects (dizziness, nausea), but may also very rarely cause anaphylaxis. If administered to children with renal impairment, it is poorly cleared and may result in very severe complications; nephrogenic systemic fibrosis (NSF) with multiorgan involvement. Hence the drug is contraindicated in children with renal impairment or immature renal function (infants under 2 years or those with <30 ml/min/1.73 m 2 ). (N.B. Radiology departments now have guidelines for gadolinium dose, weight, and BUN values, and these charts should be consulted.)