Pediatric Anesthetic Techniques: Monitoring

Monitoring

Monitoring requirements for infants and children are generally similar to those for adults with some minor modifications. Alarm limits should be appro-priately adjusted. Smaller electrocardiographic elec-trode pads may be necessary so that they do not encroach on sterile surgical areas. Blood pressure cuffs must be properly f ttedi. Noninvasive blood pressure monitors have proved to be reliable in infants and children. A precordial stethoscope pro-vides an inexpensive means of monitoring heart rate, quality of heart sounds, and airway patency. Finally, monitors may sometimes need to be first attached (or reattached) following induction of anesthesia in less cooperative patients.

Small pediatric patients have a reduced margin for error. Pulse oximetry and capnography assume an even more important role in infants and small children because hypoxia from inadequate ventila-tion remains a common cause of perioperative mor-bidity and mortality. In neonates, the pulse oximeter probe should preferably be placed on the right hand or earlobe to measure preductal oxygen saturation. As in adult patients, end-tidal CO2 analysis allows assessment of the adequacy of ventilation, confirma-tion of endotracheal tube placement, and early warning of malignant hyperthermia. Flow-through (mainstream) analyzers are usually less accurate in patients weighing less than 10 kg. Even with aspiration (sidestream) capnographs, the inspired (baseline) CO 2 can appear falsely elevated and the expired (peak) CO2 can be falsely low. The degree of error depends on many factors but can be mini-mized by placing the sampling site as close as possi-ble to the tip of the endotracheal tube, using a short length of sampling line, and lowering gas-sampling flow rates (100–150 mL/min). Furthermore, the size of some flow-through sensors may lead to kinking of the endotracheal tube or hypercapnia as a result of increased equipment dead space.Temperature must be closely monitored in pediatric patients because of the greater risk

for malignant hyperthermia and greater potential for intraoperative hypothermia or hyperthermia. The risk of hypothermia can be reduced by main-taining a warm operating room environment (26°C or warmer), by warming and humidifying inspired gases, by using a warming blanket and warming lights, and by warming all intravenous and irrigation fluids. The room temperature required for a neutral thermal environment varies with age; it is greatest in premature newborns. Note that care must be taken to prevent accidental burns and hyperthermia from overzealous warming efforts.

Invasive monitoring (eg, arterial cannulation, central venous catheterization) demands expertise and judgment. Air bubbles should be removed from pressure tubing and small volume flushes should be used to prevent air embolism, unintended heparin-ization, or fluid overload. The right radial artery is often chosen for cannulation in the neonate because its preductal location mirrors the oxygen content of the carotid and retinal arteries. A femoral artery catheter may be a suitable alternative in very small neonates, and left radial or right or left dorsalis pedis arteries are alternatives in infants. Critically ill neonates may retain an umbilical artery catheter. Internal jugular and subclavian approaches are often used for central lines. Ultrasonography should be used during placement of internal jugular catheters and provides useful information for arterial cannu-lation as well. Urinary output is an important (but neither sensitive nor specific) indicator of the ade-quacy of intravascular volume and cardiac output. Noninvasive monitors of stroke volume have only recently been tested in infants and young children.

Premature or small-for-gestational age neo-nates, and neonates who have received total paren-teral nutrition or whose mothers are diabetic, are prone to hypoglycemia. These infants should have frequent blood glucose measurements: levels below 30 mg/dL in the neonate, below 40 mg/dL in infants, and below 60 mg/dL in children and adults indi-cate hypoglycemia requiring immediate treatment. Blood sampling for arterial blood gases, hemoglo-bin, potassium, and ionized calcium concentration can be invaluable in critically ill patients, particu-larly in those undergoing major surgery or who may be receiving transfusions.