Pediatric Equipment

Forced Air Warmers

Forced air warming devices remain one of the most common and effective strategies to maintain and increase the child's temperature in the OR. These devices consist of a central unit that regulates the air temperature and forces heated air through a hose to a disposable perforated blanket that can be placed underneath or on top of the child or around the child's head. The device must be used in accordance with the manufacturer's instructions to minimize the risk of thermal injury. The device very effectively maintains the child's temperature through the combination of active convection and a plastic wrap or blanket that eliminates radiation and evaporative heat losses. Concerns have been raised that these devices develop internal microbial buildup, that they disrupt laminar airflow in the OR, and that they cause surgical infections that involve implanted material. However, despite these concerns, forced air warmers continue to be used in children without reports of increased infection rates. Nonetheless, some surgeons prefer that forced air warmers be powered on only after the child has been prepped and draped (e.g., ventriculoperitoneal catheter insertion), a practice that has been applied to many surgical types. Several manufacturers produce forced air warmers and blankets. The devices all operate in a similar manner and may be considered equivalent in effectiveness: 3M (St. Paul, MN), Celsius Medical (Madrid, Spain), Stryker (Kalamazoo, MI), and Medical Solutions, Inc. (Omaha, NE).

Warming Blankets

Warming blankets include circulating water mattresses placed underneath the child and electrical heat-generating conductive blankets that can be placed either underneath or on top of the child. When placed underneath the child, these devices offer complete access to the child without obstruction, transferring heat by conduction, accounting for only 4% of the heat loss. Warming blankets do not have the associated concern of changing airflow in the OR. Typically, these devices are also reusable and require wipe-down disinfection. Since these devices are in direct contact with the child and have a greater thermal density, care must be taken to avoid surface burns at high temperature settings. Circulating water blankets include the Blanketrol by Cincinnati Sub-Zero (Cincinnati, OH), and the Medi-Therm III by Gaymar Industries (Orchard Park, NY). Manufacturers of non-water–based blankets include Augustine Biomedical (Eden Prairie, MN), Inditherm (Rotherham, United Kingdom), and Novamed USA (Elmsford, NY).

Radiant Warmers

Overhead radiant heating units, sometimes referred to as a “french fry light,” have become less commonly used in the OR since the introduction of forced air warmers, although they remain in use in the neonatal intensive care unit (NICU) and are built in to many NICU beds. These devices use a temperature sensor on the infant to supply feedback to a servomechanism to adjust the heat output. Without this feedback or if the heating element is placed too close to the neonate, there is a risk of skin burns to the neonate and nearby staff.

Passive Heat and Moisture Exchangers

Heat and moisture exchangers (HMEs) are reflective filters interposed between the endotracheal tube and the ventilator circuit to preserve the child's temperature and airway humidity. Under the correct circumstances, these devices may maintain body temperature but they cannot increase body temperature. They are less effective at maintaining temperature compared with heated humidifiers in the airway circuit. Even the smallest exchanger can increase the airway dead space and resistance, particularly in neonates, blunting the capnogram until it is almost uninterpretable. These exchangers are effective and useful for preventing the contamination of devices attached to the airway such as pulmonary function testing equipment.

Heated Humidifiers

Heated humidifiers or heated breathing circuits are typically a sealed heated wire within one limb of the breathing circuit. Sterile water is introduced into the circuit and the servomechanism controlled heater maintains temperature. These devices are prone to hazards, such as overheating, condensation, changes in the compressible volume of the circuit, leaks in the tubing, and obstruction, if they are not connected correctly. They are superior to any other device for preventing the secretions in the airway from drying out and are universally used with ICU ventilators. However, as the circle breathing circuit supplanted the Mapleson F circuit (Jackson-Rees modification of the Ayre T-piece) in clinical anesthesia care globally, heated humidifiers became anachronistic as it could be difficult to adapt them to the circle circuit. The additional cost and complications of these devices also limit their use except for anesthesia cases of prolonged duration. Manufacturers include Armstrong Medical (Lincolnshire, IL), Carefusion (Becton Dickinson, Franklin Lakes, NJ), Dräger (Telford, PA), Fisher & Paykel (Irvine, CA), Philips Healthcare (Bothell, WA), Teleflex (Morrisville, NC), and Westmed Inc. (Tucson, AZ), among others.

Fluid and Blood Warmers

When large volumes of IV fluid are infused at a rapid rate, the child's core temperature may decrease precipitously unless a fluid warmer is used. In contrast, when IV fluid is infused at a maintenance flow rate, the effect on the child's temperature is attenuated. One strategy to deliver warmed IV fluid is to warm the IV fluid bags before the fluid is delivered. This can be achieved with blanket warmers already in use in the ORs or with specialized warmers such as the ivNow fluid warmer by Enthermics (Menomonee Falls, WI). The IV fluid bags should be used within a week or two to prevent degradation of the plastic bags. Individuals have warmed IV fluid bags in a standard microwave oven, but this practice is not recommended because hot spots, overheating, or deterioration of the container might develop.

In general, blood products are stored in refrigerated coolers. When the products are selected for use, they are warmed before administration. Fluid warmers currently marketed are designed to warm crystalloid solutions and blood products. The two main designs for these fluid warmers are a water bath and dry heat. The Level 1 Hotline device (Smiths Medical, Dublin OH) uses a heated water bath and specialized tubing with a sterile inner lumen. Warmed water circulates in the outer lumen, increasing the temperature of the fluid. The Level 1 can deliver warmed fluids with a gravity flow rate up to 83 mL/minute. The dry heat designs use either standard IV tubing or proprietary tubing sets. These are placed in contact with a heat exchanger usually made of metal because of its conductive properties. The device warms the tubing and the fluid as it passes through the tubing. The designs vary in their priming volume, flow rates, portability, and distance they can be placed from the patient. The greater the distance between the device and the patient, the greater the cooling of the fluid before it reaches the patient. Both pressurized and nonpressurized warmers can deliver large fluid flow rates that are commonly necessary for trauma and transplantation surgeries. Nonpressurized warmers that use proprietary tubing sets include the enFlow by Carefusion (Becton Dickinson, Franklin Lakes, NJ) with a 4-mL priming volume and a flow rate up to 200 mL/minute; the Medi-Temp by Stryker (Kalamazoo, MI) with a flow rate up to 500 mL/minute; and the Ranger by 3M (St. Paul, MN) with a flow rate up to 500 mL/minute. Some nonpressurized warmers that adapt to standard IV tubing sets manufactured in Germany include the Nuova/05 by Nuova GmbH (23909 Ratzeburg, Germany) and the Astoflo Plus by Stihler Electronic GmbH (Germany). For massive transfusion of blood, pressurized fluid warmers are used. The Belmont Rapid Infuser RI-2 (Belmont Medical, Billerica, MA) uses electromagnetic induction heating, has an optional blood reservoir, and infuses the warmed fluid with a rapid roller pump. This device can deliver more than 750 mL/minute of warmed blood. The Level 1 h-1200 Fast Flow Fluid Warmer (Smiths Medical, Dublin OH) uses an aluminum heat exchanger, a countercurrent water bath, has two chambers for fluid bags, and uses pressurized air to compress the IV bags and infuse fluids at flows of up to 600 mL/minute, although at the greater rates, the temperature of the IV fluid is not sustained ( Fig. 52.1 ). The flow rate of these devices is limited by the size and length of the inserted venous catheter and, to a lesser extent, by the length of the tubing before the patient ( E-Fig. 52.1 ). These devices have integrated air and pressure detectors that will automatically stop the infusion if a breech is detected. Even with the air detector, it is important to eliminate all air from the bags to avoid the possibility of infusing air into the circulation.

Controlling Exposure

Body temperature can be preserved if the child is covered to reduce radiant and convective heat losses. Plastic wrap used for food is effective, inexpensive, and translucent. Covering the infant's head is an important strategy to prevent heat loss since the infant's head has a large body surface area/volume ratio. Reflective aluminized Mylar blankets are also very effective but more expensive. Using a blanket warmer and uncovering only the necessary small portions of the child during induction and IV placement attenuates heat loss. If the child must be uncovered at any time, warming the air temperature within the OR is effective as it reduces both radiation and convective heat losses. In one study of neonatal and maternal hypothermia, fewer hypothermic neonates (<36°C) were identified when room temperature was 23°C compared with a room temperature of 20°C (5% vs. 19%). Once the neonate has been covered, the room temperature can be reduced.

Maintenance Fluids

For neonates and chronically ill infants in whom there is significant risk of hypoglycemia, a dextrose-containing fluid should be used. If the child is receiving 10% dextrose or a similar solution from the NICU, this infusion should be continued at the same rate during anesthesia in the absence of additional data. If the dextrose infusion rate is decreased, the serum dextrose concentration should be measured periodically throughout anesthesia to preclude the development of hypoglycemia. To prevent fluid overload, consider the use of a pump to control the infusion of IV fluids, with a stopcock close to the cannula to infuse medications. Some have recommended in-line filters in IV lines to prevent morbidity and mortality in neonates associated with contamination of the infusions (bacteria, endotoxins, and others). However, a Cochrane review concluded that there was insufficient evidence to recommend in-line filters in neonates to reduce morbidity and mortality. If vasoactive medications and maintenance fluids are infusing and a separate IV catheter is present, the medications should be flushed as close to the patient as possible in the second IV in order to minimize the risk of injecting boluses of vasoactive medications.

Resuscitation

If there is an anticipated need for a large volume of fluids for volume resuscitation, the largest IV that can be easily placed should be used, recognizing that attempting to place a catheter that is too large may result in failure. It is better to have two working 22-gauge IVs rather than multiple puncture sites from failed attempts with an 18- or 20-gauge IV. Table 52.1 indicates that a shorter catheter delivers a greater flow rate than a longer catheter and that a central venous catheter, which is often a long catheter, is usually limited to infuse low fluid flow rates because of resistance caused by their length. PICC lines cannot be used for resuscitation (and may prevent the rapid administration of a bolus of propofol) because of their narrow caliber and extra length (see Table 52.1 ).

Large-bore tubing used for blood transfusion or resuscitation has the best flow characteristics. There are multiple strategies to increase the IV flow rate, including using a pressure bag placed around the fluid bag, IV tubing sets with integrated bulb pumps, use of a large (60-mL) syringe and a stopcock to create a pull-push system or large prefilled syringes, and a purpose-built device such as the Level 1 h-1200 Fast Flow Fluid Warmer (Smiths Medical) or Belmont Rapid Infuser RI-2 (Belmont Instrument, Bellerica, MA). If a 20-gauge or larger catheter is already in place, it may be exchanged for an Arrow rapid infusion catheter (Teleflex, Morrisville, NC) that is typically a 7F or 8.5F (internal diameter) 2-inch-long catheter. Fluid resuscitation is limited with the commercially available IV pumps to their maximum flow rates, 999 mL/hour or 16.6 mL/minute. If a pressure infusion bag is used, the IV bag should be de-aired to prevent air from being pumped into the circulation, creating an air embolism, as the bag empties.

The temperature and viscosity of IV fluids greatly affect the infusion rate. Less viscous fluids are infused more rapidly than more viscous fluids (e.g., colloid solutions). Crystalloid solutions are the least viscous fluids followed by colloids, whole blood, and PRBCs. PRBCs may be diluted with normal saline solution to reduce viscosity, improve flow characteristics, and decrease the risk of hemolysis during a rapid infusion.

Total Intravenous Anesthesia and Vasoactive Medications

If total IV anesthesia (TIVA) or the use of vasoactive medications is necessary, they are ideally infused through a separate venous access. The speed at which the medication is administered depends on the location of the access point in the infusion line, how much priming volume is present in the tubing, and the speed at which the fluids are infusing ( Fig. 52.2 ). A carrier solution on a pump should be infused at a baseline rate because most vasoactive medications are piggy-backed into the tubing at slow infusion rates. The carrier solution should be adjusted to the child's maintenance infusion rate and the other IV fluids reduced accordingly. Multiple stopcock manifolds allow for the connection of multiple infusions as well as the carrier solution. Fig. 52.3 shows various multiple-drug infusion systems, each of which has slightly different priming volumes, which in turn affect the speed at which medications are infused. Many practitioners prime their medications and then initiate the pumps to run the fluids to the end of the manifold. When connected directly to an IV line, medications should be delivered without delay provided the carrier fluid rate is maintained at the same rate.

Establishing any IV access in infants and toddlers can be difficult, a task that becomes extremely difficult when they are in shock. When peripheral IV access cannot be established quickly and the child is critically ill, placement of an intraosseous catheter should be entertained (see also Chapter 49 , Figs. 49.6 and 49.7 ).

Luer Adapters

Luer-Lok adapters allow for the rapid and secure connection of syringes and IV fluid lines to catheters. This has particular significance in the OR as access to the arterial or venous lines are remote from the caregiver and hidden under the drapes. However, the Luer-Lok adapter is also interchangeable with epidural, spinal and nerve block catheters, feeding tubes, total parenteral nutrition lines, and even sidestream carbon dioxide (CO ₂ ) connectors. All of these have the identical six-degree Luer-Lok taper that allows them to be connected interchangeably. This universal connection has led to the accidental injection of drugs not meant for the neuroaxial space into epidural catheters, parenteral chemotherapy (vincristine) given intrathecally (more than 30 times since 1968), local anesthetics (e.g., bupivacaine) injected intravenously, a blood pressure (BP) cuff attached to a Hep-Lock IV set (Baxter Healthcare), gastric feeds, and breast milk infused through a central venous catheter, causing significant morbidity and mortality. Labeling of all catheters at the hub, color coding, and vigilance have been effective, in part, to reduce this risk. However, to address this risk formally, an international, multidisciplinary team convened in 2007 to draft a standard by which Luer-Loks will be modified such that a unique Luer-Lok design will be available for each type of Luer-Lok connection (e.g., IV, gastrointestinal, genitourinary, neurologic, anesthesia breathing circuits, and hemodynamic monitoring [BP cuffs]) that will also prevent cross-connection of tubing meant for different uses. This meeting resulted in publication of ISO-80369 standard, which after several iterations, is about to be set for implementation. This new standard will modify the six-degree Luer-Lok taper to preclude cross-connection of tubing intended for differences uses by creating non–Luer-Lok connectors for non-IV equipment larger or smaller than the standard Luer-Lok connections.

Masks

Transparent disposable plastic (latex-free) face masks are available in a wide variety of sizes for children of all ages, to deliver oxygen as well as induce and maintain inhalational anesthesia. These air-filled cushioned masks, which can be inflated to fill the cuff, replaced the old Rendell-Baker/Soucek face masks, which had a very small dead space but often failed to seal completely on the faces of some children. With the wide variability in the morphology of children's facies, especially those who are syndromic, the anesthesiologist should prepare cushioned masks that are smaller and larger than the size chosen for the child. The provider should be able to maintain a tight mask seal on the face with the least amount of dead space. Masks vary according to the manufacturer; however, there are few features that would lead us to recommend one over another. Some masks can be purchased already flavored (with fruit such as strawberry), although most anesthesiologists prefer to offer flavors (e.g., watermelon or strawberry lip balms) to the child and let him or her choose their favorite and apply the flavor to the mask. Specialized masks with a built-in port for endoscopy or fiberoptic intubation are also available for specific indications (see E-Fig. 14.13 ).

Oropharyngeal Airways

Oropharyngeal airways are hard, non-latex plastic that are preformed in different sizes from 40 mm (infant) to 100 mm (large adult). Care should be taken to choose an airway that is the correct size for the child because an airway that is too small displaces the posterior portion of the tongue or epiglottis into the glottic opening, causing upper airway obstruction. Alternatively, if the airway is too large, the airway device may cause damage to laryngeal structures, causing swelling and potential postoperative obstruction (see Fig. 14.13 ). An oral airway should always be placed midline, without rotating it as it is inserted as is commonly done in adults, since at every age, children have some loose teeth and others that are ready to fall out. Rotating the hard airway may dislodge one or more teeth, leading to a possible pulmonary aspiration. Misplaced oral airways that obstruct venous and/or lymphatic drainage of the tongue can precipitate acute macroglossia. Additional causes of acute macroglossia include retained throat packs, surgical positioning, and the presence of TEE probes.

Nasopharyngeal Airways

Nasopharyngeal airways are an additional adjunct to reduce or prevent upper airway obstruction. Latex-free nasal airways are available in sizes from 12F to 36F. Care should be taken when placing them in the nose as they may injure the mucosa or dissect adenoidal tissue free, causing bleeding. Selecting the correct size of the airway is important because an excessively large nasal airway can apply pressure to the ala of the nose, which can lead to injury and even alar necrosis. If the ala blanches when the airway is seated, it is likely too large for the diameter of the nostril and should be replaced with a smaller-diameter airway. Some nasal airways have a movable flange to prevent them from being inserted too deeply. The flange should be adjusted before it is inserted. The correct nasal airway size approximation is estimated when the airway extends from the nares to the angle of the jaw or the earlobe. In the absence of an appropriately sized nasal airway, one could cut a tracheal tube to the appropriate length. Note that a cut tracheal tube is stiffer than a commercially available nasal airway and has a greater potential for injury. Prewarming the tracheal tube using hot water may soften the tube and reduce the risk of mucosal injury. The lumen of any nasal airway is limited and can be occluded with secretions and/or blood. Therefore they should be removed as quickly as possible if airway obstruction is diagnosed.

Laryngeal Mask Airways

The reusable (Classic) Laryngeal Mask Airway (LMA, Teleflex) is a supraglottic airway device (SGA) developed by Dr. Archibald Brain in the 1980s. Reusable models of the LMA are still available, although most SGAs used today are single-use, disposable airways. Several different types of LMAs are now available, including the LMA Unique (used in emergency setting), LMA Flexible (soft, malleable wired neck), LMA ProSeal (with a second channel to direct gastric contents away from the airway), and the LMA Supreme (the Proseal with a built-in bite block). All of these airways are currently available, although high-quality studies that compared their advantages and disadvantages (with the exception of the Classic and the ProSeal) are lacking in children. The SGA is a lifesaving airway device that should be used to establish ventilation when either ventilation by face mask or tracheal intubation is difficult or impossible. These devices are usually easy to place by inserting them straight into the hypopharynx, although some prefer to rotate the LMAs 90 degrees as they insert them. Occasionally, the LMA will not advance past the posterior pharynx, especially if the bowl has been deflated. This may occur if there is a step-up in the alignment of the mucosa over the vertebral bodies against which the tip of the LMA abuts. Alternately, the tip of the bowl may have flipped backward, toward the nasopharynx, as the LMA is inserted, preventing it from advancing smoothly. To advance the LMA in both circumstances, the tip of the bowl should be lifted using your finger and the LMA then advanced. The bowl should be inflated until there is no air audible leak at ~16 to 20 cm H ₂ O peak inspiratory pressure. These airways can be used as the sole airway during anesthesia or as a conduit for bronchoscopy or fiberoptic intubation. There are several manufacturers with small to moderate differences among these devices (see also Fig. 14.18, Fig. 14.19, Fig. 14.20 ). For routine use in children with normal airways these small differences may not matter; some are specifically designed as a conduit for intubation. Supraglottic devices may have either one or two lumens. Dual-lumen SGAs are placed blindly into the oropharynx. They have two separate cuffs that can be inflated to allow isolation of the trachea (see E-Figs. 14.1 and 14.2 ). The dual-lumen devices are more typically used for prehospital providers during resuscitation and are not discussed further here. A typical single-lumen SGA is also readily placed blindly into the hypopharynx and makes a nonocclusive seal with the larynx. Single-lumen SGAs have a variety of additional features and design elements, such as nonferrous valves for use in magnetic resonance imaging (MRI); spiral reinforced and flexible, containing a thermoplastic cuff that molds to the airway; drains or sites for drainage of gastric contents; curvature to facilitate fiberoptic intubation; internal bars to prevent the epiglottis from obstructing the lumen; devices specifically designed to facilitate blind endotracheal intubation; and modifications that allow greater airway occlusive pressures during positive-pressure ventilation.

SGAs are available for all age groups from neonates and infants (<5 kg) to children and adolescents (>70 kg). Success rates for inserting the LMA on the first attempt are very high in most age groups, although some report only moderate success rates in neonates and infants (80%). In most infants and children, the epiglottis lies within the bowl of the LMA, without evidence of upper airway obstruction. In neonates and infants, it behooves the anesthesiologist to maintain very close vigilance of oxygenation and ventilation as the airway may become compromised quite suddenly and rescue measures must be adopted quickly.

When the LMA was first introduced, most practitioners used it only in children who breathed spontaneously. However, more recently many have adopted the adult practice of using low-pressure volume support and positive end-expiratory pressure (PEEP) with the LMA to minimize the effect of the dead space contributed by the LMA stem and the associated hypercarbia. We have had good success with this approach in young children.