Fig. 13.1
Physiologic factors in the full-term and premature infants that can influence their management during anesthesia and surgery. See text for details
1.
Oxygen toxicity: Human fetuses are hypoxemic with PO2 values ranging between 20 and 32 mmHg. The antioxidant mechanisms are not well developed in neonates [1] and premature infants are even more susceptible to oxygen toxicity after exposure to excessive levels of oxygen [2]. The association between oxygen exposure and retinopathy of prematurity (ROP) and bronchopulmonary dysplasia (BPD) is well established [3–7]. Several animal and human studies have also reported increased pulmonary arterial contractility [8], biochemical oxidative stress [9], and increased risk of cancer [10] after even brief exposure to 100 % oxygen in the delivery room at birth. In the past, anesthesiologists routinely used 100 % oxygen to ventilate the lungs of neonates with during surgery to avoid hypoxia or due to a lack of air. Increased awareness of oxygen toxicity has led to changes in this practice. In the OR, all neonates undergoing emergent surgery with a rapid sequence induction are still preoxygenated for several minutes to prevent desaturation while the airway is secured, although most neonates do not tolerate a face mask without objection. This practice continues today. A recent survey of 247 anesthetists in the United Kingdom demonstrated that <40 % oxygen is used during neonatal anesthesia by 52 % of respondents and >40 % oxygen is used by <16 % [11]. Few anesthesiologists administer 100 % oxygen to neonates and premature infants [11]. However, 10 % of the respondents suggested that they do not make a conscious effort to avoid 100 % oxygen during neonatal anesthesia. The use of 100 % oxygen is also associated with pulmonary atelectasis. The potential risks of desaturation during anesthesia and concern over the need for a margin of safety in light of the evidence that the incidence of desaturation including severe desaturation (<80 %) increases with decreasing age [12] have led to the use of 30–40 % oxygen during neonatal anesthesia (in the absence of significant lung disease) to maintain a target preductal oxygen saturation of ~90 % (see Complication chapter 16). The pulse oximeter should be sited on the right hand (preductal) to display the oxygen saturation. Oxygen saturations of 99–100 % are often associated with supraphysiological PaO2 and potential toxicity to the retina and lungs in neonates and, in particular, in very low birth weight (VLBW) infants. Oxygen saturations of 85–89 % have been associated with an increased mortality when compared with 91–95 % in infants <28 weeks gestation at birth, although this notion remains contentious and unresolved (see Complication chapter). Oxygen saturations should be closely monitored during mechanical ventilation of both premature and full-term neonates under anesthesia with target saturations set to ~90 %, to limit ROP and lung disease while avoiding an increase in mortality [5–7].
2.
Similarly, the use of 100 % oxygen for transport from the NICU to the OR is also contentious. The use of 100 % oxygen delays the time to serious desaturation in both infants [13] and critically ill patients during transport [14]. This allows more time for corrective action before cardiac and neurologic sequelae from hypoxia may occur. The notion of using 100 % oxygen for high-risk procedures balances the potential of a possible long-term risk of ROP and lung disease against the immediate potentially lifesaving benefits of delayed desaturation and cardiac arrest.
3.
Lung development continues during fetal life with limited surfactant production until almost 34 weeks gestation [15]. The combination of a lack of surfactant and a compliant chest wall increases the risk that the small bronchioles will collapse during expiration. Positive end expiratory pressure (PEEP) is crucial during ventilation in premature infants. Furthermore, if BPD is present, airway resistance is increased leading to an increased risk of air trapping. The use of appropriate PEEP, low rates, and prolonged expiratory times may be necessary to optimize ventilation (see Ventilation chapter 9).
4.
Respiratory control is immature in premature infants resulting in episodes of apnea and bradycardia. The risk of postoperative apnea (of prematurity) increases with infants of younger gestational and/or postconceptional age and anemia [16].
5.
Premature and full-term neonates are considered obligate nose breathers, although they are capable of mouth breathing during nasal occlusion [17]. The shift to mouth breathing in response to nasal occlusion becomes more automatic with advancing postconceptional age [18]. Nonetheless, infants with choanal stenosis and atresia and some craniofacial anomalies (e.g., Pierre Robin sequence, Crouzon syndrome) remain at risk for apnea. It is important to suction the nares and ensure the patency of the nasal passages before extubating the trachea in these infants.
6.
Uncuffed tracheal tubes (TTs) have been the standard for premature and term neonatal infants. Issues associated with the use of uncuffed TTs during anesthesia include difficulties in maintaining targeted tidal volumes during mechanical ventilation (particularly in infants with poorly compliant lungs), multiple tracheal intubations to achieve a properly sized tube, and expiratory gas leak and OR pollution [19, 20]. Two manufacturers currently supply small-diameter cuffed TTs: the Lo-Pro/Lo-Contour 3.0 mm internal diameter TT (Mallinckrodt© USA) and the 3.0 mm Microcuff© TT (Kimberly Clark, USA). These TTs have similar outer diameters as the comparable uncuffed TTs although the latter tubes have been modified to include an elliptical-shaped, more caudally placed, thin-walled cuff without a Murphy eye. Few studies have documented the safety and long-term use of these TTs in premature and full-term neonates [21]. A recent report cited three cases of stridor in young infants whose weights were less than those recommended for the 3.0 mm Microcuff TT, 3 kg, suggesting that even high-compliance cuffed TTs may cause stridor [22]. Preliminary retrospective data from the NICU support such a concern [23]. The use of cuffed TTs in premature and full-term neonates warrants further study (see Airway chapter 5).
7.
Premature and term infants may have increased pulmonary vascular resistance (PVR). When PVR increases as in the presence of hypoxia or acidosis, right-to-left shunting of blood at the patent foramen ovale (PFO) or Patent Ductus Arteriosus (PDA) may occur, resulting in cyanosis [24, 25]. Since the pCO2 may directly increase the PVR, one strategy to reduce the PVR is to reduce the pCO2. However, hypocarbia from overventilation decreases cerebral perfusion and may lead to periventricular leukomalacia (PVL) in premature infants [26].
8.
Intraventricular hemorrhage (IVH) is common in extremely low birth weight (ELBW) premature infants [27]. Friable vasculature in the subependymal region of the lateral ventricles is prominent during early gestation and involutes with advancing gestational age. Several risk factors increase the risk of IVH including wide fluctuations in PaCO2 or hypercapnia, rapid infusion of fluids and sodium bicarbonate, and increases in intrathoracic pressure (e.g., as a result of pneumothorax) [28]. Studies in ELBW infants (<1,000 g at birth) suggest that wide fluctuation in PaCO2 (i.e., difference between maximum and minimum pCO2 > 42 mmHg) during the first 4 days of life is an important risk factor for IVH [29]. Wide swings in monitored variables should be avoided during anesthesia as well, although this presents a great challenge in infants with BPD.
9.
Immaturity of the hepatic enzyme systems increases the neonate’s risk for toxicity from medications. Neonates receiving parenteral alimentation for prolonged periods are at risk for cholestatic liver disease [30] resulting in further compromise to hepatic function.
10.
Fetal accretion rates for calcium and phosphorus are high. Many growing premature infants cannot maintain similar bone mineralization after birth because of low calcium and phosphorus absorption from parenteral and enteral nutrition [31]. In addition, many extremely premature infants receive medications such as diuretics, methylxanthines, and steroids that interfere with calcium metabolism. These infants may develop osteopenia of prematurity [32] and are susceptible to pathological fractures. The risk of osteopenia and fractures increases as gestational age decreases. These fractures can occur during routine limb manipulations such as placement of an intravenous catheter. Anesthesiologists should be aware of the existence of previous pathological fractures and the current serum alkaline phosphatase levels [31, 33]. Alkaline phosphatase levels >750 IU/L may be associated with radiological features of osteopenia in some premature infants. In the 1980s, the incidence of osteopenia was 50 % in premature infants <1,000 g birth weight. Fractures were detected in as many as 24 % of these infants. With better nutrition, the incidence of osteopenia and fractures has decreased in recent years [31], although this problem persists.
11.
Glomerular filtration rate (GFR) is reduced in premature and term neonates, but improves postnatally reaching adult rates by 1–2 years of age. The use of nephrotoxic medications such as indomethacin and vancomycin may compromise renal function in some cases requiring blood sampling to determine concentrations at increased intervals between doses.
12.
During the first few postnatal days, umbilical vessels provide arterial and venous access to sick neonates. Anesthesiologists should be familiar with the location of these lines (see below).
13.
Term infants at birth have approximately 70 % fetal hemoglobin (HbF). HbF has increased affinity for oxygen resulting in a greater oxygen saturation compared with adult hemoglobin (HbA). For example, a pulse oximeter reading of 90 % is associated with a PaO2 close to 60 mmHg with HbA but maybe as low as 50 mmHg in premature infants with increased levels of HbF. Some infants receive multiple packed RBC transfusions, thereby increasing the HbA content. The oxygen dissociation curve in such infants with multiple blood transfusions resembles that of adults resulting in a reduced oxygen saturation (e.g., PaO2 of 50 mmHg will result in an oxygen saturation of 85 % in a baby that has received multiple transfusions).
14.
Premature infants have thin permeable skin and are prone to increased heat and water loss by evaporation during the first few days of life. This thin fragile skin is vulnerable to accidental loss from peeling tape.
15.
The ratio of surface area to body weight in neonates exceeds that in adults. As a consequence, the neonate is at increased risk for heat loss by radiation (39 %), convection (37 %), evaporation (21 %), and conduction (3 %) [34]. During surgery, appropriate measures to maintain thermal homeostasis must be used including a servo-controlled or thermal-neutral incubator to the suite in which the procedure/investigation will take place, increasing the room temperature, using an overhead heat lamp, thermal mattress, and forced-air warmer. Some or all of these devices may not be MRI compatible and cannot be used in that environment. The skin should remain dry and contact with wet linens should be avoided to prevent heat loss. Direct contact with the heating sources must also be avoided to minimize the risk of skin injury.
Benefits of Performing Surgery in the NICU
The most common reason for performing surgery in the NICU is to avoid comorbidities that may occur during transport of the critically ill neonate to another unit, such as the operating room (OR). There are several potential risks from transporting these infants (Table 13.1). The transport may require a change in the mode of ventilation [35]. Transporting a neonate whose lungs are ventilated with a high-frequency oscillatory ventilator (HFOV) or high-frequency jet ventilator (HFJV) is difficult and very challenging. Often, the lungs must be ventilated manually during transport and HFOV reinstituted only upon arrival in the OR. The transport incubator should be designed to maintain the neonate’s temperature [36]. The neonate requires four transfers [37] during the trip to the OR (NICU bed to the transport incubator, incubator to the OR table, OR table back to the transport incubator, and lastly from the incubator back to the NICU bed). The risks are increased with the distance to be traveled and the need to use an elevator [36]. In a report of neonatal surgical practices from the United Kingdom [38], more than one-third of the transports to the OR involve transfer to a separate building from the NICU, whereas only 3 % of the responders provide anesthesia for surgical procedures in the NICU. Furthermore, the neonate is difficult to observe during the transport. Monitors during the transport often suffer from interference or movement artifact rendering the measurements unreliable, and the frequency of false alarms may mask true critical events. This, along with the fact that it is more difficult to clinically assess the neonate in the closed incubator, may cause a delay in the diagnosis and management of complications such as hypoxia, bleeding, pneumothorax, and cardiac arrest.
Table 13.1
Risks of transporting neonate
Disrupting of stable ventilation parameters |
Loss of the airway or movement of the endotracheal tube |
Loss of IV or central line access and interruption of infusions |
Hypothermia |
Requirement for 4 transfer episodes |
Distance to operating room |
Cardiovascular instability |
The postoperative patient usually more fragile |
Difficulty in examining the neonate during transport |
Incompatibility of monitoring systems between the NICU and the OR |
Hypothermia is more common after a procedure in the OR than one in the NICU. In a comparison of 80 infants undergoing laparotomy or diaphragmatic hernia repair, the core temperature decreased by 2.2 C° in those who underwent surgery in the OR compared with 0.6 C° in those who underwent surgery in the NICU [39]. Extreme hypothermia (30 °C) has also been reported in neonates after surgery in the OR [35]. The risk of extreme hypothermia (33 °C) is more common in VLBW neonates <1,500 g. Interestingly, there are also reports of hyperthermia (>37.5 °C) in neonates who underwent surgery in the OR [24]. Hyperthermia in the perioperative period should be eschewed. Hyperthermia in the immediate postnatal period in infants with hypoxic-ischemic encephalopathy has been associated with worse outcomes [40]. Although similar data are not available for normal neonates after surgery, hyperthermia is best avoided.
Patient Indications for Surgery in the NICU
There are several patient indications for performing surgery in the NICU (Table 13.2). Neonates who are too unstable to transfer either within the hospital or between hospitals and those in whom the risk of mortality is very high with or without the operative procedure (ASA class 5) are good candidates to undergo surgery in the NICU. Performing surgery in VLBW neonates <1,500 g in the NICU has resulted in more stable clinical situation with less disruption of physiologic parameters [35]. Transporting neonates who require high-frequency (HFJV or HFOV) ventilation is difficult, requiring the presence of a respiratory therapist and neonatologist in the OR for the duration of the surgery to assist with the ventilation management as well as the transport back to the NICU. In contrast, the ventilator in the OR may be incapable of ventilating the neonate’s lungs with the same mode and parameters as were used with the NICU ventilator. Additionally, when emergent surgery is required and the OR is fully occupied, the surgery can be performed in the NICU without delay, assuming OR personnel is available.
Table 13.2
Indications for neonatal surgery in the NICU
Too unstable for transfer |
Weight <1,000 g or <1,500 g |
High-frequency oscillatory ventilation |
Jet ventilation |
Inhaled nitric oxide |
Complex conventional ventilatory requirements |
Surgical team willing to do “out-of-OR surgery” |
Emergency procedure and delay in the OR |
Logistics of Performing Surgery in the NICU
In order to provide anesthesia and perform operative procedures in the NICU, several logistic considerations need to be appreciated (Table 13.3). Consent must be obtained for the anesthetic and surgery from the parents or guardians. A thorough discussion of risks and benefits of anesthesia and surgery in very unstable infants must be completed in advance, in order to prepare for all possible options that may ensue including the need for changes in ventilation, blood transfusion, up to and including cardiopulmonary resuscitation. Although parents may be present at the infant’s bedside during routine care, we do not allow parents to be present during surgery.
Table 13.3
Logistics of performing operative procedure in the NICU
Availability of surgical equipment and lighting |
Availability of anesthesia equipment |
Location for operative procedure |
Consideration for other NICU patients |
Infection control |
Communication |
Team concept |
The surgeon and surgical team require a complete sterile surgical equipment tray, gowns, gloves, and masks. Appropriate surgical lighting must also be available, including portable overhead lights as well as surgical optical headlights and light sources [41]. Appropriate suction and cautery equipment must also be available. A full array of surgical instruments must be immediately available in the NICU in the event additional instruments are unexpectedly required urgently.
The anesthesiologist requires access to pharmacological, airway, and fluid supplies. An anesthetic workstation is usually neither available in the NICU nor required as inhalational anesthetics are infrequently used for several reasons including the absence of waste gas scavenging in the NICU. As a result, anesthesia in the NICU usually involves a total intravenous technique that consists of intermittent boluses of opioids and muscle relaxants. Infusion pumps are generally not used unless inotropes are required. Most monitors that we require are present in the NICU, although they may be difficult to access. One monitor that historically has been absent in the NICU is a capnogram. Many NICUs are now routinely using end-tidal CO2 monitors, especially in VLBW infants. If a capnogram is not present, a portable capnogram may be brought from the OR, unless the neonate is ventilated with HFO, in which case the capnogram will be of limited value. A fluid warming device is recommended if large volumes of fluids or blood are required. Emergency equipment should also be available in the NICU including a resuscitation cart.
When surgery is performed in the NICU, it occurs in the neonate’s bedside location. During surgery, all visitors and nonessential staff are cleared from the procedural area before the OR staff arrive. This should limit the risk of airborne contamination and microbial shedding resulting in infections. The use of barriers will also discourage inadvertent access to the operative procedure by unauthorized persons. Many new neonatal units have single-patient room design. Space constraint may necessitate transfer to a larger room. Some NICUs have a fully equipped procedure room with a high airflow exchange or a “twin room” with a larger area that may be utilized in the NICU unit. Using such a room requires that the infant be transferred from the incubator to the procedure room, which is usually a short distance.
Good communication among the NICU and the OR staff, the surgical team, and the anesthesiologist is very important. Moreover, establishing a close liaison with the NICU bedside nurse before anesthesia and surgery commence is very helpful to ensure that the latest laboratory values are available and within acceptable limits, that vascular access is available at a distance from the neonate, and that blood products are available. Since anesthesiologists have a limited knowledge of the layout of the NICU, it is imperative that the bedside nurse is available to provide syringes, needles, and other supplies during the surgery. Similarly, the presence of the neonatologist is extremely important in order to ensure that changes in management strategies of the neonate, such as ventilation changes, are undertaken with a thorough understanding of the child’s preexisting conditions. A cooperative environment will increase the efficiency and safety of the anesthetic and surgery. An efficient and organized surgical service for the NICU minimizes disruption of the care the nurses must provide to the other infants in the room and minimizes the time that family members of other neonates in the room are barred from visiting their infants.
Vascular Access:
Establishing adequate vascular access in neonates may be challenging. This is particularly challenging in ELBW infants (<1,000 g birth weight). In addition to peripheral venous access, some neonates may have umbilical lines and percutaneous PICC lines (peripherally inserted central catheters). Anesthesiologists should be comfortable using these access lines and should be capable of inserting lines in emergency situations. A brief review of umbilical venous and arterial lines and PICC lines is given below:
1.
Umbilical venous catheter: The umbilical vein is large and easily accessible in neonates. Many infants in the NICU have an indwelling umbilical venous line for the first 5–7 days of life. It is important to document the exact location of the tip of the umbilical venous catheter on a recent X-ray before using it during anesthesia. The optimal location of the catheter tip should be in the inferior vena cava at or just above the level of the diaphragm (see Fig. 13.2). If the catheter tip is caudal (in hepatic veins), hepatic necrosis can occur in response to the infusion of hypertonic or vasospastic solution into the liver tissue [42]. If the catheter tip is too rostral, it may be located in the right atrium, superior vena cava, foramen ovale, left atrium, pulmonary veins (Fig. 13.3), right ventricle, or pulmonary artery. These locations may be associated with complications such as pericardial effusion, pleural effusion, and cardiac arrhythmias. Umbilical venous catheters are usually 5 Fr in diameter (occasionally 8 Fr in large term infants), consisting of either single-lumen or double-lumen catheters. These catheters should not be left open to atmosphere (because of the risk of an air embolus) [42]. For emergency vascular access, vital infusions (not hypertonic solutions) may be administered slowly through an umbilical venous catheter placed in the umbilical vein (usually 2–4 cm below the skin) [42] and checking for blood return. The umbilical venous catheters traverse the falciparum ligament and are usually removed before laparotomy.
2.
Umbilical arterial catheter: An umbilical arterial catheter is often placed in a sick neonate to monitor blood pressure and to sample blood (especially arterial blood gas samples). The catheter is usually a 3.5 Fr or a 5 Fr single-lumen catheter placed in the umbilical artery and advanced into the aorta. The catheter tip is usually located either high (at the level of thoracic vertebrae 6–9) or low (at the level of lumbar vertebrae 3–4). Locating the catheter tip between thoracic vertebra 10 and lumbar vertebra 2 is best avoided because this region includes the origins of the celiac, mesenteric, and renal arteries (Fig. 13.4). If the catheter tip is located above thoracic vertebra 6, there is a risk of embolization to the carotid and subclavian arteries. Umbilical arterial catheters can also be used to deliver parenteral fluids, although vasospastic agents such as dopamine are best avoided. If there is evidence of vascular compromise (pallor in the lower limbs and buttocks), the umbilical line should be removed immediately. In neonates in whom abdominal emergencies such as spontaneous intestinal perforation (SIP) are developing, the umbilical arterial catheter should be removed before surgery. To remove an umbilical arterial catheter, the catheter should be withdrawn slowly until approximately 5 cm remains in the vessel and then tightened using an umbilical tie around the base of the umbilical cord (and not on the skin). The remainder of the catheter should be pulled out of the vessel at a slow rate of 1 cm/min (to allow vasospasm of umbilical artery). If bleeding occurs once the catheter has been removed, lateral pressure should be applied to the cord by compressing it between the thumb and first finger [43].
3.
Peripheral arterial cannulation: The most peripheral artery with good collateral flow, with low infectious risk, and that is large enough to measure systemic blood pressure should be selected for cannulation [44]. Ongoing bacteremia and fungal infections are relative contraindications to arterial cannulation because of the risk of colonization of the catheter. Common sites for peripheral cannulation include the radial, ulnar, dorsalis pedis, and posterior tibial arteries, with the right radial artery selected the most in one retrospective review of infants <5 kg [45]. Evidence for collateral flow must be checked before cannulation. This can be done by using a modified Allen test or by Doppler ultrasound [46]. Transillumination of the wrist is helpful in identifying the location of radial, ulnar, dorsalis pedis, and posterior tibial arteries. Care should be taken not to injure the ulnar nerve during ulnar arterial cannulation as it runs along the medial side of the artery. Sedation and analgesia with fentanyl are usually provided before arterial cannulation. Some also infiltrate the site before arterial cannulation with 0.5 ml of lidocaine. After aseptic precautions are followed, an Angiocath is inserted into the artery by direct puncture and advanced at a 10–15° angle to the skin with the bevel facing down [47]. When blood appears in the stylet, the cannula is advanced off the stylet and into the artery. Alternately, the needle stylet may be inserted at a 30–40° angle to the skin with the bevel facing up through the artery. The stylet is removed and the cannula is withdrawn slowly until pulsatile arterial flow is established. The cannula is then advanced into the lumen of the artery [44]. Transparent semipermeable dressing is often used to cover the site of insertion to facilitate early detection of bleeding at the site. All fingers/toes should be clearly visible to monitor for signs of vascular insufficiency. Complications of peripheral arterial cannulation in neonates include thrombosis, vasospasm, infection, hematoma, damage to peripheral nerves, and air embolism [45, 48, 49].
4.
Central venous catheterization: Placing a peripherally inserted central catheter (PICC) is a common procedure in the NICU to establish long-term central venous access in neonates. PICC lines are 1.1–5 Fr catheters of varying lengths, with the smallest single-lumen size being 1.1 Fr and the smallest double lumen being 2 Fr. In general, 1.1–2 Fr catheters are used in infants <2,500 g and those 1.9–3 Fr in those >2,500 g (http://www.nann.org/pdf/pdf/PICCGuidelines.pdf). The PICC tip should be located in the superior or inferior vena cava, outside the pericardial reflection [50]. Common indications for PICC placement include parenteral nutrition and need for long-term IV medication (antibiotics for bacterial, fungal, or viral infections). PICC has significant risks and complications (such as sepsis) and must be avoided when peripheral venous access is adequate and possible [50]. Many neonatologists prefer to place a PICC after 24 h of parenteral antibiotics or when the blood culture is no longer positive for infection. Strict aseptic precautions must be followed when placing the catheter.
A central venous catheter is usually inserted percutaneously in neonates. A cutdown or surgical technique is used only when percutaneous insertion has been unsuccessful. Adequate sedation and analgesia should be provided before beginning to insert the catheter. A slow infusion of 2–4 mcg/kg of fentanyl is preferred, although larger doses may be required for infants who have been receiving opioids and in infants whose lungs are mechanically ventilated. Infants who do not require significant respiratory support may receive non-pharmacologic comfort measures such as sucrose-dipped pacifier in addition to fentanyl. For catheter insertion by surgical cutdown, local infiltration with lidocaine is recommended.
It is important to check the position of the catheter tip before commencing surgery. The use of radio-opaque contrast improves localization of the catheter tip. The most recent chest radiograph should be evaluated for catheter position. Migration of catheters associated with complications is known to occur after insertion.
Most indwelling catheters are made of silicone or polyurethane to minimize the risk of perforation and fracture. In neonates, small gauges (1.1, 1.9, 2, and 3 Fr) are commonly used for percutaneous insertion. These catheters often cannot be used for withdrawing blood or rapidly infusing fluid boluses or anesthetic induction drugs (such as propofol) or blood products during surgery. Sterile precautions should be observed when breaking into a PICC circuit during surgery.
Fig. 13.2
Optimal position of the umbilical venous line. The tip of the umbilical venous catheter should be located in the inferior vena cava just above the level of the diaphragm
Fig. 13.3
Umbilical venous catheter advanced into the right atrium, patent foramen ovale, left atrium, and pulmonary veins (shown by dashed lines). This is an inappropriate location for an umbilical venous catheter
Fig. 13.4
Appropriate locations of the umbilical venous and arterial catheters from a lateral view. The umbilical venous catheter traverses the umbilical and portal veins and enters the inferior vena cava through the ductus venosus. The optimal location of the tip is in the inferior vena cava just below the right atrium. The umbilical arterial catheter is advanced through the umbilical, internal iliac, and common iliac arteries and advanced into the aorta. The celiac axis, superior and inferior mesenteric arteries, and renal arteries arise from the abdominal aorta at the level of thoracic vertebra T12 to lumbar vertebra L3. The umbilical arterial catheter can be positioned below this region (low line L3–L4) or above this region (T6–9, as shown in this figure)
Anesthesia Requirements
There are several important issues that the anesthesiologist should establish when planning to provide anesthesia in the NICU (Table 13.4). First, dedicated IV access should be available to the anesthesiologist for drug and fluid administration. Drugs such as antibiotics or vasopressors pressors not be co-infused in that dedicated line. Second, the anesthesia regimen most frequently used for neonates is an (high-dose) opioid technique with neuromuscular blockade. Fentanyl is the most widely used opioid in neonates and vecuronium or rocuronium the most commonly used neuromuscular blocking agent. All medications should be flushed through the line as medications are often administered at a site remote from the infant and may cause an unexpected delayed effect when the IV line is later flushed. All fluid boluses, flushes, and infusions should be carefully documented to prevent fluid overdoses. There have been some reports of the adjunct use of midazolam and propofol [61] in neonates during surgery in the NICU. The potential circulatory depression associated with the use of some of these drugs, especially in the compromised neonate, cannot be overstated.
Table 13.4
Anesthesia requirements
IV access |
Drugs |
Anesthetic technique |
Monitoring |
Ventilation |
Fluids |
The monitoring equipment in the NICU is often foreign to the anesthesiologist. Assistance is often needed from the bedside nurse or neonatologist to activate the audible pulse oximetry/ECG tones, which are not frequently used in the NICU. Blood pressure may be measured invasively via a radial or umbilical artery line, but in those in whom invasive pressure monitoring is not present, a noninvasive oscillometric blood pressure monitor should be used. The reliability of noninvasive measures of blood pressure monitoring in premature infants has been affirmed by some and questioned by others [51, 52]. Recent evidence supports applying the blood pressure cuff in either the upper or lower extremity in infants >1,000 g but may provide more accurate readings from the lower extremities in infants <1,000 g [53]. Mean and systolic blood pressures in premature and full-term neonates increase with gestational age, birth weight, and postnatal age [54]. Of importance is the observation that the systolic and mean blood pressures measured noninvasively in premature and full-term neonates asleep is 10–20 % less than the corresponding awake values [54]. This is consistent with the expected decrease in systolic blood pressure of 20–30 % after induction of anesthesia. Because complex ICU ventilators or HFOV/ HFJV is often used in the NICU, a neonatologist and respiratory therapist should be present throughout the procedure [37] to assist with ventilation, oxygenation, and ventilator-related issues. Changes in oxygenation and ventilation may occur as a result of increases in the abdominal pressure and/or decreases in lung compliance associated with surgery. Persistent changes in oxygenation and ventilation may require compensatory changes in PEEP, PIP, and mean airway pressure depending on the mode of ventilation as well as the inspired fraction of oxygen. If conventional ventilation cannot maintain adequate blood gases, it is possible that the strategy will have to be changed to perhaps HFOV [67]. Neonates whose lungs require HFOV are often monitored using transcutaneous CO2 monitoring. This monitor tracks the PaCO2 [55] although it requires recalibration periodically; the response lags compared with end-tidal capnography and its accuracy should be confirmed by comparing the results to an arterial blood gas before commencing surgery. Capnography is not routinely available in most NICUs, but the anesthesiologist should ensure that capnography is available for those neonates and VLBW infants with reasonable lung function and whose lungs are ventilated with conventional ventilators [55, 56, 99]. End-tidal CO2 does not provide accurate estimates of PaCO2 in neonates whose lungs are ventilated with HFOV (see discussion on high-frequency ventilation below).
Thermoregulation is a vital function in the neonate that may prove challenging during surgery in the NICU. Surgery is often performed in open radiant warmers with overhead radiant heaters in the NICU. However, these heaters may be less effective at maintaining thermoneutrality during surgery as the surgeons cover the neonate blocking the infants from the heat source. In the OR, the ambient temperature is often increased to 26 °C [57, 58] to prevent radiation and, to a lesser extent, convective heat losses. This is not usually possible in the NICU setting unless a designated procedure room is used. A forced-air heating blanket, which is a very effective method to prevent intraoperative hypothermia [59] better than most other strategies during surgery, is usually unavailable in the NICU. However, if it is available, it should be placed under the infant before surgery commences. A fluid warmer should be used to warm all fluids, especially if blood products are required. Often, a fluid warmer must be supplied from the OR. Hypothermia during neonatal surgery has been associated with reduced OR ambient temperature as well as with major surgical procedures [60], e.g., open abdominal procedure. Similar data from the NICU have not been forthcoming.
One major controversy regarding surgery in the NICU when this subject was initially considered was the potential risk for increased infections and sepsis. However, several small studies failed to demonstrate any increased risk associated with operating in the NICU. One study that involved repair of congenital diaphragmatic hernia in the NICU [61] reported an increased but not statistically significant change in the infection rate. However, they did demonstrate a significant increase in the inflammatory marker C-reactive protein (CRP) in the NICU operative group, suggesting that inflammation was present. Because critically ill neonates are more prone to infections as well as a greater morbidity and mortality from infection than healthy neonates, it is imperative to adhere to OR infection control policies including the use of appropriately timed (pre-incision) surgical site antibiotics irrespective of the location of the surgery [41].
There have been several published reports of neonates undergoing a variety of different operative procedures in the NICU. Most of these studies included small sample sizes, most were retrospective, and none were randomized trials evaluating outcomes. A review of the publications to date suggests that the neonates in the NICU operative group had a greater mortality than those operated in the OR [35, 39, 61, 62], although selection bias limits the external validity of these data: these neonates were sicker and required more ventilatory and inotropic support. The extent to which these differences of pre-procedural morbidity were responsible for the increased mortality is difficult to determine. A retrospective study [35] utilizing the score for neonatal acute physiology (SNAP) demonstrated that neonates undergoing surgery in the NICU had a greater preoperative SNAP score than those undergoing surgery in the OR, but that SNAP increased by 20 % in both groups during the initial 24 h post-procedure.
Despite the lack of evidence concerning improved outcomes after surgery in the NICU, it is difficult to determine whether the challenges associated with undertaking surgery in a foreign environment offset those associated with transferring the neonate to the OR [35]. As surgery is performed more frequently in the NICU on more stable neonates, the mortality rate is decreasing significantly [35]. In many centers today, surgery in the NICU is regarded as routine and safe.
Sedation and Analgesia for Common Procedures in the NICU
Critically ill neonates in the NICU undergo frequent painful procedures such as blood draws, heel sticks, and intravenous catheter placement daily [63]. Other procedures that may cause discomfort in some neonates include tracheal intubation, mechanical ventilation, and tracheal suctioning [64, 65]. Neonates who require mechanical ventilation are often sedated with a combination of fentanyl and midazolam. The American Academy of Pediatrics (AAP) recently published guidelines for premedicating neonates who require nonemergent tracheal intubation [66]. They recommended atropine, fentanyl as a slow infusion, and vecuronium/rocuronium. These guidelines recommend avoiding midazolam in premature neonates because of its prolonged half-life, hypotension, reduced cerebral blood flow, and the presence of benzyl alcohol as a preservative.
High-Frequency Ventilation:
Critically ill neonates, especially premature infants, may develop hypoxemic respiratory failure as a result of small lung volumes, poor compliance, increased intra- and extrapulmonary shunts, and ventilation perfusion mismatch. High-frequency ventilation is a commonly used lung-protection strategy that benefits oxygenation and ventilation [67]. Two types of high-frequency ventilators are used in neonates in the United States:
(a)
High-frequency oscillatory ventilation (HFOV, Sensor Medics 3100A, CareFusion Corporation, San Diego CA) utilizes a piston pump to generate oscillations. This is the only mode of ventilation in which inspiration and expiration are active. A constant distending pressure is applied to the lungs (mean airway pressure), over which small tidal volumes (amplitude) are superimposed at a rapid respiratory frequency (6–15 Hz). Typically a frequency range between 10 and 15 Hz is used in neonates. Greater frequencies are commonly used in premature infants. The frequency of oscillation influences the CO2 removal in a direction opposite to that of conventional ventilation. Greater frequencies decrease tidal volume and increase PaCO2. Decreasing the frequency and increasing the amplitude independently increase tidal volume and decrease PaCO2. The following factors should be considered if a critically ill infant who depends on HFOV requires surgery:
1.
Performing surgery while the lungs are ventilated using a HFOV may be technically difficult for the surgeon.
2.
Mean airway pressure recruits alveoli and is closely related to oxygenation. When an infant is switched from conventional ventilation to HFOV, it is recommended that the starting mean airway pressure be 2 cmH2O above the mean airway pressure on conventional ventilation.
3.
If a neonate is weaned from HFOV to conventional ventilation for surgery, adequate PEEP must be provided to maintain alveolar recruitment and oxygenation.
4.
Increased mean airway pressure can impede venous return and decrease blood pressure. If hypotension is encountered during HFOV, fluid boluses may be required. If hypotension persists, the mean airway pressure should be decreased providing the respiratory status of the neonate remains stable.
5.
Wide fluctuations in PaCO2 (especially hypocarbia) can occur during HFOV. Frequent blood gases and/or transcutaneous pCO2 monitoring provide useful indices of ventilation with HFOV; end-tidal pCO2 monitor is unreliable. The skin at the site of transcutaneous monitor application must be frequently checked to avoid burns. The site may have to be changed frequently particularly in premature infants.
(b)
High-frequency jet ventilation (HFJV, Life Pulse, Bunnell Incorporated, Salt Lake City, UT) is the second form of high-frequency ventilation in the Unites States. HFJV is particularly effective for early intervention and treatment of pulmonary interstitial emphysema. The jet ventilator provides small, high-velocity breaths and fast rates with passive exhalation. A conventional ventilator operates in tandem with the jet ventilator to maintain optimal PEEP. The conventional ventilator is attached to the regular connector of the tracheal tube, and the HFJV is connected through a special adaptor to the side port of the tube. Mean airway pressure is adjusted primarily by changing the PEEP on the conventional ventilator. Just as in the case of conventional ventilation, faster respiratory rates and greater PIP with the HFJV reduces the PaCO2. See Chapter 9 for further information [68].
Transport:
The majority of births in the United States occur in hospitals without tertiary level neonatal intensive care units. Neonates who are born extremely premature outside a tertiary hospital may require transport to a tertiary hospital (interhospital transport) soon after birth because of respiratory distress, congenital anomalies, and/or surgical problems. A transport incubator should be used for all interhospital transports. Once inside the tertiary hospital, these neonates may require transport within the facility for diagnostic or special procedures such as radiography, cardiac catheterization, or surgery [69] (intrahospital transport). Many of these neonates are critically ill, require mechanical ventilation, and are at increased risk for cardiorespiratory instability. Increased stimulation during transport can destabilize a critically ill infant. Accordingly, appropriate sedation and analgesia during transport will prevent cardiorespiratory instability.
For short transports within the hospital, critically ill infants are transported on radiant warmer beds. In these instances, the infant’s head should be covered with a hat, and the body wrapped in a plastic/vinyl insulated bag to prevent heat loss. In neonates with abdominal wall defects (gastroschisis or omphalocele) or large neural tube defects (meningomyelocele and encephalocele), sterile vinyl bags should be applied to prevent infection, hypothermia, and hypovolemia. Intrahospital transports are best managed by manually ventilating the lungs. Hand ventilation enables the operator to continuously evaluate the compliance of the lungs including early detection of accidental extubation, a tube disconnect or tracheal tube kinking, or occlusion to be detected earlier although this depends on the fresh gas flow and operator experience [70]. However if the lungs are ventilated manually, it is imperative that the operator remains focused on the ventilation (rather than steering the incubator) to ensure the respiratory rate and peak inspiratory pressure are appropriate.
It is recommended that the neonatal transport team carry medications for analgesia, sedation, and paralysis [69] including analgesics and sedatives (fentanyl, morphine, midazolam), neuromuscular blocking drugs (pancuronium and vecuronium) and reversal agents (flumazenil to reverse benzodiazepines, naloxone to reverse opioid-induced respiratory depression, neostigmine to antagonize neuromuscular blocking agents). In addition, they must have equipment to manage a sudden airway emergency including an appropriately sized laryngoscope, tracheal tubes, stylet, and ventilation circuit (Ambu bag or T-piece).
Specific Conditions Requiring Surgery in the NICU (For Further Details See Chap. 9 Thoracoabdominal Surgery)
Closure of Patent Ductus Arteriosus (PDA)
Failure of the PDA to close spontaneously or in response to medical management with indomethacin or ibuprofen is common in ELBW premature infants. Medical management appears to fail in up to two-thirds of ELBW infants [71]. When medical treatment was compared with surgical closure of the PDA as first-line therapy in premature infants, the incidence of mortality and post-closure complications were similar [72]. In some, medical treatment may be contraindicated because of intraventricular hemorrhage or renal failure. A PDA results in significant left-to-right shunting of blood causing pulmonary over-circulation, respiratory failure, prolonged ventilator dependence, congestive cardiac failure and chronic lung disease, and NEC (necrotizing enterocolitis). In these patients, surgical ligation of the PDA may be performed [71]. More recently, percutaneous closure of the PDA has been performed successfully in young neonates and may point to another approach to open surgical ligation [73].
Surgical ligation of a PDA in neonates has a low morbidity and mortality. The CXR may indicate fluid overload or evidence or a respiratory distress syndrome. The echocardiogram establishes the size of the ductus and the degree and direction of blood flow. Although surgical closure of the PDA is routinely performed in the OR, it has also been performed in the NICU [74]. The outcome from surgical ligation appears to be related to the underlying degree of pulmonary and cardiovascular disease. In a nonrandomized study of PDA ligation in the OR and NICU, it demonstrated that postoperative mortality (17 %) was due to respiratory failure and sepsis, with risk factors being surgery in the NICU and low birth weight [75]. The overall outcome of PDA ligation was early extubation (<10 days) in 30 % of neonates, late extubation (no chronic lung disease, CLD) in 22 %, and late extubation with CLD in 31 %. There was no difference between the groups in terms of early incidence of extubation suggesting that the outcome after PDA closure in neonates without severe cardiorespiratory disease is similar whether it is done in the OR or NICU. In another study of 41 PDA ligations in neonates <1500 g with a mean gestational age of 27 weeks in the NICU, no complications were attributable to anesthesia, and 5 deaths were all related to prematurity and congestive heart failure [74]. In some institutions ligation of a PDA in the NICU is considered standard. Some regional centers have a team comprising of a pediatric cardiac surgeon, pediatric anesthesiologist, and pediatric OR nurses traveling to pediatric hospitals to perform PDA ligation in the referring hospital’s NICU to avoid the interhospital transfer of the neonate [76]. There was no difference in either the preoperative complication rate or mortality between these neonates and those operated on at the surgical institution. Most importantly, by not transferring the neonates, the same neonatal team that is most familiar with the infant’s medical and social history could provide the infant’s care, and the family is minimally inconvenienced.
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