Chapter 86

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1454 PART 5 ■ Anesthetic, Surgical, and Interventional Procedures: Considerations sevoflurane, and is also associated with a decrease in heart rate. With isoflurane and sevoflurane, a reduction of peripheral vascular resistance is the main cause of the reduced blood pressure and the heart rate will be maintained or even slightly increased. 149 Most often, the degree of hypotension caused by the inhalational agents can be tolerated. However, if treatment is deemed necessary, a bolus administration of 5 to 10 mL/kg of crystalloid in the case of sevoflurane and isoflurane, 119,148 or administration of atropine if halothane is used, often suffices to correct the situation. 150 The concomitant administration of N 2 O has different effects on the MAC requirements for the three volatile anesthetics mentioned above. The addition of 60% N 2 O decreases the MAC values by 60%, 40%, and 25% for halothane, 151 isoflurane, 152 and sevoflurane, 119 respectively. To use N 2 O together with halothane in an attempt to minimize the negative cardiovascular effects of halothane appears reasonable. However, whether supplemental use of N 2 O is of significant value when isoflurane or sevoflurane is used can be debated. The preconditioning effect of sevoflurane is currently an area of great interest, and recent data has shown a myocardial pre - conditioning effect of sevoflurane in a neonatal rodent model. The mechanism behind this preconditioning effect of sevoflurane appeared to be a blockage of mitochondrial K ATP channels. 153 The effect of inhalational agents on cerebral autoregulation is also an important topic in the context of neonatal anesthesia. Recent data suggest that cerebral autoregulation is preserved up to 1.5 MAC sevoflurane as assessed by the transient hyperemic response measured by transcranial Doppler. 154 Opioids The use of moderate to high doses of opioids for maintenance of anesthesia is associated with a high degree of hemodynamic stability. This is especially useful in unstable patients or in the case of major surgery in the neonate. The use of fentanyl (10–50 g/kg) or sufentanil (35 g/kg) has been found capable of attenuating the neuroendocrine stress response and reducing morbidity; a reduc - tion in mortality has even been suggested in neonates undergoing corrective surgery for congenital heart defects. 15,24 Synthetic opioids are high clearance drugs and the metabolism is not so dependent on the maturation of the hepatic biotransformation system 155 (see Chapter 15). The terminal half-lives of fentanyl and sufentanil in the neonate are approximately 5 and 13 hours, respectively. 156 Because these drugs have a high clearance, their elimination is substantially prolonged in situations of compro - mised liver blood flow, for example, high abdominal pressure following closure of an omphalocele or gastroschisis. In this situation the terminal half-life of fentanyl has been reported to increase to 1.5 to 3 times the normal average value. 155 When a regional anesthesia has not been performed for intraoperative analgesia, the repeat injection of small boluses of fentanyl (1–2 g/kg) can be used together with a volatile agent as a balanced anesthesia technique. 157 Some caution is recommended regarding the intraoperative doses of opioids in patients having received a regional anesthetic block. If there is intraoperative need to increase the depth of anesthesia, this should preferentially be accomplished by temporarily increasing the dose of volatile agent. Otherwise the patient will be exposed to the risk of a prolonged emergence with respiratory depression, possibly necessitating postoperative ventilation, since at the time of emergence the patient will have good analgesia from the regional block and, thus, will have no stimulatory effects of any pain. Such a situation can be overcome by the administration of naloxone, but the staff in the recovery room or NICU should be aware of the risks of renarcotization if a prolonged infusion of naloxone has not been started. 5.6. Use of Regional Anesthesia Techniques The modern concept of a combination of a light general volatile anesthetic and a central or peripheral nerve block has proved to be of great benefit in neonatal surgery. 157,158 Apart from offering excellent intra- and postoperative analgesia, frequently making the perioperative administration of opioids unnecessary, regional anesthetic techniques provide muscle relaxation, making unnecessary the use of muscle relaxants except to facilitate tracheal intubation. A regional block also attenuates the magnitude of the surgically induced stress response 159 which is highly likely to be beneficial to the recovery of the patient. Retrospective data also indicate that a thoracic epidural block reduces the need for posto - perative ventilation compared to children receiving more tradi - tional postoperative analgesia with opioids. 157 A further advantage may also be earlier return of peristalsis following abdominal surgery in premature babies and neonates. 160 The use of epidural blocks has been found adequately safe in children, as shown in a large prospective audit (10,000 children), including more than 500 epidurals performed in neonates. 161 Although regional blocks offer considerable benefits in neo - nates compared to more traditional techniques, care must be taken regarding the dosing of local anesthetics in order to avoid toxi - city. 162 Generally accepted guidelines restrict a maximum bolus injection of bupivacaine to 1.5 (up to 2.0) mg/kg and a subsequent continuous infusion to maximum 0.2 mg/kg/h 163 and these dosage recommendation have recently been found to result in safe plasma levels in neonates, at least up to 48 hours postoperatively. 158 Bupivacaine plasma levels of 2 to 4 g/L are generally believed to represent the threshold for CNS toxicity in children, but signi - ficantly lower plasma levels are associated with pretoxic symptoms in awake ex-premature infants receiving a caudal block. 164 Since the metabolism of lidocaine is relatively mature in neonates this local anesthetic might be an even better option than bupivacaine in neonates if a continuous infusion technique is con sidered. Determinations of plasma levels of lidocaine are usually readily available at most laboratories, making monitoring of the treatment possible and steady state conditions following conti nuous infusion will be reached within approximately 12 hours. 165 This provides a sharp contrast to bupivacaine infusion, where plasma concentra - tions of bupivacaine are still increasing in a significant portion of neonates following 48 hours of infusion. 158 Neonates receiving continuous regional blockades postoperatively should be cared for in the NICU or in a high dependence environ ment with appro - priate monitoring, for example, ECG, pulse oxi metry, respiratory rate, pain scoring, and general behavior of the neonate. Prevention of Heat Loss/Maintenance of Normal Body Temperature Every possible effort must be made to prevent perioperative hypothermia in the neonate (see Chapter 10). This can be accomplished by combining a number of different measures (Table 86–10). If hypothermia still occurs despite precautions, attempts
CHAPTER 86 ■ Management of the Neonate: Anesthetic Considerations 1455 TABLE 86-10. Measures to Prevent Neonatal Perioperative Hypothermia 1. Avoid unnecessary exposure of the patient. Cover the baby as much as possible during anesthesia induction and line placement. 2. Use warm preparation solutions and the smallest amount necessary 3. Keep the incubator plugged in and warm during the operation. 4. Increase the operating room temperature to at least 25–26C. 5. Use an active humidifier or a heat-moisture exchanger to prevent heat and water losses from the exhaled air. 6. Active heating blanket with a prewarmed gel mattress 7. Forced convective air heating system. Do not use the highest temperature setting to avoid hyperthermia and/or skin burns. 8. Open bed incubator with overhead radiant heaters. Preferably use servocontrol mode with skin temperature probe. 9. Warm intravenous fluids. Coaxial devices are more efficient to warm fluids. 10. If intraoperative irrigation is necessary in the surgical wound, warm solutions should be used. to normalize body temperature should be undertaken as soon as possible. In order to be in control of temperature homeostasis, it is crucial to measure body temperature in all neonatal patients as part of routine monitoring. The best site for measurement of true core temperature during normal clinical conditions can be debated but convenient sites are the axilla, esophagus, rectum, and naso - pharynx. To gain further information any of the above monitoring sites can be complemented by measurement of the skin tem - perature in order to determine the degree of difference between the peripheral and the core temperature. With regards to the operating room temperature, it has recently been reported that using a room temperature of more than 23C is beneficial but will not prevent hypothermia in neonates as a single measure. 166 Intraoperative Fluid Requirements and Volume Replacement During Anesthesia Caloric, Fluid, and Electrolyte Requirements Caloric, fluid, sodium, and potassium requirements have been defined during minor surgery performed under halothane anesthesia (Table 86–11). 167 These requirements are close to those associated with the basal metabolic rate. 168 Depending on the degree of surgical trauma basal infusion rates during neonatal surgery can be set as follows: TABLE 86-11. Intraoperative Energy and Fluid Requirements 167 Intraoperative Requirements Caloric Fluid Sodium Potassium Calculated Maintenance Value 1.5 kg 5 kcal/h 2.5 kg 10 mL/h 0.045 kg 0.16 mmol/h 0.03 kg 0.10 mmol/h 1. minor surgery (e.g., inguinal hernia repair): 5 mL/kg/h; 2. moderate surgery (e.g., duodenal atresia repair): 7.5 mL/kg/h; 3. major surgery (e.g., gastroschisis repair): 10 mL/kg/h. These infusion rates will cover fluid losses due to evaporation from the wound and “third spacing” losses. These infusion rates should be viewed as guidelines only; individual adjustments will have to be made in each separate case. Glucose Administration To include or abstain from intraoperative glucose administration has been a highly debated topic during recent years. In the majo - rity of neonates it is possible to use only Ringer solutions during the operation without risking the development of hypoglycemia. 169 However, in newborns less than 48 hours ols, in babies born to diabetic mothers, following interruption of a continuous glucose infusion, and in premature or small-for-date babies, there is a definite risk of intraoperative hypoglycemia. Since the risks associated with intraoperative glucose administration are small (excluding cardiac and neurosurgical anesthesia) most practitio - ners include some amounts of glucose in the intraoperative infusion in order to safeguard against intraoperative hypoglyce - mia. Frequent intraoperative measurements of blood glucose are, however, of value regardless of infusion strategy in order to monitor glucose levels. Fluid Replacement and Suitable Solutions The composition of the intraoperative infusion fluid varies greatly between centers. A solution containing 2.5% glucose with sodium 70 mmol/L represents an acceptable standard solution for most cases. Volume replacement will mainly be governed by clinical signs such as blood pressure, urine output, and time for capillary refill, since attempts at measuring carefully the amount of intraoperative blood loss in neonates are associated with great difficulties. Neonates tolerate hypovolemia poorly and substitution with crystalloids and colloids (Ringer solution 3 mL/mL of blood loss; 5% albumin 1 mL/mL of blood loss) should be started very early to compensate for ongoing losses due to oozing from the wound edges and transudation. Substitution with packed red cells and plasma (aliquots of 5–10 mL/kg of packed red cells or plasma are given according to the estimated blood loss and the blood pressure response) should also be started early and if the child is not polycythemic at the outset of surgery, the author suggests that transfusion should be started when the blood loss exceeds 10% of the estimated blood volume. Administration of a 4 to 5% albumin solution has traditionally been the colloid of choice in the neonatal setting to treat hypo - volemia, whereas it has been strongly questioned in adults. 170 Albumin solutions contain quite large amounts of sodium. After significant administration of albumin the occurrence of hyper - natremia is exceedingly rare in the authors experience, even if surgery is performed immediately postpartum. Successful use of gelatin solutions (maximum dose of Haemaccel 40 mL/kg) in neonatal surgery has recently been reported. 171 Currently, albumin is still the colloid of choice for use in neonatal surgery until further data are available. Major hemorrhage, fortunately, is a rare event during neonatal surgery due to the meticulous hemostasis technique practiced by most pediatric surgeons. If confronted with major bleeding, rapid transfusion can most often be accomplished by rapid injection
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Chapter 86

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