Chapter 86

More documents

Recommendations

Info

1452 PART 5 ■ Anesthetic, Surgical, and Interventional Procedures: Considerations a nasogastric tube should be inserted before placement of the LMA and left open to vent the stomach. Use of the LMA allows the anesthesiologist to avoid unnecessary tracheal intubation in expremature babies with bronchopulmonary dysplasia where extubation has just recently been achieved with great difficulty. The LMA with preserved spontaneous ventilation can be used for selected cases with an anticipated anesthetic duration of less than 30 to 45 minutes. If longer interventions are planned, tracheal intubation should be performed. The LMA has also been advocated in the resuscitation situation immediately after delivery in asphyxiated term babies. If an experienced anesthesiologist performs the placement of the LMA in this situation, successful placement of the LMA is virtually always achieved at the first attempt. 124 If the position of the LMA is checked by fiberscopy, the epiglottis is visible in about 50% of cases. The clinical relevance of this finding is still open to question since only 2% of the children had complete airway obstruction. 125 The clinician should also be aware that end-tidal CO 2 readings will underestimate the PaCO 2 by as much as about 10% of the correct arterial value if the child is allowed to breath sponta - neously. 126 However, if ventilation is controlled, end-tidal CO 2 values are as accurate as if a tracheal tube were used. 127 This, together with the high prevalence of hypercapnea associated with the use of the LMA in spontaneously breathing neonates and infants, further underscores the necessity of at least intermittently assisting the ventilation manually. Tracheal Intubation As discussed above, tracheal intubation should be considered the standard method for airway management in the neonate. A number of points deserve attention: 1. Awake tracheal intubation has previously been recommended in neonates as a safe and practical method. Currently, this practice is no longer acceptable since tracheal intubation is a very stressful and painful stimulus which can definitely cause harm to the patient both in the short and long-term pers - pective. Additionally, the technique is also very stressful for the anesthetic team since the intubation conditions are far from optimal compared to the situation following a controlled anesthetic induction. 128 2. Different measures exist to achieve the appropriate degree of muscle relaxation to allow easy intubation. Succinylcholine should mainly be reserved for rapid sequence intubation and nondepolarizing muscle relaxants should be preferred under more ordinary circumstances. However, the use of nonde - polarizing muscle relaxants will cause a reduction in FRC associated with decrease dventilatory homogeneity. This can be counteracted by the use of 3 cm H 2 O of positive endexpiratory pressure (PEEP) and, thus, the use of this level of PEEP is recommended in anesthetized and paralyzed neonates. 129 Sufficient muscle relaxation can be achieved also by deeper inhalational anesthesia, but, due to the increased risks for cardiopulmonary complications, this will require quite exten - sive neonatal anesthesia experience. Since sevoflurane causes substantially less cardiovascular depression compared to halothane, sevoflurane is preferable when available. However, the slightly more pronounced respiratory depression caused by sevoflurane compared to halothane should be borne in mind. When intubation is performed during deeper inhalational anesthesia only, the use of muscle relaxants might also be completely avoided in most cases of neonatal surgery. Inspira - tory concentrations of sevoflurane and halothane necessary to achieve good intubating conditions will, however, cause a certain degree of hypotension and great caution should be observed in the unstable neonate regarding the use of deeper levels of inhalational anesthesia. However, in more stable neonates intubation during sevoflurane inhalation was found to achieve more stable hemodynamics compared to the outdated technique of awake intubation. 130 3. Since the neonatal larynx is located more anteriorly and more cephalad, with the epiglottis tending to be much floppier and to drop down over the laryngeal entrance like a theater curtain, use of a straight laryngoscope blade is recommended to gain good visualization of the vocal cords in neonates (see Chapter 38). The tip of the blade should not be placed in the vallecula as in older subjects but should lift the epiglottis. This is most easily achieved by first inserting the laryngoscope so that the tip of the laryngoscope is in the entrance the esophagus and then gently withdraw the laryngoscope until the laryngeal entrance “pops” in view. Visibility is regularly enhanced by gentle external pressure on the larynx which can be accom plished either by the anesthesiologist’s own little finger or by an assistant. 4. Several equations are available to help determine the optimal depth to which the tracheal tube should be inserted in order to avoid unintentional dislodgment of the tube or intubation of one of the mainstem bronchi (term neonate; oral intubation: 9 cm at teeth; nasal intubation: 11 cm at nose). Although helpful, such equations and guidelines are not completely reliable and the anesthesiologist must still carefully look how much of the tube is inserted during the intubation procedure and then confirm equal breath sounds and chest wall move - ments bilaterally as well as adequate end-tidal CO 2 readings before being satisfied with the positioning of the tracheal tube. 5. Due to the very compliant chest wall and the slightly stiffer lung, the neonate is prone to develop atelectasis following intubation or other situation involving muscle relaxation and cessation of manual or mechanical ventilation. In order to reexpand the atelectatic lung, a vital capacity maneuver should be performed. Based on animal experiments, a vital capacity maneuver (VCM; inflation pressure 40 cm H 2 O for 15 sec) 131 or a timed re-expansion inspiratory maneuver (TRIM; inflation pressure 30 H 2 O for 10 sec) 132 has been suggested. 6. Adequate fixation of the tracheal tube is of course very important. Since nasal intubation provides better opportunities to accomplish reliable fixation, nasal intubation should be performed in all situations with limited access to the head or if the patient is in the lateral or prone position. 7. By tradition, uncuffed tracheal tubes are used in neonates and infants and an air leak should be present at an airway pressure of approximately 20 cm H 2 O to prevent laryngotracheal trauma. With the introduction of newer materials and designs of the tracheal tubes, this traditional view is now questioned. 133 However, more data are necessary before changing the classical recommendation of using uncuffed tracheal tubes in neonates. 8. Use of an atraumatic technique and appropriate size of the tracheal tube is of paramount importance since the risk of laryngeal damage with long-term sequelae otherwise is high. 134 9. A number of diseases and syndromes are associated with difficult intubation in the neonate too (see companion textbook, Bissonnette B, Luginbuehl I, Marciniak B, editors.
CHAPTER 86 ■ Management of the Neonate: Anesthetic Considerations 1453 Syndromes: Rapid Recognition and Perioperative Implications. New York: McGraw-Hill; 2006.). In such a situation an individualized preinduction strategy should be formed to deal with this potential problem. 135 Use of Muscle Relaxants for Intubation The dose necessary to achieve adequate muscle relaxation with succinylcholine is substantially larger in neonates compared to older children and adults 136 (see Chapter 16). The most likely explanation for this larger dose requirement in neonates is the larger extracellular fluid volume (responsible for a larger volume of distribution) present in the newborn. Thus, an effective intubat - ing dose of succinylcholine in the neonate will be approximately 3 mg/kg. 136 Neonates have increased sensitivity to nondepolarizing muscle relaxants due to their reduced capacity for release of acetylcholine at the motor end-plate in neonates. 137 This increased sensitivity 138 (Figure 86–11) is, however, offset by the increase in extracellular fluid volume. Thus, the actual dose requirements per kg body weight is similar to the doses used in adults. 138 Neonates also display a faster onset time and a prolonged duration of action of these agents. 139 At present neonatal pharmacokinetic data only exists for atracurium, 138 vecuronium 140 and pancuronium, 141 mak - ing these drugs the first line choices. Of these agents only atra - curium is of intermediate duration since both vecuronium 142 and pancuronium cause long-acting muscular relaxation in neonates. Further data are necessary before the routine use of rocuronium or mivacurium can be recommended in the neonatal population. With the variable duration of the nondepolarizing muscle relaxants in neonates monitoring of neuromuscular transmission is clearly advisable. However, such monitoring is not easily accomplished in this age group. Adequate reversal of muscle relaxation should, therefore, be the rule in all neonates. In this respect it can be discussed whether nondepolarizing muscle re - laxants should be used routinely since the judicious use of halo - genated agents and regional anesthetic techniques can produce adequate muscle relaxation in most clinical situations without the concomitant use of nondepolarizing muscle relaxants. Ventilation Ventilation should almost constantly be controlled in neonates, either by manual ventilation or with the aid of a ventilator. 143 A number of pediatric anesthesia breathing circuits have been described 144 (see Chapter 23) and one of the most commonly used intraoperatively is still the Jackson–Rees modification of the Ayres T-piece system. Although very versatile, this traditional system does have certain disadvantages compared to circle absorber systems. The use of low-flow (600 mL/min) semiclosed circle ventilation has been found possible also in neonates using modern anesthesia machines. 145 A number of patients undergoing neonatal surgery have various degrees of pulmonary problems, and during surgery the need for more advanced means of mechanical ventilation might become necessary. Thus, the ventilator used during the anesthetic must be as sophisticated as the ventilator in the NICU and, at the same time, be able to deliver anesthetic gases. With the latest developments within neonatal intensive care, the neonatal anes thesiologist must also be prepared and equipped to perform anesthesia and surgery during administration of inhaled nitric oxide and/or high frequency oscillatory ventilation (HFOV). These new demands will place a great deal of responsibility on the anesthesiologist and the operation unit to learn and acquire new and sophisticated ventilators in order to meet the needs of the sick neonate. The mode of ventilation differs slightly depending on the age of the neonate and the type of surgery. Generally, pressure con - trolled ventilation is preferred in premature infants, in newborns with respiratory distress or any other pre-existing pulmonary pathology, and also during the first days of extrauterine life. Out - side the above mentioned patient categories, volume controlled ventilation can be used successfully and is especially useful in situations where surgical manipulations will interfere with intraoperative ventilation. Due to high compliance of the thoracic cage, lower compliance of the lung and higher closing volume, neonates are particularly prone to develop atelectasis during sur - gery. 146 In order to counteract this tendency for regional lung collapse, a positive-end expiratory pressure of 3 to 5 cm H 2 O should routinely be used in this setting. For shorter procedures, manual ventilation is an option. A false sense of security might be associated with this mode of ventilation, since even experienced practitioners cannot reliably sense a change in compliance only by the tactile feel of the bag. 147 Figure 86-11. Log dose-probit response regression lines for neonates (N), infants (I) and children (C). The points along the lines represent mean responses from subgroups of five patients. Maintenance of Anesthesia Volatile Agents In babies given a regional block as part of the anesthetic plan, or who are otherwise stable and not subjected to major or very painful procedures, a volatile agent is often a good choice for maintenance. Three different volatile anesthetics are commonly used: sevoflurane, isoflurane, and halothane. All of these agents negatively affect the baroreceptor reflex with halothane having the most pronounced effect. 148 The drop in blood pressure is similar for all three agents but the mechanism for this differs for halothane compared to isoflurane and sevoflurane. Halothane depresses myocardial contractility to a greater extent than isoflurane and
Page 1 and 2: Management of the Neonate: Anesthet
Page 3 and 4: CHAPTER 86 ■ Management of the Ne
Page 15: CHAPTER 86 ■ Management of the Ne
Page 27 and 28: TABLE 86-19. Typical Management of
Page 39: CHAPTER 86 ■ Management of the Ne

Chapter 86

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?