Chapter 86

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1456 PART 5 ■ Anesthetic, Surgical, and Interventional Procedures: Considerations with a normal syringe attached to the infusion line. If very substantial blood loss is anticipated preoperatively, the use of a rapid transfusion device might be indicated. 172 If transfusion is given, it is necessary to make sure that the infused components are warmed. Supplementary intravenous calcium administration might also be needed in the setting of larger transfusions of packed red cells (calcium chloride 10 mg/kg (0.05 mmol/kg) I.V., might need to be repeated. Rule of thumb: 1 mg calcium chloride/ transfused mL of packed red cells or plasma). 173 Intraoperative Complications The most frequently encountered intraoperative complications are listed in Table 86–12. Whatever the presenting symptom, airway problems should always be ruled out first, even including rein - tubation of the patient. Tachycardia and hypotension are usually indicative of hypovolemia. Bradycardia and hypotension can either be caused by anesthetic overdose, especially if halothane is used, or represent a late and very ominous sign of an unobserved complication about to escalate. However, if a thoracic epidural block has been performed, relative bradycardia and modest hypotension can be caused by blockade of the sympathetic cardio - accelerator fibers. Bradycardia and hypertension is rarely seen except in the case of an abrupt increase in afterload, as can be seen during aortic clamping/compression or following the ligation of a large patent ductus arteriosus, but in neurosurgical patients can also be a sign of increasing intracranial pressure. In this setting, the hemodynamic response is caused by a partially operative baro - receptor reflex. Tachycardia and hypertension in the absence of catecholamine producing tumors most frequently indicate insufficient levels of anesthesia (Table 86–13). Venous air embolism is always a risk in neonatal anesthesia and utmost care must be observed not to allow injection of small air bubbles or to cause air entrainment at three-way stopcocks. It must be remembered that the fetal extrapulmonary shunts might still be open or can reopen during the course of the anesthetic. Inter - mittent increases in pulmonary artery pressure due to intense surgical stimulation combined with insufficiently light anesthesia can set the stage for devastating systemic embolization due to right-to-left shunting of air bubbles through the oval foramen or the ductus arteriosus. Low urine output is a frequent problem during lengthy pro - cedures. Most commonly this is due to prerenal causes which can easily be corrected by fluid and/or volume replacement. If this does not return the urine output to an acceptable level, then a renal cause for the problem might be present. Although the neonatal TABLE 86-12. Intraoperative Complications Ventilatory Circulatory Complications Complications Miscellaneous 1. Dislodgment of 1. Hypotension 1. Hypothermia tracheal tube 2. Tracheal tube 2. Bradycardia 2. Low urine output obstruction 3. Bronchial intubation 3. Tachycardia 3. Coagulopathy 4. Pneumothorax 4. Hypertension 5. Failure of the 5. Venous air anesthetic equipment embolism TABLE 86-13. Differential Diagnosis of Intraoperative Hemodynamic Events Any Major Hemodynamic Event Tachycardia hypotension Bradycardia hypotension Tachycardia hypertension Bradycardia hypertension First Exclude Any Problems Related to Hypoxia or the Airway: 1. Ventilator circuit 2. Tracheal tube kinked or blocked by secretions 3. Dislodgment of the tracheal tube 4. Intubation of a main stem bronchus 5. Unilateral or bilateral pneumothorax Hypovolemia Reduced venous return due to surgical manipulations Overdose of volatile anesthetic Late ominous sign—collapse imminent Insufficient level of anesthesia Hypercapnea Clamping or compression of the aorta Ligation of a large ductus arteriosus Increasing intracranial pressure kidney is far from mature (see “Renal Function”) it is still capable of responding to stress induced increases of antidiuretic hormone and aldosterone. If fluid and volume replacement is believed to be accurate, then a small dose of furosemide (0.25–0.5 mg/kg) is indicated to try to enhance renal urine production. Probably the most common cause for insufficient urine output is postrenal in nature and is caused by obstruction or kinking of the Foley catheter. In this case, urine output often completely ceases or the urine production is very variable over time. Checking the patency of the Foley catheter should, thus, be the first action taken if urine output is less than anticipated. Termination of Anesthesia—Emergence Reversal of Muscle Relaxation Although adequate time is believed to have elapsed since the last dose of intermediate acting nondepolarizing muscle relaxant, all neonates should be subjected to the administration of neostigmine (50 g/kg) and glycopyrrolate (10 g/kg) in order to reverse any residual muscle relaxation. Because of inherent problems with neonatal application of nerve stimulators (e.g., type and placement of the stimulating electrodes, size of the stimulating current) monitoring of train-of-four does often not provide reliably infor mation regarding the status of the neuromuscular blockade, since almost all such monitors will not function optimally in the neonate. However, if the neonate displays any type of spontaneous muscular response, reversal can be performed without risk. Should the Trachea Be Extubated or Kept Intubated? The answer to this question is complex and should be decided individually for each patient. However, if the neonate has stable vital signs, is normothermic without any major residual effects of the anesthetic, and has good quality pain relief without any concomitant respiratory depression, tracheal extubation can often be successfully performed if the patient fulfills certain criteria:
CHAPTER 86 ■ Management of the Neonate: Anesthetic Considerations 1457 1. regular spontaneous breathing 2. vigorous movements of the limbs 3. gagging 4. eye opening or pronounced grimacing 5. stable hemodynamics, good oxygen saturation 6. Absence of significant hypothermia In any other case, the patients should be ventilated in the NICU at least overnight before extubation is attempted. However, one should remember that controlled mechanical ventilation is not without significant risks for the patient and these risks must be carefully weighed against the risk for respiratory depression/ insufficiency after attempted early extubation. Anesthetic Aspects Associated With Laparoscopic and Thoracoscopic Surgery Still, a traditional surgical technique is most often used, but lapa - roscopic surgery is becoming increasingly popular 174 and may soon be the method of choice in many institutions. If a laparosco - pic approach is used, the anesthesiologist must pay special attention to the various issues associated with the use of pneumo - peritoneum. Pneumoperitoneum Laparoscopic techniques or robotic surgery require the use of gas insufflation into the abdominal cavity. The insufflation will lead to physiologic alterations, especially if the abdominal pressure is allowed to be more than marginally increased. The choice of insufflation gas may also influence these physiologic changes, as will the choice of body positioning necessary for surgical access (e.g., extreme head-up or head-down positions). 175,176 Carbon dioxide is the most frequently used gas, since if inadvertently insufflated into the blood vessels it will be rapidly absorbed, and thus the risk of serious pulmonary gas embolism is minimized. A certain amount of the CO 2 will be absorbed via the peritoneum itself and this will cause an increased CO 2 load for the patient. By using advanced mass spectrometry, it has been shown that 10 to 20% of exhaled CO 2 after 10 minutes of pneumoperi - toneum is derived from exogenous CO 2 . 177 An increase in alveolar minute ventilation by approximately 25 to 30% is needed during normal circumstances in order to counteract the increased CO 2 load. 175 Further adjustment of minute ventilation may be needed due to cranial displacement and splinting of the diaphragm if abdominal pressures are unduly raised and/or if the patient is placed in a head-down position. Thus, in some patients the preser - vation of adequate ventilation during laparoscopic surgery can be quite challenging. Increased abdominal pressure and cranial displacement of the diaphragm will also increase the risk for atelectasis formation. To prevent undue atelectasis formation the use of volume controlled ventilation and a slightly elevated PEEP is recommended. Endotracheal intubation represents standard airway manage - ment in children undergoing laparoscopic procedures. The combined use of pneumoperitoneum and a head-down tilt will, however, produce a downward movement of the tip of the endo - tracheal tube that may result in endobronchial intubation. De - pending on the size of the child the shift of the tip can range between 1.2 to 2.7 cm. 178 Pneumoperitoneum can also cause hemodynamic instability, but if intra-abdominal pressures are maintained in the lower range (10 mmHg) the impact on hemodynamics is usually minor. In this situation, venous return will be enhanced due to displacement of blood from the splanchnic bed as well as an overall increase in systemic vascular resistance. 175 However, if intra-abdominal pres - sures are allowed to increase to about 12 mmHg, then cardiac function will be directly affected as evidenced by septal dyskine - sia 179 and furthermore preload will be reduced due to compression of the inferior vena cava. 175 Since the hemodynamic consequences of pneumoperitoneum is so closely related to the intra-abdominal pressure, it is absolutely essential to monitor the intra-abdominal pressure during the surgical procedure. The maximum tolerable intra-abdominal pressure level during laparoscopic surgery should be 6 to 8 mm Hg. 180 If greater pressures occur or are necessary for surgical access one may have to abandon the procedure and instead convert to an open approach due to safety concerns for the child. Both volatile and total intravenous anesthesia can be used for laparoscopic surgery. However, the use of nitrous oxide is sub - optimal based on the fact that nitrous oxide will easily diffuse into gas filled spaces and thereby increase the volume and/or pressure of trapped gas (cf. pneumothorax and intracranial air). Further - more, the use of nitrous oxide can both obscure the visibility for the surgeon due to expansion of the bowel as well as causing unwanted increases of the intra-abdominal pressure. All the problems listed above will obviously be more prominent in neonates and infants compared to older children. Thoracoscopy There is currently a surgical trend at certain major centres to perform tetralogy of Fallot (TOF) repair as a thoracoscopic pro - cedure. This is of cause associated with very specific anaesthetic considerations. A number of issues are similar to the situation of pneumoperitoneum but there are also some specific issues asso - ciated with thoracoscopy in neonates. 181 CONSIDERATIONS REGARDING ENDOTRACHEAL INTUBATION: Although endotracheal intubation following an inhalational in - duction with preserved spontaneous ventilation is preferred by many clinicians (in order to avoid the risk of potential gastric distension) an intravenous induction can also be used safely in most cases. It is important to place the tip of the endotracheal tube distal to the fistula, but even more important is that the tip has a reasonable safety margin to the carina. The latter is paramount since intuba tion of the right mainstem bronchus, either during intubation or secondary to movement during the positioning of the patient, will make ventilation impossible once gas has been insufflated into the right pleural cavity causing right lung collapse. It is therefore necessary to confirm the position of the tube tip both following intubation as well as after placing the patient in the final position with the right side slightly elevated for surgical access. ONE-LUNG VENTILATION (OLV): Insufflation of CO 2 into the right pleural cavity will cause the right lung to collapse, even when using the recommended insufflation pressure of 5 to 6 mmHg. This will in turn result in an increase in pulmonary vascular resistance secondary to hypoxic vasoconstriction in the right lung. The positive pressure in the right hemithorax will also cause a decrease in venous return by compression of the vena cava and may also cause direct compression of the right ventricle. Thus,
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Chapter 86

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