Chapter 86

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1446 PART 5 ■ Anesthetic, Surgical, and Interventional Procedures: Considerations maintenance infusion of 10% glucose containing 20 mmol/L sodium and 20 mmol/L potassium is usually satisfactory for the first 48 postnatal hours. If enteral feeding has not been established at this time, total parenteral nutrition should be started to ensure adequate nutrition of the baby. Temperature Control Thermoregulation in the neonate displays significant particulari - ties (see Chapter 10). Heat loss is favored by the comparatively larger body surface–to–body weight relationship, the poorly developed insulating subcutaneous fat layer, and the inability to use shivering thermogenesis. These limitations are partially compensated for by the unique thermal capacity for nonshivering thermogenesis (NST), which takes place in the neonate’s brown adipose tissue (see Chapter 10). Brown fat is mainly located be - tween the scapulae, around the blood vessels of the neck, in the axillae, in the mediastinum, and around the adrenal glands and kidneys. However, nonshivering thermogenesis is negatively influenced by the administration of volatile anesthetics. 91 Halo - thane, enflurane and isoflurane appear to cause an equipotent inhibition of thermogenesis. Concentrations of volatile anesthetics as low as 0.7% result in a 50% inhibition of the maximal thermal response 92 (Figure 86–8). Recent data also indicate that a fentanylpropofol–based anesthetic will interfere with NST. 93 Inadvertent intraoperative hypothermia has been found to cause a number of negative effects in adults, such as impaired immunologic function, increased rate of wound infections, negative influences on hepatic and renal function, and reduced drug metabolism. 94 Although no corresponding data are currently available in children, it is reason - Figure 86-8. The effects of halothane, isoflurane, and enflurane on the maximal norepinephrine-induced oxygen consumption in isolated brown adipocytes. The cells were preincubated with the indicated concentrations of the anesthetic agent, immediately transferred to an airtight oxygen electrode chamber, and then stimulated with successive additions of norepinephrine. In each of the control experiments, the maximal rate of oxygen consumption was defined. The highest rate of oxygen consumption that was reached for each concentration of each anesthetic, expressed as percent inhibition of the maximal rate of oxygen consumption, are the values shown. The results are the averages from two series of experiments. The values obtained were for cells treated with halothane: I max 89 2%, IC 50 0.7 0.04%, r 0.997; with enflurane: I max 79 4%, IC 50 0.7 0.07%, r 0.994; and with isoflurane: I max 69 3%, IC 50 0.6 0.06%, r 0.993. able to assume that these negative effects will occur also in the neonate, maybe at an ever greater degree, and hypothermia must be prevented during anesthesia and surgery in the neonate at all times (see “Prevention of Heat Loss” ). This fact is further under - scored by convincing evidence from adults pointing out that a reduction of as little as 2C will predispose to a number of post - operative complications and will also affect outcome. 95 PREOPERATIVE INVESTIGATIONS Medical History and Physical Examination Hydration Status The anesthesiologist should screen every neonate for clinical signs of dehydration, for example, reduced fontanel tension, decreased skin perfusion, reduced skin turgor, and unexplained tachycardia (see Chapter 27). Special attention should be paid to any patho - logic fluid losses, most often occurring from the gastrointestinal tract. Also signs of hypovolemia (diaphoresis, tachycardia, hypo - tension, reduced capillary refill, oliguria) must be sought. All degrees of dehydration and/or hypovolemia will have to be fully corrected before going to the operating theater, the only exception being airway obstruction and other super-emergency conditions (e.g., threatening intestinal gangrene due to malrotation volvulus). Failure to correct a negative fluid balance or to miss pre-existing hypovolemia can cause severe problems during the course of the anesthetic. Respiratory Function The presence of any respiratory symptoms must be noted. Stridor is not infrequently mistaken as expiratory stridor. Since airway obstruction is very rare unless the neonate is infected with res - piratory syncytial virus, until proven otherwise, stridor is essen - tially inspiratory in nature and represents a symptom of upper airway obstruction. Its presence should lead to further investiga - tions and consultation with an otolaryngologist. Tachypnea, grunting, jugular and costal retractions, reduced peripheral oxy - gen saturation on room air, oxygen dependence or frank cyanosis are all signs of respiratory distress. Neonatal respiratory distress can be caused by a number of different pathologies and merits consultation with a neonatologist before anesthesia. Cardiovascular Function Cardiovascular abnormalities are usually known in neonates scheduled for surgery. However, the anesthesiologist should always check for the presence of any signs and symptoms indicative of cardiovascular problems, for example, poor or excessive weight gain, failure-to-thrive problems, hepatomegaly, tachypnea, cyano - sis, heart murmur, or weak or absent femoral pulses. If such symp - toms or signs of cardiovascular abnormalities are present further consultation with the pediatric cardiologist, including an echo - cardiographic examination, is mandatory before anesthesia and surgery. A liberal attitude towards pediatric cardiology consulta - tion should be the rule in order not to miss any significant cardiovascular abnormality. Neonates undergoing correction of any congenital malformation are at increased risk of having some associated syndrome. The anesthesiologist can not be expected to be knowledgeable regarding all rare congenital syndromes but signs suggestive of Down syndrome should always be sought. The
CHAPTER 86 ■ Management of the Neonate: Anesthetic Considerations 1447 Pierre–Robin syndrome has anesthesiological implications and signs of micrognathia should be identified before going into the operating theater. Coagulation Disorders Coagulopathy is rare in neonates. However, since coagulation dis - orders can cause life-threatening bleeding intra- and postopera - tively, the anesthesiologist has to search for symptoms and signs (e.g., prolonged bleeding from skin puncture sites, spontaneous bleeding from the nasal or oral mucosa, presence of more signifi cant amount of blood during tracheal suctioning in already ventilated patients). The skin surface should also be inspected in order to identify any petechiae indicating a possible low platelet count. If the patient is suffering from uncontrolled sepsis, a coagulopathy should be suspected until proven otherwise. If coagulation problems are suspected, appropriate laboratory tests must be performed (see “Coagulation”). If these tests are not within the normal range, consultation with a coagulationist should be under taken. Laboratory Screening Hemoglobin, Blood Typing, and Compatibility Screening Neonatal hemoglobin values are considerably higher (150 to 240 g/L) than in adults (see Chapter 9). It consists mainly of fetal hemoglobin (HbF) which has a higher oxygen binding capacity (P 50 19.5 mmHg) than normal adult hemoglobin (HbA) (P 50 27 mmHg); thus, the HbF oxygen dissociation curve is displaced to the left. Due to its higher oxygen binding capacity, HbF has a decreased potential for oxygen release to the tissues. In a situation where oxygen demand is high or oxygen transport is marginal (e.g., sepsis, hypoxemia, hypovolemia, and intraoperative hemorrhage), transfusion of HbA will be beneficial. Polycythemia (normal hemoglobin range in the newborn: 150–240 g/L) can be present in certain neonates (incidence approximately 4%) and hematocrit values above 65% increase blood viscosity, which negatively influences tissue blood flow. In such a situation, exchange transfusion (20–30 mL/kg of blood exchanged for the same amount of plasma) can be discussed before surgical intervention in order to optimize the conditions for the patient. A preoperative hemoglobin and hematocrit value should be taken in all neonates scheduled for surgery, with the exception of diagnostic or very minor procedures (e.g., inguinal hernia repair). If surgery is more extensive or if there is even a small risk of significant bleeding, blood typing and compatibility screening should be performed. Blood and plasma should be ordered according to the potential needs and should be readily available before induction of anesthesia. Indications for the ordering of plasma are mainly the anticipation of major blood loss where plasma will be needed to boost coagulation or in situations where substantial third space losses are likely (e.g., gastroschisis repair). In the neonate, blood typing and compatibility screening requires determination of the neonates blood type as well as blood typing and screening of the mother. The type and screen of the mother is acceptable if the baby is less than 6 weeks old. If irregular antibodies are found in the mother, cross-matching has to be performed. Screening tests do not need to be performed in the neonate, since the neonatal immune system is not capable of producing antibodies until 3 months of age. Thus, the antibodies present in the neonate only originate from placental transfer from the mother. Electrolytes and Acid-Base Balance If the patient is scheduled for more extensive surgery the patient’s electrolyte and acid-base status must be checked before induction of anesthesia. A standard screen should include sodium, potas - sium, chloride, calcium, pH, and base excess/standard bicarbonate levels. Any significant deviation from normal values should be corrected before anesthesia and surgery. It is worth remembering that the neonatal reference values for potassium are higher than in older children and adults (day 1–2: 4.5–7.0 mmol/L; 3rd postnatal day–3 months: 4.0–6.2 mmol/L). Values outside of the normal values might be associated with the same risk for cardiac arrhythmias as in older patients. Coagulation Coagulation parameters are quite different in neonates and pre - mature babies compared to adults (Table 86–8) and can be mistaken for a coagulopathy with an increased bleeding tendency, especially regarding activated partial thromboplastin time 96 whereas neonates most often have an increased tendency for blood clotting. The theoretical background for this is still not entirely clear but can be a result of lower inhibitor levels. Thus, surgery does not have to be postponed or action taken merely on the grounds of coagulation tests outside normal adult limits. However, if coagulation parameters are outside the normal values for premature or term babies, especially also if clinical signs of coa - gulopathy are present, consultation with a coagulation expert should be undertaken. Platelet counts are similar to normal adult values in term neonates (250–300 10 9 /L) but are frequently lower in premature children (50–150 ( 10 9 /L). The function of the platelets are generally normal. The existence of thrombocytopenia should raise concern since this is often one of the initial signs of sepsis in neonates and a neonatologist should be consulted regarding the cause of a low platelet count. No specific knowledge is available for the lowest acceptable platelet count in association with neonatal surgery, but levels of at least 50 to 65 10 9 /L should most probably be required. Platelet transfusion of 5 mL/kg will increase the total platelet count by about 40 10 9 /L. In major surgery, intraoperative platelet transfusion is usually not needed until the patient has bled approximately two blood volumes, if the patient had a normal platelet count preoperatively. Due to limited reserves and a generally insufficient supply of vitamin K by breast feeding, neonates should receive supplemental vitamin K either by the oral or, preferably, by the intramuscular route (1 mg) immediately following birth. This will safeguard against the development of coagulopathy during the neonatal period. In emergent delivery situation or as a result of early transfer of the baby between hospitals, vitamin K administration can easily be forgotten. Before neonatal anesthesia and surgery it is prudent to check the patient’s notes to ensure that vitamin K has been administered. If not, coagulation parameters should be checked and vitamin K given (1 mg I.M. or I.V.). Intramuscular administration of vitamin K is preferable since I.V. administration is associated with an increased risk of side effects (mainly severe hemodynamic reactions). The effect of vitamin K is delayed (hours) and in an emergent situation transfusion of fresh frozen plasma will provide enough coagula tion factors to allow the start of the surgical intervention.
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Chapter 86

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