Chapter 86

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1448 PART 5 ■ Anesthetic, Surgical, and Interventional Procedures: Considerations TABLE 86-8. Reference Values (Mean [Boundary]) for Coagulation Tests in Term and Premature (30–36 g.w.) Babies Coagulation test Day 1 Day 5 Day 30 Adult Premature infants PT (sec) 13.0 (10.6–16.2) 12.5 (10.0–15.3) 11.8 (10.0–13.6) 12.4 (10.8–13.9) APTT (sec) 53.6 (27.5–79.4) 50.5 (26.9–74.1) 44.7 (26.9–62.5) 33.5 (26.6–40.3) TCT (sec) 24.8 (19.2–30.4) 24.1 (18.8–29.4) 24.4 (18.8–29.9) 25.0 (19.7–30.3) Fibrinogen (g/L) 2.43 (1.50–3.73) 2.80 (1.60–4.18) 2.54 (1.50–4.14) 2.78 (1.56–4.00) Coagulation inhibitors AT III (U/mL) 0.38 (0.14–0.62) 0.56 (0.30–0.82) 0.59 (0.37–0.81) 1.05 (0.79–1.31) Protein C (U/mL) 0.28 (0.12–0.44) 0.31 (0.11–0.51) 0.37 (0.15–0.59) 0.96 (0.64–1.28) Term infants PT (sec) 13.0 (10.1–15.9) 12.4 (10.0–15.3) 11.8 (10.0–14.3) 12.4 (10.8–13.9) APTT (sec) 42.9 (31.3–54.5) 42.6 (25.4–59.8) 40.4 (32.0–55.2) 33.5 (26.6–40.3) TCT (sec) 23.5 (19.0–28.3) 23.1 (18.0–29.2) 24.3 (19.4–29.2) 25.0 (19.7–30.3) Fibrinogen (g/L) 2.83 (1.67–3.99) 3.12 (1.62–4.62) 2.70 (1.62–3.78) 2.78 (1.56–4.00) Coagulation inhibitors AT III (U/mL) 0.63 (0.39–0.87) 0.67 (0.41–0.93) 0.78 (0.48–1.08) 1.05 (0.79–1.31) Protein C (U/mL) 0.35 (0.17–0.53) 0.50 (0.22–0.78) 0.63 (0.33–0.93) 0.96 (0.64–1.28) PT prothrombin time; APTT activated partial thromboplastin time; TCT thrombin clotting time; AT III antithrombin III. Adapted from Andrew et al. 144 When major surgery is planned a preoperative coagulation screen consisting of prothrombin time, activated partial thromboplastin time, and platelet count should be performed before surgery. The use of thromboelastography has recently been described also in neonates and infants. Using this technique, children with complex congenital heart disease have been found to have a functionally intact coagulation-fibrinolytic system working at a lower level than in healthy infants, indicating a reduction in the hemostatic potential with less reserve. 97 Using the same techno - logy, the effects of various colloid alternatives were analyzed in infants (3–15 kg). 98 In this investigation, the use of gelatins as an alternative to albumin was suggested since the use of hydroxyethyl starch affected the overall coagulation process the most. Diagnostic Investigations Special investigations can be required after taking the medical history and obtaining results from the laboratory testing. The most common preoperative investigations are chest radiography, echocardiography and ultrasonic head scans. Chest X-Rays Chest radiographs should be obtained in all patients with cardio - respiratory symptoms. Not only will this investigation provide the anesthesiologist with information regarding the severity of various conditions but it can also provide information if further treatment might optimize the patients condition before anesthesia and surgery. Thus, based on the chest radiograph, surgery might be postponed in order to re-expand atelectatic lung tissue or to reduce interstitial edema by intensifying diuretic treatment. Ultrasonographic Examinations Echocardiography should be performed liberally not only to search for associated congenital heart disease but also to more precisely estimate the intravascular volume status. Echocardiography is also useful in order to determine if the ductus arteriosus still remains open and to determine the possible presence of pulmonary hypertension and right-to-left shunting. Due to the existence of an open fontanel ultrasonic head scans provide the unique opportunity for investigating the intracranial contents of the neonate (for the vein of Galen for instance). In term neonates, this investigation rarely provides crucial infor - mation since intracranial hemorrhage is unusual in this group. However, premature infants have an increased risk for such hemorrhages with the highest risk seen in the most prematurely born babies. Before performing anesthesia in such premature infants, it might be wise to perform an ultrasonic head scan in order to document any pre-existing problem and, thus, escape the responsibility for any hemorrhages which have already occurred prior to the involvement of the anesthesiologist. 99 PREANESTHETIC MANAGEMENT Premedication If the neonate is judged to be in pain preoperatively, low and titrated doses of morphine are appropriate. The response to morphine in this age group is variable and doses of 10 to 20 g/kg should be administered intravenously until adequate pain relief is achieved. In case of difficult venous access where an inhalational induction is planned, subcutaneous or intramuscular atropine (10–20 g/kg; minimum 100 g) is often useful to counteract parasympathetic reflexes before the placement of a reliable venous line. In case of intravenous induction, atropine can be given intravenously (10 g/kg; minimum 100 g) just before the start of the anesthetic. Apart from these specific situations, no preme - dication is usually required in the neonatal period. Parental Presence During Induction In older patients, parental presence can be helpful, although cer - tain practitioners still find this practice questionable. 100,101 However, the neonate is not yet mentally capable of psychologic -
CHAPTER 86 ■ Management of the Neonate: Anesthetic Considerations 1449 ally benefiting from parental presence, and contrary to the standard case in older children, where the children in most circumstances are otherwise healthy and the anesthetic and the surgical procedure are not expected to be hazardous, neonatal parents are often very anxious and scared for obvious reasons. Thus, parental presence does not provide any significant benefits to the neonate, may cause unnecessary stress on the parents, and can cause problems to the anesthetic team. The decision to allow or abstain from parental presence during induction of anesthesia can only be made on a case-by-case evaluation. Monitoring Requirements Overview Because of the small size of neonatal patients a number of advanced continuous monitoring options frequently used in adult patients undergoing major surgery or who are hemodynamically unstable (e.g., pulmonary artery catheterization, transesophageal echocardiography) cannot be used in the neonatal setting. However, the need for adequate and reliable monitoring is especially important in neonates since the patient will become more or less inaccessible to the anesthesiologist following surgical draping of the patient. The minimal monitoring required for neonatal anesthesia consists of the following: pulse oximetry, capnography, noninvasive blood pressure monitoring, electrocar - diogram, and body temperature measurement. The use of a precordial or an esophageal stethoscope is viewed as essential by some practitioners and is compulsory for medical–legal reasons in certain countries. Monitoring of anesthetic gases can obviously be incorporated into standard monitoring but the anesthesiologist must be aware of the caveats with the currently available systems resulting in problems with the interpretation of the generated data. If the patient is scheduled for more extensive surgery where substantial bleeding may occur or if the patient is unstable for any reason more invasive monitoring is required. Intra-arterial blood pressure monitoring should be performed liberally under these circumstances not only since it allows accurate and on-line measurement of the blood pressure even at very low blood pressure levels but also since it permits excellent monitoring of the intravascular volume status. Hypovolemia usually causes undulations of the blood pressure tracing synchronous with ventilation due to the variability in venous return caused by ventilation. Hypovolemia also causes a change in the up-stroke of the blood pressure curve due to inadequate filling of the heart. Compared to monitoring of central venous pressure intra-arterial blood pressure monitoring is superior in the setting of judging changes in filling pressures in the neonate. Intra-arterial access also allows repeated arterial blood gas sampling and other labo - ratory analyses (e.g., hematocrit, blood glucose, sodium, potas - sium, and ionized calcium). Insertion of a single lumen or multilumen central venous catheter might be a good option to get secure venous access and allow infusions of inotropic and vasoactive drugs. In any situation at risk of air embolism, precordial Doppler monitoring, together with an esophageal stethoscope, should be used to rapidly detect and treat this complication. Continuous measurement of urine output is obviously of great importance for the monitoring of the neonate undergoing major surgery. Urine output less than 1.0 mL/ kg/h is indicative of hypovolemia. However, sudden decreases in output should be viewed with suspicion and the catheter system should immediately be check for blockage or kinking before any therapeutic measures are taken. Specific Considerations Concerning Common Monitoring Options PULSE OXIMETRY: Neonatal probes should only be used since adult probes are not reliable when peripheral vascular perfusion is poor. It is preferable to place the probe on the hand so that its access is facilitated when it has to be checked or moved to a new location in order to obtain a good tracing again. The probe and cable should be protected from interference caused by electric cautery. Use of a pulse oximeter displaying the plethysmogram and indicating changes in skin perfusion is recommended since significant additional information regarding the cause of malfunc - tion and the development of peripheral vasoconstriction due to hypovolemia or hypothermia is provided. Pulse oximetry will not provide reliable readings in the presence of either pronounced polycythemia or methemoglobinemia. CAPNOGRAPHY: Mainstream analysis will give more reliable readings that sidestream analysis for rapid ventilatory rates. At ventilatory rates above 50/min, the accuracy of both types of analyzers is substantially affected. However, it is usually possible to decrease the ventilatory rate intermittently briefly to 15 to 20/min to obtain a more reliable reading. The probe of mainstream analyzers will generate heat, thus, care must be taken to avoid contact of the probe with the skin. The advantages with main - stream analysis will, however, to a substantial extent be offset by the problems of mixture and dilution of the expired gases by the fresh gas flow. 102 A major issue in this respect is that it is impossible to use a measuring point distal to the tracheal tube connector with mainstream analysis. To obtain more reliable readings, sidestream analysis with a sampling point distal to the elbow connector should be used, with the ideal point being distal to the point where the tube connector narrows to the diameter of the tracheal tube 103 (Figure 86–9). In summary, very useful trend information can be generated both by mainstream and sidestream analyzers but the clinician must be aware of the limitations of the techniques and, when clinically indicated, control the end-tidal readings against conventional blood gas analysis. NONINVASIVE BLOOD PRESSURE MONITORING: The cuff must be appropriately sized and the arterial indicator arrow has to be in the correct place. Measurement intervals shorter than every third minute should not be routinely used, since this can cause venous stasis and petechial formation, especially in preterm babies. The calf can be used instead of the arm, depending on the circumstances. Noninvasive blood pressure monitoring provides sufficiently accurate readings in most cases and at least allows for trend observations. ELECTROCARDIOGRAPHIC TRACINGS: Cleaning the skin with an alcohol solution improves the quality of skin contact with electro - des and provides a high quality signal throughout the operation. The derivation providing the best P-wave tracing should be preferred, as it makes easier the diagnostic of nodal arrhythmia which is frequent in pediatric anesthesia. Electrocardiogram pads must be carefully removed especially in preterm infants, to avoid skin damage.
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Chapter 86

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