the premature neonate

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The Premature Neonate. Claude Abdallah , MD, MSc. Preterm Neonates. Morbidity and mortality in this population has decreased over the past 25 years. In extremely low birth weight premature neonate(

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  • The Premature Neonate

    Claude Abdallah, MD, MSc

  • Preterm NeonatesMorbidity and mortality in this population has decreased over the past 25 years. In extremely low birth weight premature neonate(
  • Airway and Work of Breathing

    Spaeth JP, O'Hara IB, Kurth CD: Anesthesia for the micropremie. Semin Perinatol 1998; 22:390-401.

  • Airway and Work of BreathingSmall airways : predispositon to obstruction and difficulty with ventilation.

    Insertion of an ETT increases resistance and work of breathing far greater for the premie (2.5 or 3 mm inside diameter [ID]): (Resistance to airflow is inversely proportional to the fifth power for large airways and to the fourth power of the radius for small airways. )

    Additional partial occlusion from loss of muscle tone during anesthesia.

  • Pediatr Crit Care Med. 2009;10(1):1-11.

  • Effect of airway pathologySubglottic stenosis, Tracheal stenosis, and Tracheobronchomalacia occur commonly in the micropremie increase further resistance to airflow and work of breathing. Also, may necessitate the placement of even a smaller ETT>> airway resistance from the stenosis distal to the endotracheal tube

  • POSTNATAL DEVELOPMENT OF THE LUNGS AND THORAXThe respiratory system is not fully developed at birth.

    The morphologic and physiologic development of the lungs continues throughout the first years of life.

    Alveolar formation begins only about the 36th week of gestation.

    Thick-walled saccular spaces decrease lung compliance.

  • Production of Surfactant

    -Begins between 23 to 24 weeks of gestation, -Remain inadequate until 36 weeks of gestation lung volumes and compliance are decreased increase intrapulmonary shunt and ventilation/perfusion mismatch and increase the risk of hypoxia.-Anesthesia further decreasesV/Q mismatch. Ventilation with continuous PEEP during anesthesia required but limited:Susceptibility to O2 toxicity, barotrauma, and development of bronchopulmonary dysplasia.

  • RAPID DESATURATION IN PREMIES?WHY?-Lung volume disproportionately small

    -Higher metabolic rates in infants: The neonatal oxygen consumption is approximately 6 ml/kg/min versus 3 ml/kg/min in the adultEven under normal circumstances the immature cardiac and respiratory systems must function near maximum to support this metabolic demand.

    -Elastic recoil pressure of the lung and thorax are lowPoorly developed thoracic muscle massIncreasing respiratory rate rather than tidal volume The diaphragm is the primary respiratory muscle has fewer high-oxidative muscle fibers and is less resistant to fatigue than the adult diaphragm. Mechanical challenge: Ribs Raised small increase in thoracic cavity volume with contraction of the diaphragm.,

  • Respiratory Control and Prematurity

    Response to hypoxia: Biphasic Ventilatory Response- Initially, ventilation increases during hypoxia, but after several minutes, - Ventilation decreases and apnea may ensue.

    Anesthetic drugs:- depress the ventilatory responses to both hypoxia and hypercapnia.

  • Anesthesiology Editorial 59:495-498, 1983Life-threatening Perioperative Apnea in the Ex-premie

    George A. Gregory and David Steward

  • Post anesthetic Care & Discharge of Neonates

    Full Term Infant (Born at PCA* 37 weeks) and otherwise healthy:If 45 weeks PCA: Overnight stay in hospital in monitored bed. Must have at least 12 hours of apnea-free period prior to discharge.

    Preterm Infant (Born at PCA 30%.

    A minimal stay of 2 hours of apnea free period in PACU is required for all these patients. If needed, they should be transported with monitoring and accompanied by a registered nurse.

  • Kurth et al, 1987Prospective study using pneumography47 premature infants37% incidence of postop. prolonged apnea in infants 32 - 55 wks. PCAInitial episode may occur as late as 12 hrs. postop.All types of surgical procedures, including NEC and VP shunts

  • How about caffeine?

  • Incidence of Perioperative Apnea and PB: Caffeine 5mg/kg Caffeine ControlsPostop. prolonged apnea none 8(73%)*with bradycardia

    Postop. PB none 2(18%)

    Postop. apnea < 15 sec 8(89%) 1(9%)

    Postop. caffeine level 5-8.6 zeromg/L (range)Periodic BreathingThree or more periods of apnea 3-15 secs. separated by < 20 secs. of normal respiration

  • Incidence of Postoperative Apnea, PB and Desaturation: Caffeine 10mg/kg Caffeine ControlsPostop. prolonged apnea none 13(8%)*

    Postop. PB >1% none 4(25%)

    Postop. desat.< 90% none 8(50%)

    Postop. caffeine level 15-19 zeromg/L (range)

  • Caffeine concentrations as low as 3-5 mg/L can decrease apneic spells in neonates, Brief apnea persistedPlasma concentrations of 8-20 mg/L are required for optimal responseNo toxicity(????) with concentrations as high as 50 mg/L

  • Survival without disability to age 5 years after neonatal caffeine therapy for apnea of prematurity. JAMA. 2012 Jan 18;307(3):275-82.

    Five-year follow-up in academic hospitals. Randomized, placebo-controlled. Caffeine for Apnea of Prematurity Study. A total of 1640 children with birth weights of 500 to 1250 g.

    The combined outcome of death or disability was not significantly different for the 833 children assigned to caffeine from that for the 807 children assigned to placebo.

  • Postoperative Apnea in Former Preterm InfantsSpinal vs General Anesthesia

  • Incidence of Postoperative Apnea and PB General Spinal Spinal + Anesthesia Anesthesia Ketamine

    Prolonged Apnea 5(31%) 0 8(89%)*with bradycardia

    PB > 1% 1 0 2

    Intubation or 0 0 0ventilation

  • Is Preoperative Transfusion Necessary?

  • Postoperative Complications Hct > 30% Hct < 30%

    Brief Apnea 0 0

    PB > 1% 0 20%

    Prolonged Apnea 21% 80%*

    Bradycardia 0 20%

  • SummaryAnemia in preterm infants increased incidence of postop. apneaAnemic infants had high HbF and low 2,3 DPGDefer elective surgeryClose postoperative monitoring

  • Anesthesiology82:809-822, 1995Postoperative Apnea in Former Preterm Infants after Inguinal Herniorrhaphy

    Metanalysis of previous studies

    Limitations:

    Small number of patientsSignificant variation of incidence of apnea between different institutionsConsiderable variation in the duration and type of monitoring and definitions of apnea

  • Predicted probability of apnea after leaving recovery room by weeks postconceptual age (weeks) for infants who did not have apnea in recovery room or anemia . Bottom marks indicate the number of data points by postconceptual age. The risk does not fall below 1% with 95% statistical confidence until 56 weeks postconceptual age.

    Anesthesiology. 82(4):809-822, April 1995.

  • Fisher DAnesthesiology82:807-808,1995.....Establishing policy regarding the postop. management of ex-premature infants undergoing inguinal hernia repair requires a decision regarding acceptable risk

  • Pediatric Anesthesia 22 (2012) 1139-1141

  • Thermoregulation & Premature NeonateSmall size and

    Increased surface-area-to-volume ratio.

    Increased thermal conductance .

    Limited range of the neutral thermal environment= Range of ambient temp. at which metabolic rate is minimal.

    Normal body temp. range for a neonate is 36.5 to 37.7C. Temp. below 36C are considered hypothermic.

    Predisposition to APNEA, BRADYCARDIA, and/or METABOLIC ACIDOSIS. Maximum ventilatory response to PCO2 decreases.

    Extubation and Transfer Criteria

  • Non Shivering Thermogenesis-Principally metabolism of brown fat (2-6% of TBW).-Brown fat differentiates at the 26 to 30 weeks gestational period. -Multinucleated cells, numerous mitochondria.-Abundant vascular supply and innervation.-COST: increases in norepinephrine (3X), glucocorticoids and thyroxine production.Prevention of hypothermia is extremely important

  • The intersection of line with the temp scale: threshold.Interthreshold range: Core temperatures not triggering autonomic thermoregulatory responses: 0.2-0.4 deg. CASessler DI: Temperature monitoring. In Miller RD (ed): Anesthesia, 4th ed. New York, Churchill Livingstone, 1994, p 1363. Thermoregulatory Thresholds

  • Effects of Mild Hypothermia-Stress response: V-C (incr. SVR, CVP).

    -Decreased RBF and GF. Cold diuresis, impaired sodium reabsorption = hypovolemia.

    Impaired coagulation: Defect in platelet fction & clotting factors.

    Leftward shift of oxy-Hb dissociation curve + BMR= deleterious effect.

    Increased wound infections (immune function & v-c). Duration of hosp. by 20%.

    Shivering: Increase in wound pain and in intraocular and intracranial pressures.

  • Effects of Anesthesia Medications on ThermoregulationVolatile anesthetics: Hypothalamus + direct vasodilatory