【正文】 ry Rapidly crosses placenta Rapidly cleared from neonatal circulation Detected low concs in breast milk Propofol and pentothol ? similar Apgar and neurobehavioural scores General Anesthesia – Ketamine 1 mg/kg Rapid onset Analgesia, hypnosis, and reliably provides amnesia Good in asthma or modest hypovolemia 1 mg/kg does NOT ? uterine tone (larger doses do) Rapidly crosses placenta Similar umbilical cord blood gas and Apgar scores with ketamine or pentothal General Anesthesia – Succinylcholine mg/kg Muscle relaxant of choice for most patients Highly ionized and water soluble, ? only small amounts cross placenta Maternal administration rarely affects neonatal neuromuscular function One study – only doses 300 mg result in significant placental transfer Pseudocholinesterase activity ? 30% in pregnancy, BUT recovery is not prolonged ? volume of distribution offsets the effect of ? activity General Anesthesia – Rocuronium 1 mg/kg Only very small amounts cross placenta Apgar and neurobehavioural scores not affected General Anesthesia – Maternal Awareness Desire to minimize neonatal depression must be balanced against risk of awareness If another agent not given ? incidence of awareness ? in direct proportion to ID interval 50% N2O/O2 alone ? 1226% awareness Awareness ? ? catecholamines ? uterine artery vasoconstriction and ? oxygen delivery to fetus General Anesthesia – Maternal Awareness Common Approaches: 50/50 N2O/O2 with MAC inhalational agent ? awareness to 1% Pregnancy ? anesthetic requirements by 3040% No adverse affect on neonatal condition No ? maternal blood loss Discontinue volatile only if there is uterine atony that is unresponsive to oxytocin General Anesthesia – Oxygen Piggott et al, BJA 1990 – 100% O2 ? higher umbilical venous blood pO2 and higher 1 minute Apgar scores, pared to 50% O2 100% O2 ? higher conc of iso, without maternal awareness or excessive bleeding Supports 100% O2 and higher volatile in cases of fetal distress Lawes et al, BJA 1988 – elective csxn – no difference in neonatal oxygenation or oute between 33% and 50% O2 Cesarean Section Under Local Potential indications: patient with severe coagulopathy, known difficult airway and requires emergency csxn No anesthesia provider immediately available and severe fetal distress ? Can begin surgery and deliver infant ? Temporary hemostasis achieved until anesthetist arrives, then induce GA to plete the surgery Cesarean Section Under Local Need: 1) Midline abdominal incision 2) Minimal use of retractors 3) Do not exteriorize the uterus Local Infiltration Anesthesia for Cesarean Section 1) Professional support person with patient 2) Infiltration with lidocaine % (total dose 500mg) 3) Intracutaneous injection in midline from umbilicus to symphysis pubis 4) Subcutaneous injection 5) Incision down to rectus fascia 6) Rectus fascia blockade 7) Parietal peritoneum infiltration and incision 8) Visceral peritoneum infiltration and incision 9) Paracervical injection 10) Uterine incision and delivery 11) GA with ETT for uterine repair and closure, if needed Cesarean Section Under Local Disadvantages: 1) Patient disfort 2) Potential for systemic toxicity and anesthesia may not be available to assist with resuscitation 3) Requires time 4) Does not provide satisfactory operating conditions for plications, eg. uterine atony, uterine laceration Once Infant Delivered Once umbilical cord clamped – oxytocin given 1020 U oxytocin in 1000 mL crystalloid and run at 4080 mU/min Bolus IV oxytocin may cause maternal hypotension and tachycardia and should be avoided Once Infant Delivered If atony does not repond to oxytocin: ? Methylergonovine mg IM ? 15methylprostaglandin F2alpha 250 ug IM or IMM Ergots: ? Severe hypertension PGF2α: ? N+V, diarrhea, fever, tachypnea, tachycardia, hypertension, bronchoconstriction ? Avoid in asthmatics Once Infant Delivered Exteriorize Uterus – What to watch for: ? Pain ? Nausea ? Hemodynamic changes ? Risk of VAE Effects of Anesthesia on Fetus and Neonate No significant difference in umbilical cord blood gas between general or regional anesthesia for elective or emergency csxn Goals: ? Effective LUD ? Ensure adequate maternal oxygenation ? Avoid maternal hyperventilation ? Avoid excessive doses of anesthetic agents ? Treat hypotension promptly Effects of Anesthesia on Fetus and Neonate Crawford – found uterine incision to delivery (UD) interval is more important than ID interval A UD interval 3 mins associated with ? incidence of low umbilical cord blood pH and Apgar scores, regardless of anesthetic techniqu