PHYSIOLOGIC AND ANATOMIC CHANGES DURING PREGNANCY AND LABOR- ANESTHETIC IMPLICATIONS ChangeAnesthetic Implications Circulation Hyperdynamic: increased reliance on sympathetic nervous system Increase in incidence and severity of hypotension after regional analgesia/anaesthesia Capillary engorgement, increase in airway edema Increased incidence of difficult airway Aortocaval compressionMore profound hypotension with parturient in the supine position Metabolism and Respiration Increase in O2 requirement and CO2 production Greater risk of desaturation after induction of general anesthesia Decrease in FRCGreater risk of desaturation after induction of general anesthesia Gastrointestinal System Reduced oesophageal---stomach barrier pressure Increased risk of aspiration pneumonitis Endocrine Increased progesterone levelsIncreased pain threshold Nervous System Increase in ß -endorphin concentrationIncreased tolerance to pain Increased susceptibility to local anestheticsDecrease in local anesthetic dose requirements Anatomic changes in the spinal columnDecrease in local anesthetic dose requirements Increased susceptibility to CNS depressantsDecrease in dose requirements for general anesthetics and adjuvants

 Myometrial hypoxia  Stretching of the cervix  Pressure on the nerve ganglia adjacent to the cervix and vagina  Traction on the tubes, ovaries and peritoneum  Traction and stretching of the supporting ligaments  Pressure on the urethra, bladder and rectum  Distention of the muscles of the pelvic floor and perineum

 MOTHER:  Relief of pain  By relieving pain the changes of ventilation, circulation, hormonal function that ordinarily accompany pain can be controlled  Freedom from fear  Safe and comfortable delivery  INFANT:  To be given a favorable physiologic milieu for delivery  To use techniques not associated with fetal depression or long term poor outcome  OBSTETRICIAN:  Reduction of pressure from patient & relatives to do something prematurely  Optimum conditions at delivery

 The method must ensure that:  The health of the mother is not endangered  The newborn should not be depressed at delivery. Drugs cross the placenta  The technique effectively controls pain  The efficiency of uterine contractions is not decreased  The ability of the patient to cooperate intelligently with the medical and nursing staff is maintained  There is no need for operative interference because of anesthesia  The method is relatively simple to use

“ to prepare a woman for labor and delivery so that she approaches the end of her pregnancy with knowledge, understanding and confidence rather than apprehension and fear”  Aims of perinatal training:  Counteract apprehension of young women caused by exaggerated tales of horror  The patient is given an opportunity to gain confidence  Exercises are taught which strengthen certain muscles and relaxes others  The patient is trained in breath control  The patient told about labor pains and analgesic options  Patient to choose the method most suitable for her away from others experiences  Emphasis on the fact that most labors are normal

 Simple analgesia:  Aspirin  Paracetamol  Non-steroidal Anti-Inflammatory Drugs  Early in pregnancy  Third trimester  Opioid analgesics:  Codeine  Pethidine/morphine

 Non-pharmacological:  Breathing exercise  TENS machine  Inhalation anesthesia: “Nitrous Oxide”  Insoluble in blood, rapid induction and recovery  Rapidly transported to maternal tissue, placenta and fetus  Effective when taken during contractions  Nontoxic  NO 50:50 O2, decreasing the chance of maternal hypoxia  Prolonged use may lead to neonatal depression  No/little effect on labor

 Systemic medications “Narcotics”… alleviate pain. If given in large doses in the latent phase < contractions & cx dilatation. When labor established, relief of pain and anxiety make the uterine contractions more efficient  S.Effect: resp. depression, ortho hypotenb, <gastric motility, nausea & vomitting. Affects neonatal neurobehavior  Morphine: 0.1mg/kg 3-4 hrs peak effect1-2 hrs (I.m.)/20 min (I.v.). Duration 4- 6 hrs. if given< 3 hrs before delivery…. Fetus affected  Demerol(meperidine, pethidine): synthetic narcotic with atropine-like action. 1mg/kg 3-4 hrs peak effect min(I.m.)/5-10 min (I.v.). Duration 3-4 hrs. the greatest effect on the fetus reached within 1.5 hrs after I.m. Narcotic effects on the newborn are best antagonised with Naloxone 5-10 micg/kg

 Paracervical block: XXXXXXXXXX  Lumber Epidural block:  Injecting of Marcaine % or others in a continuous infusion  Advantages:  Almost pain free labor  Can be kept as long as desired  Level of analgesia can be controlled  Mother is alert and cooperative. Retains ability to bear down. If forceps req.  Can be used when converting to C/S  Minimal effect on the fetus!!!!!!!!!!!!!!!!!!!

 Disadvantages:  Might mask the strength of contractions esp. with syntocinone  10% significant hypotension if lie supine. Epidural anesthesia>>20mm Hg drop in syst or diast in 30% of pnt. Due to:  Sympathetic vasomotor blockade >>> 20% drop in arteriolar resistance  Increased venous capacitation and pooling>>>decreased in venous return and COP  Uterine pressure on aorta and vena cava To prevent hypotension:  Infuse 1 L RL or Saline  Wedge under right hip to displace the uterus to the left and reduce vascular pressure  Use Ephedrine as vasopressor if required  Intravascular injection: convulsion and hypotension  If dura is punctured>> headache. Subarachnoid >>>massive motor block, hypotension and respiratory distress

 Disadvantages:  Fetal heart rate patterns may be affected  Infection at site of injection,,rare  Backache  Neurological side effect debatable  Might affect uterine contractions needing oxytocin  If large dose, would paralyze pelvic floor>> failure to rotate and mother not bearing down due to lack of sensation>>> instrumental delivery  Contraindications:  Drug allergy  Skin infection  Coagulopathy(severe PET,active Hg)  Severe supine hypotension  Certain cardiopulmonary diseases

 Inhalation Anesthesia:  Halothane, Enflorane, Isoflorane  Intravenous Anesthesia:  Thiopentone, Ketamine  Not routinely used in every days work. Mainly in private sector. Consider side effect of general anesthesia and need to be administered by anesthetist.

 Local Anesthesia:  Advantages  Disadvantages 1. Direct infiltration >>>>>>>

2. Pudendal Nerve Block

1.Topped up ongoing epidural 2.Spinal block anesthesia 3.General anesthesia >90% of C/s in UK

EpiduralSpinal Onset min min Duration & effect ContinuousSingle shot. effect lasts for 2 hours Success rate Higher incidence of patchy, one-sided blocks Block quality Less-dense sensory blockMore dense sensory block Less motor blockMore motor block Hypotension Same incidence, slower onsetSame incidence, more rapid onset Risk of PDPH Approximately 1% Risk of systemic local anesthetic toxicity Inadvertent intravenous injection may cause systemic toxicity Dose too small to cause systemic toxicity if inadvertently injected intravascular Risk of total spinal Possible with inadvertent subarachnoid injection or “overdose” epidural injection Less likely because of small drug dose Post---cesarean delivery analgesia Continuous or single-shotSingle-shot only Effects on the fetus Greater drug exposureMinimal drug exposure

BlockClinical UseAdvantage Disadvantages/Side Effects/Complications/ Spinal (saddle block) Instrumental vaginal delivery anesthesia Rapid onset analgesia with perineal motor block Single shot, not continuous Caudal blockLabor and delivery analgesiaAnother access to epidural space Technically more difficult than lumbar epidural Useful for patients with lumbar spine fusion Requires large volume of local anesthetic to provide labor analgesia to T10 level Paracervical block Early---mid 1st stage labor analgesia No motor blockNot continuous Risk of fetal bradycardia Lumbar sympathetic block Early---mid 1st stage labor analgesia No motor block. Speeds labor Not continuous. Requires bilateral injections Useful for patients with lumbar spine fusion Technically more difficult to learn Pudendal block 2nd stage analgesia; instrumental vaginal delivery anesthesia Performed by obstetrician before delivery Not continuous Complications rare Perineal infiltration Episiotomy or repair anesthesiaTechnically simpleNo motor relaxation Performed by the obstetrician as needed Complications rare

 Inhalation Anesthesia:  Halothane, Enflorane, Isoflorane  Intravenous Anesthesia:  Thiopentone, Ketamine  Aspiration of vomitus during anesthesia. Commonest morbidity  Methods to prevent its occurrence  Failed intubation  Mendelson Syndrome Can operate in relaxed state in difficult cases. If >3 min before delivering baby >>drowsy