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DR ROWAN MOLNAR ANAESTHETICS STUDY GUIDE PART VI
Part VI: Sub-Specialty Anaesthesia
PART VI: SUB-SPECIALTY ANAESTHESIA
INCLUDES:1. Paediatrics 2. Obstetrics3. Cardiothoracic4. ENT/Head & neck5. Neurosurgery
SUBSPECIALTY ANAESTHETICS A: PAEDIATRIC
“They’re not just small adults”. . . But . . .“Nor are they all just big neonates, either”
CASE STUDY IVPaediatric Hypospadias Repair
HISTORY
4 year old boy (obviously!) Grade III hypospadias & chordee For EUA/repair Background: Mild asthma & ADHD
ISSUES Preop assessment & stabilisation Premedication Induction & IV insertion Prolonged surgery Postoperative analgesia Postoperative IV & IUDC
ADULT-PAEDIATRIC DIFFERENCES Psychosocial CNS Respiratory
AirwayOther
Cardiovascular
Renal/fluids
Gastrointestinal
Hepatic/metabolic
EndocrineHaematologicalImmunologicalMusculoskeletal Integument
THE PSYCHOSOCIAL DIMENSION There are (almost) always two patients – child and
parent(s). If you don’t keep the parents happy, or at least reassured, the child won’t be either – no matter how good the anaesthetic.
Children don’t understand that you are there to help – only that you are a stranger.
Children hate needles. Parents hate their children having needles. Even without this, cannulation can be difficult. Anything that ameliorates this is good: such as premedication, EMLA to cannula sites & inhalational inductions.
Parental presence at induction can be a good idea – as long as the parent is going to cope. If in doubt, a generous premed & a goodbye outside may be a better option.
ANATOMICAL DIFFERENCES 1
Body proportionsHead largerLimbs smallerIncreased surface
area to volume ratio
CNS differencesBrain & spinal
cord relatively larger
ANATOMICAL DIFFERENCES 2: AIRWAY
Head larger Nares (relatively)
larger Larynx higher
C3 in neonate -> C6 in adult
Epiglottis longer (& softer)
Cricoid ring narrowest part of airway
PAEDIATRIC RESPIRATORY PHYSIOLOGY
Chest wall mechanics & tracheobronchial tree “floppier”.
Tidal volume/dead space same as adults in mls/kg
Respiratory rate & minute volume higher FRC similar to adult in mls/kg, but vO2 higher,
so desaturate more quickly when apnoeic. Control of respiration immature till ~ 15/12
post conceptual age – up till then vulnerable to apnoeas – especially post GA &/or narcotics.
PAEDIATRIC CVS PHYSIOLOGY REFRESHER
Fetal circulation/Postnatal transition-predelivery: systemic & pulmonary circulations in
parallel, with oxygenation via placenta & high pressure/low flow on (R) side.
-Transition at birth to systemic & pulmonary circulations in series with fall in PVR & closure of shunts.
HaemodynamicsNeonates & infants have fixed stroke volumes: CO
dependant on HR – i.e. bradycardia = hypotension & shock.
Autonomic controlDifferent in neonates & children – response to hypoxia
is bradycardia (“Diving reflex”) rather than tachycardia.
BLOOD & BODY FLUIDS Blood volume 80-90 mls/kg (adult ~ 70) Birth Hb 180-200 g/L (adult 120-160)
Falls to ~ 110 @ 6/12 then rises. Fetal haemoglobin (HbF)
Different chainsLower p50 (Hb-O2 curve shifted
left)75% of Hb at birth minimal @
6/12. Body water 75-80% in neonate (adult
65%) ECF compartment larger than ICF
(crossover @ ~ 4/12)
PAEDIATRIC THERMODYNAMICS Infants at higher risk of hypothermia Higher surface area to volume ratio Remember the four modes of heat
loss:1. Conduction2. Convection3. Radiation4. Evaporation
All four occur more when the surface area to volume ratio is higher
HEAT PRODUCTION & REGULATION
Controlled in hypothalamus Balances heat loss & heat production Heat production
Shivering – poorly developed in neonate/infant
Metabolic thermogenesis (brown fat) Thermoneutral environment;
Point of minimum O2 consumtione.g. for unclothed term baby is ~ 33°C
SUBSPECIALTY ANAESTHETICS B: OBSTETRICS
Remember, once again you have two patients – but this time they are physically connected
CASE STUDY VCaesarian Section
HISTORY
38 yr old lady, P0G1 Booked LSCS IVF pregnancy Moderate PIH/pre-ecclampsia History of back pain Wants to be awake for delivery Needle phobic
ISSUES Preop consultation Investigations Premedication Choice of anaesthetic technique Choice of IV fluids Backup anaesthetic plan Postoperative monitoring Analgesia plan
PRINCIPLES Pregnancy is a normal, but vulnerable
condition. The prregnant patient is different Delivery is hazardous Operative intervention may be required Labour & delivery can be agonisingly painful Anaesthesia inevitably has (at least some)
foetal effects/implications.
DIFFERENCES IN PREGNANCY Psychosocial CNS Respiratory
AirwayOther
Cardiovascular
Renal/fluids
GastrointestinalHepatic/
metabolicEndocrineHaematological ImmunologicalMusculoskeletal Integument
DRUGS & THE PLACENTAGeneral rule: If it crosses the blood brain
barrier, it crosses the placenta!Placental transfer:
Narcotics/Sedatives/GA agents - HIGHMuscle relaxants -Essentially nilLocal anaesthetics – Significant (in freebase
form) . . . but peak maternal plasma levels usually post delivery