Pediatric Anesthesia

 

PRINCIPLES & PRACTICE OF PAEDIATRIC ANAESTHESIA  Dr R Djagbletey KBTH

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OUTLINE 1. 2. 3.

4. 5. 6.

7. 8.

 Age Definitions Important Anatomical and Physiological points Pharmacology Equipment Practical Aspects Monitoring Summary References

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 AGE DEFINITONS DEFINITONS 

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Premature Neonate infant born less than 37 completed weeks after  conception   Neonate from 37 weeks 37 weeks post conception until 28days post delivery Infant age 1 – 1 – 12 months Child age 1 –  12 yrs    Adolescent age 10 –  18 yrs  

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IMPORTANT ANATOMICAL AND PHYSIOLOGICAL POINTS One of the important differences between paediatric and adult patients is oxygen consumption which , in infants may exceed 6ml\kg\min, twice that of adults. There are physiological adaptations in paediatric cardiac and respiratory systems to meet this increased demand. October 2010

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 Airway and Ventilation Ventilation

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relatively large head with prominent occiput and  short neck, small face and lower jaw, relatively large tongue, narrow nostrils, loose teeth or awkward dentition, large floppy horseshoe-shaped epiglottis, high anterior larynx, short trachea directed downwards and posterior, right main bronchus less angled than left.

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Obligate nose breathers until past the age of 6 wks - 4 months (secretions ,NG tubes ,temperature probes ) Soft chest wall and horizontal ribs in neonate and young infant makes breathing motions more abdominal than thoracic so any abdominal distension greatly increases the work  involved in breathing October 2010

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70% of neonatal Hb is Hb F which releases less O2 is thatifbaby lessatreserves recellular serves of olevel. f O2 Implication supply to tissues supply therehas is problem with breathing, airway or circulation. Hypoxia occurs much quicker than in adults. Narrowest part of airway is at the level of the cricoid with larynx having gradually tapering shape. Cylindrical ETT fits ring shaped cricoid well aspiration enough to from minimize air Roughly leaks from below and above. after puberty, vocal cords are narrowest part and ETT needs cuff to fit snuggly

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Disproportionate effect of tracheal mucosa oedema. Oedema of 1mm in the infants cricoid ring, of  say 4mm diameter will: reduce the airway by about 75% and increase the resistance by 16 fold

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Respiratory Function Tidal volume, Dead Space, Vital Capacity and Specific Compliance are similar in small children and adults when related to body weight. However, because metabolic rate in infants and neonates is much greater than in older children and adults, RR (and therefore Alveolar  Ventilation ) is higher. This higher alveolar ventilation ,when related to the FRC makes the FRC a less effective buffer between inspired gases and the pulmonary circulation with 2 important consequences

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 Any in ventilation quickly  leadsinterruption to hypoxemia  The fraction of anaesthetic gases in the  alveolus equilibrates with the inspired  fraction more rapidly than occurs occurs in  adults 

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Cardiovascular Heart of neonate with relatively few muscle fibres and thus less reserves of function to cope with circulatory stress

Cardiac output on(vagal the HR thus care needed to very avoiddependent bradycardia stimulation with laryngoscopy, hypoxaemia ) as the sympathetic nervous system not well developed predisposing to bradycardia.  bradycardia.  October 2010

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Some normal values in infancy and childhood (from: Sumner and Hatch 1989, Textbook of Paediatric Anaesthetic Practice)

 Age

0-1 week  3 months

6-12 months

Preschool

Haemogl 17.0obin(g/dl 22.0 )

10.512.0

11.012.0

11.512.5

Haemato crit (%) 55-70

35-40

34-41

37-41

Blood

80

75

70

volume( ml/Kg) October 2010

80

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Metabolism Hypothermia Ratio of body surface area to weight is high and heat is lost, particularly from the head. Low sub-cutaneous body fat Babies less than 3months do not shiver Thermoregulatory centre of children not well developed Hypoglycaemia Stores of glycogen in liver limited and long preoperative fasting not well tolerated. October 2010

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CNS Sensitive to respiratory depressant effect of  opioids MAC of inhalational vary with age MAC of neonate similar to that of the adult and decreases with prematurity MAC peaks at age of 1yr about 1.5 MAC of the adult. It then decreases towards adult value at onset of puberty October 2010

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Kidneys of infants immature and not able to handle sodium sugar loads of well hence care needed to or limit amounts these in IV infusions. Also the kidney of infants have limited concentrating ability.

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Water Requirements These are related to the surface area and  metabolic rate, so are greater per Kg in the  baby.  Age Total body water (% wght)  0 –  1 mnth 75%  1 –  12 mnths 70%  1- 12 yrs 65%  

October

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Maintenance fluid requirements are calculated on an hourly basis depending on the body weight. A suitable way of  working this out is as follows: 

4 ml/kg for the first 10 kg, 2 ml/kg for the second 10 kg and 1 ml/kg for each kg over 20 kg.

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PHARMACOLOGY  

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 Absorption Neonatal gastric emptying delayed and drug absorption slower with delayed peak blood concentrations. Little difference in other age groups compared to adults. Distribution Depends on relative of in body fatlife and water. Proportion of proportions water highest early so water-soluble drugs have disproportionately dis proportionately large vol of distrubution. Implication is that doses given according to weight relatively higher for younger than older children and adults

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Metabolism In neonates size of liver in relation to body weight that ofof of adults falls withafter age.the Explainstwice faster rate drug and metabolism first 2 – 2 – 3 months of life.

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Elimination GFR of full term babies 1\3 that in adults. GFR  reaches adult values by 4th month, tubular function by 7th .Thus drugs excreted by glomerular filtration or by tubular secretion have to have doses adjusted

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EQUIPMENT Breathing Circuits Ideally lightweight         

minimum number of connections easy to assemble and use deliver O2 and anaesthetic gases eliminate CO2 conserve heatand and humidity easy to clean allow scavenging of gases minimize dead space and resistance to breathing and

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facilitate monitoring concentrations of expired of airway gases. pressure and

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For Mapleson D, E, F inc T-Piece and Coaxial D (Bain ) : FGF for IPPV is 220ml\kg for babies and infants up to 20kg. For spont ventilation , it is 2 – 2 – 3 X minute volume. Manual ventilation ventilation with with T-piece T-piece appropriate for infants less than 20kg with disadvantages of   

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Hands not free Gas monitoring technically difficult and prone to inaccuracy Scavenging difficult

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Face masks

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-Rendell-BakerSoucek  -Laerdal Laryngoscopes Straight blade necessary fortipneonates young infants. With Magill, placed and posterior to epiglottis (vagal innervation). Most can also be used like a Mackintosh blade with the tip in the valleculla.

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Endotracheal Tubes Uncuffed ETT used in children under age 10 – 10 – 11. For children > in 2yrs, size of tube mm = Age\4 + 4.5 need to have range of sizes with some bigger and smaller than calculated size. For children <2 yrs : Size Age 2.5 3 Premature 3.0 -3.5 Neonate 6 Month 3.5 4.0 6 Months 1 Yr 4.0 5.0 1 2 yrs  – 

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Too tight a fit causes ischaemic damage to the tracheal cartilage. Tubes best secured to the immobile part of the face ie the maxilla Oral best related to need heightto but weight be used.tube Agelengths quite unreliable. Still listen formay equal breath sounds on both sides of chest Height (cm) + 5 OR Weight (kg) + 12 OR Age+12 10 12 2 For neonates, lengths of 7 – 7 – 9 cm at the lips depending on size.   size.

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Laryngeal Mask Airways Good alternative to face mask anaesthesia in spont breathing patients. Risk of abdominal distension with IPPV so ETT better. Size Inflation vol Weight 1 5 mls Neonate 6.5kg 2 10 mls 6.5kg 20kg  – 

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2.5 3 adult

15mls 20mls

20 30 kg 30kg small  – 

 – 

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PRACTICAL ASPECTS 

Pre-Operative Assessment  Age, maturity, surgical procedure and medical will influence infl uence the anaesthetic technique used. condition Initial assessment at Clinic or Ward. Introduction of self  to child and family. Emphasize that child will be asleep throughout procedure if GA. Discuss post-op analgesia, likely side-effects, how soon child and family will be reunited. Consider : Previous anaesthesia, Relevant Family History, Recent cough\ cold, Last oral intake, Drugs and Allergies, any loose teeth. Relevant physical examination. Sickling status and other investigations,

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Fasting Guidelines  Aim at child with empty empty stomach but not dehydrated or hypoglycemic. Bottled milk, milk formula, baby feeds and milky drinks classified as solids as milk curds and becomes solid in acidic stomach medium. Breast milk cleared relatively quickly hence shorter fasting time given Clear fluids emptied very quickly - 6 hours for solids, milk or drinks - 3 hours for breast milk  - 2 hours for clear fluids

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For premature babies and neonates, history should 

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include and evaluation of the mother’s pre pre-conception -conception condition, antenatal history, mode of delivery and any complications encountered including need for neonatal resuscitation, immediate post natal condition ( like apnoeic spells,  jaundice, cyanosis, admisions to NICU..) NICU..) drugs administered ( eg IM Vitamin K ) Also look out for congenital abnormalities esp in the cardiovascular system - congenital cardiac anomalies

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Premedication

To reduce unwanted effects of anaesthetic agents 2. To treat preoperative pain 3. To supplement anaesthesia 4. To reduce anxiety and make induction i nduction easier.  Anxiolytic may be unnecessary unnecessary esp if parent can be with child at induction. Oral premedication usually preferable Consider using EMLA or Ametop cream EXAMPLES 1.

<10kg; orally Chloral hydrate 50mg\kg or Triclofos 100mg\kg >10 kg; Midazolam 0.5mg\kg (in syrup or juice )orally (max 15mg ) Temazepam 0.5mg\kg + droperidol 0.1mg\kg orally (max 20mg\2.0mg)  20mg\2.0mg) 

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Other commonly3 prescribed are oral trimeprazine mg/kg andpre-medications diazepam 0.25 mg/kg. Intramuscular pre-medications are traumatic for children and should be avoided whenever possible  Atropine usedduring to dry direct secretlaryngoscopy secretions ions and to increase heart rate. Invaluable and bronchoscopy, squint surgery, deep halothane anaesthesia, intermittent suxamethonium and 1st dose of suxamethonium in neonates. Have it ready for orchidopexies and hernia surgery that the child has been weighed and the Ensure weight noted for drug calculation

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Estimating the weight of a large child ( 8  – 12 yrs) Weight ( Kg) = 2 [ (Age )+ 4 ] OR  = 2 [Age ] + 8

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Preparation Work out all drug le doses, blood volume,permittable volume,permittab bloodfluid loss,requirements, tube sizes , minute volumes etc. Ensure ambient temp in theatre appropriate if  anaesthetisizing neonate or small infant ( 20 – 20 – 24 C) ideally. Warming insulating material should be available. Check equipment Label syringes and check dilutions ENSURE THAT CONSENT FORM IS APPROPRIATELY  SIGNED AND WITNESSED

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Induction and Maintenance Done after putting up monitors, getting baseline values and pre-oxygenating pre-oxygenating.. Thiopentone 5 - 7mg\kg Propofol 2 5 mg\kg (add lignocaine) Ketamine 5 10 mg\kg IM, 1 2 mg\kg IV   – 

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Inhalational with Halothane in Nitrous Oxide\ Oxygen. Well tolerated with minimal airway problems. MAC ~0.9% in neonate, increases rapidly to 1.2% by 6 mnth, then gradually declines to ~ 0.8% 0.8% in the adult. Sevoflurane more expensive. is a good alternative but much more

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Muscle Relaxant Neuromuscular junction of neonate is more sensitive to NDNMBs than the adult. However, because of the increased volume of extracellular fluid and volume of  distribution in very young children, dose doesn’t change much with age. 

 Analgesics ( reduce dose under 1 yr)  Analgesics IV Fentanyl 0.5 0.5 –  – 1 mcg\kg IV Pethidine 0.5 0.5 –  – 1mg\kg IV Morphine 0.05 – 0.05 – 0.75 mg\kg

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Local Analgesia Given during GA to give post op pain relief  Caudal block  circumcision : 0.5ml\kg Bupivacaine 0.25% herniotomy : 1ml\kg Bupivacaine 0.25% orchidopexy : 1.25ml\kg Bupivacaine 0.2% Ilio-Inguinal block for groin incisions Ilio-hypogastric block for groin incisions Dorsal nerve block of penis for circumcision Skin infiltration; Bupivacaine & Lidocaine (plain ) Intercostal block for thoracotomies

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MONITORING Essential monitor is the vigilant anaesthetist constantly observing oxygenation, ventilation, perfusion, depth of  anaesthesia, and fluid balance. Precordial or Oesophageal stethoscope useful and simple monitor of heart and respiratory sounds.

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Pulse oximetry , ECG, and BP monitoring give essential information Temperature Warmed incubator pre and post op with temp regulated. Bair Hugger warming system Heated water or air blanket Use of appropriate of appropriate technology : cotton wool, foil etc  Need to monitor core temperature when using extraneous heat sources. Beware of over heating  heating  

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Blood Pressure

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Need for between correct sized cuff. Quick guide is half the distance the elbow and the shoulder. BP according to age

Normal SBP 0 -1 mnth >60 1mnth- 1yrs 1yr

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10yrs

>10yrs

>80 90+ [2(age in yrs)]

110 -130

LOWER LIMIT 50 70 70 + [2(age

90   90

in yrs)]

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 Age RR 

<30 days 5yrs 12yrs 18yrs 30

HR  150 (RR x 5)

20

18

14

100

90

70

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Blood Loss  Accurate measurement measurement difficult in small patients patients as most spillage will be on surgical drapes. Weighing swabs useless unless done when they are dry and when been soaked prior with saline. Complicated wayHb. by use of calorimeter and patients pre-op Capnography Useful guide for assessing alveolar al veolar ventilation. Main stream more reliable than side si de stream

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Basic Post Operative Care Infants and from children generallyand recover faster than adults anaesthesia surgery. The immediate postoperative care is as critical as the intra-operative care and the child should be taken to a recovery area with trained staff. The anaesthetist should report to the recovery room personnel any intra-operative problems that occurred.

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The airway should be maintained to assure adequacy of ventilation and oxygenation and any unexpected findings reported to the anaesthetist. Vital signs should be taken frequently the return first hour andward pain treated. The childinmay to the when the observations are stable, he is fully conscious and his pain is controlled.

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Analgesia  Post op Analgesia  IM Pethidine 1 – 1 – 1.5 mg\kg IM Morphine 0.1 - 0.15mg\kg IM Paracetamol 15mg\kg 6 – 8 hrly Oral\Rectal Paracetamol – Paracetamol – 40mg\kg stat, 20 - 25 mg\kg 6 – 8 hrly Oral\Rectal Diclofenac 1 mg\kg 12hrly 

Narcotic antagonist; Naloxone 10mcg\kg

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Post anaesthetic complications 

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Larngospasm Forceful involuntary spasm of laryngeal musculature caused by stimulation of superior laryngeal nerve.Avoided by extubation fully awake or while deeply anaesthetized. Usually occurs immediate post op Post-intubation croup Due tocartilage glottic ormost tracheal oedema.Region of  cricoid susceptible. Almost always occurs within 3 hours post extubation

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 Apnoea

Common in neonates and pre term babies October 2010

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Conclusion Successful paediatric anaesthetic management depends on an apprecaition of the physiological, anatomic andeach pharmacological differences between of the age groups within the paediatric range and an acceptance of the fact that paediatric patients should be respected in their own right and not treated as mere   small adults  

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REFERENCES 

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Textbook of Anaesthesia by A. R   Aitkenhead et al Clinical Anaesthesiology by G. E Morgan et al Birmingham Childrens Hospital Paediatric  Anaesthesia guide by M. A Stokes Update in Anaesthesia Issue 8 ( 1998 ) Paediatric Anaesthesia Review by L Rusy

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THANK YOU .