PRINCIPLES & PRACTICE OF PAEDIATRIC ANAESTHESIA Dr R Djagbletey KBTH
OUTLINE 1. 2. 3.
4. 5. 6.
Age Definitions Important Anatomical and Physiological points Pharmacology Equipment Practical Aspects Monitoring Summary References
AGE DEFINITONS DEFINITONS
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
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
Airway and Ventilation Ventilation
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.
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
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
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
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
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
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
Some normal values in infancy and childhood (from: Sumner and Hatch 1989, Textbook of Paediatric Anaesthetic Practice)
0-1 week 3 months
Haemogl 17.0obin(g/dl 22.0 )
Haemato crit (%) 55-70
volume( ml/Kg) October 2010
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
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
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.
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%
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.
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
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.
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
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
facilitate monitoring concentrations of expired of airway gases. pressure and
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
Hands not free Gas monitoring technically difficult and prone to inaccuracy Scavenging difficult
-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.
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 –
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.
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 –
2.5 3 adult
20 30 kg 30kg small –
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,
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
For premature babies and neonates, history should
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
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)
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
Estimating the weight of a large child ( 8 – 12 yrs) Weight ( Kg) = 2 [ (Age )+ 4 ] OR = 2 [Age ] + 8
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
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 –
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
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
2. 3. 4. 5. 6.
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
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.
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
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
>80 90+ [2(age in yrs)]
LOWER LIMIT 50 70 70 + [2(age
<30 days 5yrs 12yrs 18yrs 30
HR 150 (RR x 5)
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
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.
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.
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
Post anaesthetic complications
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
Common in neonates and pre term babies October 2010
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
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