Paediatric anaesthesia Flashcards
Define
Prematurity
Neonate
Infants
Toddlers
Prematurity < 38/40
Neonate 0 - 28 days
Infants 1 month - 1 year
Toddlers 1 - 3 years
Why is neonatal cardiac output dependent on HR and what are the implications of this
CO = HR x SV
Neonatal LV is poorly developed with a non-compliant myocardium.
Implications: poor tolerance for changes in preload and afterload
What does the neonatal rely on more (c.f. adults) for contractility
Extracellular calcium
How does autonomic innervation in the neonatal heart differ from adults and what are the implications of this
Minimal SNS
Vagal tone is more dominant
Implications: Significant bradycardia during stress (hypoxia/hypovolaemia/acidosis/large anaesthetic doses/ vagal stimulation)
What additional aetiology should always be considered in neonates
Congenital anatomical defects
-> PDA
Give the approximate normal heart rate, BP and RR for the following age groups
Term neonate 6 months 12 months 2 years 5 years 12 years
Term neonate: 140 70/40 50
6 months 120 90/60 30
12 months 120 90/60 25
2 years 100 100/60 25
5 years 90 100/60 25
12 years 70 110/60 18
What are the anatomical differences with regards to the airway and respiratory system in a neonate
Large floppy head
Large floppy tongue
Large floppy epiglottis
Vocal cords are the narrowest part of the airway (like in adults) BUT the subglottic area at the cricoid ring is the least distensible = 3 - 4 mm and the slightest amount of oedema here can cause stridor
Up to what age or children obligate nasal breathers
Neonates to 6 months
How do the tidal volumes differ between a neonate and an adult
6 - 8 ml/kg
Adult 70 kg = 500mL
Neonate = 24 mL
Why are neonates and children prone to desaturation
Children O2 consumption: 6 - 9 ml/kg/min
Children FRC much lower than in adults
Adult O2 consumption: 3 - 4 ml/kg/min
Higher FRC
How does the compliance in neonatal lungs and chest compare with adults and what are the implications of this
Immature alveoli –> reduced lung compliance
Chest wall is very compliant
Implications: Respiratory distress results in obvious tracheal tug and intercostal recession
Which is more important for neonatal ventilation: diaphragm/intercostals. What are the implications of this
Diaphragm - underdeveloped intercostals and no mechanical ‘bucket handle’ conformation established.
Implications: Increased intra-abdominal breathing hinders ventilation and oxygenation more readily.
What two aberrant (decompensatory) physiological responses occur in neonates that do not usually occur in adults
Response to stress:
CVS –> Bradycardia
RSP –> Apnoea
Why do neonates need closer observation than adults in the postoperative period?
Neonates can develop apnoea in response to surgical stress or anaesthetic drugs.
Differentiate the blood volume between neonate/infant and adult
Neonate: 100 ml/kg
Infant: 80 ml/kg
Adult: 70 ml/kg
What is neonatal Hb and what percentage of neonatal Hb is HbF versus HbA and how long does it take for HbF to be replaced by HbA and what are the implications of this
Neonate:
- Hb = 18 - 20 g/dL
- HbF is 80% at birth
- Replaced by HbA by 6/12
Implications: Physiological anaemia (Hb = 10g/dl) exists at 2 -3 months and recovers by 1 year
How does affinity for O2 of HbF differ from HbA
HbF has a higher affinity for O2 than HbA meaning it offloads O2 to tissues poorly.
How does coagulation in neonates differ from adults
Immature liver –> reduced Vit K dependent clotting factors (2, 7, 9 and 10) –> bleeding diathesis
Neonates are given Vitamin K at birth
How does the function of the Liver and Kidneys differ at birth versus adults. What are the implications of this?
- Liver and kidney are immature at birth
- Metabolism and excretion of anaesthetic drugs are reduced.
- Tendency toward hypoglycaemia (low glycogen stores)
Is the CNS immature at birth, how does this affect the senses?
Yes, not fully developed but neonates can see, smell, hear and feel pain
Drug requirements vary according to age
How do MAC values differ between Neonates / Infants / children and adults
Neonates: Similar to adults
Infants and children: Higher than adults
Adults: Similar to neonates
What is the formula for Cerebral Perfusion Pressure and how can neonates tolerate raised intracranial pressure.
What levels of CPP should be maintained in children
CPP = MAP - ICP (or CVP)
Maintain CPP > 40 mmHg in 0 - 5 years
Maintain CPP > 50 mmHg in 6 -17 years
Maintain CPP > 70 mmHg in adults
Why are neonates at significant risk for hypothermia
- Larger surface area to body mass ratio
- Large head
- Large organs close to the skin
- Unable to shiver
- Unable to move in response to cold
Only one mechanism: brown fat thermogenesis
What are the key aspects of the pre-operative assessment of the paediatric patients
- Perinatal factors: early problems/ex-premature babies
- Exclude congenital anomalies
- URTI –> Laryngospasm/breath holding / bronchospasm
Indications to postpone (evidence of acute illness):
- Fever
- Tachycardia
- Copious secretions
- LRTI - Most healthy kids undergoing minor surgery don’t require Ix
- Counsel - explain everything and get consent (including suppositories)
Which paediatric patients should not be prescribed premeds
Infants (i.e. < 1 year)
Children with OSA (enlarged tonsils/adenoids)
Airway obstruction
How should premeds be adminstered and what drugs are used in paediatrics
Re-assurance in the presence of a parent should allay anxiety. If not:
Midazolam 0.25 mg/kg (30 min before) Paradox
(Dormicum) Short act
Clonidine 4 ug/kg (60 min before) No RSP -
(Dixarit) Analgaesia
Trimeprazine 2 -3 mg/kg (120 min before) Long act
(Vallergan) Anti-em
Droperidol 0.1 mg/kg (120 min before) anti-em
(Inapsin)
Ketamine 5 -10mg/kg (60 min before) Deep sed
(Ketalar) Monitor!
What are the advantages of the Jackson-Rees modified Ayre’s T-piece and why is it specifically used in paediatrics
- Light weight
- No valves (low resistance)
- Open ended reservoir bag for manual assisted ventilation
- FGF close to child’s face –> minimal dead space and quick change in concentration of delivered gases
- No soda lime
What are the disadvantages of the Jackson-Rees modified Ayre’s T-piece
- High FGF - wasteful (FGF 2 - 3 x minute volume required for spontaneous breathing)
- e.g. Child 10kg with Vt 80 ml + RR 25 = Ve of 2 L/minute so FGF required 4 - 6 L/minute - No scavenging (pollution hazard)
- Possible very high pressures for manual ventilation
- No humidification (no soda lime)
When should a Jackson Rees Modified Ayre’s T-Piece (Mapelson F) circuit be used and why
Patients < 10kg for induction
Patients less than 10kg cannot comfortably generate pressure to breathe spontaneously in a circle system
Patient’s can then be switched over to paediatric circle system if IPPV is required.
Why is pressure-controlled ventilation used in paediatrics
- It compensates for circuit compliance and leaks
- Inherent safety feature: maximal set pressure acts as a ceiling even if lung compliance changes
MUST MONITOR Vt
What is the concept behind the design of shallow paediatric face masks
Minimize equipment dead space
How are oro-pharyngeal airways measured?
Middle of the incisors to the angle of the jaw
What size LMA is required for the following weights
< 10 kg 10 - 20 20 - 30 30 - 50 50 - 70 > 70
< 10 kg 1 - 1.5 (unreliable - use ETT) 10 - 20 2 20 - 30 2.5 30 - 50 3 50 - 70 4 > 70 5
Classify laryngoscope blades
Curved
- Macintosh
Straight (often better for neonates)
- Miller
- Seward
- Wisconsin
What is the formula to predict an appropriate
- Internal diameter ETT
- Length at teeth/gums
Internal tube diameter in mm = Age/4 + 4
(-0.5 for cuffed tubes)
Length at teeth/gums in mm = Age/2 + 12
How is the correct size(internal diameter) tube confirmed
How is correct tube length at teeth confirmed
Internal diameter:
- Easy passage through larynx
- Leak develops at 10 - 20 cmH20
- absence of leak indicates that tube is too big and should be replaced –> oedema can lead to post-intubation stridor
Length
1. Air entry and chest rise equal bilaterally
What is a useful guide to placement of ETT in paeds
Length (cm) of ETT distal to cords = internal diameter (mm) of ETT
E.g. 3mm ETT should be 3 cm distal to the cords.
What is a buretrol?
Type of infusion device that holds limited amounts of IV fluids or medications as children are less able to tolerate large fluid influx like adults. These devices also prevent flow of fluids or air once the infusion quantity is complete.
What are the two options for induction of anaesthesia in paeds
- IV induction
- EMLA + counseling –> IV - Inhalational induction
- Halothane or Sevoflurane ± N2O
What are the issues related to parental presence
- Good for anxyiolysis of the child
2. Prepare the parent for Stage 2 of anaesthesia and for the surgery to follow.
Is muscle relaxation routinely required to intubate children
No. Inhalational agent and spraying cords with 2% lidocaine and/or IV dose of propofol (1-2 mg/kg) helps abolish airway reflexes sufficiently for intubation.
Preferred: NDMR if required for surgery
SUX (avoid)
- Muscle pains
- Bradycardia
- Malignant Hyperthermia
- Anaesthesia induced rhabdomyolysis
Why should sevoflurane be changed to isoflurane for maintenance after inhalational induction with sevoflurane
- More cost effective
- Minimise incidence of post anaesthesia emergence delirium (more common with sevo)
How should replacement and maintenance fluids be calculated in the perioperative period
- Replace deficit at start: 10 ml/kg balsol
- Maintenance fluid - 4:2:1 rule
First 10kg —> 4 ml/kg/hr
Second 10kg —> 2 ml/kg/hr
Every kg > 20kg —> 1 ml/kg/hr
E.g. 25 kg child
40ml + 20ml + 5 ml = 65 ml/hr
Isotonic crystalloid
- Ringers lactate may be used
- Consider making 1 - 2.5% dextrose in infants or 5 - 10% dextrose in neonates
How much packed red cells and how much whole blood is required to raise the Hb by 1 g/dL
Packed cells: 4 ml/kg
Whole blood: 8 ml/kg
List the names and doses of medications used for analgaesia in paediatrics
- Paracetamol IV/PO/PR 15mg/kg 6hrly
- Diclofenac PR 1 mg/kg 8hrly
- Ibuprofen PO 6mg/kg 6hrly
- Morphine IV 0.1 mg/kg 4 hrly
- Fentanyl IV 1 ug/kg titrated 10 mins
- Tilidine (Valeron) SL 1mg/kg 6hrly
- Ketamine PO 5 - 10 mg/kg
- Ketamine IV 0.25 - 0.5 mg/kg
- Clonidine PO 1 - 5 ug/kg 8hrly
- Clonidine IV 1ug/kg
- Clonidine Epidural 1ug/kg
- Bupivacaine TD 2.5 mg/kg max
(Regional/local anaesthesia)
Can suppositories be broken
No
When is caudal anaesthesia performed
Any lower abdominal surgery or lower limb surgery
When are TAP blocks performed
Abdominal surgery
When are rectus sheath block performed
Midline surgery - e.g. umbilical hernia repair
When are penile blocks performed
For circumcisions
When are ilio-inguinal blocks performed
hernia repairs
When are axillary nerve blocks performed
forearm and hand surgery
What is the differential for emergence delirium in children
Pain
When can a child can be discharged from recovery and home
From recovery
1. Pain free, Normal VS, No PONV
Home
- Pain free, Normal VS, No PONV
- Oral intake, ambulating/moving legs, urinating.
- Clean and dry surgical site.
