Neonatal and paediatric anaesthesia

PAEDIATRIC ANAESTHESIA AND MY EXPERIENCE AT DSH

Capt Shoaib Bin kashemTrainee Anaesthesilogy

INTRODUCTION

• Dhaka Shishu (Children) Hospital is the largest children hospital in Bangladesh. It is a Government supported tertiary level public hospital for children with 640 beds.

• All indoor facilities including operation

• Two OT complex- General ot and Cardiac ot

SCOPES

• Children are not little adults!– Neonates: 0-30 days old– Infants: 1 month to 1 year– Children: older than 1 year–  Full term neonate: born between 37-40 weeks and

aged less than 1 month – Premature neonate: child born before 37 weeks

gestation–  Extreme preterm neonate: child born less than 28

weeks gestation• A 10-12 yrs old child thought of anatomically and

physiologically small adult

• Different Anatomy • Different Physiology • Different Pharmacology • Different psychology

Airways

• Head large– 1/3 size of adult head– 1/9 height of adult– 1/27 weight of adult

• Tongue large• Nasal passages narrow• Obligate nose breathers until 5 month

Airway difference:

Large tongueEpiglottis short and stubbyHigher located larynx Angled vocal cords Narrowest portion is cricoid cartilage

It’s Different

• Larynx– Anterior– Cephalad– C 4 level

• Epiglottis long & U shaped• Trachea short

– Neonates → 2 cm cords to carina• Cricoid → Narrowest point until 10 yrs

More rostral pediatric larynx

Infant’s larynx is higher in neck (C2-3) compared to adult’s (C4-5)

Relatively larger tongue• Obstructs airway• Obligate nasal breathers• Difficult to visualize larynx• Straight laryngoscope blade

completely elevates the epiglottis, preferred for pediatric laryngoscopy

Angled vocal cords• Infant’s vocal cords have more angled

attachment to trachea, whereas adult vocal cords are more perpendicular

• Difficulty in nasal intubations where “blindly” placed ETT may easily lodge in anterior commissure rather than in trachea

Differently shaped epiglottis

• Adult epiglottis broader, axis parallel to trachea• Infant epiglottis ohmega (Ώ) shaped and angled away from axis

of trachea• More difficult to lift an infant’s epiglottis with laryngoscope blade

Funneled shape larynx

• narrowest part of infant’s larynx is the undeveloped cricoid cartilage, whereas in the adult it is the glottis opening (vocal cord)

• Tight fitting ETT may cause edema and trouble upon extubation

• Uncuffed ETT preferred for patients < 8 years old

• Fully developed cricoid cartilage occurs at 10-12 years of age

INFANTADULT

Respiratory system

• Alveoli small & limited number– Lung compliance decreased

• Cartilaginous rib cage– Chest wall compliance increased– Chest wall collapse during inspiration and

relatively low residual volume• Chest is circular shaped with horizontal ribs

• Weaker intercostal muscle and the diaphragm– Fewer type 1 muscle cells

• Abdominal muscle strength undeveloped• Caliber of airways is relatively narrow• Large rate of o2 consumption• Ventilator drive are not well developed, so

hypoxia and hypercapnia depress respiration

CVS

In neonates Myocardium less contractile causing the ventricles to be less compliant & less able to generate tension during contraction – Limits the size of stroke volume – Cardiac output therefore rate dependant – Infant behaves as with fixed cardiac output state • Cardiac output – 300-400 ml/kg/min at birth – 200 ml/kg/min within few months

Vagal parasymphathetic tone is most dominant which makes neonates & infants more prone to bradycardias • Bradycardia: – Assc with reduced cardiac output – If assc with hypoxia, should be treated with O2 & Ventilation initially – Cardiac compression will be required in neonate with HR 60 or less OR 60-80bpm with adequate ventilatio

renal

• Decreased glomerular filtration rate– Decreased creatinine clearance– Decreased sodium excretion– Decreased glucose excretion– Decreased bicarbonate resorption– Decreased diluting capability– Decreased concentrating ability

• 600 mosm

• Meticulous attention to fluid administration

Dehydration: – Poorly tolerated – Premature infants have increased insensible losses as they have large surface area relative to weight – There is larger proportion of ECF in children (40% BW as compared to 20% in adult) • Conclusion: – Newborn kidneys has limited capacity to compensate for Volume EXCESS or Volume DEPLETION

Glucose management

• High glucose utilization– Premies 5-6 mg/kg/minute– Neonates 3-4 mg/kg/minute

• Low glycogen stores– Predisposes to hypoglycemia

• Neonates < 30 mg/dl• Infants < 40 mg/dl

– Increased risk with prematurity• Options at maintenance rate

– D5LR, D5 ½ NS, D5 ¼ NS

Thermoregulation• Greater heat loss

– Thin skin– Low fat content– High surface area/weight ratio

• No shivering until 1 yrs• Thermogenesis by brown fat• More prone to iatrogenic hypo/hyperthermia• Optimal ambient temp to prevent heat loss:

– Premature infant: 34⁰C – Neonates: 32⁰C – Adults: 28⁰C

Pharmacotherapy

• Weight “guesstimate” = 2 x (age) + 9• Total body water content increased (70-75%)

– Large volume of distribution for water soluble meds– Increased dose/kg

• Hepatic biotransformation immature• Protein binding decreased• Neuromuscular junction immature• Muscle mass in neonates smaller

– Termination of action by redistribution prolonged

Volatile anesthetics

• Minute ventilation to FRC ratio increased• Blood flow to vessel rich groups increased.

– Rapid rise in alveolar anesthetic concentration• Blood-gas coefficients lower in neonates• Inhalation induction rapid

– BP of neonates and infants more sensitive to hemodynamic effects of volatile agents

– Caution against overdose

IV or IM anaesthetics1- thiopentone sodiumLower dose in neonates than in infantsNeonates- 3-4 mg/kgInfants - 5-6 mg/kg decreased dosage in neonates is due to -- immature brain-- decreased plasma protein binding-- more permeable BBB.

increased requirement in infants due to increased cardiac output as this would be expected to reduce the first pass concentration of thiopentone arriving at the brain.

• PROPOFOL• Children required larger dose of propofol-

– Large vol of distribution– Shorter elemination half life– Higher plasma clearance– 2- 3 mg / kg

Opioids• More potent in neonates than children or adults

– Easier across blood:brain barrier– Decreased metabolic capability– Increased sensitivity of respiratory centers– Caution in neonates

• Hepatic conjugation decreased• Cytochrome P 450 pathways mature by 1 mo• Renal clearance of morphine metabolites is

decreased• Children have high rates of hepatic blood flow

– Increased biotransformation and elimination

Neuromuscular blockers

• Shorter onset time (as much as 50%)– Shorter circulation time

• Depolarizing agent– Succinylcholine

• Nondepolarizing agents– Rocuronium– Cisatricurium– Vecuronium

• Fastest onset → 30-60 secs• Children → 1-1.5 mg/kg IV, 4-6 mg/kg IM• Infants → 2-3 mg/kg IV, 4-6 mg/kg IM• Dysrhythmias

– Bradycardia and sinus arrest– Atropine 10-20 mcg/kg

• Vecuronium- .1mg/kg

Rocuronium Drug of choice for

intubation 0.6 mg/kg IV RSI 0.9-1.2 mg/kg IV

May last 90 min May be given IM

1-1.5 mg /kg Onset 3-4 min

Cisatricurium● Consistently

intermediate duration● 0.05-0.06 mg/kg IV

Reversal

• Nondepolarizing blockade can be reversed with neostigmine (0.03–0.07 mg/kg) or edrophonium (0.5–1 mg/kg) along with an anticholinergic agent (glycopyrrolate, 0.01 mg/kg, or atropine, 0.01– 0.02 mg/kg).

Preoperative considerations

History and physical• Comorbid illness• Recent URI• Murmur

– Innocent– New– Symptomatic

• Anesth problems• Labs → none routine

URI Symptoms new or chronic?

Infectious vs allergic or vasomotor Viral infection within 2 - 4 weeks of GA with

intubation increases perioperative risk Wheezing risk increased 10x Laryngospasm risk increased 5x Hypoxemia, atelectisis, recovery room stay,

admissions and ICU admissions all increased If possible, delay nonemergent surgeries

Premedication

• Sedative premedication is generally omitted for neonates and sick infants.

NPO● Clears → 2 h● Breast milk → 4 h● Formula → 6 h● Solids → 8 h

Monitoring Age & size appropriate standard monitors Precordial stethoscope

Heart rate, heart tones, respiratory quality Preductal pulse oximetry in neonates

Right extremity or earlobe EtCO2 monitor

Main-stream less accurate in < 10 kg Side-stream may falsely elevate iCO2 and

falsely lower EtCO2. Temperature

Monitoring

Face masks

Selection of laryngoscope blade: Miller vs. Macintosh

• Miller blade is preferred for infants and younger children

• Facilitates lifting of the epiglottis and exposing the glottic opening

• Care must be taken to avoid using the blade as a fulcrum with pressure on the teeth and gums

• Macintosh blades are generally used in older children

• Blade size dependent on body mass of the patient and the preference of the anesthesiologist

Endotracheal Tube

New AHA Formulas:Uncuffed ETT: (age in years/4) + 4Cuffed ETT: (age in years/4) +3

ETT depth (lip): ETT size x 3

Age Wt ETT(mm ID) Length(cm) Preterm 1 kg 2.5 6 1-2.5 kg 3.0 7-9Neonate-6mo 3.0-3.5 106 mo-1 3.5-4.0 111-2 yrs 4.0-5.0 12

Cuff vs Uncuffed Endotracheal Tube• uncuffed ETT recommended in children < 8 yrs old to

avoid post-extubation stridor and subglottic stenosis• Arguments against cuffed ETT: smaller size increases

airway resistance, increase work of breathing, poorly designed for pediatric pts, need to keep cuff pressure < 25 cm H2O

• Arguments against uncuffed ETT: more tube changes for long-term intubation, leak of anesthetic agent into environment, require more fresh gas flow > 2L/min, higher risk for aspiration

• For “short” cases when ETT size >4.0, choice of cuff vs uncuffed probably does not matter

• Cuffed ETT preferable in cases of: high risk of aspiration (ie. Bowel obstruction), low lung compliance (ie. ARDS, pneumoperitoneum) etc.

T piece vs closed circuit•Jackson-Rees modification to Ayres T piece or Mapleson F circuit•Simple, lightweight, has an open ended bag which can be occluded to apply CPAP and PEEP•Better for children <20kg (varies with anaesthetist) because easier to assess tidal volume and lung compliance, has low resistance and dead space•Disadvantage is pollution and anaesthetic gas wastage•Bag must be big enough not to restrict tidal volume but not so large that his visual and tactile monitor is lost

Breathing

Paediatric breathing circuit•Narrow tubing (15mm) which reduces compression volume and small distal connections to minimise dead space•Better conservation of heat and vapour, easy scavenging and less gas wastage but loss of feel during hand ventilation due to large compression volume

Perioperative fluid replacement● 1st 0-10 kg → 4 cc/kg/hr● 2nd 10-20 kg → 2 cc/kg/hr● > 20 kg → 1 cc/kg/hr● Calculate preoperative deficit

– Replace 50% first hour– Replace 25% second hour– Replace 25% third hour

● Minor surgery → additional 2 cc/kg/hr● Major surgery → up to additional 10 cc/kg/hr

Regional Anaesthesia

• Most commonly done caudal, SAB and penile block

• caudal block-– Penil and anal surgery– Vaginal surgery– Orchidoplexy– Hernia repair

• Bupivacain plain 1- 1.5 mg/kg• Lidocain 2-2.5 mg /kg• Doses:

0.5cc/kg for perineal surgery 0.75cc/kg for T-10 level 1cc/kg for lower thoracic level

• Penile block-– Done for any penile surgery

CONCLUSION Pediatric anesthesia involves more than simply adjusting drug doses and equipment for smaller patients. Neonates, infants, toddlers, and young children have differing anesthetic requirements. Safe anesthetic management depends on full appreciation of the physiological, anatomic, and pharmacological characteristics of each group. Indeed infants are at much greater risk of anesthetic morbidity and mortality than older children; that require unique surgical and anesthetic strategies.

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