Pediatric Anesthesia

Age groups:

• Premature: Less than 37 weeks gestational age.
• Neonate: Less than 28 days.
• Infant: 1-12 months.
• Toddlers: 1-3 years.
• Children: 3-7 years.
• Older Children: 7-12 years.
• Adolescents: 12-15 years.

Paediatric Patients Are Not Merely Small Adults

Successful anesthetic management depends on an appreciation of the physiologic, anatomic, and pharmacologic characteristics of each age group. This necessitates the need for modification of anesthetic equipment and techniques. Children are prone to illnesses that require unique surgical and anesthetic strategies.

Cardiovascular

• Noncompliant Left Ventricle (LV).
• Residual fetal circulation.
• Small veins and arteries.
• Poorly developed sympathetic and baroreceptor reflexes.
• Cardiac output rate-dependent.
• Lower Blood Pressure (BP).
• Faster heart rate.
• Reduced response to catecholamines.
• Dominant vagal reflex response.

Respiratory and Airway

• Large head and tongue.
• Narrow nasal passages.
• Anterior and cephalad larynx at C4 versus C6 in adults.
• Long epiglottis.
• Cricoid is the narrowest point (funnel shape).
• Short trachea and neck.
• Prominent tonsils and adenoids.
• Weak intercostal and diaphragm muscles.
• High resistance to airflow.
• Faster respiratory rate.
• Small tidal volume (Vt).
• Lower lung compliance.
• Greater chest wall compliance.
• Lower Functional Residual Capacity (FRC).
• Reduced response to CO2 and hypoxia.
• Increased oxygen (O2) demand.

Note: HR is approx. (RR x 5)
Age	RR	HR
<30 days	30	150
5yrs	20	100
12yrs	18	90
18yrs	14	70

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	Pre-school
Haemoglobin (g/l)	17.0-22.0	10.5-12.0	11.0-12.0	11.5-12.5
Haematocrit (%)	55-70	35-40	34-41	37-41
Blood volume (ml/kg)	80	80	75	70

Body Compositions During Growth

BODY COMPARTMENT	INFANT (% BODY WEIGHT)	ADULTS (% BODY WEIGHT)
TBW	73	60
ECF	44	15-20
BV	8-10	7
ICW	33	40
MUSCLE MASS	20	50
FAT	12	18

Age	Water requirements ml/kg/hr
0-1 yr	5
1-3 yrs	4
3-6 yrs	3
7-14 yrs	2.5
Adult	2

• Poorly Developed and Non-Compliant Myocardium
• Residual Fetal Circulation
• Difficult Venous Cannulation
• Large Floppy Head, Tongue, and Epiglottis
• The Narrowest Part of the Airway is Subglottic at the Cricoid
• Narrow Nasal Passages
• Anterior and Cephalad Larynx
• Short Trachea and Neck
• Prominent Adenoids and Tonsils
• Alveoli are Immature with Resultant Decreased Lung Compliance
• Weak Diaphragmatic Muscles
• High Resistance to Air Flow

• Immature Hepatic Biotransformation
• Decreased Protein Binding
• Increased MAC (Minimum Alveolar Concentration)
• More Sensitive to Opioids
• Large Volume of Distribution for Water-Soluble Drugs
• Immature Neuromuscular Junction
• More Susceptible than Adults to Cardiac Arrhythmias After Administration of Succinylcholine
• Rapid Induction and Recovery (Rapid Fa/Fi)

History

During the preanesthetic evaluation, it is important to consider the patient's history. This includes:

• Perinatal History
• Recent or intercurrent Upper Respiratory Tract Infection (URTI)
• Loose teeth (in school-aged children)
• Ruling out congenital anomalies
• Assessment of other medical problems

Assessment of the Psychological Make Up of the Child & Family

Anesthesia and surgery can be stressful for both the child and the family. Factors contributing to this stress include:

• Separation from Parents
• Strange Surroundings
• Painful Procedures
• Frightening Procedures
• Concerns for Survival

Honest and consistent communication between the child and parents is vital in addressing these stress factors.

Laboratory Investigations

When it comes to laboratory investigations for pediatric patients:

• Minimal Laboratory Evaluation:
• As with adults, the approach is guided by the medical history.
• Most pediatric patients require no lab evaluation.
• However, many institutions require a Hematocrit (HCT) for infants under 6 months (nadir of 10 g/dL).

Preoperative Fasting

The aim for a child is to have an empty stomach but not be dehydrated or hypoglycemic. Here are the guidelines for fasting:

• Bottled milk, milk formula, baby feeds, and milky drinks are classified as solids as milk curds and becomes solid in the acidic stomach medium.
• Breast milk is cleared relatively quickly, hence a shorter fasting time is recommended for it.
• Clear fluids are emptied very quickly.
• The fasting times are as follows:
• 6 hours for solids, milk, or drinks
• 3 hours for breast milk
• 2 hours for clear fluids

Premedications

Premedications serve various purposes in pediatric anesthesia:

1. To reduce unwanted effects of anesthetic agents
2. To treat preoperative pain
3. To supplement anesthesia
4. To reduce anxiety and make induction easier.

Anxiolytics may be unnecessary, especially if a parent can be with the child at induction. Oral premedication is usually preferable. Different types of premedications include:

• Sedative Hypnotics - Oral, Nasal & Rectal
• Oral: Midazolam (0.5-0.7 mg/kg), Ketamine (5-6 mg/kg for ages 1-6 years)
• Oral Transmucosal Fentanyl
• Nasal: Used when there is a lack of cooperation; e.g., Midazolam, Sufentanil, Ketamine
• Rectal: Methohexital and Thiopentone (onset in 10 minutes; causes respiratory depression and desaturation)
• IM (Intramuscular): Note that children do not like needles.

Anti-Nausea Medications

Nausea and vomiting (N&V) are the most frequent causes of unanticipated admission in pediatric day cases. Here are some anti-nausea medications and their recommended doses:

• Droperidol: Dose ranges from 20 to 70 µg/kg.
• Metoclopramide: Recommended dose is 0.15 mg/kg.
• Ondansetron: Recommended dose ranges from 0.05 to 0.15 mg/kg.

Additionally, it's important to assess venous access. EMLA (Eutectic Mixture of Local Anesthetics) can be applied 30-60 minutes before the induction of anesthesia to improve venous access.

Preparation

Before the procedure, it's essential to prepare meticulously:

• Work out all drug doses, fluid requirements, blood volume, allowable blood loss, tube sizes, minute volumes, etc.
• Ensure the ambient temperature in the theater is appropriate, especially when anesthetizing a neonate or small infant (ideally between 20 and 24°C). Warming and insulating materials should be available.
• Check equipment to ensure everything is in working order.
• Label syringes and check dilutions for accuracy.
• Ensure that the consent form is appropriately signed and witnessed.

Equipment

• Breathing Circuits: Ideally lightweight. For Mapleson D, E, F, including T-Piece and Coaxial D (Bain), the Fresh Gas Flow (FGF) for Intermittent Positive Pressure Ventilation (IPPV) is 220 ml/kg for babies and infants up to 15 kg. For spontaneous ventilation, it is 2 – 3 times the minute volume.
• Mapleson A: Unsuitable for IPPV. Minimal FGF for spontaneous ventilation is alveolar ventilation.
• Manual Ventilation with T-Piece: Appropriate for infants over 15 kg, with some disadvantages including hands not being free, gas monitoring being technically difficult and prone to inaccuracy, and scavenging being difficult.

Airway Management

• Face Masks:
  • Rendell-Baker-Soucek
  • Laerdal
• Laryngoscopes: Straight blades are necessary for neonates and young infants. With Magill, the tip should be placed posterior to the epiglottis to avoid vagal innervation. Most laryngoscopes can also be used like a Mackintosh blade with the tip in the vallecula.
• Endotracheal Tubes: Non-cuffed tubes are suitable for very young patients. Too tight a fit can cause ischemic damage to the tracheal cartilage.
• Laryngeal Mask Airway (LMA): LMAs are available for most patients, including neonates.

During the conduct of anesthesia in pediatric patients, several considerations are important:

• Inhalational induction is common, but it comes with challenges such as breath-holding, laryngospasm, and stomach distension. Infants are especially prone to bradycardia and hypotension.
• Halothane and sevoflurane provide rapid and smooth induction. Isoflurane and desflurane are associated with a risk of laryngospasm.
• Intravenous (IV) induction is an alternative, and the application of EMLA cream can increase cooperation and patient comfort during cannulation.
• Common IV induction agents include propofol, thiopental, methohexital, and ketamine.

Muscle Relaxants

• Suxamethonium: a higher dose requirement. Atropine is frequently used before its administration to prevent arrhythmias.
• Neuromuscular Junction Sensitivity: The neuromuscular junction of a neonate is more sensitive to non-depolarizing neuromuscular blockers (NDNMBs) than that of an adult. However, due to the increased volume of extracellular fluid and volume of distribution in very young children, the dose doesn't change significantly with age.

Analgesics

For analgesia in pediatric patients (reduce dose under 1 year), the following options are available:

• IV Fentanyl: 1 – 3 mcg/kg administered half-hourly.
• IV Morphine: 0.5 – 0.75 mcg/kg administered every 2 hours.
• IM Pethidine: 1 – 2 mg/kg.
• IM Morphine: 0.15 mg/kg.
• IM Codeine: 1 mg/kg administered every 3 – 6 hours.
• Oral/Rectal Paracetamol: Dose ranges from 20 to 40 mg/kg every 4 to 6 hours.
• IM Paracetamol: Dose is 15 mg/kg every 4 to 6 hours.
• Oral/Rectal Diclofenac: Dose ranges from 1 to 2 mg/kg every 12 hours.

Additionally, for other considerations:

• Narcotic Antagonist (Naloxone): Dose is 10 mcg/kg.
• Antiemetics: For older children, you can use Metoclopramide up to 0.5 mg/kg or Prochlorperazine 6.25 mg IM or 5–10 mg rectally. However, avoid use in children under 10 kg, and be cautious as they can cause oculogyric crises.

Fluid Therapy

Fluid therapy in pediatric patients is typically divided into three components:

• Deficit: Half of the deficit should be given in the first hour, and the remaining half should be administered over the next two hours.
• Maintenance: Maintenance fluid requirements are calculated using the formula 4-2-1-1.
• Third Space Loss/Blood Loss:

Maximum allowable blood loss (MABL) = EBV × (Starting HCT - Target Hematocrit) / Starting HCT

Where EBV is estimated blood volume.

In pediatric anesthesia, vigilant monitoring is essential. The anesthetist should constantly observe:

• Oxygenation
• Ventilation
• Perfusion
• Depth of anesthesia
• Fluid balance

A precordial or oesophageal stethoscope can be a useful and simple monitor for heart and respiratory sounds. Additionally, monitoring techniques such as pulse oximetry, ECG, and blood pressure monitoring provide essential information.

Temperature control is crucial:

• Use a warmed incubator pre and post-op with regulated temperature.
• Bair Hugger warming system.
• Utilize heated water or air blankets.
• Ensure the use of appropriate technology for temperature monitoring.

It's important to monitor core temperature when using extraneous heat sources and to be cautious about the risk of overheating.

Post-operative care in pediatric patients should involve continuous monitoring. The airway must be maintained to ensure adequate ventilation and oxygenation. Any unexpected findings should be reported to the anesthetist. Vital signs should be taken frequently during the first hour, and pain should be treated. The child can be transferred to the ward when observations are stable, they are fully conscious, and their pain is under control.

However, pediatric patients are particularly vulnerable to two post-anesthetic complications:

Laryngospasm:

This is a forceful involuntary spasm of the laryngeal musculature caused by the stimulation of the superior laryngeal nerve. It can be avoided by extubating the patient when they are fully awake or while they are deeply anesthetized. Laryngospasm typically occurs immediately post-operation.

Post-intubation Croup

Post-intubation croup can occur due to glottic or tracheal edema, with the region of the cricoid cartilage being most susceptible. It almost always occurs within 3 hours post-extubation. Severe croup can present with:

• Suprasternal retractions
• Labored respiration
• Arterial O2 desaturation

Treatment options for post-intubation croup include:

• High concentrations of humidified oxygen
• Racemic epinephrine

Children are not just little adults. However, most principles of adult anesthesia are also applicable in pediatric patients. A thorough understanding of the differences is crucial for the skilled administration of anesthesia to this challenging group of patients. The smaller they are, the less margin of reserve is present.