Neonatal & Pediatric Assessments & Anesthesia Considerations

Neonatal Classifications and Vital Statistics

• Definition of Neonate: A neonate is defined as an infant from birth to $30$ days of life.
• Gestational Age Classifications:     * Term Neonate: Born at $37\,0/7+$ weeks gestation.     * Pre-Term Neonate: Born between $23/24$ weeks (viability thresholds often depend on weight and eyelid fusion) and $36\,6/7$ weeks gestation.     * Non-viable: Born between $0$ and $22\,6/7$ weeks gestation.
• Vulnerability Factors:     * Neonates exhibit significantly increased vulnerability to external stressors compared to older children.     * Premature neonates are even more susceptible to these stressors.     * There is a $10\times$ increased risk of morbidity and mortality in neonates when compared to older pediatric populations.     * The period of highest risk for these patients is the post-operative period.
• ASA Physical Status Classification:     * Children under the age of $1$ year (< 1\text{ y/o}) are automatically categorized as ASA Class III - V.

Overview of Neonatal Organ Systems: Cardiac and Respiratory

• Cardiac System and Transitional Circulation:     * Birth/Delivery: Marks the transition from fetal to neonatal circulation.     * Clamping the Umbilical Cord: Clamping and cutting the cord increases aortic pressure, which triggers specific physiological changes:         * Lung Expansion/Increased $PaO_2$: This occurs due to a decrease in pulmonary vascular resistance.         * Pulmonary Vasodilation: Leads to the closure of the Foramen Ovale (FO) and the Ductus Arteriosus (DA) due to increased systemic vascular resistance.
• Respiratory System:     * Fetal Surfactant: Production details are referenced from previous material (Week #4 assessment).     * Airway Obstruction Risks:         * The neonatal larynx is proportionally smaller than the mouth and pharynx.         * The cricoid cartilage represents the narrowest point of the neonatal airway.         * The tracheal length is very short, measuring approximately 5\text{--}9\,\text{cm}.
• HEENT (Head, Eyes, Ears, Nose, Throat):     * Macroglossia: The neonatal tongue is large relative to the oral cavity, making it difficult to manipulate during procedures.     * Hyoid Bone: The position of the hyoid bone contributes to the difficulty in airway manipulation and increases the risk of obstruction.

Overview of Neonatal Organ Systems: Abdominal, Renal, and Neurological

• Liver Function:     * Metabolism is decreased due to an immature liver.     * Enzyme activity is significantly decreased, resulting in longer drug elimination half-lives.
• Renal Function:     * Glomerular Filtration Rate (GFR): Neonates have a decreased GFR, which leads to decreased drug elimination.     * Drug clearance capabilities typically take approximately $3\text{--}4$ weeks to mature.
• Neurological Development and Thermoregulation:     * Sensory nerve distribution is fully formed by $20$ weeks gestation.     * Functional pain pathways and pain receptors are present at birth.     * Thermoregulation Challenges: Neonates struggle with temperature control due to a lack of subcutaneous (Sub-Q) tissue and an inability to shiver.
• Autonomic Nervous System (ANS):     * The ANS is immature at birth.     * The Sympathetic Nervous System has a delayed response compared to the Parasympathetic Nervous System.     * Physiologic stress can lead to rapid and severe cardiovascular (CV) collapse.

Neonatal Anesthesia complications and Physiological Stress Responses

• Non-Shivering Thermogenesis (NST):     * This is the primary mechanism for heat production in neonates since they cannot shiver.     * Brown fat is broken down to produce heat.     * Complication: The breakdown of brown fat creates metabolic acidosis.
• Cardiovascular Complications:     * Metabolic acidosis resulting from NST leads directly to bradycardia.     * If untreated, this progresses to cardiac arrest.
• Respiratory Complications:     * Mask ventilation is inherently difficult due to the risk of airway obstruction caused by neonatal anatomy.     * Post-extubation croup: This is a frequent complication if a cuffed endotracheal (ET) tube is used in neonates.

Neonatal Anesthesia Considerations and Procedural Goals

• Primary Goals:     1. Minimize the duration of anesthesia to decrease iatrogenic effects.     2. Utilize short-acting pharmacological agents.     3. Employ a combination of local, regional, and general anesthesia, along with systemic analgesics, to reduce the overall required drug dosage.
• Respiratory and Intubation Management:     * Positioning: Do not use the "Sniffing Position" for neonatal intubation. Instead, place a rolled towel under the shoulders to aid in visual alignment of the airway.     * Intubation Technique: Use a straight blade (Miller) for placement.     * Tube Specifics: Insertional distance of the ET tube should be less than 10\,\text{cm}. Avoid the use of cuffed ET tubes in this population.     * Observation: Patients must be observed for at least $24$ hours post-operatively.
• HEENT Procedural Technique: Insert the straight blade laryngoscope on the right side of the mouth and sweep the tongue to the left.

Environmental Control and Pre-Operative Requirements for Neonates

• Temperature Maintenance (Essential):     * Pre-operative: Use radiant heat sources such as OHIO beds or Isolettes.     * Operating Room (OR): Maintain an OR room temperature of at least $26\,^{\circ}\text{C}$.     * Fluids/Gases: Use warmed irrigation fluids, warmed Intravenous Fluids (IVF), and humidified inhaled gases.     * Mechanical Barriers: Use warm blankets immediately once removed from the radiant heat source and ensure the head is covered.     * Clothing: Remove wet clothing or diapers as soon as possible to prevent heat loss.
• NPO Status and Dehydration:     * Gastric emptying is slower in neonates than in adults.     * $2\text{--}4\text{--}6\text{--}8$ Rule: Standard fasting guidelines ($2$ hours for clear liquids, $4$ hours for breast milk, $6$ hours for formula/light meal, $8$ hours for heavy meal).     * Maintenance Fluids: IVF maintenance should be started before surgery to offset potential dehydration.

Neonatal Anesthetic Drug Considerations

• Protein Binding:     * Protein binding capacity is decreased in neonates.     * This heightens the pharmacological effect of drugs because there is a higher concentration of circulating, unbound (active) medication in the body after administration.
• Inhaled Agents:     * Mask ventilation is difficult due to anatomical obstruction risks.     * Inhalation medications result in rapid induction; however, the therapeutic margin is narrow.     * There is an increased risk of CV side effects, specifically myocardial depression, due to rapid induction and the immature heart.
• Intravenous (IV) Agents:     * These agents are rapidly absorbed but have a longer duration of action due to decreased liver metabolism and renal secretion.     * Opioids: There is an increased Central Nervous System (CNS) effect due to an immature Blood-Bain Barrier (BBB). Fentanyl is generally well tolerated, while Morphine should be avoided.     * Propofol: Higher doses are actually needed for induction in neonates because of an increased volume of distribution/metabolism profile unique to this drug in this age group.
• Neuromuscular Blockade (NMB):     * Administration: There is decreased clearance and slower Acetylcholine (Ach) release at the immature synapse, leading to a smaller therapeutic window.     * Succinylcholine: Avoid use except in emergent airway situations due to the risk of severe hyperkalemia.     * Reversal: Neonates are highly vulnerable to hypoxemia due to residual muscle weakness.     * Extubation: Avoid extubation until all reflexes have returned.     * Apnea Treatment: Specific treatments include CPAP (Continuous Positive Airway Pressure) and the administration of Caffeine.

Pediatric Classifications and Organ System Maturity

• Pediatric Life Stages:     * Infant: $30$ days of life to $1$ year old.     * Toddler: $1$ to $3$ years old.     * Preschool: $4$ to $6$ years old.     * School Age: $6$ to $13$ years old.     * Adolescent: $13$ to $18$ years old.
• ASA Class: Similar to neonates, children under $1$ year old are categorized as Class III - V.
• Respiratory System:     * Increased risk for airway obstruction due to smaller anatomy.     * Additional risks include loose teeth or dental braces.
• Abdominal and Renal Maturation:     * Liver: Like neonates, early pediatric patients have decreased metabolism and enzyme activity, leading to longer drug half-lives.     * Kidneys: GFR is initially decreased, but renal function reaches adult rates between $8$ and $12$ months of age.
• Neurological: Sensory nerve distribution is formed by $20$ weeks gestation, and pain pathways are present at birth.

Pediatric Anesthesia Complications and Infection Guidelines

• Respiratory Complications:     * Use of cuffed ET tubes causes post-extubation croup.     * Bronchial airways remain reactive for $6\text{--}8$ weeks following a Lower Respiratory Infection (LRI).     * Airways can be chronically reactive in patients with a history of asthma.
• Active Infection Signs (Criteria to Delay Elective Procedures):     * Purulent drainage.     * Dry or productive cough.     * Pharyngitis.     * Fever.

Pediatric Anesthesia Management and Considerations

• Primary Goals: Exactly the same as neonatal goals (minimize duration, use short-acting drugs, use multi-modal/combination anesthesia).
• NPO Status:     * The gastric emptying rate reaches adult levels by $6$ months of age.     * $2\text{--}4\text{--}6\text{--}8$ Rule: Fasting protocol remains standard.     * Chewing Gum: No gum is permitted after midnight ($0000$).
• Pharmacological Adjustments:     * Protein Binding: Capacity is decreased until approximately $1$ year of age.     * Pre-Op Interventions:         * Prioritize non-pharmacological interventions first.         * Midazolam: Used for amnesia, anxiolysis, and hypnotic effects.         * EMLA cream: Applied prior to attempting IV access to reduce pain.

Pediatric Drug Administration and Blockade Reversal

• Inhaled Agents:     * Mask induction is commonly used for children under $8$ years old (< 8\text{ y/o}) or those without existing IV access.     * This reduces anxiety associated with IV placement.
• IV Agents:     * Preferred over mask induction if the child has not followed NPO guidelines before emergent surgery or if there is a history of Gastroesophageal Reflux Disease (GERD).     * Propofol Warning: Avoid long-term, high-dose use of Propofol due to the risk of Propofol Infusion Syndrome.     * Symptoms of Propofol Infusion Syndrome: Heart failure, dysrhythmias, fever, and acidosis.
• Neuromuscular Blockade in Pediatrics:     * Ach release is slower due to immature synapses, resulting in a narrow therapeutic window.     * Succinylcholine: Avoid use through the early teens if possible, except in emergencies, due to the risk of severe hyperkalemia.
• Reversal and Recovery:     * Patients are vulnerable to hypoventilation due to residual blockade.     * Do not extubate until reflexes have fully returned.     * Post-Operative Care: Place the patient in a lateral position, provide supplemental $O_2$, and utilize suctioning as needed.