Pediatric Anesthesia, M&M Chapter 42
Population with reduced risk for halothane-induced hepatic dysfunction
Prepubertal children
When does pediatric kidney function approach normal values?
- 6 months old - Potentially delayed until 2 years old
-How is pediatric drug dosing adjusted? - How is age a factor?
- Adjusted per kg - During early childhood, age can correlate with weight: 50th percentile weight (kg) = (Age x2) + 9
- Vital sign sensitive to volatile anesthetic - Caused by?
- Blood pressure (neonates & infants), r/t 1. Underdeveloped compensatory mechanism (vasoconstriction, tachycardia) 2. Immature myocardium is more sensitive to myocardial depressents
Pediatric patients' response to muscle relaxants in pediatric patients
- Generally faster onset (up to 50% less delay) - R/t SHORTER circulation times than adults.
- Most common mechanism of anesthesia-related cardiac arrest - Contributing factors
- Medication related - 1. CV depression from halothane, alone or in combination with other drugs, was believed to be responsible in 66% of all medication-related arrests 2.IV injection of LA, most often following a negative aspiration test during attempted caudal injection
CV mechanism that results in anesthesia-related cardiac arrest
- NO clear etiology - Congenital heart disease in more than 50% of those patients **- IF CV mechanism identified, MOST often related to hemorrhage, transfusion, or inadequate or inappropriate fluid therapy
Water content of neonates & infants compared to adults
- Neonates & infants:70-75% - Adults: 50-60%
In ped population, reversal of NDMB
- Neostigmine (0.03-0.07 mg/kg) - Edrophonium (0.5-1 mg/kg) ALONG with an anticholinergic agent (glycopyrrolate, 0.01 mg/kg, or atropine, 0.01-0.02 mg/kg).
- Is weight-adjusted drug dosing effective? - Why?
- Not completely effective, bc does NOT account for: 1. Disproportionately LARGER pediatric intravascular and extracellular fluid compartments 2. Immaturity of hepatic biotransformation pathways 3. DECREASED protein drug binding 4. HIGHER metabolic rate
What do we know about etomidate use in the pediatric population?
- Nothing significant, bc not well studied in children < 10y/o - Profile in older children is similar to adults
- Opioids are more _____ in neonates than in older children and adults. - Why?
- POTENT - 1. "easier entry" across the blood-brain barrier (unproven but popular belief) 2. Decreased metabolic capability 3. Increased sensitivity of the respiratory centers.
- Unlike adults, children may respond their first dose of succinylcholine with ______. - How can this response be avoided?
- Profound bradycardia and sinus node arrest - Atropine pretreatment (0.1 mg minimum) must ALWAYS be administered prior to succinylcholine in children.
DOA of pancuronium, vecuronium, and rocuronium in neonates
- Prolonged - Drugs are hepatically metabolized and neonates have immature hepatic function
Although recovery from a single dose of proposal is not very different than adults.... - What is the speed of recovery for a continuous propofol infusion? Clinical significance?
- RAPID - Children have shorter elimination 1/2 life and higher plasma clearance for propofol - Children may require weight-adjusted rates of infusions for anesthesia maintenance (up to 250 mcg/kg/min)
- VA blood/gas coefficients ____ in neonates? - Clinical significane?
- REDUCED (compared to adults) - Results in even FASTER induction and potentially INCREASING risk for accidental overdose
- Considered by many clinicians to be the drug of choice during routine intubation in pediatric patients with intravenous access - Why? - Can it be used for RSI?
- Rocuronium (0.6 mg/ kg intravenously) - Fastest onset of NDMB - Yes, larger doses of rocuronium (0.9-1.2 mg/kg) may be used for RSI but a prolonged duration (up to 90 min) will likely follow.
For peds patients, do metabolic parameters have a stronger correlation to SA or weight? (Review: What are metabolic parameters?)
- SURFACE AREA! Metabolic parameters: - O2 consumption - CO2 production - CO - Alveolar ventilation
Peds patients have a ______ BMI & ____ surface area per kg than adults
- Smaller BMI - Larger SA
Neonatal physical characteristics that promote environmental heat loss
- Thin skin - Low fat content - Greater SA relative to weight
Neonates have decreased protein binding for certain drugs. 1. Which ones? 2. Clinical signifiance
- Thiopental, bupivacaine, and many antibiotics 1. Thiopental: Increased free drug enhances potency and REDUCES INDUCTION dose for neonates compared to older children 2. Bupivacaine: Increase in free drug increases risk for systemic toxicity
Name developmental cardiovascular differences of neonates/infants
- Underdeveloped SNS and baroreceptor reflex - Blunted response to exogenous catecholamines - More sensitive to myocardial depression by volatile anesthetics and opioid-induced bradycardia - Incomplete compensatory vasoconstriction to hypovolemic state - No rebound tachycardia to hypotension r/t intravascular depletion
How does increased TBW affect "volume of distribution (Vd)?"
- Vd for most IV drugs is disproportionately GREATER in neonates, infants, and young children - Optimal dose (per kg) is usually greater than in older children and adults
What are developmental changes to RR, TV, and airway resistance?
- Ventilation is less efficient in neonates and infants. Increase work of breaking and muscles easily fatigued - RR increased in infants and neonates...gradually falls to adult levels by adolescence. - TV & dead space per kg nearly constant during development - Neonates and infants have increased airway resistance r/t fewer and smaller airways - Alveoli fully mature by late childhood (8 y/o) -
Why is there a variable response to NDMR amongst neonates?
1. "immature NMJ" in premature neonates can lead to increased sensitivity (unproven) 2. larger extracellular compartment can reduce drug concentrations (proven)
1. Examples of neonatal renal immaturity 2. What medical intervention is significant affected?
1. - Decreased creatinine clearance - Impaired sodium retention - Impaired glucose excretion - Impaired bicarbonate reabsorption - Reduced diluting & concentrating ability 2. Appropriate fluid administration is IMPORTANT during first few days of life
According to POCA: As with adults, two major predictors of mortality
1. ASA physical status 3-5 2. Emergency surgery.
Regarding administration of succinylcholine, children are more susceptible to:
1. Cardiac arrhythmias 2. Hyperkalemia 3. Rhabdomyolysis 4. Myoglobinemia 5. Masseter spasm 6 .Malignant hyperthermia
1. DOA of drugs for neonates 2. Caused by? 3. Examples of effected medications
1. DOA is prolonged 2. Disproportionately SMALLER muscle mass causes a delay in "redistribution to muscle" 3. Thiopental and fentanyl
1. Why do older pediatric patients have relatively greater rates of biotransformation and elimination? 2. What drugs are affected?
1. High hepatic blood flow 2. Sufentanil, alfentanil, and, possibly, fentanyl clearances may be greater in children than in adults.
- Drug clearance for neonates - Caused by?
1. Impaired renal drug clearance, hepatic metabolism, and biliary excretion 2. DECREASED GFR, hepatic blood flow and renal tubular function; IMMATURE hepatic enzyme systems
Accepted indications for succinylcholine IV administration in children
1. RSII with a "full" stomach 2. Laryngospasm not responsive to PPV . Intramuscular atropine (0.02 mg/kg) should be administered with intramuscular succinylcholine to reduce the likelihood of bradycardia
How does pediatric ventilation/perfusion affect anesthesia gas administration?
1. Rapid increase in alveolar anesthetic concentration 2. Inhalation induction occurs faster
1. What is "propofol infusion syndrome?" 2. Populations with greater incidence
1. Rhabdomyolysis, metabolic acidosis, hemodynamic instability, hepatomegaly, and multi-organ failure 2. Critically ill children and adults with long term propofol infusion (>48 hrs and >5 mg/kg/hr)
1. The only NDMB adequately studied for IM administration 2. Potential drawback
1. Rocuronium (1.0-1.5 mg/kg) 2. Requires 3-4 min for onset.
1. Which volatile anesthetic has the "same" MAC in neonates and infants? 2. Clinical significance
1. Sevoflurane 2. Preferred agent for inhaled induction in pediatric anesthesia. Greater therapeutic index (than halothane)
1. Accepted indications for succinylcholine IM in children 2. Dose 3. Clinical consideration
1. When rapid muscle relaxation is required prior to intravenous access (eg, with inhaled inductions in patients with full stomachs 2. 4-6 mg/kg 3. Concurrent IM atropine (0.02 mg/kg) administration o reduce the likelihood of bradycardia
1. Halothane sensitize the heart to ____. 2. Max dose of epinephrine in LA solution during halothane anesthesia
1. catecholamines 2. 10 mcg/kg
What measurable amount of edema can affect gas flow in children?
1mm of edema can affect gas flow in children's airways, bc small tracheal diameter
VA that causes least respiratory depression
Sevoflurane
Why should the pediatric patient be monitored with a peripheral nerve stimulator?
As with adults, to see the effect of incremental doses of muscle relaxants (usually 25-30% of the initial dose)
Why is propofol not recommended for prolonged sedation of critically-ill peds patients?
Associated with greater mortality than other agents
Atracurium and cisatracurium DOA in peds population
Since do not depend on hepatic biotransformation, reliably behave as intermediate-acting muscle relaxants.
Immediate treatment for cardiac arrest following administration of succinylcholine to a child
TREAT HYPERKALEMIA!!! Then, prolonged, heroic resuscitative efforts may be required (ex. cardiopulmonary bypass)
As with adults, a more rapid intubation can be achieved with a muscle relaxant dose that is twice the ED 95 dose.
TRUE (but you still pay for it at the end......bc prolonged DOA)
True/False: In recent years, increased concern and scientific interest in the possibility that general anesthesia and general anesthetic agents are toxic to the brains of small children.
TRUE :( Experimental date in ANIMALS are consistently worrisome, but the clinical data are (currently) inconclusive as to the extent of the risk and whether one technique is safer than another.
Clinical consideration for administration of thiopental to infants and neonates
- Children require relatively larger doses of thiopental (compared with adults) 1. SHORTER elimination 1/2 life 2. GREATER plasma clearance - Neonates are MORE sensitive to barbiturates 1. LESS protein binding 2. LONGER 1/2 life 3. IMPAIRED clearance Thiopental induction dose: Neonates: 3-4 mg/kg Infants: 5-6 mg/kg
What factors exacerbate hypoxia in neonates and infants?
- Exaggerated by the higher rate of oxygen consumption of neonates and infants - Since hypoxic and hypercapnic ventilatory drives are not well developed in neonates & infants → hypoxia and hypercapnia can cause respiratory depression
1. Drawback of Sevo and Des administration in young children
- Greater incidence of agitation or delirium upon emergence - As a result, some clinicians switch to ISO after sevo induction
- Are neonates predisposed to "hyperglycemia or hypoglycemia?" - Why? - Who is at greatest risk?
- HYPOglycemia - R/t reduced glycogen stores (impaired renal glucose secretion may offset this tendency) - "At-risk" neonates: 1. Premature, small for gestational age 2. Neonates receiving hyperalimentation 3. Offspring of diabetic mothers
Most (82%) arrests occurred during which part of anesthesia? Clinical manifestations prior to arrest.
- INDUCTION! - Bradycardia, hypotension, and a low SpO2 frequently preceded arrest.
Surgical and anesthesia factors that contribute to neonatal heat loss
- Inadequately warmed operating rooms - Prolonged wound exposure - Administration of room temp IV & irrigation fluid - Dry anesthetic gas - Anesthetic agents effect temperature regulation
Dose adjustment of succinylcholine for infants. Why?
- Infants require larger doses of sux (2-3 mg/kg) than older children and adults -Larger Vd - If dosage is based on body surface area, then discrepancy disappears
Does the neonatal liver conjugate drugs "more or less?"
- LESS - Immature liver conjugates drugs and other molecules LESS readily early in life
Respiratory mechanisms that lead to cardiac arrest include:
- Laryngospasm, airway obstruction, and diffi cult intubation (in decreasing order). **Laryngospasm most likely to occur during induction * Pts with airway obstruction or were difficult to intubate had at least one other significant underlying disease.
Emergence is fastest following which VAs?
- Sevo & Des
According to POCA: 33% of patients who suffered a cardiac arrest were ASA physical status___.
1 -2
What factors exacerbate reduced hepatic blood flow in neonates?
1. Increased intra-abdominal pressure 2. Abdominal surgery
According to POCA: 1. _____ accounted for 55% of all anesthesia-related arrests 2.____ have the greatest risk.
1. Infants 2. Younger than 1 month of age (ie, neonates)
1. ____ has the fastest clearance of all benzodiazepines. 2. BUT, clearance is significantly reduced in _____ compared with ____.
1. Midazolam 2. Clearance is signifincalt reduced in neonates compared with older children
Anatomical differences of neonates and infants (compared to adults and older children)
1. Proportionally larger head and tongue 2. Narrower nasal passages 3. Anterior and cephalad larynx 4. longer epiglottis 5. Short trachea and neck 6.Weker intercostal muscles & diaphragms 7. More horizontal and pliable ribs & protuberant abdomen 8. Glottis at vertebral level C4 (Adult level is C6)
When is atracurium or cisatracurium preferred in young infants?
For short procedures, because these drugs consistently display short to intermediate duration.
Pediatric VENTILATION factor that affects the administration of anesthetic gas
Greater minute ventilation-to-FRC ratio
Morphine sulfate, particularly in repeated doses, should be used with caution in neonates. Why?
In neonates: 1. Hepatic conjugation is reduced (cytochrome P-450 pathways mature at the end of the neonatal period) 2. Decreased renal clearance of morphine metabolites
Alternate emergency route for intramuscular succinylcholine
Intralingual administration (2 mg/kg in the midline to avoid hematoma formation)
Based on weight, older children require____doses than adults for some neuromuscular blocking agents (eg, atracurium.
Larger
MAC for halogenated agents is ______ in _____ than ____.
MAC is GREATER in INFANTS than neonates and adults.
Population with most VA induced ventilation depression
MORE in infants compared to older children
Are there reportable instances of renal toxicity from inorganic fluoride production during sevo administration to children?
NO!
Useful database for assessing pediatric anesthetic risk.
Pediatric Perioperative Cardiac Arrest (POCA) Registry -Approx 1 million cases since 1994 - Investigate cardiac arrests or death during the administration of or recovery from anesthesia
For neonates and infants- What cardiac output variant is fixed? Why? Effects on CO?
Cardiac stroke volume is relatively fixed by noncompliant and immature left ventricle. This causes cardiac output to be very sensitive to changes in heart rate
Positive airway effects of sevo and halo
Compared to other VA, these agents are LESS likely to: 1. Irritate airway 2. Cause breath holding or largyngospasm during induction
Most common equipment-related mechanisms leading to a cardiac arrest
Complication related to attempted central venous catheterization (eg, pneumothorax, hemothorax, or cardiac tamponade).
Narrowest point of pediatric airway
Cricoid cartilage (until 5 years old)
How does ketamine affect neonates and infants?
Doesn't affect them as much! - Neonates and infants may be more resistant to ketamine's hypnotic effects - Require sightly higher doses (but the doses "differences" are within the range of error in studies) Sidenote: pharmacokinetics not significantly different than adults
What occurs during neonatal/infant inspiration and expiration.
During inspiration, chest wall collapses. During expiration, decrease in FRC.
Preoperative problems caused by hypothermia
Even mild degrees of hypothermia can cause: - Delayed awakening from anesthesia - Cardiac instability - Respiratory depression r/t increased PVR - Altered response to anesthetics & NMBs
True/False: Muscle relaxants are more commonly used during induction of anesthesia in pediatric than in adult patients.
FALSE!!! - Less commonly used - In peds: LMA or ETT is usually placed after a sevo inhalation induction, placement of an intravenous catheter, and administration of various combinations of propofol, opioids, or lidocaine
Neonates have _______ incidence of GERD
Increased
What age group has greater risk of anesthetic morbidity and mortality?
Infants. Risk is generally inversely proportional to age
After weight-adjusted dosing, why do infants and young children require larger doses of "propofol?"
Larger Vd compared to adults
How does a decrease in FRC affect pediatric population?
Limits oxygen reserve during periods of apnea (ex. intubation attempts) and predisposes them to atelectasis & hypoxemia.
Age related changes in vital signs
NEONATE: 40RR, 140 HR, 65/40 12 month: 30RR, 120 HR, 95/65 3 years: 25RR, 100HR, 95/65 12 years: 20RR, 80HR, 110/80
Neonatal heat production mechanisms How are they affected by anesthesia?
Neonatal heat production via non-shivering thermogenesis: 1. Metabolism of brown fat 2. Shifting of hepatic oxidative phosphorylation to a thermogenic pathway - Metabolism of brown fat is severely limited in premature, sick neonates bc deficient fat stores - VAs INHIBIT thermogenesis in brown adipocytes
Compare peds "alveolar ventilation and FRC" to adults
Neonates, infants, and young children have: 1. relatively GREATER alveolar ventilation 2. REDUCED FRC compared to older children and adults (even after weight adjustment)
Define neonate, infant, toddler, and young children by months of age
Neonates: 0-1 month Infants: 1-12 month Toddlers: 12-24 months Young children: 2-12 years
Pediatric PERFUSION factor that affects the administration of anesthetic gas
Relatively greater blood flow to vessel-rich organs
Remifentanil clearance is ______ in neonates and infants; but, elimination half-life is _____ compared with adults.
Remifentanil clearance is INCREASED in neonates and infants; but, elimination half-life is UNALTERD compared with adults.
What group of pediatric pts are at greater risk for bradycardia that can lead to hypotension, asystole, and intraoperative death?
Sick infants undergoing during emergency or prolonged procedures
Excluding succinylcholine and cisatracurium... - Infants require _____ muscle relaxant doses than older children.
Significantly smaller
Specific antagonist for rocuronium and vecuronium (still not released in US)
Sugammadex
How does total body water (TBW) change throughout development?
TBW decreased while fat and muscle content increase with age.
Succinylcholine is avoided for routine, elective paralysis for intubation in children and adolescents.
True
Although the basal HR of neonates & infants is greater than adults- what can cause bradycardia and profound reductions in cardiac output?
activation of PARAsympathetic nervous system, anesthetic overdose, or hypoxia can quickly trigger bradycardia → profound reductions in cardiac output
What adverse CV effects are less common with sevoflurane than halothane
cardiovascular depression, bradycardia, and arrhythmias
Neonates and infants have _____ rib structure that makes their ____.
cartilaginous rib structure that makes their chest wall very compliant.
Neonates and infants have fewer and smaller ____ that reduces ______
fewer and smaller alveoli that REDUCES lung compliance
Combination of midazolam and fentanyl can cause ______ in patients of all ages.
hypotension
How do the characteristic anatomical changes of neonates and infants affect their breathing?
obligate nasal breathers (until 5 months of age)
Regarding peds, muscle relaxant with the fastest onset of action
succinylcholine (1-1.5 mg/kg) has the fastest onset in adults and children
