PEDIATRIC ANESTHETIC CONSIDERATIONS

KIDS ARE NOT SMALL ADULTS

Respiratory System Anatomy… Tongue relatively large Tongue relatively large Larynx more cephalic and anterior Larynx more cephalic and anterior  C 3-4 in child  C 4-5 in adult  Epiglottis long and stiff  Protrudes posterior at 45 o

Respiratory System Anatomy… Narrowest diameter upper airway at cricoid ring (glottis in adult) Narrowest diameter upper airway at cricoid ring (glottis in adult)  Susceptible to airway obstruction Trachea short—4-5.7cm vs. 6-8cm Trachea short—4-5.7cm vs. 6-8cm Equidistant bronchi from trachea— increased chance of endobronchial intubation Equidistant bronchi from trachea— increased chance of endobronchial intubation Lung alveoli—20 mil at birth, 300 mil age 8 Lung alveoli—20 mil at birth, 300 mil age 8

Respiratory Physiology… Alveolar ventilation: O 2 requirement Alveolar ventilation: O 2 requirement  Infant: cc/kg/min  Adult: 60cc/kg/min Increase in Va 2 o increased metabolic rate in infant Increase in Va 2 o increased metabolic rate in infant FRC (functional residual capacity) FRC (functional residual capacity) exp. reserve vol. + residual vol. exp. reserve vol. + residual vol.

Respiratory Physiology… FRC— FRC—  acts as a buffer to maintain PaO 2 during inspiration and expiration  smaller reserve  less O 2 during apnea Va/FRC (adult) = 1.5/1 Va/FRC (adult) = 1.5/1 Va/FRC (infant) = 5/1 Va/FRC (infant) = 5/1

Respiratory Physiology… Lung mechanics Lung mechanics  Increased resistance 2 o narrow nasal passage  Resp. rate increased (24-30 vs. 20) Oxygen transport (left shift) Oxygen transport (left shift)  Incr. affinity of hemoglobin for O 2  Favors uptake not unload  Less O 2 available to tissues, therefore increased HR and CO necessary

Cardiovascular Anatomy & Physiology… Ventricle in infant Ventricle in infant  Right > Left (size and thickness)  Less compliant Pulse rate is the major determinant of CO in infant Pulse rate is the major determinant of CO in infant  New born—130; adult—77 Sinus dysrhythmia common Sinus dysrhythmia common BP; infant—70/43, adult—122/80 BP; infant—70/43, adult—122/80

Cardiovascular Anatomy & Physiology… Response to hypoxia Response to hypoxia  Metab. demand for O % > adult  Va/FRC is high (5:1)  Hypoxemia can develop rapidly  Bradycardia is always initial response to hypoxia  Treat unexplained bradycardia immediately with O 2

Pediatric Pharmacology… Brain, heart, liver, and kidneys = 18% of body weight in infant vs. 5% adult Brain, heart, liver, and kidneys = 18% of body weight in infant vs. 5% adult  Larger fraction of drug distributed to these organs vs. muscle and fat Infants have less plasma protein conc. Infants have less plasma protein conc. More perm. BBB More perm. BBB Hepatic enzymes—inactive/immature Hepatic enzymes—inactive/immature GF less in infant—slower elimination of drugs and metabolites GF less in infant—slower elimination of drugs and metabolites

Pediatric Sedation… ASA status—I’s and II’s ASA status—I’s and II’s Risk factors for pediatric sedation Risk factors for pediatric sedation  Age—the younger the patient the greater the risk  Respiratory arrest is the greatest liability Rule of thumb “adults will have a cardiac arrest, children will have a respiratory arrest” Rule of thumb “adults will have a cardiac arrest, children will have a respiratory arrest”

Evaluation of Physical Risks During Sedation… History History  Syndrome associated with difficult airway?  Does the child snore at night?  Most crucial question in history  Accurate predictor of obstruction  Most common etiology is hypertrophy of adenoids and tonsils Problems with emergency airwayProblems with emergency airway

Evaluation of Physical Risks During Sedation… History History  Previous surgeries and anesthetics  Very good indicator of success/failure Physical exam Physical exam  Differences in child’s airway  Kids are smaller Smaller mouthsSmaller mouths Mallampati evaluationMallampati evaluation

Evaluation of Physical Risks During Sedation… Physical exam Physical exam  Disproportionate sized features  Relatively large epiglottis  Floppier epiglottis  Narrowest part of airway is subglottic  Glottis is prone to laryngospasm during sedation  Thyromental distance

Evaluation of Physical Risks During Sedation… Physical exam Physical exam  URI  Most children have 2-10 viral respiratory tract infections per year Is a snotty nose just a cold or day 1 of a viral infection?Is a snotty nose just a cold or day 1 of a viral infection?  More prone to laryngospasm, bronchospasm, coughing, mucus plugging

Factors Influencing the Outcome of Sedation The best success rate with children is % (20-40% failure) The best success rate with children is % (20-40% failure) Age Age Cognitive development Cognitive development Degree of expression of fear Degree of expression of fear  Flight response of crying/screaming Child temperament Child temperament

SEDATION PHARMACOLOGY Sedative Hypnotics Sedative Hypnotics Phenothiazines/Antihistamines Phenothiazines/Antihistamines Benzodiazepines Benzodiazepines Narcotics Narcotics Barbiturates Barbiturates Reversal Agents Reversal Agents

SEDATIVE HYPNOTICS CHLORAL HYDRATE

“Classic” pediatric sedative “Classic” pediatric sedative Moderately effective sedative/hypnotic Moderately effective sedative/hypnotic Mild depressant of the central nervous system Mild depressant of the central nervous system Trichloroethanol is the active metabolite Trichloroethanol is the active metabolite

CHLORAL HYDRATE Often combined with other agents Often combined with other agents No analgesic properties No analgesic properties No reversal agent No reversal agent May cause GI irritation, respiratory depression, hypotension and paradoxical excitement May cause GI irritation, respiratory depression, hypotension and paradoxical excitement Hepatic elimination Hepatic elimination

CHLORAL HYDRATE Side effects: Side effects:  Nausea  Vomiting  Diarrhea  Flatulence  disorientation  excitement  rash

CHLORAL HYDRATE DOSE DOSE  mg/kg PO ONSET ONSET  minutes PO PEAK EFFECT PEAK EFFECT  1-2 hours PO

CHLORAL HYDRATE WORKING TIME WORKING TIME  minutes DURATION DURATION  7-10 hours

ANTIHISTAMINES DIPHENHDRAMINEHYDROXYZINE

DIPHENHYDRAMINE Trade name: Benadryl Trade name: Benadryl H 1 receptor antagonist with anticholinergic and sedative effects H 1 receptor antagonist with anticholinergic and sedative effects Partially inhibits vasodilator effect of histamine on peripheral vascular smooth muscle Partially inhibits vasodilator effect of histamine on peripheral vascular smooth muscle

DIPHENHYDRAMINE USES: USES:  Antiemetic  Antivertigo  Treatment of allergic reactions  Treatment of extrapyramidal reactions

DIPHENHYDRAMINE DOSE: DOSE:  0.5 to 1 mg/kg q6h (25-50 mg) PO  maximum 300 mg/day ONSET: ONSET:  <15 minutes PO

DIPHENHYDRAMINE PEAK EFFECT: PEAK EFFECT:  2 hours PO DURATION: DURATION:  < 7 hours PO

DIPHENHYDRAMINE Children are at an increased risk of paradoxic CNS stimulant effects such as restlessness, insomnia, tremors, euphoria and seizures

HYDROXYZINE Vistaril/Atarax Vistaril/Atarax Antihistamine Antihistamine Anxiolytic Anxiolytic Sedative Sedative Hepatic elimination Hepatic elimination

HYDROXYZINE DOSE: DOSE:  mg/kg PO ONSET: ONSET:  minutes PO PEAK EFFECT: PEAK EFFECT:  minutes PO DURATION: DURATION:  2- 4 hours

PHENOTHIAZINES PROMETHAZINE

PROMETHAZINE Phenothiazine derivative Phenothiazine derivative H 1 receptor antagonist with good sedative, antiemetic, anticholinergic and antimotion sickness effects H 1 receptor antagonist with good sedative, antiemetic, anticholinergic and antimotion sickness effects Hepatic elimination Hepatic elimination

PROMETHAZINE Uses: Uses:  Antiemetic  Adjunct to other sedatives (antiemetic and co-sedative)  Used alone for mild sedation or to control gagging

PROMETHAZINE DOSE: DOSE:  1 mg/kg PO ONSET: ONSET:  minutes PO PEAK EFFECT: PEAK EFFECT:  <2 hours PO DURATION: DURATION:  2-8 hours PO

PROMETHAZINE Extrapyramidal reactions Extrapyramidal reactions Use with caution in children with severe cardiovascular or liver disease Use with caution in children with severe cardiovascular or liver disease

BENZODIAZEPINES DIAZEPAMMIDAZOLAM

DIAZEPAM DOSE: DOSE:  mg/kg PO ONSET: ONSET:  30 minutes to 1 hour PO PEAK EFFECT: PEAK EFFECT:  1 hour PO DURATION: DURATION:  hours PO

MIDAZOLAM Trade name: Versed Trade name: Versed Short acting Short acting Water soluble Water soluble Greater amnesia than with diazepam Greater amnesia than with diazepam Dose dependent respiratory and circulatory depression Dose dependent respiratory and circulatory depression Four times more potent than diazepam Four times more potent than diazepam

MIDAZOLAM DOSE: DOSE:  0.5 mg/kg PO ONSET: ONSET:  minutes PO PEAK EFFECT: PEAK EFFECT:  30 minutes PO DURATION: DURATION:  2-6 hours PO

MIDAZOLAM - INTRANASAL Not permitted with Level 1 Not permitted with Level 1 Burning of the nasal mucosa is a major drawback Burning of the nasal mucosa is a major drawback Need to make sure that the drug is absorbed through the nasal mucosa and not swallowed Need to make sure that the drug is absorbed through the nasal mucosa and not swallowed

FLUMAZENIL Trade Name: Romazicon Trade Name: Romazicon Competes with benzodiazepines for the GABA/benzodiazepine receptor Competes with benzodiazepines for the GABA/benzodiazepine receptor Has a much shorter duration of action than most of the benzodiazepines Has a much shorter duration of action than most of the benzodiazepines Used as a reversal agent for benzodiazepine agonists Used as a reversal agent for benzodiazepine agonists

FLUMAZENIL DOSE: DOSE:  IV/IM 0.1 mg or 3mcg/kg (max dose is 1 mg) ONSET: ONSET:  minutes IV PEAK EFFECT: PEAK EFFECT:  minutes IV DURATION: DURATION:  minutes IV

FLUMAZENIL Precautions Precautions  May be associated with seizures in high risk patients.  Patient may become re-sedated so need to monitor patient.  Can cause confusion and agitation

NARCOTICS MEPERIDINE

MEPERIDINE DOSE: DOSE:  1-2 mg/kg PO ONSET: ONSET:  minutes PO PEAK EFFECT PEAK EFFECT  <1 hour PO DURATION DURATION  hours PO

MEPERIDINE Do not use in patients taking MAO inhibitors Do not use in patients taking MAO inhibitors Can cause abnormal behavior or dysphoria Can cause abnormal behavior or dysphoria Use with caution in patients who are high risk or hypovolemic Use with caution in patients who are high risk or hypovolemic

NALOXONE Trade Name: Narcan Trade Name: Narcan Pure opioid antagonist Pure opioid antagonist Competitively inhibits opiates at the mu, delta, and kappa receptor sites Competitively inhibits opiates at the mu, delta, and kappa receptor sites Reverses respiratory depression, sedation, hypotension and analgesia Reverses respiratory depression, sedation, hypotension and analgesia No pharmacologic effects in absence of narcotics No pharmacologic effects in absence of narcotics

NALOXONE DOSE: DOSE:  0.01 mg/kg IV/IM/SC (titrate to response) ONSET: ONSET:  minutes IV,  minutes IM/SC PEAK EFFECT: PEAK EFFECT:  minutes IV/IM/SC DURATION: DURATION:  hours IV/IM/SC

NALOXONE Abrupt reversal may cause nausea, vomiting, diaphoresis, tachycardia, hypertension, pulmonary edema Abrupt reversal may cause nausea, vomiting, diaphoresis, tachycardia, hypertension, pulmonary edema Careful monitoring needed because duration of action of opiates may be longer than that of naloxone Careful monitoring needed because duration of action of opiates may be longer than that of naloxone