当前位置: 首页 > >

哈尔滨医科学临床麻醉学课件小儿麻醉 2

发布时间:

Pediatric Anesthesia
Department of anesthesiology Cui Xiao Guang

The provision of safe anesthesia for pediatric patients depends on a clear understanding of the physiologic, pharmacologic, and psychological differences between children and adults.

? Neonates: 0–1 months ? Infants: 1–12 months ? Toddlers: 1–3 years ? small children: 4–12 years

DEVELOPMENTAL PHYSIOLOGY OF THE INFANT

The pulmonary system 1
? The relatively large size of the infant's tongue ? The larynx is located higher in the neck ? The epiglottis is shaped differently, being short
and stubby ? The vocal cords are angled ? The infant larynx is funnel shaped, the narrowest
portion occurring at the cricoid cartilage: uncuffed endotracheal tubes; patients younger than 6 years.

The pulmonary system 2
? Alveoli increase in number and size until the child is approximately 8 years old.
? Functional residural capacity (FRC): the same with adult; induction and palinesthesia of anesthesia is rapid
? A-aDO2 is larger: functional airway closure ? Limits oxygen reserves: hypoxemia. ? The work of breathing: (In premature infants)
three times of adults, increased by cold stress or some degree of airway obstruction. RR: two times of adults

The pulmonary system 3
? Tidal volume(VT) is little; physiological dead space is 30% of VT
? Airway resistance increasing: secretion, upper airway infection
? Diaphragmatic and intercostal muscles do not achieve the adult configuration of type I muscle fibers until the child 2 years old: apnea or carbon dioxide retention and respiratory failure.
? Infants have often been described as obligate nasal breathers: <5 months of age.

The Cardiovascular System1
? In uterus: foramen ovale, ductus arteriosus (right→left) ? At birth: the fetal circulation becomes an adult-type
circulation.-- transitional circulation ? Prolonged transitional circulation:
prematurity, infection, acidosis, pulmonary disease resulting in hypercarbia or
hypoxemia (aspiration of meconium), hypothermia, congenital heart disease.

The Cardiovascular System2
? The myocardial structure of the heart is less developed, produce less compliant ventricles
? This developmental myocardial immaturity: sensitivity to volume loading, poor tolerance of increased afterload, heart rate-dependent cardiac output.

The Cardiovascular System3
? Bradycardia and profound reductions in cardiac output : activation of the parasympathetic nervous system hypoxia anesthetic overdose
? The sympathetic nervous system and baroreceptor reflexes are not fully mature.

The Kidneys
? Renal function is markedly diminished in neonates and further diminished in preterm babies because of low perfusion pressure and immature glomerular and tubular function.
? Nearly complete maturation: approximately 20 weeks after birth
? Complete maturation :about 2 years of age ? dehydration

The Liver 1
? The functional maturity of the liver is somewhat incomplete.
? Most enzyme systems for drug metabolism are developed but not yet induced (stimulated) by the drugs that they metabolize.
? Jaundice: decreased bilirubin breakdown

The Liver 2
? A premature infant's liver has minimal glycogen stores and is unable to handle large protein loads: hypoglycemia acidemia failure to gain weight when the diet contains too much protein.
? The lower the albumin value, the less protein binding and the greater the levels of free drug.

The Gastrointestinal System
? At birth, gastric pH is alkalotic; after birth the second day, pH is in the normal
? The ability to coordinate swallowing with respiration does not fully mature until the infant is 4 to 5 months of age: gastroesophageal reflux
? If a developmental problem occurs within the gastrointestinal system, symptoms will occur within 24 to 36 hours of birth. Upper --vomiting and regurgitation ; Lower --abdominal distention and failure to pass meconium.

Thermoregulation
? Thin skin, low fat content, and a higher surface relative to weight allow greater heat loss to the environment in neonates. –保温
? Thermogenesis: shivering and nonshivering (metabolism of brown fat).
? General anesthesia affects the metabolism of brown fat.--hypothermia
? Hypothermia: delayed awakening from anesthesia, cardiac irritability, respiratory depression, increased pulmonary vascular resistance, and altered drug responses.

Central nervous system
? More fat is in the central nervous system ? Permeability of Blood brain barrier is great:
opioid—decrement bilirubin—kernicterus ? MAC↑

Pharmacological Differences
? The response to medications: body composition, protein binding, body temperature, distribution of cardiac output, functional maturity of the heart, maturation of the blood-brain barrier, the relative size (as well as functional maturity) of the liver and kidneys, the presence or absence of congenital malformations

Alterations in body composition have several clinical implications for neonates
? a drug that is water soluble: larger volume of distribution and larger initial
dose (e.g., succinylcholine); ? less fat: a drug that depends on redistribution into
fat for termination of its action will have a longer clinical effect (e.g., thiopental); ? a drug that redistributes into muscle:
longer clinical effect (e.g., fentanyl); ? Others

Inhaled Anesthetics
? Nitrous oxide ? Halothane ? Enflurane ? Isoflurane ? Sevoflurane ? Desflurane

Nitrous oxide
? lower dissolubility: 含气间隙的体积增大
neonate: pneumothorax, emphysema congenital diaphragmatic hernia or
acromphalus necrotic enteritis

Enflurane
? In the introduction of anesthesia: breathholding, cough, laryngospasm
? After anesthesia: seizure-like activity

Isoflurane
? Introduction of anesthesia and analepsia: rapid
? respiratory depression, coughing, laryngospasm ? After extubate:
incidence of laryngospasm< enflurane

Sevoflurane
? induction is slightly more rapid ? anesthesia is steady ? respiratory tract irritation: small ? the production of toxic metabolites as a result of
interaction with the carbon dioxide absorbent must be considered . ? Introduction and short anesthesia: sevoflurane ? Prolonged anesthesia: elect other anesthetics

Desflurane
? respiratory tract irritation: strong laryngospasm (?50%) during the gaseous induction of anesthesia
? Concern for the potential for carbon monoxide poisoning
? Hypertension and tachycardia

Intravenous anesthetics
? Ketamine ? Thiopental ? Propofol ? Etomidate ? Benzodiazepines: diazepam, midazolam ? Opioids: morphine, fentanyl, alfentanil,
sufentanil, remifentanil

Ketamine 1
? Routes of administration: intravenous: 2 mg/kg intramuscular: 5 to 10 mg/kg rectally: 10 mg/kg orally: 6 to 10 mg/kg intranasally: 3 to 6 mg/kg

Ketamine 2
? Undesirable side effects: increased production of secretions vomiting postoperative "dreaming" hallucinations apnea laryngospasm increased intracranial pressure increased intraocular pressure

Thiopental
? Intravenous: 2.5% thiopental, 5 to 6 mg/kg ? Termination of effect occurs through
redistribution of the drug into muscle and fat ? Thiopental should be used in reduced doses
(2 to 4 mg/kg) in children who have low fat stores, such as neonates or malnourished infants.

Propofol
? Propofol is highly lipophilic and promptly distributes into and out of vessel-rich organs.
? Short duration: rapid redistribution, hepatic glucuronidation, and high renal clearance.
? Dose: 1-2 mg/kg; higher in infants younger than 2 years
? Pain: lidocaine, ketamine

Etomidate
? Pain, bucking. ? No commonly used

Diazepam
? 0.1-0.3 mg/kg, orally provides; ? may also be administered rectally ? has an extremely long half-life in neonates
(80 hours) ? Contraindicat: until the infant is 6 months of
age or until hepatic metabolic pathways have matured.

Midazolam
? Midazolam is water soluble and therefore not usually painful on intravenous administration.
? Administration: intravenous: 0.05 to 0.08 mg/kg, maximum of 0.8mg (weight<10 kg) intramuscular: 0.1 to 0.15 mg/kg, maximum of 7.5 mg oral: 0.25 to 1.0 mg/kg, maximum of 20 mg rectal: 0.75 to 1.0 mg/kg, maximum of 20 mg nasal: 0.2 mg/kg sublingual: 0.2 mg/kg

Fentanyl
? Fentanyl: rapid onset; brief duration of action
? Dosage: patient age, the surgical procedure, the health of the patient, and the use of anesthetic adjuvants.

Alfentanil
? Eliminate: more rapidly than fentanyl ? Pharmacokinetics: independent of dose ? Margin of safety: the greater the
administered dose, the greater the elimination. ? Clearance of alfentanil may be increased in children in comparison to adults

Sufentanil
? use primarily for cardiac anesthesia ? Children are able to clear sufentanil more
rapidly than adults do. ? Bradycardia and asystole: when a vagolytic
drug was not administered simultaneously.

Remifentanil
? Often use in pediatric anesthesia

Muscle Relaxants
? Depolarizing Muscle Relaxant: succinylcholine
? Nondepolarizing Muscle Relaxants : Pancuronium, Vecuronium, Atracurium , Pipecuronium, Rocuronium

Succinylcholine
? the dose required for intravenous administration in infants (2.0 mg/kg) is approximately twice that for older patients
? Intravenous administration of atropine before the first dose of succinylcholine may reduce the incidence of arrhythmias

Pancuronium
? useful for longer procedures ? no histamine is released ? The disadvantage : tachycardia ? Administration: 0.1 mg/kg

Vecuronium
? Vecuronium is useful for shorter procedures in infants and children
? no histamine is released ? Administration: 0.1mg/kg ? Duration : 20 – 30min

Atracurium
? Useful for shorter procedures in infants and children
? Particularly useful in newborns and patients with liver or renal disease. Why?
? Administration:0.3 – 0.5 mg/kg ? Duration : >30 min

Rocuronium
? Rocuronium has a clinical profile similar to that of vecuronium and atracurium
? Advantage: can be administered intramuscularly

Preoperative Preparation(1)
? The preoperative visit and preparation of the child for surgery are more important than the choice of premedication
? chart review, physical examination, and furnishing of information regarding the approximate time and length of surgery

Preoperative Preparation(2)
? evaluates the medical condition of the child, the needs of the planned surgical procedure, and the psychological makeup of the patient and family
? explain in great detail what the child and family can expect and what will be done to ensure the utmost safety

Fasting
? milk and solids: before 6 hours ? clear fluids up to 2-3 hours before induction ? Infants who are breast-fed may have their
last breast milk 4 hours before anesthetic induction

Premedication (1)
? The need for premedication must be individualized according to the underlying medical conditions, the length of surgery, the desired induction of anesthesia, and the psychological makeup of the child and family

Premeditation (2)
? A premedication is not normally necessary for the usual 6-month-old child but is warranted for a 10- to 12-month-old who is afraid to be separated from parents
? Oral midazolam is the most commonly administered premedication. An oral dose of 0.25 to 0.33 mg/kg (maximum, 20 mg)

Premeditation (3)
? Premedications may be administered orally, intramuscularly, intravenously, rectally, sublingually, or nasally
? Although most of these routes are effective and reliable, each has drawbacks

Merits and drawbacks
? Oral or sublingual : not hurt but may have a slow onset or be spit out
? Intramuscular and Intravenous : painful and may result in a sterile abscess
? Rectal : make the patient feel uncomfortable ? Nasal : irritating, although absorption is
rapid

Premeditation (4)
? Midrange doses of intramuscular ketamine (3 to 5 mg/kg) combined with atropine (0.02 mg/kg) and midazolam (0.05 mg/kg) will result in a deeply sedated patient
? Higher doses of intramuscular ketamine (up to 10 mg/kg) combined with atropine and midazolam may be administered to patients with anticipated difficult venous access to provide better conditions for insertion of the intravenous line

Induction of Anesthesia
The method of inducing anesthesia is determined by a number of factors: ◆ the medical condition of the patient, ◆ the surgical procedure, ◆ the level of anxiety of the child, ◆ the ability to cooperate and communicate (because of age, developmental delay, language barrier), ◆ the presence or absence of a full stomach, and other factors

Rectal Induction of Anesthesia
? Rectal administration of 10% methohexital reliably induces anesthesia within 8 to 10 minutes in 85% of young children and toddlers
? The main advantage: the child falls asleep in the parent‘s arms, separates atraumatically from the parents.
? The main disadvantage : drug absorption can be either markedly delayed or very rapid

Intramuscular Induction of Anesthesia
? Many medications, such as ketamine (2 to 10 mg/kg combined with atropine and midazolam), or midazolam alone (0.15 to 0.2 mg/kg), are administered intramuscularly for premedication or induction of anesthesia
? The main advantage : reliability
? the main disadvantage : painful

Intravenous Induction of Anesthesia
? Intravenous induction of anesthesia is the most reliable and rapid technique
? Intravenous induction may be preferable when induction by mask is contraindicated (e.g., in the presence of a full stomach)
? The main disadvantage : painful and threatening for the child

The Difficult Airway
? Difficult intubation: maintain spontaneous respirations; placing a stylet in the endotracheal tube; fiberoptic brochoscope.

The Child with Stridor (1)
? expiratory stridor: intrathoracic airway obstruction ,
. such as: bronchiolitis, asthma, intrathoracic foreign body
? inspiratory stridor : extrathoracic upper airway obstruction , such as: epiglottitis, laryngotracheobronchitis, laryngeal foreign body

?
When a child has upper airway obstruction (as in epiglottitis, laryngotracheobronchitis, and extrathoracic foreign body) (shaded area) and struggles to breathe against this obstruction, dynamic collapse of the trachea increases

The Child with Stridor (2)
? maintaining spontaneous respiration ? Induction of anesthesia with halothane or
sevoflurane in oxygen by mask ? With the patient lightly anesthetized and after
infiltration of local anesthetic, an intravenous line is inserted ? If stridor worsens or mild laryngospasm occurs, the pop-off valve is closed sufficiently to develop 10 to 15 cm H2 O of positive end-expiratory airway pressure.

When a child has upper airway obstruction caused by laryngospasm (A) or mechanical obstruction (B), the application of approximately 10 cm H2 O of positive endexpiratory pressure (PEEP) during spontaneous breathing often relieves the obstruction. That is, PEEP helps keep the vocal cords apart (A) and the airway open (B, broken lines)

The Child with Stridor (3)
? A child with laryngotracheobronchitis or epiglottitis usually requires an uncuffed endotracheal tube that is 0.5 to 1.0 mm (internal diameter) smaller than normal
? total airway obstruction occur and mask ventilation or endotracheal intubation not be possible ----- tracheotomy

The Child with a Full Stomach 1
? Children with a full stomach must be treated the same as adults with a full stomach
? child may be uncooperative and refuse to breathe oxygen before induction of anesthesia

The Child with a Full Stomach 2
? enrich the environment with a high flow of oxygen
? Additional equipment : two suction catheters , two appropriately sized laryngoscopes
? While the child is breathing oxygen, atropine (0.02 mg/kg, up to 0.6 mg) may be administered intravenously
? cricoid cartilage

Endotracheal Tubes
? For most children, the proper-size endotracheal tube and the proper distance of insertion relative to the alveolar ridge of the mandible or maxilla are moderately constant.

? Tube diameter (in mm) = age/4+4 ? Infant 3 months to 1 year: 10 cm ? Child 1 year: 11 cm ? Child 2 year: 12 cm ? Length of tube (in cm) = age/2+12 ? the tip of the endotracheal tube should pass
only 1–2 cm beyond an infant's glottis.

The Dedicated Pediatric Equipment
? Rendell-Baker-Soucek mask ? Ayres T tube ? Jackson Rees improved type of Ayres T tube:
have reservoir bag; airflow: [1000 ml+ 100 ml×BW(kg)] /min ( weight<10kg)
? Laryngeal mask

Epidural anesthesia
Epidural block procedures: sacral intervertebral approach (1), lumbar approach (i.e., midline route) (2), and thoracic approach (i.e., midline route) (3).

Local Anesthetics
? 0.8%~1.5% lidocaine ? 0.1%~0.2% tetracaine ? 0.25%~0.5% bupivacaine ? 0.25%~0.5% ropivacaine

Caudal anesthesia
Caudal block procedure. A, Insertion of the needle at right angles to the skin in relation to the coccyx (1) and the sacrococcygeal membrane (2). B, Cephalad redirection of the needle after piercing the sacrococcygeal membrane.

Spinal anesthesia

Local Anesthetic Plain tetracaine (1%) Dose (mg/kg) Volume (mL/kg) Duration (min) Tetracaine (1%) with epinephrine Dose (mg/kg) Volume (mL/kg) Duration (min) Bupivacaine (0.5%) Dose (mg/kg) Volume (mL/kg) Duration (min)

0–5 kg
0.5 0.05 75
0.5 0.05 120
0.5 0.1 65–75

5–15 kg
0.4 0.04 80
0.4 0.04 120
0.4 0.08 70–80

*
>15 kg
0.3 0.03 85
0.3 0.03 125
0.3 0.06 75–85

Axillary approaches
Axillary approaches to the brachial plexus: classic approach (A) and transcoracobrachialis approach (B), indicating the pectoralis major muscle (1), axillary artery (2), and coracobrachialis muscle (3).

Dose
-

Volumes for Single -Shot Procedures by Weight

Block

2–10 kg (mL/kg)

15 kg (mL)

20 kg (mL)

25 kg (mL)

30 kg (mL)

40 kg (mL)

50 kg (mL)

60 > 70 kg kg (mL) (mL)

Para scalene

1

12.5

15

17.5

20

22.5

25

27.5 30

Interscalene

1

12.5

15

17.5

20

22.5

25

27.5 30

Peri -subclavian 1

12.5

15

17.5

20

22.5

25

27.5 30

Axillary

0.5

7.5

10

10

12.5

15

17.5

20 25

Coracoid

0.5

7.5

10

10

12.5

15

17.5

20 25

Lumbar plexus * 1

15

17.5

20

20

20

20

20 20

Femoral

0.7

8

12

15

15

17.5

20

22.5 25

Fascia iliaca

1

12.5

15

17.5

20

22.5

25

27.5 30

Proximal sciatic 1

15

17.5

20

22 .5

25

27.5

30 32–35

Popliteal fossa 0.3

4

5

6

7.5

10

10

10 10

Monitoring
? The complexity of monitoring applied to pediatric patients must be consistent with the severity of the underlying medical condition and the planned surgical procedure.

Routine Monitoring
? precordial stethoscope, ↘ esophageal stethoscope,
? blood pressure cuff, ? electrocardiogram, ? temperature probe, ? pulse oximeter, ? end-tidal carbon dioxide monitor

Invasive Monitoring
? Arterial catheter ? Central venous catheter

Intravenous Fluid
? the high metabolic demands ? the high ratio of body surface area
to weight.

The basis for calculating

-

Weight (kg) Hourly Fluid Requirements (mL) 24-hr Fluid Requirements (mL)

<10

4 mL/kg

100 mL/kg

11-20

40 mL + 2 mL/kg > 10 kg

1000 mL + 50 mL/kg > 10 kg

>20

60 mL + 1 mL/kg > 20 kg

1500 mL + 20 mL/kg > 20 kg

Other
? Fluid deficits, ? Third-space losses, ? Modifications because of
hypothermia or hyperthermia, ? Requirements caused by unusual
metabolic demands

? 50% of the resulting deficit is replaced in the first hour and 25% in each of the next 2 hours.
? Loss with the surgical procedure:
from 1 mL/kg/hr for a minor surgical procedure to as much as 15 mL/kg/hr for major abdominal procedures.

The composition of the
intravenous fluid
? Child with greater hypoxic brain damage : high blood glucose levels, recommend not using glucose-containing solutions routinely, especially for brief operative procedures
? All deficits and third-space losses: A balanced salt solution (e.g., lactated Ringer's solution)
? Maintenance fluid: 5% dextrose in 0.45% normal saline minimize the chance of hypoglycemia or accidental hyperglycemia

General blood volume
? premature infant : 100 to 120 mL/kg ? full-term infant : 90 mL/kg ? child 3 to 12 months old : 80 mL/kg ? child older than 1 year : 70 mL/kg ? These are merely estimates of blood volume

Simple formula

MABL=

EBV×(Starting hematocrit – Target hematocrit) Starting hematocrit

EBV : estimated blood volume
Target hematocrit : child younger than 3 months --- >35%; child older than 3 months --- 25%-30%

Fluid replacememt and blood transfusion
? Blood loss <1/3 MABL: balanced solution; balanced solution:volume of blood loss= 3:1
? Blood loss >1/3 MABL: colloid; colloid:volume of blood loss = 1:1
? Blood loss >1MABL: blood transfusion;

Volume of PRBCs
(Desired Hct – Present Hct)×EBV×BW (kg) Volume of PRBCs(ml) =
Hematocrit of the PRBCs(~60%)

Fresh Frozen Plasma
? PT>15s or PTT> 60s: Fresh frozen plasma

Platelets
? Thrombocytopenia: <15×109/L idiopathic thrombocytopenic purpura, chemotherapy, infection, disseminated intravascular coagulopathy
? Dilution during massive blood loss: <50×109/L

Postoperative Management
? Extubate ? Laryngospasm ? Bradycardia ? Glossoptosis ? Postoperative analgesia:
>9 years, PCA <9 years, Nurse controlled analgesia(NCA) morphine, 20?g/kg/h, hypodermical injection or IM

Do not deck yourself up with fine clothew , but enrich your mind with profound knowledge
Thank you !




友情链接: