Conference Lectures

 

INHALATIONAL  INDUCTION IN PEDIATRICS : CONS

 

DR. RAVI R.
PROF. AND HOD
DEPT. OF ANAESTHESIOLOGY
J.J.M. MEDICAL COLLEGE,DAVANGERE.

 

INTRODUCTION:
Preparations for induction of anesthesia in infants and children differ considerably from those for adult patients.
There has been an increased use of intravenous anesthesia in pediatrics as a result of improved understanding of pediatric pharmacokinetics and introduction of newer shorter-acting agents.

GOALS OF GENERAL ANESTHESIA:
Rapid Induction
Use the minimal level of anesthetic that will give:
-Analgesia, unconsciousness, amnesia
Minimal depression of cardiovascular system
Rapid recovery.
The method of inducing anesthesia is determined
by a number of factors:
Medical condition of the patient,
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.

ADVERSE EFFECTS OF INHALATIONAL INDUCTION:
RISK OF OVERDOSING:
For all anesthetic agents, MAC is highest at 6 -12 months of age.
There is more rapid uptake and distribution of inhaled anesthetics in children compared to adults because of:
- Increased respiratory rate
- Increased cardiac index
- Greater proportional distribution of cardiac   
output to vessel-rich organs.
Increased MAC requirement in conjunction with rapid uptake of anesthetic makes infants and children very susceptible to anesthetic overdose.

EFFECTS ON RESPIRATION:
All inhalational anesthetics depress respiration in a dose-dependent manner.
Decrease in Tidal volume and response to carbon dioxide.
Increase in respiratory rate as anesthetic concentration increases.

Effects are most pronounced in neonates and  young infants.

 

EFFECTS ON CVS:
Neonates are more sensitive to cardiodepressant effects of inhalational anesthetics than adults.
Infants—Baroreceptors are less mature, so compensatory mechanisms for inhalational anesthetics cannot compensate.
Dose dependent depression of cardiovascular system seen as:
Bradycardia
Hypotension
Depression of myocardial contractility
Cardiac arrest during induction of anesthesia.

 

 

POSTOPERATIVE  AGITATION:
Postoperative agitation or Emergence delirium is common after Sevoflurane, Desflurane and Isoflurane up to 6–8 years of age.
Steps should be taken for prevention and treatment of agitation.
The most evident option would be, to avoid responsible inhalational agents for induction at all, and to use IV agents (e.g. Propofol) instead.

POSTOPERATIVE NAUSEA AND VOMITING:
Use of inhalational agents promotes postoperative vomiting.
Major cause of postoperative discomfort in children and main reason for admission after outpatient surgery.
Intravenous anesthesia is associated with less vomiting in the first 24 hours postoperatively than inhalational anesthetics.
RECOVERY AND POSTOP STAY:
Factors associated with duration of stay in PACU include postoperative pain, PONV and postoperative agitation and delirium.
Fast emergence and short recovery demands minimizing these.
Thus, Intravenous agents give faster recovery and emergence compared to inhalationals.

MALIGNANT HYPERTHERMIA:
An inherited disorder that can be triggered by all volatile anesthetic agents(Except Nitrous oxide).
Intravenous anesthesia is the exclusive option.
Inhalational agents have to be avoided completely.
Use of TIVA, is a must for children who may be susceptible to Malignant Hyperthermia.

COST:
Equipment required for Inhaled anesthesia is costly.
Use of low fresh gas flows maximizes rebreathing of exhaled anesthetic gas and reduces cost, but it provides less control of the level of anesthesia and is not always feasible.

OTHER DISADVANTAGES:
Slow induction and may be rejected on induction   i.e. breath-holding, respiratory irritation.
Claustrophobia associated with inhaled route.
Knowledge of equipment essential.
Hazards associated with compressed gas.
OT and environment pollution.
Difficult to transport for 'field' anesthesia.

PROBLEMS WITH INDIVIDUAL AGENTS:
NITROUS OXIDE:
Can be used only as a supplement to other anesthetics to provide complete anesthesia.
Expands gas-containing spaces, such as intestines, middle ear and pneumothorax.
Lymphocyte depression, testicular damage, defects in spermatogenesis, apoptosis.
Inactivates methionine synthase, a vitamin B12dependent enzyme essential for DNA production.
Injury to blood-forming elements or to central nervous system (Neuropathies).

HALOTHANE:
Depresses cardiovascular function in direct proportion to depth of anesthesia.

 

Cardiac depression manifested as:
-Direct negative inotropic effect on myocardium
-Bradycardia 
-Reduction in peripheral resistance
-Hypotension
-Cardiac arrest.
Sensitizes myocardium to arrhythmogenic properties of epinephrine.
Cardiac arrhythmias, particularly premature ventricular contractions.
At high concentrations, abolishes autoregulation of cerebral blood flow in response to changes in arterial blood pressure.
Depresses neural respiratory drive and increases PCO2 in children .
Spontaneous breathing under halothane increases alveolar dead space and wasted ventilation.
Halothane-associated hepatitis.(Rare)

ISOFLURANE:
Noxious smell.
Respiratory irritant.
Not an effective induction agent due to  greater incidence of Cough and laryngospasm     during induction.
Direct negative inotropic effect on myocardium.
Hypotension due to reduction in peripheral vascular resistance.
Compensatory increase in heart rate.
Depression of minute ventilation and respiratory frequency.
Carbon monoxide poisoning in presence of desiccated soda lime and Baralyme.

 

SEVOFLURANE:
Increased incidence of postanesthesia delirium and emergence agitation.
Likely to cause seizures in patients with a baseline risk for seizures.
EEG and epileptiform activities during inhalational induction in children.
Cardiodepressant activity.
Potent respiratory depressant.
Metabolized by liver, releasing free fluoride ions; risk for renal diabetes insipidus.
Administration for more than two MAC hours and at fresh gas flow rates <2 L/min may be associated with compound A formation, a nephrotoxin leading to proteinuria and glucosuria.
Exothermic reaction with desiccated CO2 absorber Baralyme, producing carbon monoxide and excessive heat can cause ignition and explosions within anesthesia circle systems and tracheobronchial burns.
Expensive.

DESFLURANE:
Pungent odor.
Poor induction agent as highly respiratory irritant.
High incidence of laryngospasm, coughing, secretions, breath holding, and oxyhemoglobin de-saturation when used for induction in children.
Transient hypertension and tachycardia resulting from sympathetic activation.
High incidence of emergence agitation and delirium.
High incidence of postoperative vomiting.
Expensive.
Requires a special heated pressurized vaporizer.
Potential for carbon monoxide poisoning If carbon dioxide absorbent becomes desiccated.

 

Key points supporting the use of TIVA:
Improved quality of emergence from anesthesia.
Reduced postoperative nausea and vomiting.
Rapid onset of action independent from alveolar ventilation.
Can be used in peripheral locations because anesthetic machine and scavenging system not needed.
Independent from airway instrumentation.
Nonpollutant to theatre environment.
Elimination of the mask and its unpleasant odors.

OTHER ADVANTAGES OF TIVA:
Anesthesia for MRI or CT scans and for radiotherapy.
When administration of inhalational agents is not an option, e.g., during transtracheal jet ventilation.
CONCLUSION:
Anesthetic management in pediatrics requires knowledge of pharmacologic and physiologic development for optimum patient management.
TIVA combined with monitoring of the hypnotic state is a very attractive choice nowadays for routine pediatric anesthesia practice.
IV technique allows a peaceful and rapid recovery.
This increases parental satisfaction and is a major step forward with respect to improved quality of care.