Anesthesia, Perioperative Care, and Sedation

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Chapter 70 Anesthesia, Perioperative Care, and Sedation

The primary purpose of general anesthesia is to suppress the conscious perception of, and physiologic response to, noxious stimuli and to render the patient unconscious. Potent drugs are used to blunt physiologic responses to what would otherwise be life-threatening trauma (surgery). Intraoperatively, the anesthesiologist is responsible for providing analgesia as well as physiologic and metabolic stability (see Table 70-1 on the Nelson Textbook of Pediatrics website at image www.expertconsult.com). This responsibility is facilitated by obtaining an adequate preanesthesia history (see Table 70-2 on the Nelson Textbook of Pediatrics website at image www.expertconsult.com). The increased risk of morbidity and mortality in the perioperative period demands the utmost vigilance. The risk is even higher in certain disease states (see Table 70-3 on the Nelson Textbook of Pediatrics website at image www.expertconsult.com).

Table 70-2 THE PREANESTHETIC HISTORY

Child’s previous anesthetic and surgical procedures:

Perinatal problems (especially for infants):

Other major illnesses and hospitalizations

Family history of anesthetic complications, malignant hyperthermia, or pseudocholinesterase deficiency

Respiratory problems:

Cardiac problems:

Gastrointestinal problems:

Exposure to exanthems or potentially infectious pathogens

Neurologic problems:

Hematologic problems:

Renal problems:

Psychosocial considerations:

Gynecologic considerations:

Current medications:

Allergies:

Dental condition (loose or cracked teeth)

When and what the child last ate (especially in emergency procedures)

Table 70-3 SPECIFIC PEDIATRIC DISEASES AND THEIR ANESTHETIC IMPLICATIONS

DISEASE IMPLICATIONS
RESPIRATORY SYSTEM
Asthma Intraoperative bronchospasm that may be severe
Pneumothorax or atelectasis
Optimal preoperative medical management is essential; preoperative steroids may be required
Difficult airway Special equipment and personnel may be required
Should be anticipated in children with dysmorphic features or acute airway obstruction, as in epiglottitis or laryngotracheobronchitis or with an airway foreign body
Patients with Down syndrome may require evaluation of the atlanto-occipital joint
Patients with storage diseases may be at high risk
Bronchopulmonary dysplasia Barotrauma with positive pressure ventilation
Oxygen toxicity, pneumothorax a risk
Cystic fibrosis Airway reactivity, bronchorrhea
Risk of pneumothorax, pulmonary hemorrhage
Atelectasis
Patient should be assessed for cor pulmonale
Sleep apnea Pulmonary hypertension and cor pulmonale must be excluded
Careful postoperative observation for obstruction required
CARDIAC
  Need for antibiotic prophylaxis for bacterial endocarditis
Use of air filters; careful purging of air from the intravenous equipment
Physician must understand the effects of various anesthetics on the hemodynamics of specific lesions
Preload optimization and avoidance of hyperviscous states in cyanotic patients
Possible need for preoperative evaluation of myocardial function and pulmonary vascular resistance
Provide information about pacemaker function and ventricular device function
HEMATOLOGIC
Sickle cell disease Possible need for simple or exchange transfusion based on preoperative hemoglobin concentration and percentage of hemoglobin S
Importance of avoiding acidosis, hypoxemia, hypothermia, dehydration, and hyperviscosity states
Oncology Pulmonary evaluation of patients who have received bleomycin, bis-chloroethyl-nitrosourea, chloroethyl-cyclohexyl-nitrosourea, methotrexate, or radiation to the chest
Avoidance of high oxygen concentration
Cardiac evaluation of patients who have received anthracyclines; risk of severe myocardial depression with volatile agents
Potential for coagulopathy
RHEUMATOLOGIC
  Limited mobility of the temporomandibular joint, cervical spine, arytenoid cartilages
Careful preoperative evaluation required
Possible difficult airway
GASTROINTESTINAL
Esophageal, gastric Potential for reflux and aspiration
Liver High overall morbidity and mortality in patients with hepatic dysfunction
Altered metabolism of some drugs
Potential for coagulopathy
Renal
  Altered electrolyte and acid-base status
Altered clearance of some drugs
Need for preoperative dialysis in selected cases
Succinylcholine to be used with extreme caution and only when the serum potassium level has recently been shown to be normal
NEUROLOGIC
Seizure disorder Avoidance of anesthetics that may lower the threshold
Optimal control ascertained preoperatively
Preoperative serum anticonvulsant measurements
Increased intracranial pressure Avoidance of agents that increase cerebral blood flow
Avoidance of hypercarbia
Neuromuscular disease Avoidance of depolarizing relaxants; at risk for hyperkalemia
Patient may be at risk for malignant hyperthermia
Developmental delay Patient may be uncooperative at induction
Psychiatric Monoamine oxidase inhibitor (or cocaine) may interact with meperidine, resulting in hyperthermia and seizures
Selective serotonin reuptake inhibitors may induce or inhibit various hepatic enzymes that may alter anesthetic drug clearance
Illicit drugs may have adverse effects on cardiorespiratory homeostasis and may potentiate the action of anesthetics
ENDOCRINE
Diabetes Greatest risk is unrecognized intraoperative hypoglycemia; if insulin is administered, intraoperative blood glucose level monitoring needed ; glucose and insulin must be provided, with adjustment for fasting condition and surgical stress
SKIN
Burns Difficult airway
Risk of rhabdomyolysis and hyperkalemia from succinylcholine
Fluid shifts
Bleeding
Coagulopathy
IMMUNOLOGIC
  Retroviral drugs may inhibit benzodiazepine clearance
Immunodeficiency requires careful infection control practices
Cytomegalovirus-negative blood products, irradiation, or leukofiltration may be required
METABOLIC
  Careful assessment of glucose homeostasis in infants

General Anesthesia

Analgesia

Providing analgesia for procedures both in and out of the operating room is a major responsibility and functions within a spectrum of care (Table 70-4). Techniques exist to provide profound pain relief during operative procedures for all patients, including the most critically ill infants. Blunting the physiologic responses to painful stimuli inhibits the stress response and its multiple deleterious physiologic and metabolic consequences. The response to painful and stressful stimuli is a potent stimulus of the systemic inflammatory response syndrome (SIRS), which leads to increased catabolism, physiologic instability, and increased mortality (Chapter 64). Appropriate use of medication, such as fentanyl anesthesia in neonates, reduces the incidence of postoperative bradycardia, hypotension, acidosis, interventricular hemorrhage, coagulation abnormalities, hypoglycemia, and death.

Table 70-4 DEFINITIONS OF ANESTHESIA CARE

MONITORED ANESTHESIA CARE

LIGHT SEDATION

Administration of anxiolysis and/or analgesia that obtunds consciousness but does not obtund normal protective reflexes (cough, gag, swallow, hemodynamic reflexes).

DEEP SEDATION

Sedation that obtunds consciousness and normal protective reflexes or possesses a significant risk of blunting normal protective reflexes (cough, gag, swallow, hemodynamic reflexes).

GENERAL ANESTHESIA

Administration of hypnosis, sedation, and analgesia that results in the loss of normal protective reflexes.

REGIONAL ANESTHESIA

LOCAL ANESTHESIA

NO ANESTHESIOLOGIST

An anesthesiologist will not be involved in the care of the child in any way.

Hypnosis and Amnesia

The blunting of both consciousness (hypnosis) and conscious recall (amnesia) is a crucial feature of pediatric anesthesia care. Awareness of painful, anxiety-provoking, and stressful conditions for children is just as deleterious, physically and psychologically, as the painful procedures themselves. Management is aimed at blunting the fear and emotional response during surgery, painful procedures (bone marrow aspiration, lumbar punctures), or nonpainful but anxiety-provoking procedures (MRI, CT). Many drugs provide anxiolysis, blunting of recall, and amnesia for such events (Table 70-5). Obtundation of consciousness may accompany the provision of analgesia. Hypnotic and sedative agents can induce altered consciousness without producing any analgesia; analgesia and obtunded consciousness are not synonymous. It is also possible to provide analgesia (local, spinal, or epidural analgesia) without obtunding consciousness.

Table 70-5 SELECTED DRUGS USED IN ANESTHESIA

DRUG USES AND IMPLICATIONS
MUSCLE RELAXANTS
Succinylcholine Used to facilitate endotracheal intubation and maintain muscle relaxation in emergency situations; now virtually never given routinely
A depolarizing neuromuscular blocking agent with rapid onset and offset properties
Associated with the development of malignant hyperthermia in susceptible patients
Degraded by plasma cholinesterase, which may be deficient in some individuals; such a deficiency may result in prolonged effect
Fasciculations may be associated with immediate increases in intracranial and intraocular pressures as well as postoperative muscle pain
Pancuronium, vecuronium, cis-atracurium, D-tubocurarine (curare) Nondepolarizing neuromuscular blockers
Have less rapid onset than succinylcholine butare longer-acting
Pancuronium is vagolytic, so may be of benefit in newborns, who have high levels of vagal tone; rarely used
Vecuronium and rocuronium are metabolized by the liver and excreted in bile; the most commonly used
Cis-atracurium is metabolized by plasma cholinesterase and therefore may be of benefit in patients with hepatic or renal disease
Curare releases histamine and is long-acting
HYPNOTICS
Propofol Rapidly acting hypnotic; amnestic, but not analgesic
Like pentothal, may cause hypotension
Causes respiratory depression
May increase the seizure threshold
Great utility in titrated doses for sedation and with local anesthetic and short-acting opioid for outpatient procedures
May suppress nausea
Associated with the often fatal propofol infusion syndrome when used in prolonged intravenous infusion (>24 hr) and therefore not used for ICU sedation in children
Etomidat Cardiovascular stability on induction with no increase in intracranial pressure
Inhibits corticosteroid synthesis and increases ICU mortality
Associated with myoclonus, potential difficulty with assisted ventilation, and pain on injection
Ketamine Hypnotic analgesic and amnestic
Causes sialorrhea and should be coadministered with an antisialagogue, such as atropine or glycopyrrolate
May be associated with laryngospasm
Causes endogenous catecholamine release, tachycardia, and bronchodilation
Increases intracranial and intraocular pressures
Decreases the seizure threshold
Thiopental Used to induce a state of unconsciousness; rarely used
Rapidly acting hypnotic, but not an analgesic
Offset is by redistribution, not by metabolism
May cause hypotension because of its myocardial depressant effects and by vasodilation
Causes respiratory depression
Releases histamine and may be associated with bronchospasm in susceptible individuals
Increases the seizure threshold
SEDATIVE-ANXIOLYTICS
Benzodiazepines May produce sedation, anxiolysis, or hypnosis, depending on the dose
May produce antegrade but not retrograde amnesia
All agents raise the seizure threshold, are metabolized by the liver, and depress respiration, especially when administered with opioids
Frequently administered as premedications
Diazepam may be painful on injection and has active metabolites
Midazolam can be administered by various routes and has a short half-life
Lorazepam has no active metabolites
Sedation effected by all benzodiazepines may be reversed by flumazenil, but respiratory depression may not be reliably reversed
Dexmedetomidine Produces anxiolysis, sedation, sympatholysis, by α2-receptor stimulation centrally; has mild analgesic properties
Side effects include hypotension and bradycardia
Increasingly used for procedural sedation
Continuous infusion for ICU sedation; currently limited to 24 hr
ANALGESIC-SEDATIVES
Opioids Gold standard for providing analgesia
May cause respiratory depression
Morphine and, to a lesser extent, hydromorphone may cause histamine release
The synthetic opioids fentanyl, sufentanil, and short-acting alfentanil may have a greater propensity to cause chest wall rigidity when administered rapidly or in high doses and are also associated with the rapid development of tolerance; these 3 drugs have particular utility in cardiac surgery because of the hemodynamic stability associated with their use
Remifentanil is an ultra–short-acting synthetic opioid that is metabolized by plasma cholinesterase; it may have particular utility when deep sedation and analgesia are required along with the ability to assess neurologic status intermittently
INHALATIONAL AGENTS
Nitrous oxide Causes amnesia and mild analgesia at low concentrations
Danger of hypoxic mixture if the oxygen concentration is not monitored and preventive safety mechanisms are not in place
Potent vapors “Complete anesthetics”—they induce a state of hypnosis, analgesia, and amnesia
All are myocardial depressants, and some are vasodilators
May trigger malignant hyperthermia in susceptible individuals
Isoflurane and enflurane are fluorinated ethers and isomers
Enflurane may lower the seizure threshold—rarely used
Halothane has been the gold standard for performing inhalation induction of anesthesia in children, but sevoflurane, a newer drug, is also well tolerated and has more rapid kinetics (onset and offset) because of its low solubility in blood. No longer available in the USA.
Sevoflurane is almost universally used for inhalation induction of anesthesia in children.
All are bronchodilators at equipotent concentrations
Isoflurane, enflurane, and especially desflurane are associated with a higher incidence of laryngospasm, when used for anesthetic induction, than sevoflurane

ICU, intensive care unit.

Sedation describes a medically induced state that is on a continuum between the fully alert, awakened state and general anesthesia (see Table 70-4). In addition to inducing unconsciousness and amnesia, general anesthesia obtunds or ablates critical physiologic reflexes; the most important are airway-protective reflexes: coughing, gagging, and swallowing. Cardiorespiratory reflexes are also obtunded with general anesthesia; respiratory depression and hemodynamic compromise may occur and may be profound. As sedation deepens toward general anesthesia, loss of airway patency, loss of airway-protective reflexes, and loss of cardiovascular stability occur. Light (minimal) sedation is anxiolysis without loss of these reflexes or airway patency. Deep sedation occurs when these reflexes are obtunded or lost (see Table 70-4). Adequate sedation in children may be accompanied by the actual or potential loss of vital reflexes. It is mandatory that those providing sedation for a child be able to detect the transition into deep sedation and general anesthesia and be prepared to manage the child’s airway and circulation, and provide cardiopulmonary resuscitation (CPR) if required.

Akinesia (Immobility or Muscular Relaxation)

Akinesia is the absence of movement. It is necessary to ensure safe and adequate operative conditions and to provide ideal conditions for advanced and meticulous surgery. Akinesia is produced with muscle relaxants (see Table 70-5). These agents facilitate respiratory management in the perioperative period and in critically ill patients. The absence of movement is neither the absence of pain nor the presence of amnesia. Whenever neuromuscular blocking agents are used, analgesia and sedation must be provided.

Physiologic Support

The need for anesthesia increases the need to monitor and support physiologic integrity and homeostasis. Sedation and anesthesia have significant and potentially life-threatening physiologic consequences (see Tables 70-4 and 70-5). Maintenance of adequate cardiorespiratory function, fluid management, electrolyte control, thermoregulation, and concern for all aspects of the child’s health are critical during anesthesia.

Induction of General Anesthesia

The goal of induction of general anesthesia is to rapidly achieve surgical anesthesia by using intravenous (IV) or, more commonly in children, inhalational induction agents. In children who are too young to tolerate the establishment of vascular access before the induction of anesthesia, it is routine to induce anesthesia by mask inhalation of volatile anesthetics. In the operating room, a child is often accompanied by the parents (parental presence during induction [PPI]) and placed on the operating room table. Before the induction of anesthesia, monitors are usually applied to the child. These include a pulse oximeter, electrocardiogram (ECG) electrodes, and, frequently, a blood pressure cuff. The child is then cautiously introduced to the face mask, which contains a high gas flow (5-7 L/min of oxygen), frequently mixed with nitrous oxide (N2O). Inhalation of nitrous oxide and oxygen for 60-90 sec induces a state of euphoria. The airway responses to inhalational anesthetics are now blunted, and sevoflurane can be introduced into the inhaled gas mixture. This leads to unconsciousness within 30-60 sec while the child continues to breathe spontaneously.

The child is now “asleep,” and the parents can be asked to leave. An IV line is then started, and comprehensive intraoperative monitoring initiated. Surgical anesthesia can be maintained by spontaneous ventilation with a mask; this is safe only when the airway is secure and patent, the stomach is empty, and the child is >6 mo of age. Procedures >1 hr are not usually performed with mask inhalational anesthesia. If these conditions are not met, if the surgeon needs to approach the airway, or if muscular paralysis is required, then the airway must be secured with endotracheal intubation. Although endotracheal intubation can be performed under deep inhalational anesthesia with respiratory depression and obtunded cough and gag reflexes, the depth of anesthesia required to ablate airway reflexes is very close to the level that induces hemodynamic instability. After anesthetic induction, IV access is secured and anesthesia is deepened with IV agents. Muscle relaxation with IV, nondepolarizing muscle relaxants is induced to facilitate endotracheal intubation. Succinylcholine is rarely if ever used. After paralysis is induced, direct laryngoscopy and airway intubation can be performed. Correct endotracheal tube placement is confirmed by direct laryngoscopy, end-tidal CO2 measurement, endotracheal tube fogging, and the finding of bilaterally equal breath sounds during positive pressure ventilation. If necessary, fiberoptic airway endoscopy and chest radiograph, in addition to these measures, can be used to confirm correct endotracheal tube placement.

After endotracheal intubation, spontaneous ventilation may be permitted, if muscle relaxants are not used or have worn off; it is routine to provide controlled mechanical ventilation. When the child is completely anesthetized, positioned for surgery, and hemodynamically stable, and maintenance anesthesia is achieved, the surgery can begin.

Inhalational Anesthetics

General anesthesia may be induced and maintained by either inhalation or the IV route. The inhalational anesthetics used in children include sevoflurane, isoflurane, and desflurane. Although halothane is the prototypical pediatric inhalational anesthetic agent, it is no longer used in the USA.

The minimal alveolar concentration (MAC) of an inhalational anesthetic is the alveolar concentration (expressed as percent at 1 atmosphere) that provides sufficient depth of anesthesia for surgery in 50% of patients. For potent inhalational agents, the alveolar concentration of an anesthetic reflects the arterial concentration of anesthetic in the blood perfusing the brain. Thus, the MAC is an indication of anesthetic potency and is analogous to the ED50 (effective dose in 50% of recipients) of a drug. MAC is age-dependent, is lower in premature infants than in full-term infants, and decreases from term through infancy to preadolescence. In adolescence, MAC again increases, falling thereafter. Inhalational anesthetic agents are poorly soluble in blood but rapidly equilibrate between alveolar gas and blood. The less soluble an anesthetic agent is in blood (low blood gas partition coefficient, or ratio of the anesthetic concentration in the blood to the alveolar gas at equilibrium), the more rapid are both the induction of and the emergence from inhalational anesthesia with that agent. Blood gas partition coefficients for sevoflurane (0.69) and desflurane (0.42) are lower than that for halothane (2.4).

Specific Anesthetics

Nitrous Oxide

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