**3. General principles of anesthesia in neonate**

children and adult. Nonshivering thermogenesis is regulated by brown fat is the primary mechanism in heat generation in the neonates [1]. Brown fat tissue is located in the posterior neck along the interscapular and vertebral regions and it is responsible for heat generation in

Cold intravenous fluids, exposure to cold sterilization solutions, drying of anesthetic gases and the direct effect of anesthetic agents on temperature regulation are the factors that

For this reason mentioned above, caution should be exercised in serious temperature changes in the perioperative period. Hypothermia may cause undesirable effects such as acidosis,

Maximum precautions should be taken to prevent hypothermia in the perioperative period.

Characteristics of neonates and infants that differentiate them adult patients are summarized

Hepatic function

for drug Respiratory changes • More rapid rise in \*

concentration Body fluid changes

• Immature biotransformation

• Decreased protein, decreased binding

• more rapid induction and recovery from inhaled anesthetics • Increased minimum alveolar

• Relatively larger volume distribution for water- soluble drugs • Immature neuromuscular junction

FA/FI

myocardial depression, and delay recovery from anesthesia [19, 20].

These precautions are mentioned in the intraoperative management section.

**Anatomical differences Physiological differences Pharmacological differences**

• Total body water content • Chest wall compliance • Ratio of body surface area to

• Functional residual capacity

body weight Decreasing parameters • Blood pressure

• Lung compliance

FA/FI: Fractional alveolar concentration/fractional inspired concentration.

**Table 1.** Characteristics of neonates and infants that differentiate them adult patient.

Table has modified by Lange Clinical Anesthesia 2015.

Increasing parameters • Heart rate (dependent cardiac output) • Respiratory rate • Metabolic rate

newborns.

• Evaporation, • Convection, • Conduction, • Radiation,

128 Selected Topics in Neonatal Care

increase this loss.

in **Table 1**.

Head and neck

tongue

Circulation

Respiratory

\*

• Relatively larger head and

• Narrower nasal passage • Anterior and cephalad larynx • Relatively longer epiglottis and

• Left ventricle –noncompliant • Transitional circulation

shorter trachea

• Weak intercostal and diaphragmatic muscles • Increased resistance to airflow

There are four different mechanisms of heat loss [18]:

Neonatal period, which is the most vulnerable time period in terms of anesthetic risk and perioperative mortality, is a challenging period for pediatric anesthetists.

Drug interactions, physiological and anatomical differences, and knowledge of risk factors are also important to reduce these risks.

What are the risks associated with neonatal anesthesia? In addition to the neonatal differences, prematurity, congenital anomalies, asphyxia at birth, and emergency situations that required surgery are risk factors. At the same time, there is a very narrow margin of error, including airway management, vascular access and drug administration. Some of these risk factors are summarized in **Table 2**.

Therefore, a safe aesthetic approach depends on a good understanding of the variables and physiological and anatomical changes taking place in the transition from fatal to neonatal life.

Anatomical differences Airway anomalies Difficult airway: Micrognathia, macroglossia, cleft palate-lift Prematurity, Immature organ and system function Respiratory Apnea (especially premature neonates) Respiratory failure, mechanical ventilatory support, supplemental oxygen Oxygenation: avoid high FiO<sup>2</sup> (high FiO2, risk of retinopathy, NEC) Cardiac Transitional circulation Persistent pulmonary hypertension Immature myocardium Parasympathetic dominance Neurological problems Intraventricular/periventricular hemorrhage (IVH, PVH) Congenital syndromes and disorders (especially associated with risk of difficult airway, comorbidities of cardiac defect) • Pierre-Robin syndrome • Treacher-Collins syndrome (mandibulofacial dysostosis) • Goldenhar syndrome • Klippel-Feil syndrome • Down syndrome Pharmacological differences Anesthetic drugs – dilutional changes, prolonged effect Fluid management Glucose: avoid hypoglycemia Intolerance for rapid fluid infusion Problems of vascular access Temperature management Prevent hypothermia Emergency surgery

**Table 2.** Risk factors in neonatal anesthesia.

#### **3.1. Effects of anesthetic drugs and inhalation anesthetics on neonates**

Effective and safe drug administration in neonates should be based on detailed knowledge on the physiological characteristics of the neonates and pharmacokinetics and pharmacodynamics of given drug. Clinical pharmacology in neonates is recognized with extensive variability. The effect of anesthetic agents varies with organ maturation, body water content and metabolic differences and, coexisting disease in neonatal patient population.

extracellular distribution volume will dilute the drug concentration, while those metabolized

Neonatal Care for Anesthesiologists http://dx.doi.org/10.5772/intechopen.71952 131

Anesthetic management in neonatal patients can be challenging but careful preoperative assessment means that a safe and smooth preparation process for the neonates and anesthetic team. This evaluation is also an approach that encourages confidence for their parents.

A careful preoperative examination allows the anesthetist to determine the risk of anesthesia based on the general state of health of newborn. It is aimed to establish an appropriate plan

Preoperative assessment in neonates should include a comprehensive examination of the neonate's perinatal history (such as prematurity, apnea-hypoxic episode history, duration of oxygen dependency, neurological damage etc.), congenital anomalies, previous anesthesia applications,

Premature, ex-premature and term neonates are highly heterogeneous group within newborn period and needs various surgical interventions. Most of them come directly from the neonatal intensive care unit (NICU) and require urgent intervention. Many unusual congenital syndromes occur in childhood. These congenital anomalies in newborn period may accompany emergency surgical procedures [24]. Congenital anomalies that may cause difficult intubation

In addition, a more detailed examination should be performed to reveal early postnatal prob-

A systematic approach to preoperative evaluation will prevent important problems from being overlooked. Many healthy neonates undergoing elective simple surgery and procedures are fit and do not require compressive physical examination. However, evaluation of the head and neck (such micrognathia, limited neck mobility, macroglossia, etc.) and cardiorespiratory examination (cardiac congenital anomalies, breathing sounds, respiratory pathologies associated with increased secretion and inflammation etc.) should be performed before surgical procedures. Also in cardiac examination, previously undiagnosed murmur with pathological qualities (e.g. loud, continuous, diastolic and or/associated with a trill)

Evaluation of the airway is critical to the delivery of safe anesthesia. In neonates with a syndrome associated with airway anomalies, the potential presence of a difficult airway (**Table 2**) (*e.g. Pierre-Robin, Goldenhar, Treacher-Collins Syndrome, cleft palate and lip, maxilla mandibular* 

Risk factors which are important in neonatal anesthesia are summarized in **Table 2**.

for anesthesia, postoperative care and analgesia in the light of acquired information.

and general state of health (acute, chronic lung disease, cardiac pathologies, etc.) [23].

should be noted and the anesthesia plan should be made accordingly.

lems that may be seen (such as hypoglycemia, infection and sepsis, etc.).

**4. Anesthesia preparation in neonates before surgical procedure**

in the liver will prolong the duration.

**4.1. Preoperative evaluation**

may be noticeable.

*synechia, etc.*) can be identified preoperatively.

Inhalation anesthesia is a commonly used anesthetic technique in neonatal population. However, intravenous and regional anesthesia methods also can be applied as anesthetic technique in this patient population. The minimum alveolar concentration (MAC) of an inhaled anesthetic is the alveolar concentration that prevents movement in 50% of patients in response to a standardized stimulus (e.g., surgical incision) and changes with age [1, 6, 21]. MAC for inhalational agents is less in neonates than in infants (up to 6 months of age [12, 21]. In newborns, cardiac and respiratory functions and blood pressure are very sensitive to volatile anesthesia. Immature myocardium and less developed compensatory mechanisms are responsible for this result. Therefore, these anesthetics can cause dose dependent cardiac and respiratory depressant effect and can be seen bradycardia, hypotension and postoperative apnea. These effects are more pronounced during the induction period [12, 22].

Intravenous anesthetic agents may be used for induction of anesthesia when inhalational anesthetics are not preferred and/or not practices.

Factors affecting the administration of intravenous anesthesia can be listed as follows:


These factors mentioned above affect the properties of the intravenous anesthetics such as duration of effect (onset and termination), doses and toxicity limits of drugs.

An opioid agent causes fewer hemodynamic changes but it should be noted that increase the risk of postoperative apnea and late-onset re-sedation in recovery in preterm and term neonates [2, 4].

Thus, it is crucial that intravenous lines are flushed and cleared of any medication (e.g. opioid, neuromuscular blocker).

Muscle relaxant may be required for some surgical procedures (especially abdominal surgical procedures such as necrotizing enterocolitis, abdominal wall defect). The response of neonates to nondepolarizing muscle relaxant is quite variable. Neuromuscular junction is immature in preterms and this increases the susceptibility to muscle relaxants. However, the large extracellular distribution volume will dilute the drug concentration, while those metabolized in the liver will prolong the duration.
