**2. Physiological feature in neonatal period**

#### **2.1. Organ and system differences in neonate**

The neonatal period shows anatomical and physiological differences when compared to adult period. In this section, will be mentioned to physiological characteristics of neonates, also anatomical differences of neonates will be discussed in the part of anesthetic management.

It is important to know the anatomical airway differences between adults and children and newborns for a complete anesthesia assessment [6]. These differences can be listed as follows:


Because of these anatomical features, nasal breathing is dominant in neonates and infants until about 5 months of age [6].

In the newborn period, many vital organ and system functions are immature [7]. In respiratory system, high pulmonary vascular resistance (PVR) which is characteristics in fetal circulation decreases by approximately 10% after labor, but the apparent decrease occurs with the first breath [8, 9]. When the transition period to the adult circulation is examined, pulmonary blood flow, increased alveolar and arterial PO2 appear to be important factors.

The characteristics of the neonatal respiratory system can be listed as follows: [1, 6].


Cardiovascular system changes are also observed during neonatal period. The circulation of a newborn infant is a dynamic state which may revert to a transitional characteristic at any time. This means that the adult series circulation accompanies fetal parallel circulation [10].

The onset of spontaneous breathing is the main factor that reduces high PVR which is characteristic of fetal circulation. This decrease in pulmonary pressure is followed by an increase in systemic vascular resistance and left atrial pressure. Some clinical situations such as hypoxia and acidosis may lead to reduction of pulmonary blood flow which causes a return the fetal circulation features that is called persistent fetal circulation (PFC) [11].

Cardiac function is heart rate dependent in healthy neonates because the immature myocardium has limited compliance [2, 12].

The parasympathetic system is predominant in neonates [10], so that vagal stimulus by laryngoscopy and hypoxia may cause bradycardia. Therefore, it should be avoided bradycardia and treated aggressively when it is observed.

Liver and kidney function are also closely related to the anesthetic management of neonates. In the neonatal period, both organs have not yet completed maturation. The liver serves a critical role in carbohydrate, protein, lipid metabolism, coagulation. And is the primary site for biotransformation of drugs [13]. Hepatic oxidation, reduction and hydrolysis maturation process is rapid and these functions reaches adult rates around 6 month of ages [14]. Because of this, newborns may metabolize drugs (include anesthetic drugs) and toxins less efficiently than adults in the early months of their lives, as the pathway of degradation is immature [1]. Also, one of the changes in early infancy is the lower concentration of total serum protein, albumin and α1-acid glycoprotein. These proteins reach the adult level at about 1 year old [14].

One of the main routes of clearance of drugs and metabolites are the kidneys too. Glomerular filtration rate (GFR), active secretion and passive reabsorption are functions that determine renal excretion of drugs [15].

The kidneys also play an important role in the maintaining of acid base homeostasis and fluid electrolyte balance. GFR and reabsorption are increase age dependent manner. A neonate's kidney takes approximately 6–12 months to achieve adult performance.

In the perioperative period, fluid electrolyte balance is affected and the metabolism of commonly used anesthetic drug altered [10]. Drug metabolism and protein binding are also reduced due to immature organ (hepatic and renal) function [16].

Maturational physiologic changes are most prominent in neonatal period and infancy. The distribution of total body fluid component in neonates is different from adults. Body fluid constitute a greater proportion of body weight in the neonate (approximately 70–75%) and higher than adults. In neonate, the intracellular and extracellular fluid compartments are approximately 45 and 33% of body weight, respectively [17]. These body component changes affect volumes of distribution of drugs.

#### **2.2. Thermoregulation**

In this chapter will be discussed issues that related to the anesthetic approach and postopera-

The neonatal period shows anatomical and physiological differences when compared to adult period. In this section, will be mentioned to physiological characteristics of neonates, also anatomical differences of neonates will be discussed in the part of anesthetic management.

It is important to know the anatomical airway differences between adults and children and newborns for a complete anesthesia assessment [6]. These differences can be listed as follows:

Because of these anatomical features, nasal breathing is dominant in neonates and infants

In the newborn period, many vital organ and system functions are immature [7]. In respiratory system, high pulmonary vascular resistance (PVR) which is characteristics in fetal circulation decreases by approximately 10% after labor, but the apparent decrease occurs with the first breath [8, 9]. When the transition period to the adult circulation is exam-

• Immature hypoxic response, lower functional residual capacity (limits oxygen reserves

• Neonatal oxygen consumption 6 cc kg−1 per minute is twice that of resting adult (this value

Cardiovascular system changes are also observed during neonatal period. The circulation of a newborn infant is a dynamic state which may revert to a transitional characteristic at any time. This means that the adult series circulation accompanies fetal parallel circulation [10].

The characteristics of the neonatal respiratory system can be listed as follows: [1, 6].

during period of apnea, rapid desaturation in prolonged intubation attempt),

appear to be important

ined, pulmonary blood flow, increased alveolar and arterial PO2

• Central control of ventilation is not fully develop,

increases 10 cc kg−1 in the first week of life).

• Peripheral feedback mechanisms are not sufficiently mature,

tive care to neonatal patients.

126 Selected Topics in Neonatal Care

**2. Physiological feature in neonatal period**

**2.1. Organ and system differences in neonate**

• Proportionately larger head and tongue,

• Narrower nasal passages,

• Shorter trachea and neck.

until about 5 months of age [6].

• A longer epiglottis,

factors.

• An anterior and cephalad larynx,

The newborn baby has a greater surface area relative to weight and a thin layer subcutaneous fat tissue [3]. These properties cause more heat loss to the environment in neonates than older 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 newborns.

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

are also important to reduce these risks.

factors are summarized in **Table 2**.

Difficult airway: Micrognathia, macroglossia, cleft palate-lift

Intraventricular/periventricular hemorrhage (IVH, PVH)

• Treacher-Collins syndrome (mandibulofacial dysostosis)

Anesthetic drugs – dilutional changes, prolonged effect

Respiratory failure, mechanical ventilatory support, supplemental oxygen

(high FiO2, risk of retinopathy, NEC)

Congenital syndromes and disorders (especially associated with risk of difficult airway, comorbidities of cardiac

Prematurity, Immature organ and system function

Apnea (especially premature neonates)

Oxygenation: avoid high FiO<sup>2</sup>

Persistent pulmonary hypertension

Transitional circulation

 Immature myocardium Parasympathetic dominance Neurological problems

• Pierre-Robin syndrome

• Goldenhar syndrome • Klippel-Feil syndrome • Down syndrome Pharmacological differences

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.

Anatomical differences Airway anomalies

Respiratory

Cardiac

defect)

perioperative mortality, is a challenging period for pediatric anesthetists.

Neonatal period, which is the most vulnerable time period in terms of anesthetic risk and

Neonatal Care for Anesthesiologists http://dx.doi.org/10.5772/intechopen.71952 129

Drug interactions, physiological and anatomical differences, and knowledge of risk factors

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

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.

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


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 increase this loss.

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

Maximum precautions should be taken to prevent hypothermia in the perioperative period. These precautions are mentioned in the intraoperative management section.

Characteristics of neonates and infants that differentiate them adult patients are summarized in **Table 1**.


\* FA/FI: Fractional alveolar concentration/fractional inspired concentration. Table has modified by Lange Clinical Anesthesia 2015.

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