Neonatal Anesthesia

Ain Shams Journal of Anesthesiology                                         Vol 4-1; Jan 2011

Neonatal Anesthesia 
Hany M. El-Zahaby, MD
Department of Anesthesia, Intensive Care and Pain Management, Faculty of
Medicine, Ain Shams University, Cairo, Egypt.
Safe and effective neonatal anesthesia is one of the most challenging tasks presented to anesthesiologists. Knowledge of  the neonate's unique features, great manual skills and continuous practice are required for the
anesthesiologist to perform such task.
Neonatal Physiology Related to Anesthesia
Nociceptive System and Stress Response
The central nervous system is incompletely developed at birth. However, studies in preterm and term
neonates reported a fully competent neuroendocrine stress reaction in response to surgical stimulation.
Neonatal pain is capable of producing a "pain memory" as a result of plasticity changes within the central
nervous system or a psychological process.
 This confirms that a nonanalgesic technique practice is no longer acceptable.  The potential incompletely developed autoregulation of cerebral blood flow together with fragile infant's cerebral blood vessels
are important factors in the development of intraventricular hemorrhage.
 The spinal cord extends to a lower segment of the spine in neonates than in older children and adults. The volume of cerebrospinal fluid and the spinal surface area are proportionally larger in neonates, whereas the amount of myelination is less than in older children and adults.
These factors explain the increased amount of local anesthetics (mg/kg) required for a successful spinal
anesthetic in infants.   Hyperoxia has been associated with retinopathy of prematurity (ROP).
 However, ROP has been reported in full-term infants, in preterm infants never exposed to greater than ambient oxygen, may affect retina of one eye only, and even in infants with congenital cyanotic heart disease who has low oxygen tension in their blood.

fiberoptic intubation

Abdominal compartment syndrome

williams airway

The Airway Intubator is cylindrical on the proximal half and open on the distal half of the lingual surface.

The Airway Intubator is indicated for use as:

• An oropharyngeal airway
• A means of intubating the trachea
• A guide for fiber optic laryngoscope placement

For adult females (Williams Airway 9cm), recommended for use up to 7.5mm I.D. Endotracheal Tubes

For adult males (Williams Airway 10cm), recommended for use up to 8.5mm I.D. Endotracheal Tubes

Non obstetric surgery during pregnancy

Non obstetric surgery during pregnancy is relatively common.

The most common indications for surgery during pregnancy are either pregnancy related or pregnancy non related. Pregnancy related surgery include interventions for cervical incompetence and surgery for ovarian cyst problems.

The most common non pregnancy related indications are acute abdominal problems( most commonly appendicitis and cholecystitis), maternal trauma and surgery for malignancies.

Anaesthetists who care for pregnant patients undergoing non-obstetric surgery must provide safeanaesthesia for both the mother and the foetus.  To maintain maternal  safety the physiological and anatomical changes of pregnancy must be considered and anaesthetic techniques and drug administration modified accordingly.  Foetal wellbeing is related to avoidance of foetal asphyxia, teratogenic drugs and preterm labour.

Physiological Changes during Pregnancy

Central Nervous System Effects

The minimal alveolar concentration (MAC) progressively decreases during pregnancy—at term, by as much as 40%—for all general anesthetic agents; MAC returns to normal by the third day after delivery. Changes in maternal hormonal and endogenous opioid levels have been implicated. Progesterone, which is sedating when given in pharmacological doses, increases up to 20 times normal at term and is probably at least partly responsible for this observation. A surge in -endorphin levels during labor and delivery also likely plays a major role

At term, pregnant patients also display enhanced sensitivity to local anesthetics during regional anesthesia; dose requirements may be reduced as much as 30%. This phenomenon appears to be hormonally mediated but may also be related to engorgement of the epidural venous plexus.

Obstruction of the inferior vena cava by the enlarging uterus distends the epidural venous plexus and increases epidural blood volume. The latter has three major effects: (1) decreased spinal cerebrospinal fluid volume, (2) decreased potential volume of the epidural space, and (3) increased epidural (space) pressure. The first two effects enhance the cephalad spread of local anesthetic solutions during spinal and epidural anesthesia, respectively, whereas the last may predispose to a higher incidence of dural puncture with epidural anesthesia

Neurosurgery in children

Neurosurgery in children

Intracranial Physiology and Pathophysiology

There are a number of anatomic differences between children and adults that affect central nervous system physiology, especially intracranial pressure (ICP).

 At birth, the dura mater is covered by the calvaria, which consist of ossified plates connected by fibrous sutures and open fontanelles. The fontanelles close by approximately 10 to18 months of age but do not fully ossify until the teenage years. Thus, the infant skull is more compliant and may slowly expand in response to increasing ICP. These same structures offer a great deal of resistance to acute elevations in ICP. Infants and young children may not exhibit clinical signs of intracranial hypertension until the process is significantly advanced and the cranium can no longer accommodate a further increase in ICP.

 By the time an infant demonstrates the classic clinical signs of elevated ICP such as bradycardia, hypertension, papilledema, and pupillary changes, the disease process is likely very advanced. In contrast to adults, infants and young children may present with vague signs and symptoms such as increased head circumference, expanding sutures, bulging fontanelles, “sundowning” of eyes, lethargy, poor feeding, irritability, and possibly lower motor deficit.

 After ossification of the fontanelles, for a time, children may be more vulnerable to brain injury from increased ICP because of a relatively higher brain tissue to blood and cerebrospinal fluid intracranial volume than in the adult.

The limits of autoregulation are also different in infants and children. In adults, normal ICP ranges between 8 and 15 mmHg, whereas in infants, it may be as low as 2 to 4 mmHg. The cerebral autoregulation limit is shifted to a significantly lower value of mean arterial blood pressure (20 to 60 mmHg). The “margin of safety” may be narrower because infants are less able to compensate for the changes in blood pressure. Global cerebral blood flow (CBF, measured as ml/min/100 g of brain tissue) in children is greater than in adults, but in infants and premature babies, it is lower. The lower limit of CBF needed to sustain neuronal integrity is unknown in these patients. In infants with pathologic conditions resulting in a shift of the intracranial compliance curve to the right, cerebrospinal fluid production alone may be a significant contributor of increased ICP. Infants are at risk for ischemia when mean arterial pressure is low, whereas systemic hypertension may result in intraventricular hemorrhage; therefore, large fluctuations in systemic blood pressure may be deleterious. The response to hyperventilation may, also, be exaggerated and ischemia may ensue with very low PCO2 levels (less than 20 mmHg).

Twin-to-twin transfusion syndrome (TTTS)

Ain Shams Journal of Anesthesiology                                         Vol 4-1; Jan 2011
99
Twin-to-twin transfusion syndrome (TTTS)
 
Mohammed Abdel-Galil Sallam MD
Department of Anesthesiology, Intensive Care, and Pain Management, Faculty of
Medicine, Ain-Shams University, Cairo, Egypt
TTTS only occurs in monozygotic
(identical) twins with a monochorionic
placenta. It is the result of an
intrauterine blood transfusion from one
twin (donor) to another twin
(recipient). The donor twin is often
smaller with a birth weight 20% less
than the recipient’s birth weight. The
donor twin is often anemic and the
recipient twin is often plethoric with
hemoglobin differences greater than 5
gm/dL. The blood transfusion from the
donor twin to the recipient twin occurs
through placental vascular anastomoses.
The most common vascular anastomosis
is a deep, artery-to-vein anastomosis
through a shared placental cotyledon.
The clinical feature es of TTTS are
the result of hypoperfusion of the donor
twin and hyperperfusion of the recipient
twin.