Neonatal Anesthesia

Hany El-Zahaby, MD

Dept. of Anesthesia, Ain Shams University

“Safe and effective anesthesia for neonates undergoing surgery is one of the most challenging tasks presented to

anesthesiologist.”

Knowledge

Manual skills

Continuous practice

+

Adequate monitoring

↓

Outcome

Age Specific ConsiderationNociceptive System And Stress Response

•The central nervous system is incompletely developed at birth.

•Fully competent neuroendocrine stress reaction in response to surgical stimulation.

•“Pain memory"

•“Programming phenomena”

•Non-analgesic technique practice is no longer acceptable.

Self-report tools of pain appropriate for different age groups

-Infant's fragile cerebral blood vessels is an important factor in the development of intraventricular hemorrhage.

-The spinal cord extends to a lower segment of the spine than in older children .

-The volume of cerebrospinal fluid and the spinal surface area are proportionally larger in neonates ► increased amount of local anesthetics (mg/kg) required for a successful spinal anesthesia in infants.

Age-specific considerations Airway Features

Age-specific considerations Fast desaturation

• High metabolic rate (5-8 ml/kg/min) • Tidal volume (6-7 ml/kg/min) • High respiratory rate (40-60 breaths/min) • High alveolar ventilation (130 ml/kg/min)• Lung compliance is less while chest wall compliance is more than

those in adults {reduced FRC and atelectasis} ►PEEP.• Diaphragm (dominating respiratory muscle ) has less oxidative type

I fibers ► susceptible for fatigue.• The work of breathing is composed of compliance and resistive

components. The compliance work relative to tidal volume is nearly the same as in adult. The resistive work increases when breathing through ETT (4th radius), and through circle system.

“Neonates and especially ex-premature infants have a tendency toward periodic breathing that is accentuated by anesthetics, increasing the risk of postoperative apnea until approximately 55-60 weeks post-conceptual age and require continuous monitoring of blood oxygen saturation and heart rate until 12- hours of apnea free period”.

ApneaApnea (1) central apnea, due to immaturity or depression of the respiratory drive; (2) obstructive apnea, due to an infant's inability to maintain a patent airway; and (3) mixed apnea, a combination of both central and obstructive apnea.

Susceptibility to Central apnea is exacerbated by hypothermia, hypoglycemia, and hypocalcemia, anemia, opioids .

• Treatment: xanthines (caffeine & theophylline)

▲ Hct

▲ FiO2

• Never give caffeine & send the neonate home as being “safe now”.• Even patients treated with naloxone require continuous monitoring

of blood oxygen saturation and heart rate until 12-hours of apnea free period.

Obstructive apnea is treated by changing the head position, inserting an oral or nasal airway, placing the infant in a prone position or by applying continuous positive airway pressure (CPAP)

Age-specific considerations Cardiovascular

• Fetal hemoglobin has higher affinity for oxygen.

• Oxygen delivery is facilitated by a high cardiac output.

• Cardiac output is more dependent on heart rate.

• Parasympathetic control of heart rate matures earlier and to a greater extent than β-adrenergic control – Do not respond to hypovolemia or an inadequate depth of anesthesia

with tachycardia

– More susceptible, to the cardiac depressant effects of volatile anesthetics

PDA

• With expansion of the lungs during the first breath, pulmonary vascular resistance decreases and blood flow to the lungs increases

• Neonatal hypoxia, hypercarbia, or acidosis increase PVR & may result in a return to the fetal-type circulatory pattern with right-to-left shunt via the PFO or PDA (PA to AO)

• Persistent PDA after declining of pulmonary vascular resistance causes left to right shunt with pulmonary hypertension and increased ventilatory support.

• PDA is diagnosed by bounding peripheral pulses, a harsh systolic ejection murmur at the left sternal border and a large pulse-pressure, Echo.

• PDA is treated by indomethacin, coiling or surgical ligation.

PPHN

• Sepsis and aspiration syndromes ► muscularization of pulmonary arterial vessels.

• Difference in preductal and postductal oxygen saturations, right-to-left shunting of deoxygenated blood via PDA.

• Ultrasonography ► PPHN + no cardiac lesion

• Treatment: oxygenation, alkalosis , inhaled NO

Prevention of Heat Loss

Radiation

Evaporation

Conduction

Convection

Prevention of Heat Loss

Room temp.: 80-85 F

Avoid unnecessary exposure & cover cotton wraps as much as possible

HME (active or passive)

IVF: warm

Active warming mattress

Cover exposed viscera with warm wet towels

Incubator: keep plugged

Age-specific considerations Renal Function

• The glomerular filtration rate is only 15% to 30% of normal adult levels.

• The kidneys' tubular function is impaired and hence sodium-retaining ability.

• Renal excretion of medications such as penicillin, gentamicin, pancuronium is impaired ►prolonged duration

The initial doses of some medications may be greater on a weight basis than for adults in order to achieve the desired blood concentration in the presence of high volume of distribution. In contrast, because of immaturity of renal function, the interval between dosages of some drugs may be increased

Caloric Consumption is about 100-120 Kcal/kg/day.

Age-specific considerations Glucose Homeostasis

• In full-term infants, a glucose infusion rate of 5 to 8 mg/kg/min is required to prevent hypoglycemia i.e. maintenance rate/h

• Excessively fasted, SGA infants, infants of diabetic mothers and infants with TPN sudden withdrawal are particularly prone to develop hypoglycemia.

• The signs and symptoms of hypoglycemia (apnea, cyanosis, seizures, tremors, high-pitched cry, irritability, limpness, lethargy, eye rolling, poor feeding, temperature instability, and sweating) in infants are often blunted and nonspecific.

• Is it then justified to use only glucose solutions during operation?

Age-specific considerations Gastrointestinal & Hepatic Function

• Prolonged gastric emptying + incompetent lower esophageal sphincters = reflux is common.

• Preterm, hypoxemic, acidotic neonates with low serum protein levels are liable to get Kernicterus (bilirubin encephalopathy) due to increased levels of unconjugated serum bilirubin.

• Furosemide & sulfonamides (high protein bound) may displace bilirubin and increase the possibility of kernicterus.

• Increased intra-abdominal pressure may compromise hepatic drug metabolism .

Preoperative Laboratory Testing

• Hematocrit • Blood typing and compatability screening • Electrolyte (sodium, potassium, chloride and calcium) and acid-base

status (pH, base excess and standard bicarbonate)

• Coagulation profile :– (APTT) at day 1 averages at 42 compared to 33 in adults.

– Platelet counts are similar to normal adult values in term neonates. The lowest acceptable platelet count for surgery in neonates is not specifically known.

– Due to limited reserves and insufficient supply of vitamin K by breast feeding, intramuscular vitamin K (1 mg) is usually given.

Age-specific considerations Fasting

Elective:Clear fluids ►2h

Breast milk ►4h

Infant formula ► 6h

Emergency:Stomach aspiration

Awake/Rapid sequence

Premedication

• Atropine (10-20µ/kg IV, minimum 100µ) to counteract parasympathetic reflexes.

• Pain (increments of morphine 10-20µ/kg IV up to 100µ/kg)

Monitoring

• Standard:

ECG

Precordial or esophageal stethoscope?

NIBP

Temperature probe

Pulse oximeter (pre & postductal)

CO2 analyzer (site of sampling)

• Direct BP (significant intravascular instability)• CVP (vasoactive drugs)• Urine output (1 ml/kg/h)

How Long Pre-oxygenation?

60 seconds 6L/min (gives 80-90 seconds before desaturation) (Morrison JE et al: Pediatric Anaesthesia1998:8;293)

Inhalation VS Intravenous Induction?

IV access + hemodynamically stable→ STP 4-8mg/kg (prolonged emergence & postoperative apnea)- Propofol 3-3.5mg/kg

IV access + hemodynamically unstable → Ketamine 1.5-3mg/kg

Difficult IV access or compromised airway → Sevoflurane or halothane

Combined technique → (opioid + nondepolarizing MR + inhalation agent)

LMA VS ETT?

LMA: less than 30-45 min with spontaneous breathing

Size 1 ( 50% misplacement, NGT, large dead space & hypercapnea, helpful for ex-premis with BPD)

ETT: “The standard practice in neonates”

Awake intubation (very stressful/painful stimulus/ suboptimal conditions/BP fluctuation)

Relaxation?

Succinyl choline (RSI) (higher doses than adults), large ECF volume

Nondepolarizing MR (similar doses as adults), sensitivity offset by large ECF

Deep inhalation anesthesia, disadvantages?

Technique?

•Oral Vs nasal? (lateral/prone/limited head access)

•Straight blade- Paraglossal

•Leak pressure? 20-25cmH2O, affected by head position & MR

•Non-cuffed/cuffed: 8y (upper abdominal & thoracic surgery, poor

lung compliance)

•After intubation → VCM (40cmH2O/15 sec) or TRIM (30cmH2O/10

sec)

The retromolar, paraglossal, or lateral approach to rigid laryngoscopy utilizing a straight blade.

Microcuff ETT

More anatomical fit Sealing at low pressuresMore distal positionGreater permeability for nitrous oxide

For neonates ≤3 kg and infants ≤1 year, ID 3.0-mmPost-intubation croup was 0.4% (2/500 children)

Spontaneous Vs controlled?

-Spontaneous: more than 6 M, less than 30 min.

Pressure Vs volume control?

-Pressure control: First few days, premature, respiratory distress or lung pathology, compensate for leaks.

-Volume control: surgical manipulations interfere with ventilation.

-Pressure control/volume guaranteed.

-Peep 3-4 is routine.

“ Whatever the technique, an expired tidal volume & PIP should be tailored to the desired levels”

Maintenance:

• All inhaled anesthetics depress baroreceptor reflex.• Halothane depress the myocardium more.• Halothane decrease the heart rate more .

(Hypotension is treated by atropine & lowering halothane)• Sevo/Isoflurane decrease PVR more (treated by 5-10ml/kg fluid

bolus).• Nitrous oxide 60% decreases MAC of halothane, isoflurane &

sevoflurane by 60%, 40% & 25% respectively.

• Narcotics: -Fentanyl 1-2µ/kg if regional block was done.-Fentanyl based anesthesia for prolonged major surgery with postoperative ventilation.-Morphine 0.05mg/kg .

“The use of light general volatile anesthetic with a central or peripheral nerve block has proved to be of great benefit in neonatal surgery”

Bosenberg AT et al, Pediatr Surg Int, 1992:7, 289

Larsson BA et al, Anesth Analg 1997:84, 501

Intraoperative Volume Replacement

Hypovolemia with blood loss accounts for 12% of causes of cardiac

arrest in OR with almost half of it due to under estimation of blood

loss.*

*Anesthesia-Related Cardiac Arrest in Children: Update from the Pediatric Perioperative Cardiac Arrest Registry

Bananker et al, Anesthesia & Analgesia, August 2007

Assessment of dehydration

Mild

(50ml/kg)

Moderate

(100ml/kg)

Severe

(150ml/kg)

Wt loss%

Behavior

Thirst

Mucous memb.

Tears

Anterior fontanel

Skin turgor

Urine output

5

Normal

Slight

Normal

Normal

Flat

Normal

<2ml/kg/hr

10

Irritable

Moderate

Dry

+

+

+

<1ml/kg/hr

15

++irrit/lethargic

Intense

Parched

Absent

Sunken

Increased

<0.5ml/kg/hr

Fluid & blood loss

Type of fluid? Dextrose? BSS? Why?

Weighing swabs before it dries.

Intraoperative blood loss should be replaced with balanced salt solution (1:3), or colloid (1:1)

Estimated maximum allowable blood loss =

EBV x (Hctstarting – Hctacceptable)

Hctstarting

Emergence

Reversal of MR after spontaneous movement even with adequate time after last dose

Extubation:

Regular spontaneous breathing

Vigorous movements of all limbs

Gagging

Eye opening or pronounced grimacing

Stable hemodynamics & good oxygen saturation

Absence of significant hypothermia

“Extubate when fully awake”

Case-specific considerationsCase 1

• A 5 days old 3.6 kg male with history of prematurity (34 W) scheduled for ventriculo-peritoneal shunt & repair of encephalocele.

Encephalocele

Wet/soft covering

Avoid pressure

Antibiotics

Prone (nasal intubation)

Blood loss

Hypothermia

Latex – free procedure

Document spontaneous breathing postoperatively

Neural tube defect with variable neural dysfunction + Hydrocephalus + Arnold Chiari type II

Case-specific considerations Case 2

• A 2 days old 2.6 kg male 36 W conceptual age coming from NICU 2.5 ET in place, ventilated on PCVG mode with moderate ventilatory setting & and acceptable ABG planed for repair of esophageal atresia with tracheoesophageal fistula.

Thoracic SurgeriesEsophageal Atresia/TEF

1cm

Thoracic SurgeriesEsophageal Atresia/TEF

1:3000M:F 25:3First fed chocking, cyanosisCHD, VACTERL association 13%

Thoracic SurgeriesEsophageal Atresia/TEF

Management:

Head up

Continuous low suction on blind pouch

Echocardiography

Antibiotics

Vit K

Next day surgery

Case-specific considerations Case 3

• 65 W postconceptual age ex-premi male baby who has been on chronic ventilatory support-sepsis-PDA-IVH-NEC-multiple medications-BPD - extubated with great difficulty in NICU & planed to have inguinal hernial repair.