Apnoea

Question 1

What are the various terms used to quantify the age of neonates

Answer 1

See picture

Question 2

how is a clinical diagnosis of apnoea of prematurity made

Answer 2

if a premature infant has a cessation of breathing for at least 20 seconds or a shorter pause associated with bradycardia (less than 100 beats per minute) or desaturation.

Question 3

How is apnoea classified

Answer 3

Apnea may be classified as central (cessation of breathing effort), obstructive (airflow obstruction usually at the pharyngeal level), or mixed.

Question 3

What is the postulated cause of apnoea

Answer 3

Etiology is likely from immature neurons in the medullary respiratory control centers as well as immaturity of the peripheral chemoreceptor triggering respiration.

Question 4

What are the most common type of apnoea events in premature infants

Answer 4

Most apneic episodes in premature infants are mixed events, when obstructed airflow results in a central apneic pause or vice versa.2

Question 4

Why do infants develop bradycardia instead of tachycardia (like adults) in response to hypoxaemia

Answer 4

Hypoxemia leads to bradycardia because newborns have a fully matured parasympathetic system and an immature sympathetic system.

Question 5

Why are premature infants more prone to hypoxia

Answer 5

Premature infants are more prone to hypoxemia given their immature control of breathing.

Question 6

Which premature infants require monitoring for apnoea and why

Answer 6

all premature infants born at less than 35-weeks gestational age require monitoring for apnea.

Virtually all infants born at less than 28 weeks gestation develop apnea of prematurity, and the incidence decreases to 85% of infants born at 30 weeks and 20% of infants born at 34 weeks gestation.2

By postconceptual age of 52 weeks, these apneic episodes typically resolve.

Question 7

What are the risk factors for apnoea of prematurity

Answer 7

Anemia
Glucose or electrolyte imbalance
PDA with a large shunt
Medications: opioids & magnesium sulfate
Gastroesophageal reflux
Elevated body temperature

Question 8

What are the main prophylactic pharmacologic treatments for apnea of prematurity and postoperative apnea. Describe dosing and important attributes of these drugs

Answer 8

The methylxanthines

1. Caffeine citrate
   - Preop: 20mg/kg PO (2 hours preop)
   - Post op: 10 mg/kg PO daily for 2 days post op
2. Anyhydrous caffeine
   - Preop: 10mg/kg PO (2 hours preop)
   - Post op: 5 mg/kg PO daily for 2 days post op
3. Aminophylline
   - Intraop: 10 mg/kg IV slowly intraop

Question 9

Describe the apnoea monitoring basics done at RXH

Answer 9

Apnoea monitoring is for 12 hours post op

It is required for term infants < 50 weeks postconceptual (postmenstrual) age

It is required for preterm infants < 60 weeks postconceptual (postmenstrual) age

Question 9

What is the mechanism of action of the methylxanthine drugs in relation to apnoea

Answer 9

Block inhibitory Adenosine A1 receptors –> excitation of respiratory center neural output

Block inhibitory Adenosine A2A receptors –> found on GABA neurons

Question 10

What are the adverze effects of the methylxanthines

Answer 10

Tachycardia
Jitteriness
Emesis

Question 11

Apart from the methylxanthines, what are other described methods of preventing and treating apnoea

Answer 11

1. Prone positioning (thoracoabdominal synchrony + stabilize chest wall)
2. Nasal CPAP at 4 - 6 cmH20
3. Blood transfusions (? increase O2 carrying capacity but uncertain evidence)
4. Temperature control
5. ?? Treating GORD

Question 12

Are small for gestational age preterm infants more likely or less likely to have apnoea of prematurity

Answer 12

Less likely

Question 13

Does regional anaesthesia eliminate the need for apnoea monitoring in infants at risk of apnoea

Answer 13

A multicenter, randomized trial comparing general anesthesia with spinal anesthesia for former preterm and term infants undergoing inguinal herniorrhaphy (GAS trial), showed no difference in the incidence of postoperative apnea (~6% in preterm infants). However, the severity of apnea and the incidence of apnea in the first 30 minutes in the PACU was lower in the spinal anesthesia group.

Additionally, the administration of drugs to prolong the duration of a spinal or caudal block such as clonidine or sedative drugs like midazolam or dexmedetomidine are associated with postoperative apnea.

Therefore, regional anesthesia does not eliminate the need for postoperative monitoring in premature infants.

Question 14

List the most common causes of bradycardia in the post anaesthesia care unit (recovery)

Answer 14

1. Apnoa and hypoxia
2. vagal responses (e.g., nasogastric tube, laryngoscopy),
3. medications (e.g., neostigmine, beta-adrenergic blockade, alpha-2-agonists, opioids such as fentanyl),
4. increased intracranial pressure and
5. high neuraxial anesthetic blockade.