This document discusses the anaesthetic considerations for premature infants undergoing surgery. It outlines the physiological differences between premature and term infants that impact anaesthesia, including differences in the airway, respiratory, cardiovascular, renal and temperature regulation systems. It provides guidance on pre-operative assessment, appropriate intra-operative monitoring and management, including fluid management and blood product transfusion thresholds. Post-operative care involves close monitoring due to the risks of apnea and other complications in the first 48-72 hours after surgery.

1. Anaesthetic consideration in
premature infant
Dalila Hussain

2. Introduction
 Premature babies are defined as those born before
37 weeks
 Categorization of prematurity by gestational age &
birth weight
Gestational
age
Birth weight
36-37 week
Borderline/
near term
<2500g
LBW
31-36 week
Moderately
premature
<1500g
VLBW
24-31 week
Severely
premature
<1000g
ELBW

3. Physiology
 Airway :
- They are obligatory nose breathers due to
high resistance to airflow through oral passage
.
- large & lax tongue- easily fall back & obstruct
airway
- Trachea length is 4cm

4. • Infant’ s larynx is higher in neck (C2-C3)
compared to adult’s (C4-C5)
- glottis @ C3 level in premature infant

5. • Large , floppy & ohmega (Ω) shaped epiglottis ,
make visualisation of glottis difficult during
intubation

6. Funneled shape of larynx;
-Narrowest part of infant’s larynx is @ cricoid ring
with an approximate 14mm2 (ETT that passes easily
through the glottic opening may be tight @ level
cricoid ring)
Tight fitting
ETT may cause
oedema

7. 
Closing volume relatively large & encroaches normal tidal volume--
predispose to:
 Airway close
 Atelectasis

Increase O2 consumption ( 6ml/kg/min)to meet high metabolic rate

Tidal volume is relatively fixed due to anatomic structure

Unable to increase tidal volume--compesating for increase respiratory
demands through raised respiratory rate -- lead to early fatigue

Minute alveolar ventilation is more dependent on increase resp. rate
than on TV

Reduce FRC which is smaller than the closing capacity --- rendering
them dependent on PEEP & prone rapid desaturation

Chemoreceptor responses are blunted

8.  Extension of head does not facilitate intubation
but even obstruct airway
 External laryngeal pressure facilitate intubation by
bringing anterior larynx into view
- Changes in head position result in ETT movement
due to shortness of trachea & large tounge
- Flexion of the neck moves the tip of tube farther
out of trachea
- Extension moves the tube farther into the trachea

9. Sniffing
position
Neck flexed
forward, head
extend on the
neck & jaw held
forward is
required for
effective
ventilation

10.  Respiratory system
-
Fetal diaphragm contain only 10% Type 1 respiratory muscle
( high oxidative & resistant to fatigue)-- contributing to
apnoea during physiological stress & fatigue more quickly
-
Alveoli form @ 17-28 weeks gestational age
-
Pulmonary capillaries form @ 28-36 weeks gestational age
-
Lung maturation @ 36 week
-
Lung surfactant produce at 32-34 weeks. Surfactant function
to :
 Lower surface tension in alveoli
 Facilitate alveolar opening
 Prevent alveolar collapse at end of expiration

11.  Prone to apnoea (pauses in breathing > 20 sec/ loss
effective breathing associated with bradycardia)
Central apnoea
Obstructive apnoea
- Diminished
- Opposition of
hypercapnic
hypopharyngeal
response
soft tissues
- Hypoxic ventilatory - Nasal occlusion
depression
- Active inhibitory
reflexes
Mixed apnoea
-obstruction followed
by central pauses

12. Risk factor for apnoea
Hypoglycaemia
Hypoxia
Hypothermia
Anaemia
Sepsis

13.  Post operation, apnoea are frequent in 1st 12 hour
& can continue until 48-72 hour
 Premature infant exposed to mechanical
ventilation & > 28 days on O2 supplementation
likely to develop bronchopulmonary dysplasia
(BPD)
 Sx of BPD :
 Increase O2 requirements
 Reduced lung compliance
 Reversible airway obstruction

14. Cardiovascular system
 The ductus arteriosus often remain patent ( PDA)
 Other pathology eg: atrial / VSD can cause
significant :
 Left to right shunting
 Progressively increased pulmonary flow
 Congestive cardiac failure

15. Hypoxia is a potent
pulmonary
vasoconstrictor
Raised pulmonary
vascular resistance (PVR)
Lead to right to left
shunting, exacerbating
hypoxia & acidosis

16.  Prolonged raise PVR lead to:
 Poor right ventricular fx
 Impaired cardiac output
 Limited oxygen delivery
 Pulmonary oedema
 Sudden death

17. Haematology
 Term baby has 18-20g/dL of Hb
 Premature baby : 13-15g/dL of Hb
 70-80% of which is HbF
 HbF has reduced ability to release oxygen
 Target haematocrit 40-45%---facilitate O2 delivery
 Estimation of blood volume in premature baby:
95ml/kg
 If less than target, may necessitate preop blood
transfusion

18. Renal
 Ability to retain Na+ @ 32 week GA
 The distal tubular response to aldosterone is low until
34 week
 ADH level are high
 Impaired ability to concentrate urine
 Drug excretion delayed due to immature renal system
 Total body water : 75-85% of body weight . Inversely
related to GA
 Marked transepidermal permeability & large body
surface area accelereate H2O loss
 Evaporative H2O increase 15 fold during 1st few days
of life compare with term babies.

19. Temperature regulation
 Increase surface area to body weight ratio
 Decrease brown fat store- limit heat production
 Non keratinised skin , extreamly susceptible to heat
loss
 Inability to shivering
 Thermoneutral environment for unclothed preterm
baby is 34 degree celcious
 @ this temp, O2 demand is minimal
 Hypohermia induced stress can lead to:
 Hypoglycaemia
 Apnoea
 Metabolic acidosis

20. Glucose homeostasis
 Have fewer glycogen stores
 Underdeveloped gluconeogenesis pathway
 Prone developing hypoglycaemia during
starvation
 Hyperglycaemia should be avoided as a
hyperosmolar state can lead to IVH, osmotic
diuresis & dehydration

21. Gastrointestinal system
 Gastro-oesophageal reflux is common resulting
from underdeveloped and incompetent lower
oesophageal sphinter.
 This lead to:
-Laryngospasm
- Chronic cough
-Laryngitis
-Tracheitis
-Apnoea
-Otitis media
-asthma
 NEC with bowel wall necrosis and perforation can
lead to systemic sepsis
 Drug metabolism is immature

22. Central nervous system
 Pain receptors develop by 20 weeks GA
 Pain pathways develop by 26 weeks.
 A foetus of 26 weeks may demonstrate a flexion
withdrawal reflex in response to pain stimulation
 Descending inhibitory pathways are immature
leading to greater pain sensitivity
 Risk factor for IVH or later neurodevelopmental
delay include :
- RDS
- Hypotension / fluctuating blood pressure,
- the use of hypertonic infusions
- aggressive volume expansion

23. Pre anaesthetic assessment
 Consult parent regarding risk of deterioration of
pulmonary function & necessitating postoperative
ventilatory support
 Particular points to ascertain are:
1)
Gestational age at birth and the current gestational
age
2)
Weight
3)
Periods of mechanical ventilation, CPAP and
oxygen therapy and the duration
4)
Apnoeas – frequency, duration, possible triggers
5)
Co-morbidities, particularly cardiac
6)
General health, growth and development
7)
Previous operations
8)
Medications

24.  Airway assessment
 If already intubated- check the ETT size & length
 Blood investigations
 If anticipated blood loss greater than 10% of blood
volume, crossmatch should be taken
 Echocardiogram must be performed before
surgery
 Minimise starvation times to prevent
hypoglycaemia and dehydration.

25. Intraoperative management
 The ambient temperature minimum 27 degree celcious
for reception of the baby
 Effective warming device eg: warming matress, warming
air blanket
 Inspired gases should be heated & humidified.
 Fluids , blood, blood products & irrigation fluid must be
warmed.
 If 360 o access to baby is required by the surgeon( eg:
laser surgery for retinopathy), access can be improved by
removing the head & foot ends of operating table.

26. ETCO2
detector
Tapes for
securing
ETT
GA
machine
Check all
the
equipment
Connector to
fit between
ETT tube &
ventilation
bag, circuit
Laryngoscope
handle
& blades: 00, 0
(premature)
ETT: portex
peadiatric
size 2.5, 3.0
& 3.5mm

27. ETT size & length
Baby weight
( kg)
Tube size
(mm)
Oral tube
length @ lip
( cm)
Nasal tube
length @
nose (cm)
Suction tube
size ( Fr)
<1.0
2.5
5.5
7.0
6
1.0
2.5-3.0
6.0
7.5
6
2.0
3.0
7.0
9.0
6
3.0
3.0
8.5
10.5
6
3.5
3.0-3.5
9.0
11.0
8
4.5
3.5
9.0
11.0
8
An alternative is to assess ET tube length by the rule of
6.
Oral tube length(cm) =: 6 + wt (kg)
Nasal tube length(cm) = 6 + (1.5 x wt)
appropriate position must always be comfirmed

28.  Monitoring:
-BP using an appropriate sized cuff
-ECG
-capnography
-temperature
- SpO2 ( 2 oximeter probes recommended)
- pt with PDA, 1 probe placed on the right hand
( pre-ductal) & the other on lower limb ( post-ductal)

29.  Inhalational induction is often preferred
 Moderate concentration of volatile can be used to ;
-
Minimized increase in PVR
-
Avoid decrease in systemic arterial presure
 Newer shorter acting agent, desflurane may useful for
recovery in a preterm infant.

Sale, in their study on premature babies under 37 weeks gestation & under 47 week undergoing
inguinal herniotomy suggested that infant wake faster from GA when maintained with desflurane as
compared with sevoflurane, but no difference in postoperative respiratory events was demonstrated
 A range of uncuffed tubes should be available
– a neonate of <1200g may need a 2.5mm tube
- 2 kg baby has tracheal tube positioned @ gum margin @ 8cm mark
 Anticipate difficult intubation if premature infant has
undergone prolong ventilation-- possibility subglottic
stenosis

30.  Exposure to high O2 levels is associated with
increase morbidity & mortality.
 Tacycardia & HTN can be detrimental in presence
of underdeveloped cerebral autoregulation.
-
Careful titration of anaesthetic & narcotic agent is necessary
 Multimodal analgesia should be use for pain relief
(eg: local anesthesia, paracetamol, opioid (fentanyl)

31. Intaoperative fluid
management
 Estimated maintenance fluid requirement:
100ml/kg/24hour
 Maintenance fluid should be isotonic.
 Premature infant often receive a glucose-containing
solution to maintain normoglycaemia.
- This should continue intraoperative

32. Blood / blood products
Required volume
Pack cell
ml = desired increment in Hb
(g/dL) x weight (kg) x 3
Platelet
10-20ml/kg
FFP
10-20ml/kg
cryoprecipitate
5-10ml/kg
Replace on going loss:
-Superficial surgery: 1-2ml/kg/hour
-Thoracotomy : 4-7ml/kg/hour
-Abdominal surgery :5-10ml/kg/hour
Do not introduce
air bubbles into
circulation which
may transverse
right to left shunts
Sign fluid depletion:
Hypotension, tacycardia, increase core peripheral
temperature, delayed capillary refill time, reduce heart
sound

33. Post operative care
 Remain intubated??? Or extubate???
-
Decision should consider the preoperative state of the baby as
well as the type of surgery performed.
-
If plan for extubate, baby should fully awake & managing
adequate TV without support
 Post operation, apnoea are frequent in 1st 12 hour & can
continue until 48-72 hour
 Monitor in high dependency unit for at least 12 hours
post operatively and for a further 12 hours following
any apnoeic period.

34. References
 Anaesthesia for the preterm infant – Anaesthesia UK
 Kawshala Peiris, David Fell,..The Prematurely Born Infant and
Anaesthesia, Oxford Journal: Volume 9, Issue 3, Pp 73-77
 Sale SM, Read JA ,..Prospective Comparison of Sevoflurane and
Desflurane in Premature Infant undergoing inguinal
herniotomy, Br J Anaesth.2006 Jun; 96 (6): 774-8. Epub 2006 Apr
28
 Guy Bayley, Special consideration in the premature and expremature infant, Anaesthesia and Intensive care medicine 12:3,
2010 Elsevier Ltd
 Bharti Taneja, Vinish Srivastava, Physiological and anaesthetic
consideration for the preterm neonate undergoing surgery ,2012;
1:14
 Neonatal Handbook