Preterm anesthetic consideration
anesthetic implications in preterm
Published on: Mar 4, 2016
Transcripts - Preterm anesthetic consideration
Dr. Varun kumar varshney
Premature babies - born before 37 weeks
Gestational Age determines the extent of
• ALVEOLI develop 17-28 WKS
• Pulmonary capillaries 28-36 wks
• Before 32-34 wks surfactant deficeint
more prone to RDS
• mechanical ventilation
• more than 28 days of oxygen supplementation BPD
CONTROL OF RESPIRATION /APNOEA
• Chemoreceptor blunted response
• Normal biphasic response to hypoxaemia
replaced by apnoea.
• incidence higher in preterm.
• Apnoea pause more than 20 sec alone
or less than 20 sec + bradycardia
• Preterm - 10% type 1 fibre diaphragm and intercostal muscles
apnoea at time of physiological stress.
• After operation, apnoeas are frequent in the first 12 h
and can continue until 48–72 h.
Large sized tongue
Larynx : more cephalic, funnel shape
Epiglottis : short, stubby, omega shaped,
angled over laryngeal inlet
Vocal cords angled
Cricoid cartilage : Narrowest portion
• No doughnut is required
• Straight blades preferred
Tube that easily passes the vocal cords
may be tight in the subglottic region
Uncuffed tubes preferred
Cuffed tubes : leak maintained around cuff
(with or without inflation) to prevent trauma
resulting in subglottic oedema and
subsequent post-extubation stridor.
• Chest wall
Lungs : non compliant
Alveoli thick walled at birth
Dead space ventilation similar to adults
Oxygen consumption 2-3 times higher
Work of breathing 3 times that in adults ----
increased by cold stress / airway obstruction
Hypoxic and hypercapnic drives not well developed
Depress respiration in these patients
Weaker intercostal muscles,diaphragm
Horizontal , pliable ribs
Diaphragmatic and intercostal muscles
Low type 1 muscle fibres – ability to perform repeated
• Early fatigue
Limited respiratory reserve
Horizontal ribs prevent ‘bucket handle’ action
seen in adult breathing : limit increase in VT
Ventilation primarily diaphragmatic
Bulky abdominal organs , stomach filled
with gases from poor bag mask ventilation –
impinge on contents of the chest , splint diaphragm
reducing adequate ventilation
Chest wall more compliant : low FRC
FRC decreases with apnoea , anaesthesia causing lung
Closing volume larger than FRC until 6-8 years
Causes an increased tendency for airway closure at end
Thus, neonates generally need IPPV
during anaesthesia and would benefit from a
higher respiratory rate and the use of PEEP.
CPAP during spontaneous ventilation improves
oxygenation and decreases work of breathing
Apnoea common post op in premature infants
Stroke volume - fixed by noncompliant and immature LV
CO sensitive to HR changes
Activation of parasympathetic nervous system,
anesthetic overdose, or hypoxia -- trigger bradycardia --
profound reductions in CO
Sympathetic nervous system
Blunted response to exogenous catecholamines
Immature heart -- more sensitive to depression by volatile
anesthetics and opioid-induced bradycardia
Not fully mature
• DUCTUS ARTERIOSUS- remain patent
• Flip flop circulation.
• Left---rt circulation.
increased pulmonary flow.
congestive cardiac failure.
Bradycardia associated with hypoxia : treat with oxygen
and ventilation initially
Patent ductus contracts in 1st few days of life
fibrose within 2-4 weeks
Closure of foramen ovale is pressure dependent
closes in the first day of life
Neonatal pulmonary vasculature reacts to rise in Pa02 and
pH and fall in PaCO2 at birth
Alterations in pressure and with response to hypoxia and
acidosis : reversion to transitional circulation may occur in
the first few weeks after birth.
A term baby has 18–20 g /dl of haemoglobin (Hb);
in prematurity, this can be 13–15 g/ dl,
70–80% of which is HbF.
•Fetal Hb has a reduced ability to release oxygen;
•Compensation the relatively high blood volume,
Hb concentration, and cardiac output .
•This compensation is much less in the preterm baby.
A target haematocrit of 40–45% facilitates oxygen delivery; this
may necessitate earlier perioperative blood transfusion
EARLY BLOOD TRANSFUSION
TARGET HAEMOCRIT 40-45%
Metabolism and temperature
Vulnerable to hypothermia
Large body surface area to weight ratio
thin skin (non keratinized)
decrease brown fat (nonshivering thermogenesis)
Low body temperature
Decreased cardiac output
Increased duration of action of drugs
Decrease in platelet function
Increase in the risk of infection
Heat lost during anaesthesia mostly via radiation
Also by conduction, convection and evaporation
Optimal ambient temperature to prevent heat loss
34ºC for premature infant
32ºC for neonates
28ºC in adolescents and adults.
Peri-operative heat loss is vital
Placing baby on warming mattress and warming the surgical
unit (80° F or warmer) : conduction
Keeping infant in incubator and covered with blankets :
convection. Cover head too.
Evaporation : humidification of inspired gases,
use of plastic wrap to decrease water loss through skin,
warming of skin disinfectant solutions.
Hot air blankets : most
effective means of
Anesthetics alter many
thermogenesis in neonates.
Renal function diminished due to
-Small perfusion pressures
-Immature glomerular Fxn
-Immature tubular function
Nearly complete maturation -- ≈ 20 weeks after birth
Complete maturation -- 2 years of age
Free water and solute clearance impaired in PRETERM
More prone to dehydration
T1/2 of medications -prolonged (antibiotics)
• Preterm infants impaired ability to concentrate urine, so
cannot tolerate under and over hydration.
• They are unable to retain sodium
prone to hyponatraemia.
• Water loss is common in preterm infants
due to the large body surface area and thin skin,
particularly in the first few days of life.
prone to hyponatraemia.
Functional maturity of the liver- incomplete
Metabolic enzyme developed but not inducible.
With growth of infant ability to metabolize medications ↑
(1) Hepatic blood flow ↑, more drug delivered
(2) Enzyme systems develop , induced
Cytochrome P450 system ≈ 50% adult values at birth.
CYP3A : present at adult values at birth
Other cytochromes absent or reduced
Phase II reactions : involve conjugation to facilitate renal
Often impaired in neonates(preterm)
Jaundice (decreased bilirubin breakdown)
long drug t1/2
the half-life of morphine and benzodiazepines is several days
Preterm infant’s liver - minimal glycogen stores
Unable to manage large protein loads
Thus increased tendency :
failure to gain weight when diet contains too much
Birth -- gastric pH is alkalotic
Day 2 -- pH in normal physiologic range
Coordination of swallowing with respiration
under developed in preterm
High incidence of gastroesophageal reflux
Hypoglycaemia : common in preterm
less glycogen store
underdeveloped glucogenic pathway.
May lead to neurological damage
Glucose levels : monitored regularly
Infusion of 10% glucose may be used.
Neonates - appreciate pain
(increased HR , BP , neuro-endocrine response)
Narcotics depress the ventilation response to a rise in PaC02.
BBB poorly formed : barbiturates, opioids, antibiotics and
bilirubin cross --- prolonged duration of action
Central nervous system
• Intraventricular haemorrhage
occurs in 25% of very low birth weight infants
within the first 72 hours of life.
Intraventricular haemorrhage complicated by ventricular
dilation, progress to hydrocephalus.
• Recently anaesthetic agents effect on the developing
brain leading to later memory and learning impairment.
• SO, only essential surgery should be
performed in early life.
Ketamine should probably be avoided in premature babies
Cerebral vessels in preterm infant : thin walled, fragile--
Awake airway manipulations
Retinopathy of prematurity
More common in preterm infants
• cause vasoconstriction of retinal vessels
high concentrations of supplemental oxygen,
• lead to retinal detachment, fibrosis
blindness in children,
• prevented avoiding exposure to high concentration of 02.
Total body water -- preterm infants > term infant
Water soluble drug - large Vd - requires large loading dose
Fat , muscle content ↑ with age
Drug redistributing into fat have long clinical effect
Drug redistributing into muscle
Small safety margin between anaesthetic overdose
and inadequate depth of anaesthesia
Anaesthetic requirement preterm < term neonates
Infants : higher MAC than older children or adults
Uptake more rapid : increased RR , CI
Non volatile anaesthetics
Larger doses of Propofol –
Shorter elimination t1/2
Higher plasma clearance
“Propofol infusion syndrome” (>48hrs duration ,
Thiopental : larger dose in children
- Shorter elimination t1/2
- Greater plasma clearance
Neonate ( 3-4mg/kg)
- Less protein binding
More potent in preterm
Easier entry across BBB
Decreased metabolic capability
Increased sensitivity of respiratory centers
Detailed history from both the parents .
Points to be asked-
• Gestational age at birth and the current gestational age
• Periods and duration of mechanical ventilation,
• Apnoeas – frequency, duration, possible triggers
• Co-morbidities, particularly cardiac
Greater risk for aspiration –
Low gastric pH
High residual volumes
Type Fasting time (hrs)
Clear liquids 2
Breast milk 4
Infant formula 6
Solid (fatty or fried) foods 8
• ADVANTAGES OF THESE LIBERAL GUIDELINES-
- Prevent dehydration and hypoglycemia
- Reduce the risk of aspiration
• platelets count,
• coagulation profile
A crossmatch should be taken where blood loss
is anticipated to be greater than 10% of blood volume.
All premature babies should have an echocardiogram
performed before surgery
Premedication is not required
However, atropine should be considered to pre-empt
• The PRETERM may already be intubated and
ventilated prior to arrival in the operating theatre.
• A range of uncuffed tubes should be available.
• If the infant has undergone prolonged ventilation,
there is a possibility of subglottic stenosis.
• An orogastric tube is useful after intubation
to decompress the stomach and to minimise
splinting of the diaphragm and facilitate ventilation.
• AVOID excessive oxygen concentrations predispose to
retinopathy of prematurity.
• A balanced anaesthetic technique should be used
• For pain, Paracetamol is commonly used.
• NSAIDs for analgesia are C/I due to renal
• NSAIDs may cause premature closure of a PDA.
• Where opiates are necessary, short acting such as fentanyl.
• The use of local anaesthetic techniques is encouraged
local infiltration by the surgeon or
caudal, epidural or spinal.
• Should have all the necessary equipment and staff for this.
• Ideally 2 oxygen saturation probes
• one on the right hand and
• one on the lower limb
to compare pre ductal and post ductal levels.
• ECG via neonatal electrodes, non-invasive blood pressure,
capnography and temperature monitoring are mandatory.
• The theatre pre-warmed to achieve a temperature 25°C.
Active warming by such as overhead heaters should be used
as well as a paediatric heat moisture exchange.
• All fluid and blood products warmed prior
• irrigation fluid is warmed prior to use.
• prevent unnecessary exposure.
• Surgical drapes lightweight, preferably plastic allow the
baby to be clearly seen.
• Blood glucose closely monitored.
• a widely accepted cut off is a blood sugar of <2.6mmol/L.
• Glucose can be given as a bolus of 1-2ml/kg of 10% glucose.
• Regular blood sugars should be checked in order to confirm
nomal glucose level
Plan for awake intubation
Return of gag reflex
Responsive and purposeful
• Ideally, fluid
acid–base, electrolyte corrected before reaching ot
Hb deficits should be
• The estimated maintenance fluid requirement of a preterm
infant is 100 ml /kg/24 h21.
• During surgery, the maintenance fluid should be isotonic (e.g.
Hartmann’s solution, 0.9% sodium chloride).9
• Preterm infants often receive a glucose-containing solution
to maintain normoglycaemia continue during surgery.
• Estimation of blood loss can be difficult
• replacement can be guided by
capillary Hb and haematocrit
perceived ongoing and anticipated losses, and
• The extremely premature and those with cyanotic heart disease
need a haematocrit of 35–40% to maintain oxygenation.
• As a transfusion guideline, the volume of packed cells
required(ml)=desired increment in Hb (g dl21)*weight (kg)*3
• Platelets and fresh frozen plasma is given as
10–20 ml /kg21, and cryoprecipitate as 5–10 ml /kg21.
• Third-space losses 1–2 ml/ kg/hfor superficial surgery,
4–7 ml /kg/ hfor thoracotomy, and
5–10 ml/ kg /hfor abdominal surgery.9
• Hypotension, diminished heart sounds, tachycardia,
increased core-peripheral temperature gradient, and
delayed capillary refill suggest fluid depletion.
• Urine output is a good indicator of fluid
status and perfusion; an output of 0.5–2 ml/kg /h is the
• However, monitoring such small volumes is difficult.
• If an arterial line is in situ, the position of
the dicrotic notch and the area under
the arterial waveform can give valuable
information to guide fluids.
• Care must be taken during drug injections
not to introduce air bubbles into the circulation
Which may traverse right-to-left shunts.
As little as 0.2–0.4 ml kg can BE DANGEROUS
MABL = EBV * Starting haematocrit – Target haematocrit
Preterm : 120ml/kg
Term : 90ml/kg
Child(3-12mths) : 70-80ml/kg
Child (›1yr) : 70ml/kg
A decision whether to extubate or not????
consider the preoperative state of the baby
type of surgery performed.
If plans extubate, fully awake and
managing adequate tidal volumes without support.
period. apnoea-major concern
Premature babies under 60 weeks gestational age
need high dependency unit for at least 12 hours
and for a further 12 hours following any apnoeic
Continuous apnoea alarm monitoring must be available
IV caffeine at 10mg/kg
CPAP may well be useful at this stage