Preoperative management: Extremes of age and Emergency Surgery

Question 1

How is AIRWAY management different in children?

Answer 1

1. Large head - tips head forward (stabilize with ring)
2. Neutral position best for maintaining airway with FM
3. Avoid pressure soft tissues of the floor of mouth (FM)
4. Large tongue
5. Larynx anterior and cephalad
6. Large and floppy epiglottis (straight blade posterior)
7. Airway narrowest cricoid ring (Uncuffed tubes used)

Question 2

Outline the differences in the child respiratory system that are relevant to the anaesthetist

Answer 2

Compliant chest wall –> reduced FRC (small reservoir) and encroaching CC–> VQ mismatch

Diaphragmatic ventilation (poorly developed intercostals)

Higher RR = Higher WOB combined with immature ventilatory control –> small children require intubation and controlled ventilation

Question 3

Outline the differences in the child CVS that are relevant to the anaesthetist

Answer 3

HR higher
BP lower
CO higher
SVR lower
Blood volume higher 
neonates 90 ml/kg; children; 80 ml/kg; adults 70 ml/kg

Question 4

Outline the differences in the Nervous system of children relevant to the anaesthetist

Answer 4

Preterm infant: Cerebral vessels friable –> intraventricular haemorrhage (change of BP/physiological stress)

Increased MAC required
- peaks at 1 year (50% greater than adult MAC) and falls to reach adult level by puberty

Reduced Ach at NMJ

• Less sensitive to SUX (give more)
• More sensitive to NDMR (give less)

Question 5

Outline the differences in the Renal system of children relevant to the anaesthetist

Answer 5

Normal number nephrons but immature so:

1. GFR is reduced
2. Reduced ability to regulate Na
   - Sodium load in IV fluid administration
   - Hypotonic solutions (susceptible)
3. Reduced ability to concentrate urine - quicker dehydration

Question 6

Outline the differences in the Hepatic system of children relevant to the anaesthetist

Answer 6

NEWBORN liver is immature taking at least 2 MONTHS to achieve normal function

1. Reduced drug metabolism leading to prolonged duration of action
2. Hypoglycaemia risk (reduced glycogen stores and impaired gluconeogenesis) - avoid excessive starvation
3. Impaired coagulation –> reduced synthesis of Vit K dependent factors

Question 7

Outline the differences in the Metabolic system of children relevant to the anaesthetist

Answer 7

OXYGEN
- Higher VO2 in children (weight adjusted) –> apnoea leads to hypoxia faster

TEMPERATURE

• Surface area to body ratio is 2 - 2.5 larger than in an adult –> greater radiant heat loss.
• -> warm operating theatres and insulate with warming devices

Newborns cannot shiver, they use brown fat initiated by catecholamines

Question 8

How is AIRWAY management in the elderly altered

Answer 8

Frequently edentulous

• easier laryngoscopy
• difficult BVM

Question 9

Outline the differences in the Respiratory system of the elderly relevant to the anaesthetist

Answer 9

IRV, ERV, Surface area for gas exchange fall
Closing capacity increases to encroach on FRC –> age related decline in PaO2

PaO2 (kPa) = 13.3 - (age/30)

Poor upper airway tone and reduced ability to cough –> aspiration and chest infection more common

Question 10

Outline the differences in the CVS in the elderly relevant to the anaesthetist

Answer 10

CO - decreases by 1% a year from the age of 30

HR max - declines with age

Ventricles stiffen (endocardial fibrosis) -> ventricular filling more dependent on atrial contraction

Loss of SA node pacemaker cells –> increase likelihood of dysrhythmias

Reduced large vessel elasticity –> Increased SBP and MAP

Question 11

Outline the differences in the Nervous system in the elderly relevant to the anaesthetist

Answer 11

CNS
Higher functions: Increased delirium

Increased CNS sensitivity to all CNS depressant drugs
- MAC declines to reach about 60% of initial value by 80 years

ANS
Impaired ANS –> impaired response to circulatory disturbance

Question 12

Outline the differences in the Renal system in the elderly relevant to the anaesthetist

Answer 12

GFR decreases by 1% a year from age 30
- Creatinine may not rise (decrease skeletal muscle mass) –> modest rises in serum creatinine may indicate significant renal impairment

Deterioration RENAL HOMEOSTATIC MECHANISMS
(Aldosterone and ADH)
- More prone to effects of fluid overload and hypovolaemia

Perioperative renal failure is more common in the elderly

Question 13

Outline the differences in the Hepatic system in the elderly relevant to the anaesthetist

Answer 13

Hepatic mass
Hepatic blood flow
–>Both reduce by about 40% by the age of 90 –> reduced clearance and prolonging the effects of drugs metabolized by the liver
(opioids, benzodiazepines, NMBs)

Question 14

Can propofol be used for all ages?

Answer 14

Not licensed for use < 3 years

Question 15

When is a T-piece required and why?

Answer 15

For children < 20 kg: valveless system to reduce the work of breathing

Question 16

Why is knowledge of the surgical diagnosis (the magnitude and urgency of the surgery) important

Answer 16

This dictates the time available and the extent to which derangements can be corrected preoperatively.

Question 17

Outline approach and targets for preoperative resuscitation in emergency cases

Answer 17

Situation - Summary
Background - SAMPLE Hx
Actions - Whats been done
Recommendations - Whats being planned

Determines time available for preoperative resuscitation:

Airway: Assess and plan
Breathing: Optimize oxygenation and ventilation
Circulation:
- HR < 100
- SBP > 100
- Urine output > 0.5 ml/kg/hour
- Metabolic acidosis should correct with improved CO

Haemostatic resuscitation in trauma
INR > 1.5 -> FFP
Hb < 8 - 10 g/dl in an actively bleeding -> PRBCs
Calcium < 0.8 -> calcium gluconate
Platelets < 50 -> platelets
platelet dysfunction (e.g. drugs, urea) -> DDAVP +/- platelets

Disability: Assess and plan (GCS)
Exposure: Rx glucose. Prevent hypothermia. Reduce blood loss

Some cases require admission to HDU/ICU preoperatively for aggressive resuscitation guided by invasive monitoring