24.6 Cigarette Smoking

Question 1

a) List the effects of cigarette smoking on the cardiovascular system and on oxygen delivery, outlining the pathophysiological mechanisms involved. (12 marks)

Answer 1

Cardiovascular:
1.&raquo_space; Hypertension:
raised circulating catecholamine levels and accelerated atherosclerosis
formation increase left ventricular afterload,
resulting in left ventricular hypertrophy,
diastolic dysfunction
and, ultimately, heart failure.

2. > > Tachycardia:
   raised circulating catecholamine levels
   due to stimulation of nicotinic receptors.
3. > > Peripheral vascular disease:
   accelerated atherosclerosis formation.
4. > > Ischaemic heart disease:
   accelerated atherosclerosis formation and
   prothrombotic state
   (due to carbon monoxide,
   nicotine and other chemicals
   in cigarette smoke causing
   polycythaemia,
   enhanced platelet action,
   increased fibrinogen levels).
5. > > Heart failure: subsequent to infarction,
   ischaemia and cardiac muscle damage.

Oxygen delivery:
» Airway conditions related to smoking
that result in reduced oxygen
availability within the alveolus and
reduced effective gas exchange.
Hypoxic hypoxia.

> > Carboxyhaemoglobin formation:
haemoglobin has a 250-fold increased
affinity for carbon monoxide compared
to oxygen, thus reducing oxygen
carriage. Anaemic hypoxia.

> > Shift of oxygen dissociation curve to left:
carbon monoxide shifts the
dissociation curve reducing the
ability of hemoglobin to release oxygen.
Anaemic hypoxia.

> > Inhibition of cytochrome oxidase by carbon monoxide, reducing oxygen dependent
synthesis of ATP in mitochondria.
Histotoxic hypoxia.

The combined effect is reduced oxygen delivery to the myocardium during a
time of increased need, resulting in increased risk of ischaemia, which further
promotes carboxyhaemoglobin formation, further reducing myocardial
oxygen delivery, increasing the risk of perioperative ischaemia and infarction.

Question 2

b) List the effects of cigarette smoking on the respiratory system, other than those you have outlined
above, that are relevant to the conduct of general anaesthesia. (4 marks)

Answer 2

> > Pre-existing airways disease
as a result of smoking such as cancer,
chronic obstructive pulmonary disease.

> > Increased upper airway irritability:
breath-holding, laryngospasm at
induction and instrumentation.

> > Increased lower airway reactivity,
bronchospasm, mucus secretion.

> > Impaired mucociliary transport
and secretion clearance:

risk of atelectasis,
postoperative pneumonia,
shunt.

> > Accelerated rate of FEV1 reduction with age: **significantly reduced level
predictive of postoperative
respiratory complications.

> > Increased closing capacity.

> > Increased risk of
pulmonary embolism due
to hypercoagulability:

thromboembolic preventative
measures to be taken.

Question 3

c) What advice would you give a smoker 24 hours before a scheduled procedure under general
anaesthesia and why? (4 marks)

Answer 3

To stop smoking for the remaining
24 hours preoperatively and,
ideally, to stop thereafter:

> > Circulating catecholamine levels**
return to normal within 1 hour and
carboxyhaemoglobin clearance occurs
within 24 hours, thus massively
improving oxygen delivery to
all tissues including the myocardium,
reducing the risk of perioperative ischaemic event.

As oxygen carriage improves,
physiological reserve to cope
with perioperative periods of
inadvertent hypoxia improves.

> > Postoperatively, ongoing smoking
is known to be associated with
poor tissue healing,
including wounds,
anastomoses, flaps.

Blood hypercoagulability will start to
improve as carbon monoxide levels fall,
reducing risk of postoperative thrombotic events.