66. Post-operative hypotension

Question 1

You are asked to see a 40-year-old lady in recovery after an elective right
hemicolectomy. The nurse is concerned because her blood pressure is
80/40. What are the causes of hypotension in recovery?

Answer 1

Mean arterial pressure is determined by the formula

MAP = CO × SVR.

Cardiac output is determined by heart rate and stroke volume (which is dependent on
pre-load, after-load, and contractility). Therefore, hypotension may be caused
by:

Question 2

Therefore, hypotension may be caused
by:

Answer 2

1. Reduced SVR:
2. Low heart rate:
3. Reduced pre-load:
4. Reduced contractility:

Question 3

Reduced SVR:

Answer 3

Residual anaesthetic agents.

Sympathetic blockade from spinal or epidural anaesthesia.

Opioids.

Systemic inflammatory response or sepsis.

Hypothermia or pyrexia.

Anaphylaxis or anaphylactoid reactions.

Actions of patient’s normal medication especially ACEIs and Angiotensin 2 blockers.

Hypercapnia (though sympathetic stimulation usually produces hypertension).

Question 4

Low heart rate:

Answer 4

High epidural or spinal block with cardiac sympathetic block.

Myocardial ischaemia or infarction (particularly inferior).

Pre-operative beta-blockade or digoxin (particularly if hypokalaemic).

Opioids.

Hyperkalaemia.

Hypothermia.

Profound hypoxia

Question 5

Reduced pre-load:

Answer 5

Absolute hypovolaemia due to bleeding or other intra-operative losses.

Relative hypovolaemia due to vasodilatation. Similar to causes of reduced SVR.

Obstruction to venous return such as tension pneumothorax or right to left obstruction due to pulmonary embolism.

Question 6

Reduced contractility:

Answer 6

Myocardial ischaemia or infarction
Hypoxia
Hypocalcaemia
Hyperkalaemia
Hypothermia
Beta-blockade
Cardiac insufficiency in TUR syndrome

Question 7

The commonest causes of Low MAP peri-operatively are:

Answer 7

Volume related (relative or absolute)
as volume is the biggest
determinant of cardiac output.

A low SVR – as many anaesthetic drugs affect SVR.

Question 8

How would you approach this problem?

Answer 8

would familiarise myself with the patient’s history and peri-operative
records to identify relevant factors such as cardiac history, pre-operative
medication, pre-operative and intra-operative blood pressure, anaesthetic
agents and techniques used, and intra-operative fluid loss and fluid management.

I would also perform an Airway, Breathing and Circulation assessment of
the patient and rectify problems as I identified them.

Question 9

Tell me what you would be looking for in each part of your examination
and what you would do?

Answer 9

Airway

Look for obstruction leading to respiratory failure. I would
give supplementary oxygen to all patients:

Mechanical obstruction due to low conscious level or
residual neuromuscular blockade. Use airway opening
manoeuvres and airway adjuncts. Naloxone or neostigmine
may be indicated.
Laryngospasm. PEEP should be applied via a bag and mask.
Propofol may be useful to loosen the spasm, but
suxamethonium should be available if re-intubation
becomes necessary.
Physical obstruction due to retained airway packs or vomitus.
Airway oedema. May warrant re-intubation and
dexamethasone.

Question 10

Breathing

Answer 10

Look, listen and feel noting respiratory rate, pattern, breath sounds, and oxygen saturation:

Hypo-ventilation due to residual anaesthesic agents, opioids
or neuromuscular blockade. Naloxone or neostigmine may
be indicated.

Pulmonary oedema. Diuretics, nitrates and facial CPAP can
be used but may compromise blood pressure. Severe cases
will require re-intubation.

Aspiration.

Pneumothorax. If tension pneumothorax is suspected,
needle thoracocentesis in the second intercostal space
followed by formal intercostal drainage is indicated.

Atelectasis.

Hypo-ventilation due to high spinal. May require
re-intubation and sedation until block descends.

Pulmonary embolism.

Question 11

Circulation

Answer 11

Look, listen and feel noting heart rate, rhythm, blood
pressure, capillary refill, urine output, drains output, fluid
management, and evidence of occult bleeding:

Hypovolaemia due to haemorrhage or other flood loss. Treat
with fluid resuscitation and blood products as needed. May
require surgical input if bleeding.

Vaso-dilatation. First line treatment should be fluid
resuscitation but vasopressors may be required. Adrenaline
may be required if anaphylaxis is suspected

Cardiac insufficiency. Signs of ischaemia or infarction should
be sought and an ECG performed. Correction of hypoxia,
hypovolaemia, hypothermia, and electrolyte imbalance may
improve cardiac output. Inotropes may be required.