8.01 - Pre-Operative Care

Question 1

Name the crystalloids commonly used in fluid prescriptions.

Answer 1

• 5% dextrose solution
• 0.9% sodium chloride solution (normal saline)
• Hartmann’s solution

Question 2

Outline the features of 5% dextrose solution, and therefore the clinical indications of prescription.

Answer 2

• hypotonic and isosmotic
• fluid containing only dextrose and water

Dextrose is rapidly taken up into cells to be metabolised; remaining free water equilibrates across all the body compartments.

As only a small proportion of fluid stays within the intra-vascular space, 5% dextrose solution has no role in fluid resuscitation of a patient, only in fluid maintenance regimes*.

*the main advantage of dextrose is being able to maintain hydration without administering an excess of electrolytes, and it can be prescribed with supplementary potassium if required.

Question 3

Outline the features of normal saline solution, and therefore the clinical indications of prescription.

Answer 3

• isotonic solution
• contains water, Na+ and Cl-

Normal saline solution equilibrates throughout both the intravascular and interstitial spaces, making it useful in both fluid resuscitation and maintenance regimes.

Normal saline solution can be prescribed with supplementary potassium if required.

Question 4

Why is normal saline solution contraindicated when used as a lone fluid maintenance?

Answer 4

Excessive saline replacement can result in a hyperchloraemic acidosis.

Question 5

Outline the features of Hartmann’s solution, and therefore the clinical indications of prescription.

Answer 5

• isotonic solution
• contains water, Na+, Cl-, K+, HCO3- and Ca2+

Hartmann’s solution distributes throughout the intravascular and interstitial spaces, making it useful for both fluid resuscitation and fluid maintenance.

Question 6

Outline the clinical features of colloid fluid solutions, and therefore their indications of prescription.

Answer 6

Colloids are rarely used in surgical practice, as clinical trials have shown their limited benefit in resuscitation alongside a small risk of anaphylaxis.

Colloids contain proteins with large molecular weights, aiming to maintain a high plasma oncotic pressure to keep fluid within the intravascular compartment.

Question 7

What are the principles upon which fluids are prescribed?

Answer 7

• resuscitation
• maintenance
• replacement

Question 8

a) What percentage of total body weight is water?

b) What percentage of total body water distributes into the intracellular fluid?

c) What percentage of total body water distributes into the extracellular fluid?

d) What percentage of ECF stays in the intravascular space?

e) What percentage of ECF moves into the interstitium?

Answer 8

a) 66%

b) 66%

c) 33%

d) 20%

e) 80%

Question 9

Why is aggressive fluid resuscitation often needed to maintain intravascular volume in a septic patient?

Answer 9

Tight junctions between the capillary endothelial cells break down and vascular permeability increases, increasing hydrostatic pressure and reducing oncotic pressure. This leads to fluid leaving the vasculature and entering the tissue.

In order to maintain the intravascular volume, large volumes of intravenous fluids therefore need to be given.

Question 10

Outline the sources of our fluid input.

Answer 10

• 60% from fluids via the enteric route (major)
• 20% from food
• 20% from metabolic processes

When a patient is nil by mouth (NBM), it is important that all sources are replaced via the parenteral route.

Question 11

Give the values for

a) daily fluid input

b) daily fluid output

c) net fluid balance

in a 70kg man

Answer 11

a) 2.5L

b) 2.5

c) +/- 0L

Question 12

Approximately how much fluid output is via sensible losses (ie. urine output)?

Answer 12

1.5L per day (60%)

Question 13

What are the insensible sources for fluid output?

Answer 13

• respiration
• sweating
• faeces

In unwell patients, who may be febrile, tachypnoeic, or having increased bowel output, insensible losses will rise.

Question 14

How can fluid depletion be clinically detected?

Answer 14

• dru mucous membranes
• reduced skin turgor
• decreasing urine output (<0.5ml/kg/hr)
• orthostatic hypotension
• increased capillary refill time
• tachycardia
• hypotension

Question 15

How can fluid overload be clinically detected?

Answer 15

• raised JVP
• peripheral or sacral oedema
• pulmonary oedema

Question 16

According to current NICE guidelines, give the daily requirements of:

a) water

b) Na+

c) K+

d) glucose

Answer 16

a) 25ml/kg/day

b) 1.0mmol/kg/day

c) 1.0mmol/kg/day

d) 50g/day

Question 17

Give a typical fluid maintenance regime for a 70kg health male.

Answer 17

1. 500ml 0.9% saline with 20mmol/L K+ to be run over 8 hours.
2. 500ml 5% dextrose with 20mmol/L K+ to be run over 8 hours.
3. 500ml 5% dextrose with 20mmol/L K+ to be run over 8 hours.

Question 18

How should fluid deficit be corrected?

Answer 18

Prescribe maintenance fluids plus fluids for resuscitation.

A fluid challenge of either 250ml or 500ml over 15-30mins, depending on a patients size and co-morbidities, should be commenced to resuscitate fluids.

Question 19

Outline the significance of Rhesus D (RhD) group in blood transfusions.

Answer 19

If a RhD- female patient is given RhD blood, they begin to make RhD antibody. This causes potential problems during pregnancy*.

The anti-D antibodies can cross the placenta, therefore if the foetal circulation contains RhD+ blood, the antibodies will bind to the Rhesus D antigens on the foetal erythrocytes. This causes the foetal immune system to attack and destroy its own erythrocytes leading to foetal anaemia (ie. haemolytic disease of the newborn).

*as the patient themselves do not have Rhesus D antigens on their erythrocytes, the anti-D antibodies will not cause a reaction for the patient themselves.

Question 20

Outline the significance of ABO group in blood transfusions.

Answer 20

The ABO group refers to the presence of A and/or B antigens on the surface of red blood cells. The human body produces antibodies to bind to the surface antigens (A or B) that are NOT present on the host’s red blood cell surface membrane.

Question 21

Give the ABO blood group type that are:

a) universal donors

b) universal acceptors

Answer 21

a) O-ve: the donor’s erythrocytes do not have A, B or RhD antigens on the surface membrane, meaning there are no surfaces for the antigens to attack.

b) AB+ve: the recipient has A, B and RhD antigens on the surface of erythrocytes, meaning they produce no A, B or RhD antibodies. They therefore cannot mount an immune response to the donor blood.

Question 22

Which blood tests should be performed prior to blood transfusion?

Answer 22

• group and save (G&S): determines the patient’s blood group (ABO and RhD) and screens the blood for any atypical antibodies. No blood can be issued based upon G&S results. A G&S is recommended if blood loss is not anticipated, but blood may be required should there be greater blood loss than expected.
• crossmatch (X-match): physically mixing the patient’s blood with the donor’s blood, in order to see if any immune reaction takes place. If it does not, the donor blood is issued and can be transfused to the patient. An X-match is done if blood loss is anticipated.

Question 23

Which cannulas should blood products be administered through?

Answer 23

• green (18G)
• grey (16G)

A smaller cannula can cause the cells to haemolyse due to the sheering forces in the narrow tube. You must ensure all blood products are administered through a blood-giving set (as contains a filter in the chamber), rather than a normal fluid giving set.

Question 24

What are the different types of blood products?

Answer 24

• packed red cells
• platelets
• fresh frozen plasma (FFP)
• cryoprecipitate

Question 25

What are the:

a) major constituents

b) indications

c) duration over which it is administered

of packed red cells?

Answer 25

a) red blood cells

b) acute blood loss; chronic anaemia; symptomatic anaemia

c) 2-4 hours; must be completed within 4 hours of coming out of the store.

Note patients given red blood cells may produce autoantibodies to donor surface antigens, therefore a new G&S must be sent before any future transfusions.

Question 26

What are the:

a) major constituents

b) indications

c) duration over which it is administered

of platelets?

Answer 26

a) platelets

b) haemorrhagic shock; thrombocytopenia; bleeding with thrombocytopenia

c) 30 minutes

Question 27

What are the:

a) major constituents

b) indications

c) duration over which it is administered

of fresh frozen plasma?

Answer 27

a) clotting factors

b) disseminated intravascular coagulation (DIC); haemorrhage secondary to liver disease; massive haemorrhages

c) 30 minutes; commonly given after the 2nd unit of packed red cells in massive haemorrhage.

Question 28

What are the:

a) major constituents

b) indications

c) duration over which it is administered

of cryoprecipitate?

Answer 28

a) fibrinogen, vWF, Factor VIII and fibronectin

b) DIC with fibrinogen <1g/L; von Willebrands disease; massive haemorrhage

c) 15/30 minutes

Question 29

What are the possible general complications of blood transfusions?

Answer 29

• clotting abnormalities (dilution effect; FFP and platelets administered to mitigate risk)
• hypocalcaemia
• hyperkalaemia
• hypothermia
• infection

Question 30

What is an acute haemolytic reaction?

Answer 30

A serious reaction caused by transfusion of the incorrect blood type (ABO incompatibility), whereby donor red blood cells are destroyed by the recipient’s preformed antibodies, resulting in haemolysis.

Question 31

What is transfusion-associated circulatory overload (TACO)?

Answer 31

Occurs when blood-products are over-transfused, causing fluid overload. This is often a common problem in those who are already overloaded, for example cardiac failure.

Patients at risk of overload can be prescribed 20mg furosemide prophylactically during the transfusion to prevent TACO.

Question 32

What is transfusion related acute lung injury (TRALI)?

Answer 32

A form of acute respiratory distress syndrome (ARDS), a non-cardiogenic cause of pulmonary oedema. TRALI has high mortality and requires specialist and intensive care input urgently.

Question 33

What pre-operative advise should be given to patients regarding fasting?

Answer 33

• no food 6 hours before surgery
• no clear fluids 2 hours before surgery

Fasting ensures that the stomach is empty in contents, reducing the risk of aspiration.

Question 34

List the medications commonly stopped as part of pre-operative management.

Answer 34

• clopidogrel (stopped 7 days prior to surgery due to bleeding risk)
• hypoglycaemics
• oral contraceptive pill or HRT (stopped 4 weeks before surgery due to DVT risk)
• warfarin (stopped 5 days prior to surgery due to bleeding risk)

Question 35

List the medications commonly altered as part of pre-operative management.

Answer 35

• subcutaneous insulin switched to variable rate IV insulin infusion (VRIII)
• long-term steroids must be continued (risk of Addisonion crisis); if the patient cannot take these orally, switch to IV

Question 36

How is DVT prevented in the surgical patient?

Answer 36

• low-molecular weight heparin prescribed prophylactically
• anti-embolic stocking prescribed
• early mobility following surgery

Question 37

Generally, which surgeries warrant antibiotic prophylaxis?

Answer 37

• othopaedic
• vascular
• gastrointestinal

Question 38

How should a surgical patient with diabetes mellitus be managed generally?

Answer 38

Patients with DM should be first on the list where possible, to avoid prolonged fasting.

Blood glucose (BM) should be checked regularly throughout the procedure.

Patients on insulin will be placed on variable rate intravenous insulin infusion (VRIII).

Patients taking oral hypoglycaemics should stop the day before surgery.

Patients with diet-controlled DM require no peri-operative management.

Question 39

Generally outline the definitions of the following ASA grades:

ASA I

ASA II

ASA III

ASA IV

ASA V

ASA E

Answer 39

ASA I: normal healthy patient

ASA II: mild systemic disease

ASA III: severe systemic disease

ASA IV: severe systemic illness that is a constant threat to life

ASA V: moribund, who is not expected to survive without the operation

ASA E: suffix added if an emergency operation.