8.01 - Pre-Operative Care Flashcards
Name the crystalloids commonly used in fluid prescriptions.
- 5% dextrose solution
- 0.9% sodium chloride solution (normal saline)
- Hartmann’s solution
Outline the features of 5% dextrose solution, and therefore the clinical indications of prescription.
- 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.
Outline the features of normal saline solution, and therefore the clinical indications of prescription.
- 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.
Why is normal saline solution contraindicated when used as a lone fluid maintenance?
Excessive saline replacement can result in a hyperchloraemic acidosis.
Outline the features of Hartmann’s solution, and therefore the clinical indications of prescription.
- 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.
Outline the clinical features of colloid fluid solutions, and therefore their indications of prescription.
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.
What are the principles upon which fluids are prescribed?
- resuscitation
- maintenance
- replacement
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?
a) 66%
b) 66%
c) 33%
d) 20%
e) 80%
Why is aggressive fluid resuscitation often needed to maintain intravascular volume in a septic patient?
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.
Outline the sources of our fluid input.
- 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.
Give the values for
a) daily fluid input
b) daily fluid output
c) net fluid balance
in a 70kg man
a) 2.5L
b) 2.5
c) +/- 0L
Approximately how much fluid output is via sensible losses (ie. urine output)?
1.5L per day (60%)
What are the insensible sources for fluid output?
- respiration
- sweating
- faeces
In unwell patients, who may be febrile, tachypnoeic, or having increased bowel output, insensible losses will rise.
How can fluid depletion be clinically detected?
- dru mucous membranes
- reduced skin turgor
- decreasing urine output (<0.5ml/kg/hr)
- orthostatic hypotension
- increased capillary refill time
- tachycardia
- hypotension
How can fluid overload be clinically detected?
- raised JVP
- peripheral or sacral oedema
- pulmonary oedema
According to current NICE guidelines, give the daily requirements of:
a) water
b) Na+
c) K+
d) glucose
a) 25ml/kg/day
b) 1.0mmol/kg/day
c) 1.0mmol/kg/day
d) 50g/day
Give a typical fluid maintenance regime for a 70kg health male.
- 500ml 0.9% saline with 20mmol/L K+ to be run over 8 hours.
- 500ml 5% dextrose with 20mmol/L K+ to be run over 8 hours.
- 500ml 5% dextrose with 20mmol/L K+ to be run over 8 hours.
How should fluid deficit be corrected?
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.
Outline the significance of Rhesus D (RhD) group in blood transfusions.
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.
Outline the significance of ABO group in blood transfusions.
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.
Give the ABO blood group type that are:
a) universal donors
b) universal acceptors
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.
Which blood tests should be performed prior to blood transfusion?
- 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.
Which cannulas should blood products be administered through?
- 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.
What are the different types of blood products?
- packed red cells
- platelets
- fresh frozen plasma (FFP)
- cryoprecipitate
What are the:
a) major constituents
b) indications
c) duration over which it is administered
of packed red cells?
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.
What are the:
a) major constituents
b) indications
c) duration over which it is administered
of platelets?
a) platelets
b) haemorrhagic shock; thrombocytopenia; bleeding with thrombocytopenia
c) 30 minutes
What are the:
a) major constituents
b) indications
c) duration over which it is administered
of fresh frozen plasma?
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.
What are the:
a) major constituents
b) indications
c) duration over which it is administered
of cryoprecipitate?
a) fibrinogen, vWF, Factor VIII and fibronectin
b) DIC with fibrinogen <1g/L; von Willebrands disease; massive haemorrhage
c) 15/30 minutes
What are the possible general complications of blood transfusions?
- clotting abnormalities (dilution effect; FFP and platelets administered to mitigate risk)
- hypocalcaemia
- hyperkalaemia
- hypothermia
- infection
What is an acute haemolytic reaction?
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.
What is transfusion-associated circulatory overload (TACO)?
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.
What is transfusion related acute lung injury (TRALI)?
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.
What pre-operative advise should be given to patients regarding fasting?
- 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.
List the medications commonly stopped as part of pre-operative management.
- 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)
List the medications commonly altered as part of pre-operative management.
- 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
How is DVT prevented in the surgical patient?
- low-molecular weight heparin prescribed prophylactically
- anti-embolic stocking prescribed
- early mobility following surgery
Generally, which surgeries warrant antibiotic prophylaxis?
- othopaedic
- vascular
- gastrointestinal
How should a surgical patient with diabetes mellitus be managed generally?
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.
Generally outline the definitions of the following ASA grades:
ASA I
ASA II
ASA III
ASA IV
ASA V
ASA E
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.