pre-op management Flashcards
What is the composition of the following fluids:
0.9% saline
5% dextrose
0.18% NaCl/ 4% dextrose
A 1% solution contains 1g per 100ml of solvent
- 0.9% saline is 150 mmol/L of Na and 150 mmol/L of Cl
- 5% dextrose is 50g of dextrose
- 0.18% NaCl/4% dextrose is 40g of dextrose and 30mmol/L of Na and 30mmol/L of Cl
How does 0.18% NaCl/4% Dextrose distribute across body compartments?
Theorectically this fluid is 1 part 0.9% NaCl (200ml) and 4 parts 5% Dextrose (800ml)
IV fluids need to be isotonic so as not to damage red blood cells. However 4% Dextrose/0.18% Saline is hypertonic, why is this and why can it be used as a fluid?
Initially dilutes osmolality of extracellular fluid but once cell has used the dextrose, the remaining saline and electrolytes act isotonic
5% dextrose is isotonic as the dextrose is metabolised to water
Why is there a normal postoperative phase of oliguria?
Surgery is trauma which causes ADH and cortisol release which causes more water to be reabsorbed in the kidney so less urine produced
Why are many surgical patients in fluid/electrolyte deficits?
- Vomiting from intestinal obstruction: vomiting causes loss of isotonic fluid leaving space in gut for more to be sequestered so many patients in hypovolaemic shock as lost a lot of fluid from ECF
- Peritonitis: large surface area so if inflammad can give off litres of fluid as normal blood flow is 150ml/min and SA is 2m2
- Fistulae
- Bleeding
What are some useful biochemical markers for dehydration in a patient who is vomiting due to a bowel obstruction?
Raised haematocrit (>55%)
Raised serum urea
Raised serum urea in comparison to creatinine as urea can be reabsorbed but creatinine cannot
What are some of the reasons colloids are not often used?
High cost
Risk of anaphylaxis
Increased risk of coagulopathy
What are some of the different enteral feeding options?
TPN is used when intestinal failure (e.g perforations or short gut from resection) or cannot access jejunum
Hierarchy of feeding
Tube enterostomies are used long term when need feeding over 4 weeks. PEG better as can be used for night feeds with less risk of aspiration
What causes low albumin levels?
Chronic inflammation
Protein losing enteropathy
Proteinuria
Hepatic dysfunction
NOT MALNUTRITION
What are the consequences of poor pain control?
- Slower recovery time due to reluctant to mobilise
- Inadequate ventilation leading to possible subsequent atelectasis and hospital-acquired pneumonia as they are not breathing as deeply as they would if they were not in pain
- Cardiovascular: tachycardia, hypertension
- GI: ileus, N+V, urinary retention, ileus
What are the side effects of NSAIDs?
Work by decreasing synthesis of prostaglandins so decreased inflammation
IGRAB
interactions with other drugs
gastric ulcerations
renal impairment
asthma sensitivity
bleeding risk
side effects of opioids
dry mouth
eurphoria
sedation
constipation
nausea and vomiting
respiratory depression
when do PEs classically occur?
10-12 days post op
how can post op DVT be prevented
pre-op mobilisation
post - op mobilisation
stop thrombotic drugs
TED stockings
How does the dose of dalteparin vary if a patient is renally impaired? (eGFR<30)
Need to use a lower dose (2/3 of body weight if treating VTE) OR
Use UFH
How long is dalteparin prophylaxis given for?
- Normal surgery: give dose 1-2 hours before surgery then every 24 hours whilst at risk of VTE
- Major orthopaedic surgery (e.g THR/TKR): consider Dalteparin for up to 35 days after surgery if high risk
What are some contraindications of mechanical VTE prophylaxics (AES and IPC)?
Peripheral arterial disease
Peripheral oedema
Local skin conditions.
How do you reverse the following anticoagulants?
Dabigatran
LMWH
Rivaroxaban
Warfarin (reversal needed for procedure in 5 days)
Warfarin (immediate reversal)
Warfarin (reversal needed for procedure next day)
short half life but idarucizumab can be used
Witholding usually sufficient due to short half life but protamine can be use
Withold drug 24 hours as not reversal, can try PCC
Withhold drug and bridge with LMWH till 24 hours before
- Prothrombin Complex Concentrate
- Vitamin K
When do you need to do bridging therapy when stopping warfarin for surgery?
If high risk of VTE (e.g VTE within last 3/12, AF with previous stroke or TIA, or mitral mechanical heart valve) then bridge
Start LMWH and stop 24 hours before surgery if surgery has high bleeding risk
Start warfarin again at night after surgery that day
Q
How long before surgery do you need to stop aspirin and clopidogrel?
Aspirin: 7-10 days before
Clopidogrel: 7 days before
wells score for DVT and what is the management?
- If 1 or less DVT is unlikely but do D-Dimer to rule out. D-dimer can also be raised in recent surgery/trauma, pregnancy, liver disease, infection, prolonged hospital stay
- If 2 or more DVT likely so do US
mx: DOACs first line or dabigatran
How are PEs investigated and managed?
Ix
- Wells Score less than or equal to 4: PE unlikely, but D-dimer test to exclude
- Wells Score greater than 4: PE likely and confirm diagnosis with CTPA scan (or V/Q scan in those with poor renal function).
Can do ECG to rule out MI differential and may have S1Q3T3
Mx
- Interim anticoagulation: offer apixaban or rivaroxaban first line for 5 days then dabigatran for 5 days
If CTPA is negative stop anticoagulation
If CTPA positive keep on anticoagulation for 3 months if unprovoked, longer if provoke
If haemodynamically unstable give oxygen, continuous UFH infusion and consider systemic thrombolytic therapy
When diabetic patients are due to have surgery, how is their blood glucose control altered to their normal regime? (use flowchart)
If expected to miss more than one meal put on variable rate intravenous insulin infusion of soluble human insulin in sodium chloride 0.9 % (sliding scale)
Need to run intravenous glucose-containing ‘substrate solution’ alongisde it
Need to check BM hourly, especially for first 12 hours of VRII, to see if in range of 6-10 mmol/L (4-12 acceptable)
Conversion back to s/c insulin when patient can eat and drink with no N+V with overlap of 30 minutes
How can you tell if a diabetic patient is hypoglycaemic whilst under anaesthesia and what are the consequences of this?
There is no way, you just have to monitor BM!! Sugars often go up in surgery due to stress response
Risk of brain injury and seizures as not aerobically respiring
