Anaesthetics Flashcards
What are the normal ranges for sodium and potassium in the blood and why is there such a difference?
Sodium: 135-145mmol/L
Potassium: 3.5-5.0mmol/L
Sodium mostly exists in the extracellular compartment (ECF and blood), potassium mostly exists in the intracellular compartment
What are the daily requirements of water, glucose, sodium and potassium?
Important things to remember when prescribing maintenance fluids?
DAILY REQUIREMENTS 24 HOURS
WATER 25-30 ml/kg/day
K+/Na+/Cl- 1 mmol/kg/day
Glucose 50-100 g/day of glucose to limit starvation ketosis
- will not address the patient’s nutritional needs
- reduce flow rate to 20-25 ml/kg/day if renal impairment/heart failure/ frail/elderly/malnourished (re-feeding syndrome)
- reduce maintenance if also eating and drinking
What kinds of things cause FLUID LOSS?
Poor oral intake (elderly, dysphagia, unconsciousness, fasting NBM) Increased requirements (Trauma, burns, post-operative) Increased loss (fever, sweating, bleeding, D+V, renal loss, drugs, NG tube or stoma loss or billary drainage loss)
How do we classify fluid loss?
As mild, moderate or severe
MILD
- 4% body weight, loss of skin turgor and dry mucus membranes
MODERATE
- 5-8% body weight, oliguria, tachycardia and hypotension
SEVERE
- >8% body weight, profound oliguria and CVS collapse
What are some crystalloids and what are some examples?
They are water soluble substances dissolved in solution. They can be rapidly administered but can cause pulmonary oedema
NaCl 0.9%
Dextrose
Haartmans
What is in NaCl and what are some risks?
(0.9% mean 9g in 100ml) - contains 154mmol/L Na and 154mmol/L Cl
So about the right amount of sodium but there is a risk of hyperchloraemic acidosis
What is in dextrose and when should it be used?
5% = 50g per L water
Good if people have glucose requirements
What is in Haartman’s and what are some benefits of using it?
Na - 131 Cl - 111 K - 5 Ca 2 Lactate 29
-reduses risk of hypokalaemia and hyperchloreamia
What are some examples of colloids? Where are they sometimes used?
Gelfusin Voluven Volulyte Albumin Sometimes used in trauma but rarely elsewhere
What is a fluid challenge?
Getting IV access with a wide bore cannula and administering 250-500mL of fluid as quickly as possible (usually 10-15mins) and monitoring for a response (BP, HR, UOP, JVP)
If an unwell patient hasn’t improved after 3 fluid challenges then need senior support
What is maintenance fluid?
What is an example of a good maintenance fluid regimen in a 70kg man?
MAINTAINANCE FLUID
-total amount of fluid in a day, presuming everything else is normal (e.g. no dehydration, no drugs that will effect)
0.9% NaCl + 40mmol K over 8 hours
5% dextrose + 20mmol K over 8 hours
5% dextrose + 20mmol K over 8 hours
Why will people need more than just maintenance fluid after surgery?
People loose fluids during surgery (on average 600-900mL) so they will need some extra fluids before they’re placed on a maintenance regime
How do you manage fluid therapy in fever?
Add 10% extra fluids for every degree of fever
What should you ask in the history section of a pre-operative assessment?
- what is your understanding of the op?
- who do you live with at home? well supported?
- can you normally independently care for yourself?
- Current illness (health in the past 2 weeks, any new problems or infections)
-Vision and hearing
-Dental care
-Neuro (epilepy and stroke)
-Neck and jaw (trauma, movements, RA/OA)
Cardiac
-how far are you able to walk? (should be 4+ METS)
-how do you sleep at night?
-chest pain?
-MI/HF/diabetes/HTN/valve problems/arrythmias
Resp
-SOB
-cough?
chest infections?
COPD/asthma/infections/sleep apnoea
GI
-reflux/indigestion/heartburn/liver/kidney problems
Anaesthetic history (personal and family-MH/suxapnoea) Drug hx and allergies Social history (smoking, alcohol, drugs, pregnancy, blood products)
ICE
What ongoing medical conditions in particular should you ask about during anaesthetic history?
Any drugs you should avoid with certain conditions?
epilepsy/stroke/ heart attacks/diabetes/HTN/asthma/COPD/liver or kidney disease. Always ask how well controlled these are
Diabetes-done give Dexamethasone
Renal failure-dont give Rocuronium/NSAIDS/morphine
What should you examine in a pre-operative assessment? (4)
Examination pre-op
- Neck movement, jaw opening and dental health (dentures, caps, crowns or loose teeth)
- Mallampati score
- ASA score
- General examination (listen to heart and chest, feel abdomen, feel peripheries, feel calves for swelling or tenderness)
- Pregnancy test
What is the mallampati score?
I - complete visualisation of soft palate
II - Complete visualisation of uvula
III - Can only see base of uvula
IV - Cannot see soft palate
What is the ASA-GRADING for surgery?
How does emergency surgery change ASA grade?
1 - Healthy patient, no ongoing disease. Non smoker and no/minimal alcohol
2 - Mild/mod chronic disease with no functional impairment (e.g. well controlled diabetes, HTN, smoker or social drinker)
3 - Severe chronic disease with functional impairment e.g. angina or COPD
4- Severe chronic disease with constant threat to life e.g angina, ESRD or liver disease
5 - Moribund patient who is unlikely to survive with or without operation
6 - Brainstem dead patient for organ donor transplant
EMERGENCY BUMPS YOU UP BY ONE
What are the surgical grades for the operation?
Minor - skin excision/ toenail removal/ absess drainage/cystoscopy
Intermediate - hernia repair/tonsillectomy/ knee arthroscopy/varicose veins
Major/complex - emergency laparotomy/ hysterectomy/ thyroidectomy/joint replacement/thoracic operational/ radical neck dissection
In MAJOR surgery, what investigations would everyone get?
-FBC for all ASAs
For ASA 2+
-Kidney function (or ASA1 at risk AKI) and ECG (or ASA 65+)
group and save would be useful if expected blood loss
What are some extra investigations for specific things in pre-operative assessment?
LFTs for liver or billiard op
Sickle cell screen for Afro-Caribbean patients
TFTs if they’re on thyroxine
CXR if ICU care might be required
Echo if they’ve got valve problem or murmur
Spirometry if lung disease
What must you correct before the operation if found to be abnormal?
INR (with vit K or prothrombin complex)
Anaemia
What is the general rule for stopping medications before an operation?
In general omit on the day of operation and resume the day after
What more specific medications must be stopped before operation?
COCP - stop 4 weeks before
Aspirin/clopidogrel - stop 7 days before
Warfarin-stop 5 days before (give therapeutic dose LMWH in interim)
LMWH - stop 48h before (hep infusion if at risk)
DOACs - stop 24h before
Insulin - don’t have morning dose
Metformin-can continue on day (dont cause hypo)
Oral hypoglycaemic - avoid on day of op
Diuretics/ACE-is - avoid on day of op
Long-term steroids - consider switch to hydrocortisone higher dose
What are the fasting guidelines before an operation?
- No food for 6 hours before (have dinner nil else)
- No breastmilk for 4 hours before
- Only clear fluids (black tea, purples juice) until 2 hours before (30ml only for tablets)
- Children allowed water 1 hour before
- No alcohol 24 hours before
How much oxygen can be given through nasal cannulas?
1-6L (most commonly 2L)
24-40% O2
How much oxygen can be given through a simple face mask (hudson)?comment on flow and FiO2
Flow 5-10L (CO2 can accumulate if the flow is less than 5L)
FiO2 35-60%
Not very reliable
Can humidify to help with comfort
What demonisations are there of venturi devices? In whom are they commonly used?
BLUE 24% WHITE 28% YELLOW 35% RED 40% GREEN 60%
Non rebreather mask (80-95%)
Good in CO2 retainers (COPD, long term rep condition) to control concentration of O2
How much oxygen can be given through a non rebreathe mask? comment on flow and FiO2
Non re breath mask
-15L and probably gives up to around 80-95% - this is about as good as we can get unless we artificially ventilate someone
What options do we have if the patient need assistance with ventilation?
Ventilation options
- BAG-VALVE MASK
- NIV
- ET tube or airway adjunct or igel
How do you measure a Gedell airway?
SOFT TO SOFT
-tragus to corner of mouth
What are the average sizes of NP tubes? When should they not be used
NASOPHARYNGEAL TUBES (little finger of patient)
6-7mm for women
7-8mm for men
Do not use if any suspicion of basal skull fracture
What are some examples of supraglottic airways?
Laryngeal mask airway (LMA) and iGEL
When are LMAs preferably used and how do you insert an LMA?
-Used in shorter surgeries when an ET tube is not required -or if you cannot intubate someone (easier to put in)
NOT A DEFINITIVE AIRWAY
-Reflexes should be suppressed e.g. with propofol then insert with the curve of the airway (no need to rotate)
What kind if airway is an ET tube? How are the sized
ET tube
- Definitive (no aspiration risk)
- Sized by internal diameter of tube - 7/8mm for women, 8/9mm for men
What is the process of inserting an ET tube?
- preoxygenate the patient
- Wait for the neuromuscular blockage (90-120s)
- Place the patient in the sniffing the morning air position
- Hold laryngoscope in L hand
- Insert the laryngoscope in the R hand corner of the mouth and slide it down between the tongue and the epiglottis
- then lift with your whole arm up and to the left
- Aim to visualise the vocal cord
- Insert the tube to just beyond the vocal cords
- should be 23 cm for men and 21 cm for women, measured at the central incisors
- Inflate the cuff of the tube, attach to the bag valve mask and look for signs that it is in the right place
What signs are there that the ET tube is in the right place?
ET tube
- see it go in right place (through vocal cords)
- misting tube
- EtCO2 properly traced (5 clear traces)
- symmetrical rise and fall of chest
- ausciltation reveals air in chest, not in abdomen
What are some possible complications of ET tubing?
- Breaking teeth with the laryngoscope
- Incorrectly positioned tube (into oesophagus) if in doubt take it out
- Right lung intubation if put too far down
- Laryngospasm - especially if someone has asthma or COPD
What are the three types of anaesthetic?
Local, Regional, General
When putting someone under a general anaesthesia what three things do you need to achieve?
AMNESIA - unconscious and won’t remember
AKINESIA - cannot move
ANALGESIA - won’t be in pain or have a pain response
How do we achieve amnesia in general anaesthesia?
AMNESIA
- INDUCTION AGENTS INITIALLY (propofol, thiopentone, etomiidate and ketamine) these last 4-10 mins
- Then maintained with VOLATILE AGENTS or TIVA
benefits and unwanted effects of Propofol?
Propofol 1.5-2.5mg/kg
Benefits
-Excellent suppression of airway reflexes
-Good at preventing PONV
Unwanted effects
- Causes a marked drop in HR and BP (give vast active)
- Also can be painful to inject because it is lipid based
- Unwanted movements
What type of drug is thiopentone?
when would you be more likely to use thiopnetone?
unwanted effects thiopentone (inc effects on BP and HR)
when would you not use thiopentone?
Thiopentone 4-5mg/kg
-This is a BARBITUATE
Uses
- It works much faster than propofol and thus is often used in RSI (emergency surgery/risk of aspiration)
- It also has anti-epileptic properties and is quite neuroprotective
Unwanted effects
- Drops BP but INCREASES HR
- rash and bronchospasm
- requires intra-arterial injection (lead to gangrene and thrombus)
Avoid
-Avoid in porphyria
What effects does ketamine have?
what are some unwanted effects? (inc effects on BP and HR)
Ketamine 1-1.5mg/kg
- It is a DISSOCIATIVE ANAESTHETIC (anterograde anaethsesia) and is also profoundly analgesic
- it is quite slow to act (90s)
Unwanted effects
- INCREASES HR and BP
- bronchodilation
- can causes PONV and EMERGENCE PHENOMENON (vivid dreams and hallucinations)
Benefits of Etomidate?
WHos it good for?
Unwanted effects of Etomidate?
Etomidate 0.3mg/kg
- rapid onset
- good haemodynamic stability (good for pens with cardiovascular conditions)
- lowest incidence of hypersensitivity
Unwanted effects
- pain on injection
- spontaneous movements
- post op NV
- ADRENOCORTICAL SUPPRESION (cortisol is suppressed for up to 72 hours suggesting it should not be used in very unwell who need the stress response)
What agents are used to maintain anaesthesia?
Volatile agents (desflurane, isoflurane, enflurane, sevoflurane and NO)
What is minimum alveolar concentration?
MAC - this is the minimum concentration of gas required to eliminate a reaction to a standard stimulus
What are the MACs of nitrous oxide, sevoflurane, isoflurane, desflurane and enflurane?
Nitrous oxide 104% Sevoflurane 2% Isoflurane 1.15% Desoflurane 6% Enflurane 1.6%
How does pain affect people under anaesthesia?
They don’t FEEL pain because this is a conscious interpretation. However, they do have nociceptors stimulated which can cause the physiological response of increased HR and BP. That’s why it’s important to give someone analgesics
What are some examples of short acting analgesics used to suppress response to laryngoscope?
Fentanyl, ramifentanil, alfentanyl