Anaesthesiology SC001: Is He Fit For Surgery? Pre-operative Assessment Flashcards
Peri-operative management in Anaesthesia
- Pre-operative care
- Medical optimisation
- Cardioprotection - Intra-operative
- Choice of technique / drugs / fluids - Post-operative
- Analgesia / ICU / Medical therapy
Aim:
- ↓ Peri-operative morbidity + costs by identifying patients at high risk of developing complications —> these patients may benefit from:
1. Further testing
2. Alternative management strategies (Medical / Surgical) - Pharmacological intervention
Purpose of pre-operative visit
Should be done as soon as decision to surgery is made
- Assessment of patient
- Identification + optimisation of co-morbidities (illness not related to need for surgery)
- Assessment of risk of surgery / anaesthesia - Rapport + relieve anxiety
- Appropriate instructions to patients
- What will happen
- Pain management - Facilitates planning of anaesthesia + peri-operative care
- GA / Regional / Epidural etc.
- Improvement in outcome - Pre-medication
- To reduce anxiety
Components of pre-operative visit
- History (obtained personally / questionnaire)
Patient assessment: - Co-existing diseases
- Medications / other therapies / drug allergies
- Specific anaesthetic related issues before
- Fasting / associated problems
- P/E
- Investigations
Medications assessment
- Identification
- Drugs that need to be stopped / modified
- **Oral hypoglycaemics —> **Switch to Insulin (∵ patient will be fasted before surgery, surgery can trigger stress response —> release catecholamines, glucocorticoid —> causing **hyperglycaemia —> insulin requirement may be ↑ peri-operatively)
- Anticoagulants (e.g. **Warfarin: long duration of action + difficult to reverse —> need to change to something more titratable)
(- Aspirin?) (Permanent effect on platelet aggregation inhibition, but can be cardioprotective in patients for secondary prevention) - Drugs that may need to be measured
- Digoxin
- Anticonvulsants - Recreational drugs
- may interact with anaesthetic drugs - Oral contraceptives
- no need to be stopped - Indwelling devices
- Dentures
- Prosthetic heart valves
- Pacemakers
—> may need prophylactic antibiotics
Specific anaesthetic related issues
- Previous anaesthetic history / mishaps
- Allergies
- Family history
- Worries / requests
- Discussion / Explanation of anaesthetic methods
- GA / Regional / LA sedation - Consent
- Plan for post-operative analgesia
- PCA, epidural etc.
Fasting
Why?
- Less likely to regurgitate / aspirate
—> Gastric volume + content (solid / liquid) + pH
—> affect consequence of aspiration
How long?
- Drinking clear fluids —> 95% emptied in 1 hour —> ∴ **2 hours fasting before considered safe (esp. paediatric)
—> Give **carbohydrate load 1-2 hours before surgery —> Help mitigate stress response during surgery
- Solids - liquefaction —> emptying highly variable —> ***6 hours recommended
Risk factors for delayed gastric emptying:
- Trauma, pain, drugs (e.g. opioids)
- Emergency surgery
Risk
Potential that a chosen action / activity (including the choice of inaction) will lead to an undesirable outcome
- implies that a choice has an influence on the outcome
- almost any human endeavour carries some risk
Life is risky:
Micromort:
—> 1 in million chance of sudden death: same as flipping a coin 20 times with same outcome
- translate small risks into whole numbers that can be immediately compared
—> e.g. risk of death from GA in emergency operation = 1 in 100,000 —> ***10 micromorts per operation (other examples: skydiving, decorating at home on a high ladder)
—> 1 day in hospital: 75 micromorts
Microlife:
- ***30 mins of life expectancy = one millionth of your life
- 2 cigarettes: one microlife lost
- ***accumulate from day to day —> do not go away
Surgery risk and rewards
Risk:
- Mortality
- Morbidity
- Medicolegal
- Cognitive function (∵ surgical stress response)
Reward:
- Prevention of mortality (cure for cancer / AAA)
- Improved QoL (joint replacement / cataract removal)
- Palliation (bowel obstruction)
How do we make risk based decisions?
- Behavioural + organisation psychology underpin our understanding of risk based decision making
—> why are we irrationally more scared of sharks / terrorist than we are of motor vehicles / medications? - In decision theory: regret (and anticipation of regret) can play a significant part in decision-making, distinct from risk aversion (preferring the status quo in case one becomes worse off)
- All decision-making must consider **cognitive bias, **cultural bias, ***notational bias
—> acceptance of obviously wrong answers simply because it is socially painful to disagree (consensus opinion)
—> herd instinct - It is earlier to avoid a personally unnecessary risk but our job is to accept risks, albeit trying to minimise it
Shared decision making
- Explain the problem in brief and find out what the patient understands
- Go through pros + cons of available options including uncertainty
- Focus on patients’ values + preferences
- Do not judge their decision but understand + ensure it is based on correct information + that they are not put under any undue pressure
- Involve friends / family is useful
- Sometimes decisions are reached quickly / sometimes they need deferring for more time + more information
Conundrum:
- Do patients (or relatives) really know what is best for them?
- Economics
—> Should we consider financial implications of very high risk surgery
—> How to quantify this?
—> In economically developed counties, the justice system consider a human life “priceless”, thus illegalising any form of slavery
Medicolegal aspect of risk
- Full + frank discussion before procedure
- Consent
- Shared decision making does not mean frightening patients with risk
- It is NOT your risk
- Mortality / morbidity is not necessarily negligent
Risk assessment
- Aerobic capacity can be estimated by history (e.g. flight of stairs) / directly measured by CPX
- History of PVD, CVA, CHF, MI, Renal disease (Serum Creatinine >150 umol/L) each independently ↑ risk of during by 1.5 times
- History of TIA / Angina ↑ risk of dying by 1.2 times
- Risk of post-operative morbidity is double the risk of post-operative mortality
Cardiopulmonary exercise testing
- Standard ECG stress test + Metabolic gas exchange analysis
- Gold standard for assessments of functional capacity
- Can help determine cause of dyspnea on exertion: Circulatory vs Pulmonary vs Peripheral etiologies
Complications of anaesthesia
- High incidence of peri-operative cardiac morbidity / mortality
—> 1% MI
—> 0.3 % CVS deaths
—> rate will be much higher with operations e.g. vascular surgery
Identification of high risk patients
- History + P/E
- Exercise capacity
- Functional stratus - Surgical procedure?
- Risk indices
- ASA classification
- Revised Goldman / National surgical quality improvement program database (ACS)
- Gupta (recent)
American Society of Anaesthesiologist (ASA) classification
Very subjective
Identification of high-risk patients
—> predict perioperative risks
—> Correlates well with outcome:
Class 1: A normal **healthy patient
Class 2: Patient with **mild systemic disease
Class 3: Patient with **severe systemic disease
Class 4: Patient with severe systemic disease that is a **constant threat to life
Class 5: A moribund patient **not expected to survive without the operation
Class 6: **Emergency
Functional capacity
- Simple, inexpensive assessment
- Major determinant of peri-operative risk
- 1 MET = Exercise consumption of resting adult
- ***>7 MET without ischaemia = Low risk
- ***Inability to climb 2 stairs is associated with a PPV of 89% for cardiopulmonary complications
Basis for testing
- Evidence-based medicine
—> systematic review of RCTs e.g. AHA / ACC - Bayesian analysis
—> a test is most useful in a population with a moderate probability (30-70%) of disease - Avoid unnecessary, costly, potentially hazardous investigations
- Poor PPV of non-invasive stress test
- Considerable risk of coronary angiography / coronary revascularisation —> may not be protective —> ↑ risk of peri-operative MI
—> apparent risk reducing interventions may paradoxically ↑ risk (e.g. PCI)
—> may be expensive - Peri-operative plaque stabilisation by pharmacological means may be as important in prevention of PMI as an ↑ in myocardial O2 supply / ↓ in myocardial O2 demand
Medical therapy for Cardioprotection
- Aspirin
- Secondary prevention
- ↑ bleeding may negate benefits - Beta blockers
- Continue therapy
- Probably no benefit from initiation - Statins
Diabetes
- Modern epidemic
- 25% require surgery
- 5x ↑ peri-operative mortality
- 2-4x ↑ heart disease / stroke
—> 65% die from heart disease / stroke
—> frequently associated with silent ischaemia
—> risk of PTE ↑ 6x - Resistant to pre-conditioning
- Impaired leukocyte function, including altered chemotaxis + phagocytic activity —> ***risk of infection
- Glycaemia control improves outcome
—> but does ***NOT need to be very aggressive / tight (otherwise hypoglycaemic)
—> 80-150 mg/dL
—> healing, infection, MI
Enhanced Recovery After Surgery (ERAS) program
Evidence-based multidisciplinary care pathway aimed at:
- ↓ length of stay + complications
- ↓ variability (by standardisation of care, protocols)
- ↓ cost
- Improving quality of care
- Increasing value = Quality divided by Cost
Pre-operative:
- Preadmission counselling
- No / Selective bowel preparation
- Oral fluid (Carbohydrate loading)
- No prolonged fasting
- Antibiotic prophylaxis
- Thromboprophylaxis
- No pre-medication
Intra-operative:
- Goal-directed fluid therapy
- Epidural anaesthesia / analgesia
- Short acting anaesthetic agents
- Short incision, no drains
- Warm air body heating / Maintanance of normothermia (body warmer / warm IV fluid)
- Avoidance of Na / fluid overload
Post-operative:
- No NG tube
- Epidural anaesthesia / analgesia
- Prevention of N+V
- Avoidance of Na / fluid overload
- Early removal of urine catheters
- Early oral nutrition
- Non-opioid analgesics / Multimodal analgesia (minimise SE of opioid)
- Early mobilisation
- Stimulation of gut mobility
- Audit of compliance
Summary
- Understand relative risk / benefit
- Shared decision making
- Clinical evaluation + Selective investigation
- Simple interventions effective + safe
- Communication / Team work
- Time out before surgery - Care pathways are useful
- ERAS
- EBPOM
