Anaesthesiology: The Preoperative Assessment Flashcards
Pre-operative assessment clinic (PAC)
Day 0 = Day of surgery
Aim of pre-op assessment: 1. Formulate ***anaesthetic plan + ***analgesic plan 2. ***Optimise patient condition 3. Determine ***fitness for surgery 4. Decide ***post-op placement 5. Plan ***fasting, pre-medication 6. Establish ***rapport —> ↓ Hospital stay, bed occupancy, economic + psychological impact
Component:
1. History (past + present) from patient, relatives, care-provider
- Medical history
—> CVS, Respiratory, GI, RA, DM, Neuromuscular, Renal, Liver, OSA
- Previous anaesthetic + surgery
- P/E
- Airway
- Respiratory system
- CVS system - Order / Review appropriate investigation
- Explain anaesthetic plan
- Obtain consent with explanation of risks
Triage of PAC
Patients at **low risk of complications during anaesthesia + surgery (ASA class 1, 2 patients / Uncomplicated surgery e.g. duration, blood loss, post-op pain)
1. No-co-existing medical problems
2. Have a co-existing medical problem that is well-controlled + not impact daily activities (e.g. HT)
3. No history / predicted anaesthetic difficulty
4. Requiring surgery in which complications is minimal
—> listed as **Day surgery (same day admission +/- same day discharge, day surgery centre)
Higher risks patients:
1. Co-existing disease that impaired ADL
2. Discovery of previously undiagnosed medical problems (e.g. HT, DM, murmurs)
3. Medical problems less than optimally managed (e.g. Angina, COPD)
—> Sent for further investigations (ECG, Lung function test, Echo, CT)
—> Refer to appropriate specialist for advice + management before re-assessment
—> Pre-op admission for assessment for list anaesthetist / specialist anaesthetist / pre-op optimisation
PAC:
- Once patient admitted for surgery —> their intended surgery are ***not cancelled because deemed unfit / medical problems not adequately treated
- Time between surgery and PAC should NOT >3 months (4-6 weeks optimal)
- Obtain consent
Pitfalls:
- Need coordination between surgeon, anaesthetist, nurses, ward, patient —> preferably sessions on same day for patients’ convenience
- Fasting time difficult to decide (esp. paediatric / morning / afternoon session)
- List anaesthetist may not agree on mode of anaesthetic —> review + explain
- Interval changes: new developments, new investigations, patient leave
- Q/A sheet, check list, video
History: CVS system
Equire about:
- Primary disease
- End-organ involvement
Ask about symptoms:
- IHD
- frequency
- severity
- predictability of angina
- Previous history of MI: greater risk of further infarction, peri-op risks ↓ as time elapsed since original event
- Uncomplicated MI with normal exercise tolerance: elective surgery may need to be delayed by 6-8 weeks
- Complicated MI, infarction size, residual angina, arrhythmias —> need cardiac assessment
- PCI / pacemaker / anticoagulant - Heart failure
- ↑ risk of peri-operative cardiac morbidity / mortality - HT
- treatment + control
- Mild HT: 140-159/90-99 —> no evidence that delaying surgery for treatment affects outcome
- Moderate HT: 160-179/100-109 —> consider **review of treatment, if unchanged requires **close monitoring to avoid swings during surgery + anaesthesia
- Severe HT: >180/>109 —> **postpone elective surgery ∵ risk of **myocardial ischaemia, arrhythmia + intracranial haemorrhage
- Emergency surgery —> **acute control + **invasive monitoring
- Consider end organ involvement
—> Heart hypertrophy, Heart failure
—> Renal: RFT
—> Retina - Valvular heart disease
- AS in elderly
- congenital heart disease into adulthood - Conduction defects / Arrhythmias
- Peripheral vascular disease
- previous DVT, PE
History: Respiratory system
- Symptoms
- Asthma
- COPD
- Infection
- Restrictive lung disease
- Pre-existing lung disease: ↑ risk of peri-operative **chest infection (esp. if obese / have upper abdominal / thoracic surgery)
- If acute URTI (consider Stage of disease, Urgency of surgery, Patient expectations) —> surgery / anaesthesia may be **postponed unless life-threatening condition - Exercise tolerance
- prediction of post-op morbidity / mortality —> surgery provokes similar physiological responses to exercise (i.e. ↑ tissue O2 demand —> require ↑ O2 delivery + CO)
- run for bus? How far walk uphill? How many stairs can climb before stopping? Can do housework? Able to care for yourself (ability to perform ADL before stopping due to chest pain / SOB: **indication of cardiac + lung reserve)
- subjective (depend on patient motivation, tend to over-estimate their abilities)
- objective: **Specific Activity Scale
Metabolic equivalents of activity (MET), Specific Activity Scale
1 MET = Energy used at test
1 MET = Metabolic equivalents of O2 consumption
1-4 MET = Standard light home activities walk around the house, Walk 1-2 blocks on level ground at 3-5 km/hr
5-9 MET = Climb a flight of stairs, walk up a hill, walk on level ground at >6 km/hr, run a short distance, moderate activity (gold, dancing, mountain walk)
>=10 MET = Strenuous sports (swimming, tennis, bicycle), heavy professional work
NYHA classification of cardiac function of **Specific Activity Scale classification:
Class 1:
- can perform activities requiring **>=7 MET
- joy, walk at 5 mph, ski, play squash, basketball, shovel soil
Class 2:
- can perform activities requiring ***>=5 MET but <7 MET
- unable at 4 mph / level ground, garden, rake, weed, have sexual intercourse with stopping
Class 3:
- can perform activities requiring ***>=2 MET but <5 MET
- perform most household chores, play gold, push the lawn mover, shower
Class 4:
- cannot perform activities requiring >=2 MET
- cannot dress without stopping due to symptoms
- cannot perform class 2 activity
History: Other important considerations
- Indigestion, heart burn, reflux
- possibility of ***hiatus hernia if exacerbated on bending forwards (lying flat will ↑ risk of regurgitation + aspirations) - RA
- joint deformities limit **positioning for surgery
- cervical spine (C1/2 subluxation), TM joint involvement —> complicate **airway management
- chronic anaemia
- drugs: steroids, NSAID, DMARDs - DM + End organ involvement (Microvascular disease)
- IHD, Renal dysfunction, Autonomic + Peripheral neuropathy
- ↑ risk of ***peripheral complications (e.g. hypotension, infection) - Neuromuscular disorders
- poor respiratory function (FVC <1L) —> predispose to **chest infection + ↑ chance of requiring respiratory support post-op (consider regional)
- poor bulbar function —> predispose **aspirations
- medico-legal implications: what if block does not regress as projected —> need thorough explanation + examination - Chronic renal failure
- anaemia
- electrolyte abnormality
- altered drug excretion
—> co-ordinate surgery + dialysis - Hepatic dysfunction
- coagulopathy
- altered drug metabolism: Opioids - OSA
History: Previous anaesthetic + surgery
- Problems with anaesthesia
- N+V
- awareness
- jaundice
- delayed recovery
- prolonged hypotension - History of difficult intubation
- History of delayed recovery
- Difficult IV access, bleeding
- Check previous record
- Potential anaesthesia problems (e.g. cardiac, pulmonary, spine)
History: Family history
- ***Malignant hyperthermia
- ***Pseudocholinesterase deficiency
- Previous ICU admission
History: Drug history, allergies, Social history
- Smoking
- ↑ peri-operative complication
- ↓ ciliary function
—> stopping 8 weeks improve airway
—> stopping 2 weeks ↓ airway irritability
—> stopping 2 days ↓ CO level - Alcohol
- enzyme induction: drug tolerance
- post-op alcohol withdrawal syndrome - Drug abuse
- difficult IV
- HIV, HBV, HCV carrier
- drug withdrawal syndrome post-op (cocaine) - Pregnancy
- X-ray in 1st trimester
- 1st trimester: greater chance of abortion (though risk of spontaneous abortion is high, elective Suxamethonium use during 2nd trimester)
- ↑ risk of regurgitation / aspiration ∵ ↑ intra-abdominal pressure + delayed gastric emptying
American Society of Anaesthesiologist (ASA) classification
Identification of high-risk patient
—> 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
***Pre-operative management
- Fasting
- Type of anaesthetic + consent
- Any consultation + extra investigation
- Drugs
- Pre-medication
- Post-operative placement
- based on:
—> pre-morbid status
—> nature + length of operation
—> intra-op + post-op events
- Fasting
- ↓ Volume of gastric contents —> ↓ Pulmonary aspiration risk
- Factors predisposing to regurgitation / aspiration usually occurs at **induction / **emergency, occasionally intra-op
- Gastric volume + content (solid / liquid) + pH —> affect consequence of aspiration
***Guidelines for pre-op fasting:
- Clear fluids: 2 hours
- Breast milk: 4 hours
- Light meal: 6 hours
(- Regular meal: 8 hours)
(2468 rule)
Management:
1. Assert fasting time
- Identify high risk patients
- RSI (Rapid sequence induction) for high risk patients / emergency surgery
- Prophylaxis: Chemical control of gastric volume + pH
- Antacids (neutralise acidity)
—> particulate antacids not recommended
—> ***Na citrate administered shortly before induction
- H2 blockers / PPI (↓ stomach acidity)
—> pregnancy: ***Ranitidine 150mg evening before + 2nd dose 2 hours pre-op + Na citrate shortly before induction - Metoclopramide (↑ gastric motility, seldom used)
- Empty gastric contents before induction
- ***Suction NG tube
—> not routinely inserted in all patients —> open esophageal gastric sphincter
Pre-operative medications
- Rapport: Full explanation + consent
- ***Pain relief
- Sedation, ***Anxiolytics in ADHD
- ***DVT prophylaxis (but caution: prolonged bleeding)
- Regurgitation + Aspiration prophylaxis
- Drug + pre-existing disease
- DM, HT, Psychiatric drugs, Drug abuse, Anticoagulants for IHD, AF, Herbal medicine - Pacemaker programming
- EMLA cream (for paediatric)
P/E
- System based, concentrate on CVS + Resp system
- Other systems if problems relevant to anaesthetic / identified in history
- ***Vascular access (e.g. AV fistula on arm, axillary dissection done before)
- ***Airway assessment
***Airway examination
Try to predict patients with difficult airway (Bag-mask ventilation, LMA insertion, ETT intubation)
—> cannot intubate / ventilate —> crisis —> go-to-algorithm
- Regional anaesthetic can bypass airway —> but what if it fails / complications occur / resuscitation —> Plan B/C
History:
- Patients with history of difficult intubation at previous anaesthetic
P/E:
- **Anatomical features suggesting ***Difficult intubation:
1. Limited mount opening
- Receding chin
- small / regressed mandible - Position, number, health of teeth
- loose dentures
- protruding incisors
- missing upper incisors - Size + Motility of tongue
- tongue relax and fall back under GA / LOC —> obstruct airway
- lower mandible large enough to contain tongue
- CA tongue stuck to floor of mouth - Soft tissue swelling at front of neck
- goiter with deviation of trachea and obstructs esophagus
- tumour
- Ludwig’s angina - Deviation of larynx / trachea
- Limitation in flexion / extension of cervical spine
- previous fusion
- C1/2 subluxation
- unstable from trauma
- ankylosing spondylosis - Retropharyngeal abscess
P/E:
- Mallampatti score
- Patient sitting upright open their mouth widely + maximally protrude tongue
- View of pharyngeal structures graded 1 - 4 —> Grade 3 + 4 suggests difficult intubation - Thyromental distance
- with head fully extended on neck —> distance between bony point of chin and prominence of thyroid cartilage —> distance of ***>7 cm suggest easy Direct laryngoscopy - Neck extension
- Dental condition
- Celden test
- Wilson score
- Sternomastoid distance
- Neck circumference (Bull neck: too much loose tissue in oropharynx to displace)
Difficult intubation:
- overall incidence 5.2%, failed intubation 0.15%
