Risk, consent and preop assessment in CVS and RSP disease Flashcards
How can very common/common/uncommon/rare/very rare be described to a patient during the consent process
Very common - 1 in 10 (One person in your family)
Common - 1 in 100 (One person on your street)
Uncommon - 1 in 1000 (One person in a village)
Rare - 1 in 10 000 (One person in a town)
Very rare - 1 in 100 000 (One person in a city)
Describe the common side effects of regional and general anaesthesia
GA + RA
PONV Dizziness Headache Itching Aches and pains Pain at injection areas Bruising and soreness
GA
Sore throat
Confusion and memory loss
Describe the uncommon side effects to GA and RA
GA + RA
Bladder problems
Slow breathing
Worsening of existing medical problem
GA
Chest infection
Damaged teeth/tongue/lips
Awareness
Describe the rare side effects to GA
GA + RA
Serious allergy to drugs
Nerve damage
Death
Equipment failure
GA
Eye damage
Who makes the decision regarding capacity
The health professional proposing the treatment
Can an anaesthetist refuse a Jehovah’s witness in the elective situation?
Yes but he must refer the case to a suitably qualified colleague who is prepared to do the case
In what situations might a Jehovahs witness accept blood products for transfusion
- Autologous (cell-saver) blood
- Cardiopulmonary bypass with non-hematogenous primes
- Epidural blood patch may be acceptable to some
Should blood be given to the child of a Jehovah’s witness in a life-threatening emergency when the child is unable to give competent consent against the wishes of the parents
Yes.
List the ways of minimizing awareness during anaesthesia
- Choose LA/RA and stay awake
- Pre-op - Equipment check
- Pre-op monitoring check (pt, disconnection alarms, drug monitoring)
- Brain activity monitors
- Avoid muscle relaxants –> awareness is less common in spontaneously breathing patients
How common is awareness and what proportion feel pain
1 in 1000 have some degree of awareness
1 in 3000 feel pain
What are the reasons for awareness
Misjudgement of anaesthetic doses needed or equipment malfunction
High risk operations (for awareness)
- Caesarian section (attempt to avoid drugs affecting baby)
- Emergency surgery (severe illness)
- Cardiac surgery
Chronic opioids/ETOH
Compare the benefits of GA vs benefits of RA
Benefits of RA
- Postoperative analgaesia (epidural)
- Decreased blood loss
- Decreased risk VTE
- Decreased PONV
- Reduced chest infection risk
- Earlier return to eating and drinking
Benefits of GA
1. Unconscious during surgery
(analgaesia available post op: PCA/IM/PO/PR)
What are the two major causes of mortality in the first 28 days after surgery and why is this the case
Cardiac (59%)
Respiratory (35%)
O2 consumption after surgery can increase by up to 40%. Any disease which affects the cardiac and respiratory systems may mean that the patient is unable to increase oxygen delivery to meet the increased demand.
Stratify cardiovascular risk based on history and examination
High risk
IHD - MI < 3 month - Unstable angina Decompensated heart failure Arrhythmias (symptomatic/uncontrolled) Severe AS or MS
Intermediate risk
- Previous MI
- Stable angina Compensated HF
- Previous stroke
- DM
Describe metabolic equivalents
1 metabolic equivalent (or MET) is equal to the oxygen consumed by an individual at rest and during normal activity. In a 70 kg male this equates to an O2 consumption of about 250 ml/min.
2-3 METS: light house work
4 METS: Climbing one flight of stairs/running a short distance
> 10 METS: highly strenuous sport: tennis/soccer
When can METS not be assessed
Patient’s with limited mobility
When does heart failure occur
When the heart is unable to provide adequate tissue perfusion in the presence of normal filling pressures.
What is the mortality rate for a patient with decompensated heart failure - undergoing a high risk operation such as an emergency laparotomy?
20 -30%
Describe the pathophysiology of angina and at what level of narrowing of the coronary artery lumen this occurs
O2 extraction in the heart is very high at rest (OER = 0.6)
Exercise/stress –> increased myocardial O2 demand which is normally met by increased coronary blood flow. But this is not possible in atherosclerosis and the onset of angina usually occurs when lumen obstruction approaches 70%
How do MIs occur in the perioperative period?
O2 demand supply imbalance
50% are caused by excessive demand: Major surgery, stress, pain –> SNS –> tachycardia and hypertension –> increased O2 demand
50% are caused by sudden reduced supply: Unstable atherosclerotic plaque haemorrhage/rupture causing thrombosis and occlusion
In what % of patients over 65 is valvular heart disease diagnosed and what is the most common type
4%
Aortic stenosis
Aortic stenosis and mitral stenosis versus regurgitant valve disease: which condition tolerates anaesthesia and which condition is very high risk for anaesthesia and why
Aortic stenosis and mitral stenosis: Very high risk as they are associated with a fixed cardiac output state and are unable to compensate for falls in SVR or increase the metabolic demands caused by the stress of major surgery
Regurgitant valve disease often tolerate anaesthesia well –> reduction in SVR reduces regurgitant fraction and improves forward flow
How can severity of stenotic valve lesions be quantified
Doppler echocardiography: identifies increased flow velocity across stenotic valves from which pressure gradients and severity of stenosis may be estimated
What happens if patients with aortic stenosis develop tachycardia or lose sinus rhythm?
Usually calcification –> increased afterload –> LVH –> decreased LV wall compliance –> atrial contractions now contribute 40% (instead of 20%) to ventricular filling
Therefore:
- Tachycardia is poolry tolerated
- Loss of sinus rhythm may cause a critical reduction in cardiac output
Why can aortic stenosis be associated with angina in the absence of coronary artery disease
Due to left ventricular hypertrophy and fixed CO state
What are the symptoms of aortic stenosis
Angina
Effort syncope
Dyspnoea
What are the signs of aortic stenosis
EJECTION OF FLOW RESTRICTED
- Slow rising pulse
- Reduced pulse pressure
- Ejection systolic murmur
What is the normal aortic valve area?
2.6 - 3.5 cm^2
Classify the severity of aortic stenosis
MILD
- Valve area: >1.5 cm^2
- Mean gradient: <25 mmHg
MODERATE
- Valve area: 1.0 - 1.5 cm^2
- Mean gradient: 25 - 40 mmHg
SEVERE
- Valve area: < 1.0 cm^2
- Mean gradient: > 40 mmHg
What are the symptoms of mitral stenosis
Dyspnoea, palpitations, fatigue.
If pulmonary hypertension develops:
- bronchitis
- haemoptysis
- pulmonary oedema
What happens if patients with mitral stenosis develop tachycardia or lose sinus rhythm?
Critical decrease in cardiac output –> acute pulmonary oedema
What is the normal valve area of the mitral valve
4 - 6 cm^2
Classify the severity of mitral stenosis
MILD
- Valve area: 1.5 - 2.5 cm^2
MODERATE
- 1.0 - 1.5 cm^2
SEVERE
- <1.0 cm^2
Describe the management of pre-operative (non-cardiac surgery) patients with AORTIC stenosis
SYMPTOMATIC:
AV replacement prior to major elective surgery
ASYMPTOMATIC:
Major surgery (with marked fluid shifts) thoracic/abdominal/major orthopedic
with AV gradients > 40 mmHg –> referred for AV replacement
Intermediate or minor surgery
–> do well if managed carefully with invasive monitoring
Describe the management of pre-operative (non-cardiac surgery) patients with MITRAL stenosis
SYMPTOMATIC:
MV replacement considered prior to major elective surgery
ASYMPTOMATIC:
Usually tolerate elective surgery well
Define atrial fibrillation
Arrhythmia
Uncoordinated atrial activation
Poor atrial mechanical function
Irregular ventricular response
Why is cardiac output reduced in patients with AF
Well timed atrial contraction normally contributes 20% of ventricular filling
What are the common causes of AF
Majority: Idiopathic AF
IHD
MV disease
Thyrotoxicosis
What is the greatest risk associated with AF
Arterial thromboembolism (Clots forming in the left atrium)
- Stroke
- Acute gut ischaemia
- Acute limb ischaemia
How does anticoagulation with warfarin change the risk of stroke in atrial fibrillation
It halves the risk of stroke
List the three important aspects of perioperative AF management
- Rate control < 100 (improves LV filling and reduces O2 demand)
- Anticoagulation: Warfarin should be stopped four days prior to surgery (minimal risk of bleeding when INR< 1.5)
- ECHO: for patients with functional impairment
- Quantify ventricular performance
- Measures left atrial size
- Identifies Mitral Valve disease
Under what circumstances can elective surgery proceed in the poorly controlled hypertensive patient
BP < 180/110 and NO TARGET ORGAN DAMAGE
Hypertension in the absence of target organ damage does not increase perioperative CVS complications
What should be done if the BP for the patient is > 180/110 in the patient awaiting elective surgery
Delay surgery for four weeks and control BP
Which patients with a newly diagnosed murmur should have an ECHO
Ideally all patients
> 4 METS, N ECG, N CXR –> tolerate minor and intermediate surgery but will require ECHO if major surgery is planned
Any patient with < 4 METS (poor functional capacity) –> ECHO
What are the respiratory complication rates of body cavity surgery (thoracic and upper abdominal) and why is this the case
20 - 40% (compared to 2 - 5% in lower abdominal surgery)
What happens to FRC during general anaesthesia and why
Decreases by 20%
Supine + muscle relaxation
Upward displacement of diaphragm downward displacement of lower ribs.
What can potentially reduce pulmonary complications in major abdominal surgery
Effective epidural anaesthesia
Describe the common causes of COPD
Congenital
- alpha 1 antitrypsin deficiency
Acquired
- cigarette smoking
- other fumes/dusts
Define Chronic Bronchitis
Chronic Bronchitis is characterised by breathlessness and a productive morning cough for at least 3 months of the year in two consecutive years
Productive morning cough x3 months for two consecutive years
Describe the pathophysiology of chronic bronchitis
Small airway obstruction is caused by mucosal oedema, mucus hypersecretion secondary to glandular hypertrophy.
Describe the common clinical characteristics associated with chronic bronchitis
“Blue bloaters”
Overweight Poor respiratory effort Chronic CO2 retention Hypoxaemia Pulmonary hypertension Right Ventricular Failure
Define emphysema
Progressive and irreversible expansion of alveoli with eventual destruction o the alveolar tissue.
What causes small airway obstruction in emphysema
Loss of elastic recoil of small airways which normally holds the airways open during expiration
Describe the clinical features of emphysema
“Pink puffers”
Thin
Maintain reasonable oxygenation
Increased VE
Always SOB
Define asthma
Recurrent reversible episodes of airway obstruction, caused by mucosal swelling, mucus hypersecretion and bronchoconstriction
What is extrinsic and intrinsic asthma
Extrinsic –> in response to an external allergen
Intrinsic –> occurs in adults and has overlap with COPD
How are well controlled asthmatics managed in the perioperative phase
Good control –> tolerate anaesthesia well
Poor control –> tolerate anaesthesia poorly
Continue all medications if controlled or change or add to get control
B2 agonist (Salbutamol) Antimuscarinic (ipratroprium bromide) Inhaled Steroids (Beclometasone)
How are poorly controlled asthmatics managed in the perioperative period
Preoperative steroids (prednisolone 30 -60 mg daily x 4-5 days)
If already taking > 10mg prednisolone daily (very poor control) –> supplement hydrocortisone perioperatively
Exclude chest infection
What effects does smoking have on the airways
- Sensitised/irritable airway (smokers cough)
- Increased mucus production (chemicals inhaled)
- Impaired ciliary function (secretion clearance reduced)
- Narrowed airways
- reflex bronchoconstriction (chemicals)
- increased mucus production (chemicals)
What occurs more commonly during anaesthetics in smokers?
- Bronchospasm
- Laryngospasm
- Coughing
- O2 desaturation
- Postoperative chest infection
- Reduced O2 carrying capacity (COHb 2 -12%)
- SNS activation by nicotine
How long before surgery should smoking be discontinued to reduce morbidity from complications to that of non-smokers
8 weeks
How does smoking affect the oxygen carrying capacity. How can this be mitigated
Reduces the oxygen carrying capacity as levels of COHb are between 2 - 12% (normal <1.5%)
Abstinence for 12 hours will improve O2 carrying capacity (T1/2 of COHb is 4h) and reduce SNS activation by nicotine (t1/2 < 60 min)
How is the FEV1/FVC ratio interpreted?
FEV1/FVC < 70% in obstructive lung disease
FEV1/FVC > 70% in restrictive lung disease (Normal is 80%)
If measurements indicate an obstructive pattern then the measurements should be completed again 10 minutes after an inhaled bronchodilator
How is PEFR interpreted in an anaesthetic context?
Coughing is ineffective when PEFR < 200 L/min
PEFR falls during obstructive episodes
How are the absolute values of FEV1 and FVC interpreted in an anaesthetic context?
FEV1 of less than 0.8 L and a FVC of less than 1 liter indicates that the patient’s cough will be poor and suggests the likely need for respiratory support following major surgery
What is the name of the instrument used to measure the FEV1 and the FVC
Vitalograph - plots expired volume versus time
What is DLCO
Another name for DLCO is transfer factor
This is the carbon monoxide diffusing capacity - it is an indication of the efficiency of gas exchange across the alveolar capillary membrane.
CO is extremely soluble in blood and hence never reaches equilibrium with capillary blood. This means that diffusion is independent of perfusion and hance CO is used because the amount that diffuses into the blood reflects the diffusion capacity rather than the pulmonary perfusion
What diseases reduce DLCO
Interstitial lung diseases
Pulmonary fibrosis
Scleroderma
Sarcoidosis
All increase the thickness of the alveolar capillary membrane and hence reduce the DLCO
What happens to the DLCO in emphysema and why?
In reduces. Alveolar destruction leads to a reduced surface area for gas exchange
How can the DLCO be interpreted in an anaesthetic context?
DLCO of less than 60% predicted is associated with increased risk of pulmonary complications after major surgery
What are CXR findings in pulmonary fibrosis
Bilateral ground glass appearance
When should an ABG be performed preoperatively?
Patients breathless on minimal exertion
Hypoxic on room air
To look for CO2 retention
To quantify degree of hypoxia
Summarise the criteria indicating severe respiratory disease
Breathlessness on minimal exertion
Hypoxia on room air (SaO2<95%)
PaCO2 > 6.0 kPa
FEV1 < 0.8 L
FVC < 1 L
DLCO < 60%
What should the postoperative plan for patients with indications of severe respiratory disease include?
Initial postoperative care should be in HDU/ICU
If postoperative ventilatory support becomes necessary, non-invasive ventilation can be considered
Is coronary sinus blood oxygen content the same as mixed venous blood?
Mixed venous blood O2 content = 15ml O2/100ml blood
Coronary sinus blood O2 content = 9 ml O2/100ml blood
Myocardium has an OER of 0.6 compared to peripheral tissue of 0.75
