Anaesthetics

INFORMED CONSENT IN ANAESTHESIA

1. Bolam Test
a. Dr’s duty of care to inform a pt of the risks involved in any proposed procedure or tx was discharged….if the dr has acted in accordance w practice accepted as proper by a responsible body of medical men skilled in that particular art
b. Outmoded
2. Rogers vs whitaker (Australia)
a. Duty to disclose even where a consumer makes no specific enquiry
b. A minimum, not a maximum standard
c. Duty to provide the info that would reasonably be reqd by a person in the position of the pt
d. Applies to NZ
3. Health and Disability Commissioner Act 1994
a. No health care procedure shall be carried out w/o informed consent
b. Elements of informed consent under the code
i. Right 5 - Effective communication
1. communication in a form, lang and manner enabling the consumer to u/stand the info provided; this includes the right to a competent interpreter where necessary and reasonably practicable
2. a shared dialogue – responsive to the needs, wishes, capacities and expressed concerns of the particular (unique ) consumer
3. right to an evt that enables both consumer and provider to communicate openly, honestly and effectively
a. extending consultation times so that questions can be asked and answered
b. plain language rather than medical jargon
c. visual or written explanations, diagrams, models
d. support persons and whanau
e. sensitivity to religious or cultural needs, values and beliefs
4. the provider is not in breach if they have taken reasonable action in the circumstances to give effects to the rights and comply with duties
a. circumstances can means the consumers clinical circumstances or the providers resource constraints
ii. Right 6 – the right to be fully informed → Provision of all necessary info – including options, risks and benefits
1. concept of choice
2. code envisages consumers taking an active role in decision-making rather than simply acquiescing in decision made on their behalf by providers
iii. Freely given and competent consent

Four Essential Features
1. Competent patient
2. Provision of sufficient info for the pt to be fully informed
What procedure is
Who is doing it
Risks – rare + serious, common + minor, relevant to pt
Pt needs to u/stand info + apply it to their situation
3. Effective Communication – includes opportunity for pt to clarify
4. It is obtained in a context which allows voluntary choice
Ideally documented

OXYGEN THERAPY

1. Goal of O2 therapy → prevent tissue hypoxia
2. O2 Cascade (see diagram)
3. Recognising hypoxaemia
a. Non-specific features
i. Altered mental state
ii. Dyspnea or tachypnea
iii. Central cyanosis
iv. Dysrrhythmias
v. Coma
b. Central cyanosis
i. Reqiores 15 g/l reduced Hb for recogntion
c. Pulse oximetry and ABGs
4. Indications for O2 therapy
a. A/w problems
b. Cardiac or respiratory arrest
c. Hypoxaemia – PaO2 <8 kPa, SaO2 <92%
d. Hypotension – SBP <100
e. Low CO states
f. Metabolic acidosis
g. Respiratory distress – RR >24
5. Mechanisms of tissue hypoxia
a. Arterial hypoxaemia
i. Low inspired PaO2 – high altitude
ii. Alveolar hypoventilation – sleep apnea, opiate o/d
iii. Ventilation-perfusion mismatch – acute asthma, atelectasis
iv. R→L shunts
v. Diffusion problems
b. Failure of oxyhemoglobin transport
i. Inadequate tissue perfusion
ii. Low Hb conc
iii. Abnormal O2 dissociation curve – haemoglobinopathies, high COHb
iv. Histotoxic poisoning – eg cyanide, septicaemia
6. Physiology of hypoxaemia
a. CVS – tachycardia, pulm HTN
b. Resp – tachypnea
c. Haemotological – EPO induced polycythemia
d. Neuro – confusion, ↑ cerebral blood flow
7. Oxyhemoglobin dissociation curve (see diagram)
8. Alveolar hypoventilation (see diagram)
9. Alveolar Gas equation
a. PaO2 = PiO2 – PaCo2 / RQ
b. RQ = respiratory quotient (normally 0.8)
10. O2 Delivery devices
a. High flow fixed performance devices - Venturi effect
i. Adapters to face mask – determine FiO2
ii. Side port diameter determines degree of mixing with room air
b. Low flow variable performance devices
11. Type 2 Respiratory failure and hypoxic drive
a. Use fixed performance devices
i. Reliable FiO2
ii. Risk of rebreathing w low flow devices
b. Failure to correct hypoxaemia is unacceptable
c. Pts relying on hypoxic drive are uncommon
d. Monitoring of tx is essential
12. High flow O2 masks
a. Accurately deliver low FiO2 (24-35%)
b. FiO2 unaffected by ventilatory pattern
c. Rebreathing not a problem
d. May reduce risk of CO2 retention
e. Humidification necessary
13. Low flow O2 masks
a. Concentrations up to 60% achieved w moderate O2 flow rate (6-10 L/min)
b. Used mainly in type 1 respiratory failure
c. At low flow rates (<5 L/min), rebreathing may occur bec exhaled air not flushed
d. Difficult to achieve low Fio2
e. Humidification necessary at higher flow rates
14. Hudson mask
a. Variable performance (determined by rate and depth of breathing)
i. 1 L/min → 24%
ii. 2 L/min → 28%
iii. 3 L/min → 32%
iv. 4 L/min → 36%
b. At low flow rates (<5 L/min), rebreathing may occur as exhaled air not flushed
c. Humidification necessary at higher flow rates
15. Nasal prongs
a. Simple and convenient – pt can eat and drink
b. FiO2 dependent on flow rate (1-6 L/min) and minute vent volume
c. Fio2 25-35% in hypopharynx at 2 L/min flow
d. Humidification not necessary <4 L/min
e. Local irritation and dermatitis at high flow rates
16. Humidification
a. Oro and nasopharynx provides humidification at flow rates <4 L/min
17. Dangers of O2 therapy
a. Pulmonary oxygen toxicity – FiO2 >0.6
b. Supports combustion → Ø smoking
c. Paul-bert effect (hyperbaric O2)
i. Cerebral vasoconstriction
ii. Epileptic fits
d. Alveolar hypoventilation if pt reliant on hypoxic ventilatory drive
18. Monitoring O2 therapy
a. Pulse Ox – simple, safe, continuous, only SaO2 provided, artefacts, unreliable if fingers cold, low output states, nail polish (use ear probe)
b. ABGs – invasive, intermittent, PO2, PCo2, pH, HCO3- and more
19. Stopping O2 therapy
a. Adequate oxygenation in room air – PaO2 >8 kPa, SaO2 >92%
b. Resolution of tissue hypoxia – acid-base status normalised, normal organ perfusion
20. Summary
a. O2 is life saving
b. It should be prescribed in writing specifying flow rate and method of delivery
c. Failure to tx hypoxaemia for fear of causing CO2 retention is unacceptable
d. Careful and regular monitoring is reqd

MAORI – OPERATING THEATRE

1. General principles
a. Oral language is very impt
b. Tribal affiliations
c. Recognition of tangata whenua status
d. Many Maori pts and their families will want religious ceremonies conducted at times of importance such as prior to surgical procedures
e. Concepts of tapu/noa (sacred/profane)
f. Head is tapu → potential for conflict in the OT w need for masks, nasal and oral tubes
g. Concept of body shyness (whakama) → also extends to bodily secretions, will need sensitivity in the OT
h. Retention of body parts
i. A need to reclaim the body for return to marae for grieving is paramount
j. Organ donation is not a culturally simple proposition
k. Patient consent – pt is likely to want whanau involvement in major decision making
l. Food and the pre-op pt – requirements for fasting prior to surgery needs to be emphasized as food is seen as a vital ingredient at the bedside of the fasting pt before surgery
m. Informed consent – but consider Maori language and the provision of an interpreter
n. Has been a shift from reasonable doctor to reasonable patient

PERI-OPERATIVE FLUID MANAGEMENT

1. Principle of fluid therapy is to maintain tissue perfusion
2. Distribution of TBW – 42L
a. TBW = ICF 28 L (BW x 0.4) / ECF 14 L (BW x 0.2)
b. ECF = Interstitial fluid 11 L (BW x 0.15) + Intravascular fluid 3 L (BW x 0.05)
3. Composition of fluid c/ments
a. Na and Cl → mostly plasma and interstitial
b. K → mostly intracellular
4. Daily water balance
a. Intake – ingested fluid 1300 ml, sold food 800 ml, metabolic water 400 ml
b. Output – skin 500 ml, lungs 400 ml, urine 500 ml, faeces 100 ml
5. Daily water requirements for a 70 kg man = 2500 ml/day
a. 1st 10 kg = 10 x 100 ml/kg = 1000 ml
b. 2nd 10 kg = 10 x 50 ml/kg = 500 ml
c. Subsequent Kg = 50 x 20 ml/kg = 1000 ml
6. Daily electrolyte requirements
a. Na = 0.5-1 mmol/kg/day
b. K = 0.5-1 mmol/kg/day
7. IV Fluids
a. A Colloid has protein like mass – good intravascular persistence, prolonged hemodynamic stabilisation, ½ life 90 mins
b. A Crystalloid is just an ionic solution – poor intravasc persistence, transient hemodynamic stabilisation but cheap, ½ life 30 mins
8. Crystalloids
a. Saline 0.9% - Na 154 mmol/l
b. Saline 0.45%
c. Glucose 4% / Saline 0.18% - Na 31 mmol/l
d. Glucose 5% - nil Na
e. Hartmans solution (or ringers lactae) – Na, K, Ca, Cl, HCO3- (as lactate)
9. Practical crystalloid therapy
a. If you infuse NaCl 0.9% 1000 ml – all the Na will remain in the ECF
i. As NaCl is isotonic, there is no change in ECF osmolality and no water exchange occurs across the cell membrane
ii. NaCl expands ECF only
iii. Intravascular vol will only be ↑ by 250 ml
b. If you infuse glucose 5% 1000 ml, the glucose will enter the cell and be metabolised
i. The water expands both ECF and ICF in proportion to their volumes
ii. The ECF vol will ↑ by 333 ml
iii. Intravascular vol will only ↑ by approx 100 ml
c. Plasmalyte
i. Crystalloid
ii. First line fluid
iii. Use in expanding intrasvascular space (ECF)
iv. Ratio 4:1 to loss
v. Isotonic
10. Gelatins eg Gelafusin
a. Colloid
b. Effective vol expander
c. Moderate intravascular life
d. Some anaphylaxis
e. Ratio 2:1 loss
f. Ketastarch – stays even longer in circ
11. Dextrose saline
a. Supplies daily Na
b. Hypotonic
c. Iso-osmolar
d. Need to add isotonic solution for losses
e. K+
f. Beware hyponatremia (unlikely in surgical pts where Na retention occurs)
12. Blood
a. Give early in active bleeding
b. Discuss before giving in stable pts
c. Risks may outweigh benefits in fit pts
d. General guidelines
i. When hemodynamically stable – rare to need blood if Hb >100 g/dl, usual to need blood if Hb <70 g/do
13. Practical fluid therapy
a. Replacement of intravasc vol
b. Maintenance therapy
c. Replace e/lyte deficit
14. Assessment of intravascular depletion
a. 5% → thirst, dry mucous membranes, UO 1-2 ml/kg/hr
b. 10% → tachycardia, oliguria, UO 0.5-1 ml/kg/hr
c. 15-20% → tachycardia, hypotension, severe oliguria, UO <0.5 ml/kg/hr
15. Use plasmalyte or colloids to restore perfusion
a. Hypotension
b. Tachycardia
c. Oliguria
d. Cool peripheries
e. Known blood loss
16. Dehydration
a. Plasmalyte
b. Give 50% bolus to tx deficit – eg if 10% depleted, give a 2L bolus stat
c. Reassess
d. Ongoing infusion
17. Suggested intravasc vol replacement
a. Plasmalyte 1000 ml over 30 mins then reassess
b. Gelofusin 500 ml over 15 mins then reassess
c. Don’t simply incr rate slightly
d. No place for dextrose saline
e. Modify your fluid mgt w the changing patient needs
f. HF is not a contraindication for fluid replacement – these pts still require fluids
18. Intravascular vol replacement
a. Best estimate of the vol required is the pts response
b. After therapy started, observe →
i. Vital signs
ii. U/O >0.5 ml/kg/hr
iii. CVP
19. Fluid and E/lyte therapy
a. Surgical pts have –
i. Maintenance vol requirements
ii. On going losses
iii. Vol excess/deficits
iv. Maintenance e/lyte requirements
v. E/lyte deficiencies/excess
b. Ongoing losses
i. Eg – NG tube, drains, fistulae, third space losses
ii. Conc similar to plasma
iii. Replace w isotonic fluids
20. Control of vol status
a. Effective circ volume – portion of ECF that pefuses organs, usu equates to intravasc vol
b. Third space loss – abnormal shift of fluid from intravasc to tissues – eg bowel obstruction, pancreatitis
21. Giving Fluids
a. Type of loss
b. Degree of deficit
c. Blood loss
d. Co-morbidities
e. Response to replacement
22. Therapeutic endpoints
a. Goal – normal hemodynamic parameters, normal e/lyte concentration
23. Post-op fluid therapy
a. Check IV regime ordered in op form
b. Assess for deficits by checking I/O chart and vital signs
c. Calculate maintenance requirements
d. Usu K not started in first 24 hrs
e. Monitor carefully vital signs and U/O
24. Cardiac, renal and liver failure
a. Still must resuscitate
b. Endpoint are less predictable
c. Monitor more intensively – ICU, invasive monitoring
25. Summary
a. Assess and reassess
b. Use salt rich solutions to resuscitate
c. Use water + Na and K for maintenance
d. Blood if actively bleeding and anemic
e. Beware hyponatremia

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