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Anaesthetics Study Guide


UNSW School of Medicine Liverpool Clinical School Year VI Critical Care Rotation Anaesthetics Study Guide Blair Munford, BMedSc, MB,ChB, FFARACS, FANZCA – PowerPoint PPT presentation

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Title: Anaesthetics Study Guide

Anaesthetics Study Guide
  • UNSW School of Medicine
  • Liverpool Clinical School
  • Year VI Critical Care Rotation

Blair Munford, BMedSc, MB,ChB, FFARACS,
FANZCA Senior Specialist Anaesthetist, Liverpool
Aims of Anaesthetic Attachment
  • To understand the scope of the practice of
  • To understand the role of the anaesthetist as
    part of the surgical or procedural team.
  • To gain exposure to airway management and other
    procedural skills
  • To understand the importance of the perioperative
    process including pre-anaesthetic assessment,
    investigations, and optimisation.
  • To understand post anaesthetic care including
    pain management, and the indications for
    specialised postanaesthetic monitoring support.
  • To revise/enhance key concepts simple
    competencies in emergency assessment and
    resuscitation, including CPR/BLS/ALS.
  • For those interested, to acquire insight into
    anaesthetics as a medical career option.

Introductory Case Study
  • Dont play with that!
  • A simple paediatric case - NOT

My first ever weekend on duty as an anaesthetics
registrar . . .
  • Case transferred from country hospital for
  • 3 year old girl, previously well
  • Mixed total/partial toe amputation
  • (From playing with grandfathers axe!)
  • 18 hours ago, fasted since
  • IV in situ, IV fluids running.
  • Has had antibiotics/narcotic analgesics.
  • No problem, even for a junior registrar, right?

What happened next . . .
  • To OT as scheduled.
  • Rapid sequence induction, uneventful anaesthesia.
  • Extubated near awake at end (in hindsight, too
  • Vomited undigested food, developed laryngospasm,
  • Re-paralysed, intubated, pharynx sucked out,
    suction down ET tube no evidence aspiration
  • Awoken re-extubated uneventfully.

The lessons from this
  • Specific Beware occult delayed gastric emptying
    predictable in hindsight.
  • General
  • There is minor surgery but there is no minor
  • Anaesthetic practice is more than just being able
    to give an anaesthetic just like being a 747
    captain is more than just holding the controls!

Part I Scope Development of Anaesthetic
Imagine a world without anaesthesia . . .
What medicine was like prior to the invention of
  • Surgical operations performed rarely only as a
    last resort. Death was the expected and usual
    outcome, from shock, haemorrhage, or infection.
  • When surgery unavoidable, patient was held down
    by assistants surgeons operated as fast as
    possible. The first incision was often
    deliberately brutal in the hope that the patient
    would faint, allowing less haste.
  • No analgesia in labour interventional/operative
    obstetrics essentially unknown except post
    mortem (original meaning of Caesarean Section)

Without anaesthesia . . .
  • Surgical advances would have been minimal.
  • Childbirth would remain a major risk for baby
    and/or mother.
  • Concepts of intensive care resuscitation would
    not have developed.
  • Pain - acute and chronic - would have remained an
    inevitable part of life.

  • Without doubt the development of anaesthesia has
    been one of the top ten medical advances of all
  • Some have even ranked it as the most important
    medical invention ever.
  • Others rank it amongst greatest discoveries of
    any type in human history.

But what is anaesthesia?
  • A state that encompasses (1)analgesia plus (2)
    arreflexia (muscle relaxation or lack of
    movement) and (in the case of general
    anaesthesia) (3) hypnosis enabling painful or
    distressing procedures to be performed humanely.
  • This is the Triad of Anaesthesia

The other triad of anaesthesia
  • THE MISSION IS (in order of importance)
  • Preserve life
  • Relieve suffering
  • Provide optimum conditions for procedure
  • (Any fool can do the third by ignoring the first.
    Doing the second by ignoring the first is called
    euthanasia. The art is in being able to provide
    all three.)

Anaesthesia can be
  • Cerebral
  • Sedation/analgesia
  • General
  • Inhalational/spontaneous ventilating
  • Balanced/controlled ventilation
  • Neuro-interruptive
  • Local
  • Regional
  • Neuraxial

(Or some combination of two or more of these)
Classification of Anaesthetics
Spontaneous ventilation
Controlled ventilation
Nerve/plexus block
Spinal blocks
Epidural cervical, thoracic, lumbar, caudal
Single shot, intermittent, continuous
Local anaesthetic, narcotic/adjuvant, combination
But wait . . . theres more
Scope of Anaesthetic Practice
  • Anaesthesia for surgery
  • Sedation/anaesthesia for other procedures
  • Obstetric analgesia/anaesthesia services
  • Pre-anaesthetic assessment perioperative
  • Acute Chronic Pain Services
  • Vascular access services Central venous lines,
    et al.
  • Resuscitation Trauma team/MET/Prehospital
  • Teaching Procedural skills/resuscitation/analgesi
  • Intensive Care practice/cover/support
  • Operating theatre management/coordination
  • Critical care transport
  • (Its a broad church!)

Part II Perioperative Medicine The way of the
What is perioperative medicine?
  • Integrated multidisciplinary management of the
    surgical or procedural patients hospital
    admission stay.

Perioperative system includes
  • Identification of patient requiring procedure
  • Referral to perioperative service
  • Screening for level of workup required
  • Pre-anaesthetic assessment/plan
  • Referral investigations as required.
  • Admission at appropriate pre-op interval
  • Post-operative drug/fluid/other therapy
  • Appropriate post op level of care stay
  • Discharge at earliest appropriate point

But why?
  • Minimize unnecessary pre-op bed days.
  • Minimize preoperative cancellations
  • Enable more predictable bed occupancy
  • Minimize pseudo-urgent blood tests other
  • Improve post operative care shorten post
    operative stay

The Pre-anaesthetic Consultation
  • What? Targeted history examination,
    formulation of anaesthetic/perioperative plan.
  • Who? Ideally by the anaesthetist for the
    procedure (not always possible).
  • Whom? All patients should have some form of this.
  • When? At the earliest appropriate opportunity
    (Obviously this varies on a case by case basis)
  • Why? To enable optimimum pre-anaesthetic
    preparation, risk minimisation, informed consent,
    and allaying of anxiety.

Pre-operative preparation may include
  • Use if required, not one size fits all
  • Aims
  • Ameliorate anxiety
  • Usually with a benzodiazepine such as temazepam
  • Relieve pain predominantly in the acute setting
    usually with narcotics.
  • Prevent reflux/aspiration - in at risk patient
  • Usually (a) H2 blocker or PPI 6-8 hrs preop if
    possible, then (b) non particulate antacid
    immediately preop.
  • Treat other medical conditions
  • e.g. asthma prophylaxis.

Most regular medications are continued, including
on the day of surgery
  • Exceptions include
  • Oral hypoglycaemics
  • Antithrombotic agents (mostly)

ASA Physical Status
  • ASA 1 Healthy patient
  • ASA 2 Mild or controlled systemic disease
  • ASA 3 Significant systemic disease
  • ASA 4 Severe systemic disease current or
    constant threat to life
  • ASA 5 Moribund patient unlikely to survive with
    or without procedure
  • ASA 6 Brain dead patient (organ donor)
  • /- E Emergency procedure

Relevance of this?
  • Risk stratification
  • Workload/resource utilisation planning
  • Remuneration aspects

Perioperative (Preanaesthetic) Clinic
Surgical clinic
Surgeon refers case
Nurse Clinic
Satisfied with it decides to send it back to
her for mx
Decides to further investigate. May cancel,
postpone, refer case or decide to do it
Checked up, satisfied as fit suitable Decides
to proceed with planned time, date procedure
Not certainsends only case notes to
anaesthetist to review it
Not quite satisfied takes over review mx
  • The Doctor takes a quick history, leading
    questions are allowed as major diagnoses should
    already be known
  • Asks for hypertension, diabetes, asthma,epilepsy,
    previous anaesthetics, allergies, complications,
    medications being used
  • A quick examination is done, Ix like Xray, ECG,
    UES Blood ix are done
  • ASA categorised, anaesthesia decided
  • Explained to patient about anaesthetics, risks,
    PCA possible complications

  • Based on History
  • Examination, Investigation . . .
  • Decision

To postpone the procedure till fully
investigated optimised
To cancel the procedure
To do the planned procedure
  • Perioperative management

Diabetic patient for vascular surgery
  • 65 year old man, BMI 35
  • Type II DM, 15 yrs, on OHGs, poor control
  • Smoker 60 pack years
  • Hypertension
  • Hypercholesterolaemia
  • Ischaemic heart disease
  • Diabetic nephropathy, (eGFR 30mls/min)
  • For (R) femoro-popliteal bypass

  • What are the issues and risks here?

  • 1.What are the issues and risks here?
  • 2. How can we optimise him preoperatively?

  • 1. What are the issues and risks here?
  • 2. How can we optimise him preoperatively?
  • 3. What are our anaesthetic options problems?

  • 1. What are the issues and risks here?
  • 2. How can we optimise him preoperatively?
  • 3. What are our anaesthetic options problems?
  • 4. How do we manage him postoperatively?

Part III Safety Monitoring in Anaesthesia
Safety in anaesthesia is paramount
  • When it goes right, no-one remembers. . . When
    it goes wrong, no-one forgets
  • . . . So the aim is to make anaesthesia as
    forgettable as possible!

Safety Initiatives in Anaesthesia
  • Anaesthetists have been the leaders in safety
    initiatives in medicine e.g.
  • Privileged reporting investigation of deaths
    under or associated with anaesthesia in most
  • Systematic reporting of incidents and near misses
  • Collegial policies on minimum standards for
    facilities, equipment, monitoring, staffing,
  • Publication of algorithms e.g difficult airway
    management malignant hyperthermia
  • Simulation contingency training e.g. difficult
    airway workshops, emergency management of
    anaesthetic crises (EMAC) course.

Principles of Safety
  • Recognise risk pre anaesthetic consultation
  • Avoid risk if possible e.g. can procedure be
    done under LA?
  • Mitigate risk optimise patient condition,
    select safest technique/agents/resources e.g
    cardiac anaesthetic postop ventilation.
  • Plan be prepared for emergencies e.g.
    predrawn emergency drugs, backup airway plan.
  • Observe/monitor for deviations crises.
  • Respond in a timely appropriate fashion.
  • Call for help/backup if required.

The price of safety is eternal vigilance
  • Clinical observation is the cornerstone of
    patient monitoring
  • ANZCA Policy statements (several)
  • OR . . .
  • The best patient monitor is still the one
    between your ears so make sure its switched
    on my take on the above.

Monitoring in anaesthesia
  • Basic (all/most patients)
  • Pulse oximetry
  • ECG
  • Noninvasive (cuff) BP
  • Capnography
  • Oxygen concentration
  • Agent monitoring
  • Airway pressures
  • Temperature
  • Others as indicated
  • Invasive arterial BP
  • Precordial stethescope
  • Ventilator alarm(s)
  • Nerve stimulator
  • BIS/entropy
  • Spirometry
  • CVP
  • Swann Ganz (PAP)
  • Transoesophageal echo

Pulse oximetry
  • First monitor I put on most patients first I
    usually look at.
  • If this is OK, then patient has a pulse, a
    survivable blood pressure (at least 60/) and is
    oxygenating their blood.
  • But if its not right, its not very specific
    i.e. it may be as simple as a dislodged probe, or
    as serious as a cardiac arrest.
  • Doesnt guarantee tissue oxygenation may be
    relatively normal in extreme anaemia, carboxy-
    haemoglobinaemia, cyanide posoning, etc.

  • Good monitor for
  • Arrhythmias/ectopics
  • Some electrolyte abnormalities (K Ca)
  • Ischaemic/strain changes
  • (Provided leads are placed correctly!)
  • Does not monitor
  • Volume status
  • Cardiac output
  • Blood pressure
  • Remember it is entirely possible to die
  • with a relatively normal ECG!

Noninvasive arterial blood pressure (NIBP)
  • Usually automated
  • Convenient but not reliable
  • Dependant on correct cuff size position
  • Not continuous
  • Usually under-estimates true hyper-
    over-estimates true hypotensive values.
  • Interferes with IV infusions pulse oximetry
  • Should not be placed on limb with AV fistula or

  • Gold standard for verification of ETT
  • Can also give information on
  • Dead space/V-Q mismatching
  • Adequacy of ventilation
  • Spontaneous respiratory effort during controlled
  • Rebreathing circuit problems or inadequate gas
  • Venous return, RV function pulmonary blood flow
    e.g. thrombotic, gas or fat embolism

Oxygen monitoring
  • Monitors machine rather than patient.
  • The only specific monitor of oxygen supply
  • (Other safety features assume/depend on the gas
    from O2 outlets cylinders actually being
  • N.B. Before adoption/mandating of oxygen
    monitoring, all reported ( thankfully very rare)
    wrong gas anaesthetic incidents (misconnected
    pipelines or incorrectly filled cylinders)
    resulted in the death of the first patient
    exposed in every case.

Anaesthetic agent monitoring
  • Identifies (hopefully confirms!) anaesthetic
    agent being used
  • Measures inspiratory expiratory concentrations
  • Expiratory (alveolar) concentration enables
    calculation of MAC fraction or multiple i.e.
    estimation of anaesthetic depth.
  • Now mandatory when inhalational anaesthetic
    agents are used.

Temperature monitoring
  • Anaesthesia promotes hypothermia by
  • Decreased metabolic rate -gt decreased heat
  • Redistribution of blood flow -gt increased heat
  • Patients may need temperature support
  • Passive (prevent heat loss)
  • Active warming forced air/ heated IV fluids
  • What you support you must monitor
  • Ideally monitor core temperature
  • Nasopharyngeal/oesophageal/bladder/PV
  • Better than
  • Skin/axillary/oral/rectal

  • Airway manometry
  • Usually analogue gauge on circle circuit
  • Monitors inflation pressure
  • With IPPV can help identify
  • Airway obstruction
  • Bronchospasm
  • Circuit leaks/faults
  • Ventilator monitor
  • Mandatory when mechanical IPPV employed.
  • Usually integrated into ventilator w/automatic
  • High (overpressure) low (disconnect) functions

  • Precordial stethescope
  • Traditional monitor
  • Still used in some paediatric cases
  • Can monitors
  • Heart respiratory rate
  • Breath sounds presence quality.
  • Only as good as the person listening to it!
  • Direct arterial pressure monitoring
  • Invasive procedure, but
  • Gold standard for real time haemodynamic
  • Accurate, reliable.
  • Immediate warning of hypo/hypertension of any

  • Nerve stimulator
  • Used with muscle relaxants (neuromuscular
  • Electrical stimulus to nerve then observation of
    innervated muscle.
  • Commonest site Ulnar nerve
  • Nondepolarising block characterised by fade
    weakening of contraction with (4) successive
    impulses train of four.
  • Assesses - Density of block
  • Return of function
  • Point of safe reversal
  • Depth of Anaesthesia monitoring
  • Uses simplified EEG recording algorithm to
    produce number related to level of conciousness
    (lower nodeeper anaesthesia)
  • Two methods bispectral edge (BIS) and entropy.
  • Role/value still controversial
  • Probably indicated for
  • TIVA (as no MAC to monitor)
  • Patient with a history of awareness
  • Where lightest possible plane of anesthesia

Other monitors
  • Central venous line.
  • - Mostly used for drug infusions but can also
    measure CVP as a (not very accurate) guide to
    volume status.
  • Pulmonary artery (Swann Ganz) catheter
  • Can estimate LV filling pressure (preload) a
    better guide to functional volume status than CVP
  • Also can measure cardiac output by thermodilution.
  • Trans-Oesphageal Echo-cardiography (TOE)
  • Has become the gold standard cardiac function
    monitor. Able to estimate
  • Ejection fraction/stroke volume/cardiac output
  • LV RV Preload/pressures
  • Diastolic dysfunction (early index of ischaemia)
  • Spirometry
  • Measurement of pressure volume loops hence work
    of breathing in controlled, spont. asstd

  • Gynaecological laparoscopy

Patient with polycystic ovaries for laparoscopic
cystotomies as day case procedure
(No Transcript)
  • 25 year old woman
  • Height 165cm, weight 80kg
  • BMI 29.5
  • Typical PCOS history/findings.
  • Allergies nil
  • Rx Metformin 0.5G b.d.
  • Previous GA E/O wisdom teeth OK
  • O/Ex Overweight, otherwise unremarkable.

Common lies told by surgeons - number 2 Just a
quick laparoscopy!
  • What are the issues and risks here?

Anaesthetic issues
  • Medical condition
  • Prolonged surgery
  • Laparoscopy/pneumoperitoneum
  • Trendellenberg
  • Analgesia
  • PONV

Quiet victory
  • Largely uneventful anaesthesia/surgery
  • Problems maintaining normocarbia without
    excessive airway pressures when head down
  • Mild permissive hypercapnoea, corrected at end
  • Polymodal antiemetic therapy no PONV
  • Comfortable on combined analgesia
  • Home as day case.
  • A typical straightforward case that was
    expected to go well - did - so is not memorable
    to anyone but the anaesthetist who worked hard to
    make it that way.

There are a million stories in the naked city,
this is one of them. - The Naked City, US
crime drama series
  • The practice, safety reputation of anaesthesia
    is built on thousands of such cases far more so
    than the glamorous emergency cases heroic

Part IV Anaesthetic Equipment Airway
Introduction to/overview of the Anaesthetic
  • Consists of three main parts
  • A cocktail bar
  • This is the backbar which blends piped /or
    bottle gasses O2, N2O air, and the vapour of
    (usually one only) volatile anaesthetic agent
    (liquid) to produce the desired blend.
  • A delivery service
  • This is the breathing circuit which delivers
    the fresh gas mixture to the patient and removes
    carbon dioxide. (There are three main classes of
    circuits discussed later)
  • A bunch of hangers on
  • These are all the ancillaries attached to the
    anaesthetic machine but not part of its core
    function typically suction system, patient
    monitors, drawers/trays for airway equipment, and
    a mechanical ventilator for hands-free controlled

A Note of Caution
  • Modern anaesthetic machines are complex devices
    that require special knowledge to operate.
  • In particular, knowledge of the pharmacology of
    inhaled anaesthetic agents is essential.
  • Undetected mishaps can be rapidly fatal.
  • A thorough check prior to use, appropriate for
    the particular machine, by an experienced person,
    is vital.
  • Some parts of the circuit e.g. filters hoses,
    need to be changed after every or certain cases,
    or a different type of circuit may be selected
    attached. An abbreviated re-check must be carried
    out after any such change.

Anaesthetic Circuits
  • Three principal types
  • Drawover or semi-open systems where
    non-rebreathing valves are used to ensure
    unidirectional flow of gas. Principally now used
    in resuscitation field anaesthetic systems,
    because of the ability to use ambient air instead
    of (some or even all) pressurised gas supply.
  • Simple or semi-closed systems with pressurised
    fresh gas inflow, reservoir tube bag in one of
    several different configurations. (Sometimes
    called Maplesen systems, after the man who
    classified evaluated the different
    configurations). The patient breathes to fro
    through the reservoir tube bag the system
    relies on an adequate fresh gas flow to minimise
    rebreathing. Commonest example the
    Jackson-Rees T-piece (Maplesen F) paediatric
  • Circle, or closed circuit systems which use one
    way valves to direct expired gas through a carbon
    dioxide absorber. This gas can then be
    supplemented with only enough fresh gas mix to
    replenish the oxygen and anaesthetic agents taken
    up, and then rebreathed. This is the commonest
    type of anaesthetic circuit in modern practice.

  • The commonest anaesthetic circuit most medical
    nursing staff will ever use is the
    non-rebreathing resuscitation bag (Laerdal bag
    or similar) . . .
  • . . . to give the commonest anaesthetic and
    resuscitation drug of all Oxygen

Another rule of three The triad of resuscitation
  • Or . . . Alternatively
  • (The triad of resuscitation my own version)
  • Air goes in out
  • Blood goes round round
  • Variations on the first two are a BAD THING

  • Note that airway always comes first
  • Airway isnt everything . . .
  • . . . but without it everything else is nothing.
  • This is why anaesthetists are good people to have
    around at a resuscitation and why a grounding
    in anaesthesia is good training for emergencies.

Airway Control Why?
  • Prevent obstruction
  • Anatomical/foreign body
  • Protect against aspiration
  • Vomit/blood/secretions
  • Permit controlled ventilation
  • With paralysis/deep anaesthesia
  • Where ventilatory support required
  • Enable special manoeuvres
  • e.g IPPV PEEP for thoracotomy, laryngeal
    surgery with microlaryngeal tube, single lung
    deflation with double lumen ET tube.

Classification of airways
The winner, and still champion
  • Endotracheal intubation (usually oral), remains
    the gold standard for airway management, . . .
    but . . .
  • It is also the most difficult to master and
    carries the highest risk.
  • Remember An unrecognised oesophageal intubation
    has a 100 mortality

Emergency Airway Management (in anaesthesia
Rapid sequence intubation or unmodified
(cold) intubation if apnoeic arreflexic
Other techniques Fibreoptic intubation Supraglott
ic airway Surgical airway
Rapid Sequence Intubation How to do it properly
  • Preoxygenation 3mins or 5 VC breaths.
  • IV induction agent titrated to effect
  • Cricoid pressure 30N.
  • Suxamethonium 1.5mg/kg (IBW).
  • or Modified RSI 0.9mg/kg rocuronium
  • No bag mask ventilation (unless hypoxic)
  • Intubation confirmation of placement
  • (then only then) Cricoid pressure released.

  • Remember (1) every intubation attempt is a
    potential failed intubation.
  • You should always have a backup plan
  • - i.e. a failed intubation drill.
  • Backup begins even before you start - with
    preoxygenation for every IV induction
  • Remember (2) People dont die of failure to
    intubate, but of failure to oxygenate

nasopharyngeal airway if necessary
Supraglottic rescue airway e.g. LMA SUCCESSFUL?
  • Bag mask ventilation
  • Repeat attempt /or alternate technique to

Subglottic (surgical) airway
Non endotracheal airways
  • Theres more to anaesthetic airways than just ET
  • Laryngeal masks (of various types) are the most
    widely used airways in modern anaesthetic
  • Classic (original) its various copies
    reuseable or single use.
  • Reinforced kink resistant more flexible upper
    lumen to permit alternative positioning after
    insertion for oral/facial procedures.
  • Proseal - second lumen to communicate with
    oesophagus allow drainage of gastric contents
    or placement of gastric tube.
  • Intubating modified shape, more rigid,
    lacking apeture bars to enable passage of a
    special ET tube through it.

Non endotracheal airways II
  • Advantages of laryngeal masks
  • Hands free (compared to face mask/oral airway)
  • Easier to insert become proficient at compared
    to ETT
  • Tolerated at lighter plane of anaesthesia than
  • Good protection against top aspiration - of
  • Pressure support in some cases IPPV can be
  • Disadvantages of laryngeal masks
  • Less secure airway - more prone to dislodgement
    than ETT
  • No protection against laryngospasm
  • Poor protection against bottom aspiration of
    gastric contents (Except Proseal)
  • Not guaranteed to permit satisfactory IPPV
    especially where high pressures required.

Remember, the traditional facemask/chin lift /-
Geudels airway is still an acceptable possibly
even underutilised technique for short simple
Part V Anaesthetic Drugs Pharmacology, Use
Related Issues
Classification of drugs used for anaesthesia
  • The Big Five
  • Inhalation anaesthetic agents gasses/vapours
  • IV anaesthetic agents alias Hypnotics or
    induction agents
  • Narcotic ( other) analgesics
  • Muscle relaxants neuromuscular blocking agents
  • Local anaesthetic agents
  • Other agents are often given as part of
    anaesthesia e.g. antiemetics autonomic
    agents, but are not conventionally regarded as
    anaesthetic agents per se.

Pharmacology 1 Inhalational Anaesthetic Agents
  • Inhaled therefore delivered via apparatus
  • Gasses or volatile liquids
  • Moderate to high lipid solubility solvents
  • Effects related to physical properties
  • (rather than to a generic chemical structure)
  • Effects on multiple organ systems
  • Actual mode of action not yet fully elucidated,
    but thought to be by dissolving into cell
    membranes causing secondary changes in
    configuration of ion channels.

Currently Used Inhalational Anaesthetics (shown
in their international colour codes)
  • Nitrous oxide (N20) a gas. Insufficiently
    potent to produce full anaesthesia on its own,
    but is rapid acting, pleasant to inhale is the
    only currently used agent that is also analgesic.
  • Sevoflurane
  • Desflurane all liquids that are flourinated
  • Isoflurane
  • Earlier volatile agents such as ether, chloroform
    halothane have been superceded due to issues
    such as flammability, slow recovery, toxicity.

Practical Pharmacology of Inhalational Agents
  • Used for induction sometimes (predominantly in
    children) maintenance of anaesthesia in the
    majority of cases - either alone, or in
    combination with narcotics muscle relaxants.
  • Modern flourinated agents are good hypnotics,
    provide a degree of muscle relaxation at high
    doses, but not analgesia.
  • In contrast, nitrous oxide is analgesic, but
    doesnt decrease muscle tone, and is a poor
    hypnotic except at very high (i.e. hypoxic)
  • The combination of a volatile agent, e.g.
    sevoflurane, with a 5050 nitrous oxide/oxygen
    mix is a useful combination that combines the
    attributes of both agents.

Practical Pharmacology of Inhalational Agents (2)
  • Sevoflurane has superceded isoflurane as probably
    the most widely used agent, has also superceded
    halothane as the agent of choice for inhalational
    induction in children.
  • All currently used agents have relatively low
    solubility in blood tissue meaning that their
    partial pressures rise fall quickly, producing
    more rapid induction emergence.
  • The classical stages of anaesthesia are still
    seen with modern agents including the delerium
    phase characterised by restlessness risk of
    laryngospasm. This stage is usually seen on
    emergence, or with inhalational inductions in

Practical Pharmacology of Inhalational Agents (3)
  • Nitrous oxide, as a gas is delivered by a
    flowmeter (as are O2 air the 3 flowmeters on
    a typical modern anaesthetic machine). A linkage
    between the N20 oxygen flowmeters stops the
    delivery of any mixture lt25O2. Most anaesthetic
    machines also only allow delivery of either
    N20/O2 or air/O2, not all 3 none allow air/N2O
    (a hypoxic mixture).
  • Volatile agents are delivered by vapourisers
    devices which add a precise percentage of vapour
    to the gas mixture. Modern vapourisers are agent
    specific and colour coded/labelled accordingly.
    They have numerous mechanisms to ensure accurate
    delivery, plus safety measures such as keyed
    filling systems that match only the correct
    bottle and machines that can have more than one
    vapouriser fitted must have interlocks that
    prevent more than one being turned on.

Pharmacology 2 IV anaesthetic induction
  • Used for
  • Induction of anaesthesia
  • Sole agent for brief procedures
  • By infusion for longer procedures - in place of
    inhaled agents i.e. total intravenous
    anaaesthesia TIVA

Classification of intravenous agents
  • Barbiturates Thiopentone
  • Benzodiazepines Midazolam
  • Dissociative agents Ketamine
  • Others- Propofol
  • Alpha-2 agonists Dexmetomidine . . . maybe
    the next big thing

General features of IV agents
  • Lipid soluble
  • High volume of distribution (Vd)
  • Initial distribution to VRG
  • Offset of (initial) effect predominantly by
  • More complex when used as infusions
  • (Computerised multicompartment pharmacokinetic
    modelling required)

  • Most widely used agent now
  • Rapid(ish) onset offset
  • Shorter elimination halftime
  • Less CVS respiratory depression
  • Doesnt predispose to laryngospasm
  • ED50 for induction 2 mg/kg
  • Suitable kinetics for infusion

Other IV agents
  • First widely used agent
  • Rapid onset initial offset by redistribution
  • Long elimination halftime
  • CVS resp depressant
  • Laryngospasmogenic
  • ED50 5mg/kg
  • Still used for RSI
  • The correct dose of thiopentone is enough (and
    no more!!)
  • Low CVS resp depressant
  • Anxiolytic, good initial adjuvant agent, not
    often used as sole agent
  • Dissociative agent
  • Phencyclidine derivative
  • Cardiorespiratory stimulant (in vivo)
  • Maintains airway reflexes
  • Analgesic in subanaesthetic doses
  • The disaster anaesthetic

Total intravenous anaesthesia TIVA
  • Not practical until introduction of propofol ,
    with its short elimination half life, meaning
    minimal accumulation with infusion.
  • Usually target controlled infusion using
    computerised algorithm in syringe pump software.
    Operator enters patient weight, age, desired
    blood level.
  • Often used in combo with remifentanil
    cisatracurium infusions for long cases (these
    also have good kinetics for use by infusion).

TIVA good bad
  • Advantages
  • Good for cases of long or uncertain duration
  • Less effects on CBF ICP than volatile agents
  • Less likely to cause PONV then either volatiles
    or N2O.
  • Disadvantages
  • Long setup time
  • More expensive
  • Multiple syringe pumps required
  • No direct measure of blood or effect site

Pharmacology 3 Narcotic Analgesics Acute Pain
  • A Definition of Pain
  • An unpleasant localised sensory experience
    perceived as actual or potential tissue damage.
  • May be acute or chronic

Classification of Analgesics
  • Conduction blockade
  • Opiods
  • Paracetamol
  • NSAIDs COX2s
  • Miscellaneous agents
  • Complementary/Non pharmacological

An opiod is a drug that exhibits agonist activity
at opiate (endorphin/enkephalin) receptors. A
classification of opiods includes
  • Opiates (naturally occuring constituents of
    opium) their derivatives
  • e.g. morphine, codeine, diamorphine (heroin)
  • Synthetic opiods
  • e.g. pethidine, fentanyl cogeners, oxycodone
  • Partial agonists
  • e.g. pentazocine Fortral, buprenorphine
  • N.B. This classification does not include the
    narcotic antagonists e.g. naloxone Narcan
    naltrexone however these are closely related,
    being n-allyl substituted derivatives (hence
    their names)of opiods

Properties of opiods
  • Analgesia
  • Spinal ( µ/?) supraspinal (µ)
  • Respiratory depression
  • Sedation/euphoria (addiction potential)
  • Emesis
  • Depression of GI motility
  • Pruritis
  • Urinary retention
  • No difference in respiratory depression between
    equi-analgesic doses of any narcotic agonists

So the differences between opiods are less in
their analgesic efficacy than in
  • Onset
  • Duration
  • Potency/dose
  • Histamine release
  • Autonomic effects
  • Chest wall rigidity
  • Effective routes of administration

Routes of administration of opiods
  • Intravenous (a) Boluses titrated to effect
    e.g recovery pain protocol (b) Infusions
    require close monitoring due to potential for
    overdose as narcotic requirements fall away.
  • (c) PCA now widely used. Intrinsically
    safer than infusions, plus positive psychological
    effect of patient knowing they are in control.
  • Neuraxial - Epidural or intrathecal (spinal)
    usually in combination with regional anaesthesia,
    but may also be stand alone technique for
    postoperative analgesia. Risk of late onset
    respiratory depression if agent migrates into
    intracranial CSF in significant amount (highest
    with morphine, but this is also the longest
  • IM/SC decreasing importance with availability
    of PCA better oral agents, multimodal
  • Oral variable bioavailability e.g. oxycodone
    high, morphine 15 due to first pass
  • Sublingual(buprenorphine) /Intranasal(fentanyl)
    lipid soluble agents fairly rapidly absorbed
    this route avoids first pass effect ( injection)
  • Transcutaneous e.g. fentanyl patches for
    chronic pain

Problems with opiods
  • Respiratory depression/cough suppression
  • Tolerance
  • Abuse/addiction potential
  • Accountability/access/supply difficulties
  • - consequent to abuse potential.
  • Nausea vomiting
  • Constipation

Multimodal analgesia options
  • Regional/local blockade (if possible)
  • Paracetamol
  • NSAID or COX2
  • Basal opiod (e.g. oxycontin) or tramadol
  • (or both)
  • prn or PCA opiod
  • Other
  • Clonidine or ketamine

Pharmacology 4 Neuromuscular blockers
  • Purely paralysing agents no analgesic or
    hypnotic activity.
  • Two types based on modes of action
  • Depolarising (Suxamethonium)
  • Versus
  • Nondepolarising
  • (NDNMBs, several available)

Why use paralysing drugs at all?
  • Permit procedures at a lighter plane of
    anaesthesia hence less CVS depression
  • Intubation ventilation
  • Surgery
  • Permit IPPV without interference
  • Lower airway pressures by increasing chest wall
  • Lower O2 consumption in critical periods

Properties of NMBDs
  • Highly polar molecules
  • Low VD ( ECF volume)
  • Do not cross BBB/placenta
  • Renally excreted (with exceptions)
  • Range of actions at other ACh receptors
  • Histamine releasers (most)
  • Decrease VO2 /ATP heat production

Sux versus the NDNMBDs
  • Suxamethonium
  • Rapid onset (30s)
  • Fasciculations
  • Transient rise in ICP, IOP, IAP/IGP, K.
  • Rapid offset (usually)
  • by hydrolysis in plasma
  • Unpredictable effects in repeat dosing
  • Nondepolarisers
  • Slower onset (3-7m)
  • No fasciculations
  • Little to no effect on ICP, etc.
  • Varying durations with different drugs
  • OK for prolonged use by boluses or infusion

Nondepolarising relaxants
  • First generation
  • Curare/tubocurarine
  • Alcuronium
  • Metocurine
  • Gallamine
  • Pancuronium
  • Modern agents
  • Vecuronium
  • Atracurium
  • cisAtracurium
  • Rocuronium
  • Mivacurium

Brown curare derivatives Blue aminosteroids
(the oniums) Green benzisoquinolines (the
Side effects of suxamethonium
  • Raises serum K
  • Exaggerated action K rise in denervation,
    burns, muscle injury
  • Prolonged action with pseudochlinesterase
  • Histamine release
  • Anaphylaxis (15000)
  • Myalgia
  • MH trigger
  • Masseter spasm
  • Phase II block
  • Raises ICP
  • Raises IOP
  • Bradycardia
  • (Usually in infants
  • or with 2nd dose)

Problems with nondepolarisers
  • Slow onset not usually a major problem
  • Slow offset (situation/agent dependant)
  • Awareness
  • Hypothermia reduced heat production
  • Autonomic side effects
  • Interactions
  • Failure to reverse/recurarisation

Paralysis obviously mandates controlled
  • Modern anaesthetic machines are all equipped with
  • Usual mode is volume controlled (delivers a set
    size of breath, a set number of times a minute)
    with or without PEEP.
  • Most can also give, or be adapted to give,
    pressure controlled ventilation, which is the
    mode of choice for paediatric patients (who
    usually have uncuffed tubes, and hence a small

The Physiology of Controlled Ventilation
  • Spontaneous ventilation sucks Controlled
    ventilation blows
  • Maintains constant minute volume enables
    titration to desired pCO2 vital in neurosurgery
    acidotic patients.
  • Uptake of volatile agents therefore usually
    higher than in spontaneously breathing patient -gt
    more CVS depression.
  • Recruits alveoli prevents collapse minimises
  • Raises mean intrathoracic pressure hence RAP,
    so reduces venous return cardiac output
    especially in head up position with
    pneumoperitoneum e.g. laparoscopic
  • Risk of barotrauma esp. w/high tidal volume or

Pharmacology 5 Local anaesthetic agents
  • Local anaesthetics are membrane stabilisers that
    block depolarisation in nerves
  • Non specific blockers of
  • All sensory fibres (not just pain)
  • Motor fibres
  • Autonomic fibres (mainly sympathetics in most
  • Hence can produce analgesia arreflexia in the
    distribution of the nerves blocked.
  • Lower concentrations of LA agents effect
    predominantly smaller axons pain (Ad C
    fibres), temperature, autonomic (unmyelinated
    sympthetic post-ganglionic fibres)

Your friendly local anaesthetic molecule Think
of a person standing in the water keeping
their head high dry
  • Head benzene ring (lipophilic)
  • Body (intermediate chain) with either ester or
    amide link.
  • Tail (feet) hydrophilic due to tertiary
    nitrogen capable of accepting proton rendering
    molecule water soluble. (This is the form it is
    in in the ampoule)

The voyage of the molecule Lignocaine

Sodium channel
Freebase lignocaine diffuses across cell membrane
Understand this, and you will know
  • Why local anaesthetics sting on injection
  • (because of the low pH needed to maintain ionised
  • Why their onset of action is not immediate
  • (because of the buffering/diffusion/reionisation
  • Why local anesthesia is poorly effective in
    inflamed/ infected tissue
  • (because of the lack of buffering capability in
    acidotic tissue)
  • Why LAs exhibit tachyphylaxis
  • (exhaustion of buffering capability)
  • ( why cocaine users end up needing nose
    reconstructions from repeated insult to the
    nasal septum from an acid substance that is also
    a vasoconstrictor - which inhibits circulatory
    dilution of the acid load)

Local Anaesthetic Agents
  • Lignocaine (Xylocaine)
  • Bupivicaine (Marcain)
  • Ropivicaine (Naropin)
  • Levobupivicaine (Chirocaine)
  • Prilocaine (Citanest)
  • Max dose
  • Plain (Adr)
  • 4 (7) mg/kg
  • 2 mg/kg
  • 3-4mg/kg
  • 4 mg/kg
  • 7(9) mg/kg

Local Anaesthetic Problems
  • Failed block - multiple causes
  • High block (spinals/epidurals)
  • CNS toxicity
  • at high dose or with inadvertent IV injection
  • Selective cardiotoxicity (bupivicaine)
  • Needle/injection trauma
  • Nerve damage
  • Other e.g pneumothorax

Adjuvant agents used with LAs
  • Adrenaline prolongs blockade, allows increased
    dose (lignocaine/prilocaine)
  • Bicarbonate Decreases acidity - speeds onset of
  • Hyaluronidase Aids diffusion (Eye brachial
    plexus blocks)
  • Glucose (spinals) to produce hyperbaric
  • Narcotics (neuraxial) synergistic analgesia
  • Other analgesics e.g clonidine in neuraxial

Modes of Local Anaesthesia
  • (a) Peripheral
  • Surface
  • Topical (incl EMLA)
  • Nebulised
  • Intrapleural/peritoneal
  • Infitration
  • Intravenous regional
  • Nerve/plexus blocks
  • Multiple types
  • (b) Neuraxial
  • Epi(extra)dural
  • Single shot vs catheter
  • Bolus vs infusion
  • LA only vs combinations
  • Includes caudal blocks
  • Spinal/subarachnoid
  • Usually single shot
  • LA only or LA/narcotic
  • Combination (CSE)

Some common nerve/plexus blocks
  • Intercostal blocks
  • Ilio-inguinal block
  • Dorsal penile nerve block
  • Pudendal nerve block
  • Femoral (/- LCNT) block
  • Ankle blocks
  • Eye blocks
  • Peribulbar, retrobulbar, Sub-Tenons
  • Superficial cervical plexus block
  • Brachial plexus blocks
  • Axillary, supraclavicular, interscalene
  • Paravertebral blocks

Spinal Anaesthesia
  • Relatively quick, defined end-point for placement
  • Small volume of LA
  • Usually single shot fire forget
  • Block level depends on spread varies with
  • Volume
  • Speed of injection
  • Baricity
  • Minimal respiratory effects unless high block
  • Autonomic effects - Vasodilatation _at_ T12 up
  • - Bradycardia _at_ T4 up

Epidural Anaesthesia
  • Alone, or with GA, or as CSE.
  • Cervical (rare), thoracic, lumbar, caudal
  • Usually catheter placement (except caudal)
  • High volumes LA /- adjuvants.
  • Band phenomenon.
  • Autonomic effects similar to spinal, but slower

Considerations in regional blockade
  • Consent/communication
  • IV access
  • Adjuvant sedation/analgesia
  • Time involved
  • Failed block/backup plan
  • Management of side effects/reactions

Part VI Sub-Specialty Anaesthesia
  • Paediatrics
  • Obstetrics
  • Cardiothoracic
  • ENT/Head neck
  • Neurosurgery

Subspecialty Anaesthetics A Paediatric
  • Theyre not just small adults
  • . . . But . . .
  • Nor are they all just big neonates, either

Case Study IV
  • Paediatric Hypospadias Repair

  • 4 year old boy (obviously!)
  • Grade III hypospadias chordee
  • For EUA/repair
  • Background Mild asthma ADHD

  • Preop assessment stabilisation
  • Premedication
  • Induction IV insertion
  • Prolonged surgery
  • Postoperative analgesia
  • Postoperative IV IUDC

Adult-Paediatric Differences
  • Psychosocial
  • CNS
  • Respiratory
  • Airway
  • Other
  • Cardiovascular
  • Renal/fluids
  • Gastrointestinal
  • Hepatic/metabolic
  • Endocrine
  • Haematological
  • Immunological
  • Musculoskeletal
  • Integument

The Psychosocial Dimension
  • There are (almost) always two patients child
    and parent(s). If you dont keep the parents
    happy, or at least reassured, the child wont be
    either no matter how good the anaesthetic.
  • Children dont understand that you are there to
    help only that you are a stranger.
  • Children hate needles. Parents hate their
    children having needles. Even without this,
    cannulation can be difficult. Anything that
    ameliorates this is good such as premedication,
    EMLA to cannula sites inhalational inductions.
  • Parental presence at induction can be a good idea
    as long as the parent is going to cope. If in
    doubt, a generous premed a goodbye outside may
    be a better option.

Anatomical Differences 1
  • Body proportions
  • Head larger
  • Limbs smaller
  • Increased surface area to volume ratio
  • CNS differences
  • Brain spinal cord relatively larger

Anatomical Differences 2 Airway
  • Head larger
  • Nares (relatively) larger
  • Larynx higher
  • C3 in neonate -gt C6 in adult
  • Epiglottis longer ( softer)
  • Cricoid ring narrowest part of airway

Paediatric Respiratory Physiology
  • Chest wall mechanics tracheobronchial tree
  • Tidal volume/dead space same as adults in mls/kg
  • Respiratory rate minute volume higher
  • FRC similar to adult in mls/kg, but vO2 higher,
    so desaturate more quickly when apnoeic.
  • Control of respiration immature till 15/12 post
    conceptual age up till then vulnerable to
    apnoeas especially post GA /or narcotics.

Paediatric CVS Physiology Refresher
  • Fetal circulation/Postnatal transition
  • -predelivery systemic pulmonary circulations
    in parallel, with oxygenation via placenta high
    pressure/low flow on (R) side.
  • -Transition at birth to systemic pulmonary
    circulations in series with fall in PVR closure
    of shunts.
  • Haemodynamics
  • Neonates infants have fixed stroke volumes CO
    dependant on HR i.e. bradycardia hypotension
  • Autonomic control
  • Different in neonates children response to
    hypoxia is bradycardia (Diving reflex) rather
    than tachycardia.

Blood body fluids
  • Blood volume 80-90 mls/kg (adult 70)
  • Birth Hb 180-200 g/L (adult 120-160)
  • Falls to 110 _at_ 6/12 then rises.
  • Fetal haemoglobin (HbF)
  • Different chains
  • Lower p50 (Hb-O2 curve shifted left)
  • 75 of Hb at birth ? minimal _at_ 6/12.
  • Body water 75-80 in neonate (adult 65)
  • ECF compartment larger than ICF
  • (crossover _at_ 4/12)

Paediatric Thermodynamics
  • Infants at higher risk of hypothermia
  • Higher surface area to volume ratio
  • Remember the four modes of heat loss
  • Conduction
  • Convection
  • Radiation
  • Evaporation
  • All four occur more when the surface area to
    volume ratio is higher

Heat production regulation
  • Controlled in hypothalamus
  • Balances heat loss heat production
  • Heat production
  • Shivering poorly developed in neonate/infant
  • Metabolic thermogenesis (brown fat)
  • Thermoneutral environment
  • Point of minimum O2 consumtion
  • e.g. for unclothed term baby is 33C

Subspecialty Anaesthetics B Obstetrics
  • Remember, once again you have two patients but
    this time they are physically connected

Case Study V
  • Caesarian Section

  • 38 yr old lady, P0G1
  • Booked LSCS
  • IVF pregnancy
  • Moderate PIH/pre-ecclampsia
  • History of back pain
  • Wants to be awake for delivery
  • Needle phobic

  • Preop consultation
  • Investigations
  • Premedication
  • Choice of anaesthetic technique
  • Choice of IV fluids
  • Backup anaesthetic plan
  • Postoperative monitoring
  • Analgesia plan

  • Pregnancy is a normal, but vulnerable condition.
  • The prregnant patient is different
  • Delivery is hazardous
  • Operative intervention may be required
  • Labour delivery can be agonisingly painful
  • Anaesthesia inevitably has (at least some) foetal

Differences in Pregnancy
  • Psychosocial
  • CNS
  • Respiratory
  • Airway
  • Other
  • Cardiovascular
  • Renal/fluids
  • Gastrointestinal
  • Hepatic/metabolic
  • Endocrine
  • Haematological
  • Immunological
  • Musculoskeletal
  • Integument

Drugs the Placenta
  • General rule If it crosses the blood brain
    barrier, it crosses the placenta!
  • Placental transfer
  • Narcotics/Sedatives/GA agents - HIGH
  • Muscle relaxants -Essentially nil
  • Local anaesthetics Significant (in freebase
    form) . . . but peak maternal plasma levels
    usually post delivery

  • Analgesia for labour
  • Anaesthesia for operative delivery
  • Emergency
  • Semiurgent
  • Planned
  • Anaesthesia for post partum complications
  • Neonatal resuscitation

Analgesic options
  • Inhalational N2O as Entonox (5050 N20/O2) or
    via blender (up to 70 N2O Caution!)
  • Narcotics
  • IM/SC prn pethidine favoured by midwives
  • Infusions not often used
  • PCA remifentanil drug of choice.
  • Epidural usually initial bolus then either
  • (a) Infusion /or (b) bolus top-ups or (c)
  • Other regional/local blocks e.g. pudendal block
    for second stage.

Anaesthetic Options for Caesarean
  • Regional
  • Spinal vs Epidural
  • Spinal quicker unless epidural already in situ
    only needing top-up.
  • Most mothers want to be awake.
  • Beware the failed or patchy block.
  • General
  • Technique of choice for emergency LSCS
  • Fastest
  • Better in hypovolaemia
  • Riskier for mother on raw figures, but
  • GA population includes failed regionals most
    emergency cases.
  • So are we comparing apples to oranges?

No difference (surprisingly) in foetal outcomes
between GA RA
Subspecialty Anaesthetics C/D Cardiothoracic
  • What do these surgical disciplines have in common?

Remember the basic rules
  • Air goes in out
  • Blood goes round round
  • Variations on this are a BAD THING
  • . . . BUT (you knew there had to be a but
    somewhere, didnt you) . . .
  • ENT, Thoracic, Cardiac anaesthesia all require
    some flexibility of these rules!

Anaesthetic Factors in ENT/Oral Surgery the A to
  • Airway - shared with surgeon . . . And theyre
    not good sharers sometimes!
  • Bleeding even a little in the airway is a BAD
  • Children make up a large proportion of patients
  • Disruptions see Airway!
  • Extubation strategies deep versus awake deep
    prevents coughing but leaves patient without
    airway protection light ensures airway
    protection but patient coughing may exacerbate
    likelihood of bleeding.
  • (No easy answer to this has to be case by case

Airway Management Options in ENT/Oral Surgery
  • None (!)
  • Venturi ventilation
  • Nasal tubes
  • RAE tubes
  • MLT tubes
  • Laryngeal masks (yes!)
  • Subglottic airway i.e tracheostomy

Anaesthetic Factors in Thoracic Surgery
  • Open thorax mandates IPPV /- PEEP
  • Pre existing lung disease
  • Lung isolation requirements
  • Intraoperative hypoxia (lung isolation by
    definition creates a major shunt)
  • Postoperative issues
  • Respiratory support
  • Analgesia

Lung separation techniques
  • Endobronchial intubation
  • (but this time not inadvertent!)
  • Double lumen ET tubes
  • Bronchial blockers
  • Other (generally bodgie) methods

Anaesthetic Factors in Cardiac Surgery
  • Cardiopulmonary bypass
  • Cardiopulmonary bypass!
  • Cardiopulmonary bypass!!
  • (Scary, scary, scary stuff)

Cardiopulmonary bypass (CPB) for dummies
  • Pump plus oxygenator
  • (Heart lung machine)
  • Cardioplegia
  • (High K solution to cause cardiac standstill)
  • Hypothermia
  • (Enables prolonged ischaemic times)

Problems with CPB
  • Non-pulsatile flow can cause paradoxical
    circulatory responses
  • Hypothermia/pH issues What is the right pH in
    hypothermia to maintain acid base status?
  • Red cell trauma from pump rollers impellers,
    (especially bubble type) oxygenators
  • Cardiac restarting/Weaning from bypass
  • Post CPB syndrome confusion cognitive
    impairment, sometimes long-term or permanent.

Other Anaesthetic Factors in Cardiac Surgery
  • Pre-existing cardiac disease well, obviously!
  • Co-morbidities - high incidence CVD, PVD,
    diabetes, renal impairment, etc.
  • Concurrent medications likely to be multiple
  • Monitoring In patient on CPB there is no ECG,
    pulse (oximetry), conventional BP, or expired CO2
    there to monitor. Can monitor MAP generated by
    bypass, ABGs, BIS/entorpy

Subspecialty Anaesthetics E Neurosurgical
  • Its not rocket science . . .
  • . . . but it is brain surgery

Special considerations in neurosurgical