dr rowan molnar anaesthetics study guide part iii
TRANSCRIPT
DR ROWAN MOLNAR ANAESTHETICS STUDY GUIDE PART 3
Gynaecological laparoscopy
PATIENT WITH POLYCYSTIC OVARIES FOR LAPAROSCOPIC CYSTOTOMIES AS DAY CASE PROCEDURE
HISTORY 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 saves.
PART IV: ANAESTHETIC EQUIPMENT& AIRWAY MANAGEMENT
INTRODUCTION TO/OVERVIEW OF THE ANAESTHETIC MACHINE
Consists of three main parts:1. “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.
2. “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)
3. “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 ventilation.
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:1. 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.
2. 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 circuit.
3. 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.
REMEMBER: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
A – AIRWAYB – BREATHING
C – CIRCULATION
Or . . . Alternatively:
(The triad of resuscitation – my own version)1. Air goes in & out2. Blood goes round & round3. Variations on the first two are a BAD
THING
Note that airway always comes first
Airway isn’t 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 anaesthesiaWhere ventilatory support required
Enable special manoeuvrese.g IPPV & PEEP for thoracotomy, laryngeal
surgery with microlaryngeal tube, single lung deflation with double lumen ET tube.
CLASSIFICATION OF AIRWAYS
SUPRAGLOTTIC TRANSGLOTTIC SUBGLOTTIC
Oropharyngeal airway
Orotracheal tube Cricothyrotomy
Nasopharyngeal airway
Nasotracheal tube Transtracheal jet catheter
Laryngeal Mask Airways (various)
Intubating LMA (w/ETT placed thru it)
Tracheostomy
Combitube/PTL * (85% of placements oesophageal)
(Combitube/PTL) - if one of the 15% placed tracheally
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 & RESUSCITATION)
Rapid sequence intubation
[or unmodified (“cold”)
intubation if apnoeic & arreflexic]
Other techniques:Fibreoptic intubationSupraglottic airwaySurgical airway
>90% <10%
RAPID SEQUENCE INTUBATION:HOW TO DO IT PROPERLY
Preoxygenation: 3mins or 5 VC breaths. IV induction agent – titrated to effectCricoid 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 don’t die of failure to intubate, but of failure to oxygenate
Supraglottic rescue airway e.g. LMA
SUCCESSFUL?
Subglottic (surgical) airway
1. Bag mask ventilation2. Repeat attempt &/or
alternate technique to intubate
SUCCESSFUL?
FIRSTLY MAINTAIN OXYGENATION!
FAILED INTUBATION DRILLCAN YOU MASK VENTILATE? [With Geudels &/or nasopharyngeal
airway if necessary]
NO
NO
YES
NO
NON ENDOTRACHEAL AIRWAYS
There’s more to anaesthetic airways than just ET tubes!
Laryngeal masks (of various types) are the most widely used airways in modern anaesthetic practice:
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 ETT.
Good protection against “top” aspiration - of saliva/mucus.
Pressure support & in some cases IPPV can be given.
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 +/- Geudel’s airway is still an acceptable – possibly even underutilised – technique for short simple cases.