dr rowan molnar anaesthetics study guide part ii

DR ROWAN MOLNAR PART II: PERIOPERATIVE MEDICINE“THE WAY OF THE FUTURE”

WHAT IS PERIOPERATIVE MEDICINE?

“Integrated multidisciplinary management of the surgical or procedural patient’s 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

investigations 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 PREMEDICATION

Use if required, not “one size fits all”Aims:

1. Ameliorate anxiety Usually with a benzodiazepine such as

temazepam2. Relieve pain – predominantly in the acute setting –

usually with narcotics. 3. 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.

4. Treat other medical conditionse.g. asthma prophylaxis.

MOST REGULAR MEDICATIONS ARE CONTINUED, INCLUDING ON THE DAY OF SURGERY

Exceptions include:(a) Oral hypoglycaemics(b) 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

Nurse Clinic

Checked up, satisfied as fit & suitable

Decides to proceed with planned time, date & procedure Not certain;sends

only case notes to anaesthetist to review it

Satisfied with it; decides to send it back to her

for mx

Not quite satisfied; takes over review & mx

Decides to further investigate. May cancel, postpone, refer case or

decide to do it

Surgeon refers case

Preanaesthetic Clinic

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

Preanaesthetic ClinicBased on: HistoryExamination, Investigation . . .Decision:

To do the planned

procedure

To postpone the procedure till fully

investigated optimised

To cancel the procedure

CASE STUDY II

Perioperative management

DIABETIC PATIENT FOR VASCULAR SURGERY

HISTORY 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 & MONITORINGIN 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 ANAESTHESIAAnaesthetists have been the leaders in safety

initiatives in medicine – e.g. : Privileged reporting & investigation of deaths

under or associated with anaesthesia in most states.

Systematic reporting of incidents and near misses Collegial policies on minimum standards for

facilities, equipment, monitoring, staffing, & training.

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 it’s switched on” – my take on the

above.

MONITORING IN ANAESTHESIABasic (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 it’s not right, it’s not very specific – i.e. it may be as simple as a dislodged probe, or as serious as a cardiac arrest.

Doesn’t guarantee tissue oxygenation – may be relatively normal in extreme anaemia, carboxy- haemoglobinaemia, cyanide posoning, etc.

ELECTROCARDIOGRAM 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 pressureRemember: it is entirely possible to

die with a relatively normal ECG!

NONINVASIVE ARTERIAL BLOOD PRESSURE (NIBP) MONITORING

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 lymphoedema.

CAPNOGRAPHY“Gold standard” for verification of ETT

placement. Can also give information on:

Dead space/V-Q mismatching Adequacy of ventilation Spontaneous respiratory effort during controlled

vent’n. Rebreathing: circuit problems or inadequate gas

flow. 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 oxygen)

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 -> decreased heat production

Redistribution of blood flow -> increased heat loss 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 obstructionBronchospasmCircuit leaks/faults

Ventilator monitor

Mandatory when mechanical IPPV employed.

Usually integrated into ventilator w/automatic activation.

High (overpressure) & low (disconnect) functions

Precordial stethescope

“Traditional” monitor Still used in some

paediatric cases Can monitors:

Heart & respiratory rateBreath sounds presence

& quality.Only as good as the

person listening to it!

Direct arterial pressure

monitoringInvasive procedure,

but: Gold standard for real

time haemodynamic assessment

Accurate, reliable. Immediate warning

of hypo/hypertension of any aetiology.

Nerve stimulator

Used with muscle relaxants (neuromuscular blockers):

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 no=deeper 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 essential

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. & ass’t’d ventilation