iThoughts

Equipment 1

Circulation

BP

7 Non-invasive

Palpation
Cuff + manometer

Korotcoff sounds

1: tapping = systolic
2: soft swishing
3: louder
4: dramatic decrease in sound
5: loss of sound
Diastolic = 4/5

von-Recklinghausen oscillotometer

2 cuffs
Anaeroid barometers
Mechanically amplified to needle

Automated oscillometers

DINAMAP

Components

Solenoid valve
Pressure transducer
Microchip

Oscillation

Start = systolic
Max = MAP
No further change = diastolic

Issues

Sizing

Should be 20% wider than arm diameter

Inaccurate in arrythmias and movement
Takes a minute
Can damage tissue

Finapress

LED absorbance measured, pressure around finger keeps it constant

Radial accelerometry
Doppler

Invasive

Components

Cannula
Tubing
Heparinised saline
Transducer

Pressure moves diaphragm in transducer which alters the tension and therefore resistance in a strain gauge, this is amplified by a Wheatstone bridge and displayed as a waveform
types

wire strain gauge

as pressure increases, length decreases and cross sectional area increases —> reducing resistance

bonded strain gauge

as pressure increases, length increases and cross sectional area decreases —> increasing resistance

capacitive

as pressure increases, capacitor plate moves closer to 2nd plate, increases capacitance —> reducing resistance

Signal processor
Amplifier

gain

changes amplitude

interference reduction

common mode rejection

removes interference at measuring and reference electrode

bandwidth

removes high/low frequency interference

Display

Waveform

Slow rise = poor contractility
High dicrotic notch = vasoconstriction
Low dicrotic notch = low vascular resistance
Area under curve to notch = stroke volume

Issues

Offset drift (common)

corrected by zeroing

Slope drift (uncommon)

corrected by adjusting gain

Resonance & damping

Optimal damping = 0.64
minimum natural frequency = 20-40Hz (approx. 10x input frequency from heart rate) (to avoid resonance)

CO

5 Non-invasive

Clinical
Thoracic impedance
Transthoracic doppler
MRI
NICO

Fick principle w. CO2

1 Minimally invasive

Oesophageal doppler

40cm
measures flow in descending aorta

3 Invasive

Pulmonary artery catheter

inflated w. 1mL of air!
methods

Fick principle

CO = oxygen consumption / (`CaO2 - CmvO2)

Thermodilution

method: known volume of cold saline injected into right atrium, thermistor measures temp in pulmonary artery
calculation: semi-logarithmic temp change over time plotted then area under curve is entered into the Stewart-Hamilton equation to calculate CO
GOLD STANDARD
underestimates: too much injectate, thrombus on catheter

Dye dilution

indocyanine green
Calculation: semi-log plot, extrapolate straight line to allow for recirculation

risks

pulmonary infarction
arrythmias

PICCO
LIDCO

ECG

calibration

x

paper speed = 25mm/s
so 1mm = 40ms, 5mm = 200ms

y

1mm = 0.1mV, 5mm = 0.5mV

Leads

Limb

RA, RL, LA, LL

Bipolar

I, II, III (coronal plane)
Count number of L's for which is which!

Unipolar

Augmented

AvR, AvL, AvF (coronal plane)

Chest

V1 - V6 (horizontal plane)

Measured from imaginary midpoint (Einthoven's triangle)

CM5

enables detection of 80% of LV ischaemia
RA moved to manubrium
LA moved to V5
LL moved to clavicle
lead 1 selected (between manubrium and V5)

axis

normal = -30 —> +90
RAD

RBBB, RVH, normal variant

LAD

inferior MI, LBBB, pregnancy

Waves

P

atrial depolarisation

Q

normal septal depolarisation

when QRS to L of 60 degrees

I, aVL, V5, V6

when QRS to right of 60 degrees

II, III, aVF

MI

in V1-3, >2mm deep, >25% of QRS or >1mm wide

R

upright in all waves except aVR and V1

abnormalities

heart block

PR

1st
2nd

I (Wenkebach)

progressive prolongation
may be normal in athletes w. high vagal tone

II

2:1 or 3:1

3rd

bundle branch

LBBB
LAHB
LPHB
RBBB
bifasicular block

RBBB + a fasicular block
seen as RBBB + LAD

trifasicular block

bifasicular block + 1st degree HB
risk of complete HB

delta waves

upward deflection before Q
WPW

(also get shortening of PR)

J waves

upward deflection after S
hypothermia, SAH, hypercalcaemia

U waves

deflection after T wave
digoxin, hypokalamia, hypercalcaemia, hyperthyroidism

QT prolongation

hypocalcaemia, hypokalaemia, hypomagnesaemia, amiodarone, antihistamines, antipsychotics, macrolides, Romano-Ward syndrome, Lervell Lange Nielson syndrome
‘HHHAAM RALLY’
also anything that prolongs QRS!!!

ST

inferior

II, III, aVF
normally R coronary occlusion

anterior

subtypes

septal

V1-V2

LAD

anterior

V2-V4

LAD

lateral

V4-V6, aVL
smaller branches of LAD/circumflex

anteroseptal

LAD

anterolateral

LAD

worst prognosis

posterior

V7-V9
big horizontal ST depression in V1-V3

miscellaneous

AAGBI 2007 recommendations of standards of monitoring

Continuous presence of an anaesthetist
General

ECG
Sats
NIBP
Airway pressures
Gas analysis

Regional

ECG
Sats
NIBP

Recovery

Sats
NIBP

filters

blood

200um
blood, platelets, FFP, cryo

standard

15um
fluids, HAS, stem cells, IVIG

Specific IV drug filter (e.g. For phenytoin

0.22um

drawing up needles

5um

epidurals and HMEFs

0.2um

ETT

one lung ventilation

double lumen tube

e.g. Robershaw tube
L side tube is better as the R side give off R upper lobe bronchus early which may then be occluded

Cannulae

flow rates

14G

300mL/min

16G

150mL/min

18G

100mL/min

20G

50mL/min

22G

25mL/min

spinal needles

Quinke

cuts
opening at tip = less likely to fail
higher risk of PDPH (8%), nerve damage and coring

Whitacre

1951
atraumatic pencil point
PDPH 3%, more convincing ‘dural click’
increased resistance, increased risk of accidental injection into epidural space

Sprott

1987
modified atraumatic pencil point
larger aperture = less resistance, more tapered tip = less trauma
aperture further from tip = higher risk of failure

Ballpen (Rusch)

stylet point needle
opening at the tip, does not need to be in as far as Whitacre or Sprott
still risk of injecting into epidural space

epidurals

Tuohy needle

8cm
16-18g
Lee markings start at 3cm

catheter

18 - 20g
915mm long
4-5cm should be in epidural space
3 lateral holes at the end

loss of resistance syringe

cryoprobe

energy required to overcome van der Waals forces between gas molecules comes from kinetic energy of rapidly expanding gas as it is expelled, causing a drop in temperature to -70 C
it is adiabatic as no heat is added or removed

similar mechanism when a bike tyre heats up on pumping and when cylinders get cold in use

Cleaning

Spaulding classification

Critical

Enter tissue

Require sterilisation

removal of all organisms and spores ‘GAGE’

2% glutaraldehyde
autoclave
gamma radiation
ethylene oxide

Semi-critical

Contact mucous membranes or damaged skin

Require high level disinfection

removal of all organisms except spores ‘CHAPG’

0.5 - 5% chlorhexidine
hydrogen peroxide
60% alcohol
pasteurisation
2% glutaraldehyde

Non-critical

Contact intact skin

Require cleaning

removal of foreign material ‘WUL’

washing
USS bath
low temp steam

—> decontamination = cleaning followed by disinfection or sterilisation