Cardiovascular
Monitoring and Support
Introduction
Arterial Access
CVP Measurement
PA Catheterisation
Cardiac Function
Cardiac Support for Drugs
Guide to Pressures
Introduction
Monitoring aims to avoid tissue hypoxia through rapid, accurate and
reproducable measurements.
- gets a total body view rather than specific viscera information
- note that the gut is prone to hypoxia and can drive the inflammatory
response
--> hence many ICU physicians try to deliver oxygen at greater than
normal rates.
- one approach is to treat plasma lactate and negative base excess to
achieve this.
- another is to treat certain viscera via tonomotry.
Indications
for invasive monitoring
- failure to restore homeostasis with simple techniques
- procedures that may profoundly change preload / afterload
- use of vasoactive drugs that influence preload, afterload or
myocardial function.
- low perfusion state or at risk of such.
What can be monitored?
Intra-arterial BP
- systolic, mean and diastolic.
CVP
- rough guide to systemic preload (provisos)
Pulmonary artery P
- systolic, mean and diastolic.
Pulmonary artery occlusion / wedge P
- indicates systemic preload
Cardiac output
- or 'index' corrects any variable for pt size.
Transducers
Mechanical signals from target are converted by an electrical signal
via a transducer
- this must be zeroed and calibrated
- minimise interference, eg kinking of catheters or blockage of vessels
by clot.
Safeguards
For any technique:
- know the practical anatomy soundly
- be competent
- explain it to the pt
- be aseptic
- know complications & contraindications
- benefit must outweight risk
- nurses must know how to manage lines
- everything should be carefully labelled
- attendents shd be familiar with monitors
- lines must be dressed aseptically and changed appropriately.
Arterial Access
See notes
CVP
Measurement
CVP?
CVP is the venous pressure entering the RA
- lying flat the best reference point is the mid-axillary line.
- next best is 2nd IC space at sternal edge (5cm above atrium)
--> always take readings with pt supine and from same point.
Measurement
Either with a liquid manometer with steril dextrose 5%
- cheap, effective & simple
- but slower response
- fluctuates with respirations to confirm its activity
Or an electronic transducer
- faster, can display the mean P
Indications
Fluid replacement when concern re over-transfusion
- or when conventional access is impossible
Measuring effect of vasoactive drugs
Aid RVF diagnosis
Remember:
- no indication of LV Function
- does not equal intravascular volume
Pitfalls
Inaccuracy
- failing to zero or calibrate
- placing it in the RV
- tricuspid incompitance, AV dissociation, nodal rhythms.
Variations
- in intravascular volume, sympatehtic tone, and CO
- eg during PPV
--> falsy high RV filling pressure given.
Complications
- damage to veins and adjacent structures
- vessel rupture / haemorrhage, haemothorax, tension pneumo (esp in PPV
pts), air embolism, extravascular placement, knotting, breakage,
neurapraxia, arterial puncture, tracheobronchial puncture, sepsis.
- ie be skilled and experienced.
--> before using it, check for easy aspiration of blood.
See notes on insertion
PA
Catheterisation
Indications
Pre-op in high risk surgical pts
Post op MI or cardiogenic shock
Vasoactive drug use to manipulate preload, afterload or O2 transport
Fluid management in multi-trauma, SIRS/sepsis / multi-organ failure
Diagnosis of ARDS
Via Swann Ganz or PA catheter
- multi-lumen, have an inflatable balloon just proximal to their tip.
- three lumen: i) to inflate balloon; ii) measure pressure at tip; iii)
measure pressure from SVC or right atrium.
Pressure can be transduced
- from central veins, RA, RV and pulmonary artery as the catheter
passes through all of these.
- as it is pushed through, it eventually is halted by the decreased
lumen of the PA branches
- ie becomes 'wedged'.
- pressure here reflected as the PCWP (pulm cap wedge P)
--> ie an index of LA Pressure.
--> reflects end-diastolic P, the true preload.
- (only if normal LV compliance mitral valve function)
Cardiac output calculation
- inject a known volume of cold saline at known temperature via a port
in the RA, filters out to wedge, where temp drop is proportional to CO.
- values are divided by body surface area (BSA) to get cardiac index to
elinate effect of body size.
Other variables
CVP, PAWP, CI, BSA, HR, MAP and bld sampling are done as above.
- so can be calculated defined variables for management of complicated
cases.
- eg systemic vascular resistance (SVR), PVR, SV, LV stroke-work index,
DO2 (O2 delivery) and VO2 (O2 uptake).
Complications
Dysrhythmia during insertion
Valcular damage or infection
Pulmonary emvolus, infarction of rupture of pulmonary artery
Knotting of catheter within the heart
Infection, haematoma, thrombosis.
Pitfalls
Correct placement (confirm byCXR, PAWP < mean PAP, wedged
PaO2>mixed veinous PaO2, should flush)
High intrathoracic P will falsely elevated PAWP.
- so will mitral regurge
Catheter can migrate
Do not leave the balloon
inflated after PAWP measurement.
Cardiac Function Measurement
Because PA catheters are invasive and risky, non-invasive methods are
used also.
TOE
Disposable probe shows waveform, used to calculate preload, SV,
afterload.
- however must be tubed to tolerate it.
PiCCO
(pulse contour cardiac output with indicator dilution)
- peripheral cannulae dilution info fed into a computer, wihch
calculates heart functions.
Cardio Support
for Drugs
Normally, CO determined by preload, afterload, HR, rhythm,
contractility, and O2 supply vs demand.
- pressure-volume loops show effects of altered heart function
If the CI remains low after correcting hypovolaemia, inotropic drugs
are used to increase contracility and O2 supply vs demand
- inotropes
- should reduce afterload and preload, decreasing wall tension,
promoting coronary flow, O2 delivery and reducing O2 consumption.
--> this ideal does not exist.
Adrenaline, noradrenaline and dobutamine are used
--> all upward left-shift the Starling curve.
Should be used only when full monitoring is available
--> and never if hypovolaemia present.
Are discussed elsewhere
Guide
to Pressures
BP
|
LV
filling P
|
Cardiac
Index
|
Condition
|
Therapy
|
<100
|
<10
|
<2.5
|
Hypovolaemia
|
Volume
|
<100
|
10-20
|
>2.5
|
Sepsis
|
Pressors
|
100-150
|
>20
|
>2.5
|
Pulm
congestion
|
GTN,
diuretic
|
<100
|
>20
|
<2.5
|
LV
failure
|
Vasodilators
|
<80
|
>20
|
<2.0
|
Cardio
shock
|
Inotropes,
vasodilators
|