ICM - CO monitoring Flashcards
What forms of cardiac output monitoring are there?
Invasive and non-invasive.Non-invasive:- Fluid challenge and response in SVV (LiDCO rapide)- TTEInvasive:- Pulse contour wave analysis i) LiDCo - requires arterial line ii) PiCCO - requires special arterial line- TOE- Pulmonary artery catheter- Oesophageal doppler
What are the principles of pulse contour wave analysis?
The arterial waveform in combination with the dilution of the injectate can be used to interpret cardiac function.The stroke volume is proportional to the area under the curve up to the dichrotic notch.Measured values include:- Heart rate- blood pressure- MAPCalculated information include:- stroke volume- cardiac outputDerived information includes:- SVRI- cardiac index- oxygen delivery index
What is stroke volume and what is stroke volume variability and how can its interpretation guide patient care?
Stroke volume is the volume of blood ejected from the left ventricle during systole (EDV - ESV).SVV is the variability in stroke volume during the ventilatory cycle.Normal SVV is 5-10%If elevated trial response to fluid bolus until SVV in normal range.
What is Fick’s principle with respect to cardiac output?
The amount of oxygen taken up by the tissues is dependent upon the delivery (CO) and the concentration difference (the arterial-venous gradient)Therefore VO2 = (CO x Ca) - (CO x Cv).Ca is arterial line O2Cv is pulmonary catheter O2VO2 is the difference between inspired and expired oxygen concentrations.This can be rearranged to get CO= VO2 / (Ca - Cv)
Describe the features of a Swan-Ganz/pulmonary artery catheter?
8Fr catheter usually 110cm longWorking distally to proximally:1. Distal lumen used to measure PCWP and mixed venous sampling2. Balloon for inflation when floating the catheter (1.5ml air).3. Thermistor4. Heating coil5. Proximal lumen for measuring CVP and for cold injectate for thermodilution.
What information can we obtain from using pulmonary artery catheters?
- Measured variables- CVP- right atrial pressure- right ventricular pressure- pulmonary artery pressure- PCWP- SvO2- core temperature2. Derived variables- Cardiac output- Stroke volume- Stroke volume index- systemic vascular resistance- systemic vascular resistance index- pulmonary vascular resistance- pulmonary vascular resistance index
What are the complications of pulmonary artery catheters?
- Complications from central access- introducing infection- arterial puncture/damage- pneumothorax- venous thrombosis formation2. Complications from floating the catheter- arrhythmias- valvular trauma- misplacement- knotting of catheter3. Complications from the PAC being insitu- pulmonary artery rupture- PE- pulmonary infarctionPAC-man trial 2005 showed 10% complication rate and no benefit in outcomes.
Describe how oesophageal doppler works?
A probe is inserted into the oesophagus with a doppler probe pointing to the descending thoracic aorta at about 35-40cm.The doppler probe produces a doppler trace by tracking red cell movement to produce a velocity-time trace giving:- peak velocity- mean acceleration- stroke distance (AUC)From these derived values can be obtained:- stroke volume (by multiplying stroke distance by cross sectional area)- flow time corrected (by knowing the velocity and distance)
Describe the important features of a central venous pressure trace.
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a = highest peak, resulting from atrial contraction at end-diastole.c = close of the tricuspid valvex = atrial relaxationv = v(f)illing of the atriay = opening of tricuspid valve
Describe the important features of a central venous pressure trace.
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How does the cardiac bypass machine work?
The machine involves drawing blood from a cannula in the right atrium (or other variations of the right sided circulation), and returning blood to a cannula in the ascending aorta.
Between this time, the blood has CO2 removed and O2 added, to replicate the lungs’ function, and is returned at an appropriate flow and pressure, to replicate the heart’s function.
The circuit contains of an accessory limb -> venous reservoir ->systemic pump -> heat exchanger -> gas exchanger
One of the primary functions of CPB is to take over the main function of the lungs; gas exchange.
This involves oxygenation of the blood, and removal of CO2.
The majority of modern CPB machines achieve this through membrane oxygenators.
What is cardioplegia?
Cardioplegia refers to the paralysis of the heart muscle through the administration of ‘toxic’ solution.
Is is the main form of myocardial protection used in cardiac surgery.
In cardiac surgery, blood flow to the myocardium often has to be interrupted.
If the myocardium continued its usual, very high, metabolic activity, then it would very quickly become substrate deplete and start to die.
The cardioplegia solution typically involves a high concentration of potassium chloride, usually in 20 mmol/L concentration.
This causes a reduction in the resting membrane potential of the myocardium and loss of excitability.
It is usually administered intermittently every 15-30 minutes in order to maintain cardioplegia whilst also allowing good operating conditions.
What are some of the complications of CPB?
HAEMATOLOGICAL
activation of coagulation, complement, kallikrein system
-> fibrinolysis, decreased platelet function
-> bleeding
-> transfusion risks
platelet aggregation and thrombocytopaenia
coagulopathy due to dilution, hypothermia, acidosis, drugs and platelet dysfunction)
anaemia (blood loss from circuit, hemolysis)
systemic heparinisation and exposure to protamine
CENTRAL NERVOUS SYSTEM
emboli (gas, debris, calcium)
poor cerebral perfusion
-> ischaemia, CVA (watershed or focal), seizures, spine ischemia, long-term cognitive impairment (1-5%)
phrenic nerve palsy
RENAL
AKI -> oliguria, elevated creatinine
renin-angiotensin-aldosterone activation and vasopressin release -> oliguria
post-bypass diuresis (also hypothermia)
HYPOTHERMIA
myocardial depression
arrhythmias
diuresis
altered pharmacokinetics
CARDIOVASCULAR
SIRS response involving activation of neutrophils, complement, kallikrein system and release of TNF -> vasodilation, hypotension and tachycardia
RV dysfunction due to protamine induced pulmonary hypertension
myocardial stunning
myocardial ischemia due to graft failure, air embolus, non-pulsatile flow or hypotension
injury or dissection of vessels from cannulation (aorta, femoral)
leukocyte release -> capillary leakage
systemic microemboli -> can affect any organ (ischemia, MODS)
RESPIRATORY
ALI/ ARDS secondary to SIRS, neutrophil activation and decreased surfactant
left lower lobe collapse due to failed lung re-expansion and/or phrenic nerve palsy
increased PVR due to protamine
neutrophil activation -> pulmonary dysfunction
GASTROINTESTINAL
ischemic gut, acalculous cholecystitis, hepatitis, or pancreatitis
METABOLIC
hypothermia and glucagon release -> unsulin resistance and hyperglycaemia
electrolyte disturbance
IMMUNE
allergy (e.g. to protamine)
SIRS response due to exposure to bypass circuit leading activation of WBCs, complement, the clotting cascade, cytokines and cell adhesion molecules
