CVS Support

Question 1

CVS complications on ICU

Answer 1

VTE (DVT and PE)

Question 2

VTE (venous thromboembolism)

Answer 2

this includes deep vein thrombosis (DVT) and a pulmonary embolism (PE)

assessment and prophylaxis

prevention:
LMWH (enoxaparin)
Intermitten pneumatic compression devices (flowtrons) which regularly inflate and squeeze the legs to promote blood flow

Question 3

what does cardiac function consist of?

Answer 3

Preload
Afterload
Contractility
Heart rate

Question 4

what is preload?

Answer 4

the amount that the heart muscle is stretched when filled with blood just before a contraction.

(the load or stretch in the ventricle pre contraction. It is related to the volume of blood in the ventricle at the end of diastole, just before the ventricle contracts)

Question 5

what is afterload?

Answer 5

Afterload is the resistance that the heart must overcome to eject blood from the left ventricle, through the aortic valve and into the aorta.

You can think of afterload as being the load or resistance after the aortic valve – how much resistance there is to pushing blood through the aortic valve. Common causes of raised afterload are hypertension and aortic stenosis

Question 6

what are:

• contractility
• HR
• SVR
• Stroke volume
• Cardiac output

Answer 6

Contractility refers to the strength of the heart muscle contraction.

Heart rate is the number of heartbeats per minute.

Systemic vascular resistance is the resistance in the systemic circulation that the heart must overcome to pump blood around the body.

Stroke volume is the volume of blood ejected during each beat.

Cardiac output is the volume of blood ejected by the heart per minute. The formula is:
Cardiac output = stroke volume x heart rate

Question 7

what is MAP (mean arterial pressure)

Answer 7

the average blood pressure throughout the entire cardiac cycle, including both systole and diastole. Mean arterial pressure is a product of cardiac output and systemic vascular resistance. Low arterial pressure may be the result of low cardiac output or low systemic vascular resistance.

(systole is only 1/3 of the cardiac cycle so MAP gets a more general overview as to how perfused the heart and organs are)

An adequate mean arterial pressure is essential for tissue perfusion throughout the body. Low mean arterial pressure results in tissue hypoperfusion, leading to hypoxia, anaerobic respiration, lactate production and damage to the tissue.

Question 8

basic non invasive monitoring of cardiac function in ICU

Answer 8

basic non-invasive monitoring:
Heart rate
Peripheral blood pressure
Pulse oximetry (oxygen saturations)
Continuous ECG monitoring

Question 9

intense monitoring of cardiac function on ICU

Answer 9

Invasive blood pressure monitoring via an arterial line (a special cannula inserted into an artery)

Arterial blood gas analysis taken from an arterial line

Central venous pressure via a central venous catheter in the vena cava/right atrium

Central venous oxygen saturation measured using blood samples from a central venous catheter

Pulmonary wedge pressure via a pulmonary artery catheter (indicates the left atrial pressure) (rarely done)

Pulmonary artery oxygen saturation via a pulmonary artery catheter (rarely done)

Echocardiogram (transoesophageal or transthoracic) (TOE)

*Pulse contour cardiac output (PiCCO) monitors cardiac output via a central venous catheter and thermodilution arterial line
Oesophageal Doppler monitor assesses the blood flow through the thoracic aorta to estimate stroke volume and cardiac output

Question 10

fluid status

Answer 10

optimising fluid status is an important part of maintaining cardiac function (consider this before starting on inotrope and vasopressor meds)

Question 11

CVP and preload

Answer 11

central venous pressure can be measured via a central venous catheter into the vena cava / right atrium. this is often used as an estimate measure of preload i.e it shows how much blood is avaialbleto fill the heart before a ventricular contraction.

If the central venous pressure is low, the heart has less blood filling the ventricles for each contraction.

giving extra IV fluids will help increase CVP and help the heart fill with blood in diastol so increasing preload and SV will increase cardiac output

Question 12

fluid overload

Answer 12

this can crease congestion in the circulation which can result in congestive heart failure, pulmonary oedema and increased mortality.

Question 13

what are ionotropes?

Answer 13

medications that alter the contractility of the heart.

positive inotropes: increase the contractility of the heart > increases CO and MAP. used in patients with a low cardiac output e.g. due to HF, recent MI or post heart surgery

most postiive ionotropes are catecholamines meaning they stimulate the sympathetic nervous system via alpha and beta adrenergic receptors

Question 14

positive inotropes

- catecholamine: MOA and examples

Answer 14

catecholamines: simulate the sympathetic nervous system via alpha and beta-adrenergic receptors

examples:
Adrenaline
Dobutamine
Isoprenaline
Noradrenaline (weak inotrope and mostly a vasopressor)
Dopamine (not an inotrope at lower infusion rates)

Question 15

other positive ionotropes

- MOA and examples

Answer 15

Milrinone is a positive inotrope that works as a phosphodiesterase-3 inhibitor.

Levosimendan is another positive inotrope that works by increasing the heart muscle’s sensitivity to calcium.

Question 16

how are positive ionotropes delivered?

Answer 16

through a central venous catheter. They are only used where patients can be closely monitored (e.g., ICU). Doses are titrated in response to changes in the patient’s clinical condition, mean arterial pressure, central venous pressure and cardiac output.

Question 17

negative ionotropes

Answer 17

reduces contractility of hte heart

i.e beta blockers, ca2+ channel blockers, flecanide

Question 18

vasopressors

Answer 18

medications which causes vasoconstriction (narrows blodo vessels) to increase SVR and consequently MAP (and tissue perfusion)

indications: i.e severe sepsis

Question 19

examples of common vasopressors

Answer 19

Noradrenaline (given as an infusion via a central line)
Vasopressin (given as an infusion via a central line)
Adrenaline (given as an infusion via a central line or as a bolus in an emergency)
Metaraminol (given as a bolus or an infusion)
Ephedrine (given as a bolus)
Phenylephrine (given as a bolus or an infusion)

vasopressin isantidiuretic hormone (ADH) which causes contraction of smooth muscle in the blood vessels and stimulates water reabsorption from the collecting ducts in the kidneys.

Question 20

antimuscarinic meds

Answer 20

used to treat bradycardia (i.e in operations) which works by blocking the acetylcholine receptor

i.e glycopyronium
atropine

Question 21

intra aortic balloon pump

Answer 21

this is a temporary measure used while the underlying condition is managed.

A catheter is inserted into the arterial system, usually via the femoral artery, up to the descending thoracic aorta. At the tip of the catheter is an inflatable balloon. The balloon is intermittently inflated and deflated by a special machine, synchronised to the heart contractions. Helium is used to inflate the balloon.

During diastole, when the heart is relaxing, the balloon is inflated. This pushes blood backwards into the coronary arteries, improving coronary perfusion.

During systole, when the heart is contracting, the balloon is deflated. Deflating the balloon creates a vacuum effect, as empty space is created that the balloon previously filled. This reduces the afterload and increases cardiac output. (less resistance = easier to contract?)

In summary, an intra-aortic balloon pump:

Increases coronary blood flow
Reduces afterload
Increases cardiac output