Cardiac output
HR X Stroke vol.
Stroke vol.
Compromise of preload, after load, and contractility of the heart
Preload
- Volume of blood within the left ventricle just before it contracts
- Major determinant = state of systemic venous constriction or dilation
Afterload
Resistance to left ventricle ejection of blood at the point of peak tension in the wall of the ventricle (aka resistance to blood flow from the left ventricle into the systemic arterial tree)
- affected by systemic vascular resistance
- dilated artery = decreases resistance = decrease after load
Elevated heart rate
Volume loss, pain, hypoxemia, hypocapnia, sepsis, or decreasing vascular resistance
- Diseases: hyperthyroidism, pheochromocytomas, heart conditions
- causes insufficient ventricular filling time
- 2x the normal rate is worrying
Decrease heart rate
- CO and BP will fall
- half of normal is concerning
- Causes: high vagal (10th nerve in the medulla oblongata) tone, atrioventricular conduction disturbances, hyperkalemia, severe hypothermia, drugs, organophosphate or carbamate (pesticides/insecticides) toxicity, increased intracranial pressure
Pulse elevation - femoral artery
- highest arterial pressures in the body
- last location for a pulse to fade as BP drops
- can be felt even at 40mmHg
Pulse elevation - dorsal pedal pulse
- more difficult to palpate
* MAP of 60-70mmHg
Pulse wave
Difference between the systolic pressure and diastolic pressure
Weak thready pulse
- due to poor cardiac output
- caused by: hypovolemia, poor contractility, tachycardia, poor ventricular diastolic performance, arrhythmia, or aortic stenosis
Pulse deficit
- heartbeat with no associated pulse
* no. 1 cause: premature arrhythmias
Arterial blood pressure
- evaluates pressure of blood flow within an artery
* product of cardiac output, vascular capacity and blood volume
How does the body temporarily maintain blood pressures in the face of blood loss and decreasing flow?
- Via the adrenomedullary and neurohormonal stress reactions
- catecholamines and renin-angiotensin system
- Arterial pressures wont drop till these compensatory reactions are exhausted
Oscillometric method
- cuff size is important
- some pressure applied by cuff is lost to tissue compression
- narrow cuffs more severely affected than wider cuffs
- optimum cuff size 40-60% of limb circumference
- need to encircle at least 60% of the limb
- hindleg: dorsal pedal artery or cranial tibial artery
- take 5 readings and discard the highest and lowest
- cold patients: poor circulation to their extremities = poor readings
Doppler (ultrasonic) method
- shave for good skin contact
- best superficial artery sites: just above palmar metacarpal or plantar metatarsal or ventral coccygeal artery
- cuff should be inflated to at least 30mmHg above the last audible sound using sphygmomanometer
- first sound = systolic pressure
- at the point where the short pulsation sound change to a more continuous “swishing” sound = diastolic pressure
Direct monitoring
- dorsal metatarsal artery
- ventral coccygeal artery
- palmar metacarpal artery
Normal values
systolic 100-160mmHg
Diastolic 60-110mmHg
Mean Arterial 80-120mmHg
Pulse pressure 40-80mmHg
Hypotension causes
Hypovolemia, poor CO, or systemic vasodilation
- Hypovolemia
- extracellular fluid deficits
- vascular vol. deficits
- Poor CO
- myocardial failure
- valvular disease
- pericardial tamponade
- severe bradycardia or tachycardia or arrhythmia
- Peripheral vasodilation
- sepsis, anaphylaxis, vasodilator year drugs
Hypertension can cause what
Retinal detachment
Hemorrhage
Increased intracranial pressure
Excessive after load
MAP calculation
*Diastole is twice as much as systole
MAP= ((2xdiastole) + systolic ) / 3
Or
MAP = diastolic + (systolic - diastolic) NOT THE SAME!!!
CVP
- 0-5cm water or 0-3mmHg
- Affected by intravascular vol., venous tone, and compliance, intrathoracic pressure and cardiac function
- Trends rather than numbers
Primary indication for CVP monitoring
*Assessing fluid therapy (renal, pulmonary dz, cardiac dz, septic shock)
Colloid oncotic pressure (COP)
- Measurement of holding power of fluids within the vascular fluid compartment
- Affected by conditions:
- hypoproteinemia
- conditions that increase capillary permeability
- Decrease in COP:
- results in 3rd spacing of fluids
- Values below 3.5g/dl = need to start colloids
- colloids will affect refractometer readings
Normal COP
18-25mmHg
