Body Fluid and Haemodynamics Flashcards
What are the methods of arterial blood pressure monitoring?
- Non-invasive - oscillometry method (automated), Korotkoff sound (manual)
- Invasive - intra-arterial line
What are the pros and cons of non-invasive blood pressure (NIBP) monitoring?
Pros
1. Closely approximates IABP during normotension
Cons
1. Lag time
2. Not reliable in severe hypotension or hypertensive crisis
3. Inaccurate in peripheral vasoconstriction (vasopressor use, cold, etc)
What is the principle of automated blood pressure machine?
Oscillometry method
Arterial pulses produce oscillations
Maximum oscillation amplitude occurs at MAP
Systolic and diastolic BP derived from rate of change of oscillation amplitude based on company algorithm
What are possible causes of errors in automated BP measurement?
- Inappropriate cuff size
- Motion artifact
- Arrhythmias
- Blood pressure at extremes (hypertensive or hypotensive crisis)
What are the indications of IABP?
- Haemodynamic instability
- Strict BP control
- Inability to obtain NIBP
How are pressure monitoring systems zeroed and leveled?
Zeroing transducer - referenced to atmospheric pressure
- Exposing transducer to atmospheric pressure by opening stopcock of transducer and pressing zero button on monitor
Leveling transducer - aligns plane of measurement with area of interest (heart) to account for hydrostatic pressure
- Leveled to midaxillary line, 4th ICS, or 5cm posterior to sternal notch -> approximates RA
What are the components of normal arterial waveform? (6)
Does the location of measurement changes end result?
Systolic events - LV ejection
A. Systolic upstroke - LV ejects blood into arterial system
B. Peak systolic pressure
C. Systolic decline
Diastolic event
D. Dicrotic notch (incisura) - AV closure, beginning of diastole
E. Diastolic run-off
F. End-diastolic pressure
Peripheral locations (radial) differs from central (aortic root)
- Higher systolic pressure
- Lower diastolic pressure
- Small reduction in MAP
- Delayed dicrotic notch
Aortic valve lesions on arterial waveform
- Aortic stenosis and aortic regurgitation
Aortic stenosis
- Delayed systolic upstroke
- No dicrotic notch
- Narrowed pulse pressure
Aortic regurgitation
- Low diastolic pressure
- Widened pulse pressure (diastolic runoff occurs back into LV)
- Bisiferens pulse - 2 systolic peaks
What are the indications for central venous catheter (CVC) placement?
- Infusion of concentrated vasoactive or vein irritating medication
- Total parenteral nutrition
- Monitor CVP
- Inadequate peripheral venous access
- Sitting craniotomy - aspiration of entrained air
What are the components of CVP waveform? (5)
What is volume responsiveness
Ability to augment SV (and CO) with IV fluid administration in end-organ malperfusion
- Closely related to the patient’s point on Frank-Starling curve
Volume responsiveness if SV increases 10-15%
Refer to FACET protocol
Principle of body fluid distribution
Total body water is 60% of body weight in males, 50% in female
40% of fluid is in intracellular space
(30% in females - larger subcutaneous tissue and smaller muscle mass)
20% in extracellular space
- 15% interstitial
- 5% plasma
TBW decreases with age
- Newborn: 75-80% water
How do you calculate maintenance fluid requirement?
- Holliday-Segar Formula (esp children)
100 mL/kg/day for first 10kg
50 mL/kg/day for next 10kg
20 mL/kg/day for subsequent kg
(first 20kg = 1500mL) - Estimation from daily losses
- Sensible losses + insensible losses about 2-2.5L/day - equivalent to 30-35 mL/kg in acute patients
- Physiologically
> Water: 1 mL/kg/hour
> Glucose 1-1.5 g/kg/day
> Potassium: 1 mmol/kg/day
What are sensible and insensible fluid losses?
A. Sensible losses (measurable)
- Faeces - 200mL
- Urine - based on urine output, typically 0.5-1mL/kg/hr (800-1500mL)
- Sweat - variable
B. Insensible losses (not measurable)
- Skin - 600mL
- Lungs - 200mL
Estimation of acute blood loss crystalloid replacement
3:1 rule
3mL crystalloid given for each 1mL blood loss
- Compensates for crystalloid lost into interstitial space
Composition of NS vs Hartman (RL)
- Composition
- Hartman solution is more physiologic for acute volume replacement
- Normal saline is not preferred as it can result in hyperchloraemic metabolic acidosis
