Exam 3 - Ultrafiltration & Endocrine Response To CPB Flashcards
How does volume overload lead to mortality
Overload -> increase pre/afterload -> increase LV hypertrophy -> increase CHF -> Mortality
Ultrafiltration
- hemoconcentration (increase [RBC])
- removes water and low weight solutes
- uses transmembrane CONVECTION pressure gradient across membrane
- high to low pressure (positive pressure side to negative pressure side)
Advantages of hemoconcentration
- Increase [protein] and [RBC]
- Remove inflammatory mediators
- Decrease lung water
- Improve operative homeostasis
- Reduced postop vent support
Hemoconcentrator design
- hollow fiber
- blood on inside
- Dialysate on outside
- can be used with or without vacuum
- blood side generates pressure that pushes body water out
Hollow fiber bundle diameter
180-200 um
Microporous membrane thickness
5-10 um
Convection
- fluid flow through membrane driven by pressure gradient
Diffusion
- movement across membrane due to differences in solute concentration on each side (concentration gradient)
- Blood side has high [solute]
- Ultrafiltration uses both diffusion AND convection
Overall change in [solute] using ultrafiltration
- There is none
- removes water and diffusable solutes in equal concentrations
- BUT protein / cells / protein bound solutes not removed
- so concentration of blood side goes up
Principles of ultrafiltration
- need blood flow and pressure gradient
- sieving coefficient (pore size vs weight of solute)
- rate of filtration based on flow rate and transmembrane pressure
Transmembrane pressure (TMP)
- gradient between blood and ultrafiltrate compartment
- TMP should not exceed 500-600 mmHg
Ultrafiltration coefficient
- Kuf
- how efficient filtration is
- typical rates 2-50 ml/hr/mmHg
- increase blood flow / TMP = increase removal
- decrease Hct / plasma protein = increase removal
Sieving coefficient
- [ultrafiltrate solute] to [blood solute]
- 0 to 1.0
- 1 = solute will pass
- 0 = solute will not pass
- ease at which given solute will travel across filter membrane
CUF
- Conventional Ultrafiltration
- basic type normally used using pressure gradient
- will increase Hct
- level in reservoir will drop
Z-BUF
- Zero balanced ultrafiltration
- Equal input and output
- replaces ultrafiltrate volume with electrolyte solution
- can use normosol, plasma-lite, LR, etc
- used to reduce cytokines / compliment levels (reduce inflammatory response)
- used during re-warming (peak of inflammatory response)
- treats hyperkalemia
- need to add bicarb
MUF
- Modified ultrafiltration
- used following termination of CPB
- volume from circuit back to patient
- mainly used on pediatrics
- brings down CVP
Where can ultrafiltration filters go in circuit?
- O2 recirculation line
- Cardioplegia circuit
Post-CPB pump blood
- residual blood is hemoconcentrated
- reduce need for bank blood transfusion
Parameters to think of w/ ultrafiltration
- Flow
- Pressure
- Volume
- may need to increase flow to keep pressure up since filter is another shunt
- can add vacuum to [hemo] to increase removal rate
Things to be wary of w/ [hemo]
- volume level
- pink effluent means too high TMP (hemolysis)
- vacuum increase removal but also hemolysis
- [Hemo] is a shunt and must be off if pump is off
Dialysis
- mainly uses diffusion but also convection
- runs countercurrent
- concentration gradient made by using dialysate solution
Dialysate solution
- contains chemicals in [ ] ‘s similar to blood
- flows countercurrent
- substances that need to stay in blood are in same [ ] as blood in dialysate solution
Purpose of dialysis
- treat renal failure
- remove waste products from blood
- return blood chemistry values back to normal
ARF
- acute renal failure
- kidney may recover
- CPB is cause of injury
- can be put on dialysis to recover
CKD
- chronic kidney disease
- long/slow process where kidneys lose function
ESRD
- end stage renal disease
- kidneys shut down permanently
- permanent dialysis
Renal failure
- decrease in GFR (how well kidneys are filtering)
- elevated BUN and Creatinine levels
- GFR goes down with age
Dialysis access
- AV fistula (connection of artery to vein)
- made by vascular surgeon
- used to remove and return blood during dialysis
- safer for patient
Heart and lungs on CPB
- not perfused
- not able to secrete hormones
- not part of normal drug metabolism
Exposure to circuit on CPB
- trauma to cellular components
- removal of plasma proteins
- stimulation of immune response
Hemodilution and CPB
- altered [ ] of electrolytes, hormones, serum proteins
Hypothermia and CPB
- decreased rate of all reactions
- disruption of hormonal responses
Non-pulsatile flow and CPB
- may change flow distribution to organs
- may change flow distribution within organs
CPB and stress hormones
- stimulate release
- cortisol
- increased levels of hormones post CPB
Vasopressin
- ADH
- Hold onto water volume
- Very potent
- If high [ ]:
- increase PVR
- increase renal vascular resistance (less filtration / renal volume)
- decrease coronary blood flow
- decrease contractility
- stimulate releases of von Willebrand factor (clotting)
What stimulates ADH release
- increased plasma osmolarity
- decrease in blood volume / pressure (CPB)
- hypoglycemia
- stress / pain
- angiotensin
- anesthesia / surgery
- ACE inhibitors
- SIADH = syndrome of inappropriate ADH release
ADH and CPB
- Greatly increases release
- persists hours post-op
- caused by:
- drop in blood volume on initiation
- drop in LA pressure (vent)
- hypotension
Prevention of ADH on CPB
- pulsatile flow (not really)
- anesthesia w/ synthetic opioids (not completely)
- regional anesthesia (only on non-cardiac)
- THESE all decrease ADH but doesn’t stop completely on CPB
Catecholamines
- Epi (x10 on CPB) - peak at target temp
- NE (x4 on CPB) - peak at clamp removal / rewarm
- increase on CPB
- from adrenal medulla
- from sympathetic / central nerve terminal (NE only)
- potent vasoconstrictor
Prevention of Epi and NE on CPB
- “just enough” anesthesia (deeper is better)
- proposal infusion
- opioid plus epidural versus opioid alone
- anesthesia plays big role in prevention of catecholamines
- magnitude of increase can be dropped but not eliminated
Adrenal cortical hormones
- Cortisol
- stress hormone
- corticosteroid
- increases blood sugar
- Adrenocorticotropic hormone
- corticotropic
- increases cortisol release
- Both increased during CPB
Prevention of adrenal cortical hormones on CPB
- deeper levels of anesthesia
- add epidural
- not clear if increased levels good or bad
Glucose and CPB
- regulated by insulin / glucagon
- [ ] altered w/ CPB
- increase at initiation (hyperglycemia)
- insulin levels drop (hypoinsulinemia)
- insulin resistance (bad in DMII)
- PRBC add a ton of glucose (400-700 g/dL)
Atrial Natriuretic factor (ANF)
- Reduces blood volume
- release triggered by atrial distention (should be none)
- cause:
- increase GFR
- inhibits renin
- reduce atrial BP
- inhibits aldosterone
ANF and CPB
- [ ] reduced during … no volume in heart
- [ ] rise during rewarm and post-op… heart fills
- normal values lost during bypass and early post-op
Renin-angiotensin-aldosterone
- regulates BP / volume
- Kidneys release renin when:
- drop in Na
- drop volume
- low renal flow
- Sympathetic release during pain / stress / emotion
Renin-Angiotensin-Aldosterone pathway
- Renin converts angiotensinogen to angiotensin I (in blood)
- ACE converts angiotensin I to angiotensin II (in lungs)
Angiotensin II
- increase BP
- vasoconstrictor
- increase release of aldosterone
Aldosterone
- increase absorption of H2O / Na
- increases BP
- CPB increases hypertension which increases all these levels
Eicosanoids
- prostaglandin-thromboxane
- metabolized by lungs
Prostaglandin H2
- produces PGEs (vasodilator)
- produces TXA2 (vasoconstrictor)
Prostaglandin and Thromboxane and CPB
- levels increase during and drop shortly after
- no consistent effect found
Histamine
- inflammatory response
- vasodilator
- triggered by:
- opioids
- muscle relaxers
- antibiotics
- heparin
- protamine
- increased during CPB
Calcium
- maintained by bones/kidney
Ca and CPB
- changes caused by:
- blood products (deplete Ca)
- prime (few contain Ca)
- albumin (drops ionized Ca)
- Give extra Ca when:
- termination
- ionized Ca reduced
- need to increase contractility and BP
- NOT too much… stone heart
Mg
- need to actually administer Mg to increase levels
- needed as factor for enzymes and membrane stability
- Albumin binds Mg and drops levels
- hemodilution drops levels
- takes a while to come back up (no native hormone)
- Supplemental Mg is GOOD…suppresses arrhythmias
K
- changes caused by:
- cardioplegia
- anesthesia
- prime
- renal function
- pH
- hypothermia (drop when cool…up when warm)
- hyperkalemia not uncommon
- albumin may help reduce decrease in [ ]
- Normal is 3.5-5…..shoot for 4.5