Deliberate Hypotension Flashcards
What are the 3 different BP goals used depending on the institution for deliberate hypotension? (systolic goal vs. MAP goal vs. % reduction from baseline)
- reduction of systolic BP to 80-90mmHg
- MAP 50-65mmHg
- 30% reduction of baseline MAP (this is what TC said was the best choice to go by)
5 main benefits of DH
- reduced blood loss
- facilitation of surgical dissection
- reduction of oozing beneath skin flaps
- prevention of aneurysmal rupture
- reduction in intravascular tension
What benefits occur bc of the reduced blood loss associated with DH
- conserve blood supply
- avoidance of transfusion reactions
- decreased transmission of blood-borne disease
What benefits related to the facilitation of surgical dissection are seen in DH
- idnetifies malignant vs. nonmalignant tissue and vital structures
- reduces the amount of cauterized tissue, debris, and wound infection
- reduction in operative time
What specific surgical specialty benefits from reducing oozing beneath skin flaps?
Better plastics outcome, improved wound healing
What are the 6 common indications for DH
- Neurosurgery
- Large ortho cases- total hip, spinal fusions, arthroplasty
- surgery on large tumors-pelvic
- Head or Neck, maxillo-facial, middle ear
- plastics
- patients in whom transfusion is undesirable
What has allowed for the decrease in contraindications for DH
Improved drugs and monitoring
Contraindications for DH
- Hypovolemia
- Severe anemia
- untreated hypertension
- realtive contraindications : H/O cerebrovascular disease, renal dysfunction, liver dysfunction, severe peripheral claudication, MI, or angina
Is DH safe in treated HTN patients?
Yes, treatment returns cerebral autoregulation toward normal
DH in untreated HTN is associated with increased risk of death
Arterial bleeds are related to what BP parameter?
reduced by?
abolished by?
MAP
reduced by decreased MAP and HR
Abolished by tourniquet
Capillary Bleedis dependent on?
reduced by?
- Dependent on local flow in the capillary bed
- reduced by decreased BP and local vasoconstriction
Venous bleed related to?
abolished by?
- related to venous return, venous tone, and dependent posture
- aboilshed by spinal or epidural and direct vasodilators
How can body positioning be used to achieve hypotension
- Operative site above the level of the heart
- For each 2.5cm of vertical height above the heart, the local arterial pressure is reduced by 2mmHg
How does PEEP contribute to hypotension
decreased venous return
How does PPV cause hypotension
decreased venous return and CO
What effect on BP does decreasing SV and HR have
decreased BP duh
What 2 mechanical methods can be used to decrease BP
- tourniquets
- local infiltration with epinephrine
What 2 things are crucial to monitor with the use of tourniquets
- Duration: 60min upper limb, 90min lower limb
- Pressure: 250mmHg in the arm, 300mmHg in leg
Pharmacologic methods to achieve DH (6)
- volatiles
- sympathetic ganglionic blockers
- Alpha-blockers
- Beta-blockers
- vasodilators
- spinal and epidural anesthesia
Isoflurane can be used for DH, but what response has the greatest effect on BP?
~plz reword, my brain is strugglin~
Vasodilation
Effects of using Iso for DH (6)
- minimal effect on myocardial contractility
- vasodilation effect easily adjusted
- great for a moderate reduction in BP
- less on an effect on ICP than halothane
- decreased CMRO2
- minimizes reflex vasoconstriction or tachycardia
Iso effect on CO?
Nitro effect on CO?
both maintain CO
Iso likelihood of causing tachycardia? Nipride?
Iso- rare
Nipride-frequent
Iso effect on pulmonary shunting? Nipride?
iso-unchanged
nipride- increases pulmonary shunting
iso effect on cerebral blood flow? nipride?
both maintain per that chart but also the vasodilator ppt says Nipride increases CBF sooooooooooooooooooooooooooooooooooooooooooooo cool
iso effect on CMRO2? nipride?
iso-decreases
nipride- unchanged
Iso’s effect on cerebrovascular CO2 reactivity? nipride?
iso- preserves
nipride- impairs
Monitoring of EEG and SSEP with iso? nipride?
iso- may not be possible
nipride- no interference
hepatic blood flow with iso? nipride?
both are maintained
prolonged recovery with iso? nipride?
iso: possible dependent on dose and duration
nipride: none
What is more precise, the use of Iso or nipride for DH?
Nipride is more precise
Is the onset time with iso or nipride faster? what is the negative to the fast onset?
Nipride has a quicker onset at the expense of possible overshoot
Which agent iso or nipride is associated with rebound hypertension
Nipride
What agent is associated with the risk of toxic metabolites iso or nipride? what is the metabolite?
Nipride- can rarely produce cyanide and thiocynate toxicity
How can Sevo be used with DH?
- minimize HR fluctuations that occur with the use of nitro, nicardipine, or alprostadil to achieve hypotension
- decreased sympathetic activity
Trimethaphan( Arfonad) response that makes it a possible DH medication?
Interruption of sympathetic outflow, vasodilation
-historical, not still used for DH today
benefit of pretreating with clonidine
reduces the required infusion of PGE 1 needed to maintain DH and reduces the blood loss by 45%
Alpha-adrenergic blockers used for DH (2)
- Phentolamine(Regitine)
- Droperidol
Alpha-adrenergic blockers effects (both a positive and a negative)
positive- vasodilation
negative- increased HR and myocardial oxygen demand due to beta stimulation (makes alpha-blockers not a good choice)
What is the big advantage with the use of beta-blockers for DH
decreased HR and CO
How are beta-blockers typically used for DH (with what other drugs?)
Used with vasodilators to abolish reflex tachycardia
T/F beta-blockers help prevent wide variations in BP
true
What are the downsides to the use of labetalol for DH
- not as potent
- masks the adrenergic response to acute blood loss
- long duration lasts in postop period
propranolol pretreatment has what positive effects?
reduced dose of SNP and the rebound HTN upon discontinuation
What beta blocker is associated with reducing plasma renin activity? what does that result in?
- Esmolol
- results in improved stability and greater reduction in CO
2 causes for caution with the use of sodium nitroprusside
- increased ICP
- cyanide toxicity
Is sodium nitroprusside good for short periods?
Yes
“dial-a-pressure”
Are there adverse effects on myocardial contractility with the use of nitroprusside?
No
What can you pretreat with to reduce the dose of SNP and avoid rebound HTN?
- propranolol
- captopril
- enalapril
Does nitro have a more or less dramatic decrease in BP compared to Nipride?
less dramatic decrease
Does nitro decrease systolic or diastolic more?
systolic
Compared to nipride, does nitro have better or worse coronary artery perfusion?
better coronary artery perfusion
Does nitro increase ICP?
Yes, but not as bad at SNP
benefits of 3inch transdermal NTG patch for DH
- moderate hypotension
- reduced blood loss by 50%
- reduced need for transfusion
Does spinal/epidural anesthesia have vasodilating effects on arterial, venous, or both?
both due to sympathectomy
What regional block is required to prevent tachycardia during DH
T1-T4
What plexus is blocked during lower abdominal and pelvic surgery
pelvic venous plexus
Can you use epi in your spinal/epidural if using it for DH?
No, if epi is added to the local it can counteract the hypotensive effect
Is it better to reduce Bp by decreasing SVR or CO? why?
decreasing SVR so blood flow to tissues is maintined
What are the principal hazards of DH
Ischemia of the brain and myocardium
What is the safest lower limit of BP during DH and why?
50-55mmHg in a normotensive patient bc that is the lowest pressure at which autoregulation of CBF is maintained
When MAP falls below___, CBF no longer responds to changes in PaCO2
50mmHg
During normotension, CBF changes linearly with PaCO2 when the PaCO2 is ___?
20-70mmHg
What should be avoided to maintain the balance of myocardial oxygen supply and demand?
- tachycardia
- myocardial depression
- coronary artery perfusion alteration
During DH why is there an increase in dead space ventilation and what happens to the PaCO2?
Decreased perfusion causes the increased dead space ventilation which results in increased PaCO2
Decreased PaO2 due to increased shunt seen with what drug and what type of lungs?
~halp idk how to word this info bc my lil brain does not understand
- Seen with nipride but not with iso
- Seen in normal lungs, but not with COPD
The effects of DH on PaCO2 and PaO2 make what necessary?
controlled ventilation and increased oxygenation
At what MAP does GFR begin to decrease
MAP< 75
When MAP drops below 75 and GFR decreases, are the metabolic needs of the kidneys still met? What symptom is seen?
Yes metabolic needs still met but oliguria occurs
Is a rapid recovery of UOP seen when DH is d/c?
rapid recovery only in normovolemic patients
T/F strict maintenance of UOP during DH is crucial
false, it is not neccessary
Renal function is better preserved with a combo of iso and __ than a higher concentration of iso alone
labatelol
How is liver perfusion affected during DH
- altered d/t limited autoregulation for the hepatic artery and no autoregulation for the portal venous circulation
- increased sympathetic outflow causes splanchnic vasoconstriction and decreased flow to the liver and intestine
decreased blood flow to the eyes during DH leads to what complications
- blurry vision
- blindness(rare)
What 3 interventions are used to help reduce likelihood of eye injury during DH
- careful positioning to avoid increased intraocular pressure (neutral position)
- maintain Hgb
- colloid instead of crystalloid to minimize edema
What should you look for on EKG that would indicate inadequate myocardial perfusion
ST depression and ectopic beats
What leads are the best to look at for signs of ischemia
Lead 2 and V5
How does DH effect temp
vasodilation causes rapid loss of body heat
Where should your transducer of your artline be leveled during DH
the level at internal carotid/circle of Willis to monitor CPP
(tragus of the ear)
Is ETCO2 accurate during DH, why or why not?
Not accurate d/t increased dead space, decreased CO, and no changes in body metabolism
a sudden decrease in ETCO2 during DH case could indicate what?
PE
In regards to ETCO2 and CBF, what should be avoided to prevent cerebral vasoconstriction and decrease CBF
hyperventilation
T/F there is an increase in mortality associated with DH compared to other anesthetics
false, no difference in mortality
complications seen with DH
- dizziness, prolonged awakening, cerebral artery thrombosis
- renal thrombosis
- anuria, oliguria
- postop bleeding
- inadequate or excessive hypotension
What type of DH is desired for plastic, maxilo-facial, and ENT cases
- slow onset
- sustained moderate hypotension with slow return to normal
When massive blood loss is anticipated what type/characteristics of DH are desired
moderate sustained hypotension with reduced HR
When clipping cerebral aneurysm what type/characteristics of DH are desired?
profound hypotension with short period of excessively small pressures
What drug should be avoided during DH
atropine
Is more or less sedation/analgesia required during DH
generous sedation or analgesia
PACU considerations following DH procedure
- raise HOB
- avoid CO2 retention
- avoid hypoxia
What position should be avoided unless arterial pressure is being measured at the level of the circle of willis
severe head up position
don’t know how to ask this but important fact:
Don’t reduce the systolic pressure during the case to less than the pre-op diastolic pressure
:)
SNP advantages
- potent
- reliable
- rapid onset and recovery
- CO well preserved
SNP disadvantages
- reflex tachycardia
- rebound HTN
- pulm shunting
- cyanide toxicity
Dexmedetomidine advantages
- dose dependent sedation and analgesia with associated hypotension
- decreases IV/inhalational anesthetic requirements
- smooth emergence
Dexmedetomidine disadvantages
- bradycardia
- heart block
Esmolol advantages
useful to control tachycardia
esmolol disadvantages
potential for significant cardiac depression
advantages of nitroglycerin for deliberate hypotension
- preserves myocardial blood flow
- reduces preload
- preserves tissue oxygenation
NTG disadvantages
increases ICP
highly variable dosage requirements
Nicardipine advantages for deliberate hypotension
preserves cerebral blood flow
Nicardipine disadvantages
trick- nothing according to that chart
Remi + propofol advantages
- reduces middle ear blood flow (remi)
- decreased PONV (propofol)
remi + propofol disadvantages
- no analgesic effect once remi infusion d/c
- postop secondary hyperalgesia
