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1)
RECOMMENDATIONS
a)
General Approach
i)
All anesthetized patients should be consistently monitored using
indirect oscillometric or doppler blood pressure monitors
(1)
Main priority is to maintain systolic blood pressure (SAP) at or
above 90 mm Hg
(a)
80 mmHg is often discussed as a minimum SAP
(2)
Mean arterial pressure (MAP) should be maintain at or above 70 mm
Hg
(3)
Diastolic blood pressure is the least accurate of the blood pressures
measured by the indirect oscillometric method.
ii)
Oscillometric Monitors
(1)
Are less labor intensive than Doppler monitors but tend to be less
consistent in their ability to register blood pressures for smaller patients
(2)
Set to automatically cycle every 2 to 3 minutes
(a)
1 minute cycles tend to create an ischemic challenge to the
extremity
(3)
Cuff width should be 40% of limb circumference for dogs and cats
(a)
Excessively wide cuffs will lead to an under-estimation of blood
pressure
(b)
Excessively narrow cuffs will lead to an over-estimation of blood
pressure
(4)
Location of cuff is important
(a)
Most consistent cuff location for small patients is the mid-foreleg
(i)
Don’t hesitate to try all locations as needed
(b)
Good locations for larger animals include metacarpus, metatarsus,
and distal tibia just above tarsus
(c)
The tail base may be an adequate site for some patients including
cats
iii)
Doppler
(1)
More consistently effective when monitoring small patients
(2)
Measures systolic pressure only
(a)
In cats there is some evidence that you are measuring MAP rather
than SAP especially if cuff width is too large
(3)
Locations include ventral tail, caudal metacarpus, and caudal
metatarsal area
(4)
Hair is generally clipped at the probe site
(a)
The depression in the probe must be filled with aquasonic coupling
gel
(b)
Once you hear the swishing sound, tape the probe in place
(i)
Both excessive and inadequate pressure can create difficulties
measuring pressures
(5)
It is often possible to obtain readings by first wetting the site
with alcohol, then applying coupling gel to the site and the probe without
clipping any hair
(6)
The cuff is placed just proximal to the probe
(a)
Cuff width is as important with doppler BP measurement as with
oscillometric BP measurement
(i)
Cuff width should be 40% of limb circumference for dogs
(ii)
Cuff width should be 30% of limb circumference for cats
(iii)
Excessively wide cuffs will lead to an underestimation of blood
pressure
(iv)
Excessively narrow cuffs will lead to an overestimation of blood
pressure
b)
Pre-anesthetic Medications
i)
An opioid alone or with a benzodiazepine usually provides the best
maintenance of optimal blood pressures
ii)
Effective premeds, with an emphasis on opioid analgesics, are an
extremely important first step in handling a patient in a fashion that
helps best preserve tissue perfusion
c)
Induction
i)
Induction agents for maintenance of the most optimal blood
pressures
(1)
Etomidate
(2)
Hydromorphone or oxymorphone with diazepam (canines)
d)
Maintenance
i)
If blood pressures are too low:
(1)
Decrease inhalant anesthetic level if possible
(a)
If systolic pressures are at least 80 mm Hg, awaiting surgical
stimulation is a reasonable short term option
(b)
Consider an IV bolus of fentanyl 0.002 mg/kg (0.001 mg/lb) or
hydromorphone 0.10 mg/kg (0.05 mg/lb)
(c)
Consider an IV bolus of diazepam 0.2 mg/kg (0.1 mg/lb)
(2)
Increase fluid rate if possible
(a)
Increase from 10 ml/kg/hr to 20 ml/kg/hr (5 ml/lb/hr to 10 ml/lb/hr)
(i)
Consider a quick bolus of 10 ml/kg (5 ml/lb) over 5 minutes
(3)
Relocate monitor site (mainly pertains to oscillometric monitors)
(a)
Verify proper cuff selection
(4)
Hetastarch
(a)
Dogs
(i)
5 ml/kg (2.5 ml/lb) over 5 minutes
1.
Can be repeated with caution until SAP reaches 80 mmHg or a total
of 20 ml/kg/day (10 ml/lb/day) is reached
(b)
Cats
(i)
2 ml/kg (1 ml/lb) over 5 minutes
1.
Can be repeated with caution until SAP reaches 80 mmHg to a total
of 20 ml/kg/day (10 ml/lb/day)
(5)
Consider administering dobutamine or dopamine
(a)
Dobutamine
(i)
Dog – 0.001 to 0.010 mg/kg/min (0.0005 to 0.005 mg/lb/min)
(ii)
Cats - use low end of dog dose range
(iii)
Recipe for 0.002 mg/kg/min (0.001 mg/lb/min) dose
1.
4.8 ml @ 12.5 mg/ml = 60 mg
2.
Add to 250 ml 0.9% saline for 0.24 mg/ml
3.
Give 0.5 ml/kg/hour
a.
Requires infusion pump or syringe pump for accurate delivery
(iv)
For
Excel Dobutamine CRI spreadsheet click here
(v)
Discontinue dobutamine if significant increase in heart rate or if
any arrhythmias develop
(b)
Dopamine (available in multiple
strengths)
(i)
Dog – 0.002 to 0.010 mg/kg/min (0.001 to 0.005 mg/lb/min)
(ii)
Cats - use low end of dog dose range
(iii)
Recipe for 0.002 mg/kg/min (0.001 mg/lb/min) dose
1.
1.5 ml @ 40 mg/ml = 60 mg
2.
Add to 250 ml 0.9% saline for 0.24 mg/ml
3.
Give 0.5 ml/kg/hour
a.
Requires infusion pump or syringe pump for accurate delivery
(iv)
For
Excel Dopamine CRI spreadsheet click here
(v)
Discontinue dopamine if significant
increase in heart rate or if any arrhythmias develop
(7)
For dogs, consider switching from
isoflurane/sevoflurane to:
(a)
Hydromorphone or oxymorphone as a periodic bolus with periodic
boluses of diazepam (see Anesthetic Maintenance section for details on
Hydromorphone and Oxymorphone maintenance guidelines)
(b)
Fentanyl and midazolam CRI
(i)
Ketamine and lidocaine may be added to the CRI unless there is a
specific contraindication
(c)
For cats these protocols may be used
to reduce the inhalant need but it is unlikely to be a successful strategy
without additional anesthetic agents
e)
Support
i)
See above
2)
PRECAUTIONS
a)
Pre-anesthetic Medications
i)
Acepromazine can cause hypotension
(1)
This is a dose dependent effect
b)
Induction
i)
Administering propofol too rapidly can cause myocardial depression
and a transient decrease in blood pressure
c)
Maintenance
i)
Any inhalant agent is capable of causing significant hypotension at
surgical anesthetic levels
(1)
Switching inhalant agents may be beneficial
(2)
Switching to injectable agents may be beneficial
d)
Support
i)
As needed base upon above discussion
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