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Veterinary Anesthesia & Analgesia Support Group |
| Practical Information for the Compassionate Veterinary Practitioner |
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| Blood Pressure Management Basics | ||
| Dr. Bob Stein | ||
1) RECOMMENDATIONS
a) General Approach
i) All anesthetized patients should be consistently monitored using indirect oscillometric, doppler, or direct blood pressure monitor (1) Our goal is to maintain systolic blood pressure (SAP) at or above 90 mm Hg and mean arterial pressure (MAP) above 70 mmHg (a) 80 mmHg is often considered the minimum acceptable SAP while 60 mmHg is often considered the minimum acceptable MAP (3) Diastolic blood pressure is the least accurate of the blood pressures measured by the indirect oscillometric method and usually ommitted from practical discussions regarding BP monitoring ii) Oscillometric Monitors (1) Are often 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) 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 IV fluid bag based Dobutamine CRI calculator 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 IV fluid bag based Dopamine CRI/MCI calculator click here (v) Discontinue dopamine if significant increase in heart rate or if any arrhythmias develop (5) Consider administering 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) (c) Cautionary note: (i) The author does not recommend using a colloid fluid bag beyond the day it was opened (6) For the toughest of the tough cases, 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) (i) Ketamine, lidocaine, and (dex)medetomidine may be added to the CRI unless there is a specific contraindication (ii) For cats, this protocol may be used to reduce the inhalant need but it is unlikely to be a successful strategy without additional anesthetic agents like ketamine, porpofol, etomidate, or alfaxalone (b) Fentanyl and midazolam CRI (i) Ketamine, lidocaine, and (dex)medetomidine may be added to the CRI unless there is a specific contraindication (ii) For cats, this protocol may be used to reduce the inhalant need but it is unlikely to be a successful strategy without additional anesthetic agents like ketamine, porpofol, etomidate, or alfaxalone (c) Propofol CRI/MCI infusions (i) Opioid/lidocaine/ketamine/midazolam/(dex)medetomidine may be added to the CRI unless there is a specific contraindication (d) Etomidate CRI/MCI infusions (i) Opioid/lidocaine/ketamine/midazolam/(dex)medetomidine may be added to the CRI unless there is a specific contraindication (e) Alafaxalone CRI/MCI infusions (i) Opioid/lidocaine/ketamine/midazolam/(dex)medetomidine may be added to the CRI unless there is a specific contraindication 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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