Veterinary Recommendations for Anesthesia and Analgesia

This Guidance Document is to establish recommendations for anesthesia and analgesia for use in research animals.

 

PRINCIPLES OF ANESTHESIA AND ANALGESIA

1. The proper anesthetic and analgesic agents must be used in order to eliminate or reduce the potential for pain and distress during the peri-operative period.

2. Withholding anesthesia or analgesia must be justified and approved in the IACUC protocol.

3. A multimodal approach to analgesia should be employed to offer the best broad-spectrum pain control possible. This includes the use of different categories of analgesics in combination to address different sources of pain perception/stimulation.

For example, a surgical procedure may use a local anesthetic block of lidocaine and bupivacaine at the incision site, and systemic administration of an NSAID for inflammatory pain and an opioid.

4. According to the 8th edition of the Guide for the Care and Use of Laboratory Animals (NRC), "Guidelines for the selection and proper use of analgesic and anesthetic drugs should be developed and periodically reviewed and updated as standards and techniques are refined."

 

ANESTHESICS

1. Inhalant Anesthetics

a. The inhalant anesthetics include gases such as isoflurane and sevoflurane. These anesthetics require an anesthetic machine set-up. In addition, use of a scavenger system is required to prevent personnel exposure to the waste anesthetics. For short procedures it may be possible to administer inhalant anesthesia via a drop jar. For this procedure a cotton ball or gauze soaked with the anesthetic is placed in a jar with the animal. This procedure must be performed under a fume hood, the animal CANNOT contact anesthetic, and can only be done for minor quick procedures. Animals will recover quickly after removal from jar.

b. Advantages: safe and reliable, predictable and rapid control of anesthetic depth, not controlled substances

c. Disadvantages: induction must be closely monitored, personal training, special equipment required, potential risk to staff (if not appropriately scavenged)

2. Injectable anesthetics

a. Injectable general anesthetics include ketamine/xylazine and pentobarbital. Most of the commonly used agents are administered via intraperitoneal (IP) injection (figure 4).

b. Local anesthetics are often delivered subcutaneously along the incision site. They could also be used in nerve blocks or epidural administration. Local anesthetics are not adequate as the only analgesic for any surgical procedure unless scientifically justified in the protocol.

c. Advantages: They can be used without expensive supporting equipment such as the anesthesia machines required with the use of inhalants, they are easily transported, and are relatively inexpensive.

d. Disadvantages: Prolonged recovery times. The animal will have to metabolize the drug in order to completely recover from anesthesia. In addition, once the agent is injected, the anesthetic depth cannot be adjusted throughout the procedure except to achieve a deeper anesthetic plane by giving additional drug if the animal demonstrates signs of arousal. Animals which are sick or compromised may have a difficult time with these anesthetics due to changes in their ability to metabolize the drugs. Also, many of the commonly used injectable anesthetics are controlled substances which will require the laboratory comply with all rules regarding controlled substances and obtain a DEA license.

3. Monitoring Anesthetic Depth

Anesthetic depth should be gauged prior to conducting any surgical manipulation and throughout the surgical procedure. Loss of reflexes (e.g., pedal, corneal, palpebral) can be used to assess appropriate anesthetic plane. There should not response to toe pinch. Signs of Inadequate anesthetic depth include purposeful movement, reflexes present, response to painful stimulus, or twitching whiskers. Equipment (e.g. pulse oximeter) may also be used to monitor depth of anesthesia. Changes in heart rate, respiratory rate, or blood pressure may indicate whether an animal is at too light or too deep of an anesthetic plane. Depth of anesthesia should be assessed every 10-15 minutes during surgery.

 

ANALGESIA

1. Pain assessment and Analgesia

Assessing pain is difficult in animals. Some animals are species of prey and are adapted to hide signs of pain and distress. Clinical signs associated with pain are species specific, but some common signs of all species include changes in appearance such as hunched, scruffy, porphyrin staining (rats/mice), or changes in activity, including less active or inactive, hyperactive or pacing, abnormal postures such as back arching, belly pressing, wound guarding, or writhing. Also, decreased appetite, isolation from cage mates, exaggerated or decreased response to handling, vocalization can be used to gauge pain and distress. Recently, there has been some focus on assessing rodent facial expression or grimace scale in order to assess pain (Figure 1). It is important to pay close attention to the animal's appearance and behavior post-surgery in order to observe subtle changes that may indicate the need for additional pain management.

Analgesia should be administered to ALL post-surgical animals unless otherwise justified in the protocol. If there is concern regarding an animal's clinical condition post-surgery and additional analgesia is necessary, contact DLAR veterinary staff for further guidance on treating the animal.

Whenever possible multimodal analgesia is recommended. This involves providing a more 'balanced analgesia' through multiple methods or modalities. Local anesthetics at the incision site are often used in conjunction with a stronger opioid or NSAID analgesic.

 

RECOMMENDATIONS BY PROCEDURE

See specific doses, routes, and frequencies in the formularies below.

1. Rodent laparotomy (example major surgery)

Anesthesia induction via isoflurane in an induction chamber at 3-5% followed by isoflurane via facemask at 2-4%. Buprenorphine or other moderate to strong analgesic is given immediately after induction prior to patient prep to allow adequate time to reach therapeutic levels. Subsequently, moderate to strong analgesia is administered at appropriate intervals for 48 hours minimum post-operatively. Rodents are monitored closely thereafter to evaluate for signs of pain, and additional analgesia is given until evidence of pain is no longer present.

2. Rodent subcutaneous implant or vascular catheter placement (example minor surgergy)

Anesthesia induction via ketamine-xylazine. Carprofen is given immediately after induction prior to patient prep to allow adequate time to reach therapeutic levels. Carprofen is given as directed for 24 hours minimum post-operatively. Rodents are monitored closely thereafter to evaluate for signs of pain, and additional analgesia is given until evidence of pain is no longer present.

3. Swine laparotomy

Anesthesia induction via ketamine-acepromazine. Pre-emptive analgesia is given immediately after induction prior to patient prep to allow adequate time to reach therapeutic levels; buprenorphine (for moderate pain; time to effect - 30 minutes IV & 60 minutes IM) and NSAID (time to effect - 60 minutes IV or IM). Following endotracheal intubation, anesthesia is maintained with isoflurane. Local anesthetics, lidocaine and bupivacaine, are given SC at the location of planned incision. Post-operative analgesia, buprenorphine and NSAID, is given at appropriate intervals for at least 48 hours postoperatively. Swine are monitored closely postoperatively to evaluate for signs of pain, and additional analgesia is given until evidence of pain is no longer present.

4. Dog thoracotomy

Anesthesia induction via ketamine-diazepam. Pre-emptive analgesia is given immediately after induction prior to patient prep to allow adequate time to reach therapeutic levels; buprenorphine (for severe pain; time to effect - 30 minutes IV & 60 minutes IM) and NSAID (time to effect - 60 minutes IV or IM). A fentanyl transdermal patch is secured on skin (time to effect - 12-24 hours). Following endotracheal intubation, anesthesia is maintained with isoflurane. Local anesthetics, lidocaine and bupivacaine, are given SC at the location of planned incision. Once skin incision is made, an intercostal nerve block is performed. Post-operative analgesia is given at appropriate intervals for at least 72 hours postoperatively, buprenorphine for 12-24 hours until fentanyl takes effect, fentanyl transdermal patch in place for 72 hours, and NSAID for 3-5 days. Dogs are monitored closely postoperatively to evaluate for signs of pain, and additional analgesia is given until evidence of pain is no longer present.

 

Neonatal Rodents (mice and rats)

Neonatal rodents must have adequate anesthesia and analgesia when undergoing surgical procedures. It is important to balance safety with effectiveness when using anesthetics in neonatal animals. Neonates have an immature hepatic/renal system which can lead to prolonged anesthesia and a narrow margin of safety when using injectable medications. Inhalant anesthetics (isoflurane/sevoflurane) or hypothermia (<7 days of age) are the recommended methods of anesthesia in neonatal rodents. Opioid analgesics have been used successfully in neonatal rodents. However, these drugs should be administered at the lower end of the published dose range to avoid complications.

Hypothermia Anesthesia
Age Altheicial rodents up to 7 days old
Induction 2-4 minutes. Protect pup by placing into finger of a glove or paper lined test tube. This will avoid skin damage caused by direct contact with ice/cold water. Immerse pup in ice water or place on crushed ice (2-3˚C or 35-37˚F). Observe pups closely during induction.
Maintenance Up to 15 minutes anesthesia. Remove pups from ice bath when adequate anesthesia is achieved (immobile/lethargic). The pup can be maintained by placing on an ice pack covered with latex/paper towel.
Recovery Up to 1 hour. Avoid rapid warming during the recovery period. Recommend re-warming using an incubator set at 90-95˚F (32-25˚C) or in a paper-lined cage set over a circulating warm water blanket. Electric heating blankets and heat lamps are not recommended.
Additiona Considerations Fiber optic lighting should be used during surgical procedure to help maintain hypothermia (incandescent lamps can warm surgical field). Steps should be taken to avoid rejection by dam post-surgery. Recommend: remove blood/disinfectants from pup after surgery (wipe with wet gauze and dry), make sure neonate is completely recovered (warm, pink, breathing, moving), place neonates in bedding/nesting material from home cage to obtain appropriate scent, and return neonates as a group to home cage.

 

FORMULARY FOR MOST COMMONLY USED SPECIES AND DRUGS

Mouse and Rat Formulary

Analgesics Dose (mg/kg) Route Freq Comments
  Mouse Rat      

Acetaminophen

Oral dose

Water bottle

 

 

1-2 mg/ml drinking water

100-300

 

6 mg/ml drinking water

PO

 

 

PO

q4h

Not adequate as a sole analgesic except for very minor pain. May be combined with another class of analgesic for post-op pain.

 

Change water every other day. Water must be placed on cage 48 hours prior to painful procedure in order for rats to acclimate.

Recommended:

Buprenorphine

0.05 - 0.1 0.01 - 0.05 SC q12h Excellent for moderate to severe pain.
Carprofen 5 5 SC q24h

Good for mild to moderate pain.

Meloxicam 1 - 5 1 - 2 PO, SC q24h  
Tramadol 20 - 40 5 - 20 IP   For chronic or severe pain. Literature does not define recommended dosing interval in rodents. In other species administered up to TID. Start at BID dosing.
Anesthetics Dose (mg/kg) Route Duration Comments
  Mouse Rat      
Recommended: Isoflurane 2 - 5 % 2 - 5 % Inhalation   Gold standard anesthetic. Must have appropriate equipment to use safely (precision vaporizer and scavenging).

Ketamine/ xylazine

90 - 100

10

60

0.4

IP 30 - 45 min Ketamine combinations are the next best anesthetic if isoflurane cannot be used. Do not re-dose xylazine; if additional dose needed provide ~1/3 dose ketamine
Ketamine/ medetomidine

50 - 75

1 - 10

60

0.4

IP  
Ketamine/ xylazine/ acepromazine

100

2.5

2.5

40

8

4

IM, IP  
Pentobarbital 30 - 90 30 - 60 IP 60 - 120 min Not readily available.
Tribromoethanol 250 Not recommended IP   Very short term anesthesia, not recommended for survival procedures; inappropriate storage or mixing may result in toxicity.
Reversal Agents Dose (mg/kg) Route Duration Comments
  Mouse Rat      
Yohimbine 0.2 0.2 IP NA Reverses xylazine
Atipamazole 1 1 SC NA Reverses xylazine and medetomidine
Local Anesthetics Dose (mg/kg) Route Duration Comments
  Mouse Rat      
Bupivicaine/ Lidocaine mixture

1.5 mg/kg

0.5 mg/kg

1.5 mg/kg

0.5 mg/kg

SC 4 - 8 hrs Slow onset, long duration Mix together in same syringe for infiltration around incision
<1 hr Rapid onset, short duration

 

 

Dog Formulary

Analgesics Dose (mg/kg) Route Frequency Comments
OPIOIDS        
Recommended: Burprenorphine 0.01 - 0.03 IV/IM/SC Q6h Mild to moderate pain
Fentanyl transdermal

<10 kg 25 µg/h

10 - 25 kg 50 µg/h

>25 kg 100 µg/h

dermal patch q72h Severe pain; 24 hours for maximal effect
NSAIDS/OTHER        
Recommended: Carprofen

2.2

4.4

PO/IV/SC

Q12h

Q24h

Excellent synergistic effect with opioids
Meloxicam

0.2 mg/kg once, then

0.1 mg/kg

IV/SC/PO q24h Excellent synergistic effect with opioids
Acetaminophen 10 - 15 PO q6-8h Antipyretic, mild pain
Anestetics Dose (mg/kg) Route Frequency Comments
INHALATION        
Recommended: Isoflurane

3 - 5 % induction

1 - 3 % maintenance

Inhalation continuous Must use precision isoflurane vaporizer
Sevoflurane

5 - 7 % induction

2 - 4 % maintenance

Inhalation continuous Must use precision sevoflurane vaporizer
INJECTABLE        
Ketamine/ diazepam

5.0 mg/kg

0.25 mg/kg

IV in same syringe As needed Use for anesthetic induction; duration 20 - 30 minutes
Ketamine/ midazolam

5.0 mg/kg

0.25 mg/kg

IV in same syringe As needed Use for anesthetic induction; duration 20 - 30 minutes
Propofol

5.5 - 8.0 mg/kg* = induction

0.4 mg/kg/min* = maintenance

IV

 

IV

Slowly to effect

 

Continuous rate infusion (CRI)

Must administer slowly over 30-60 seconds to avoid apnea, hypotension. Rapid recovery in 10-20 minutes
Pentobarbital* 25 - 30 mg/kg IV Slowly to effect; single or intermittent bolus Single dose duration approximately 45 minutes
Local Anesthetics Dose (mg/kg) Route Frequency Comments

Bupivacaine/ Lidocaine mixture

1.5 mg/kg

0.5 mg/kg

SC Once Mix in same syringe for infiltration or local nerve block. Bupivacaine has slow onset (20-30 minutes), longer duration (4-8 hours); Lidocaine has rapid onset (5-10 minutes), shorter duration (1-2 hours).
Neuromuscular Blocking Dose (mg/kg) Route Frequency Comments
Pancuronium

0.05 - 0.1 mg/kg, then

0.01 mg/kg

IV Once, then as needed Duration of effect 30 - 45 minutes
Reversal Agents Dose (mg/kg) Route Frequency Comments

Atropine

Neostigmine methylsulfate

0.02 mg/kg

0.04 mg/kg

IV

Once

No more than 3 times

Reverses neuromuscular block; give atropine first

 

Swine Formulary3

Analgesics Dose (mg/kg) Route Frequency Comments
OPIOIDS        

Recommended: Buprenorphine

0.01 - 0.05 IV/IM/SC q8-12h Mild to moderate pain
Butorphanol 0.1 - 0.3 IM/SC q4-6h Mild to moderate pain
Fentanyl transdermal 5 µg/kg/h dermal patch q72h Severe pain; dosage variable depending upon breed, age, patch location, heat, moisture, procedure
NSAIDS        
Recommended: Carprofen

2.0

3.0 - 4.0

PO/IV/SC/IM

q12-24h

q24h

Excellent synergistic effect with opioids
Meloxicam 0.1 mg/kg 0.4 mg/kg PO/IV/SC q24h Excellent synergistic effect with opioids
Anesthetics Dose (mg/kg) Route Frequency Comments
INHALATION        
Recommended: Isoflurane

3 - 5 % induction

1.5 - 3 % maintenance

Inhalation continuous Must use precision isoflurane vaporizer
Sevoflurane

5 - 7 % induction

3 - 4 % maintenance

Inhalation continuous Must use precision sevoflurane vaporizer
INJECTABLE        

Ketamine/ acepromazine

22 - 33 mg/kg

1.1 mg/kg

IM/SC Once Use for anesthetic induction; duration 30 minutes; slightly cardio-depressant
Ketamine/ midazolam

33.0 mg/kg

0.5 mg/kg

IM/SC Once Use for anesthetic induction; duration 45-60 minutes; profoundly hypothermic due to peripheral vasodilation; terminal procedures only
Ketamine/ xylazine

20 mg/kg

2 mg/kg

IM/SC Once Use for anesthetic induction; use anticholinergic to reverse cardiodepression/heart block
Telazol® (tiletamine/zolazepam) 2.0 - 8.8 mg/kg IM/SC Once 20 minutes immobilization; use for minor surgery & anesthetic induction; hypothermia, cardiodepression
Telazol® xylazine

4.4 mg/kg

2.2 mg/kg

IM/SC Once Use for anesthetic induction and intubation; not recommended for cardiovascular studies
Propofol

0.83 - 1.66 mg/kg induction

14 - 20 mg/kg/min* maintenance

IV

 

 

IV

Slowly to effect

 

Continuous rate infusion (CRI)

Must administer slowly over 30-60 seconds to avoid apnea, hypotension. Effective sedation and muscle relaxation with minimal cardiodepression at lower dosages; poor analgesia at lower dosages
Reversal agents Dose (mg/kg) Route Frequency Comments
Yohimbine 0.05 - 0.1 mg/kg IV Slowly Once Reverses sedative, cardiodepression, analgesic effects of xylazine
Local anesthetics Dose (mg/kg) Route Frequency Comments
Bupivacaine/ Lidocaine mixture

I.5 mg/kg

0.5 mg/kg

SC Once Mix in same syringe for infiltration or local nerve block. Bupivacaine has slow onset (20-30 minutes), longer duration (4-8 hours); Lidocaine has rapid onset (5-10 minutes), shorter duration (1-2 hours).
Neuromuscular Blocking Dose (mg/kg) Route Frequency Comments
Pancuronium 0.02 - 0.15 mg/kg IV Once, then as needed Duration of effect 30-45 minutes
Reversal agents Dose (mg/kg) Route Frequency Comments

Atropine

Neostigmine methylsulfate

0.02 mg/kg

0.04 mg/kg

IV

Once

No more than 3 times

Reverses neuromuscular block; give atropine first

 

Cat Formulary

Analgesics Does (mg/kg) Route Frequency Comments
OPIOIDS        
Recommended: Buprenorphine 0.01 - 0.03 IV/IM/SC/PO (sublingual)

q6h

q6-12h

Mild to moderate pain
Fentanyl transdermal 25 µg/h dermal patch q72h Severe pain; 6 - 12 hours for maximal effect
NSAIDS        
Recommended: Meloxicam 0.1 mg/kg IV/SC/PO once, then 0.05 mg/kg PO IV/SC/PO q24h Excellent synergistic effect with opioids; chronic dosing PO only
Anesthetics Dose (mg/kg) Route Frequency Comments
INHALATION        
Recommended: Isoflurane

3 - 5 % induction

1 - 3 % maintenance

Inhalation continuous Must use precision isoflurane vaporizer
Sevoflurane

5 - 8 % induction

2 - 4 % maintenance

Inhalation continuous Must use precision sevoflurane vaporizer
INJECTABLE        
Ketamine/ diazepam

5.0 mg/kg

0.25 mg/kg

IV in same syringe As needed Use for anesthetic induction; duration 20 - 30 minutes
Ketamine/ midazolam

5 - 10 mg/kg

0.2 - 0.4 mg/kg

IM in same syringe As needed Use for anesthetic induction; duration 20 - 30 minutes
Ketamine/ xylazine

10

1

IM Once Administer xylazine first as stimulation of chemoreceptor trigger zone frequently causes vomiting; wait 10 minutes, then administer ketamine
Reversal Agents Dose (mg/kg) Route Frequency Comments
Yohimbine 0.05 - 0.1 mg/kg IV slowly Once Reverses sedative, cardiodepression, analgesic effects of xylazine
Local Anesthetics Dose (mg/kg) Route Frequency Comments
Bupivacaine/ Lidocaine mixture

1.5 mg/kg

0.5 mg/kg

SC Once Mix in same syringe for infiltration or local nerve block. Bupivacaine has slow onset (20-30 minutes), longer duration (4-8 hours); Lidocaine has rapid onset (5-10 minutes), shorter duration (1-2 hours).
Neuromuscular Blocking Dose (mg/kg) Route Frequency Comments
Pancuronium 0.05 - 0.1 mg/kg, then 0.01 mg/kg IV

Once

No moe than 3 times

Duration of effect 30-45 minutes
Reversal Agents Dose (mg/kg) Route Frequency Comments

Atropine 

Neostigmine methylsulfate

0.02 mg/kg

0.04 mg/kg

IV

Once

No more than 3 times

Reverses neuromuscular block; give atropine first
Edrophonium 0.5 mg/kg IV

Once

No more than 5 times

Reverses neuromuscular block; complete reversal takes 5-45 minutes

 

Rabbit Formulary

Analgesics Dose (mg/kg) Route Frequency Comments
OPIOIDS        
Recommended: Buprenorphine 0.01 - 0.05 IV/SC q6-12h Mild to moderate pain
Fentanyl transdermal ½ 25 µg/h patch for 3 kg rabbit1 dermal patch q72h Severe pain; do not cut patch, cover ½ not in use
NSAIDS        
Recommended: Meloxicam 0.3 - 0.6 mg/kg SC/PO q24h Excellent synergistic effect with opioids
Carprofen

2 - 4 mg/kg

1.0 - 2.2 mg/kg1

SC

PO

q24h

q12h

Excellent synergistic effect with opioids
Anesthetics Does (mg/kg)  Route Frequency Comments
INHALATION        
Recommended: Isoflurane

3 - 5 % induction

1 - 3 % maintenance

Inhalation continuous Must use precision isoflurane vaporizer
INJECTABLE        
Recommended: Ketamine/ Xylazine

35 - 50 mg/kg

5 -10 mg/kg

IM If additional doses needed to prolong anesthesia provide 1/3 dose ketamine only Minor surgery only; lower doses used for anesthetic induction when isoflurane used for anesthetic maintenance
Ketamine/ Medetomidine

15 - 25 mg/kg

0.25 - 0.5 mg/kg

SC/IM   Minor surgery only; used for anesthetic induction when isoflurane used for anesthetic maintenance

Ketamine/

Xylazine/

Buprenorphine

35 mg/kg

5 mg/kg

0.03 mg/kg

IM If additional doses needed to prolong anesthesia provide 1/3 dose ketamine only Minor surgery only; used for anesthetic induction when isoflurane used for anesthetic maintenance

Ketamine/

Medetomidine/

Buprenorphine

35 mg/kg

0.5 mg/kg

0.03 mg/kg

IM If additional doses needed to prolong anesthesia provide 1/3 dose ketamine only Minor surgery only; used for anesthetic induction when isoflurane used for anesthetic maintenance
Reveral Agents Dose (mg/kg) Route Frequency Comments
Atipamezole 5X medetomidine (same volume as medetomidine) IM preferred/ IV   More specific for reversal of medetomidine that xylazine
Yohimbine 0.2 - 1.0 mg/kg1 IV slowly/ IM Once Reverses sedative, cardiodepression, analgesic effects of xylazine
Local Anesthetics Dose (mg/kg) Route Frequency Comments

Bupivacaine/ 

Lidocaine mixture

I.5 mg/kg

0.5 mg/kg

SC Once Mix in same syringe for infiltration or local nerve block. Bupivacaine has slow onset (20-30 minutes), longer duration (4-8 hours); Lidocaine has rapid onset (5-10 minutes), shorter duration (1-2 hours).

References

Primary reference:

Fish RE et al. Anesthesia and Analgesia in Laboratory Animals, 2nd edition, 2008.

Other references:

1. Carpenter J. Exotic Animal Formulary, 4th ed, 2012.

2. (denoted by * in table) Kuehn N. North American Companion Animal Formulary, 9th ed, 2010.

3. Swindle, MM. Swine in the Laboratory: Surgery, Anesthesia, Imaging, and Experimental Techniques, 2nd Ed, 2007.

4. Langford DJ, Bailey AL, Chanda ML, Clarke SE, Drummond TE, Echols S, Glick S, Ingrao J, Klassen-Ross T, Lacroix-Fralish ML, Matsumiya L, Sorge RE, Sotocinal SG, Tabaka JM, Wong D, van den Maagdenberg AM, Ferrari MD, Craig KD, Mogil JS. 2010. Coding of facial expressions of pain in the laboratory mouse. Nature methods 7:447-449.

 

Figure 1. Mouse Grimace Scale4

 

 

Date: December 1, 2013

Revised: October 7, 2015