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Experiences with morphine injected into the subarachnoid space in sheep
A E Wagner1, C I Dunlop, A S Turner
1Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, USA.
Abstract:
The effects of morphine (M), 0.1 mg/kg, administered into the lumbosacral subarachnoid space of sheep used for experimental stifle surgery, were investigated. In a pilot study, preservative-free morphine was administered to three sheep, morphine containing preservatives to two sheep, and saline (S) to one sheep. After recovery from anesthesia, all five sheep administered M displayed rear limb weakness. One sheep, which had received morphine containing preservatives, also licked and chewed incessantly at its flank and hindquarters during recovery. A group of 24 sheep was used to study the effects of morphine containing preservatives, injected intrathecally, on recovery from general anesthesia and hindlimb orthopedic surgery. Eight sheep received M, eight sheep received S, and eight sheep had a needle placed in the subarachnoid space without any injection (N). Times from end of anesthesia to standing varied greatly and did not differ significantly among groups (P = .73), with M sheep averaging 119 minutes; S sheep, 87 minutes; and N sheep, 83 minutes. One sheep administered M licked and chewed at its hindquarters during recovery. Another group of 24 sheep was used to study the effects of morphine containing preservatives, injected intrathecally, on postoperative lameness. Treatments were as described previously. Sheep were videotaped intermittently for 36 hours after surgery, and each sheep was scored as follows: 0 = not lame; 1 = slightly lame; and 2 = very lame. The average lameness scores, which did not differ significantly among groups (P = .21), were: M sheep, 1.07; S sheep, 0.81; and N sheep, 0.68. One sheep administered M displayed extensor spasms of the hindlimbs, and could not stand until several hours after surgery. We conclude that subarachnoid morphine at the dosage used produces no apparent benefit in sheep which have had stifle surgery, and in fact may cause detrimental side effects, such as hindlimb weakness, and pruritus or irritation of the hindquarters.
Insights
Subarachnoid morphine in sheep undergoing stifle surgery did not improve recovery or reduce lameness. Instead, it caused adverse effects like hindlimb weakness and skin irritation, suggesting no benefit and potential harm.
Area of Science:
- Veterinary Surgery
- Anesthesiology
- Pharmacology
Background:
- Intrathecal morphine is used for postoperative pain management.
- The efficacy and safety of subarachnoid morphine in sheep undergoing stifle surgery require investigation.
Purpose of the Study:
- To evaluate the effects of subarachnoid morphine on recovery and lameness in sheep after stifle surgery.
- To identify potential adverse effects of intrathecal morphine in this surgical model.
Main Methods:
- Sheep received intrathecal injections of morphine (with preservatives), saline, or no injection (needle only).
- Recovery times (anesthesia to standing) and postoperative lameness scores were assessed.
- Videotaping and clinical observations were used to monitor sheep for adverse effects.
Main Results:
- No significant differences in time to standing or lameness scores were observed between morphine, saline, and control groups.
- Sheep receiving morphine exhibited hindlimb weakness, pruritus, and, in one case, extensor spasms.
- Adverse effects included licking/chewing of hindquarters and difficulty standing.
Conclusions:
- Subarachnoid morphine at 0.1 mg/kg provided no apparent benefit for stifle surgery recovery in sheep.
- Morphine administration was associated with detrimental side effects, including hindlimb weakness and pruritus.
- The use of subarachnoid morphine in this context is not recommended due to lack of efficacy and potential harm.