Comparison of Carbon Dioxide Laser Modalities for Removal of Polymethylmethacrylate Cement

Polymethylmethacrylate (PMMA) cement is routinely used in a number of surgical procedures performed on human beings and animals. As the use of PMMA increases in veterinary medicine, the need for its removal during “revision” surgeries also increases. Common indications for removal of PMMA are infection, aseptic loosening, and fracture of the cement. Polymethylmethacrylate cement is often applied in areas of the body where typical mechanical methods of removal are dangerous or impossible. Cement placed near the spinal canal for the treatment of caudal cervical malformation-malarticulation syndrome or deep within the femoral medullary canal for total hip prostheses are examples. The ability to safely and easily remove cement should lower intraoperative complication rates associated with revision surgeries.

The vaporization efficiency for removal of PMMA cement for three carbon dioxide laser modalities (continuous wave only, with Swift-Lase™ attachment, and with Fiberlase™ wave guide) were determined, as well as heat transferred to periosteal surface during PMMA cement vaporization, and gross pathology to the cortical bone at the maximum vaporization efficiency power. Cefazolin sodium was added to half of the samples to determine if the ablation ablation rate of PMMA would be affected. The C02 laser with wave guide was the most efficient modality for vaporization at 25 watts, and produced significantly less heat transfer to the periosteal surface than the heat of polymerization of the PMMA cement. Cefazolin sodium appeared to slightly decrease the vaporization efficiency, and all of the lasers produced gross and histologic lesions to the bone.

Three laser types were compared for their ability to efficiently and safely remove polymethylmethacrylate (PMMA) cement. Vaporization rates were determined. The most efficient wattage for each laser modality was used to compare the heat transferred during PMMA removal as well as the pathology created by application of each laser modality to the cortical bone. The CO2 laser with wave guide at 25 watts was the most efficient modality for vaporization of PMMA cement, and produced significantly less heat transfer to the periosteal surface than the CO2 laser and the CO2 laser with Swift-Lase™.

Effects of butorphanol and carprofen on the minimal alveolar concentration of isoflurane in dogs

OBJECTIVE

To evaluate the effects of butorphanol and carprofen, alone and in combination, on the minimal alveolar concentration (MAC) of isoflurane in dogs.

DESIGN

Randomized complete-block crossover study.

ANIMALS

6 healthy adult dogs.

PROCEDURE

Minimal alveolar concentration of isoflurane was determined following administration of carprofen alone, butorphanol alone, carprofen and butorphanol, and neither drug (control). Anesthesia was induced with isoflurane in oxygen, and MAC was determined by use of a tail clamp method. Three hours prior to induction of anesthesia, dogs were fed a small amount of canned food without any drugs (control) or with carprofen (2.2 mg/kg of body weight [1 mg/lb]). Following initial determination of MAC, butorphanol (0.4 mg/kg [0.18 mg/lb], i.v.) was administered, and MAC was determined again. Heart rate, respiratory rate, indirect arterial blood pressure, endtidal partial pressure of CO2, and saturation of hemoglobin with oxygen were recorded at the time MAC was determined.

RESULTS

Mean +/- SD MAC of isoflurane following administration of butorphanol alone (1.03 +/- 0.22%) or carprofen and butorphanol (0.90 +/- 0.21%) were significantly less than the control MAC (1.28 +/- 0.14%), but MAC after administration of carprofen alone (1.20 +/- 0.13%) was not significantly different from the control value. The effects of carprofen and butorphanol on the MAC of isoflurane were additive. There were not any significant differences among treatments in regard to cardiorespiratory data.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that administration of butorphanol alone or in combination with carprofen significantly reduces the MAC of isoflurane in dogs; however, the effects of butorphanol and carprofen are additive, not synergistic.

Cardiorespiratory responses and plasma cortisol concentrations in dogs treated with medetomidine before undergoing ovariohysterectomy

OBJECTIVE

To evaluate effects of medetomidine on anesthetic dose requirements, cardiorespiratory variables, plasma cortisol concentrations, and behavioral pain scores in dogs undergoing ovariohysterectomy.

DESIGN

Randomized, prospective study.

ANIMALS

12 healthy Walker-type hound dogs.

PROCEDURE

Dogs received medetomidine (40 micrograms/kg [18.2 micrograms/lb] of body weight, i.m.; n = 6) or saline (0.9% NaCl) solution (1 ml, i.m.; 6) prior to anesthesia induction with thiopental; thiopental dose needed for endotracheal intubation was compared between groups. Ovariohysterectomy was performed during halothane anesthesia. Blood samples were obtained at various times before drug administration until 300 minutes after extubation. Various physiologic measurements and end-tidal halothane concentrations were recorded.

RESULTS

In medetomidine-treated dogs, heart rate was significantly lower than in controls, and blood pressure did not change significantly from baseline. Plasma cortisol concentrations did not increase significantly until 60 minutes after extubation in medetomidine-treated dogs, whereas values in control dogs were increased from time of surgery until the end of the recording period. Control dogs had higher pain scores than treated dogs from extubation until the end of the recording period.

CONCLUSION AND CLINICAL RELEVANCE

Administration of medetomidine reduced dose requirements for thiopental and halothane and provided postoperative analgesia up to 90 minutes after extubation. Dogs undergoing ovariohysterectomy by use of thiopental induction and halothane anesthesia benefit from analgesia induced by medetomidine administered prior to anesthesia induction. Additional analgesia is appropriate 60 minutes after extubation.