Measurement of peripheral muscle oxygen saturation in conscious healthy horses using a near-infrared spectroscopy device.

OBJECTIVE: Maintaining adequate muscle tissue oxygenation is of paramount importance during equine general anesthesia. The objectives of this study were to assess the feasibility, reliability and repeatability of near-infrared spectroscopy (NIRS) muscle oximetry using the Inspectra m650 in conscious healthy adult horses. STUDY DESIGN: Prospective, observational study. ANIMALS: A group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018. METHODS: The probe of an Inspectra m650 NIRS tissue oximeter was placed on the hairless surface of five muscle sites (omotransversarius, triceps long head, extensor carpi ulnaris, vastus lateralis and lateral digital extensor) on the left side of the body of each standing, unsedated horse. Each site had muscle oxygenation (StO2) recordings measured in triplicate and statistical modeling used to assess the reading reliability and repeatability within and between muscle sites. RESULTS: The readings acquired at the vastus lateralis and extensor carpi ulnaris muscle sites had highly repeatable values [mean (90% confidence interval): StO2, 95% (93.8%, 96.5%) and 93% (91.6%, 93.9%), respectively; intraclass correlation coefficients, 0.92 and 0.80, respectively]. These two sites also had high reliability (represented by the percentage of successful readings; 70% and 86%, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: The use of NIRS muscle oxygenation technology is a clinically feasible means to assess tissue oxygenation in horses. The vastus lateralis and extensor carpi ulnaris muscle sites provided the most reliable and repeatable readings when using the Inspectra m650 machine in horses.

Evaluation of tissue hemoglobin saturation (StO2) using near-infrared spectroscopy during hypoxemia and hyperoxemia in Beagle dogs.

OBJECTIVE: To determine the relationship between tissue oxygen saturation (StO2) and oxygen delivery (D˙O2) during hypoxemia and hyperoxemia. STUDY DESIGN: Prospective, randomized study. ANIMALS: Eight purpose-bred Beagle dogs. METHODS: Dogs were anesthetized with isoflurane, ventilated to eucapnia, and instrumented for thermodilution cardiac output, invasive mean arterial pressure (MAP), sartorius muscle StO2 and airway gas monitoring. Dogs were administered rocuronium to facilitate mechanical ventilation and esmolol to minimize anesthetic effects on cardiac output. Instrumentation and baseline data collection were at 0.21 fractional inspired oxygen (FIO2). Dogs were evaluated at high (0.40 then 0.95) and low (0.15 then 0.10) FIO2 sequences in random order with a 60 minute rest period at FIO2 0.21 between sequences. Target FIO2 was achieved by manipulating nitrogen and oxygen flow rates. Data collected at each FIO2, after a 10 minute period of stabilization, included heart rate (HR), MAP, cardiac index (CI) and StO2. Arterial oxygen content (CaO2) and oxygen delivery index (D˙O2I) were calculated at each FIO2. Data analysis included Pearson's correlation analysis and mixed-model anova (p < 0.05). RESULTS: There were no significant differences in HR, MAP or CI across all FIO2 values. Significant decreases occurred in mean ± standard deviation StO2 (90 ± 4% to 69 ± 18%; p = 0.0001), D˙O2I (458 ± 70 to 281 ± 100 mL minute(-1) m(-2); p = 0.0008) and CaO2 (13.2 ± 1.53 to 8.4 ± 2.05 mL dL(-1); p = 0.0001) from FIO2 0.21 to 0.10, but not at remaining FIO2 values. The correlation between StO2 and D˙O2I across all FIO2 values was strong (r = 0.97; p = 0.0013) and linear. CONCLUSIONS AND CLINICAL RELEVANCE: In this model of hypoxemia and hyperoxemia, the strong correlation between StO2 and D˙O2I suggests that StO2 can be used to estimate D˙O2.

Evaluation of tissue oxygen saturation with near-infrared spectroscopy during experimental acute hemorrhagic shock and resuscitation in dogs.

OBJECTIVE: To evaluate tissue oxygen saturation (Sto2) by use of near-infrared spectroscopy in experimental acute hemorrhagic shock and resuscitation in dogs. ANIMALS: 14 healthy adult purpose-bred Beagles. PROCEDURES: Dogs were anesthetized with isoflurane via facemask, anesthesia was maintained with propofol and rocuronium bromide, and dogs were mechanically ventilated to maintain normocapnia. Dogs were studied under normovolemia (baseline), hypovolemia with target mean arterial blood pressure < 40 mm Hg achieved and maintained steady for 10 minutes (hypovolemia T1), then 20 minutes later (hypovolemia T2), following resuscitation with shed blood (after transfusion), and after administration of 20 mL of hetastarch/kg (hypervolemia). Conditions were executed sequentially during a single anesthetic episode, allowing stabilization between states (10 minutes). Hemoglobin concentration, mean arterial blood pressure, arterial blood gas concentrations, cardiac index, oxygen delivery indexed to body surface area, and Sto2 were monitored. RESULTS: From baseline to hypovolemia T1, there was a significant reduction in mean ± SD oxygen delivery index (619 ± 257 mL/min/m(2) to 205 ± 76 mL/min/m(2)) and Sto2 (94 ± 4.4% to 78 ± 12.2%). Following resuscitation, Sto2 (80 ± 8.5% vs 92 ± 6.45%) and oxygen delivery index (211 ± 73 mL/min/m(2) vs 717 ± 221 mL/min/m(2)) significantly increased, returning to baseline values. Hypervolemia had no effect on Sto2 or oxygen delivery index. A strong correlation (r = 0.97) was detected between mean oxygen delivery index and Sto2 across all time points. CONCLUSIONS AND CLINICAL RELEVANCE: Under the conditions of this study, there was a strong correlation between Sto2 and oxygen delivery, suggesting that Sto2 may be used to estimate oxygen delivery.

Effect of hind limb position on the craniocaudal length of the lumbosacral space in anesthetized dogs.

OBJECTIVE: To investigate whether rostral extension of the hind limbs increases the cranio-caudal dorsal interlaminar distance between the seventh lumbar vertebra and the sacral bone (LS distance) in sternally recumbent anesthetized dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: Eighteen dogs (eight neutered males, three intact males, six spayed females, one intact female) of various breeds, weighing 4-34 kg and ranging in age from 1 to 13 years. METHODS: Each dog was grouped by size: small (≤ 10 kg), medium (15-20 kg) or large (≥ 25 kg). Each dog was anesthetized and positioned in sternal recumbency. Computed tomography (CT) of the lumbosacral area was performed with the hind limbs resting on the stifle and the feet extended posteriorly, and then with the hind limbs extended rostrally. LS distance, craniocaudal dorsal interlaminar distance between sixth and seventh lumbar vertebra (L6-L7 distance), length of L7 vertebral body and lumbosacral angle (LS angle) were measured on a reconstructed mid-sagittal CT image from the two hind limb positions. The measurements from the two hind limb positions for the whole dog population and by size were compared using Student's T tests. Diagnostic interpretation of the CT images was performed. RESULTS: The length of L7 was taken as the reference value as it was not affected by hind limb position. LS distance, L6-L7 distance and LS angle were significantly higher when the hind limbs were extended rostrally in all three size groups. The CT images of ten dogs showed clinically undetected osteoarthrosis of the ileo- and lumbosacral area. CONCLUSIONS AND CLINICAL RELEVANCE: Rostral extension of the hind limbs significantly increases LS and L6-L7 distance and LS angle even in dogs with clinically undetected osteoarthrosis of the ileo- and lumbosacral area, and may enhance the ease of lumbosacral epidural injection in sternally recumbent anesthetized dogs.

Comparison of three different inhalant anesthetic agents (isoflurane, sevoflurane, desflurane) in red-tailed hawks (Buteo jamaicensis).

OBJECTIVE: To compare isoflurane, sevoflurane and desflurane for inhalant anesthesia in red-tailed hawks (Buteo jamaicensis) in terms of the speed and characteristics of induction; cardiovascular and respiratory parameters while anesthetized; and speed and quality of recovery. STUDY DESIGN: Prospective, cross over, randomized experimental study. ANIMALS: 12 healthy adult red-tailed hawks. METHODS: Anesthesia was induced with isoflurane, sevoflurane or desflurane in oxygen via face mask in a crossover, randomized design with a 1 week washout period between each treatment. Hawks were tracheally intubated, allowed to breathe spontaneously, and instrumented for cardiopulmonary monitoring. Data collected included heart rate, respiratory rate, end-tidal CO(2) , inspired and expired agent, SpO(2,) temperature, systolic blood pressure, time to intubation and time to recovery (tracking). Recovery was subjectively scored on a 4 point scale as well as a summary evaluation, by a single blinded observer. RESULTS: No significant difference in time to induction and time to extubation was noted with the administration of isoflurane, sevoflurane or desflurane. Time to the ability of the bird to follow a moving object with its eyes (tracking) was significantly faster with the administration of sevoflurane and desflurane. All recoveries were scored 1 or 2 and were assessed as good to excellent. No significant difference was noted in heart rate, blood pressure and temperature among the three inhalants. Administration of isoflurane resulted in lower respiratory rates. CONCLUSIONS AND CLINICAL RELEVANCE: Overall, although isoflurane remains the most common inhaled anesthetic in avian practice, sevoflurane and desflurane both offer faster time to tracking, while similar changes in cardiopulmonary function were observed with each agent during anesthesia of healthy red-tailed hawks.

Comparison of two anesthetic protocols for feline blood donation.

OBJECTIVE: To compare hemodynamic variables during, and recovery quality following, anesthesia for feline blood donation using intramuscular ketamine-midazolam-butorphanol (KMB) versus inhaled sevoflurane in oxygen (SEV). STUDY DESIGN: Prospective blinded, randomized, crossover study. ANIMALS: Twenty healthy, client-owned, mixed breed cats, aged 4-8 years, weighing 5.2-6.4 kg. METHODS: Cats were anesthetized with KMB for one donation and SEV for another. Heart rate (HR), respiratory rate (f(R)), pulse quality, mucous membrane color, capillary refill time, arterial hemoglobin saturation with oxygen (SpO(2)), and noninvasive arterial blood pressure (Doppler) were assessed by a blinded observer every 1 minute during collection. A nonblinded anesthesiologist delivered drugs and responded to hemodynamic changes. Each donation consisted of 55 mL of whole blood drawn via jugular puncture over 5-22 minutes. Donors received 60 mL subcutaneous lactated Ringer's solution before recovery. Donors were monitored for a minimum of 4 hours post-donation, before returning home. Owners, unaware of anesthetic protocol, completed a questionnaire regarding their cat's behavior during the 24 hours following donation. RESULTS: Both protocols provided adequate restraint but were complicated by significant hypotension, requiring intervention in 16 (84%) SEV cats, and eight (42%) KMB cats. KMB cats experienced post-procedure hyperthermia, with body temperatures >103.5 degrees F. All animals responded to symptomatic therapy within 2 hours. Owners noted a significantly faster return to normal behavior at home following SEV. CONCLUSION: All cats experienced hypotension, with many animals requiring intervention. There was no significant difference between protocols in incidence and severity of hypotension. The primary post-procedure complication was hyperthermia with KMB. CLINICAL RELEVANCE: As a result of the potential for hypotension during blood donation, intravenous (IV) access and blood pressure monitoring are recommended for all anesthetized donor cats, regardless of the anesthetic protocol. Post-procedure hyperthermia is a risk with KMB, so temperature monitoring is recommended. Return to normal behavior is faster with SEV.

Use of a wireless system to measure invasive arterial blood pressure in ponies - preliminary study.

OBJECTIVE: To evaluate the feasibility and functionality of intra-carotid wireless device implantation in ponies, and to investigate its short-term complications. STUDY DESIGN: Prospective preliminary study. ANIMALS: Five mixed breed, adult, intact male ponies weighing 104 +/- 28.8 kg (mean +/- SD) underwent surgery. Arterial blood pressure data were continuously collected from four animals. METHODS: General anesthesia was induced on two consecutive days. On the first day, an intra-arterial wireless device was implanted in the right carotid artery. On the next day, a transcutaneous intra-arterial catheter was placed in the left facial artery. Data from both sources were collected. Post-mortem examination was performed. RESULTS: Surgical time was 27.1 +/- 11.85 minutes. All catheters remained in place with some extra vascular migration. Complications included mild seroma and hematoma. CONCLUSION: The wireless system allowed continuous monitoring in ponies throughout anesthesia and at rest and may allow for the recording of arterial blood pressure and heart rate when it would be difficult to achieve with a conventional system (e.g. during recovery from anesthesia). CLINICAL RELEVANCE: The wireless invasive blood pressure monitor may allow continuous measurements when only intermittent measurements would be feasible with a wired system.