Predicting the effect of fresh gas flow on tidal volume in volume-controlled mechanically ventilated dogs.

OBJECTIVES: To determine if the tidal volume (VT) delivered (VTDEL) to canine patients being mechanically ventilated by a volume-controlled ventilator differed from the volume set on the ventilator (VTSET) at three fresh gas flow (FGF) rates. To determine if VTDEL could be accurately predicted by an FGF-based mathematical model. STUDY DESIGN: Prospective proof-of-concept study. ANIMALS: A total of 23 adult client-owned dogs undergoing elective orthopedic surgery. METHODS: Dogs were anesthetized and ventilated with a volume-controlled mechanical ventilator with constant respiratory rate (fR) of 10 breaths minute-1, inspiratory-to-expiratory ratio of 1:2 [fraction of inspiratory time (TI) in one respiratory cycle (Ttot) 1:3], and VTSET as body weight (kg) × 15 (mL kg-1). VTDEL was measured in 20 dogs at three FGF (500, 1000 and 4000 mL minute-1). A mathematical model was used to calculate predicted volume (VTPRED) for each animal at each FGF: VTSET + {FGF × [(TI/Ttot)/fR]}. Linear repeated measures models were fit comparing VTDEL to VTSET and to VTPRED by FGF. RESULTS: VTDEL was significantly higher than VTSET at every FGF (p < 0.05), and differences were larger at higher FGF (p < 0.001). There were no statistically significant differences between VTDEL and VTPRED at FGF rates of 500 and 4000 mL minute-1 and, although the mean VTDEL was statistically significantly higher than VTPRED at FGF 1000 mL minute-1 (p = 0.017), the mean difference of 9 mL was not clinically significant. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs on volume-controlled ventilators may be ventilated at a higher VTDEL than intended depending on the FGF settings. Ventilation of small animals at high FGF could inadvertently induce pulmonary damage. A mathematical equation can be used to achieve a desired VTDEL by adjusting VTSET values based on FGF, fR and TI/Ttot.

Randomized, blinded, controlled clinical trial to assess gastroesophageal reflux and regurgitation in dogs undergoing general anesthesia after hydromorphone premedication with or without acepromazine or dexmedetomidine.

OBJECTIVE: To investigate whether premedication with hydromorphone alone or combined with acepromazine or dexmedetomidine affects the incidence of gastroesophageal reflux (GER) and regurgitation in dogs undergoing general anesthesia for elective orthopedic surgery. ANIMALS: 39 healthy client-owned dogs undergoing general anesthesia for elective orthopedic surgery between November 2016 and November 2018. PROCEDURES: For this prospective, randomized, controlled, blinded clinical trial, dogs were randomly assigned to be premedicated with hydromorphone (0.1 mg/kg, IM) alone (group H [control group]) or with either acepromazine (0.05 mg/kg, IM; group AH) or dexmedetomidine (6 µg/kg, IM; group DH) before undergoing general anesthesia induced with propofol and maintained with isoflurane. A pH sensor-tipped probe was used to identify episodes of GER (esophageal pH < 4 or > 7.5 for ≥ 30 seconds). Results for GER, regurgitation, vomiting, propofol dose, and durations of food withholding and anesthesia were compiled and compared across groups. RESULTS: There were 13 dogs in each group, and no meaningful differences were detected in age, body weight, sex, breed, or durations of anesthesia or food withholding across groups. Overall, 16 of the 39 (41%) dogs developed GER: 9 in group H, 6 in group AH, and 1 in group DH. The incidence of GER was significantly lower for group DH versus group H. Six of the 39 (15%) dogs regurgitated: 4 in group H and 2 in group AH. CONCLUSIONS AND CLINICAL RELEVANCE: The combined use of dexmedetomidine and hydromorphone as premedication may be a better choice to reduce GER in healthy dogs undergoing orthopedic surgery than would the use of hydromorphone with or without acepromazine. Additional research is warranted.

Iatrogenic ocular trauma associated with infraorbital block performed for rhinoscopy in a cat: case report and preliminary imaging findings.

OBJECTIVES: This paper describes a case of endophthalmitis in a feline patient caused by globe penetration during an infraorbital block performed to provide analgesia during rhinoscopy, and presents additional imaging and dissection data demonstrating risk of iatrogenic ocular trauma during infraorbital blocks in cats when the infraorbital canal is entered. METHODS: Case records and accompanying histopathologic reports were reviewed for the feline patient. Separately, two feline cadavers were imaged using CT following placement of 5/8" 25 G needles or 1" 22 G over the needle catheters in the infraorbital canal. Infraorbital blocks with injection of trypan blue dye followed by dissection were performed in two further feline cadavers to assess the potential for globe penetration and to provide preliminary information regarding the potential efficacy of infraorbital blocks for analgesia during rhinoscopy. RESULTS: Clinical and histopathologic findings support inadvertent globe penetration during infraorbital block as the cause for endophthalmitis in the feline patient described. CT imaging and dye injection studies further demonstrate the risks involved with this local anesthetic technique in cats. CONCLUSIONS AND RELEVANCE: Further study is needed to assess the safety and efficacy of infraorbital blocks performed for rhinoscopy in cats. Catheters may be safer anesthetic delivery devices than needles. Extreme caution should be used when entering the infraorbital canal in cats.

Sedative effects of alfaxalone and hydromorphone with or without midazolam in cats: a pilot study.

OBJECTIVES: The aim of this pilot study was to compare the quality of sedation and ease of intravenous (IV) catheter placement following sedation using two intramuscular (IM) sedation protocols in cats: hydromorphone, alfaxalone and midazolam vs hydromorphone and alfaxalone. METHODS: This was a prospective, randomized and blinded study. Cats were randomly assigned to receive an IM injection of hydromorphone (0.1 mg/kg), alfaxalone (1.5 mg/kg) and midazolam (0.2 mg/kg; HAM group), or hydromorphone (0.1 mg/kg) and alfaxalone (1.5 mg/kg; HA group). Sedation scoring (0-9, where 9 indicated maximum sedation) was performed at 0, 5, 10, 15 and 20 mins from the time of injection. At 20 mins, an IV catheter placement score (0-10, where 10 indicated least resistance) was performed. RESULTS: Twenty-one client-owned adult cats were included in this study. Sedation and IV catheter placement scores were compared between groups using Wilcoxon rank sum tests. Peak sedation was significantly higher (P = 0.002) in the HAM group (median 9; range 7-9) than in the HA group (median 7; range 3-9), and IV catheter placement scores were significantly higher (P = 0.001) in the HAM group (median 9.5; range 7-10) compared with the HA group (median 7; range 4-9). Spearman correlations were calculated between IV catheter placement score and sedation scores. There was a significant positive correlation of average sedation over time (correlation 0.83; P <0.001) and sedation at 20 mins (correlation 0.76; P <0.001) with a higher, more favorable IV catheter placement score. CONCLUSIONS AND RELEVANCE: These preliminary results suggest that the addition of midazolam to IM alfaxalone and hydromorphone produced more profound sedation and greater ease of IV catheter placement than IM alfaxalone and hydromorphone alone.

Postoperative regurgitation and respiratory complications in brachycephalic dogs undergoing airway surgery before and after implementation of a standardized perianesthetic protocol.

OBJECTIVE: To determine whether implementation of a standardized perianesthetic protocol was associated with reduced incidence of postoperative regurgitation, pneumonia, and respiratory distress in brachycephalic dogs undergoing general anesthesia for airway surgery. ANIMALS: 84 client-owned dogs. PROCEDURES: A perianesthetic protocol that included preoperative administration of metoclopramide and famotidine, restrictive use of opioids, and recovery of patients in the intensive care unit was fully implemented for brachycephalic dogs in July 2014. Medical records of brachycephalic dogs (specifically Boston Terriers, French Bulldogs, English Bulldogs, and Pugs) undergoing anesthesia for airway surgery before (group A) and after (group B) protocol implementation were reviewed. Patient characteristics, administration of medications described in the protocol, surgical procedures performed, anesthesia duration, recovery location, and postoperative development of regurgitation, pneumonia, and respiratory distress were recorded. Data were compared between groups. RESULTS: The proportion of dogs with postoperative regurgitation in group B (4/44 [9%]) was significantly lower than that in group A (14/40 [35%]). No intergroup differences in patient characteristics (including history of regurgitation), procedures performed, or anesthesia duration were found. Rates of development of postoperative pneumonia and respiratory distress did not differ between groups. A history of regurgitation was associated with development of postoperative regurgitation. CONCLUSIONS AND CLINICAL RELEVANCE: Implementation of the described protocol was associated with decreased incidence of postoperative regurgitation in brachycephalic dogs undergoing anesthesia. Prospective studies are warranted to elucidate specific causes of this finding.

Effects of fentanyl administration on locomotor response in horses with the G57C µ-opioid receptor polymorphism.

OBJECTIVE To determine the locomotor response to the administration of fentanyl in horses with and without the G57C polymorphism of the µ-opioid receptor. ANIMALS 20 horses of various breeds and ages (10 horses heterozygous for the G57C polymorphism and 10 age-, breed-, and sex-matched horses that did not have the G57C polymorphism). PROCEDURES The number of steps each horse took was counted over consecutive 2-minute periods for 20 minutes to determine a baseline value. The horse then received a bolus of fentanyl (20 µg/kg, IV), and the number of steps was again counted during consecutive 2-minute periods for 60 minutes. The mean baseline value was subtracted from each 2-minute period after fentanyl administration; step counts with negative values were assigned a value of 0. Data were analyzed by use of a repeated-measures ANOVA. RESULTS Data for 19 of 20 horses (10 horses with the G57C polymorphism and 9 control horses without the G57C polymorphism) were included in the analysis. Horses with the G57C polymorphism had a significant increase in locomotor activity, compared with results for horses without the polymorphism. There was a significant group-by-time interaction. CONCLUSIONS AND CLINICAL RELEVANCE Horses heterozygous for the G57C polymorphism of the µ-opioid receptor had an increased locomotor response to fentanyl administration, compared with the response for horses without this polymorphism. The clinical impact of this finding should be investigated.

Evaluation of risk factors, including fluconazole administration, for prolonged anesthetic recovery times in horses undergoing general anesthesia for ocular surgery: 81 cases (2006-2013).

OBJECTIVE--To determine risk factors for prolonged anesthetic recovery time in horses that underwent general anesthesia for ocular surgery. DESIGN--Retrospective cohort study. ANIMALS--81 horses that underwent general anesthesia for ocular surgery between 2006 and 2013. PROCEDURES--Descriptive information recorded included the ocular procedure performed, concurrent fluconazole treatments, analgesic and anesthetic agents administered, procedure duration, use of sedation for recovery, and recovery time. Data were analyzed for associations between recovery time and other variables. RESULTS--81 horses met inclusion criteria. In 72 horses, anesthesia was induced with ketamine and midazolam; 16 horses treated concurrently with fluconazole had significantly longer mean recovery time (109 minutes [95% confidence interval {CI}, 94 to 124 minutes]) than did 56 horses that were not treated with fluconazole (50 minutes [95% CI, 44 to 55 minutes]). In 9 horses anesthetized with a protocol that included ketamine but did not include midazolam, there was no difference between mean recovery time in horses that either received (59 minutes [95% CI, 36 to 81 minutes]; n = 5) or did not receive (42 minutes [95% CI, 16 to 68 minutes]; 4) fluconazole. Other variables identified as risk factors for prolonged recovery included duration of anesthesia and use of acepromazine for premedication. CONCLUSIONS AND CLINICAL RELEVANCE--Fluconazole administration was associated with prolonged anesthetic recovery time in horses when ketamine and midazolam were used to induce anesthesia for ocular surgery. Duration of anesthesia and premedication with acepromazine were also identified as risk factors for prolonged recovery time.

A comparison of epidural morphine with low dose bupivacaine versus epidural morphine alone on motor and respiratory function in dogs following splenectomy.

OBJECTIVE: To compare post-operative motor function in dogs that received epidural morphine and low dose bupivacaine versus epidural morphine alone following splenectomy. STUDY DESIGN: Prospective, randomized study. ANIMALS: 16 client owned dogs undergoing routine splenectomy. METHODS: Following splenectomy dogs were randomly allocated into one of two groups. The morphine group (MOR) was administered epidural morphine (0.1 mg kg(-1)); the morphine-bupivacaine group (MORB) received epidural morphine (0.1 mg kg(-1)) and low dose bupivacaine [0.25 mg kg(-1), (0.167%)]. The adjusted final volume was 0.15 mL kg(-1) in both groups. Motor function and pain assessment were performed at pre-determined times using a simple numerical motor score and the University of Melbourne Pain Scale (UMPS) respectively. An arterial blood gas was performed 2 hours following epidural administration to check for respiratory compromise. If patients scored >7 on the UMPS or were deemed painful by the observer they were administered hydromorphone intravenously and dose and time of rescue analgesia were recorded. RESULTS: There were no statistically significant differences in motor scores, pain scores, amount of rescue analgesia administered or PaCO2 between treatment groups. No dogs demonstrated respiratory depression or profound motor dysfunction at any time point during the study. 9/16 (56%) dogs did not require rescue analgesia during the first 18 hours following splenectomy. CONCLUSIONS AND CLINICAL RELEVANCE: The combination of low dose bupivacaine (0.25 mg kg(-1)) and morphine (0.1 mg kg(-1)) when administered epidurally has little effect on post-operative motor function. This combination can be used without concern of motor paralysis in healthy animals.

Identification of single nucleotide polymorphisms within exon 1 of the canine mu-opioid receptor gene.

OBJECTIVE: To determine the presence and frequency of single nucleotide polymorphisms (SNPs) within exon 1 of the canine mu-opioid receptor (MOR) gene. STUDY DESIGN: Prospective genetic analysis. ANIMALS: Seventy-five dogs of various breeds. METHODS: DNA was isolated from dog blood. Polymerase chain reaction (PCR) was performed to amplify exon 1 of the canine MOR gene using primers derived from a published sequence. PCR products of anticipated size were identified by gel electrophoresis, isolated and sequenced. RESULTS: Two SNPs were found within the examined region. One is 15 base pairs (bp) upstream (C-15A) of the protein-coding portion of the gene. The second is at position 207 (C207T); a synonymous mutation predicting unaltered protein sequence. The overall prevalence of the C-15A SNP was 43% (64/150 alleles). The overall prevalence of the C207T SNP was 26% (39/150 alleles). CONCLUSIONS AND CLINICAL RELEVANCE: Absence of haplotypes containing both an adenosine at position -15 and a thymine at position 207 suggests that these polymorphisms occurred independently from each other. How these SNPs influence variations in responses seen after opioid administration to dogs remain to be determined, however, our data indicates the C-15A SNP may play a role in opioid dysphoria.

Use of wound soaker catheters for the administration of local anesthetic for post-operative analgesia: 56 cases.

OBJECTIVE: To describe the administration of local anesthetic through wound soaker catheters for post-operative veterinary patients and to characterize complications. STUDY DESIGN: Retrospective study of hospital records. ANIMALS: Records of patients in which a wound soaker catheter was placed post-operatively between November 1, 2004 and July 1, 2006 at a veterinary teaching hospital. Records in which a limb amputation was performed between January 1, 2002 and August 1, 2007 and in which a wound soaker catheter was not placed were reviewed for historic control. RESULTS: A total of 56 cases were identified in which a wound soaker catheter was placed post-operatively including 52 dogs, 2 cats, and 2 goats. Twenty canine cases were identified in which limb amputation was performed and no wound soaker catheter was placed. The majority of surgical procedures for which a wound soaker catheter was placed included thoracic limb amputation (46.4%) and pelvic limb amputation (35.7%). Wound soaker catheters remained in place for an average of 1.6 +/- 0.5 days. Feline and caprine patients received intermittent bupivacaine boluses every 6 hours. Canine patients received continuous lidocaine infusions. Complications included disconnection of the catheter from the infusion (7.7%), one seroma, and one suspected lidocaine neurotoxicity. Incisional infections were noted in 3/56 (5.3%) limb amputations with wound soaker catheters placed which was not higher than the incisional infection rate found in the historic control cases 3/20 (15%). CONCLUSION AND CLINICAL RELEVANCE: Use of the wound soaker catheter was a viable means of providing local analgesia in post-operative veterinary patients. Studies are needed to evaluate efficacy of pain management, and to further investigate techniques for catheter placement and maintenance which may help to optimize the analgesia achieved using this technique.

Evaluation of compliance among nursing staff in administration of prescribed analgesic drugs to critically ill dogs and cats.

OBJECTIVE: To investigate the prescription of analgesic drugs to hospitalized critically ill dogs and cats and determine compliance of nursing staff in administering the prescribed analgesics. DESIGN: Cross-sectional study. ANIMALS: 272 dogs and 79 cats hospitalized in an intensive care unit during a 2-month period. PROCEDURE: Patient treatment orders were examined daily for details regarding prescribed and administered analgesic drugs. RESULTS: A mean of 39% of cats and dogs in the intensive care unit were prescribed analgesic drugs each day, the most common of which were opioids. Local anesthetic drugs, nonsteroidal anti-inflammatory drugs, and ketamine were prescribed less frequently. Cats were less likely than dogs to receive analgesics after traumatic injury, but the difference was not significant. There was no difference between species in frequency of prescription of analgesic drugs after surgery. Most patients were prescribed a single class of analgesic drug; only 13% had orders for multiple analgesics. Of the patients for which analgesics were prescribed, 64% received them exactly as prescribed, 23% had at least 1 reduction in dosing, and 13% had at least 1 increase in dosing. When a decrease in dosing occurred, the drugs were opioids in each instance, whereas when drug dosing was increased, the drugs were of various types. CONCLUSIONS AND CLINICAL RELEVANCE: Discrepancies sometimes existed between the dose of analgesic prescribed and that administered. This appeared to occur primarily because of concerns about adverse effects of opioid drugs. Strategies to reduce these effects may improve pain management in critically ill dogs and cats.