Alex Dugdale

Retrospective study of the risk factors and prevalence of colic in horses after orthopaedic surgery

The records of 496 orthopaedic operations on 428 horses were reviewed to estimate the prevalence of, and identify the risk factors for, the development of colic in horses after surgery. Colic was defined as any recognised sign of abdominal pain that could not be attributed to a concurrent disease. Fourteen of the horses developed colic; eight of them were undiagnosed, three were classified as impactions, one as tympanic colic of the colon, one as incarceration of the small intestine in the epiploic foramen, and one as left dorsal displacement of the colon in the nephrosplenic space. Morphine was associated with a four-fold increased risk of colic compared with the use of no opioid or butorphanol, and out-of-hours surgery was also associated with an increased risk.

Post anaesthetic colic in horses: a preventable complication?

REASONS FOR PERFORMING STUDY There is little information on the prevalence of, and risk factors associated with, post anaesthetic colic (PAC) in horses undergoing nonabdominal operations. OBJECTIVES To undertake the first prospective study of prevalence of PAC and identify risk factors in its development in nonabdominal procedures. METHODS A multicentre prospective case-control study was conducted, on every horse undergoing anaesthesia for a nonabdominal procedure between April 2004 and June 2005. Colic cases were defined as any horse with recognised signs of abdominal pain within 72 h of general anaesthesia that could not be attributed to any concurrent disease. Five control horses per case were selected randomly from the study population at all hospitals. Multivariable logistic regression analysis was used to examine the relationship between predictor variables and the risk of developing PAC. RESULTS The estimated mean prevalence of PAC in the study population was 5.2% (95% CI, 2.8, 8.0). However, the prevalence of colic varied between each centre. The most commonly diagnosed cause of colic was impaction. Multivariable analyses showed that the centre involved and the type of surgery performed were associated with an increased risk of PAC. Preoperative food deprivation and the use of opioid drugs were confounding factors. CONCLUSIONS Prevalence of PAC varied significantly between the 4 hospitals studied; there may be hospital-related covariates that account for this. The type of surgery performed influenced the risk of PAC. POTENTIAL RELEVANCE Identifying the risk factors for PAC is a prerequisite for its prevention. This study indicates horses at increased risk of PAC that might benefit from a more critical evaluation of post anaesthetic gastrointestinal function and/or the provision of preventative measures. Further investigation is required to explain the variation in prevalence of PAC between centres.

Strong Stability and Host Specific Bacterial Community in Faeces of Ponies

The horse, as a hindgut fermenter, is reliant on its intestinal bacterial population for efficient diet utilisation. However, sudden disturbance of this population can result in severe colic or laminitis, both of which may require euthanasia. This study therefore aimed to determine the temporal stability of the bacterial population of faecal samples from six ponies maintained on a formulated high fibre diet. Bacterial 16S rRNA terminal restriction fragment length polymorphism (TRFLP) analyses of 10 faecal samples collected from 6 ponies at regular intervals over 72 hour trial periods identified a significant pony-specific profile (P<0.001) with strong stability. Within each pony, a significantly different population was found after 11 weeks on the same diet (P<0.001) and with greater intra-individual similarity. Total short chain fatty acid (SCFA) concentration increased in all ponies, but other changes (such as bacterial population diversity measures, individual major SCFA concentration) were significant and dependent on the individual. This study is the first to report the extent of stability of microbes resident in the intestinal tract as represented with such depth and frequency of faecal sampling. In doing so, this provides a baseline from which future trials can be planned and the extent to which results may be interpreted.

Prospective evaluation of postoperative pain in cats undergoing ovariohysterectomy by a midline or flank approach.

Twenty entire female cats were randomly assigned to two groups of 10; the cats in one group underwent ovariohysterectomy by a midline approach and the cats in the other group by a flank approach. Cats were assessed for signs of pain and scores were assigned pre- and postoperatively. There was a tendency for the cats neutered by a flank approach to be in more pain postoperatively (P=0·05). The final pain score for cats in either group was equal to or lower than their baseline score.

Reported morbidities following 861 anaesthetics given at four equine hospitals

POSTANAESTHETIC morbidity prolongs convalescence, thus increasing costs to the client, and can lead to death. Most information available on postanaesthetic morbidity in horses relates to musculoskeletal disorders, such as postanaesthetic myopathy or fractures (Richey and others 1990, Young and Taylor 1993). More recently, the prevalence of postanaesthetic colic after non-abdominal procedures has been estimated retro spectively (Senior and others 2004, 2006, Andersen and others 2006). Information relating to other types of post-anaesthetic morbidity is scarce. This short communication describes a multi-centre prospective study conducted to esti-mate the prevalence of and identify risk factors for reported morbidities in horses undergoin g non-abdominal procedures at four equine hospitals in the

Suspected venous air embolism in a horse

A horse which had had a caecal impaction for 10 days was treated by means of an ileocaecostomy but failed to respond satisfactorily. Before a second laparotomy was performed it was observed to have dislodged the extension set from a jugular catheter and air was heard being sucked into the vein. It became very agitated but was anaesthetised again and the impaction was removed through an incision in the apex of the caecum. After recovering from the anaesthesia it developed severe signs of pruritus which subsided only after 12 hours. These signs were considered most likely to have resulted from a venous air embolism.

Does pethidine affect the cardiovascular and sedative effects of dexmedetomidine in dogs

OBJECTIVES To investigate pethidines effects on sedation and cardiovascular variables in dogs premedicated with dexmedetomidine. METHODS Sixty American Society of Anesthesiologists (ASA) I dogs were presented for routine neutering. Heart rate was measured at admission. Dogs were randomly assigned to one of the five groups to decide premedication; group D5+P (dexmedetomidine 5 microg/kg plus pethidine 5 mg/kg), D10+P (dexmedetomidine 10 microg/kg plus pethidine 5 mg/kg) with three control groups, D5 (dexmedetomidine 5 microg/kg), D10 (dexmedetomidine 10 microg/kg) or P (pethidine 5 mg/kg). Heart rate was measured at 3, 5, 10 and 20 minutes after preanaesthetic medication. Simple descriptive scores for sedation were assigned after 20 minutes. Anaesthesia was induced using propofol and maintained using isoflurane in oxygen. Heart rate was recorded throughout anaesthesia. RESULTS Sedation scores after preanaesthetic medication were significantly higher (P<0.001) in groups D5+P and D10+P compared with the other three groups. D5+P and D10+P groups tended to have lower heart rates in dogs at all time points after premedication compared with groups containing only pethidine or dexmedetomidine at the relevant dose. CLINICAL SIGNIFICANCE Greater sedation is achieved using combinations of dexmedetomidine and pethidine compared with each drug alone. Pethidine does not attenuate the alpha-2 adrenergic-induced bradycardia.

The ins and outs of ventilation 1. Basic principles

ALTHOUGH the rhythmic squeezing of a bag is still the basic method of providing controlled ventilation in veterinary patients, there are many automatic mechanical ventilators now available, each boasting some advantage over another. This article discusses important physiological aspects of controlled ventilation and, in particular, their bearing on ventilator requirements for anaesthesia and intensive care. An article in the next issue will describe how some of the available machines can be used for the ventilatory support of anaesthetised animals.

The ins and outs of ventilation: 2. Mechanical ventilators

THIS article discusses some of the commonly available machines that can be used for ventilatory support of anaesthetised patients. An article in the last issue of In Practice (April 2007, volume 29, pp 186-193) reviewed physiological aspects of mechanical ventilation. An appreciation of these factors is important for understanding the features and limitations of the ventilator in use.

Treatment of recurrent luxation of the shoulder in an alpaca

LUXATION of the shoulder is an uncommon condition in large animals (Semevolos and others 1998), and has not pre-viously been reported in alpacas. Alpacas are raised primarily as companion animals, and have similar orthopaedic prob-lems to cattle. The mild temperament and relatively small body size of these animals make them excellent candidates for the treatment of orthopaedic problems (Kaneps 1996).This short communication describes the clinical presenta-tion and surgical treatment of recurrent lateral luxation of the shoulder in an alpaca by greater tubercle osteotomy and bicipital tendon transposition, using a technique previously described in dogs (Hohn and others 1971, Piermattei 1997, Engen 1998, Talcott and Vasseur 2003).A four-year-old male alpaca, bodyweight 60 kg, had a history of recurrent luxation of the shoulder. The initial lux-ation had occurred seven months previously, after a fight with another male alpaca. The luxated joint was easily reduced under sedation using 6 mg (0·1 mg/kg) xylazine (Rompun; Bayer), and the animal was reported be sound between each episode.On examination, the alpaca did not show any lameness at the walk, and manipulation of the shoulder was not resented in extension or flexion. There was no swelling or thickening of the soft tissues. Lateral luxation was easily induced manu-ally, resulting in a non-weight-bearing lameness, but any lux-ation could be easily reduced without sedation. Craniocaudal and lateromedial radiographs of the shoulder were taken in sternal and lateral recumbency, respectively. There were no visible osteoarthritic or other changes affecting the shoulder joint with the joint reduced.The alpaca was not allowed food for 24 hours before surgery, and water was withheld for at least eight hours. After place-ment of a 14 G catheter into the right jugular vein (Intraflon 2; Vygon), 6 mg xylazine was administered intravenously to sedate the animal. Anaesthesia was induced with 140 mg (2·3 mg/kg) ketamine (Ketaset; Fort Dodge Animal Health) and 5 mg (0·08 mg/kg) diazepam (Diazepam; Hameln Pharmaceuticals), administered intravenously. The alpaca became recumbent, but needed additional increments of ket-amine, as well as the local application of lidocaine (Xylocaine Spray; Astra) on to the larynx, to facilitate intubation of the trachea using a cuffed endotracheal tube with an inter-nal diameter of 7·5 mm. Anaesthesia was maintained with sevoflurane (SevoFlo; Abbott) in 100 per cent oxygen, admin-istered via a small animal circle breathing system. Flunixin (60 mg) (Meflosyl; Fort Dodge Animal Health) and 6 mg morphine (Morphine Sulfate; Celltech) were administered 10 ml/kg/hour Hartmann’s solution intravenously through-out the period of anaesthesia.The alpaca was positioned in right lateral recumbency. After the usual aseptic precautions, a craniolateral para-humeral incision was made, beginning 6 cm dorsal to the shoulder joint and extending to a point midway down the humeral shaft. The skin and subcutaneous tissues were then reflected, and the lateral border of the brachiocephalic mus-cle was retracted medially, exposing the cranial aspect of the proximal humerus and the insertions of the supraspinatus, deltoid and superficial and deep pectoral muscles (Fig 1). The insertion of the superficial pectoral muscle was transected. The tissues over the bicipital groove and the intertubercular ligament were incised. The biceps tendon was freed from the surrounding fascia by blunt dissection proximally, and the muscle body was separated from surrounding tissue distally.Two holes were drilled through the greater tubercle, 1·5 cm apart, using a 2 mm drill bit perpendicular to the humerus axis, exiting on its medioproximal aspect. The glid-ing holes were enlarged with a 3·5 drill bit to a depth of 1·5 cm. The pilot hole was drilled with a 2·5 mm drill bit through the opposite cortex. A depth gauge was used to obtain the correct length of screw before tapping the pilot hole with a 3·5 tap. Two 3·5 mm cortical screws, 4·8 and 5·5 cm long, were driven in place to assess correct positioning and length, and they then were removed. A 7 mm thick osseous flap, 2·5 cm long and 1·5 cm wide, was made with an oscillating saw from the greater tubercle, to include the insertion of the supraspinatus muscle. The flap was retracted and separated proximally from the surrounding tissues by blunt dissection (Fig 2).The bicipital tendon was transposed laterally and the bone flap from the greater tubercle was fixed in position with the screws (Fig 3). The wound was flushed with saline. The brachiocephalic muscle was reattached and the subcutane-ous tissues were closed in a simple continuous pattern with 2·0 braided lactomer (Polysorb 2.0; Syneture). The skin was closed with simple interrupted sutures of polypropylene (Prolene 0; Ethicon). A stent bandage was applied on the skin. The alpaca was placed into sternal recumbency with its head held up and blankets were used to treat the hypother-mia (rectal temperature 35·7°C at the end of the pro cedure). The endotracheal tube was removed once the animal’s swallowing reflex returned, but the head was kept supported in an elevated position until full consciousness was achieved. A moderate bloat developed during the procedure, but it resolved once the animal was placed into sternal recum-bency and no reflux was observed. A dose of 6 mg morphine intramuscularly, followed by 0·6 mg (0·01 mg/kg) buprenor-