The Patient

While there may be important geographical/regional differences in equine patients and an individual veterinarian or equine clinical establishment may focus on a particular patient type, in the broadest sense equine patients considered for orthopedic‐ procedures span groupings according to age, gender, breed (including consideration of physical size, body build, and demeanor), life‐stage, use, and degree of physical activity and fitness. For example, they include mini‐horses, donkeys, race/performance horses, mules, and draft horses; they may be domesticated or not (e.g. feral, and zoological‐based). This chapter will focus on systemically healthy foals and physically active (athletic) adult horses such as, Thoroughbred racehorses, working Quarter horses, performing Warmbloods, and endurance‐focused Arabians. Developmental deformities at various stages and degrees are most commonly observed in foals and yearlings while exercise‐related acute or chronic joint, ligament, tendon, or bony conditions of the appendicular skeleton are most often seen in adults.

At times, adult horses are engaged in sport or work‐performance disciplines that result in extreme degrees of physical exertion immediately prior to injury and the need for emergency intervention (e.g. break down in a flat race). In such cases, decisions require heightened awareness of altered physiological and pharmacological impacts on anesthetic and surgical management

A smaller subgroup of both foals and adult horses may be presented with joint infections or a localized infection occurring as a result of orthopedic trauma especially of long bones, e.g. limb fractures (closed or compounded). Other health‐related confounders may accompany such orthopedic considerations and should be considered when developing an anesthetic plan.

Individuals of a still smaller group of aged adult horses are presented for diagnostic and/or surgical management in an attempt to preserve quality of life and/or to support breeding or other very specific owner interests. The degree of individual patient health may vary widely but often is at an extreme stage of chronic orthopedic disease or malfunction necessitating special care as for example assistance with mobility and chronic pain management.

Finally, horses of any age may present for surgical management of fractures or bony displacement.

Environment of Patient Care

Along with aforementioned patient considerations, the environment available for the care of equine patients with orthopedic deformities and injuries has an undeniable influence on the individualized plan for anesthetic management, health care personnel, and the facilities being most prominent in this regard, but geographic and/or extremes of climatic considerations may also be a factor.

For purposes of this discussion, health care personnel are identified as primary care providers, i.e. licensed veterinarians, and allied and supportive care personnel that may include both licensed and unlicensed animal nurses and/or animal health technicians with and without advanced training or experience either with handling horses and/or providing anesthesia‐related care.

For purpose of highlighting focused clinical knowledge and experience, primary care providers may be identified in one or both of the species and clinical specialty focus groupings. Each grouping is further defined in Table 7.1. which also relates providers to practice facilities. Obviously, in comparison to the large multi‐provider equine hospital‐based facilities, casual providers would be expected to have less focused knowledge and experience regarding a breath of equine orthopedic conditions and would not have the facilities to successfully manage them. Such expectations also apply to management plans for both general anesthetic and anesthetic recovery.

Before leaving this topic, it is important to note that especially in relation to major and/or uncommon orthopedic procedures, specialist anesthesia providers and/or equine surgeons may be called to travel to distant (often unfamiliar) facilities to collaborate (with potentially unfamiliar health care personnel) and assist in the operative care of a patient. In such circumstances and in support of optimal outcome, unique patient considerations and specialized procedural needs of the consultant(s) along with facility capabilities should be discussed by the primary professional health care team prior to (if possible) the arrival of consultant specialists.

Patient Positioning for Orthopedic Care and Associated Choice of Anesthetic Technique

Orthopedic interventions may be performed in standing and recumbent patients using regional and/or general anesthesia. Orthopedic procedures performed in sedated standing equine patients are increasing in both number and diversity (Auer 2012; Honnas 1991; Madron et al. 2013; Modesto et al. 2015; O’Brien and Hunt 2014; Payne and Compston 2012; Russell and Maclean 2006; Sullins 1991). This development is due to the clear advantages of minimizing patient risk of general anesthesia and recumbency (including transition to and from recumbency), and cost of care. Disadvantages of standing surgery relate to patient, personnel, and facility safety, and potential impact on surgical technique. While some of these procedures can be quite challenging to both anesthetist and surgeon, improvements in drugs, knowledge, and skill (both anesthesia and surgically related), and improved physical facilities have meaningfully supported such change. Regardless, not surprisingly success in this type of patient management is heavily dependent upon careful patient selection and health provider knowledge and skill.

General anesthesia remains most commonly used for extensive orthopedic procedures in the horse. While general anesthesia‐induced recumbency reduces incidence of physical injury to health care providers and facilitates surgery‐related procedural accuracy, it is a patient risk modifier due to the impact of recumbency (including improper positioning), and drug action on normal physiological (especially circulatory, respiratory, and GI) function and perhaps most importantly, the need for the patient to transition to standing posture in a smooth and atraumatic manner.

Induction of general anesthesia, especially for less routine orthopedic procedures, requires careful a priori planning by the anesthesia/surgical team. Ideally, the entire team is present at the time of induction to facilitate and/or observe the patient’s response to the environment and drugs administered. Induction experiences differ widely and are markedly influenced by facilities and clinician preferences and in this regard, we hasten to share our opinion. While more discussion on pharmacology considerations of general anesthetic induction will follow, Table 7.2 provides an overview of physical techniques of transitioning the patient from standing to recumbency. Without question, the tilt‐table and sling techniques in Figures 7.1 and 7.2 (Category II techniques, Table 7.2) offer the most control in body positioning but at a significant economic cost and requirement for personnel knowledge/familiarity and skill. Indeed, the authors consider Category I techniques usually ill‐suited for less routine, technically involved orthopedic surgical procedures (e.g. long bone fractures) and lack of such conditions is strong reason, if possible, for referral to facilities that include such patient management possibilities. If on the other hand and all things considered, a Category II technique is not possible or perhaps situation‐undesirable, the head/tail technique (Category I) is often the technique of choice. For example, with the patient’s head and tail secured with ropes, the fractured limb is positioned against the wall. Then as anesthetic induction proceeds and the patient begins to show signs of drug‐induced relaxation, attendants should attempt to keep the patient’s head elevated while pulling the body into lateral recumbency. Such management should result in less strain at the limb fracture site. This is in contrast, for example, of using a squeeze door/wall for induction of a hind limb long bone fracture where a likely assumed sternal posture on induction will cause inappropriate greater stress at the fracture site.

Before leaving discussion of positional changes, it is important to note that successful fracture repair requires free access to the affected limb and in some cases the ability to apply traction for fracture reduction. These requirements may affect strategic management of anesthetic monitoring (e.g. blood pressure, electrocardiographic and/or muscle twitch monitoring) and may add variability of procedure‐induced noxious stimulation, both impacting anesthetic management. Operative limb positioning and immobility should also be addressed. either by physical (e.g. rope) and/or pharmacological (e.g. analgesics, neuromuscular blocking drugs) means.

The magnitude of circulatory and respiratory dysfunction associated with general anesthesia is of special note during dorsal recumbency and time in this posture contributes further complication risk and as a result encourages further thought in the planning process (Muir and Hubbell 2008). For example, dorsal recumbency likely will increase the magnitude of lung ventilation/perfusion imbalance associated with general anesthesia and in unmitigated circumstances likely reduce the magnitude of arterial oxygenation (Muir and Hubbell 2008). It will also likely increase blood volume within both the calvarium and spinal canal which in turn increases local pressure, and potential for reduced regional blood flow and associated reduced tissue perfusion (Brosnan et al. 2002, 2003, 2008, 2011; Steffey 2008; Steffey et al. 2015). Conversely, blood flow to the lower portions of the limbs and feet may be reduced, perhaps to a harmful degree, as a result of dorsal body positioning with limbs a variable height above heart level and/or as a result of placement of a tourniquet.

Choice of Anesthetic Technique

For most types of orthopedic surgery in foals and adults, techniques of anesthetic management follow age‐related techniques commonly applied to patients admitted for non‐orthopedic (except perhaps gastrointestinal related) surgical procedures performed by the practice. The details of anesthetic management of foals may be found elsewhere (Chapter 13) in this textbook, and their care in most cases would be similar to that of other non‐gastrointestinal surgery. An example of a circumstance likely requiring some modification is a long bone fracture proximal to the carpus or hock in which significant associated hemorrhage has occurred

Adult horses with serious orthopedic trauma including long bone fracture and “breakdown” injuries are often “mentally” and physically stressed and may show signs of substantial pain. As a result, confounding drugs may be “on board” at time of presentation and influence especially the early course anesthetic management. Alternatively, some patients may have not been previously treated and especially under climatically challenging conditions present recumbent and in shock. These circumstances require heightened attention to peri‐operative monitoring, analgesic and fluid therapy, and management of anesthetic recovery.

In a perfect world, anesthesia technique selection is a collaborative decision between the anesthesia staff’s analysis of the situation and animal risk, and the surgical staff’s needs relative to safety, surgical skill and knowledge, considerations for outcome, and financial implications. It is the opinion of the authors that the “donation of staff body parts” in an effort to mitigate financial responsibility should no longer enter the decision process within the context of this topic. The most important factors guiding decisions are the needs of the patient‐client pair, and the health care team’s ability to optimize those needs within the knowledge, and skill‐set of the team assembled and available facilities. Collectively, this informs the “individualized” management plan.

Standing surgical intervention is a technique that should be in the repertoire of any clinical practice (private and university‐based) providing orthopedic surgical care. The technique should be strongly considered as an option in cases where recovery is a concern due to fracture configuration, patient limitations, or facility and equipment limitations. Once the option for standing intervention is considered the best path for success, a few steps should be taken to increase the likelihood of success. The patient should be brought to the surgical area and lightly sedated. The limb should be clipped and a gross scrub performed under the influence of this light sedation to assess the animal’s response to mild stimulation in the area of the fracture and noise that will be present during the procedure. If the patient appears to remain a good candidate, then the operative region should be desensitized. This next step again allows the team to determine if the horse’s responses to more moderately painful stimuli are still acceptable to consider them a standing surgical candidate. Information on local and regional analgesic drugs and techniques appropriate for orthopedic procedures may be found elsewhere.

Inhalation anesthesia with injectable adjuvants is often the technique of choice although for some relative short, particularly secondary procedures (e.g. cast change) total intravenous anesthesia may be an appropriate alternative. Variations to the relatively straightforward inhalation anesthetic maintenance format relate largely to circumstances such as: (i) use of local or regional anesthesia in conjunction with general anesthesia to reduce anesthetic requirement and/or use of peri‐operative analgesia specific to the horse’s orthopedic problem, (ii) patient and/or orthopedic complaint‐specific post‐anesthetic recovery considerations, and (iii) anticipated surgical needs for prolonged general anesthesia, immobility, and recumbency, e.g. long bone fracture, or less familiar surgical procedures.

Choice of Anesthetic Drugs

Drugs that form the basis for general anesthesia are commonly grouped according to administration technique, i.e. injectable and inhalation. Drugs administered by injection are further categorized according to the route by which they are given as for example local or regional as opposed to systemic. Bolus intravenous injection and/or continuous rate (intravenous) infusion (i.e. CRI) are most common, but intramuscular or subcutaneous routes may also be employed under specific conditions.

With the commercial loss of ultrashort‐acting barbiturates to much of the world, the two most common drugs used for injectable anesthesia of equines are ketamine and propofol. These drugs are typically administered after an alpha‐2 adrenergic drug such as xylazine or detomidine (Table 7.3) to minimize undesirable effects. A benzodiazepine or guaifenesin may be additionally used with these agents to further enhance a smooth transition to recumbency and reduce the dose of other medications. Isoflurane, sevoflurane, and desflurane are inhalation anesthetics currently available for equine anesthesia (halothane is at best regionally limited).

Globally and pending availability and cost, there are many “preferred” drug and drug dose combinations that may be used in the anesthetic management of horses with orthopedic conditions. However, as the purpose of this chapter is not to provide in‐depth pharmacologic review of drugs important to the present subject, readers are referred elsewhere for further information (Carruthers et al. 2018; Grimm et al. 2015; Miller 2018; Muir and Hubbell 2008; Riviere and Papich 2018). In considering drug selection, readers of a broadly circulated text such as these must recognize that although consideration of drug classes from which specific drugs are selected is conducted on the basis of both drug and specific patient characteristics, this is also heavily influenced by clinician training and experience, as well as regional drug availability and cost, i.e. although the knowledge may be global, the drug may not be.

Monitoring Requirements for Major Orthopedic Surgery

Contemporary monitoring of otherwise healthy patients during general anesthetic management for routine or uncomplicated orthopedic surgery lasting up to about 2–3 hours generally focuses on common clinical signs of anesthesia along with more in‐depth observations of circulatory and respiratory function (Muir and Hubbell 2008). Hemodynamic monitoring usually at the least includes regular observation and recording (at least every five minutes) of heart rate and rhythm (electrocardiogram), palpation of a peripheral pulse and at least indirect measurement of systemic arterial blood pressure; direct blood pressure monitoring is strongly recommended for inhaled anesthetic maintained recumbency lasting more than 30–45 minutes. Respiratory (or mechanical ventilation) rate is similarly quantitated and recorded, and subjective observations are made of breathing rhythm (spontaneous ventilation) and depth. Serial observations of body temperature are informative, and pulse oximetry and monitoring of inspired and end‐expired anesthetic gas and carbon dioxide are desirable and indeed, routine in many private‐ and most university‐based referral equine hospitals.

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