Cold Therapy Pain Management for Warm Blooded Animals
How and Why Polar Powder Pain Relief Cold Packs are better

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The therapeutic application of cold appears to be widely used for the treatment of a variety of painful and inflammatory conditions.. The application of cold to an injured or painful area is hardly a new therapeutic concept. The Greek physician Hippocrates wrote about the use of cold therapy to control pain and swelling in the 4th century B.C. The Roman physician Galen described the use of cold compresses for analgesia following soft tissue injuries in the 1st century A.D. During the Middle Ages, ice was used for preoperative anesthesia. Cold therapy in the form of ice has been used extensively in the athletic training environment for the treatment of sports injuries for many years. n human medicine, cold therapy is commonly used to treat acute soft tissue injuries and to help reduce symptoms of inflammation at the end of exercise In addition, cold therapy appears to have significant analgesic effects and is also used to help alleviate pain in post-surgical patients.


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Cold therapy can be used in the various phases of pathological processes. In the acute inflammatory phase after soft-tissue injury (up to 48 hours after trauma) cold plays an important role in the control of the inflammatory response. Cold therapy can be used during the repair phase after soft tissue injuries as well (between 48 hours and six weeks after injury). In human medicine, application of cold during the repair phase is referred to as "cryokinetics." The analgesic effect of cold makes it possible to start exercising an injured limb while it is partially desensitized. In humans, this allows early weight bearing on the injured limb at a time when collagen is organizing and remodeling. It's also proposed that motion of the injured limb increases blood flow to the injured area. Cold therapy is also a therapeutic option in the treatment of several chronic conditions such as tendonitis, bursitis, trigger points and muscle spasms. 

Cold therapy is commonly used in the treatment of inflammation and soft tissue injuries in the horses, dogs and other pets. The application of cold has been recommended in the treatment of acute tendon injuries for all warm blooded animals for suspensory desmitis and other non-specific areas of swelling and inflammation. It has also been advocated in pre-exercise therapy. 

It is generally assumed that cryo-therapy causes small blood vessels on the body surface to constrict. This effect may help reduce hemorrhage and edema. Edema acts as a negative metabolic factor for cells surrounding the initial injury site because of the longer transport route for oxygen to reach the cells. Edema may cause capillary constriction due to increased extra cellular pressure.  Cold therapy may also slow hematoma formation due to decreased blood flow. Blood vessel constriction is a reflex mechanism aimed at minimizing the loss of heat by the body and is mediated by both the autonomic nervous system and local hormonal control.

Following initial vasoconstriction, vasodilation occurs. This appears to be a protective mechanism to maintain viability of body tissues at low temperatures. When tissue temperature falls below 18 C, the initial reduction in blood flow is followed by a compensatory increase in blood flow. This appears to be due to dilation of muscle blood vessels.  This vasodilatory response varies between different types of tissue and, in humans, appears to be greatest in areas subjected to frostbite.  Reflex vasodilation was not recognized after thirty minutes of cold therapy at 39.2 F .

Anti-inflammatory effects. It is also assumed that cold reduces the inflammatory response after soft tissue injuries by reducing pain and post-injury edema. It is believed that cold reduces inflammation by inhibiting histamine, neutrophil activation, collagenase activity and synovial leukocytes.1

Hypometabolism. The decrease in inflammatory response seen after the application of cold is enhanced due to decreased tissue metabolism, which limits secondary tissue damage due to hypoxia.  Some studies suggest that this hypometabolism is more important than the vascular response in limiting the extent of tissue injury.  For example, enzymatic activity in the knee joints of human patients with rheumatoid arthritis increases four times with an increase in temperature from a normal 33 C to 36 C. Studies have shown that metabolic enzyme activity is decreased by about 50 per cent when the temperature is lowered by 10 C.

Reduced muscle spasm. Cold decreases activity of the muscle spindle, which in turn decreases muscle spasticity.30 Cold also makes muscle tissue stiffer and results in changes in viscosity and plasticity of the various tissues. There seems to be a direct relationship between the cooling temperature and the muscle performance.2

Decreased nerve conduction velocity. Decreased nerve conduction velocity has been documented as a result of the application of cold. This is thought to contribute to the reported analgesic effects of cold (see below).

It is generally thought that cold decreases swelling, however, numerous studies have shown that application of cold actually increases subcutaneous edema. Greater swelling occurred in limbs following application of cold in both injured and uninjured limbs in an experimental model of ligament injury in pigs.   Increased swelling was shown with the application of cold for treatment of postacute ankle sprains in people.  Increased subcutaneous swelling may be due to the fact that cutaneous veins and arteries appear to react differently to cold, with veins staying constricted atlower temperatures.   Increased subcutaneous swelling following application of cold may also be due to increased permeability of superficial lymph vessels.  It should be noted that many clinical studies related to the use of cold in humans do not indicate increased swelling following the application of cold, perhaps because first aid combines cold with compression and elevation.

Cyrotherapy is proposed to help preserve the elastic properties of collagen in soft tissue injuries. Cooling results in enhanced stiffness and stability in injured tissue.  This effect could be potentially detrimental, however. Increased tissue stiffness and analgesic effects could conceivably make tissues less pliable and impede the normal protective mechanisms that pain provides, thus rendering the tissue more susceptible to injury during vigorous exercise. Tissue elasticity is critical to normal tendon function, for example, and anything that would increase tissue stiffness would presumably be contraindicated as it could conceivably predispose to injury.   The use of cryotherapy is considered contraindicated in humans prior to exercise because the increased collagen stiffness results in a decrease in muscle flexibility.

Cold has been frequently shown to have an analgesic effect. Clinical and experimental research on pain and pain threshold indicates that pain reduction occurs after the tissues are cooled to 10C to 15C; however the duration of pain relief is uncertain.  The mechanism for pain relief may include breaking the pain-spasm cycle or decreasing nerve conduction velocity. The decrease in nerve conduction velocity appears to be proportional to the decrease in tissue temperature rather than the changes in local circulation. Nerve conduction is continually slowed down when temperatures fall, until finally, nerve fibers cease conducting altogether. The application of cold also appears to act as a counter irritant producing a shower of nerve impulses that makes receptors momentarily refractory to pain impulses. Other proposed mechanisms for cold-induced pain relief include a decreased production of pain-producing substances locally,  interference with gate control pain mechanisms (cold might provide as strong sensory input which "closes the gate" and reduces the transmission of painful stimuli and release of endorphins with a resulting influence on opioid receptors in the central nervous system.

TIME OF APPLICATION  In the treatment of acute injuries, cryotherapy is best initiated as soon as possible after the onset of the injury. In studies on human ankle injuries, cryotherapy initiated on the day of injury (day 0) or on day 1 allowed for an earlier resumption of full activities that did cryotherapy begun on day two.

LENGTH OF APPLICATION  There appears to be a general consensus in human medicine that the optimum duration of cold therapy is from 20 to 30 minutes.  The effects of cold application are seen rather quickly. Investigators using triple-phase technetium-99m scintigraphs (bone scans) were able to show that the topical application of ice for 20 minutes decreased skeletal blood flow in the human knee by an average of 19.3% and soft tissue blood flow by 25.8%.  In another study that attempted to increase blood flow, cold packs were applied to human ankles for 25 minutes and the responses were measured using strain gauge plethysmography. That study found decreased blood flow during the 25 minutes of cold application and for 25 minutes after removal of the ice packs.  In another study, to produce a measurable, albeit small (5.1%) decrease in blood flow and metabolism in the deep tissues of a human knee joint, specifically the bones, only 5 minutes of ice application were necessary. A maximal response was produced within 25 minutes of icing, fourfold greater than that seen at 5 minutes. There was a mean increase in arterial blood flow at 10 minutes, suggesting a possible reflex vasodilation in the arterial blood vessels in response to cooling, with subsequent decreases again noted at 15, 20 and 25 minutes of cooling. 

Clinical studies from human medicine seem to agree that cryotherapy does improve recovery from injuries. It should be noted, however, that many of these studies combine cryotherapy with other therapies such as compression, limb elevation and analgesic therapy. Cold does reduce the temperature of the tissues to which it is applied. In addition, other physiologic processes, such as neuromuscular action, nerve conduction and plasticity of tissues are also affected by cold. It is not clear if it is important to cool injured temperatures to a point near freezing or if more moderate cooling methods are equally effective. Cold may also have negative effects. Increased swelling of the subcutaneous tissues may be seen after application of cold therapy. In experimental situations, cold can increase as well as decrease the inflammatory reaction. Excessive application of cold to tissue has the potential to cause tissue damage or nerve injury.

The therapeutic application of cold appears to be widely used for the treatment of a variety of painful and inflammatory conditions.. The application of cold to an injured or painful area is hardly a new therapeutic concept. The Greek physician Hippocrates wrote about the use of cold therapy to control pain and swelling in the 4th century B.C. The Roman physician Galen described the use of cold compresses for analgesia following soft tissue injuries in the 1st century A.D. During the Middle Ages, ice was used for preoperative anesthesia. Cold therapy in the form of ice has been used extensively in the athletic training environment for the treatment of sports injuries for many years.

In human medicine, cold therapy is commonly used to treat acute soft tissue injuries and to help reduce symptoms of inflammation at the end of exercise In addition, cold therapy appears to have significant analgesic effects and is also used to help alleviate pain in post-surgical patients.

Cold therapy can be used in the various phases of pathological processes. In the acute inflammatory phase after soft-tissue injury (up to 48 hours after trauma) cold plays an important role in the control of the inflammatory response. Cold therapy can be used during the repair phase after soft tissue injuries as well (between 48 hours and six weeks after injury). In human medicine, application of cold during the repair phase is referred to as "cryokinetics." The analgesic effect of cold makes it possible to start exercising an injured limb while it is partially desensitized. In humans, this allows early weight bearing on the injured limb at a time when collagen is organizing and remodeling. It's also proposed that motion of the injured limb increases blood flow to the injured area. Cold therapy is also a therapeutic option in the treatment of several chronic conditions such as tendonitis, bursitis, trigger points and muscle spasms. 

Cold therapy is commonly used in the treatment of inflammation and soft tissue injuries in the horses, dogs and other pets. The application of cold has been recommended in the treatment of acute tendon injuries for all warm blooded animals for suspensory desmitis and other non-specific areas of swelling and inflammation. It has also been advocated in pre-exercise therapy. 


It is generally assumed that cryo-therapy causes small blood vessels on the body surface to constrict. This effect may help reduce hemorrhage and edema. Edema acts as a negative metabolic factor for cells surrounding the initial injury site because of the longer transport route for oxygen to reach the cells. Edema may cause capillary constriction due to increased extra cellular pressure.  Cold therapy may also slow hematoma formation due to decreased blood flow. Blood vessel constriction is a reflex mechanism aimed at minimizing the loss of heat by the body and is mediated by both the autonomic nervous system and local hormonal control.

Following initial vasoconstriction, vasodilation occurs. This appears to be a protective mechanism to maintain viability of body tissues at low temperatures. When tissue temperature falls below 18 C, the initial reduction in blood flow is followed by a compensatory increase in blood flow. This appears to be due to dilation of muscle blood vessels.  This vasodilatory response varies between different types of tissue and, in humans, appears to be greatest in areas subjected to frostbite.  Reflex vasodilation was not recognized after thirty minutes of cold therapy at 39.2 F .

Anti-inflammatory effects. It is also assumed that cold reduces the inflammatory response after soft tissue injuries by reducing pain and post-injury edema. It is believed that cold reduces inflammation by inhibiting histamine, neutrophil activation, collagenase activity and synovial leukocytes.1

Hypometabolism. The decrease in inflammatory response seen after the application of cold is enhanced due to decreased tissue metabolism, which limits secondary tissue damage due to hypoxia.  Some studies suggest that this hypometabolism is more important than the vascular response in limiting the extent of tissue injury.  For example, enzymatic activity in the knee joints of human patients with rheumatoid arthritis increases four times with an increase in temperature from a normal 33 C to 36 C. Studies have shown that metabolic enzyme activity is decreased by about 50 per cent when the temperature is lowered by 10 C.

Reduced muscle spasm. Cold decreases activity of the muscle spindle, which in turn decreases muscle spasticity.30 Cold also makes muscle tissue stiffer and results in changes in viscosity and plasticity of the various tissues. There seems to be a direct relationship between the cooling temperature and the muscle performance.2

Decreased nerve conduction velocity. Decreased nerve conduction velocity has been documented as a result of the application of cold. This is thought to contribute to the reported analgesic effects of cold (see below).

It is generally thought that cold decreases swelling, however, numerous studies have shown that application of cold actually increases subcutaneous edema. Greater swelling occurred in limbs following application of cold in both injured and uninjured limbs in an experimental model of ligament injury in pigs.   Increased swelling was shown with the application of cold for treatment of postacute ankle sprains in people.  Increased subcutaneous swelling may be due to the fact that cutaneous veins and arteries appear to react differently to cold, with veins staying constricted atlower temperatures.   Increased subcutaneous swelling following application of cold may also be due to increased permeability of superficial lymph vessels.  It should be noted that many clinical studies related to the use of cold in humans do not indicate increased swelling following the application of cold, perhaps because first aid combines cold with compression and elevation.

Cyrotherapy is proposed to help preserve the elastic properties of collagen in soft tissue injuries. Cooling results in enhanced stiffness and stability in injured tissue.  This effect could be potentially detrimental, however. Increased tissue stiffness and analgesic effects could conceivably make tissues less pliable and impede the normal protective mechanisms that pain provides, thus rendering the tissue more susceptible to injury during vigorous exercise. Tissue elasticity is critical to normal tendon function, for example, and anything that would increase tissue stiffness would presumably be contraindicated as it could conceivably predispose to injury.   The use of cryotherapy is considered contraindicated in humans prior to exercise because the increased collagen stiffness results in a decrease in muscle flexibility.

Cold has been frequently shown to have an analgesic effect. Clinical and experimental research on pain and pain threshold indicates that pain reduction occurs after the tissues are cooled to 10C to 15C; however the duration of pain relief is uncertain.  The mechanism for pain relief may include breaking the pain-spasm cycle or decreasing nerve conduction velocity. The decrease in nerve conduction velocity appears to be proportional to the decrease in tissue temperature rather than the changes in local circulation. Nerve conduction is continually slowed down when temperatures fall, until finally, nerve fibers cease conducting altogether. The application of cold also appears to act as a counter irritant producing a shower of nerve impulses that makes receptors momentarily refractory to pain impulses. Other proposed mechanisms for cold-induced pain relief include a decreased production of pain-producing substances locally,  interference with gate control pain mechanisms (cold might provide as strong sensory input which "closes the gate" and reduces the transmission of painful stimuli and release of endorphins with a resulting influence on opioid receptors in the central nervous system.

TIME OF APPLICATION  In the treatment of acute injuries, cryotherapy is best initiated as soon as possible after the onset of the injury. In studies on human ankle injuries, cryotherapy initiated on the day of injury (day 0) or on day 1 allowed for an earlier resumption of full activities that did cryotherapy begun on day two.

LENGTH OF APPLICATION  There appears to be a general consensus in human medicine that the optimum duration of cold therapy is from 20 to 30 minutes.  The effects of cold application are seen rather quickly. Investigators using triple-phase technetium-99m scintigraphs (bone scans) were able to show that the topical application of ice for 20 minutes decreased skeletal blood flow in the human knee by an average of 19.3% and soft tissue blood flow by 25.8%.  In another study that attempted to increase blood flow, cold packs were applied to human ankles for 25 minutes and the responses were measured using strain gauge plethysmography. That study found decreased blood flow during the 25 minutes of cold application and for 25 minutes after removal of the ice packs.  In another study, to produce a measurable, albeit small (5.1%) decrease in blood flow and metabolism in the deep tissues of a human knee joint, specifically the bones, only 5 minutes of ice application were necessary. A maximal response was produced within 25 minutes of icing, fourfold greater than that seen at 5 minutes. There was a mean increase in arterial blood flow at 10 minutes, suggesting a possible reflex vasodilation in the arterial blood vessels in response to cooling, with subsequent decreases again noted at 15, 20 and 25 minutes of cooling. 

Clinical studies from human medicine seem to agree that cryotherapy does improve recovery from injuries. It should be noted, however, that many of these studies combine cryotherapy with other therapies such as compression, limb elevation and analgesic therapy. Cold does reduce the temperature of the tissues to which it is applied. In addition, other physiologic processes, such as neuromuscular action, nerve conduction and plasticity of tissues are also affected by cold. It is not clear if it is important to cool injured temperatures to a point near freezing or if more moderate cooling methods are equally effective. Cold may also have negative effects. Increased swelling of the subcutaneous tissues may be seen after application of cold therapy. In experimental situations, cold can increase as well as decrease the inflammatory reaction. Excessive application of cold to tissue has the potential to cause tissue damage or nerve injury.

RE:  HORSES:    Equine limbs treated with a 4 C cold bandage for 30 minutes demonstrated a 6 C difference (measured by thermography) between treated and untreated limbs immediately after removal of the bandage. The dorsal metacarpus was the slowest area to rewarm with a difference between treated and untreated limbs of 4 C after four hours.16 In human medicine, the extent of the decrease in tissue temperature is dependent on the method of cooling, length of treatment and the temperature of the cooling agent that is used.30 The recommendation for 20 - 30 minutes of therapy appears to be based on studies where the cooling agent applied is ice. Ice, which is applied at a temperature of 0 C, has the potential to injure tissue. Application of cold can be for much longer periods of time if the temperature is controlled and allows for continuous cryotherapy, a relatively new treatment modality

(see below).

METHOD OF APPLICATION

There are many ways by which cold can be applied to the equine limb.

Hose. Although simple to apply and relatively available, cold water directed through a hose is a time-consuming and relatively ineffective method for applying cryotherapy.[xxxiv]

Tub, Whirlpool or Turbulator Boot. Water immersion is an effective way of providing cold therapy to horse limbs. Numerous studies have demonstrated that cold water immersion causes a profound decrease in tissue temperature.32, [xxxv], [xxxvi], Application of these devices is less time consuming than is use of a hose, however, horses may still need to be monitored to make sure that they do not upset the devices. Crushed ice can be added to the water to increase the cold effect of the therapy. A thermometer would be useful for monitoring the temperature applied by these methods so as to prevent tissue injury.

Ice cup. A Styrofoam cup filled with water and placed in the freezer can be used as an effective way to apply ice to a localized area. Ice massage is indicated to decrease pain and inflammation in a localized area. Ice massage is applied by rubbing ice over the painful area for 7 to 10 minutes or until analgesia is produced.30 The rim of the cup is peeled away and the target area is massaged with the exposed ice. The Styrofoam makes a nice insulator for the ice. A tongue depressor inserted into the water can also be used as a handle when massaging the affected area.

Gel wraps and chemical ice envelopes. Numerous products are available composed of gels that can be cooled in the refrigerator and then applied directly to the horse's limb or chemical ice envelopes that contain a chemical which is broken within a package, with the resulting endothermic reaction cooling the pack. Although convenient, one study found that the standardized application of melting ice cooled better than did either of these methods.[xxxvii]

Crushed ice and water in a plastic bag. This easy and inexpensive way to apply cold has the advantage of being able to mold to limb contours.34

Continuous cold therapy. There are two major disadvantages of the above-listed methods of application of therapeutic cold. First is their inability to maintain a constant temperature over a prolonged period of time. All of the methods listed above lose effectiveness as they are warmed by the heat of the limb. Second is that when ice at 0 C, is used as the cooling modality there is a potential for tissue injury if the modality is applied for an excessive period to time. Thus, in the human field, machines have been developed which allow a continuous application of temperature-controlled cold. Continuous cold application offers the additional advantage of controlling the vasoconstriction:vasodilation cycle that occurs with intermittent applications of cold. Several studies indicate that when compared to intermittent application of cold therapy, continuous cold therapy of from 7 to 10 C reduces pain, decreases analgesic intake and decreases swelling.[xxxviii], [xxxix], [xl] However, another study concluded that continuous cold therapy had no effects in relief of pain from total knee arthroplasty.[xli]

Pressure and cold. The combination of pressure and cold is an excellent combination for the treatment of injured limbs. Compressive dressing is thought to reduce the amount of swelling by altering the intracellular and extracellular pressure relationships.40 Adjunctive compression also significantly augments local tissue hyperthermia.23 However, it may also enhance the risk of hypothermic injury if applied injudiciously.

OTHER VARIABLES

Many other variables influence actual tissue temperatures reached in a clinical situation:[xlii]

form of ice. Chipped ice appears to be more effective at cooling than do ice cubes or chunks of ice.37

temperature of ice. The colder the ice, the greater the cooling effect but the greater the potential to cause surface tissue injury.

pressure applied to pack. As previously noted, pressure increases the efficiency of cold delivery.

surface area of pack. The greater the area covered with cold, the more profound the temperature decrease.

anatomical site where the pack is applied. This relates to the vascularity of the targeted tissues and the thickness of subcutaneous fat. The more vascular the tissue, the larger the layer of insulating fat, the more inefficient the delivery of cold. For example, temperature changes in sheep thighs have been shown to be depth dependent; after a single treatment, temperatures rise rapidly at first but after 2 hours do not regain pretreatment values. During a subsequent application, the temperatures of the deep tissues continue to fall whereas the superficial tissue falls again to similar values as on the first application.38 As a general rule, the skin cools first, followed by the subcutaneous tissue. Both cool before joints and muscle, with the former cooling more slowly than the latter11 and the effects of cold being less pronounced in either muscle or joint than in the skin or subcutaneous tissues although they tend to persist longer.3 Most studies indicate that muscle temperature continues to drop after the cooling modality has been removed.2

nature of lesion (extent of vascular damage). For example, temperatures in sheep thighs did not fall as much after trauma as they did in pretrauma experiments. This was attributed to an increase in blood flow through the injured tissues.38

duration of application. As a general rule, the longer that cold is applied, the colder the tissue gets.

Given all of the variables involved, the ideal and most efficient application of cold therapy to the equine limb would appear to combine the ability to control temperature, the ability to apply pressure and the ability to apply coverage to a large area, using readily available materials (i.e., ice and water).

At least one such device is available on the equine market.[1]

COMPLICATIONS OF CRYOTHERAPY

In the equine veterinary literature, complications from cryotherapy do not appear to have been reported. In the human literature, the most frequently reported complications are frost-bite and cold induced nerve palsy. Frost-bite the cutaneous reaction that occurs when ice or cold is applied to the skin for an extended time period. The risk of frost-bite in humans is reduced by applying a wrap next to the skin and by not extending the use of cold therapy for longer than 45 minutes.1 Nerve palsy appears to be more likely to occur in large areas were nerves are located directly beneath the skin, most frequently involving the peroneus and ulnar nerves of the human knee and elbow, respectively.[xliii] Neither condition has been reported in the horse following the use of cryotherapy, perhaps because of the thick skin and insulating hair layer.

SUMMARY

Clinical studies from human medicine seem to agree that cryotherapy does improve recovery from injuries. It should be noted, however, that many of these studies combine cryotherapy with other therapies such as compression, limb elevation and analgesic therapy. Cold does reduce the temperature of the tissues to which it is applied. In addition, other physiologic processes, such as neuromuscular action, nerve conduction and plasticity of tissues are also affected by cold. It is not clear if it is important to cool injured temperatures to a point near freezing or if more moderate cooling methods are equally effective. Cold may also have negative effects. Increased swelling of the subcutaneous tissues may be seen after application of cold therapy. In experimental situations, cold can increase as well as decrease the inflammatory reaction. Excessive application of cold to tissue has the potential to cause tissue damage or nerve injury.

The lower limbs of the horse are almost ideally suited to the application of cold therapy. Being roughly cylindrical, cold can be easily and conveniently applied using a number of different bandaging techniques. Newer technologies make the application of cold easier, more convenient and more effective. There are many applications of cold therapy to equine limbs. However, one common application in human medicine, the use of cold post-surgery, appears not to have been used to a great extent in equine surgery. There appear to be ample opportunities to perform equine-specific clinical research demonstrating the applications of the various techniques of cold therapy to the horse.

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