Rationale for hyperbaric oxygen therapy in traumatic injury and wound care in small animal veterinary practice.

Hyperbaric oxygen therapy is in wide use in human medicine around the world. Although hyperbaric oxygen therapy is available for veterinary use, it is still significantly underutilised. The physical principles, gas laws and physiologic mechanisms by which hyperbaric oxygen therapy is therapeutic, especially in traumatic injuries and complicated wound care, are discussed. Then, considerations are offered for the implementation of hyperbaric oxygen therapy in veterinary practices. Finally, a review of clinical indications for veterinary practices, including a presentation of select literature, is provided. Applying hyperbaric oxygen therapy in an earlier and more consistent manner could improve short- and long-term outcomes in complicated wounds. The authors also hope this information may stimulate interest in the design of future, prospective studies for the various clinical situations described.

Effect of high arterial carbon dioxide tension on efficiency of immunoglobulin G absorption in calves.

OBJECTIVES: To determine whether high PaCO2 reduced apparent efficiency of IgG absorption (AEA) in calves and whether assisted ventilation of calves with high PaCO2 increased AEA. ANIMALS: 48 Holstein calves. PROCEDURES: Arterial and venous blood samples were collected 1, 13, and 25 hours after birth; an additional venous sample was collected at 37 hours after birth. Arterial samples were analyzed for PaCO2, PaO2, pH, and bicarbonate and base excess concentrations; venous samples were analyzed for plasma IgG concentrations. On the basis of 1-hour PaCO2, calves were assigned to nonrespiratory acidosis (PaCO2 < 50 mm Hg; n = 19) or respiratory acidosis (PaCO2 > or = 50 mm Hg; 29) groups. Calves in the respiratory acidosis group were assigned randomly to receive no further treatment (n = 17) or to be given 5 minutes of assisted ventilation (12). All calves received between 1.8 and 2 L of colostrum 2, 14, 26, and 38 hours after birth. Plasma volume and AEA were determined 25 hours after birth. RESULTS: 1-hour PaCO2 had no effect on AEA or on plasma IgG concentrations determined 13, 25, or 37 hours after birth. Artificial ventilation had no effect on plasma IgG concentration or AEA. CONCLUSIONS AND CLINICAL RELEVANCE: Lack of effect of 1-hour PaCO2 on AEA and IgG concentration indicated that calves compensated for moderate acid-base imbalances associated with birth. Calves born with high PaCO2 achieved adequate plasma IgG concentrations if fed an adequate amount of high-quality colostrum early in life. The effect of artificial ventilation on PaCO2 was temporary and did not increase AEA.

Effect of high volume epidural morphine, ketamine and butorphanol on halothane minimum alveolar concentration in ponies.

This study determined the effects of epidurally administered morphine, ketamine and butorphanol on halothane minimum alveolar concentration (MAC) in ponies. Seven ponies were anaesthetised with thiopentone and succinylcholine, intubated and anaesthesia maintained with halothane. Ventilation was controlled and blood pressure was maintained within normal limits. Following the determination of baseline halothane MAC for the pelvic and thoracic limbs the ponies were given morphine (0.1 mg/kg bwt), ketamine (0.8 or 1.2 mg/kg bwt), butorphanol (0.05 mg/kg bwt) or saline, epidurally, to a final volume of 0.15 ml/kg bwt. The halothane MAC for the pelvic and thoracic limbs was redetermined following each treatment. The baseline halothane MAC for the control group was mean +/- s.e. 0.85 +/- 0.02% and no significant change occurred after saline administration. Morphine significantly (P = 0.002) decreased MAC from, mean +/- s.e. 0.90 +/- 0.05% to 0.77 +/- 0.06% in the pelvic limb. Ketamine significantly decreased MAC in the pelvic limb from mean +/- s.e. 0.86 +/- 0.06% to 0.71 +/- 0.04%, and 0.82 +/- 0.03% to 0.71 +/- 0.02%, for the low (P = 0.008) and high dose (P = 0.001), respectively. No significant change in MAC occurred following butorphanol. No treatment reduced halothane MAC for the thoracic limb.

Effect of acepromazine and butorphanol on halothane minimum alveolar concentration in ponies.

The effect of i.v. acepromazine (0.05 mg/kg bwt), butorphanol (0.05 mg/kg bwt) and a combination of acepromazine and butorphanol on halothane minimum alveolar concentration (MAC) was determined in 7 mixed-breed ponies. Ventilation was controlled, and blood pressure and temperature were maintained within normal limits. Following the determination of baseline MAC, treatments were administered to each pony in a random manner. The control treatment was normal saline. The baseline halothane dMAC for the control group was 0.91 +/- 0.04%, and no significant change occurred after saline administration. Acepromazine decreased (P = 0.0001) the halothane MAC from mean +/- s.e. 0.92 +/- 0.02% to 0.58 +/- 0.04%, and the combination of acepromazine and butorphanol, decreased (P = 0.003) halothane MAC, from mean +/- s.e. 0.95 +/- 0.04% to 0.59 +/- 0.06%. This represents a decrease of 36.9 and 37.8%, respectively. However, the difference between these 2 treatments was not significant. Butorphanol did not significantly change the mean group value for MAC; nevertheless, 3 ponies had an increase, one a decrease, while the MAC did not change in the remaining 3 ponies following butorphanol treatment.

Cerebrospinal fluid acid-base status during normocapnia and acute hypercapnia in equine neonates.

OBJECTIVE: To determine normal acid-base status of the CSF and to compare it with changes during acute hypercapnia in equine neonates. ANIMALS: 10 clinically normal foals between 1 and 12 days old. PROCEDURE: CSF and arterial and venous blood samples were collected every 15 minutes during 45 minutes of normocapnia and 90 minutes of hypercapnia in isoflurane-anesthetized foals. CSF samples were collected via a subarachnoid catheter placed in the atlanto-occipital space. RESULTS: Comparison of blood and CSF gases during normocapnia indicated that CSF was significantly more acidic than blood. The lower pH was attributable to higher CO2 and lower bicarbonate concentrations than those in blood. During hypercapnia, CSF CO2 increased and pH decreased parallel to changes in blood, but changes were not a great as similar changes in venous blood, indicating that some degree of buffering occurs in the CSF of foals. CONCLUSIONS: Normal CSF acid-base status in equine neonates is similar to that in other domestic species. The blood-brain and blood-CSF interfaces in neonates allow rapid diffusion of CO2, but allow only slow diffusion of bicarbonate. Equine neonates are capable of buffering respiratory-induced acid-base changes in the CSF, but the buffering capacity is less than that of the vascular compartment. CLINICAL RELEVANCE: Neonatal foals may develop severe respiratory compromise, resulting in hypoxemia and hypercapnia. Because the ability of the CSF to buffer acid-base changes in neonates is reduced, hypercapnia may contribute to the CNS abnormalities that often develop in sick neonates. Thus, normal blood gas values should be maintained in diseased equine neonates.

Blood ionized calcium concentrations in horses before and after the cross-country phase of three-day event competition.

Blood ionized calcium (Ca2+) and pH; plasma lactate concentrations; and total protein, total calcium (CaT), albumin, and phosphorus concentrations in serum were determined in 40 healthy horses before (T1), at the finish line (T2), and 10 minutes after the finish (T3) of the cross-country phase of a 3-day-event competition. Mean (+/- SEM) Ca2+ concentrations decreased from 6.22 +/- 0.04 mg/dl at T1 to 5.04 +/- 0.07 mg/dl at T2 (P < or = 0.05). This decrease was accompanied by a nonsignificant increase in CaT between T1 and T2. The mean (+/- SEM) percent ionization of calcium decreased significantly (P < or = 0.05), from 50.9 +/- 2.75% at T1 to 40.3 +/- 3.58% at T2. Significant increases in mean albumin, total protein, phosphorus, and lactate concentrations and a significant decrease in mean pH were observed at T2 (P < or = 0.05). At T3, mean Ca2+ and percent ionization had increased, but remained significantly less than resting values. Mean CaT was significantly decreased at T3, compared with values at T1 and T2. Correlation of mean Ca2+ concentration with all other measured variables at each time was evaluated; correlation coefficients between mean Ca2+ and all other variables were low (r2 < or = 0.38), indicating low biological significance.

Heart rate response and plasma lactate concentrations of horses competing in the cross-country phase of combined training events.

The exercise intensity of horses (n = 175) competing in the cross-country phase of 4 combined training events at 5 levels of competition [novice (N), training (T), preliminary (P), intermediate (I) and advanced (A)] was investigated. Environmental conditions varied from cool and humid (mean +/- s.d. temperature and humidity = 12.1 degrees C +/- 0.6 and 88.4% +/- 8.9 RH) to moderately hot and humid (27.8 degrees C +/- 2.1 and 62.5% +/- 7.8 RH). Heart rates (beats/min) were recorded continuously at 5 s intervals with a heart monitor. Mean +/- s.d. heart rates (beats/min) for each level of competition were: 154.4 +/- 19.2 beats/min (n = 45) (N), 160.4 +/- 28.1 beats/min (n = 47) (T), 160.6 +/- 33 beats/min (n = 53) (P), 181 +/- 26.6 beats/min (n = 29) (I) and 194.6 +/- 4.2 beats/min (n = 4) (A). Plasma lactate concentration was determined at rest in a random sampling of horses (n = 36) from all competitions and within 60 s of completion of the cross-country phase in all horses. Mean +/- s.d. lactate concentration at rest was 0.98 +/- 0.3 mmol/l. Mean +/- s.d. lactate concentrations (mmol/l) of horses after exercise were: N = 8.1 +/- 7, T = 11.5 +/- 4.7, P = 17.6 +/- 6.1, I = 19 +/- 6.7 and A = 21.3 +/- 7.3. Mean plasma lactate increased significantly (P < 0.001) as levels of competition increased, although there were few significant differences in heart rate between levels. Rectal temperatures were taken immediately after completion of the cross-country phase and 10 min later. Mean +/- s.d. rectal temperatures were significantly higher 10 min after completion of the cross-country than those taken immediately after cross-country (P < 0.001). Rectal temperatures 10 min after completion of exercise were significantly higher as the level of competition increased for N through I (P < 0.001). Rectal temperatures 10 min after completion of exercise were correlated with ambient temperatures (r = 0.22, P = 0.01). There was no significant correlation between either pulse or respiratory rate taken immediately after completion of exercise with heart rate during the course.

Haematological and biochemical changes in horses competing in a 3 Star horse trial and 3-day-event.

Haematological and biochemical changes in horses competing in the Endurance Test (Phase T and D) of an advanced Horse Trial (HT, n = 22) and the Endurance Test (Phases A-D) of an advanced (CCI) 3-day-event (TD, n = 11) over a similar course on the same day were studied. Environmental conditions during the event were cool (5.5-11.1 degrees C). Blood samples were collected from the horses in each group the evening prior to the Endurance Test, within 60 s after, and 10 min after, completion of Phase D (cross-country jumping). The following were determined in the blood samples and compared between the 2 groups of horses: packed cell volume (PCV), serum total protein [TP], serum albumin [ALB], plasma lactate [lactate], serum total calcium [TCa], plasma ionised calcium [Ca+2], serum inorganic phosphate [PO4], plasma pH, plasma sodium [Na], plasma potassium [K], serum chloride [Cl], serum urea nitrogen [SUN], serum creatinine [Cr] and serum glucose concentrations and aspartate aminotransferase (AST) and creatine kinase (CK) activities. The PCV and [Cr] were higher in the TD group and approached significance (P = 0.063 and P = 0.057, respectively). The [TP], [ALB], [Na], glucose concentration and CK, and AST were significantly higher and [Cl] and [PO4] were significantly lower in the TD group after exercise when compared to the HT group. It was deduced from these data that the horses competing in the 3-day-event experienced greater fluid and electrolyte losses, reduced glomerular filtration, higher glycogenolysis and had greater leakage of enzymes from working muscles during competition than horses competing in the horse trial.

Effects of shortening the steeplechase phase (phase B) of a 3-day-event.

Thirty-four horses competing in the Endurance Test of a 3-day-event were divided into 3 groups: horses in Group 1 (n = 15) competing in a 3.5 min steeplechase phase; horses in Group 2 (n = 13) in a 3 min steeplechase phase (Phase B) and horses in Group 3 (n = 6) in a 2.5 min steeplechase phase. The shortening of Phase B was associated with a lengthening of Phase C so that the total distance of the event for all horses was 14,940 m. Bodyweight (BW) was measured and total body water (TBW) and water loss estimated. Blood samples were collected from the horses prior to the Endurance Test, at the end of Phase B, the 4 km marker on Phase C (C4K), the end of Phase C, and 20 min after the completion of Phase D for measurement of packed cell volume (PCV), total plasma protein [TPP], lactate, ionised calcium, pH, sodium, potassium, chloride, total calcium and glucose concentrations, and aspartate aminotransferase, creatine kinase and lactate dehydrogenase activities. Mean +/- s.d. ambient environmental temperature during the Endurance Test was 25.3 +/- 1 degrees C (range 20.3 degrees C-29.7 degrees C). Mean relative humidity was 43.8 +/- 2.4% (range 39%-48.6%) and the average 'comfort index' (CI) was 121. There were no significant differences between the groups competing in the Endurance Test, despite the shorter Phase B. However, there were significant decreases in BW, TBW, net exchangeable cations, chloride, ionised calcium, and pH. The sodium and total calcium concentrations remained at near pre-event values. The PCV, TPP, lactate, potassium, glucose, aspartate aminotransferase, and lactate dehydrogenase activity increased during the Endurance Test, when compared to pre-event values. Horses competing in this competition experienced significant fluid and electrolyte losses, reduced glomerular filtration, increased glycogenolysis and had significant leakage of enzymes from working muscles during competition. These changes could not be reduced by shortening Phase B and lengthening Phase C.

Weight, water, and cation losses in horses competing in a three-day event.

Body weight of 48 horses competing in a 3-day event was measured the day before the event (baseline), following the dressage phase of the event (day 1), after the endurance phases of the event (day 2), and 18 to 24 hours after the endurance phases (day 3). Plasma sodium and potassium concentrations were measured the evening before, immediately after, and 10 minutes after the endurance phases. Total body water, water loss, and net exchangeable cation loss were then calculated. Body weight and total body water were significantly decreased, compared with baseline values, at all times during the event, and significant water loss was detected. The largest changes were recorded after the endurance phases of the event. Water deficits were still detected 18 to 24 hours after the endurance phases of the event. Mean plasma sodium concentration was significantly increased immediately after the endurance phases of the event, compared with concentration measured the evening before, and remained increased after the 10-minute recovery period, presumably because of dehydration. Mean plasma potassium concentration was significantly increased immediately after the endurance phases of the event, compared with concentration measured the evening before, but was not increased after the 10-minute recovery period.

Magnesium attenuates pulmonary hypertension due to hypoxia and group B streptococci.

We investigated whether hypermagnesemia alleviates hypoxic or group B streptococcal (GBS) pulmonary hypertension (PH). Hypoxic PH was induced and maintained in 14 lambs by continuous ventilation with 12% oxygen. GBS PH was induced and maintained in 16 lambs by the continuous infusion of 5-10 x 10(8) colony-forming units.kg-1.h-1 of GBS. After the onset of PH, lambs were randomized to receive either magnesium sulfate (MgSO4, intermittent boluses of 0.38 mmol/kg, with a continuous infusion of 0.15 mmol.kg-1.h-1) or a similar volume of normal saline. Hypermagnesemia lowered pulmonary arterial pressure (PAP) and delayed the fall in systemic arterial pressure and stroke volume index seen in the control animals (each P < 0.05). At a serum magnesium concentration ([Mg]) of 2.75 +/- 0.25 mmol/l, PAP was 27 +/- 3 compared with 40 +/- 4 Torr in the control animals ([Mg] = 0.87 +/- 0.06 mmol/l; P < 0.05). In the GBS PH trial, hypermagnesemia prevented the continued increase in PAP seen in the control animals. At [Mg] = 2.15 +/- 0.07 mmol/l, PAP fell 2 +/- 1 Torr from prerandomization values, whereas it rose 4 +/- 2 Torr in the control animals ([Mg] = 0.59 +/- 0.07 mmol/l; P < 0.05). However, during the same time the systemic arterial pressure fell further in the magnesium-treated animals (-19 +/- 1 vs. -2 +/- 5 Torr). MgSO4 attenuates PH in both models but may cause systemic hypotension in sepsis.

Albumin quotient, IgG concentration, and IgG index determinations in cerebrospinal fluid of neonatal foals.

Total protein (TP), albumin, and IgG concentrations were measured in CSF from the atlanto-occipital (AO) and lumbosacral (LS) sites and in serum of 15 clinically normal neonatal foals < or = 10 days old (mean, 7.0 days). The albumin quotient (AQ; CSF albumin/serum albumin x 100) and IgG index ([CSF IgG/serum IgG] x [serum albumin/CSF albumin]), indicators of blood-brain barrier permeability and intrathecal IgG production, respectively, were then calculated. Mean +/- SD values obtained from the foals of this study were: serum albumin, 2,900 +/- 240 mg/dl; serum IgG, 1,325 +/- 686 mg/dl; AO CSF total protein (TP), 82.8 +/- 19.2 mg/dl; LS CSF TP, 83.6 +/- 16.1 mg/dl; AO CSF albumin, 52.0 +/- 8.6 mg/dl; LS CSF albumin, 53.8 +/- 15.7 mg/dl; AO CSF IgG, 10.2 +/- 5.5 mg/dl; LS CSF IgG, 9.9 +/- 5.7 mg/dl; AO AQ, 1.86 +/- 0.29; LS AQ, 1.85 +/- 0.51, AO IgG index, 0.52 +/- 0.28; and LS IgG index, 0.48 +/- 0.27. Significant difference between values for the AO and LS sites was not found. A CSF albumin concentration > 85.2 mg/dl or AQ > 2.4, as determined by mean +/- 2 SD, may indicate increased blood-brain barrier permeability. An IgG index value > 1.0 may indicate intrathecal IgG production. Values obtained for foals of this study should serve as baseline for comparison in the evaluation of blood-brain barrier permeability and intrathecal IgG production in neonatal foals with neurologic disease.

Alterations in blood viscosity in horses competing in cross country jumping.

Packed cell volume and plasma total protein (TP), serum albumin (Alb) and globulin (Glb), and plasma ionized calcium (PCa) concentrations, blood viscosity (BV), and plasma viscosity (PV) were measured in 42 horses at rest and after the cross country jumping phase of a horse trial competition. The BV and PV were determined at 6 shear rates (230, 115, 46, 23, 11.5, 5.75 s-1), using a digital rotational cone and plate microviscometer. A paired t-test was used to determine differences between PCV, TP, Alb, Glb and PCa values at rest and after exercise. The PCV, TP, Alb, and Glb values increased (P < 0.05) in horses after exercise. The PCa concentration decreased (P < 0.05) in horses after exercise. Mean BV and PV in the 42 horses at rest and after exercise were fitted to an asymptotic function. Significant (P < 0.05) correlation at all shear rates was seen between BV at rest and PCV, TP, Alb, Glb, and PCa values at rest; and between BV after exercise and PCV, TP, Alb, Glb, and PCa values after exercise. Significant correlation was not seen between PV at rest and TP, Alb, Glb, and PCa at rest, or between PV after exercise and TP, Alb, Glb, and PCa concentrations after exercise at any shear rate.

Use of end-tidal CO2 tension to predict arterial CO2 values in isoflurane-anesthetized equine neonates.

End-tidal carbon dioxide tension (PetCO2) and arterial carbon dioxide tension (PaCO2) were determined and compared in isoflurane-anesthetized spontaneously breathing equine neonates. End-tidal carbon dioxide and PaCO2 values increased with respect to time. Difference between values of PetCO2 and PaCO2 increased over time. End-tidal carbon dioxide tension was useful to predict changes in and was more closely correlated with PaCO2 early in the anesthetic period (T less than or equal to 60 minutes). The dead space volume to tidal volume (Vd/Vt) ratio increased with respect to time, indicating increase in physiologic dead space in isoflurane-anesthetized foals. The data indicate that the increased difference between widening of the PetCO2 and PaCO2 values over time may have been attributable to hypoventilation and decreased pulmonary capillary perfusion of alveoli.

Chemical restraint and analgesia in the horse.

Chemical restraint in the standing horse is used for a variety of procedures in veterinary medicine. The choice of agent depends on the physical status, temperament, and size of the patient; the procedure to be performed; and safety for the patient, veterinarian, and owner. The combination of certain agents may provide more desirable restraint and analgesia than does the use of individual agents. The use of analgesics in the horse is not without side effects, some of which may be detrimental to the patient's condition. Analgesics should be chosen with these untoward effects in mind. Draft breeds possess differences that may provide a challenge to the practitioner. One such difference is their clinically apparent increased sensitivity to tranquilizers and sedative-hypnotics; consequently, reduced dose regimens for chemical restraint should be employed initially.

Work intolerance in a horse with thyroid carcinoma.

A thyroid carcinoma was diagnosed in a 14-year-old competitive trail horse with a 3-month history of work intolerance. Abnormal findings included low base-line triiodothyronine (T3) and thyroxine (T4) values, a large thyroid gland and decreased work tolerance. Nuclear medicine scanning revealed displacement of the right thyroid gland by a mass. Needle biopsy of the mass revealed neoplastic changes compatible with thyroid carcinoma. After removing the tumor surgically, T3 and T4 values returned to normal. Subsequently, the horse was able to compete successfully. Horses with work intolerance combined with a large thyroid gland may develop a thyroid carcinoma. In such horses, T3 and T4 values should be determined; if abnormal values are detected, needle biopsy and scintigraphic evaluation should be considered.

Management of thermal injuries in large animals.

The pathophysiology and histopathology of thermal burns in large animals is very similar to that in humans. Burns are classified as first degree, superficial and deep second degree, third degree, and fourth degree, depending upon the depth of thermal injury. Most severe burns will produce a local and a systemic response--both of which must be properly treated to increase the patient's chances for survival. The systemic response is mainly characterized by hypovolemia, fluid and electrolyte loss, protein loss, pulmonary edema, increased caloric requirements, and depressed immune responses. The local response is one of inflammation, vasospasm fluid accumulation, and electrolyte shifts depending upon the extent of the thermal injury. In all burn cases, the total patient should be evaluated. There is a tendency to focus on the wound, and systemic problems may be overlooked. In many cases, the thermal wound cannot be accurately evaluated for a few days, especially in large animals. An attempt should be made to estimate the depth of the burn, because treatment will vary accordingly. The treatment method must consider several problems. These include evaporative fluid and electrolyte loss, protection against mechanical injury, prevention of bacterial invasion and infection, maintenance of body temperature, and removal of nonviable tissue while leaving viable germinal tissue for healing. Thermal injuries in large animals present several additional problems. Many burns in large animals involve a large surface area, which increases the fluid, electrolyte, and caloric losses. Because most veterinary hospitals are not equipped to control the patient's surroundings, extensive bacterial contamination of the burn is of major concern. Patient restraint must also be a consideration to prevent further injury of the healing wound. Many patients are pruritic, and proper measures must be taken to prevent self-mutilation. There is also a lack of technically trained personnel to monitor and properly treat burn patients.