Haemodynamic effects of small volume hypertonic saline in experimentally induced haemorrhagic shock

A comparison of the haemodynamic benefits of small volume hypertonic saline (2,400 mOsm/litre) versus isotonic saline (300 mOsm/litre) was conducted in 12 adult horses using a haemorrhagic shock model. The horses were anaesthetised and intravascular catheters placed for the measurement of haemodynamic data. Mean systemic arterial pressure was then reduced to 50 to 60 mmHg by controlled haemorrhage and maintained at that level for 40 mins. Cardiac output, stroke volume, mean systemic arterial pressure, plasma volume and urine production decreased significantly following blood loss. Hypertonic or isotonic saline was administered randomly by intravenous infusion and haemodynamic data recorded for a 2 h period. Treatment with hypertonic saline produced rapid elevations in cardiac output, stroke volume, mean systemic and pulmonary arterial pressures, cardiac contractility and urine output, and was accompanied by expansion of the plasma volume. The changes in cardiac output and stroke volume were maintained for the duration of the recording period, whereas increases in mean systemic arterial pressure were not as remarkable. Infusion of isotonic saline caused only transient increases in cardiac output and mean systemic and pulmonary arterial pressure, and cardiac output; urine output and plasma volume did not change. This study indicates that hypertonic saline produces haemodynamic improvements in experimentally induced haemorrhagic shock in horses.     

Respiratory and metabolic effects of massive administration of isotonic saline solution in heaves-affected and control horses

REASONS FOR PERFORMING STUDY: It has been suggested that rapid administration of isotonic saline solution relieves airway obstruction in heaves-affected horses, but the efficacy and tolerability of this treatment is poorly documented. OBJECTIVES: To determine the respiratory and metabolic effects of a rapid administration of isotonic saline solution in control horses and those with heaves. METHODS: Thirty litres isotonic saline solution were administered i.v. to 5 control (Group C) and 9 heaves-affected horses (Group H). Pulmonary function testing and arterial blood gas analysis were performed prior to saline infusion, at 90 and 180 mins after starting the infusion, and 1, 3, 6 and 10 days later. PCV, plasma total solids, plasma electrolytes (Na+, Cl- and K+) and venous blood gas analysis were performed prior, during and after saline infusion. RESULTS: Rapid saline administration was shown to have no beneficial effects on lung function during infusion in Group H. On the contrary, they had significantly increased pulmonary resistance (RL) at 180 mins following the initiation of saline administration compared to baseline. In Group C, saline administration resulted in a significant increase in RL at 180 mins and a significant decrease in PaO2 at 90 mins. These results suggest a transient decrement in lung function caused by rapid saline administration. Group H had a metabolic alkalosis with hypochloraemia at baseline compared to control horses. This resolved following i.v. saline administration and returned to baseline within 6 h after treatment had been discontinued. CONCLUSION: The administration of saline to Group H did not improve airway function significantly, but resulted in mild and transient side effects. POTENTIAL RELEVANCE: Rapid administration of isotonic saline alone is not an effective therapy for heaves in horses.     

Effect of hypertonic and isotonic saline solutions on plasma constituents of conscious horses.

Blood constituents and vascular volume indices were determined in 5 standing horses by use of 2-period crossover experimental design. Horses were either administered hypertonic (2,400 mosm/kg of body weight, i.v.) or isotonic (300 mosm/kg, i.v.) saline solution. Each solution was administered at a dosage of 5 ml/kg (infusion rate, 80 ml/min). Samples for determination of PCV, plasma volume, blood volume, plasma osmolality, total amount of plasma protein and plasma concentrations of protein, Na, K, and Cl were collected at 0 hour (baseline, before fluid infusion) and 0.5 hour (at the end of fluid infusion), and subsequently, at 0.25- or 0.5-hour intervals for 4.5 hours. All horses were given the predetermined dose of fluids by 0.5 hour after beginning the saline infusion. Values of P < or = 0.05 were considered significant. Administration of hypertonic saline solution was associated with decreased mean body weight by 4.5 hours, but weight change after isotonic saline administration was not significant. Other than body weight and plasma protein concentration, between-trial difference (treatment effect) was not observed for any measured variable or index. The F values indicated that increasing the number of horses would have not changed these results. A time effect was evident across both trials, so that mean (+/- SD) plasma volume increased (12.3 +/- 1.07%) and mean plasma protein concentration (-12.1 +/- 1.03%) and PCV (-11.9 + 0.67%) decreased proportionately and transiently in association with administration of either fluid at that volume. Other time effects included increased plasma osmolality and Na and Cl concentrations. Blood volume estimates and total amount of plasma protein remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Treatment of Dogs in Hemorrhagic Shock by Intraosseous Infusion of Hypertonic Saline and Dextran

Under isoflurane anesthesia, 50% of the calculated blood volume was removed from 11 dogs. After 30 minutes, five dogs were treated with hypertonic saline and dextran (HSD) (5 mL/kg) followed by isotonic saline solution (2 mL/kg) intraosseously. Six dogs (controls) received isotonic saline (7 mL/kg) intraosseously. All treatments were administered through the medullary cavity of the tibia over a 30-minute period. Cardiac output, mean arterial pressure, central venous pressure, packed cell volume, total protein, and blood gases were monitored for 4 hours. Cardiac output, mean arterial pressure, and circulating volume (indicated by packed cell volume and total protein) were significantly improved after administration of HSD. We conclude that intraosseous infusion of HSD is efficacious in treating hemorrhagic shock and believe the technique may prove to be useful in clinical situations when intravenous lines cannot be established rapidly.     

Cardiovascular and pulmonary effects of hetastarch plus hypertonic saline solutions during experimental endotoxemia in anesthetized horses

BACKGROUND: Small volume resuscitation has been advocated as a beneficial therapy for endotoxemia in horses but this therapy has not been investigated in a prospective manner. The objective of this study was to determine the cardiopulmonary effects of small-volume resuscitation using hypertonic saline solution (HSS) plus Hetastarch (HES) during experimental endotoxemia in anesthetized horses. HYPOTHESIS: Treatment of horses with induced endotoxemia using HES-HSS does not alter the response of various cardiopulmonary indices when compared to treatment with either small- or large-volume isotonic crystalloid solutions. ANIMALS: Eighteen healthy horses were randomly assigned to 1 of 3 groups. Anesthesia was maintained with halothane. Endotoxemia was induced by administering 50 microg/kg of Escherichia coli endotoxin IV. The horses were treated over 30 minutes with 15 mL/kg of balanced polyionic crystalloid solution (control), 60 mL/kg of balanced polyionic crystalloid solution (ISO), or 5 mL/kg of HSS followed by 10 mL/kg of HES (HSS-HES). METHODS: Prospective randomized trial. RESULTS: Cardiac output (CO) after endotoxin infusion increased significantly (P < .05) from baseline in all groups, whereas mean central venous pressure increased significantly (P < .05) in the ISO group only. Mean pulmonary artery pressure increased from baseline (P < .05) in horses treated with isotonic fluids and HSS-HES. There was no effect of treatment with HSS-HES on CO, systemic vascular resistance (SVR), mean arterial pressure, blood lactate concentrations, or arterial oxygenation. CONCLUSIONS AND CLINICAL IMPORTANCE: The use of HSS-HES failed to ameliorate the deleterious hemodynamic responses associated with endotoxemia in horses. The clinical value of this treatment in horses with endotoxemia remains unconfirmed.     

Effect of hydroxyethyl starch solution in normal horses and horses with colic or acute colitis

Hydroxyethyl starch (HES) solution is an effective colloidal infusion solution in humans for treatment of hypovolaemic shock, but it has not been compared with fluids currently available for use in horses. On the basis of plasma-expanding effect of HES in normal horses, a 10% medium-molecular 200/0.5 solution of HES was subsequently tested in hypovolaemic horses. Six normal horses were given five protocols of a single infusion of HES at varying dosage rates (5, 10, 15 ml HES/kg), as well as isotonic saline (15 ml/kg) and hypertonic saline (4 ml/kg b.w.). Dehydrated horses suffering from acute colitis or those which had been treated surgically for ileus of the small or large intestine were given an i.v. infusion of 10 ml HES/kg in combination with 10 ml saline/kg. Clinical data and blood samples for testing were taken before the infusion, and then 10 min, 1 h, 2, 4, 6, 8, 10, 12 and 24 h after infusion (a.i.). A significant decrease in haematocrit was observed in protocol 1-5 for a period of up to 4, 4, 10 h, 10 min and up to 10 min; in group of colitis, during the entire 24-h testing period, and in groups of ileus of small intestine and of large intestine, up to 4 and 10 h a.i. HES decreases better and longer-lasting haematocrit and total protein than either isotonic or hypertonic saline. Half-life of HES increases due to higher dosage (5.83, 7.63 and 11.48 h) and distribution is exclusively intravascular. In normal horses of protocol 1-3 using HES aPTT, sodium and potassium were within the physiological range. Serum amylase activity is increased in horses using HES. On the basis of this clinical study, the decreasing effect of urea and creatinine in colic patients after surgery and fewer instances of postoperative ileus a dosage of 10 ml HES/kg could be recommended.     

Influence of preinduction methoxamine, lactated Ringer solution, or hypertonic saline solution infusion or postinduction dobutamine infusion on anesthetic-induced hypotension in horses

A controlled study of the cardiovascular responses in horses anesthetized with acepromazine (0.05 mg/kg of body weight, IV), guaifenesin (100 mg/kg, IV), thiamylal (5.0 mg/kg, IV), and halothane in O2 (1.2 to 1.4% end-expired concentration) was performed to determine whether hypotension could be prevented by use of various treatments. Six horses were given 5 treatments in a randomized sequence: no treatment (control), methoxamine (0.04 mg/kg, IV), lactated Ringer solution (20.0 ml/kg, IV), 7.5% hypertonic saline solution (4.0 ml/kg, IV), or constant infusion of dobutamine (5.0 mg/kg/min, IV) during anesthesia. Heart rate, ECG, blood pressure, central venous pressure, cardiac output, blood gas analysis, PVC, and plasma total protein concentration were measured during the study. Compared with the control value, an increase in blood pressure during halothane administration was observed after administration of lactated Ringer solution, hypertonic saline solution, or dobutamine (P less than 0.05). The improved blood pressure response to hypertonic saline solution and dobutamine was related to an increase in cardiac output, which was statistically significant (P less than 0.05). Other statistically significant differences in cardiopulmonary responses among treatments were not observed during anesthesia. The PCV was increased in response to dobutamine infusion, and plasma total protein concentration was reduced in response to administration of hypertonic saline or lactated Ringer solution.     

Effect of suckling isotonic or hypertonic solutions of sodium bicarbonate or glucose on abomasal emptying rate in calves

OBJECTIVE: To determine and compare the abomasal emptying rates in calves suckling milk replacer or an isotonic or hypertonic solution of NaHCO(3) or glucose. ANIMALS: 5 male Holstein-Friesian calves that were < 30 days of age. PROCEDURES: Calves were fed 2 L of milk replacer or isotonic (300 mOsm/L) or hypertonic (600 mOsm/L) solutions of NaHCO(3) or glucose containing acetaminophen (50 mg/kg). Venous blood samples and transabdominal ultrasonographic abomasal dimensions were obtained periodically after feeding, and abomasal luminal pH was continuously monitored by placement of a luminal pH electrode through an abomasal cannula. Abomasal emptying rate was assessed by the time to maximal plasma acetaminophen concentration, ultrasonographic determination of the half-time of abomasal emptying, and the time for luminal pH to return to within 1 pH unit of the preprandial value. RESULTS: Hypertonic NaHCO(3) solution was emptied slower than an isotonic NaHCO(3) solution, isotonic glucose solution was emptied slower than an isotonic NaHCO(3) solution, and hypertonic glucose solution emptied slower than an isotonic glucose solution. CONCLUSIONS AND CLINICAL RELEVANCE: An electrolyte solution for oral administration with a high osmolarity and glucose concentration may lead to a slower resuscitation of dehydrated diarrheic calves because such solutions decrease the abomasal emptying rate and therefore the rate of solution delivery to the small intestine. Whether slowing of the abomasal emptying rate in dehydrated diarrheic calves suckling an oral electrolyte solution is clinically important remains to be determined.     

Furosemide and sodium bicarbonate-induced alkalosis in the horse and response to oral KCl or NaCl therapy

Metabolic alkalosis was induced in 10 clinically normal horses by administration of furosemide (1 mg/kg of body weight, IM) followed 4.5 hours later by sodium bicarbonate (NaHCO3; 500 g in 8 L water) via nasogastric tube. Furosemide diuresis resulted in a mean weight loss of 21.1 kg, which was associated with small, but significant, increases in venous blood pH, bicarbonate, and plasma protein concentrations (P less than 0.001), while plasma potassium, chloride, and calcium concentrations declined significantly (P less than 0.001). Oral administration of the hypertonic NaHCO3 solution resulted in clinical evidence of hypovolemia, which was accompanied by a marked increase (P less than 0.001) in plasma protein concentration. Seven of the 10 horses developed signs of neuromuscular excitability, as evidenced by muscle fasciculations, and 5 of the horses developed diaphragmatic flutter. Hypernatremia was transiently induced, but it resolved as the horses were allowed access to water. The alkalosis induced by furosemide and NaHCO3 was profound and persisted for a 24-hour period and was associated with marked hypochloremia and hypokalemia. Partial replacement of the electrolyte deficits and correction of the metabolic alkalosis was attempted, using 1,000 mEq of NaCl or KCl given as an isotonic solution via nasogastric tube. In the KCl-treated group, there was a prompt and significant decline in venous blood pH and bicarbonate concentration (P less than 0.001) accompanied by a significant increase in plasma potassium concentration (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a hypertonic saline solution and dextran 70 combination in the treatment of diarrhoeic dehydrated calves

Thirty dehydrated diarrheic calves aged 2-45 days were used to study the effects of small volume intravenous 7.2% hypertonic saline and 6% dextran 70 solution in combination with alkalinising oral fluids and to compare this therapy with the large volume intravenous isotonic saline with alkalinising oral fluid treatment. This study included a total of 30 diarrhoeic dehydrated calves aged 2-45 days. After routine clinical and haematological examinations, the calves were allotted to two treatment groups. Isotonic saline solution (32 ml/kg, i.v.) with an oral electrolyte solution (22 ml/kg, p.o.) were administered to group I (control), and the combination of 7.2% hypertonic saline in 6% dextran 70 solutions (HSD) (4 ml/kg, i.v.) with an oral electrolyte solution (50 ml/kg, p.o.) were administered to group II (test). Additionally, an oral electrolyte solution (50 ml/kg, p.o.) was readministered to both groups at 12 h of the study. The clinical and haematological examinations of all calves were performed both before and after the treatment at the 1/2, 1, 2, 4, 12 and 24 h. The capillary refill time, peripheral pulse quality, dehydration degrees, mental status, haematocrit rates, haemoglobin and plasma values after treatment were found to be statistically different compared with the values before treatment. In comparison with group I, group II is observed to have shorter capillary refill time at 1, 4 and 12 h (P < 0.001) and better peripheral pulse quality at 1/2 (P < 0.05), 1, 2, 4 and 12 h (P < 0.001). Moreover, the degree of dehydration in group II, was significantly improved at 2 (P < 0.01), 4 and 12 h. Results of the study indicated that administration of low volumes of hypertonic sodium chloride and dextran 70 solution combinations with oral electrolyte solutions was concluded as quicker, practical, economical and most importantly an effective way for the treatment of dehydrated diarrhoeic calves.     

Hypertonic saline.

A key feature in the successful resuscitation of dehydrated or endotoxemic ruminants is the total amount of sodium administered. Administration of small volumes of HS and HSD offer major advantages over large volumes of isotonic saline because HS and HSD do not require intravenous catheterization or periodic monitoring, and are therefore suitable for use in the field. Hypertonic saline and HSD exert their beneficial effect by rapidly increasing preload and transiently decreasing afterload. Contrary to early reports, HS and HSD decrease cardiac contractility and do not activate a pulmonary reflex. The osmolality of HS and HSD should be 2400 mOsm/L (7.2% NaCl solution, 8 times normal plasma osmolality). Use of HS and HSD solutions of different osmolality to 2400 mOsm/L should be avoided at all costs, as too low a tonicity removes the main advantages of HS (low cost, decreased infusion time), whereas too high a tonicity may cause rapid vasodilation and decreased cardiac contractility, resulting in death. Rapid administration (> 1 mL/kg-1/min-1) of HS (2400 mOsm/L) should be avoided, as the induced hypotension may be fatal when coupled with a transient decrease in cardiac contractility. For treating dehydrated adult ruminants, HS (2400 mOsm/L, 4-5 mL/kg i.v. over 4-5 minutes) should be administered through the jugular vein and the cow allowed to drink water. This means that 2 L of HS should be administered to adult cattle. HSD should be administered in conjunction with isotonic oral electrolyte solutions to all calves 8% or more dehydrated (eyes recessed > or = 4 mm into the orbit, cervical skin tent duration > 6 seconds) or calves with reduced cardiac output (fetlock temperature < 29 degrees C when housed at 10-24 degrees C). For treating dehydrated calves, HSD (2400 mOsm/L NaCl in 6% dextran-70, 4-5 mL/kg i.v. over 4-5 minutes) should be administered through the jugular vein and the calf allowed to suckle an isotonic oral electrolyte solution. This means that 120-200 mL of HSD of HSD should be administered to a calf. HSD should be routinely administered to severely depressed or comatose calves, as HSD provides the fastest method of resuscitation while rapidly reversing the effects of hyperkalemia.     

Preoperative administration of hydroxyethyl starch or hypertonic saline to horses with colic

BACKGROUND: Hypertonic saline and hydroxyethyl starches have been proposed as alternatives to isotonic crystalloids for reversal of hypovolemia in horses with colic. However, no direct comparison of these fluids has been performed in a clinical setting. HYPOTHESIS: Preoperative administration of hypertonic saline or pentastarch would produce similar effects on intra operative hemodynamics in horses with colic. ANIMALS: Thirty horses requiring colic surgery were enrolled in this prospective, randomized, open-label clinical trial. Inclusion criteria were owner consent, and at least 2 of 3 clinicopathologic abnormalities: packed cell volume >45%, plasma total solid concentration >8.0 g/dL, and blood lactate concentration >2.5 mM. METHODS: Study horses were randomly assigned to receive 4 mL/kg hypertonic saline or pentastarch before induction of anesthesia. Hemodynamic measurements were recorded every 30 minutes during anesthesia. Cardiac output (CO) was measured by the lithium dilution method. CO and stroke volume (SV) were indexed by body weight. Data were analysed using repeated measures analysis of variance (ANOVA). Post hoc comparisons were performed using the Bonferroni test. RESULTS: Cardiac index (CI) was higher in the pentastarch group compared with the hypertonic saline group from 30 to 150 minutes after induction (P = .04). SV index was higher in the pentastarch group at 30 (P = .025) and 60 minutes (P = .04). Mean arterial pressure of horses in both groups was lower at 90 minutes compared with 30 and 60 minutes. CONCLUSIONS AND CLINICAL IMPORTANCE: Preoperative administration of pentastarch results in better CI than hypertonic saline, for 150 minutes after anesthetic induction. The effect of this improved global blood flow on regional perfusion or clinical outcome remains to be elucidated.     

The effect of 7.2% hypertonic saline solution on the duration of sodium gradient between the cerebrospinal fluid and the venous circulation in the dog

To determine the duration of water movement from cerebrospinal fluid (CSF) into venous blood by the infusion of 7.2% hypertonic saline solution (HSS), the sodium gradient between venous blood and CSF were examined. Venous sodium concentrations remained higher than that in CSF for duration of 60 min following HSS infusion. By 90 min, the CSF sodium concentration reached the equilibrium with venous sodium concentration. Those data suggests that the duration of time during which water moved from CSF into capillaries in brain by the gradient of sodium concentration was less than 90 min.     

Iatrogenic hypocalcaemia during parenteral fluid therapy of diarrhoeic calves

Acid-base balance and electrolyte concentrations, including ionised calcium, were monitored during intravenous fluid therapy of 11 collapsed diarrhoeic suckler calves aged five to 10 days. Six healthy calves of similar age and type were used to provide control data. All the diarrhoeic calves were severely acidotic (TCO2<12 mmol/litre). Isotonic sodium bicarbonate (1-3 per cent) was administered until the metabolic acidosis was half corrected, as indicated by the TCO2 increasing to 17 to 24 mmol/litre when the infusion was changed to an extracellular volume replacement fluid containing 144 mmol/litre Na+, 35 mmol/litre HCO3-, 4 mmol/litre K+ and 113 mmol/litre Cl- which was administered until the calf was discharged. Milk feeding was started as soon as the calf had a suck reflex. The treatment was successful in 10 calves. At admission the diarrhoeic calves were hypocalcaemic compared with the control calves, but their ionised calcium was significantly higher, with significantly less calcium being protein bound. Treatment with isotonic sodium bicarbonate resulted in a significant improvement in acid-base balance, but both total and ionised calcium decreased significantly, the decrease in ionised calcium being proportionately greater owing partly to a significant increase in the protein binding of calcium. The mean total, bound and ionised calcium concentrations were all significantly lower in the treated calves after they had received isotonic sodium bicarbonate than in the control calves. Further treatment with replacement fluid had no significant effect on any of the parameters apart from pCO2 which increased significantly. Milk feeding had no significant effect on plasma calcium concentrations. The calves' mean ionised calcium concentration was significantly lower at the end of the treatment than before it, but there was no difference in the mean total and bound calcium concentrations. The calves' mean plasma potassium and magnesium concentrations decreased significantly during the course of the treatment.     

Cardiovascular effects of 7.2% hypertonic saline solution in halothane anaesthetized ponies

The haemodynamic effects of intravenously (iv) administered hypertonic saline solution (7.2%, 4 ml/kg of body weight [bwt]) were investigated in normovolaemic ponies during halothane anaesthesia (dorsal recumbent position, intermittent pressure ventilation). Heart rate, arterial blood and pulmonary artery pressures, cardiac output, and arterial blood gases were measured throughout the experiment while related haemodynamic parameters (cardiac index, systemic and pulmonary vascular resistance, stroke volume, ventricular work) were calculated.
A transient decrease in arterial blood pressure occurred during the administration of the hypertonic solution. Significant increases in cardiac output and index, stroke work, and systolic arterial pressure were observed 5 min after the administration of the hypertonic infusion. A gradual normalization of the increased parameters occurred afterwards. Heart rate and arterial blood gases remained constant throughout the study. No clinical side-effects, except for an increase in urinary production in the recovery period, were seen during and after anaesthesia.     

Effects of small- and large-volume resuscitation on coagulation and electrolytes during experimental endotoxemia in anesthetized horses

BACKGROUND: Small-volume resuscitation (SVR) has been advocated in place of large-volume isotonic resuscitation for the treatment of endotoxemia in horses. The effects of this type of therapy during experimental endotoxemia on electrolytes and coagulation have not been evaluated in the horse. As part of a larger project, the objective of this study was to determine the effects of SVR (hypertonic saline solution [HSS] plus hetastarch [HES]) on coagulation and serum electrolytes concentration, and to compare SVR with large- and small-volume isotonic resuscitation during experimental endotoxemia in anesthetized horses. HYPOTHESIS: SVR does not affect coagulation parameters or serum electrolyte concentrations when compared with either small- or large-volume isotonic crystalloids. ANIMALS: Horses were randomly assigned to 1 of 3 groups. Under halothane anesthesia, endotoxemia was induced by administering 50 microg/kg Escherichia coli endotoxin i.v. The horses were treated for 30 minutes with 15 mL/kg of balanced polyionic crystalloid solution (control), 60 mL/kg of balanced polyionic crystalloid solution (ISO), or 5 mL/kg of HSS followed by 10 mL/kg HES (HSS-HES). METHODS: Prospective randomized trial. RESULTS: Significant differences in coagulation parameters were not found among the groups. Thrombocytopenia was severe in all 3 groups. Serum ionized calcium concentration significantly decreased from baseline in control and ISO groups but not in the HSS-HES group. CONCLUSIONS AND CLINICAL IMPORTANCE: These results suggest that the HSS-HES combination, at the dosage used in this study had no adverse effects on coagulation beyond those produced by endotoxemia. HSS-HES may have a protective effect against endotoxemia-induced ionized hypocalcemia.     

Circulatory and blood gas changes accompanying the development and treatment of induced laminitis

A peripheral vasodilatory agent, isoxsuprine hydro-chloride, was evaluated in a controlled study for its efficacy in the treatment of acute equine laminitis. Eight healthy, adulthorses of variable age and sex were used in the trial. Acute laminitis was induced in 5 of the horses by oral carbohydrate overload. Intravenous isoxsuprine therapy (1.8 mg/kg) was initiated in 3 of the horses receiving carbohydrate overload at first sign of clinical lameness and repeated at 12-hour intervals. Intravenous saline placebos were administered on a similar schedule to 2 control horses which also received a carbohydrate overload. The remaining 3 horses served as further controls. Local and systemic responses to induction of laminitis and isoxsuprine administration were assessed by subjective evaluation of clinical lameness in a double blind trial; nuclear scintigraphy and radiography of the distal forelimbs; and assessment of physical, hematological and biochemical parameters.

Pronounced tachycardia, hypotension and sweating accompanied the intravenous infusion of isoxsuprine. The 3 horses treated with isoxsuprine following the induction of laminitis showed a more rapid improvement in soundness than horses receiving saline placebos. No horse developed rotation of the third phalanx in response to the diet Nuclear scintigraphy indicated that blood perfusion patterns within the hoof of laminitic horses altered with isoxsuprine therapy, but an overall increase or decrease in perfusion was not apparent. Alterations in serum enzyme and electrolyte profiles with the onset of laminitis generally concurred with findings previously reported for this model of the disease. No change in coagulation profiles accompanied the onset of laminitis or isoxsuprine administration. Blood gas analysis indicated an increase in median palmar vein oxygen partial pressure (PO₂) levels with onset of laminitis. A concurrent decrease in the median palmar arteriovenous oxygen partial pressure difference (AVO₂) was significant at the P<0.01 level. There was no difference in median palmar vein PO₂ values between thoseanimals receiving isoxsuprine and those receiving saline placebo therapy. Results of the trialindicated that isoxsuprine may be beneficial in the treatment of acute laminitis. Further controlled studies are appropriate.     

Effect of hypertonic vs isotonic saline solution on responses to sublethal Escherichia coli endotoxemia in horses

Cardiovascular responses to sublethal endotoxin infusion (Escherichia coli, 50 micrograms/ml in lactated Ringer solution at 100 ml/h until pulmonary arterial pressure increased by 10 mm of Hg) were measured 2 times in 5 standing horses. In a 2-period crossover experimental design, horses were either administered hypertonic (2,400 mosm/kg of body weight, IV) or isotonic (300 mosm/kg, IV) NaCl solution after endotoxin challenges. Each solution was administered at a dose of 5 ml/kg (infusion rate, 80 ml/min). Complete data sets (mean arterial, central venous, and pulmonary arterial pressures, pulmonary arterial blood temperature, cardiac output, total peripheral vascular resistance, heart rate, plasma osmolality, plasma concentration of Na, K, Cl, and total protein, blood lactate concentration, and PCV) were collected at 0 (baseline, before endotoxin infusion), 0.25, 1, 1.5, 2, 2.5, 3, 3.5, 4, and 4.5 hours after initiation of the endotoxin infusion. Blood constituents alone were measured at 0.5 hour and cardiovascular variables alone were evaluated at 0.75 hour. By 0.25 hour, endotoxin infusion was completed, a data set was collected, and saline infusion was initiated. By 0.75 hour, saline solutions had been completely administered. Mean (+/- SEM) cardiac output decreased (99.76 +/- 3.66 to 72.7 +/- 2.35 ml/min/kg) and total peripheral resistance (1.0 +/- 0.047 to 1.37 +/- 0.049 mm of Hg/ml/min/kg) and pulmonary arterial pressure (33.4 +/- 0.86 to 58.3 +/- 1.18 mm of Hg) increased for both trials by 0.25 hour after initiation of the endotoxin infusion and prior to fluid administration. For the remainder of the protocol, cardiac output was increased and total peripheral resistance was decreased during the hypertonic, compared with the isotonic, saline trial.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of xylazine on cerebrospinal fluid pressure in conscious horses.

Lumbosacral CSF pressure was measured in 6 horses via a catheter inserted through the lumbosacral space. Heart rate, facial artery pressure, central venous pressure, and CSF pressure were measured before IV injection of a saline solution control, for 15 minutes after saline solution injection, and for 60 minutes after the IV injection of 1.1 mg of xylazine/kg of body weight. Arterial pH and blood gases were analyzed before saline solution injection, 15 minutes after saline solution injection, and at 15, 30, and 60 minutes after xylazine injection. Constant craniocervical posture was maintained during sedation. Lumbosacral CSF pressure was significantly decreased for 15 minutes after xylazine injection. Diastolic arterial pressure was significantly increased 4 minutes after xylazine administration and diastolic and mean arterial pressure were increased at 6 and 8 minutes after xylazine administration. Small increases in systolic arterial blood pressure and central venous pressure, and a small decrease in heart rate were observed. There were no significant differences in the arterial blood gas values. It was concluded that IV injection of xylazine causes a decrease in intracranial pressure in healthy conscious horses. The effects may be different in horses with neurologic disease or cerebral trauma.     

Effects of continuous rate intravenous infusion of butorphanol on physiologic and outcome variables in horses after celiotomy

A randomized, controlled, blinded clinical trial was performed to determine whether butorphanol administered by continuous rate infusion (CRI) for 24 hours after abdominal surgery would decrease pain and surgical stress responses and improve recovery in horses. Thirty-one horses undergoing exploratory celiotomy for abdominal pain were randomly assigned to receive butorphanol CRI (13 microg/kg/h for 24 hours after surgery; treatment) or isotonic saline (control). All horses received flunixin meglumine (1.1 mg/kg IV q12h). There were no significant differences between treatment and control horses in preoperative or operative variables. Treatment horses had significantly lower plasma cortisol concentration compared with control horses at 2, 8, 12, 24, 36, and 48 hours after surgery. Mean weight loss while hospitalized was significantly less for treatment horses than control horses, whether expressed as total decrease in body weight (13.9+/-3.4 and 27.9+/-4.5 kg, respectively) or as a percentage decrease in body weight (2.6+/-0.7 and 6.3+/-1.1%, respectively). Treatment horses were significantly delayed in time to first passage of feces (median times of 15 and 4 hours, respectively). Treatment horses had significantly improved behavior scores during the first 24 hours after surgery, consistent with the conclusion that they experienced less pain during that time. Butorphanol CRI during the immediate postoperative period significantly decreased plasma cortisol concentrations and improved recovery characteristics in horses undergoing abdominal surgery.