Haematological, serum electrolyte and blood gas effects of small volume hypertonic saline in experimentally induced haemorrhagic shock

The effects of treatment with small volume hypertonic (2400 mOsm/litre) and isotonic (300 mOsm/litre) saline on serum electrolyte and biochemical concentrations, haemograms and blood gases were evaluated in 12 horses using a haemorrhagic shock model. Intravascular catheters were placed surgically for sample collection prior to anaesthesia. Controlled haemorrhage was initiated and continued until mean systemic pressure reached 50 to 60 mmHg. Hypertonic or isotonic saline (2 litres) was administered by intravenous infusion and data collected for 2 h. Following haemorrhage, packed cell volume (PCV), haemoglobin, blood glucose concentrations and erythrocyte numbers increased whereas plasma total protein and albumin concentrations decreased. Infusion of hypertonic saline resulted in a further decrease in total protein and albumin concentrations. Glucose concentrations and other haematological variables were unaffected. Isotonic saline administration did not affect electrolyte, total protein or albumin concentrations. Concentrations of sodium and chloride were unaffected by hypotension but increased significantly following hypertonic saline treatment, exceeding normal values during the immediate post treatment period. Serum osmolality increased concurrently. No significant changes in arterial and venous blood gas values were observed with haemorrhage or isotonic saline treatment. A transient decrease in arterial and venous blood pH and a sustained decrease in venous bicarbonate and base excess concentrations occurred following hypertonic saline administration. No significant increases in any serum biochemical concentrations occurred during hypotension or following infusion of either isotonic or hypertonic saline. These results demonstrate that small volume hypertonic saline can be administered safely to horses without producing extreme changes in electrolyte concentrations, blood gases or haematological parameters.     

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.     

Hemodynamic response of endotoxemic calves to treatment with small-volume hypertonic saline solution

The hemodynamic effects of hypertonic saline solution (HSS) resuscitation on endotoxic shock were examined in pentobarbital-anesthetized calves (8 to 20 days old). Escherichia coli (055:B5) endotoxin was infused IV at dosage of 0.1 microgram/kg of body weight for 30 minutes. Endotoxin induced large decreases in cardiac index, stroke volume, maximal rate of change of left ventricular pressure (+dP/dtmax), femoral and mesenteric arterial blood flow, glomerular filtration rate, urine production, and mean aortic pressure. Severe pulmonary arterial hypertension and increased pulmonary vascular resistance were evident at the end of endotoxin infusion. Treatment with HSS (2,400 mosm of NaCl/L, 4 ml/kg) or an equivalent sodium load of isotonic saline solution (ISS: 300 mosm of NaCl/L, 32 ml/kg) was administered 90 minutes after the end of endotoxin administration. Both solutions were infused IV over a 4- to 6-minute period. Administration of HSS induced immediate and significant (P less than 0.05) increase in stroke volume and central venous pressure, as well as significant decrease in pulmonary vascular resistance. These effects were sustained for 60 minutes, after which all variables returned toward preinfusion values. The hemodynamic response to HSS administration was suggestive of rapid plasma volume expansion and redistribution of cardiac output toward splanchnic circulation. Plasma volume expansion by HSS was minimal 60 minutes after resuscitation. Administration of ISS induced significant increase in cardiac index, stroke volume, femoral arterial blood flow, and urine production. These effects were sustained for 120 minutes, at which time, calves were euthanatized. Compared with HSS, ISS induced sustained increase in mean pulmonary arterial pressure and only a small increase in mesenteric arterial blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 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)     

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.     

Haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia

In order to evaluate the haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia (RCHV), 12 trotters with RCHV were compared with 9 normovolaemic (NV) trotters. Haemodynamic data were recorded during exercise at 4 different speeds on a treadmill. Oxygen uptake was determined with an open bias flow system. Pulmonary artery pressure (PAP), systemic artery pressure (SAP), heart rate, packed cell volume (PCV) and plasma lactate and haemoglobin ([Hb]) concentrations were measured. Arteriovenous O2 content difference, cardiac output, stroke volume, pulmonary vascular resistance (PVR) and total systemic resistance (TSR) were calculated. Oxygen uptake, arteriovenous O2 content difference, heart rate, cardiac output, stroke volume, TSR and lactate did not differ between groups. The RCHV horses had significantly higher both mean diastolic and systolic PAP compared to NV horses and this difference increased with higher workload. Further, a higher SAP, PVR, PCV and [Hb] were found in RCHV horses during the course of exercise. Eleven of the RCHV horses, but none of the NV, showed exercise-induced pulmonary haemorrhage on endoscopic examination. The increase in red cell volume, resulting in a high PCV and high total blood volume, is suggested to be an important contributor to both the increased blood pressures in pulmonary and systemic circulation during exercise and to the development of exercise-induced pulmonary haemorrhage in RCHV horses.     

Effects of dobutamine on cardiovascular function and oxygen delivery in standing horses

Dobutamine is routinely used to improve cardiovascular function in anaesthetized horses. However, dobutamine in conscious horses is insufficiently investigated. Ten research horses that were already instrumented for a preceding trial were included into the study. Cardiovascular variables were recorded and blood samples taken after instrumentation (Baseline), before starting dobutamine and after 10 min of dobutamine infusion (2 µg kg⁻¹ min⁻¹). A significant increase in systemic blood pressure, mean pulmonary artery pressure and right atrial pressure, and a decrease in heart rate were observed with dobutamine compared with baseline measurements. Arterial and mixed venous haemoglobin and oxygen content, as well as mixed venous partial pressure of oxygen increased. No significant changes in cardiac output, stroke volume, systemic vascular resistance, arterial partial pressure of oxygen, or oxygen consumption, delivery and extraction ratio were detected. Concluding, dobutamine increased systemic blood pressure without detectable changes in stroke volume, cardiac output or systemic vascular resistance in conscious horses.     

Effects of slow infusion of a low dosage of endotoxin on systemic haemodynamics in conscious horses

The effects of intravenous (iv) infusion of endotoxin for 60 mins at a cumulative dosage of 0.03 micrograms/kg bodyweight on systemic arterial, right atrial and pulmonary arterial pressures, heart rate, cardiac output, and derived pulmonary vascular resistance and total peripheral vascular resistance were compared to the effects of iv infusion of saline solution in four healthy horses. Heart rate was increased significantly after endotoxin infusion, although diastolic arterial pressure, systolic arterial pressure, electronically averaged arterial pressure, cardiac output, total peripheral resistance, and right atrial pressure did not change significantly. Average pulmonary arterial pressure was increased significantly by endotoxin infusion. This was accompanied by a trend toward increased diastolic pulmonary arterial pressure (P = 0.1), systolic pulmonary arterial pressure (P = 0.08) and pulmonary vascular resistance (P = 0.07). These results suggest that low dosages of endotoxin produce pulmonary hypertension without causing hypotensive, hypodynamic shock.     

Hemodynamic Effects of Atropine, Dobutamine, Nitroprusside, Phenylephrine, and Propranolol in Conscious Horses

The authors investigated the cardiovascular effects of low doses of nitroprusside, dobutamine, and phenylephrine and a beta-adrenergic blocking dose of propranolol in conscious, healthy horses with and without prior atropine administration. A parasympathetic blocking dose of atropine produced significant increases in heart rate and arterial pressures, and decreased stroke volume, ejection fraction, pulse pressure, and right-ventricular end-diastolic pressure and volume. Cardiac output was not changed by atropine administration. Nitroprusside reduced arterial pressures to a greater extent in atropinized horses but increased heart rate in both atropinized and non-atropinized horses. Dobutamine increased mean arterial pressure in both non-atropinized and atropinized horses but increased heart rate, diastolic arterial pressure, and systemic vascular resistance only in atropinized horses. Propranolol did not affect any of the hemodynamic variables that were measured. Phenylephrine, in the presence of beta-adrenergic blockade, increased mean arterial pressure and reduced cardiac output. This study showed that low doses of nitroprusside, dobutamine, and phenylephrine produce significant hemodynamic effects in conscious, healthy horses and that these effects are modified by prevailing parasympathetic tone.     

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.     

Cardiopulmonary effects of a ketamine hydrochloride/acepromazine combination in healthy cats.

The effect of a ketamine hydrochloride/acepromazine combination on the cardiopulmonary function of 11 healthy cats was studied. Test parameters included cardiac output, measured by thermodilution, heart rate, respiratory rate, arterial blood pressure (systolic, diastolic and mean) and arterial blood gas analysis. Values for systemic vascular resistance, cardiac index and stroke volume were calculated. The cardiac output, cardiac index, stroke volume, arterial blood pressure and arterial blood pH decreased significantly (p less than 0.006). The arterial CO2 increased significantly (p less than 0.006). All changes occurred during the five to 45 minute postinduction time period. The heart rate, respiratory rate, arterial O2 and systemic vascular resistance were not significantly altered. The anesthetic regime maintained an adequate plane of surgical anesthesia for 30-45 minutes.     

Cardiovascular effects of continuous propofol infusion in horses

We examined the influence of propofol infusion on cardiovascular system at the rate of 0.14, 0.20 and 0.30 mg/kg/min in six adult Thoroughbred horses. The cardiovascular parameters were heart rate (HR), mean arterial pressure (MAP), mean right atrial pressure (MRAP), stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR), pre-ejection period (PEP) and ejection time (ET). In order to keep the ventilation conditions constantly, intermittent positive pressure ventilation was performed, and the partial arterial CO(2) pressure was maintained at 45 to 55 mmHg during maintenance anesthesia. SV showed a significant dose-dependent decrease however, CO did not show significant change. SVR decreased significantly at higher dose. PEP was prolonged and PEP/ET increased significantly at the highest dose. From these results, it became clear that SV decreases dose-dependently due to decrease of cardiac contractility during anesthesia with continuous propofol infusion in horses. On the other hand, since MAP and CO did not show significant changes, total intravenous anesthesia with propofol was suggested to be suitable for long-term anesthesia in horses.     

Hemodynamic and metabolic alterations associated with intravenous infusion of a combination of adenosine triphosphate and magnesium chloride in conscious horses.

OBJECTIVE: To determine hemodynamic and metabolic effects of IV infusion of ATP-MgCl2 combination and maximal safe IV infusion rate in conscious horses. ANIMALS: 6 adult female horses. PROCEDURE: All horses received an IV infusion of ATP-MgCl2 combination, beginning at a rate of 0.05 mg of ATP/kg of body weight/min, which was increased by 0.05 mg/kg/min increments at 10-minute intervals until a rate of 1.0 mg/kg/min was achieved. Data were collected prior to the start of the infusion, at the end of each infusion rate, and at 15-minute intervals for the next hour after discontinuation of the infusion. Measured or calculated hemodynamic variables included cardiac output, cardiac index, heart rate, stroke volume, systemic and pulmonary arterial pressures, and systemic and pulmonary vascular resistances. Arterial blood gas tensions, CBC, plasma biochemical profiles, urine volume and specific gravity, and selected clinical signs of disease also were evaluated. RESULTS: Intravenous infusion of ATP-MgCl2 significantly increased cardiac output, decreased systemic vascular resistance, and caused mild pulmonary hypertension. Magnitude of the hemodynamic alterations was dependent on rate of infusion. Maximal safe infusion rate for these horses was 0.3 mg/kg/min. All horses became lethargic, and their appetites diminished during the infusion; 5 horses had mild signs of abdominal discomfort. Flank sweating was observed in all horses as infusion rate increased. Urine volume and specific gravity and hematologic, biochemical, and arterial blood gas alterations were detected during and after infusion. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous administration of ATP-MgCl2 in healthy, conscious, adult horses caused various metabolic and hemodynamic alterations that were without appreciable detrimental effects.     

Effects of norepinephrine and a combined norepinephrine and dobutamine infusion on systemic hemodynamics and indices of renal function in normotensive neonatal thoroughbred foals

BACKGROUND: Norepinephrine is a potent vasopressor that increases arterial blood pressure but may have adverse effects on renal blood flow. The combination of norepinephrine and dobutamine may lead to improved renal perfusion compared to an infusion of norepinephrine alone. The effects of these drugs in the normotensive neonatal foal have not been reported. HYPOTHESIS: Norepinephrine increases arterial blood pressure. Adding dobutamine to a norepinephrine infusion will change the renal profile during the infusions without changing the arterial blood pressure. ANIMALS: Eight conscious Thoroughbred foals were used in this study. METHODS: Each foal received norepinephrine (0.1 microg/kg/min), combined norepinephrine (0.1 microg/kg/min) and dobutamine (5 microg/kg/min), and a control dose of saline in a masked, placebo-controlled study. Heart rate, arterial blood pressure (direct), and cardiac output (lithium dilution) were measured, and systemic vascular resistance, stroke volume, cardiac index, and stroke volume index were calculated. Urine output, creatinine clearance, and fractional excretion of sodium, potassium, and chloride were measured. RESULTS: Norepinephrine and a combined norepinephrine and dobutamine infusion increased arterial blood pressure and systemic vascular resistance and decreased heart rate and cardiac index as compared to saline. The combination resulted in higher arterial pressure than norepinephrine alone. There was no significant difference in urine output, creatinine clearance, or fractional excretion of electrolytes with either infusion as compared to saline. CONCLUSIONS AND CLINICAL IMPORTANCE: These data suggest that norepinephrine and a combined norepinephrine and dobutamine infusion cause unique hemodynamic effects without affecting indices of renal function, and this effect warrants further investigation.     

Effects of saffan on cardiopulmonary function in healthy cats.

The effects of saffan on cardiopulmonary function were evaluated in eight healthy adult cats. Measured values were cardiac output by thermodilution, heart rate by electrocardiogram, arterial blood gases, respiratory rate and systolic, diastolic and mean arterial blood pressures by arterial catheterization. Calculated values included cardiac index, stroke volume and systemic vascular resistance. Statistical analysis employed paired t-tests comparing pre saffan anesthetic induction and post saffan anesthetic parameters over a 120 minute time sequence. Thirty min after saffan induction, significant depression in cardiac output was evident while stroke volume was significantly depressed at 45 and 60 min, systolic blood pressure at 15 min and respiratory rate at 5, 10 and 15 min. No significant changes occurred in cardiac index, heart rate, arterial blood gases, diastolic and mean arterial blood pressure or systemic vascular resistance. It was concluded that saffan causes significant depression of cardiopulmonary function in normal adult cats.     

Intravenous administration of hypertonic sodium chloride solution with dextran or isotonic sodium chloride solution for treatment of septic shock secondary to pyometra in dogs.

OBJECTIVE: To determine effects of i.v. administration of hypertonic saline (7.5% NaCl) solution with 6% dextran 70 (HSSD) or isotonic saline (0.9% NaCl) solution (ISS) to dogs with septic shock secondary to pyometra. DESIGN: Prospective, randomized, clinical study. ANIMALS: 14 client-owned dogs with septic shock secondary to pyometra. PROCEDURE: Prior to emergency ovariohysterectomy, catheters were placed in pulmonary and femoral arteries of each dog to evaluate hemodynamic and oxygenation status. Immediately prior to surgery, 7 dogs received HSSD (4 ml/kg [1.82 ml/lb] of body weight, i.v.) and 7 dogs received ISS (32 ml/kg [14.54 ml/lb], i.v.) during a 5-minute period. Measurements of hemodynamic and oxygenation variables were obtained before and 5 and 20 minutes after administration of fluids. RESULTS: Mean arterial pressure (MAP) increased significantly 5 and 20 minutes after administration of HSSD, whereas ISS did not affect MAP. However, cardiac output, cardiac index, and oxygen delivery increased and hematocrit decreased after both treatments. Oxygen consumption and extraction rate and degree of acidosis did not improve after either treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous administration of small volumes of HSSD to dogs with septic shock secondary to pyometra resulted in improvement of hemodynamic and oxygenation status. Although cardiac output, cardiac index, and oxygen delivery improved after administration of a volume of ISS equal to 8 times that of HSSD, MAP increased to > 80 mm Hg only after treatment with HSSD. Administration of HSSD may be an effective treatment for septic shock in dogs.     

Effects of hypertonic saline on myocardial contractility in anaesthetized pigs

The cardiac effects of hypertonic saline (HS, 7.5% NaCl) were evaluated using a number of indices derived from the left ventricular (LV) pressurevolume relationship. Left ventricular end-systolic elastance (elastance), the slope of the endsystolic pressure-volume relationship, end-systolic elastance normalized for enddiastolic volume (elastance(_norm), the rate of rise of LV pressure (dP/dt_max), and dP/dt_max/end-diastolic volume were used to assess myocardial contractility. Pigs were anaesthetized with isoflurane and instrumented for haemodynamic measurements, LV pressure, and volume (conductance catheter) determinations. Elastance was determined during transient (8–10 s) caudal vena caval balloon occlusion. Following instrumentation, the end-tidal isoflurane concentration was reduced and maintained at 1 minimum alveolar concentration (1.5%). Pigs were randomly administered either 0.9% NaCl (n= 7) or HS (n =9) at a dose of 4 ml/kg, over 3 min into the right atrium. There were no significant differences in LV or haemodynamic measurements between isotonic saline and HS treated pigs at any time point. Elastance, elastance(_norm) and dP/dt_max/end-diastolic volume did not change in either treatment group. In contrast, dP/dt_max) increased significantly (P < 0.015) at 5 min compared to baseline after treatment with HS. End-diastolic volume increased significantly from 5 to 30 min following treatment with HS. Left ventricular end-diastolic pressure increased significantly at 5 and 60 min in HS treated pigs. Central venous and pulmonary arterial wedge pressures, and cardiac index increased significantly at 5 min after treatment with HS. Total peripheral resistance decreased significantly at 5 min, followed by a return to baseline in the HS group. These results suggest that HS is not a positive inotrope in the anaesthetized pig and that increases in cardiac index are primarily due to an increased preload.     

Effect of phenylbutazone on the haemodynamic, acid-base and eicosanoid responses of horses to sustained submaximal exertion

The systemic haemodynamic and acid-base effects of the administration of phenylbutazone (4·4 mg kg⁻¹ intravenously) to standing and running horses were investigated. Phenylbutazone, or a placebo, was administered to each of six mares either 15 minutes before, or after 30 minutes of a 60-minute submaximal exercise test which elicited heart rates approximately 55 per cent of maximal, and to the same horses at rest. The variables examined included the cardiac output, heart rate, systemic and pulmonary arterial pressures, right atrial and right ventricular pressures, and arterial and mixed venous blood gases and pH. Serum sodium, potassium and chloride concentrations, and plasma thromboxane B₂, 6-keto-prostaglandin F_1α (6-keto-PGF_1α), and prostaglandin E₂ (PGE₂) concentrations were measured in separate studies using similar protocols in the same horses. Running produced increases in heart rate, cardiac output, mean arterial and right ventricular pressure, and decreases in total peripheral resistance. The acid:base responses to exertion were characterised by respiratory alkalosis. Exertion did not significantly influence plasma 6-keto-PGF_1α or PGE₂ concentrations but plasma thromboxane B₂ concentrations were increased significantly by 60 minutes of exertion in the untreated horses. This exercise-induced increase in plasma thromboxane B₂ concentration was inhibited by the previous administration of phenylbutazone, but phenylbutazone did not produce detectable changes in systemic haemodynamic or acid-base variables in either standing or running horses.     

Effects of norepinephrine and combined norepinephrine and fenoldopam infusion on systemic hemodynamics and indices of renal function in normotensive neonatal foals

Background: Norepinephrine increases arterial blood pressure but may have adverse effects on renal blood flow. Fenoldopam, a dopamine-1 receptor agonist, increases urine output in normotensive foals. The combination of norepinephrine and fenoldopam may lead to improved renal perfusion compared with an infusion of norepinephrine alone. The combined effects of these drugs have not been reported in the horse.
Hypothesis: Norepinephrine will alter the hemodynamic profile of foals without affecting renal function. Addition of fenoldopam will change the renal profile during the infusions without changing the hemodynamic profile.
Animals: Five conscious pony foals.
Methods: Each foal received norepinephrine (0.3 μg/kg/min), combined norepinephrine (0.3 μg/kg/min) and fenoldopam (0.04 μg/kg/min), and a control dose of saline in a masked, placebo-controlled study. Heart rate (HR), arterial blood pressure (direct), and cardiac output (lithium dilution) were measured, and systemic vascular resistance (SVR), stroke volume, cardiac index (CI), and stroke volume index were calculated. Urine output, creatinine clearance, and fractional excretion of electrolytes were measured.
Results: Norepinephrine and a combined norepinephrine and fenoldopam infusion increased arterial blood pressure, SVR, urine output, and creatinine clearance and decreased HR and CI compared with saline. The combination resulted in higher HR and lower arterial blood pressure than norepinephrine alone.
Conclusions and Clinical Importance: Norepinephrine might be useful for hypotensive foals, because in normal foals, this infusion rate increases SVR without negatively affecting renal function (creatinine clearance increased). Fenoldopam does not provide additional benefit to renal function. These findings warrant further investigation.