Arterial lactate concentration, hospital survival, sepsis and SIRS in critically ill neonatal foals.

REASONS FOR PERFORMING STUDY: Blood lactate concentration has been shown to be a useful clinical indicator in human patients, but has not been formally investigated in critically ill foals. OBJECTIVE: To investigate the association of blood lactate with hospital survival, markers of cardiovascular status, metabolic acid base status, sepsis and systemic inflammatory response syndrome (SIRS). METHODS: A database containing clinical, haematological, plasma biochemical and hospital outcome data on neonatal foals referred to an intensive care unit in 2000-2001 was analysed. Seventy-two foals for which arterial lactate was measured at admission were included in the study. RESULTS: Sixty-one foals had an admission lactate concentration > 2.5 mmol/l. Admission lactate was statistically associated with hospital survival, mean arterial pressure, blood creatinine concentration, bacteraemia, anion gap, lactate concentration at 18-36 h after admission and evidence of SIRS, but not with packed cell volume or heart rate. Lactate at 18-36 h was also associated with survival and evidence of SIRS. Anion gap, base excess, base excess due to unidentified anions (BEua), simplified strong ion gap or bicarbonate correctly classified foals for presence of hyperlactaemia (> 5 mmol/l) in < or = 80% of animals. CONCLUSIONS: Admission blood lactate gives important prognostic information. Lactate should be measured rather than assumed from the anion gap, base excess, BEua, simplified strong ion gap or bicarbonate. POTENTIAL RELEVANCE: Blood lactate concentrations at admission are clinically relevant in neonatal foals and warrant further investigation. This should include the clinical value of measuring changes in lactate in response to treatment.

Clinical assessment of gas exchange in mature horses.

There are limited methods of assessing pulmonary function in horses at rest. We developed clinical techniques to measure gas exchange efficiency in horses and evaluated 3 groups of horses that were 1) asymptomatic based on auscultation with rebreathing, transtracheal aspirate cytology, and thoracic radiographs (n = 6), 2) asymptomatic at rest but symptomatic with rebreathing (n = 11) and 3) symptomatic at rest (n = 9). Blood samples were obtained from the transverse facial artery and jugular vein. Maximal end-tidal CO2 tension (PETCO2) was measured by an infrared capnograph through a facemask. Alveolar O2 tension, dead space fraction (V(D)/V(T)), and physiological shunt fraction (Q(S)/Q(T)) were calculated using standard formulae. Arterial O2 tension in Group 1 horses (mean +/-s.d.103+/-3 mmHg) was significantly higher than in Group 2 or Group 3 horses. Q(S)/Q(T) in Group 1 horses (0.37+/-0.98%) was significantly lower than in Group 2 and Group 3 horses. Mean +/-s.d.V(D)/V(T) in Group 1 horses (-18.2+/-3.1) was significantly lower than Group 3 horses but not Group 2 horses.

Cardiopulmonary changes associated with abdominal insufflation of carbon dioxide in mechanically ventilated, dorsally recumbent, halothane anaesthetised horses.

The use of laparoscopy for the diagnosis or therapeutic management of abdominal disease in the horse has distinct advantages when it allows the horse to remain standing. However, distending the abdomen by insufflation of a biologically active gas in an anaesthetised horse may add to the physiological challenge of general anaesthesia and recumbency. The cardiopulmonary responses to abdominal insufflation with carbon dioxide (CO2) to 15 mmHg pressure were evaluated in 6 horses in dorsal recumbency anaesthetised with halothane in oxygen and subjected to laparoscopic colopexy. Vaporiser settings targeted a fractional expired halothane of 1.5 MAC and a clinically acceptable depth of anaesthesia. Pressure and rate controlled positive pressure ventilation was adjusted to an ETCO2 of 35 mmHg before abdominal insufflation and was not changed thereafter. Cardiopulmonary data were collected before, at 30 and 60 min during and 30 min after CO2 insufflation. ANOVA for repeated measures followed by Tukey's protected t test were used to determine differences. Partial pressure of oxygen and pH of arterial blood, tidal volume and systemic vascular resistance decreased during abdominal insufflation and laparoscopic surgery whereas mean arterial blood pressure, right atrial pressure, cardiac index, stroke index, partial pressure of CO2 in arterial blood and end tidal respiratory gases, and calculated physiological shunt increased significantly. Only systemic vascular resistance returned to the pre-insufflation level after desufflation. The hypercapnia, acidosis and apparent increase in cardiac work that accompany CO2 pneumoperitoneum for laparoscopic surgery could place the anaesthetised horse at additional risk of perioperative complications.

Comparison of lithium dilution and thermodilution cardiac output measurements in anaesthetised neonatal foals.

Knowledge of cardiac output is expected to help guide the treatment of hypotension associated with critical illness and/or anaesthesia in neonatal foals. However, a practical and safe method of measuring cardiac output has not been described for the foal. Lithum dilution, a new method of cardiac output determination not requiring cardiac catheterisation, has recently been reported in mature horses. We compared this method to thermodilution in isoflurane-anaesthetised foals age 30-42 h and found good agreement between the 2 methods in a range of cardiac outputs 5.4-20.4 l/min. The lithium dilution technique is a practical and reliable method of measuring cardiac output in anaesthetised neonatal foals, and warrants investigation in critically ill conscious foals.

Treatment of ischaemic jejunum with topical and intraluminal Carolina Rinse.

Carolina Rinse Solution (CRS) was applied topically and intraluminally to ischaemic (Group 1; n = 5) and distended equine jejunum (Group 2; n = 5). Mesenteric blood flow, ORC (osmotic reflection coefficient), wet weight to dry weight ratios (WW/DW), serosal thickness, and neutrophil accumulation in the serosa were measured. After 60 min ischaemia followed by reperfusion (Group 1), mesenteric blood flow remained greater than baseline values. The mean ORC was similar to that previously reported in normal bowel or ischaemic intestine treated with CRS by arterial perfusion. The ORC after distention and decompression (Group 2) increased and was similar to that previously reported in a comparable untreated experimental model. The WW/DW after both ischaemia and distention increased compared to specimens collected from noninstrumented jejunum proximal to the experimental segments in the same horses. There was no difference in neutrophil numbers in the serosa of either ischaemic or distended intestine compared to the noninstrumented proximal jejunum. CRS-treated ischaemic intestine maintained microvascular permeability similar to that reported for normal intestine whereas treated distended intestine did not. Combined topical and intraluminal application of CRS to ischaemic intestine may reduce complications due to acute inflammation during reperfusion.

Effects of intraluminal distention and decompression on microvascular permeability and hemodynamics of the equine jejunum.

OBJECTIVE: To determine whether intraluminal distention and subsequent decompression of the equine jejunum affects intestinal blood flow, hemodynamics, and microvascular permeability. ANIMALS: 5 healthy adu t horses. PROCEDURES: Horses were anesthestized and underwent exploratory laparotomy. Two jejunal segments were identified as sham-operated or instrumented segments. After baseline values were obtained, intraluminal distention was created in the experimental segment to induce an ntraluminal pressure of 18 cm H2O. After 120 minutes of distention, the intestine was decompressed for 120 minutes. Mesenteric blood flow, oxygen delivery, oxygen consumption, microvascular permeability, wet weight-to-dry weight ratio, neutrophil infiltration, and vascular resistance were determined and comparisons made among control, sham-operated, and experimental segments. RESULTS: Mean jejunal blood flow was 21.4 ml/min per kg. There was a significant decrease in mesenteric bood flow to the distended intestine (13.4 ml/min per kg). Blood flow increased significantly during the decompression period (340% of baseline blood flow). Intraluminal distention and subsequent decompression resulted in a significant increase in microvascular permeability, as determined by the osmotic reflection coefficient. Oxygen delivery and oxygen content decreased significantly during the distention period and increased during decompression. Morphologic evaluation revealed a significant increase in edema and neutrophil infiltration after distention and decompression, compared with results for the sham-operated or control segments. CONCLUSIONS AND CLINICAL RELEVANCE: Intraluminal distention and decompression of the equine jejunum results in low-flow ischemia and edema, which may contribute to adhesions and ileus in the postoperative period after surgery for obstructions of the small intestines.

Effect of preanesthetic medication on ease of endoscopic intubation of the duodenum in anesthetized dogs.

The effects of preanesthetic medication on ease of duodenal endoscopic intubation in dogs was evaluated. One of 12 combinations of preanesthetic medications (using atropine, glycopyrrolate, morphine, meperidine, acepromazine, and 0.9% NaCl solution) was administered IM to each of 12 dogs in a trial. Twelve endoscopic trials were performed so that each dog received each treatment combination once. Anesthesia was induced with thiamylal administered IV and maintained with halothane vaporized in oxygen. Electrocardiographic recordings, indirect blood pressure measurements, end-tidal carbon dioxide partial pressures, and halothane concentrations were monitored during the anesthetic period. The ease with which the fiberoptic endoscope was passed into the proximal portion of the duodenum was qualitatively score on the basis of time and maneuvering effort. None of the preanesthetic combinations made intubation of the duodenum significantly easier than that with 0.9% NaCl solution (control). Only the combination of morphine and atropine induced gastro-pyloric conditions that resulted in significantly higher (more difficult) endoscopic scores than those after preanesthetic medication with 0.9% NaCl solution.

Consolidating pneumonia and pneumothorax in a horse.

A 3-year-old Thoroughbred mare with signs of acute abdominal pain and chronic pneumonia was found to have pneumothorax. A single application of suction was successful in resolving the pneumothorax. The underlying pneumonia was treated with long-term antibiotic administration selected on the basis of results of bacteriologic culture and antimicrobial susceptibility testing of a transtracheal aspirate. The pneumonia resolved, and the mare returned to competition as a show hunter.

A review of the pathophysiology of exercise-induced pulmonary haemorrhage in the equine athlete.

In the United States, more than 75% of equine athletes are reported to suffer from exercise-related haemorrhage of the respiratory tract (Voynick and Sweeney, 1986; Sweeney et al., 1990). Fiberoptic endoscopy has traced the source of blood to beyond the bifurcation of the trachea. In 1981, the term exercise-induced pulmonary haemorrhage (EIPH) was introduced (Pascoe et al., 1981). Racehorses of all breeds, polo ponies and three-day event horses of mixed heritage, even foxhunters, may 'bleed' (Voynick and Sweeney, 1986; Pascoe et al., 1981; Sweeney and Soma, 1983; Hillidge, 1986). Any horse working at speeds greater than 240 m/min is at risk (Voynick and Sweeney, 1986). The impact of exercise-induced pulmonary haemorrhage is difficult to assess. Most attempts to demonstrate statistically a negative correlation between EIPH and performance have been unrewarding, largely due to the number of uncontrollable variables (Pascoe et al., 1981; Raphel and Soma, 1982). In racing thoroughbreds (Mason et al., 1983) and standard breeds (MacNamara et al., 1990) approximately half as many EIPH-positive as EIPH-negative horses were placed in their races. Based on extensive intrapulmonary haemorrhage, a 3-year prospective study of sudden deaths in exercising thoroughbreds concluded that 9 out of 11 deaths were attributable to EIPH (Gunson et al., 1988). By correlation of clinical signs, thoracic radiographs, ventilation/perfusion scintigraphy, gross and subgross pathology and histopathology in 26 affected thoroughbreds, EIPH has been associated with chronic small airway inflammation, proliferation of subpleural, peribronchial and septal bronchial arterioles, interstitial connective tissue fibrosis and alveolar septal disruption in the dorsocaudal lung lobes (O'Callaghan et al., 1987). From this work it was proposed that the initial insult of EIPH started as focal, dorsocaudal pulmonary peribronchial inflammation which resulted in bronchial arterial neovascularization. Haemorrhage then occurred when, during exercise, bronchial blood pressure increased in fragile capillary buds. The incidence of bronchitis/bronchiolitis, regardless of aetiology, has been estimated to be 30% in non-racing equine athletes and close to 100% in one group of racing thoroughbreds (Sweeney et al., 1989). Histological study of lungs from horses with mild, moderate and severe chronic small airway disease consistently revealed a greater density of lesions in the diaphragmatic lobes (Winder and von Fellenberg, 1988). To understand further the aetiology and/or pathophysiology of EIPH, we will first explore some aspects of general mammalian and specific equine pulmonary and bronchial vascular anatomy and physiology. Exercise-related changes in these systems in normal and EIPH-positive horses will be briefly reviewed.(ABSTRACT TRUNCATED AT 400 WORDS)

Retrospective assessment of dobutamine therapy for hypotension in anesthetized horses.

Dobutamine was infused (1.7 micrograms/kg/minute) into 200 anesthetized horses as treatment for hypotension. The horses had been premedicated with xylazine, and anesthesia was induced with guaifenesin and ketamine and maintained with halothane. One hundred fifty-seven horses (79%) responded with an average increase in systolic blood pressure of at least 10 mm Hg within 10 minutes. A cardiac arrhythmia developed in 56 horses (28%) after dobutamine administration: 34 with sinus bradycardia, 18 with atrioventricular block, 2 with premature atrial contractions, and 2 with atrioventricular dissociation. Dobutamine intravenous infusion was effective treatment for hypotension in horses anesthetized with halothane.

Effect of pharmacological agonists on contractile responses in aortic rings derived from endotoxaemic rats.

To investigate the vascular smooth muscle dysfunction of septic shock, in vitro isometric responses to phenylephrine (PE) and acetylcholine (ACh) were evaluated in aortic rings, with and without endothelium (+/-E), removed from male Wistar rats 1.5, 3 and 6 h after intravenous (i.v.) administration of 5 mg/ kg lipopolysaccharide (LPS) or vehicle. A reduction in maximum contraction (+/-E) and sensitivity (-E) to PE were identified at 6 but not at 1.5 or 3 h. Maximum relaxation to ACh (+E) was not affected by LPS treatment but sensitivity was increased at 1.5 and 3 h. Having identified 6 h as the time at which the most pronounced changes were observed, further studies at this interval found that maximum contraction to potassium chloride (+/-E), prostaglandin F2 alpha (+E) and detomidine (-E) and relaxation to salbutamol (-E) were less in aortic rings from endotoxaemic rats. Sensitivity to KCl (+/-E), PGF2 alpha (-E) and detomidine (-E) was also reduced. Relaxation to sodium nitroprusside and atrial natriuretic peptide was not changed. These results suggest that attenuated pressor responses to a variety of vasoactive agents may be expected in patients 6 h after systemic exposure to endotoxin and that this vasoplegia may influence the vascular side-effects of therapeutic agents.

Atracurium as an adjunct to halothane-oxygen anesthesia in a llama undergoing intraocular surgery. A case report.

Atracurium (0.2 mg/kg intravenously [IV]) was administered to a llama anesthetized with halothane in oxygen, to insure immobilization of the globe during intraocular surgery. Recovery of neuromuscular function was facilitated by administration of edrophonium (0.5 mg/kg IV).

The recovery of horses from inhalant anesthesia: a comparison of halothane and isoflurane.

OBJECTIVE: Recovery is one of the more precarious phases of equine general anesthesia. The quality and rate of recovery of horses from halothane and isoflurane anesthesia were compared to determine differences in the characteristics of emergence from these commonly used inhalant anesthetics. EXPERIMENTAL DESIGN: Prospective, randomized blinded clinical trial. SAMPLE POPULATION: A total of 96 Thoroughbred and 3 Standardbred racehorses admitted for elective distal forelimb arthroscopy. METHODS: All horses were premedicated with intravenous xylazine, induced with guaifenesin and ketamine, and maintained on a large animal circle system fitted with an out of the circle, agent specific vaporizer. Recoveries were managed by a blinded scorer with a standardized protocol. A 10 category scoring system was used to assess each horse's overall attitude, purposeful activity, muscle coordination, strength and balance from the time of arrival in recovery to standing. Times to extubation, sternal recumbency and standing were recorded. Median recovery scores and mean times to extubation, sternal and standing were compared using the Mann-Whitney U test and student's t test, respectively. RESULTS: The median score for horses recovering from halothane was lower (20.0; range, 10 to 57) than that for horses recovering from isoflurane (27.5; range, 10 to 55). Horses in the two groups were extubated at similar mean times (halothane, 11.3 +/- 5.5 and isoflurane, 9.5 +/- 5.2 minutes) but horses recovering from isoflurane achieved sternal recumbency (halothane, 37.7 +/- 12.1 and isoflurane, 24.7 +/- 8.8 minutes) and stood (halothane, 40.6 +/- 12.9 and isoflurane, 27.6 +/- 9.6 minutes) sooner than those recovering from halothane. CONCLUSIONS: The recovery of horses from isoflurane anesthesia was more rapid but less composed than that from halothane. CLINICAL RELEVANCE: The quality of recovery following isoflurane was worse than after halothane anesthesia using the criteria chosen for this study. However, the range of recovery scores was similar for both groups and all horses recovered without significant injury.