Effects of isotonic crystalloid resuscitation on fluid compartments in hemorrhaged rats.

Redistribution of fluid after isotonic crystalloid resuscitation from hemorrhage may result not only in interstitial edema but also in cellular edema. We measured the extent to which shock and resuscitation altered fluid compartments in different organs. Nephrectomized, anesthetized rats were randomly divided into a Control group (n = 10) and a Hemorrhage plus Resuscitation group (H/R, n = 10). Rats were subjected to 60 min hemorrhagic hypotension (50 mmHg) followed by a 60 min resuscitation period with .9% NaCl infused as needed to maintain mean arterial pressure at 80% of baseline. A 2 h 51Cr-EDTA distribution space was used to estimate extracellular fluid volume (ECFV) and a 5 min 125I-albumin distribution space was used to measure plasma volume (PV). After euthanasia, total tissue water was measured by wet/dry weight analysis and interstitial fluid volume (ISFV) and cell water were calculated for selected organs. Resuscitation volume was two times the shed blood volume, but resulted in a PV equal to that of the Controls. There were no significant differences in whole animal ECFV or ISFV, although the mean values in the H/R group were greater than that of the Control group. The mean values for total tissue water for each tissue in the H/R group were larger than the respective means of the Control tissues but was significantly greater for only the heart (3639 +/- 56 microL/g vs. 3493 +/- 24 microL/g, mean +/- S.E., p < .05). In all H/R tissues, mean values for ISFV were also larger; this difference was significant for only the liver and small intestines (744 +/- 62 vs. 518 +/- 29 microL/g and 1117 +/- 155 vs. 706 +/- 58 microL/g, respectively). Heart cell water was significantly larger in H/R than Controls (2900 +/- 60 microL/g vs. 2738 +/- 27 microL/g). These data suggest that resuscitation of hemorrhage using isotonic crystalloid normalizes overall PV and ECFV but also causes interstitial expansion in selected gut tissues and cellular edema in the heart.

Kindling with rapidly recurring hippocampal seizures.

Bipolar electrodes, stereotactically implanted in the hippocampus of adult rats, were used to deliver 10 s trains of suprathreshold tetanic electrical stimuli every few minutes. As indices of seizure intensity, durations of the afterdischarges triggered by these stimuli were measured, and the accompanying behaviors were scored on a 5-point scale. After 2-3 h, prolonged afterdischarges appeared in conjunction with severe limbic seizures, separated by periods of approximately 60 min. After 3-9 h, the stimulation was withheld until the following day. Upon reinstitution of the stimuli, intense seizures were seen at the onset, and the cycle time between them was shortened. Enhanced responsiveness to a fixed stimulus persisted for several months, the longest period tested. In addition, the enhanced epileptogenicity showed transference and was not stimulus-specific. These studies, using stimuli with low intertrain frequency and short interstimulus intervals, establish a robust and rapidly-developing model of epileptogenesis in the hippocampus that is comparable to traditional kindling.

Paravertebral thoracolumbar anaesthesia in 10 horses.

The caudal border of the last rib was used as a reliable point of orientation while performing paravertebral thoracolumbar anaesthesia (PTLA) on 10 horses undergoing standing flank laparotomy. The local anaesthetic in all horses was 2% lidocaine. The PTLA procedure was completed in 9.8 +/- 1.8 mins (mean +/- sd). Sedation was provided by a combination of intravenous morphine with xylazine or detomidine. Overall analgesia, provided by the combination of PTLA and sedation, was rated as excellent in 2 horses and good in 6 horses. In the remaining 2 horses, overall analgesia was rated as fair because of incomplete analgesia at the ventral portion of the incision. Total time, from start of PTLA to end of surgery was 143.5 +/- 24.2 mins. Five horses responded mildly to suturing of the ventral portion of the incision. Apart from 1 horse which developed transient, unilateral hindlimb weakness intraoperatively, no other complications were noticed. We conclude that PTLA can easily be performed in the horse and, combined with systemic sedation, is an effective and safe method of providing analgesia for standing flank laparotomy.

Cortisol suppression in cats after induction of anesthesia with etomidate, compared with ketamine-diazepam combination.

OBJECTIVE: To evaluate duration and magnitude of adrenocortical function suppression after administration of etomidate to cats. ANIMALS: 15 purpose-bred, healthy cats. PROCEDURE: Cats were allotted to 2 groups. Anesthesia was induced with etomidate (ET, 2 mg/kg of body weight, i.v.; n = 8) or a mixture (KD, n = 7) of ketamine (5 mg/kg; i.v) and diazepam (0.25 mg/kg, i.v.). Anesthesia was maintained with halothane in all cats for 2 hours. ACTH gel (2.2 U/kg, i.m.) was administered 30 minutes after anesthesia induction. Blood samples for cortisol assay were taken before anesthesia induction (T -30), and before (T0) and at 30, 60, 120, 180, 300, and 420 minutes after ACTH administration. Anesthesia was discontinued after the T120 sample was obtained. RESULTS: After anesthesia induction, median (interquartile range [Q1-Q3]) cortisol values were significantly lower in the ET group (4 [3 to 4] micrograms/dl) at T0, compared with T -30 values and with T0 values in the KD group (5 [3 to 9] micrograms/dl). After ACTH administration, cortisol values in the ET group continued to decrease two- to threefold below T -30 values and remained decreased over the 2-hour anesthesia period. After ACTH administration, cortisol values increased twofold for 2 hours in the KD group, compared with T -30 values. One hour after anesthesia recovery, cortisol values in the ET group (3 [2 to 3] micrograms/dl) remained significantly lower than values in the KD group (9 [7 to 11] micrograms/dl) and preanesthesia values. By T300, both groups had cortisol concentration near 7 micrograms/dl, similar to preanesthesia values. CONCLUSION: Induction of anesthesia with etomidate caused suppression of adrenocortical function during 2 hours of halothane anesthesia and 1 hour of recovery in cats. Cortisol concentration did not return to baseline until after 2 additional hours. CLINICAL RELEVANCE: Results from these healthy cats suggest profound suppression of important stress hormones after anesthesia induction with etomidate, use of which could put critically ill cats at further risk.

Evaluation of quantitative acid-base balance and determination of unidentified anions in swine.

Arterial blood samples were collected from 19 anesthetized pigs before and after hemorrhage was induced. Blood gas tensions and concentrations of sodium, potassium, chloride, lactate, and total protein were measured. Results indicated that hydrogen ion (H+) concentration calculated from a specific formula was a biased and imprecise estimate of measured H+ concentration. The bias was 5.45 nEq/L, with limits of agreement from -7.92 to 18.83 nEq/L. Because albumin is the fraction of plasma protein most important in acid-base balance, the agreement between predicted and measured H+ concentration was reevaluated, using an albumin charge estimate and a reference swine albumin-to-globulin ratio. This improved the ability of the formula to predict H+ concentration; the bias decreased to 1.33 nEq/L with limits of agreement from -12.16 to 9.49 nEq/L. The formula and a simplified approach for clinical application were biased and unacceptably imprecise estimators of lactate (L-) concentration. The formula approach underestimated L- concentration by 2.8 (-12.4, 6.7) mEq/L, whereas the simplified method overestimated L- concentration by 5.0 (-3.8, 13.9) mEq/L.

Effects of tromethamine buffer on coagulation variables and ionized calcium concentration in dogs.

OBJECTIVE: To evaluate coagulation variables in 2 groups of dogs after tromethamine administration. ANIMALS: 13 Beagles. PROCEDURES: Both groups of dogs received a 30-minute IV infusion of 10 ml of 0.3M tromethamine/kg of body weight. In unsedated dogs (group 1, n = 8), prothrombin time, activated partial thromboplastin time, normalized ionized calcium concentration, platelet numbers, and platelet function were measured prior to treatment, at the end of the infusion, and 1 hour after the infusion. In xylazine-sedated dogs (group 2, n = 5), buccal mucosal bleeding time and plasma percentage of von Willebrand factor antigen were measured before and 1 hour after infusion, and fibrin degradation products concentration was measured 1 hour after infusion. Platelet function was assessed by determining platelet aggregation and by measuring ATP release from the aggregating platelets over 6 minutes, using a whole blood aggregometer, with 20, 10, and 5 microM ADP and 5 and 10 micrograms of collagen/ml as platelet activation agonists. RESULTS: There was no significant change in any of the variables measured in either group of dogs, compared with baseline values. CONCLUSIONS AND CLINICAL RELEVANCE: When administered to healthy dogs, tromethamine does not change the coagulation indices measured.

Acid-base, metabolic, and hemodynamic effects of sodium bicarbonate or tromethamine administration in anesthetized dogs with experimentally induced metabolic acidosis.

OBJECTIVE: To evaluate buffering capacity and side effects of equivalent doses of tromethamine (THAM) and sodium bicarbonate (BIC). ANIMALS: 18 purebred dogs. PROCEDURE: Acidosis was induced by having dogs breathe a hypoxic gas mixture (FIO2 = 0.10) until arterial base balance < or = -7.5 mEq/L was reached. Dogs then received a 30-minute infusion of 5% BIC (n = 6) or 0.3M THAM (n = 8), and FIO2 increased to 0.30. Drug doses were calculated to correct base balance to zero. RESULTS: During hypoxia, for BIC- and THAM-treated groups, median (interquartile range [Q1, Q3]) pHa and arterial base balance decreased to 7.16 (7.07, 7.38) and 7.19 (7.11, 7.31), -14 (-16, 9) and -12 (-16, -11) mEq/L, respectively, and mixed venous lactate concentration increased to 7 (2, 15) and 6 (3, 13) mmol/L, respectively. Immediately after each infusion, acid-base and cardiopulmonary variables returned toward baseline. For respective BIC- and THAM-treated groups, pHa increased to 7.37 (7.26, 7.44) and 7.40 (7.33, 7.49) and base balance increased to 0 (-4, 7) and 0 (-4, 2) mEq/L. Lactate concentration decreased only slightly to 5 (2, 6) and 5 (2, 9) mmol/L, but continued to decrease throughout the study. The only significant (P < or = 0.05) difference between groups was hypernatremia after BIC administration that persisted for 60 minutes. The PaCO2 in BIC-treated dogs increased immediately after infusion, compared with values during hypoxia. Standardized ionized calcium values initially decreased in both groups, but returned to baseline by 60 minutes. CONCLUSION: The buffering capacity of THAM is equal to that of BIC, although THAM does not cause the transient hypernatremia or hypercapnia observed after BIC administration. Hypocalcemia may be transient after administration of either solution. Thus, THAM is an acceptable alternative to BIC for treatment of metabolic acidosis in selected anesthetized dogs.

Effects of a highly concentrated hypertonic saline-dextran volume expander on cardiopulmonary function in anesthetized normovolemic horses.

Conventional fluid resuscitation is unsatisfactory in a small percentage of equine emergency surgical cases because the large volumes of fluids required cannot be given rapidly enough to adequately stabilize the horse. In anesthetized horses, the volume expansion and cardiopulmonary effects of a small volume of highly concentrated hypertonic saline-dextran solution were evaluated as an alternative initial fluid choice. Seven halothane-anesthetized, laterally recumbent, spontaneously ventilating, normovolemic horses were treated with a 25% NaCl-24% dextran 70 solution (HSD) at a dosage of 1.0 ml/kg of body weight, IV, infused over 10 minutes, and the effects were measured for 120 minutes after infusion. Plasma volume expansion was rapid and significant (from 36.6 +/- 4.6 ml/kg to 44.9 +/- 4.8 ml/kg), and remained significantly expanded for the duration of the experiment. Packed cell volume, total blood hemoglobin, and plasma protein concentrations significantly decreased, confirming rapid and sustained volume expansion with hemodilution. Cardiac index and stroke index immediately increased and remained high for the entire study (from 69.6 +/- 15.3 ml/min/kg to 106.6 +/- 28.4 ml/min/kg, and from 1.88 +/- 0.49 ml/beat/kg to 2.50 +/- 0.72 ml/beat/kg, respectively). Systemic vascular resistance significantly decreased immediately after HSD infusion and remained decreased for the duration of the study (from 1.41 +/- 0.45 mm of Hg/ml/min/kg to 0.88 +/- 0.22 mm of Hg/ml/min/kg). Arterial and venous blood oxygen content decreased significantly because of hemodilution, but actual oxygen transport transiently increased at the 10-minute measurement before returning toward baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Duration of action and hemodynamic properties of mivacurium chloride in dogs anesthetized with halothane.

OBJECTIVE: To describe onset and duration of neuromuscular blockade induced by mivacurium chloride and its associated hemodynamic effects at 3 dosages in healthy dogs. ANIMALS: 7 Labrador Retrievers. PROCEDURE: Anesthesia was induced with thiopental and maintained with halothane in oxygen, and dogs were mechanically ventilated to end-tidal P(CO)2 between 35 and 40 mm Hg. Core temperature, end-tidal P(CO)2, and halothane concentration were kept constant throughout the experiment. Neuromuscular function was assessed by evaluation of the train-of-four response to a supramaximal electrical stimulus of 2 Hz applied to the ulnar nerve every 10 seconds. Blood for determination of plasma cholinesterase activity was obtained prior to administration of mivacurium, a bolus of which was administered IV, using a randomized Latin-square design for dosages of 0.01, 0.02, and 0.05 mg/kg of body weight. RESULTS: All dogs had typical plasma cholinesterase activity. After administration of mivacurium, differences were not evident between groups in heart rate, systolic, mean, or diastolic blood pressure, change at any time in heart rate, systolic, mean, or diastolic blood pressure, or pH. Interval from onset to 100% neuromuscular blockade was 3.92+/-1.70, 2.42+/-0.53, and 1.63+/-0.25 minutes at dosages of 0.01, 0.02, and 0.05 mg/kg, respectively. Duration of measurable neuromuscular blockade was 33.72+/-12.73, 65.38+/-12.82, and 151.0+/-38.50 minutes, respectively. Time of onset and duration of effect differed significantly among dosages. CONCLUSIONS AND CLINICAL RELEVANCE: Mivacurium provides good hemodynamic stability at the dosages tested. In dogs, this drug has a rapid onset and long duration of effect.

Pharmacokinetic variables of mivacurium chloride after intravenous administration in dogs.

OBJECTIVE: To determine pharmacokinetic variables of mivacurium chloride after IV administration in dogs. ANIMALS: 5 healthy Labrador Retrievers. PROCEDURE: Anesthesia was induced with thiopental and maintained with halothane in oxygen. Dogs were ventilated mechanically to an end-tidal P(CO)2 value between 35 and 40 mm Hg. Heart rate, direct blood pressure, and arterial pH were recorded throughout the experiment. Core temperature, end-tidal P(CO)2, and halothane concentration were kept constant throughout the experiment. Paired blood samples for determination of plasma cholinesterase activity were collected prior to administration of a bolus of mivacurium (0.05 mg/kg of body weight), which was administered IV during a 2-second period. Arterial blood samples were obtained for determination of plasma mivacurium concentration 0, 1, 3, 5, 10, 30, 60, 120, 150, and 180 minutes after administration of mivacurium. Blood was collected into tubes containing EDTA and 0.25% echothiophate. Mivacurium concentration was determined, using reversed-phase high-performance liquid chromatography. RESULTS: For the trans-trans isomer, mean +/- SEM volume of distribution was 0.18+/-0.024 L/kg, median half-life was 34.9 minutes (range, 26.7 to 53.5 minutes), and clearance was 12+/-2 ml/min/kg. For the cis-trans isomer, values were 0.31+/-0.05 L/kg, 43.4 minutes (range, 31.5 to 69.3 minutes), and 15+/-2 ml/min/kg, respectively. Values for the cis-cis isomer were not calculated, because it was not detectable in plasma 60 minutes after mivacurium administration in all 5 dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The transtrans and cis-trans isomers of mivacurium have a long half-life and slow clearance in healthy dogs anesthetized with halothane.

Anesthetic and postanesthetic management of sea turtles.

OBJECTIVE: To examine the physiologic effects of inhalation anesthesia in aquatic turtles to improve anesthetic techniques and postanesthetic monitoring. DESIGN: Retrospective case series. ANIMALS: 9 Kemp's ridley sea turtles. PROCEDURE: Isoflurane was used as the general anesthetic during 14 minor surgical procedures. Turtles were orotracheally intubated, and a surgical plane of anesthesia was maintained with 2.7 +/- 0.4% (mean +/- SE) isoflurane. The duration of anesthesia was 131 +/- 12 minutes. Pulse rate, blood pressure, blood gases (PaO2 and PaCO2) and pH, blood lactic acid concentration, and capnography were used to evaluate the physiologic responses of sea turtles to isoflurane. RESULTS: An isoflurane concentration of 3.4 +/- 0.3% provided anesthetic induction in 7 +/- 1 minutes. The mean duration of the recovery phase was 241 +/- 31 minutes. The duration of the recovery phase was not affected by the duration of anesthesia, type of carrier gas, method of ventilatory weaning, or use of selected pharmacologic agents. The recovery phase was characterized by hypoxemia, progressive acidemia, hypercapnia, and lactic acidosis. Awakening in the turtles was preceded by a characteristic tachycardia and tachypnea. All sea turtles recovered from isoflurane anesthesia without apparent adverse effects within 24 hours. CLINICAL IMPLICATIONS: Isoflurane appears to be safe and effective in providing surgical anesthesia in turtles that require a timely return to an aquatic environment. This study should assist veterinarians in predicting the physiologic responses of aquatic turtles to inhalation agents.

Surface-induced hypothermia in dogs: 19 cases (1987-1989).

Surface-induced hypothermia is used to protect tissues from ischemic events during surgery. In a review of 19 clinical cases in dogs, the technique was used to enable intracardiac surgery (4 dogs) and to facilitate removal of extensive thoracic or abdominal masses (15 dogs). For 16 dogs (84%), anesthesia was induced with an opioid/benzodiazepine combination and maintained with a balanced technique by use of an opioid, a neuromuscular blocking agent, and isoflurane in oxygen. Dogs were cooled in an ice bath to a mean esophageal temperature of 27.8 +/- 1.4 C. Mean anesthesia time was 4.04 +/- 1.37 hours. Hypothermic-induced adverse effects, such as increased blood viscosity, increased myocardial irritability, and shivering, were managed by hemodilution, manipulation of acid-base balance, and administration of opioid and neuromuscular blocking agents. Complications requiring treatment included severe hypotension (74%), arrhythmias (47%), hypoxemia (42%), and acidemia (58%). Six dogs (32%) went into cardiac arrest and all were successfully resuscitated once the surgical procedure was completed. One dog was euthanatized during surgery, another died after surgery, and the 17 remaining dogs (90%) were discharged from the hospital to their owners. The technique appears beneficial in selected cases to decrease the morbidity and mortality associated with the risk of prolonged ischemia and life-threatening hemorrhage.

Perioperative management and mortality rates of dogs undergoing cesarean section in the United States and Canada.

OBJECTIVE: To describe dogs undergoing cesarean section in the United States and Canada, to determine perioperative management, and to calculate survival proportions. DESIGN: Multicenter prospective case series. ANIMALS: 3,908 puppies from 808 dams. RESULTS: Survival rates immediately, 2 hours, and 7 days after delivery were 92, 87, and 80%, respectively, for puppies delivered by cesarean section (n = 3,410) and 86, 83, and 75%, respectively, for puppies born naturally (498). For 614 of 807 (76%) litters, all puppies delivered by cesarean section were born alive. Maternal mortality rate was 1% (n = 9). Of 776 surgeries, 453 (58%) were done on an emergency basis. The most common breeds of dogs that underwent emergency surgery were Bulldog, Labrador Retriever, Boxer, Corgis, and Chihuahua. The most common breeds of dogs that underwent elective surgery were Bulldog, Labrador Retriever, Mastiff, Golden Retriever, and Yorkshire Terrier. The most common methods of inducing and maintaining anesthesia were administration of isoflurane for induction and maintenance (n = 266; 34%) and administration of propofol for induction followed by administration of isoflurane for maintenance (237; 30%). CLINICAL IMPLICATIONS: Mortality rates of dams and puppies undergoing cesarean section in the United States and Canada are low. Knowledge of mortality rates should be useful to veterinarians when advising clients on the likelihood of puppy and dam survival associated with cesarean section.

Periparturient and neonatal anesthesia.

Small animal patients may need to be anesthetized in the periparturient period for emergency, nonobstetric reasons, elective ovariohysterectomy, or cesarean section. In each case, the physiologic changes in the dam must be accounted for in designing an anesthetic protocol, but the requirements of the fetuses will be different. Subsequent to birth, the neonatal animal may need to be anesthetized, and the unique physiology and pharmacology at this age is described.

Neonatal critical care.

The first few minutes after a neonate's birth may determine the quality of its entire life. Immediate care includes prevention of hypothermia, clearing of nasal and oral passages, stimulation of ventilation and oxygenation, and, in a few cases, advanced life support. Any additional stress during the first weeks of life can also result in neonatal morbidity and mortality. Care of the diseased newborn must focus not only on treatment of the underlying disease but on aggressive supportive care. A safe, warm, clean, proper environment and adequate nutrition are essential.

General anesthetic techniques in swine.

General anesthesia techniques for swine can be challenging due to the animal's temperament, anatomic traits, physical condition, and the environment in which the clinician may be working. Taking these factors into consideration, this article provides specific information on preanesthetic considerations, venous catheterization, drug selection, monitoring, perioperative complications and therapy, recovery, and analgesia.