Fetal oxygen content is restored after maternal hemorrhage and fluid replacement with polymerized bovine hemoglobin, but not with hetastarch, in pregnant sheep.

UNLABELLED: We investigated the ability of hemoglobin-based oxygen carrying solutions (HBOCs) to alleviate fetal hypoxemia from maternal hemorrhage. Fifteen pregnant ewes (132-day gestational age) were hemorrhaged 20 mL/kg over 1 h; they were randomized to receive 20 mL/kg IV of HBOC, hetastarch (HTS), or autologous blood (BLD) (n = 5 each) over 30 min and were monitored for 2 h. Hemorrhage significantly (P < or = 0.05) decreased maternal mean blood pressure (from 98 to 48 mm Hg, median), arterial oxygen content (from 12.2 to 11.1 mL/dL), and fetal arterial oxygen content (from 8.1 to 3.9 mL/dL). Fluid replacement restored maternal blood pressure in all groups, although maternal oxygen content immediately returned to baseline only after BLD or HBOC. Maternal oxygen saturation decreased after HBOC (from 98% to 88%). Fetal oxygen content rapidly returned to baseline with either BLD (7.1 mL/dL) or HBOC (8.0 mL/dL) but was never restored with HTS (4.7 mL/dL), and, 60 min after fluid replacement, it was higher with HBOC (8.3 mL/dL) than with HTS (4.7 mL/dL). Fetal plasma-free hemoglobin did not change after HBOC. In conclusion, maternal fluid replacement with HBOC or BLD effectively restored fetal oxygenation, primarily by restoring maternal oxygen content, whereas HTS did not. IMPLICATIONS: Hemoglobin solutions eliminate many limitations of blood transfusions. Our results show that fluid replacement with either blood or a hemoglobin solution, compared with hetastarch, restored fetal oxygenation in pregnant ewes after hemorrhage. If applicable to women, these results suggest a potential for the use of hemoglobin solutions in obstetrics.

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.

Perioperative risk factors for puppies delivered by cesarean section in the United States and Canada.

The purpose of this study was to evaluate perioperative risk factors affecting neonatal survival after cesarean section. Data from 807 cesarean-derived litters (3,908 puppies) was submitted by 109 practices in the United States and Canada. Survival rates immediately, two hours, and seven days after delivery were 92% (n=3,127), 87% (n=2,951), and 80% (n=2,641), respectively, for puppies delivered by cesarean section (n=3,410) and were 86% (n=409), 83% (n=366), and 75% (n=283), respectively, for puppies born naturally (n=498). Maternal mortality rate was 1% (n=9). Of 776 surgeries, 453 (58%) were done on an emergency basis. The most common breed of dog was bulldog (n=138; 17%). 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 (n=237; 30%). A model of cesarean-derived puppies surviving to birth, between birth and two hours, and between two hours and seven days was designed to relate litter survival to perioperative factors. The following factors increased the likelihood of all puppies being alive: the surgery was not an emergency; the dam was not brachycephalic; there were four puppies or less in the litter; there were no naturally delivered or deformed puppies; all puppies breathed spontaneously at birth; at least one puppy vocalized spontaneously at birth; and neither methoxyflurane nor xylazine was used in the anesthetic protocol.

Intravenous infusion of magnesium sulfate and regional redistribution of fetal blood flow during maternal hemorrhage in late-gestation gravid ewes.

OBJECTIVES: Even though magnesium sulfate is commonly prescribed for women with preeclampsia as prophylaxis against seizure and for women with preterm labor as a tocolytic agent there is limited information about its effects on the fetus. It is of particular concern that women with preeclampsia or in premature labor are at high risk for abruptio placentae with consequent compromise of fetal oxygenation. Magnesium sulfate is a vasodilator and thus may exert cardiovascular effects on the fetus. The goal of this study was to evaluate the effects of magnesium sulfate on fetal organ blood flow, especially regional cerebral blood flow, during the stressful condition of maternal hemorrhage. STUDY DESIGN: Studies were performed with 11 long-term instrumented pregnant ewes and their fetuses at 121 to 128 days' gestation (term, 147 days' gestation). Animals were randomly allocated to either the experimental (n = 5) or the control (n = 6) group. After a 60-minute baseline period, experimental fetuses received intravenous magnesium sulfate diluted in 0.9% sodium chloride (0.3 g loading dose, then 0.3 g/h at a rate of 3 mL/h) and control fetuses were infused with an equivalent volume of intravenous 0.9% sodium chloride. After 60 minutes of this infusion-only period, the infusions were continued and ewes were intermittently bled 4 times at a rate of 5 mL/kg for 10 minutes with 5 minutes between hemorrhages. The total blood lost at the end of the hemorrhage-plus-infusion hour was 20 mL/kg. The infusions were continued and the sheep were observed for 1 hour after this period (posthemorrhage period). At the end of baseline, infusion-only, and hemorrhage-plus-infusion periods, fetal and maternal blood pressures and blood gas values were measured and fetal organ blood flows were determined through a fluorescent microsphere technique. Repeated-measures analysis of variance and Wilcoxon tests were used to determine the significance of changes in hemodynamic, blood gas, and organ blood flow parameters between different time points within each group. Comparisons between groups were made with rank sum tests (Mann-Whitney tests). RESULTS: There were no significant differences between groups or within groups for baseline and infusion-only measurements in any measured hemodynamic or hematologic factor. Mean maternal blood pressure decreased significantly (P <.05) after hemorrhage, with similar median decrements in both control and experimental groups of 41 mm Hg (interquartile range, 24-57 mm Hg) and 41 mm Hg (interquartile range, 12-43 mm Hg), respectively. There were no significant differences between groups in fetal blood gas values or hemodynamic parameters. Fetal arterial PO(2) decreased significantly after hemorrhage plus infusion, with similar mean (+/-SEM) decreases in control and experimental groups of 5.9 +/- 1.4 mm Hg and 4.5 +/- 1.5 mm Hg, respectively. Fetal pH also decreased significantly in both groups. After hemorrhage plus infusion there were significant increases in fetal regional cerebral and myocardial blood flows in both groups. Adrenal blood flow increased significantly from baseline (214%, 183%-294%) in the control group after hemorrhage plus infusion but not in the experimental group. No other difference in organ blood flow between control and experimental groups was observed. Significant regional variations in cerebral blood flow were not observed in either group at any time. CONCLUSIONS: In these initially healthy, late-gestation fetal lambs magnesium sulfate exposure did not impair cardiac output redistribution, nor did it cause fetal death in response to maternal hemorrhage.

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.

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.

The effects of equivalent doses of tromethamine or sodium bicarbonate in healthy horses.

OBJECTIVE: To describe the effects of tromethamine, a putative treatment for metabolic acidosis, and to compare its biochemical effects with those of sodium bicarbonate. DESIGN: Randomized intervention study with repeated measures. ANIMALS: 16 healthy horses, 3 to 17 years old, weighing 391 to 684 kg. METHODS: Ten horses received 3 mEq/kg tromethamine and six received 3 mEq/kg sodium bicarbonate. Samples of venous blood and cerebrospinal fluid (CSF) were collected at intervals before and after drug administration. Heart rate and breathing rate were also recorded at intervals. RESULTS: Median standard base excess increased significantly (P < .05) from baseline immediately after both bicarbonate and tromethamine. These increases were not significantly different between treatments. Standard base excess returned toward baseline but remained significantly increased 3 hours after infusion of either treatment. After tromethamine, there was a significant decrease in plasma sodium concentration that lasted for at least 90 minutes. After sodium bicarbonate, no change in plasma sodium concentration was detected. Both sodium bicarbonate and tromethamine increased carbon dioxide tension in venous blood and CSF. Despite venous alkalemia, the pH of CSF decreased after both treatments. CONCLUSIONS: Tromethamine and sodium bicarbonate have similar alkalinizing ability. Tromethamine causes hyponatremia, whereas both tromethamine and sodium bicarbonate increase carbon dioxide tension in venous blood and CSF. CLINICAL RELEVANCE: If hyponatremia, hypercarbia, and acidosis of the CSF occur after tromethamine is given to horses with existing metabolic acidosis, some of the potential advantages of tromethamine may prove theoretical rather than practical.

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.

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.

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.

Two cases of pneumothorax during mechanical ventilation in Vietnamese potbellied pigs.

This case report describes pneumothorax associated with positive pressure ventilation in two Vietnamese potbellied pigs while under general anesthesia. A discussion of possible causes and barotrauma/volutrauma follows. The cause of pneumothorax in both cases was probably an interaction of intermittent positive pressure ventilation with some factor unique to these two pigs.

Phenylephrine-induced ventricular arrhythmias in dogs with inherited sudden death.

INTRODUCTION: Dogs with an inherited predisposition to sudden death display ventricular arrhythmias having certain characteristics, such as pause dependence, that are suggestive of early afterdepolarization-induced triggered activity. We hypothesized that alpha-adrenergic stimulation may facilitate the development of these arrhythmias by inducing a reflex bradycardia and by exerting a direct myocardial effect. METHODS AND RESULTS: Twenty affected dogs and 7 unaffected dogs were studied. The incidence and severity of ventricular arrhythmias were determined after administration of phenylephrine (0.01 mg/kg IV), with or without pretreatment with propranolol (0.1 to 0.3 mg/kg IV), atropine (0.04 mg/kg IV), or prazosin (0.5 mg/kg IV). Third-degree heart block was induced by AV nodal ablation in 4 affected dogs. Phenylephrine increased ventricular arrhythmias in affected dogs, with or without pretreatment with propranolol, but did not induce ventricular arrhythmias in unaffected dogs. In dogs with intact AV nodal conduction, atropine increased sinus rate, which suppressed baseline and phenylephrine-induced arrhythmias. In dogs with heart block, arrhythmias were increased during baseline and after phenylephrine, with or without pretreatment with atropine. Prazosin and overdrive ventricular pacing suppressed phenylephrine-induced arrhythmias. CONCLUSION: Phenylephrine increases ventricular arrhythmias in dogs with inherited sudden death via both an induction of reflex bradycardia and a direct myocardial effect. Superimposition of heightened alpha-adrenergic and vagal tone may facilitate the development of sudden death in these animals.

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.