Effects of single hyperinflation using a sustained high pressure manoeuvre during inhalation anaesthesia in horses.

The effect of a single hyperinflation using a sustained high-pressure manoeuvre (SHPM) during inhalation anaesthesia was evaluated in horses. Twenty-eight client-owned male horses were recruited; 14 were operated on in dorsal recumbency and 14 in lateral recumbency. For each category, horses were randomly allocated to either the 'breathing spontaneously' or 'mechanically ventilated' group. After 30 min of anaesthesia, baseline cardiorespiratory parameters were collected and a SHPM of 50 cmH2O during 50s was undertaken. In the group of horses breathing spontaneously and positioned in dorsal recumbency, venous admixture developed significantly more than in other groups and a single SHPM only partially and transiently improved arterial oxygenation. No benefit of the respiratory manoeuvre was observed in the other groups.

Isoflurane but not halothane minimum alveolar concentration-sparing response of dexmedetomidine is enhanced in rats chronically treated with selective α2-adrenoceptor agonist.

Halothane minimum alveolar concentration (MAC)-sparing response is preserved in rats rendered tolerant to the action of dexmedetomidine. It has been shown that halothane and isoflurane act at different sites to produce immobility. The authors studied whether there was any difference between halothane and isoflurane MAC-sparing effects of dexmedetomidine in rats after chronic administration of a low dose of this drug. Twenty-four female Wistar rats were randomly allocated into four groups of six animals: two groups received 10 µg/kg intraperitoneal dexmedetomidine for five days (treated groups) and the other two groups received intraperitoneal saline solution for five days (naive groups) prior to halothane or isoflurane MAC determination (one treated and one naive group of halothane and one treated and one naive group of isoflurane). Halothane or isoflurane MAC determination was performed before (basal) and 30 min after an intraperitoneal dose of 30 µg/kg of dexmedetomidine (post-dex) from alveolar gas samples at the time of tail clamp. Administration of an acute dose of dexmedetomidine to animals that had chronically received dexmedetomidine resulted in a MAC-sparing effect that was similar to that seen in naive animals for halothane; however, the same treatment increased the MAC-sparing response of dexmedetomidine for isoflurane. Isoflurane but not halothane MAC-sparing response of acutely administered dexmedetomidine is enhanced in rats chronically treated with this drug.

Cardiorespiratory and minimum alveolar concentration sparing effects of a continuous intravenous infusion of dexmedetomidine in halothane or isoflurane-anaesthetized rats.

Dexmedetomidine (DEX) is a highly selective alpha(2)-adrenoceptor agonist in both the central and peripheral nervous systems. Its cardiorespiratory effects have been described; however, these effects have not been reported when it is used in combination with volatile anaesthetics in rats. The cardiovascular and respiratory actions of a continuous intravenous infusion of 0.25 microg/kg/min of DEX administered to rats anaesthetized at 1 minimum alveolar concentration (MAC) of either halothane (HAL) or isoflurane (ISO) were studied. Twenty-eight rats were grouped into four treatment groups: HAL alone, ISO alone, DEX + HAL and DEX + ISO. The MAC(HAL) or MAC(ISO) was determined in each rat from alveolar gas samples at the time of tail clamping. Control MAC values, expressed as mean +/- standard deviation, were 1.31 +/- 0.1% for HAL and 1.46 +/- 0.05% for ISO. DEX reduced HAL MAC from 1.31 +/- 0.1% to 0.36 +/- 0.22% (72 +/- 17% MAC reduction) and ISO MAC from 1.46 +/- 0.05% to 0.83 +/- 0.2% (43 +/- 14% MAC reduction). Heart rate (HR) was decreased in both DEX groups at 1 MAC, with no differences between HAL and ISO. The mean arterial pressure was significantly depressed in the DEX + ISO group compared with the ISO only group. This difference in mean arterial blood pressure (MABP) was not seen between the DEX + HAL and HAL only groups. Respiratory depression was minor at 1 MAC with both inhalant anaesthetics. DEX reduced the MAC of HAL to a degree greater than it decreased the MAC of ISO. The effects of DEX on HR and ventilation were similar in rats anaesthetized with HAL or ISO at 1 MAC; however, hypotension was more pronounced when DEX was combined with ISO at 1 MAC.

Effect of alkalinization on the local analgesic efficacy of ketamine in the abaxial sesamoid nerve block in horses.

The objective of this study was to determine the effects of the alkalinization on the local analgesic efficacy of 1% ketamine in the abaxial sesamoid nerve block in horses. Thirty-six mature healthy horses were randomly assigned to four groups for the following treatments; an abaxial sesamoid block with 5 mL of saline solution (control saline); an abaxial sesamoid block with 5 mL of a solution containing 1% ketamine (KETs 1%); an abaxial sesamoid block with 5 mL of a solution containing saline solution and 0.5 mEq of sodium bicarbonate (control bicarbonate); and an abaxial sesamoid block with 5 mL of a solution containing 1% ketamine and 0.5 mEq of sodium bicarbonate (KETb 1%). All blocks were performed in one randomly selected front leg. To determine analgesia, hoof withdrawal from thermal stimulus from radiant heat lamp was assessed. Before each block, the hoof withdrawal reflex latency (HWRL) (time between lamp illumination and withdrawal of the hoof) was determined; after the block, local analgesic effects were determined using the heat lamp at 2 and 5 min after the injection and then every 5 min for 1 h. In KETs 1% group, there were significant increases in HWRL between basal values and values from 2 to 10 min after an abaxial sesamoid block. In KETb 1% group, significant increases in HWRL was collected between the basal value and values from 2 to 25 min following an abaxial sesamoid block. In KETs 1% group, of the nine horses, four had an abaxial sesamoid block that was unsuccessful. However, in KETb 1% group, only one of the nine horses had an abaxial sesamoid nerve block that was unsuccessful. The alkalinization of a 1% ketamine solution produced a more consistent and persistent local analgesia in horses when compared with 1% ketamine solution alone.

Effects of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses.

REASONS FOR PERFORMING STUDY: Recovery from inhalant anaesthesia in the horse is a critical and difficult period to manage; however, several factors could help to obtain a calm recovery period including choice of anaesthetic and analgesic procedure used and the conditions under which anaesthetic maintenance and recovery occur. OBJECTIVES: The objective of this study was to evaluate and compare the quality of recovery in horses administered saline, xylazine, detomidine or romifidine during recovery from isoflurane anaesthesia. METHODS: Six mature and healthy horses were premedicated with i.v. xylazine and butorphanol, and anaesthesia induced using ketamine. After 2 h of inhalant anaesthesia with isoflurane vaporised in oxygen, saline solution, xylazine (0.1 mg/kg bwt), detomidine (2 microg/kg bwt) or romifidine (8 pg/kg bwt) were administered. The quality of recovery of each horse and the degree of sedation and ataxia were evaluated. Cardiovascular and respiratory parameters were recorded, and arterial blood samples obtained and analysed for pH, PO2 and PCO2 during recovery. RESULTS: Quality of recovery was better in groups treated with alpha-2 adrenergic receptors agonists, showing less ataxia. Degree of sedation was greater in the romifidine group. CONCLUSIONS: We concluded that the administration of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses prolonged and improved the quality of recovery without producing significant cardiorespiratory effects. POTENTIAL CLINICAL RELEVANCE: Administration of alpha-2 adrenoceptor agonists after inhalent anaesthesia could prevent complications during the recovery period.

Optical aggregometry versus the PFA-100: experimental studies in pigs treated with propofol.

An experimental study of platelet aggregation was performed in 22 male Landrace x Large-White crossbred pigs treated with propofol at different doses, to compare the results of optical aggregometry with those of the PFA-100 (Dade Int., Miami, FL, USA), a new platelet function analyzer. Platelet aggregation was analyzed in basal blood samples by both methods, after which the pigs were divided into three groups: G1, anaesthetic induction with propofol (2 mg/kg intravenously (i.v.)); G2, anaesthetic induction with propofol (2 mg/kg i.v.), followed by a second dose of 1.5 mg/kg; and G3, anaesthetic induction with propofol (2 mg/kg i.v.), followed by 1 h of continuous i.v. infusion at 13 mg/kg/h. Four minutes after propofol injection, blood samples were again taken from each group and studied by both methods. In groups G2 and G3, both methods showed reduced platelet aggregation, while in group G1 neither evidenced an anti-aggregating effect of propofol. Under our experimental conditions: (1) the propofol effect on platelet aggregation depends on the plasma concentration; (2) the results obtained with the two methods are comparable; (3) PFA-100 may provide an alternative to optical aggregometry for detecting the effects of anaesthetic agents ex vivo.

Trasplante de pulmón experimental: desarrollo de un modelo anestésico en el cerdo / Experimental lung transplantation: a model of anesthesia developed in the pig

Introducción. Actualmente, el cerdo es el animal de experimentación y el modelo quirúrgico experimental elegido por su gran similitud con el hombre, lo que hace necesario un constante desarrollo paralelo de las técnicas anestésicas que se emplean en esta especie. Material y métodos. En 20 cerdos se realizaron 10 trasplantes de pulmón unilaterales, tras haber sufrido el pulmón 3 h de isquemia. La técnica anestésica empleada incluyó propofol + fentanilo + midazolam + pancuronio. Resultados. No se observaron variaciones estadísticamente significativas en ninguno de los parámetros cardiovasculares ni respiratorios registrados, a excepción del gasto cardíaco, que disminuyó de forma estadísticamente significativa de 3,4 ñ 1,1 l/min en el momento basal, hasta 2,8 ñ 0,9 l/min en el momento 1 h posreperfusión. La presión parcial de oxígeno en sangre venosa mixta experimenta una disminución en este mismo momento. La presión parcial de CO2 arterial sufrió un incremento significativo en el momento de la neumonectomía. Conclusiones. El protocolo anestésico empleado mantiene una estabilidad cardiovascular y respiratoria adecuada para la realización del trasplante pulmonar; tan sólo el gasto cardíaco se reduce a los 60 min de la finalización del trasplante, lo que en principio se puede atribuir al síndrome de isquemia-reperfusión (AU)

Reduction of isoflurane MAC with buprenorphine and morphine in rats.

Preoperative analgesics are being increasingly used to provide analgesia in the intraoperative and postoperative period. Opioids reduce anaesthetic requirements, although the effect varies with the different drug and species. The aim of this work was to determine whether buprenorphine reduces the minimum alveolar concentration (MAC) of isoflurane in a dose-related fashion, and whether this effect is similar to morphine when clinical doses of both drugs are used in the rat. Thirty-six male Wistar rats were anaesthetized with isoflurane, and MAC was determined before and after the administration of either buprenorphine or morphine. MAC of isoflurane was determined from alveolar gas samples when a standard noxious stimulus, in the form of a tail clamp, was applied. The duration and degree of reduction of the MAC of isoflurane were recorded. Basic cardiovascular and respiratory measurements were also recorded. Buprenorphine (10, 30 and 100 microg/kg) and morphine (1, 3 and 10 mg/kg) reduced in a dose-dependent fashion the MAC of isoflurane by 15%, 30% and 50%, respectively. Buprenorphine resulted in less cardiovascular and respiratory depression and had a longer-lasting action than morphine. In conclusion, buprenorphine has a dose-related isoflurane sparing effect in the rat similar to that caused by morphine at clinical doses of both drugs.

Aspirin synergistically potentiates isoflurane minimum alveolar concentration reduction produced by morphine in the rat.

BACKGROUND: The combination of opioids and nonsteroidal antiinflammatory drugs is more analgesic than the summed effect of each drug administered separately. This synergism has been used to obtain analgesia in the postoperative period at doses at which side effects are minimal. The aim of this study is to evaluate the analgesic interaction between aspirin and morphine in the rat during isoflurane anesthesia. The reduction in minimum alveolar concentration of isoflurane (MAC(ISO)) was used as an objective measure of the analgesic potency of individual drugs and their use in combination. METHODS: Thirty-seven male Wistar rats were anesthetized with isoflurane in oxygen, and the MAC(ISO) was determined before and after the intravenous administration of aspirin and morphine. Rats were administered morphine alone (1, 3, and 10 mg/kg) or morphine (1 and 3 mg/kg) and aspirin (30 mg/kg). The MAC(ISO) was determined from alveolar gas samples at the time of tail clamp. The duration of MAC(ISO) reduction was recorded. RESULTS: Aspirin did not have an effect on MAC(ISO), (average, 1.35+/-0.1%), whereas the combination of morphine (1 and 3 mg/kg) and aspirin (30 mg/kg) produced a reduction in the dose of morphine needed to produce the same degree of MAC(ISO) reduction. Actual MAC(ISO+drug) data were as follows: 1 mg/kg morphine, 1.17+/-0.14%; 3 mg/kg morphine, 0.98+/-0.15%; 1 mg/kg morphine plus aspirin, 0.90+/-0.04%; 10 mg/kg morphine, 0.63+/-0.13%; and 3 mg/kg morphine plus aspirin, 0.64+/-0.06%. CONCLUSIONS: The synergistic effects of aspirin and morphine allow a clinically significant reduction in the requirements of isoflurane and isoflurane plus morphine, and these drug combinations may decrease the side effects associated with the use of single higher, equianalgesic doses of these drugs.

Epidural injection of ketamine for perineal analgesia in the horse.

OBJECTIVE: To determine the analgesic, sedative, and cardiopulmonary effects of epidural ketamine in the horse. ANIMAL POPULATION: Six healthy horses (three males and three females) weighing between 350 and 450 kg. METHODS: Three doses of ketamine were selected (0.5, 1, 2 mg/kg). Two months before the beginning of experiments, the carotid artery was exteriorized, and 1 week before experiments began, an epidural catheter was placed percutaneously in all animals with the tip located 12 cm cranially in the midsacrum. One week later, either saline (control) or one of three doses of ketamine was injected epidurally. Each animal received each ketamine dose and saline in random order at 1-week intervals. Ketamine was diluted in saline 0.9% before the experiment, and the volume used was adjusted to horse size and correlated to clinically used volumes. All the animals received a standard noxious stimulus consisting of needle insertion into the skin and deep muscle using a 3-point scale for scoring the response. A second scale was used to score the degree of sedation. The response to a noxious stimulus, the degree of sedation, and arterial blood pressure were assessed at previously determined intervals: before drug and 2, 5, 10, and 15 minutes and every 15 minutes to 210 minutes after ketamine or saline administration. Arterial blood samples were drawn for blood gas analysis before drug and at 15, 30, 60, and 90 minutes. RESULTS: All the tested doses of ketamine were effective in producing analgesia of the tail, perineum, and upper hindlimb. Total tail and perineal analgesia times were similar depending on dosage (30 minutes for 0.5 and 1.0 mg/kg and 75 minutes for 2.0 mg/kg). A sedative effect of ketamine was also observed in a dose-response manner with a peak effect between 15 and 30 minutes postadministration. No cardiopulmonary effects were observed with any dose of ketamine. CONCLUSIONS: Results indicate that epidurally administered ketamine in the horse produces local spinal and central nervous system effects with analgesia and sedation but minimal cardiopulmonary effects. CLINICAL RELEVANCE: Further studies are required to determine whether the analgesia is sufficient for surgery.

Anesthetic potency of desflurane in the horse: determination of the minimum alveolar concentration.

OBJECTIVE: To determine the minimum alveolar concentration (MAC) of desflurane (DES) in the horse. STUDY DESIGN: Prospective study. ANIMALS: Six healthy adult horses (three males and three females) weighing 370 +/- 16 kg and aged 9 +/- 2 years old. METHODS: Anesthesia was induced with DES vaporized in oxygen via a face mask connected to a large-animal, semiclosed anesthetic circle system. The horses were endotracheally intubated and positioned in right lateral recumbency. Inspired and end-tidal DES were monitored using a calibrated Ohmeda RGM 5250 multigas analyzer (Ohmeda-BOC, Spain). The MAC of desflurane that prevented gross purposeful movement in response to 60 seconds of noxious electrical stimulation of oral mucous membranes was determined. RESULTS: The time from the start of DES administration to lateral recumbency was 6.1 +/- 0.9 min. The MAC of DES in these horses was 7.6 +/- 0.4%. Time required for the animal to regain sternal recumbency after 98 +/- 4 minutes of anesthesia was 6.6 +/- 0.5 minutes and the time to standing was 14.3 +/- 2.7 minutes. CONCLUSIONS: The MAC of desflurane in these horses was 7.6 +/- 0.4%. DES provided a rapid induction to, and recovery from, anesthesia. CLINICAL RELEVANCE: Desflurane offers the potential for more precise control during anesthesia, and may allow a faster and uneventful recovery. It is important to know the MAC of an inhalant to use it clinically.

Improved distribution of pulmonary flush solution to the tracheobronchial wall in pulmonary transplantation.

This report describes the experimental results obtained with conventional (pulmonary artery, PA) flushing versus retrograde perfusion (via left atrium, LA) using 99mTc-labeled macroaggregated albumin (MAA-99mTc) to ascertain the distribution throughout the tracheobronchial (TB) tree in 10 Large-White pigs. Lung preservation was achieved with 4 degrees C Euro-Collins solution (60 ml/kg) instilled via PA (n = 5) or LA (n = 5). Simultaneously, MAA-99mTc was given using the same respective route and the isotope uptake quantified at different TB levels after heart-lung block harvest and dissection of all tissue adjacent to TB: proximal and distal trachea and right and left main bronchi. Retrograde distribution resulted in a significantly higher 99mTc count compared to the PA route (p < 0.01).

Actions of xylazine in young swine.

OBJECTIVE: To determine sedative, analgesic, and basic cardiovascular effects of xylazine administered to pigs. ANIMALS: 6 two-month-old Landrace x Large White pigs. PROCEDURE: Xylazine was administered i.v. at increasing dosages (1, 2, 4, 8, and 16 mg/kg of body weight) to otherwise unmedicated, conscious pigs, and the aforementioned effects were determined before xylazine administration and 2, 5, 10, and 15 minutes later. Then a higher xylazine dosage was given after the 15-minute measurements were taken. RESULTS: None of the xylazine dosages induced sufficient analgesia to prevent painful response to tail clamping; considerable excitation with vocalization and without appreciable sedative effect was observed at all dosages. At lower dosages, cardiovascular effects were characterized by bradycardia and biphasic blood pressure response; initial hypertension was followed by hypotension. At higher dosages, severe hypotension with moderate bradycardia was followed by marked bradycardia and return to normal baseline values or slight increase in blood pressure. CONCLUSION: Xylazine did not induce adequate sedative or analgesic effects in pigs at any dosage tested; however, cardiovascular effects were considerable. These effects of xylazine differ from those observed in other domestic species.

[Cardiorespiratory and analgesic effects of continuous infusion of propofol in swine as experimental animals]. / Efectos cardiorrespiratorios y analgésicos de la infusión continua de propofol en el cerdo como animal de experimentación.

HYPOTHESIS AND OBJECTIVES: To study the effects of 3 doses of continuous infusion of propofol on heart rate (HR), arterial pressure (AP), cardiac output (CO), pulmonary artery pressure (PAP), pulmonary capillary pressure (PCP), central venous pressure, flow volume, minute volume, arterial gases and analgesic effect. MATERIAL AND METHODS: Eighteen Landrace-Large-White pigs were randomly assigned to 3 groups of 6 based on dose of propofol used. An intravenous dose of 2 mg/kg propofol was followed by the continuous infusion corresponding to each group: group I (GI) received 9 mg/kg/h, group II (GII) received 11 mg/kg/h and group III (GIII) received 13 mg/kg/h, each for a period of 1 hour. Variables were recorded 5, 15, 30, 45 and 60 min after the intravenous induction dose. When the infusion was withdrawn, the time elapsing before recovery of sternal decubitus (SDT) position was recorded for each animal. RESULTS: The following changes from baseline values were statistically significant: AP and PAP increased and PaO2 and MV decreased in GI, with SDT recovery after 27 +/- 4 min; PA increased and FV decreased in GII, while SDT recovery was at 29 +/- 5 min; and diastolic arterial pressure, PCP, CO and HR decreased in GIII. All the pigs in the last group experienced apnea requiring mechanical ventilation and SDT was recovered after 63 +/- 7 min. PCP was significantly higher in GII and GIII than in GI. None of the doses produced an analgesic effect.

Cardiopulmonary and analgesic effects of xylazine, detomidine, medetomidine, and the antagonist atipamezole in isoflurane-anesthetized swine.

The cardiovascular and respiratory effects of three alpha(2)-adrenergic agonists (xylazine 2mg/kg of body weight; detomidine, 40 micrograms/kg; medetomidine, 40 micrograms/kg) and their specific antagonist, atipamezole (200 micrograms/kg) were examined in young, isoflurane-anesthetized (1.3% end-tidal concentration) swine (weight range, 15 to 35 kg). The intravenous administration of all three alpha(2)-agonists caused an initial significant (P < 0.05) but short-lived increase in arterial blood pressure. Atipamezole also increased blood pressure, and this effect persisted throughout the period of observation. All agonists caused a sustained significant bradycardia, whereas atipamezole significantly increased heart rate (30 +/- 7 beats per min). The cardiac index tended to transiently decrease 5 to 10 min after agonist injection (significant only for xylazine at 2 min after injection) from an average pre-injection value of 166 ml/kg per min and did not change in response to atipamezole. None of the drugs significantly modified arterial blood gas (PaO2, PaCO2) or pH values. Xylazine and medetomidine but not detomidine or atipamezole manifested short-lived analgesic properties in response to clamping of the interdigital fold.

Hepatic resuscitation after warm anoxia: one approach for increasing the donor pool for liver transplantation.

The deleterious effects of warm anoxia on the liver are seen to be irreversible if cooling and transplantation (LT) follow immediately after. The aim of our study is to demonstrate that livers subjected to anoxia may be suitable for LT if a period of resuscitation is interposed before the cooling process. Forty female Large White pigs were used. Preservation (Euro-Collins solution) and LT technique were the same in all 20 procedures. All donors underwent clamping of the porta hepatis at the end of harvesting dissection. In the so-called "resuscitated" groups (AR and BR), the clamp was released for a period of time before the liver was cooled. Then, all livers underwent 2 h of cold ischemia followed by LT. Ultrastructural study showed better maintenance of mitochondria and sinusoidal cell integrity in resuscitated livers after LT. Liver synthesis of total adenine nucleotides, graft function and recipient survival were found to be better in the "resuscitated" groups. In conclusion, anoxic livers may be retrieved for LT if a resuscitation period (i.e. aerobic perfusion) is allowed prior to cold preservation. Longer periods of warm anoxia are needed to further support these preliminary results.

Cardiopulmonary and analgesic effects of epidural lidocaine, alfentanil, and xylazine in pigs anesthetized with isoflurane.

To determine cardiopulmonary and analgesic effects of lidocaine, alfentanil, and xylazine in pigs anesthetized with isoflurane, 18 healthy Landrace-Large White pigs were studied (six for each drug). General anesthesia was induced with isoflurane in O2 and maintained with 1% to 1.2% end-tidal ISO, ensuring presence of a pain response before epidural drug administration. Heart rate (HR), arterial blood pressures (AP), cardiac output (CO), pulmonary arterial pressure, pulmonary capillary wedge pressure (PCWP), central venous pressure, respiratory rate (RR), tidal volume (TV), minute volume (MV), arterial blood gas data, core temperature (CT), and analgesic effects (by picking the lumbar area and the abdominal wall) were determined at various times (2, 5, 15, 30, 45, 60, and 90 minutes) after epidural administration of lidocaine (5 mg/kg), alfentanil (5 micrograms/kg), or xylazine (0.2 mg/kg), all diluted in NaCl 0.9% to 0.5 mL/kg. Statistical analysis included two-way analysis of variance for repeated measures and the least significant difference test for determining differences among means. A probability level of P < .05 was used. The following results were statistically significant decreases in systolic AP, HR, TV, RR, MV, CT, pH, PaO2, and TCO2 and increases in PCWP, PaCO2, and HCO3 after LID. After ALF, only CT and HCO3 decreased. Core temperature and TV decreased after XYL. Lidocaine provided 45 to 60 minutes of analgesia. Alfentanil had no analgesic effects, and xylazine provided 90 minutes of analgesia. The authors conclude that xylazine, when injected epidurally, provides suitable analgesia in isoflurane-anesthetized pigs.