Clinical and Histological Effects of the Intrathecal Administration of a Single Dose of Dexmedetomidine in Rabbits.

BACKGROUND: There is experimental evidence that dexmedetomidine has neuroprotective effects. So, it could be expected that its intrathecal or epidural administration presents no harm. However, whether dexmedetomidine is neurotoxic to the spinal cord remains to be fully elucidated. OBJECTIVE: To evaluate the effect of preservative-free dexmedetomidine administered as a subarachnoid single injection on the spinal cord and meninges of rabbits. STUDY DESIGN: Research article. SETTING: Experimental research laboratory. METHODS: Twenty young adult female rabbits, each weighing between 3200 and 4900 g, and having a spine length between 36 and 40 cm, were divided by lot into 2 groups (G): 0.9% saline in G1 and preservative-free dexmedetomidine in G2 (dose of 10 µg). After intravenous anesthesia with ketamine and xylazine, the subarachnoid space was punctured at S1-S2 under ultrasound guidance, and a random 5 µl.cm-1 of spinal length (0.2 mL) of solution (saline or dexmedetomidine) was injected. The animals remained in captivity for 21 days under medical observation and were sacrificed by decapitation. The lumbosacral spinal cord portion was removed for immunohistochemistry to assess the glial fibrillary acidic protein (GFAP), and histology was assessed using hematoxylin and eosin (HE) stain. RESULTS: None of the animals had impaired motor function or decreased nociception during the period of clinical observation. None of the animals from the control group showed signs of injuries to meninges. In the dexmedetomidine group, however, 9 animals presented with signs of meningeal injury. The main histological changes observed were areas with meningeal thickening and lymphoplasmocitary infiltration in the pia-mater and arachnoid. Further histological examination also revealed adherence areas among the pia and arachnoid. There was no signal of injury in neural tissue in any animal of both groups. LIMITATIONS: Evaluation of the possible analgesic effects of the intrathecal dexmedetomidine was not performed. CONCLUSION: On the basis of the present results, dexmedetomidine administered in the subarachnoid space in a single dose of 10 µg is capable of producing histological changes over the meninges of rabbits.

Fluid resuscitation using the intraosseous route: infusion with lactated Ringer's and hetastarch.

OBJECTIVE: The effectiveness of the intraosseous (IO) route for fluid resuscitation remains uncertain. This study compares IO infusion rates and estimated volume expansion using clinically relevant infusion pressures with lactated Ringer's (LR) and hetastarch (HES). METHODS: IO needles were placed in the sternum or tibia for infusion of HES and LR in 8 Yorkshire pigs. Pressures were recorded at variable flow rates and linear regression used to identify flow rates at 100 and 400 mm Hg. Volume expansion was calculated for a 10-minute infusion. RESULTS: Mean LR flow rates (mL x min(-1)) were 24/111 (tibia--100/400 mm Hg) and 8/34 (sternum--100/400 mm Hg). The HES flow rates (mL x min(-1)) of 10/44 (tibia--100/400 mm Hg) and 6/26 (sternum--100/400 mm Hg) were significantly lower or -40% (p < 0.01) of the LR flow rates into the tibia and -70% (p < 0.05) into the sternum. Mean volume expansion (mL) for a 10-min infusion of LR was estimated to be 80/369 (tibia--100/400 mm Hg) and 27/112 (sternum--100/400 mm Hg). In comparison, HES volume expansion was -20% higher for the tibia (p > 0.05) and 110% to 120% higher for the sternum (p < 0.05). CONCLUSION: HES flow rates are lower than LR flow rates in the sternum and tibia of swine. Sternal infusion of HES is likely to provide greater estimated intravascular volume expansion than LR despite the lower infusion rates.

Clinical and histological effects of the intrathecal administration of methylprednisolone in dogs.

BACKGROUND: Methylprednisolone is one of the most commonly used steroids for management of chronic back pain via epidural injection. Its inadvertent injection into the intrathecal space is associated with complications such as adhesive arachnoiditis. OBJECTIVE: The present study aimed to assess the clinical and histological changes associated with the injection of methylprednisolone into the intrathecal space of dogs. STUDY DESIGN: A randomized, double blind, controlled animal trial. METHODS: After approval by the animal research ethics committee, 14 dogs were studied in a randomized double blind controlled trial. They were assigned to one of 2 groups: Group I received 1 mL of 0.9% normal saline; Group II received 1 mL (1.15mg/kg) of methylprednisolone into the intrathecal space. Animals were clinically evaluated for 21 days, and then sacrificed. The lumbar and sacral portions of their spinal cords were removed for histological examination. RESULTS: In Group I, there were no clinical or histological changes. All animals in Group II showed no clinical changes but all exhibited histological changes in the spinal cord. The main histological changes consisted of meningeal thickening and lymphocytic infiltrates in the blood vessels. In 3 animals, adhesion of pia, arachnoid, and dura matter was noted and the nerve roots were surrounded by fibrosis. In one animal, necrosis of the spinal cord was evident. LIMITATIONS: The limitations of the present study include: small sample of animals (n=14), relative short clinical follow-up (21 days), and use of a commercially available drug solution, which is not preservative free. CONCLUSION: The present study demonstrated that the intrathecal administration of commercially available methylprednisolone was responsible for causing histological changes in the spinal cord and meninges of the animals studied.

Anestesia em paciente obstétrica portadora de anemia falciforme e traço talassêmico após plasmaféresis: relato de caso / Anesthesia in obstetric patient with sickle cell anemia and thalassemic trait after plasmapheresis: case report

JUSTIFICATIVA E OBJETIVOS: A plasmaféresis é a técnica de tratamento de escolha para pacientes com anemia hemolítica grave. Uma de suas conseqüências é a depleção de colinesterase plasmática, o que interfere na metabolização de alguns bloqueadores neuromusculares de uso corrente na prática anestesiológica. RELATO DO CASO: Paciente com 26 anos, estado físico ASA IV, gestação de 30 semanas e 3 dias, portadora de anemia falciforme, traço talassêmico e alo-imunização para antígenos de alta freqüência. Apresentou crise de falcização, sendo transfundida com derivado sangüíneo incompatível. Evoluiu com hemólise maciça, sendo admitida com hemoglobina de 3 g/dL e hematócrito de 10 por cento, icterícia intensa, taquicardia, apatia e descoramento. Na avaliação hematológica concluiu-se ser situação de inexistência de sangue compatível para transfusão. Foi tratada com corticoterapia, imunoglobulinas e plasmaféresis. No segundo dia de internação, evoluiu com insuficiência renal aguda e edema pulmonar agudo, piora do estado geral e instabilidade hemodinâmica. Indicada a resolução da gestação em decorrência do quadro clínico da paciente e do sofrimento fetal agudo que se sobrepôs. A paciente foi admitida na sala de operações consciente, dispnéica, pálida, ictérica, SpO2 de 91 por cento em ar ambiente, freqüência cardíaca de 110 bpm e pressão arterial de 110 x 70 mmHg, em uso de dopamina (1 æg.kg-1.min-1) e dobutamina (10 æg.kg-1.min-1). Optou-se por anestesia geral balanceada, com alfentanil (2,5 mg), etomidato (14 mg) e atracúrio (35 mg) e isoflurano. Não se observou intercorrências anestésico-cirúrgicas. Ao final, a paciente foi encaminhada à UTI, sob intubação orotraqueal, e em uso de drogas vasoativas, tendo sido extubada após 3 horas. CONCLUSÕES: Este caso mostrou-se um desafio para a equipe, visto que a paciente apresentava instabilidade hemodinâmica e alteração do coagulograma, condições que contra-indicam a anestesia regional; além disto, a plasmaféresis potencialmente depleta os estoques de colinesterases plasmáticas, o que interfere na anestesia. Entretanto, o arsenal medicamentoso disponível permitiu o manuseio seguro desta situação.

[Anesthesia in obstetric patient with sickle cell anemia and thalassemic trait after plasmapheresis: case report]. / Anestesia em paciente obstétrica portadora de anemia falciforme e traço talassêmico após plasmaféresis: relato de caso.

BACKGROUND AND OBJECTIVES: Plasmapheresis is the technique of choice for severe hemolytic anemia patients. A consequence is plasma cholinesterase depletion, which interferes with metabolism of some neuromuscular blockers currently used in anesthesiology. CASE REPORT: Pregnant patient, 26 years old, physical status ASA IV, 30 weeks and 3 days gestational age, with sickle cell anemia, thalassemic trait and allo-immunization for high frequency antigens. Patient presented sickling crisis being transfused with incompatible blood. Patient evolved with massive hemolysis being admitted with 3 g/dL hemoglobin and 10% hematocrit, severe jaundice, tachycardia, apathic and pale. Hematological evaluation has concluded for the inexistence of compatible blood for transfusion. Patient was treated with steroids, immunoglobulins and plasmapheresis. In the second admission day patient evolved with acute renal failure and pulmonary edema, general state worsening and hemodynamic instability. Gestation resolution was indicated due to patient's clinical conditions and consequent acute fetal suffering. Patient was admitted to the operating room conscious, pale, with dyspnea, jaundice, 91% SpO2 in room air, heart rate of 110 bpm and blood pressure of 110 x 70 mmHg, under dopamine (1 microg.kg-1.min-1) and dobutamine (10 microg.kg-1.min-1). We decided for balanced general anesthesia with alfentanil (2.5 mg), etomidate (14 mg), atracurium (35 mg) and isoflurane. There were no anesthetic-surgical intercurrences. Patient was referred to ICU after surgery completion under tracheal intubation and vasoactive drugs, being extubated 3 hours later. CONCLUSIONS: This case was a challenge for the team since patient was hemodynamically instable with coagulogram abnormalities counterindicating regional anesthesia. In addition, plasmapheresis potentially depletes plasma cholinesterase reserves, interfering with anesthesia. However, available drug armamentarium has allowed for the safe management of this situation.