Effects of prone position on alveolar dead space and gas exchange during general anaesthesia in surgery of long duration.

BACKGROUND AND OBJECTIVE: We investigated the effects of prone position on respiratory dead space and gas exchange in 14 anaesthetized healthy patients undergoing elective posterior spinal surgery of more than 3 h of duration. METHODS: The patients received a total intravenous anaesthetic with propofol/remifentanil/cisatracurium. They were ventilated at a tidal volume of 8-10 mL kg(-1), zero positive end-expiratory pressure and an inspired oxygen fraction of 0.4. Physiological, airway and alveolar dead spaces were calculated by analysis of the volumetric capnography waveform. Measurements were made in supine position (20 min after the beginning of mechanical ventilation) and 30, 120 and 180 min after turning to prone position. RESULTS: We found that the alveolar dead space/tidal volume ratio did not change. PaO(2)/F(i)O(2) increased, although not statistically significantly. Dynamic compliance was reduced due to a reduction in tidal volume and an increase in plateau pressure. CONCLUSIONS: Patients undergoing surgery in prone position for a duration of 3 h under general anaesthesia including muscle relaxation and mechanical ventilation without positive end-expiratory pressure have stable haemodynamics and no significant changes in the alveolar dead space to tidal volume ratio. Oxygenation tended to improve.

[Clinical effect of mivacurium in morbidly obese patients]. / Efecto clínico del mivacurio en pacientes con obesidad mórbida.

OBJECTIVES: To compare the clinical effect of mivacurium in morbidly obese and normal-weight patients. PATIENTS AND METHODS: Ten morbidly obese patients (body mass index >40) and 10 normal-weight patients (body mass index, 21-24) with normal plasma cholinesterase levels. Anesthesia was provided with propofol and remifentanil in continuous infusion and a mixture of oxygen and nitrous oxide. Mivacurium was administered at a dose based on the patient's weight (0.15 mg x kg(-1)). The neuromuscular block was monitored by train-of-four (TOF) acceleromyography after stimulation of the cubital nerve at the forearm. We measured the onset time (time from administration of the muscle relaxant to 95% twitch depression), duration of block (times from dosing to 5% recovery after the first twitch [T1] of a TOF stimulus and to a TOF ratio of 80%), and the recovery indices (time between 25% and 75% recovery after T1 and between recovery of TOF ratios of 25% and 80%). Groups were compared with the Student t test. RESULTS: Mean (SD) onset time was similar in the 2 groups (normal weight 2.73 [1] minutes vs morbidly obese 1.91 [0.6] minutes). Other measures of duration and recovery were also similar in the 2 groups, respectively: duration of dose-T1 5%, 12.23 (2.1) vs 11.45 (3) minutes; dose-TOF ratio 80%, 24.71 (4.6) vs 24.81 (5) minutes); recovery index T1 25%-75%, 6.45 (2) vs 5.56 (1) minutes; recovery of TOF ratio T1 25%-80%, 9 (2) vs 10.11 (2) minutes. CONCLUSION: We found no differences in the clinical effect of mivacurium between morbidly obese and normal-weight patients when doses were based on real weight.

Efecto clínico del mivacurio en pacientes con obesidad mórbida / Clinical effect of mivacurium in morbidly obese patients

OBJETIVOS: Comparar el efecto clínico del mivacurioen pacientes con obesidad mórbida y pacientes con normo-peso.PACIENTES Y MÉTODOS: Se estudiaron 10 pacientescon obesidad mórbida (Índice de masa corporal(IMC)>40) y 10 pacientes con normo-peso (IMC 21-24)con actividad de colinesterasa plasmática normal. Laanestesia se realizó con propofol y remifentanilo eninfusión continua y mezcla de O2/N2O. Se administró0,15 mg Kg-1 de mivacurio en base al peso real delpaciente. El bloqueo neuromuscular se monitorizó poraceleromiografía tras estimulación del nervio cubital anivel del antebrazo. Se registró la instauración del bloqueo(tiempo desde la dosis a la depresión de la respuestadel estímulo simple del 95%), duración del bloqueo(tiempos desde la dosis hasta la recuperación de laprimera respuesta del TOF (T1) del 5% y del TOF ratio(TOFr) del 80% y los índices de recuperación T1 25-75% y T1 25%-TOFr 80%. Los grupos se compararoncon la prueba t-Student.RESULTADOS: Los grupos fueron similares en la instauracióndel bloqueo (normo-peso 2,73±1 min vs obesidadmórbida 1,91±0,6 min), en su duración (Dosis-T1 5%:12,23±2,1 vs 11,45±3 min; Dosis-TOFr 80%: 24,71±4,6 vs24,81±5 min) y en los parámetros de recuperación (T1 25-75%: 6,45±2 vs 5,56 ± 1 min; T1 25%-TOFr 80%: 9±2 vs10,11±2 min).CONCLUSIÓN: No encontramos diferencias en el efectoclínico del mivacurio entre pacientes con obesidad mórbiday pacientes con normo-peso cuando se dosifica enfunción del peso real

OBJECTIVES: To compare the clinical effect of mivacuriumin morbidly obese and normal-weight patients.PATIENTS AND METHODS: Ten morbidly obese patients(body mass index >40) and 10 normal-weight patients(body mass index, 21-24) with normal plasma cholinesteraselevels. Anesthesia was provided with propofol andremifentanil in continuous infusion and a mixture ofoxygen and nitrous oxide. Mivacurium was administeredat a dose based on the patient's weight (0.15 mg·kg-1).The neuromuscular block was monitored by train-offour(TOF) acceleromyography after stimulation of thecubital nerve at the forearm. We measured the onsettime (time from administration of the muscle relaxant to95% twitch depression), duration of block (times fromdosing to 5% recovery after the first twitch [T1] of aTOF stimulus and to a TOF ratio of 80%), and the recoveryindices (time between 25% and 75% recovery afterT1 and between recovery of TOF ratios of 25% and80%). Groups were compared with the Student t test.RESULTS: Mean (SD) onset time was similar in the 2groups (normal weight 2.73 [1] minutes vs morbidly obese1.91 [0.6] minutes). Other measures of duration and recoverywere also similar in the 2 groups, respectively: durationof dose-T1 5%, 12.23 (2.1) vs 11.45 (3) minutes; dose-TOF ratio 80%, 24.71 (4.6) vs 24.81 (5) minutes); recoveryindex T1 25%-75%, 6.45 (2) vs 5.56 (1) minutes; recoveryof TOF ratio T1 25%-80%, 9 (2) vs 10.11 (2) minutes.CONCLUSION: We found no differences in the clinicaleffect of mivacurium between morbidly obese and normalweightpatients when doses were based on real weight