Nitrous oxide does not produce a clinically important sparing effect during closed-loop delivered propofol-remifentanil anaesthesia guided by the bispectral index: a randomized multicentre study.

BACKGROUND: Nitrous oxide (N2O) offers both hypnotic and analgesic characteristics. We therefore tested the hypothesis that N2O administration decreases the amount of propofol and remifentanil given by a closed-loop automated controller to maintain a similar bispectral index (BIS). METHODS: In a randomized multicentre double-blind study, patients undergoing elective surgery were randomly assigned to breathe 60% inspired N2O (N2O group) or 40% oxygen (AIR group). Anaesthesia depth was evaluated by the proportion of time where BIS was within the range of 40-60 (BIS40-60). The primary outcomes were propofol and remifentanil consumption, with reductions of 20% in either being considered clinically important. RESULTS: A total of 302 patients were randomized to the N2O group and 299 to the AIR group. At similar BIS40-60 [79 (67-86)% vs 76 (65-85)%], N2O slightly decreased propofol consumption [4.5 (3.7-5.5) vs 4.8 (4.0-5.9) mg kg(-1) h(-1), P=0.032], but not remifentanil consumption [0.17 (0.12-0.23) vs 0.18 (0.14-0.24) µg kg(-1) min(-1)]. For the subgroups of men, at similar BIS40-60 [80 (72-88)% vs 80 (70-87)%], propofol [4.2 (3.4-5.3) vs 4.4 (3.6-5.4) mg kg(-1) h(-1)] and remifentanil [0.19 (0.13-0.25) vs 0.18 (0.15-0.23) µg kg(-1) min(-1)] consumptions were similar in the N2O vs AIR group, respectively. For the subgroups of women, at similar BIS40-60 [76 (64-84)% vs 72 (62-82)%], propofol [4.7 (4.0-5.8) vs 5.3 (4.5-6.6) mg kg(-1) h(-1), P=0.004] and remifentanil [0.18 (0.13-0.25) vs 0.20 (0.15-0.27) µg kg(-1) min(-1), P=0.029] consumptions decreased with the co-administration of N2O. CONCLUSIONS: With automated drug administration titrated to comparable BIS, N2O only slightly reduced propofol consumption and did not reduce remifentanil consumption. There was a minor gender dependence, but not by a clinically important amount. Clinical trial registration This study was registered at ClinicalTrials.gov, number NCT00547209.

[The "high concentration" oxygen mask: a dangerous defect]. / Masque à oxygène "haute concentration": une malfaçon dangereuse.

Three cases of unidirectional valve inversion in airtight oxygen masks are reported. These defects were discovered before use on a patient. One of the masks was tested on a healthy volunteer. It resulted in the rupture of the reservoir bag, with a oxygen leak and decrease in FiO2. Checking the valve before use is therefore mandatory, and fabrication procedures should be revised.

[Severe confusion following a theophylline-cimetidine combination]. / Etat confusionnel grave lors de l'association théophylline-cimétidine.

Cimetidine and theophylline were given together to a 67 year old chronic bronchitic post-operatively: the patient became very confused, shook of all his limbs, vomited, and presented a tachycardia. The greater than normal blood levels of theophylline (27.8 mg . 1(-1) confirmed its involvement in this clinical state. But, as there was no real overdose, the simultaneous administration of cimetidine was probably responsible for inducing this state. Three days after stopping this treatment, the disorder had completely disappeared.

[Urinary excretion of creatinine and 3-methylhistidine in multiply injured patients]. / Excrétion de créatinine et de 3,méthylhistidine urinaire chez les polytraumatisés.

The daily urinary excretion of 3,methylhistidine (3,MeHis) was measured in eight severely injured patients for periods of at least two weeks to at most one month after the trauma. The patients were fed with 0.20 +/- 0.05 g X kg-1 X 24 h-1 of nitrogen and 25 +/- 5 kcal X kg-1 X 24 h-1 given as glucose. The pattern of 3,MeHis and creatinine excretion as well as the weight loss suggested the following: 1) the muscle protein breakdown in these patients was approximately twice the normal value (the mean 3,MeHis excretions were respectively 7.98, 7.21, 6.26 and 5.14 mumol X kg-1 X 24 h-1 for the four week study period, compared with the normal value of 3.73); 2) the creatinine excretion decreased slowly. This showed the magnitude of muscle wasting in these patients who, in one month, could lose up to 20% of their initial weight. Various factors could be responsible for increasing and extending the muscle protein catabolism: the importance of muscle damage, the metabolic response to neurotrauma, sepsis and prolonged immobilization. In these conditions, it would seem useless and even harmful to try, at all costs, to obtain a positive nitrogen balance. The authors suggest therefore an average intake of 0.2 g X kg-1 X 24 h-1 of nitrogen, which should be sufficient to meet the requirements for protein synthesis.

[Aneurysm of the abdominal aorta and preoperative disseminated intravascular coagulation]. / Anévrysme de l'aorte abdominale et coagulation intravasculaire préopératoire.

A case of abdominal aortic aneurysm associated with preoperative signs of disseminated intravascular coagulation is reported. The 69-year-old female patient presented with spontaneously appearing petechiae and bruising. She had 0.95 g.l-1 fibrinogen, 105 G.l-1 platelets, and 100 micrograms.ml-1 fibrin and fibrinogen degradation products. Investigations revealed an 80 mm diameter aneurysm of the abdominal aorta, extending from the coeliac trunk to the iliac arteries. Heparin 7,000 IU.day-1 resulted in a biological improvement for a week only. At that time, levels of coagulation factors were: 92% factor II, 88% factor V, 100% factors VII and X, 100% antithrombin III. Surgical cure of the aneurysm was nevertheless carried out. Twenty standard units of platelets, 8 g fibrinogen, four units of fresh frozen plasma, five homologous and two autologous red cell units were transfused during the procedure. No coagulation factors were necessary during the postoperative course, which was uneventful. The management of coagulation factor infusions, before or after aortic cross-clamping, is discussed.