The cuff method: a pilot study of a new method of monitoring neuromuscular function.

BACKGROUND: A new method of monitoring neuromuscular blockade based on a modified blood pressure cuff that incorporates stimulating electrodes was compared with mechanomyography (MMG) ('gold standard'). METHODS: Forty adults and 20 children (ASA I-II) underwent neuromuscular blockade monitoring on the contralateral arms and on the same arm using the new cuff method and MMG. Only train-of-four (TOF) ratios > 0.1 and T(1) heights > 0 were studied. Supramaximal stimulation was also assessed. A device based on a PC with an analogue-to-digital conversion card was used to control and synchronize MMG and the cuff method. The agreement between both methods was assessed using the statistical method of Bland and Altman. RESULTS: When TOF ratios were >0.7, the bias between the two methods was -0.04 with the limits of agreement ranging from -0.21 to -0.12 (95% CI -0.06 to -0.02). The T(1) > 0 heights bias was -0.01 with the limits of agreement ranging from -0.26 to 0.24 (95% CI -0.02 to -0.003). The sensitivity of the cuff method was 88%, with a specificity of 85% and an accuracy of 86%. CONCLUSION: This pilot study indicates that the cuff method could be useful to monitor neuromuscular blockade according to the bias and limits of agreement compared with MMG, particularly when the degree of blockade was evaluated by TOF ratios > 0.7. The new cuff method is easy and simple to use. However, further studies in a larger number of patients are necessary to confirm these favourable preliminary results.

Atelectasia pulmonar secundaria a arrancamiento adenoideo, una complicación infrecuente de la intubación nasotraqueal / Pulmonary atelectasia secondary to adenoid uprooting. A rare complication of nasotracheal intubation

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Selective versus non-selective neural stimulation in the monitoring of muscular relaxation during general anesthesia.

AIM: The depth of muscular relaxation during general anesthesia is monitored through the analysis of the contraction evoked by selective electrical stimulation of a peripheral nerve. The aim of this study was to compare the method of selective stimulation (SS) to a new method based on non-selective electrical stimulation (NSS) delivered over the muscle. METHOD: Electrical stimuli were delivered as train-of-four impulses to the ulnar nerve (SS) and to the ventral aspect of the contralateral forearm (NSS). The muscular responses of the adductor pollicis brevis (SS) and the forearm supinator longus (NSS) were studied at 30-60 s intervals with piezoelectric transducers before and after the administration of atracurium bolus doses of 0.5 mg/kg to patients under general anesthesia. SS and NSS evoked muscular responses were quantitized as percentages of the control response and compared with linear correlation and concordance analysis. RESULTS: Twenty patients were studied. Basal and post-atracurium muscular responses were similar for the SS and the NSS methods. Precision between SS and NSS was >85% and accuracy >92%. Concordance was: basal <15%, relaxation <5%, recovery <10%. CONCLUSION: NSS is equivalent to SS for muscular relaxation monitoring during general anesthesia. This has important implications to simplify muscular relaxation monitor design.

Mathematical analysis of epidural space location.

BACKGROUND: The location of epidural space for local anaesthetic injection can be difficult. The aim of this study was to define the mathematical function of the pressure changes in the syringe during puncture of the epidural space. Knowledge of pressure changes might be of help to the anesthetist who attempts to ascertain the location of the needle, and it is essential to the design of a device with which to locate epidural space. METHODS: Epidural punctures were performed in 20 patients, using an 18-Tuohy needle connected to a 10 ml syringe. The epidural space was located by the loss of resistance technique. Pressure variations within the injection system during epidural puncture were measured and digitized at 250 Hz. Pressure curves were analyzed for amplitude and rate of a decay after entry of the needle into the epidural space. RESULTS: Pressure increased as the needle passed through skin, subcutaneous fat and muscle. The maximal pressure was observed when the needle perforated the ligamentum flavum (689 +/- 124 cm H2O). When the needle entered the epidural space, an exponential decrease in pressure was observed in all patients (R2 = 0.99; tau = 2.1 +/- 0.9 seconds). End-residual pressure was 22 +/- 12 cm H2O. The change in pressure observed when the needle entered the epidural space fitted a negative exponential function (y = e-x/2.08). CONCLUSIONS: Pressures within the injection system for epidural puncture can reach 1100 cm H2O. Location of the epidural space is characterized by an exponential decay to and end-residual pressure below 50 cm H2O, with a constant time of approximately 2 seconds.