Effect of weight gain during pregnancy on heart rate variability and hypotension during caesarean section under spinal anaesthesia.

The purpose of this study was to assess the effect of antenatal weight gain on baseline heart rate variability and incidence of hypotension in singleton parturients with a normal pre-pregnancy body mass index, presenting at term for elective caesarean section under spinal anaesthesia. Sixty-six parturients, of ASA physical status 1-2, were allocated to one of three groups according to their weight gain during pregnancy: < 11 kg; 11-16 kg; and > 16 kg. Mean (SD) approximate entropy of baseline heart rate was significantly higher in the < 11 kg group (0.27 (0.11)) compared with the 11-16 kg group (0.14 (0.08)) and the > 16 kg group (0.14 (0.07)) (both p < 0.001). The incidence of hypotension in the < 11 kg group (17/22; 77%) was significantly higher than in the 11-16 kg group (7/22; 32%) (p = 0.006) and the > 16 kg group (8/22; 36%) (p = 0.01). We conclude that weight gain < 11 kg during pregnancy is associated with increased baseline heart rate variability and a higher incidence of hypotension at the time of elective caesarean section under spinal anaesthesia.

Tracheal intubation following training with the GlideScope compared to direct laryngoscopy.

SUMMARY: Tracheal intubation using direct laryngoscopy has a high failure rate when performed by untrained medical personnel. This study compares tracheal intubation following direct laryngoscopy by inexperienced medical students when initially trained by using either the GlideScope, a video assisted laryngoscope, or a rigid (Macintosh) laryngoscope. Forty-two medical students with no previous experience in tracheal intubation were randomly divided into two equal groups to receive training with the GlideScope or with direct laryngoscopy. Subsequently, each medical student performed three consecutive intubations on patients with normal airways that were observed by a anaesthetist who was blinded to the training method. The rates of successful intubation were significantly higher in the Glidescope group after the first (48%), second (62%), and third (81%) intubations compared with the Macintosh group (14%, 14% and 33%; p = 0.043, 0.004 and 0.004, respectively). The mean (SD) times for the first, second, and third successful tracheal intubations were significantly shorter in the Glidescope group (59.3 (4.4) s, 56.6 (7.1) s and 50.1 (4.0) s) than the Macintosh group (70.7 (7.5) s, 73.7 (7.3) s and 67.6 (2.0) s; p = 0.006, 0.003 and 0.0001, respectively). Training with a video-assisted device such as the GlideScope improves the success rate and time for tracheal intubation in patients with normal airways when this is performed by inexperienced individuals following a short training programme.

Changes in resistances of endotracheal tubes with reductions in the cross-sectional area.

BACKGROUND AND OBJECTIVES: Partial obstruction of endotracheal tubes due to accumulation of secretions and mucus plugs can increase the tube resistance and subsequently impose increased resistive load on the patient. This study was performed to determine the changes in the resistance of endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm with different degrees and locations of endotracheal tube narrowing. METHODS: Reductions of 10%, 25%, 50% and 75% in the endotracheal tube's cross-sectional areas were created at different sites along the axes of the tube connected to an artificial lung. While ventilating with a constant inspiratory flow, a 1 s end-inspiratory occlusion manoeuvre was applied and the resulting plateau pressure was determined. The resistance was calculated as (peak airway pressure--plateau pressure)/peak inspiratory flow. RESULTS: Significant increases in the endotracheal tube's resistances were observed as the tube's cross-sectional area reduction was increased from 25% to 50% and from 50% to 75% for the 7.5 mm endotracheal tube, from 25% to 50% for the 8.0 mm endotracheal tube, and from 50% to 75% for the 8.5 mm endotracheal tube. Changes of the endotracheal tube resistances were not affected by the site of cross-sectional area reductions along the axes of the tubes. CONCLUSIONS: For endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm, significant changes in the tubes resistances are observed when the partial obstructions of the tubes exceed certain critical values. The location of the partial obstruction did not affect the changes in the endotracheal tube resistances.

Evaluation of hemostasis by the Clot Signature Analyzer: a potentially valuable device for the anesthesiologist.

Rapid detection of hemostatic defects presents a challenge for the anesthesiologist who must balance anesthetic and surgical considerations for maintaining adequate platelet and coagulant factors, while keeping allogenic blood exposure to a minimum. The Clot Signature Analyzer, a point-of-care device capable of rapid response and easy interpretation is described here. Its applicability in two obstetrical patients with platelet dysfunction is discussed.

Electromyographic assessment of ulnar nerve motor block induced by lidocaine.

STUDY OBJECTIVE: To determine the differences in the onset time and duration of motor block produced by lidocaine 1% and lidocaine 2% via a quantitative and objective method, the measurement of compound muscle action potentials (CMAPs). STUDY DESIGN: Prospective study. SETTING: Main operating rooms of a university hospital. PATIENTS: 20 consecutive patients undergoing surgery not requiring intraoperative muscle relaxation. INTERVENTIONS: General anesthesia with unilateral ulnar nerve block was administered. In patients' nondominant (experimental) arms, an insulated block needle was placed adjacent to the ulnar nerve at the wrist while continuous nerve stimulation was delivered to ensure its proper placement. Through this needle, lidocaine 1% or lidocaine 2% was injected. The dominant (control) arm received no injection. MEASUREMENTS AND MAIN RESULTS: Monitoring of ulnar nerve-evoked CMAPs was performed simultaneously on both arms. Ulnar nerve function was assessed at baseline and then at 10-second intervals by automatically measuring the amplitude of the evoked CMAPs on a two-channel electromyogram. The mean (+/- SEM) baseline CMAP amplitude prior to injection of lidocaine 1% was 3.10 +/- 0.87 mV and 3.06 +/- 0.89 mV for the experimental and control ulnar nerves, respectively (p = NS); for lidocaine 2%, baseline CMAP amplitude was 3.58 +/- 1.39 mV and 3.70 +/- 1.46 mV, respectively (p = NS). Over the course of the study, the control CMAP amplitude varied by < 12%. At the experimental ulnar nerve, 90% CMAP decrease after injection of lidocaine 1% and lidocaine 2% occurred 7.5 +/- 2 minutes and 5 +/- 1.5 minutes, respectively (p = NS), whereas maximal blockade was achieved after 15 +/- 3 minutes and 11 +/- 5 minutes, respectively (p = NS). Recovery of CMAP to 90% of baseline occurred 184 +/- 31 minutes after injection of lidocaine 1% and 248 +/- 30 minutes following lidocaine 2% (p = NS). CONCLUSION: The present study describes a technique that can be used in vivo to objectively measure the speed of onset and duration of local anesthetic-induced motor blockade. Although statistically not different, lidocaine 2% demonstrated a faster onset and longer duration of ulnar nerve motor block than lidocaine 1%.