François Lenfant

Could heart rate variability predict outcome in patients with severe head injury? A pilot study.

Despite major improvements in the resuscitation of patients with head injury, the outcome of patients with head trauma often remains poor and difficult to establish. Heart rate variability (HRV) analysis is a noninvasive tool used to measure autonomic nervous system (ANS) activity. The aim of this prospective study was to investigate whether HRV analysis might be a useful adjunct for predicting outcome in patients with severe head injury. Twenty patients with severe head trauma (Glasgow Coma Scale [GCS] ≤ 8) underwent 24-hour electrocardiogram recording 1 day after trauma and again 48 hours after withdrawal of sedative drugs. Heart rate variability was assessed, in both time domain and spectral domain. The authors initially compared (on Day 1) HRV in patients who progressed to brain death to HRV in survivors; then during the awakening period compared HRV in surviving patients with good recovery (GCS ≥ 10) to HRV in patients characterized by a worsened neurologic state (GCS < 10). Statistical analysis used the Kruskal-Wallis test, P < .05. To assess whether HRV could predict evolution to brain death, receiver operating characteristic (ROC) curves were generated the day after trauma for Total Power, natural logarithm of high-frequency component of spectral analysis (LnHF), natural logarithm of low-frequency component of spectral analysis (LnLF), and root mean square for successive interval differences (rMSSD). Seven patients died between Day 1 and Day 5 after trauma. Six of those had progressed to brain death. In these six patients, at Day 1, Global HRV and parasympathetic tone were significantly higher. Referring to the area under the rMSSD ROC curve, HRV might provide useful information in predicting early evolution of patients with severe head trauma. During the awakening period, global HRV and the parasympathetic tone were significantly lower in the worsened neurologic state group. In conclusion, HRV could be helpful as a predictor of imminent brain death and a useful adjunct for predicting the outcome of patients with severe head injury.

Prediction of difficult tracheal intubation: time for a paradigm change.

Background:It has been suggested that predicting difficult tracheal intubation is useless because of the poor predictive capacity of individual signs and scores. The authors tested the hypothesis that an accurate prediction of difficult tracheal intubation using simple clinical signs is possible using a computer-assist model. Methods:In a cohort of 1,655 patients, the authors analyzed the predictive properties of each of the main signs (Mallampati score, mouth opening, thyromental distance, and body mass index) to predict difficult tracheal intubation. They built the best score possible using a simple logistic model (SCOREClinic) and compared it with the more recently described score in the literature (SCORENaguib). Then they used a boosted tree analysis to build the best score possible using computer-assisted calculation (SCOREComputer). Results:Difficult tracheal intubation occurred in 101 patients (6.1%). The predictive properties of each sign remain low (maximum area under the receiver operating characteristic curve 0.70). Using receiver operating characteristic curve, the global prediction of the SCOREClinic (0.74, 95% CI: 0.72–0.76) was greater than that of the SCORENaguib (0.66, 95% CI: 0.60–0.72, P < 0.001) but significantly lower than that of the SCOREComputer (0.86, 95% CI: 0.84–0.91, P < 0.001). The proportion of patients in the inconclusive zone was 71% using SCORENaguib, 56% using SCOREClinic, and only 32 % using SCOREComputer (all P < 0.001). Conclusion:Computer-assisted models using complex interaction between variables enable an accurate prediction of difficult tracheal intubation with a low proportion of patients in the inconclusive zone. An external validation of the model is now required.

Comparison of single-use and reusable metal laryngoscope blades for orotracheal intubation during rapid sequence induction of anesthesia: a multicenter cluster randomized study.

Background:Single-use metal laryngoscope blades are cheaper and carry a lower risk of infection than reusable metal blades. The authors compared single-use and reusable metal blades during rapid sequence induction of anesthesia in a multicenter cluster randomized trial. Methods:One thousand seventy-two adult patients undergoing general anesthesia under emergency conditions and requiring rapid sequence induction were randomly assigned on a weekly basis to either single-use or reusable metal blades (cluster randomization). After induction, a 60-s period was allowed to complete intubation. In the case of failed intubation, a second attempt was performed using the opposite type of blade. The primary endpoint was the rate of failed intubation, and the secondary endpoints were the incidence of complications (oxygen desaturation, lung aspiration, and/or oropharynx trauma) and the Cormack and Lehane score. Results:Both groups were similar in their main characteristics, including the risk factors for difficult intubation. The rate of failed intubation was significantly decreased with single-use metal blades at the first attempt compared with reusable blades (2.8 vs. 5.4%, P < 0.05). In addition, the proportion of grades III and IV in Cormack and Lehane score were also significantly decreased with single-use metal blades (6 vs. 10%, P < 0.05). The global complication rate did not reach statistical significance, although the same trend was noted (6.8% vs. 11.5%, P = not significant). An investigator survey and a measure of illumination pointed that illumination might have been responsible for this result. Conclusions:The single-use metal blade was more efficient than a reusable metal blade in rapid sequence induction of anesthesia.

In vivo and in vitro antioxidant properties of furosemide.

The aim of this study was to investigate in vivo and in vitro antioxidant properties of furosemide. In vitro, human red blood cells were submitted to oxidative stress (AAPH), in absence or in presence of different concentrations of furosemide. Potassium efflux was measured in order to quantify the oxidative stress after the action of AAPH on red blood cells. Allophycocyanin assay was also used to investigate antioxidant capacities of furosemide. For the in vivo experiment, male Wistar rats were used. A control group (n = 5) was treated by a daily intraperitoneal injection of saline solution (0.2 ml); 2 other groups (J0 and J+) were treated for 7 days by one daily intraperitoneal injection of furosemide (0.10 mg/kg/day). In the J+group, the injection of furosemide was done one hour before the experiment, while in the J0 group the last injection of furosemide was done on the 6th day and an injection of saline was performed one hour before the experiment. On the day of experiment, a laparotomy was performed under general anesthesia and blood was collected from abdominal aorta. Oxidative stress and antioxidant capacities were evaluated on Wistar rat red blood cells and plasma. In vitro results (oxidative challenge with AAPH) showed that oxidative stress was decreased in presence of furosemide. This was due to a potent free radical scavenging effect of furosemide. In vivo studies confirmed that furosemide had antioxidant properties. These data may be of great relevance in clinical practice, considering the use of large doses of furosemide in patients presenting pathology involving the production of free radicals.

Comparison of two techniques for retrograde tracheal intubation in human fresh cadavers.

Background:During retrograde tracheal intubation, the short distance existing between the cricothyroid membrane and vocal cords may be responsible for accidental extubation. The insertion of a catheter into the trachea before the removal of the guide wire may help to cope with this problem. This work was conducted to study the impact of such a modification on the success rate and the duration of the procedure. Methods:Procedures of retrograde tracheal intubation following the classic and modified techniques were randomly performed in cadavers (n = 70). The duration of the procedure from the puncture of the cricothyroid membrane to the inflation of the balloon of the endotracheal tube was measured, and, at the end of the procedure, the position of the endotracheal tube was checked under laryngoscopy. The procedure was considered to have failed if it had taken more than 5 min or when the endotracheal tube was not positioned in the trachea. Results:The mean time to achieve tracheal intubation was similar in both groups (123 ± 51 vs. 127 ± 41 s; not significant), but intubation failed significantly more frequently with the classic technique (22 vs. 8 failures; P < 0.05). All failures were related to incorrect positioning of the endotracheal tube. In four cases, both techniques failed. Conclusions:This efficient, simple modification of the technique significantly increases the success rate of the procedure, without prolonging its duration. These data should be confirmed in clinical conditions but may encourage a larger use of the retrograde technique in cases of difficult intubation.

The influence of extracorporeal circulation on the susceptibility of erythrocytes to oxidative stress

Extracorporeal circulation (ECC), a necessary and integral part of cardiac surgery, can itself induce deleterious effects in patients. The pathogenesis of diffuse damage of several tissues is multifactorial. It is believed that circulation of blood extracorporeally through plastic tubes causes a whole body inflammatory response and a severe shear stress to blood cells. The aim of this study was to evaluate the level of oxidative stress and its deleterious effect on red blood cell (RBC) before (pre-ECC), immediately after (per-ECC) and 24 h after an ECC (24 h post-ECC). Several indicators of extracellular oxidative status were evaluated. The ascorbyl free radical (AFR) was directly measured in plasma using electron spin resonance (ESR) spectroscopy and expressed with respect to vitamin C levels in order to obtain a direct index of oxidative stress. Allophycocyanin assay was also used to investigate the plasma antioxidant status (PAS). Indirect parameters of antioxidant capacities of plasma such as vitamin E, thiol and uric acid levels were also quantified. RBC alterations were evaluated through potassium efflux and carbonyl levels after action of AAPH, a compound generating carbon centered free radicals. No changes in plasma uric acid and thiols levels were observed after ECC. However, vitamin E levels and PAS were decreased in per-ECC and 24 h post-ECC samples. Vitamin C levels were significantly lower in 24 h post-ECC and the AFR/ vitamin C ratio was increased. Differences in results had been noted when measurements took account of hemodilution. Increases of uric acid and thiols levels were observed after ECC. Vitamin E levels were not modified. However after hemodilution correction a significant decrease of vitamin C level was noted in 24 h post-ECC samples as compared to per-ECC sample. Whatever the way of measurement, vitamin C levels decreased suggesting the occurrence of ECC induced-oxidative stress. Concerning RBC, in the absence of AAPH, extracellular potassium remained unchanged between pre-, per- and 24 h post-ECC. AAPH induced a significant increase in extracellular potassium and carbonyls levels of RBC membranes, which was not modified by ECC. These results suggest the absence of alterations of RBC membrane during ECC despite the occurrence of disturbances in PAS. Such protection is of particular importance in a cell engaged in the transport of oxygen and suggests that RBC are equipped with mechanisms affording a protection against free radicals.

Oxygen delivery during transtracheal oxygenation: a comparison of two manual devices.

BACKGROUND:The Manujet™ and the ENK Oxygen Flow Modulator™ (ENK) deliver oxygen during transtracheal oxygenation. We sought to describe the ventilation characteristics of these 2 devices. METHODS:The study was conducted in an artificial lung model consisting of a 15-cm ringed tube, simulating the trachea, connected via a flow analyzer and an artificial lung. A 15-gauge transtracheal wire reinforced catheter was used for transtracheal oxygenation. The ENK and Manujet were studied for 3 minutes at respiratory rates of 0, 4, and 12 breaths/min, with and without the artificial lung, in a totally and a partially occluded airway. Statistical analysis was performed using analysis of variance followed by a Fisher exact test; P < 0.05 was considered significant. RESULTS:Gas flow and tidal volume were 3 times greater with the Manujet than the ENK (approximately 37 vs 14 L · min−1 and 700 vs 250 mL, respectively) and were not dependent on the respiratory rate. In the absence of ventilation, the ENK delivered a 0.6 ± 0.1 L · min−1 constant gas flow. In the totally occluded airway, lung pressures increased to 136 cm H2O after 3 insufflations with the Manujet, whereas the ENK, which has a pressure release vent, generated acceptable pressures at a low respiratory rate (4 breaths/min) (peak pressure at 27.7 ± 0.7 and end-expiratory pressure at 18.8 ± 3.8 cm H2O). When used at a respiratory rate of 12 breaths/min, the ENK generated higher pressures (peak pressure at 95.9 ± 21.2 and end-expiratory pressure at 51.4 ± 21.4 cm H2O). In the partially occluded airway, lung pressures were significantly greater with the Manujet compared with the ENK, and pressures increased with the respiratory rate with both devices. Finally, the gas flow and tidal volume generated by the Manujet varied proportionally with the driving pressure. DISCUSSION:This study confirms the absolute necessity of allowing gas exhalation between 2 insufflations and maintaining low respiratory rates during transtracheal oxygenation. In the case of total airway obstruction, the ENK may be less deleterious because it has a pressure release vent. Using a Manujet at lower driving pressures may decrease the risk of barotrauma and allow the safe use of higher respiratory rates.

Phone call simulator.

For Emergency Medical Communication Centres (EMCCs), the dentification of life-threatening situations and appropriate disatch remain crucial elements.1 To this end, we need to develop etter indicators to dispatch the right ambulance to the right atient. For this challenge, education and training of healthcare orkers have to be improved.2 Simulation is a reliable, validated ethod to enhance educational messages and to enable training n safe conditions. In addition, it can also be used for research, and ertification. Until now, no apparatus has been developed to simuate conversations. We describe here a new tool that does just this nd a method for its use in medical education. SimulPhone© is a new phone call simulator that recreates the nvironment of an EMCC. Trainees and trainers use a different comuter interface. The trainee is equipped with a headset to answer irtual phone calls. He talks with the simulator as if it were a real erson. The phone calls are modelled on medical emergency scearios. All of the answers of the virtual caller are pre-recorded by an ctor. The trainee also has to manage a standard computer interface hat simulates the major tasks performed in EMCC prioritisation take notes, dispatch the proper medical service and manage the ifferent responders). During the simulation, the trainer clicks on the question asked y the trainee, and the SimulPhone© plays the corresponding re-recorded answer. According to the scenario, the software anticpates the potential question asked by the trainee and always roposes the most likely responses. In the case where no preecorded answer is available, the trainer clicks on a tool box. This ool box contains different peripheral answers to peripheral quesions that give no further information. The tool box can also be used hen the trainee comes out of the scenario. The trainer must be xperienced in handling emergency calls to enhance the coherence f the scenario. The software records every question asked and the advice given nd the different times. The notes and decisions of the trainee are lso recorded. Using a simulator in education requires guidelines and speialists to build the scenarios.3 However, EMCC, have neither. ecommendations and the gold standard will be based on the perormance of experts. We will use the cognitive nature of expertise, escribed by Patel,4 to identify experts by their way of reasoning. hese will be selected from a wide population of EMCC workers ho will be tested with a psychometric simulator. In order to validate SimulPhone© as a psychometric tool, we ill first test it as a measurement tool. The data will be analysed

Effect of Cricoid Pressure Compared With a Sham Procedure in the Rapid Sequence Induction of Anesthesia: The IRIS Randomized Clinical Trial

Importance The use of cricoid pressure (Sellick maneuver) during rapid sequence induction (RSI) of anesthesia remains controversial in the absence of a large randomized trial. Objective To test the hypothesis that the incidence of pulmonary aspiration is not increased when cricoid pressure is not performed. Design, Setting, and Participants Randomized, double-blind, noninferiority trial conducted in 10 academic centers. Patients undergoing anesthesia with RSI were enrolled from February 2014 until February 2017 and followed up for 28 days or until hospital discharge (last follow-up, February 8, 2017). Interventions Patients were assigned to a cricoid pressure (Sellick group) or a sham procedure group. Main Outcomes and Measures Primary end point was the incidence of pulmonary aspiration (at the glottis level during laryngoscopy or by tracheal aspiration after intubation). It was hypothesized that the sham procedure would not be inferior to the cricoid pressure. The secondary end points were related to pulmonary aspiration, difficult tracheal intubation, and traumatic complications owing to the tracheal intubation or cricoid pressure. Results Of 3472 patients randomized, mean (SD) age was 51 (19) years and 1777 (51%) were men. The primary end point, pulmonary aspiration, occurred in 10 patients (0.6%) in the Sellick group and in 9 patients (0.5%) in the sham group. The upper limit of the 1-sided 95% CI of relative risk was 2.00, exceeding 1.50, failing to demonstrate noninferiority (P = .14). The risk difference was −0.06% (2-sided 95% CI, −0.57 to 0.42) in the intent-to-treat population and −0.06% (2-sided 95% CI, −0.56 to 0.43) in the per protocol population. Secondary end points were not significantly different among the 2 groups (pneumonia, length of stay, and mortality), although the comparison of the Cormack and Lehane grade (Grades 3 and 4, 10% vs 5%; P <.001) and the longer intubation time (Intubation time >30 seconds, 47% vs 40%; P <.001) suggest an increased difficulty of tracheal intubation in the Sellick group. Conclusions and Relevance This large randomized clinical trial performed in patients undergoing anesthesia with RSI failed to demonstrate the noninferiority of the sham procedure in preventing pulmonary aspiration. Further studies are required in pregnant women and outside the operating room. Trial Registration ClinicalTrials.gov Identifier: NCT02080754