Martin R. Lessard

Effects of pressure-controlled with different I:E ratios versus volume-controlled ventilation on respiratory mechanics, gas exchange, and hemodynamics in patients with adult respiratory distress syndrome.

Background:Pressure-controlled (PCV) and pressure-controlled inverse ratio ventilation (PCIRV) have been proposed instead of volume-controlled conventional ratio ventilation (VC) with positive end-expiratory pressure (PEEP) for patients with adult respiratory distress syndrome (ARDS). The advantages advocated with the use of PCIRV are to decrease airway pressures and to improve gas exchange. However, most studies did not compare PCIRV and VC while keeping both the level of ventilation and end-expiratory alveolar pressure (total-PEEP) constant. Methods:Nine patients with moderate to severe ARDS (lung injury score 2.83 ± 0.18) had their lungs ventilated with VC, PCV with a conventional ratio (I:E 1:2; PC 1/2), and PCIRV (I: E 2:1 and 3:1; PC 2/1 and PC 3/1, respectively). Ventilator settings were adjusted to keep tidal volume, respiratory rate, Fio2, and total-PEEP constant in every mode. With each mode, a complete set of ventilatory, hemodynamic, and gas exchange parameters was obtained after 30 min. Results:In PC 3/1, the data obtained could not be strictly compared to the other modes because total-PEEP was higher despite external-PEEP being set at zero. For the other modes (VC, PC 1/2, and PC 2/1), despite differences in peak airway pressures, no difference was noted for end-inspiratory and end-expiratory static airway pressures (which better reflect alveolar pressures) nor for lung and respiratory system compliance. Arterial oxygenation deteriorated slightly with PC 2/1 despite a higher mean airway pressure, whereas alveolar ventilation tended to be slightly, but not significantly, improved (lower Paco2). A decrease in systolic and mean arterial pressure also was observed with PC 2/1 without other significant hemodynamic change. Conclusions:In this prospective controlled study, no short-term beneficial effect of PCV or PCIRV could be demonstrated over conventional VC with PEEP in patients with ARDS.

Complications associated with the use of the Esophageal-Tracheal Combitube

PurposeTo report four cases of subcutaneous emphysema, pneumomediastinum and pneumoperitoneum associated with the use of the Esophageal-Tracheal Combitube® (ETC) during prehospital management of cardiac arrest.Clinical featuresBetween September 1994 and April 1996, 1139 patients were resuscitated with the ETC and the semiautomated external defibrillator as part of the CPR protocol for prehospital management of cardiac arrest by basic emergency medical technicians. Eight of these patients presented with subcutaneous emphysema. Four of them, declared dead after arrival in the emergency room (ER), had autopsy studies. In two, autopsy revealed large (6 and 6.5 cm respectively) longitudinal transparietal lacerations of the anterior wall of the oesophagus. Multiple superficial lacerations of the oesophagus were also present in another patient, while no lesion of the airway or the oesophagus was found in the last patient.ConclusionThese cases suggest that subcutaneous emphysema, pneumomediastinum and pneumoperitoneum might be complications associated with the use of the ETC. At least in two cases, oesophageal laceration appears to be the mechanism by which these complications occurred.ObjectifRapporter quatre cas d’emphysème sous-cutané, de pneumothorax et de pneumopéritoine associés à l’usage du Combitube® durant la réanimation pré-hospitalière de l’arrêt cardiaque.Aspects cliniquesEntre septembre 1994 et avril 1996, 1139 patients ont été réanimés en utilisant le Combitube® et un défibrillateur externe semi-automatique dans le cadre d’un protocole de RCR pour la prise en charge des arrêts cardiaques par des techniciens médicaux d’urgence ayant une formation de base. Huit de ces patients ont présenté de l’emphysème sous-cutané. Quatre d’entre eux, décédés après leur arrivée à la salle d’urgence, eurent des autopsies. Chez deux, l’autopsie a montré d’importantes lacérations longitudinales transpariétales (6 et 6,5 cm respectivement) de la paroi antérieure de l’œsophage. Des lacérations superficielles multiples étaient aussi présentes chez le troisième patient, alors qu’aucune lésion ni des voies aériennes ni de l’œsophage ne fut retrouvée chez le dernier patient.ConclusionCes cas suggèrent une association entre l’emphysème sous-cutané, le pneumo-médiastin et le pneumopéritoine comme complications de l’utilisation du Combitube®. Au moins chez deux patients, des lacérations oesophagiennes semblent être le mécanisme de ces complications.

Submental endotracheal intubation : An alternative to tracheotomy in patients with Midfacial and panfacial fractures

BACKGROUND The submental route for endotracheal intubation has been proposed as an alternative to tracheotomy in the surgical management of patients with maxillofacial trauma. The purpose of this study was to review our experience with this procedure. METHODS Medical records of 25 patients who had surgical reduction of midfacial or panfacial fractures while securing their airway with submental intubation were reviewed. After standard orotracheal intubation, a passage was created by blunt dissection with a hemostat clamp through the floor of the mouth in the submental area. The proximal end of the orotracheal tube was pulled through the submental incision. Surgery was completed with minimal interference from the endotracheal tube. At the end of surgery, the tube was pulled back to the usual oral route. RESULTS Mean duration of surgery was 7.9 hours (range, 2-16 hours). Mean duration of postoperative mechanical ventilation was 5.2 days (range, 1-24 days). Fourteen of these patients required prolonged (>24 hours) postoperative mechanical ventilation because of associated injuries. Two patients later required a tracheotomy because of prolonged respiratory failure. One patient died of multiple organ failure. One complication of the submental intubation was observed: a superficial infection of the submental wound. CONCLUSION Submental intubation is a simple technique associated with a low morbidity. It is an attractive alternative to tracheotomy in the surgical management of selected cases of maxillofacial trauma.

Cricoid Pressure Does Not Increase the Rate of Failed Intubation by Direct Laryngoscopy in Adults

Background:Cricoid pressure (CP) is applied during induction of anesthesia to prevent regurgitation of gastric content and pulmonary aspiration. However, it has been suggested that CP makes tracheal intubation more difficult. This double-blind randomized study evaluated the effect of CP on orotracheal intubation by direct laryngoscopy in adults. Methods:Seven hundred adult patients undergoing general anesthesia for elective surgery were randomly assigned to have a standardized CP (n = 344) or a sham CP (n = 356) during laryngoscopy and intubation. After anesthesia induction and complete muscle relaxation, a 30-s period was allowed to complete intubation with a Macintosh No. 3 laryngoscope blade. The primary endpoint was the rate of failed intubation at 30 s. The secondary endpoints included the intubation time, the Cormack and Lehane grade of laryngoscopic view, and the Intubation Difficulty Scale score. Results:Groups were similar for demographic data and risk factors for difficult intubation. The rates of failed intubation at 30 s were comparable for the two groups: 15 of 344 (4.4%) and 13 of 356 (3.7%) in the CP and sham CP groups, respectively (P = 0.70). The grades of laryngoscopic view and the Intubation Difficulty Scale score were also comparable. Median intubation time was slightly longer in the CP group than in the sham CP group (11.3 and 10.4 s, respectively, P = 0.001). Conclusions:CP applied by trained personnel does not increase the rate of failed intubation. Hence CP should not be avoided for fear of increasing the difficulty of intubation when its use is indicated.

Risk of cross-infection related to the multiple use. of disposable syringes

The rate of blood contamination of IV tubings used in anaesthesia practice was investigated. Only IV tubings started in the operating room were studied. First, 300 tubings of three different types were tested at the three distal injection sites. The contamination rate was 3.3 per cent at the injection site closest to the IV cathétér and 0.3 per cent at the furthest. The presence of a checkvalve did not affect the contamination rate. Second, 300 third injection sites fixed at a level equal to or above the IV cathétér were tested. None of them was contaminated. Finally, in order to evaluate whether changing the needle alone could prevent the contamination of syringes, injections were made into a tubing where blood was flowing. Thirty-four per cent of the syringes tested positive for blood. We conclude that IV tubings have a significant contamination rate in usual practice. This rate decreases as the distance from the IV cathétér increases. The use of the third site fixed at a level equal to or above the IV cathétér carries a lower risk of contamination. Changing the needle alone is a useless procedure to prevent crosscontamination.RésuméLe taux de contamination sanguine des tubulures des intraveineuses installées en salle d’opération a été étudié. Premièrement, 300 tubulures ont été testées au trois premiers sites d’injection. La présence de sang a été détéctée dans 3.3 pour cent des sites d’injection proximaux et dans seulement 0.3 pour cent des sites distaux. La présence d’une valve antireflux n’a pas modifié l’incidence de contamination. Dans un deuxième temps, on a recherché la présence de sang au troisième site d’injection de 300 tubulures fixées à un niveau égal ou supérieur au cathétér veineux. Aucun de ces sites n’était contaminé. Finalement, I’efficacité de la pratique de changer seulement les aiguilles pour prévenir la contamination des seringues a été verifiee. Trentequatre pour cent des seringues testées étaient contaminées. En conclusion, le taux de contamination sanguine des tubulures est significatif dans la pratique anesthésique quotidienne. Ce taux diminue en s’éloignant du cathétér veineux. L’utilisation du troisiéme site d’injection, fixé a un niveau égal ou supérieur au cathétér veineux, comporte un risque inférieur de contamination. Enfin, changer uniquement les aiguilles est une pratique inutile pour prévenir la contamination des seringues.

Isoflurane-induced hypotension in orthognathic surgery

The effect of isoflurane-induced hypotension on reduction of blood loss, improvement of surgical field, and postoperative edema was investigated in 52 patients undergoing combined maxillary and mandibular osteotomies. Anesthesia was maintained with fentanyl, N2O, O2, and isoflurane. Deliberate hypotension was induced by increasing isoflurane inspired concentration. Blood loss in the hypotensive group (MAP 55–65 mm Hg) was significantly less than that in the control group (MAP 75–85 mm Hg): 454.0 ± 211.3 mL versus 755.3 ± 334.6 mL (P < 0.001). Fewer patients had to be transfused in the hypotensive group, 12.0% versus 44.4% (P < 0.02). The surgical field was significantly improved by the hypotensive technique, but operative time was not shortened. Subjective and objective measurements of postoperative edema failed to show any effect of deliberate hypotension. Our data suggest that isoflurane-induced hypotension effectively reduces blood loss and the number of transfusions in orthognathic surgery.

WEANING FROM VENTILATORY SUPPORT

Resumption of spontaneous unassisted breathing after an episode of acute respiratory failure often is achieved without major difficulty. In a significant number of patients however, weaning from mechanical ventilation is a long and difficult process that markedly increases the duration of mechanical ventilation and consumes a significant fraction of critical care resources. Some criteria have been suggested to predict early and more accurately the moment the patient is ready to be separated from the ventilator. At the present time, the f/VT ratio (rapid shallow breathing index) appears to yield the best predictive power. None of these indices, however, is powerful enough to be relied on solely, and their use should be limited to that of aids to the critical care physician. The inability to sustain spontaneous ventilation usually is the consequence of an imbalance between respiratory demand and respiratory muscle capacity. Increased elastic workload, increased resistive workload, and increased VE are the main causes of excessive demand imposed on the respiratory system. Respiratory muscle pump failure usually relates to peripheral nerve dysfunction or muscular dysfunction. Left ventricular dysfunction also is an important cause of weaning failure. The usual methods of weaning from mechanical ventilation are T-piece trials with abrupt definitive discontinuation of mechanical ventilation if tolerated or with progressive intermittent trials, IMV, and PSV. All have their advantages and disadvantages, and the method of weaning per sé is not the only critical factor. Although their conclusions were different regarding the best method of weaning, however, two recent clinical trials suggest that ventilatory management has a major influence on the outcome of weaning from mechanical ventilation in difficult-to-wean patients. The global management of such patients requires a systematic approach with consideration of all factors involved in the process of separation from the ventilator. New computer-assisted systems already are tested and, in the future, may provide a significant advantage in the management of weaning from mechanical ventilation.

Efficacy of a T-piece system and a continuous positive airway pressure system for apnea testing in the diagnosis of brain death

Objective:To prospectively compare three methods of apnea testing for the confirmation of brain death. Design:Prospective, randomized, crossover study. Setting:Intensive care unit of a tertiary care university hospital. Patients:Twenty adult patients requiring apnea testing for confirmation of brain death. Interventions:Ten minute apnea testing was repeated in random order for every patient with the three oxygenation systems: oxygen catheter inserted through the endotracheal tube (oxygen 6 L/min), T-piece system (oxygen 12 L/min), and continuous positive airway pressure (CPAP) system 10 cm H2O (oxygen 12 L/min). Measurements and Main Results:Arterial blood was drawn at 0, 2, 5, and 10 mins of each test. Compared with baseline, Paco2 increased by 30.6 ± 7.4, 30.0 ± 7.3 and 30.2 ± 7.5 mm Hg during the apnea period (p = .96), reaching 73.3 ± 8.3, 71.6 ± 11.1, and 72.7 ± 9.0 mm Hg at the end of the apnea test (p = .73) for the oxygen catheter, the T-piece, and the CPAP, respectively. Pao2 decreased less with the CPAP compared with the oxygen catheter or the T-piece (−22.4 ± 76, −99.1 ± 158, and −91.6 ± 133 mm Hg, respectively, p < .01). In two patients, apnea testing could not be completed with the oxygen catheter and the T-piece because of desaturation, although it could be completed with the CPAP. Conclusions:The T-piece and the CPAP systems are effective alternatives to the standard oxygen catheter technique for apnea testing. Oxygenation was best maintained with the CPAP system, which can be useful in some patients.

Alfentanil causes less postoperative nausea and vomiting than equipotent doses of fentanyl or sufentanil in outpatients.

BACKGROUND The relative potencies of alfentanil, fentanyl, and sufentanil as a risk factor for postoperative nausea and vomiting have not been determined. They were compared in a randomized study designed to obtain equipotent plasma concentrations of these three opioids at the beginning of the recovery period. METHODS The study included 274 patients treated on an outpatient basis. The steady state opioid plasma concentration providing a predicted 50% reduction of the minimum alveolar concentration of isoflurane was used to determine the relative potency of the opioids. The opioids were prepared in equal volumes at concentrations of alfentanil 150 microg/ml, fentanyl 50 microg/ml, and sufentanil 5 microg/ml and were administered in vol/kg. Anesthesia was induced in a blinded fashion with a bolus of the study opioid (0.05 ml/kg) and 4-6 mg/kg thiopental and was maintained with isoflurane (0.6-1%) in a nitrous oxide-oxygen mixture with a continuous infusion of the study opioid (0.06 ml x kg(-1) x h(-1)). If necessary, up to five additional boluses of opioid (0.02 ml/kg) could be given. This opioid administration protocol was tested by pharmacokinetic simulations. RESULTS The incidence of postoperative nausea and vomiting was not different in the postanesthesia care unit, but in the ambulatory surgery unit it was significantly lower for alfentanil compared with fentanyl and sufentanil (12, 34, and 35%, respectively P < 0.005). Pharmacokinetic modeling showed that the end-anesthesia opioid plasma concentrations were approximately equipotent in the three groups. However, modeling does not support that the difference between groups in the postoperative period can be explained by a more rapid disappearance of alfentanil from the plasma. CONCLUSIONS Alfentanil, compared with approximately equipotent doses of fentanyl and sufentanil, is associated with a lower incidence of postoperative nausea and vomiting in outpatients.

A microbiological study of the contamination of the syringes used in anaesthesia practice

In many operating theatres, it is common practice to reuse disposable plastic syringes with the same needles for several injections to different patients during the same day. This practice could lead to bacterial contamination of these syringes, making them an infection hazard to patients. We did a microbiologic survey of 100 of the most frequently reused syringes in our operating rooms anda control group of 100 single-use syringes. Only three of the syringes were contaminated in each group. None of the patients exposed to the syringes having a positive culture showed any sign of sepsis. Our data suggest that reusing plastic syringes is not associated with an increase in the incidence of bacterial contamination. However, contamination of the syringes by patients’ blood, with the risk of crossinfections, remains a possibility and further studies are needed to evaluate this potential hazard.RésuméDans plusieurs salles ďopération, les mêmes seringues de plastique jetables avec ľaiguille sont réutilisées pour plusieurs injections à différents patients durant une même journée. Cette pratique pourrait entraîner une contamination bactérienne de ces seringues et exposer des patients à des risques ďinfection. Nous avons effectué une étude microbiologique de cent seringues parmi les plus fréquemment réutilisées dans notre milieu ainsi qu’un groupe contrôle de cent seringues n’ayant été utilisées qu’une seule fois. Seulement trois des seringues se sont révélées contaminées dans chacun des groupes. Aucun des patients exposés à ces seringues n’a présenté de signes de bactériémie. Nos résultats suggérent que la réutilisation des seringes de plastique n’est pas associée à une plus grande fréquence de contamination bactérienne. Cependant la contamination des seringues par du sang des patients avec le risque associé ďinfection croisée demeure une possibilité et ďautres études sont nécessaires afin ďévaluer ce risque.