The impact of an algorithm-guided management of preoperative anemia in perioperative hemoglobin level and transfusion of major orthopedic surgery patients.

The aim of this study was to evaluate a laboratory-guided therapeutic algorithm of preoperative anemia. 335 patients with elective hip or knee arthroplasty were included in this retrospective before-after study. Group I (n = 101) underwent conventional preoperative procedures before algorithm implementation. Group II (n = 234) underwent algorithm-guided preoperative anemia management. A hemoglobin-level of 13 g/dL was the therapeutic cut-off for men and women. Reticulocyte hemoglobin content (CHr) and soluble transferrin receptor (sTfR)/log ferritin ratio were used in the form of the Thomas plot. Iron deficiency (ID) was substituted with 1000 mg iron intravenous (i.v.) and 10000 international units (I.U.) of erythropoiesis-stimulating agent (ESA) subcutaneous (s.c.) or i.v., anemia of chronic disease (ACD) (without functional ID) with 40000 I.U. ESA s.c. or i.v and additionally 200 mg iron i.v. Substituted anemic patients in Group II (n = 32) showed a distinctly higher preoperative (Hb-median 13 versus 11.95 g/dL) (P < 0.01) and postoperative (Hb-median 9.75 versus 9.0 g/dL) (P < 0.05) Hb level compared with untreated anemic patients in Group I (n = 24). In Group II red blood cell (RBC) units (35 units/234 patients) were reduced by 44% compared with Group I (27 units/101 patients). Algorithm-guided preoperative anemia management raises perioperative Hb-level and reduces blood use.

Head position angles to open the upper airway differ less with the head positioned on a support.

INTRODUCTION: The aim of the study was to assess the effects of positioning the head on a support on "head position angles" to optimally open the upper airway during bag-valve mask ventilation. METHODS: We ventilated the lungs of anesthetized adults with a bag-valve mask and the head positioned with (n = 30) or without a support (n = 30). In both groups, head position angles and ventilation parameters were measured with the head positioned in (1) neutral position, (2) in a position deemed optimal for ventilation by the investigator, and (3) in maximal extension. RESULTS: Between groups ("head with/without a support") and between head positions within each group, head position angles and ventilation parameters differed (P < .0001, respectively). However, head position angles and ventilation parameters between head positions differed less "with a support" (P < .001), and ventilation parameters improved with a support compared with the head-without-a-support group (P < .001). CONCLUSIONS: In the head-with-a-support group, when compared with the head-without-a-support group, head position angles differed less, indicating a decreased potential for failure during bag-valve mask ventilation with the head on a support. Moreover, in the head-with-a-support group, ventilation parameters differed less between head positions, and ventilation improved. These findings suggest a potential benefit of positioning the head on a support during bag-valve mask ventilation.

Automated emergency ventilation devices in a simulated unprotected airway.

BACKGROUND: Automated ventilation devices are becoming more popular for emergency ventilation, but there is still not much experience concerning the optimal ventilation mode. METHODS: In a bench model representing a non-intubated patient in respiratory and cardiac arrest, we compared a pressure-cycled with a time- and volume-cycled automated ventilation device in their completely automated modes. The main study endpoints were inspiratory time, respiratory rate, stomach inflation, and lung tidal volumes. RESULTS: The pressure-cycled device inspired for 6.7 s in the respiratory arrest setting (respiratory rate 5.6/min), and never reached its closing pressure in the cardiac arrest setting (respiratory rate 1 breath/min). The time- and volume-cycled device inspired in both settings for 1.7 s (respiratory rate 13 breaths/min). In the respiratory arrest setting, mask leakage was 620 ± 20 mL for the pressure-cycled device vs. 290 ± 10 mL for the time- and volume-cycled device (p < 0.0001); lung tidal volume was 1080 ± 50 mL vs. 490 ± 20 mL, respectively (p < 0.0001); and there was no stomach inflation for either device. In the cardiac arrest setting, pressure-cycled device mask leakage was 5460 ± 60 mL vs. 240 ± 20 mL (p < 0.0001) for the time- and volume-cycled device (p < 0.0001); stomach inflation was 13,100 ± 100 mL vs. 90 ± 10 mL, respectively (p < 0.0001); and lung tidal volume 740 ± 60 mL vs. 420 ± 20 mL, respectively (p < 0.0001). CONCLUSION: In a simulated respiratory arrest setting, ventilation with an automated pressure-cycled ventilation device resulted in lower respiratory frequency and larger tidal volumes compared to a time- and volume-cycled device. In a simulated cardiac arrest setting, ventilation with an automated pressure-cycled ventilation device, but not a time- and volume-cycled device, resulted in continuous gastric insufflation.

Head-position angles in children for opening the upper airway.

AIMS: Inexperienced health-care-providers may encounter severe problems to ventilate an unconscious child. Designing a ventilating device that could indicate how to open an upper airway correctly may be beneficial. Neutral position in young children and slight head extension in older children is recommended, although the optimal head angle is not clear. Thus, we compared effects of neutral head position and extension, measuring head-position angles and ventilation parameters. METHODS: Sixty-one children scheduled for tonsillectomy were enrolled, and were ventilated with pressure-controlled ventilation after anaesthesia induction. RESULTS: Children were divided into two groups: 1-5 years old (pre-school children, n=38) and 6-10 years old (school children, n=23). In neutral (mean+/-SD: 1.3+/-6.0) vs. head-extension position (13.2+/-6.0; P<0.001) in pre-school children, tidal volumes (132+/-44,137+/-49 ml), peak-expiratory flow (300+/-90 vs. 310+/-100 mls(-1)) and expiratory airway resistance (20+/-8 vs. 18+/-6c mH(2)O s l(-1)) were comparable (P=NS). In neutral (-0.4+/-5.4) vs. head-extension position (15.7+/-6.4; P<0.001) in school children, expiratory airway resistance (17+/-7 vs. 13+/-5 cmH(2)O s l(-1); P=0.048) differed, while tidal volume (224+/-93 vs. 230+/-92 ml) and peak-expiratory flow (427+/-181 vs. 381+/-144 ml s(-1)) were comparable (P=NS). CONCLUSIONS: Head-extension and neutral head-position angles differed in pre-school and school children. In pre-school children, neutral head position or head extension with an angle of -1 degrees or 13 degrees , and in school children head extension of 16 degrees , may be used to achieve optimal ventilation of an unprotected airway.

Anaesthesia in prehospital emergencies and in the emergency room.

AIMS: To review anaesthesia in prehospital emergencies and in the emergency room, and to discuss guidelines for anaesthesia indication; pre-oxygenation; anaesthesia induction and drugs; airway management; anaesthesia maintenance and monitoring; side effects and training. METHODS: A literature search in the PubMed database was performed and 87 articles were included in this non-systematic review. CONCLUSIONS: For pre-oxygenation, high-flow oxygen should be delivered with a tight-fitting face-mask provided with a reservoir. In haemodynamically unstable patients, ketamine may be the induction agent of choice. The rocuronium antagonist sugammadex may have the potential to make rocuronium a first-line neuromuscular blocking agent in emergency induction. An experienced health-care provider may consider prehospital anaesthesia induction. A moderately experienced health-care provider should optimise oxygenation, fasten hospital transfer and only try to intubate a patient in extremis. If intubation fails twice, ventilation should be resumed with an alternative supra-glottic airway or a bag-valve-mask device. A lesser experienced health-care provider should completely refrain from intubation, optimise oxygenation, fasten hospital transfer and only in extremis ventilate with an alternative supra-glottic airway or a bag-valve-mask device. With an expected difficult airway, the patient should be intubated awake. With an unexpected difficult airway, bag-valve-mask ventilation should be resumed and an alternative supra-glottic airway device inserted. Senior help should be called early. In a "can-not-ventilate, can-not-intubate" situation an alternative airway should be tried and if unsuccessful because of severe upper airway pathology, a surgical airway should be performed. Ventilation should be monitored continuously with capnography. Clinical training is important to increase airway management skills.

The mouth-to-bag resuscitator during standard anaesthesia induction in apnoeic patients.

AIM: Ventilation of a non-intubated emergency patient by inexperienced rescuers with a standard bag-valve device may result in high inspiratory flow rates and subsequently high airway pressures with stomach inflation. Therefore, a self-inflating bag has been developed that requires lay rescuers to blow up a single-use balloon inside an adult bag-valve device, which, in turn, displaces air within the bag towards the patient. This concept has been compared to standard adult bag-valve devices earlier in bench models but not in patients. METHODS: An anaesthetist who was blinded to all monitor tracings ventilated the lungs of 40 apnoeic patients during routine anaesthesia induction either with a standard bag-valve device or with the mouth-to-bag resuscitator in a random order. Study endpoints were peak inspiratory flow rates, peak airway pressure, tidal volumes and inspiratory time. RESULTS: Peak inspiratory flow was 40+/-10lmin(-1) for the standard bag-valve device versus 33+/-13lmin(-1) for the mouth-to-bag resuscitator (P<0.0001); peak airway pressure was 17+/-5cmH(2)O versus 14+/-5cmH(2)O (P<0.0001); inspiratory tidal volume was 477+/-133ml versus 644+/-248ml (P<0.001) and inspiratory time was 1.1+/-0.3s versus 1.9+/-0.6s (P<0.0001). CONCLUSION: Employing the mouth-to-bag resuscitator during simulated ventilation of a non-intubated patient in respiratory arrest significantly decreased peak inspiratory flow and peak airway pressure and increased inspiratory tidal volume and inspiratory times compared to a standard bag-valve device.

Ventilation strategies in the obstructed airway in a bench model simulating a nonintubated respiratory arrest patient.

BACKGROUND: The Smart Bag MO(R) is an adult flow-limited bag-valve device designed to reduce the risk of stomach inflation in an unprotected airway. Its properties in severe airway obstruction are as yet unknown. METHODS: In a bench model, we evaluated respiratory mechanics and delivered tidal volumes although ventilating at airway resistances of 4, 10, and 20 cm H(2)O . L(-1) . s(-1) once with a flow-limited bag-valve device and once with a standard bag-valve device to simulate a respiratory arrest patient with an unprotected airway. RESULTS: Inspiratory times were always longer with the flow-limited bag-valve device than with the standard bag-valve device. Lung tidal volume in the simulated unobstructed airway was 750 +/- 70 mL using the flow-limited bag-valve device versus 780 +/- 30 mL using the standard bag-valve device (n.s.); in the simulated medium obstructed airway it was 800 +/- 70 versus 850 +/- 20 mL (n.s.), and in the simulated severely obstructed airway it was 210 +/- 20 versus 170 +/- 10 mL (P < 0.01). Peak airway pressure in the simulated unobstructed airway was 15 +/- 2 cm H(2)O using the flow-limited bag-valve device versus 22 +/- 4 cm H(2)O using the standard bag-valve device (P < 0.01); in the simulated medium obstructed airway it was 22 +/- 1 versus 39 +/- 7 cm H(2)O (P < 0.01), and in the simulated severely obstructed airway it was 26 +/- 1 versus 61 +/- 3 cm H(2)O (P < 0.01). Stomach inflation in the simulated unobstructed airway was 0 mL/min using both bag-valve devices; in the simulated medium obstructed airway it was 0 mL/min for the flow-limited bag-valve device versus 200 +/- 20 mL/min for the standard bag-valve device (P < 0.01), and in the simulated severely obstructed airway it was 0 versus 1240 +/- 50 mL/min (P < 0.01). CONCLUSION: In a simulated severely obstructed unprotected airway, the use of a flow-limited bag-valve device resulted in longer inspiratory times, higher tidal volumes, lower inspiratory pressures, and no stomach inflation compared with a standard bag-valve device.

Effects of stomach inflation on haemodynamic and pulmonary function during spontaneous circulation in pigs.

AIM: Stomach inflation during mask ventilation is frequent, but the effects on haemodynamic and pulmonary function are unclear. We evaluated the effects of stomach inflation on haemodynamic and pulmonary function during spontaneous circulation in a porcine model. METHODS: Randomised prospective animal study. After randomisation, in 23 domestic pigs the stomach was inflated every 90s with 0L (control; n=8), 0.5L (n=7) or 1L (n=8) ambient air. RESULTS: After 22.5min, i.e. 8.5L in the 0.5L and 17L in the 1L stomach inflation group, stomach inflation increased central venous pressure (median) (control: 10mmHg vs. 1L: 23mmHg, P<0.05) and mean pulmonary artery pressure (control: 24mmHg vs. 1L: 45mmHg, P<0.05). As a result stroke volume index decreased (control: 135mL/kg vs. 0.5L: 90mL/kg, P<0.05; vs. 1L: 72mL/kg, P<0.05). Stomach inflation also decreased static pulmonary compliance (control: 24mL/cmH(2)O vs. 0.5L: 8mL/cmH(2)O, P<0.05; vs. 1L: 3mL/cmH(2)O, P<0.05), which increased peak airway pressure (control: 28cmH(2)O vs. 0.5L: 69cmH(2)O, P<0.05; vs. 1L: 73cmH(2)O, P<0.05). Additionally, arterial oxygen partial pressure (control: 305mmHg vs. 0.5L: 140mmHg, P<0.05; vs. 1L: 21mmHg, P<0.05) and systemic oxygen delivery (control: 53mLO(2)/min vs. 1L: 19mLO(2)/min, P<0.05) decreased. Stomach inflation increased mortality (control: 0/8 vs. 1L: 5/8, P<0.05). CONCLUSIONS: Stomach inflation with 1L when compared to 0.5L increments resulted in faster haemodynamic and pulmonary failure and increased mortality. Stomach inflation may cause a hyper-acute abdominal compartment syndrome.

Effects of stomach inflation on haemodynamic and pulmonary function during cardiopulmonary resuscitation in pigs.

AIM: Stomach inflation during cardiopulmonary resuscitation (CPR) is frequent, but the effect on haemodynamic and pulmonary function is unclear. The purpose of this study was to evaluate the effect of clinically realistic stomach inflation on haemodynamic and pulmonary function during CPR in a porcine model. METHODS: After baseline measurements ventricular fibrillation was induced in 21 pigs, and the stomach was inflated with 0L (n=7), 5L (n=7) or 10L air (n=7) before initiating CPR. RESULTS: During CPR, 0, 5, and 10L stomach inflation resulted in higher mean pulmonary artery pressure [median (min-max)] [35 (28-40), 47 (25-50), and 51 (49-75) mmHg; P<0.05], but comparable coronary perfusion pressure [10 (2-20), 8 (4-35) and 5 (2-13) mmHg; P=0.54]. Increasing (0, 5, and 10L) stomach inflation decreased static pulmonary compliance [52 (38-98), 19 (8-32), and 12 (7-15) mL/cmH(2)O; P<0.05], and increased peak airway pressure [33 (27-36), 53 (45-104), and 103 (96-110) cmH(2)O; P<0.05). Arterial oxygen partial pressure was higher with 0L when compared with 5 and 10L stomach inflation [378 (88-440), 58 (47-113), and 54 (43-126) mmHg; P<0.05). Arterial carbon dioxide partial pressure was lower with 0L when compared with 5 and 10L stomach inflation [30 (24-36), 41(34-51), and 56 (45-68) mmHg; P<0.05]. Return of spontaneous circulation was comparable between groups (5/7 in 0L, 4/7 in 5L, and 3/7 in 10L stomach inflation; P=0.56). CONCLUSIONS: Increasing levels of stomach inflation had adverse effects on haemodynamic and pulmonary function, indicating an acute abdominal compartment syndrome in this CPR model.

Influence of ventilation strategies on survival in severe controlled hemorrhagic shock.

OBJECTIVE: To investigate the effect of different ventilation settings on hemodynamic stability in severe controlled hemorrhagic shock. DESIGN: Prospective, randomized, controlled animal study. SETTING: Research laboratory in a university hospital. SUBJECTS: Approximately 35-45 kg domestic pigs. INTERVENTIONS: Twenty-four domestic pigs were bled 45 mL/kg (estimated 65% of their calculated blood volume) and then ventilated with either 0 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 0 respiratory rate 14), or with 5 cm H2O positive end-expiratory pressure, a respiratory rate of 28 ventilations/min, and a tidal volume reduced by half (positive end-expiratory pressure 5 respiratory rate 28), or with 5 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 5 respiratory rate 14). After 1 hr study phase surviving animals, received fluid resuscitation and were monitored for further 1 hr. MEASUREMENTS AND MAIN RESULTS: Pulmonary variables, hemodynamic variables, and short-term survival. There were no significant differences in mean arterial blood pressure and cardiac index after hemorrhage. After 20 mins of different ventilation strategies mean arterial blood pressure was 40 +/- 3 mm Hg in the positive end-expiratory pressure 0 respiratory rate 14 group, vs. 24 +/- 6 mm Hg the positive end-expiratory pressure 5 respiratory rate 28 group (p < 0.05) vs. 19 +/- 3 mm Hg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Cardiac index was 65 +/- 5 mL/min/kg in the positive end-expiratory pressure 0 respiratory rate 14 group vs. 37 +/- 5 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 28 group(p < 0.01) and 20 +/- 3 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Mean airway pressure and positive end-expiratory pressure correlated strongly with mean arterial blood pressure and cardiac index. None of the positive end-expiratory pressure 0 respiratory rate 14 animals died in the study phase, whereas six of seven positive end-expiratory pressure 5 respiratory rate 28 animals, and all seven positive end-expiratory pressure 5 respiratory rate 14 animals died. CONCLUSIONS: In this porcine model of severe hemorrhagic shock, reduction of positive end-expiratory pressure was the most important ventilation strategy component influencing hemodynamic stability. Reducing mean airway pressure by decreasing tidal volumes and increasing respiratory rates seemed to have less influence on cardiopulmonary function and survival than 0 cm H2O positive end-expiratory pressure.

Preoperative administration of esomeprazole has no influence on frequency of refluxes.

STUDY OBJECTIVE: To examine the effect of esomeprazole in a fixed time setting on gastric content volume, gastric acidity, gastric barrier pressure, and reflux propensity. DESIGN: Randomized, controlled, double-blind trial. SUBJECTS: 21 healthy, ASA I physical status volunteers. INTERVENTION: Esomeprazole was given 12 hours and one hour before investigation. Before the study, a multichannel intraluminal impedance catheter, pH monitoring data logger (PHmetry) catheter, and an intragastric-esophageal manometry catheter were placed nasally after topical anesthesia. MEASUREMENTS: Gastric acidity and gastric content volume were determined by PHmetry after aspiration of gastric contents over a nasogastric tube. Gastroesophageal reflux and intragastric-esophageal barrier pressure were investigated by multichannel intraluminal impedance measurement, PHmetry, and intragastric-esophageal manometry. MAIN RESULTS: The pH of gastric contents was significantly (P < 0.001) higher after esomeprazole (mean [25th-75th percentile], 4.2 [3.9-4.8] vs 2.0 [1.9-2.7]), and gastric content volume was significantly (P < 0.001) lower (5.0 mL [3.0-12.0] vs 15 mL [10.0-25.0]) in comparison to placebo. No significant difference between esomeprazole and placebo was found with respect to number of refluxes per person, duration of reflux, or barrier pressure. CONCLUSION: Esomeprazole in a fixed time setting can markedly increase the pH of gastric contents and decrease gastric content volume, but has no influence on the frequency, duration of refluxes, or gastroesophageal barrier pressure.

Minimizing stomach inflation versus optimizing chest compressions.

In a bench model, we evaluated a bag-valve device (Smart Bag MO) with limited maximum inspiratory gas flow developed to reduce the risk of stomach inflation in an unprotected airway. During simulated cardiopulmonary resuscitation with uninterrupted chest compressions, ventilation with the "disabled" Smart Bag MO or an adult self-inflating bag-valve device provided only adequate tidal volumes if inspiratory time was 0.5 s. Ventilation with the "enabled" Smart Bag MO, even in ventilation windows of 0.5 s, provided inadequate tidal volumes during simulated cardiopulmonary resuscitation and would result in hypoventilation in a patient.

Guided insertion of the ProSeal laryngeal mask airway is superior to conventional tracheal intubation by first-month anesthesia residents after brief manikin-only training.

In the following pilot study, we compared conventional laryngoscope-guided tracheal intubation (tracheal intubation) and laryngoscope-guided, gum elastic bougie-guided ProSeal laryngeal mask airway insertion (guided ProSeal) for airway management by first-month anesthesia residents after brief manikin-only training. Five first-month residents with no practical experience of airway management were observed performing these techniques in 200 ASA I-II anesthetized, paralyzed adults. Each resident managed 40 patients, 20 in each group, in random order. The number of insertion attempts, effective airway time, ventilatory capability during pressure-controlled ventilation set at 15 cm H2O, airway trauma, and skill acquisition were studied. Data were collected by unblinded observers. Insertion was more frequently successful (100% versus 65%) and effective airway time was shorter (41 +/- 24 s versus 89 +/- 62 s) in the guided ProSeal group (both P < 0.0001). Expired tidal volume was larger (730 +/- 170 mL versus 560 +/- 140 mL) and end-tidal CO(2) lower (33 +/- 4 mm Hg versus 37 +/- 5 mm Hg) in the guided ProSeal group during pressure controlled ventilation (both P < 0.0001). Blood staining was more frequent on the laryngoscope (24% versus 2%; P < 0.0001) in the tracheal intubation group. There was evidence for skill acquisition in both groups. We conclude that laryngoscope-guided, gum elastic bougie-guided insertion of the ProSeal laryngeal mask airway is superior to conventional laryngoscope-guided tracheal intubation for airway management in terms of insertion success, expired tidal volume, and airway trauma by first-month anesthesia residents after brief manikin-only training. The guided ProSeal technique has potential for cardiopulmonary resuscitation by novices when conventional intubation fails.

Influence of negative expiratory pressure ventilation on hemodynamic variables during severe hemorrhagic shock.

OBJECTIVE: Outcome after trauma with severe hemorrhagic shock is still dismal. Since the majority of blood is present in the venous vessels, it might be beneficial to perform venous recruiting via the airway during severe hemorrhagic shock. Therefore, the purpose of our study was to evaluate the effects of negative expiratory pressure ventilation on mean arterial blood pressure, cardiac output, and short-term survival during severe hemorrhagic shock. DESIGN: Prospective study in 21 laboratory animals. SETTING: University hospital research laboratory. SUBJECTS: : Tyrolean domestic pigs. INTERVENTIONS: After induction of controlled hemorrhagic shock (blood loss approximately 45 mL/kg), 21 pigs were randomly ventilated with either zero end-expiratory pressure (0 PEEP; n = 7), 5 cm H2O positive end-expiratory pressure (5 PEEP; n = 7), or negative expiratory pressure ventilation (up to -30 cm H2O at the endotracheal tube during expiration; n = 7). MEASUREMENTS AND MAIN RESULTS: Mean (+/-sd) arterial blood pressure was significantly higher in the negative expiratory pressure ventilation swine when compared with the 0 PEEP (38 +/- 5 vs. 27 +/- 3 mm Hg; p = .001) and the 5 PEEP animals (38 +/- 5 vs. 20 +/- 6 mm Hg; p < .001) after 5 mins of the experiment. Cardiac output was significantly higher in the negative expiratory pressure ventilation swine when compared with the 0 PEEP (3.1 +/- .4 vs. 1.9 +/- .9 L/min; p = .001) and 5 PEEP animals (3.1 +/- .4 vs. 1.2 +/- .8 L/min; p < .001) after 5 mins of the experiment. All seven negative expiratory pressure ventilation animals, but only three of seven 0 PEEP animals (p = .022), survived the 120-min study period, whereas all seven of seven 5 PEEP animals were dead within 35 mins (p < .001). Limitations include that blood loss was controlled and that the small sample size limits the evaluation of survival outcome. CONCLUSIONS: When compared with pigs ventilated with either 0 PEEP or 5 PEEP, negative expiratory pressure ventilation during severe hemorrhagic shock improved mean arterial blood pressure and cardiac output.

Effects of face mask ventilation in apneic patients with a resuscitation ventilator in comparison with a bag-valve-mask.

Bag-valve-mask ventilation in an unprotected airway is often applied with a high flow rate or a short inflation time and, therefore, a high peak airway pressure, which may increase the risk of stomach inflation and subsequent pulmonary aspiration. Strategies to provide more patient safety may be a reduction in inspiratory flow and, therefore, peak airway pressure. The purpose of this study was to evaluate the effects of bag-valve-mask ventilation vs. a resuscitation ventilator on tidal volume, peak airway pressure, and peak inspiratory flow rate in apneic patients. In a crossover design, 40 adults were ventilated during induction of anesthesia with either a bag-valve-mask device with room air, or an oxygen-powered, flow-limited resuscitation ventilator. The study endpoints of expired tidal volume, minute volume, respiratory rate, peak airway pressure, delta airway pressure, peak inspiratory flow rate and inspiratory time fraction were measured using a pulmonary monitor. When compared with the resuscitation ventilator, the bag-valve-mask resulted in significantly higher (mean+/-SD) peak airway pressure (15.3+/-3 vs. 14.1+/-3 cm H2O, respectively; p=0.001) and delta airway pressure (14+/-3 vs. 12+/-3 cm H2O, respectively; p<0.001), but significantly lower oxygen saturation (95+/-3 vs. 98+/-1%, respectively; p<0.001). No patient in either group had clinically detectable stomach inflation. We conclude that the resuscitation ventilator is at least as effective as traditional bag-valve-mask or face mask resuscitation in this population of very controlled elective surgery patients.

Middle ear pressure changes during anesthesia with or without nitrous oxide are similar among airway devices.

We tested the hypothesis that middle ear pressure (MEP) is influenced by the choice of airway device during anesthesia with or without nitrous oxide (N2O) in the gas mixture. Eighty consecutive anesthetized, paralyzed ventilated patients (ASA physical status I-II, 18-65 yr) were randomly allocated for airway management with the orally inserted tracheal tube, classic laryngeal mask airway, ProSeal laryngeal mask airway, or laryngeal tube suction with or without N2O 66% in the gas mixture. MEP was measured from both ears in random order by a blinded observer before induction of anesthesia and every 10 min for 70 min. In the N2O groups, N2O was changed to air after 40 min. There were no differences in MEP among the airway devices in the N2O or air groups. MEP was unchanged in the air groups but increased in the N2O groups with N2O (P < 0.0001) and decreased with air (P < 0.02). Baseline values for MEP were similar, but MEP was always higher for the N2O groups (P < 0.001). We conclude that the choice of airway device does not influence MEP among orally inserted tracheal tube, classic laryngeal mask airway, ProSeal laryngeal mask airway, and laryngeal tube suction during anesthesia with or without N2O in the gas mixture.

Signs of inflammation after sciatic nerve block in pigs.

Nerve stimulators are widely used to assist with peripheral nerve blocks but do not eliminate the risk of nerve injury. We evaluated the histologic findings 6 h after sciatic nerve block with bupivacaine in pigs. When a motor response was still obtained with a current <0.2 mA (n = 10), the postmortem microscopic evaluation revealed lymphocytes and granulocytes sub-, peri-, and intraneurally in 5 (50%) of 10 pigs. No signs of inflammation were observed when the muscle contraction was achieved with a current between 0.3 and 0.5 mA (P = 0.03). In conclusion, the current required to elicit a motor response, the position of the needle tip, and the subsequent likelihood of nerve damage merit further evaluation.