Percutaneous transtracheal emergency ventilation during respiratory arrest: comparison of the oxygen flow modulator with a hand-triggered emergency jet injector in an animal model

The oxygen flow modulator is a device for percutaneous transtracheal emergency ventilation. Simulating a respiratory arrest situation, we studied the effects of this device in comparison with a hand-triggered emergency jet injector during pulmonary resuscitation. Nine pigs were anesthetized and mechanically ventilated. After surgical exposure, an emergency transtracheal airway catheter was inserted into the trachea. Ventilation was stopped until SpO2 was below 70%. Each animal was subsequently randomly ventilated via the transtracheal airway catheter with either the hand-triggered emergency jet injector or the oxygen flow modulator. After 10 minutes, respiratory and hemodynamic parameters were recorded. Ventilation was stopped again until SpO2 reached 70%, and the animal was ventilated with the second device. With both devices, pulmonary resuscitation was successful. Whereas PaO2 differed not significantly between the two devices, PaCO2 was lower during percutaneous transtracheal ventilation with the hand-triggered emergency jet injector.     

Percutaneous transtracheal jet ventilation for cardiopulmonary resuscitation: evaluation of a new jet ventilator

This study compared percutaneous transtracheal jet ventilation (PTJV) at a frequency (f) of 20/min, with high-frequency positive-pressure ventilation (HFPPV) at f of 60/min, and endotracheal intubation and intermittent positive-pressure ventilation (ET IPPV) at f of 10/min in apneic dogs. Fifty-four emergency medicine trainees (EMTs) attempted PTJV via a 14-gauge Angiocath attached to a hand-held jet ventilator, f of 20/min, and ET IPPV using an Ambu bag, f of 10/min. Twenty-nine other EMTs attempted cricothyrotomy using a prototype nonkinkable catheter (Arrow) and a new jet ventilator, Bronchovent, f of 60/min, equipped with a pressure sensor which stops ventilation at pressures greater than 20 cm H2O. Adequate oxygenation was achieved by all 3 groups, but only the HFPPV group avoided respiratory alkalosis. There was a higher equipment failure rate (catheter kinking and dislodgment) in the PTJV group. In the HFPPV group, the Bronchovent's pressure-limiting sensor stopped ventilation when the catheter was kinked or out of position, reducing the extent of subcutaneous emphysema and barotrauma. With further catheter improvements, HFPPV Bronchovent may offer a safe and reliable method of ventilating patients during CPR in the field.     

Sustained oxygenation without ventilation in paralyzed pigs with high-flow tracheal oxygen

OBJECTIVES: It is generally assumed that ventilation is necessary for oxygenation. This study tested if paralyzed animals without respirations can maintain arterial oxygenation when administered high-flow oxygen delivered by a catheter in the trachea. METHODS: DESIGN: Prospective observational study. SETTING: University research laboratory. PARTICIPANTS: 3 anesthetized/paralyzed swine weighing 29.5 +/- 4.2 kg. INTERVENTIONS/OBSERVATIONS: Pigs were intubated, anesthetized with intravenous tiletamine and a pentobarbital drip. A femoral arterial line was placed to record arterial blood gases and vital signs every 5 minutes. Respiratory paralysis was obtained with vecuronium 150 microg/kg and repeated at any sign of movement. A catheter was placed in the trachea to deliver oxygen at 15 L/min. Outflow gas from the endotracheal tube was analyzed for O2 and CO2. O2 was discontinued at 75 minutes. The institutional animal care and use committee approved the protocol. RESULTS: All pigs survived to 75 minutes. PaO2 was more than 100 mm Hg throughout the study period. Mean PaCO2 was 37.4 +/- 2.8 mm Hg at baseline, 146 +/- 59 at 30 minutes, then rose above 200 mm Hg in all pigs by 45 minutes. Mean arterial pH fell from 7.47 +/- 0.04 at onset to 6.75 +/- 0.06 at 75 minutes. When oxygen was terminated at 75 minutes, PaO2 fell to 16.5 +/- 7.6 mm Hg within 5 minutes, and all pigs were sacrificed within 10 minutes. For outflow gas, O2 was more than 98% and expired CO2 less than 1% throughout the study period. CONCLUSIONS: Paralyzed, unventilated pigs receiving high-flow oxygen via a tracheal catheter remained alive after 75 minutes, although a profound respiratory acidosis developed.     

Percutaneous transcricoid jet ventilation compared with surgical cricothyroidotomy in a sheep airway salvage model

BACKGROUND: We developed a large animal model of the "cannot intubate/cannot ventilate" (CNI/V) scenario to compare percutaneous transcricoid manual jet ventilation (MJV) with surgical cricothyroidotomy (SC). METHODS: Twelve sheep weighing 40-80 kg were assigned to MJV or SC groups. After sedation, intubation, and line placement, CNI/V was simulated by removing the tracheal tube and inducing paralysis with vecuronium. When SaO2 reached 80% (t=0), MJV catheter insertion or SC was initiated. Upon successful airway placement, ventilation began using 100% oxygen at 20 breaths/min. MJV was administered at 50 psi. HR, BP, SaO2, pH, PCO2, and PO2 were recorded at t=0, 30, 60, 90, 120, 150, 180, 300, 600, and 1200 s. Data were reported as mean+/-S.E.M. over the whole observation period. Baseline values were compared using Student's t-tests. Repeated-values ANOVA was used for post-procedure group comparisons. Statistical tests were two-tailed and alpha was set at 0.05. RESULTS: Body weights were not significantly (P=0.08) different between MJV (65+/-6 kg) and SC (52+/-3 kg) groups. Baseline respiratory and hemodynamic variables were also not significantly different. Median procedure time for MJV (20 s) and SC (24 s) was not significantly (P=0.69) different. Post-procedure values were not significantly different for SaO2 (P=0.65), pH (P=0.70), PCO2 (P=0.47), PO2 (P=0.84), MAP (P=0.09), or HR (P=0.16) over the entire 20 min resuscitation period. CONCLUSION: Using a realistic model of CNI/V we found no difference in respiratory or hemodynamic variables between MJV and SC. Adequate ventilation and perfusion was maintained solely by MJV for up to 20 min.     

Hyperoxia in lethal methemoglobinemia: effects on oxygen transport, tissue oxygenation, and survival in pigs

BACKGROUND: Treatment of severe methemoglobinemia includes the avoidance of methemoglobin-inducing drugs, the application of methylene blue, and the administration of supplementary oxygen. However, the efficacy of the latter on oxygen transport, tissue oxygenation, and survival in the treatment of extreme methemoglobinemia is ambiguous. The objective was to assess whether using hyperoxic ventilation as the sole therapeutic intervention (i.e., ventilation with pure oxygen, Fio2 1.0) improves the short-term (6-hr) survival rate during otherwise lethal methemoglobinemia. DESIGN: Prospective, randomized, controlled study. SETTING: Experimental animal laboratory of a university hospital. SUBJECTS: Fourteen anesthetized, mechanically ventilated pigs. INTERVENTIONS: After induction of profound methemoglobinemia (60 +/- 2%) by the injection of 15 mg/kg 4-dimethylaminophenol, artificial ventilation either was continued with room air (G 0.21, n = 7) or was changed over to hyperoxic ventilation (G 1.0, n = 7). A constant level of methemoglobinemia was maintained by continuous infusion of 4-dimethylaminophenol throughout a 6-hr follow-up period. MEASUREMENTS AND MAIN RESULTS: All animals died within the 6-hr follow-up period, but survival time was prolonged in animals ventilated with pure oxygen (G 0.21, 105 +/- 30 mins; G 1.0, 210 +/- 64 mins, p < .05). No differences were encountered between G 0.21 and G 1.0 with respect to the investigated variables of macrohemodynamics, oxygen transport, and tissue oxygenation. CONCLUSIONS: Hyperoxic ventilation has negligible effects on oxygen transport and tissue oxygenation during lethal methemoglobinemia; nevertheless, survival was increased without severe adverse reactions provoked by hyperoxic ventilation.     

Physiologic effects of transtracheal open ventilation in postextubation patients with high upper airway resistance

OBJECTIVE: To investigate whether transtracheal open ventilation (TOV), pressure control ventilation (PCV) through a minitracheotomy tube (internal diameter 4 mm), is an effective method of inspiratory assistance under high upper airway resistance in postextubation patients; to compare, in a lung model study, TOV with other methods. DESIGN: Clinical study: A prospective, controlled, crossover study. Lung model study: A prospective laboratory trial. SETTING: Clinical study: A six-bed general intensive care unit in a teaching hospital. Lung model study: Animal research laboratory. PATIENTS: Clinical study: Eleven postextubation patients, who had undergone minitracheotomy for sputum retention between January 1997 and December 1997. SUBJECT: Lung model study: Two-bellows-in-a-box lung model, which included ordinary and high levels of upper airway resistance. INTERVENTIONS: Clinical study: Ventilatory settings were: assist/control (A/C) mode, 2 breaths/min of A/C back-up rate, 35-40 cm H2O of PCV, 0.6-0.8 secs of inspiratory time, and 0 cm H2O of positive end-expiratory pressure. The ventilatory parameters of TOV were compared with those of spontaneous breathing (SB). Lung model study: Effect of TOV on inspiratory assistance was compared with those of SB, open minitracheotomy, 5 L/min of transtracheal gas insufflation, and 5 and 10 cm H2O of pressure support ventilation (PSV), which simulated noninvasive positive ventilation. TOV ventilatory settings were: A/C mode; 30, 40, and 50 cm H2O of PCV, 0.9 secs of inspiratory time, and 0 cm H2O of positive end-expiratory pressure. At each ventilatory setting, we adjusted the inspiratory effort of the model to give a tidal volume of 0.5 L. MEASUREMENTS AND MAIN RESULTS: Clinical study: TOV was performed for 76.6 +/- 38.6 hrs (mean +/- sd) over 5.6 +/- 2.6 days without major complication. Peak tracheal pressure, which was measured distal to the minitracheotomy tube in six patients by a catheter pressure transducer, was 4.33 +/- 0.59 cm H2O. Inspiratory tidal volume delivered by the ventilator was 0.51 +/- 0.06 L. Respiratory rate during TOV was lower than during SB. According to esophageal pressure and respiratory inductive plethysmography, TOV reduced the patient's inspiratory work and improved the breathing pattern. Lung model study: Mean tracheal pressure during TOV and 10 cm H2O of PSV were positive values and they had larger inspiratory assistance according to the pressure-time product of pleural pressure. Although high upper airway resistance reduced the inspiratory assistance of PSV, it did not change the effects of TOV. CONCLUSIONS: TOV effectively reduced patient's inspiratory work and was more useful than open minitracheotomy and transtracheal gas insufflation. TOV also improved the breathing pattern. TOV may be useful for resolving some postextubation respiratory problems and avoiding the need for reintubation.     

Simultaneous use of membrane oxygenation and high-frequency jet ventilation in acute pulmonary failure

A 16-yr-old female suffering acute, rapidly progressive combined respiratory and cardiac failure that was unresponsive to conventional volume-cycled ventilation, was stabilized with the simultaneous short-term use of veno-venous membrane oxygenation and high-frequency jet ventilation. Percutaneously introduced cannulas afforded rapid vascular access for membrane oxygenation, minimal wound problems during the perfusion, and easy decannulation. This is the first reported combined use of high-frequency jet ventilation and extracorporeal membrane oxygenation, and the first reported percutaneous initiation of veno-venous bypass. The patient remained alive and well 4 months after therapy.     

俯卧位吸氧对COPD急发期病人氧合作用的影响及护理

慢性阻塞性肺气肿 ,简称慢阻肺 (COPD)。急性发作期病人由于支气管黏膜炎症水肿加重 ,痰液堵塞支气管腔 ,潮气量减低 ,导致总的肺泡通气量不足[1] ,表现为明显的低氧血症。氧疗可以防止动脉血氧的急剧变化 ,从而改善病人的预后。研究显示 ,俯卧位能增加功能残气量 ,改善通气血流比值 ,减少分流 ,改善膈肌的运动[2 ,3 ] ,对改善肺炎、ARDS以及慢性呼吸功能不全基础上发生的急性呼吸衰竭等病人的氧合状态 ,提高存活率有明显的治疗作用[4,5] 。为此 ,本研究在氧疗时辅以俯卧位应用于COPD急性发作期病人 ,旨在观察俯卧位对改善COPD急性发…     

Hemodynamic effects of high-frequency jet ventilation in dogs with a chronically banded pulmonary artery

Two to seven weeks after banding the main pulmonary artery, the hemodynamic effects of high-frequency jet ventilation (HFJV) and conventional mechanical ventilation (CMV) were studied in dogs with and without PEEP. In comparison with CMV, HFJV significantly increased cardiac index, stroke index (SI), left ventricular stroke work index, and oxygen delivery index, and decreased pulmonary vascular resistance index both with and without PEEP; however, there were significant decreases in PaO2 and increases in intrapulmonary physiologic shunt ratio in HFJV without PEEP. SI without PEEP was significantly greater with HFJV when the peak airway pressure was synchronized with the diastole in pulmonary arterial pressure (PAP) than with CMV and with HFJV synchronized with the systole in PAP. These findings suggest that HFJV has hemodynamic advantages over CMV in dogs with chronically banded pulmonary artery and dilated right ventricle.     

Hemodynamic effects of continuous positive-pressure ventilation and high-frequency jet ventilation with positive end-expiratory pressure in normal dogs

The hemodynamic effects of high-frequency jet ventilation (HFJV) at 60, 120, 240, and 480 breath/min, and conventional ventilation at 15 breath/min were compared in 6 anesthetized, paralyzed dogs, at 0, 10, and 20 cm H2O of positive end-expiratory pressure (PEEP). On HFJV at the same inspired oxygen, PaCO2, and PEEP levels, hemodynamic function improved significantly. Cardiac output was higher, whereas transmural CVP and pulmonary vascular resistances were lower. The improvement was primarily related to a decrease in mean airway pressure, particularly at higher PEEP levels. When PEEP was applied, hemodynamic function improved even when mean airway pressure was maintained constant. The findings suggest that lung volume was smaller during HFJV, and/or that lung volume changes during each respiratory cycle contributed to differences in venous return and ventricular function.     

Different effects of early endotoxaemia on hepatic and small intestinal oxygenation in pigs

Objective Study on simultaneous O₂ supply/uptake relationships in liver and gut during endotoxaemia, to determine whether signs of dysoxia develop uniformly in the splanchnic region.Design Animal study to assess the early effects of endotoxaemia on oxygenation of both liver and small intestine.Interventions Eight anaesthetized pigs received a continuous portal venous infusion of lipopolysaccharide (0.5 g·kg^–1·h^–1) for 6 h. Systemic, pulmonary and splanchnic haemodynamics as well as systemic and splanchnic O₂ supply/uptake relationships were determined.Results There was a multiphasic haemodynamic response pattern characterized by an early (within the 1st h) and a subsequent more prolonged phase (between the 2nd and 6th h) of decreases and recovery of hepatic arterial, portal venous and superior mesenteric arterial blood flows (electromagnetic flow probes) and splanchnic O₂ deliveries. Unrelated to perfusion pressure and O₂ delivery, there were early and sustained decreases in ileal mucosal surface partial pressure of oxygen (PO₂) (multiwire PO₂ electrode) and pH (tonometry). This was not reflected by ileal serosal surface PO₂, O₂ uptake and arteriomesenteric venous pH and partial pressure of carbon dioxide (PCO₂) gradients. There was little evidence of concomitant hepatic dysoxia as evaluated by surface PO₂.Conclusions The study demonstrates early and sustained regional (mucosa) intestinal hypoxia with little evidence of simultaneous hepatic dysoxia during initial endotoxaemia.     

Cerebral blood flow and cerebral oxygen consumption in patients with COPD on mechanical ventilation

Objective To investigate the effect of PaCO₂ on cerebral blood flow (CBF) in chronic obstructive pulmonary disease (COPD).Design Before-after trial.Setting General ICU in a regional hospital.Patients 7 patients undergoing mechanical ventilation because of an exacerbation of COPD.Intervention CBF and cerebral metabolic rate of oxygen (CMRO₂) of COPD were measured before and after hyperventilation and were compaired by those of normal patients. CBF was measured by the Kety-Schmidt technique using 15% N₂O.Measurements/results Hyperventilation produced a significant reduction in CBF in COPD with no concomitant change in CMRO₂. CMRO₂ in COPD was significantly lower than those in normal patients. The regression equation was shifted significantly more to the right in COPD.Conclusion The sensitivity of CBF in CO₂ remained but CMRO₂ was reduced markedly in COPD patients.     

Twice-daily mixed regular and NPH insulin injections with new jet injector versus conventional syringes: pharmacokinetics of insulin absorption

The purpose of the present study was to evaluate the feasibility of using a jet injector in a split and mixed regular and NPH insulin regimen and to compare serum glucose and free-insulin profiles obtained with the injector and the conventional syringe and needle. Twelve insulin-dependent diabetic patients were hospitalized for 5 days. After a stabilization day, six patients received their insulin injection with the injector for 2 days and with the syringe and needle for the following 2 days; the regimen was reversed for the other six patients. Diet, exercise, and insulin dosage remained constant. The serum glucose levels with the injector were consistently lower than those obtained with the syringe at all times of the day except at 5:00 a.m. and 7:30 a.m., when mean values were similar for both treatments. Free-insulin levels were higher with the injector from 10:30 a.m. to 4:30 p.m. These findings suggest that insulin absorption is faster and possibly greater with the injector than with the syringe. When switching from a syringe to an injector insulin program, insulin dose adjustment may be necessary.     

Retention of ventilation skills of emergency nurses after training with the SMART BAG compared to a standard bag-valve-mask

BACKGROUND AND PURPOSE: Studies show that nurses retain resuscitation skills poorly and that retention of ventilation skills is particularly difficult. We formed the hypothesis that the SMART BAG (SB, O-Two Medical Technologies Inc., Canada), i.e. a bag-valve-mask device with a pressure/flow responsive valve, would assist nurses in providing more efficient ventilation six months after training. MATERIALS AND METHODS: Prior to training, 39 emergency nurses performed CPR for 2 min, in pairs, using a standard bag-valve-mask device (STBVM, Laerdal, Norway) to assess their base line skills. A CPR training manikin (Simulaids, USA) equipped with a PEEP valve in the oesophagus set at 20 cm H2O was used to measure inspiratory time, tidal volume (Vt), peak pressure and gastric insufflation (GI). Immediately following training they were tested using an O-Two STBVM and a SB. Half of the nurses were retested after three months, the other half after six months. Efficient ventilation was defined as a mean Vt>400 ml and GI<50 ml in 1 min. RESULTS: Before training, only 16% of nurses ventilated efficiently: 63% had GI and 28% had Vt<400 ml. Three months after training the efficiency of the STBVM and the SB was high (81 and 75%, respectively). Six months after training, there was a trend towards higher efficiency for the SB (63%) compared to the STBVM (25%) (p=0.07). For instances with the STBVM producing a Vt>400 ml, those without GI had a lower peak pressure than those with GI (7.8 cm H2O versus 17.7 cm H2O, p=0.0001) and showed a trend towards a longer inspiratory time (1.28 s versus 1.08 s, p=0.08). Of all efficient ventilations with a STBVM, 26% had a Vt>600 ml. CONCLUSIONS: Six months after training, nurses ventilated at least as efficiently with the SB, compared with the STBVM. This illustrates the ability of the SB to compensate for the deterioration over time in skill. On the other hand, training with a STBVM should focus primarily on prolonging the inspiratory time, and therefore the peak pressure, whilst maintaining an adequate Vt.     

一种新高频通气方法对实验性急性呼吸窘迫综合征的疗效观察

在高频喷射通气（ＨＦＪＶ）治疗犬实验性急性呼吸窘迫综合征（ＡＲＤＳ）时，采用连续ＨＦＪＶ基础上间歇叠加深吸气（ＨＦＪＶ＋ＤＩ）的新通气方法，以期为ＡＲＤＳ的治疗寻找一种新途径。用油酸复制犬ＡＲＤＳ模型，并随机分为３组。ＨＦＪＶ＋ＤＩ组（ｎ＝１０）：在连续ＨＦＪＶ基础上每隔１０分钟加入１次深吸气；常规机械通气组（ＣＭＶ，ｎ＝１０），给予０．７８５ｋＰａ（１ｋＰａ＝１０．２０ｃｍＨ２Ｏ）呼气末正压（ＰＥＥＰ）治疗；对照组（ｎ＝１０），未予通气治疗。每隔１小时测定１次氧合及血流动力学指标，共观察５小时。注射油酸后，动脉氧分压（ＰａＯ２）由１２．４００ｋＰａ（１ｋＰａ＝７．５ｍｍＨｇ）降至６．５６０ｋＰａ（Ｐ＜０．０１），动脉二氧化碳分压（Ｐａ－ＣＯ２）未见明显变化。通气治疗后，ＣＭＶ和ＨＦＪＶ＋ＤＩ均使ＰａＯ２明显升高，ＰａＣＯ２无明显变化（Ｐ＞０．０５），ＨＦＪＶ＋ＤＩ的氧释放指数（ＤＯ２Ｉ）明显高于ＣＭＶ组（Ｐ＞０．０５），心脏指数（ＣＩ）在ＣＭＶ组及ＨＦＪＶ＋ＤＩ组均明显减低（Ｐ＜０．０５）。提示：ＨＦＪＶ＋ＤＩ时ＰａＯ２的提高大于ＣＩ下降所致的不利影响，在改善组织缺氧方面明显优于ＣＭＶ时加用ＰＥＥＰ     

Effect of a self-directed learning package on emergency nurses' knowledge of assessment of oxygenation and use of supplemental oxygen

Emergency nurses frequently and independently make decisions regarding supplemental oxygen. The importance of these decisions for patients is highlighted by the well documented association between respiratory dysfunction and adverse events. This study aimed to: (i) examine the effect of educational preparation on emergency nurses' knowledge of assessment of oxygenation, and the use of supplemental oxygen; (ii) explore the impact of existing knowledge on decisions related to the implementation of supplemental oxygen; and (iii) explore nurses' characteristics that were associated with effectiveness of the educational preparation. A pretest/post-test, controlled, quasi-experimental design was used in this study. Educational preparation was effective in increasing emergency nurses' knowledge. Baseline level of knowledge was predictive of reports of independent decisions regarding the implementation of oxygen. There was a significant positive relationship between postgraduate qualification in emergency nursing and the effect of education, and significant negative relationships between effect of education and baseline level of knowledge and daily decisions to implement supplemental oxygen.     

Hemodynamic effects of different lung-protective ventilation strategies in closed-chest pigs with normal lungs

OBJECTIVE: The benefits of lung-protective ventilation strategies used for acute respiratory distress syndrome in subjects with normal lungs are uncertain. The purpose of this study was to investigate the hemodynamic effects of conventional lung-protective ventilation (CLPV) and high-frequency oscillatory ventilation (HFOV) in a normal lung animal model. DESIGN: Prospective laboratory investigation. SETTING: Animal laboratory in a university medical center. SUBJECTS: Seven landrace pigs (mean weight 41 kg). INTERVENTIONS: Pigs were ventilated at random conventionally with positive end-expiratory pressure 2-3 cm H2O and tidal volume 10-12 mL/kg (control), with CLPV (positive end-expiratory pressure 10 cm H2O, tidal volume 6 mL/kg), or with HFOV. Hemodynamics were analyzed after insertion of biventricular conductance catheters and a pulmonary artery catheter. MEASUREMENTS AND MAIN RESULTS: The protective strategies led to higher mean airway pressures and severe hypercapnia with acidosis, which was only significant with CLPV. Compared with control, oxygenation was worse with CLPV and HFOV. With HFOV and CLPV, mean arterial pressure, cardiac output, and stroke volume decreased significantly; pulmonary arterial elastance increased. The slope of the end-diastolic pressure volume relationship for the left and right ventricle remained unchanged (preserved ventricular function), whereas the intercept increased with both protective strategies (augmented intrathoracic pressure); left and right end-diastolic volumes decreased significantly. CONCLUSIONS: In the absence of a fluid resuscitation strategy, CLPV and HFOV caused decreased mean arterial pressure, cardiac output, and stroke volume and worsened oxygenation in this normal lung animal model. This resulted primarily from a biventricular decrease in preload.     

Comparison of manually triggered ventilation and bag-valve-mask ventilation during cardiopulmonary resuscitation in a manikin model

Background

To compare a novel, pressure-limited, flow adaptive ventilator that enables manual triggering of ventilations (MEDUMAT Easy CPR, Weinmann, Germany) with a bag-valve-mask (BVM) device during simulated cardiac arrest.

Methods

Overall 74 third-year medical students received brief video instructions (BVM: 57 s, ventilator: 126 s), standardised theoretical instructions and practical training for both devices. Four days later, the students were randomised into 37 two-rescuer teams and were asked to perform 8 min of cardiopulmonary resuscitation (CPR) on a manikin using either the ventilator or the BVM (randomisation list). Applied tidal volumes (V_T), inspiratory times and hands-off times were recorded. Maximum airway pressures (P_max) were measured with a sensor connected to the artificial lung. Questionnaires concerning levels of fatigue, stress and handling were evaluated. V_T, pressures and hands-off times were compared using t-tests, questionnaire data were analysed using the Wilcoxon test.

Results

BVM vs. ventilator (mean ± SD): the mean V_T (408 ± 164 ml vs. 315 ± 165 ml, p = 0.10) and the maximum V_T did not differ, but the number of recorded V_T < 200 ml differed (8.1 ± 11.3 vs. 17.0 ± 14.4 ventilations, p = 0.04). P_max did not differ, but inspiratory times (0.80 ± 0.23 s vs. 1.39 ± 0.31 s, p < 0.001) and total hands-off times (133.5 ± 17.8 s vs. 162.0 ± 11.1 s, p < 0.001) did. The estimated levels of fatigue and stress were comparable; however, the BVM was rated to be easier to use (p = 0.03).

Conclusion

For the user group investigated here, this ventilator exhibits no advantages in the setting of simulated CPR and carries a risk of prolonged no-flow time.     

The effects of inversed ratio ventilation (IRV) on arterial oxygenation during mechanical ventilation in patients with acute respiratory failure.

We investigated the effects of inversed ratio ventilation by altering the inspiratory:expiratory (I:E) ratio and assessing the time course changes in the intrapulmonary shunting (Qs/Qt) in 14 patients with acute respiratory failure. Stepwise prolongation of the I:E ratio from 1:1.9 to 2:1 and then to 2.6 or 4:1 was applied when PEEP failed to raise the PaO2 above 80 mmHg while breathing oxygen. A significant decrease in Qs/Qt was observed following prolongation of the I:E ratio from 1:1.9 (Qs/Qt = 45 +/- 9%) to 2:1 (Qs/Qt = 29 +/- 9%) but not with further prolongation of the I:E ratio (Qs/Qt = 27 +/- 7%). Improvement of the pulmonary ventilation/perfusion imbalance became more marked with continued IRV and a significant increase in PaO2 was observed at 6 h after initiating prolongation of the inspiratory time (P less than 0.05). There were no significant changes in hemodynamics, PaCO2, or peak inspiratory pressure during IRV. This ventilatory pattern may be indicated when PEEP fails to improve PaO2, but prolongation of the inspiratory time above an I:E ratio of 2:1 did not produce a greater improvement in Qs/Qt and further increases in PaO2 did not occur after more than 10 h of IRV in our 14 patients.