BACKGROUND:/st> Needle cricothyrotomy and subsequent transtracheal jet ventilation (TTJV) is one of the last options to restore oxygenation while managing an airway emergency. However, in cases of complete upper airway obstruction, conventional TTJV is ineffective and dangerous. We transformed a small, industrial ejector into a simple, manual ventilator providing expiratory ventilation assistance (EVA). METHODS:/st> An ejector pump was modified to allow both insufflation of oxygen and jet-assisted expiration through an attached 75 mm long transtracheal catheter (TTC) with an inner diameter (ID) of 2 mm by alternately occluding and releasing the gas outlet of the ejector pump. In a lung simulator, the modified ejector pump was tested at different compliances and resistances. Inspiration and expiration times were measured and achievable minute volumes (MVs) were calculated to determine the effect of EVA. RESULTS:/st> The modified ejector pump shortened the expiration time and an MV up to 6.6 litre min(-1) could be achieved through a 2 mm ID TTC in a simulated obstructed airway. CONCLUSIONS:/st> The principle of ejector-based EVA seems promising and deserves further evaluation.

In managing an obstructed upper airway, an emergency transtracheal ventilation device needs to function as a bidirectional airway, allowing both insufflation of oxygen and egress of gas. The aim of the present study was to determine the capability of two self-assembled, three-way stopcock based jet devices and the Oxygen Flow Modulator to function as a bidirectional airway in conjunction with a small lumen catheter. For each device the effective pressures at the catheter's tip during the expiratory phase and the achievable minute volumes were determined in a laboratory set-up. Using the three-way stopcock based jet devices, changing the connection position of the transtracheal catheter from the in-line port to the side port of the three-way stopcock resulted in a decrease of expiratory pressure at the catheter's tip from a dangerous mean (SD) of 71.1 (0.08) cmH(2)O to -14.71 (0.05) cmH(2)O. Yet this negative expiratory pressure did not facilitate the egress of gas. All devices tested impeded the expiratory outflow and hence decreased the achievable minute volume. This decrease in minute volume was smallest with the Oxygen Flow Modulator.

We conducted a one-year prospective study involving a prehospital Emergency Medical Service in the Netherlands to investigate the incidence of failed or difficult prehospital endotracheal intubation. During the study period the paramedics were asked to fill in a registration questionnaire after every endotracheal intubation. Of the 26,271 patient contacts, 256 endotracheal intubations were performed by paramedics in one year. Endotracheal intubation failed in 12 patients (4.8%). In 12.0% of 249 patients, a Cormack and Lehane grade III laryngoscopy was reported and a grade IV laryngoscopy was reported in 10.4%. The average number of endotracheal intubations per paramedic in one year was 4.2 and varied from zero to a maximum of 12. The median time between arrival on the scene and a positive capnograph was 7 min.38 s in the case of a Cormack and Lehane grade I laryngoscopy and 14 min.58 s in the case of a Cormack and Lehane grade 4 laryngoscopy. The incidence of endotracheal intubations performed by Dutch paramedics in one year was low, but endotracheal intubation was successful in 95.2%, which is comparable with findings in international literature. Early capnography should be used consistently in prehospital airway management.

The results of different studies investigating the use of unilateral spinal anaesthesia are confusing and partly inconsistent. Some authors doubt whether it is possible to create a strictly unilateral block (i.e. motor, sensory and sympathetic) at all, while others claim that such a procedure is standard, especially for ambulatory anaesthesia. This review considers those factors which are relevant, plausible and proven.

BACKGROUND AND OBJECTIVES: The dependence of unilateral spinal anesthesia on injection flow is controversial. We hypothesized that it is possible to achieve strictly unilateral sympathetic block (as assessed by temperature measurements of the limbs) and unilateral sensory and motor block, respectively, during spinal anesthesia by a slow and steady injection of a hyperbaric local anesthetic solution. METHODS: Forty-four patients (American Society of Anesthesiologists [ASA] physical status I-III) undergoing surgery of one lower extremity were randomly assigned to one of two groups. Dependent on the patients' height, 1.4 to 1.7 mL hyperbaric bupivacaine 0.5% was injected manually with the patient in the lateral decubitus position, which was maintained for 30 minutes after injection. Injection flow was approximately 0.5 mL/min in group I ("air-buffered" injections performed by 4 mL air between the local anesthetic and the syringe's plunger, n = 25) and approximately 7.5 mL/min in group II ("conventional" injections, n = 19). Sympathetic block was defined as a temperature increase of more than 0.5 degrees C at the foot. Any reduction in the ability to move the hip, knee, or ankle as well as loss of temperature discrimination and/or pinprick even in one dermatome on the nondependent side was considered as a bilateral block. RESULTS: Before surgery, significant differences (P <.05) were observed for unilateral motor paralysis (92% in group I v 68.4% in group II), unilateral sensory block (48.0% v 10.5%), and unilateral sympathetic block (72% v 42.1%). Strictly unilateral spinal anesthesia was found to be significantly more frequent in group I (40% v 5.3%). Significant hemodynamic differences between the groups were not detected. CONCLUSIONS: For hyperbaric spinal anesthesia, the injection flow is an important factor in achieving unilateral sympathetic block. A slow injection proves useful to restrict spinal anesthesia to the side of surgery.

Various in vitro models have been introduced for comparative examinations of post-dural-puncture trauma and measurement of liquor leakage through puncture sites. These models allow simulation of subarachnoid, but not of peridural, pressure. A new two-chamber-model realizes the simulation of both subarachnoid and peridural pressure and allows observation of in vitro punctures with video-documentation. Frame grabbing and (computer-aided) image analysis show new aspects of spinal puncture effects. Therefore, post-dural-puncture trauma and retraction can be objectively visualized by this method, which has not previously been demonstrated. METHODS: Two-chamber-model consists of two short aluminium cylinders. Native human dura patches (8X8 mm) from fresh cadavers are put (correctly oriented) between two special polyamide seals. Mounted between the upper and lower cylinder, these seals stretch the dura patch, which remains flexible and even in all directions. After filling of the lower (subarachnoid) and upper (peridural) chamber with Ringer lactate solution, positive or negative physiological pressure can be adjusted by way of two (Ringer lactate solution filled) infusion lines in each chamber. Puncturing is performed at an angle of 57 degrees to the dura. The model allows examination with epi-illumination and transmitted (polarized) light. In vitro punctures are observed through an inverted camera lens with an CCD-Hi8 video camera (Canon UC1HI) looking into the peridural chamber and documented by means of an S-VHS video recorder (Panasonic NV-FS200EG). After true-colour frame grabbing by a video digitizer (Fast Screen Machine II), single video frames can be optimized and analysed with a 486-66 MHz computer and conventional software (Corel Draw 3.0, Photostyler 1.1a, DDL Aequitas 1.00b). Punctures demonstrated in this paper have been done under simulation of a transdural gradient of 20 cm water similar to the situation of a recumbent patient (15 cm water in the subarachnoid and -5 cm water in the peridural chamber). The punctures were followed by short-time observation for up to 10 minutes. RESULTS: By making it possible to obtains a picture of the puncture site at 20-ms intervals (because of the PAL norm of 50 half-frames/s), video-documentation has become accepted as superior to conventional photography. When the Ringer lactate solution in the subarachnoid chamber is stained with methylene blue, transdural leakage can easily be observed. The result of this documentation technique demonstrate that not dural puncture can be atraumatic, when a 29-G Quincke needle is used. Calculation on the difference between a digitized video frame before and after the puncture clearly illustrates the dural trauma. Owing to their non-cutting tip, as expected, pencil-point needles leave diffuse changes across the dura patch, whereas a more local trauma was observed after puncturing with cutting-tip needles. The same computer calculation between two video frames allows examination of post-puncture-dural retraction of the puncture site. In this connection, we found that relevant dural retraction is a phenomenon limited to the first minute after puncture. Thin spinal needles with so-called modern tips (e.g. Whitacre, Atraucan) can minimize the post-dural-puncture trauma, whereas thicker, conventional, spinal needles (Quincke) leave considerable dural defects. CONCLUSIONS: The two-chamber-model presented allows easy simulation of physiological subarachnoid and peridural pressure. The Ringer lactate solution in the subarachnoid chamber corresponds to the liquor, whereas that in the peridural chamber corresponds to the intercellular (peridural) space. The tension of the dural patch between the polyamide seals is similar to the situation in an anotomical model observed by spinaloscopy (in an earlier study). With the video documentation and computer-aided analysis technique introduced, dural trauma and retraction of the puncture site can be examined and demo

Restriction of sympathetic denervation during spinal anesthesia may minimize hemodynamic alterations. Theoretically, the use of nonisobaric anesthetics may allow unilateral anesthesia and thus restrict sympathetic denervation to one side of the body. The present prospective study investigates the incidence of unilateral spinal anesthesia using hyperbaric bupivacaine 0.5%(1.4 mL, 1.6 mL, 1.8 mL, or 2.0 mL) injected via a 29-gauge Quincke needle with a pump-controlled injection flow of 1 mL/min. In 96 consecutive patients undergoing unilateral surgery of the lower extremities, spinal anesthesia was performed in the lateral decubitus position, which was maintained for 20 min postinjection. Increases in foot temperature of at least 0.5 degrees C were defined as sympathetic blockade. The incidence of unilateral block was not significantly influenced by the amount of bupivacaine. For all 96 patients, the incidence of unilateral sympathetic and complete motor block was 69% and 77%, respectively. Frequency of unilateral sensory block (assessed by pinprick and temperature discrimination) was significantly lower (28%). Strict unilateral spinal anesthesia was achieved in 24 cases (25%). Twenty minutes after injection of the local anesthetic, mean arterial blood pressure decreased significantly in patients with bilateral sympathetic blockade from 87 +/- 8 to 83 +/- 8 mm Hg (P < 0.01) but not in patients with unilateral sympathetic blockade (from 87 +/- 11 to 85 +/- 10 mm Hg). In conclusion, low-flow injection (1 mL/min) of hyperbaric bupivacaine 0.5% via a 29-gauge Quincke needle prevented bilateral sympathetic blockade in more than 69% of the patients. The data further suggest that loss of temperature discrimination alone is not a reliable estimation of sympathetic block.

An improved darkfield-illumination system for comfortable and convenient use of oblique incidence epi-illumination is described. The illuminator employs a new means for altering the position of the aperture diaphragm allowing a subtle adjustment of both the direction and the angle of the incident light bundle. The efficacy of this device for surface imaging is demonstrated in human chromosomes. The device permits an improved visualization of subtle Giemsa bands and the detection of sub-bands, which have not yet been described in the International System for Human Cytogenetic Nomenclature-High Resolution Banding.

BACKGROUND We have developed a technique for measuring a characteristic of the tracheal tube (TT)-trachea interface: the leak conductance (LC). This study aimed to validate the technique in the laboratory and to compare LC with measurements of fractional volume loss (FVL) in neonates undergoing mechanical ventilation. METHODS LC, expressed as leak flow at a lung pressure of 10 cm H(2)O, was derived remotely from ventilator pressure and flow signals. Validation was by simulating breathing circuits for 10 models in which LC was measured directly. LC was compared with FVL for different settings of PEEP, inspired pressure, and time at plateau pressure. Clinically, LC was measured for 135 infants admitted to paediatric intensive care after cardiac surgery and compared with FVL. RESULTS No significant differences were found between direct and remote laboratory measurements of LC (P>0.05). FVL varied with PEEP, plateau pressure, and time at plateau (P<0.05) but LC did not (P>0.05). The between-patient standard deviation (sd) of LC (0.4 litre min(-1)) exceeded the within-patient sd of lc (0.05 litre min(-1); P<0.05); the between-patient sd of FVL (22.1%) exceeded the within-patient sd of FVL (1.3%; P<0.05). The median LC was 0.38 (inter-quartile range 0.29-0.46) litre min(-1). LC was correlated with FVL (r=0.82; 95% confidence interval 0.76-0.88) but wide ranges of FVL were observed for patients with similar LC. CONCLUSIONS LC can be derived remotely and was correlated with FVL, a conventional proxy for tube fit. It may be a better measure of TT fit than FVL.

OBJECTIVE To evaluate oxygen flow through several transtracheal devices in native and right angle kinked states. MATERIAL AND METHOD Eight catheter-over-needle, and two oxygen conveyance devices (Enk Flow Modulator 10 L/min flow and Manujet III Jet device 15, 30, 50 psi) were examined. Oxygen flow from each catheter was measured five times with three insufflation patterns [continuous insufflation, one second insufflation/one second pause (1:1), one second insufflation/three second pause (1:3)] in both native, and 90 degree kinked condition. RESULTS During continuous insufflation, all but the 20G catheter delivered flows of more than 7 L/m with all conveyance pressures. With a 1:1 insufflation/pause ratio, catheters smaller than 16G were able to deliver 7 L/min flow only with driving pressures of 30 and 50 psi. With a 1:3 insufflation ratio, no catheter could deliver adequate flow with 15 psi (manujet) or with the Enk Flow modulator Only the Cook catheter and 14G Ravussin were capable at 30 psi. Only the Cook Transtracheal Jet Ventilation Catheter could deliver adequate flow in kinked position, but only at 50 psi. CONCLUSION Needle-catheters designed for vascular access are marginally capable of effective TJV. The Cook Transtracheal Jet Ventilation catheter proved to be the most robust device in the kinked state, but only when combined with a high-pressure oxygen conveyance system.

Closed endotracheal suction interferes with mechanical ventilation received by infants, but the change to ventilation may be different when ventilator modes that target expired tidal volume (VT(e)) are used. To measure airway pressure and tidal volume distal to the endotracheal tube (ETT) during and after closed suction in a volume-targeted ventilation mode with the Dräger Babylog 8000+, and to determine the time until VT(e) returns to the baseline level. In this benchtop study, closed suction was performed on 2.5- to 4.0-mm ETTs connected to a test lung. 5-8 French suction catheters were used at suction pressures of 80-200 mm Hg during tidal-volume-targeted ventilation. During catheter insertion and suction, circuit inflating pressure increased and tidal volume was maintained, except when a large catheter relative to the ETT was used, in which case tidal volume decreased. End-expiratory pressure distal to the ETT was reduced during suction by up to 75 cm H(2)O while circuit end-expiratory pressure was unchanged. Reduction in end-expiratory pressure distal to the ETT was greatest with large catheters and high suction pressures. Following suction, circuit and tracheal inflating pressures increased and tidal volume increased before returning to baseline in 8-12 s. Closed endotracheal suction interferes with ventilator function in volume-targeted mode, with substantially negative intratracheal pressure during suction, and the potential for high airway pressures and tidal volumes following the procedure. These effects should be considered and pressure limits set appropriately whenever using volume-targeted ventilation.

HASH(0x13466680)

UNLABELLED Volume-assured non-invasive ventilation (NIV) theoretically guarantees minute ventilation with circuit leak compensation unlike other modes of NIV. Bench testing demonstrated that minute ventilation was maintained with varying lung compliance and resistance with minimal effect from circuit leak, confirming for the first time the core features of volume-assured NIV. BACKGROUND AND OBJECTIVE Volume-assured non-invasive positive pressure ventilation (va-NIPPV) is a novel mode designed to adapt pressure support (PS) to achieve a target minute ventilation (TgV). This may optimize ventilation; however, no data confirm that va-NIPPV compensates appropriately for the changes in pulmonary mechanics and circuit leak seen in clinical practice. Bench testing assessed these principles. METHODS A ventilator featuring a va-NIPPV mode was studied. A test lung with varying compliance and resistance, and pneumotachograph were used. Eight lung model settings were chosen:(i) low resistance and high compliance;(ii) low resistance and low compliance;(iii) high resistance and high compliance; and (iv) high resistance and low compliance, all with and without additional circuit leak. An expiration valve, respiratory rate of 15, inspiratory time of 1 s and PS between 3 and 21 cm H2O were used. Va-NIPPV was tested with varying TgV after establishing the range of minute ventilation possible in a pressure preset mode. RESULTS At a TgV of 10 L/min, va-NIPPV delivered minute ventilation of (median (interquartile range)): 11 (10.9-11, 10.2 (10.2-10.3), 12.4 (12.4-12.4) and 11.2 (10.9-11.2) L/min in test lung settings 1, 2, 3 and 4, respectively. Additional leak between 8-33 L/min had little effect. Similar results were seen at other TgV, within the ventilator's PS capabilities. CONCLUSIONS These data confirm that va-NIPPV is able to approximate a preset TgV with varying lung compliance and resistance, and that additional circuit leak has little effect on the delivered minute ventilation.

BACKGROUND:/st> Needle cricothyrotomy and subsequent transtracheal jet ventilation (TTJV) is one of the last options to restore oxygenation while managing an airway emergency. However, in cases of complete upper airway obstruction, conventional TTJV is ineffective and dangerous. We transformed a small, industrial ejector into a simple, manual ventilator providing expiratory ventilation assistance (EVA). METHODS:/st> An ejector pump was modified to allow both insufflation of oxygen and jet-assisted expiration through an attached 75 mm long transtracheal catheter (TTC) with an inner diameter (ID) of 2 mm by alternately occluding and releasing the gas outlet of the ejector pump. In a lung simulator, the modified ejector pump was tested at different compliances and resistances. Inspiration and expiration times were measured and achievable minute volumes (MVs) were calculated to determine the effect of EVA. RESULTS:/st> The modified ejector pump shortened the expiration time and an MV up to 6.6 litre min(-1) could be achieved through a 2 mm ID TTC in a simulated obstructed airway. CONCLUSIONS:/st> The principle of ejector-based EVA seems promising and deserves further evaluation.

BACKGROUND Oxygen supplies capable of supporting transtracheal jet ventilators can be lifesaving. There is not much information about which oxygen sources (readily available inside and outside operating rooms) have sufficient driving pressure for transtracheal jet ventilation. METHODS We measured driving pressures (upstream or residual oxygen pressure) in a specially designed jet ventilation test system with a 2.25-mm (14-gauge) i.v. catheter. High-pressure oxygen sources evaluated included wall-mounted (Puritan, Allied Health, Precision, and Datex-Ohmeda) and anesthesia machine auxiliary oxygen flowmeters and oxygen flush valves from anesthesia machines (Draeger Narkomed 2B, Narkomed 4, Datex-Ohmeda Excel, and Datex-Ohmeda Modulus). RESULTS All 4 types of wall-mounted oxygen flowmeters, opened past their highest scale settings (15 L/min), delivered sufficient working pressures (range, 103-282 kPa; 16-41 psi). Working pressures from auxiliary oxygen flowmeters mounted on Datex-Ohmeda machines were adequate to support jet ventilation (range, 189-248 kPa; 27-36 psi), whereas those on tested Draeger machines did not supply sufficient pressure for jet ventilation: Narkomed 2B, 14-28 kPa (2-4 psi); Narkomed 4, 24-28 kPa (3-4 psi). Working pressures delivered by oxygen flush valves on tested Draeger machines were adequate to support jet ventilation, ranging from 96 to 117 kPa (14-17 psi), whereas pressures generated by tested Datex-Ohmeda flush valves were not (ranging from 50 to 62 kPa, 7-9 psi). CONCLUSION Oxygen sources other than dedicated jet ventilator connectors to high-pressure pipeline oxygen may supply adequate working pressure, but each type of oxygen source needs testing to ensure that it supplies adequate working pressure.

In managing an obstructed upper airway, an emergency transtracheal ventilation device needs to function as a bidirectional airway, allowing both insufflation of oxygen and egress of gas. The aim of the present study was to determine the capability of two self-assembled, three-way stopcock based jet devices and the Oxygen Flow Modulator to function as a bidirectional airway in conjunction with a small lumen catheter. For each device the effective pressures at the catheter's tip during the expiratory phase and the achievable minute volumes were determined in a laboratory set-up. Using the three-way stopcock based jet devices, changing the connection position of the transtracheal catheter from the in-line port to the side port of the three-way stopcock resulted in a decrease of expiratory pressure at the catheter's tip from a dangerous mean (SD) of 71.1 (0.08) cmH(2)O to -14.71 (0.05) cmH(2)O. Yet this negative expiratory pressure did not facilitate the egress of gas. All devices tested impeded the expiratory outflow and hence decreased the achievable minute volume. This decrease in minute volume was smallest with the Oxygen Flow Modulator.

BACKGROUND Resource planning is essential for successful transport of the mechanically ventilated patient. Mechanically ventilated patients require adequate oxygen supplies to ensure transport is completed without incident. The LTV-1000 portable ventilator utilizes a program to calculate oxygen cylinder duration, based on cylinder size, fraction of inspired oxygen (F(IO(2))), and current minute ventilation. We evaluated the accuracy of the cylinder-duration algorithm in a laboratory setting. METHODS The LTV-1000 was attached to a test lung. Lung compliance was set at 0.04 L/cm H(2)O, and airway resistance was 5.0 cm H(2)O/L/s. We tested 7 different combinations of ventilator settings a minimum of 2 times each. With each setting, minute ventilation was kept at 10 L/min. Breath type, positive end-expiratory pressure, and F(IO(2)) were varied to evaluate the accuracy of the algorithm across a range of clinical scenarios. The cylinder-duration calculation from the ventilator program and manual calculation was determined at each setting and compared to the actual cylinder duration. RESULTS The ventilator algorithm and the manual calculation underestimated the actual cylinder duration by 12 +/- 3% with each test. The range of differences between calculated and actual cylinder duration was 2-26 min across the 7 conditions. CONCLUSION Actual cylinder duration averaged 12% longer than the cylinder duration estimated by the algorithm of the LTV-1000. One explanation is that the E cylinders may contain more liters of oxygen than indicated by the sticker on the side of the tank. Additionally, the bias flow during expiration is affected by inspiratory-expiratory ratio and respiratory rate. Clinicians should be aware of these differences when planning for patient transport.

In parts of the world where supplies of oxygen and electricity are erratic, ventilating patients' lungs can be problematic. Should the electricity supply fail, gas driven ventilators have an advantage as they can continue functioning. However, many are extravagant in their requirement for the driving gas. The Glostavent ventilator was designed to minimise these requirements. We measured the duration of ventilation achieved by the Glostavent ventilator using an E-size oxygen cylinder at a range of minute volumes, and the inspired oxygen concentration achieved by recycling the driving gas. The period of mechanical ventilation from a single E-size cylinder ranged from 11 h 8 min (SD 4 min) with a minute volume of 7 l min(-1) to 18 h 15 min (SD 7 min) with a minute volume of 3 l min(-1). The mean fractional inspired oxygen concentration achieved by recycling the driving gas without further inspired oxygen supplementation was 0.33. We conclude that the Glostavent ventilator performs as efficiently and cost effectively as predicted.