A prototype small-bore ventilation catheter with a cuff: cuff inflation optimizes ventilation with the Ventrain.

BACKGROUND: Ventilation through small-diameter tubes typically precludes use of a cuff as this will impede the necessary passive outflow of gas alongside the tube's outer surface. Ventrain assists expiration and enables oxygenation and normoventilation through small-bore cannulas or catheters, particularly in obstructed airways. A small-bore ventilation catheter (SBVC; 40 cm long, 2.2 mm inner diameter) with a separate pressure monitoring lumen and a cuff was developed. Efficacy of oxygenation and ventilation with Ventrain through this catheter was investigated in sealed and open airways in a porcine cross-over study. METHODS: Six pigs were ventilated with Ventrain (15 l/min oxygen, frequency 30 breaths per min, I : E-ratio 1 : 1) through the SBVC, both with the cuff inflated and deflated. Prior to each test they were ventilated conventionally until steady state was achieved. RESULTS: With an inflated cuff, PaO2 rose instantly and remained elevated (median [range] PaO2 61 [52-69] kPa after 30 min; P = 0.027 compared to baseline). PaCO2 remained stable at 4.9 [4.2-6.2] kPa. After cuff deflation, PaO2 was significantly lower (9 [5-28] kPa at 10 min, P = 0.028) and interventional ventilation had to be stopped prematurely in five pigs as PaCO2 exceeded 10.6 kPa. Pulmonary artery pressures increased markedly in these pigs. Intratracheal pressures were kept between 5 and 20 cmH2 O with the cuff inflated, but never exceeded 2 cmH2 O after cuff deflation. CONCLUSION: The SBVC combines the benefits of a small diameter airway and a cuff. Cuff inflation optimizes oxygenation and ventilation with Ventrain.

Ventrain: an ejector ventilator for emergency use.

BACKGROUND: A small, flow-regulated, manually operated ventilator designed for ventilation through a narrow-bore transtracheal catheter (TTC) has become available (Ventrain, Dolphys Medical BV, Eindhoven, The Netherlands). It is driven by a predetermined flow of oxygen from a high-pressure source and facilitates expiration by suction. The aim of this bench study was to test the efficacy of this new ventilator. METHODS: The driving pressure, generated insufflation, and suction pressures and also the suction capacity of the Ventrain were measured at different oxygen flows. The minute volume achieved in an artificial lung through a TTC with an inner diameter (ID) of 2 mm was determined at different settings. RESULTS: Oxygen flows of 6-15 litre min(-1) resulted in driving pressures of 0.5-2.3 bar. Insufflation pressures, measured proximal to the TTC, ranged from 23 to 138 cm H(2)O. The maximal subatmospheric pressure build-up was -217 cm H(2)O. The suction capacity increased to a maximum of 12.4 litre min(-1) at an oxygen flow of 15 litre min(-1). At this flow, the achievable minute volume through the TTC ranged from 5.9 to 7.1 litres depending on the compliance of the artificial lung. CONCLUSIONS: The results of this bench study suggest that the Ventrain is capable of achieving a normal minute volume for an average adult through a 2 mm ID TTC. Further in vivo studies are needed to determine the value of the Ventrain as a portable emergency ventilator in a 'cannot intubate, cannot ventilate' situation.

Ventilation through a small-bore catheter: optimizing expiratory ventilation assistance.

BACKGROUND: Emergency ventilation through a small-bore transtracheal catheter can be lifesaving in a 'cannot intubate, cannot ventilate' situation. Ejectors, capable of creating suction by the Bernoulli principle, have been proposed to facilitate expiration through small-bore catheters. In this bench study, we compared a novel, purpose-built ventilation ejector (DE 5) with a previously proposed, modified industrial ejector (SBP 07). METHODS: The generated insufflation pressures, suction pressures in static and dynamic situations, and also suction capacities and entrainment ratios of the SBP 07 and the DE 5 were determined. The DE 5 was also tested in a lung simulator with a simulated complete upper airway obstruction. Inspiratory and expiratory times through a transtracheal catheter were measured at various flow rates and achievable minute volumes were calculated. RESULTS: In a static situation, the SBP 07 showed a more negative pressure build-up compared with the DE 5. However, in a dynamic situation, the DE 5 generated a more negative pressure, resulting in a higher suction capacity. Employment of the DE 5 at a flow rate of 18 litre min(-1) allowed a minute volume through the transtracheal catheter of up to 8.27 litre min(-1) at a compliance of 100 ml cm H(2)O(-1). The efficiency of the DE 5 depended on the flow rate of the driving gas and the compliance of the lung simulator. CONCLUSION: In laboratory tests, the DE 5 is an optimized ventilation ejector suitable for applying expiratory ventilation assistance. Further research may confirm the clinical applicability as a portable emergency ventilator for use with small-bore catheters.

Achieving an adequate minute volume through a 2 mm transtracheal catheter in simulated upper airway obstruction using a modified industrial ejector.

BACKGROUND: 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: 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: 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: The principle of ejector-based EVA seems promising and deserves further evaluation.

A bench study of ventilation via two self-assembled jet devices and the Oxygen Flow Modulator in simulated upper airway obstruction.

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.

Hemodynamic stability ensured by a low dose, low volume, unilateral hypobaric spinal block: modification of a technique.

We report the case of an 89-year-old female with a history of arterial hypertension, intermittent rapid atrial fibrillation and severe aortic valve stenosis, suffering from femoral neck fracture. Hyperbaric unilateral spinal anesthesia is a known technique to obtain stable hemodynamics combined with the possibility of continuous neurologic evaluation and preservation of cognitive functions. Because a hyperbaric unilateral technique can be very painful in case of traumatic hip fracture, a low dose, low volume, unilateral hypobaric spinal block may be an adequate alternative. In the present case report, a unilateral hypobaric spinal anesthesia was performed using 5 mg of bupivacaine in a 1.5 mL volume and a slow and steady, "air-buffered", directed injection technique, to allow an urgent hip arthroplasty. During surgery the patient was kept in the lateral recumbent position. Hemodynamics remained stable throughout the entire procedure without any need for vasoconstrictors. The impact of aortic valve stenosis combined with atrial fibrillation on anesthetic management and our considerations to opt for a unilateral hypobaric spinal anesthesia are discussed.

Success rate of unilateral spinal anesthesia is dependent on injection flow.

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.

Unilateral spinal anaesthesia: gadget or tool?

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.

[A new two-chamber model for examination and demonstration of transdural fluid leakage after spinal anesthesia]. / Ein neues Zwei-Kammer-Modell zur Untersuchung und Demonstration transduraler Liquorverluste nach Spinalanästhesien.

UNLABELLED: 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

Unilateral spinal anesthesia using low-flow injection through a 29-gauge Quincke needle.

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-illuminator for direct surface imaging of chromosomes.

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.

[Subdural intra-arachnoid spread of local anesthetics. A complication of spinal anesthesia]. / Subdurale, intraarachnoidale Ausbreitung von Lokalanästhetika. Eine Komplikation der Spinalanästhesie.

Accidental subdural injections and catheterisations are a complication of epidural and spinal anaesthesia. The incidence of subdural spread in myelographies is estimated to be over 10% by the spinal technique. With spinaloscopy in an anatomic human model, we analysed the puncture process and the influence of different needle types on the incidence of subdural injection. We compared 22-gauge Sprotte, Quincke, and 18-gauge Tuohy needles in median and paramedian approaches with various bevel orientations. METHOD. The studies were performed in a preserved and recently expired cadaver donated to the Institut für Anatomie, Westfälische Wilhelms-Universität, Münster. The spinal column from T12 to S1, together with the back musculature (in order to preserve the normal curvature of the spine), were removed from the cadaver. Spinaloscopy was performed with a 4-mm endoscope with a 0 degree optic (Storz, Tuttlingen, Germany). All observations were made in the lumbosacral region of the dissected preparation. The endoscope was inserted from the caudal end of the spinal canal and, depending on the observations being made, the spinal canal was filled with air or artificial cerebrospinal fluid (CSF). To obtain information on the distribution of local anaesthetics injected into the subarachnoid space, 0.5% bupivacaine was coloured with a small amount of 1% methylene blue. The distribution of the coloured anaesthetic was clearly visible during and after injection. RESULTS. Needle insertion: Multiple observations were made using median or paramedian advancement of the needle into the spinal canal. With all needles, including the pencil-point, we saw an unexpected inward movement of the dura to the epidural space before penetration. This dural movement was independent of the direction of the dural fibres in the lumbar area. Distribution of local anaesthetics: Our observations indicate that difficulty with injecting drugs occurred when needle insertion was stopped too close to the dura, especially with the Sprotte needle. After manually registered penetration of the dura, the lateral opening of the needle only partially penetrates the dura. This allows CSF to appear in the needle hub, and injection into the vertical subdural space is possible. In all cases with the Sprotte needle, we could reproduce deposition of methylene-blue-coloured local anaesthetics into the subdural space. With the Quincke and Thuohy needles, it was not possible to deposit local anaesthetics into the subdural space in this model. CONCLUSION. Spinaloscopy was done in a non-fixated anatomic preparation of a spinal column with a 4-mm, 0 degree endoscope. From these observations we conclude that both manually registered penetration of the dural and the appearance of CSF in the needle hub can mimic correct needle position. Especially with the lateral opening of the Sprotte needle, deposition of local anaesthetics in the subdural space is possible.

[Spinal endoscopy in the detection of problems caused by continuous spinal anesthesia]. / Spinaloskopie zur Darstellung von Problemen bei der Anwendung der kontinuierlichen Spinalanästhesie.

Continuous spinal anaesthesia has a number of advantages, but there are a number of drawbacks as well: difficulties in threading the catheter, distribution of the local anaesthetics and the development of cauda equina syndrome. Spinaloscopy was done to visualize the fate of catheters during and after their insertion, as well as the distribution of local anaesthetics injected through these fine-bore catheters. METHOD. The studies were conducted in preserved and fresh cadavers donated to the Anatomic Institute for Medical Studies. The spinal column from T12 to S1, together with the back musculature (in order to preserve the normal curvature of the spine) were removed from the cadaver. Spinaloscopy was done with a 4 mm endoscope with a 0 degree optic (Storz, Tutlingen, FRG). All observations were made from the lumbosacral region of the dissected preparation. In this fashion, it was possible to observe the insertion of the spinal needle used to introduce the catheter into the subdural space. The distribution of local anaesthetics injected through a 22-gauge spinal needle or a 28-gauge catheter was shown by injecting 0.5% hyperbaric bupivacaine colored with a small amount of 1% methylene blue. Pictures were taken 15, 30 and 45 s after beginning the injection. RESULTS. Difficulty in threading the catheter: our observations indicate that the difficulty in inserting microbore catheters is most likely due to inserting the needle too far. It is impossible for the catheter to bend and be inserted into the subarachnoid space. In many cases the catheter encountered the anterior wall of the spinal canal and would slide along various structures. Distribution of the drug: the injection is better dispersed with a 22-gauge needle and it completely fills the subarachnoid space. The local anaesthetics injected through the 28-gauge nylon catheter (Kendall Healthcare, Mansfield, Mass.) are distributed in the dependent portions of the spinal canal. If high doses and a high concentration are injected, the distribution pattern may result in an overconcentration in some parts of the subarachnoid space. Possibility of trauma: the catheter stretches around the roots, the potential for trauma is that untoward stress may be applied to the root, either during full insertion of the catheter or during its withdrawal. CONCLUSION. Spinaloscopy was done in a non-fixated anatomic spinal column preparation with a 4 mm 0 degree endoscope (Storz, Tuttlingen, FRG). Based on our observations, we conclude: The catheter should only be inserted 2 cm into the subarachnoid space. This may decrease the risk of malpositioning. After the tip of the catheter has reached the subarachnoid space, the stylet should be with drawn 2 or 3 cm to minimize the risk of nerve injury and/or bleeding.