A prospective, randomized evaluation of the effects of epidural needle rotation on the distribution of epidural block

We evaluated the effects of turning the tip of the Tuohy needle 45 degrees toward the operative side before threading the epidural catheter (45 degrees -rotation group, n = 24) as compared to a conventional insertion technique with the tip of the Tuohy needle oriented at 90 degrees cephalad (control group, n = 24) on the distribution of 10 mL of 0.75% ropivacaine with 10 microg sufentanil in 48 patients undergoing total hip replacement. The catheter was introduced 3 to 4 cm beyond the tip of the Tuohy needle. A blinded observer recorded sensory and motor blocks on both sides, quality of analgesia, and volumes of local anesthetic used during the first 48 h of patient-controlled epidural analgesia. Readiness to surgery required 21 +/- 6 min in the control group and 17 +/- 7 min in the 45 degree-rotation group (P > 0.50). The maximum sensory level reached on the operative side was T10 (T10-7) in the control group and T9 (T10-6) in the 45 degree-rotation group (P > 0.50); whereas the maximum sensory level reached on the nonoperative side was T10 (T12-9) in the control group and L3 (L5-T12) in the 45 degree-rotation group (P = 0.0005). Complete motor blockade of the operative limb was achieved earlier in the 45 degree-rotation than in the control group, and motor block of the nonoperative side was more intense in patients in the control group. Two-segment regression of sensory level on the surgical side was similar in the two groups, but occurred earlier on the nonoperative side in the 45 degree-rotation group (94 +/- 70 min) than in the control group (178 +/- 40 min) (P = 0.0005). Postoperative analgesia was similar in the 2 groups, but the 45 degree-rotation group consumed less local anesthetic (242 +/- 35 mL) than the control group (297 +/- 60 mL) (P = 0.0005). We conclude that the rotation of the Tuohy introducer needle 45 degrees toward the operative side before threading the epidural catheter provides a preferential distribution of sensory and motor block toward the operative side, reducing the volume of local anesthetic solution required to maintain postoperative analgesia. IMPLICATIONS: Turning the Tuohy introducer needle 45 degrees toward the operative side before threading the epidural catheter is a simple maneuver that produces a preferential distribution of epidural anesthesia and analgesia toward the operative side, minimizing the volume of local anesthetic required to provide adequate pain relief after total hip arthroplasty.     

三种扩皮送鞘法在肿瘤患者PICC置管中的应用效果观察

目的 探讨三种扩皮送鞘法在超声引导下改良塞丁格技术PICC置管中的应用效果,为临床操作提供参考。方法 将384例肿瘤科行PICC置管患者随机分为A、B、C三组,各128例。A组采用微插管鞘中的扩张器与传统穿刺针的外鞘组装后直接扩张穿刺点后送鞘的钝性分离法;B组采用扩张器与导管鞘组件扩张穿刺点后送鞘的钝性分离法;C组采用扩皮刀扩张穿刺点后推进血管鞘的方法。比较三组患者一次性送鞘成功率、置管后24 h穿刺点渗血情况及置管术中疼痛评分。结果 A组和C组一次性送鞘成功率100%,B组一次性送鞘成功率95.31%。三组穿刺点渗血情况、局部渗液发生率比较,差异有统计学意义（均P<0.01）,A组和B组显著低于C组。A组和B组术中疼痛评分低于C组。结论 采用微插管鞘中的扩张器与传统穿刺针的外鞘组装后直接扩张穿刺点后送鞘的钝性分离法行PICC置管,不仅一次性送鞘成功率高,且患者置管术中疼痛及术后穿刺点局部渗血渗液等并发症发生率较低。     

A pulmonary artery catheter does not affect the intravascular electrocardiogram from the air aspiration introducer sheath

The air aspiration introducer sheath allows the use of a pulmonary artery (PA) catheter for monitoring during sitting neurosurgical procedures while providing a means of air aspiration that is more efficient than aspiration from the proximal and distal ports of the PA catheter alone. To place the 25-cm long introducer sheath safely into the right atrium, the PA catheter should be positioned first and used as a guide for the introducer sheath, which is then advanced into the atrium and positioned by observation of the intravascular electrocardiogram (IVECG). Placement of the introducer sheath with the IVECG has been described previously without a PA catheter in the lumen of the introducer sheath. In this study, performed in dogs, we have demonstrated that the presence of a PA catheter in the lumen of the introducer sheath does not affect the IVECG recorded from the introducer sheath.     

A prospective randomised trial comparing insertion success rate and incidence of catheterisation‐related complications for subclavian venous catheterisation using a thin‐walled introducer needle or a catheter‐over‐needle technique

In clinical practice, both a thin‐walled introducer needle and catheter‐over‐needle technique can be used to allow insertion of a guidewire during central venous catheterisation using the Seldinger technique. We compared the incidence of catheterisation‐related complications (arterial puncture, haemothorax, pneumothorax, haematoma and catheter tip malposition) and insertion success rate for these two techniques in patients requiring right‐sided subclavian central venous catheterisation. A total of 414 patients requiring infraclavicular subclavian venous catheterisation were randomly allocated to either a thin‐walled introducer needle (needle group, n = 208) or catheter‐over‐needle technique (catheter group, n = 206). The catheterisation‐related complication rate was lower in the needle group compared with the catheter group (5.8% vs. 15.5%; p = 0.001). Overall insertion success rates were similar (97.1% and 92.7% in the needle and catheter groups respectively; p = 0.046), although the first‐pass success rate was higher in the needle group (62.0% vs. 35.4%; p < 0.001). We recommend the use of a thin‐walled introducer needle technique for right‐sided infraclavicular subclavian venous catheterisation.     

Treatment of air embolism with a special pulmonary artery catheter introducer sheath in sitting dogs

The treatment of venous air embolism by aspiration from central venous catheters is well established. However, some anesthesiologists prefer to use a pulmonary artery catheter to monitor patients undergoing a neurosurgical procedure in the sitting position. While offering certain advantages, pulmonary artery catheters may be of limited use in the treatment of venous air embolism because the small diameter of the proximal port is poorly suited for efficient air aspiration. The authors have designed a special pulmonary artery catheter introducer sheath which can be positioned by intravascular electrocardiography to provide an efficient and effective means of air aspiration, while permitting the simultaneous use of a pulmonary artery catheter for pressure monitoring. The flow characteristics of this sheath, with and without side holes, were tested in vitro by measuring the time required to aspirate 50 ml of blood. The introducer sheath was compared to a Sorenson CVP catheter, a Bunegin-Albin Air Aspiration CVP Catheter, and the proximal port of a pulmonary artery catheter. The rank order of flow rate was: Bunegin-Albin CVP greater than introducer sheath without side holes = introducer sheath with side holes greater than Sorenson CVP greater than pulmonary artery catheter (P = 0.0001). The introducer sheath was then compared to a pulmonary artery catheter for the treatment of a 4 ml/kg venous air embolism in sitting, anesthetized dogs. The mean proportion of air retrieved by the sheath with or without side holes, 57% and 80%, respectively, was significantly greater than that retrieved by simultaneous aspiration of atrial and distal ports of the pulmonary artery catheter, 16% (P = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Management of an unusual complication during placement of a pulmonary artery catheter

We describe an unusual complication during flotation of a pulmonary artery catheter through a preexisting percutaneous introducer sheath. A malfunctioning pulmonary artery catheter, which was placed through an introducer sheath in the right internal jugular vein, was removed. Attempts at repositioning a second pulmonary artery catheter met with resistance, and we were unable to either advance or withdraw it. Chest radiograph showed a bent introducer sheath going from the right internal jugular vein into the right subclavian vein and a pulmonary artery catheter loop. Under continuous fluoroscopy, the introducer sheath and the pulmonary artery catheter were withdrawn as one unit, which resulted in relaxation of the acute angulation in the introducer sheath and allowed the pulmonary artery catheter to unfold, thus facilitating their complete extraction. We conclude that complications may occur during placement of a pulmonary artery catheter through a well positioned introducer sheath and that fluoroscopy is a valuable tool for safe management of such a complication.     

Differences in arterial and venous thromboelastography parameters: potential roles of shear stress and oxygen content

OBJECTIVE: To investigate potential mechanisms for the differences in thromboelastography variables observed between arterial blood samples and venous blood samples. DESIGN: Prospective cohort study. SETTING: University hospital. PARTICIPANTS: Patients undergoing cardiac surgery (n = 33). INTERVENTIONS: After the withdrawal of 10 mL of discarded blood (>3 deadspace volumes), 3 blood samples were withdrawn simultaneously from the central venous port of the pulmonary artery catheter (CVP), the radial arterial catheter (ART), and the side port of the 9F sheath introducer (SI). MEASUREMENTS AND MAIN RESULTS: Thromboelastography was done simultaneously on each sample. All thromboelastography analyses were performed with 1% celite and heparinase according to the manufacturer's guidelines. A total of 80 ART, SI, and CVP comparisons were obtained. Mean hematocrit values were not different between sampling sites (27 +/- 4 v 27 +/- 4 v 27 +/- 3). Thromboelastography R time values (mean +/- SD) were CVP, 8 +/- 3; ART, 10 +/- 3; and SI, 13 +/- 5 (p = 0.004). Thromboelastography maximal amplitude (MA) values (mean +/- SD) were CVP, 60.4 +/- 11.7; ART, 56.2 +/- 11.4; and SI, 50.5 +/- 13.2 (p = 0.008). Calculated maximal shear stresses were CVP, 48 dyne/cm(2); ART, 36 dyne/cm(2); and SI, 0.3 dyne/cm(2). Blood samples obtained from the CVP (highest shear stress) resulted in faster (shorter R) and stronger (larger MA) coagulation compared with the arterial site (intermediate shear stress) and sheath introducer (lowest shear stress). CONCLUSION: These data show that differences exist in thromboelastography values between arterial and venous blood samples and, more importantly, show that the differences observed are not related to differences in oxygen content. These differences seem to be related to differences in catheter lumen diameter and, presumably, shear forces.     

Balloon embolectomy catheter-induced arterial injury: a comparison of four catheters

This study compared four brands of balloon embolectomy catheters with respect to their mechanical characteristics and the histologic responses they elicit. Seventy-two 4F Becton-Dickinson, Edwards, Electro-Catheter, and Shiley catheters were studied. In vitro studies of penetration forces demonstrated that the forces required for arterial puncture were greatest for Shiley (295 +/- 22 gm) and least for Edwards catheter tips (217 +/- 11 gm) (p less than 0.05). This indicates that the Shiley catheter is least likely to puncture vessels in patients. Studies of balloon eccentricity showed that none of the balloons distended with excessive eccentricity. Studies of balloon emptying time demonstrated that the silicon Becton-Dickinson balloon required more than two times as long (5.7 +/- 1.2 seconds) as all other balloons to empty. Balloon emptying time reflects the ability of the surgeon to rapidly adapt the balloon to changing vessel diameter in patients. Shear forces were studied in cylindrical segments of arteries in vitro. Initial shear forces were significantly different among all catheters, Becton-Dickinson greater than Edwards greater than Shiley greater than Electro-Catheter (p less than 0.05). In contrast, during catheter withdrawal dynamic shear forces were similar among the four brands of catheters. Balloon embolectomies were performed in vivo in the common carotid and common femoral arteries in 18 anesthetized dogs. Histologic examinations of the vessels exposed to 50, 100, and 200 gm shear forces showed that myointimal hyperplasia increased with rising shear forces for all catheters (p less than 0.05), but that there were no differences in the degree of myointimal hyperplasia elicited by the different brands of catheters.(ABSTRACT TRUNCATED AT 250 WORDS)     

A newly designed disposable introducer sheath for a ventricular fiberscope.

We have developed a disposable plastic introducer sheath for use with a flexible endoscope during intraventricular procedures. The sheath is composed of a thin polypropylene tube passing through the center of a plastic stopper. The tube serves as a sheath through which the fiberscope is introduced into the ventricle. The stopper seats in the burr hole and prevents downward and lateral movement of the tube. The sheath can be placed safely in the ventricle with a drainage catheter used as an introducing guide. We used this sheath system in 10 patients and found it very useful. Manipulation of the fiberscope was not hindered, copious irrigation was allowed, and the sheath remained stable on the skull. This new introducer sheath may contribute to the increased use of a flexible endoscope in neuroendoscopic procedures.     

The Effect of Urethral Introducer Tip Catheters on the Incidence of Urinary Tract Infection Outcomes in Spinal Cord Injured Patients

Purpose

We attempted to determine whether an introducer tip catheter reduces urinary tract infection in spinal cord injured patients on intermittent catheterization.

Materials and Methods

The introducer tip catheter bypasses the colonized 1.5 cm. of the distal urethra. Enrolled patients were prospectively entered into the study in alternate groups depending on whether they reflex voided: group 1-on intermittent catheterization with the introducer tip catheter but not voiding spontaneously or wearing an external urinary catheter, group 2-same as group 1 but using a nonintroducer tip catheter; group 3-on intermittent catheterization with the introducer tip catheter, voiding by reflex and wearing an external urinary catheter, and group 4-same as group 3 but using a nonintroducer tip catheter.

Results

Statistical significance was shown when comparing patients using versus not using the introducer tip catheter regardless of whether an external urinary catheter was worn (p = 0.0121). A greater difference was noted between patients using and not using the introducer tip catheter in the intermittent catheterization only group (p = 0.0093).

Conclusions

The introducer tip catheter decreased urinary tract infections in hospitalized men with spinal cord injury on intermittent catheterization.     

Spinal anesthesia performance conditions and side effects are comparable between the newly designed Ballpen and the Sprotte needle: results of a prospective comparative randomized multicenter study

In this study, we examined the characteristics of a newly designed spinal needle (Ballpen [B]) with a pencil-like tip formed by a stylet that is withdrawn after penetration of the dura. The main goal was to examine whether the use of the B needle could reduce performance time by improved puncture conditions in comparison with the Sprotte (S) needle. Seven-hundred patients at 4 hospitals received single-dose spinal anesthesia with a 25-gauge B or S needle and 0.5% bupivacaine. The performance time of spinal anesthesia was defined as the time between insertion of the introducer needle and the first identification of cerebrospinal fluid in the hub of the spinal needle. Failed spinals were assessed when patients required general anesthesia. On postoperative Day 2-4, all patients were visited and interviewed. Groups did not differ with respect to demographics, puncture site, and dose of bupivacaine. Performance time was 98 +/- 145 s in Group B and 103 +/- 159 s in Group S (P = 0.68). The failure rate in Groups B and S was 3.8% and 3.9%, respectively, and the incidence of postdural puncture headache was 1.8% and 0.9% (P = 0.50), respectively. We conclude that there was no difference in technical variables or outcome between the B and S needles. IMPLICATIONS: This multicenter study examined characteristics of the newly designed Ballpen needle with the Sprotte needle in 700 patients undergoing lower abdominal or extremity surgery in single-dose spinal anesthesia. Technical variables and side effects were comparable between both noncutting spinal needles.     

A microsurgical technique for catheter insertion in the rat femoral artery

Purpose:To modify a surgical catheterization method using the bent needle introducer in small animals.Methods:Eight-week-old male Lewis rats were used in the study. A needle introducer was created by bending a 21G injection needle at 45°. The bent needle introducer was used for catheter insertion into the left femoral artery of the rats under anesthesia. As a control, a catheter was directly inserted into the blood vessel without the introducer. The insertion time of each method was measured. Blood pressure and heart rate were measured 24 h after catheter insertion using the telemetry system.Results:Using the introducer, the catheter was successfully inserted within a short time in all rats. Without the introducer, a longer duration was required for catheter insertion. The frequency of the insertion with no catheter-based errors with the introducer tended to be higher than that without the introducer. The mean arterial pressure and heart rate 24 h after catheter insertion in each group were almost the same.Conclusions:We developed a surgical catheterization method using the introducer in small animals. This could potentially reduce the frequency of the insertion with catheter-based errors and insertion time.Key words: Catheterization, Microsurgery, Telemetry, Vital Signs, Rats     

In vitro assessment of a novel dual probe ultrasonic intracorporeal lithotriptor

PURPOSE: The Cyberwand (Cybersonics, Erie, Pennsylvania) is a novel intracorporeal lithotrite that uses coaxial ultrasonic elements operating at 2 frequencies. We compared this device to the LithoClast(R) Ultra, which we previously noted is the most efficient commercially available intracorporeal lithotripsy device. MATERIALS AND METHODS: An in vitro test system was used to assess the efficiency of stone penetration for the Cyberwand and the LithoClast Ultra. The devices were mounted upright with the probe tip up in a modified irrigation sheath. A gypsum artificial stone was centered on the probe tip and a mass was placed atop the stone to provide a constant force. The manufacturer recommended setting was selected for the Cyberwand, while for the LithoClast Ultra a pneumatic frequency of 12 Hz with an ultrasonic power setting of 100% was selected, representing optimal settings in previous in vitro tests. The time required for complete stone penetration was measured. Differences in mean stone penetration times were compared using ANOVA. RESULTS: Mean +/- SD penetration time for the Cyberwand was significantly shorter than for the LithoClast Ultra (4.8 +/- 0.6 vs 8.1 +/- 0.6 seconds, p <0.0001). Neither device showed any difficulties with overheating, occlusion or another malfunction. CONCLUSIONS: Initial assessment using our hands-free in vitro test system, in which stone penetration time is not affected by operator bias, suggests that the Cyberwand is an efficient lithotrite. These promising results justify in vivo testing.     

The epidural structure changes during deep breathing

PURPOSE: Previous experience has suggested that the insertion of an epidural catheter becomes easier when the patient takes a deep breath. The purpose of this study is to investigate the effects of respiration on the epidural space. METHODS: We examined the epidural space using a flexible epiduroscope in 20 patients undergoing thoracic epidural anesthesia. A 17-gauge Tuohy needle was inserted using the paramedian technique and the loss-of-resistance method with 5 ml air. The epiduroscope was introduced into the epidural space via the Tuohy needle. Each patient was requested to take a deep breath when the epiduroscope was positioned at the needle tip and at approximately 10 cm cephalad from the needle tip within the epidural space. The changes in the epidural structure during deep breathing at each site were then measured. RESULTS: In 80% of the patients, fatty tissue occupied the needle tip. Through the patients' maximal inspiration, the fatty tissue moved and a visible cavity expanded at the needle tip. Cross section area of the visible cavity at the needle tip was greater at the maximal inspiratory level than at the resting expiratory level: 12.1 +/- 6.7% vs 2.8 +/- 2.1% (mean +/- SD, P < 0.0001). In all patients, the visible cavity within the epidural space, which had already been expanded by injected air, became more expanded after maximal inspiration. Cross section area of the visible cavity at the 10 cm cephalad position was greater at the maximal inspiratory level than at the resting expiratory level: 20.6 +/- 10.0% vs 7.0 +/- 5.3% (P < 0.0001). CONCLUSION: Epiduroscopy showed that deep breathing expanded the potential cavity of the epidural space. We suggest that the changes in the epidural structure during deep breathing may assist in the insertion of an epidural catheter.     

B型超声波引导行经皮肾穿刺造瘘术88例

目的：总结应用B超引导下行经皮肾穿刺造瘘术的经验。方法：分析使用B超线阵扫描探头实时引导，配以穿刺导向器和经改良的套迭式金属扩张管鞘，行经皮肾穿刺造瘘手术88例104侧肾的分析临床资料。结果：肾穿刺成功率100％，满意放置导管造瘘成功率96.2％(100／104)，无严重并发症。结论：实时B超引导下行经皮肾穿刺造瘘术成功率高，创伤小，安全，可靠。合理设置经皮肾穿刺通道和适当的扩张皮肾通道技巧是手术成功的关键技术。     

Effect of catheter material on the incidence of urethral strictures.

The aetiology of urethral strictures in patients catheterised for short periods at the time of surgery is the subject of some debate. The occurrence of epidemics of strictures associated with certain batches of latex catheters, and the demonstrable in vitro cytotoxicity of latex in general, have supported the suggestion that catheter material (and in particular latex) has an important role. We have looked retrospectively at 299 patients undergoing transurethral resection of the prostate gland by 1 urologist, 135 of whom had a latex catheter and 164 a plastic one; 19 patients developed strictures over the next 12 months with no proven difference attributable to the catheter material. The study provides no evidence that the short-term use of latex catheters is associated with stricture formation.     

Preliminary evaluation of a valved introducer sheath for the insertion of tunneled hemodialysis catheters

This brief technical report describes our initial experience using the FlowGuard valved introducer sheath during the insertion of tunneled hemodialysis catheters in 15 patients. The incorporation of a silicone valve into the introducer sheath is intended to minimize blood loss and decrease the risk of air embolism during the catheter insertion procedure. Our preliminary experience demonstrated that the FlowGuard sheath is a substantial improvement when compared to standard introducer sheaths. However, an asymptomatic air embolus did occur in one patient. This article describes several caveats for the use of this new product.     

Introducers and protective sleeves may increase thrombogenicity of pulmonary artery catheters

OBJECTIVE: To investigate the cause of clot formation on the surface of non-heparin coated/bonded pulmonary artery catheters. DESIGN: A controlled, unblinded, open-labeled study. SETTING: Research laboratory at Tulane School of Medicine, New Orleans, LA. PARTICIPANTS: Rhesus and African Green monkeys. INTERVENTIONS: Anesthetized monkeys (n = 24) were assigned to one of two groups. The first group (group A) had a pulmonary artery catheter inserted into a femoral vein through a cutdown without passage through an introducer or protective sleeve before insertion. In the second group (group B), the pulmonary artery catheter was passed through an introducer and protective sleeve before insertion in the femoral vein. After the study, the animals were returned to the primate breeding colony. Laboratory values were measured for each animal, and electron micrographs were taken of selected pulmonary artery catheters before and after passage of these catheters through the introducer sheath and/or protective sleeve. MEASUREMENTS AND MAIN RESULTS: Between the two groups, there was a significant difference in fibrinogen level, but not in hematocrit, prothrombin time, partial thromboplastin time, and platelet count. Clots were visible on 11 of 12 catheters in group B, which was statistically significant (p < 0.01), compared with only 3 of 12 catheters in group A. The average clot weight was 0.014+/-0.014 g in group A (range, 0.00 to 0.170 g), which was statistically significant (p < 0.01), compared with 0.216 < 0.058 g in group B (range, 0.000 to 0.620 g). Electron micrographs taken after catheters were passed through an introducer and/or protective sleeve showed that both significantly altered the surface of the catheter. The surface of the catheter was smooth and homogenous in appearance before insertion. Conversely, both the introducer and protective sleeve produced marked furrowing and a nodular appearance on the catheter surface, as shown by electron micrographs. CONCLUSION: The data from this study show that the incidence of clot formation and amount of clot formed on the surface of non-heparin-coated pulmonary artery catheters are significantly greater after passage through an introducer and/or protective sleeve. The electron micrographs also show that both introducers and protective sleeves abraded the catheters and were associated with thrombus formation on the catheter. Designing less traumatic valves on these devices is warranted and recommended.     

In vitro assessment of lithoclast ultra intracorporeal lithotripter

PURPOSE: The Lithoclast Ultra (Boston Scientific Corporation, Natick, MA) enables the simultaneous application of ultrasonic and pneumatic modalities for the fragmentation and removal of stones during percutaneous nephrolithotomy (PCNL). We evaluated the effectiveness of this unit using a hands-free in vitro testing system. MATERIALS AND METHODS: An in vitro test system was used to assess the efficiency of stone penetration when the Lithoclast Ultra was operated at different settings of ultrasonic power and pneumatic frequency. The pneumatic and ultrasonic handpieces were assembled, the probes were inserted into an irrigation sheath (Cook Urological, Spencer, IN), and the complete unit was mounted upright (probe tip up). A gypsum artificial stone (mean length 12.8 +/- 0.6 mm; mean diameter 7.6 +/- 0.1 mm) was centered on the probe tip. A weight (63.4 g) was placed atop the stone to provide a constant force. Pneumatic frequency settings of 12, 8, 4, and 1 Hz were tested in conjunction with ultrasonic power settings of 100%, 70%, and 40%. The times required for complete stone penetration were assessed for each combination of settings. Differences in mean stone penetration times were compared using ANOVA. RESULTS: The combination of 12 Hz and 100% produced the fastest mean stone penetration time (8.9 +/- 1.1 seconds). Stone penetration times decreased significantly with increases in pneumatic frequency (P< 0.001) as well as with increases in ultrasonic power (P= 0.001). When analyzing the effect of each modality on the total improvement in penetration time, increasing the pneumatic frequency accounted for approximately 80% of the performance improvement. The stone penetration times were better than those of the most efficient ultrasonic device previously evaluated using this test system. CONCLUSIONS: The Lithoclast Ultra exhibited excellent stone penetration efficiency when evaluated with a hands-free in vitro test system. Increases in either pneumatic frequency or ultrasonic power significantly improve penetration times, with the pneumatic modality contributing the majority of the effect.     

The effect of introducer gauge,design and bevel direction on the deflection of spinal needles

This study was performed to determine how the use of an introducer affects the extent to which a needle deflects during a spinal or combined spinal-epidural injection. A polystyrene block was used to simulate the paraspinal area of the back. A line was drawn perpendicular to the edge of the block to use as a guide and to measure the deflection. The use of an introducer needle decreased the deflection in all the bevelled needles (p < 0.001). Depending on the direction of both the bevels, the deflection decreased as the introducer bevel was changed from the same direction, to right-angles to bevel direction and then to a direction opposite to that of the spinal needle (p < 0.05). Deflection was decreased when a thick introducer was used (p < 0.001). The use of an introducer increased the deflection of the pencil-point needle only in the deflection direction of the introducer (p < 0.001). The 18-gauge Tuohy needle with a "backhole" deflected more than the corresponding needle without a backhole (p < 0.001), and the spinal needle inserted through the Tuohy needle with a backhole deflected more (p = 0.002). Besides the tip type and gauge, the deflection of a spinal needle depends upon the use of introducer, its gauge and bevel direction. The deflection of a Tuohy needle depends upon its design, gauge and the presence of a backhole.