John Dolan

The rectus sheath block: accuracy of local anesthetic placement by trainee anesthesiologists using loss of resistance or ultrasound guidance.

Background and Objectives: The aim of this study was to compare the accuracy of local anesthetic placement in the rectus sheath block when performed by trainee anesthetists using loss of resistance (LOR) or ultrasound guidance. Methods: Eighty-one patients undergoing laparoscopic surgery were randomly assigned to undergo rectus sheath block by either LOR or ultrasound guidance. Trainee anesthesiologists were also randomly assigned to provide the rectus sheath block by LOR or by using ultrasound. The placement of local anesthetic was recorded using ultrasound. Results: The placement of local anesthetic by LOR was accurate in 45% of attempts but was superficial and deep to the rectus sheath in 34% and 21% of punctures, respectively. Accurate placement of local anesthetic within the rectus sheath decreased significantly as body mass index increased. Ultrasound guidance significantly improved the accuracy of needle placement, with 89% of abdominal punctures being correctly placed at the time of first injection of local anesthetic. An additional fascial plane lying at variable distance above the anterior layer of the rectus sheath was commonly observed. Conclusions: Ultrasound guidance improves the accuracy of local anesthetic placement when undertaking the rectus sheath block. An additional fascial plane above the anterior layer of the rectus sheath may be wrongly perceived as the anterior layer of the rectus sheath when the block is undertaken without the aid of ultrasound.

Persistent median artery and veins in patients undergoing elective day case hand surgery.

To the Editor: T hank you for the opportunity to respond to the comments by Dr Chelly. He expresses concerns about the sterility of the block procedure and the risk of infection spreading to the operated knee, and he questions the relevance of the quadriceps weakness caused by the femoral nerve blockade in the consequent risk of falling. We chose to place the perineural catheter postoperatively because, in our setting, the compression dressing does not reach so high on the patient’s thigh that it interferes with the sterility of the procedure, and it shortens the preparation time before surgery. The midthigh approach is at least a hand’s width away from the wound dressing and the aseptic dressing was not broken or touched during placement of the perineural catheter. We consider the risk of catheter infection and the potential spread to the knee to be extremely low in this procedure. Furthermore, the catheter could probably be removed at the end of the first postoperative day because the analgesic benefit from the catheter injections seems to be negligible on the second postoperative day. The issue, in our hospital, regarding quadriceps weakness is not primarily the risk of falling, although we consider this a serious and potentially dangerous event, but the patient’s ability to fulfill the physiotherapeutic goals, where early mobilization, beginning on the day of surgery, has a high priority in a fast-track setting. Quadriceps weakness, caused by the femoral nerve blockade, will interfere with early mobilization, especially on the day of surgery. The combination of local infiltration analgesia and the saphenous nerve blockade did not cause quadriceps weakness and did not hamper early mobilization while providing adequate analgesia. Our study was perhaps underpowered to show that this favorable effect has longer duration for the following postoperative days.

Ultrasound-guided interfascial injection for peripheral obturator nerve block in the thigh.

To the Editor: Identification of vascular structures during regional anesthesia procedures with ultrasound can help to identify target nerves and plan for an appropriate needle approach to avoid puncture and intravascular injection. Arteries can be identified by their relative resistance to collapse from pressure exerted by the ultrasound probe along with the characteristic pulsatile flow demonstrated by color or pulse wave Doppler. Veins often go unidentified, leading to patient morbidity and potential mortality. Because of their ease of collapse with minimal ultrasound probe pressure and their low-velocity-flow states that are not always well represented on ultrasound by color Doppler, veins can be difficult to recognize with ultrasound. We describe a novel technique to identify small or collapsed veins using any standard ultrasound with color Doppler. Once an area is identified that could contain venous structures, color Doppler is activated. During real-time ultrasound, any distal part of the patient’s corresponding extremity is compressed or squeezed. This compression of the distal muscles and veins significantly increases venous blood flow that is then represented more reliably by color Doppler on ultrasound (Fig. 1). This technique may be repeated several times for complete evaluation of veins in an area and is well tolerated by patients. Other techniques can be used to visualize low-flow blood vessels such as probe tilt, adjustment of pulse repetition frequency, and increasing color gain, but none of these are effective in evaluating veins that are collapsed. Squeezing a distal extremity, as described here, results in the ability to evaluate both low-flow and completely collapsed venous structures. We have found this distal compression technique to be very useful in the identification of veins that are often closely associated with nerves. We routinely use this technique in the axillaq and the popliteal regions by squeezing the arm and calf, respectively.

Accurate placement of ultrasound-guided lateral popliteal-sciatic perineural catheters.

To the Editor: I read with interest the article by Mariano et al describing the placement of ultrasound-guided perineural catheters for continuous lateral popliteal-sciatic nerve block. Catheters were initially advanced 5 cm beyond the needle tip and gradually withdrawn to a position inferred by the injection of air boluses. However, the positive or negative predictive values of this test remain unknown. A suboptimal location of the ultrasound-guided catheters in this study may be suggested by mean postoperative pain scores of 4.5 (range, 0Y7.1), which are significantly higher than those in other studies using neurostimulation to place continuous popliteal-sciatic catheters for pain control. Their relatively superficial location and transverse trajectory ensures that long-axis ultrasound images of perineural catheters are readily obtained during the lateral approach to the poplitealsciatic nerve (Fig. 1). Catheters can be continually visualized, and the spread of local anesthetic around the sciatic nerve can also be confirmed. Sonographic placement of perineural catheters may offer a number of advantages compared to landmark-based neurostimulation techniques alone. However, significant improvement in postoperative pain scores may be difficult to confirm if, as in the study by Mariano et al, ultrasonography is used to simply infer catheter position rather than to view the catheter in real time and to confirm precise placement of the catheter tip and spread of local anesthetic within the perineural sheath.