Effect of neuropeptide Y on hemodynamics of the rabbit lung

We evaluated the effect of neuropeptide Y (NPY) on the hemodynamics of the isolated rabbit lung perfused at constant flow and outflow pressure. Doses of 10(-8) and 10(-7) M NPY increased pulmonary arterial pressure (Ppa) from 11.5 +/- 1.0 (SE) mmHg to, respectively, 16.4 +/- 1.5 and 26.0 +/- 3.8 mmHg (P < 0.05, n = 5 mmHg lungs), with 78 +/- 4% of the increase at 10(-7) M resulting from an increased arterial resistance. At the latter dose, pulmonary capillary pressure increased from 5.8 +/- 0.9 to 9.4 +/- 1.0 mmHg (P < 0.05). When administered in the presence of norepinephrine, 10(-8) and 10(-7) M NPY (n = 6) produced extreme increases in Ppa to 66.1 +/- 20.5 and 114.7 +/- 25.5 mmHg, respectively, that were due primarily to an increased arterial resistance. To determine the significance of circulating NPY as a pulmonary vasoactive agent, we measured plasma NPY-like immunoreactivity in anesthetized rabbits after massively activating the sympathetic nervous system with veratrine. NPY-like immunoreactivity increased from 74 +/- 10 to 111 +/- 10 (SE) pM (P < 0.05). Thus, although NPY is a potent vasoconstrictor in the rabbit lung, it is not likely that plasma NPY concentrations rise sufficiently, even after massive sympathetic nervous system activation, to produce pulmonary vasoconstriction in the intact rabbit.

Continuous parasacral sciatic nerve block: two case reports

OBJECTIVE

This study investigated the use of a continuous parasacral sciatic nerve block for anesthesia and postoperative analgesia for lower extremity surgery.

METHODS

A continuous parasacral sciatic nerve block was performed in two patients (triple ankle arthrodesis and below-knee amputation). The sacral plexus was identified using an insulated Tuohy needle and a nerve stimulator. A catheter was placed near the elements of the sacral plexus via the Tuohy needle.

RESULTS

In both patients, surgical anesthesia was successfully established through the parasacral catheter with lidocaine 1% (1/200,000 epinephrine), and postoperative analgesia was successfully established with a bolus of bupivacaine 0.375% (1/200,000 epinephrine) and maintained with a continuous infusion of bupivacaine 0.1% (8 mL/h) for 48 hours.

CONCLUSION

We conclude that continuous parasacral sciatic nerve block can provide anesthesia and long-term analgesia for operative procedures of the foot and leg.

The parasacral sciatic nerve block

BACKGROUND AND OBJECTIVES

The clinical utility of a new parasacral approach for conduction block of the sciatic nerve was investigated, with critical examination of onset, extent, and success rates when this block was used for surgical procedures below the knee.

METHODS

Thirty ASA I-III patients presenting for surgery on the lower limb were enrolled. All received 30 mL of 1.5% lidocaine with 1:200,000 epinephrine following nerve stimulator identification of the sciatic nerve at < or =0.2 mA or less. Trans-sartorial saphenous nerve blocks were performed to provide anesthesia to the medial leg.

RESULTS

Overall success for surgical anesthesia with this block was 97%. All components of the sacral plexus could be blocked with this approach, and 93% of patients displayed evidence of obturator nerve motor block. However, no patient displayed evidence of obturator sensory anesthesia that could be mapped. Saphenous nerve blocks were 100% effective in providing surgical anesthesia for the procedures performed.

CONCLUSIONS

The parasacral approach to the sciatic nerve exhibits a high success rate, resulting in anesthesia of the entire sacral plexus and generally in motor block of the obturator nerve was an interesting observation.

Saphenous nerve anaesthesia--a nerve stimulator technique

PURPOSE

This two part study was undertaken to assess both the feasibility of identifying the saphenous nerve with a nerve stimulator and to assess the efficacy of saphenous nerve anaesthesia with electrical isolation of the nerve.

METHODS

(Part I): In Part I we studied 25 volunteers. Each had saphenous nerve blocks performed using a nerve stimulator (NS) and loss of resistance (LOR) technique. We recorded 10 cm linear visual analogue pain scores on completion of the blocks, time to completion of the blocks, onset time, and success of the blocks. (Part II): Clinical utility of the NS technique of saphenous nerve block was investigated. We evaluated the NS technique in 21 consecutive patients having surgery below the knee.

RESULTS

(Part I): The LOR technique successfully produced saphenous nerve anaesthesia in 18/25 (72%) volunteers and the NS technique was successful in all volunteers (25/25-P < 0.05). The nerve stimulator approach required more time to complete (NS 13 +/- 7 min vs LOR 8 +/- 2 min; P < 0.05). Visual analogue pain scores differed (P < 0.05) with a median of 1.0 cm for the LOR technique and a median of 2 cm for the NS technique. (Part II): The saphenous nerve block was successful in 20/21 (95%) of the patients.

CONCLUSIONS

(Part I): The first part of the study established the feasibility of electrical identification of the saphenous nerve and demonstrated that the NS technique could be utilized to provide superior anaesthesia of the saphenous nerve when compared with a previously validated LOR technique. (Part II): The clinical utility of the NS technique of saphenous nerve block was successfully demonstrated.

Femoral nerve block. Single injection versus continuous infusion for total knee arthroplasty

BACKGROUND AND OBJECTIVES

This study was conducted to ascertain whether there is any advantage to the continuous-infusion femoral 3-in-1 nerve block over the single-injection femoral nerve block for postoperative analgesia after total knee arthroplasty.

METHODS

A double-blind, randomized, controlled study was made of 33 patients undergoing total knee arthroplasty, who were randomized into three groups. Group 1 received a single-injection femoral 3-in-1 nerve block with 20 mL 0.5% bupivacaine with 1:200,000 epinephrine. Group 2 had a catheter placed in the femoral nerve sheath, through which a continuous femoral 3-in-1 nerve block was established. Group 3 patients served as controls. All blocks were performed and assessed prior to induction of standardized general anesthesia. All patients received morphine via patient-controlled analgesia. Pain was recorded on a 100-mm visual analog scale at rest and with motion of the knee. Opioid consumption and side effects were recorded; P = .05 was considered statistically significant.

RESULTS

In the recovery room, pain scores with motion were lower in the single-injection and continuous-infusion groups (P < .05). There were no significant differences between any of the groups regarding pain scores or morphine requirements beyond the recovery room. The incidence of nausea was higher in the control group. There were no differences between the groups with respect to overall patient satisfaction.

CONCLUSIONS

We were unable to confirm improvements in analgesia provided by continuous-infusion femoral 3-in-1 nerve block for total knee arthroplasty except in the recovery room.

Lateral femoral cutaneous nerve block revisited. A nerve stimulator technique

BACKGROUND AND OBJECTIVES

Regional block of the lateral femoral cutaneous nerve (LFCN) often has disappointing success rates despite the large volumes of local anesthetic used. This study was undertaken to investigate the utility of using a nerve stimulator (NS) to localize and block the LFCN.

METHODS

After obtaining institutional approval and informed consent, the authors proceeded with a two-stage study. In stage 1, 20 ASA 1 volunteers underwent LFCN block by both a fan and a NS technique in a prospective, randomized, crossover study utilizing strict criteria for success and extent of block. To predict clinical utility, 20 patients underwent LFCN block by the NS technique using the same assessment criteria (stage 2). Statistical analysis for the comparisons was completed employing the Fisher's exact or paired t-test as appropriate. P < .05 was considered significant.

RESULTS

The NS technique significantly improved the success of LFCN block over the fan technique (100% vs. 40%, P = .00002). The extent of successful blocks was no different with the two techniques. Success in stage 2 was similar to that in stage 1 (85%) predicting clinical utility.

CONCLUSIONS

A NS can be used to localize a purely sensory nerve; such as the LFCN, and improve success rates in regional anesthesia.

Superior laryngeal nerve block: an anatomical study

Superior laryngeal nerve anaesthesia is frequently used to facilitate endotracheal intubation in the awake patient. We have modified the transcutaneous approach to this nerve block to employ a short bevel needle. This improves tactile perception in performing the procedure thus simplifying identification of the correct depth of injection. This study was designed to determine the anatomical basis of superior laryngeal nerve anaesthesia and to estimate the success rate using our modified technique. At autopsy, 20 cadavers had nerve block performed substituting 0.02% methylene blue for local anaesthetic. Dissection was then performed to identify the anatomical structures stained by the simulated local anaesthetic. Additional dissections were performed in formalin-fixed cadavers. We found that the dye was injected into the paraglottic space bounded laterally by the thyrohyoid membrane and thyroid cartilage, medially by the laryngeal submucosa, caudad by the conus elasticus, cephalad by the hyoid bone, and anteriorly and posteriorly by the anterior and posterior thyrohyoid ligaments, respectively. The internal laryngeal nerve, the sensory branch of the superior laryngeal nerve, passed through this compartment and was heavily stained with simulated local anaesthetic. Resistance to the passage of the short bevel needle was provided by the lateral glossoepiglottic fold, not the thyrohyoid membrane as we had expected. Of 40 injections, 39 were deemed successful for a success rate of 97.5%. We conclude that this is a simple and highly successful technique for performing superior laryngeal nerve anaesthesia.

Haemoglobin Hammersmith precludes monitoring with conventional pulse oximetry

We report a case of a 15-yr-old North American Indian female with haemoglobin Hammersmith, scheduled for elective tonsillectomy, whose arterial oxygen saturation could not be reliably monitored perioperatively because of technical limitations of conventional dual wavelength pulse oximetry. The patient was chronically icteric. She had an atrial septal defect with a small L-->R shunt demonstrated by echocardiography. On arrival in the operating room pulse oximetry (Nellcor-Model N100) demonstrated a saturation of 45% whilst breathing room air. Her oxygen saturation increased to 60% whilst breathing 100% oxygen via a face mask. An arterial blood gas performed whilst breathing 100% oxygen revealed a PaO2 of 418 mmHg. Tonsillectomy was completed uneventfully under general anaesthesia. The pulse oximeter did not provide any clinically useful information throughout the case. In conclusion, conventional dual wavelength pulse oximeters cannot give an accurate estimate of oxygenation in patients with haemoglobin Hammersmith. Assessment of oxygenation in these patients requires alternative monitoring techniques.

Can parturients distinguish between intravenous and epidural fentanyl?

We tested the hypothesis that the sedative, euphoric, and analgesic effects of intravenous fentanyl would distinguish intravenous from epidural administration. One hundred ASA I and II labouring parturients received 100 micrograms fentanyl either iv or via an epidural catheter in a double-blind, randomized, cross-over fashion. Nineteen anaesthetists (8 staff and 11 residents) participated and correctly guessed the route of administration of the fentanyl in 61/66 intravenous doses and in 69/75 epidural doses yielding a sensitivity of 92.4%, a specificity of 92.0%, a positive predictive value of 91.0%, and a negative predictive value of 93.2%. Of the 41 patients that were crossed over, 38 (92.7%) were able to detect a difference between the routes of administration. Most patients experienced prompt, short-lived symptoms with iv fentanyl but no important differences in fetal heart rate pattern or in maternal desaturation were seen between the groups. This study suggests that subjective symptoms will accurately distinguish intravenous from epidural fentanyl administration in labouring parturients (P < 0.001), and should serve as a safe and reliable intravenous test dose for epidural anaesthesia in the obstetric population.

Temporal changes in left ventricular function after massive sympathetic nervous system activation

Intense activation of the sympathetic nervous system (SNS) decreases the contractile state of the rabbit left ventricle (LV). In this study, we determined the time course of LV dysfunction after massive central activation of the SNS in dogs. Veratrine (40-80 micrograms/kg) was injected intracisternally to activate the SNS in six chloralose-anesthetized dogs, and LV end-diastolic pressure (LVEDP), cardiac output, heart rate, and aortic pressure (Pa) were measured at 30-min intervals for 3 h. Pa increased from 147 +/- 8 (SE) to 272 +/- 7 mmHg (1 mmHg = 133.3 Pa) within 15 min, then declined to 148 +/- 16 mmHg by 1 h LV function curves (stroke work versus LVEDP or stroke work verus LV transmural pressure) showed a marked decrease in slope and a shift to the right within minutes after activating the SNS, which persisted for the duration of the experiment. These data indicate that LV contractility was diminished in these animals. No changes in LV function were observed in three dogs serving as time-matched controls. In three additional dogs, LV pressure was raised to a degree similar to that observed after SNS activation by constricting the ascending aorta for 1 h. These animals exhibited only modest shifts in the LV function curve during and after aortic constriction. Mean plasma catecholamine concentration increased by one to two orders of magnitude in animals after SNS activation, but only minor changes were observed in the other two groups. We conclude that myocardial contractility declines markedly soon after massive SNS activation and is not solely a function of the initial hypertensive period.

The femoral 3-in-1 block revisited

STUDY OBJECTIVE

To estimate the frequency of successful conduction blockade of the femoral, lateral femoral cutaneous, and obturator nerves following a femoral 3-in-1 block.

DESIGN

Prospective observational study.

SETTING

Operating room at Royal University Hospital, Saskatoon, Saskatchewan.

PATIENTS

32 patients having lower extremity surgery.

INTERVENTIONS

Femoral 3-in-1 nerve blocks were performed on all patients.

MEASUREMENTS AND MAIN RESULTS

Sensation and motor power in all 3 nerve distributions (femoral, lateral femoral cutaneous, obturator) were assessed before and after each femoral 3-in-1 nerve block. By our criteria, the femoral nerve block was successful in 26 of 32 patients (81%). The lateral femoral cutaneous nerve was successfully blocked in 25 of 26 patients (96%). Incidentally, the saphenous nerve which is classically described as the terminal branch of the femoral nerve, was successfully blocked in 20 of 26 patients (77%). The obturator nerve block was successful in only 1 of 26 patients (4%).

CONCLUSIONS

The femoral 3-in-1 nerve block does not block the parent trunk of the obturator nerve.

Transsartorial approach for saphenous nerve block

Blockade of conduction in the saphenous nerve is important in providing surgical anaesthesia in the lower leg. Unfortunately, previously described techniques have lacked clinical effectiveness in practice. We developed a transsartorial approach for conduction block of the saphenous nerve. We first confirmed its potential clinical utility in 12 cadaveric specimens by demonstrating that the saphenous nerve was consistently stained by injections of methylene blue. Subsequently, we compared the relative rates of successful saphenous nerve block and the extent of conduction block provided by three techniques: (1) transsartorial saphenous nerve block (TSSNB), (2) above knee femoral paracondylar field block (FPFB), and (3) below knee field block (BKFB) of the saphenous nerve in 20 ASA I volunteers. The transsartorial saphenous nerve block proved to be highly successful (80% success rate) and was superior to the other two approaches in providing cutaneous analgesia to pinprick in the saphenous nerve distribution (P < 0.05). The success rates of the BKFB and FPFB were 65% and 40% respectively. A successful block with the transsartorial approach provided complete anaesthesia of the medial malleolus in 94% of subjects whilst the BKFB and FPFB provided complete anaesthesia of the medial malleolus in less than 40% of the successful blocks. We recommend the transsartorial approach for more effective block of the saphenous nerve.

Reevaluation of the sciatic nerve block

BACKGROUND AND OBJECTIVES

Sciatic nerve blocks are perceived as unreliable, technically demanding, and uncomfortable. With strict criteria to define success rates, we designed a study to examine the efficacy of two techniques of sciatic nerve block.

METHODS

All blocks were performed by a novice in sedated patients using an insulated needle and a nerve stimulator.

RESULTS

Overall success with both techniques was 87.5%. One transient neurologic deficit attributed to the sciatic nerve block was observed; otherwise, the technique provided satisfactory anesthesia without complications.

CONCLUSIONS

Patient acceptance was excellent.

Circulating neuropeptide Y does not produce pulmonary hypertension during massive sympathetic activation

We tested the possibility that neuropeptide Y (NPY) may contribute to the pulmonary hypertension that occurs after massive sympathetic activation produced by intracisternal veratrine administration in the chloralose-anesthetized dog. In six dogs, veratrine caused arterial NPY-like immunoreactivity (NPY-LI) to rise from 873 +/- 150 (SE) pg/ml to peak values of 3,780 +/- 666 pg/ml by 60-120 min. (In 3 animals, adrenalectomy significantly reduced the increases in NPY-LI.) In five additional dogs, we infused porcine NPY for 30 min in doses that increased arterial NPY-LI to 8,354 +/- 1,514 pg/ml and observed only minor changes in pulmonary hemodynamics. In three isolated perfused canine left lower lung lobe (LLL) preparations, increasing doses of NPY were administered, producing levels of plasma NPY-LI, at the highest dose, that exceeded those observed after veratrine administration by three orders of magnitude. No changes in LLL arterial or double-occlusion capillary pressures were observed at any dose. Similarly, no changes in LLL hemodynamics were observed in three additional lobes when NPY was administered while norepinephrine was being infused. We conclude that it is unlikely that NPY plays a role as a circulating vasoactive agent in producing the pulmonary hypertension and edema that occur in this model.