Robert McCarthy

Angiotensin-converting Enzyme Inhibitors Increase Vasoconstrictor Requirements After Cardiopulmonary Bypass

Preoperative use of angiotensin-converting enzyme (ACE) inhibitors is common and has been associated with hypotension at separation from cardiopulmonary bypass (CPB). This study prospectively examined the influence of chronic preoperative ACE inhibitor use and other perioperative factors on the incidence of vasoconstrictor therapy required to maintain systolic blood pressure at more than 85 mm Hg despite a normal cardiac output after CPB in 4301 adults undergoing elective coronary artery and/or valve surgery. Hypothermic, nonpulsatile CPB and either opioid or ketamine-benzodiazepine anesthesia were common features of the operations. At least two vasoconstrictor infusions (phenylephrine, norepinephrine, or dopamine) were required for low perfusion pressure despite adequate cardiac output after CPB in 7.7% of 519 ACE-inhibited patients and 4.0% of 3782 patients not receiving ACE inhibitors (P = 0.0001). In the first 4 h after arrival in the intensive care unit, the need for vasoconstrictor infusions to treat hypotension with adequate cardiac output did not differ, although more ACE-inhibited patients (6.4%) exhibited low values of systemic vascular resistance (<600 dyne centered dot s centered dot cm-5) than patients not receiving ACE inhibitors (2.8%; P = 0.0002). Logistic regression analysis identified preoperative ACE inhibitor use, congestive heart failure, poor left ventricular function, duration of CPB, reoperative surgery, age, and opioid anesthesia as independent risk factors for requiring >or=to 2 vasoconstrictor infusions after CPB. No other preoperative drug therapy significantly altered this outcome. (Anesth Analg 1995;80:473-9)

Nerve stimulator-assisted evoked motor response predicts the latency and success of a single-injection sciatic block.

Variable onset latency of single-injection sciatic nerve block (SNB) may result from drug deposition insufficiently close to all components of the nerve. We hypothesized that this variability is caused by the needle tip position relative to neural components, which is objectified by the type of evoked motor response (EMR) elicited before local anesthetic injection. One-hundred ASA I–II patients undergoing reconstructive ankle surgery received infraglutealparabiceps SNB using 0.4 mL/kg (maximum 35 mL) of levobupivacaine 0.625%. The endpoint for injection was the first elicited EMR: inversion (I), plantar flexion (PF), dorsiflexion (DF), or eversion (E) at 0.2–0.4 mA. The frequencies of the EMRs were: I 40%, PF 43%, E 14%, and DF 3%. SNB was considered complete if both tibial and common peroneal nerves were blocked and failed if either analgesia to pinprick was not observed at 30 min or anesthesia at 60 min. Patients with an EMR of I demonstrated shorter mean times (±95% confidence interval [CI]) to complete the block with 8.5 (95% CI, 6.2–10.8) min compared to 27.0 (95% CI, 20.6–33.4) min after PF (P < 0.001) and 30.4 (95% CI, 24.9–35.8) min after E (P < 0.001). No rescue blocks were required in group I compared with 24% (P = 0.001) and 71% (P < 0.001) of patients in groups PF and E, respectively. We conclude that EMR type during nerve stimulator-assisted single-injection SNB predicts latency and success of complete SNB because the observed EMR is related to the positioning of the needle tip relative to the tibial and common peroneal nerves.

The Association Between Propofol-Induced Loss of Consciousness and the SNAP™ Index

The SNAP™ is a processed electroencephalogram monitor that uses an algorithm based on low- and high-frequency spectral components to derive a SNAP™ index. In this study we sought to determine the relationship of the SNAP™ index with loss of consciousness in subjects receiving a bolus of propofol. Unpremedicated subjects were randomized to receive 1 of 11 doses of IV propofol (0, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, or 2.4 mg/kg; n = 20 per group). The SNAP™ index was recorded when the subject became unconscious (end-point) or at 160 s after the injection. Sixty-five percent of subjects achieved the end-point (defined as the time at which the subject dropped a weighted syringe). The 50% effective dose for propofol was 0.97 mg/kg (95% confidence interval [CI], 0.86–1.07 mg/kg). The median awake SNAP™ index was 92 (range 78–99) and did not differ between subjects who reached the end-point and those who did not. The end-point SNAP™ index decreased from baseline in the subjects who dropped the syringe to a median of 76 (range, 57–94) at doses ≥1.0 mg/kg but was not different among doses. The index was not different from baseline at 160 s in subjects who did not reach the end-point. Binary logistic regression models predicted a SNAP™ index 95% effective dose for loss of consciousness of 71 (95% CI, 63–74) and 19 (95% CI, 16–22) for changes in SNAP™ index from baseline. The areas under the receiver operator characteristic curves for these models were 0.837 and 0.864. The SNAP™ index correlated with propofol-induced loss of consciousness. It appears to be a useful indicator of loss of consciousness and should be further investigated as a monitor of anesthesia depth.

Oxygen-Free Atomic Layer Deposition of Indium Sulfide

Atomic layer deposition (ALD) of indium sulfide (In2S3) films was achieved using a newly synthesized indium precursor and hydrogen sulfide. We obtain dense and adherent thin films free from halide and oxygen impurities. Self-limiting half-reactions are demonstrated at temperatures up to 225 °C, where oriented crystalline thin films are obtained without further annealing. Low-temperature growth of 0.89 Å/cycle is observed at 150 °C, while higher growth temperatures gradually reduce the per-cycle growth rate. Rutherford backscattering spectroscopy (RBS) together with depth-profiling Auger electron spectroscopy (AES) reveal a S/In ratio of 1.5 with no detectable carbon, nitrogen, halogen, or oxygen impurities. The resistivity of thin films prior to air exposure decreases with increasing deposition temperature, reaching <1 Ω·cm for films deposited at 225 °C. Hall measurements reveal n-type conductivity due to free electron concentrations up to 10(18) cm(-3) and mobilities of order 1 cm(2)/(V·s). The digital synthesis of In2S3 via ALD at temperatures up to 225 °C may allow high quality thin films to be leveraged in optoelectronic devices including photovoltaic absorbers, buffer layers, and intermediate band materials.

Effect of Intrathecal Bupivacaine Dose on the Success of External Cephalic Version for Breech Presentation: A Prospective, Randomized, Blinded Clinical Trial

Background: Breech presentation is a leading cause of cesarean delivery. The use of neuraxial anesthesia increases the success rate of external cephalic version procedures for breech presentation and reduces cesarean delivery rates for fetal malpresentation. Meta-analysis suggests that higher-dose neuraxial techniques increase external cephalic version success to a greater extent than lower-dose techniques, but no randomized study has evaluated the dose–response effect. We hypothesized that increasing the intrathecal bupivacaine dose would be associated with increased external cephalic version success. Methods: We conducted a randomized, double-blind trial to assess the effect of four intrathecal bupivacaine doses (2.5, 5.0, 7.5, 10.0u2009mg) combined with fentanyl 15 &mgr;g on the success rate of external cephalic version for breech presentation. Secondary outcomes included mode of delivery, indication for cesarean delivery, and length of stay. Results: A total of 240 subjects were enrolled, and 239 received the intervention. External cephalic version was successful in 123 (51.5%) of 239 patients. Compared with bupivacaine 2.5u2009mg, the odds (99% CI) for a successful version were 1.0 (0.4 to 2.6), 1.0 (0.4 to 2.7), and 0.9 (0.4 to 2.4) for bupivacaine 5.0, 7.5, and 10.0u2009mg, respectively (P = 0.99). There were no differences in the cesarean delivery rate (P = 0.76) or indication for cesarean delivery (P = 0.82). Time to discharge was increased 60u2009min (16 to 116u2009min) with bupivacaine 7.5u2009mg or higher as compared with 2.5u2009mg (P = 0.004). Conclusions: A dose of intrathecal bupivacaine greater than 2.5u2009mg does not lead to an additional increase in external cephalic procedural success or a reduction in cesarean delivery.