Nigel M. Bedforth

The Effects of Sevoflurane and Nitrous Oxide on Middle Cerebral Artery Blood Flow Velocity and Transient Hyperemic Response

UNLABELLED We studied the effects of sevoflurane, with and without nitrous oxide, on the indices of cerebral autoregulation (transient hyperemic response ratio and the strength of autoregulation) derived from the transient hyperemic response (THR) test. Twelve patients (ASA physical status I or II) aged 18-40 yr presenting for routine non-neurosurgical procedures were recruited. The middle cerebral artery blood flow velocity was continuously recorded using transcranial Doppler ultrasonography. Preinduction THR tests were performed before the patients were anesthetized with alfentanil, propofol, and vecuronium. End-tidal carbon dioxide concentration and mean arterial pressure (to within 10% with a phenylephrine infusion) were maintained at their preinduction values. THR tests were performed sequentially at the following end-tidal sevoflurane concentrations: 2.2% in oxygen, 3.4% in oxygen, 3.4% with 50% nitrous oxide in oxygen, and 2.2% with 50% nitrous oxide in oxygen. Neither 2.2% nor 3.4% sevoflurane significantly affected cerebral autoregulation. The addition of 50% nitrous oxide to the 2.2%, but not the 3.4%, concentration of sevoflurane increased middle cerebral artery blood flow velocity and decreased autoregulatory indices significantly. IMPLICATIONS Transient hyperemic response is preserved during sevoflurane anesthesia but is significantly impaired when nitrous oxide is added to the lower concentration of sevoflurane (2.2%). These findings have implications for neurosurgical patients undergoing general anesthesia.

Cerebral hemodynamic response to the introduction of desflurane: A comparison with sevoflurane.

Rapid increases in the inspired concentration of desflurane cause transient increases in heart rate and blood pressure. Desflurane also impairs cerebral autoregulation at clinical concentrations. Sevoflurane does not share these hemodynamic side effects. We compared the cerebral and systemic hemodynamic responses to the introduction of desflurane or sevoflurane after the induction of anesthesia with propofol. Twenty healthy adult patients scheduled for nonneurological surgery were recruited. After the induction of anesthesia with propofol, either desflurane or sevoflurane (n = 10 per group) was introduced at 7.2% or 2.2%, respectively, and increased to 10.8% or 3.3%, respectively, 2 min later. Middle cerebral artery blood flow velocity was measured continuously by using a 2-MHz transcranial Doppler ultrasound probe. Heart rate and blood pressure were recorded at 1-min intervals during the 12-min study period. Those patients receiving desflurane had significantly greater middle cerebral artery blood flow velocities, heart rates, and blood pressures than those receiving sevoflurane (P < 0.01). Implications The introduction of desflurane after the induction of anesthesia leads to significant disturbances in cerebral and systemic hemodynamics suggesting loss of cerebral autoregulation and cerebral hyperemia. This may have implications for patients undergoing anesthesia for intracranial surgery.

Three-Dimensional, Multiplanar, Ultrasound-Guided, Radial Nerve Block

Objective: We describe the use of 3-dimensional, multiplanar ultrasound imaging for peripheral nerve block. Case Report: To illustrate the potential usefulness of the technique, we present a case in which real-time 3-dimensional, multiplanar ultrasound was used to assist in the performance of a radial nerve block. Conclusions: Three-dimensional, multiplanar ultrasound in real-time has the potential to improve nerve identification and accuracy of needle placement in regional anesthesia.

Survey of intrathecal opioid usage in the UK

Background and objective: Intrathecal opioids are now used routinely in the UK for intra‐ and postoperative analgesia. The opioids of choice have altered over recent years and the dosage regimens used can vary between institutions. Concerns over safety have been reduced probably because much lower doses of opioids are now being used. This survey explored the practice of intrathecal opioid usage in the UK. Methods: We sent a questionnaire survey to 270 anaesthetic departments and received 199 replies, a response rate of 73.7%. Results: Intrathecal opioids were used in 175 (88.4%) departments. Of these departments, 107 (61.1%) had local guidelines or protocols in place. Opioids such as diamorphine (used in 136 (78.2%) of departments) and fentanyl (129 (74.1%)) with a shorter duration of action are now more commonly used than morphine (37 (21.3%)) for intrathecal analgesia. In 96 (54.5%) departments, patients were nursed on regular surgical wards following administration of spinal opioids. Conclusions: The use of low‐dose lipophilic intrathecal opioids for postoperative analgesia is widespread in the UK. Patients are commonly nursed in low‐dependency post‐anaesthetic care areas. The low incidence of adverse events reported by the respondents along with the popularity of the technique suggests that low‐dose spinal opioid administration is safe.

Real-time Three-dimensional Ultrasound-guided Central Venous Catheter Placement

We present the first description of real-time 3-dimensional ultrasound for insertion of a central venous catheter in a surgical patient. An HD11 XE™ ultrasound machine with a V8-4 transducer (Philips Medical Systems, Bothell, WA) was used throughout. Three-dimensional multiplanar and volume-rendered views allowed us to simultaneously view the neck anatomy in 3 orthogonal planes. Needle entry into the vein and subsequent catheter placement were also visualized. We were able to rotate the views in real time, thereby enabling visualization of the catheter within the lumen of the vein. The ability to see simultaneous real-time short- and long-axis views along with volume perspective without altering transducer position is an exciting development with the potential to confer a safety benefit to the patient. Although the operator is required to assimilate more information, the limitations we encountered were mainly related to processing power and transducer size, which we expect will be overcome with advancing technology.

Assessing Neuromuscular Block at the Larynx: The Effect of Change in Resting Cuff Pressure and a Comparison with Video Imaging in Anesthetized Humans

UNLABELLED Neuromuscular block (NMB) at the larynx has been assessed by measuring the cuff pressure (CP) in an endotracheal tube (ETT) placed between the vocal cords. In this study, we evaluated the decrease in resting cuff pressure (RCP) after the administration of rocuronium and the effect of this decrease on the assessment of NMB, and we compared CP measurement with an alternative technique, video imaging (VI). In 20 patients, NMB was determined at the hand by mechanomyography and at the larynx initially by CP and subsequently by VI, recording images using a fiberoptic bronchoscope via a laryngeal mask. Train-of-four stimuli were applied at both sites. After baseline measurements, the ETT was replaced, and rocuronium was infused to achieve a steady-state 50% (n = 10) or 75% (n = 10) block at the hand. CP measurements were recorded before and after restoration of RCP to prerocuronium pressure, followed by further VI measurements. The mean RCP decreased from 21 +/- 4 to 12 +/- 5 mm Hg after rocuronium. At 50% block at the hand, the CP estimate of block at the larynx with reduced RCP was 62% +/- 18%, and that after restoring RCP was 29% +/- 13%; VI estimated 27% +/- 14% block. At 75% block at the hand, CP and VI estimated 52% +/- 11% and 46% +/- 9% block, respectively (RCP maintained). We conclude that RCP decreases after the administration of rocuronium, that restoring RCP significantly alters CP estimates of NMB, and that VI is in agreement with CP measurement if RCP is maintained at prerelaxant values. IMPLICATIONS In this study, we show that a muscle relaxant-induced decrease in resting tension at the larynx may confound the assessment of neuromuscular block by cuff pressure measurement. The preliminary data suggest that video imaging may provide a suitable alternative to cuff pressure measurement to assess neuromuscular block at the larynx.

Delineation of distal ulnar nerve anatomy using ultrasound in volunteers to identify an optimum approach for neural blockade

Background and objective Ultrasound can provide novel approaches to neural blockade independent of surface landmarks. We elucidated the sonoanatomy of the ulnar nerve in the forearm of healthy volunteers in order to identify an optimum site for neural blockade. Methods One hundred forearms were scanned; the shape, depth from skin and cross-sectional area of the nerve were noted at the elbow, forearm and wrist. Results The nerve was visualized in all volunteers and had a maximum depth of 18.9 mm from the skin. The mean distance between the nerve and artery, 2 cm proximal to the point where the two structures met in the forearm, was 8.5 mm (95% confidence interval 8.1–8.9 mm). This was approximately at the junction between the proximal 2/5 and distal 3/5 of the forearm. Conclusion Our study demonstrates that ultrasound can be utilized to identify the ulnar nerve and artery in the forearm. This implies that traditional landmarks will not be required prior to neural blockade. We have suggested a point for blockade of the nerve to reduce risk of vascular puncture.

Visuospatial Ability as a Predictor of Novice Performance in Ultrasound-guided Regional Anesthesia

Background: Visuospatial ability correlates positively with novice performance of simple laparoscopic tasks. The aims of this study were to identify whether visuospatial ability could predict technical performance of an ultrasound-guided needle task by novice operators and to describe how emotional state, intelligence, and fear of failure impact on this. Methods: Sixty medical student volunteers enrolled in this observational study. The authors used an instructional video to standardize training for ultrasound-guided needle advancement in a turkey breast model and assessed volunteers’ performance independently by two assessors using composite error score (CES) and global rating scale (GRS). The authors assessed their “visuospatial ability” with mental rotation test (MRT), group embedded figures test, and Alice Heim group ability test. Emotional state was judged with UWIST Mood Adjective Checklist (UMACL), and fear of failure and general cognitive ability were judged with numerical reasoning test. Results: High CES scores (high error rate) were associated with low MRT scores (&rgr; = −0.54; P < 0.001). Better GRS scores were associated with better MRT scores (&rgr; = 0.47; P < 0.001). Regarding emotions, GRS scores were low when anxiety levels were high (&rgr; = −0.35; P = 0.005) and CES scores (errors) were low when individuals reported feeling vigorous and active (&rgr; = −0.30; P = 0.01). Conclusions: An MRT predicts novice performance of an ultrasound-guided needling task on a turkey model and as a trait measure could be used as a tool to focus training resources on less-able individuals. Anxiety adversely affects performance. Therefore, both may prove useful in directing targeted training in ultrasound-guided regional anesthesia.

Patient satisfaction with perioperative care among patients having orthopedic surgery in a university hospital.

This survey aimed to validate the English version of the multidimensional Leiden Perioperative Patient Satisfaction questionnaire (LPPSq) and use it to assess patient satisfaction with perioperative care and the influence of type of anesthesia. One hundred patients having orthopedic surgery under regional and general anesthesia verbally consented to participate. Different aspects of satisfaction were assessed (eg, provision of information, and staff-patient relationship). The reliability estimate of the LPPSq (Cronbach’s-α) was good (0.94). Overall, patient satisfaction score was 86.7%, lowest was for information (80.8%) and highest for staff-patient relationships (90.3%). Patients were more satisfied with the provision of information regarding regional anesthesia.

Anesthesiologists’ perception of patients’ anxiety under regional anesthesia

The aim of this survey is to report anesthesiologists’ perception of patients’ anxiety under regional anesthesia, its frequency, effects and causes, and the strategies employed to reduce it. Electronic questionnaires were sent to all grades of anesthesiologists in Nottingham, UK. The response rate for the survey was 79%. Over half of the anesthesiologists in our region believe that anxiety during regional anesthesia is not common. Surgery and anesthesia, followed by block failure were reported by anesthesiologists as the most common causes of patients’ anxiety. Frequently employed techniques to manage anxiety were communication or sedation. Most respondents felt that regional anesthesia provides good analgesia and patient satisfaction. However, 20% felt that regional anesthesia is painful or unpleasant for patients, perhaps explaining the reluctance by some anesthesiologists to perform regional anesthesia.