Sevoflurane-induced isoelectric EEG and burst suppression: differential and antagonistic effect of added nitrous oxide
The objective of this study was to investigate whether nitrous oxide influenced the ED50 of sevoflurane for induction of isoelectric electroencephalogram (ED50isoelectric) differently from its influence on the ED50 of sevoflurane for electroencephalogram burst suppression (ED50burst). In a prospective, randomised, double-blind, parallel group, up–down sequential allocation study, 77 ASA physical status 1 and 2 patients received sevoflurane induction and, after tracheal intubation, were randomly allocated to receive sevoflurane with either 40% oxygen in air (control group) or 60% nitrous oxide in oxygen mixture (nitrous group). The ED50isoelectric in the two groups was determined using Dixon's up and down method, starting at 2.5% with 0.2% step size of end-tidal sevoflurane. The electroencephalogram was considered as isoelectric when a burst suppression ratio of 100% lasted > 1 min. The subsequent concentrations of sevoflurane administered were determined by the presence or absence of isoelectric electroencephalogram in the previous patient in the same group. The ED50isoelectric in the nitrous group 4.08 (95%CI, 3.95–4.38)% was significantly higher than that in the control group 3.68 (95%CI, 3.50–3.78)% (p < 0.0001). The values for ED50burst were 3.05 (95%CI, 2.66–3.90)% and 3.02 (95%CI, 3.00–3.05)% in nitrous group and control group, respectively (p = 0.52). The addition of 60% nitrous oxide increases ED50isoelectric, but not the ED50burst of sevoflurane. Neither result indicates an additive effect of anaesthetic agents, as might be expected, and possible reasons for this are discussed.
A randomised double-blind trial of phenylephrine and metaraminol infusions for prevention of hypotension during spinal and combined spinal–epidural anaesthesia for elective caesarean section
Prophylactic vasopressor administration is commonly recommended to reduce maternal hypotension during spinal anaesthesia for caesarean section. Metaraminol has undergone limited investigation in obstetric anaesthesia for this purpose, particularly in comparison with phenylephrine. In this multicentre, randomised, double-blind, non-inferiority study, we compared prophylactic phenylephrine or metaraminol infusions, started immediately after spinal anaesthesia, in 185 women who underwent elective caesarean section. Phenylephrine was initially infused at 50 μg.min−1, and metaraminol at 250 μg.min−1. The primary outcome was the difference in umbilical arterial pH between groups; secondary outcomes included other neonatal acid-base measures, and maternal haemodynamic changes. The mean (SD) umbilical arterial pH was 7.28 (0.06) in the phenylephrine group vs. 7.31 (0.04) in the metaraminol group (p = 0.0002). The estimated mean (95%CI) pH difference of 0.03 (0.01–0.04) was above the pre-determined lower boundary of clinical non-inferiority, and also met the criterion for superiority. Umbilical artery lactate concentration was 2.8 (1.2) mmol.l−1 in the phenylephrine group vs. 2.3 (0.7) mmol.l−1 in the metaraminol group (p = 0.0018). Apgar scores did not significantly differ between groups. There was a higher incidence of hypotension, defined as systolic arterial pressure <90% baseline, in the phenylephrine group; there was a higher incidence of hypertension and severe hypertension (systolic arterial pressure >110% and >120% baseline, respectively) in the metaraminol group. There was no significant difference between groups in the incidence of nausea, vomiting or maternal bradycardia. We conclude that, when used as an infusion to prevent hypotension after spinal anaesthesia for elective caesarean section, metaraminol is at least non-inferior to phenylephrine with respect to neonatal acid-base outcomes.
We investigated the flow rates of 25-G and 27-G spinal needles, of 90-mm and 120-mm lengths, from Vygon, BD, B. Braun and Pajunk; the needles had either a Luer connector, or a Surety® or UniVia® non-Luer connector. We used a bench-top model of entering the spinal space, pressurised to 35 cmH2O to simulate cerebrospinal fluid pressure in the sitting position. We examined the time to first appearance of simulated cerebrospinal fluid in the needle hub, as well as the amount of fluid collected over 120 s after the needle was introduced. The mean (SD) times to first appearance of fluid in the needle hub of Luer spinal needles varied from 0.36 (0.22) s for the 25-G 90-mm BD to 3.14 (0.72) s for the 27-G 120-mm B. Braun, and in the non-Luer spinal needles from 0.22 (0.17) s for the 25-G 90-mm B. Braun to 2.99 (0.71) s for the 27-G 120-mm Pajunk. There was a significant difference in the time to first appearance of fluid in the needle hub between Luer and non-Luer needles of the same type for seven of 14 comparisons made, of which four showed slower appearance of fluid in the non-Luer version. In some of these cases, the time to appearance of fluid was nearly twice as long with the non-Luer counterpart. The mean (SD) weight of fluid collected in 120 s using the Luer spinal needles varied from 0.21 (0.05) g for the 27-G 120-mm Pajunk to 1.21 (0.18) g for the 25-G 90-mm Vygon, and using the non-Luer spinal needles from 0.25 (0.05) g for the 27-G 120-mm Pajunk to 1.55 (0.05) g for the 25-G 90-mm B. Braun. All of the needle types showed a greater weight of fluid collected using the non-Luer compared with the Luer version, with six of the 14 needle types showing a significant difference. Significant variations in flow were also seen between the same needle type from different manufacturers. We conclude that changing from Luer to non-Luer versions of spinal needles does not merely change the hub design and connection, but may introduce important differences in function.
A randomised crossover simulation study comparing the impact of chemical, biological, radiological or nuclear substance personal protection equipment on the performance of advanced life support interventions
Recent incidents involving chemical, biological, radiological and nuclear substances have stressed the importance of sufficient personal protection equipment for medical first-responders. Modern lightweight, battery-independent, suit ensembles may prove superior to the current protective suit used in the UK. This study compared the powered respiratory protective suit (PRPS ensemble) with a lightweight suit consisting of a SARATOGA® Multipurpose CBRN Protective Coverall Polyprotect 12 in conjunction with the Avon C50 Respirator/Avon CBRNF12CE filter canister and butyl rubber protective gloves (Polyprotect 12 ensemble). Thirty anaesthetists carried out a standardised resuscitation scenario either unprotected (control) or wearing the PRPS or Polyprotect 12 ensembles in a randomised, crossover simulation study. Treatment times for five simulated advanced life support interventions (application of monitoring; bag/mask ventilation; tracheal intubation; drug and fluid administration; and external pacing) were measured. Wearer comfort was also assessed for the two protective suits by questionnaire. All participants accomplished the treatment objectives of all study arms without adverse events. Total mean (SD) completion time for the five interventions was significantly longer for the PRPS compared with the Polyprotect 12 ensemble (204 (53) s vs. 149 (36) s, respectively; p < 0.0001). Participants rated mobility, noise, heat, vision, dexterity and speech intelligibility significantly better in the Polyprotect 12 ensemble compared with the PRPS ensemble. The combination of a lightweight Polyprotect 12 suit and an Avon C50 air-purifying respirator is preferable to the powered respiratory protective suit during simulated emergency life support, due to a combination of shorter task completion times and improved mobility, communication and dexterity.
A randomised trial of peri-operative positive airway pressure for postoperative delirium in patients at risk for obstructive sleep apnoea after regional anaesthesia with sedation or general anaesthesia for joint arthroplasty
Previous pilot work has established an association between obstructive sleep apnoea and the development of acute postoperative delirium , but it remains unclear to what extent this risk factor is modifiable in the ‘real world’ peri-operative setting. In a single-blind randomised controlled trial, 135 elderly surgical patients at risk for obstructive sleep apnoea were randomly assigned to receive peri-operative continuous positive airway pressure (CPAP) or routine care. Of the 114 patients who completed the study, 21 (18.4%) experienced delirium. Delirium was equally common in both groups: 21% (12 of 58 subjects) in the CPAP group and 16% (9 of 56 subjects) in the routine care group (OR = 1.36 [95%CI 0.52–3.54], p = 0.53). Delirious subjects were slightly older – mean (SD) age 68.9 (10.7) vs. 64.9 (8.2), p = 0.07 – but had nearly identical pre-operative STOP-Bang scores (4.19 (1.1) versus 4.27 (1.3), p = 0.79). Subjects in the CPAP group used their devices for a median (IQR [range]) of 3 (0.25–5 [0–12]) nights pre-operatively (2.9 (0.1–4.8 [0.0–12.7]) hours per night) and 1 (0–2 [0–2]) nights postoperatively (1.4 (0.0–5.1 [0.0–11.6]) hours per night). Among the CPAP subjects, the residual pre-operative apnoea–hypopnea index had a significant effect on delirium severity (p = 0.0002). Although we confirm that apnoea is associated with postoperative delirium, we did not find that providing a short-course of auto-titrating CPAP affected its likelihood or severity. Voluntary adherence to CPAP is particularly poor during the initiation of therapy.
The accuracy of timed maximum local anaesthetic dose calculations with an electronic calculator, nomogram, and pen and paper
Forty anaesthetists calculated maximum permissible doses of eight local anaesthetic formulations for simulated patients three times with three methods: an electronic calculator; nomogram; and pen and paper. Correct dose calculations with the nomogram (85/120) were more frequent than with the calculator (71/120) or pen and paper (57/120), Bayes Factor 4 and 287, p = 0.01 and p = 0.0003, respectively. The rates of calculations at least 120% the recommended dose with each method were different, Bayes Factor 7.9, p = 0.0007: 14/120 with the calculator; 5/120 with the nomogram; 13/120 with pen and paper. The median (IQR [range]) speed of calculation with pen and paper, 38.0 (25.0–56.3 [5–142]) s, was slower than with the calculator, 24.5 (17.8–37.5 [6–204]) s, p = 0.0001, or nomogram, 23.0 (18.0–29.0 [4–100]) s, p = 1 × 10−7. Local anaesthetic dose calculations with the nomogram were more accurate than with an electronic calculator or pen and paper and were faster than with pen and paper.
Pain Assessment in INTensive care (PAINT): an observational study of physician-documented pain assessment in 45 intensive care units in the United Kingdom
Pain is a common and distressing symptom experienced by intensive care patients. Assessing pain in this environment is challenging, and published guidelines have been inconsistently implemented. The Pain Assessment in INTensive care (PAINT) study aimed to evaluate the frequency and type of physician pain assessments with respect to published guidelines. This observational service evaluation considered all pain and analgesia-related entries in patients’ records over a 24-h period, in 45 adult intensive care units (ICUs) in London and the South-East of England. Data were collected from 750 patients, reflecting the practice of 362 physicians. Nearly two-thirds of patients (n = 475, 64.5%, 95%CI 60.9–67.8%) received no physician-documented pain assessment during the 24-h study period. Just under one-third (n = 215, 28.6%, 95%CI 25.5–32.0%) received no nursing-documented pain assessment, and over one-fifth (n = 159, 21.2%, 95%CI 19.2–23.4)% received neither a doctor nor a nursing pain assessment. Two of the 45 ICUs used validated behavioural pain assessment tools. The likelihood of receiving a physician pain assessment was affected by the following factors: the number of nursing assessments performed; whether the patient was admitted as a surgical patient; the presence of tracheal tube or tracheostomy; and the length of stay in ICU. Physician-documented pain assessments in the majority of participating ICUs were infrequent and did not utilise recommended behavioural pain assessment tools. Further research to identify factors influencing physician pain assessment behaviour in ICU, such as human factors or cultural attitudes, is urgently needed.
A consistent message within critical care publications has been that a restrictive transfusion strategy is non-inferior, and possibly superior, to a liberal strategy for stable, non-bleeding critically ill patients. Translation into clinical practice has, however, been slow. Here, we describe the degree of adherence to UK best practice guidelines in a regional network of nine intensive care units within Wessex. All transfusions given during a 2-month period were included (n = 444). Those given for active bleeding or within 24 h of major surgery, trauma or gastrointestinal bleeding were excluded (n = 148). The median (IQR [range]) haemoglobin concentration before transfusion was 73 (68–77 [53–106]) g.l−1, with only 34% of transfusion episodes using a transfusion threshold of < 70 g.l−1. In a subgroup analysis that did not study patients with a history of cardiac disease (n = 42), haemoglobin concentration before transfusion was 72 (68–77 [50–98]) g.l−1, with only 36% of transfusion episodes using a threshold of < 70 g.l−1 (see Fig. 3). Most blood transfusions given to critically ill patients who were not bleeding in this audit used a haemoglobin threshold > 70 g.l−1. The reason why recommendations on transfusion triggers have not translated into clinical practice is unclear. With a clear national drive to decrease usage of blood products and clear evidence that a threshold of 70 g.l−1 is non-inferior, it is surprising that a scarce and potentially dangerous resource is still being overused within critical care. Simple solutions such as electronic patient records that force pause for thought before blood transfusion, or prescriptions that only allow administration of a single unit in non-emergency circumstances may help to reduce the incidence of unnecessary blood transfusions.
An investigation into the effects of real vs. stimulated cases and level of experience on the distribution of visual attention during induction of general anaesthesia
In anaesthesia, patient simulators have been used for training and research. However, insights from simulator-based research may only translate to real settings if the simulation elicits the same behaviour as the real setting. To this end, we investigated the effects of the case (simulated case vs. real case) and experience level (junior vs. senior) on the distribution of visual attention during the induction of general anaesthesia. We recorded eye-tracking data from 12 junior and 12 senior anaesthetists inducing general anaesthesia in a simulation room and in an actual operating room (48 recordings). Using a classification system from the literature, we assigned each fixation to one of 24 areas of interest and classified the areas of interest into groups related to monitoring, manual, and other tasks. Anaesthetists gave more visual attention to monitoring related areas of interest in simulated cases than in real cases (p = 0.001). We observed no effect of the factor case for manual tasks. For other tasks, anaesthetists gave more visual attention to areas of interest related to other tasks in real cases than in simulated cases (p < 0.001). Experience level did not have an effect on the distribution of visual attention. The results showed that there were differences in the distribution of visual attention by between real and simulated cases. Therefore, researchers need to be careful when translating simulation-based research on topics involving visual attention to the clinical environment.
Haemodynamic changes to a midazolam–fentanyl–rocuronium protocol for pre-hospital anaesthesia following return of spontaneous circulation after cardiac arrest
Following the return of spontaneous circulation after out-of-hospital cardiac arrest, neurological dysfunction, airway or ventilatory compromise can impede transport to early percutaneous coronary intervention, necessitating pre-hospital or emergency department anaesthesia to facilitate this procedure. There are no published reports of the ideal induction agents in these patients. We sought to describe haemodynamic changes associated with induction of anaesthesia using a midazolam (0.1 mg.kg−1), fentanyl (2 μg.kg−1) and rocuronium (1 mg.kg−1) regimen developed using expert opinion, and adherence to the protocol by our pre-hospital teams. We performed a retrospective review of haemodynamic data recorded during induction of anaesthesia in patients following return of spontaneous circulation, over a 30-month period. We analysed the changes in systolic blood pressure and heart rate using a repeated-measures design, as well as the rate of new hypotension or hypertension. Sixty-four patients had four consecutive measurements for analysis (one pre-induction and three post-induction). Systolic blood pressure at all three post-induction measurements was significantly lower than the pre-induction value. Heart rate did not differ between any time-points. New episodes of hypotension (systolic pressure <90 mmHg) occurred in four (6%) patients at the first measurement post-induction (95%CI 2–15%) and 10 (16%) at the third measurement (95%CI 8–27%). Three patients (5%; 95%CI 1–13%) had a hypertensive response. The median (IQR[range]) dose of midazolam given at induction was 0.04 (0.03-0.05 [0.01 to 0.10]) mg.kg−1. Adherence to recommended fentanyl and rocuronium doses was high. Overall, systolic blood pressure was reduced following induction of anaesthesia, and systolic pressures < 90 mmHg occurred more often at measurements made later (up to 9 min) after induction. Changes in heart rate, and new hypertension were uncommon.
The analgesic efficacy of pre-operative bilateral erector spinae plane (ESP) blocks in patients having ventral hernia repair
Laparoscopic ventral hernia repair is an operation associated with significant postoperative pain, and regional anaesthetic techniques are of potential benefit. The erector spinae plane (ESP) block performed at the level of the T5 transverse process has recently been described for thoracic surgery, and we hypothesised that performing the ESP block at a lower vertebral level would provide effective abdominal analgesia. We performed pre-operative bilateral ESP blocks with 20–30 ml ropivacaine 0.5% at the level of the T7 transverse process in four patients undergoing laparoscopic ventral hernia repair. Median (range) 24-h opioid consumption was 18.7 mg (0.0–43.0 mg) oral morphine. The highest and lowest median (range) pain scores in the first 24 h were 3.5 (3.0–5.0) and 2.5 (0.0–3.0) on an 11-point numerical rating scale. We also performed the block in a fresh cadaver and assessed the extent of injectate spread using computerised tomography. There was radiographic evidence of spread extending cranially to the upper thoracic levels and caudally as far as the L2–L3 transverse processes. We conclude that the ESP block is a promising regional anaesthetic technique for laparoscopic ventral hernia repair and other abdominal surgery when performed at the level of the T7 transverse process. Its advantages are the ability to block both supra-umbilical and infra-umbilical dermatomes with a single-level injection and its relative simplicity.
Ultrasound-guided approach to nerves (direct vs. tangential) and the incidence of intraneural injection: a cadaveric study
This study evaluated the incidence of nerve puncture and intraneural injection based on the needle approach to the nerve (direct vs. tangential). Two expert operators in regional anaesthesia performed in-plane ultrasound-guided nerve blocks (n = 158) at different levels of the brachial plexus in cadavers, aiming either directly for the nerve (n = 77) or tangentially inferior to the nerve (n = 81). After reaching the outer limit of the nerve, the needle was intentionally advanced approximately 1 mm in both approaches, and 0.2–0.5 ml of saline was injected. Each operator classified (in real time) the needle tip and injectate as intraneural or not. Video clips showing the final position of the needle and the injection were evaluated in the same manner by seven independent expert observers who were blinded to the aims of this study. In addition, 20 injections were performed with ink for histological evaluation. Intraneural injections of saline were observed by the operator in 58% (45/77) of cases using the direct approach and 12% (10/81) of cases using the tangential approach (p < 0.001). The independent observers agreed with the operator in a substantial number of cases (Cohen's kappa index 0.65). Histological studies showed intraneural spread in 83% (5/6) of cases using the direct approach and in 14% (2/14) of cases using the tangential approach (p = 0.007). No intrafascicular injections were observed. There was good agreement between the operators’ assessment and subsequent histological evaluation (Cohen's kappa = 0.89). Simulation of an unintentional/accidental advancement of the needle ‘beyond the edge’ of the nerve suggests significantly increased risk of epineural perforation and intraneural injection when a direct approach to the nerve is used, compared with a tangential approach.
Effects of acute controlled changes in end-tidal carbon dioxide on the diameter of the optic nerve sheath: a transorbital ultrasonographic study in healthy volunteers
Transorbital ultrasonographic measurement of the diameter of the optic nerve sheath is a non-invasive, bed-side examination for detecting raised intracranial pressure. However, the ability of the optic nerve sheath diameter to predict acute changes in intracranial pressures remains unknown. The aim of this study was to examine the dynamic changes of the optic nerve sheath diameter in response to mild fluctuations in cerebral blood volume induced by changes in end-tidal carbon dioxide. We studied 11 healthy volunteers. End-tidal carbon dioxide was controlled by a model-based prospective end-tidal targeting system (RespirAct™). The volunteers' end-tidal carbon dioxide was targeted and maintained for 10 min each at normocapnia (baseline); hypercapnia (6.5 kPa); normocapnia (baseline 1); hypocapnia (3.9 kPa) and on return to normocapnia (baseline 2). A single investigator repeatedly measured the optic nerve sheath diameter for 10 min at each level of carbon dioxide. With hypercapnia, there was a significant increase in optic nerve sheath diameter, with a mean (SD) increase from baseline 4.2 (0.7) mm to 4.8 (0.8) mm; p < 0.001. On return to normocapnia, the optic nerve sheath diameter rapidly reverted back to baseline values. This study confirms dynamic changes in the optic nerve sheath diameter with corresponding changes in carbon dioxide, and their reversibly with normocapnia.