Associations Between Age and Dosing of Volatile Anesthetics in 2 Academic Hospitals

BACKGROUND

The inverse relationship between age and dose requirement for potent volatile anesthetics is well established, but the question of whether anesthetic providers consider this relationship in practice remains unanswered. We sought to determine whether there is an association between patient age and the mean dose of volatile anesthetic delivered during maintenance of anesthesia.

METHODS

This was a retrospective cross-sectional study of patients receiving a single potent volatile anesthetic at 2 academic hospitals using data recorded in an anesthesia information management system. Multivariate linear models were constructed at each hospital to examine the relationship between age and mean minimum alveolar concentration (MAC) fraction delivered during the maintenance of anesthesia.

RESULTS

A total of 7878 cases at the 2 hospitals were included for analysis. For patients aged <65 years, we observed decreasing doses of volatile anesthetics as age increased. Per decade, mean delivered MAC fraction decreased by an estimated 1.8% (95% confidence interval, 1.5-2.2, P < 0.0001), smaller than the 6.7% decrease suggested by previous studies of human anesthetic requirements. At age >65 years, the magnitude of the inverse association between age and MAC fraction was higher (3.8% decrease per decade; 95% confidence interval, 2.9-4.7).

CONCLUSIONS

Increasing age is associated with decreased absolute doses of potent volatile anesthetics, an association that seems to strengthen as patients enter the geriatric age range. The observed decreases in absolute anesthetic dose were less than those predicted by previous research and therefore represent an overall increase in "age-adjusted dose" as patients grow older.

Intraoperative burst suppression is associated with postoperative delirium following cardiac surgery: a prospective, observational study

Background

Postoperative delirium (POD) occurs frequently after cardiac surgery and is associated with increased morbidity and mortality. We analysed whether perioperative bilateral BIS monitoring may detect abnormalities before the onset of POD in cardiac surgery patients.

Methods

In a prospective observational study, 81 patients undergoing cardiac surgery were included. Bilateral Bispectral Index (BIS)-monitoring was applied during the pre-, intra- and postoperative period, and BIS, EEG Asymmetry (ASYM), and Burst Suppression Ratio (BSR) were recorded. POD was diagnosed according to the Confusion Assessment Method for the Intensive Care Unit, and patients were divided into a delirium and non-delirium group.

Results

POD was detected in 26 patients (32%). A trend towards a lower ASYM was observed in the delirium group as compared to the non-delirium group on the preoperative day (ASYM = 48.2 ± 3.6% versus 50.0 ± 4.7%, mean ± sd, p = 0.087) as well as before induction of anaesthesia, with oral midazolam anxiolysis (median ASYM = 49.5%, IQR [47.4;51.5] versus 50.6%, IQR [49.1;54.2], p = 0.081). Delirious patients remained significantly (p = 0.018) longer in a burst suppression state intraoperatively (107 minutes, IQR [47;170] versus 44 minutes, IQR [11;120]) than non-delirious patients. Receiver operating analysis revealed burst suppression duration (area under the curve = 0.73, p = 0.001) and BSR (AUC = 0.68, p = 0.009) as predictors of POD.

Conclusions

Intraoperative assessment of BSR may identify patients at risk of POD and should be investigated in further studies. So far it remains unknown whether there is a causal relationship or rather an association between intraoperative burst suppression and the development of POD.

Trial registration

clinicaltrials.gov NCT01048775

The psychological and neurocognitive consequences of critical illness. A pragmatic review of current evidence

Mortality rates alone are no longer a sufficient guide to quality of care. Due to medical advances, patients are surviving for longer following critical illness and major surgery; therefore, functional outcomes and long-term quality of life are of increasing consequence. Post-operative cognitive dysfunction has been acknowledged as a complication following anaesthesia for many years, and interest in persistent cognitive dysfunction following a critical illness is growing. Psychological and neurocognitive sequelae following discharge from intensive care are acknowledged to occur with sufficient significance to have recently coined the term 'the post-intensive care syndrome'. Rehabilitation following critical illness has been highlighted as an important goal in recently published national UK guidelines, including the need to focus on both physical and non-physical recovery. Neuropsychological and cognitive consequences following anaesthesia and critical illness are significant. The exact pathophysiological mechanisms linking delirium, cognitive dysfunction and neuropsychological symptoms following critical illness are not fully elucidated but have been studied elsewhere and are outside the scope of this article. There is limited evidence as yet for specific peri-operative preventative strategies, but early management and rehabilitation strategies following intensive care discharge are now emerging. This article aims to summarise the issues and appraise current options for management, including both neuroprotective and neurorehabilitative strategies in intensive care.

Emergence from general anaesthesia and evolution of delirium signs in the post-anaesthesia care unit

BACKGROUND

Emergence from anaesthesia is often accompanied by signs of delirium, including fluctuating mental status and inattention. The evolution of these signs of delirium requires investigation since delirium in the post-anaesthesia care unit (PACU) may be associated with worse outcomes.

METHODS

Adult patients emerging from anaesthesia were assessed for agitated emergence in the operating room using the Richmond Agitation-Sedation Scale (RASS). The Confusion Assessment Method for the Intensive Care Unit was then used to evaluate delirium signs at PACU admission and during PACU stay at 30 min, 1 h, and discharge. Signs consistent with delirium were classified as hyperactive vs hypoactive based upon a positive CAM-ICU assessment and the concomitant RASS score. Multivariable logistic regression was utilized to assess potential risk factors for delirium during PACU stay including age, American Society of Anesthesiologists classification, and opioid and benzodiazepine exposure.

RESULTS

Among 400 patients enrolled, 19% had agitated emergence. Delirium signs were present at PACU admission, 30 min, 1 h, and PACU discharge in 124 (31%), 59 (15%), 32 (8%), and 15 (4%) patients, respectively. In patients with delirium signs, hypoactive signs were present in 56% at PACU admission and in 92% during PACU stay. Perioperative opioids were associated with delirium signs during PACU stay (P=0.02).

CONCLUSIONS

A significant proportion of patients develop delirium signs in the immediate postoperative period, primarily manifesting with a hypoactive subtype. These signs often persist to PACU discharge, suggesting the need for structured delirium monitoring in the PACU to identify patients potentially at risk for worse outcomes in the postoperative period.

General anesthetic and the risk of dementia in elderly patients: current insights

In this review, we aim to provide clinical insights into the relationship between surgery, general anesthesia (GA), and dementia, particularly Alzheimer’s disease (AD). The pathogenesis of AD is complex, involving specific disease-linked proteins (amyloid-beta [Aβ] and tau), inflammation, and neurotransmitter dysregulation. Many points in this complex pathogenesis can potentially be influenced by both surgery and anesthetics. It has been demonstrated in some in vitro, animal, and human studies that some anesthetics are associated with increased aggregation and oligomerization of Aβ peptide and enhanced accumulation and hyperphosphorylation of tau protein. Two neurocognitive syndromes that have been studied in relation to surgery and anesthesia are postoperative delirium and postoperative cognitive dysfunction, both of which occur more commonly in older adults after surgery and anesthesia. Neither the route of anesthesia nor the type of anesthetic appears to be significantly associated with the development of postoperative delirium or postoperative cognitive dysfunction. A meta-analysis of case-control studies found no association between prior exposure to surgery utilizing GA and incident AD (pooled odds ratio =1.05, P=0.43). The few cohort studies on this topic have shown varying associations between surgery, GA, and AD, with one showing an increased risk, and another demonstrating a decreased risk. A recent randomized trial has shown that patients who received sevoflurane during spinal surgery were more likely to have progression of preexisting mild cognitive impairment compared to controls and to patients who received propofol or epidural anesthesia. Given the inconsistent evidence on the association between surgery, anesthetic type, and AD, well-designed and adequately powered studies with longer follow-up periods are required to establish a clear causal association between surgery, GA, and AD.

Neurological complications of surgery and anaesthesia

Injury to the central and peripheral nervous systems is often permanent. As such, adverse neurological outcomes of surgery and anaesthesia can be devastating for patients and their families. In this article, we review the incidence, risk factors, outcomes, prevention, and treatment of a number of important neurological complications in the perioperative period.

Perioperative management in order to minimise postoperative delirium and postoperative cognitive dysfunction: Results from a Swedish web-based survey

Cognitive side-effects such as emergence agitation (EA), postoperative delirium (POD) and postoperative cognitive dysfunction (POCD) are not infrequently complicating the postoperative care especially in elderly and fragile patients. The aim of the present survey was to gain insight regarding concern and interest in prevention and treatment strategies for postoperative delirium and dysfunction, and the use of EEG-based depth-of-anaesthesia monitoring possibly reducing the risk for cognitive side effects among anaesthesia personnel.

METHODS

A web-based validated questionnaire was sent to all Swedish anaesthesiologists and nurse anaesthetists during summer 2013. The questionnaire consisted of 3 sections, subjective preferences, routines and practices related to the perioperative handling of EA, POD, POCD.

RESULTS

The response rate was 52%. Cardiovascular/pulmonary risks where assessed as importance by 98, 97% of responders while 69% considered the risk of neurocognitive side-effects important. When asked explicitly around cognitive side-effects 89%, 37% and 44% assessed awareness, POC and POD respectively of importance. EEG-based depth-of-anaesthesia monitors were used in 50% of hospitals. The responders were not convinced about the benefits of such monitors even in at-risk patients. Structured protocols for the management of postoperative cognitive side-effects were available only in few hospitals.

CONCLUSION

Swedish anaesthesia personnel are concerned about the risk of postoperative cognitive side-effects but are more concerned about cardiovascular/pulmonary risks, pain, PONV and the rare event of awareness. Most respondents were not convinced about the use of depth-of-anaesthesia monitors. There is a need to improve knowledge around risk factors, prevention and management of postoperative cognitive side effects.

A pilot study for a prospective, randomized, double-blind trial of the influence of anesthetic depth on long-term outcome

BACKGROUND

Deep general anesthesia has been associated with increased mortality in 5 observational studies. The association may be causal or an epiphenomenon due to increased anesthetic sensitivity in high-risk patients. We conducted a pilot study to assess the feasibility of performing a definitive randomized controlled trial. The aims of the study were to determine whether anesthetic depth targeting in a high-risk group was feasible and to document anesthetic doses and arterial blood pressures associated with "deep" and "light" general anesthesia.

METHODS

ASA physical status III and IV patients, aged ≥60 years, having surgery lasting ≥2 hours, with expected hospital stay ≥2 days, and receiving general anesthesia were randomly allocated to a Bispectral Index (BIS) or spectral entropy (SE) target of 35 ("low" group) or 50 ("high" group). The primary end point was mean BIS or SE. Secondary end points were postanesthesia care unit length of stay and pain scores, quality of recovery score, hospital length of stay, postoperative complications, and death. A composite end point of postoperative complications (pneumonia, myocardial infarction, stroke, pulmonary embolism, heart failure, and death) was determined at 1 year.

RESULTS

One hundred twenty-five patients were recruited. The mean of the median BIS/SE values for each patient during the maintenance phase of anesthesia in the low and high groups was significantly different: 39 vs 48 (mean difference 8 [95% confidence interval {CI95}, 6 to 10], P < 0.001). There was also a significant difference in mean volatile anesthetic administration (minimum alveolar concentration): 0.98 vs 0.64 (mean difference -0.35 [CI95, -0.44 to -0.26], P < 0.001) and target propofol concentrations: 4.0 vs 3.1 μg/mL (mean difference -0.8 [CI95, -1.2 to -0.3], P = 0.004). Intraoperative mean arterial blood pressures were similar (85 vs 87 mm Hg; mean difference 2 [CI95, -2 to 6], P = 0.86), and there were no differences in short-term recovery characteristics or hospital length of stay. There was a significant difference in the incidence of wound infection at 30 days (13% vs 3%; risk difference -10% [CI95, -21 to -0.1], P = 0.04). At 1 year, the composite rates of complications in the low and high groups were 28% and 17% (risk difference -11 [CI95, -25 to 4], P = 0.15) and mortality rates were 12% and 9%, respectively (risk difference -2 [CI95, -14 to 9], P = 0.70).

CONCLUSIONS

This pilot study demonstrated that depth of anesthesia targeting with BIS or SE was achievable in a high-risk population with adequate separation of processed electroencephalogram monitor targets. The expected incidence of postoperative complications and mortality occurred. We conclude that a large, multicenter, randomized controlled trial is feasible.

Postoperative delirium in a substudy of cardiothoracic surgical patients in the BAG-RECALL clinical trial

BACKGROUND

Postoperative delirium in the intensive care unit (ICU) is a frequent complication after cardiac or thoracic surgery and is associated with increased morbidity and mortality.

METHODS

In this single-center substudy of the BAG-RECALL trial (NCT00682825), we screened patients after cardiac or thoracic surgery in the ICU twice daily for delirium using the Confusion Assessment Method for the ICU. The primary outcome was the incidence of delirium in patients who had been randomized to intraoperative Bispectral Index (BIS)-guided and end-tidal anesthetic concentration-guided depth of anesthesia protocols. As a secondary analysis, a Bayesian stochastic search variable selection strategy was used to rank a field of candidate risk factors for delirium, followed by binary logistic regression.

RESULTS

Of 310 patients assessed, 28 of 149 (18.8%) in the BIS group and 45 of 161 (28.0%) in the end-tidal anesthetic concentration group developed postoperative delirium in the ICU (odds ratio 0.60, 95% confidence interval, 0.35-1.02, P= 0.058). Low average volatile anesthetic dose, intraoperative transfusion, ASA physical status, and European System for Cardiac Operative Risk Evaluation were identified as independent predictors of delirium.

CONCLUSIONS

A larger randomized study should determine whether brain monitoring with BIS or an alternative method decreases delirium after cardiac or thoracic surgery. The association between low anesthetic concentration and delirium is a surprising finding and could reflect that patients with poor health are both more sensitive to the effects of volatile anesthetic drugs and are also more likely to develop postoperative delirium. Investigation of candidate methods to prevent delirium should be prioritized in view of the established association between postoperative delirium and adverse patient outcomes.

Cognitive dysfunction following desflurane versus sevoflurane general anesthesia in elderly patients: a randomized controlled trial

As life expectancy increases, more patients ≥65 years undergo general anesthesia. Anesthetic agents may contribute to postoperative cognitive dysfunction, and incidence may differ with anesthetic agents or intraoperative anesthesia depth. Responses to anesthetic adjuvants vary among elderly patients. Processed electroencephalography guidance of anesthetic may better ensure equivalent cerebral suppression. This study investigates postoperative cognitive dysfunction differences in elderly patients given desflurane or sevoflurane using processed electroencephalography guidance.

IRB approved, randomized trial enrolled consenting patients ≥65 years scheduled for elective surgery requiring general anesthesia ≥120 minute duration. After written informed consent, patients were randomly assigned to sevoflurane or desflurane. No perioperative benzodiazepines were administered. Cognitive impairment was measured by an investigator blinded to group assignment using mini-Mental Status Examination (MMSE) at baseline; 1, 6, and 24 hours after the end of anesthesia. Mean arterial pressure was maintained within 20% of baseline. Anesthetic dose was adjusted to maintain moderate general anesthesia per processed electroencephalograpy (Patient State Index 25 to 50). The primary outcome measure was intergroup difference in MMSE change 1 hour after anesthesia (median; 95% confidence interval).

110 patients consented; 26 were not included for analysis (no general anesthesia; withdrew consent; baseline MMSE abnormality; inability to perform postoperative MMSE; data capture failure); 47 sevoflurane and 37 desflurane were analyzed. There were no significant differences in patient characteristics; intraoperative mean blood pressure (desflurane 86.4; 81.3 to 89.6 versus sevoflurane 82.5; 80.2 to 86.1 mmHg; p = 0.42) or Patient State Index (desflurane 41.9; 39.0 to 44.0 versus sevoflurane 41.0; 37.5 to 44.0; p = 0.60) despite a lower MAC fraction in desflurane (0.82; 0.77 to 0.86) versus sevoflurane (0.96; 0.91 to 1.03; p < 0.001). MMSE decreased 1 hour after anesthesia (p < 0.001). The decrease at one hour was larger in sevoflurane (−2.5; −3.3 to −1.8) than desflurane (−1.3; −2.2 to −0.5; p = 0.03). MMSE returned to baseline by 6 hours after anesthesia.

AAI-guided anaesthesia is associated with lower incidence of 24-h MMSE < 25 and may impact the IL-6 response

INTRODUCTION

Trauma stress and neuro-inflammation caused by surgery/anaesthesia releases cytokines. This study analysed impact of Auditory Evoked Potential Index (AAI) depth-of-anaesthesia titration on the early plasma IL-6 release after eye surgery under general anaesthesia.

METHOD

This is a subgroup analysis of a prospective randomized study on the effect of auditory evoked potential guided anaesthesia for eye surgery. Plasma IL-6 levels taken before, 5 and 24 h after end of surgery from 450 patients undergoing elective ophthalmic surgery under desflurane anaesthesia were analysed. Minimal mental state examination (MMSE) was also tested at 24-h.

RESULTS

IL- 6 increased significantly at both 5 and further at 24 h after surgery (3.2, 4.5 and 5.1 base-line, 5 and 24-h respectively), the IL-6 increase showed different patterns between the 2 groups; IL-6 was significantly increased in the control group of patients between preoperative baseline and 24 h after surgery (p = 0.008) also between 5 h and 24 h, (p = 0.006) after surgery while the AAI-group had only minor non-significant changes. The 18 patients that showed a 24-h MMSE score less than 25 had a significant higher 24-h IL-6 compared to the 390 patients with a MMSE score > 24 (p = 0.002).

CONCLUSION

The IL-6 increase after surgery was less pronounced in patients where anaesthesia was titrated by AAI compared to anaesthesia adjusted on clinical signs only. IL-6 were also found to be higher in patients with a MMSE < 25 at 24-h. Further studies are warranted evaluating the role of depth of anaesthesia monitoring on the risk for early cognitive impairment and neuro-inflammation.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NA/study were conducted between January 2005-April 2008.