Post-operative atelectasis - a randomised trial investigating a ventilatory strategy and low oxygen fraction during recovery.

BACKGROUND: Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy with a combination of 1) continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and 2) a reduced end-expiratory oxygen concentration during recovery would reduce post-operative atelectasis. METHODS: Sixty patients were randomized into two groups. During anaesthesia induction, inspiratory oxygen fraction (FIO2) was 1.0, and depending on weight, CPAP 6, 7 or 8 cmH2O was applied in both groups via facemask. During maintenance of anaesthesia, a laryngeal mask airway (LMA) was used, and PEEP was 6-8 cmH2O in both groups. Before removal of the LMA, FIO2 was set to 0.3 in the intervention group and 1.0 in the control group. Atelectasis was studied by computed tomography (CT) approximately 14 min post-operatively. RESULTS: In one patient in the group given an FIO2 of 0.3 before removal of the LMA a CT scan could not be performed so the patient was excluded. The area of atelectasis was 5.5, 0-16.9 cm(2) (median and range), and 6.8, 0-27.5 cm(2) in the groups given FIO2 0.3 or FIO2 1.0 before removal of the LMA, a difference that was not statistically significant (P = 0.48). Post-hoc analysis showed dependence of atelectasis on smoking (despite all were clinically lung healthy) and American Society of Anesthesiologists class (P = 0.038 and 0.015, respectively). CONCLUSION: Inducing anaesthesia with CPAP/PEEP and FIO2 1.0 and deliberately reducing FIO2 during recovery before removal of the LMA did not reduce post-operative atelectasis compared with FIO2 1.0 before removal of the LMA.

Improvements in logistics could increase survival after out-of-hospital cardiac arrest in Sweden.

OBJECTIVES: In a review based on estimations and assumptions, to report the estimated number of survivors after out-of-hospital cardiac arrest (OHCA) in whom cardiopulmonary resuscitation (CPR) was started and to speculate about possible future improvements in Sweden. DESIGN: An observational study. SETTING: All ambulance organisations in Sweden. SUBJECTS: Patients included in the Swedish Cardiac Arrest Registry who suffered an OHCA between January 1, 2008 and December 31, 2010. Approximately 80% of OHCA cases in Sweden in which CPR was started are included. INTERVENTIONS: None RESULTS: In 11 005 patients, the 1-month survival rate was 9.4%. There are approximately 5000 OHCA cases annually in which CPR is started and 30-day survival is achieved in up to 500 patients yearly (6 per 100 000 inhabitants). Based on findings on survival in relation to the time to calling for the Emergency Medical Service (EMS) and the start of CPR and defibrillation, it was estimated that, if the delay from collapse to (i) calling EMS, (ii) the start of CPR, and (iii) the time to defibrillation were reduced to <2 min, <2 min, and <8 min, respectively, 300-400 additional lives could be saved. CONCLUSION: Based on findings relating to the delay to calling for the EMS and the start of CPR and defibrillation, we speculate that 300-400 additional OHCA patients yearly (4 per 100 000 inhabitants) could be saved in Sweden.

Oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia.

BACKGROUND: atelectasis is a common consequence of pre-oxygenation with 100% oxygen during induction of anaesthesia. Lowering the oxygen level during pre-oxygenation reduces atelectasis. Whether this effect is maintained during anaesthesia is unknown. METHODS: during and after pre-oxygenation and induction of anaesthesia with 60%, 80% or 100% oxygen concentration, followed by anaesthesia with mechanical ventilation with 40% oxygen in nitrogen and positive end-expiratory pressure of 3 cmH(2) O, we used repeated computed tomography (CT) to investigate the early (0-14 min) vs. the later time course (14-45 min) of atelectasis formation. RESULTS: in the early time course, atelectasis was studied awake, 4, 7 and 14 min after start of pre-oxygenation with 60%, 80% or 100% oxygen concentration. The differences in the area of atelectasis formation between awake and 7 min and between 7 and 14 min were significant, irrespective of oxygen concentration (P<0.05). During the late time course, studied after pre-oxygenation with 80% oxygen, the differences in the area of atelectasis formation between awake and 14 min, between 14 and 21 min, between 21 and 28 min and finally between 21 and 45 min were all significant (P<0.05). CONCLUSION: formation of atelectasis after pre-oxygenation and induction of anaesthesia is oxygen and time dependent. The benefit of using 80% oxygen during induction of anaesthesia in order to reduce atelectasis diminished gradually with time.

Population pharmacokinetics of sevoflurane in conjunction with the AnaConDa: toward target-controlled infusion of volatiles into the breathing system.

BACKGROUND: The Anesthetic Conserving Device (AnaConDa) uncouples delivery of a volatile anesthetic (VA) from fresh gas flow (FGF) using a continuous infusion of liquid volatile into a modified heat-moisture exchanger capable of adsorbing VA during expiration and releasing adsorbed VA during inspiration. It combines the simplicity and responsiveness of high FGF with low agent expenditures. We performed in vitro characterization of the device before developing a population pharmacokinetic model for sevoflurane administration with the AnaConDa, and retrospectively testing its performance (internal validation). MATERIALS AND METHODS: Eighteen females and 20 males, aged 31-87, BMI 20-38, were included. The end-tidal concentrations were varied and recorded together with the VA infusion rates into the device, ventilation and demographic data. The concentration-time course of sevoflurane was described using linear differential equations, and the most suitable structural model and typical parameter values were identified. The individual pharmacokinetic parameters were obtained and tested for covariate relationships. Prediction errors were calculated. RESULTS: In vitro studies assessed the contribution of the device to the pharmacokinetic model. In vivo, the sevoflurane concentration-time courses on the patient side of the AnaConDa were adequately described with a two-compartment model. The population median absolute prediction error was 27% (interquartile range 13-45%). CONCLUSION: The predictive performance of the two-compartment model was similar to that of models accepted for TCI administration of intravenous anesthetics, supporting open-loop administration of sevoflurane with the AnaConDa. Further studies will focus on prospective testing and external validation of the model implemented in a target-controlled infusion device.

Cognitive dysfunction after minor surgery in the elderly.

BACKGROUND: Major surgery is frequently associated with postoperative cognitive dysfunction (POCD) in elderly patients. Type of surgery and hospitalization may be important prognostic factors. The aims of the study were to find the incidence and risk factors for POCD in elderly patients undergoing minor surgery. METHODS: We enrolled 372 patients aged greater than 60 years scheduled for minor surgery under general anesthesia. According to local practice, patients were allocated to either in- (199) or out-patient (173) care. Cognitive function was assessed using neuropsychological testing preoperatively and 7 days and 3 months postoperatively. Postoperative cognitive dysfunction was defined using Z-score analysis. RESULTS: At 7 days, the incidence (confidence interval) of POCD in patients undergoing minor surgery was 6.8% (4.3-10.1). At 3 months the incidence of POCD was 6.6% (4.1-10.0). Logistic regression analysis identified the following significant risk factors: age greater than 70 years (odds ratio [OR]: 3.8 [1.7-8.7], P = 0.01) and in- vs. out-patient surgery (OR: 2.8 [1.2-6.3], P = 0.04). CONCLUSIONS: Our finding of less cognitive dysfunction in the first postoperative week in elderly patients undergoing minor surgery on an out-patient basis supports a strategy of avoiding hospitalization of older patients when possible.

Ceasing routine use of nitrous oxide-a follow up.

BACKGROUND: The role of nitrous oxide in modern anaesthesia is questioned. The routine use of nitrous oxide was almost completely stopped in our department after November 1, 2000, and we now report some consequences. METHODS: Staff completed a questionnaire after 6 months, and we analysed the use of hypnotics and opioids after 12 months. The cost of drugs for the year after stopping nitrous oxide was compared with the cost 2 yr before. RESULTS: Less than half of the 55 staff members who answered the questionnaire used nitrous oxide in the 6 months after the stop, and they did so on only a few occasions. Half of the staff members thought the benefit of nitrous oxide was small. Most supported the change. The use of opioids was stable during the study period, and there was an annual increase of 12-14% in the use of hypnotics during the 3 yr. CONCLUSIONS: The staff questionnaire showed a strong acceptance of the new policy, and the use of other anaesthetic agents did not increase as expected. Has the value of nitrous oxide been overestimated?

The sevoflurane saving capacity of a new anaesthetic agent conserving device compared with a low flow circle system.

BACKGROUND: An anaesthetic agent conserving device (ACD) has been added to a Bain system to approach the agent-saving capacity of a low flow circle system. METHODS: Randomly selected ASA physical status I patients received a standardized anaesthetic with sevoflurane in air/O2 through either a circle system with 1.5 l/min fresh gas flow (n = 8), or through a Bain system with an added ACD with fresh gas flow 4.4-6.4 l/min (n = 8). A target controlled infusion of remifentanil was used for analgesia. RESULTS: The median sevoflurane consumption was 19.7 and 22.0 ml/MAC/h with the low flow circle system and the Bain system + ACD, respectively (P=0.10, Mann-Whitney U-test), or when adjusted for weight 0.25 and 0.28 ml/MAC/h/kg (P=0.26, Mann-Whitney U-test). CONCLUSION: The expenditure of sevoflurane with a Bain system + ACD was close to that in a circle system with 1.5 l/min fresh gas flow. It is thereby possible to use sevoflurane to all its potential, performing for example rapid alterations in end-tidal concentration using high fresh gas flows by combining a Bain system with an ACD. Although the price is not decided for this not yet commercially available device, a potential for a lower cost exists. Additionally, there will be no concerns of toxic compounds produced in the absorber.

Intraoperative awareness: detected by the structured Brice interview?

BACKGROUND: Awareness is a rare complication in general anesthesia, but its consequences are stressful. Efforts must be undertaken to prevent, diagnose, and, if occurring, treat it. The incidence of awareness is higher following anesthesia involving the use of muscle relaxants. As a part of a quality assurance program at our short-stay surgery all patients exposed to general anesthesia are routinely subjected to a Brice interview, which aims to evaluate our standard anesthetic technique regarding awareness. METHODS: The Brice interview was used prospectively in 5216 patients given a propofol/opioid anesthetic for day-case or short-stay surgery. Neuromuscular blocks were used only for surgical needs, not routinely. All patients were interviewed on discharge from the recovery room. A second interview, according to Brice, was undertaken by telephone 3-7 days later in the case of a notable intraoperative event, or otherwise after postoperative patient complaints. All patients were also interviewed by telephone 1-2 days postoperatively. RESULTS: None of the patient interviews indicated awareness. This was also the case in five non-relaxed patients who had an incident of light anesthesia with eye opening and gross motor response without forewarning. Neuromuscular blockade was used in 7% of patients. DISCUSSION: We were unable to detect intraoperative awareness. The anesthetic regimen, including minimal use of muscle relaxants, might be beneficial for awareness prevention. Alternatively, the diagnostic power, the timing of the Brice interview, or the number of interviews performed may be questioned.

A new device to reduce the consumption of a halogenated anaesthetic agent.

We report the first clinical application of a new anaesthetic agent-saving device. The principles of a heat-moisture exchanger have been further developed to create a device that reduces inhalational agent consumption. Sixteen patients were randomly allocated to receive isoflurane through either a vaporiser or through the agent-saving device. A coaxial Mapleson D system (Bain) was used in both groups. A standard ventilatory setting was used, aiming for normocapnia. Mean (SD) isoflurane consumption was 24.5 (2.8) ml x MAC-hour(-1) with the vaporiser, compared with 15.2 (3.0) ml x MAC-hour(-1) with the new device (p < 0.05). This corresponded to a 40% saving in the consumption of isoflurane. The amount of isoflurane that was scavenged to the atmosphere was reduced by an average of 55%.

Unintentional hypotension from lidocaine infiltration during orthognathic surgery and general anaesthesia.

BACKGROUND: A probable causal relationship between submucosal infiltration of lidocaine, with adrenaline 12.5 microg x mL(-1), and untoward arterial hypotension during general anaesthesia for orthognathic surgery was investigated in two parts. METHODS: The first part of the study was open and non-randomised. The patients served as their own controls, receiving 5.4 mL saline/adrenaline before mandibular or maxillary surgery on the first side of the jaw and 5.4 mL lidocaine (2%)/adrenaline on the other side a minimum of 40 min later. Nine patients received in total 11 pairs of injections of the study drugs. In Part Two, 50 mg or 100 mg of lidocaine with adrenaline was infiltrated in an observer-blinded and randomised order in either side of the jaw in another 13 patients. RESULTS: A significant and dose-dependent blood pressure decrease was observed after infiltration of lidocaine/adrenaline, but not after saline/adrenaline. The heart rate increased significantly after both types of injections, most pronounced after saline/adrenaline. Mean arterial blood pressure decreased on average 11% and 23% with lidocaine 50 mg and 100 mg, respectively (P<0.05, ANOVA). CONCLUSION: Lidocaine induced dose-dependent arterial hypotension when combined with a defined level of general anaesthesia. The causative mechanism is unclear.

The Combitube for failed intubation--instructions for use.

The Combitube is easy to use, but it might be years between occasions for use, and most likely the situation is stressful. Then, normal routines might be forgotten. We illustrate that the Combitube instructions would be improved by including a recommendation of cuff pressure monitoring.

[Dosage of anesthetics--a tricky question]. / Narkosdosering--en svår balansgång.

The optimal dosage of anaesthetic agents may be difficult. Not only does the intensity of surgical stimuli vary during a surgical procedure, but drug sensitivity varies between subjects exposed to comparable stimuli. Moreover, clinically monitored body reactions do not always reflect the balance between central nervous system effects of the surgical stimuli and of the anaesthetic agent. Therefore, the specialist in anaesthesiology requires access to additional methods of monitoring to enable dosage to be optimised for each patient, minute by minute, thus improving the chances of maintaining an appropriate depth of anaesthesia. Two electro-encephalographic techniques are presented in the article, and aspects of under- and over-dosage of anaesthetic agents are discussed.

Evidence of cerebral dysfunction associated with isoflurane- or propofol based anaesthesia for orthognathic surgery, as assessed by biochemical and neuropsychological methods.

A relationship has previously been described between individual mean isoflurane concentrations and the release of a marker of neuronal injury, adenylate kinase (AK), into the cerebrospinal fluid (CSF) after anaesthesia and orthognathic surgery. Likewise, reduced mental performance has been detected. Twenty-nine patients scheduled for orthognathic surgery were assigned to isoflurane- or propofol based anaesthesia, which was adjusted to a defined level with the aid of processed EEG and quantitative surface EMG. In the case of a mean arterial pressure (MAP) < 50 mmHg a phenylephrine infusion was started to keep the MAP above the minimal level, otherwise no regard was paid to the blood pressure, which never exceeded normal values. A lumbar puncture for CSF sampling was performed approximately 20 h postoperatively. The CSF sample was analysed for AK activity. Neuropsychological tests were performed the day prior to surgery and again in the period 4-8 weeks postoperatively. Five patients were re-examined by psychometry 12-30 months later. A release of AK into CSF was confirmed, equal in both groups. Correlation with the anaesthetic dose given was poor. Five patients from each group failed significantly in the postoperative neuropsychological tests. They differed in several demographic respects from the others. When five of the failed patients were re-examined 12-30 months later, three patients still performed poorly in the tests. Biochemical and neuropsychological disturbances were recorded in several patients objected to orthognathic surgery. The underlying mechanisms are unclear, including the role of the anaesthetic drugs or surgery itself.

Cerebral normoxia in the rhesus monkey during isoflurane- or propofol-induced hypotension and hypocapnia, despite disparate blood-flow patterns. A positron emission tomography study.

BACKGROUND: Due to a few reports of cerebral dysfunction in connection with isoflurane-induced hypotension and concomitant hypocapnia, positron emission tomography (PET) was used to measure cerebral oxygenation and blood flow during similar conditions with isoflurane or propofol. METHODS: The short-lived radionuclide 15O was used for measurement of cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF) and oxygen extraction ratio (OER) regionally in rhesus monkeys during normotensive/normocapnic and hypotensive/hypocapnic conditions, mean arterial pressure 100-110 and 50-65 mmHg and PaCO2 4.4-5.4 and 3.4-4.4 kPa, respectively. Isoflurane or propofol anaesthesia was given (n = 4 in both groups), supported with 70% nitrous oxide and preceded by ketamine anaesthesia (baseline). RESULTS: PET revealed wide variations in CBF between regions during isoflurane anaesthesia, particularly in comparison with propofol anaesthesia, while rCMRO2 decreased globally in a dose-dependent manner during both isoflurane and propofol anaesthesia. The metabolism-flow coupling was intact during propofol but not during isoflurane anaesthesia. Hypotension reduced rCBF, and rOER increased globally with both study drugs when changing from normo- to hypotension. However, this rOER increase was not significant when using PaCO2 as a covariate, and rOER was never above an arbitrary limit for hypoxia of 70%. Thus, hypocapnia, rather than hypotension, was responsible for the somewhat higher rOER measured. CONCLUSION: PET indicated adequate cerebral oxygenation during isoflurane and propofol anaesthesia, despite disparate blood-flow patterns. Hypotension and concomitant moderate hyperventilation reduced rCBF, but did not result in hypoxia.

Low frequency of adenylate kinase release into cerebrospinal fluid during balanced, normotensive anaesthesia and a non-orthognathic surgical procedure.

Activity of strictly intracellular enzymes in the cerebrospinal fluid (CSF) may indicate leakage from dysfunctional brain cells. Increased activity of adenylate kinase (AK) in the CSF is indicative of brain cell injury arising from several sources, among them orthognathic surgery. The mechanism in the latter case is obscure, but the use of an oscillating saw which generates vibrations, and the site of surgery close to the brain may be contributing factors. Anaesthesia may also play a role. In the present study, CSF-AK activity was measured after hysterectomy and was compared with activity after orthognathic surgery in two other studies. Four of 19 patients (21%) in the present study expressed pathological activity, compared with 34 of 47 (72%) orthognathic patients in the two other studies. No firm conclusion may be drawn from historical comparisons, and the difference in activity seen between the two types of surgery might not necessarily be the result of surgical factors. Until this is investigated further, however, we conclude that there may be a difference in postoperative CSF-AK activity between orthognathic and lower abdominal surgery.