Fj Smith

Attention and working memory in resident anaesthetists after night duty: group and individual effects

Aims: To investigate the effects of a single period of night duty on measures of attention and working memory in a group of residents (registrars) in anaesthesiology. Emphasis was placed on individual deficits using a reference point of the equivalent effect of a blood alcohol concentration (BAC) >0.05% determined by other researchers. Methods: There were 33 subjects aged 26–42 years. Night duty was performed on a weekly basis. Baseline assessments were conducted at either 08 15 or 08 55 preceding night duty and repeated 24–25 hours later, just after the completion of duty. Questionnaires included items regarding duration of sleep and the Stanford Sleepiness Scale. A battery of four reaction time (RT) tasks of increasing difficulty, lasting approximately 35 minutes, was administered on a personal computer. These ranged from simple RT to progressively more complex RT tasks incorporating working memory. A significant change was regarded as >15% deterioration in respect of speed or accuracy. Results: The mean duration of sleep preceding night duty was 7.04 hours and 1.66 hours during the period of night duty. Intergroup comparisons revealed significant prolongation in mean response speed in the first three tests. Mean accuracy was significantly reduced only in respect of the two more complex tests. A >15% deterioration in response speed occurred in up to 30% of subjects on a single task, rising to 52% (17/33) overall. Deterioration occurred in a patchy distribution in most subjects, involving no more than one or two of the four tasks. As regards accuracy, the prevalence of deterioration increased with task complexity. Conclusions: Results are in general agreement with previous group analyses. A new dimension was added by the analysis of a broad spectrum of individual response to sleep deprivation. The effects of sleep loss in residents cannot be overlooked, even in a relatively benign work schedule.

Entropy of the electroencephalogram as applied in the M-Entropy S/5™ Module (GE Healthcare) during increases in nitrous oxide and constant sevoflurane concentrations

Abstract Background: It has been suggested that spectral entropy of the electroencephalogram as applied in the M-Entropy S/5TM Module (GE Healthcare) does not detect the effects of nitrous oxide (N2O). The aim of this study was to investigate the effect on entropy by graded increases in N2O concentrations in the presence of a constant concentration of sevoflurane, in the absence of surgical stimulation. Method: This single-blind, randomised study was conducted at an altitude of approximately 1 400 m. Patients received sevoflurane 2% (1.7% at sea level) and N2O, at end-tidal concentrations of 0%, 10%, 20%, 30%, 40%, 50%, 60% or 70% (equivalent to 8.5%, 17%, 25.5%, 34%, 42.6%, 51.1% and 59.6% at sea level). Entropy was measured before, during and after N2O administration. The absolute changes and ratios of entropy relative to the baseline were calculated. Between- and within-group comparisons were made using analysis of variance and covariance. Results: None of the entropy variables differed significantly within and between groups before and after N2O administration. Within-group analysis revealed that entropy during N2O administration was significantly lower than before or after N2O administration (P < 0.007). While a minor clinical but statistically significant linear relationship was observed between increasing N2O concentration and decreasing entropy from N2O 0% to 60%, a steeper and clinically important decrease (relative change > 20%) was noted at N2O > 60% (> 51% at sea level). Conclusions: The M-Entropy Module S/5TM responds to increasing concentrations of N2O in the presence of 2% (1.7% at sea level) sevoflurane, in the absence of surgical stimulation. There is a linear relationship between increasing N2O concentrations and decreasing entropy with a steep and clinically important decrease at N2O > 60% (> 51% at sea level). The influence of ambient pressure on the partial pressures, which determine the effects of anaesthetic agents, must be taken into account.

The effect of positive end-expiratory pressure on pulse pressure variation

Abstract Objectives: To determine the effect of different levels of positive end-expiratory pressure (PEEP) on pulse pressure variation (PPV). Design: An observational study. Setting: Operating theatres of a tertiary training hospital. Subjects: Ventilated patients who required intra-arterial blood pressure monitoring. Outcome measures: PPV during different levels of PEEP. Method: Patients were anaesthetised by means of a standard technique and ventilated with a tidal volume of 9 ml/kg ideal body mass. The PPV was calculated at PEEP levels of 2, 5, 8 and 10 cmH2O. PPV was compared at the various PEEP levels. Results: PPV at a PEEP of 8 cmH2O and 10 cmH2O was significantly larger than that at 2 cmH2O (p-value < 0.001). PPV at a PEEP of 10 cmH2O was significantly larger than that at 8 cmH2O (p-value < 0.001). PPV at a PEEP of 8 cmH2O was larger than that at 5 cmH2O (p-value = 0.002). PPV at a PEEP of 2 and 5 cmH2O did not differ significantly (p-value = 0.194). Conclusion: We have demonstrated that, in patients with normal lungs, PEEP has a significant influence on PPV. PPV may be overestimated if PEEP ≥ 8 cmH2O is applied in patients who are ventilated with a tidal volume of 9 ml/kg. It is recommended that in patients with healthy lungs PPV should be measured at a standardised PEEP of ≤ 5 cmH2O.

Attenuation of the haemodynamic response to placement of the Mayfield skull pin head holder: alfentanil versus scalp block

Summary Introduction: Application of the Mayfield clamp causes a significant haemodynamic response. Different methods have been used to attenuate this response. We compared two of these methods, namely alfentanil bolus (Group A) and nerve block of the scalp (Group B). METHOD: Twenty-two patients entered the study. Anaesthesia was standardised using thiopental, sufentanil, vecuronium, isoflurane, oxygen and air. Group A patients received alfentanil 10 mg kg−1 90 seconds before clamp placement and group B patients received a scalp block with lignocaine 4–5 mg kg−1 as a 1% solution after intubation. Blood pressure and pulse rate were recorded before, during and 30 s, 60 s, 120 s, 240 s and 480 s after clamp placement. RESULTS: For group A, the mean maximum changes in systolic, diastolic and mean arterial blood pressure, and heart rate were, 34%, 39%, 35% and 20% respectively. The corresponding values for Group B were 9% (p=0,004), 16% (p=0,009), 13% (p=0,0066) and 10% (p=0,0901) respectively. CONCLUSION: The scalp block is significantly more effective in attenuating the blood pressure response to clamp placement (p<0.05).

Induction of anaesthesia with propofol according to the adjusted ideal body mass in obese and non-obese patients: an observational study

Background: Obesity changes body composition including fat free mass (FFM), regarded as the “pharmacologically active mass”. Scaling drug doses to obese patients by total body mass (TBM) results in overdose. We aimed to determine the success rate of inducing anaesthesia in normal, overweight and obese patients with propofol, using an adjusted body mass scalar (ABM), which embodies the increased FFM of obese patients. Methods: Ninety-six patients were divided into three groups according to body mass index (BMI): normal, overweight and obese. Propofol 2 mg/kg ABM was administered according to the equation: ABM = IBM + 0.4(TBM – IBM), where IBM = ideal body mass. Induction success was assessed clinically and by electroencephalographic spectral entropy. Results: The groups were similar regarding gender, age, height and IBM. One patient was morbidly obese (BMI = 44). State entropy (SE) decreased to < 60 in 33/33, 28/29 and 33/34 patients in the normal-weight, overweight and obese groups respectively, an overall success rate of 97.5% (95% confidence interval 92.7% to 99.4%). Median lowest achieved SE values and median times that SE remained < 60 did not differ between groups, however the individual values ranged widely in all three groups. Induction failed in the two patients whose SE did not decrease to < 60 (one overweight and one obese). Conclusions: The ABM-based propofol induction dose has a high success rate in normal, overweight and obese patients. Further studies are required to determine the feasibility among morbidly obese patients.

Head size and body mass in infants with hydrocephalus.

nephrine is locally infiltrated. First, epinephrine doses: the hemodynamic effects of epinephrine are dose-dependent. Although both a and b-adrenoceptors are stimulated, b2 vasodilatory effects are most sensitive. When epinephrine-containing solutions are infiltrated, exogenous epinephrine is absorbed into blood circulation, which probably influences the forthcoming blood pressure. Yang et al observed intranasal infiltration of epinephrine both 20 and 40 mg induced significant decline in MAP 1.5 minutes later in the patients scheduled for endoscopic sinus surgery. However, only epinephrine 40 mg could lead to significant increase in MAP 3 minutes later, whereas epinephrine 20 mg resumed MAP to normal at this time. Second, anesthesia depth: the performance of epinephrine infiltration, eliciting pain and other stimulations, can activate a stress reaction. This stress reaction may excite the sympathetic-adrenomedullar system, enhance the exciting degree of adrenergic nerve, increase the endogenous epinephrine and norepinephrine, and therefore elevate blood pressure. In another study by Yang et al, the authors found that depth of anesthesia affects the MAP response after epinephrine infiltration. Compared to deeper general anesthesia (BIS 36), lighter anesthesia (BIS 42) lead to less decrease in MAP 1.5 minutes after initiation of epinephrine administration with greater rebound in MAP at the 3 minute mark. One should also note if the surgery is performed during the observational time frame, blood pressure is to be more significantly influenced. Third, observational time points: as mentioned above, the epinephrineinduced changes of blood pressure are time-related. For example, when scalp epinephrine was applied, the average time from the beginning of local infiltration to the lowest MAP was 102 seconds and to the highest was 202 seconds. Therefore, without appropriate observational time points, one may miss the subtle difference of blood pressure after epinephrine infiltration. In conclusion, infiltration locations, epinephrine doses, anesthesia depth, and observational time points are all contributing factors for changes in blood pressure when epinephrine infiltration is applied on scalp or nasal mucosa under general anesthesia.

Haemodynamic response to laryngoscopy with and without tracheal intubation

ABSTRACT Introduction Tracheal intubation is accompanied by an increased blood pressure and heart rate. The aim of this study was to find the most important source of this haemodynamic response, namely laryngoscopy or intubation. Method A standard induction technique was used for all patients. Eighty patients were randomly allocated to one of two groups, one group to undergo laryngoscopy followed by intubation (Group I), and the other laryngoscopy only of duration similar to intubation (Group L). Blood pressure and heart rate were recorded in the ward, before induction of anaesthesia and one, two, three, and four minutes after instrumentation. Results The instrumentation times did not differ significantly (p = 0.20). Over time mean arterial pressures were significantly higher in Group I than in Group L (p = 0.038). Over time the ratios of mean blood pressure and heart rate relative to the preoperative heart rate were significantly greater in Group I than in Group L (p < 0.01). Conclusion Blood pressures and heart rates were significantly greater after laryngoscopy followed by intubation than after laryngoscopy of the same duration not followed by intubation. The induction technique, consisting of lignocaine, alfentanil, and propofol, may have attenuated expected increases in blood pressure but not increases in heart rate after intubation.

Effect of nitrous oxide on spectral entropy during sevoflurane anaesthesia at an altitude of 1 400 metres

Introduction Spectral entropy is a monitor of the level of anaesthesia. No change in entropy was recorded with N2O alone, despite a loss of consciousness, but entropy decreased when N2O was added to sevoflurane.

The use of ketamine in cancer palliation

ABSTRACT Cancer pain is caused by continuous tissue injury, which may be due to surgery, infiltration of the surrounding organs including nerves, as well as from mucositis after chemo- or radiotherapy. Nerve involvement, chronic opioid therapy and continuous nociceptive input cause hyperalgesia. Chronic stimulation of the dorsal root neurons leads to hyperalgesia and resistance (tolerance) to μ opioid analgesics (hyperalgesia-tolerance). The NMDA receptor antagonist ketamine reverses tolerance to morphine. Ketamine aggravates the sedative effect of opioids and other drugs used for neuropathic pain, such as sodium valproate and amitriptyline. The pain experienced by cancer patients needs a multimodal approach, including ketamine. Although ketamine appears to be a useful analgesic, the literature dealing with ketamine as an analgesic lacks randomised controlled trials.

Analgesia after total hip replacement: epidural versus psoas compartment block

ABSTRACT Background The objective of this paper is to evaluate the effectiveness of a psoas compartment block, as compared with an epidural, for postoperative analgesia following total hip replacement surgery. The research design was a double-blinded randomised control trail, in the setting of a university hospital. Methods Patients scheduled for hip arthroplasty received either a psoas compartment or epidural infusion of bupivacaine. The outcome measures that were examined were postoperative pain, local anaesthetic and morphine consumption, and side effects. Results There was no significant difference between the two groups regarding postoperative pain. Local anaesthetic and opiate consumption was significantly higher in the psoas compartment block group. Postoperative morphine as covariate had a significant influence on the mean postoperative pain. There was no significant difference between side effects in each group. Conclusion Epidural analgesia was more effective than the psoas compartment block after hip replacement surgery. Although pain did not differ significantly, local anaesthetic and opiate consumption was significantly higher in the psoas compartment group.