Anaesthetic management of patients with sleep apnoea syndrome

Purpose

Sleep apnoea syndrome (SAS) is a relatively common, potentially fatal, disorder. Patients with SAS exhibit repetitive, often prolonged episodes of apnoea during sleep, with serious nocturnal and diurnal physiologic derangements. Several anecdotal reports and clinical studies have documented anaesthetic-related occurrence of fatal and near-fatal respiratory complications in these patients. The purpose of this article is to outline the potential problems encountered in anaesthetic management of adult SAS patients, and to suggest a practical approach for anaesthesia both for incidental and specific procedures.

Principal findings

SASs have many implications for the anaesthetist. First, SAS patients are exquisitely sensitive to all central depressant drugs, with upper airway obstruction or respiratory arrest occurring even with minimal doses. Thus sedative and opioid premedication should be omitted as should the intra and postoperative use of opioids be limited or avoided. All anaesthetic drugs should be administered by titration to desired effect, preferably using short-acting drugs. When feasible, continuous regional anaesthesia using a catheter is the technique of choice. Where possible nonopioid analgesics or local anaesthetics should be used for postoperative analgesia. Perioperative monitoring for apnoea, desaturation, and dysrhythmias is essential. Secondly, SAS patients have a potentially difficult airway. Awake intubation is the safest approach to airway control. Extubation should only be tried in the fully conscious patient with intact upper airway function and under controlled situations. Thirdly, the cardiorespiratory complications of SAS and the presence of associated diseases can adversely influence anaesthetic management.

Conclusion

Perioperative risks attending SAS patients emphasize the importance of their detection, perioperative evaluation and planning.     

The development of scales to measure knowledge and preference for diet and physical activity behavior in 4- to 8-year-old children

Although there is a sizable literature on determinants of health-related habits in adults, relatively little attention has been paid to influences on health habits in children. The purpose of this study was to (a) develop practical, reliable, and valid measures of knowledge of and preference for cardiovascular disease-related diet and exercise behaviors in children, and (b) assess parental influences on children's knowledge and preference. Eighty-one 4- to 8-year-old children from diverse ethnic backgrounds and their parent or legal guardian participated. Children were presented with 15 attractive photo-pairs of foods. One photograph was of a "healthful" food or activity, and the other was "unhealthful." They were asked to identify which food/activity of the pair they preferred, and which one they thought was more healthy. Children were retested after 1 week to determine test-retest reliability. Validity of the preference tests was determined by giving the child actual choices of the same activity and food pairs. Validity of knowledge tests was determined by testing children after an educational intervention session. The alpha coefficients, test-retest reliabilities, and validity data generally indicated that food preference and knowledge tests had adequate psychometric properties, but the physical activity scales did not. Very few parental influences on health-related behavior were detected.     

The renal cytochrome P-450 arachidonic acid system

In addition to cyclooxygenase and lipoxygenase, arachidonic acid (AA) is metabolized by the cytochrome P-450 monooxygenase system. The kidney is one of the major extrahepatic tissues that display cytochrome P-450 enzyme activities, in particular the cortex, specifically the proximal tubule demonstrate the highest concentration. AA is metabolized by the renal cytochrome P-450 epoxygenase and /-1 hydroxylases to epoxyeicosatrienoic acids and /-1 alcohols (20- and 19-mono-hydroxyeicosatetraenoic acids), respectively. These metabolites possess a broad spectrum of biological and renal effects which include: vasodilation, vasoconstriction, inhibition and stimulation of Na⁺–K⁺-ATPase, inhibition of ion transport mechanisms, natriuresis, inhibition of renin release and stimulation of cell growth. These metabolites are endogenous constituents of the kidney and are present in urine with increasing concentration under pathological conditions such as pregnancy-induced hypertension. The cytochrome P-450-dependent metabolism of AA is specifically localized to the proximal tubule and exhibits developmental changes, i.e., renal production of metabolites is very low in the fetus, newborn and up to 3 weeks of age, after which a remarkable increase in enzyme activities is observed. These characteristics call attention to the importance of this enzyme system in producing cellular mediators for regulating renal function in normal and diseased states.     

Bone Mineral Density in Hemophilia Patients

Patients with hemophilia suffer from low bone mineral density (BMD) due to several risk factors including arthropathy and resulting immobility. Recent studies have shown variable frequency of low BMD in this group of patients. This study attempts to assess the prevalence of low BMD (osteoporosis and osteopenia) and the associated risk factors in a group of Iranian hemophilia patients. Patients with moderate or severe hemophilia underwent BMD measurement by dual energy X-ray absorptiometry. The results were correlated with other variables including physical activity, calcium intake and demographic data. Forty two patients with the mean age of 31 years (range 18–72) completed the study. The prevalence of osteoporosis in the spine and the left femoral neck was 23.8 and 14.6 %, respectively, and osteopenia in the spine and femoral neck was seen in 45.2 and 31.7 % of the patients, respectively based on the WHO T-score criteria. We found only cigarette smoking to be significantly related to low BMD (P < 0.001). There were two cases of pathologic fracture at femoral neck and forearm (4.8 %). Low BMD is very common in patients with hemophilia. Appropriate assessment of BMD and control of predisposing factors such as prophylactic factor replacement (to prevent hemarthrosis) and cessation of cigarette smoking are warranted.     

Bubble dynamics in boiling histotripsy

Boiling histotripsy is a non-invasive, cavitation-based ultrasonic technique which uses a number of millisecond pulses to mechanically fractionate tissue. Though a number of studies have demonstrated the efficacy of boiling histotripsy for fractionation of solid tumours, treatment monitoring by cavitation measurement is not well studied because of the limited understanding of the dynamics of bubbles induced by boiling histotripsy. The main objectives of this work are to (a) extract qualitative and quantitative features of bubbles excited by shockwaves and (b) distinguish between the different types of cavitation activity for either a thermally or a mechanically induced lesion in the liver. A numerical bubble model based on the Gilmore equation accounting for heat and mass transfer (gas and water vapour) was developed to investigate the dynamics of a single bubble in tissue exposed to different High Intensity Focused Ultrasound fields as a function of temperature variation in the fluid. Furthermore, ex vivo liver experiments were performed with a passive cavitation detection system to obtain acoustic emissions. The numerical simulations showed that the asymmetry in a shockwave and water vapour transport are the key parameters which lead the bubble to undergo rectified growth at a boiling temperature of 100°C. The onset of rectified radial bubble motion manifested itself as (a) an increase in the radiated pressure and (b) the sudden appearance of higher order multiple harmonics in the corresponding spectrogram. Examining the frequency spectra produced by the thermal ablation and the boiling histotripsy exposures, it was observed that higher order multiple harmonics as well as higher levels of broadband emissions occurred during the boiling histotripsy insonation. These unique features in the emitted acoustic signals were consistent with the experimental measurements. These features can, therefore, be used to monitor (a) the different types of acoustic cavitation activity for either a thermal ablation or a mechanical fractionation process and (b) the onset of the formation of a boiling bubble at the focus in the course of HIFU exposure.     

Comparison of radiographic and magnetic resonance imaging findings of early osteoarthritis of the rabbit knees: an experimental study

The objectives of the present study were to describe radiographic and magnetic resonance imaging (MRI) findings of early osteoarthritis and their relationships at the same time. A total number of ten rabbits were used and randomly divided into two equal groups. In one group, cranial cruciate ligament (CCL) of the left knee was transected to produce experimental osteoarthritis and in the other group, only the articular capsule was entered as sham operation (arthrotomy group). All of the left knees were examined by MRI and radiography before operation to exclude preexisting abnormalities and serve as control. One month postoperation, two conventional radiographic views and MR imaging were performed under general anesthesia. Statistical analysis of the MRI results revealed that there was a significant difference between the CCL-transected group with arthrotomy and control groups. There was no significant difference in the radiographic findings between the operated, arthrotomy and control groups. It was concluded that osteoarthritic changes of the joints can be detectable 1?month postinjury by MRI. Meniscal degeneration and subchondral bone irregularity are detectable diagnostic signs.