An inventory of Canadian anesthesiology. Human research from 1995 through 1999.

PURPOSE: The year 2000 provides a symbolic opportunity to assess the past initiatives in anesthesia research. As in many other fields, medical research has benefited from utilizing computerized data bases to facilitate enumerating areas of interest. We have created a baseline survey of past research in the fields of anesthesia, anesthetics, analgesia, and analgesics to highlight Canadian studies. METHODS: The survey was undertaken using the Medical Literature Analysis and Retrieval System (MEDLARS) medical literature archive for the years 1995 through 1999. The principal categories and sub-categories of MEDLARS' anesthesia classifications were counted for 70 countries contributing to the archive. RESULTS: Canadian contributions ranged from 141 (1992) to 185 (1999) and represented annually 3% of the world total in the anesthesia categories. The greatest number of studies (30-38%) were about adults aged 19 to 44 yr, and there were between 4% and 14% more studies of females than males. "Pharmacology" and "therapeutic use" were the most frequent topics, lidocaine, fentanyl, and propofol were the most studied anesthetics, and non-steroidal anti-inflammatories, opium, morphine, and fentanyl were the most studied analgesics. Among the types of studies, those classified as "quality of health care" occurred most frequently (16%). Canadian trends closely follow world trends. CONCLUSION: The collected counts provide a comprehensive overview of research trends for the past five years.

Effects of propofol on cerebral oxygenation during cardiopulmonary bypass in children.

PURPOSE: Neurologic complications occur following cardiopulmonary bypass surgery. We conducted a randomized, controlled, single-blind study to determine the effect of propofol on the redox status of cytaa3, and to evaluate its potential for decreasing neurologic complications. METHODS AND MATERIALS: Twenty-four children (median age: 3.3 yr; median weight: 14.4 kg) scheduled for elective cardiopulmonary bypass surgery were assigned to either the experimental group (Group P, given sufficient propofol to eliminate brain electrical activity as measured on EEG (i.e. burst suppression)) or the control group (Group C, no propofol). Near infrared spectroscopy data were collected at one-second intervals throughout the surgical procedures. Pre- and postoperative neurologic examinations were completed by a physician blinded to the group to which the patient was assigned. Change in cytochrome aa3 data at 10-min intervals (10, 20, 30, 40 min) following start of bypass were compared between groups by repeated measures analysis of variance. RESULTS: The patterns of change in redox state of cytochrome were different between the two groups (P < 0.002). The pattern of change within Group P was similar to that in hypothermic patients in Group C. There were correlations between change in cytaa3 redox status and temperature in the control subjects. There were no gross neurologic complications in either group. CONCLUSIONS: Propofol appears to stabilize the energy supply/demand equilibrium of the brain during cardiopulmonary bypass surgery and thus theoretically could reduce the incidence or severity of neurologic complications.

Canadian anesthesia physician resources: 1996 and beyond.

PURPOSE: To report physician resource information from the 1996 national anesthesia physician and residency programme surveys in Canada. The findings are used to discuss the potential effects on availability of future specialist anesthesia services in Canada. METHODS: Twenty-six hundred and ninety-three physicians (2,206 specialists, 487 family physicians) providing anesthesia services were surveyed. Information on demographics and patterns of clinical practice were sought. Anesthesia programme directors provided trainee information. Projections of the potential number of practicing anesthesiologists to 2026 were made based on the number of available training positions and age distribution of anesthesiologists. RESULTS: There was a 58.3% response rate to the national survey. Since 1986 there has been a 10% increase in the number of specialist anesthesiologists. Marked regional variations in age distribution and changes in the number of specialist anesthesiologists were noted. Most specialists remain in the region or province of postgraduate training. Sixty percent of specialists were either re-entry trainees or international medical graduates. Changes in anesthesia practice patterns have resulted in 40% of the anesthesiologist's work now occurring outside of the operating room. Anesthesia training positions have decreased by at least 15%. The population of Canada is projected to increase by 33.8% between 1996 and 2026. If current government and position allocation policies continue, it is projected there will be 0% increase in the number of specialist anesthesiologists over the same time period. CONCLUSIONS: Changes in anesthesia practices have exacerbated the current shortages of anesthesiologists. These shortages will worsen if the number of, and restrictions to, available residency positions is unchanged.

Comparison of electrohydraulic lithotripters with rigid and pressure-release ellipsoidal reflectors. II. Cavitation fields.

Dramatically different cavitation was produced by two separate acoustic pulses that had different shapes but similar duration, frequency content, and peak positive and negative pressure. Both pulses were produced by a Dornier HM-3 style lithotripter: one pulse when the ellipsoidal reflector was rigid, the other when the reflector was pressure release. The cavitation, or bubble action, generated by the conventional rigid-reflector pulse was nearly 50 times longer lived and 3-13 times stronger than that produced by the pressure-release-reflector pulse. Cavitation durations measured by passive acoustic detection and high-speed video agreed with calculations based on the Gilmore equation. Cavitation intensity, or destructive potential, was judged (1) experimentally by the size of pits in aluminum foil detectors and (2) numerically by the calculated amplitude of the shock wave emitted by a collapsing bubble. The results indicate that the trailing positive spike in the pressure-release-reflector waveform stifles bubble growth and mitigates the collapse, whereas the trough after the positive spike in the rigid-reflector waveform triggers inertially driven growth and collapse. The two reflectors therefore provide a tool to compare effects in weakly and strongly cavitating fields and thereby help assess cavitation's role in lithotripsy.

Model experiment to study sonic boom propagation through turbulence. Part II. Effect of turbulence intensity and propagation distance through turbulence.

A model experiment was reported to be successful in simulating the propagation of sonic booms through a turbulent atmosphere [B. Lipkens and D. T. Blackstock, J. Acoust. Soc. Am. 103, 148-158 (1998)]. In this study the effect on N wave characteristics of turbulence intensity and propagation distance through turbulence are investigated. The main parameters of interest are the rise time and the peak pressure. The effect of turbulence intensity and propagation distance is to flatten the rise time and peak pressure distributions. Rise time and peak pressure distributions always have positive skewness after propagation through turbulence. Average rise time grows with turbulence intensity and propagation distance. The scattering of rise time data is one-sided, i.e., rise times are almost always increased by turbulence. Average peak pressure decreases slowly with turbulence intensity and propagation distance. For the reported data a threefold increase in average rise time is observed and a maximum decrease of about 20% in average peak pressure. Rise times more than ten times that of the no turbulence value are observed. At most, the maximum peak pressure doubles after propagation through turbulence, and the minimum peak pressure values are about one-half the no-turbulence values. Rounded waveforms are always more common than peaked waveforms.

Comparison of electrohydraulic lithotripters with rigid and pressure-release ellipsoidal reflectors. I. Acoustic fields.

The most common lithotripter, a Dornier HM-3, utilizes an underwater spark to generate an acoustic pulse and a rigid ellipsoidal reflector to focus the pulse on the kidney stone to be comminuted. The pulse measured in water with a PVDF membrane hydrophone at the external focus of the ellipsoid was a 1-microsecond positive-pressure spike followed by a 3-microsecond negative-pressure trough. When we replaced the rigid reflector in our experimental lithotripter with a pressure-release reflector, the pulse was a 1.6-microsecond trough followed by a 0.6-microsecond positive spike. The waveforms are nearly time inverses (i.e., their spikes and troughs are reversed). The frequency spectra, the maximum peak positive pressures P+ (42 MPa, rigid and 43 MPa, pressure-release), and the maximum peak negative pressures P- (-12 MPa and -14 MPa) are comparable. The maximum P- occurred 20 mm closer to the reflector than did the maximum P+, for both reflectors. However, the spatial maxima of the peak pressures (P+ and P-) produced by the pressure-release reflector were located 20 mm nearer to the reflector than those produced by the rigid reflector. Qualitative explanation of the waveforms and the location of pressure maxima as well as comparison to previous theoretical and experimental results is given. The alternate waveform produced by the pressure-release reflector may be a tool in determining the role of cavitation in lithotripsy because cavitation is highly sensitive to waveform.

Bioeffects of positive and negative acoustic pressures in vivo.

In water, the inertial collapse of a bubble is more violent after expansion by a negative acoustic pressure pulse than when directly compressed by a positive pulse of equal amplitude and duration. In tissues, gas bodies may be limited in their ability to expand and, therefore, the relatively strong effectiveness of negative pressure excursions may be tempered. To determine the relative effectiveness of positive and negative pressure pulses in vivo, the mortality rate of Drosophila larvae was determined as a function of exposure to microsecond length, nearly unipolar, positive and negative pressure pulses. Air-filled tracheae in the larvae serve as biological models of small, constrained bubbles. Death from exposure to ultrasound has previously been correlated with the presence of air in the respiratory system. The degree of hemorrhage in murine lung was also compared using positive and negative pulses. The high sensitivity of lung to exposure to ultrasound also depends on its gas content. The mammalian lung is much more complex than the respiratory system of insect larvae and, at the present time, it is not clear that acoustic cavitation is the physical mechanism for hemorrhage. A spark from an electrohydraulic lithotripter was used to produce a spherically diverging positive pulse. An isolated negative pulse was generated by reflection of the lithotripter pulse from a pressure release interface. Pulse amplitudes ranging from 1 to 5 MPa were obtained by changing the proximity of the source to the biological target. For both biological effects, the positive pulse was found to be at least as damaging as the negative pulse at comparable temporal peak pressure levels. These observations may be relevant to an evaluation of the mechanical index (MI) as an exposure parameter for tissues including lung since MI currently is defined in terms of the magnitude of the negative pressure in the ultrasound field.

Intraoperative hyperthermia in a paediatric patient with cystinosis.

Cystinosis is a rare autosomal recessive inherited disorder of amino acid metabolism. Little is known of the affects of general anaesthesia on the disease (Tobias 1993) and complications relating to anaesthesia have not been previously reported. Infantile cystinosis presents as progressive renal failure and the Fanconi syndrome and metabolic bone disease often develop. We describe the case of a child who presented with signs of apparent malignant hyperthermia (MH) under general anaesthesia and was treated with dantrolene. During a repeat 'trigger-free' general anaesthetic he developed a fever which responded to paracetamol. The metabolic effects of cystinosis and its similarity to MH will be discussed.

Propofol anaesthesia reduces early postoperative emesis after paediatric strabismus surgery.

Propofol anaesthesia may reduce postoperative emesis. The purpose of this study was to compare the incidence of emesis after propofol anaesthesia with and without nitrous oxide, compared with thiopentone and halothane anaesthesia, in hospital and up to 24 hr postoperatively, in outpatient paediatric patients after strabismus surgery. Seventy-five ASA class I or II, unpremedicated patients, aged 2-12 yr were randomly assigned to one of three groups: Thiopentone, 6.0 mg.kg-1 i.v. induction followed by halothane and N2O/O2 for maintenance (T/H); propofol for induction, followed by propofol and oxygen for maintenance (P/O2); and propofol for i.v. induction, followed by propofol infusion and N2O/O2 for maintenance (P/N2O). All received vecuronium, controlled ventilation, and acetaminophen pr. Morphine was given as needed for postoperative analgesia. There were no differences in age, weight, number of eye muscles operated upon, duration of anaesthesia or surgery. The P/N2O group (255 +/- 80 micrograms.kg-1 x min-1) received less propofol than the P/O2 group (344 +/- 60 micrograms.kg-1 x min-1) (P < or = 0.0001) and had shorter extubation (P < 0.001) and recovery (P < 0.01) times. Emesis in the hospital, in both the P/N2O (4.0%) and P/O2 group (4.0%) was less than in the T/H group (32%) (P < 0.01). Antiemetics were required in four patients in the T/H group (16.0%). Overall emesis after surgery was not different among the groups: T/H (48%), P/O2 (28%) and P/N2O (42%). The use of propofol anaesthesia with and without N2O decreased only early emesis. This supports the concept of a short-acting, specific antiemetic effect of propofol.

Tracheal extubation in children: halothane versus isoflurane, anesthetized versus awake.

The authors compared the incidence of respiratory complications and arterial hemoglobin desaturation during emergence from anesthesia in children whose tracheas were extubated while they were anesthetized or after they were awake and to whom halothane or isoflurane had been administered. One hundred children 1-4 yr of age undergoing minor urologic surgery were studied. After a standard induction technique, patients were randomized to receive either isoflurane or halothane. In 50 patients tracheal extubation was performed while they were breathing 2 MAC of either halothane or isoflurane in 100% oxygen. The remaining 50 patients received 2 MAC (volatile agent plus nitrous oxide) during the operation, but tracheal extubation was delayed until they were awake. A blinded observer recorded the incidence of respiratory complications and continuously measured hemoglobin saturation for 15 min after extubation. When tracheal extubation occurred in deeply anesthetized patients, no differences were found between the two volatile agents. When tracheal extubation of awake patients was performed, the use of isoflurane was associated with more episodes of coughing and airway obstruction than was halothane (P less than 0.05). Awake tracheal extubation following either agent was associated with significantly more episodes of hemoglobin desaturation than was tracheal extubation while anesthetized.

The acoustic fields of the Wolf electrohydraulic lithotripter.

Electric sparks are used as the sources for both intra- and extracorporeal shock wave lithotripters. Upon ignition, a pressure pulse, headed by a shock, is generated that propagates as a spherically diverging wave. Simultaneously, a bubble is created that, in the case of the Wolf Model 2137.50 Electrohydraulic Lithotripter, expands to a radius of approximately 5 mm and collapses spontaneously after approximately 1 msec. Upon rebound, the bubble generates a second pressure pulse that is almost equal in amplitude and acoustic energy to the first shock wave. Measured pressures are almost entirely positive and decrease in amplitude with the reciprocal of the distance from the source. For the Wolf lithotripter at its maximum output setting, the pressure amplitude at a distance of 3 cm from the spark is typically 3 MPa.

Analysis of an anaesthetic gas scavenging system hazard.

The collapse of the reservoir bag in a circle circuit was observed during anaesthesia. This resulted from the incomplete closure of the pressure relief valve on the absorber whie it was connected to the scavenging system. Although the scavenging system was operating and installed according to the manufacturer's recommendations and to the CSA standard on Anaesthetic Gas Scavenging Systems (Z168.8), the patient was not protected from this hazard. Introducing an air break into the scavenging interface device will protect the patient. However, such a system would not meet the CSA standard and would make the relief valves on the scavenging interface device unnecessary.

Anaesthetic implications of the trismus pseudocamptodactyly (Dutch-Kentucky or Hecht Beals) syndrome.

The trismus pseudocamptodactyly syndrome is a relatively rare, autosomal dominant condition first described in 1969. Affected patients classically present with two main features: limited excursion of the mandible and flexion deformity of the fingers that occurs with wrist extension (pseudocamptodactyly). Foot deformities and a shorter-than-normal stature may also be present. The underlying abnormality is short muscle tendon units, which prevent normal growth and development. We reviewed the anaesthetic experience in three paediatric patients with the trismus pseudocamptodactyly syndrome and the pertinent clinical findings in three other members of the same family, spanning three generations. Limited mandible excursion was present in all six cases, but was not obvious preoperatively in the patients because of its subtle presentation. All three cases were successfully managed using mask anaesthesia with spontaneous ventilation, avoiding muscle relaxants. Attempts to visualize the larynx under anaesthesia were unsuccessful in two cases. Blind nasotracheal intubation was successful in one patient. Postoperatively, there were no problems with the airway.

Inner medullary hemodynamics in dogs with aortocaval fistula.

To investigate the role of medullary hemodynamics and vasoactive hormones in sodium retention in dogs with aortocaval fistula, we examined papillary plasma flow (PPF), solute content, and renal output of renin, norepinephrine, and prostaglandin E2 (PGE2) in anesthetized normal and fistula dogs. During hydropenia, cardiac output was elevated and systemic vascular resistance reduced in fistula dogs, accompanied by markedly increased renal output of renin, norepinephrine, and PGE2. In fistula dogs the blunted diuretic and natriuretic response to saline loading was not due to impaired myocardial contractility. During hydropenia and after saline loading, glomerular filtration rate (GFR) and renal blood flow were similar in normal and in fistula dogs; however, PPF was significantly lower in fistula dogs, accompanied by significantly greater papillary tissue osmolality and sodium content. These findings indicate that in fistula dogs enhanced medullary sodium reabsorption is associated with decreased PPF and stimulation of the renin-angiotensin and adrenergic nervous system. Furthermore, the reduced PPF obviates medullary solute washout during saline loading, and may contribute to the blunted diuretic and natriuretic response.

Negative pressure in the middle ear in children after nitrous oxide anaesthesia.

A study was conducted to measure the pressure in the middle ear in healthy children, following nitrous oxide anaesthesia. Premedication with chloral hydrate and scopolamine orally was similar in all patients and awake patients received thiopentone 4-5 mg X kg-1 for induction of anaesthesia. All received nitrous oxide (66 per cent) in oxygen and halothane or isoflurane as required. Exposure to nitrous oxide varied from 17-100 minutes, mean 47 minutes. All patients developed negative pressure in one or both ears in the first day following anaesthesia. This is a higher incidence than previously reported and may be explained by the inability of children to equilibrate negative middle ear pressure via the eustachian tube.