Medical oxygen and air travel.

This report responds to a resolution that asked the American Medical Association (AMA) to take action to improve airport and airline accommodations for passengers requiring medical oxygen. Information for the report was derived from a search of the MEDLINE database and references listed in pertinent articles, as well as through communications with experts in aerospace and emergency medicine. Based on this information, the AMA Council on Scientific Affairs determined that commercial air travel exposes passengers to altitude-related hypoxia and gas expansion, which may cause some passengers to experience significant symptoms and medical complications during flight. Medical guidelines are available to help physicians evaluate and counsel potential passengers who are at increased risk of inflight hypoxemia. Supplemental oxygen may be needed for some passengers to maintain adequate tissue oxygenation and prevent hypoxemic complications. For safety and security reasons, federal regulations prohibit travelers from using their own portable oxygen system onboard commercial aircraft. Many U.S. airlines supply medical oxygen for use during flight but policies and procedures vary. Oxygen-dependent passengers must make additional arrangements for the use of supplemental oxygen in airports. Uniform standards are needed to specify procedures and equipment for the use of medical oxygen in airports and aboard commercial aircraft. Revision of federal regulations should be considered to accommodate oxygen-dependent passengers and permit them to have an uninterrupted source of oxygen from departure to destination.

Inflight medical emergencies.

This report responds to resolutions asking the American Medical Association (AMA) to develop recommendations for the use of medical equipment and technology onboard commercial airlines. Information for the report was derived from a search of the MEDLINE database and references listed in pertinent articles, as well as through communications with experts in aerospace and emergency medicine. Based on this information, the AMA Council on Scientific Affairs determined that, while inflight morbidity and mortality are uncommon, serious events do occur, which require immediate emergency care. Management of serious problems requires an integrated emergency response system that ensures rapid notification of medical personnel on the ground, assistance from appropriately trained flight crews and passenger volunteers (if available), and adequate medical supplies and equipment to stabilize the victim. Physicians have an important role in the preflight evaluation and counseling of potential passengers who are at risk of inflight medical complications, and in providing inflight medical assistance. Some U.S. and foreign air carriers are upgrading inflight emergency medical kits and placing automated external defibrillators aboard aircraft. Few data are available regarding the effectiveness of such improvements in improving health or survival outcomes. Recent federal legislation requires assessment of the extent of inflight medical emergencies, including the adequacy of emergency medical supplies and equipment carried onboard commercial airliners. This legislation also should alleviate liability concerns by providing immunity for physicians and others who render inflight medical assistance.

Crossover use of donated blood for autologous transfusion: report of the Council on Scientific Affairs, American Medical Association.

BACKGROUND: Controversy exists concerning whether the costs and potential risks outweigh the potential benefits of "crossover" use in the general blood supply of unutilized blood that was donated for autologous transfusion. STUDY DESIGN AND METHODS: Published articles and reports were identified through systematic search of MEDLINE and review of references cited in previously identified articles, textbooks, and reports. Consultation was made with experts in blood donation and transfusion. Additional peer review was received from the American Medical Association (AMA) Council on Scientific Affairs RESULTS: Concern over infectious disease transmission has led to increased interest in and support for autologous transfusion for individuals having planned surgeries. Different requirements exist for collection, labeling, and screening of blood to be used for autologous versus allogeneic transfusions; therefore, procedures for diverting autologous blood donations to the general blood supply involve considerable expense. Several cost-effectiveness studies of autologous blood donation and transfusion conclude that currently this "crossover" appears to be an expensive procedure yielding little increased benefit from a societal perspective. CONCLUSIONS: The recommendations in this report were adopted as AMA Policy at the AMA Annual Meeting in June 1997. The AMA does not encourage blood collection programs to "cross over" units donated for autologous use to the allogeneic blood supply. Practice guidelines are needed, and should be utilized to ensure parsimony in the use of autologous blood donations and transfusions.

Changes in blood flow and vascular resistance in the arm and leg during spinal anaesthesia and vasopressor therapy with methoxamine.

The effects of subarachnoid block with hyperbaric bupivacaine 0.5% on forearm and calf blood flow and vascular resistance were examined using venous occlusion plethysmography in 10 fit patients. Following blockade there was an increase in mean (SD) calf blood flow from 2.0 (0.4) to 2.6 (1.2) ml.100 ml-1.min-1 (p = 0.057), a decrease in mean (SD) calf vascular resistance from 55 (15) to 38 (14) R units (p < 0.01), a decrease in mean (SD) forearm blood flow from 3.1 (1.2) to 1.8 (0.9) ml.100 ml-1.min-1 (p < 0.01) and an increase in mean forearm vascular resistance from 38 (16) to 62 (24) R units (p < 0.01). Methoxamine 2 mg was administered intravenously when the mean arterial blood pressure decreased by 15%. There was a resultant marked increase in mean (SD) forearm blood flow from 1.8 (0.9) to 3.0 (0.8) ml.100 ml-1.min-1 (p < 0.001) but a decrease in mean (SD) calf blood flow from 2.6 (1.2) to 2.1 (1.4) ml.100 ml-1.min-1 (p = 0.11). Correspondingly, the mean (SD) forearm vascular resistance decreased from 62 (24) to 46 (17) R units (p < 0.01) with an increase in mean (SD) calf vascular resistance from 38 (14) to 56 (22) R units (p < 0.01). These findings indicate that whereas methoxamine produces the anticipated constrictor response in the calf vessels it causes a simultaneous reduction in vascular resistance in the forearm.

The effect of intravenous clonidine on the forearm circulation.

The effect of two doses of clonidine on forearm blood flow was compared with an inert treatment using mercury strain gauge venous occlusive plethysmography. In the clonidine treated groups, forearm blood flow was unaffected in the resting state, but decreased sharply with tracheal intubation. In the saline group, blood flow increased with intubation. Forearm vascular resistance increased in the clonidine treated groups, but decreased in the saline group. These results suggest that clonidine has a peripheral action in anaesthetised normotensive individuals, and is not a purely centrally acting drug.

Cardiovascular effects of intravenous clonidine. Partial attenuation of the pressor response to intubation by clonidine.

The effect of clonidine on the pressor and heart rate response to tracheal intubation was studied in a placebo-controlled, randomised, double-blind trial. Thirty patients were pretreated with either clonidine 1.25 micrograms/kg, or clonidine 0.625 microgram/kg or an equivalent volume of normal saline, given intravenously 15 minutes before induction of anaesthesia. The attenuation of the pressor response to intubation of both clonidine groups was statistically significant compared to the saline group. Neither dose of clonidine completely abolished the increase in either heart rate or blood pressure. There was no difference in attenuation between the clonidine treatments; this indicated that the lower dose may be the more appropriate.

The effects of propofol and thiopentone on forearm circulation.

Some effects of propofol and thiopentone induction on the peripheral circulation of healthy patients are examined using mercury strain gauge venous occlusion plethysmography of the forearm. Results indicate that both drugs produce a statistically significant decrease in mean arterial blood pressure and forearm blood flow. Forearm vascular resistance remains unchanged after either drug. These data suggest that bolus dose induction of anaesthesia with propofol does not cause arterial vasodilatation of the limb and that a cause for the reduction in mean arterial pressure must be sought elsewhere.

Use of auditory evoked responses as a measure of recovery from benzodiazepine sedation.

The amplitude of the P300 component of auditory evoked responses was found to be depressed by benzodiazepine sedation and was subsequently used to monitor the recovery of volunteers sedated with midazolam. The amplitude of the evoked responses was found to be highly correlated with blood midazolam levels but to be no more sensitive than standard psychomotor testing in assessing recovery from sedation.

Electroconvulsive therapy and serum potassium.

In 54 patients presenting for electroconvulsive therapy, the concentration of serum potassium was measured before and after the induced convulsion modified with a standard anaesthetic technique of methohexitone and suxamethonium. It was found that there was a statistically significant rise in serum potassium, but that the duration of convulsion had no significant effect on that rise in serum potassium. In a further 11 patients, methohexitone alone was administered without ECT, and it was found that serum potassium fell. Methohexitone, suxamethonium and ECT in combination cause a rise in serum potassium which is not clinically important unless pre-induction level is abnormally high, and prolonged convulsion does not exaggerate this rise.

Midazolam sedation for outpatient fibreoptic endoscopy: evaluation of alfentanil supplementation.

Alfentanil, a short-acting opioid, was used as an adjuvant to midazolam for sedation of 30 outpatients undergoing upper gastrointestinal endoscopy. The operating conditions and recovery times were compared with those of a similar group of 30 patients sedated with midazolam only. The use of alfentanil resulted in improved operating conditions and a more rapid recovery. Patient acceptance was high.

Suxamethonium induced myalgia and the effect of pre-operative administration of oral aspirin. A comparison with a standard treatment and an untreated group.

Eighty-four fit, unpremedicated patients who presented for routine surgery and received a standard anaesthetic technique were allocated randomly to three equal groups. Group 1 received tubocurarine 0.05 mg/kg before induction of anaesthesia. Group 2 received soluble aspirin 600 mg orally one hour before surgery, while Group 3 received no pretreatment. Aspirin prophylaxis produced a significant reduction in the incidence of subsequent suxamethonium-induced myalgia and the improvement was similar to that achieved with tubocurarine pretreatment. Pre-operative oral administration of aspirin effectively reduces muscle pains and avoids many of the complications associated with pretreatment with non-depolarising agents.

Halothane and isoflurane in outpatient anaesthesia. A comparison of recovery.

The speed and quality of recovery after anaesthesia were studied in 60 outpatients. Anaesthesia was induced using propofol and maintained by nitrous oxide in oxygen supplemented with either halothane or isoflurane. Initial clinical recovery was significantly faster in the halothane group but no differences were found during subsequent psychomotor testing. Minor postoperative side effects were common in both groups.

Postoperative gastric emptying in outpatient anesthesia: the effect of opioid supplementation.

Acetaminophen (paracetamol) 20 mg/kg was administered orally to 45 gynecological outpatients who had received either alfentanil 5 micrograms/kg, fentanyl 1 microgram/kg, or no analgesic supplement immediately prior to the induction of general anesthesia. Postoperative gastric emptying, assessed by acetaminophen absorption, was significantly inhibited in those given alfentanil. This inhibition is unlikely to be of great clinical importance and was much less than that found in previous studies using longer-acting opioids such as morphine.

Recovery from outpatient anaesthesia: a comparison of incremental propofol and propofol-isoflurane.

Propofol was used to induce anaesthesia in 60 patients undergoing minor outpatient gynaecological procedures. Maintenance was with 66% nitrous oxide in oxygen, plus either isoflurane or 10-mg increments of propofol. Recovery was assessed using both clinical and psychomotor criteria and the results compared with those obtained in a non-anaesthetized control group. As far as the two test groups were concerned, initial recovery was more rapid in the incremental propofol group but, by 1 h after surgery, there were no differences between all three groups.

A comparison of propofol and methohexitone as induction agents for day case isoflurane anaesthesia.

The induction and recovery characteristics of equivalent doses of propofol and methohexitone were compared in 50 patients undergoing day case isoflurane anaesthesia. Propofol induction was smoother but was associated with greater cardiorespiratory depression. Both the speed and quality of recovery were superior with propofol compared with methohexitone.