Biomedical subjects
Publications and source records attributed to D M Gaba.
The pressure/volume characteristics of the bronchial cuff of a polyvinylchloride (PVC) double-lumen endobronchial tube (DLT) was compared with the inflatable cuff of a bronchial blocker. At the volumes needed to seal a series of rigid model bronchi the PVC DLT bronchial cuff consistently generated significantly lower pressures than the bronchial blocker cuff.
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The authors have developed a course in Anesthesia Crisis Resource Management (ACRM) analogous to courses in Crew (Cock-pit) Resource Management (CRM) conducted in commercial and military aviation. Anesthesiologists do not typically receive formal training in crisis management although they are called upon to manage life-threatening crises at a moment's notice. Two model demonstration courses in ACRM were conducted using a realistic anesthesia simulation system to test the feasibility and acceptance of this kind of training. Anesthesiologists received didactic instruction in dynamic decision-making, human performance issues in anesthesia, and in the principles of anesthesia crisis resource management. After familiarization with the host institution's operating rooms and with the simulation environment, they underwent a 2-h simulation session followed by a debriefing session which used a videotape of their simulator performance. Participants rated the course as intense, helpful to their practice of anesthesiology, and highly enjoyable. Several aspects of the course were highly rated, including: videotapes of actual anesthetic mishaps, simulation sessions, and debriefing sessions. Scores on written tests of knowledge about anesthesia crisis management showed a significant improvement following the first course (residents) but not the second course (experienced anesthesiologists). Although the ultimate utility of this training for anesthesiologists cannot easily be determined, the course appeared to be a useful method for addressing important issues of anesthesiologist performance which have previously been dealt with haphazardly. The authors believe that ACRM training should become a regular part of the initial and continuing education of anesthesiologists.
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Sixteen ASA class II or III male patients (aged, 52 to 66 years) undergoing elective cardioversion were randomly assigned to receive either thiopental or etomidate according to an observer-blinded, parallel study design. The appropriate drug was administered in 2-mL aliquots every 15 seconds until the patient no longer responded to verbal commands, at which time cardioversion was attempted. The total dose for induction was 0.22 +/- 0.2 mg/kg and 3.2 +/- 0.4 mg/kg for etomidate and thiopental, respectively. The cardiorespiratory data after induction were evaluated for maximal percent change from baseline. The baseline heart rate was 106 +/- 6 beats/min and 98 +/- 8 beats/min for the etomidate and thiopental groups, respectively (mean +/- SEM). The heart rate decreased 5% after induction with etomidate and increased 7% with thiopental (P less than 0.05). The baseline mean arterial pressure (MAP) was 96 +/- 3 mm Hg and 105 +/- 11 mm Hg for the etomidate and thiopental groups, respectively (mean +/- SEM). The MAP decreased 4% with etomidate and 3% with thiopental. Respiratory rate was significantly increased by 22% after etomidate compared with a 22% decrease in respiratory rate with thiopental (P less than 0.05). Seven of eight patients in the thiopental group required only one countershock, whereas four of eight patients in the etomidate group required only one shock. One patient in each group could not be successfully cardioverted. Recovery time and clinical side effects were similar between groups except for mild myoclonus in the etomidate group. Titration to effect of either etomidate or thiopental provided satisfactory anesthesia for elective cardioversion in hemodynamically stable patients.(ABSTRACT TRUNCATED AT 250 WORDS)
Eight experienced anesthesiologists (faculty or private practitioners) were presented with the same simulated critical incidents that had previously been presented to 19 anesthesia trainees. The detection and correction times for these incidents were measured, as was compliance with Advanced Cardiac Life Support (ACLS) guidelines during cardiac arrest, and the occurrence of unplanned incidents. Experienced personnel tended to react more rapidly than did trainees, but differences between second-year anesthesia residents (CA2) and experienced anesthesiologists were not statistically significant. There was a high variability in performance between incidents and within each group. Unplanned errors and management flaws still occurred with experience subjects. The response to incidents during anesthesia is a complex process that involves multiple levels of cognitive activity and is vulnerable to error regardless of experience. Most trainees seemed to acquire adequate response routines by the end of the CA2 year. Formal reasoning appeared to play a minor role in responding to intraoperative events, but the exact nature of the anesthesiologist's cognition remains to be thoroughly investigated.
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In analyzing recordings of first- and second-year residents performing anesthesia in a comprehensive anesthesia simulation environment (CASE 1.2), we noted the occurrence of unplanned incidents. Utilizing a modified critical incident technique, we documented 132 unplanned incidents during 19 simulations (range 3-14, mean 6-947). Ninety-six (73%) of the incidents were considered simple incidents, and 36 (27%) were considered critical incidents. The incidents were classified as either human errors (65.9%), equipment failures (3%), fixation errors (20.5%), or unknown causes (10.6%). Human errors accounted for 87 of the incidents (range 1-12, mean 4.579), fixation errors accounted for 27 of the incidents (range 0-3, mean 1.421), and equipment failures accounted for only four of the incidents (range 0-2, mean 0.211). There was a significant (P less than 0.025) difference overall between resident groups, although no one class differed significantly from the others. The data confirm that most incidents are due to human error rather than equipment failure, and document fixation errors as a frequent cause of incidents in anesthesia. The data indicate that although most incidents are simple and do not progress into more serious incidents, human error remains ubiquitous, and that formal training and education should include recognition of events and the responses to them, in addition to prevention.
Workload is an important determinant of human performance during complex dynamic tasks. We indirectly measured the mental workload of nine anesthesia residents during 19 cases using a secondary (subsidiary) task paradigm in which performance on an extra task (problems in mathematical addition occurring approximately every 45 s) was used as a probe of a subject's "spare capacity." Excess response time (above baseline) correlated with activities like "manual task" and "speaking with the attending anesthesiologist." The addition problem was either skipped or had a high excess response time (greater than 30 s) in 40% of presentations. The complexity of a case and the experience level of the resident interacted in determining the workload. Subjective workload ratings confirmed that induction of and emergence from anesthesia were periods of highest workload, with "attention" as the dominant cognitive requirement. The anesthesiologist's spare capacity may often be limited during anesthesia. These types of workload measurement techniques should be applied in controlled studies to better define the factors that increase workload.
While adverse outcomes linked to anesthesia are uncommon in healthy patients, they do occasionally happen. There is rarely a single cause. Anesthesia and surgery bring the patient into a complex world in which innumerable small failings can converge to produce an eventual catastrophe. And for all the technology involved, the anesthesiologist remains the cornerstone of safe anesthesia care, protecting the patient from harm regardless of its source. Responding to the demands of the operating room environment requires on-the-spot decision making in a complex, uncertain, and risky setting. Only responsible, professional human beings acting in concert can perform this task; no machine that we devise now or in the foreseeable future will suffice. I have outlined the components of a dynamic decision-making process that successfully protects patients in almost all cases. However, being human, anesthesiologists do make errors along the way--errors we are just beginning to understand. Sometimes these errors are due to faulty vigilance or incompetence, but usually they are made by appropriately trained, competent practitioners. Anesthesiologists can err in many ways, and recognizing these ways makes it easier to analyze the events leading to an anesthetic accident. More importantly, it better equips us to eliminate or minimize them in the future--and this is the real challenge.
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Pressure damage to respiratory mucosa from overinflation of bronchial cuffs has been implicated as a cause of bronchial rupture, a rare but devastating complication of double-lumen endobronchial tubes (DLTs). We compared the pressure/volume characteristics of the bronchial cuffs of three different polyvinylchloride (PVC) DLTs and an equivalent sized red-rubber Robertshaw DLT. At the volume needed to seal effectively our bronchial model, two of the three PVC tube cuffs tested generated significantly less pressure than did that of the cuffs of the third PVC and the red-rubber Robertshaw tubes.
Using a comprehensive anesthesia simulation environment (CASE 1.2) we studied the response of anesthesia trainees (10 first-year residents and 9 second-year residents) to five simulated critical incidents: 1) endobronchial intubation; 2) kinked IV; 3) atrial fibrillation with hypotension; 4) breathing circuit disconnection; 5) cardiac arrest. Simulations were videotaped, and the response times for detecting and initiating correction of the problems were measured. Different problems had significantly different response characteristics. Breathing circuit disconnection and cardiac arrest were quickly detected (21 +/- 17 seconds; 7 +/- 5 seconds), and correction was begun quickly, although major errors in managing the cardiac arrest occurred in 58% of cases. Endobronchial intubation and atrial fibrillation took longer than the other problems to detect (105 +/- 142 seconds; 111 +/- 158 seconds) and to correct (555 +/- 358 seconds; 365 +/- 121 seconds). Intravenous kink was detected more slowly (238 +/- 269 seconds) but once discovered was quickly corrected. The response of different individuals was highly variable; experience level was a significant factor for correction (P = 0.03) but not for detection of problems overall. Because of high individual variation, experience was not a significant factor in correcting any signal problem. The data suggest that some types of problems are harder to handle than others and that individuals vary widely in their problem-handling abilities. Experience is a beneficial factor in anesthesia problem solving but not in a simple fashion. Vigilant detection of problems is only the first step in a complex response pathway that might be strengthened by improved protocols and repeated practice.
The effect of L-phenylisopropyladenosine (L-PIA), the A1 adenosine agonist, on the depth of anesthesia was investigated in halothane-anesthetized rats. L-PIA treatment reduced the minimum anesthetic concentration (MAC) of halothane that prevented 50% of animals from moving in response to a painful stimulus by 49%. MAC experiments performed with L-PIA given in conjunction with A1 adenosine receptor antagonists which either permeate the blood-brain barrier (8-phenyltheophylline [8-PT] or do not (8-sulphophenyltheophylline [8-So-PT]) indicate that central mechanisms are involved. Noradrenergic neurotransmission was diminished following L-PIA administration in halothane-anesthetized rats in all brain regions. These data suggest that acute L-PIA treatment decreases central noradrenergic neurotransmission and may represent the mechanism for the decrease in halothane dose to achieve an anesthetic endpoint anesthetic response to halothane.
The authors studied the reduction in anesthetic requirement (MAC) and the hemodynamic effects of the highly selective alpha 2-adrenergic agonist azepexole in isoflurane-anesthetized dogs. Eleven male beagles were anesthetized with isoflurane in oxygen. After a 2-h equilibration period, they determined isoflurane MAC and baseline hemodynamic function. Azepexole (at 0.1, 0.3, and 1.0 mg/kg) was administered via a right atrial port over 15 min, while each dog was given isoflurane at the MAC dose for that animal. Twenty minutes after the end of infusion, at a time when hemodynamic variables were stable, they reassessed hemodynamic function. They then determined isoflurane MAC again. In other experiments, dogs were pretreated with either idazoxan (the alpha 2-adrenergic antagonist; n = 5) or naloxone (the opiate antagonist; n = 7) prior to the administration of azepexole. Isoflurane MAC was determined before and after each dose of azepexole. Isoflurane MAC decreased as the dose of azepexole increased, to the extent that at the highest dose (1 mg/kg) the decrement in MAC was more than 85%. This reduction of MAC caused by azepexole could be completely prevented by pretreatment with idazoxan, while naloxone was without effect. Azepexole did not change mean arterial blood pressure, but caused heart rate and cardiac output to progressively decrease. The MAC-reducing effect of azepexole appears to be mediated by alpha 2 adrenoreceptors. Given the extent of the reduction of MAC, it is unlikely that inhibition of central noradrenergic neurotransmission through agonism of presynaptic alpha 2 adrenoreceptors is the sole explanation, since complete disruption of central noradrenergic tracts decreases MAC by only 40%.(ABSTRACT TRUNCATED AT 250 WORDS)
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Simulation is used extensively in industries that involve routine, but risky activities. The authors describe an anesthesia simulation environment that provides a re-creation of the anesthesiologist's task environment in a real operating room. The system provides appropriate inputs to standard monitoring equipment in common use during anesthesia, including ECG (with arrhythmias); invasive systemic arterial, pulmonary arterial, and central venous pressures (all coupled to ECG arrhythmias); automated cuff blood pressure; pulse oximetry; mass spectrometry; breathing circuit spirometry; and oxygen analysis. An intubation/thorax mannequin allows tracheal intubation and tube manipulation, and provides for simulation of occlusion, malposition, or disconnection of the tracheal tube, as well as regurgitation of gastric contents. The simulation is comprehensive in that it is "hands-on" and requires actual performance of most interventions using actual equipment. The simulation is conducted by a systems operator and a simulation director; the latter also acts in the roles of surgeon and circulating nurse. The simulator outputs are determined by a "script" that defines the consequences of routine anesthetic actions and pre-established critical incidents. Decisions about timing and override of the script are made by the simulation director. This control system offers maximum flexibility while maintaining clinical realism. The simulator experiences were judged as highly realistic by 21 subjects. Limitations in this version have centered on the mannequin (e.g., no patient movement, minimal or confusing physical signs) and will be addressed in future versions of the system. The authors suggest that anesthesia simulation can be accomplished at nominal expense and has major potential for training, continuing education, certification, and research.