The effect of deteriorating visual acuity and contraction of visual fields on performance by anesthesiologists is not known. Boucek et al. (1) demonstrated that wearing laser goggles resulted in an increased frequency of medication sorting errors and a deterioration of performance by anesthesiologists. Gaba (2) reported that there is rarely one cause of an adverse outcome but rather that most adverse outcomes evolve through a series of events that join to create a catastrophe. He reported that esophageal or endobronchial intubation were among the most frequently cited critical incidents of anesthesia that resulted in seemingly preventable anesthetic misadventures (2).
We wondered how a decline in visual acuity or a contraction of visual fields would affect an anesthesiologist’s ability to intubate the trachea. We theorized that a deterioration in visual acuity or a contraction of visual fields might lead to esophageal or endobronchial intubation, which in turn might initiate a critical incident.
The Sir Mortimer B. Davis Jewish General Hospital (SMBD-JGH) is a McGill University Teaching Hospital in which 12 fellowship certified anesthesiologists participated in this study. Consent was obtained from all anesthesiologists. Two adult intubating mannequins (A) Laerdal Adult Intubation Model (Asmund S. Laerdal Co., Stavanger, Norway) and (B) Ambu Intubation Trainer (Laryngeal Mask Co. Ltd, Brondby, Denmark) were placed on standard operating room (OR) tables in a vacated OR. Mannequin A had “lungs” that would inflate whereas Mannequin B had only a trachea distal to the anatomical upper airway.
The anesthesiologists were brought individually into the OR and asked to intubate each of the mannequins under six different conditions. Five sets of custom-made ophthalmologic goggles were used to simulate the vision impairments. These were obtained from the SMBD-JGH low-vision clinic. The goggles had been made specifically for low-vision simulation in conformance with accepted standards. The vision impairment affected near vision as well as far and Condition 2 was the most severe impairment of all. The six conditions were:
- Condition 1: Anesthesiologist’s usual vision. Those anesthesiologists who wore corrective lenses (glasses or contact lenses) fitted the ophthalmologic goggles over their lenses. No anesthesiologist had any other obvious visual impairment.
- Condition 2: Represented conditions of central-vision loss with 20/500 bilaterally (oculus uterque [O.U.]) and a 24° central scotoma bilaterally (i.e., diabetic retinopathy, optic neuritis, etc.).
- Condition 3: Represented conditions of peripheral-field loss with 20/20 O.U. and a 7° visual field (i.e., glaucoma, retinitis pigmentosa, etc.).
- Condition 4: Represented conditions of peripheral-field loss with 20/20 O.U. and a 3.5° visual field.
- Condition 5: Represented conditions of central-vision loss with 20/200 O.U. and a 12° central scotoma bilaterally.
- Condition 6: Represented conditions of right ocular media opacity and 20/70 left eye (oculus sinister) (i.e., corneal problems, cataracts, etc.).
The same trained anesthesia technician (STT) was present for all intubations, simulating the normal practice. She stood to the right of the anesthesiologist and gave him or her a fresh laryngoscope. The batteries were fully charged and the laryngoscope light was on. Once the anesthesiologist had identified the larynx, she handed him or her a lubricated 7.5-mm internal diameter endotracheal (ETT) tube. The mannequin was then intubated. The technician handed the anesthesiologist a 10-mL syringe to inflate the ETT tube cuff and a Laerdal bag (Asmund S. Laerdal Co.) to “ventilate the patient.”
The anesthesiologist was timed by stopwatch from the moment he or she grasped the laryngoscope until he or she was satisfied that the ETT tube was in the trachea and he or she was ventilating both lungs. Bilateral lung ventilation was confirmed by either stethoscope (Mannequin A) or visual inspection (Mannequin A or B). The sequence of the six conditions for intubation for each mannequin was generated by a random sequence computer program. Each anesthesiologist was asked to intubate each of the mannequins three times in the same randomized sequence. Mannequin A was always intubated first. Variables such as the position of the mannequin head, use of stylet, and laryngoscope blade size were managed according to the preference of each anesthesiologist.
Simple means and standard deviations were calculated for the various times to intubation. A multiple analysis of variance was used to determine the effects of anesthesiologist, mannequin, trial, and visual condition on the time to intubate. A Dunnett post test adjustment was applied for multiple comparisons. A level of P < 0.05 was considered significant. The data were analyzed by using the SAS system (SAS Institute, Cary, NC).
The 12 anesthesiologists ranged in age from 33 to 61 yr and they had been specialty certified from 1 to 27 yr. All anesthesiologists completed the trials on Mannequin A but two refused to continue the trials on Mannequin B and were removed from the model. The times to intubation on Mannequin A for these two anesthesiologists were within the range of the other subjects. The mean (±sd) time in seconds for successful intubation of Mannequin A for conditions 1–6 were respectively: 16.0 ± 3.3, 31.9 ± 10.4, 26.4 ± 9.0, 26.4 ± 7.7, 22.4 ± 5.1, 25.5 ± 16.9. Two anesthesiologists were unable to intubate under Condition 2.
The mean (±sd) time in seconds for successful intubation of Mannequin B for conditions 1–6 were respectively: 16.6 ± 6.6, 26.9 ± 10.0, 21.4 ± 9.2, 21.4 ± 5.8, 21.5 ± 7.7, 17.7 ± 5.1. One anesthesiologist was unable to intubate under Condition 2.
Multiple analysis of variance revealed highly significant differences among the four predictors (anesthesiologist, mannequin, trial, and condition). Interactions were first included in the models. No interactions were found to be significant, and were removed from the models (Table 1).
There were 6 esophageal intubations in the study—4 occurred under Condition 2, and 1 each occurred in Conditions 4 and 6 (Table 2).
This is the first study attempting to identify the impact of vision impairment on an anesthesiologist’s ability to intubate the trachea. We found that although there was a significant difference in the time it took to successfully intubate between the two trials, this difference narrowed rapidly by the second mannequin. In other words, the anesthesiologists learned to adapt rapidly.
Our study was designed to simulate the clinical situation in several ways. We were in a standard OR with the usual lighting and positioning of the “patient.” We assisted the anesthesiologist as per routine. The anesthesiologist was given his or her choice of laryngoscope, blade, and stylet. We tried to optimize the intubating conditions for each anesthesiologist. However, a significant weakness of our study was that the visual impairment was imposed acutely and left no time for accommodation or chronic adaptation. We used plastic mannequins whose “tissue compliance” differs considerably from humans. The internal airway structure of the mannequins is also quite crude. Furthermore, the OR was quiet, with no electrocardiogram or pulse oximetry or other health professionals, unlike the usual clinical situation. The extra noise, commotion, or interperson airway variability in the clinical situation might negatively affect a vision-impaired anesthesiologist’s ability to visualize the larynx. Intubations under vision-impaired conditions in vivo might therefore be much more challenging.
It is true that vision impairment prolonged the time to successful intubation and there were esophageal intubations. This extra uncertainty in placing the ETT tube might result in increased morbidity. However, the mean time to successful intubation even with the most severe vision impairment tested was still relatively quick. Furthermore, the vision impairment was immediate and did not evolve over time. A chronic vision impairment might have led to adaptive behavior of the anesthesiologists and may not have resulted in as significant a difference in time to intubation. Other medical acts could be affected as well, but no other medical technique is as commonly practiced or entails such a dramatic difference between success and failure. We did not assess time to successful IV insertion, for example, because the morbidity associated with unsuccessful IV cannulation, although real, does not carry the same consequences as unsuccessful ETT intubation. We also did not measure response times to various alarms under the impaired-vision conditions. Because vision is so important to anesthesiologists (3), such a study might be informative.
Clinical examples in which acute vision impairment of these severities might occur include diabetic retinopathy with hemorrhage or exudative macular degeneration. We thought that acute severe vision impairment would prevent anesthesiologists from being able to intubate, or that intubation would take so long that patients would be at risk. We were surprised by the quality and speed of intubation under the five abnormal conditions. However, two anesthesiologists would not complete Mannequin B and one anesthesiologist was never able to intubate under Condition 2. We explain this as an individual response to a challenge. We think some anesthesiologists would react by “quitting” whereas others would persevere and use whatever clues/tricks they could to complete the task. We think the implication of this study is that anesthesiologists who develop acute severe vision impairment might have more difficulty intubating, which could initiate more critical incidents. However, this conclusion is not necessarily applicable to those with chronic vision impairment.
In summary, in this study, we assessed the time to successful intubation under an anesthesiologist’s usual vision and five vision-impaired conditions. We demonstrated that anesthesiologists adapted rapidly to the vision-impaired conditions but were not quite as capable at intubating under the vision-impaired conditions. The effects of chronic vision impairment remain undetermined.
The authors gratefully acknowledge the assistance of Mr. William Stewart of Vitaid Pharmaceuticals and Mr. Louis Belle-Isle of Vanier Community College in loaning the mannequins for this study. The authors thank the members of the SMBD-JGH Department of Anesthesia for cooperating unhesitatingly in the study. The authors also gratefully acknowledge the secretarial assistance of Mrs. Sarah Scholl in the preparation of the manuscript.
1. Boucek C, Freeman JA, Bircher NG, Tullock W. Impairment of anesthesia task performance by laser protection goggles. Anesth Analg 1993; 77: 1232–7.
2. Gaba DM. Human error in anesthetic mishaps. Int Anesthesiol Clin 1989; 27: 137–47.
3. Gurushanthaiah K, Weinger MB, Englund CE. Visual display format affects the ability of anesthesiologists to detect acute physiologic changes: a laboratory study employing a clinical display simulator. Anesthesiology 1995; 83: 1184–93.
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