Anesth Analg 2001;92:166-171
© 2001 International Anesthesia Research Society
NEUROSURGICAL ANESTHESIA
Intraoperative Monitoring in Neuroanesthesia: A National Comparison Between Two Surveys in Germany in 1991 and 1997
Sabine Himmelseher, MD*,
Ernst Pfenninger, MD ,
Christian Werner, MD*, and
for the Scientific Neuroanesthesia Research Group of the German Society of Anesthesia and Intensive Care Medicine
*Klinik für Anaesthesiologie, Technische Universitaet Muenchen, Munich; and Universitaetsklinik für Anaesthesiologie, Klinikum der Universitaet Ulm, Ulm, Germany
Address correspondence and reprint requests to Sabine Himmelseher, Klinik für Anaesthesiologie, Klinikum rechts der Isar, Technische Universitaet Muenchen, Ismaningerstr. 22, D-81675, Muenchen, Germany. Address e-mail to S.Himmelseher{at}lrz .tu-muenchen.de.
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Abstract
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Two surveys initiated by the Neuroanesthesia Research Group of the German Society of Anesthesia and Intensive Care Medicine examined the practice of intraoperative monitoring during intracranial procedures in Germany in 1991 and 1997. Questionnaires were mailed to departments that were registered members of the German Society of Anesthesia and Intensive Care Medicine and that provided neuroanesthesia service on a routine basis in 1991. In 1997, the survey was repeated in the 1991 respondents. In 1991, 68 departments and in 1997, 44 departments returned completed questionnaires, indicating a response rate of 87% for 1991 and of 65% for 1997. Compared with 1991, the standards for monitoring, such as surveillance of oxygenation, ventilation, circulation, and body temperature, were universally applied in adult and pediatric patients in 1997. Overall, there was a 20% increase in neuromuscular blockade monitoring and in the use of electroencephalography and evoked potentials in 1997 compared with 1991. Further brain-specific monitoring was rarely provided in 1997. Overall, jugular venous oximetry was used in 20% and transcranial Doppler ultrasonography in 15% of responding hospitals. To detect venous air embolism in sitting patients, 75% of all responding hospitals used precordial Doppler ultrasonography in both years, whereas transesophageal echocardiography was more often used in 1997 (38%) as compared with 1991 (17%).
Implications: Standards of anesthetic monitoring were surveyed in neuroanesthesia in Germany in 1991 and 1997. Central nervous system monitoring was not the standard of practice.
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Introduction
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Neurosurgical patients are at increased risk of secondary injury to the central nervous system (CNS) (1–3). Because the incidence and duration of secondary insults may have a significant impact on unfavorable neurologic outcome (4–6), timely detection and treatment of intraoperative complications is of special importance for neuroanesthesiologists (7). This is supported by the results of the American Society of Anesthesiologists’ Closed Claims Study, in which adverse outcome after injury after anesthesia was deemed preventable with the use of better monitoring modalities (3).
To assess the status of intraoperative monitoring in neuroanesthesia in Germany, the Scientific Neuroanesthesia Research Group of the German Society of Anesthesia and Intensive Care Medicine (DGAI) initiated a nationwide survey on the practice of monitoring during neuroanesthetics in 1991. The availability of a large sample size on the practice of monitoring performed in routine patient care should provide a general platform for continuing improvement in the safety and quality of care rendered to neuroanesthesiological patients. In view of the introduction of new cerebral monitoring technologies into clinical practice, the survey was repeated in the same hospitals in 1997. The repeat survey also aimed at analyzing the effects of recommendations set for monitoring patients who were in the sitting position. These were published on behalf of the German Neuroanesthesia Research Group in 1995 (8).
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Methods
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The 1991 survey was conducted in all anesthesiology departments in Germany that were registered members of the DGAI and that provided neuroanesthesia service on a routine basis. A questionnaire was mailed to department chairs indicating the purpose and importance of the survey. To update information and to identify differences from 1991, the survey was repeated in the 1991 respondents in 1997. The survey’s results on use of anesthetic techniques and drugs in neuroanesthesia in Germany in 1991 vs 1997 were reported elsewhere (9).
In the general section of the survey, information on the characteristics of the hospital was requested. In the specific section of the survey, details of intraoperative monitoring practices during tumor surgery in the supine position, during aneurysm surgery in the supine position, during tumor and aneurysm surgery in the sitting position, and during procedures in the pediatric population (aged 0–5 yr) were addressed. To explore individual practices, respondents were encouraged to indicate alternative methods of surveillance, as performed in their hospital.
The surveys asked structured questions with sets of defined answers, with the option of using only one or a combination of several answers. Figure 1 shows a part of the original questionnaire as an example for the design of the questions. All questions could be answered anonymously.
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Figure 1. Example of section in original questionnaire: monitoring during aneurysm surgery in the supine position.
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Questionnaires that were returned within 10 wk after mailing were used in the analyses, including those with partially completed surveys. All responses were processed anonymously. Results were tabulated, and to allow for comparisons between 1991 and 1997, percentages of use of monitoring techniques, as indicated in the tables, were calculated. In the results, a use of "X%" indicates that X% of hospitals regularly used a particular monitor all the time. If there were marked differences in the response gained from university institutions, community hospitals, and hospitals with private holders, results were stratified by type of hospital.
Because new cerebral monitoring modalities have been introduced into practice between 1991 and 1997, the 1991 survey was slightly expanded to include some of this current technology.
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Results
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Seventy-eight questionnaires were mailed in 1991, and 68 questionnaires were sent in 1997. In 1991, 68 departments, and in 1997, 44 departments returned completed questionnaires, indicating an 87% response rate for 1991 and a 65% response rate for 1997. There was no difference between the years in the proportion of types of hospitals responding. The characteristics of the responding hospitals are presented in Table 1. Table 2 shows that the standard anesthetic monitors, including body temperature monitoring, were almost always used in 1991, whereas they were universally applied in 1997. Overall, there was a 20% increase in neuromuscular blockade monitoring in 1997 compared with 1991. As indicated in Table 3, neuromuscular blockade monitors were more commonly used during aneurysm surgery in the supine position and during all procedures in the sitting position in 1997. Overall, there was a 20% increase in the use of electroencephalography (EEG) and evoked potentials (EP) in 1997 compared with 1991, but both were still infrequently used ( Table 4). Other CNS monitoring was rarely provided in 1997. Overall, jugular venous oximetry was used in 20% and transcranial Doppler ultrasonography (TCD) in 15% of responding hospitals. When applied, the TCD was used more frequently in university institutions ( Table 5). To detect venous air embolism in sitting patients, 75% of all responding hospitals used precordial Doppler ultrasonography in both years, whereas transesophageal echocardiography (TEE) was more often used in 1997 (38%) as compared with 1991 (17%). University institutions applied the precordial Doppler less often and the TEE more frequently in 1997 than in 1991 ( Table 6), whereas community hospitals and hospitals with private holders used the precordial Doppler more often in 1997 than in 1991. With regard to the status of monitoring in pediatric patients, Table 7 shows a similar change in use of monitors as that observed for adult patients.
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Discussion
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Our analysis is the first assessment of monitoring during neuroanesthesia in Germany. Although the designate for neuroanesthesiology completed the surveys, some limitations must be considered. Because we did not apply mechanisms to ensure that answers were based on actual practice or on the perception of what members of the department were doing, it is possible that the intention to monitor, rather than reality, was sometimes reported. To facilitate honest responses, questions were to be answered anonymously.
Our recovery rate of 87% of surveys in 1991 and of 65% in 1997 was similar to that reported by a British (10) and a German (11) survey on monitoring in the sitting position in neurosurgery and more than the response rate for a survey of members of the Society of Neurosurgical Anesthesia and Critical Care regarding anesthesia for carotid endarterectomy (CEA) (12). The many surveys performed in German anesthesiology in recent years, with the result of a "certain tiredness" from answering questionnaires by anesthesiologists, is the most likely reason for the decreased recovery rate we obtained in 1997. To prevent a bias in our report’s information caused by possible changes in the population of respondents, we calculated the percentages of values on the basis of the numbers of hospitals responding for the individual monitors. In addition, because the proportion of the hospitals responding to the two surveys was comparable, we regard a comparison of the 1991 data versus the 1997 data as reasonable.
Because our surveys did not include questions asking for reasons of changes in monitoring practice, we cannot claim cause for use or change of use of specific techniques. Nevertheless, several developments are interesting to note. In comparison with 1991, the standards for monitoring as recommended by the American Society of Anesthesiologists (13), including monitoring of systemic oxygenation, ventilation, hemodynamics, and body temperature (13–15), were implemented as a standard in German neuroanesthesia in 1997. Because there is evidence that secondary injury to the brain is an critical issue in determining neurological outcome (4–6), the use of standard monitors and the frequent invasive blood pressure measurements could indicate that this has generally been recognized. Pulmonary artery catheters were used by a small percentage of responding hospitals, and some of the hospitals noted that they restricted use to special indications, such as monitoring Triple-H therapy in subarachnoid hemorrhage (16), possibly because indications for pulmonary artery catheters have not changed between surveys. In contrast, body temperature monitoring was much more common in 1997 than in 1991. However, because we did not differentiate between the site of temperature measurements, the temperatures assessed did not necessarily reflect brain temperature values (7,17).
There was a 20% increase in use of the EEG/EP in 1997 compared with 1991. It is conceivable that this relates to the renewed interest in the EEG on the basis of its noninvasive nature and improved hardware, including readily available computed EEG values (18). Because monitoring of EP can assess the integrity of neural pathways during neurovascular procedures (19), it is surprising that this method was used by only 35% of all respondents during aneurysm surgery in 1997. However, our results must not be compared with the rate of EEG monitoring during CEAs. Whereas CEAs are sometimes conducted by vascular surgeons without involvement of anesthesiologists, our surveys focused on craniotomies performed under neuroanesthesiological care only.
In 1997, <30% of responding hospitals used jugular venous oximetry to assess the balance between cerebral oxygen delivery, oxygen consumption, and the cerebral lactate oxygen index. This could relate to the invasive nature of the technique, the frequency of complications, or poor-quality data (20–22). Despite these pitfalls, any prompt detection of brain desaturation allows for immediate and specific treatment to decrease the extent of ischemic events. This is justified by the current view that a decrease in brain oxygenation may occur despite a maintenance of arterial blood pressure and adequate oxygen supply to the brain (6,22). Although TCD is a feasible and noninvasive modality for detecting relative changes in cerebral blood flow (7,23), only 25% of university institutions indicated its use. This may be explained by the focus of our study, which concerned intraoperative monitors rather than an evaluation of the domains of TCD, such as detection of vasospasm in subarachnoid hemorrhage (7,23).
Prevention and management of venous or paradoxical air embolism with patients in the sitting position is a crucial issue in neuroanesthesiology (2,24). The German Neuroanesthesia Research Group therefore set recommendations in 1995 that allowed for a timely detection of air embolism (8). Electrocardiography, capnography, pulse oximetry, invasive arterial and central venous blood pressure monitors, and the precordial Doppler were established as standard, obligatory monitors; TEE was regarded as an optional monitor. Comparing the 1997 results with the modalities recommended in 1995, the standard monitors were used in all responding hospitals of our study. However, whereas university institutions used the precordial Doppler less often and the TEE more frequently, community hospitals and hospitals with private holders more often used the precordial Doppler in 1997 compared with 1991. It thus appears likely that when TEE was used, precordial Doppler ultrasonography was not applied additionally. Unfortunately, the recommended combination of capnometry and, at least, either the precordial Doppler or TEE, was not performed in all responding hospitals in 1997. Our results thus compare with a German survey indicating a 69% use of the precordial Doppler and a 4% use of TEE in the sitting position in 1995 (11). A 1991 survey in British centers found a 60% use of precordial Doppler ultrasonography, without mentioning TEE (10).
In summary, the standards for basic anesthetic monitoring are established in neuroanesthesia in Germany. CNS monitoring was not a standard of practice in 1997, suggesting economic restraints, lack of confidence, or training in the various methods. Future study should aim at improving availability of information on monitoring practices during neuroanesthesia and effects on the occurrence of adverse neurological outcome.
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Acknowledgments
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The authors acknowledge Dr. G. Cunitz, Klinik für Anaesthesie und operative Intensivtherapie, Knappschaftskrankenhaus Ruhr-Universitaet, Bochum, and Dr. D. Heuser, Klinik für Anaesthesiologie und operative Intensivmedizin, Klinikum der Stadt Nuernberg, Germany, for participation in designing the 1991 survey. The authors and the Scientific Neuroanesthesia Research Group of the DGAI thank all responding hospitals that spent their time to complete and return the questionnaires of the surveys.
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Accepted for publication September 19, 2000.
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Abstract
Introduction
