J Neurosurg Anesthesiol
Volume 26, Number 3, July 2014
2. Dou W, Lin N, Ma W, et al. Transsphenoidal surgery in a patient with acromegaly and McCune–Albright syndrome: application of neuronavigation. J Neurosurg. 2008;108:164–169. 3. Chakravarty C, Yadav N, Ali Z, et al. Upper lip bite test in a patient with McCune Albright syndrome with acromegaly. J Clin Neurosci. 2010;17:258–259. 4. Dumitrescu CE, Collins MT. McCune-Albright syndrome. Orphanet J Rare Dis. 2008; 3:1–12. 5. Leet AI, Chebli C, Kushner H, et al. Fracture incidence in polyostotic fibrous dysplasia and the McCune-Albright syndrome. J Bone Miner Res. 2004;19:571–577.
Hypotension Artifact With Somatosensory-evoked Potential Monitoring To JNA Readers: Artifacts in the physiological monitoring of patients undergoing surgery where somatosensory-evoked potentials (SSEP) and other electrophysiological monitors have been described. In one report, hypotension was noted when the SSEP stimulation induced ventricular tachycardia in a patient with a pacemaker.1 Eipe and Bertram described a motion artifact in the arterial line tracing in a patient during SSEP stimulation that did not change the blood pressure reading.2 Artifacts in the electrocardiogram (ECG) and pulse oximetry have been observed with electrical stimulation of the peripheral nerve or from motion of the hand during motor stimulation.1,3,4 We noticed an alteration in the arterial line tracing associated with SSEP stimulation that was associated with a substantial reduction in the indicated systolic and diastolic blood pressure that was not true hypotension.
history of treated hypertension, chronic opioid use, and previous lumbar spine surgery. He was pretreated with 2 mg midazolam intravenously and taken to the operating suite where ECG, noninvasive blood pressure, and pulse oxygen saturation monitors were applied. After mask oxygenation anesthesia was induced with 200 mg propofol, 100 mg fentanyl, and 50 mg rocuronium and the trachea intubated. Total intravenous anesthesia was begun with infusions of propofol (165 to 175 mg/kg/ min), sufentanil (0.2 to 0.4 mg/kg/h), and lidocaine 2 mg/min. Desflurane (3%) was used briefly before positioning of the patient prone for the procedure. Once anesthetized a radial arterial line was placed and monitored using a BA50 monitoring module on a General Electric Daytex-Ohmeda Aisys Anesthesia Machine (Madison, WI). During the procedure it was noted that the arterial line systolic blood pressure recording would repeatedly decrease about 30 mm Hg over the 10 to 15 seconds after the initiation of SSEP monitoring. During this time the apparent height of the tracing did not change but small peaks were seen in the arterial line tracing similar to the small peaks seen in the oxygen saturation tracing (Fig. 1). The blood pressure as assessed by a noninvasive device was unchanged. Once the SSEP stimulation was concluded the blood pressure reading returned to the prestimulation level over the next 10 to 15 seconds.
Correspondence
RECOMMENDATIONS AND CONCLUSIONS In this case the blood pressure reading seems to be associated with the anesthesia monitor averaging the small pulsations associated with the SSEP stimulation with the larger arterial pulsations resulting in a lower than actual blood pressure reading. This could have resulted in a desire to elevate the blood pressure as hypotension is associated with spinal cord ischemia. This is similar to the desire to treat apparent supraventricular tachycardia resulting from the artifact of SSEP stimulation.3 In this case treatment was not instituted. Consistent with an artifact, the ECG did not show a corresponding artifact but the pulse oximetry did show an alteration which suggested that the artifact was caused by the mechanical motion resulting from the stimulation.5 The other indication of possible artifact in the arterial line was the pulse reading of 144 from the arterial tracing. Of note this may explain that the blood pressure recordings by the neurophysiological technician were lower than the actual blood pressure as the technician recorded the blood pressure during the SSEP acquisition period. As noted by Adhikary and Manickam,4 this mechanical effect could be eliminated by changing the location of the arterial line or the use of muscle relaxation, however, neither of these options were possible during this case because of
PRESENTATION A 40-year-old male with lumbar disk degeneration presented for prone posterior lumbar spine surgery. He had a The authors have no funding or conflicts of interest to disclose. r
2014 Lippincott Williams & Wilkins
FIGURE 1. The electrocardiogram, radial arterial line, and finger-pulse oximeter tracing before (A) and during (B) somatosensory-evoked potentials stimulation in this case. www.jnsa.com |
269
Correspondence
prone positioning and the need for monitoring electromyography and motor-evoked potentials. To the best of our knowledge, an associated decrease in blood pressure with SSEP monitoring has not been reported. Unnecessary treatment of hypotension from SSEP monitoring artifact could result in hypertension and bleeding in the operative field during spinal surgery. Therefore, we recommend “ruling out” SSEP artifact as a cause of hypotension before instituting treatment. Tod B. Sloan, MD, MBA, PhD Matthew Victor, MD Department of Anesthesiology, University of Colorado School of Medicine, Aurora, CO
REFERENCES 1. Regan JJ, McAfee PC, Achuff SC. The induction of cardiac arrhythmia and hypotension from spinal cord monitoring. A case report. Spine (Phila Pa 1976). 1986;11:1031–1032. 2. Eipe N, Bertram S. An unusual arterial waveform. J Neurosurg Anesthesiol. 2008;20: 68–69. 3. Marco AP, Rice K. Pseudoarrythmia from evoked potential monitoring. J Neurosurg Anesthesiol. 2001;13:143–145. 4. Adhikary SD, Manickam BP. Unusual waveforms during SSEP monitoring—facts and artifacts. J Neurosurg Anesthesiol. 2008; 20:207. 5. Patel SI, Souter MJ. Equipment-related electrocardiographic artifacts: causes, characteristics, consequences, and correction. Anesthesiology. 2008;108:138–148.
Ideal Blood Pressure Management and our Specialty To the Editor: Drummond et al1 are to be congratulated for their important addition to the literature discussing the relationship between perioperative and ambulatory blood pressure measurements and the effects that the often high-stress environment of the presurgical period may have on that relationship. I have 4 points to add to their excellent piece of clinical research: The author has no funding or conflicts of interest to disclose.
270 | www.jnsa.com
J Neurosurg Anesthesiol
(1) They note in their discussion that their observations were similar to a small 18-person study that found a day-of-surgery bias in mean arterial pressure of +5 mm Hg over ambulatory measurements. These findings also agree, in outline, with our larger study of 2807 veterans in which the day-of-surgery bias compared with primary care blood pressures was, on average, a modest +5.5 mm Hg systolic and +1.5 mm Hg diastolic.2 (2) Regarding the history of defining acceptable ranges of intraoperative blood pressures in terms of a percentage reduction from baseline, perhaps the earliest appearance of this conventional wisdom in the peer-reviewed literature came from a 1923 article from the preeminent anesthesiologist Elmer I. McKesson3 who suggested that intraoperative shock should be treated with intravenous normal saline until the blood pressure returned to within 90% of baseline. McKesson’s statement and similar guidelines have been promulgated over the years, often with limited evidence. As an echo of this tradition of poorly grounded pronouncements, McKesson’s original 1923 article itself remained entirely unreferenced until 2012.4 (3) In addition to the phenomenon of white-coat hypertension, our specialty should also be aware of the increasingly recognized inverse phenomenon of “masked hypertension.” Masked hypertension is present when otherwise hypertensive people (as determined by a gold-standard ambulatory blood pressure monitoring device) repeatedly demonstrate blood pressures in the normal range specifically within health care contexts.5 It may be projection that leads anesthesiologists to be more anxious to assume that our hypertensive patients are “just nervous” than we are to ask which of our apparently normotensive patients are in fact masked hypertensives who should also be treated differently while under our care.
Volume 26, Number 3, July 2014
(4) Most importantly, while Drummond and colleagues address the important question of how clinicians should account for whitecoat hypertension in defining the elusive “true baseline blood pressure” as a guide to intraoperative management, we should be cautious not to overlook perhaps the most important blood pressure intervention we could provide for our hypertensive patients— namely, prompt postoperative referral to an outpatient specialist for improved longitudinal control of hypertension.6 Although further studies are needed to establish the effectiveness of such referrals, other multidisciplinary preventive health efforts have been shown to improve chronic disease outcomes in several health care contexts, including the treatment of hypertension. The potential health benefits resulting from improved treatment of hypertension among surgical patients would far outweigh any possible improvements in perioperative outcomes that might result from slight modifications in our intraoperative blood pressure management. The need is clear. For example, in our own study referenced above,2 6.8% of patients who were not seen in a primary care within 6 months after surgery presented with day-of-surgery systolic blood pressures Z160 mm Hg, a level that carried >95% specificity for the finding of elevated ambulatory clinic blood pressure. Although defining ideal intraoperative goals for blood pressure is important for our specialty, the best goal for our patients may simply be to identify undertreated hypertension to promote timely postoperative primary care follow-up. Robert B. Schonberger, MD, MA Department of Anesthesiology Yale School of Medicine Yale University, New Haven, CT
REFERENCES 1. Drummond JC, Blake JL, Patel PM, et al. An observational study of the infuence of “white-coat hypertension” on day-of-surgery r
2014 Lippincott Williams & Wilkins
Volume 26, Number 3, July 2014
2. Dou W, Lin N, Ma W, et al. Transsphenoidal surgery in a patient with acromegaly and McCune–Albright syndrome: application of neuronavigation. J Neurosurg. 2008;108:164–169. 3. Chakravarty C, Yadav N, Ali Z, et al. Upper lip bite test in a patient with McCune Albright syndrome with acromegaly. J Clin Neurosci. 2010;17:258–259. 4. Dumitrescu CE, Collins MT. McCune-Albright syndrome. Orphanet J Rare Dis. 2008; 3:1–12. 5. Leet AI, Chebli C, Kushner H, et al. Fracture incidence in polyostotic fibrous dysplasia and the McCune-Albright syndrome. J Bone Miner Res. 2004;19:571–577.
Hypotension Artifact With Somatosensory-evoked Potential Monitoring To JNA Readers: Artifacts in the physiological monitoring of patients undergoing surgery where somatosensory-evoked potentials (SSEP) and other electrophysiological monitors have been described. In one report, hypotension was noted when the SSEP stimulation induced ventricular tachycardia in a patient with a pacemaker.1 Eipe and Bertram described a motion artifact in the arterial line tracing in a patient during SSEP stimulation that did not change the blood pressure reading.2 Artifacts in the electrocardiogram (ECG) and pulse oximetry have been observed with electrical stimulation of the peripheral nerve or from motion of the hand during motor stimulation.1,3,4 We noticed an alteration in the arterial line tracing associated with SSEP stimulation that was associated with a substantial reduction in the indicated systolic and diastolic blood pressure that was not true hypotension.
history of treated hypertension, chronic opioid use, and previous lumbar spine surgery. He was pretreated with 2 mg midazolam intravenously and taken to the operating suite where ECG, noninvasive blood pressure, and pulse oxygen saturation monitors were applied. After mask oxygenation anesthesia was induced with 200 mg propofol, 100 mg fentanyl, and 50 mg rocuronium and the trachea intubated. Total intravenous anesthesia was begun with infusions of propofol (165 to 175 mg/kg/ min), sufentanil (0.2 to 0.4 mg/kg/h), and lidocaine 2 mg/min. Desflurane (3%) was used briefly before positioning of the patient prone for the procedure. Once anesthetized a radial arterial line was placed and monitored using a BA50 monitoring module on a General Electric Daytex-Ohmeda Aisys Anesthesia Machine (Madison, WI). During the procedure it was noted that the arterial line systolic blood pressure recording would repeatedly decrease about 30 mm Hg over the 10 to 15 seconds after the initiation of SSEP monitoring. During this time the apparent height of the tracing did not change but small peaks were seen in the arterial line tracing similar to the small peaks seen in the oxygen saturation tracing (Fig. 1). The blood pressure as assessed by a noninvasive device was unchanged. Once the SSEP stimulation was concluded the blood pressure reading returned to the prestimulation level over the next 10 to 15 seconds.
Correspondence
RECOMMENDATIONS AND CONCLUSIONS In this case the blood pressure reading seems to be associated with the anesthesia monitor averaging the small pulsations associated with the SSEP stimulation with the larger arterial pulsations resulting in a lower than actual blood pressure reading. This could have resulted in a desire to elevate the blood pressure as hypotension is associated with spinal cord ischemia. This is similar to the desire to treat apparent supraventricular tachycardia resulting from the artifact of SSEP stimulation.3 In this case treatment was not instituted. Consistent with an artifact, the ECG did not show a corresponding artifact but the pulse oximetry did show an alteration which suggested that the artifact was caused by the mechanical motion resulting from the stimulation.5 The other indication of possible artifact in the arterial line was the pulse reading of 144 from the arterial tracing. Of note this may explain that the blood pressure recordings by the neurophysiological technician were lower than the actual blood pressure as the technician recorded the blood pressure during the SSEP acquisition period. As noted by Adhikary and Manickam,4 this mechanical effect could be eliminated by changing the location of the arterial line or the use of muscle relaxation, however, neither of these options were possible during this case because of
PRESENTATION A 40-year-old male with lumbar disk degeneration presented for prone posterior lumbar spine surgery. He had a The authors have no funding or conflicts of interest to disclose. r
2014 Lippincott Williams & Wilkins
FIGURE 1. The electrocardiogram, radial arterial line, and finger-pulse oximeter tracing before (A) and during (B) somatosensory-evoked potentials stimulation in this case. www.jnsa.com |
269
Correspondence
prone positioning and the need for monitoring electromyography and motor-evoked potentials. To the best of our knowledge, an associated decrease in blood pressure with SSEP monitoring has not been reported. Unnecessary treatment of hypotension from SSEP monitoring artifact could result in hypertension and bleeding in the operative field during spinal surgery. Therefore, we recommend “ruling out” SSEP artifact as a cause of hypotension before instituting treatment. Tod B. Sloan, MD, MBA, PhD Matthew Victor, MD Department of Anesthesiology, University of Colorado School of Medicine, Aurora, CO
REFERENCES 1. Regan JJ, McAfee PC, Achuff SC. The induction of cardiac arrhythmia and hypotension from spinal cord monitoring. A case report. Spine (Phila Pa 1976). 1986;11:1031–1032. 2. Eipe N, Bertram S. An unusual arterial waveform. J Neurosurg Anesthesiol. 2008;20: 68–69. 3. Marco AP, Rice K. Pseudoarrythmia from evoked potential monitoring. J Neurosurg Anesthesiol. 2001;13:143–145. 4. Adhikary SD, Manickam BP. Unusual waveforms during SSEP monitoring—facts and artifacts. J Neurosurg Anesthesiol. 2008; 20:207. 5. Patel SI, Souter MJ. Equipment-related electrocardiographic artifacts: causes, characteristics, consequences, and correction. Anesthesiology. 2008;108:138–148.
Ideal Blood Pressure Management and our Specialty To the Editor: Drummond et al1 are to be congratulated for their important addition to the literature discussing the relationship between perioperative and ambulatory blood pressure measurements and the effects that the often high-stress environment of the presurgical period may have on that relationship. I have 4 points to add to their excellent piece of clinical research: The author has no funding or conflicts of interest to disclose.
270 | www.jnsa.com
J Neurosurg Anesthesiol
(1) They note in their discussion that their observations were similar to a small 18-person study that found a day-of-surgery bias in mean arterial pressure of +5 mm Hg over ambulatory measurements. These findings also agree, in outline, with our larger study of 2807 veterans in which the day-of-surgery bias compared with primary care blood pressures was, on average, a modest +5.5 mm Hg systolic and +1.5 mm Hg diastolic.2 (2) Regarding the history of defining acceptable ranges of intraoperative blood pressures in terms of a percentage reduction from baseline, perhaps the earliest appearance of this conventional wisdom in the peer-reviewed literature came from a 1923 article from the preeminent anesthesiologist Elmer I. McKesson3 who suggested that intraoperative shock should be treated with intravenous normal saline until the blood pressure returned to within 90% of baseline. McKesson’s statement and similar guidelines have been promulgated over the years, often with limited evidence. As an echo of this tradition of poorly grounded pronouncements, McKesson’s original 1923 article itself remained entirely unreferenced until 2012.4 (3) In addition to the phenomenon of white-coat hypertension, our specialty should also be aware of the increasingly recognized inverse phenomenon of “masked hypertension.” Masked hypertension is present when otherwise hypertensive people (as determined by a gold-standard ambulatory blood pressure monitoring device) repeatedly demonstrate blood pressures in the normal range specifically within health care contexts.5 It may be projection that leads anesthesiologists to be more anxious to assume that our hypertensive patients are “just nervous” than we are to ask which of our apparently normotensive patients are in fact masked hypertensives who should also be treated differently while under our care.
Volume 26, Number 3, July 2014
(4) Most importantly, while Drummond and colleagues address the important question of how clinicians should account for whitecoat hypertension in defining the elusive “true baseline blood pressure” as a guide to intraoperative management, we should be cautious not to overlook perhaps the most important blood pressure intervention we could provide for our hypertensive patients— namely, prompt postoperative referral to an outpatient specialist for improved longitudinal control of hypertension.6 Although further studies are needed to establish the effectiveness of such referrals, other multidisciplinary preventive health efforts have been shown to improve chronic disease outcomes in several health care contexts, including the treatment of hypertension. The potential health benefits resulting from improved treatment of hypertension among surgical patients would far outweigh any possible improvements in perioperative outcomes that might result from slight modifications in our intraoperative blood pressure management. The need is clear. For example, in our own study referenced above,2 6.8% of patients who were not seen in a primary care within 6 months after surgery presented with day-of-surgery systolic blood pressures Z160 mm Hg, a level that carried >95% specificity for the finding of elevated ambulatory clinic blood pressure. Although defining ideal intraoperative goals for blood pressure is important for our specialty, the best goal for our patients may simply be to identify undertreated hypertension to promote timely postoperative primary care follow-up. Robert B. Schonberger, MD, MA Department of Anesthesiology Yale School of Medicine Yale University, New Haven, CT
REFERENCES 1. Drummond JC, Blake JL, Patel PM, et al. An observational study of the infuence of “white-coat hypertension” on day-of-surgery r
2014 Lippincott Williams & Wilkins
