Armin Schubert

Side Effects of Mild Hypothermia

Mild hypothermia is increasingly touted as a low risk clinical measure in brain protection. This article reviews potential adverse effects of mild hypothermia by organ System and suggests a risk assessment framework for clinical decision making.

Mild Hypothermia as a Protective Therapy during Intracranial Aneurysm Surgery: A Randomized Prospective Pilot Trial

OBJECTIVE To conduct a pilot trial of mild intraoperative hypothermia during cerebral aneurysm surgery. METHODS One hundred fourteen patients undergoing cerebral aneurysm clipping with (n = 52) (World Federation of Neurological Surgeons score < or =III) and without (n = 62) acute aneurysmal subarachnoid hemorrhage (SAH) were randomized to normothermic (target esophageal temperature at clip application of 36.5 degrees C) and hypothermic (target temperature of 33.5 degrees C) groups. Neurological status was prospectively evaluated before surgery, 24 and 72 hours postoperatively (National Institutes of Health Stroke Scale), and 3 to 6 months after surgery (Glasgow Outcome Scale). Secondary outcomes included postoperative critical care requirements, respiratory and cardiovascular complications, duration of hospitalization, and discharge disposition. RESULTS Seven hypothermic patients (12%) could not be cooled to within 1 degrees C of target temperature; three of the seven were obese. Patients randomized to the hypothermic group more frequently required intubation and rewarming for the first 2 hours after surgery. Although not achieving statistical significance, patients with SAH randomized to the hypothermic group, when compared with patients in the normothermic group, had the following: 1) a lower frequency of neurological deterioration at 24 and 72 hours after surgery (21 versus 37-41%), 2) a greater frequency of discharge to home (75 versus 57%), and 3) a greater incidence of good long-term outcomes (71 versus 57%). For patients without acute SAH, there were no outcome differences between the temperature groups. There was no suggestion that hypothermia was associated with excess morbidity or mortality. CONCLUSION Mild hypothermia during cerebral aneurysm surgery is feasible in nonobese patients and is well tolerated. Our results indicate that a multicenter trial enrolling 300 to 900 patients with acute aneurysmal SAH will be required to demonstrate a statistically significant benefit with mild intraoperative hypothermia.

Relation between perioperative hypertension and intracranial hemorrhage after craniotomy.

Background Previous data suggest that systemic hypertension (HTN) is a risk factor for postcraniotomy intracranial hemorrhage (ICH). The authors examined the relation between perioperative blood pressure elevation and postoperative ICH using a retrospective case control design. Methods The hospital’s database of all patients undergoing craniotomy from 1976 to 1992 was screened. Coagulopathic and unmatchable patients were excluded. There were 69 evaluable patients who developed ICH postoperatively (n = 69). A 2-to-1 matched (by age, date of surgery, pathologic diagnosis, surgical procedure, and surgeon) control group without postoperative ICH was assembled (n = 138). Preoperative, intraoperative, and postoperative blood pressure records (up to 12 h) were examined. Incidence of perioperative HTN (blood pressure ≥ 160/90 mmHg) and odds ratios for ICH were determined. Results Of the 11,214 craniotomy patients, 86 (0.77%) suffered ICH, and 69 fulfilled inclusion criteria. The incidence of preoperative HTN was similar in the ICH (34%) and the control (24%) groups. ICH occurred 21 h (median) postoperatively, with an interquartile range of 4–52 h. Sixty-two percent of ICH patients had intraoperative HTN, compared with only 34% of controls (P < 0.001). Sixty-two percent of the ICH patients had prehemorrhage HTN in the initial 12 postoperative hours versus 25% of controls (P < 0.001), with an odds ratio of 4.6 (P < 0.001) for postoperative ICH. Hospital stay (median, 24.5 vs. 11.0 days), and mortality (18.2 vs. 1.6%) were significantly greater in the ICH than in the control groups. Conclusions ICH after craniotomy is associated with severely prolonged hospital stay and mortality. Acute blood pressure elevations occur frequently prior to postcraniotomy ICH. Patients who develop postcraniotomy ICH are more likely to be hypertensive in the intraoperative and early postoperative periods.

Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring.

EVOKED potentials (EPs) are the electrophysiologic responses of the nervous system to sensory or motor stimulation. Stimulating the nervous system initiates the transmission of neural signals that may be recorded as EPs from various points along the stimulated pathway. Intraoperative monitoring (IOM) of EP has gained popularity because EPs reflect the functional integrity of neural pathways in anesthetized patients undergoing surgical procedures that place nervous system structures in jeopardy. EPs monitored intraoperatively include somatosensory evoked potentials (SSEPs), brainstem auditory evoked potentials (BAEPs; also referred to as auditory brainstem responses), visual evoked potentials (VEPs), and motor evoked potentials. Additional EP modalities include dermatomal sensory evoked potentials, electrocochleography, and electromyography. Intraoperative EP changes may result from surgical injury or ischemia of the specific neural pathway, or they may be due to nonspecific physiologic or pharmacologic influences. Physiologic factors that may influence EPs include temperature, blood pressure, hematocrit, acid– base balance, and oxygen and carbon dioxide tensions. Anesthetic drugs and sedatives are the most common pharmacologic causes of nonspecific EP changes. This review discusses the physiologic and pharmacologic factors (including newer anesthetic agents and adjuncts) that influence sensory evoked potentials (SEPs), focussing on SSEPs, BAEPs, and VEPs. For ease of reference and to allow better comparisons between anesthetic agents, the discussion of anesthetic effects is separated from physiologic effects. The review intends to help clinicians recognize the important confounding perturbations so that intraoperative changes in SEPs can be interpreted optimally. It also aims to guide anesthetic planning so that reliable intraoperative EP monitoring can be accomplished during effective and safe anesthesia.

Bispectral Index monitoring correlates with sedation scales in brain-injured patients

Objective:Monitoring critically ill, brain-injured patients with a decreased level of consciousness is challenging. Our goal is to determine in this population the correlation between the Bispectral Index (BIS) and three commonly used sedation agitation scales: the Richmond Agitation-Sedation Scale (RASS), the Sedation-Agitation Scale (SAS) and the Glasgow Coma Scale (GCS) scores. Design:Prospective, single-blinded observational study. Setting:Eight-bed neurology-neurosurgery intensive care unit at the Cleveland Clinic Foundation. Patients:Thirty critically ill patients admitted to the neurointensive care unit with primary brain injury and a decreased level of consciousness. Measurements and Main Results:Patients were prospectively evaluated for level of consciousness using the RASS, SAS, and GCS every hour and simultaneously were monitored continuously with a BIS monitor for 6 hrs. A Spearman’s correlation coefficient was used to correlate the BIS scores with clinical scales. In 15 patients monitored with the newer BIS XP version, the BIS values correlated significantly with the RASS (R2 = .810; p < .0001), SAS (R2 = .725; p < .0001), and GCS (R2 = .655; p < .0001). In 15 patients monitored with the older BIS 2.1.1 software, the correlation was as follows: for RASS, R2 = .30 (p < .008), for SAS: R2 = .376 (p < .001), and for GCS: R2 = .274 (p < .015). This correlation was maintained in patients who received sedative medications. Conclusions:A statistically significant correlation existed between BIS values and the RASS, SAS, and GCS scores in critically ill brain-injured patients, with and without sedation. The newer BIS XP software package may be a useful adjunctive tool in objective assessment of level of consciousness in brain-injured patients.

Is Depth of Anesthesia, as Assessed by the Bispectral Index, Related to Postoperative Cognitive Dysfunction and Recovery?

We randomized 74 patients to either a lower Bispectral Index (BIS) regimen (median BIS, 38.9) or a higher BIS regimen (mean BIS, 50.7) during the surgical procedure. Preoperatively and 4–6 wk after surgery, the patients’ cognitive status was assessed with a cognitive test battery consisting of processing speed index, working memory index, and verbal memory index. Processing speed index was 113.7 ± 1.5 (mean ± se) in the lower BIS group versus 107.9 ± 1.4 in the higher BIS group (P = 0.006). No difference was observed in the other two test battery components. Somewhat deeper levels of anesthesia were therefore associated with better cognitive function 4–6 wk postoperatively, particularly with respect to the ability to process information.

Effects of Anesthetic Agents and Physiologic Changes on Intraoperative Motor Evoked Potentials

Motor evoked potentials (MEPs) have shown promise as a valuable tool for monitoring intraoperative motor tract function and reducing postoperative plegia. MEP monitoring has been reported to contribute to deficit prevention during resection of tumors adjacent to motor structures in the cerebral cortex and spine, and in detecting spinal ischemia during thoracic aortic reconstruction. 1–6 Many commonly used anesthetic agents have long been known to depress MEP responses and reduce MEP specificity for motor injury detection. Although new stimulation techniques have broadened the spectrum of anesthetics that can be used during MEP monitoring, certain agents continue to have dose-dependent effects on MEP reliability. Understanding the effects of anesthetic agents and physiologic alterations on MEPs is imperative to increasing the acceptance and application of this technique in the prevention of intraoperative motor tract injury. This review is intended as an overview of the effects of anesthetics and physiology on the reproducibility of intraoperative myogenic MEP responses, rather than an analysis of the sensitivity and specificity of this monitoring method in the prevention of motor injury.

The Influence of Scalp Infiltration with Bupivacaine on Hemodynamics and Postoperative Pain in Adult Patients Undergoing Craniotomy

After craniotomy, hypertension may contribute to intracerebral hemorrhage.We studied whether scalp infiltration with bupivacaine during craniotomy reduces postoperative pain and hypertension. In a double-blind fashion, 36 adult patients (ASA physical status II or III) undergoing elective craniotomy were randomly assigned to receive scalp infiltration with either bupivacaine (0.25%) and epinephrine (1:200,000) or saline/epinephrine (1:200,000) for skeletal fixation, skin incision, and wound closure. Heart rate (HR) and mean arterial pressure (MAP) were measured after anesthesia induction, after skull-pin insertion, after scalp infiltration, during dural closure, during skin closure, on admission to postanesthesia care unit (PACU), and 1 h after admission. Visual analog pain scores were recorded in the PACU. MAP was significantly greater in the saline group at scalp infiltration. HR was significantly faster in the saline group at dural and skin closure. The bupivacaine group reported significantly less pain than the saline group at PACU admission and 1 h after admission. Pain scores did not correlate with hemodynamic measurements. We conclude that scalp infiltration with 0.25% bupivacaine with 1:200,000 epinephrine blunts certain intraoperative hemodynamic responses and reduces postoperative pain but has no effect on postoperative hemodynamics. Implications: We sought to evaluate whether scalp infiltration with bupivacaine and epinephrine at the beginning and end of craniotomy would afford more intra- and postoperative hemodynamic stability and influence immediate postoperative pain. We found that intraoperative hemodynamics were not influenced greatly; however, craniotomy patients do have significant postoperative pain, which does not seem to have an influence on hemodynamics in the postanesthesia care unit. (Anesth Analg 1998;87:579-82)

The effect of ketamine on human somatosensory evoked potentials and its modification by nitrous oxide

The effect of ketamine alone and in combination with N2O (70% inspired) on median nerve somatosensory evoked potentials (SSEPs) was investigated in 16 neurologically normal patients undergoing elective abdominopelvic procedures. The anesthetic regimen consisted of ketamine (2 mg/kg iv bolus followed by continuous infusion at a rate of 30 micrograms.kg-1.min-1) [corrected], neuromuscular blockade (atracurium), and mechanical ventilation with 100% oxygen. SSEP recordings were obtained immediately preinduction and at 2, 5, 10, 15, 20, and 30 min postinduction. Thereafter, N2O was added with surgical incision and maintained for 15 min. At 5-min intervals, SSEP recordings were again taken during and after N2O. With minor exceptions, mean cortical and noncortical latencies as well as noncortical-evoked potential amplitude were unaffected by either ketamine or N2O. Ketamine induction increased cortical amplitude significantly with maximal increases occurring within 2-10 min. For example, at 5-min postinduction, mean N1-P1 amplitude increased from 2.58 +/- 1.05 (baseline) to 2.98 +/- 1.20 microV and P1-N2 amplitude increased from 2.12 +/- 1.50 (baseline) to 3.99 +/- 1.76 microV. Throughout the 30-min period after ketamine induction, mean P1-N2 amplitude increased generally by more (57-88%) than did mean N1-P1 amplitude (6-16%). N2O added to the background ketamine anesthetic produced a rapid and consistent reduction in both N1-P1 and P1-N2 amplitude. Thus, at 1 min after N2O, mean N1-P1 amplitude decreased from 2.74 +/- 1.11 to 1.64 +/- 0.63 microV, while P1-N2 amplitude decreased from 3.32 +/- 1.52 to 1.84 +/- 0.87 microV.(ABSTRACT TRUNCATED AT 250 WORDS)

High-throughput operating room system for joint arthroplasties durably outperforms routine processes.

Background:Recent publications have focused on increased operating room (OR) throughput without increasing total OR time. The authors hypothesized that a system of parallel processing for lower extremity joint arthroplasties sustainably reduces nonoperative time and increases throughput. Methods:The high-throughput parallel processing strategy included neuraxial anesthesia performed in an “induction room” adjacent to the OR, patient selection, an additional circulating nurse, and end-of-case transfer of care to a recovery room nurse who transported the patient from the OR to recovery. Instruments and supplies were prepared in a dedicated sterile setup area. Data were extracted from administrative databases. Group comparisons used standard statistical methods; statistical process control was used to evaluate performance over time. Results:There were 688 historic control cases from 299 days over 16 months, and 905 high-throughput cases from 304 days spanning 24 consecutive months starting September 1, 2004. Throughput increased from 2.6 ± 0.7 (mean ± SD) to 3.4 ± 0.8 arthroplasties per day per room. Nonoperative time decreased by 36 min (or 50%) per case. Operative time also decreased by 14 min (12%) per case. The end time for the high-throughput OR day was only 16 min later than control. Nonoperative time, operative time, and throughput remained significantly improved after 2 yr of operation. Contribution margin increased 19.6%. Conclusion:Reorganizing the perioperative work process for total joint replacements sustainably increased OR throughput. Because joint arthroplasties generated a positive margin greater than the incremental cost, the high-throughput system improved financial performance.