Mary Ann Cheng

The Effect of Prone Positioning on Intraocular Pressure in Anesthetized Patients

Background Ocular perfusion pressure is commonly defined as mean arterial pressure minus intraocular pressure (IOP). Changes in mean arterial pressure or IOP can affect ocular perfusion pressure. IOP has not been studied in this context in the prone anesthetized patient. Methods After institutional human studies committee approval and informed consent, 20 patients (American Society of Anesthesiologists physical status I–III) without eye disease who were scheduled for spine surgery in the prone position were enrolled. IOP was measured with a Tono-pen® XL handheld tonometer at five time points: awake supine (baseline), anesthetized (supine 1), anesthetized prone (prone 1), anesthetized prone at conclusion of case (prone 2), and anesthetized supine before wake-up (supine 2). Anesthetic protocol was standardized. The head was positioned with a pinned head-holder. Data were analyzed with repeated-measures analysis of variance and paired t test. Results Supine 1 IOP (13 ± 1 mmHg) decreased from baseline (19 ± 1 mmHg) (P < 0.05). Prone 1 IOP (27 ± 2 mmHg) increased in comparison with baseline (P < 0.05) and supine 1 (P < 0.05). Prone 2 IOP (40 ± 2 mmHg) was measured after 320 ± 107 min in the prone position and was significantly increased in comparison with all previous measurements (P < 0.05). Supine 2 IOP (31 ± 2 mmHg) decreased in comparison with prone 2 IOP (P < 0.05) but was relatively elevated in comparison with supine 1 and baseline (P < 0.05). Hemodynamic and ventilatory parameters remained unchanged during the prone period. Conclusions Prone positioning increases IOP during anesthesia. Ocular perfusion pressure could therefore decrease, despite maintenance of normotension.

Visual Loss after Spine Surgery: A Survey

OBJECTIVE To survey a large number of neurosurgical spine surgeons for data regarding the presence of risk factors in patients experiencing visual loss after spine surgery. METHODS A survey was sent to current members (as of 1997) of the American Association of Neurological Surgeons/Congress of Neurological Surgeons, Section on Disorders of the Spine and Peripheral Nerves, with questions focusing on intraoperative factors that may predispose patients to perioperative visual loss. RESULTS Two hundred ninety surveys were returned, and 24 patients with visual loss after spine surgery were reported by 22 surgeons. Although many of these patients had probable causative factors for visual loss after surgery (e.g., hypotension, low hematocrit level, coexisting disease), some did not (n = 8). CONCLUSION These results suggest the necessity of a high index of suspicion for evolving perioperative visual loss even in the absence of risk factors.

INTRAVENOUS AGENTS AND INTRAOPERATIVE NEUROPROTECTION: Beyond Barbiturates

The authors discuss the role of intravenous anesthetic agents in brain protection. The newer intravenous anesthetics, etomidate and propofol, have been proposed as neuroprotective agents. Thiopental remains the drug of choice, however, for use prior to intraoperative ischemic events. The anesthetic ketamine presents surprising similarities to other N-methyl-D-aspartate receptor inhibitors, but remains controversial in its use in neurologically compromised patients.

Anesthesia for carotid endarterectomy: a survey.

Summary Indications for carotid endarterectomy (CEA) have been expanded recently, and a consensus statement has been made regarding these changes. However, the debate regarding the “ideal” anesthetic for CEA remains on-going. This study was designed to evaluate the actual anesthetic techniques used by anesthesiologists for CEA. A total of 426 1-page questionnaires were mailed to all current (1995) members of the Society of Neurosurgical Anesthesia and Critical Care (SNACC). Of these, 216 (50.7%) were completed and returned. The majority of these respondents (84.7%) administered general anesthesia (GA) for CEA. Regional anesthesia (RA) was the anesthetic method of choice for 16.7%, whereas 2.8% each chose either local anesthesia (LOC) or a combined regional/general (RA/GA) technique. Despite the controversial role of nitrous oxide in neuroanesthesia, 74.6% of those returning the survey use nitrous oxide during CEA. Intraoperative neuromonitoring use was reported by 90% of the respondents, with the electroencephalography (EEG) the favored modality (67.5%). Specific intraoperative neuroprotective measures were provided by only 22.2% of all respondents, with barbiturates as the favorite method (50.0%). The technique of intraoperative hypertension is practiced by a majority of those surveyed (61.1%), with the most common target blood pressures being either preoperative baseline or preoperative baseline plus 20%. Although there is some trend towards nonintensive care setting for postoperative care, the intensive care remains the location of choice for overnight care of CEA patients (71.8%). The results of this study show that despite arguments for RA over GA, the majority of anesthesiologists surveyed choose GA for CEA.

Large-dose propofol alone in adult epileptic patients : Electrocorticographic results

The primary objective of this study was to evaluate the electrophysiologic effects of large-dose propofol, used as the sole anesthetic in patients with epilepsy. Nine patients with medically intractable complex partial epilepsy undergoing a three-stage approach to the surgical management of epilepsy were recruited. Stage I involved placement of the intracranial electrode array, while Stage II consisted of extraoperative localization of the seizure focus. The patients were studied during induction of anesthesia for Stage III (removal of electrodes and resection of seizure focus). Unpremedicated patients were induced with a propofol infusion (0.5 mg centered dot kg-1 centered dot min-1) until one of the following occurred: 1) electrical seizure activity, 2) burst suppression, or 3) total dose of 10 mg/kg. Electrocorticography (ECoG) was recorded continuously during this period. Two patients were excluded from the study after experiencing delayed awakening after the Stage I procedure. Both had received propofol along with other anesthetics. No ECoG evidence of seizure activity was detected in the seven patients completing the study. Burst suppression was attained in six patients using a mean dose of 5.7 mg/kg +/- 2.6. We conclude that large-dose propofol alone does not trigger electrical epileptiform activity on the ECoG of seizure patients. (Anesth Analg 1996;83:169-74)

Anesthesia and epilepsy.

The patient with epilepsy is an anesthetic challenge. New drugs and surgical procedures are being used to treat epilepsy. Certain anesthetics have been reported to cause perioperative seizures. This discussion will focus on advances in the treatment of epilepsy, as well as the pro- and anti-convulsant effects of the newer anesthetic agents.