The incidence of pneumocephalus after supratentorial craniotomy. Observations on the disappearance of intracranial air.

BACKGROUND: Pneumocephalus occurs in a variety of clinical settings and has important anesthetic implications, particularly if N2O is used. One common cause of pneumocephalus is a craniotomy or craniectomy, and therefore, patients undergoing these neurosurgical procedures may be at increased risk for the development of tension pneumocephalus if N2O is used during a subsequent anesthetic. However, because the rate at which a postoperative pneumocephalus resolves has not been well defined, the duration of this risk period is unknown. METHODS: Department of Anesthesia billing codes were used to identify all patients undergoing supratentorial craniotomy between 1986 and 1990. This list was cross-indexed with Department of Radiology data to generate a list of patients who had had a computed tomographic scan of the head performed on or after the day of their surgery. From this list, 240 scans were examined for the presence of intracranial air. The magnitude of pneumocephalus, if present, was ranked as large, moderate, small, or trace. RESULTS: Air was seen in all scans obtained in the first 2 post-operative days. Sixty-six percent of these pneumocephali were judged to be moderate or large. The incidence of pneumocephalus decreased to 75% by postoperative day 7. During the 2nd and 3rd postoperative weeks, the incidence of pneumocephalus decreased to 59.6 and 26.3%, respectively. The size of the pneumocephali also decreased. Still, 11.8% of the scans obtained during the 2nd postoperative week had pneumocephali that were judged to be moderate or large. CONCLUSIONS: These data indicate that all patients have pneumocephalus immediately after a supratentorial craniotomy. Although the incidence and size of pneumocephali decrease over time, a significant number of patients have an intracranial air collection large enough to put them at risk for complication if N2O is used during a second anesthetic in the first 3 weeks after the first procedure. This information should be considered in the evaluation of the patient and in the selection of anesthetic agents.

An analysis of the factors leading to crossed gas lines causing profound hypercarbia during general anesthesia.

With increasing use of laparoscopic techniques to facilitate surgical procedures in closed cavities, our institution has installed piped-in carbon dioxide (CO2) in most of our operating rooms. This case report describes an occurrence of a nitrous oxide hose being connected to a CO2 outlet, resulting in profound hypercarbia. The factors, human and mechanical, leading to this error are discussed, as well as the process of diagnosis and the subsequent treatment.

A prospective, comparative trial of three anesthetics for elective supratentorial craniotomy. Propofol/fentanyl, isoflurane/nitrous oxide, and fentanyl/nitrous oxide.

BACKGROUND: Different anesthetic agents have different effects on cerebrovascular physiology. However, the importance of these differences in neuroanesthetic practice are unclear. In an effort to determine whether important clinical differences are present, the authors compared three anesthetic techniques in 121 adults undergoing elective surgical removal of a supratentorial, intracranial mass lesion. METHODS: Patients were assigned randomly to one of three groups. In group 1 (n = 40), anesthesia was induced with propofol and maintained with fentanyl (approximately 10 micrograms/kg load, 2-3 micrograms.kg-1.h-1 infusion) and propofol (50-300 micrograms.kg-1.min-1). In group 2 (n = 40), anesthesia was induced with thiopental and maintained with isoflurane and nitrous oxide. Up to 2 micrograms/kg fentanyl was given after replacement of the bone flap. In group 3 (n = 41), anesthesia was induced with thiopental and maintained with fentanyl (approximately 10 micrograms/kg load, 2-3 micrograms.kg-1.h-1 infusion), nitrous oxide, and low-dose isoflurane, if required. Blood pressure, heart rate, expired gas concentrations, and ventilatory parameters were recorded automatically in all patients. Epidural intracranial pressure (ICP) was measured via the first burr hole, brain swelling was rated at the time of dural opening, and emergence was monitored closely. Preoperative computed tomography or magnetic resonance imaging scans were evaluated, and pre- and postoperative neurologic exams were performed by a neurosurgeon unaware of group assignments. Total hospital stay (days) and total hospital cost (exclusive of physician charges) also were reviewed. RESULTS: During induction, higher heart rates were seen in isoflurane/nitrous oxide patients, whereas mean arterial pressure was approximately 10 mmHg less during the maintenance phase (compared with both other groups). Otherwise, there were few intergroup hemodynamic differences. While there were no clinically important intergroup differences in mean ICP (+/- SD)-group 1, ICP = 12 +/- 7 mmHg; group 2, 15 +/- 12 mmHg; group 3, ICP = 11 +/- 8 mmHg-more isoflurane/nitrous oxide patients (nine, group 2) had an ICP > or = 24 mmHg than in the other groups (two each). Emergence was, overall, more rapid with fentanyl/nitrous oxide. For example, the median time until the patient could be awakened by quiet verbal command, e.g., "Open your eye," was 5 min, versus 10 min in the other groups. There were no relationships between ICP and any measurement of emergence (e.g., time to response to commands). Seven of 41 (17%) fentanyl/nitrous oxide patients vomited in the early postoperative period, compared with only 1 of 40 (2.5%) of those given propofol/fentanyl and 2 of 40 (5%) receiving isoflurane/nitrous oxide (P = 0.03). There were no differences in the incidence of new postoperative deficits, total hospital stay, or cost. CONCLUSIONS: Although there are modest differences among the three tested anesthetics, short-term outcome was not affected. These results indicate that, despite their respective cerebrovascular effects, all of the anesthetic regimens used were acceptable in these patients undergoing elective surgery.

Effect of music therapy in the postanesthesia care unit: a nursing intervention.

This study examined the effect of music on pain, hemodynamic variables, and respiration in the PACU, and the impact of music on patients' recall of their PACU experience. Sixty patients scheduled for thyroid, parathyroid, or breast surgery under general anesthesia were studied. Patients were randomly assigned into three groups: group 1, control, not wearing headphones; group 2, wearing headphones but hearing no music; and group 3, wearing headphones and listening to music. A visual analogue pain scale was used to rate patients' perception of pain. There was no difference in pain level, morphine requirement, hemodynamics, respiration, or length of stay in the PACU among the 3 groups, yet the music group was able to wait significantly longer before requiring analgesia on the nursing unit. Patients who listened to music perceived their PACU experience as significantly more pleasant than the patients in the other two groups as recalled both 1 day and 1 month later.

Ventilatory frequency influences accuracy of end-tidal CO2 measurements. Analysis of seven capnometers.

An accurate high-frequency response is mandatory when end-tidal CO2 (PETCO2) is monitored during pediatric general anesthesia. The purpose of this study was to assess the accuracy of six infrared-based capnometers and one multiplexed mass spectrometer available at our institution at increasing frequency. Capnometers studied were the Datascope Accucap, Hewlett-Packard 47210A capnometer, Narkomed 3 Capnomed, Novametrix Capnogard model 1250, Perkin-Elmer Advantage, Puritan-Bennett Datex CO2 monitor, and Traverse Medical Monitor model 2200 capnometer. Changes in CO2 concentration were generated by a solenoid valve switching between 100% O2 and 7% CO2 in O2. Frequencies, 8-101 cycles/min were chosen to stimulate a range that might be generated by children during general endotracheal anesthesia. At every rate the displayed PETCO2 was recorded. Differences in displayed PETCO2 from known CO2 ranged from -16.4 to +6.6. At or below frequencies of 31 cycles/min, four capnometers overreported and three underreported PETCO2. At frequencies above 31 cycles/min, six capnometers underreported and one overreported PETCO2. Errors may be clinically significant if they influence ventilator settings for patients.

Accuracy of a central mass spectrometer system at high respiratory frequencies.

We have shown that in a laboratory setting the long lengths of sampling catheters necessary to access a central mass spectrometer restrict the high-frequency response of the system. Reported here are the results from a clinically operating Perkin-Elmer Advantage system. The sampling catheter was 50 meters long and the sampling flow was 240 ml/min. Rapid changes in carbon dioxide concentration were created by an electronically operated solenoid valve switching between 6.94% CO2 in 50% O2 balance N2 and 100% O2. The frequency of this simulated breathing was varied between 10 and 100 breaths/min with the ratio of inspiration to expiration fixed at 1:2. Data were taken from the terminal in the operating room. Errors greater than 5% of the true value occurred at 35 breaths/min for the indicated inspired concentration and 73 breaths/min for the indicated expired concentration. For critical situations in which respiratory frequencies exceed 40 breaths/min, a centrally located mass spectrometer may not be adequate for measuring CO2 because of errors introduced by the long sampling catheters.

Venturi jet ventilation for microlaryngoscopy: technique, complications, pitfalls.

Our experience with Venturi jet ventilation as the method of anesthesia in 872 cases of microlaryngeal surgery is presented. Our indications and exact technique are presented, as well as a review of our complications. Possible pitfalls and their avoidance are discussed. With attention to detail and good clinical judgement on the part of anesthesiologist and surgeon, Venturi jet ventilation can be safe and efficient with minimal complications.

A database system for abstract selection for a major anesthesia society meeting.

Until the present time, record keeping for abstract selection for major anesthesia meetings has been performed by manual methods - paper, pen, and typewriter. We describe the construction and implementation of a microcomputer based system to facilitate data recording, form-letter generation, and program construction. Based on MicroPro's WordStar, InfoStar, MailMerge series, the database has reduced the total effort required to construct the final program from 1.5 hours per abstract submitted for the 1984 meeting to 0.7 hours for the 1986 meeting. Problems encountered were mastery of the system by operating personnel, floppy disk overflow, and data loss of unknown etiology. The significant time savings attest to the value of the system.

Frequency response of long mass-spectrometer sampling catheters.

It was hypothesized that the long lengths of sampling catheters required when a mass spectrometer is multiplexed to more than one operating room limit the upper frequency at which a gas concentration may be determined accurately. This possibility has not been investigated. Known step changes of CO2 were generated by a solenoid valve driven by an electronic timer that was adjustable from 0.1 to 10 Hz. The valve alternated between 100% O2 and 7% CO2 in 50% O2 and balance N2. CO2 concentration was monitored by a mass spectrometer after the gas passed through a 3.7 m Teflon catheter or through 30 m Teflon, nylon, polyethylene (PE), or polyvinylchloride (PVC) catheters. Gas flow for all catheters was adjusted to 1.1 ml/s. The peak-to-peak output of the mass spectrometer was read from a storage oscilloscope. The 3.7 m catheter caused a 10% error at 5.5 Hz (330/min). In sharp contrast, 30 m catheters made from Teflon, PVC, and PE caused errors greater than 10% at only 0.6 Hz (36/min). The 30 m nylon catheter passed 1.1 Hz (66/min) with a 10% error. Teflon, PVC, and PE are not suitable materials from which to make long catheters sampling CO2. Because the frequency response of the nylon catheter appeared similar to that of a low-pass filter, an electronic circuit was designed and tuned to extend the high-frequency response of the catheter. With the circuit in place, the frequency at which a 10% error occurred in the measurement of CO2 improved from 1.1 Hz (66/min) to 2.2 Hz (132/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Low frequency jet ventilation for tracheal resection.

Low frequency jet ventilation was used successfully for maintaining normal ventilation during tracheal resection for stenosis. Following resection of the stenosis around the endotracheal tube, the tube was withdrawn and the proximal end of a sterile double lumen nasogastric tube with the distal end removed passed over the ether screen. The larger lumen was connected to a Saunders jet apparatus and the smaller to a CO2 analyzer. With the distal end held in the lumen of the distal tracheal stump, jet ventilation was initiated at a rate of 20/min at a pressure sufficient to obtain adequate chest rise and fall. Adequate CO2 removal was verified by monitoring the expired level and blood gases. We obtained normal arterial and end tidal gas tensions by this method which allowed the surgeon complete freedom to anastomose the posterior and lateral tracheal walls.

Supraglottic jet ventilation for laser surgery of the larynx in children.

To investigate the efficacy and safety of supraglottic jet ventilation for laser surgery on the larynx, ten studies were performed in seven children scheduled for laser excision of juvenile laryngeal papillomata. The children were anesthetized using halothane, nitrous oxide, fentanyl 3 micrograms/kg, and a succinylcholine infusion. After the Leonard-Jako laryngoscope was in place, jet ventilation with 70% nitrous oxide in oxygen was begun through a 12-gauge Medicut intravenous cannula inserted in the right-hand light channel of the laryngoscope. Tracheal, inspired, and end-tidal oxygen, nitrous oxide, nitrogen, and carbon dioxide were determined by mass spectrometry simultaneously with arterial blood gases. Oxygen and carbon dioxide levels were always within normal limits, the end-tidal to arterial differences averaging 50 +/- 9 and 2 +/- 1 (SEM) mm Hg, respectively. Room air entrainment averaged 32 +/- 2%. The end-tidal nitrous oxide averaged 39 +/- 2%. The advantages of this technique are that it leaves the larynx completely free for the surgeon and it eliminates the possibility of endotracheal tube ignition. Supraglottic jet ventilation for this surgical procedure was determined to be effective and relatively safe.

Conscious sedation for procedures under local or topical anesthesia.

For many surgical procedures in otolaryngology general anesthesia is not required, but it is difficult to block completely all noxious sensations with local or topical anesthesia. Intravenously administered antianxiety and analgesic drugs can make the procedure more tolerable for the patient. A technique of conscious sedation based upon titrating diazepam to specific eye signs and fentanyl to specific end points is described. Safety is maintained by ensuring that the patient is always in verbal contact with the surgeon. The rationale for administering the sedative before the narcotic is presented along with the treatment of side effects and untoward responses to the drugs.

Electroencephalographic monitoring during general anesthesia.

This paper presents a concise review of the recent advances in the field of electroencephalographic monitoring during administration of general anesthetics. It presents the history and background of this technique and describes the principles of electroencephalographic monitoring and its mathematical analysis. It concludes with a discussion of the techniques currently available for the display of the electroencephalogram as a monitoring tool and describes current clinical applications.

Ventilatory and mental effects of alfentanil and fentanyl.

Forty healthy, young volunteers received intravenously, in a double-blind and random fashion, 7.5 or 15 micrograms/kg of alfentanil, 1.5 or 3 micrograms/kg of fentanyl, or saline. The ventilatory response to CO2 was measured before and at 4, 20, 30, 50, 80, and 120 min post-treatment. Mental and psychomotor functions were measured before and at 10, 40, 100, 130, and 180 min post-treatment. Low and high-dose fentanyl caused significant respiratory depression up to 30 and 80 min post-treatment, respectively, while there was no depression with low-dose alfentanil and only at 4 min with high-dose alfentanil. The fentanyl to alfentanil potency ratio for respiratory depression was 13:1. High-dose fentanyl caused more intense and prolonged mental effects than other treatments. Neither drug affected learning or recall, although high-dose fentanyl impaired motor activity. Nausea and vomiting rates were similar between high-dose alfentanil and low-dose fentanyl.

How often may a Read rebreathing test be repeated?

The minimum duration of the rest period between repeated Read rebreathing tests required to prevent interference between tests is yet unknown. Four male and four female volunteers performed eight Read rebreathing CO2 response tests in a period of 2.5 h. The test-to-test interval was as short as 10 min. No major differences in slope or intercept were found according to time in either the group as a whole or as male and female groups taken separately. There was a slight but nonsignificant depression in slope for the 3rd to 5th tests. The females responded less to a CO2 challenge than did the males. It is concluded that a test-to-test interval as short as 10 min does not effect the results of the Read rebreathing test.

Fentanyl-O2-N2O rigidity and pulmonary compliance.

Induction of anesthesia with fentanyl has been associated with such extreme rigidity as to cause failure of bag-and-mask ventilation. The etiology of this failure has not been investigated. Therefore, fentanyl-induced rigidity was studied in 5 control patients to establish the dose at which ventilation became impossible and in 5 patients with tracheostomies to investigate changes in pulmonary compliance. Anesthesia was induced with 3 micrograms/kg/min fentanyl to a total of 30 micrograms/kg. In control patients, failure to maintain bag-and-mask ventilation occurred at a mean fentanyl dose of 17 micrograms/kg. In patients with tracheostomies, compliance decreased 16% below baseline levels with fentanyl-100% O2 and an additional 22% with 60% N2O, returning to baseline levels after paralysis. It is concluded that the site of the cause of inability to maintain bag-and-mask ventilation after fentanyl lies above the trachea, specifically at the glottis. Glottic rigidity causes glottic closure and upper airway obstruction.