Simulating blocks in treatment planning calculations.

It is difficult to make an accurate calculation of dose distribution incorporating blocks using a ray model. One approach is to simulate the blocking in a treatment planning distribution by using negatively weighted beams. A second is to employ an external contour. The parameters of the negative beam or contour can be adjusted using empirical dosimetric data. This paper discusses the calculation of the dose distributions using negatively weighted beams and external contours, compares them with measurements in and around blocked areas for a range of field sizes, block sizes, and depths of interest in treatment planning applications, for 60Co, 6 MV, and 10 MV beams, and assesses their applicability.

Three-dimensional conformal radiation therapy in locally advanced carcinoma of the prostate: preliminary results of a phase I dose-escalation study.

PURPOSE: The acute morbidity of doses of 64.8-75.6 Gy and preliminary observations of late complications and tumor response using 3-dimensional conformal radiation therapy in carcinoma of the prostate are assessed. METHODS AND MATERIALS: 123 patients (Stage A2-12, B1-17, B2-43, C-51) were irradiated to the prostate and seminal vesicles using a 3-dimensional conformal radiation therapy technique. The median follow-up time was 15.2 months. The minimum tumor dose was 64.8-66.6 Gy in 49 patients, 70.2 Gy in 46, and 75.6 Gy in 28. Toxicity was scored according to the Radiation Therapy Oncology Group morbidity grading system. RESULTS: This technique of 3-dimensional conformal radiation therapy was well-tolerated with minimal acute morbidity. Only 32% of patients had grade 2 or 3 acute morbidity requiring short-term medication for relief of urinary symptoms or diarrhea. Only one patient (0.8%) has so far developed a severe (grade 4) late complication. Serum prostate specific antigen concentrations normalized in 67% of patients (64/96) within 1-14 months (median 4.5 months) after treatment and were progressively decreasing at last measurement in an additional 22% (21/96). Abnormal rising prostate specific antigen levels were observed in 15 patients, 11 of whom have already developed other evidence of relapsing disease. CONCLUSION: Acute toxicity for the doses tested with this 3-dimensional conformal radiation therapy technique is reduced compared to traditional treatment techniques, and the initial tumor response as assessed by prostate specific antigen measurement is highly encouraging with prostate specific antigen levels returning to normal in the majority of patients. Based on these results, a further increase of the dose to 81 Gy has been implemented in accordance with the schema of an ongoing Phase I dose-escalation study.

Carotid endarterectomy in elderly patients.

Between 1971 and 1989, 749 carotid endarterectomies were performed at our institution for symptomatic carotid occlusive disease in patients older than 70 years of age. Of these procedures, 693 were done in patients 71 through 80 years of age, and 56 were done in patients between the ages of 81 and 90 years. The neurologic morbidity and perioperative mortality in the former group were 2.9% and 1.4%, respectively, whereas in the latter group the corresponding values were 5.4% and 0%, respectively. For the entire group, the neurologic morbidity was 3.1% and the mortality was 1.3%. Of the 23 new postoperative neurologic deficits, 19 (83%) occurred in high-risk patients with severe preoperative neurologic or medical risks, and 14 (61%) of these deficits were minor. In selected elderly patients with symptomatic hemodynamically significant carotid occlusive disease, endarterectomy seems to be a safe procedure that is associated with acceptably low perioperative morbidity and mortality.

Ventriculoatrial shunt distal catheter placement using transesophageal echocardiography: technical note.

Accurate placement of the distal end of a ventriculoatrial shunt at the cavo-atrial junction is important for long-term shunt function as well as for avoiding cardiac arrhythmias, thrombus formation, and damage to myocardial tissue. Standard methods of intraoperative localization, including chest x-ray, pressure measurements, and electrocardiogram recording, can be inaccurate. By using intraoperative transesophageal echocardiography, the distal end of the catheter can be localized to the cavo-atrial junction.

Repair of a cerebral artery aneurysm in a patient with persistent truncus arteriosus.

We describe the anesthetic management of a 19-year-old woman with persistent truncus arteriosus who presented for cerebral artery aneurysm clipping. The anatomy and pathophysiology of persistent truncus arteriosus are reviewed to provide a basis for the choice of anesthetic agents and monitoring devices in this patient. The hazards of induced hypotension in the patient with truncus arteriosus are also discussed.

Brain relaxation and cerebrospinal fluid pressure during craniotomy for resection of supratentorial mass lesions.

Neurosurgery can be complicated by the clinical situation commonly referred to as "tight brain," in which the brain presses against the inner table of the skull or protrudes through the craniotomy site. We report here a retrospective study of 32 patients who had undergone elective craniotomy for resection of supratentorial mass lesions. We determined the relationship between lumbar cerebrospinal fluid pressure (CSFP) and brain relaxation and whether brain relaxation varies with anesthetic technique. Patients had received one of four anesthetic techniques: 1 MAC isoflurane (ISO), 1 MAC desflurane (DES), 50% N2O with 0.5 MAC ISO, or 50% N2O with 0.5 MAC DES. Lumbar CSFP had been recorded before the induction of anesthesia (baseline) and immediately prior to dural incision. Charts were retrospectively reviewed for evidence of tight brain, which was considered present if mannitol had been administered, CSF had been drained via the lumbar needle, or the surgical dictation noted the brain was tight at the time of dural incision. Tight brain occurred in 10 of 32 patients. CSFP (mean +/- SD) was significantly greater in the tight than in the nontight group both at baseline (11 +/- 5 vs. 8 +/- 3 mm Hg, p < 0.05) and immediately prior to dural incision (13 +/- 7 vs. 9 +/- 4 mm Hg, p < 0.05). Tight brain did not occur in any patient with CSFP < 6 mm Hg, but it did occur in all patients with CSFP > 17 mm Hg. Within the range of 6-17 mm Hg, CSFP was not predictive of brain relaxation. Tight brain was more common in patients receiving 1 MAC ISO or DES (9 of 20 patients; 45%) than in patients receiving 0.5 MAC ISO or DES with 50% N2O (1 of 12 patients; 8%, p < 0.05). We conclude that in patients undergoing elective craniotomy for resection of a supratentorial mass lesion, brain relaxation is not predictive of CSFP. Although CSFP values at the extremes of the observed distribution ( > 17 mm Hg or < 6 mm Hg) did correlate with brain relaxation, within the range of 6-17 mm Hg, CSFP did not predict brain relaxation. Additionally, the data from this study suggest that in patients undergoing elective craniotomy for resection of a supratentorial mass lesion, tight brain may occur with a lower frequency in patients receiving 0.5 MAC ISO or DES with 50% N2O than in patients receiving 1 MAC ISO or DES.

Morning admission to the hospital for surgery the same day. A practical problem for the blood bank.

Morning admissions for surgery the same day are increasing because of economic incentives. These admissions permit less time for red cell serologic preparation before surgery than do the more conventional methods of patient admission. During a 4-month period, serologic problems arose in 70 of 2859 cases. In 36 of the 70 cases, the sample arrived at the blood bank about the time of the beginning of the operation; in 19 of these 36 cases, the operation had begun before serologic resolution, and in 7 of these 19, the antibody was found to be of hemolytic potential. It was concluded that administrative and logistic changes need to be made to ensure sufficient time for the serologic testing necessary for safe transfusion support for same-day surgical admissions.

Labetalol and esmolol in the control of hypertension after intracranial surgery.

The postoperative course of patients emerging from general anesthesia after intracranial surgery is frequently complicated by hypertension. This study examined the comparative efficacy of esmolol and labetalol in treating increases in blood pressure during emergence and recovery from anesthesia after intracranial surgery. Both esmolol and labetalol were equally effective in controlling systolic blood pressure on emergence and in the recovery room in patients undergoing intracranial surgery. However, decreases in heart rate were significantly more frequent in the immediate postoperative period in patients given labetalol. An increase in blood pressure after intracranial surgery appears to be a transitory phenomenon adequately treated with a short-acting antihypertensive agent such as esmolol.

Detection and hemodynamic consequences of venous air embolism. Does nitrous oxide make a difference?

Volume expansion of intravascular air by nitrous oxide (N2O) may improve the sensitivity of monitors used to detect venous air embolism (VAE) and/or exacerbate hemodynamic changes following VAE. The purpose of this study was to determine if the administration of N2O alters the sensitivity (i.e., threshold of detection) of monitors used to detect VAE or the hemodynamic consequences of VAE. Twenty-one dogs were monitored for VAE with precordial Doppler ultrasound, transesophageal echocardiography (TEE), changes in end-tidal carbon dioxide tension (ETCO2), and changes in pulmonary artery pressure (PAP). Venous air was infused at rates between 0.005 and 0.4 ml.kg-1.min-1 during 1 MAC (total anesthetic level) of isoflurane with and without 50% N2O (group 1, n = 7) or isoflurane with and without 75% N2O (group 2, n = 7). The mean quantity of infused air necessary to elicit a positive response in both the presence and absence of N2O was calculated for each monitor. Positive responses were defined as follows: unmistakable audible change in frequency on Doppler ultrasound, visualization of densities consistent with air bubbles in the right cardiac chambers or outflow tract on TEE, a decrease in ETCO2 greater than or equal to 2 mmHg, and an increase in mean PAP greater than or equal to 3 mmHg. In group 3 (n = 7), venous air was infused at rates between 0.1 and 0.8 ml.kg-1.min-1 during 1 MAC (total anesthetic level) of isoflurane with and without 50% N2O. In group 3, N2O administration was discontinued immediately upon Doppler detection of VAE and air infusion continued until mean arterial pressure (MAP) decreased by 10 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Fifty percent nitrous oxide does not increase the risk of venous air embolism in neurosurgical patients operated upon in the sitting position.

Although nitrous oxide (N2O) should theoretically increase the severity of venous air embolism (VAE), data confirming this hazard in clinical situations are not available. The effect of 50% N2O on the incidence and severity of VAE and on the emergence time from anesthesia was evaluated in 300 neurosurgical patients operated upon while in the sitting position. Of these, 110 patients underwent craniectomy for posterior fossa pathology and 190 patients underwent cervical spine surgery (CSS). Patients were randomized to receive either 50% N2O in oxygen (O2) (N2O group) or O2 (no-N2O group) as part of an isoflurane-fentanyl-based anesthetic. In patients in the N2O group, N2O administration was discontinued immediately upon Doppler-detection of VAE and was reinstituted in not less than 30 min after resolution of the episode. The incidence of Doppler-detected VAE was significantly greater in the craniectomy group than the CSS group (43% vs. 7%, respectively; P less than 0.001). N2O had no effect on the incidence of VAE or the severity of VAE as judged by the magnitude of the reduction in blood pressure during hemodynamically significant episodes of VAE, the volume of gas aspirated from the right atrial catheter during episodes of VAE, or the magnitude of the decrease in end-tidal carbon dioxide tension during episodes of VAE. Hemodynamically significant episodes of VAE (i.e., episodes associated with a reduction in systolic blood pressure of greater than or equal to 15 mmHg) occurred in 17 of the 61 patients experiencing VAE (28%) and was not different between the N2O and no-N2O groups. Similarly, hemodynamically significant episodes of VAE (n = 18) accounted for 15% of all episodes of VAE (n = 118) and was not different between the N2O and no-N2O groups. Emergence time was not significantly different between the N2O and no-N2O groups, with mean times of 2 +/- 6 and 3 +/- 7 min (+/- SD), respectively. Emergence time was significantly longer in the craniectomy group than in the CSS group (5 vs. 1 min, respectively; P less than 0.001). Within the craniectomy group, the incidence of Doppler-detected VAE was significantly less in patients with previous surgery at the operative site (21%) compared to patients without previous surgery at the operative site (47%). Postoperatively, no complications could be related to the use of N2O or directly attributed to the occurrence of VAE.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of desflurane and isoflurane on cerebrospinal fluid pressure in humans with supratentorial mass lesions.

Desflurane, a new volatile anesthetic, produces cerebral vasodilation. The purpose of this study was to compare the effects of 1 MAC desflurane with those of isoflurane on cerebrospinal fluid pressure (CSFP) in patients with supratentorial mass lesions and a mass effect on computerized tomography (CT scan). Twenty adult patients undergoing craniotomy for removal of supratentorial mass lesions were studied. Ten patients received desflurane and 10 patients received isoflurane. Prior to induction of anesthesia, a radial artery catheter was inserted and a 19-G needle was inserted into the lumbar subarachnoid space to measure CSFP. Baseline arterial blood gases and CSFP were measured with the patient awake and unmedicated. Anesthesia was induced with thiopental (6-9 mg/kg) and muscle relaxation achieved with vecuronium (0.2 mg/kg). The lungs of all patients were hyperventilated to achieve an arterial CO2 tension of 24-28 mmHg. Anesthesia was maintained with 1 MAC volatile anesthetic, either 7.0% desflurane or 1.2% isoflurane in an air:O2 mixture to maintain an inspired O2 fraction (FIO2) of 0.50. Patients were not administered any other anesthetic until the dura was incised. Mean arterial pressure was kept within 20% of the patient's mean ward values with the use of esmolol or phenylephrine. CSFP, mean arterial pressure, end-tidal CO2 concentration (PETCO2), hemoglobin O2 saturation, and cerebral perfusion pressure were recorded with the patient awake, immediately postinduction with thiopental, postintubation, after institution of the volatile anesthetic, and every 5 min until the dura was incised. There was no difference in the mean (+/- SD) awake CSFP between the desflurane (11 +/- 4 mmHg) and the isoflurane (10 +/- 2 mmHg) groups.(ABSTRACT TRUNCATED AT 250 WORDS)