192 ABSTRACTS

measures could be applied. Therefore, 10 anesthetized, para- lyzed dogs (15.9--48.2 kg), initially ventilated with conven- tional mechanical ventilation (CMV) using room air, were studied. CMV was stopped and a 1- or 5-ram id catheter with a constant flow (V) of O, ranging from 0.2 to 3.0 1/rain was inserted to within 1 cm of the carina. With all flow rates, Pug2 and Paco~ initially increased with time; the rate of increase of Pao~ was greater and that of Pace= was less, with increasing V. In three dogs studied at flow rates of 2.0 or 3.0 l/rain, arterial blood gases reached a plateau after about 2 h: pH - 6.87; Poe2 - 164 mmHg; and Po2 "- 363 mmHg (mean values). These studies were stopped at between 4 and 5 h, with no dogs showing any signs of cardiovascular or other decompensation. Results in which catheter position was studied indicated that as long as the catheter tip was at or past the carina, gas transport was similar to that observed when the catheter tip was 1 cm proximal to the carina. The authors conclude that TRIO at low flow rates can produce sufficient gas exchange to support life for prolonged periods in apneic dogs. (Reprinted with permission.)

Local Application of l~Xenon for Measurement of Regional Cerebral Blood Flow (rCBF) during Halothans, Enflurane, and laoflurane Anesthesia in Humans. Eintrei C. Lesz- niewski W. and Carlsson C. Anesthesiology 63:391, 1985.

It is well known that halothane causes an increase in cerebral blood flow (CBF). In this study the effects of halothane, enflurane, and isoflurane on regional cerebral blood flow (rCBF) in humans were determined in the pres- ence of 70% N,O at a combined MAC concentration of 1.5. CBF was determined in 24 patients from the washout of locally applied U)Xenon with the use of an external scintilla- tion. All 24 patients (control n - 6, halothane n - 6, enflurane n - 6, and isofturane n - 6) were undergoing neurosurgical procedures. All patients were anesthetized with thiopental, fentanyl, droperidol, and 70% N20 in oxygen and paralyzed with pancuronium. The measurements were performed after the dura had been opened and before defini- tive surgery. The first measurement was done in the absence of any volatile agent, and the wash-out curve was registered for 6 rain. The second measurement was done after one of the volatile agents had been added for at least 20 rain and had reached a concentration of 0.58% for halothane, 1.14% for enflurane, or 1.0% for isoflurane in the expiratory gases in order to obtain about 1.5 MAC with~ach volatile anesthetic. The anesthetic concentrations were measured with the Eng- str~im multigas analyzer EMMA ®. The physiologic variables changed very little throughout the period of observation. Body temperature, heart rate, blood pressure, Pace2, and Pap: were stable. Ephedrine was used to maintain a stable arterial pressure. At approximately 1.5 MAC, halothane (plus N20) increased rCBF to nearly three times (166%) the control value, while enflurane induced only a slight increase (35%) in rCBF. Isoflurane caused no increase of rCBF at approxi- mately 1.5 MAC (-5%). The authors conclude that isoflu- rane may well be a better alternative than halothane or enflurane during neurosurgieal operations in patients with increased intracranial pressure. (Key words: Anesthesia: neurosurgical. Anesthetics, volatile: halothane; enflurane; isoflurane. Brain: blood flow; intracranial pressure.) (Re- printed with permission.)

Factors Influencing Pulmonary Volumes and COs Elimina- tion During High-frequency Jet Ventilation. Rouby J J, Simonneau G. Benhamou D, et al. Anesthesiology 63:473, 1985.

An external spirometric method using a differential linear transformer was used to measure tidal volume (V,) and to determine factors influencing CO2 elimination and HFJV- induced "PEEP effect" in 15 critically ill patieats under HFJV. V¢ increased with increasing driving pressure (DP) and decreasing frequency (f) and was influenced little by changes in I/E ratio. CO2 elimination, as reflected by the measurement of Pacer was mainly influenced by the absolute level of Vr rather than by the product Vr x frequency (Pacc~ - 5715/V1, r - 0.75, P < 0.05). The primary phenomenon explaining HFJV-induced "PEEP effect" was intrapulmonary gas trapping due to incomplete exhalation of the first V T administered: the spontaneous relaxation times of these first Vx were longer than expiratory time allotted to the ventilatory settings. HFJV-induced "PEEP effect" increased with l /E ratio, DP, and fund was markedly influenced by the mechanical properties of the total respiratory s)stem. At given ventilatory settings, H FJV-inducod "'PEEP effect" was greater in patients with a normal or elevated time constant of the total respiratory system (¢RS) than in patients with a low rRS. These results suggest that HFJV should not be used in patients with chronic obstructive pulmonary disease and asthma, and should be prcferentiafly administered to patients having stiff lungs or decreased chest wall compliance. (Key words: Carbon dioxide: elimination. Lung: volume. Ventila- tion: high-frequency jet.) (Reprinted with permission.)

Circulatory Responses to Baroreflexes, Valsalva Maneuver, Coughing, Swallowing, and Nasal Stimulation During Acute Cardiac Sympathectomy by Epidural Blockade in Awake Humans. Takeshirna R and Dohi S. Anesthesiology 63:500, 1985.

Reflex circulatory responses are chiefly governed by the integrated functions of both sympathetic and parasympa- thetic nervous systems at any moment. To examine how sympathetic denervation of the important effoctor organ, the heart, modifies such reflex responses, the authors compared circulatory responses to arterial baroreflexes, the Valsalva maneuver (VM), coughing (C), swallowing (S), and nasal stimulation (NS) before and after cervical epidural blockade using 10 ml of 1.5% lidocaine in awake, healthy humans.

The cervico-thoracic sympathetic denervation (sensory block of C4-T0 caused a slight suppression of the baroreflex sensitivity assessed by increases in RR intervals to increased systolic blood pressure with a presser test (pheaylephrine) in all eight subjects studied; the mean slopes of the regression lines were 29.1. ± 9.8 ms • mmHg -t before the blockade and 17.2 ± 6.3 ms • mmHg -t after the blockade (P < 0.05). However, the baroreflex sensitivity to a depressor test (nitro- glycerin) remained unchanged following the blockade. Fur- thermore, the responses in heart rate and blood pressure to VM (Phases II and IV) and the responses in heart rate to C, S, and NS were partially suppressed after the blockade (P < 0.05). Despite these suppressions, the overall responses to VM, C, S, and NS remained unchanged after the blockade. No predominant parasympathetic responses such as profound