Franz Lackner

Mild Intraoperative Hypothermia Prolongs Postanesthetic Recovery

Background: Intraoperative hypothermia is common and persists for several hours after surgery. Hypothermia may prolong immediate recovery by augmenting anesthetic potency, delaying drug metabolism, producing hemodynamic instability, or depressing cognitive function. Accordingly, the authors tested the hypothesis that intraoperative hypothermia prolongs postoperative recovery. Methods: Patients undergoing elective major abdominal surgery (n = 150) were anesthetized with isoflurane, nitrous oxide, and fentanyl. They were randomly assigned to routine thermal management (hypothermia) or extra warming (normothermia). Postoperative surgical pain was treated with patient‐controlled analgesia. Fitness for discharge from the post‐anesthesia care unit was evaluated at 20‐min intervals by investigators blinded to group assignment and postoperative core temperatures. Scoring was based on a modification of a previously published system that included activity, ventilation, consciousness, and hemodynamic responses. Patients were considered fit for discharge when they sustained a score of 80% (13 points) for at least two consecutive measurement periods. Results: Morphometric characteristics and anesthetic management were similar in each group. Final intraoperative core temperatures differed by [nearly =] 2 [degree sign] Celsius: 34.8 +/‐ 0.6 versus 36.7 +/‐ 0.6 [degree sign] Celsius (mean +/‐ SD, P < 0.001). Postoperative pain scores and postoperative use of patient‐controlled opioid were similar. Hypothermic patients required [nearly =] 40 min longer (94 +/‐ 65 vs. 53 +/‐ 36 min) to reach fitness for discharge, even when return to normothermia was not a criterion (P < 0.001). Duration of recovery in the two groups differed by [nearly =] 90 min when a core temperature > 36 [degree sign] Celsius was also required (P < 0.001). Conclusion: Maintaining core normothermia decreases the duration of postanesthetic recovery and may, therefore, reduce costs of care.

Postoperative pain and subcutaneous oxygen tension

Surgical patients randomly assigned to standard pain control had postoperative subcutaneous oxygen partial pressures that were significantly less than patients given better pain treatment. Our data suggest that control of postoperative pain is a major determinant of surgical-wound infection and should be given the same consideration as maintaining adequate vascular volume and normothermia.

Rapid tracheal intubation with vecuronium: the priming principle

Following the administration of a single 0.1 mg/kg dose of vecuronium bromide, satisfactory conditions for tracheal intubation developed in 156 ± 12 s (mean ± SEM), and the clinical duration of the initial dose was 36 ± 2 min. When the initial dose of vecuronium was administered in two increments, a 0.015 mg/kg “priming” dose, followed 6 min later by a 0.050 mg/kg “intubating” dose, intubation time decreased to 61 ± 3 s and clinical duration to 21 ± 1 min. The priming dose that had no unpleasant effect on premedicated, awake patients could be administered 3–4 min before, and the intubating dose 2 to 3 min after induction of anesthesia. With the described technique, comparable intubating conditions could be obtained just as rapidly with vecuronium as with succinylcholine chloride, without subjecting the patients to the side effects of and the complications occasionally encountered with succinylcholine. An added advantage of the use of a priming dose is that it will reveal undiagnosed, pathologic, or idiopathic increase of sensitivity to nondepolarizing muscle relaxants.

Comparable Postoperative Pulmonary Atelectasis in Patients Given 30% or 80% Oxygen during and 2 Hours after Colon Resection

BACKGROUND High concentrations of inspired oxygen are associated with pulmonary atelectasis but also provide recognized advantages. Consequently, the appropriate inspired oxygen concentration for general surgical use remains controversial. The authors tested the hypothesis that atelectasis and pulmonary dysfunction on the first postoperative day are comparable in patients given 30% or 80% perioperative oxygen. METHODS Thirty patients aged 18-65 yr were anesthetized with isoflurane and randomly assigned to 30% or 80% oxygen during and for 2 h after colon resection. Chest radiographs and pulmonary function tests (forced vital capacity and forced expiratory volume) were obtained preoperatively and on the first postoperative day. Arterial blood gas measurements were obtained intraoperatively, after 2 h of recovery, and on the first postoperative day. Computed tomography scans of the chest were also obtained on the first postoperative day. RESULTS Postoperative pulmonary mechanical function was significantly reduced compared with preoperative values, but there was no difference between the groups at either time. Arterial gas partial pressures and the alveolar-arterial oxygen difference were also comparable in the two groups. All preoperative chest radiographs were normal. Postoperative radiographs showed atelectasis in 36% of the patients in the 30%-oxygen group and in 44% of those in the 80%-oxygen group. Relatively small amounts of pulmonary atelectasis (expressed as a percentage of total lung volume) were observed on the computed tomography scans, and the percentages (mean +/- SD) did not differ significantly in the patients given 30% oxygen (2.5% +/- 3.2%) or 80% oxygen (3.0% +/- 1.8%). These data provided a 99% chance of detecting a 2% difference in atelectasis volume at an alpha level of 0.05. CONCLUSIONS Lung volumes, the incidence and severity of atelectasis, and alveolar gas exchange were comparable in patients given 30% and 80% perioperative oxygen. The authors conclude that administration of 80% oxygen in the perioperative period does not worsen lung function. Therefore, patients who may benefit from generous oxygen partial pressures should not be denied supplemental perioperative oxygen for fear of causing atelectasis.

The Threshold for Thermoregulatory Vasoconstriction during Nitrous Oxide/Isoflurane Anesthesia Is Lower in Elderly Than in Young Patients

Background:Thermoregulatory vasoconstriction minimizes further core hypothermia during anesthesia. Elderly patients become more hypothermic during surgery than do younger patients, and take longer to rewarm postoperatively. These data indicate that perianesthetic thermoregulatory responses may be especially impaired in the elderly. Accordingly, the authors tested the hypothesis that the thermoregulatory threshold for vasoconstriction during nitrous oxide/isoflurane anesthesia is reduced more in elderly than in young patients. Methods:The authors studied 12 young patients aged 30–50 yr and 12 elderly patients aged 60–80 yr. All were undergoing major orthopedic or open abdominal surgery. Anesthesia was induced with thiopental and fentanyl, and maintained only with nitrous oxide (70%) and isoflurane (0.6–0.8%). Core temperature was measured in the distal esophagus. Fingertip vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients. A gradient of 4° C identified significant vasoconstriction, and the core temperature triggering vasoconstriction identified the thermoregulatory threshold. Results:The vasoconstriction threshold was significantly less in the elderly patients (33.9 ± 0.6° C) than in the younger ones (35.1 ± 0.3° C) (P < 0.01). The gender distribution, weight, and height of the elderly and young patients did not differ significantly. The end-tidal isoflurane concentration at the time of vasoconstriction did not differ significantly in the two groups. Conclusions:These data indicate that thermoregulatory responses in the elderly are initiated at temperatures ≈ 1.2° C less than that in younger patients. Thus, it is likely that elderly surgical patients become more hypothermic than do younger patients, at least in part, because they fail to trigger protective thermoregulatory responses.

The esophageal tracheal combitube: Preliminary results with a new airway for CPR

We developed the esophageal tracheal combitube (ETC), a plastic twin-lumen tube, one lumen resembling an esophageal obturator airway (EOA), the other resembling an endotracheal airway (ETA). Ventilation is possible after either esophageal or tracheal placement of the ETC. A specially designed pharyngeal balloon replaces the mask of the EOA and provides sufficient seal, preventing the escape of air through the mouth and nose. The effectiveness of ventilation with the ETC in esophageal position was tested in a crossover study comparing ETC and ETA during routine operations in 31 patients. Blood gas measurements showed a significantly higher (P less than .001) mean arterial oxygen tension during ventilation with the ETC. The reason for this is not yet clear. Preliminary investigations during CPR in 21 arrest patients indicate that the ETC is as effective as the ETA.

Morphometric Influences on Intraoperative Core Temperature Changes

Intraoperative core hypothermia develops in three characteristic phases:1) core-to-peripheral redistribution of body heat that is most prominent during the first hour after induction of anesthesia; 2) subsequent slow linear decrease in core temperature resulting largely from heat loss exceeding metabolic heat production; and 3) core temperature plateau resulting when thermoregulatory vasoconstriction decreases cutaneous heat loss and constrains metabolic heat to the core thermal compartment. Accordingly, we tested the hypotheses that: 1) core cooling does not depend on body fat (BF) or the ratio of weight-to-surface area (Wt/SA) during the initial redistribution phase; 2) the core cooling rate is a function of the Wt/SA ratio during the second phase; and 3) the rate of core cooling during the plateau phase (after vasoconstriction) will be determined by the percentage of BF. In 40 patients undergoing elective colon surgery, the amount of redistribution hypothermia was inversely proportional to the percentage of BF (Delta TC = 0.034 centered dot BF - 2.2, r2 = 0.63) and the Wt/SA ratio (Delta TC = 0.052 centered dot Wt/SA - 3.35, r2 = 0.66). The core cooled linearly during the second phase, and the cooling rate was inversely proportional to the Wt/SA ratio (rate = 0.035 centered dot (Wt/SA) - 2.2, r2 = 0.29). Thermoregulatory vasoconstriction was effective in virtually all patients independent of their morphology, and produced a fourfold reduction in the core cooling rate. These results indicate that patient morphometric characteristics substantially influence intraoperative core temperature changes, and that the effect depends on the hypothermia phase. (Anesth Analg 1995;80:562-7)

Risk factors for severe bacterial infections after valve replacement and aortocoronary bypass operations: analysis of 246 cases by logistic regression

Risk factors for severe bacterial infections, that is, deep sternal wound infection, pneumonia, septicemia, and prosthetic valve endocarditis, were evaluated in 246 consecutive patients undergoing valve replacement (N = 84) or aortocoronary bypass operation (N = 162). Multiple logistic regression analysis was applied to determine the ability of putative risk factors to predict infection. The risk factors considered were age, sex, diabetes mellitus, duration of cardiopulmonary bypass (CPB), duration of operation, amount of blood restored on the day of operation, repeat thoracotomy for bleeding, intraaortic balloon pumping, reoperation, emergency operation, and the professional status of the surgeon. Severe infections occurred in similar frequency after valve replacement (8/84; 9.5%) and aortocoronary bypass (11/162; 6.8%). For patients who had a bypass procedure, repeat thoracotomy was the only factor significantly associated with infection (p = 0.0004). However, the classification analysis revealed that this variable alone is too unspecific for a reliable prediction. Univariate analysis indicated that restoration of more than 2,500 ml of blood (p = 0.0001), reoperation (p = 0.0821), duration of operation (p = 0.0061), duration of CPB (p = 0.0318), and intraaortic balloon pumping (p = 0.0281) were associated with infection following valve replacement. A model with three variables emerged from the multiple logistic regression: after correction for blood restoration, reoperation, and duration of CPB, no other variable was of additional predictive value. For patients who underwent valve replacement, the model performed well in predicting complications. The classification analysis revealed a high correspondence between observed and predicted instances of infection: it correctly predicted 75% of the patients with infection and 96% of those without infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Esophageal tracheal combitube, endotracheal airway, and mask: comparison of ventilatory pressure curves.

The esophageal tracheal Combitube (ETC) is a new airway especially designed for airway maintenance and ventilation in unconscious patients such as those requiring CPR. The ETC may be used as an esophageal obturator or an endotracheal airway. Previous studies yielded a significantly higher mean arterial oxygen tension (PaO2) during ventilation using an ETC in the esophageal position compared to a conventional endotracheal airway (ETA). To investigate this phenomenon, endotracheal and airway opening pressures were examined in 12 patients in randomized order during ventilation with an ETC in the esophageal position, with an ETA, and with a mask, respectively. In this study again the PaO2 was higher with ETC compared to ETA. The following differences in intratracheal pressure and flow could be found for ETC when compared to ETA: smaller rising pressure during inspiration, prolonged expiratory flow time, and formation of a small positive end expiratory pressure (PEEP). These factors may be responsible for the improved oxygen tension with ETC. Comparing mask to ETC ventilation, PaO2 did not differ; however, mean arterial carbon dioxide tension was higher during mask ventilation.

Evaluation of the oesophageal-tracheal double-lumen tube (Combitube) during general anaesthesia

ZusammenfassungFragestellungEvaluation auf Sicherheit und Verlässlichkeit und Wirksamkeit des Combitube (Tyco Healthcare, Brunn am Gebirge, Österreich) während Allgemeinanästhesie.Patienten und Methoden250 Patienten, die eine Allgemeinanästhesie erhielten, wurden in die Studie eingeschlossen. Die verschiedenen Operationstypen, die Dauer der Operationen, Leichtigkeit der Einführung, und potentielle Komplikationen wurden registriert. Zudem wurden maximale Beatmungsdrücke und das Ausmaß der Leckage ermittelt.ErgebnisseDie Dauer der Operationen variierte zwischen 20 und 410 Minuten. Mehr als 96% der blinden Combitube Einführungen waren beim ersten Versuch nach einer durchschnittlichen Zeit von 18±5 Sekunden (12 bis 24 Sekunden) erfolgreich. Bei 99% der Patienten war es möglich, eine adäquate Oxygenation und Ventilation aufrecht zu erhalten. Alle Patienten waren während der Gesamtdauer der Operationen hämodynamisch stabil, mit einer pulsoximetrisch gemessenenen Sauerstoffsättigung von 97±2%. Der end-tidal gemessene Kohlendioxid-Partialdruck war 38±6 mm Hg. Die Leckage betrug auch bei Beatmungsdrücken von bis zu 40 cm H2O nicht mehr als 5%. Bei 18 Patienten (7,2%) fanden sich oberflächliche Schleimhaut-Lazerationen ohne anhaltende Folgeschäden. Es wurden keine schwerwiegenden Komplikationen während der Studie beobachtet.ZusammenfassungDie Beatmung via Combitube während Allgemeinanästhesie erscheint sicher und effektiv. Der Einsatz des Combitube sollte jedoch in Hinblick auf einen zukünftigen Notfalleinsatz bei elektiven Eingriffen trainiert werden.SummaryObjectivesEvaluation of safety and effectiveness of the Combitube during general anaesthesia.Patients and methods250 patients undergoing general anaesthesia were enrolled in the study. The respective types and duration of surgery, ease of insertion of the Combitube, and potential complications were recorded. Maximum ventilatory pressures and leak fraction were also evaluated in this study.ResultsDuration of surgery varied between 20 and 410 min. More than 96% of the blind Combitube insertions were successful at the first attempt, with a mean time of less than 18±5 seconds (range 12–24 seconds). In 99% of patients the Combitube worked well, and adequate oxygenation and ventilation was possible. All patients were haemodynamically stable during the entire duration of surgery. In all patients, pulse oximetry showed an oxygen saturation of 97±2% and an end-tidal carbon dioxide of 38±6 mm Hg. Leak fraction, calculated as a fraction of the inspired volume, did not increase to more than 5% up to a ventilation pressure of 40 cm H2O. Superficial laceration occurred in 18 patients (7.2%) without further sequelae. No severe injuries were observed during the study period.ConclusionVentilation via the Combitube appears to be safe and effective during general anaesthesia. Practice in elective cases is a requirement for successful use in an emergency situation.