Effects of pain stimulation on bispectral index, heart rate and blood pressure at different minimal alveolar concentration values of sevoflurane.

BACKGROUND: The aim of the present study was to examine the level of unconsciousness measured with bispectral index (BIS) at different minimal alveolar concentration (MAC) levels of sevoflurane, and to study the hemodynamic and BIS reactions during noxious stimulation with transcutaneous electrical nerve stimulation (TENS) and an ice water pain test (IWP). METHODS: This study was approved by the Ethics Committee and was performed on 10 healthy, young volunteers (six males and four females), ASA physical status I. Anesthesia was induced and maintained with sevoflurane in an oxygen/air mixture. The volunteers were spontaneously breathing, but if necessary, ventilation was mechanically supported. TENS and IWP were performed at 1.0, 1.5 and 2.0 MAC of sevoflurane. RESULTS: At 1.0 MAC, there was a significant increase in BIS during pain stimulation both with IWP (P<0.03) and with TENS (P<0.005), but at 1.5 MAC there were no changes. A marked variation in BIS was seen at 2.0 MAC, with periods of burst suppression and periods of high BIS values despite clinical signs of deep anesthesia. These marked variations in BIS were seen before, during and after pain stimulation. One volunteer (# 8) had a short episode of convulsions at 2.0 MAC. CONCLUSION: BIS, heart rate and blood pressure increased during pain stimulation at 1.0 MAC but not at 1.5 MAC of sevoflurane. There was a remarkable variation in BIS at 2.0 MAC of sevoflurane, with BIS values indicating wakefulness despite clinical signs of deep anesthesia. This BIS variation is probably caused by epileptogenic activity due to sevoflurane.

Dexamethasone is as effective as ondansetron for the prevention of postoperative nausea and vomiting following breast surgery.

INTRODUCTION: Postoperative nausea and vomiting remain a common problem following breast surgery. This study assesses whether dexamethasone is as effective as ondansetron in the control of postoperative nausea and vomiting (PONV). METHODS: Eighty ASA I-III patients undergoing breast surgery for carcinoma of the breast were included in the study. Following premedication with diazepam 5-10 mg, patients were induced with fentanyl 50 micro g and propofol 2-2.5 mg kg-1. A larynx mask was inserted and anesthesia maintained with sevoflurane in oxygen and nitrous oxide. Patients were then randomly divided into two groups: Group D (dexamethasone) was given 4 mg dexamethasone i.v. after induction and Group O (ondansetron) was given 4 mg ondansetron at the same time point. Postoperatively, nausea, vomiting and pain were recorded at 1-h intervals during 4 h, and thereafter every 4 h during 24 h. RESULTS: The incidence of PONV during 24 h was 37% and 33% in Group D and Group O, respectively (NS). No differences were found between the groups in the incidence of postoperative nausea, vomiting or pain at the different time intervals. No differences were found in the incidence of PONV in smokers vs. non-smokers. No side-effects of these drugs were observed. CONCLUSIONS: Ondansetron 4 mg or dexamethasone 4 mg are equally effective in the prevention of postoperative nausea and vomiting following breast surgery. Other factors being similar, the difference in cost between these drugs would favor the use of dexamethasone instead of ondansetron when monotherapy against PONV is used.

Perioperative gastric emptying is not a predictor of early postoperative nausea and vomiting in patients undergoing laparoscopic cholecystectomy.

UNLABELLED: It is not known whether patients with postoperative nausea and vomiting (PONV) have delayed gastric emptying compared with patients without PONV. We compared the perioperative rate of gastric emptying in patients experiencing PONV with the rate in those without PONV immediately after laparoscopic cholecystectomy. Gastric emptying was studied by the acetaminophen method. Acetaminophen is not absorbed from the stomach but is rapidly absorbed from the small intestine, and the rate of gastric emptying therefore determines the rate of absorption of acetaminophen administered into the stomach. Forty patients (ASA physical status I and II) were included in the study. After the induction of anesthesia, a gastric tube was positioned in the stomach and 1.5 g of acetaminophen dissolved in 200 mL of water was administered. Venous blood samples for the determination of serum acetaminophen concentrations were taken before and at 15-min intervals during a period of 180 min after the administration of acetaminophen. Twenty-six patients experienced nausea during the first 4 h postoperatively. The other 14 patients had no nausea. There were no statistically significant differences in the maximal acetaminophen concentration, the time taken to reach the maximal concentration, or the area under the serum acetaminophen concentration time curves from 0 to 60, 0-120, and 0-180 min between the groups of patients with or without PONV. We did not find any relationship between postoperative gastric emptying and PONV, and therefore gastric emptying is not a predictor of PONV. IMPLICATIONS: The incidence of postoperative nausea and vomiting is frequent after laparoscopic cholecystectomy. This study has shown that perioperative gastric emptying is not a predictor of early postoperative nausea and vomiting in patients undergoing laparoscopic cholecystectomy.

Circulatory effects of isoflurane during acute hypercapnia.

Acute respiratory acidosis results in increases in cardiac output and in systemic and pulmonary arterial blood pressures. The aim of this investigation was to determine if isoflurane modifies these effects. Nine patients (ASA II or III) scheduled for major surgery took part in the investigation. After the induction of general anesthesia, CO2 was added to the inspiratory gas mixture. After 15 min, ventilation with addition of CO2 (PaCO2 8-9 kPa) isoflurane (3%) was added. Hemodynamic measurements were made to study the effects of acute hypercapnia and the effects of isoflurane during hypercapnia. The addition of carbon dioxide resulted in increases in cardiac output, systemic and pulmonary arterial blood pressures, and right and left ventricular stroke work. The addition of isoflurane during hypercapnia decreased systemic arterial blood pressure, but pulmonary arterial blood pressure was unaffected, cardiac output and stroke volume did not change, and left but not right ventricular stroke work decreased. In conclusion, acute pulmonary hypertension induced by hypercapnia was not affected by isoflurane but, despite increased right ventricular stroke work, there were no signs of right ventricular failure.

Comparative studies of IPPV and HFPPV with PEEP in critical care patients. I: A clinical evaluation.

The effects of the ventilatory patterns of a conventional ventilator (SV-900) and a low-compression ventilator (system H) were studied in 12 patients with respiratory failure (RF). Volume-controlled ventilation at frequencies (f) of 20 breath/min (SV-20) with SV-900, and 20 (H-20) and 60 (H-60 = high-frequency positive-pressure ventilation, HFPPV) breath/min with system H was given. Inspiration constituted 25% (with an inspiratory pause of 10%) of the ventilatory cycle with SV-900 and 22% with system H. Intratracheal (ITP), intrapleural, systemic and pulmonary arterial (PAP), and central venous (CVP) pressures were measured at normoventilation. During H-60, normoventilation was provided with smaller tidal volumes and lower mean intratracheal pressures than during SV-20 and H-20. Cardiac index and oxygen transport were not affected by changes in ventilatory pattern. The respiration-synchronous variations in CVP, PAP, and pulmonary capillary wedge pressure (WP) during ventilation at 20 breath/min were abolished during HFPPV. In the most severely ill patients, long-term HFPPV was uneventful. Airway suctioning during ventilation with oxygen was an important feature of the pneumatic valve principle (system H). The results of this study indicate that volume-controlled HFPPV is as efficient and as well accepted by the patient as conventional ventilation (SV-20).

Comparative studies of IPPV and HFPPV with PEEP in critical care patients. II: Studies on intrapulmonary gas distribution.

The ventilatory patterns of a conventional ventilator for volume-controlled ventilation (SV-900) and a low-compression ventilator utilizing the pneumatic valve principle for pressure/flow-generated, volume-controlled ventilation (system H) were studied in a lung model and in 10 patients with respiratory failure. System H was used at frequencies of 20 (H-20) and 60 (H-60 = high-frequency positive-pressure ventilation [HFPPV]) breath/min, and SV-900 at a frequency of 20 (SV-20) breath/min. With system H, inspiration constituted 22% (no inspiratory pause) and with SV-900, 25% (with 10% inspiratory pause). System H delivers an instantaneous accelerating flow which rapidly decelerates during the second part of the inspiratory phase. Maximal flow rates studied were 1.3 (H-60), 0.9 (H-20), and 0.7 (SV-20) L/sec. Thus, HFPPV delivers an effective tidal volume with highest linear velocity. This increased velocity increases gas mixing by increasing turbulence in conducting airways. In the 10 patients with respiratory failure, intrapulmonary gas distribution (measured as the nitrogen washout delay) was improved from 106% during SV-20 to 74% with H-60 (p less than 0.05). H-60 also increased carbon dioxide elimination in the 2 patients with the most severe pulmonary dysfunction.

Clinical evaluation of high-frequency positive-pressure ventilation (HFPPV) in patients scheduled for open-chest surgery.

Comparisons were made in 10 patients scheduled for thoracotomy between a prototype of a low-compressive system (Bronchovent Special) for volume-controlled, high-frequency positive-pressure ventilation (HFPPV; fixed frequency of 60/min; fixed relative insufflation time of 22%), and a conventional respirator (SV-900) for intermittent positive-pressure, volume-controlled ventilation at a frequency of 20/min, after induction of anesthesia, but before surgery. With both ventilator systems intratracheal, intrapleural, systolic, diastolic, and mean arterial systemic and central venous pressures were measured at normoventilation (normocarbia). Mean intratracheal pressure and mean intrapleural pressure were significantly lower with volume-controlled HFPPV (1.3 +/- 0.5 and -4.0 +/- 2.1 (SD) cm H2O, respectively) than with conventional volume-controlled ventilation with SV-900 (2.1 +/- 1.2 and -3.0 +/- 1.5 cm H2O, respectively). No significant differences between the two ventilators were found with respect to arterial systemic and central venous pressures, arterial oxygen and carbon dioxide tensions, or alveolar-arterial oxygen tension difference. With the thorax open, during volume-controlled HFPPV the exposed lung was moderately expanded and exhibited only minor movements during insufflation. Repeated blood gas analyses during surgery showed normocarbia and good oxygenation even during compression of the exposed lung. After compression the lung was readily re-expanded with the aid of a brief period of positive end-expiratory pressure (PEEP). Thus, even relatively low intrapulmonary pressures during volume-controlled HFPPV without PEEP are adequate to keep the open-chest lung expanded during intrathoracic surgery. This creates optimal conditions for the surgeons.