Summary

As atelectasis occurs in most patients during general anaesthesia and may be one of the major causes for the development of hypoxaemia and nosocomial pneumonia, its prevention may be considered as an important objective in perioperative management. The major causative mechanisms are the loss of respiratory muscle tone, compression and gas absorption. Vital capacity manoeuvres have been proposed as a means to eliminate atelectasis in the vast majority of patients and restore normal pulmonary gas exchange during general anaesthesia. In this review we describe the pathogenesis of atelectasis in the perioperative period and discuss in the light of recent published investigations the suitability of the vital capacity manoeuvre as a tool during general anaesthesia. Reviewing the current literature, a vital capacity manoeuvre during general anaesthesia may only be useful under specific circumstances when mechanical ventilation with a high inspiratory fraction of oxygen is required or during cardiac surgery at the end of cardiopulmonary bypass to reduce the amount of atelectasis and to maintain adequate gas exchange.

Summary

Background and objective: In cases of aspiration of gastric contents the risk of pneumonitis is dependent on the pH and volume of the gastric contents. Omeprazole and rantidine each decrease gastric volume and increase gastric pH. We evaluated the efficacy of preoperative administration of omeprazole (60 mg) or ranitidine (150 mg) in the prophylaxis of aspiration pneumonitis.

Methods: Data were obtained from 75 elective female surgical patients randomly allocated to one of three groups, who received either omeprazole 60 mg orally, or ranitidine 150 mg orally, or neither, on the evening prior to, and on the morning of, surgery. Gastric volume and pH was measured using blind aspiration.

Results: Both pH <2.5 and volume >25 mL were present in none of the patients in either the ranitidine or omeprazole groups, compared to 15 of 25 control patients (P < 0.0001).

Conclusions: Preoperative oral administration of omeprazole (60 mg) or ranitidine (150 mg) reduced residual gastric content volume and increased pH >2.5, possibly reducing the effects of pulmonary aspiration of gastric contents.

Summary

Background and objective: A multicentre study was conducted to compare three methods of inhalation induction with sevoflurane in adult premedicated patients.

Methods: One-hundred-and-twenty-five adult patients of ASA I–II were scheduled for short elective surgical procedures (<90 min) under general anaesthesia with spontaneous ventilation of the lungs via a laryngeal mask airway. Patients were randomly assigned to one of three groups: conventional stepwise inhalation induction group (Group C) or vital capacity rapid inhalation induction groups at 4.5% (Group VC4.5) or at 8% sevoflurane (Group VC8). Before anaesthetic induction, fentanyl 1 μg kg−1 was given and the face mask applied with the anaesthetic breathing system primed with sevoflurane 4.5% or 8% in the respective vital capacity groups. Loss of eyelash reflex, time to cessation of finger tapping, laryngeal mask insertion, side-effects and adequacy of induction were recorded.

Results: The time to loss of eyelash reflex was significantly shorter in both vital capacity groups vs. the control group: VC8: 68 ± 7 s; and VC4.5: 94 ± 6.5 s vs. C: 118 ± 6.4 s (P < 0.0001). Significant differences were found in all pairwise comparisons for time to cessation of tapping: Group VC8 (62 ± 7 s), Group VC4.5 (85 ± 6 s) and Group C (116 ± 6 s; P < 0.0001). The time to laryngeal mask insertion was significantly shorter in the Group VC8 (176 ± 13 s) compared with the other two groups, Group VC4.5 (219 ± 13 s) and Group C (216 ± 9 s). There were no significant differences in the incidence of side-effects between the three groups.

Conclusions: Inhalation induction of anaesthesia with sevoflurane with the three techniques tested is safe, reliable and well accepted by the patients. The vital capacity rapid inhalation group primed with sevoflurane 8% was the fastest method with no relevant side-effects.

Summary

Background and objective: We tested the hypothesis that disturbances of the visual pathway persist following general anaesthesia, even after normal clinical discharge criteria have been met.

Methods: We performed full-field flash electroretinography in the right eye of 10 unpremedicated ASA I patients who underwent N2O/sevoflurane anaesthesia. Electroretinograms were recorded preoperatively, immediately after discharge from the recovery room and 2 h after discontinuation of sevoflurane. The time at which postanaesthesia discharge score first exceeded 9 was also noted. Data were analysed using paired, one-tailed Student's t-test.

Results: Latency of the b-wave on the photopic electroretinogram was greater at each postoperative time point (30.5 ± 0.9 and 30 ± 1.3 ms), compared to preoperative values (29.2 ± 0.8 ms, P < 0.001 and P = 0.04, respectively). The A–B amplitude of the b-wave was less postoperatively (220.3 ± 52.7 and 210.3 ± 42.7 μV) compared to values before operation (248.1 ± 57.6 μV, P = 0.03 and P = 0.01, respectively). Oscillatory potential latencies were greater at each postoperative time point (21.4 ± 0.5 and 20.8 ± 0.6 ms) compared to before operation (20.4 ± 0.4 ms, P < 0.001 and P = 0.03, respectively). Oscillatory potential amplitudes were less at the first postoperative time point (17.5 ± 6.1 μV), compared to preoperative values (22 ± 6.4 μV, P = 0.04).

Conclusions: Postoperative electroretinogram abnormalities are consistently present in patients who have undergone N2O/sevoflurane anaesthesia. These abnormalities persist beyond the time at which standard clinical discharge criteria have been met.

Summary

Background and objective: The kneeling prone position is often used for low back surgery in order to decrease intraoperative bleeding and increase the surgical exposure of the vertebral canal. The aim of this study was to assess effects of the kneeling prone position on respiratory gas exchange focusing on oxygen consumption and early changes in oxygenation.

Methods: Thirty ASA I–II patients scheduled for low back surgery in the kneeling prone position were studied. Anaesthesia was maintained with isoflurane, 1.2% end-tidal concentration. Respiratory gas exchange was measured with indirect calorimetry.

Results: When the patients were turned into the kneeling prone position their oxygenation was immediately improved – measured by arterial oxygen tension and arterial oxygen saturation. The oxygen uptake rate did not change from a baseline supine level of 76 mL min−1 m−2, but the carbon dioxide excretion rate decreased from a baseline supine value of 71 mL min−1 m−2 to 66 mL min−1 m−2 at 5 and 10 min after the kneeling prone position was adopted. Alveolar ventilation decreased in the kneeling prone position.

Conclusions: The present study demonstrates that the kneeling prone position improves oxygenation and that the mechanisms involved are fast in onset. Furthermore, the prone position does not change oxygen consumption although alveolar ventilation is significantly reduced. The changes in alveolar ventilation could possibly be the result of circulatory changes caused by the prone position, but further studies are needed to clarify that hypothesis.

Summary

Background and objective: The use of midazolam for conscious sedation is an accepted method of anxiety control in restorative dentistry. A lack of predictability in its effects requires the dose of midazolam to be adjusted to individual patient's requirements. We determined whether patient-controlled sedation was a suitable alternative to operator-controlled sedation in restorative dentistry.

Methods: A randomized crossover clinical trial involving 35 consecutive patients undergoing similar dental procedures. Patients were randomly given midazolam, administered either by the patient or by the operator at the first visit and the alternative option on the second visit. All patients were ASA I–II and their ages ranged between 20 and 48 yr. Blood pressure, heart rate, oxygen saturation and patient satisfaction were recorded.

Results: The onset time and initial dose for sedation were similar with the two methods of administration and the sedation scores and vital signs were satisfactory. In the patient-controlled group the mean total dose of midazolam was 7.9 (±4.2 SD) mg cf. 4.2 (±1.8 SD) mg in the operator-controlled group (P < 0.05). The time to fitness for discharge (15.4 (± 11.9 SD) min) was greater in the patient-controlled group cf. the operator-controlled group (8.5 (±9.5 SD) min), P < 0.05.

Conclusion: This study shows that patient-controlled sedation is a suitable alternative to operator-controlled sedation in the management of anxious dental patients.

Summary

Background and objective: The transcerebral double-indicator dilution technique is a recently developed method to measure global cerebral blood flow at bedside. It is based on bolus injection of ice-cold indocyanine green dye and simultaneous recording of resulting thermo- and dye-dilution curves in the aorta and the jugular bulb. However, with this method 40 mL of ice-cold solution is administered as a bolus. Therefore, this prospective clinical study was performed to elucidate the effects of repeated administration of indicator on absolute blood temperature and on cerebral blood flow and metabolism.

Methods: The investigation was performed in nine male patients scheduled for elective coronary artery bypass grafting. Absolute blood temperature was measured in the jugular bulb and in the aorta before and after repeated measurements using the transcerebral double-indicator dilution technique.

Results: During the investigated time course, the blood temperature in the jugular bulb, compared to the aorta, was significantly higher with a mean difference of 0.21°C. The administration of an ice-cold bolus reduced the mean blood temperature by 0.06°C in the jugular bulb as well as in the aorta. After the transcerebral double-indicator dilution measurements a temperature recovery to baseline conditions was not observed during the investigated time period. Cerebral blood flow and cerebral metabolism did not change during the investigated time period.

Conclusions: Repeated measurements with the transcerebral double-indicator dilution technique do not affect absolute jugular bulb blood temperatures negatively. Global cerebral blood flow and metabolism measurements remain unaltered. However, accuracy and resolution of this technique is not high enough to detect the effect of minor changes of physiological variables.

Summary

Background and objective: To investigate the clinical application of a mathematical model of pulmonary gas exchange, which ascribes hypoxaemia to shunt and ventilation/perfusion mismatch. Ventilation/perfusion mismatch is quantified by ΔPO2, which is the drop in oxygen pressure from alveoli to lung capillaries. Shunt and ΔPO2 were used to describe changes in oxygenation after coronary artery bypass grafting.

Methods: Fourteen patients were studied 2–4 h after surgery and on postoperative days 2, 3 and 7. On each occasion inspired oxygen fraction was changed in four to six steps to obtain arterial oxygen saturation (SaO2) in the range of 90–100%, enabling construction of FeO2/SaO2 curves. Measurements of ventilation, circulation and oxygenation were entered in a previously described mathematical model of pulmonary gas exchange.

Results: We found that oxygenation was most impaired 3 days after surgery. By fitting the mathematical model to the FeO2/SaO2 curve, we found that shunt remained constant throughout the study period. However, ΔPO2 increased from 0.5 kPa (median, range 0–3.8) 2–4 h after surgery, to 3.2 kPa (range 1.2–6.4, P < 0.05) on day 2, and to 4.0 kPa (range 1.2–8.3) on day 3. On day 7, ΔPO2 decreased to 2.2 kPa (range 0–3.5, P < 0.05).

Conclusions: Ventilation/perfusion mismatch (ΔPO2), rather than shunt, explains the changes in postoperative oxygenation. The model of pulmonary gas exchange may serve as a useful and potentially non-invasive clinical tool for monitoring patients at risk of postoperative hypoxaemia.

Summary

Background and objective: To evaluate the temporal changes in respiratory physiological dead space and dynamic compliance of the respiratory system during non-abdominal, upper abdominal and lower abdominal surgery under general anaesthesia with intermittent positive pressure ventilation.

Methods: Thirty-four adult patients were studied (non-abdominal surgery, n = 8; upper abdominal surgery, n = 13 and lower abdominal surgery in lithotomy position, n = 13). Physiological dead space was measured using the single breath carbon dioxide test. The physiological dead space to tidal volume ratio (VD/VT), dynamic compliance of respiratory system, expiratory tidal volume and respiratory rate were measured 10 min after tracheal intubation, and 30, 60 and 120 min later.

Results: In lower abdominal surgery group, VD/VT was significantly increased at 120 min compared with 0 min (P = 0.005) and 30 min (P = 0.009). There were no significant differences in VD/VT between the three groups at any time point. Compliance decreased significantly in patients with upper abdominal (120 min) and lower abdominal surgery (60 and 120 min), but there were no significant changes during non-abdominal surgery.

Conclusions: We found that the VD/VT increased in patients undergoing lower abdominal surgery in lithotomy and head down tilt, and compliance decreased in those undergoing upper abdominal and lower abdominal surgery over time.

Summary

Background and objective: Platelet function abnormalities influence the haemostatic defect in patients with liver failure. Patients after orthotopic liver transplantation present thrombocytopaenia associated with bleeding problems, which may be aggravated by the interaction of hydroxyethyl starches with platelets.

Methods: From 12 patients after liver transplantation venous blood samples (3 mL) were taken before, 20 and 120 min after infusion of hydroxyethyl starch of medium molecular weight (200 kDa/0.5) 6% 10 mL kg−1 over a period of 30 min. Surface expression of glycoprotein IIb/IIIa and P-selectin were quantified by flow cytometry as well as the percentage of platelet–leucocyte complexes.

Results: A significant decrease of P-selectin expression following administration of hydroxyethyl starch after 120 min (89.1 ± 4.2%, P = 0.029) and a corresponding significant reduction in the formation of platelet– monocyte complexes (81.1 ± 7.8%, P = 0.001) were observed. There was no alteration in the glycoprotein IIb/IIIa expression after hydroxyethyl starch infusion.

Conclusions: Infusion of hydroxyethyl starch 200 kDa/0.5 in clinically relevant doses does not alter glycoprotein IIb/IIIa expression in thrombocytopaenic patients with pre-existing platelet dysfunction after orthotopic liver transplantation. Accordingly, infusion of hydroxyethyl starch may have a beneficial effect on microvascular graft perfusion through the resulting haemodilution and reduced P-selectin expression with subsequent reduced leucocyte–platelet complexes and endothelial adhesion.

Summary

Background and objective: Differences in sensitivity to anaesthetic drugs may exist among human races. Allelic variants for drug metabolizing isoenzymes and other pharmacokinetic/pharmacodynamic differences may account for a variable response to anaesthetic drugs. This study was designed to investigate comparatively the anaesthetic requirements and the recovery trends of three different ethnic groups: Caucasians, African blacks and Brazilians.

Methods: The anaesthetic depth and recovery of groups of 45 patients undergoing total intravenous anaesthesia with propofol and fentanyl were compared. The bispectral index and clinical parameters were used to assess the depth of anaesthesia. The bispectral index, the response to verbal stimuli and the eye opening time were used to assess recovery.

Results: After stopping propofol, the bispectral index values of Caucasians returned to the baseline in about 10.8 ± 4 min, that of Kenyan African blacks in 18 ± 7 min and that of Brazilians in a highly variable time ranging from 5 to 25 min, (14.9 ± 9.9). The time from discontinuation of propofol and fentanyl infusion to eye opening was 18.8 ± 7.1 min in African blacks (P < 0.01) and 13.5 ± 8.8 min in Brazilians (P > 0.05) vs. 11.6 ± 4.5 min in Caucasians. Time to respond to verbal commands was 16.8 ± 8 min in African blacks (P < 0.01) and 12.8 ± 8.1 min in Brazilians (P > 0.05) vs. 9.9 ± 4.5 min in Caucasians.

Conclusions: The recovery of Kenyan African blacks from anaesthesia with propofol and fentanyl is much slower, in comparison with Caucasians. The recovery time of Brazilians is much more variable, in comparison with Caucasians.