Effects of age and exercise on physiological dead space during simulated dives at 2.8 ATA.

Physiological dead space (Vds), end-tidal CO(2) (Pet(CO(2))), and arterial CO(2) (Pa(CO(2))) were measured at 1 and 2.8 ATA in a dry hyperbaric chamber in 10 older (58-74 yr) and 10 younger (19-39 yr) air-breathing subjects during rest and two levels of upright exercise on a cycle ergometer. At pressure, Vd (liters btps) increased from 0.34 +/- 0.09 (mean +/- SD of all subjects for normally distributed data, median +/- interquartile range otherwise) to 0.40 +/- 0.09 (P = 0.0060) at rest, 0.35 +/- 0.13 to 0.45 +/- 0.11 (P = 0.0003) during light exercise, and 0.38 +/- 0.17 to 0.45 +/- 0.13 (P = 0.0497) during heavier exercise. During these conditions, Pa(CO(2)) (Torr) increased from 33.8 +/- 4.2 to 35.7 +/- 4.4 (P = 0.0059), 35.3 +/- 3.2 to 39.4 +/- 3.1 (P < 0.0001), and 29.6 +/- 5.6 to 37.4 +/- 6.5 (P < 0.0001), respectively. During exercise, Pet(CO(2)) overestimated Pa(CO(2)), although the absolute difference was less at pressure. Capnography poorly estimated Pa(CO(2)) during exercise at 1 and 2.8 ATA because of wide variability. Older subjects had higher Vd at 1 ATA but similar changes in Vd, Pa(CO(2)), and Pet(CO(2)) at pressure. These results are consistent with an effect of increased gas density.

How much are patients willing to pay to avoid postoperative nausea and vomiting?

Postoperative nausea and vomiting (PONV) are unpleasant experiences. However, there is no drug that is completely effective in preventing PONV. Whereas cost effectiveness analyses rely on specific health outcomes (e.g., years of life saved), cost-benefit analyses assess the cost and benefit of medical therapy in terms of dollars. We hypothesized that patients were willing to pay for a hypothetical new drug that would eliminate PONV. Eighty elective day surgical patients using general anesthesia participated in the study. After their recovery in the postanesthetic care unit, they were asked to complete an interactive computer questionnaire on demographics, the value of avoiding PONV, and their willingness to pay for an antiemetic. Patients were willing to pay US$56 (US$26--US$97; median, 25%--75%) for an antiemetic that would completely prevent PONV. Patients who developed nausea (n = 21; 26%) and vomiting (n = 9; 11%) were willing to pay US$73 (US$44--US$110) and $100 (US$61--US$200; median, 25%--75%), respectively (P < 0.05). Seventy-six percent of patients considered avoiding postoperative nausea and 78% of patients considered avoiding vomiting as important (> or = 50 mm on a 0--100-mm visual analog scale). Nausea or vomiting in the postanesthetic care unit, greater patient income, previous history of PONV, more importance placed on avoiding nausea and vomiting, increasing age, and being married are independent covariates that increase the willingness to pay estimates. Patients associated a value with the avoidance of PONV and were willing to pay between US$56 and US$100 for a completely effective antiemetic.

Thromboelastography as a perioperative measure of anticoagulation resulting from low molecular weight heparin: a comparison with anti-Xa concentrations.

UNLABELLED: Low molecular weight heparin (LMWH) is commonly used to prevent postoperative thromboembolism. Currently, there is no convenient test to measure the degree of anticoagulation from LMWH. This prospective study examines the relationship of thromboelastography and serum anti-Xa concentration in patients treated with enoxaparin. Twenty-four adult patients scheduled for orthopedic surgery using epidural anesthesia were enrolled. Epidural catheters were removed the morning after surgery before the commencement of subcutaneous enoxaparin 30 mg twice daily. Venous blood samples were obtained at 1) the induction of anesthesia (baseline), 2) immediately before the third dose of enoxaparin postoperatively (Day 2-trough), 3) 4 h after the third dose postoperatively (Day 2-peak), and 4) immediately before the fifth dose postoperatively (Day 3-trough). Whole blood samples were obtained for thromboelastography, activated clotting time, and anti-Xa level analyses at each of the four time intervals. At the four sample intervals, the r time (mean +/- SEM). (20 +/- 1, 25 +/- 2, 51 +/- 6, 31 +/- 3 mm) and the k time (9 +/- 0. 7, 12 +/- 1, 27 +/- 5, 14 +/- 2 mm) of the thromboelastograph were significantly correlated with the expected peak and trough levels of LMWH and serum anti-Xa levels (P: < 0.05). At the Day 3-trough, thromboelastograph r times exceeded the normal range in 6 of 25 patients (25%). Prolongation of r time and k time on postoperative Day 3 may indicate an exaggerated response to LMWH. Thromboelastography is a test that could potentially correlate with the degree of anticoagulation produced by low molecular weight heparin. IMPLICATIONS: Thromboelastography is a test that could potentially correlate with the degree of anticoagulation produced by low molecular weight heparin. The r time from the thromboelastogram correlates with serum anti-Xa concentration.

Subarachnoid meperidine (Pethidine) causes significant nausea and vomiting during labor. The Duke Women's Anesthesia Research Group.

BACKGROUND: The combined spinal-epidural (CSE) technique using bupivicaine-fentanyl has become an established method of pain control during parturition. One limitation is the relatively short duration of effective analgesia produced by bupivicaine-fentanyl. In contrast, subarachnoid meperidine has been shown to provide a long duration of anesthesia in nonobstetric patients. Therefore, the authors tested the hypothesis that subarachnoid meperidine produces a significant increase in the duration of analgesia compared with bupivicaine-fentanyl. METHODS: Based on a power analysis of preliminary data, the authors intended to recruit 90 patients for the study, randomized to three groups: 2.5 mg bupivicaine-25 microg fentanyl, 15 mg meperidine, or 25 mg meperidine. However, after enrolling 34 patients, the study was discontinued because of a significant increase in nausea or vomiting in the study patients. RESULTS: Nausea or vomiting was substantially increased in both meperidine groups compared with the bupivicaine-fentanyl group: 16 with nausea or vomiting in the meperidine groups (n = 21), compared with 1 in the bupivicaine-fentanyl group (n = 11), P = 0.0011. The mean duration of analgesia provided by 25 mg meperidine was 126 +/- 51 min, compared with 98 +/- 29 min for bupivicaine-fentanyl and 90 +/- 67 min for 15 mg meperidine. These data were not significant (P = 0.27). CONCLUSIONS: Although intrathecal meperidine could potentially prolong subarachnoid analgesia during labor, its use was associated with a significant incidence of nausea or vomiting. These data do not support the use of subarachnoid meperidine in doses of 15 or 25 mg for labor analgesia.

A randomized, double-blinded comparison of ondansetron, droperidol, and placebo for prevention of postoperative nausea and vomiting after supratentorial craniotomy.

UNLABELLED: Nausea or vomiting occurs frequently after craniotomy. Because of the need for frequent postoperative neurological assessment, an effective antiemetic with minimal sedative side effects is needed. Therefore, we compared ondansetron to droperidol in a randomized, double-blinded, placebo-controlled study. A total of 60 adults requiring elective supratentorial craniotomy received standardized IV anesthesia with 4 mg of ondansetron, 0.625 mg of droperidol, or placebo at skin closure. The incidence of postoperative nausea, emesis, pain and sedation scores, and rescue antiemetic use were recorded at 0, 0.5, 1, 4, 8, 12, 24, and 48 h. All groups were demographically similar. Differences existed for cumulative 8, 12, and 24 h incidences of nausea (24 h, P = 0.03) and emesis (24 h, P = 0.04). Within 4 h, when maximal effect could be expected from treatment, 20% of the ondansetron group, 25% of the droperidol group and 50% of the placebo group received rescue antiemetic (P = 0.12). No differences in pain (P = 0.82) or sedation (P = 0.74) scores were detected. Both ondansetron and droperidol prevent nausea; however, only droperidol reduces emesis after supratentorial craniotomy. The dose of droperidol used was not more sedating than ondansetron. Sustained reduction in nausea and emesis over 24 h indicates a preemptive benefit of prophylactic antiemetic in this surgical population. IMPLICATIONS: Nausea and vomiting after brain surgery are particularly troubling, because effective treatment may cause sedation, making postoperative neurological assessment difficult. Our study shows that both ondansetron and droperidol are effective in reducing nausea, and that droperidol is particularly effective in reducing vomiting. Neither drug caused more sedation than placebo.

Changes in the auditory evoked potentials and the bispectral index following propofol or propofol and alfentanil.

BACKGROUND: Midlatency auditory evoked potentials (MLAEP) show graded changes with increasing doses of hypnotics but little change with opioids. The effect of their combination on the MLAEP was evaluated. Also, the bispectral index (BIS) was compared with the ability of MLAEP to correlate with sedation and predict loss of consciousness. METHODS: Twenty healthy volunteers were randomly assigned to receive stepped increases in propofol concentration (10 subjects) or propofol plus alfentanil 100 ng/ml (10 subjects). At baseline and at each targeted effect site concentration the mean MLAEP, BIS, measures of sedation, and drug concentration were obtained. The relation among MLAEP, BIS, and sedation score was determined. The prediction probability (Pk) was calculated and compared for BIS and MLAEP. RESULTS: The BIS and MLAEP patterns showed significant changes (Pa and Nb decreased in amplitude and increased in latency) with increasing level of sedation (P < 0.0001). The BIS correlated better with sedation scores (0.884) than did the MLAEP (P < 0.05). Pa and Nb latencies showed the best correlation with sedation levels (0.685 and 0.658, respectively). The addition of alfentanil did not affect the relation between MLAEP and loss of consciousness (P > 0.15). The BIS (Pk = 0.952) was a better predictor of loss of consciousness than were Pa and Nb amplitude (P < 0.05) but were comparable to Pa and Nb latency (Pk = 0.869 and 0. 873, respectively). CONCLUSION: MLAEP changes, like the BIS, correlate well with increasing sedation produced by propofol, and these changes in the MLAEP are independent of the presence of an opioid. Among all the MLAEP parameters, Pa and Nb latencies are the best predictors of increasing sedation and loss of consciousness.

Comparison of remifentanil with alfentanil or suxamethonium following propofol anaesthesia for tracheal intubation.

Sixty ASA physical status I and II, premedicated patients were administered propofol 2 mg x kg-1 and remifentanil 2 microg x kg-1 (group R), alfentanil 50 microg x kg-1 (group A) or suxamethonium 1 mg x kg-1 (group S) as a rapid bolus. One minute after study drug administration, tracheal intubation was performed. Intubation conditions were then scored. Excellent or good conditions were observed in only 35% in group R compared with groups S and A (100% and 85%, respectively; p < 0.001). The haemodynamic response to tracheal intubation was blunted in groups R and A compared with group S (p < 0.001). The mean heart rate in groups R and A was significantly lower than group S (p < 0.001). We conclude that remifentanil 2 microg x kg-1 given as a rapid bolus will not produce intubating conditions as good as those obtained with alfentanil 50 microg x kg-1 or suxamethonium 1 mg x kg-1 if administered after propofol 2 mg x kg-1.

Dosing study of remifentanil and propofol for tracheal intubation without the use of muscle relaxants.

Sixty ASA I and II patients, premedicated with midazolam, were administered propofol 2 mg x kg-1 and remifentanil 3 microg x kg-1 (group R3), remifentanil 4 microg x kg-1 (group R4) and remifentanil 5 microg x kg-1 (group R5). Laryngoscopy and intubation were performed 1 min after the administration of the study drugs and the intubating conditions were assessed. Good to excellent conditions were observed in 12 patients in group R3 compared with 19 patients each in groups R4 and R5 (p = 0.004). Significant reductions in mean arterial pressure (MAP) and heart rate (HR) after administration of the study drug were observed in each group, p < 0.01. There was, however, no difference in mean MAP and HR between the three groups at all time points. We conclude that remifentanil 4-5 microg x kg-1 may reliably provide good to excellent conditions for tracheal intubation when administered after propofol 2 mg x kg-1.

Acute myocardial beta-adrenergic receptor dysfunction after cardiopulmonary bypass in patients with cardiac valve disease. Duke Heart Center Perioperative Desensitization Group.

BACKGROUND: Patients with cardiac valve disease (CVD) frequently have congestive heart failure (CHF) and chronic myocardial beta-adrenergic receptor (beta AR) desensitization. Cardiac surgery requiring cardiopulmonary bypass (CPB) is associated with increased plasma catecholamine concentrations, which might worsen myocardial beta AR function. We therefore tested the hypothesis that acute beta AR dysfunction occurs during CPB in patients with CVD. METHODS AND RESULTS: After informed consent, 50 patients were enrolled. Right atrial biopsy samples were obtained at initiation and conclusion of CPB to assess beta AR density and adenylyl cyclase (AC) activity. Plasma catecholamine concentrations increased 3-fold during CPB (P < 0.01). Although beta AR density remained constant, isoproterenol-stimulated AC activity decreased significantly (approximately 30%; P < 0.005). AC activity decreased 22% and 24% with direct G protein (NaF) or AC (manganese) activation, respectively. Patients with or without preoperative CHF exhibited similar degrees of acute myocardial beta AR dysfunction during CPB. CONCLUSIONS: Acute myocardial beta AR dysfunction occurs during CPB in patients with severe CVD requiring surgical correction, with or without preexisting CHF. The primary underlying mechanism involves functional uncoupling of the beta AR signal transduction pathway at the level of the AC moiety. This information should facilitate development of agents designed to prevent acute myocardial beta AR dysfunction during CPB, potentially leading to improved outcome in this high-risk population.

Acute depression of myocardial beta-adrenergic receptor signaling during cardiopulmonary bypass: impairment of the adenylyl cyclase moiety. Duke Heart Center Perioperative Desensitization Group.

BACKGROUND: Previously the authors showed that myocardial beta-adrenergic (betaAR) function is reduced after cardiopulmonary bypass (CPB) in a canine model Whether CPB results in similar effects on betaAR function in adult humans is not known. Therefore the current study tested two hypotheses: (1) That myocardial betaAR signaling is reduced in adult humans after CPB, and (2) that administration of long-term preoperative betaAR antagonists prevents this process. METHODS: After they gave informed consent, 52 patients undergoing aortocoronary surgery were enrolled. Atrial biopsies were obtained before CPB and immediately before discontinuation of CPB. Plasma catecholamine concentrations, myocardial betaAR density, and functional responsiveness (basal, isoproterenol, zinterol, sodium fluoride, and manganese-stimulated adenylyl cyclase activity) were assessed. RESULTS: Catecholamine levels increased significantly during CPB (P < 0.005). Myocardial betaAR adenylyl cyclase coupling decreased during CPB, as evidenced by a 21% decrease in isoproterenol-stimulated adenylyl cyclase activity (750 [430] pmol cyclic adenosine monophosphate per milligram total protein 15 min before CPB compared with 540 [390] at the end of CPB, P = 0.0062, medians [interquartile range]) despite constant betaAR density. Differential activation along the betaAR signal transduction cascade localized the defect to the adenylyl cyclase moiety. Administration of long-term preoperative betaAR antagonists did not prevent acute CPB-induced myocardial betaAR dysfunction. CONCLUSIONS: These data indicate that the myocardial adenylyl cyclase response to betaAR agonists decreases acutely in adults during aortocoronary surgery requiring CPB, regardless of whether long-term preoperative betaAR antagonists are administered. The mechanism underlying acute betaAR dysfunction appears to be direct impairment of the adenylyl cyclase moiety. Similar increases in manganese-stimulated activity before and at the end of CPB show preserved adenylyl cyclase catalytic activity, suggesting that other mechanisms (such as decreased protein levels or altered isoform expression or function) may be responsible for decreased adenylyl cyclase function.

Remifentanil prevents an increase in intraocular pressure after succinylcholine and tracheal intubation.

We have studied changes in intraocular pressure (IOP) in 30 patients after succinylcholine (suxamethonium) and tracheal intubation following administration of propofol 2 mg kg-1 and either remifentanil 1 microgram kg-1 (group R) or saline (group S). IOP was measured before induction, before administration of succinylcholine and the study drug, before intubation and for every 1 min after intubation for 5 min. There was a significant decrease in IOP in group R compared with group S from the time of administration of the study drugs to the end of the study (P < 0.006).

Comparison of two paediatric resuscitation charts for ease of use.

We have compared the ease and speed of use of two published paediatric resuscitation charts, the Burke and Bowden chart and the Oakley chart. Twenty general anaesthetists each answered 11 questions on resuscitation data for five paediatric patients of different weights, heights and ages. Data was recorded for the five patients using one chart and then repeated for the same patients using the second with the order of use of chart being randomised (n=100 patients for each chart). There were significantly fewer patients for whom mistakes were made with the Burke and Bowden chart compared to the modified Oakley chart (21 and 46, respectively, P < 0.001). Only one physician recorded the resuscitation data correctly for all five patients with each chart. The Burke and Bowden chart was also statistically significantly faster to use than the Oakley chart (52.7 s (range 31-103) versus 64 s (range 44-115), respectively (P < 0.001)). A change in format and content of each chart may be required to make them both more user friendly especially when used under stress.

Postoperative nausea and vomiting. A retrospective analysis in patients undergoing elective craniotomy.

Nausea and vomiting are important complications after craniotomy, for which there are little published epidemiologic data. We retrospectively examined the incidence of postcraniotomy nausea and vomiting to define risk factors. Medical records from 199 adults undergoing elective craniotomy were identified. Data extracted from surgery and the initial 48 hours postoperatively included gender, age, supratentorial versus infratentorial craniotomy, type of anesthesia (general versus monitored anesthesia care), intraoperative fentanyl dose, duration of anesthesia, antiemetic administration intraoperatively and postoperatively, and incidence of postoperative nausea, emesis, and opioid use. Postoperative nausea was recorded in 99 patients (50%) and emesis in 78 patients (39%). Postoperative opioids were administered to 170 patients (85%). Antiemetics were given intraoperatively to 13 patients (7%) and postoperatively to 121 patients (61%). More women (61%) than men (37%) had nausea (P = 0.001); emesis (women = 46%; men = 31%, P = 0.03); and postoperative antiemetic use (women = 69%; men = 51%, P = 0.013). The incidence of postoperative nausea (P = 0.04) and vomiting (P = 0.06) was greater in patients having infratentorial surgery. Emesis was more frequent in younger patients (P = 0.03). Postoperative nausea and vomiting were independent of anesthetic duration, fentanyl dose, or postoperative opioid use and occurred with similar frequency after general anesthesia or monitored anesthesia care. We conclude that postoperative nausea and vomiting occur frequently after craniotomy. Infratentorial surgery, female gender, and younger age are significant risk factors for this complication.