Mukadder Orhan-Sungur

Does supplemental oxygen reduce postoperative nausea and vomiting? A meta-analysis of randomized controlled trials.

BACKGROUND:Studies on the ability of supplemental oxygen to decrease the incidence of postoperative nausea and vomiting (PONV) are inconsistent, with initial studies suggesting benefit while subsequent trials demonstrate no decrease in PONV. METHODS:To clarify whether supplemental oxygen is an effective and reliable method to reduce PONV, we performed a systematic review (MEDLINE, Cochrane Library, hand searching and bibliographies, with no language restriction, through March 2006) of randomized, controlled trials comparing perioperative 80% versus 30%–40% Fio2 on the incidence of PONV. For this systematic review, PONV was defined as any nausea, retching, and/or vomiting in the first 24 h after surgery. The end-points were early PONV (0–6 h), late PONV (6–24 h), and overall PONV (0–24 h). Data from 10 trials with 1729 patients were included in our meta-analysis: 860 received 80% Fio2 and 869 received 30%–40% Fio2. RESULTS:In patients who received 80% Fio2,the relative risk (95% confidence intervals) of experiencing early PONV was 0.91 [0.71–1.16]; late PONV, 0.88 [0.69–1.11]; and overall PONV, 0.91 [0.77–1.06]. Results were similar for early, late, and overall nausea and vomiting. CONCLUSIONS:The positive results of two initial studies reducing the risk for PONV in patients given 80% Fio2 were not confirmed by any of the subsequent trials. Considering all available evidence, 80% Fio2 should no longer be considered an effective or reliable method to reduce overall PONV.

Effects of supplemental oxygen and dexamethasone on surgical site infection: a factorial randomized trial

BACKGROUND Tissue oxygenation is a strong predictor of surgical site infection. Improving tissue oxygenation should thus reduce wound infection risk. Supplemental inspired oxygen can improve tissue oxygenation, but whether it reduces infection risk remains controversial. Low-dose dexamethasone is often given to reduce the risk of postoperative nausea and vomiting, but steroid-induced immunosuppression can increase infection risk. We therefore tested the hypotheses that supplemental perioperative oxygen reduces infection risk and that dexamethasone increases it. METHODS Using a factorial design, patients having colorectal resections expected to last ≥2 h were randomly assigned to 30% (n=270) or 80% (n=285) inspired oxygen during and for 1 h after surgery, and to 4 mg intraoperative dexamethasone (n=283) or placebo (n=272). Physicians blinded to group assignments evaluated wounds postoperatively, using US Centers for Disease Control criteria. RESULTS Subject and surgical characteristics were similar among study groups. Surgical site infection incidence was similar among groups: 30% oxygen 15.6%, 80% oxygen 15.8% (P=1.00); dexamethasone 15.9%, placebo 15.4%, (P=0.91). CONCLUSIONS Supplemental oxygen did not reduce surgical site infection risk. The preponderance of clinical evidence suggests that administration of 80% supplemental inspired oxygen does not reduce infection risk. We did not observe an increased risk of surgical site infection with the use of a single low dose of dexamethasone, indicating that it can be used for nausea and vomiting prophylaxis without promoting wound infections. CLINICAL TRIAL REGISTRATION ClinicalTrials.gov number: NCT00273377.

Suppression of shivering during hypothermia using a novel drug combination in healthy volunteers.

Background:Hypothermia may be beneficial in stroke victims; however, it provokes vigorous shivering. Buspirone and dexmedetomidine each linearly reduce the shivering threshold with minimal sedation and no respiratory depression. This study tested the hypotheses that the combination of buspirone and dexmedetomidine would (1) synergistically reduce the shivering threshold, (2) synergistically reduce the gain and maximum intensity of shivering, and (3) produce sufficient inhibition to permit cooling to 34°C without excessive hypotension or sedation. Methods:Eight healthy men were randomly assigned on 4 days to (1) no drug, (2) buspirone (60 mg orally), (3) dexmedetomidine (intravenous infusion to target plasma concentration of 0.6 ng/ml), or (4) combination of buspirone and dexmedetomidine at same doses. Lactated Ringers solution (approximately 3°C) was infused intravenously to decrease tympanic membrane temperature by 1.5°C/h. Shivering threshold was defined as an increase in oxygen consumption greater than 20%. Sedation was evaluated using the Observers Assessment of Sedation/Alertness scale. Results:Mean arterial pressure and heart rate were slightly lower on dexmedetomidine and combination days. Likewise, the level of sedation was statistically different on these 2 days but clinically unimportant. Buspirone reduced the shivering threshold from 36.6°C ± 0.4°C to 35.9°C ± 0.4°C, dexmedetomidine reduced it to 34.7°C ± 0.5°C, and the combination to 34.1 ± 0.4°C. The interaction effect of 0.04°C was not significant. The gain of shivering and maximum shivering intensity were similar on each day. Conclusions:The combination of buspirone and dexmedetomidine additively reduced the shivering threshold. Thus, supplementing dexmedetomidine with buspirone blocks shivering and causes only minimal sedation.

New circulating-water devices warm more quickly than forced-air in volunteers.

BACKGROUND:Newer circulating-water systems supply more heat than forced-air, mainly because the heat capacity of water is much greater than for that of dry warm air and, in part, because they provide posterior as well as anterior heating. Several heating systems are available, but three major ones have yet to be compared directly. We therefore compared two circulating-water systems with a forced-air system during simulation of upper abdominal or chest surgery in volunteers. METHODS:Seven healthy volunteers participated on three separate study days. Each day, they were anesthetized and cooled to a core temperature near 34°C, which was maintained for 45–60 min. They were then rewarmed with one of three warming systems until distal esophageal core temperature reached 36°C or anesthesia had lasted 8 h. The warming systems were 1) energy transfer pads (two split torso pads and two universal pads; Kimberly Clark, Roswell, GA); 2) circulating-water garment (Allon MTRE 3365 for cardiac surgery, Akiva, Israel); and 3) lower body forced-air warming (Bair Hugger #525, #750 blower, Eden Prairie, MN). Data are presented as mean ± sd; P < 0.05 was statistically significant. RESULTS:The rate of increase of core temperature from 34°C to 36°C was 1.2°C ± 0.2°C/h with the Kimberly Clark system, 0.9°C ± 0.2°C/h with the Allon system, and 0.6°C ± 0.1°C/h with the Bair Hugger (P = 0.002). CONCLUSIONS:The warming rate with the Kimberly Clark system was 25% faster than with the Allon system and twice as fast as with the Bair Hugger. Both circulating-water systems thus warmed hypothermic volunteers in significantly less time than the forced-air system.

Effects of nitrous oxide on intraoperative bowel distension.

Purpose of review To evaluate evidence and present an objective view on the effect of nitrous oxide on bowel function. Recent findings We determined in a metaanalysis that the chance of having intraoperative bowel distension was increased about two fold in patients receiving nitrous oxide as the anaesthetic carrier gas compared with those receiving nitrogen or oxygen. In a separate logistic regression analysis, we found that the duration of nitrous oxide exposure was a key factor in explaining this difference, as well as the variability of previously published data. In contrast to bowel distension, surgical operating conditions were not hindered by the use of nitrous oxide; however, the number of patients analysed for operating conditions was much less than that for bowel distension data. Summary Nitrous oxide causes clinically and statistically recognizable bowel distension. This distension, however, does not always exacerbate the surgical conditions, nor does it appear to delay bowel movement or hospital discharge. Although no major problems were noted in bowel functions other than distension, we recommend avoiding nitrous oxide administration during prolonged bowel operations.

Neuromuscular Block Differentially Affects Immobility and Cortical Activation at Near-Minimum Alveolar Concentration Anesthesia

BACKGROUND: Anesthesia-induced immobility and cortical suppression are governed by anatomically separate, but interacting, areas of the central nervous system. Consequently, larger volatile anesthetic concentrations are required to suppress cortical activation than to abolish movement in response to noxious stimulation. We examined the effect of decreased afferent input, as produced by neuromuscular block (NMB), on immobility and cortical activation, as measured by Bispectral index (BIS) of the electrocardiogram, in the presence of noxious stimulation during approximately minimum alveolar concentrations (MACs) of desflurane anesthesia. METHODS: The effect of NMB on the median effective end-tidal concentration of desflurane (EtDes50, or MACtetanus) for immobility was estimated using the up-and-down method and isolated forearm technique in 24 healthy volunteers. Each volunteer sequentially received saline, mivacurium, and succinylcholine in a randomized order, while EtDes concentration during each of the treatments was determined based on the movement response of the previous volunteer on the same treatment. Nonlinear mixed-effects modeling was used to evaluate the effect of NMB on BIS versus EtDes concentration relationship at baseline and after noxious stimulation, while the frontal electromyogram (EMGBIS) effect on BIS was also modeled as a covariate. Cardiovascular responses to noxious stimulation were compared across treatments. RESULTS: Succinylcholine and mivacurium significantly reduced MACtetanus (95% confidence interval) from 5.00% (4.85%–5.13%), during saline, to 4.05% (3.81%–4.29%) and 3.84% (3.60%–4.08%), respectively. Noxious stimulation significantly, although minimally, increased BIS response during all treatments. Succinylcholine increased BIS independently of an effect on EMGBIS. Succinylcholine administration increased cardiovascular activity. Interestingly, although cardiovascular reaction to the noxious event was ablated by mivacurium, cortical response, as determined by BIS, was retained. CONCLUSIONS: Both succinylcholine and mivacurium enhanced immobility during near-MAC anesthesia. All treatments were associated with a small, although significant, BIS increase in response to noxious stimulation, whereas succinylcholine increased BIS independently of noxious stimulation or EMGBIS. Mivacurium suppressed autonomic response to a noxious event.

Bispectral index dynamics during propofol hypnosis is similar in red-haired and dark-haired subjects.

BACKGROUND:We have previously shown that red hair is associated with increased desflurane requirement for immobility, compared with dark hair. The effect of red hair on IV anesthetic requirement remains unknown. We tested the hypothesis that the propofol concentration in the effect site associated with half maximal electroencephalogram response, Ce50, is at least 50% higher in subjects with red hair. METHODS:We modeled the propofol concentration versus electroencephalogram response relationship using a 2-step approach in 29 healthy dark- and red-haired volunteers receiving a propofol infusion to produce loss of consciousness. Bispectral Index (BIS) was the measure of drug effect. The parameters of a 3-compartment pharmacokinetic model were fit to measured arterial propofol concentrations. The relationship between effect-site propofol concentration (Ce) and BIS was characterized using a sigmoid Emax model. Model performance and accuracy of the estimated parameters were evaluated using accepted metrics and bootstrap resampling. The effect of hair color on the Ce50 for BIS response in the final model was assessed using a threshold of 6.63 (P < 0.01) in reduction of −2 log likelihood. The influence of body weight on the model was also assessed. RESULTS:The inclusion of hair color as a model covariate did not improve either the pharmacokinetic or the pharmacodynamic model. A separate analysis for the dark- and red-haired subjects estimated a median (95% confidence interval) Ce50 BIS of 2.71 &mgr;g/mL (2.28–3.36 &mgr;g/mL) and 2.57 &mgr;g/mL (1.68–3.60 &mgr;g/mL), respectively. Body weight was a significant covariate for the CL1 and V1. CONCLUSIONS:Red hair phenotype does not affect the pharmacokinetics or pharmacodynamics of propofol.