Papiya Sengupta

Endotracheal tube cuff pressure in three hospitals, and the volume required to produce an appropriate cuff pressure

BackgroundCuff pressure in endotracheal (ET) tubes should be in the range of 20–30 cm H2O. We tested the hypothesis that the tube cuff is inadequately inflated when manometers are not used.MethodsWith IRB approval, we studied 93 patients under general anesthesia with an ET tube in place in one teaching and two private hospitals. Anesthetists were blinded to study purpose. Cuff pressure in tube sizes 7.0 to 8.5 mm was evaluated 60 min after induction of general anesthesia using a manometer connected to the cuff pilot balloon. Nitrous oxide was disallowed. After deflating the cuff, we reinflated it in 0.5-ml increments until pressure was 20 cmH2O.ResultsNeither patient morphometrics, institution, experience of anesthesia provider, nor tube size influenced measured cuff pressure (35.3 ± 21.6 cmH2O). Only 27% of pressures were within 20–30 cmH2O; 27% exceeded 40 cmH2O. Although it varied considerably, the amount of air required to achieve a cuff pressure of 20 cmH2O was similar with each tube size.ConclusionWe recommend that ET cuff pressure be set and monitored with a manometer.

The New Perilaryngeal Airway (CobraPLA™) Is as Efficient as the Laryngeal Mask Airway (LMA™), But Provides Better Airway Sealing Pressures

The Laryngeal Mask Airway (LMA) is a frequently used efficient airway device, yet it sometimes seals poorly, thus reducing the efficacy of positive-pressure ventilation. The Perilaryngeal Airway (CobraPLA) is a novel airway device with a larger pharyngeal cuff (when inflated). We tested the hypothesis that the CobraPLA was superior to the LMA with regard to insertion time and airway sealing pressure and comparable to the LMA in airway adequacy and recovery characteristics. After midazolam and fentanyl administration, 81 ASA physical status I–II outpatients having elective surgery were randomized to receive an LMA or CobraPLA. Anesthesia was induced with propofol (2.5 mg/kg IV), and the airway was inserted. We measured 1) insertion time; 2) adequacy of the airway (no leak at 15-cm-H2O peak pressure or tidal volume of 5 mL/kg); 3) airway sealing pressure; 4) number of repositioning attempts; and 5) sealing quality (no leak at tidal volume of 8 mL/kg). At the end of surgery, gastric insufflation, postoperative sore throat, dysphonia, and dysphagia were evaluated. Data were compared with unpaired Student’s t-tests, χ2 tests, or Fisher’s exact tests; P < 0.05 was significant. Patient characteristics, insertion times, airway adequacy, number of repositioning attempts, and recovery were similar in each group. Airway sealing pressure was significantly greater with CobraPLA (23 ± 6 cm H2O) than LMA (18 ± 5 cm H2O, P < 0.001). The CobraPLA has insertion characteristics similar to the LMA but better airway sealing capabilities.

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.

Women Have the Same Desflurane Minimum Alveolar Concentration as Men: A Prospective Study

Background Women generally report greater sensitivity to pain than do men, and healthy young women require 20% more anesthetic than healthy age-matched men to prevent movement in response to noxious electrical stimulation. In contrast, minimum alveolar concentration (MAC) for xenon is 26% less in elderly Japanese women than in elderly Japanese men. Whether anesthetic requirement is similar in men and women thus remains in dispute. The authors therefore tested the hypothesis that the desflurane concentration required to prevent movement in response to skin incision (MAC) differs between men and women. Methods Using the Dixon “up and down” method, the authors determined MAC for desflurane in 15 female and 15 male patients (18–40 yr old) undergoing surgery. Results MAC was 6.2 ± 0.4% desflurane for women versus 6.0 ± 0.3% for men (P = 0.31), a difference of only 3%. These data provide 90% power to detect a 9% difference between the groups. Conclusions The MAC of desflurane did not differ between young men and women undergoing surgery with a true surgical incision. Although pain sensitivity may differ in women versus men, MAC of desflurane does not.

The timing of acupuncture stimulation does not influence anesthetic requirement.

Studies suggest that acupuncture is more effective when induced before the induction of general anesthesia than afterwards. We tested the hypothesis that electro-acupuncture initiated 30 min before the induction reduces anesthetic requirement more than acupuncture initiated after the induction. Seven volunteers were each anesthetized with desflurane on 3 study days. Needles were inserted percutaneously at four acupuncture points thought to produce analgesia in the upper abdominal area and provide generalized sedative and analgesic effects: Zusanli (St36), Sanyinjiao (Sp6), Liangqiu (Sp34), and Hegu (LI4). Needles were stimulated at 2 Hz and 10 Hz, with frequencies alternating at 2-s intervals. On Preinduction day, electro-acupuncture was started 30 min before the induction of anesthesia and maintained throughout the study. On At-induction day, needles were positioned before the induction of anesthesia, but electro-acupuncture stimulation was not initiated until after the induction. On Control day, electrodes were positioned near the acupoints, but needles were not inserted. Noxious electrical stimulation was administered via 25-gauge needles on the upper abdomen (70 mA; 100 Hz; 10 s). The desflurane concentration was increased 0.5% when movement occurred and decreased 0.5% when it did not. These up-and-down sequences continued until volunteers crossed from movement to no movement four times. The P50 of logistic regression identified desflurane requirement. Desflurane requirement was similar on the Control (mean ± sd; 5.2% ± 0.6%), Preinduction (5.0% ± 0.8%), and At-induction (4.7% ± 0.3%; P = 0.125) days. This type of acupuncture is thus unlikely to facilitate general anesthesia or decrease the requirement for anesthetic drugs.

Doxapram only slightly reduces the shivering threshold in healthy volunteers

We determined the effects of doxapram on the major autonomic thermoregulatory responses in humans. Nine healthy volunteers were studied on 2 days: control and doxapram (IV infusion to a plasma concentration of 2.4 ± 0.8, 2.5 ± 0.9, and 2.6 ± 1.1 &mgr;g/mL at the sweating, vasoconstriction, and shivering thresholds, respectively). Each day, skin and core temperatures were increased to provoke sweating, then reduced to elicit peripheral vasoconstriction and shivering. We determined the sweating, vasoconstriction, and shivering thresholds with compensation for changes in skin temperature. Data were analyzed with paired t-tests and presented as mean ± sd; P < 0.05 was considered statistically significant. Doxapram did not change the sweating (control: 37.5° ± 0.4°C, doxapram: 37.3° ± 0.4°C; P = 0.290) or the vasoconstriction threshold (36.8° ± 0.7°C versus 36.4° ± 0.5°C; P = 0.110). However, it significantly reduced the shivering threshold from 36.2° ± 0.5°C to 35.7° ± 0.7°C (P = 0.012). No sedation or symptoms of panic were observed on either study day. The observed reduction in the shivering threshold explains the drug’s efficacy for treatment of postoperative shivering; however, a reduction of only 0.5°C is unlikely to markedly facilitate induction of therapeutic hypothermia as a sole drug.

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.