Ryu Komatsu

Learning curves for bag-and-mask ventilation and orotracheal intubation: an application of the cumulative sum method.

Background:In this study, the authors determined the success and failure rates for interns learning bag-and-mask ventilation and orotracheal intubation. Their goal was to determine the amount of experience needed to perform these procedures correctly. Methods:The authors recorded 695 bag-and-mask ventilations and 679 orotracheal intubations performed by 15 inexperienced interns during their 3 month-long anesthesia rotations. Learning curves for each procedure for each intern were constructed with both the standard and risk-adjusted cumulative sum methods. The average number of procedures required to attain a failure rate of 20% was estimated for each technique. Results:Fourteen of 15 interns attained acceptable failure rates at bag-and-mask ventilation after 27 ± 13 procedures, with a median (95% confidence interval) of 25 (15–32) procedures to cross the decision limit when considering all 15 interns. Nine of 15 interns attained acceptable failure rates at orotracheal intubation after 26 ± 8 procedures, with a median of 29 (22–not estimable) procedures to cross the limit when considering all interns. The proportion of interns who attained acceptable failure rates for mask ventilation was greater than for tracheal intubation (93% vs. 60%, P = 0.025). Overall, our interns achieved a bag-and-mask ventilation failure rate of 20% or better after a median of 25 procedures; approximately 80% of interns achieved the goal after 35 procedures or less. Conclusions:Participating interns developed mask ventilation skills faster than orotracheal intubation skills, and there was more variability in the rate at which intubation skills developed. A median of 29 procedures was required to achieve an 80% orotracheal intubation success rate.

Accuracy of postoperative end-tidal Pco2 measurements with mainstream and sidestream capnography in non-obese patients and in obese patients with and without obstructive sleep apnea.

Background:Obtaining accurate end-tidal carbon dioxide pressure measurements via nasal cannula poses difficulties in postanesthesia patients who are mouth breathers, including those who are obese and those with obstructive sleep apnea (OSA); a nasal cannula with an oral guide may improve measurement accuracy in these patients. The authors evaluated the accuracy of a mainstream capnometer with an oral guide nasal cannula and a sidestream capnometer with a nasal cannula that did or did not incorporate an oral guide in spontaneously breathing non-obese patients and obese patients with and without OSA during recovery from general anesthesia. Methods:The study enrolled 20 non-obese patients (body mass index less than 30 kg/m2) without OSA, 20 obese patients (body mass index greater than 35 kg/m2) without OSA, and 20 obese patients with OSA. End-tidal carbon dioxide pressure was measured by using three capnometer/cannula combinations (oxygen at 4 l/min): (1) a mainstream capnometer with oral guide nasal cannula, (2) a sidestream capnometer with a nasal cannula that included an oral guide, and (3) a sidestream capnometer with a standard nasal cannula. Arterial carbon dioxide partial pressure was determined simultaneously. The major outcome was the arterial-to-end-tidal partial pressure difference with each combination. Results:In non-obese patients, arterial-to-end-tidal pressure difference was 3.0 ± 2.6 (mean ± SD) mmHg with the mainstream capnometer, 4.9 ± 2.3 mmHg with the sidestream capnometer and oral guide cannula, and 7.1 ± 3.5 mmHg with the sidestream capnometer and a standard cannula (P < 0.05). In obese non-OSA patients, it was 3.9 ± 2.6 mmHg, 6.4 ± 3.1 mmHg, and 8.1 ± 5.0 mmHg, respectively (P < 0.05). In obese OSA patients, it was 4.0 ± 3.1 mmHg, 6.3 ± 3.2 mmHg, and 8.3 ± 4.6 mmHg, respectively (P < 0.05). Conclusions:Mainstream capnometry performed best, and an oral guide improved the performance of sidestream capnometry. Accuracy in non-obese and obese patients, with and without OSA, was similar.

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.

Comparison of the intubating laryngeal mask airway and laryngeal tube placement during manual in‐line stabilisation of the neck

We compared the placement of the laryngeal tube (LT) with the intubating laryngeal mask airway (ILMA) in 51 patients whose necks were stabilised by manual in‐line traction. Following induction of anaesthesia and neuromuscular blockade, the LT and ILMA were inserted consecutively in a randomised, crossover design. Using pressure‐controlled ventilation (20 cmH2O inspiratory pressure), we measured insertion attempts, time to establish positive‐pressure ventilation, tidal volume, gastric insufflation, and minimum airway pressure at which gas leaked around the cuff. Data were compared using Wilcoxon signed‐rank tests; p < 0.05 was considered significant. Insertion was found to be more difficult with the LT (successful at first attempt in 16 patients) than with the ILMA (successful at first attempt in 42 patients, p < 0.0001). Time required for insertion was longer for the LT (28 [23–35] s, median [interquartile range]) than for the ILMA (20 [15–25] s, p = 0.0009). Tidal volume was less for the LT (440 [290–670] ml) than for the ILMA (630 [440–750] ml, p = 0.013). Minimum airway pressure at which gas leak occurred and incidence of gastric insufflation were similar with two devices. In patients whose necks were stabilised with manual in‐line traction, insertion of the ILMA was easier and quicker than insertion of the LT and tidal volume was greater with the ILMA than the LT.

The intubating laryngeal mask airway facilitates tracheal intubation in the lateral position.

Although the difficulty of tracheal intubation in the lateral position has not been systematically evaluated, airway loss during surgery in a laterally positioned patient may have hazardous consequences. We explored whether the intubating laryngeal mask airway (ILMA) facilitates tracheal intubation in patients with normal airway anatomy, i.e., Mallampati grade ≤3 and thyromental distance ≥5 cm, positioned in the lateral position. We evaluated whether this technique can be used as a rescue when the airway is lost during the middle of surgery in laterally positioned patients with respect to success rate and intubation time. Anesthesia was induced with propofol, fentanyl, and vecuronium in 50 patients undergoing spine surgery for lumbar disk herniation (Lateral) and 50 undergoing other surgical procedures (Supine). Patients having disk surgery (Lateral) were positioned on their right or left sides before induction of general anesthesia, and intubation was performed in that position. Patients in the control group (Supine) were anesthetized in supine position, and intubation was performed in that position. Intubation was performed blindly via an ILMA in both groups. The time required for intubation and number and types of adjusting maneuvers used were recorded. Data were compared by the Mann-Whitney U test, Fisher’s exact test, &khgr;2 test, or unpaired Student’s t-test, as appropriate. Data presented as mean (sd). Demographic and airway measures were similar in the two groups, except for mouth opening, which was slightly wider in patients in the lateral position: 5.1 (0.9) versus 4.6 (0.7) cm. The time required for intubation was similar in each group (≈25 s), as was intubation success (96%). We conclude that blind intubation via an ILMA offers a frequent success rate and a clinically acceptable intubation time (<1 min) even in the lateral position.

Airway scope and StyletScope for tracheal intubation in a simulated difficult airway.

BACKGROUND: Direct laryngoscopy is difficult when the cervical spine is immobilized. The Airway Scope® and StyletScope® are new laryngoscopes designed to facilitate intubation under these circumstances. Thus, in patients wearing a rigid cervical collar to simulate a difficult airway, we tested the hypothesis that the intubation success rates of the Airway Scope and StyletScope are similar, but that intubation with Airway Scope is faster. METHODS: Adult patients requiring tracheal intubation as part of anesthesia were enrolled. After anesthesia induction and muscle relaxation, patients’ necks were stabilized with a rigid Philadelphia collar and patients were randomly assigned to tracheal intubation with Airway Scope (n = 50) or StyletScope (n = 50). Overall intubation success rate, time required for intubation, the number of attempts required for successful intubation, and airway complications related to intubation were recorded. RESULTS: Overall intubation success rates were 98% with Airway Scope and 96% with StyletScope. Intubation was 19 s faster with Airway Scope (32[8] s; mean) versus StyletScope (51[29] s). The number of required intubation attempts was similar with each device: 26/18/5 (first/second/third attempt) for Airway Scope versus 26/17/5 for StyletScope. The incidence of mucosal trauma and lip injury was similar, except esophageal intubation occurred only with StyletScope (n = 6); neither dental injury nor hypoxia occurred. CONCLUSIONS: Both the Airway Scope and StyletScope offer high success rates in a simulated difficult airway achieved by a rigid collar. However, the Airway Scope is faster and less likely to cause esophageal intubation.

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.