Amy Shanks

Incidence and predictors of difficult and impossible mask ventilation.

Background:Mask ventilation is an essential element of airway management that has rarely been studied as the primary outcome. The authors sought to determine the incidence and predictors of difficult and impossible mask ventilation. Methods:A four-point scale to grade difficulty in performing mask ventilation (MV) is used at the authors’ institution. They used a prospective, observational study to identify cases of grade 3 MV (inadequate, unstable, or requiring two providers), grade 4 MV (impossible to ventilate), and difficult intubation. Univariate and multivariate analyses of a variety of patient history and physical examination characteristics were used to establish risk factors for grade 3 and 4 MV. Results:During a 24-month period, 22,660 attempts at MV were recorded. 313 cases (1.4%) of grade 3 MV, 37 cases (0.16%) of grade 4 MV, and 84 cases (0.37%) of grade 3 or 4 MV and difficult intubation were observed. Body mass index of 30 kg/m2 or greater, a beard, Mallampati classification III or IV, age of 57 yr or older, severely limited jaw protrusion, and snoring were identified as independent predictors for grade 3 MV. Snoring and thyromental distance of less than 6 cm were independent predictors for grade 4 MV. Limited or severely limited mandibular protrusion, abnormal neck anatomy, sleep apnea, snoring, and body mass index of 30 kg/m2 or greater were independent predictors of grade 3 or 4 MV and difficult intubation. Conclusions:The authors observed the incidence of grade 3 MV to be 1.4%, similar to studies with the same definition of difficult MV. Presence of a beard is the only easily modifiable independent risk factor for difficult MV. The mandibular protrusion test may be an essential element of the airway examination.

Predictors of postoperative acute renal failure after noncardiac surgery in patients with previously normal renal function.

Background:The authors investigated the incidence and risk factors for postoperative acute renal failure after major noncardiac surgery among patients with previously normal renal function. Methods:Adult patients undergoing major noncardiac surgery with a preoperative calculated creatinine clearance of 80 ml/min or greater were included in a prospective, observational study at a single tertiary care university hospital. Patients were followed for the development of acute renal failure (defined as a calculated creatinine clearance of 50 ml/min or less) within the first 7 postoperative days. Patient preoperative characteristics and intraoperative anesthetic management were evaluated for associations with acute renal failure. Thirty-day, 60-day, and 1-yr all-cause mortality was also evaluated. Results:A total of 65,043 cases between 2003 and 2006 were reviewed. Of these, 15,102 patients met the inclusion criteria; 121 patients developed acute renal failure (0.8%), and 14 required renal replacement therapy (0.1%). Seven independent preoperative predictors were identified (P < 0.05): age, emergent surgery, liver disease, body mass index, high-risk surgery, peripheral vascular occlusive disease, and chronic obstructive pulmonary disease necessitating chronic bronchodilator therapy. Several intraoperative management variables were independent predictors of acute renal failure: total vasopressor dose administered, use of a vasopressor infusion, and diuretic administration. Acute renal failure was associated with increased 30-day, 60-day, and 1-yr all-cause mortality. Conclusions:Several preoperative predictors previously reported to be associated with acute renal failure after cardiac surgery were also found to be associated with acute renal failure after noncardiac surgery. The use of vasopressor and diuretics is also associated with acute renal failure.

Development and validation of an acute kidney injury risk index for patients undergoing general surgery: results from a national data set.

Background:The authors sought to identify the incidence, risk factors, and mortality impact of acute kidney injury (AKI) after general surgery using a large and representative national clinical data set. Methods:The 2005–2006 American College of Surgeons– National Surgical Quality Improvement Program participant use data file is a compilation of outcome data from general surgery procedures performed in 121 US medical centers. The primary outcome was AKI within 30 days, defined as an increase in serum creatinine of at least 2 mg/dl or acute renal failure necessitating dialysis. A variety of patient comorbidities and operative characteristics were evaluated as possible predictors of AKI. A logistic regression full model fit was used to create an AKI model and risk index. Thirty-day mortality among patients with and without AKI was compared. Results:Of 152,244 operations reviewed, 75,952 met the inclusion criteria, and 762 (1.0%) were complicated by AKI. The authors identified 11 independent preoperative predictors: age 56 yr or older, male sex, emergency surgery, intraperitoneal surgery, diabetes mellitus necessitating oral therapy, diabetes mellitus necessitating insulin therapy, active congestive heart failure, ascites, hypertension, mild preoperative renal insufficiency, and moderate preoperative renal insufficiency. The c statistic for a simplified risk index was 0.80 in the derivation and validation cohorts. Class V patients (six or more risk factors) had a 9% incidence of AKI. Overall, patients experiencing AKI had an eightfold increase in 30-day mortality. Conclusions:Approximately 1% of general surgery cases are complicated by AKI. The authors have developed a robust risk index based on easily identified preoperative comorbidities and patient characteristics.

Prediction and outcomes of impossible mask ventilation: A review of 50,000 anesthetics

Background:There are no existing data regarding risk factors for impossible mask ventilation and limited data regarding its incidence. The authors sought to determine the incidence, predictors, and outcomes associated with impossible mask ventilation. Methods:The authors performed an observational study over a 4-yr period. For each adult patient undergoing a general anesthetic, preoperative patient characteristics, detailed airway physical exam, and airway outcome data were collected. The primary outcome was impossible mask ventilation defined as the inability to exchange air during bag-mask ventilation attempts, despite multiple providers, airway adjuvants, or neuromuscular blockade. Secondary outcomes included the final, definitive airway management technique and direct laryngoscopy view. The incidence of impossible mask ventilation was calculated. Independent (P < 0.05) predictors of impossible mask ventilation were identified by performing a logistic regression full model fit. Results:Over a 4-yr period from 2004 to 2008, 53,041 attempts at mask ventilation were recorded. A total of 77 cases of impossible mask ventilation (0.15%) were observed. Neck radiation changes, male sex, sleep apnea, Mallampati III or IV, and presence of beard were identified as independent predictors. The receiver-operating-characteristic area under the curve for this model was 0.80 ± 0.03. Nineteen impossible mask ventilation patients (25%) also demonstrated difficult intubation, with 15 being intubated successfully. Twelve patients required an alternative intubation technique, including two surgical airways and two patients who were awakened and underwent successful fiberoptic intubation. Conclusions:Impossible mask ventilation is an infrequent airway event that is associated with difficult intubation. Neck radiation changes represent the most significant clinical predictor of impossible mask ventilation in the patient dataset.

3,423 emergency tracheal intubations at a university hospital: airway outcomes and complications.

Background: There are limited outcome data regarding emergent nonoperative intubation. The current study was undertaken with a large observational dataset to evaluate the incidence of difficult intubation and complication rates and to determine predictors of complications in this setting. Methods: Adult nonoperating room emergent intubations at our tertiary care institution from December 5, 2001 to July 6, 2009 were reviewed. Prospectively defined data points included time of day, location, attending physician presence, number of attempts, direct laryngoscopy view, adjuvant use, medications, and complications. At our institution, a senior resident with at least 24 months of anesthesia training is the first responder for all emergent airway requests. The primary outcome was a composite airway complication variable that included aspiration, esophageal intubation, dental injury, or pneumothorax. Results: A total of 3,423 emergent nonoperating room airway management cases were identified. The incidence of difficult intubation was 10.3%. Complications occurred in 4.2%: aspiration, 2.8%; esophageal intubation, 1.3%; dental injury, 0.2%; and pneumothorax, 0.1%. A bougie introducer was used in 12.4% of cases. Among 2,284 intubations performed by residents, independent predictors of the composite complication outcome were as follows: three or more intubation attempts (odds ratio, 6.7; 95% CI, 3.2–14.2), grade III or IV view (odds ratio, 1.9; 95% CI, 1.1–3.5), general care floor location (odds ratio, 1.9; 95% CI, 1.2–3.0), and emergency department location (odds ratio, 4.7; 95% CI, 1.1–20.4). Conclusions: During emergent nonoperative intubation, specific clinical situations are associated with an increased risk of airway complication and may provide a starting point for allocation of experienced first responders.

Prevention of intraoperative awareness with explicit recall in an unselected surgical population: a randomized comparative effectiveness trial.

Background:Intraoperative awareness with explicit recall occurs in approximately 0.15% of all surgical cases. Efficacy trials based on the Bispectral Index® (BIS) monitor (Covidien, Boulder, CO) and anesthetic concentrations have focused on high-risk patients, but there are no effectiveness data applicable to an unselected surgical population. Methods:We conducted a randomized controlled trial of unselected surgical patients at three hospitals of a tertiary academic medical center. Surgical cases were randomized to alerting algorithms based on either BIS values or anesthetic concentrations. The primary outcome was the incidence of definite intraoperative awareness; prespecified secondary outcomes included postanesthetic recovery variables. Results:The study was terminated because of futility. At interim analysis the incidence of definite awareness was 0.12% (11/9,376) (95% CI: 0.07–0.21%) in the anesthetic concentration group and 0.08% (8/9,460) (95% CI: 0.04–0.16%) in the BIS group (P = 0.48). There was no significant difference between the two groups in terms of meeting criteria for recovery room discharge or incidence of nausea and vomiting. By post hoc secondary analysis, the BIS protocol was associated with a 4.7-fold reduction in definite or possible awareness events compared with a cohort receiving no intervention (P = 0.001; 95% CI: 1.7–13.1). Conclusion:This negative trial could not detect a difference in the incidence of definite awareness or recovery variables between monitoring protocols based on either BIS values or anesthetic concentration. By post hoc analysis, a protocol based on BIS monitoring reduced the incidence of definite or possible intraoperative awareness compared with routine care.

Preoperative and intraoperative predictors of cardiac adverse events after general, vascular, and urological surgery.

Background:The authors sought to determine the incidence and risk factors for perioperative cardiac adverse events (CAEs) after noncardiac surgery using detailed preoperative and intraoperative hemodynamic data. Methods:The authors conducted a prospective observational study at a single university hospital from 2002 to 2006. All American College of Surgeons–National Surgical Quality Improvement Program patients undergoing general, vascular, and urological surgery were included. The CAE outcome definition included cardiac arrest, non-ST elevation myocardial infarction, Q-wave myocardial infarction, and new clinically significant cardiac dysrhythmia within the first 30 postoperative days. Results:Four years of data demonstrated that of 7,740 noncardiac operations, 83 patients (1.1%) experienced a CAE within 30 days. Nine independent predictors were identified (P ≤ 0.05): age ≥ 68, body mass index ≥ 30, emergent surgery, previous coronary intervention or cardiac surgery, active congestive heart failure, cerebrovascular disease, hypertension, operative duration ≥ 3.8 h, and the administration of 1 or more units of packed red blood cells intraoperatively. The c-statistic of this model was 0.81 ± 0.02. Univariate analysis demonstrated that high-risk patients experiencing a CAE were more likely to experience an episode of mean arterial pressure < 50 mmHg (6% vs. 24%, P = 0.02), experience an episode of 40% decrease in mean arterial pressure (26% vs. 53%, P = 0.01), and an episode of heart rate > 100 (22% vs. 34%, P = 0.05). Conclusions:In comparison with current risk stratification indices, the inclusion of intraoperative elements improves the ability to predict a perioperative CAE after noncardiac surgery.

Perioperative Stroke and Associated Mortality after Noncardiac, Nonneurologic Surgery

Background:Stroke is a leading cause of morbidity and mortality in the United States and occurs in the perioperative period. The authors studied the incidence, predictors, and outcomes of perioperative stroke using the American College of Surgeons National Surgical Quality Improvement Program. Methods:Data on 523,059 noncardiac, nonneurologic patients in the American College of Surgeons National Surgical Quality Improvement Program database were analyzed for the current study. The incidence of perioperative stroke was identified. Logistic regression was applied to a derivation cohort of 350,031 patients to generate independent predictors of stroke and develop a risk model. The risk model was subsequently applied to a validation cohort of 173,028 patients. The role of perioperative stroke in 30-day mortality was also assessed. Results:The incidence of perioperative stroke in both the derivation and validation cohorts was 0.1%. Multivariate analysis revealed the following independent predictors of stroke in the derivation cohort: age ≥62 yr, history of myocardial infarction within 6 months before surgery, acute renal failure, history of stroke, dialysis, hypertension, history of transient ischemic attack, chronic obstructive pulmonary disease, current tobacco use, and body mass index 35–40 kg/m2 (protective). These risk factors were confirmed in the validation cohort. Surgical procedure also influenced the incidence of stroke. Perioperative stroke was associated with an 8-fold increase in perioperative mortality within 30 days (95% CI, 4.6–12.6). Conclusions:Noncardiac, nonneurologic surgery carries a risk of perioperative stroke, which is associated with higher mortality. The models developed in this study may be informative for clinicians and patients regarding risk and prevention of this complication.

Incidence, predictors, and outcome of difficult mask ventilation combined with difficult laryngoscopy: A report from the multicenter perioperative outcomes group

Background:Research regarding difficult mask ventilation (DMV) combined with difficult laryngoscopy (DL) is extremely limited even though each technique serves as a rescue for one another. Methods:Four tertiary care centers participating in the Multicenter Perioperative Outcomes Group used a consistent structured patient history and airway examination and airway outcome definition. DMV was defined as grade 3 or 4 mask ventilation, and DL was defined as grade 3 or 4 laryngoscopic view or four or more intubation attempts. The primary outcome was DMV combined with DL. Patients with the primary outcome were compared to those without the primary outcome to identify predictors of DMV combined with DL using a non-parsimonious logistic regression. Results:Of 492,239 cases performed at four institutions among adult patients, 176,679 included a documented face mask ventilation and laryngoscopy attempt. Six hundred ninety-eight patients experienced the primary outcome, an overall incidence of 0.40%. One patient required an emergent cricothyrotomy, 177 were intubated using direct laryngoscopy, 284 using direct laryngoscopy with bougie introducer, 163 using videolaryngoscopy, and 73 using other techniques. Independent predictors of the primary outcome included age 46 yr or more, body mass index 30 or more, male sex, Mallampati III or IV, neck mass or radiation, limited thyromental distance, sleep apnea, presence of teeth, beard, thick neck, limited cervical spine mobility, and limited jaw protrusion (c-statistic 0.84 [95% CI, 0.82–0.87]). Conclusion:DMV combined with DL is an infrequent but not rare phenomenon. Most patients can be managed with the use of direct or videolaryngoscopy. An easy to use unweighted risk scale has robust discriminating capacity.

Perioperative peripheral nerve injuries: a retrospective study of 380,680 cases during a 10-year period at a single institution.

Background:Peripheral nerve injuries represent a notable source of anesthetic complications and can be debilitating. The objective of this study was to identify associations with peripheral nerve injury in a broad surgical population cared for in the last decade. Methods:At a tertiary care university hospital, the quality assurance, closed claims, and institution-wide billing code databases were searched for peripheral nerve injuries over a 10-yr period. Each reported case was individually reviewed to determine whether a perioperative injury occurred, defined as a new sensory and/or motor deficit. The location and type of the injury were also identified. Nerve complications as a result of the surgical procedure itself were excluded, and an expert review panel assisted in the adjudication of unclear cases. Patient preoperative characteristics, anesthetic modality, and surgical specialty were evaluated for associations. Results:Of all patients undergoing 380,680 anesthetics during a 10-yr period, 185 patients were initially identified as having nerve injuries, and after review, 112 met our definition of a perioperative nerve injury (frequency = 0.03%). Hypertension, tobacco use, and diabetes mellitus were significantly associated with perioperative peripheral nerve injuries. General and epidural anesthesia were associated with nerve injuries. Significant associations were also found with the following surgical specialties: Neurosurgery, cardiac surgery, general surgery, and orthopedic surgery. Conclusions:To our knowledge, this is the largest number of consecutive patients ever reviewed for all types of perioperative peripheral nerve injuries. More importantly, this is the first study to identify associations of nerve injuries with hypertension, anesthetic modality, and surgical specialty.