Predicting difficult intubation: a multivariable analysis.

PURPOSE: To develop a clinically useful and valid model for predicting difficult laryngoscopic tracheal intubation in patients with seemingly normal airways by adhering to the principles of multivariable model development. METHODS: This was an observational study performed at a tertiary-care teaching hospital. Preoperatively, 444 randomly selected patients requiring tracheal intubation for elective surgery were assessed. In addition, 27 patients in whom tracheal intubation was difficult, but were not assessed preoperatively, were assessed postoperatively. One assessor, blinded to the intubation information, collected the predictor variables. A reliable definition for difficult intubation was used and all attempts were made to eliminate sources of bias. Multivariable modeling was performed using logistic regression and the model was validated using the bootstrapping technique. RESULTS: Of the 461 patients included in the analysis, 38 were classified as difficult to intubate. Multivariable analysis identified three airway tests that were highly significant for predicting difficult tracheal intubation. These were: 1) "mouth opening", 2) "chin protrusion", and 3) "atlanto-occipital extension". Using these tests, a validated, highly reliable and predictive model is produced to determine the probability of difficult intubation for patients. At a selected probability cut-off value, the model is 86.8% sensitive and 96.0% specific. CONCLUSION: A simple and accurate multivariable model, consisting of three airway tests, is produced for predicting difficult laryngoscopic tracheal intubation. Additional studies will be required to determine the accuracy and feasibility of this model when applied to a large sample of new patients by multiple anesthesiologists.

Inter-observer reliability of ten tests used for predicting difficult tracheal intubation.

PURPOSE: To determine inter-observer reliability of ten preoperative airway assessment tests used for predicting difficult tracheal intubation. METHOD: We prospectively assessed 59 patients undergoing elective surgery requiring tracheal intubation at a large metropolitan teaching hospital. Two experienced observers independently conducted the airway assessment tests on the same group of patients. Inter-observer reliability was examined using Kappa (K) and intraclass correlation coefficient (ICC). RESULTS: Two tests--mouth opening (ICC = 0.93) and chin protrusion (ICC = 0.89)--had excellent inter-observer reliability. Seven tests--thyromental distance (ICC - 0.74), subluxation (K = 0.66), atlanto-occipital extension distance (ICC = 0.67) and angle (K = 0.66), profile classification (K = 0.58), ramus length (ICC = 0.53), oropharyngeal best view (K = 0.49)--were moderately reliable. One test--Mallampati technique of assessing oropharyngeal view (K = 0.31)--had poor reliability. CONCLUSION: Many of the preoperative airway tests have only moderate inter-observer reliability. This may provide some insight into why previous research has failed to show that the tests accurately predict difficult tracheal intubation.

Choice of anaesthetic regimen influences haemodynamic response to cemented arthroplasty.

Haemodynamic changes during bilateral cemented arthroplasty (BCA) were compared in dogs anaesthetized with isoflurane/N2O (ISOF) or diazepam/fentanyl (100 microg x kg(-1))N2O(FENT). Eight animals were anaesthetized with each regimen. After establishing monitoring and recording baseline values, BCA was performed. Haemodynamic measurements included aortic blood pressure (ABP), pulmonary artery pressure (PAP), right and left atrial pressures, and cardiac output. These were recorded at 30, 60, 180 and 300 sec after BCA. Lungs were removed and examined postmortem using quantitative morphometry. Groups demonstrated similar increases in PAP (ISOF 15 +/- 2 to 32 +/- 7, FENT 19 +/- 4 to 38 +/- 13; P> 0.05 between groups, P< 0.05 vs baseline). The proportion of lung vasculature occluded by fat was not different between groups (ISOF 9.63 +/- 3.38%, FENT 8.85 +/- 2.20%). Stroke volume decreased similarly in both groups (P> 0,05 between groups, P< 0.05 vs baseline). However, ABP decreased within one minute of BCA in ISOF (111 +/- 17 to 55 +/- mmHg, P< 0.05 and two of eight dogs died. All FENT dogs survived and hypotension (118 +/- 20 to 102 +/- 24 mmHg) was transient and less severe (P< 0.05 vs ISOF). Increased heart rate (HR) was noted in FENT following BCA (73 +/- 8 to 108 +/- 25 beats x min(-1); P< 0.05). Baseline HR was higher in ISOF (P< 0.05) and no increase in HR was noted. Systemic vascular resistance decreased in ISOF (P< 0.05), but not FENT (P> 0.05 vs baseline, P< 0.05 vs ISOF). To assess the role of slower baseline HR in FENT (73 +/-8) versus ISOF (131 +/- 5), six FENT dogs were paced (130 beats x min(-1)) with epicardial leads and an AV sequential pulse generator to simulate the ISOF group's baseline HR. Haemodynamic stability was maintained in this group in spite of a more rapid baseline HR. The choice of anaesthetic regimen strongly influenced acute haemodynamic changes in response to BCA.

Critical respiratory events in the postanesthesia care unit. Patient, surgical, and anesthetic factors.

BACKGROUND: Previous studies have noted a high incidence of adverse outcomes in the postanesthesia care unit (PACU), but few have examined associated factors and patient outcomes. To determine the frequency of acute, unanticipated respiratory problems and to examine the associated patient, surgical, and anesthetic factors, we prospectively collected preoperative, intraoperative, and postoperative data on 24,157 consecutive PACU patients who received a general anesthetic during a 33-month period. METHODS: A PACU critical respiratory event (CRE), was defined as any unanticipated hypoxemia (hemoglobin oxygen saturation < 90%), hypoventilation (respiratory rate < 8 breaths/min or arterial carbon dioxide tension > 50 mmHg) or upper-airway obstruction (stridor or laryngospasm) requiring an active and specific intervention (ventilation, tracheal intubation, opioid or muscle relaxant antagonism, insertion of oral/nasal airway or airway manipulation). These problems were documented by PACU nurses whereas data on case-mix, surgical factors, and intraoperative management were retrieved from the anesthetic record. Significant patient, surgical, and anesthetic factors were identified by logistic regression analysis. Other morbidity experienced by patients with a CRE was also noted. RESULTS: For patients given general anesthesia the risk of a CRE was 1.3% (hypoxemia 0.9%, hypoventilation 0.2%, airway obstruction 0.2%). Preoperative factors that increase risk were age > 60 yr, male gender, diabetes, and obesity (P < 0.05). Patients who underwent operative procedures on an emergency basis and whose operation was longer than 4 h were also at increased risk, but those undergoing perineal procedures were at lower risk (P < 0.05). Anesthetic risk factors (P < 0.05) included opioid premedication (relative odds 1.8), sedatives preoperatively (2.0), fentanyl > 2.0 micrograms.kg-1.h-1 as the sole opioid (1.9), fentanyl used in combination with morphine (1.6) and atracurium > or = 0.25 mg.kg-1.h-1 (2.2). Patients in whom anesthesia was induced with thiopental (relative odds 2.5), compared with those who received propofol for induction, were also at increased risk of a CRE. Patients with a CRE stayed longer in PACU, had higher rates of unanticipated admissions to the intensive care unit and were more likely to have PACU cardiac problems (P < 0.01). CONCLUSIONS: A CRE is relatively rare. Multiple patient and surgical factors and specific aspects of anesthetic management are associated with the occurrence of a CRE in the PACU.

Hypotension during cemented arthroplasty. Relationship to cardiac output and fat embolism.

An episode of hypotension is common during cemented joint replacement, and has been associated with circulatory collapse and sudden death. We studied the mechanism of hypotension in two groups of six dogs after simulated bilateral cemented arthroplasty. In one group, with no lavage, the insertion of cement and prosthesis was followed by severe hypotension, elevated pulmonary artery pressure, decreased systemic vascular resistance and a 21% reduction in cardiac output. In the other group, pulsatile intramedullary lavage was performed before the simulated arthroplasties. Hypotension was less, and although systemic vascular resistance decreased, the cardiac output did not change. The severity of the hypotension, the decrease in cardiac output and an increase in prostaglandin metabolites were related to the magnitude of pulmonary fat embolism. Pulsatile lavage prevents much of this fat embolism, and hence the decrease in cardiac output. The relatively mild hypotension after lavage was secondary to transient vasodilation, which may accentuate the hypotension caused by the decreased cardiac output due to a large embolic fat load. We make recommendations for the prevention and management of hypotension during cemented arthroplasty.

Ibuprofen pretreatment does not prevent hemodynamic instability after cemented arthroplasty in dogs.

A bilateral cemented arthroplasty (BCA) in anesthetized mongrel dogs creates pulmonary fat and marrow embolism. A transient increase in plasma concentration of 6-keto prostaglandin F1 alpha and thromboxane B2 has been associated with hemodynamic instability after BCA. We tested whether intravenous ibuprofen (20 mg/kg) could inhibit prostaglandin production, pulmonary hypertension, and decreased arterial blood pressure in this model. We found a decrease in cardiac output from 3.0 +/- 0.5 to 2.2 +/- 1.3 L/min (mean +/- 1 SD) after BCA with a flow probe placed at thoracotomy around the ascending thoracic aorta. Systemic arterial blood pressure decreased from 140 +/- 11 to 100 +/- 15 mm Hg (P less than 0.0001), and pulmonary artery pressure increased from 17.7 +/- 3.3 to 37.1 +/- 9.4 mm Hg (P less than 0.0001). Similar hemodynamic changes were noted in 12 dogs without thoracotomy. Pretreatment with ibuprofen did not significantly attenuate the acute hemodynamic changes despite inhibiting prostaglandin generation. We conclude that decreased arterial blood pressure after BCA is associated with a decrease in cardiac output and that inhibition of prostaglandin production with ibuprofen does not prevent either pulmonary hypertension or systemic hypotension.

Development of a computerized database for the study of anaesthesia care.

To record, tabulate and report problems associated with anaesthesia, we have developed an information collection system and computer software to follow all patients attended by an anaesthetist at a teaching hospital in Canada. For the last 15 mo, data for 17,000 patients have been collected and the system is ongoing. Data collection is from three sources: carbonless copies of the handwritten Operating Room (OR) and Post Anaesthetic Care Unit (PACU) records, other hospital databases, and postoperative visits. Adverse events (observations which differ from specific physiological variables, or require an intervention and do not normally occur during the routine conduct of anaesthesia), are defined directly on each OR and PACU record. These events are recorded when they occur by the attending anaesthetist or the PACU nurse. All data are verified by a research nurse and an anaesthetist. Computer software, developed from DBase IV, is used to track 95 individual items on preoperative status and anaesthetic technique and another possible 1,450 selections for drugs, physicians, airways, surgical procedures and events for each patient. Data are analyzed with SAS software and reports generated to link the casemix and process with outcome. Comparison of data entered into the computer programme to a retrospective chart review revealed discrepancies of less than 0.5%. Collection, verification and computer entry takes five minutes per patient and the on-going cost is estimated at $4 per patient record. Analysis of the information collected in this database has been useful for research of adverse outcome following anaesthesia, resident expertise profiles, and the administrative management of an anaesthesia department.

Prostanoid production and pulmonary hypertension after fat embolism are not modified by methylprednisolone.

Bilateral cemented arthroplasty (BCA) in anaesthetized mongrel dogs produces particulate fat and marrow embolism of the lung. Methylprednisolone sodium succinate (MPSS) has been advocated for post-traumatic fat embolism to prevent acute lung injury. We used the BCA procedure to produce acute fat and marrow embolism, and tested the efficacy of MPSS (30 mg.kg-1) in preventing physiological and pathological markers of acute lung injury. Dogs (n = 6) pre-treated with MPSS demonstrated similar acute increases in pulmonary artery pressure (PAP) within one minute of BCA (17.8 +/- 7.3 mmHg) as the untreated (control n = 7) dogs (18.6 +/- 12.6). Pulmonary vascular resistance (PVR) increased to the same degree in both groups (455 +/- 323 and 319 +/- 137 dyne.sec.cm-5) and PaO2 decreased by 18.3 +/- 6.4 mmHg in the control group as opposed to 12.4 +/- 7.7 mmHg in the MPSS group within five minutes of BCA. Circulating arterial and mixed venous plasma concentrations of thromboxane B2 (TxB2) increased within one minute of BCA in both groups with no increase in the transpulmonary gradient. Arterial plasma 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) increased (0.91 +/- 0.29 ng.ml-1 and 0.87 +/- 0.43 ng.ml-1) in both groups one minute after BCA. Mixed venous 6-keto PGF1 alpha plasma concentration also increased, but a significant transpulmonary 6-keto PGF1 alpha gradient was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Emerging public health issues in Alaska: occupational and environmental health.

The principal purpose of this article is to examine selected Alaskan occupational and environmental health problems and associated issues. Specifically, we focus on two traditional areas of interest in occupational and environmental health: 1) Job-related injuries, illnesses, and fatalities, and 2) accidental spills and uncontrolled waste sites involving hazardous materials. In 1986 the Alaska Department of Labor reported 13,154 recordable occupational injuries and illnesses among workers in the private sector. The injury rate for private sector workers was 10.2 cases per 100, compared to a rate of 7.9 for the U.S. private sector as a whole. There are approximately 550 known hazardous waste sites in Alaska identified by military, other federal, or state sources. One study documents 1,330 hazardous materials incidents in Alaska during a one year period. Effective public health policy for these occupational and environmental health hazards requires the development of an adequate database and a specific plan of action for the future.

Early dentinogenesis in mice: von Korff fibres and their possible significance. A preliminary study by light and electron microscopy.

By light and electron microscopy we have confirmed the collagenous nature of von Korff fibres in early dentinogenesis in mice. Each fibre array begins as an argyrophil 'stem' lying between the outermost cells of the dental papilla, with finer divisions passing into the papilla. With the appearance of odontoblasts, a cone-like 'spray' of nonargyrophil fibres in continuity with the stem spreads peripherally between these cells to the dental epithelial basement membrane. After the sprays become immured in dentine matrix, the stems are removed. Later, new stems appear. Sprays are restricted to enamel-bearing parts of teeth. The possible nature and functions of von Korff fibres are discussed.

A study of the kinetics of microsporogenesis in Campelia zanonia (L.) H.B.K.

During maturation, microspores pass through a series of morphologically distinguishable stages or compartments. A study has been made of the systematic fluctuations in the frequency of microspores in these compartments, when plants are grown under rigidly controlled conditions. A new approach to the construction of cumulative flux rate curves is described; these give the number of cells passing the compartment boundaries per unit time. The curves obtained indicate that simple models, which assume constant flux rates and compartment transit times, will not explain the observations. It is evident that not only do microspores mature at different rates, but that the maturation rate of individual microspores varies during the developmental sequence. The overall process may be controlled by the intimate relationship which exists between the microspores and the tapetal periplasmodium in the Tradescantiae.