An audit of the diagnostic accuracy of rotational thromboelastometry for the identification of hypofibrinogenaemia and thrombocytopenia during cardiopulmonary bypass.

We audited the diagnostic accuracy of ROTEM® (TEM Innovations, GmbH, Munich, Germany) measurements of hypofibrinogenaemia (fibrinogen <1.5 g/l) and thrombocytopenia (platelet count <100 x 109/l) in 200 adult non-transplant patients during cardiopulmonary bypass (CPB). Blood samples were obtained for FIBTEM (assay for the fibrin part of the clot), PLTEM (calculated platelet-specific component), and laboratory measurements simultaneously. Our thresholds for FIBTEM and PLTEM were A10 (clot firmness 10 minutes after clotting time) ≤8 mm, and <35 mm respectively. We also calculated the accuracy of smaller thresholds and earlier indices. We found that FIBTEM A10 ≤8 mm had low sensitivity (0.62) for hypofibrinogenaemia. With the 13% hypofibrinogenaemia prevalence in our sample, the positive predictive value (PPV) was 0.47. In contrast, FIBTEM A10 ≤8 mm had higher specificity (0.90) (negative predictive value [NPV] 0.94). Of the other FIBTEM values analysed, only A5 ≤6 mm had similar or superior accuracy. The PLTEM results were less encouraging (sensitivity 0.81, specificity 0.62). With our prevalence of thrombocytopenia (also 13%), the PPV was only 0.24. However, the NPV was high (0.96). Of the other PLTEM values analysed, only A5 <25 mm had similar or superior accuracy. These findings indicate that during CPB FIBTEM A10 ≤8 mm and PLTEM A10 <35 mm have greater accuracy in identifying the absence of hypofibrinogenaemia and thrombocytopenia respectively than their presence. On the basis of these results we would be reassured by FIBTEM A10 values >8 mm and PLTEM A10 values ≥35 mm, but would continue to use laboratory measurements for confirmation. We would not use FIBTEM A10 ≤8 mm or PLTEM A10 <35 mm values alone to guide replacement therapy unless clinical conditions warranted an immediate decision before laboratory measurements were available.

Prevalence of major vessels anterior to the trachea at sites of potential front-of-neck emergency airway access in adults.

BACKGROUND: Several case reports have described anatomical variations that can cause difficulty with front-of-neck airway access, such as major vessels anterior to the trachea. The prevalence of these anomalies is unknown. METHODS: We screened 500 consecutive thoracic computed tomography (CT) scans in adult patients performed independently in any public hospital in Western Australia. The prevalence of major vessels anterior to the trachea in the anterior triangle of the neck was determined. RESULTS: In the suprasternal notch, 264 CT scans (53%) demonstrated part of a major vessel anterior to the trachea, most commonly the brachiocephalic artery. At 10, 20, and 30 mm above the suprasternal notch, respectively, 126 (25%), 48 (9%), and 5 (1%) CT scans showed a major vessel anterior to the trachea. None showed a major vessel anterior to the cricothyroid membrane. In the suprasternal notch, a major vessel was anterior to the trachea in 10 of 120 CT scans (8%) that had a manubrio-cricoid distance <25 mm, and 108 of 116 CT scans (93%) that had a manubrio-cricoid distance >50 mm. In a logistic-regression model, increased length of trachea above the manubrium was a strong predictor of major vessels anterior to the trachea in the suprasternal notch, whilst sex, age, thoracic kyphosis, tracheal diameter, and the origin of the brachiocephalic artery were not strong predictors. CONCLUSIONS: It is common for patients to have some portion of a major vessel anterior to the trachea at sites where an emergency tracheostomy might be performed.

An audit of the statistical validity of conclusions of clinical superiority in anaesthesia journals.

Making a statistically valid conclusion of the superiority of a clinical intervention in a clinical trial requires not only a statistically significant P value, but also adequate a priori power and an observed effect size larger than the clinically important value specified in the sample size calculation. We scrutinised the five most highly cited clinical trials reporting one or more conclusions of clinical superiority published in Anesthesiology, the British Journal of Anaesthesia, Anaesthesia, Anesthesia and Analgesia and Anaesthesia and Intensive Care in 2011 or 2012 to determine how many met all three requisite criteria. In the 25 articles, there were a total of 36 unconditional conclusions of the superiority of a clinical intervention. All were supported by a statistically significant P value. However, only 15 (41.6%) met all three requisite statistical criteria to support clinical superiority. The remainder included secondary outcomes without specific reference to their observational nature, and primary outcomes whose observed effect size was smaller than the clinically important value specified in the sample size calculation. These findings indicate that clinicians should closely scrutinise conclusions of clinical superiority in anaesthesia journals. Many will be 'hypothesis-generating observations' without adequate statistical support for a conclusion of clinical superiority in their own right.

Measuring the quality of anaesthesia from a patient's perspective: development, validation, and implementation of a short questionnaire.

BACKGROUND: The primary aim of this study was to develop and validate a short psychometric instrument to assess the patient's perception of the quality of anaesthesia. METHODS: In Part 1, the Perception of Quality in Anaesthesia (PQA) questionnaire was developed, pilot tested, and validated. Attributes of high-quality anaesthesia were identified using a process that restricted input to patients and members of the public. In Part 2, patient cohorts completed the PQA before, and after, a 6 month period where anaesthetists were given individualized performance data using questions from the PQA. RESULTS: In Part 1, items in the PQA were identified and ranked by 120 patients and members of the public. Validity and reliability of the PQA was assessed by 714 patients. Principal component analysis showed that the PQA comprised five factors: attention/gentleness; pain management; information/confidence; postoperative nausea or vomiting (PONV); and concerns addressed. In Part 2, there were 2046 patient participants in the pre-feedback cohort, 4251 in the feedback cohort, and 1421 in the post-feedback cohort. Unsatisfactory experience in at least one PQA factor was described by 45.2% [95% confidence interval (CI) 43.1-47.4%] during the pre-feedback period, and 35.0% (95% CI 32.6-37.6%) during the post-feedback period. CONCLUSIONS: We developed and validated a patient-derived questionnaire to measure the patient's perception of anaesthesia quality. PONV, postoperative pain management, and communication with the anaesthetist are the most important features of the patient's experience. Feedback of PQA performance scores to anaesthetists can lead to improved patient experience.

Comparison of the Pentax Airway Scope and McGrath Videolaryngoscope with the Macintosh laryngoscope in tracheal intubation by anaesthetists unfamiliar with videolaryngoscopes: a manikin study.

Videolaryngoscopes are becoming widely available and have been suggested as a replacement for the Macintosh in cases of cervical instability or even for use in the first instance. There is limited existing data on the use of videoscopes by experienced anaesthetists who are inexperienced in the use of videoscopes. We used a manikin model to compare time to intubation between the Macintosh blade, Pentax Airway Scope and the McGrath videolaryngoscope in a simulated urgent intubation by 23 experienced anaesthetists with no prior experience in the use of these videoscopes. We also measured the number of attempts and success of intubation within three minutes. Ease of device use and laryngoscopic view obtained were also recorded. We found that all participants could intubate the manikin within three minutes, with a median of one attempt using the Pentax Airway Scope. Only 48% of participants (n=11) could intubate within three minutes using the McGrath videolaryngoscope and required a median of three attempts. This difference occurred despite the majority of anaesthetists obtaining a Grade 1 Cormack and Lehane view with both videoscopes. We demonstrated that anaesthetists who were naive to these videoscopes can successfully intubate the trachea using the Pentax Airway Scope but not the McGrath videolaryngoscope.

Laryngoscopy force in the sniffing position compared to the extension-extension position.

Laryngoscopy is sometimes easier with the patient's head and neck in the extension-extension position (head extension with the neck extended by the head section of the table bent down at 30 degrees) rather than the classical 'sniffing the morning air' position. We therefore tested the hypothesis that the axial force required for laryngoscopy is less in the extension-extension than the sniffing position. We measured the force axial to the handle of a Macintosh 3 laryngoscope in 20 subjects under general anaesthesia who had been given neuromuscular blocking drugs. Measurement of force was made in the sniffing position and the extension-extension position. The mean (SD) axial force required in the extension-extension position was lower than in the sniffing position (19.6 (7.8) N versus 23.6 (8.6) N, p = 0.04). In the setting of routine tracheal intubation, less force is required when the patient is in the extension-extension position than in the sniffing position.

Effect of open-chest surgery in the lateral position on blood propofol concentration during target-controlled infusion of propofol.

Our research hypothesis was that single lung ventilation during thoracic surgery in the lateral position increases the blood concentration of propofol during target-controlled infusion. Thirty adult patients in two tertiary referral hospitals undergoing open-chest surgery were studied. Anaesthesia was induced and maintained with propofol using a Diprifusor (Graseby 3500) computer-controlled pump set to deliver a blood concentration of 4 tg.ml(-1). Blood samples were taken with the patient positioned in (1) the supine position 20 minutes after induction (supine); (2) the lateral position just prior to one-lung ventilation (lateral); (3) the lateral position five minutes after commencing one-lung ventilation (OLV5) and (4) the lateral position 20 minutes after commencing one-lung ventilation (OLV20). Propofol concentrations were determined by high performance liquid chromatography. The target-controlled infusion target level was maintained at 4 microg.ml(-1) during the study period for all cases. The mean (SD) propofol blood concentration (microg.ml(-1)) at each stage was 5.5 (1.5) supine, 5.3 (1.1) lateral, 5.3 (1.2) OLV5 and 5.1 (1.2) OLV20. Repeated measures ANOVA showed an F value 1.9, lambda 5.5 and P value 0.15. Post hoc analysis did not identify a significant difference between the sample times. During target-controlled infusion of propofol, mean blood propofol concentrations did not change significantly from those obtained with the patient supine after up to 50 minutes in the lateral position during thoracic surgery, or 20 minutes after commencing one-lung ventilation.

The relationship between oxygenator exhaust P(CO2) and arterial P(CO2) during hypothermic cardiopulmonary bypass.

During cardiopulmonary bypass the partial pressure of carbon dioxide in oxygenator arterial blood (P(a)CO2) can be estimated from the partial pressure of gas exhausting from the oxygenator (P(E)CO2). Our hypothesis is that P(E)CO2 may be used to estimate P(a)CO2 with limits of agreement within 7 mmHg above and below the bias. (This is the reported relationship between arterial and end-tidal carbon dioxide during positive pressure ventilation in supine patients.) During hypothermic (28-32 degrees C) cardiopulmonary bypass using a Terumo Capiox SX membrane oxygenator, 80 oxygenator arterial blood samples were collected from 32 patients during cooling, stable hypothermia, and rewarming as per our usual clinical care. The P(a)CO2 of oxygenator arterial blood at actual patient blood temperature was estimated by temperature correction of the oxygenator arterial blood sample measured in the laboratory at 37 degrees C. P(E)CO2 was measured by connecting a capnograph end-to-side to the oxygenator exhaust outlet. We used an alpha-stat approach to cardiopulmonary bypass management. The mean difference between P(E)CO2 and P(a)CO2 was 0.6 mmHg, with limits of agreement (+/-2 SD) between -5 to +6 mmHg. P(E)CO2 tended to underestimate P(a)CO2 at low arterial temperatures, and overestimate at high arterial temperatures. We have demonstrated that P(E)CO2 can be used to estimate P(a)CO2 during hypothermic cardiopulmonary bypass using a Terumo Capiox SX oxygenator with a degree of accuracy similar to that associated with the use of end-tidal carbon dioxide measurement during positive pressure ventilation in anaesthetized, supine patients.

The effects of recent aspirin ingestion on platelet function in cardiac surgical patients.

OBJECTIVE: To examine the effects of the preoperative aspirin-free interval on platelet function in cardiac surgical patients. DESIGN: Prospective clinical investigation. SETTING: University-affiliated teaching hospital. PARTICIPANTS: Patients undergoing elective coronary artery bypass graft surgery (n = 100). INTERVENTIONS: The patients were divided into 3 groups based on the number of days since they last ingested aspirin: < or =2 days, 3 to 7 days, and >7 days. Preoperative platelet function was assessed in all patients using platelet aggregation responses to arachidonic acid, 5 microg/mL, and Platelet Function Analyser (PFA100) collagen/epinephrine closure times. MEASUREMENTS AND MAIN RESULTS: Patients who ceased aspirin < or =2 days preoperatively had weaker platelet aggregation responses (18.5% +/- 7% maximum aggregation, mean +/- SD, n = 36) than patients who ceased aspirin 3 to 7 days preoperatively (68.8% +/- 29%, n = 48, p < 0.001) or >7 days preoperatively (68.3% +/- 28%, n = 16, p < 0.001). Similarly, patients who ceased aspirin < or =2 days preoperatively had longer PFA100 closure times (168 +/- 52 sec) than patients who ceased aspirin 3 to 7 days preoperatively (122 +/- 43 sec, p < 0.001) or >7 days preoperatively (128 +/- 42 sec, p < 0.01). The percentage of abnormal responses was also greatest in the aspirin < or =2 days group. CONCLUSION: Cardiac surgical patients who ingest aspirin < or =2 days preoperatively have greater impairment of platelet function than patients who have a longer preoperative aspirin-free interval.

Low serum S100beta protein levels following coronary artery surgery with or without cardiopulmonary bypass.

BACKGROUND: S100beta protein has been used as a serum marker of brain injury during cardiac surgery. Previous studies may have been confounded by the re-transfusion of shed mediastinal blood, which has a high concentration of S100beta. AIM: To examine serum S100beta levels in coronary artery surgery patients in whom re-transfusion of shed mediastinal blood was avoided, and to compare levels with and without cardiopulmonary bypass (CPB). METHODS: Serum S100beta levels were measured preoperatively, pre-heparin, post-protamine and 24 h postoperatively in 31 patients undergoing elective coronary artery surgery with (n = 14) or without (n = 17) CPB. The postoperative values were compared to their preoperative controls using two-tailed paired t-tests. RESULTS: There was a minor increase in serum S100beta post-protamine in the CPB group only (0.41 ng/mL; P < 0.01). All other levels in both groups were within normal limits. CONCLUSIONS: Coronary artery surgery without CPB is not associated with an increase in serum S100beta. The observed increase in the CPB group was four- to ninefold lower than levels previously reported. A possible explanation for the lower level was the avoidance of retransfusing shed mediastinal blood. If elevated S100beta levels are thought to represent a cerebral insult caused by CPB, the magnitude of the insult might be less than previously assumed.