A proposal for a new scoring system to predict difficult ventilation through a supraglottic airway.

BACKGROUND: The aim of this study was to propose and validate a new clinical score to predict difficult ventilation through a supraglottic airway device. METHODS: The score was proposed from our previously reported derivation data, and we prospectively validated the score in 5532 patients from November 2013 to April 2014. Predictive accuracy of the score was compared by the area under the receiver operating characteristic (ROC) curve (AUC). We assigned point values to each of the identified four risk factors: male, age >45 yr, short thyromental distance, and limited neck movement, their sum composing the score. The score ranged between 0 and 7 points. The optimal predictive level of the score was determined using ROC curve analysis. RESULTS: The AUC of the score was 0.75 (95% CI 0.66 to 0.84) in the validation data set, and was similar to that in the derivation data set (0.80; 95% CI 0.75 to 0.86). In derivation and validation data sets, the incidence of low risk categories (scores 0-3) was 0.42% vs 0.32% and of high risk categories (scores 4-7) was 3% vs 1.7% respectively. A score 4 or greater is associated with a six to seven fold increased risk of difficult ventilation through a supraglottic airway device. CONCLUSIONS: The new score for prediction of difficult ventilation through a supraglottic airway device is easy to perform and reliable, and could help anaesthetists plan for difficult airway management.

Miniaturized versus conventional cardiopulmonary bypass and acute kidney injury after cardiac surgery.

INTRODUCTION: Acute kidney injury (AKI) is a serious complication after coronary artery bypass grafting (CABG). There are conflicting reports whether a miniaturized cardiopulmonary bypass (MCPB) system is associated with a lower AKI incidence compared with conventional cardiopulmonary bypass (CCPB). It is unknown if AKI risk factors differ between the two groups. We assessed if MCPB decreases AKI after CABG and compared the risk factors between both groups. METHODS: Sixty-eight Asian patients presenting for elective CABG at a tertiary heart centre were enrolled. They were randomly assigned to MCPB (n=34) or CCPB group (n=34) and followed up in a single-blinded, prospective, randomized, controlled trial. The primary outcome was Acute Kidney Injury Network stage 1 AKI. RESULTS: The AKI incidence was 21.5% and was not significantly different between patients undergoing MCPB versus CCPB (21.9% versus 21.2%, p=0.948). The first CPB haematocrit was independently associated with AKI in the MCPB group (Relative Risk [RR]=0.484, 95% Confidence Interval [CI]=0.268-0.876, p=0.016); post-operative blood loss and inflammation were independently associated with AKI in the CCPB group (RR=1.005, 95%CI=1.003-1.007, p<0.001; RR=1.018, 95%CI=1.010-1.028, p<0.001). CONCLUSION: The MCPB system is not associated with a lower incidence of AKI in Asian patients undergoing CABG. Risk factors for AKI differed between patients using the MCPB and CCPB systems.

Incidence of and risk factors for difficult ventilation via a supraglottic airway device in a population of 14,480 patients from South-East Asia.

Difficult airway practice guidelines include the use of a supraglottic airway device as part of the armamentarium to provide and maintain ventilation and oxygenation. We retrospectively reviewed 14 480 patients aged ≥ 18 years who underwent general anaesthesia. We identified 74 (0.5%) patients whose lungs were identified as having been difficult to ventilate via a supraglottic airway device, and 29 (0.2%) patients in whom device placement failed. Multivariate analysis identified four risk factors for difficult ventilation via a supraglottic airway device: male sex (OR 1.75, 95% CI 1.07-2.86, p = 0.02); age > 45 years (OR 1.70, 95% CI 1.01-2.86, p = 0.04); short thyromental distance (OR 4.35, 95% CI 2.31-8.17, p < 0.001); and limited neck movement (OR 2.75, 95% CI 1.02-7.44, p = 0.04). Adverse respiratory events including oxygen desaturation, hypercapnoea, laryngospasm, and bronchospasm occurred in 17 patients (22%). The incidence of difficult ventilation via a supraglottic airway device was 0.5% in a large cohort of South-East Asian patients.

The inflammatory response between miniaturised and conventional cardiopulmonary bypass after cardiac surgery in an Asian population.

INTRODUCTION: We compared the systemic inflammatory response of the MCPB system to the CCPB system with cell salvage and phosphorylcholine-coated tubing amongst Asian patients undergoing coronary artery bypass grafting. METHODS: Seventy-eight patients were randomly assigned to the MCPB or the CCPB groups equally and followed up in a prospective, single-blinded, randomised, controlled trial. Levels of TNF-α, IL-6, CRP and LDH were measured peri-operatively. RESULTS: The systemic inflammatory response was similar in both groups (TNF-α: p=0.222; IL-6: p=0.991; CRP: p=0.258). Only haemolysis was significantly higher in the CCPB group (LDH: p=0.011). The MCPB system was twice more expensive, but had a near 4-fold cost saving in tranfusions. Overall, the MCPB system cost 20% more than the modified CCPB system. CONCLUSION: These results corroborate with studies that demonstrated the avoidance of cardiotomy suction rather than the MCPB system, itself, leads to an attenuated inflammatory response. The absence of obvious clinical benefit and the higher costs involved with the MCPB system would preclude its routine use.

Association of ethnicity and acute kidney injury after cardiac surgery in a South East Asian population.

BACKGROUND: Postoperative acute kidney injury (AKI) is a frequent and serious complication after cardiac surgery. Clinical factors alone have failed to accurately predict the incidence of AKI after cardiac surgery. Ethnicity has been shown to be a predictor of AKI in the Western population. We tested the hypothesis that ethnicity is an independent predictor of AKI in patients undergoing cardiac surgery in a South East Asian population. METHODS: A total of 1756 consecutive patients undergoing cardiac surgery were prospectively recruited. Among them, data of 1639 patients met the criteria for analysis. There were 1182 Chinese, 195 Indian, and 262 Malay patients. The main outcome was postoperative AKI, defined as a 25% or greater increase in preoperative to a maximum postoperative serum creatinine level within 3 days after surgery. RESULTS: Five hundred and seventy-nine patients (35.3%) developed AKI after cardiac surgery. Ethnicity was shown to be an independent predictor of AKI after cardiac surgery with Indians and Malays having a higher risk of developing AKI when compared with Chinese patients (odds ratio: Indian vs Chinese 1.44, Malay vs Chinese 1.51). CONCLUSIONS: Indians and Malays have a higher risk of developing AKI after cardiac surgery than Chinese in a South East Asian population. Ethnicity was shown to be an independent predictor of AKI after cardiac surgery.

A comparison of screen-based simulation and conventional lectures for undergraduate teaching of crisis management.

In our institution, we introduced a screen-based simulator to our undergraduate lectures on medical crisis management. We hypothesised that this novel use of the screen-based simulator would be as effective as our conventional lectures. To test this we randomly divided medical students into two groups. Students in Group A were taught medical crisis management (heart failure and anaphylaxis) using a screen-based simulation program projected onto a shared screen, with a facilitator guiding the students through the scenarios. Simultaneously, students in Group B were lectured the same content without the screen-based simulation. Both groups were allotted exactly one hour Several days later, students were tested on their management of anaphylaxis using the Human Patient Simulator. A blinded marker assessed them on diagnosis, resuscitation, specific treatment, call for help and for reassessment of the patient. Students also answered a questionnaire on their experience. Sixty-four students participated in the study. Both groups had similar overall scores. However students in Group A scored better in the specific treatment category by a factor of 1.7. Students in both groups rated their learning experiences highly. This study showed that screen-based simulation was as effective as conventional lectures and might be even more effective in some areas.

Deep hypothermic circulatory arrest in adults undergoing aortic surgery: local experience.

INTRODUCTION: The aim of our study was to evaluate the efficacy and safety of deep hypothermic circulatory arrest (DHCA) as a method of cerebral protection during aortic surgery. MATERIALS AND METHODS: We carried out a retrospective review of 59 consecutive patients (48 men, 11 women) undergoing elective or emergency aortic surgery requiring DHCA from January 1999 to April 2002 in 2 tertiary care hospitals. Data regarding demographics, clinical characteristics, operation type, duration of circulatory arrest, nasopharyngeal temperatures, use of retrograde cerebral perfusion and central nervous system (CNS) morbidity and perioperative mortality were collected and analysed. RESULTS: There were 47 (79.7 %) operations for aortic dissections and 12 (20.3 %) for aortic aneurysms. The mean duration of circulatory arrest was 42 +/- 23 minutes. The lowest nasopharyngeal temperature at the time of arrest was 16.5 degrees +/- 1.9 degrees C. Eight (13.6 %) patients had a new irreversible neurologic deficit postoperatively. These patients had a mean circulatory arrest time of 50 +/- 28 minutes. Temporary neurologic dysfunction occurred in 8 (13.6 %) patients. Intra-hospital mortality was 22 %. The mean circulatory arrest time for patients who died was 54 +/- 24 minutes. CONCLUSION: DHCA is a simple and effective method of CNS protection in aortic surgery with satisfactory outcomes. With increased surgical and anaesthetic experience, as well as selective use of adjuncts of cerebral protection, reductions in mortality and neurological morbidity will likely be achieved in the future.

Cerebral embolization during cardiac surgery: impact of aortic atheroma burden.

BACKGROUND: Aortic atheromatous disease is known to be associated with an increased risk of perioperative stroke in the setting of cardiac surgery. In this study, we sought to determine the relationship between cerebral microemboli and aortic atheroma burden in patients undergoing cardiac surgery. METHODS: Transoesophageal echocardiographic images of the ascending, arch and descending aorta were evaluated in 128 patients to determine the aortic atheroma burden. Transcranial Doppler (TCD) of the right middle cerebral artery was performed in order to measure cerebral embolic load during surgery. Using multivariate linear regression, the numbers of emboli were compared with the atheroma burden. RESULTS: After controlling for age, cardiopulmonary bypass time and the number of bypass grafts, cerebral emboli were significantly associated with atheroma in the ascending aorta (R2=0.11, P=0.02) and aortic arch (P=0.013). However, there was no association between emboli and descending aortic atheroma burden (R2=0.05, P=0.20). CONCLUSIONS: We demonstrate a positive relationship between TCD-detected cerebral emboli and the atheromatous burden of the ascending aorta and aortic arch. Previously demonstrated associations between TCD-detectable cerebral emboli and adverse cerebral outcome may be related to the presence of significant aortic atheromatous disease.

Teaching first-year medical students physiology: does the human patient simulator allow for more effective teaching?

BACKGROUND: Although the Human Patient Simulator (HPS) is an effective teaching tool in many medical fields, literature supporting its use in the teaching of physiology to medical students is lacking. This study investigated the effectiveness of HPS-based teaching of cardiovascular physiology to first-year medical students. METHODS: Two hundred and ten first-year medical students were scheduled to our HPS laboratory with the purpose of demonstrating "physiology in action". Students were divided into groups of 19-25 each, and attended a lecture followed by a HPS session. Using a theatre-type simulator complete with mannequin, anaesthesia machine and monitors (METI, Sarasota FL), the scenarios of hypovolaemia, sepsis, and cardiac failure were run to demonstrate the physiological changes that occur with changes in preload, afterload, and cardiac contractility. Each student was given a true/false test before, and again after the HPS session, followed by a survey of their learning experience. RESULTS: There was marked improvement in test scores after the HPS session (82.1% vs. 64.6%, P < 0.001). Most of the students felt that HPS was a better teaching tool (94.5%) and raised more questions (76.5%) than lectures. They wanted more topics to be taught this way (96%), as they could apply and re-enforce textbook knowledge, and visualise real-time changes. However, they felt that their experience could have been enhanced with more time and smaller groups. DISCUSSION: HPS is an excellent teaching tool as it stimulates student curiosity and makes knowledge acquisition and understanding easier. It is highly desirable to be incorporated into the teaching of physiology.

A painful pulsatile abdominal mass in a young man with elevated blood pressures: an unusual presentation of phaeochromocytoma.

We report an unusual presentation of phaeochromocytoma in a young man with a painful, pulsatile abdominal mass and elevated blood pressures. This led to a delay in diagnosis and resulted in the administration of triggers of catecholamine release, possibly causing a catecholamine surge. This caused the development of catecholamine-induced cardiomyopathy and multiple organ failure, requiring inotropic and ventilatory support, intra-aortic balloon pump and dialysis. Fortunately, his condition reversed with supportive treatment and alpha-adrenergic blockade. This illustrates the importance of having a high index of suspicion of phaeochromocytoma, especially in young patients with elevated blood pressures.

Effect of apolipoprotein E genotype on cerebral autoregulation during cardiopulmonary bypass.

BACKGROUND AND PURPOSE: The presence of the apolipoprotein E epsilon4 (apoE4) allele has been associated with cognitive decline after cardiac surgery. We compared autoregulation of cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO(2)), and arterial-venous oxygen content difference [C(A-V)O(2)], during cardiopulmonary bypass (CPB) in patients with and without the apoE4 allele to help define the mechanism of association with cognitive decline. METHODS: One hundred fifty-four patients underwent coronary artery bypass grafting with CPB, nonpulsatile flow, and alpha-stat management. CBF was measured by using (133)Xe washout methods. C(A-V)O(2), CMRO(2), and oxygen delivery were calculated. Pressure-flow autoregulation was tested by using 2 CBF measurements at stable hypothermia: the first at stable mean arterial pressure (MAP) and the second 15 minutes later, when MAP had increased or decreased >/=20%. Metabolism-flow autoregulation was tested by varying the temperature and measuring the coupling of CBF and CMRO(2). RESULTS: In patients with (n=41) or without (n=113) the apoE4 allele, there were no differences in CBF, CMRO(2), C(A-V)O(2), pressure-flow and metabolism-flow autoregulation corrected for age, gender, non-insulin-dependent diabetes, hemoglobin, CPB time, and temperature. CONCLUSIONS: We conclude that apoE genotype does not affect global CBF and oxygen delivery/extraction during CPB, which suggests that other mechanisms are responsible for the apoE isoform-related neurocognitive dysfunction seen in patients undergoing CPB.

Comparison of sevoflurane with propofol for laryngeal mask airway insertion in adults.

UNLABELLED: We performed a prospective, randomized, controlled trial to compare the quality and ease of laryngeal mask airway (LMA) insertion after either rapid inhaled sevoflurane or i.v. propofol induction of anesthesia. Seventy-six unpremedicated ASA physical status I or II patients were anesthetized with either a single vital capacity breath of sevoflurane 8% or i.v. propofol 3 mg/kg, which produced equally rapid loss of consciousness (40.5 +/- 13.9 vs 37.7 +/- 9.9 s; P > 0.05). The LMA was inserted more rapidly in patients in the propofol group (74 +/- 29 vs 127 +/- 35 s; P < 0.01) and required fewer attempts (1.2 vs 1.6; P < 0.05) than the sevoflurane group. There was a greater incidence of initially impossible mouth opening in the sevoflurane group (45% vs 21%; P < 0.05). Once mouth opening was possible, the degree of attenuation of laryngeal reflexes was similar. The overall incidence of complications related to LMA insertion, especially apnea (32% vs 0%; P < 0.01), was more frequent in the propofol group (82% vs 26%; P < 0.01). There were four failures of LMA insertion in the propofol group and none in the sevoflurane group. Both groups had stable hemodynamic profiles and good patient satisfaction. We conclude that sevoflurane vital capacity breath induction compares favorably with i.v. propofol induction for LMA insertion in adults. However, prolonged jaw tightness after the sevoflurane induction of anesthesia may delay LMA insertion. IMPLICATIONS: In this randomized, controlled trial, we compared the ease of insertion of the laryngeal mask airway in adults after induction of anesthesia with either a sevoflurane vital capacity breath technique or propofol i.v.. We conclude that sevoflurane compares favorably with propofol, although prolonged jaw tightness may delay laryngeal mask airway insertion.

Single vital capacity inhalational anaesthetic induction in adults--isoflurane vs sevoflurane.

PURPOSE: To evaluate whether isoflurane is as suitable as sevoflurane for the single vital capacity breath (VCB) method of inhalational induction in patients premedicated with midazolam. METHODS: A randomised, controlled, double-blind study involving 67 ASA I-II patients aged between 18-50 yr undergoing elective surgery under general anaesthesia. All participants received premedication with 0.03 mg.kg-1 midazolam i.v. Using a primed circle absorber circuit, inhalational induction of anaesthesia was performed with the single VCB method using either isoflurane 3.5% or sevoflurane 7.5% in nitrous oxide 67% in oxygen, representing approximately equivalent MAC-multiples of 3.6 MAC. Isoflurane was compared with sevoflurane in terms of rapidity, efficacy, safety and acceptability of induction. RESULTS: With the single VCB method, sevoflurane produced a faster (45 +/- 21 vs 71 +/- 22 sec, P < 0.01), more successful (100% vs 75.8%, P < 0.01) induction of anaesthesia, with fewer induction-related complications (11.8% vs 84.8%, P < 0.01) than did isoflurane. There was also greater patient acceptability of induction with sevoflurane (76.4% vs 42.4%, P < 0.05). CONCLUSION: In adults given midazolam premedication, isoflurane is not as suitable as sevoflurane for single VCB inhalational anaesthetic induction technique as it is associated with slower, more complicated induction and less patient acceptability.

Acute hyponatraemia secondary to cerebral salt wasting syndrome in a patient with tuberculous meningitis.

A 30-year-old HIV-positive man presented with acute hydrocephalus secondary to tuberculous meningitis, for which an external ventricular drain was inserted. He developed marked natriuresis in the postoperative period, which resulted in acute hyponatraemia (131 to 122 mmol/l) and a contraction of his intravascular volume. A diagnosis of cerebral salt wasting syndrome was made, and he responded to sodium and fluid loading. This case highlights the differentiation of cerebral salt wasting syndrome from the more commonly occurring syndrome of inappropriate anti-diuretic hormone secretion as the aetiology of the hyponatraemia.