Anaesthesia and Intensive Care

Patient inflating valves combined with self-inflating bags are known to all anaesthetists as resuscitation devices and are familiar as components of draw-over anaesthesia systems. Their variants are also commonplace in transfer and home ventilators. However, the many variations in structure and function have led to difficulties in their optimal use, definition and classification. After reviewing the relevant literature, we defined a patient inflating valve as a one-way valve that closes an exit port to enable lung inflation, also permitting exhalation and spontaneous breathing, the actions being automatic. We present a new classification based on the mechanism of valve opening/closure; namely elastic recoil of a flexible flap/diaphragm, sliding spindle opened by a spring/magnet or a hollow balloon collapsed by external pressure. The evolution of these valves has been driven by the difficulties documented in critical incidents, which we have used along with information from modern International Organization for Standardization standards to identify 13 ideal properties, the top six of which are non-jamming, automatic, no bypass effect, no rebreathing or air entry at patient end, low resistance, robust and easy to service. The Ambu and the Laerdal valves have remained popular due to their simplicity and reliability. Two new alternatives, the Fenton and Diamedica valves, offer the benefits of location away from the patient while retaining a small functional dead space. They also offer the potential for greater use of hybrid continuous flow/draw-over systems that can operate close to atmospheric pressure. The reliable application of positive end-expiratory pressure/continuous positive airway pressure remains a challenge.

Sepsis remains as a leading cause of death in critically ill patients. Unfortunately, there have been very few successful specific therapeutic agents that can significantly reduce the attributable mortality and morbidity of sepsis. Developing novel therapeutic strategies to improve outcomes of sepsis remains an important focus of ongoing research in the field of critical care medicine. Apoptosis has recently been identified as an important mechanism of cell death and evidence suggests that prevention of cell apoptosis can improve survival in animal models of sepsis and endotoxaemia. In this review article, we summarise the critical role of apoptosis of the immune cells in the pathophysiology of sepsis and propose that blocking cell-signaling pathways leading to apoptosis may present a promising specific therapy for sepsis. Various methods to inhibit apoptosis including the cell surface Fas receptor pathway inhibitors, caspase inhibitors, over-expression of anti-apoptotic genes and small interfering ribonucleic acid therapy are discussed.

Interventional neuroradiology is a rapidly expanding field, and the complexity and duration of these procedures makes anaesthetic support essential to their success. Such has been the development in this area that the American Heart Association has published a scientific statement on the indications for these procedures. A detailed understanding of patient pathology, the technical aspects of the interventions and their associated risks, and the remote location in which they are performed are important for providing expert anaesthetic care. The aim of this article is to provide a description and contemporary analysis of the common interventional neuroradiology procedures relevant to the anaesthetist. This article will cover the management of intracranial aneurysms, cerebral vasospasm following intracranial haemorrhage, intracranial and spinal arteriovenous malformations, idiopathic intracranial hypertension, carotid artery stenting, intra-arterial thrombolysis for stroke and endovascular treatment of intracranial atherosclerosis. Protection from ionising radiation and acute kidney injury are also discussed.

We compared the effectiveness of three anaesthetic regimens (propofol alone, propofol with remifentanil and sevoflurane alone), with respect to seizure duration and seizure quality in patients undergoing electroconvulsive therapy.

Thirty-nine patients underwent a total of 234 electroconvulsive therapy treatments in this prospective, observer blinded, crossover study. Each patient received either propofol 1 mg/kg alone (Group P), propofol 0.5 mg/kg and remifentanil 1 μg/kg (Group R), or sevoflurane alone 6% (Group S) for their initial electroconvulsive therapy session. The patients subsequently received an alternative regimen in their next session, such as from propofol 1 mg/kg alone to propofol 0.5 mg/kg and remifentanil 1 μg/kg, from propofol 1 mg/kg alone to propofol 0.5 mg/kg and remifentanil 1 μg/kg to sevoflurane alone 6%, or from sevoflurane alone 6% to a continuing alternation between drugs at each session, until their sixth session. Muscle paralysis was achieved with 1 mg/kg succinylcholine. Seizure duration, postictal suppression index, early and midictal amplitude were recorded. The mean motor and electroencephalogram seizure durations were significantly longer in Groups P and R compared to Group S (P <0.001). The postictal suppression index and early and midictal amplitude values were not significantly different among the groups.

These findings indicate that the three anaesthetic regimens had similar effects on seizure quality parameters, although sevoflurane was associated with shorter seizure durations than propofol or propofol-remifentanil.

The aim of this paper is to describe a linked patient blood management (PBM) data system and to demonstrate its usefulness by presenting the blood usage data obtained.

Our existing datasets already collected much of the required information in relation to PBM. However, these datasets were not linked. A patient identifier was used to link the Patient Administration System with the Laboratory Information System. Data linkage was achieved by linking the Laboratory Information System with the Patient Administration System records where blood transfusion or laboratory result date/time fell between admission and discharge date/time. The two datasets were then consolidated into the PBM data system.

Blood usage data obtained from the system showed that between August 2008 and July 2009 there were 59,627 patient completed separations in the pilot hospital. Of the total transfused units, 62% were red blood cells (RBC), followed by fresh frozen plasma (22%), cryoprecipitate (9%) and platelets (8%). Around 50% of RBC transfusions were administered to patients >70 years of age. General medicine represented 21% of RBC usage, followed by haematology (19%), orthopaedics (17%) and general surgery (16%). Patients with 100 g/1 pre-transfusion haemoglobin received 9% of RBC transfusions and patients with 71–100 g/1 pre-transfusion haemoglobin received 73% of RBC transfusions. The post-transfusion haemoglobin in RBC transfusions exceeded 100 g/1 in 33% of patients.

Databases were successfully linked to produce a powerful tool to monitor blood utilisation and transfusion practices within a pilot PBM program. This will facilitate effective targeting of PBM strategies and ongoing monitoring of their impact.

Benefits and advantages of tracheostomy have been vigorously debated. There is a lack of consensus as to whether perceived clinical improvement is attributable to fundamental changes in respiratory dynamics. We compare the effect of tracheostomy versus endotracheal tube on dead space, airway resistance and other lung parameters in critically ill ventilated patients.

Data collected included patients who were admitted to surgical, burn and neurosurgical intensive care units at the University of North Carolina. Twenty-four intubated patients were included in our analysis with various aetiologies of respiratory failure. Tracheostomy was deemed necessary either for severe neurological devastation or failure to wean from the ventilator. The diameter of the endotracheal tubes ranged from 6–8 mm and the tracheostomy tube diameters were from 6.4–8.9 mm. Internal diameters between endotracheal tube and tracheostomy tubes, ventilator settings and sedation were kept consistent throughout the study. Respiratory parameters were measured using the Respironics’ non-invasive cardiac output 2 device (Phillips, Andover, MA) immediately prior to tracheostomy and repeated within 24 hours of tracheostomy.

Only two (8%) of the patients had slight improvement (>6% decrease in dead space). The average dead space of endotracheal versus tracheostomy tubes was 41±12.6% and 40±14.6%, respectively (P=0.75). The remaining 22 patients (92%) had no significant change in dead space, compliance or other respiratory parameters. This study shows that there is no significant difference in respiratory mechanics and dead space with a tracheostomy versus endotracheal tube.

The number of patients in buprenorphine opioid substitution therapy (BOST) or methadone opioid substitution therapy (MOST) programs is increasing. If these patients require surgery, it is generally agreed that methadone should be continued perioperatively. While some also recommend that buprenorphine is continued, concerns that it may limit the analgesic effectiveness of full mu-opioid agonists have led others to suggest that it should cease before surgery.

However, no good evidence exists for either course of action. Therefore, we undertook a retrospective cohort study comparing pain relief and opioid requirements in the first 24 hours after surgery in 22 BOST and 29 MOST patients prescribed patient-controlled analgesia.

There were no significant differences in pain scores (rest and movement), incidence of nausea or vomiting requiring treatment, or sedation between the BOST and MOST patient groups overall, or between those patients within each of these groups who had and had not received their methadone or buprenorphine the day after surgery. There were also no significant differences in patient-controlled analgesia requirements between BOST and MOST patient groups overall, or between patients who did or did not receive MOST on the day after surgery. BOST patients who were not given their usual buprenorphine the day after surgery used significantly more patient-controlled analgesia opioid (P=0.02) compared with those who had received their dose. These results confirm that continuation of buprenorphine perioperatively is appropriate.

The purpose of this study was to assess whether simulation training can improve the clinician's ability to predict the effect of bivalirudin infusion.

Six clinicians with experience using bivalirudin and six without experience (Groups Exp and NoExp) entered predictions for partial thromboplastin time while viewing a running display of clinical data obtained retrospectively from intensive care unit patients who had received bivalirudin infusion after cardiac surgery. All clinicians entered guesses for the same sequence of 30 patients. Average guessing-errors were analysed using analysis of variance and linear regression.

All physicians evaluated 30 patients (813 partial thromboplastin time guesses overall) in less than two hours. Average errors in Groups Exp and NoExp decreased from 9.4 and 11.7 seconds in the first tercile, to 8.2 and 8.4 seconds in the last tercile of patients, respectively. The guessing-errors of Group NoExp were significantly higher than Group Exp in the first and second terciles, with no significant difference in the third tercile. Linear regression indicated a significantly steeper learning curve in Group NoExp than Exp.

Brief simulation training using retrospective patient data improved the ability of inexperienced clinicians to predict the effect of bivalirudin as compared to experienced clinicians.

There is widespread variation as to the method of presentation of informed anaesthetic consent with little empirical data on the nature of communication and how much information is retained. At a dedicated anaesthesia pre-admission clinic, 149 patients undergoing elective surgery under general anaesthesia were both verbally informed and shown written information about four major and three minor anaesthesia risks. The major risks were death, pneumonia, heart attack and stroke. The minor risks were dental damage, nausea and vomiting. On the day of scheduled surgery, retention of information about these anaesthetic risks was examined. Thirty-eight patients (26%) could not recall any anaesthesia risks, 55 patients (37%) could not recall any major risks and 126 patients (84%) could not recall any minor risks. Our findings indicate that patients should receive a second explanation on the day of surgery, even if informed consent was provided only two weeks earlier.

Spontaneous coronary artery dissection is a rare and often fatal condition of pregnancy. The long-term morbidity is unknown, but a small cohort of patients develop severe ventricular dysfunction as a consequence. We describe a 37-week gestation parturient who presented with cardiogenic shock secondary to spontaneous left main coronary artery dissection. Despite rapid diagnosis, stabilisation with an intra-aortic balloon pump and prompt transfer to a tertiary centre for emergency caesarean delivery and coronary artery bypass grafting, the patient developed a severe postoperative dilated ischaemic cardiomyopathy. There is little information about the long-term outcomes and the specific anaesthesia management of combined emergency caesarean delivery and cardiac surgery in pregnancy for spontaneous coronary artery dissection. Therefore, we outline our multidisciplinary management of this critically ill pregnant woman.

This case report describes an asymptomatic healthy male professional athlete who underwent general anaesthesia for a routine orthopaedic operation. Peri-procedure, pronounced ST elevation suggestive of myocardial ischaemia manifested on the electrocardiogram lasting for four hours post-procedure, upon which the athlete developed deep and diffuse inferolateral T-wave inversion. These changes resolved spontaneously and the patient remained clinically stable throughout. This case demonstrates the clinical conundrum facing anaesthetists attempting to differentiate between repolarisation anomalies that are commonly observed in high-level athletes and those of inherited cardiac pathology, namely hypertrophic cardiomyopathy, which is the leading cause of sudden cardiac death in young athletes.