Anaesthesia and Intensive Care Medicine最新文献

Heart and lung transplantation rates continue to rise with median survival rates of 11 years and 7.4 years, respectively, with transplantation becoming the definitive therapy for end-stage disease of each system. Indications for lung transplantation are categorized as suppurative, obstructive, restrictive and pulmonary vascular. Surgical options include single lung, bilateral sequential single lung, and heart–lung transplantation. Each has their own intraoperative challenges, especially at induction, commencement of positive pressure ventilation, one lung ventilation, pulmonary artery clamping and lung reperfusion. A double lumen tube and a period of one lung ventilation are generally required for cases performed without cardiopulmonary bypass. Strategies to reduce pulmonary pressures and support right ventricular function are important. Perioperative fluids are minimized and lung protective strategies implemented to optimize lung function. Thoracic epidural anaesthesia is commonly used for postoperative pain management. The most common indication for heart transplantation is non-ischaemic cardiomyopathy. Ventricular assist devices and inotropic infusions are often used as a bridge to transplantation. Communication between donor and recipient teams is critical. Reversal of anticoagulation and alteration of implanted medical devices may be necessary. Anaesthetic management requires invasive monitoring, optimization of ventricular function and preparation for coagulopathy. Right ventricular dysfunction is the leading cause of early mortality.

The nephron is the functional unit of the kidney involved in the critical interplay of fluid and electrolyte homeostasis by glomerular filtration, selective tubular reabsorption, and secretion. This article will discuss the structure and function of each segment of the nephron, and the physiology pertaining to the formation of urine.

The traditional approach to acid–base physiology is based on the Henderson–Hasselbalch equation which is derived from the CO₂/HCO₃^- buffer system. It is becoming increasingly recognized that this is an incomplete analysis, as it focuses on only one of the six reactions involving H⁺. It can lead to the incorrect assumption that CO₂ and HCO₃^- are independently adjusted factors, that ultimately determine pH. In 1983, Peter Stewart, a Canadian physiologist, proposed that a fuller understanding of acid–base physiology required consideration of biological fluids as a complex dynamic system, with the interactions of all the chemical species involved considered. He showed that the true independent variables controlling the pH of any given fluid compartment are the difference in the concentration of ‘strong ions’; the total concentration of ‘weak acid’; and the PCO₂. Importantly, H⁺ and HCO₃^- are dependent variables and it is incorrect to think of them as being specifically regulated to manipulate pH. This review will discuss the importance of pH homeostasis and highlight the implications of the Stewart approach in our understanding of acid–base control mechanisms and disorders. In particular, the true mechanisms by which the kidney regulates plasma pH will be discussed, emphasizing key misconceptions that have been propagated because of the traditional approach.

This short article aims to deliver a basic understanding of the fundamentals of data types and the application of descriptive statistics. Frequency distribution, including the normal (Gaussian) distribution, is covered alongside statistical testing and the basics of correlation and regression. Meta-analysis and systematic review are introduced.

The kidneys are vital organs in the management of fluid balance, waste product removal, electrolyte homeostasis, acid–base balance, and endocrine function. Waste products removed by the kidney are urea, uric acid and creatinine; other foreign products with similar physio-chemical properties are also excreted. Urea and uric acid are by-products of protein metabolism and creatinine is generated by the metabolism of creatine compounds from muscle. The kidney regulates fluid and electrolyte balance through controlling the composition and volume of urine. In the proximal convoluted tubule and the loop of Henle, 90% of sodium, potassium, calcium and magnesium are reabsorbed. Acid–base balance is achieved by regulating the excretion of hydrogen ions and bicarbonate buffering. The kidney also has several endocrine functions including the production of renin and erythropoietin as well as hydroxylation of vitamin D. The kidneys receive 25% of cardiac output, generating 170–200 litres of ultrafiltrate daily. Urine output is approximately 1.5 litres/day, which is concentrated ultrafiltrate through selective reabsorption of solutes and water. In this article we will discuss tests frequently used to assess renal function.

Kidneys have a major role in maintaining homeostasis of body fluids, electrolytes concentrations, acid–base balance, and osmolality. This role is achieved by the functional unit of the kidneys, which is the nephron, through four consequent mechanisms: filtration, reabsorption, secretion, and excretion. Additionally, kidneys synthesize two hormones – erythropoietin and renin – and participate in calcium homeostasis. It is essential to recognize and manage acute or chronic kidney dysfunction to avoid further deterioration of kidneys and electrolytes imbalance, which both can be fatal.

The lower urinary tract function is to store and void urine (micturition) that has been produced by the kidneys and transferred to the bladder via the ureters. The lower urinary tract consists of the bladder, urethra and (in males) the prostate. A complex interaction of central, autonomic and somatic innervation enables micturition to be under voluntary control. Common disorders of micturition include bladder outflow obstruction and overactive bladder syndrome, and management of these disorders may include conservative, pharmacological or surgical interventions.

Urological procedures vary from minor ambulatory operations to ultra-major surgeries, and many are in elderly patients. This article highlights the preoperative assessment, intraoperative management, specific complications, and postoperative management of selected common procedures, namely transurethral resection of the prostate (TURP), percutaneous nephrolithotomy (PCNL), nephrectomy, robotic assisted laparoscopic prostatectomy and radical cystectomy. Paediatric procedures are not covered.

The homeostatic and excretory functions of the kidney are dependent on its perfusion, totalling 20–25% of cardiac output, and the process of glomerular ultrafiltration. Renal blood flow (RBF) is directly proportional to the trans-renal gradient which is autoregulated across a mean arterial pressure of 50–150 mmHg in a normotensive person. Selective molecular filtration in the glomerulus is achieved by the glomerular filtration barrier and is related to the size, shape, and electrical charge of molecules. The process of ultrafiltration is determined by the balance between hydrostatic and colloid osmotic pressures in the glomerular capillary and Bowman's space, and is affected by renal plasma flow, altered surface area and changes in afferent and efferent renal arteriole vascular resistance. The phenomenon of renal plasma flow autoregulation minimizes changes in the volume of ultrafiltration through myogenic and tubuloglomerular feedback mechanisms. Glomerular filtration rate can be measured using exogenous inulin, or estimated (eGFR) from creatinine clearance, several equations can be used to calculate eGFR but their limitations in estimating the true excretory function of the kidney need to be taken into consideration.

Acute kidney injury (AKI) is a common complication of acute illness and can affect between 30% and 60% of critically ill patients. It is associated with significant morbidity and mortality as well as a high cost to healthcare systems. There are a broad range of causes of AKI which should be considered in a systematic fashion, to avoid missing multiple potential causative factors. These include pre-renal causes from hypovolaemia, intrinsic renal causes such as glomerular diseases and post-renal obstructive causes. In the intensive care unit, two-thirds of AKI cases result from renal hypo-perfusion, sepsis and nephrotoxic agents; up to 5% will require renal replacement therapy. Modalities of renal replacement therapy include intermittent haemodialysis, peritoneal dialysis and continuous haemofiltration. Continuous haemofiltration is usually preferred in the intensive care setting, as it has greater haemodynamic stability and greater capacity to extract fluid from patients with fluid overload. Anticoagulation options can be achieved with systemic anticoagulation such as heparin or regional anticoagulation with citrate.