Anaesthesia and Intensive Care Medicine最新文献

Tight control of acid–base balance is fundamental to many core physiological processes. $pH$ affects the transmembrane movement of charged ions and the conformation of proteins and consequently, acidosis and alkalosis can cause multi-system adverse effects in the human body.

The most clinically relevant concepts to understanding human acid–base physiology are the Bronsted–Lowry theory, $pH$, ${pK}_a$ (which has a significant influence on local anaesthetic pharmacokinetics) and the Henderson–Hasselbalch equation. The human body has evolved multiple endogenous buffer systems to maintain exquisite control of intra-cellular and extracellular $pH$, including proteins, haemoglobin, phosphate and the bicarbonate system.

Bicarbonate is one of the most important buffer systems and is involved in both respiratory and renal control of acid–base balance through a series of reactions mediated by carbonic anhydrase. The renal system is an important medium to long term regulator of acid base balance through its ability to excrete hydrogen ions and retain bicarbonate. Systemic metabolic derangements and exogenous drugs can disrupt the renal acid–base system and will be discussed in this article.

Adequate tissue perfusion and cellular function is dependent on the maintenance of effective circulatory volume and serum osmolality, respectively. As sodium is the principal extracellular cation with the inability to pass freely across the cellular membrane, it therefore has the greatest effect on extracellular fluid osmolality. The extracellular fluid (ECF) volume can increase or decrease independent of the surrounding osmolality indicating that control of plasma osmolality and volume occur through distinct physiological processes. Disorders in sodium balance with consequent effect on osmolality come about mainly due to disturbances in water homeostasis rather than an abnormality of sodium intake or excretion.

To aid the digestion and absorption of nutrients, the gastrointestinal (GI) tract uses a carefully coordinated series of muscular contractions. These contractions serve to propel luminal contents through the tract, as well as churning and mixing them with enzymatic secretions to aid digestion. Smooth muscle of the GI tract exhibits fluctuations in its membrane potential that can lead to action potentials and muscle contraction. These fluctuations, known as the basal electrical rhythm, can range from around three to five per minute in the stomach to 20 per minute in the small intestine. They can be influenced by neural and hormonal input and form the basis of most muscular contractions in the GI tract. The pattern of contractions varies in different parts of the tract to serve the distinct functions of each region, for example, the stomach exhibits a reflex relaxation of muscle to accommodate a meal, while in the small intestine, segmental, mixing contractions predominate.

Many patients presenting for surgery are established on anti-hypertensive medication or may require additional manipulation of blood pressure perioperatively. This article aims to explore the pharmacology of antihypertensives in relation to cardiovascular physiology, focusing on the effects on the renin–angiotensin system and the autonomic nervous system. The most recent guidance for the stepwise treatment for hypertension is reviewed, aiming to provide anaesthetists with the relevant knowledge to manage hypertensive patients perioperatively.

Arrhythmias are a common problem in the critically ill and they can have significant effects on patient outcome. They often require immediate and swift action, and it is therefore essential that clinicians have a structured approach to the recognition and management of arrhythmias. Here, we provide a framework for the appropriate management of the more frequently encountered cardiac arrhythmias in critical care. We include the most recent algorithms from the 2021 Resuscitation Council Guidelines for reference.

Around 3.7 million people worldwide die each year from cardiac arrhythmias. Despite advances in catheter ablation therapies and implantable devices, there have been few advances in pharmacological therapy. Advances in the understanding of channel subtypes has led to the proposed modification of the Vaughan Williams classification system. However, each drug has a unique pharmacokinetic profile meaning that often the class of a drug bears little clinical relevance. Many drugs also have sites of action outside of their class which may account for the generation of proarrhythmias. The advances in understanding of specific ion channel subtypes may provide the opportunity for target-specific drugs with improved safety profiles.

Digestion and absorption describe the breakdown of food into small particles and their movement from the gastrointestinal (GI) lumen into the body. The main groups of nutrients absorbed from food are carbohydrates, proteins, and lipids. Water, minerals, and vitamins are also absorbed by the GI tract along with orally administered drugs. Carbohydrates are enzymatically broken down into monosaccharides, which are absorbed across the small intestinal epithelium by passive (fructose) and active (glucose and galactose) mechanisms. Similarly, proteins are broken down from polypeptide chains into individual amino acids or dipeptides and tripeptides. Their absorption depends on their chemical properties and occurs via passive and active processes that utilize a variety of membrane transporters. Lipids and lipid-soluble vitamins require bile salts for emulsification to aid absorption. Water follows osmotic gradients generated by the absorption of nutrients. Since the processes of digestion and absorption require mechanical and chemical processes that can damage the mucosa, the GI tract has evolved several defence mechanisms, including a mucous barrier and regular renewal of the epithelial lining.

The gastrointestinal (GI) tract comprises a long tube with anatomical and functional specializations, beginning at the mouth and ending at the anus. The histology of the tract wall is relatively regular from the oesophagus to the large intestine and comprises mucosa, submucosa, muscularis and serosa layers. The tract functions primarily in digestion and absorption of nutrients, which begins in the mouth with the chewing and mixing of food with saliva. Small boluses of food are then swallowed during a complex reflex process and make their way through the oesophagus to the stomach, where they can be stored while further digestion takes place. Gastric contents are slowly emptied into the small intestine, where the majority of digestion and absorption occurs, before any undigested components are moved into the large intestine. The final absorption of water and electrolytes takes place here to produce a stool that only contains around 100–200 ml of water. The large intestine has a diverse bacterial population that contributes to digestion and can influence the health of an individual. Each component of the digestive tract has secretions that contribute to digestive function, as well as immunity and the excretion of waste.

Cardiovascular comorbidities are amongst the most important modifiable risk factors in patients undergoing non-cardiac surgery. Likewise, cardiac complications are a leading cause of all perioperative morbidity and mortality. Major adverse events include acute myocardial ischaemia, infarction, congestive cardiac failure, arrhythmias, and cardiac arrest. Preoperative assessment and planning aims to minimize these risks. Although testing is important, it must be rationalized lest resources are misused and undue delays ensue. Current thinking in preoperative therapy, intraoperative management and postoperative care is discussed. Although most patients with cardiac disease have ischaemic heart disease, other specific cardiac conditions and principles of their management are briefly considered.