Anaesthesia & Intensive Care

Self-assessment Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Viyayanand Nadella

Neurological and humoral control of blood pressure Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Soumitra K. Ghosh, Jaideep J. Pandit Abstract There is a relationship between arterial blood pressure, cardiac output and vascular resistance described mathematically, that helps us to understand short-term control of blood pressure in terms of a hydraulic system. Arterial baroreceptors are specialized sensors which mediate a rapid response to sudden changes in pressure through interaction with the autonomic nervous system. This in turn influences heart rate, inotropic state and vascular tone, altering distribution of blood between arterial and venous systems, thus compensating for acute changes in total blood volume. Total blood volume is controlled predominantly by the kidney, with the renin–angiotensin–aldosterone system acting as both the 'sensor' of blood pressure/volume (via renin release in the juxtaglomerular apparatus) and the 'effector' of blood pressure/volume (via aldosterone secretion by the adrenal cortex). Overall control is shared; the baroreceptors being responsible for mediating short-term changes, and renal mechanisms determining the long-term control of blood pressure. These systems have to be adaptable in order to deal with physiological variation in the delivery of blood to tissues from rest to exercise, and with the large shifts in blood volume seen in acute haemorrhage. Pathophysiological changes in these systems lead to maladaptive responses, with systemic hypertension the most commonly seen.

Applied cardiovascular physiology Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Carla Gould, Jon Hopper Abstract Maintaining an equilibrium between oxygen supply and demand is a principal function of the cardiovascular system. In times of altered metabolic demand mechanisms exist to maintain the balance between supply and demand. Exercise, haemorrhage and pregnancy all lead to changes in oxygen demand and subsequently modification of cardiac output. During isotonic exercise, metabolic demands of muscle are greatly increased. Sympathetic stimulation and inhibition of the parasympathetic system lead to increases in heart rate and venous return, increasing cardiac output. This allows a proportional increase in blood flow to the exercising muscle. Cardiac output increases throughout pregnancy. In the first and second trimesters this rise is mainly due to an increase in stroke volume, however during the later stages of pregnancy stroke volume reaches a plateau and further increase in cardiac output is mediated by a rising heart rate. In contrast, during haemorrhage, decreased venous return leads to a reduction in cardiac output, with a baroreceptor response due to the drop in arterial blood pressure. The tachycardia and vasoconstriction which follows are compensatory mechanisms in an attempt to preserve blood pressure. The Valsalva manoeuvre illustrates several aspects of reflex control of the cardiovascular system and allows non-invasive assessment and quantification of control mechanisms. Changes in stroke volume during the respiratory cycle can be used to predict fluid responsiveness and can be measured as pulse pressure variation or stroke volume variation.

Anaesthesia for carotid surgery Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Michael Stallard, Indran Raju Abstract Carotid endarterectomy (CEA) is a surgical procedure to prevent strokes in patients with atheromatous disease at the carotid bifurcation. The effectiveness of CEA has been established in large clinical trials. Patients should have surgery performed within 2 weeks from the onset of symptoms. This time frame presents challenges to the anaesthetist and surgeon in terms of risk stratification and optimization of patients. Optimization includes blood pressure control and use of antiplatelet and lipid-lowering therapy. CEA can be carried out under general anaesthesia or regional anaesthesia with the advantages and disadvantages of both techniques discussed. Understanding surgical technique and the implications for anaesthesia is important, specifically the use of carotid shunting, eversion technique and patch angioplasty. Cerebral perfusion monitoring can be used during CEA to reduce neurological morbidity and mortality. The gold standard for monitoring remains an awake patient where sensory, motor and higher mental functions can be assessed continuously. Intraoperative and postoperative management may involve haemodynamic and neurological complications such as stroke, cerebral hyperperfusion syndrome, heart failure and myocardial infarction. Compromise to the airway can occur as a result of oedema or haematoma and the latter may require exploration in theatre.

Anaesthesia for the ruptured aortic aneurysm Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Matthew Cheesman, Andrew Maund Abstract The perioperative management of ruptured abdominal aortic aneurysms (RAAA) remains a core anaesthetic competency. Changes such as service centralization, aneurysm screening and the developing role of emergency endovascular aneurysm repair (EVAR) are altering the demands upon anaesthetists. Whereas previously on-site general anaesthesia for resuscitative open aneurysm repair (OAR) was standard, now transfer, choice of surgical technique and options for anaesthetic management may need to be considered. We present the key components of emergency anaesthesia for both OAR and EVAR and describe clinical dilemmas arising at preoperative and intraoperative stages.

Anaesthesia for open abdominal aortic surgery Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Alastair Duncan, Adam Pichel Abstract The prevalence of abdominal aortic aneurysm (AAA) and the number of patients undergoing aneurysm repair is increasing. The UK has worked tirelessly to reduce its operative mortality rates for elective open AAA repair with the introduction of a quality improvement programme. Reducing death from ruptured aortic aneurysm has been the focus of the national screening programme. Despite the increased prevalence of disease and intervention, the popularity of open repair has diminished since the advent of endovascular repair (EVAR). The short-term benefits of EVAR when compared to open repair are well described; however, the long-term survival benefits, freedom form re-intervention and cost effectiveness of EVAR are not proven. The choice of technique for emergency AAA repair is contentious, with the more traditional approach of open repair being rapidly overtaken by endovascular options. In this article we provide an overview of the evidence supporting the different treatment options, outline current approaches to risk stratification, describe the key physiological changes that occur during open repair and describe an overview of the approach to perioperative management.

Postoperative care and analgesia in vascular surgery Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Shaun McMahon, Rachael L. Bird Abstract Patients undergoing major vascular surgery are high risk for myocardial infarction, renal failure, respiratory complications and death. Invasive procedures confer greater risk of complication, with patients undergoing open aortic surgery being at highest risk. Endovascular procedures are less invasive, yet not devoid of potentially serious complications. Reduction of myocardial oxygen demand is key: stabilizing cardiovascular parameters, maintaining normothermia, adequate volume resuscitation and effective analgesia. Continuation of preoperative risk-reduction strategies including aspirin, beta-blockers and statin therapies are critical, and should be continued in the postoperative period. Maintaining a high index of suspicion for procedure-specific complications is essential in order to reduce morbidity and mortality in these patients.

Anaesthesia for vascular surgery on the extremities Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Richard J. Telford Abstract Peripheral arterial surgery is challenging, operations are frequently long and associated with insidious blood loss. Because of the high incidence of comorbidities these patients are a high-risk group with a high incidence of morbidity and mortality. They key to successful outcome is meticulous attention to detail by all those professions involved in their care.

Anaesthesia for endovascular aneurysm repair Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): John Barrett, Sian Jones Abstract A patient with an abdominal aortic aneurysm can have surgical management through either an open or endovascular approach. The use of an endovascular approach has benefits for the patient by being a less invasive approach with initially lower mortality and morbidity and lower lengths of hospital stay, although longer term outcomes match open techniques. The endovascular technique requires more specialist equipment, including stents and imaging equipment. In the UK they are usually performed in specialist hospitals with teams of interventional radiologists, vascular surgeons and anaesthetists working together. Patients presenting for endovascular repair of their abdominal aortic aneurysm can present the anaesthetist with range of complex comorbidities which require specific management and optimization pre-operatively. The intraoperative management of the patient can vary, depending on patient, surgical and anaesthetic factors, from local anaesthetic, regional techniques or general anaesthesia. The postoperative complications are generally minimal, but the patients require lifelong follow up, making the procedure more expensive than an open procedure.

Risk modification and preoperative optimization of vascular patients Publication date: May 2019 Source: Anaesthesia & Intensive Care Medicine, Volume 20, Issue 5 Author(s): Ben A. Goodman, Adam Pichel, Gerard R. Danjoux Abstract Major vascular surgery is associated with a high risk of morbidity and mortality. Targeted optimization of organ systems most likely to suffer morbidity should be made prior to elective surgery. Risk modification can reduce both perioperative and long-term complications. This article summarizes currently accepted best practice for risk modification and preoperative optimization prior to vascular surgery.