Effects of general anesthesia on the body

Introduction

At the end of the nineteenth century, barely 50 years after ether anaesthesia was first clemonstrated in 1846, and rapidly became utilised throughout the Western world, August Bier discovered that a class of drugs (local anaesthetics) could stop neural transmission and halt sensation in the area of supply of the affected nerves. Regional anaesthesia thus became an alternative to general anaesthesia. And since that time, the debate over the relative safety of the two techniques has persisted. There have been phases in this history where one has achieved popularity over the other, and vice versa. Nowadays we strive to assess safety and efficacy on the basis of valid scientific evidence rather than on personal experience, expert opinion and anecdotal evidence. However, we cannot expect evidence to make broad generalisations for us--that would be as absurd as asking whether rainy days are better than sunny days. In evidence-based medicine, we need focused questions that apply to the patient population, the treatment and the standards of care that are relevant to the issue of interest. In the case of the regional versus general anaesthesia debate, the broader issue of whether one is safer than the other will not be answered: what we must ask is in which circumstances one anaesthetic choice has advantages over another.

With different surgical procedures and patient populations, an effect of side effect of anaesthesia can be favorable or unfavorable. For example, sympathectomy, vasodilatation and venous pooling from neuraxial blockade reduce venous return to the heart, which compounds the hypotension. Profound hypotension and reduced preload can be devastating for a frail elderly patient. The same phenomena can reduce intraoperative blood loss by reducing local blood flow to the surgical site--usually an advantage. Some advantages of the regional anaesthesia option are simply related to avoidance of general anaesthesia. For example, the high risk of acid regurgitation and aspiration during general anaesthesia for Caesarean section makes this a procedure for which regional anaesthesia is likely to be beneficial. Using regional rather than general anaesthesia for carotid endarterectomy has the advantage of the patient being awake during carotid artery clamping.

Discussion

The surgical procedures for which the two techniques are indicated may be distinctly different. Sole neuraxial anaesthesia is commonly used for extremity, body surface surgery, and non-extensive intraabdominal and pelvic procedures, whereas adjunctive neuraxial anaesthesia is more commonly used for major intraabdominal and intrathoracic procedures and for postoperative analgesia. The dense sympathetic blockade provided by intraoperative neuraxial anaesthesia results in improved lower extremity blood flow, lesser incidence of hypercoagulability, and reduced cardiac work. Hence, the incidence of deep venous thrombosis, pulmonary embolism, and cardiac events may be reduced. On the other hand, postoperative epidural analgesia, using low dose local anaesthetics with opioids, likely has different benefits, largely related to superior analgesia, continuous low-dose local anaesthetic effects, and avoidance of systemic opioids. Thus postoperative neuraxial analgesia is likely to result in improved bowel mobility, improved coughing and breathing, earlier ambulation, and consequently a lower incidence of ...