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The Virtual Anaesthesia Textbook

Pre-operative Assessment and Pre-medication

Last modified 9/11/2014. Comments to: Chris Thompson

Contents:


Preamble

Dealing with the need for assessments, laboratory investigations, and logistics of preparing patients for surgery is a major challenge for anaesthetists and requires Cupertino between Anaesthetists, Surgeons, Primary Care Physicians, other consulting physicians, and hospitals. Many changes have been made in recent years because of the great increases in outpatient and same day admit surgery but there is still no consensus on how to provide optimum preoperative preparation. There has been no system of risk assessment to guide practitioners in determining the type of pre-operative assessments needed. I have chosen to divide the topic into 1) specific anaesthetic concerns that are rarely an issue outside of anaesthesia, 2) patient considerations that may be of importance even for minor surgery, and 3) issues specific to the proposed surgery.


General Approach

Important background documents are the American College of Cardiology / American heart Association Guidelines for Perioperative Cardiovascular Evaluation for Non-cardiac Surgery. Also the American College of Physicians Position Papers which are divided into two parts: PART I Guidelines for Assessing and Managing the Perioperative Risk from Coronary Artery Disease Associated with Major Non-cardiac Surgery and PART II Perioperative Assessment and Management of Risk from Coronary Artery Disease (Palda and Detsky).

These sites focus on cardiac problems but the approach taken should provide a model for other areas of preoperative preparation.

John Loadsman has basic lecture notes on Preoperative Assessment.

E-Medicine has a detailed review.


Communicating with and Educating Patients

Communication can be a challenge when there are language problems.

Teaching patients about anaesthesia and what to expect during their time in hospital is important. The Canadian Anaesthesia Society has a good patient oriented discussion called Anesthesia and You. John Loadsman has provided Anaesthesia and the Sleep Apnoea Sufferer. AllAboutAnaesthesia.com.au provides concise patient information guides and advice.


Risk Assessment

Anaesthetists have long been in a position to provide an assessment of risk and in recent years a number of approaches have been taken to allow for a semi-quantitative approach to risk. The Goldman Index (original abstract) is an example of  such a risk scoring system. Here is an on-line risk calculator.

Dr. Gravestein in the newsletter of the Anesthesia Patient Safety Foundation has a fall 1995 editorial How Safe is Safe? where he compares anaesthesia to flying.

Studies that have looked at mortality from all causes for all cases in the peri-operative period produce numbers around 1 per 1000 . If one looks at just anaesthesia related causes it is closer to 1 per 10,000.(6) These numbers include critically ill patients having complex surgery and therefore are not applicable to many if not most patients.

The mortality numbers for relatively healthy patients and for outpatient procedures are very much lower and safer than most of our day to day activities such as driving a car.

A Mayo clinic prospective study of 45000 outpatients having surgery(7) suggested a 1 in 22000 perioperative death rate (within one month of surgery) but it was difficult to ascertain whether this was any different than the expected death rate in this population without surgery. They conclude that outpatient mortality is rare.

The Australian and New Zealand College of Anaesthetists have published the results of several studies on Anaesthesia Related Mortality in Australia. They were able to conclude that mortality attributable to anaesthesia was no less than 1 in 68,000. They admit that likely not all deaths were tracked or reported. Even so this is evidence of great improvement in recent years.

Conversely, morbidity and mortality for patients undergoing procedures such as emergency abdominal vascular surgery remains high.

Risk assessments underscore the need to assign risk depending on the patients health and proposed surgery . This is not always easy to do but general principles have evolved and certain areas such as patients with coronary artery disease have been studied a great deal in recent years. When attempts are made to separate out the various causes of mortality and morbidity generally patient problems are the most important, followed by surgical problems, and then anaesthesia problems.

Cohen and others have shown that patient related preoperative characteristics such as ASA Physical Status , age, sex, emergency surgery, and major surgery are significant predictors of mortality. For a ASA Class IV patient the death rate approaches 76 per 1000. The presence of significant medical disease is a much greater predictor of problems than the type of surgery or anaesthesia to the point that it seems anaesthetic related factors are almost inconsequential compared to patient and surgical factors.

To understand risk assessment an understanding of statistics and probability is helpful since the significance of assessments and testing done to assign risk depends very much on the prior probability of disease in the patient (see the chapter on statistics in this textbook). When one looks at pure anaesthetic problems that lead to morbidity and mortality, airway problems and failure to provide adequate ventilation leading to hypoxia are important. Fortunately the number of critical incidents involving anaesthetics alone are decreasing due to continuous oxygen saturation and end-tidal C02 monitoring. This is unlikely to have a major affect on overall mortality since anaesthetic critical incidents cause only a small part of perioperative mortality.


Guidelines and Advisories

Roizen ASA 2002 article. ASA 2012 Practice Advisory


Anaesthetic Considerations.


Surgical Considerations


Preoperative Medications


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visitors since April 29th 2000.

Original concept for the Virtual Anaesthesia Textbook by:
Dr. Chris Thompson
MBBS FANZCA
Senior Staff Specialist Anaesthetist
Royal Prince Alfred Hospital
Sydney Australia