Assessment of the obese patient

Dr Jonathan Redman
Lecture Abstract : 2013 Conference

Obesity is becoming an ever increasing problem, the most recent government figures show that 26% of the UK’s adult population are obese (BMI>30) with over 3% designated as morbidly obese (BMI >40) This will equate to an average of >13,000 morbidly obese patients living in the catchment area of your local District General Hospital.

The vast majority of obese patients presenting for surgery are relatively healthy and their risk is similar to that of normal weight patients. The aim of preoperative assessment is to identify the presence of obesity related morbidity and hence the high-risk patient and minimise the risk of postoperative complication. Obesity not only results in altered respiratory, cardiovascular, endocrine physiology but importantly can result in a chronic inflammatory response driven by visceral adipose tissue. In certain circumstances, this inflammatory state can confer protective effects in the perioperative period known as the obesity paradox. More specifically the obesity paradox describes the reduction in perioperative cardiac morbidity and mortality up to a BMI of 40. 

The key areas I will focus on in more detail within the talk are highlighted below.

Respiratory System
Airway and intubation
A thorough airway assessment should be performed in attempt to identify those patients with a potentially difficult airway.  In reality the incidence of difficult intubation is no different from the general population on the proviso that the patient is suitably positioned sitting up in a ramped position for laryngoscopy.
Bag and mask ventilation may prove difficult and risk factors include Age>50, history of snoring, increasing BMI, presence of beard, lack of teeth.

Obstructive Sleep Apnoea (OSA)
OSA is common in the obese and is often undiagnosed. Severe OSA is present in 10-20% of morbidly obese patients and if untreated can lead to pulmonary hypertension and heart failure. Strong predictors of OSA include loud snoring, large collar size, hypertension, and the presence of diabetes, male gender and older age. 

A well, evaluated screening tool is the STOP-BANG questionnaire, which seeks the presence of these predictive factors. A STOP-BANG value of 5 or more is said to be a strong predictor of the presence of OSA and if identified preoperatively the perioperative management of the patient should be tailored to minimise the risk of post-operative OSA (i.e. sit up, avoid opioids, apply oxygen and use regional technique). A clear pathway for referral for specialist sleep studies should be identified and CPAP treatment offered as soon as is possible.

Cardiovascular system
The risk of an adverse perioperative cardiac event in obese patients is related to the nature and severity of their underlying heart disease, associated comorbidities, and the type of surgery undertaken. Such comorbidities include hypertension, hyperlipidaemia, ischaemic heart disease, right heart failure secondary to obstructive sleep apnoea and obesity related cardiomyopathy. Patients with obesity should be assessed as any other patient group and the requirement for cardiac based investigations should be made on their comorbidity, functional capacity and magnitude of the anticipated surgery. Functional capacity assessment is accepted as one of the key risk predictors in post-operative outcome for major surgery. There are a number of modalities of assessment (shuttle walking, stair climbing, cardiopulmonary exercise testing etc.) but in the immobile obese population this is not always possible. 

Endocrine
It is well known that the prevalence of increased insulin resistance is strongly associated with increasing BMI. This must be identified and tightly controlled throughout the perioperative period. Some obese patients will develop the metabolic syndrome which significantly increases the perioperative cardiac risk. There are various definitions but essentially it is a constellation of central obesity, Insulin resistance and Dyslipidaemia and Hypertension. The presence of a metabolic syndrome and obesity increases complications and mortality in those with a BMI>50.

Useful References:

1) Seet E, Chung F. Obstructive sleep apnea: preoperative assessment. Anesthesiology Clin. 2010;28:199-215.

2) Chung SA et al. A systematic review of obstructive sleep apnea and its implications for anesthesiologists. Anesth Analg. 2008; 107(5):1543-63.

3) DeMaria EJ, Portenier D, Wolfe L. Obesity surgery mortality risk score: proposal for a clinically useful score to predict mortality risk in patients undergoing gastric bypass. Surg Obes Relat Dis 2007;3:134-40.

4) Berrington de Gonzalez A et al. Body-mass index and mortality among 1.46 million white adults. N Engl J Med;363:2211-9.

5)  Dindo D, Muller MK, Weber M, Clavien PA. Obesity in general elective 
surgery.Lancet 2003;361:2032-5.

6) Glance LGet al Perioperative outcomes among patients with the modifiedmetabolic 
sndrome who are undergoing noncardiac surgery. Anesthesiology 2010;113:859-72.

7) Fox WT et al. Prevalence of difficult intubation in a bariatric population, using the 
beach chair position. Anaesthesia. 2008 Dec:63(12):1339-42 

8) F.Chung et al. High STOP-BANG score indicates  high probability of obstructive sleep apnoea. British journal of Anaesthesia 2012. 108(5); 768-75.