As it has been realised that western diagnosis criteria for obese and metabolic syndrome do not hold true for Asian patients, anaesthesia care providers should be completely aware of the pathphysiology, risks and difficulties encountered by obese patients during the bariatric surgeries.
The word ‘bari’ is the plural of ‘baros’. In Greek, ‘baros’ means weight / burden / load or heaviness. From this stems ‘Baris’ referring to the obese or fat / heavy / overweight people.
Obesity has reached epidemic levels within a short span of time with an alarming rise in the number of Type 2 diabetics globally. Asia Pacific itself has seen an upsurge of more than 50 million Type 2 diabetics with no signs of regression. It has also been seen that specifically in Asia the comorbidities, especially diabetes and cardiovascular disease, develop at a lower BMI and develop significant complications leading to fatality at a low age.
It has been observed that a weight loss of even 10 per cent significantly lowers the comorbidities, which is significantly seen in case of obstructive sleep apnoea wherein a weight loss of even 10 per cent might decrease the sleep apnoea by 50 per cent. Because bariatric surgery has become common these days, it is imperative that anaesthesia care providers be knowledgeable about the pathophysiology, risks and difficulties encountered during their care. Problems include difficulties with intravenous access, tracheal intubation and extubation, appropriate use of narcotics, muscle relaxants and other drugs. Based on Body Mass Index (BMI), humans may be classified as non-obese, overweight, obese, morbidly obese and super-morbidly obese.
As a single independent factor, obesity is responsible for OSA in 60–90 per cent of the population with this disorder. OHS is different from OSA in that there is no cessation of airflow. Both OSA and OHS repeatedly disrupt sleep due to increased ventilatory effort induced arousal and causes daytime sleepiness and cardiopulmonary dysfunction.
Pulmonary function tests may be necessary to note effects on lung capacities and airflow mechanics. Arterial blood gases will indicate if the patient is retaining carbon dioxide or has hypoxemia. The presence of polycythemia will suggest long-standing hypoxemia. A chest x-ray will evaluate the anatomical status of the lung and cardiac structures
Patients with NASH may have elevated liver enzymes, increase in triglycerides, hepatomegaly and cirrhosis.
The risk of DVT is doubled in obesity (48 per cent vs. 23 per cent) when compared to lean individuals during abdominal surgery. This automatically increases the likelihood of Pulmonary Embolus (PE) and is reported as being between 2.4-4.5 per cent following bariatric surgery. To reduce the risk of DVT and PE in obese patients, most surgical protocols favour the use of anticoagulant prophylaxis and pneumatic compression lower extremity stockings.
The morbidly and super-morbidly obese are particularly challenging patients because of their size. In addition to routine evaluation, areas of concern in this patient group are as follows:
Intravenous access – The presence of excessive subcutaneous tissue decreases the easy visibility of peripheral veins. Portable ultrasound equipment may be required for identification and cannulation of peripheral veins
Preoperative airway assessment – Obese patients are more difficult to mask ventilate and intubate. This is because of their size, presence of a neck that has a widened circumference, is shorter and the presence of excessive pharyngeal tissue with a tongue that has a large base. It is imperative that every obese patient be carefully examined for the feasibility of mask ventilation and intubation including aspiration risk. Neither obesity nor body mass index has been associated with difficult intubation. Large neck and Mallampati score are the only two predictors of potential intubation problems. Also, patients with a Mallampati score greater than or equal to three have increased difficulty with tracheal intubation. Other routine assessments namely, jaw and neck mobility, dental status, patency of nostrils, and inspection of oropharynx should be done prior to implementation of an anaesthesia care plan for obese patients.
Patients undergoing bariatric surgery are prone to slipping off the table, so they must be securely strapped to the table.
Anaesthetic pharmacology – The physiological changes associated with obesity lead to alterations in distribution, binding and elimination of many drugs. Many doses have to be calculated according to the ideal body weight or more accurately according to the lean body mass. In 20 to 40 per cent of obese individuals, ideal body weight and lean body mass are not identical. This is because increase in body weight may be due to an increase in lean body mass.
Extubation – Obese patients must be extubated when they are fully awake and after they have returned of motor power. It is less threatening to extubate those that were not difficult to mask ventilate and or intubate. Factors that play a role in determining successful extubation include the severity of obstructive sleep apnoea, duration and type of procedure. Either facemask, nasal Continuous Positive Airway Pressure (CPAP) or Bi-level Positive Airway Pressure (BiPAP) support with oxygen may be required in some patients following extubation. This is usually the case for those with a history of sleep apnoea or those using CPAP before surgery and supplemental oxygen is usually required.
Caring for obese patients remains a challenge for anaesthesia providers. Some patients require special care in a low-cost obesity care unit while others may need prolonged care in the intensive care unit.
The various associated health hazards
Sunitha Goel is a Consultant Anaesthesiologist in Saifee Hospital, Dr L.H. Hiranandani Hospital, Cumbala Hill Hospital and Breach Candy Hospital. She was awarded Industry Leadership Award in 2004.