The Big Principles Of Obesity

Have you ever considered the implications of transferring a critically ill person with obesity? Obesity has a range of pathophysiological consequences, all of which may be amplified during critical illness, but on top of this there will also be a number of practical considerations during transfer…

• These effects tend to be more pronounced as BMI increases. However, BMI is a limited description of obesity and does not consider the distribution of adipose tissue which is an important determinant of morbidity.
• Those with a high waist-to-hip ratio (so-called ‘apple’ shape) are at higher risk of metabolic syndrome compared to people with a low waist-to-hip ratio (‘pear’-shaped distribution).
• Here we will explore the impact of obesity on different body systems and the implications for inter-hospital transfer.

Airway Management

• It is well recognised that airway management in the patient with obesity may be challenging for the following reasons:
  • facemask ventilation may be hampered by increased soft tissue around the neck
  • obese patients desaturate rapidly (for reasons explored below)
  • there is an increased risk of gastric reflux and aspiration

Patients with obesity were found to be twice as likely to develop airway complications in the Fourth National Audit Project (NAP4).

• Therefore, it is even more important in the patient with obesity to ensure endotracheal and tracheostomy tubes are properly secured with a lower threshold to intubate these patients prior to transfer.
• A pre-determined emergency airway plan is vital prior to any transfer.
• If emergency airway management is required, the following adaptations should be considered:

1. Airway adjuncts and a two-person technique to assist facemask ventilation
2. Ramping of the patient using pillows to optimise view at laryngoscopy
3. Use of a videolaryngoscope

• There are dedicated guidelines available on the conduct of anaesthesia in the patients living with obesity.

Respiratory Management

• Obesity has a number of effects on respiratory physiology, including:

1. A reduction in total lung volume and functional residual capacity (FRC)
2. Significant basal atelectasis leading to shunt
3. Reduced chest wall compliance and diaphragmatic splinting due to raised intra-abdominal pressures

Importantly, patients with high BMI have an increased utilisation of oxygen due to a higher basal metabolic rate. These factors significantly reduce the time to desaturation following the induction of anaesthesia

• During transfer, PEEP should be applied and maintained in mechanically ventilated patients, including clamping the endotracheal tube during disconnection of the breathing circuit to prevent PEEP loss.
• Cephalad displacement of the diaphragm can also be exaggerated during ambulance transfer as a result of deceleration forces, which can reduce compliance.

It is important to position the patient head-up to improve lung mechanics and reduce atelectasis

• Given the higher incidence of obstructive sleep apnoea and obesity hypoventilation syndrome caution should be exercised when administering sedative agents to non-ventilated patients due to the risk of airway obstruction and respiratory acidosis.

Cardiovascular Management

• Obesity is associated with increased risk of cardiovascular morbidity including systemic and pulmonary hypertension, arrhythmias, ischaemic heart disease, heart failure, venous thromboembolism and stroke.
• Patients living with obesity have increased cardiac output and cardiac workload, which can be worsened by pain and anxiety during transfer by producing a sympathetic response.
• Inter-hospital transfer may provoke cardiovascular instability, particularly in hypovolaemic patients, which may be poorly tolerated in obesity.

Be mindful of undiagnosed cardiovascular co-morbidities and ensure patients are adequately fluid resuscitated beforehand to prevent hypotension

• On longer transfers, it might be appropriate to mitigate venous thromboembolism risk using intermittent calf compression and ensuring adequate hydration.

Other Considerations

• Obesity is strongly associated with increased insulin resistance and the development of type 2 diabetes. Consider blood glucose monitoring for longer transfers.
• Patients with high BMI are at higher risk of pressure sores. Ensure pressure points are padded, particularly in sedated patients, and that they are properly and safely secured into the stretcher.

References