Anaesthetic management for a patient with morbid obesity

Arop Kual, senior anaesthetist at the Princess Marina Hospital in Botswana, and authors,  share a case report to address the important key issues relevant to peri-operative anaesthetic management of the obese patient presenting for general surgery

The purpose of this case report is to describe our experience in anaesthetic management of a patient with morbid obesity undergoing general surgery. The obese patient is most likely prone to develop peri-operative impairments of respiratory and cardiovascular functions. Moreover, the obese patient might stand a chance of airway problems at times of tracheal intubation. The difficulties in moving and positioning the patient and difficulties in gaining access for monitoring and venous cannulation add to the problems. Anaesthesia and surgery may present a considerable risk for the obese patient and should not be undertaken lightly without full understanding of the potential’s problems. This case report addresses the important key issues relevant to peri-operative anaesthetic management of the obese patient presenting for general surgery.

 

Case Report

Anaesthesia in the morbidly obese patient can present many challenges. The concern of most anaesthetists is airway management. It is traditionally thought that obese patients stand a chance of difficult airway or difficult intubation [1]. Besides the many challenges in our settings, such as the limited advance airway equipment for managing a difficult airway scenario; this made the case more interesting and challenging although we had a backup of a fibreoptic video-intubating laryngoscope which we would borrow from the ENT team in case we failed to intubate with the standard ordinary blade laryngoscope.

We describe a 165-Kg morbidly obese female patient (25 years old) whose height was 163.5 cm and {Body mass index (BMI) > 61.1 kg / m²} who underwent ventral hernia repair. The body max index was calculated using the following formula: BMI = body weight (in kg)/height² (in meters).

Pre-operative anaesthetic evaluation revealed Mallampati Class III with almost an absent neck, the thyromental distance was estimated to be < 6 cm, and there was limited range of motion of her head and neck. All lab variables and vital signs were within normal ranges.

The patient was positioned supine and all monitors were attached (Pulse oximetry, NIBP and ECG). The patient was pre-oxygenated with 100% O₂ via facemask. She was then pre-medicated with Metoclopramide 10 mg IV and anaesthetised with Propofol 200 mg IV and Suxamethonium 100 mg IV. The first intubation attempt was unsuccessful as the use of a smaller laryngoscope blade (size 4 Macintosh) could not help in visualising the cords properly. In the second attempt the patient was intubated with size 7.00 mm endotracheal tube (ETT) using size 5 Macintosh blade. A size 3 oropharyngeal airway was also inserted. The patient was ventilated mechanically using a volume control mode with a tidal volume of 1000 mls at a rate of 6mls – 8mls / minute, Sevoflurane 0-3.5 % was given. The peak inspiratory pressure was 35 cmH₂O and the I:E ratio of 1:2. A non-depolarising muscle relaxant (Atracurium 50 mg in total) was used during mechanical ventilation.

The patient remained hemodynamically stable during surgery and the emergence from anaesthesia was uneventful. She was ultimately extubated and transferred to Post-Anaesthesia Care Unit (PACU). At the PACU the patient was ventilated with only a nasal cannula without any difficulty post-operatively. The whole anaesthesia course was uneventful.

 

Discussion

The World Health Organization (WHO) regards a BMI of less than 18.5 as underweight and may indicate malnutrition, while a BMI equal to or greater than 25 is considered overweight and above 30 is considered obese. These ranges of BMI values are valid only as statistical categories.

To date, there are no reports of large patients as ours being anaesthetised and operated at Princess Marina Hospital. The anaesthetic management of an obese patient can be a real challenge to the anaesthestist, the surgeon and the whole operating team. There are several management strategies that must be considered when planning an anaesthetic for a morbidly obese patient. An operating room with sufficient space is required. Positioning of the patient should not be taken lightly as once anaesthetised; morbidly obese patients are difficult to move to any position. In the absence of lifting equipment such as Maxi Slide made it difficult in our case. Ideally two operating tables should be placed side by side to accommodate the patient [2]. In this case report only one table was used as the absence of a bariatric table made it difficult in our case.

Appropriate preparation of the airway management equipment and devices is essential as a difficult airway scenario must be anticipated in such patients. A difficult airway trolley should be readily availed. Mechanical ventilation is also another challenge as the obese patient tend to be associated with high intra-abdominal pressure and decreased functional residual capacity (FRC), end-expiratory lung volume, and total lung capacity (TLC). During general anaesthesia with muscle paralysis due to the use of muscle relaxants, there is a further reduction of lung volumes that is causally related to increasing BMI.

 

Pharmacokinetics & pharmacodynamics

Obesity results in variation in drug pharmacokinetic & pharmacodynamic profiles, thus making drug dosing challenging as most of the data on drug dosing are from non-obese patients [3]. The increase in extracellular volume, the larger fat mass and lean body weight all affect drug pharmacokinetics. Added to the above mentioned, the volume of distribution of lipophilic drugs is greater than in normal-weight patients, whereas the hydrophilic drugs do not vary as much. The choice to use ideal body weight (IBW) or total body weight to calculate drug dosages is not always clear. For example paralytics are dosed based on IBW and most analgesics are based on lean body weight. Due to the large doses required with the increased distribution volume and the risk of prolonged effects after discontinuation, lipophilic drugs such as barbiturates, benzodiazepines, and volatile inhalation agents, should be used with caution or minimally in obese patients. Anaesthesia can be easily maintained by either intravenous anaesthesia (IV) or inhalation anaesthesia.

The ideal inhalational anesthetic has a short onset and short, reliable recovery profile. Desflurane is the inhalational agent of choice in obese patients, but sevoflurane can also be used as in this case report, because it has similar results to desflurane.

 

Pulmonary System

Obese patients are at increased risk of having difficult to handle airways, as bag mask valve ventilation and intubation can be challenging. While increased BMI does not predict difficulty with laryngoscopy or tracheal intubation, greater neck circumference (>40 cm) and higher Mallampati score (>3) were better predictors of difficult intubation.

Although most patients in a supine position may successfully undergo tracheal intubation, other adjuncts, such as flexible fiberoptic wake-up intubation, video –assisted laryngoscopy and laryngeal mask airway (LMA), should be readily available.

As the FRC in obese patients is diminished, lengthy periods of apnea are not tolerated and patients easily deoxygenate ⁽⁴⁾. It is therefore recommended that preoxygenation be used for denitogenation using 100% fraction of inspired oxygen (FiO₂).

In the preintubation process, it is often suggested that the use of continuous positive airway pressure (CPAP) at 10 cmH₂O to reduce the development of atelectasis. A typical intubation position for obese patients, using shoulder towels, is the reverse Trendelenburg or head-up position 25 to 40 degrees.

With the rise in BMI, obese patients with decreased forced expiratory capacity, FRC, and expiratory reserve capacity show a restrictive trend.

Lung volume, and compliance with the lung and chest wall also decrease. For obese patients an increase for oxygen intake, respiratory resistance, and breathing function is observed.

These changes result in gas trapping with mismatching ventilation-perfusion, hypoxemia, and atelectasis which gets worse with anaesthesia and paralysis. Furthermore, there is a higher incidence of obstructive sleep apnea (OSA), with concentrations of bariatric patients varying from 30 to 93%.

The American Association of Clinical Endocrinologists (AACE), the Obesity Society (TOS), and the American Society for Metabolic and Bariatric Surgery (ASMBS) support polysomnographic preoperative screening and preoperative CPAP in patients at risk. But the preoperative CPAP in this patient was not done.

It has been shown that preoperative CPAP decreases severe hypoxemia, pulmonary vasoconstriction, hospital length of stay and postoperative complications.

Postoperative CPAP decreases the risk of restrictive pulmonary disease and acute respiratory distress syndrome.

The use of postoperative CPAP therapy is recommended when pulse oximetry reaches 90% while sleeping and IV medications are no longer required for pain relief. There are no specific guidelines on ventilator methods or modes for obese patients; however, in the anaesthesiology literature recommendations require the use of at least 10 cmH₂O of post-end expiratory pressure (PEEP) after induction.

Respiratory rate should be balanced to retain pneumoperitoneum absorbed normocapnia and offload carbon dioxide.

The use of high tidal volumes, PEEP and critical capacity manoeuvre to improve ventilation and oxygenation was recorded, although [5] showed little gain in high tidal volumes in an attempt to sustain FRCs. Extubation should be done after the defensive airway reflexes have been assessed and the recovery of muscle strength has been assessed, the patient is fully awake and able to execute commands and in the reverse Trendelenburg position. Once extubated, continuous pulse oximetry is used to detect subclinical periods of desaturation.

Following major surgery, supplemental oxygen should be given, with some physicians suggesting treatment times of at least 24 to 48 hours. Nasal CPAP was also prescribed postoperatively, in addition to supplemental oxygen particularly in this patient.

 

Cardiovascular System

Obesity is a significant coronary heart disease risk factor and above all Obesity patients will undergo a heart examination prior to elective surgery; Left ventricular hypertrophy, since they are at higher risk for critical hypertension, pulmonary hypertension, and heart obstruction [6].

Work-up should cover chest X-ray, 12-lead echocardiography and polysomnography in patients with OSA. The recommendations for Echocardiography, Spirometry, AACE / TOS / ASMBS, only if the patient has additional risk factors, and arterial blood gases. Their guidance recommends “heart disease-prone patients”.

Perioperative beta-blockers are recommended in healthy or suspected coronary artery disease patients. If contraindicated. “Several side effects of beta-blockade, however, such as impaired tolerance to glucose, decreased insulin resistance and other metabolic anomalies, can be dangerous in highly obese patients or patients with metabolic syndrome. Other medicinal products including antihypertensives can be continued preoperatively. Routine intraoperative hemodynamic surveillance should be started using telemetry and controlling blood pressure.

Blood pressure armrests should be long enough to encircle at least 75% of the arm and the width of 40% of the arm. Arm invasive monitoring of arterial or pulmonary catheters may be needed in superobese patients with serious cardiopulmonary disease (> 60 BMI), all with access difficulties, and poor noninvasive cuff readings in patients.

Transesophageal intraoperative echocardiography is recommended to be used but no data exist supporting routine implementation. The American College of Cardiology (ACC) and the American Heart Association (AHA) Task Force 2007 suggest postoperative cardiac monitoring in patients with single or multiple coronary artery risk factors.

 

Conclusion

Obesity is increasing in Botswana especially among female patients from our experience. This poses a high risk to patients undergoing anaesthesia and surgery. It is a concern for anaesthetists, surgeons and nurses to thoroughly assess and prepare for the possible risks associated with such kind of patients. It is anticipated that this case report explained the key issues in the management of obese patients who might require a multi-disciplinary team for a successful surgery and hospital stay providing a relevant reference for practicing anaesthetists, surgeon and nurses involved in the perioperative management of such challenging cases and increasingly uprising in patient population.

 

 

 

References

1. Myatt, J., & Haire, K. (2018). Airway management in obese patients. Current Anaesthesia & Critical Care, February 2010. https://doi.org/10.1016/j.cacc.2009.09.004
2. FISHER, A., WATERHOUSE, T. D., & ADAMS, A. P. (1975). Obesity: its relation to anaesthesia. Anaesthesia, 30(5), 633–647. https://doi.org/10.1111/j.1365-2044.1975.tb00924.x
3. Baerdemaeker, L. De, & Margarson, M. (2016). Best anaesthetic drug strategy for morbidly obese patients. 119–128. https://doi.org/10.1097/ACO.0000000000000286
4. Boyce, J. R., Ness, T., & Gleysteen, J. J. (2003). A Preliminary Study of the Optimal Anesthesia Positioning for the Morbidly Obese Patient. 4–9.
5. Cullen, A., & Ferguson, A. (2012). Perioperative management of the severely obese patient: A selective pathophysiological review. Canadian Journal of Anesthesia, 59(10), 974–996. https://doi.org/10.1007/s12630-012-9760-2
6. Leonard, K. L., Davies, S. W., & Waibel, B. H. (2015). Perioperative Management of Obese Patients. Surgical Clinics of NA, 95(2), 379–390. https://doi.org/10.1016/j.suc.2014.10.008

 

Authors

Arop MD Kual, Senior Anaesthesiologist, Department of Anaesthesia & ICU (Princess Marina Hospital), Nkhabe Chinyepi, General Surgeon, Department of General Surgery (University of Botswana), Katlo Rainy Diane, Medical Officer, Department of Anaesthesia & ICU (Princess Marina Hospital), Karabo Ngwako, resident in general surgery, Department of General Surgery (University of Botswana), Rashid Lwango, Medical Officer – Department of General Surgery (University of Botswana), Gaborone – (Botswana)