Blog with interesting cases and/or problems related to anesthesia with discussion based on best evidence in the literature.

April 9, 2016

A patient with BMI of 54 reqiures Quad tendon repair in ASC

A few days ago I was called and told that our friendly Orthopedic surgeon wanted to repair a Quad tendon in a patient with a BMI of 54.  This is significant, because for years the ASC where this case was posted had a policy that no patient with a BMI greater than 50 could have a procedure at the facility.  This had resulted in multiple cases where surgeons were forced to take their cases elsewhere.  For some it is a minor inconvenience, however, for others, it becomes a real problem because they have little alternatives.
I had recently requested to the medical director that this policy be revisited.  In response to this, I was asked to evaluate this patient on the day of the procedure and determine if it was suitable case to be in on an outpatient setting.

Morbid obesity has generally been recognized as a risk factor for anesthesia.  In fact, right or wrong, I have a practice of assigning any patient with a BMI greater than 40 an ASA score of III.  On the other hand, should surgery automatically be proscribed in an ASC based upon the sole fact that a BMI is greater than 50?  Is there evidence to support this practice?  The reasoning for this policy as presented to me by several of my partners is that patient safety should be the first priority.  Of course this presupposes that my first priority is not patient safety; but beyond this fact, is this really true based on the evidence available to us.  I agree, that certainly it would seem that patients with a higher BMI might have a higher risk of complications with anesthesia.  But does our intuition in this regard bear out when the evidence is reviewed?

Most anesthesiologists consider airway difficulty to be a prime consideration when approaching a morbidly obese patient.  However, in reality, morbid obesity (MO) does not predict difficult laryngoscopy [1].  Brodsky and associates concluded that MP score and neck circumference were the only real predictors of difficult intubation [1]. Others have created scoring tools that consider a variety of different physical factors that could predict difficult intubations.  Ame and Colleagues [2] produced a new scoring system based on a multifactorial analysis and were able to predict difficult intubations with greater than 90% sensitivity and specificity.  MO was not on their list.

LEMON airway assessment
L=Look externally (facial trauma, large incisors, beard, large tongue)
E=evaluate the 3-3-2 rule (incisor distance [3 finger breadths], hyoid-mental distance [3 finger breadths], thyroid-hyoid distance [2 finger breadths]).
M=mallampati score greater than or equal 3
O=Obstruction (presence of any condition like epiglottitis, peritonsiallar abscess, trauma)
N=neck mobility (limited neck mobility)
Most anesthesiologists assume that pulmonary complications are increased after anesthesia in the MO patient.  However, patient's weight, BMI, or preoperative lung function tests are not accurate predictors of posteroperative complications [3]. Others have found that in patients with co existing pulmonary disease the rate of pulmonary complications is 38% vs. 12% in obese patients in upper abdominal surgery [4].  However, in other types of surgery such as minor surgery of the foot, ankle or knee, there may not be any differences between groups. In obese patients without co existing pulmonary complications having open cholecystectomy, mortality is not different from their normal weight counterparts [5]. However, in patients with obesity with co existing cardiorespiratory disease or significant CO2 retention, and have undergone prolonged procedures or who have developed pyrexia after the operation have a higher risk of requiring postoperative MV [6].

Obstructive Sleep Apnea may be more common in obese patients, however, there are many obese patients who do not have OSA, and vice versa.  Nevertheless, a patient with significant obesity, BMI greater than 50 for example who present for ambulatory surgery with a diagnosis of OSA needs further review as there are multiple studies that suggest that the combination of super obesity and OSA combined place patients at higher risk after anesthesia.  The ASA has created a scoring tool that can serve as an aid to the clinician evaluating a MO ambulatory patient with OSA.  It should be noted that this tool is not a requirement, but a guideline used to assess the overall situation.

ASA ambulatory OSA scoring tool

A. Severity of Sleep Apnea (based on sleep study or clinical indicators)
None -          0 pts
Mild -           1 pt
Moderate -   2 pts
Severe -        3 pts
B. Invasiveness of surgery and anesthesia
Superficial surgery under local/pnb no or minmal sedation -         0 pts
Superficial surgery w/ mod sedation/GA -                                   1 pt
Peripheral surgery w/ neuraxial anesthesia mod sedation -            1 pt
Perpheral surgery w/ GA  -                                                         2 pts
Airway surgery w/ mod sedation -                                               2 pts
Major Surgery, General Anesthesia -                                           3 pts
Airway Surgery, General Anesthesia-                                           3 pts
C. Requirements for postoperative opioids
None -   0 pts
low-dose oral opioids -     1 pts
high dose oral opioids  -     3 pts

To score: Add points from Section 'A' to either section 'B' or 'C' (not both), whichever is greatest.  Subtract one point for patients who are compliant with CPAP before and will use after.  Add 1 point if a patietn with mild or moderate OSA has a resting PaCO2 greater than 50 mmHg.
A score of 4 indicates possible increased perioperative risk, scores of 5 to 6 may be at significantly increased perioperative risk from OSA.

Furthermore, the ASA Task force on Practice Guidelines state that patients with a known dx of OSA, but optimized comorbid medical conditions can be considered for ambulatory surgery if they are able to use a CPAP device in the post operative period. They also state, "patients with a presumed diagnosis of OSA with optimized comorbidities can be considered for ambulatory surgery, if post operative pain can be managed predominantly with nonopioid techniques".

While the above can serve as a guide in the overall assessment of a patient presenting for ambulatory surgery it should be considered along with other data gathered prior to surgery.  In fact, a recent systematic review was conducted in ambulatory surgery patients with OSA [7].  Although, there were more frequent oxygen desaturation episodes requiring oxygen supplementation, there were no differences between the OSA and non-OSA patients with respect to anesthesia-related complications, unanticipated hospital admission and mortality.

Recently Joshi and colleagues published an article referencing a systematic review of the literature addressing the selection of adult obese patients scheduled for ambulatory surgery including 23 studies. This review revealed that BMI alone is an inadequate criteria to predict perioperative complications or unplanned admission.  A sub category in this review contained patients who were super obese (BMI greater than 50 kg/m2).  Joshi stated, ...(these patients) " might be associated with a higher risk of postoperative complications, particularly if these patients have significant comorbidities such as OSA, obesity-related hypoventilation syndrome, pulmonary hypertension, resistant systemic hypertension, significant coronary artery disease, resistant cardiac failure, bleeding disorder and chronic renal failure on dialysis."  This comment references a study of laparoscopic bariatric procedures and might not be relevant to surgeries that are more superficial.  Furthermore, this was a retrospective review of cases performed including gastric bypass.  In the methods section the authors admit that the superobese patients were not comparable to the non superobese population having a greater burden of co morbidities.  In addition, this study considered  many end points that are not relevant to perioperative anesthesia complications.

In general, the weight of the evidence suggests that evaluating each patient individually leads to more rational clinical decisions.  Joshi emphasized this point as it relates to the obese patient presenting for ambulatory surgery in another article writing, "BMI or weight should not be used as a sole determinant of suitability for ambulatory surgery. However, the super obese population may require greater attention with respect to preopative evaluation and optimization as well as perioperative care."

I elected to proceed with the case provided that I could do it under spinal anesthesia with a peripheral nerve block.  I was told that the facility had a policy that patients had to remain for eight hours after spinal bupivacaine to ensure that the level had worn off prior to discharge.  They said this would not be permitted since this would be the last case and nurses needed to go home prior to the eight hour cut off.  I therefore, elected to do a lidocaine spinal with peripheral nerve block.  I confirmed with the surgeon that the surgery would be less than one hour.  Unfortunately, the case lasted 2 hours and the patient required some supplemental anesthesia with ketamine and propofol.  In the recovery room it was determined that he had a good obturator block, with sparing of the femoral nerve.

Lidocaine spinal anesthesia has gone out of favor due to an increased incidence of transient neurological symptoms (TNS).  Therefore, multiple studies have been performed looking for alternatives.  Chiu, Carpenter and colleagues published recovery times for lidocaine with and without epinephrine [8]. Resolution of the sensory block occurred after 123 min with 50 mg lidocaine and after 136 min with 75 mg. These same authors were able to demonstrate that with the addition of epinephrine sensory anesthesia is extended by 30 minutes.  Unfortunately, adding 0.2 mg of epinephrine also increased the time to void by one hour [8]. However, by adding 20 mcg fentanyl to lidocaine the duration of sensory anesthesia was increased by 181% without prolonging recovery time [9]. The problem with TNS however, continues to weigh on the use of lidocaine.  An epidemiological study of this phenomenon attempted to identify risk factors for TNS in over 1000 patients [11].  They concluded that only outpatient status and lithotomy position were significant risk factors for TNS with morbid obesity slightly increasing risk.  The rate of TNS after lidocaine was only 3% (comparable to the 1% with bupivacaine) in inpatients not in the lithotomy position vs. 24.3% incidence in outpatients in the lithotomy position.  Importantly, sex, age, history of back pain, lidocaine dose or concentration, were not associated with a higher incidence of TNS.  TNS was also not associated with the type or size of the needle used for injection. While the data in this study indicated that decreasing the dose will not reduce the incidence of TNS, the smallest dose evaluated was any dose less than 50 mg.  Another study found a lower incidence of TNS when 20 mg (plus fentanyl) was compared to 50 mg lidocaine [10]. This has lead to the proposal  that super low dose lidocaine spinals with fentanyl can be used safely in outpatient settings. Others have looked at the mechanism of injury that occurs in TNS. They note that studies in volunteers with TNS have found that nerve function in these patients is normal, however, the conduction of nerve impulses are irreversibly changed in models of lidocaine neurotoxicity.  Therefore, it is believed by some that TNS results from the severe neuromuscular block allowing for musculoskeletal stretch when the patient is in the lithotomy position. It is known that in a lidocaine induced neurotoxicity model, both total dose and concentration correlate with increasing toxicity.

Currently it seems prudent to avoid lidocaine when possible in the outpatient setting, but if required, lower doses (i.e. lower than 50 mg) is recommended.
Bupivacaine spinal anesthesia in the outpatient setting has also lost favor due to unpredictability in duration leading to delays in discharge from recovery. Fortunately, recent studies looking at ultra low dose bupivacaine have been able to circumvent the issue of prolonged block to some degree. A systematic review attempted to determine the feasibility of using bupivacaine in the outpatient setting [12].  They authors conclude that low doses of hyperbaric bupivacaine (4-5 mg) can effectively produce spinal anesthesia with unilateral positioning in knee arthroscopy.  They also found that bilateral spinal blocks with bupivacaine 5 mg led to high failure rate. In studies with doses of 6 to 7.5 mg there was no significant difference in failure rate, but did increase recovery time. They found that at doses of between 4 to 5 mg bupivacaine there was a widely variable time to recovery between 170 to 240 min. In this same review, they were able to confirm that using adjuvant opioids reduced the dose of bupivacaine necessary while improving quality of anesthesia, however, this was at the cost of increased post operative pruritus.   In a head to head comparison with 2 chloroprocaine, 7.5 mg of hyperbaric bupivacaine was found to require 5 1/2 hours for complete sensory regression.  In another study of low dose bupivacaine, time to void was only 2 hours and 45 min when fentanyl (20 mcg) was added to 5 mg bupivicaine with a success rate of 100% [13]. Unfortunately, it is well noted that there is large differences between patients in their time to readiness for discharge after the same bupivacaine dose.  A significant concern when bupivacaine is used for spinal anesthesia is urinary retention.  Therefore, many outpatient centers have a policy that patients must be able to void prior to discharge if they have received spinal anesthesia. However, this shotgun approach to medicine may not be best. Mulroy and colleagues [14], were able to demonstrate that after short acting local anesthetics for spinal or epidural anesthesia, or low dose bupivacaine (no more than six milligrams), patients could be discharged home prior to voiding with no risk of urinary retention at home.  Patient's at higher risk for urinary retention were excluded from this study. This would include patients undergoing inguinal hernia repair, anorectal surgery, urologic surgery or patients older than 70 years old.   The study also prohibited the use of epinephrine which is associated with a higher incidence of urinary retention.  In this study, patients receiving spinal bupivacaine had an average PACU time of 173 min vs. 155 min for lidocaine. Pavlin and colleagues, demonstrated that other risk factors for urinary retention included urinary catheterization, excessive IV fluid administration, pain and anxiety [15].
After considering all the data above, it is clear that routine spinal anesthesia in the outpatient setting is likely not beneficial. However, spinal anesthesia should not be outright proscribed by facilities based on outmoded ideas or unjustifiable fears. Furthermore, mandatory requirements for patients stay after spinal is not helpful nor evidence based. Studies to date indicate that spinal bupivcaine can be used in the ambulatory setting without increased risk. Furthermore,  policies dictating arbitrary and inflexible approaches to every patient may be a disservice to patients.








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2. Ame, J et al. Br J Anaesth 1993;70 (suppl): A1.
3. Shenkman, Z Shir Y and Brodsky JB. Br J Anaesth 1993; 70: 356.
4. Buckley FP, et al. Anaesthesia 1983; 38: 840-51.
5. Pemberton LB et al. Amer J Surg 1971;121:87-90.
6. Cooper JR et al. Semin Anesth 1987; 6: 260-70.
7. Joshi GP, Ankichetty S, Gan TJ, Chung F. Anesth Analg 2012; 115: 1060.
8. Chiu AA, Liu S, Carpenter RL et al.  Anesth Analg 1995; 80: 735-9.
9. Liu S, Chiu AA, Carpenter RL et al. Anesth Analg 1995; 80: 730-4.
10. Ben-David B, et al. Anesth Analg 2000; 91:865
11. Freedman JM, et. al. Anesthesiology  1998; 89: 633
12. Nair GS, Abrishami A, Lermitte J, and Chung F. BJA 2009; 102:307-15.
13. Ben-David B, Solomon E, Levin H, et al. Anesth Analg 1997; 85:560.
14. Mulroy MF, Salinas FV, Larkin KL, et al. Anesthesiology 2002;97: 315-9.
15. Pavlin DJ, Rapp SE, Polissar NL et al. Anesth Analg 1998;87:816-26.

1 comment:

Neha Hooda said...

I just wanted to make a quick comment to say GREAT blog!….. I’ll be checking in on a regularly now….Keep up the good work


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