What is OSA? Why does OSA matter? And does STOP BANG help us truly identify OSA?

OSA is:

  • cessation of airflow >10sec, 5+x/hr + 4% desat in SaO2
  • definitions vary, but >15x /hr is diagnostistic
  • dx by polysomnography
  • Apnea/hypopnea index (AHI), which is derived from the total number of apneas and hypopneas divided by the total sleep time (mild up to 15, severe >30)


Obstructive Sleep Apnea (OSA) matters because:

  • harder to intubate, harder to ventilate
  • increased prevalance of cardiac disease: Afib, arrhythmias, stroke, CHF, cardiomyopathy, pulmonary hypertension, CAD
  • periop complications higher, including airway obstruction, hypoxemia, atelectasis, pneumonia
  • more sensitive to respiratory depressant effect of opioids and hypnotics


Is STOP BANG Helpful?

The literature shows…

“The sensitivities of the STOP questionnaire with apnea-hypopnea index greater than 5, greater than 15, and greater than 30 as cutoffs were 65.6, 74.3, and 79.5%, respectively. When incorporating body mass index, age, neck circumference, and gender into the STOP questionnaire, sensitivities were increased to 83.6, 92.9, and 100% with the same apnea-hypopnea index cutoffs.”


And what are these complications?

Mostly pulmonary, with a few possible cardiac events mixed in as noted in this study in Chest, cited in Miller’s 8th edition(


Variables ODI4% Age, yr Sex BMI, kg/m2 Type of Surgery Complication
ODI 4%< 5 0.2 27 F 46.7 Laparoscopic gastric bypass surgery Transient episodes of unspecified tachyarrhythmia during the first 3 postoperative days
3.0 52 F 59.4 Laparoscopy with conversion to open ventral herniorrhaphy and adhesiolysis Hypoxemia treated with supplemental oxygen and BPAP
ODI 4%≥ 5 5.5 49 F 26.2 Total abdominal hysterectomy and right salpingoophorectomy cystoscopy with placement of ureteral catheters Hypoxemia was observed on postoperative day 3 and treated with oxygen supplementation; atelectasis was noted
6.0 49 F 39.1 Total abdominal hysterectomy and bilateral oophorectomy Intraperitoneal bleeding was treated with embolization
6.2 39 F 44.9 Laparoscopic gastric bypass surgery Intraperitoneal bleeding which resolved without surgery
7.6 61 M 33.5 Sigmoid colon resection Hypoxemia and hypotension.
12.9 64 M 37.0 Mitral valve replacement Hypotension and junctional escape rhythm
13.0 57 M 38.9 Laparoscopic colonic polypectomy Atelectasis
14.5 58 F 41.6 Total abdominal hysterectomy and bilateral oophorectomy Atelectasis
18.6 62 M 37.3 Left inguinal herniorrhaphy Wheezing observed which required treatment with bronchodilators
24.6 49 F 28.1 Total abdominal hysterectomy and bilateral oophorectomy Pneumonia
26.3 53 F 47.9 Gastric bypass surgery GI bleeding
31.9 50 M 29.6 Radical prostatectomy Hypoxemia treated with CPAP
34.1 62 F 31.4 Total abdominal hysterectomy and bilateral oophorectomy Atelectasis
34.2 69 M 36.9 Laparoscopic right hemicolectomy Pulmonary embolism; superior mesenteric vein thrombosis
36.4 55 F 49.5 Exploratory laparotomy, adhesiolysis, small bowel resection, partial hepatic resection, gastric bypass Chest pain (MI was ruled out)
82.4 66 F 46.8 Total abdominal hysterectomy and bilateral oophorectomy Hypoxemia treated with CPAP


F = female; M = male; BPAP = bilevel positive airway pressure. See Table 1 for abbreviation not used in the text.

lefort !

A nice rundown of Anesthetic considerations available at Continuing Education in Anesthesia, Critical Care and Pain (2014):

A few of the key points:

  • Nasal intubation preferred, and smooth extubation is essential
  • Watch out for local anesthestic toxicity, and they use lots of epinephrine
  • PONV is critical to avoid – use copious anti-emetics and go for TIVA
  • Remifentanil helps smoothen anesthetic and smoothens extubation
  • P/O ICU is historical, blood loss is minimal
  • Severe malocclusion can be intubation difficult
  • Surgeons prefer induced hypotension to minimize bleeding, remi helps this
  • Know post-op if patient will have wired jaw (clippers at bedside in pacu)
Quite the jaw thrust
Quite the jaw thrust (from Elsevier, via article cited)

Dry Lungs?

Fluid in Thoracic Surgery: Time to move overthrow Immortan Joe?
Fluid in Thoracic Surgery: Time to overthrow Immortan Joe?

The Classic Teaching from Miller 8th Edition ch 66 Anesthesia for Thoracic Surgery

Total positive fluid balance in the first 24-hour perioperative period should not exceed 20 mL/kg.

For an average adult patient, crystalloid administration should be limited to less than 3 L in the first 24 hours.

No fluid administration for third-space fluid losses during pulmonary resection.

Urine output greater than 0.5 mL/kg/h is unnecessary.

If increased tissue perfusion is needed postoperatively, it is preferable to use invasive monitoring and inotropes rather than to cause fluid overload.

And so the above was also consistent with the clinical teaching at my institution. Keep them dry, regardless of whether it was a wedge resection, lobectomy or esophagectomy (I haven’t had the pleasure of a pneumonectomy yet).

But further reading in Barash (Clinical Anethesia Fundamentals), calls this into question in ch 34 Anesthesia for Thoracic Surgery, with the following one liner broadside:

“Fluid management for all thoracic procedures should follow either a restricted or a goal-directed protocol. However, recently, concerns about acute kidney injury have called into question the strategy of fluid restriction in thoracic surgery.”

And later in the same chapter, a “Did You Know?” sidebar reinforces the same point, specifically mentioning esophageal surgery and the controversy around restrictive fluid management.

When asked about this in the operating room, the Thoracic Surgery team even indicated that anesthesiologists in this practice are being too restrictive, especially with the esophagectomies (which are for the most part, abdominal surgery).

So what is one to make of this?

Digging into the literature, there was a nice summary of the controversy and recent data at Current Opinion in Anaesthesiology  (doi: 10.1097/ACO.0b013e32835c5cf5) from a team of anesthesiologists at Yale. The article provides a nice run down on the basis of the fluid restrictive strategies (mainly studies from the 198os) and how these studies were performed before the advent of lung protective ventilation strategies (6-8cc/kg and use of peep). They do agree that fluid restriction in Pneumonectomy is logical:

In pneumonectomy, the whole cardiac output will be directed to the remaining lung. This volume in the presence of a decreased vital capacity may overwhelm the remaining lung’s protective mechanisms resulting in a rise in the pulmonary capillary filtration pressure.

However, this may not be the case in lesser lung resections, with a restrictive therapy threatening to cause Acute Kidney Injury. In fact, the belief that renal injury is low in thoracic surgery appears misplaced, as old data only counted kidney injury if patients required renal replacement therapy. Newer evidence shows thoracic patients are at higher risk of AKI than previously thought and that this may cause increased M&M in the longer term.

The authors then go on to promote a Normovolemia and Goal-Directed fluid therapy regiment. One study showed a simple normovolemia method of replacing ongoing losses and use of maintenance fluids i/o and post-op until PO intake, reduced both AKI and extravascular lung water (EVLW). The goal-directed therapy targets Cardiac Index through either Thermodilution, PiCCO, Transesophageal Doppler, SVV or PPV.  The authors point out that while controversy remains, there is some evidence showing no increase in EVLW with goal-directed fluid therapy when lung protective ventilation strategies are used.

The remainder of the article goes into the colloid vs. crystalloid debate, which is beyond the scope of this post, and it appears there is no evidence of which is better to use in thoracic surgery (potential for future research questions!).

So in conclusion, it appears that Dry Lungs may not be the Best Lungs and Best Kidneys for Thoracic Surgery.