ASA Scientific Papers Emphasize Patient Safety

Glenn S. Murphy, MD; Jeffery S. Vender, MD

Over 1,300 scientific abstracts were presented at this year’s American Society of Anesthesiologists Annual Meeting in New Orleans. Nearly 100 of these abstracts presented data directly related to patient safety. The following will highlight and summarize a few of the many interesting studies that were presented at these poster sessions.

Airway Management

Ovassapian et al. (A-1214) evaluated the status of the lingual tonsils in 33 patients with unexpected failed intubation over an 11-year period. Using a fiberoptic pharyngoscope, the investigators observed that every patient with failed intubation had enlarged lingual tonsils that displaced the epiglottis posteriorly. The authors recommend that patients with unexpected failed intubation should be evaluated for lingual tonsil hyperplasia.

Foss et al. (A-1133) reviewed the airway characteristics of 92 patients who reported a history of a previous difficult intubation. The most common diagnoses associated with this history included oral tumors, morbid obesity, cervical fusion/instability, sleep apnea, angioedema, and radiation changes. On physical exam, approximately one-third of patients demonstrated a Mallampatti Class 4 airway and one-quarter of patients had decreased motion of the neck. Fifteen patients (16.3%) had no diagnosis or physical findings suggestive of a potentially difficult airway. These data demonstrate that many patients who are difficult to intubate may have no findings on history or physical exam to suggest the cause of this potentially life-threatening complication.

Previous retrospective studies have reported a high incidence of postoperative airway obstruction following anterior cervical spine surgery. Venna et al. (A-1171) reviewed the records of 180 patients selected by the surgeon as being at risk for postoperative upper airway edema following anterior cervical corpectomies, arthrodesis, discectomy, and other reconstructive procedures of the upper cervical spine. Conservative airway management was used in all patients, which included postoperative intubation, passing a cuff leak test, and the demonstration of no significant upper airway edema on laryngoscopy. Despite this careful management, 12 patients had post extubation stridor, 5 patients required reintubation, 2 patients required tracheostomy, and 2 deaths occurred due to failed reintubation. Further study is needed to define patients at risk for airway obstruction following cervical spine surgery.

Percutaneous tracheostomy has gained widespread acceptance as a method of achieving long-term airway maintenance. There are a number of contraindications to the performance of this procedure, including difficult cervical anatomy. Byhahn et al. (A-1213) examined the safety and complications of percutaneous tracheostomy in obese (BMI >27.5 kg/m2) and morbidly obese (BMI >35.0 kg/m2) patients. Over a 4-year period, a total of 63 obese and 10 morbidly obese patients were studied. Significant complications included paratracheal dilation on cannula placement, difficult cannula placement leading to hypoxemia, major bleeding, posterior wall tracheal perforation, and cardiac arrest. The incidence of complications was 11.1% in the obese patients, which corresponds to the overall complication rates reported for this procedure. However, a three-fold increase in the incidence of complications (30%) was observed in the morbidly obese patients. These results confirm the authors’ hypothesis that the risk of complications occurring during the performance of percutaneous tracheostomy is increased in the morbidly obese patient.

Postoperative Complications

Hypothermia predisposes surgical patients to numerous complications in the postoperative period. Scheck et al. (A-1122) studied the development of hypothermia in patients undergoing abdominal surgery during transport from the operating room to the ICU. Only 3 of 32 patients who left the operating room normothermic remained normothermic until admission to the ICU; statistically significant reductions in body temperatures occurred during transport of the subjects who were normothermic at the end of surgery. The authors recommend that attention should be focused on measures which reduce heat loss during this vulnerable period.

The incidence and causes of visual loss after anesthesia and surgery remain poorly defined. Roth et al. (A-1170) reviewed the records of 223,796 anesthetics over a 15-year period. Visual loss occurred in 4 patients for an incidence of 1/56,000 or 0.002%. The incidence was 50-times higher in patients following spine surgery in the prone position. There were no differences between affected patients and matched unaffected controls in hemodynamic or fluid management. Although visual loss is a rare complication after surgery, it is far more common after prone spine surgery, and may be related to patient-specific factors which are not influenced by the anesthesia provider (see POVL story).

A higher incidence of adverse events has been reported to occur late at night. Mollenholt et al. (A-1181) prospectively studied the temporal distribution of postoperative adverse events over a 1-year period. A statistically significant increase in adverse events was reported to occur between the hours of 16:30-23:55 (4.8%) and 24:00-7:30 (6.5%) when compared to the daytime hours 7:35-16:25 (3.6%). Since the groups did not differ in ASA status or duration of surgery, the authors speculate that some aspect of anesthesia practice may play a role in the over-representation of adverse events in the early and late evening.

Ulnar neuropathy is the most frequent perioperative nerve injury. Morell et al. (A-1182) measured current perception thresholds to assess ulnar nerve dysfunction in a group of 80 volunteers. Following baseline measurements, the subject’s arm was flexed at the elbow to 110¡ or placed on a rigid surface with pressure on the ulnar groove. Significant alterations in current perception thresholds were produced with arm flexion and direct pressure on the ulnar nerve. C fibers were impaired by direct pressure and flexion, Ad fibers were impaired by direct pressure, and A§ fibers were unaffected by study conditions. Gender differences were found in unmyelinated C fibers subjected to direct pressure, which may help to explain the male propensity for postoperative ulnar nerve dysfunction.

Occupational Hazard

The National Institute of Occupational Safety and Health has recommended exposure limits to trace concentrations of nitrous oxide (25 ppm) and volatile anesthetics (2 ppm). Bueck et al. (A-1081) determined actual exposure of PACU and ICU staff to nitrous oxide and volatile agents. Over an 8-hour work shift, occupational exposure of the PACU staff to desflurane and sevoflurane exceeded the NIOSH thresholds; exposure to nitrous oxide and isoflurane was within recommended limits. In the ICU, where no air conditioning was present, measured levels of desflurane and isoflurane exceeded NIOSH limits by 2- to 3-fold. ICU and PACU personnel should be aware of possible exposure to trace levels of volatile anesthetics. The use of frequent air circulation may reduce occupational exposure.

Aspiration

Pulmonary aspiration of gastric contents is considered a rare but potentially preventable complication of anesthesia and surgery. Neelakanta et al. (A-1193) reviewed all of the cases of aspiration that occurred during a 5-year period. Medical records were examined to determine if any patient-specific or surgical related risk factors were present in patients with clinically observed aspiration. Seven patients (out of a total of 135,550 anesthetics) had documented aspiration of gastric contents into the tracheobronchial tree. All 7 cases occurred in non-obstetric adult patients during elective surgical procedures. Three patients required ICU admission, but all were discharged. Risk factors for aspiration (esophageal/GI surgery, obesity) were present in 6 of the 7 patients. These results demonstrate that pulmonary aspiration is a rare event, and that risk factors for aspiration were documented in most of the patients who developed this complication.

Hyperkalemia

Patients with chronic renal insufficiency or failure often present to the operating room with elevated serum potassium levels. Hyperkalemia is considered a contraindication to anesthesia, as it may predispose the patient to cardiac dysrhythmias. Olson et al. (A-1195) reviewed the Duke anesthesiology database to determine if hyperkalemia in patients presenting for vascular access surgery was a risk factor for perioperative complications. Of the 1472 cases on the surgeon list, 44 of the cases had a documented preoperative potassium level greater than 6.0 mmol/l. Twelve of these patients proceeded directly to surgery. There was no clinical or electrocardiographic evidence of hyperkalemia and no perioperative complications noted in this group of patients. Therefore, asymptomatic hyperkalemia may not be an absolute contraindication to vascular access surgery.

Avoiding the Carotid Artery

Unintentional puncture of the common carotid artery (CCA) is the most common complication occurring during cannulation of the internal jugular vein (IJV). Head rotation can affect the relationship between the CCA and the IJV. Lieberman et al. (A-1176) used ultrasound guidance to determine how changes in head position affect the risk of contact with the IJV and CCA. Forty-nine volunteers were studied. An ultrasound imager was placed on landmarks for a central and anterior approach to the IJV. The subjects’ heads were rotated from 0¡ to 60¡, and investigators recorded if the ultrasound beam crossed the CCA or the IJV. Optimal head rotation was defined as the angle which maximized IJV contact and limited the risk of CCA contact to less than 10%. This was found to be 45¡ in most of the subjects. However, in subjects with a high body surface area or body mass index, optimal head rotation was 30%. These results suggest that the degree of head rotation during IJV cannulation can improve success rates and reduce the risk of CCA puncture.

These brief summaries represent only a portion of the abstracts that were presented on patient safety at the American Society of Anesthesiologists 2001 Annual Meeting. All of the abstracts from this years poster sessions may be viewed at the Anesthesiology website at www.anesthesiology.org.

Dr. Murphy is Assistant Professor of Anesthesiology at Northwestern University and Director of Cardiac Anesthesia at Evanston Northwestern Healthcare. Dr. Vender is Professor of Anesthesiology at Northwestern University and Chairman at Evanston Northwestern Healthcare, Evanston, IL.