Jay B. Brodsky

Morbid Obesity and Tracheal Intubation

The tracheas of obese patients may be more difficult to intubate than those of normal-weight patients. We studied 100 morbidly obese patients (body mass index >40 kg/m2) to identify which factors complicate direct laryngoscopy and tracheal intubation. Preoperative measurements (height, weight, neck circumference, width of mouth opening, sternomental distance, and thyromental distance) and Mallampati score were recorded. The view during direct laryngoscopy was graded, and the number of attempts at tracheal intubation was recorded. Neither absolute obesity nor body mass index was associated with intubation difficulties. Large neck circumference and high Mallampati score were the only predictors of potential intubation problems. Because in all but one patient the trachea was intubated successfully by direct laryngoscopy, the neck circumference that requires an intervention such as fiberoptic bronchoscopy to establish an airway remains unknown. We conclude that obesity alone is not predictive of tracheal intubation difficulties.

Surgery during pregnancy and fetal outcome

As many as 2% of all pregnant women undergo surgery during gestation, but there are few reports of the effects of anesthesia and surgery on fetal outcome. The present paper presents information on 287 women who had surgery during pregnancy. Surgery during early pregnancy was associated with a significant increase in the rate of spontaneous abortion compared to the rate in a control group that did not have surgery. There were no differences in the incidence of congenital abnormalities in this offspring of women who had surgery during early pregnancy. The data suggest that elective surgery be deferred during early pregnancy to minimize potential fetal loss.

Tracheal Diameter Predicts Double-lumen Tube Size: A Method for Selecting Left Double-Lumen Tubes

Linear regression analysis (method of least squares) was used to evaluate tracheal width as related to patient height, weight, and age. The relationship between gender and tracheal width was assessed with analysis of variance. P < 0.05 was considered statistically significant.

Airway rupture from double-lumen tubes

A DOUBLE-CUFFED double-lumen endobronchial tube (DLT) was used for the first time during thoracic surgery almost 50 years ago to isolate and selectively ventilate the lungs. The benefits of DLTs in terms of improved surgical exposure mad their ability to isolate and protect the lungs during thoracic operations are now widely recognized. Although DLTs are safe and easy to use, complications occur. Table 1 lists the complications associated with DLTs. The most common problems involve tube placement. Rarely, the trachea or bronchus is injured, and even then, trauma to the airway is usually minor, resulting in laryngitis or tracheal irritation. More serious airway damage was a recognized complication of the original red rubber (RR) DLTs. When the softer plastic polyvinylchloride (PVC) DLTs were introduced in the early 1980s, it was initially befieved that these tubes were safer than RR tubes. 1,2 However, reports of airway injury from PVC DLTs soon appeared. The medical literature on airway disruption with DLTs was reviewed to try to identify factors associated with this potentially devastating complication.

Left double-lumen tubes: clinical experience with 1,170 patients

MODERN DISPOSABLE plastic double-lumen tubes (DLTs) are generally safe and easy to use.1,2 However, a misplaced or improperly used DLT can jeopardize any procedure and even injure the patient. This article reviews considerations for the selection and placement of left-sided DLTs based on data collected from a large series of patients undergoing thoracic procedures requiring one-lung ventilation (OLV) at this institution. Although the information presented represents the authors’ experience at a single center, others can apply many of the lessons in their own practices. With the permission of the Human Subjects Committee at Stanford University Medical Center, over an 8-year period from 1993 and 2001, 1,170 consecutive patients undergoing anesthesia for noncardiac, general thoracic surgical procedures were studied. All patients were anesthetized by anesthesia residents under the supervision of one of the authors (JBB). At the time of operation, patient sex, height, weight, site, and type of surgical procedure were recorded. When the patient’s chest radiograph (CXR) was available the width of trachea, and in some patients the width of the left bronchus, were measured. The size of the DLT selected, the depth of placement of the DLT in the bronchus, and the volume of air used to inflate the bronchial cuff were recorded. Data are reported as the mean standard deviation unless indicated otherwise. Relationships between parameters were analyzed using regression analysis. Any difficulties encountered, complications, or changes in tube position during the procedure were also noted. Data for measured parameters were not complete for some patients.

Methods for Single-Lung Ventilation in Pediatric Patients

We reviewed published values for airway measurements in children (Table 1) (1,2). Data from the first study was derived by analyzing fresh autopsy specimens of intact tracheo-bronchial trees from 160 children between the ages of 6 mo and 16 yr (1). Thin cross-sections of the airways were made at various levels and photographed on color slides. By using a metric rule photographed with the specimen, measurements were read from the projected slides. The second set of data was obtained from chest computed tomographic examinations of 130 children from 1–21 yr of age (2). The trachea is elliptical in shape, with the frontal diameter exceeding the sagittal diameter. Because the sagittal dimension is the “limiting” diameter and determines the largest tube that will fit, the sagittal measurement was used as our value for tracheal diameter. Data for bronchial dimensions were calculated using measured tracheal-to-bronchial ratios in children (3). Tube dimensions were obtained from each manufacturer and by direct measurement by a biomedical engineer using calipers accurate to within 0.025 mm.

The Dose of Succinylcholine in Morbid Obesity

The appropriate dose of succinylcholine (SCH) in morbidly obese patients is unknown. We studied 45 morbidly obese (body mass index >40 kg/m2) adults scheduled for gastric bypass surgery. The response to ulnar nerve stimulation of the adductor pollicis muscle at the wrist was recorded using the TOF-Watch SX® acceleromyograph. In a randomized double-blind fashion, patients were assigned to one of three study groups. In Group I, patients received SCH 1 mg/kg ideal body weight, in Group II 1 mg/kg lean body weight, and in Group III 1 mg/kg total body weight. After SCH administration, endotracheal intubating conditions were scored. The recovery from neuromuscular block was recorded for 20 min. There was no difference in the onset time of maximum neuromuscular blockade among groups, but maximum block was significantly less in Group I. The recovery intervals were significantly shorter in Groups I and II. In one third of the patients in Group I, intubating conditions were rated poor, whereas no patient in Group III had poor intubating conditions. Our study demonstrates that for complete neuromuscular paralysis and predictable laryngoscopy conditions, SCH 1 mg/kg total body weight is recommended.

Estimating Blood Volume in Obese and Morbidly Obese Patients

Preoperative assessment of blood volume (BV) is important for patients undergoing surgery. The mean value for indexed blood volume (InBV) in normal weight adults is 70 mL/kg. Since InBV decreases in a non-linear manner with increasing weight, this value cannot be used for obese and morbidly obese patients. We present an equation that allows estimation of InBV over the entire range of body weights.

Exposure to Nitrous Oxide and Neurologic Disease among Dental Professionals

Questionnaires, mailed to approximately 30,000 dentists and an equal number of dental assistants requesting information regarding professional exposure to anesthetics and health problems, showed an increased incidence of neurologic complaints in dental professionals who worked with nitrous oxide. The most striking differences were noted in individuals reporting symptoms of numbness, tingling, and/or muscle weakness. For dentists heavily exposed to nitrous oxide, the rate of these complaints was 4-fold greater than for nonanesthetic-exposed dentists. For dental assistants heavily exposed to nitrous oxide, a 3-fold increase in these same complaints was noted. In view of recent evidence that nitrous oxide abuse may lead to polyneuropathy, the results suggest that occupational exposure to nitrous oxide by both dentists and dental assistants may be associated with similar neuropathy.

Lean Body Weight Scalar for the Anesthetic Induction Dose of Propofol in Morbidly Obese Subjects

BACKGROUND: The unique anesthetic risks associated with the morbidly obese (MO) population have been documented. Pharmacologic management of these patients may be altered because of the physiologic and anthropometric changes associated with obesity. Unfortunately, studies examining the effects of extreme obesity on the pharmacology of anesthetics have been sparse. Although propofol is the induction drug most frequently used in these patients, the appropriate induction dosing scalar for propofol remains controversial in MO subjects. Therefore, we compared different weight-based scalars for dosing propofol for anesthetic induction in MO subjects. METHODS: Sixty MO subjects (body mass index ≥40 kg/m2) were randomized to receive a propofol infusion (100 mg · kg−1 · h−1) for induction of anesthesia based on total body weight (TBW) or lean body weight (LBW). Thirty control subjects (body mass index ⩽25 kg/m2) received a propofol infusion (100 mg · kg−1 · h−1) based on TBW. Syringe drop was used as the marker for loss of consciousness (LOC), at which point the propofol infusion was stopped. The propofol dose required for syringe drop and time to LOC were recorded. RESULTS: Total propofol dose (mg/kg) required for syringe drop and time to LOC were similar between control subjects and MO subjects given propofol based on LBW. MO subjects receiving a propofol infusion based on TBW had a significantly larger propofol dose and significantly shorter time to LOC. There was a strong relationship between LBW and total propofol dose received in all 3 groups. CONCLUSION: LBW is a more appropriate weight-based scalar for propofol infusion for induction of general anesthesia in MO subjects.