Is lower esophageal contractility a reliable indicator of the adequacy of opioid anesthesia?

Abstract

Assessing the adequacy of anesthesia in the patient who is without neuromuscular blockade is usually based on somatic as well as sympathetic and hemodynamic responses to stimulation. Because somatic responses are lost in the patient with neuromuscular blockade, a method is needed to replace these signs as an indicator of inadequate anesthesia. This study attempted to determine the relationship between lower esophageal contractility and somatic signs in detecting inadequate fentanyl anesthesia in 20 patients who were undergoing coronary artery surgery and who were hemodynamically stable in the preoperative period. Premedication included midazolam, 0.05 mg/kg intramuscularly, and ranitidine, 2 mg/kg orally. Anesthesia was induced with fentanyl, 50 µg/kg, and maintained by an infusion of fentanyl, 0.2 µg · kg⁻¹ · min⁻¹. After endotracheal intubation, a disposable 24-F esophageal monitoring probe equipped with provoking and measuring balloons was inserted, and both the amplitude of provoked and the rate of spontaneous lower esophageal contractions were displayed and recorded. Inadequate anesthesia was indicated by defined somatic signs in response to noxious stimulation. The presence of these responses was correlated with the amplitude of the provoked and the rate of the spontaneous contractions at five specific times during the period preceding initiation of cardiopulmonary bypass. A total of 208 episodes of stimulation were recorded: at insertion of the nasal temperature probe (n=8), at skin penetration by towel clips (n=25), at skin incision (n=20), at sternotomy (n=20), and during multiple episodes of electrocauterization (n=135). These provoked 23 somatic responses. The fentanyl concentration in plasma of the 20 patients during the study period was 30±10 ng/ml (mean±SD). The rate of the spontaneous contractions at times of response (6.0±4.8 contractions per 3-minuteperiod, mean±SD) was significantly greater than that at times of no response (2.6±3.0 contractions per 3-minute period), whereas there was no significant difference in the amplitude of provoked contractions (18.2±11.4 versus 16.2±8.5 mm Hg). The most favorable cutoff point was determined to be a rate of 6 contractions per 3-minute period. This produced a false-positive rate of 11.9% and a sensitivity (true-positive rate) of 52.2%. We conclude that the use of lower esophageal contractility is not reliable for detection of inadequate anesthesia when an opioid (fentanyl) is used as the primary anesthetic agent.