Capnographs rapidly and reliably detect esophageal intubation—a cause of anesthetic catastrophe—but do not reliably detect mainstem bronchial intubation.
Postoperative residual paralysis remains a problem in postanesthesia care, producing potentially injurious airway and respiratory function compromise and increasing length of stay and cost in the postanesthesia care unit (PACU).
The previous chapter reviewed routine hemodynamic monitoring used by anesthesiologists. This chapter examines the vast array of techniques and devices used perioperatively to monitor neuromuscular transmission, neurological condition, respiratory gas exchange, and body temperature.
RESPIRATORY GAS EXCHANGE MONITORS
PRECORDIAL & ESOPHAGEAL STETHOSCOPES
Prior to the routine availability of gas exchange monitors, anesthesiologists used a precordial or esophageal stethoscope to ensure that the lungs were being ventilated, to monitor for circuit disconnections, and to auscultate heart tones to confirm a beating heart. Although largely supplanted by other modalities, the finger on the pulse and auscultation remain frontline monitors, especially when technology fails. Chest auscultation remains the primary method to confirm bilateral lung ventilation in the operating room, even though detection of an end-tidal CO2 waveform is definitive to exclude esophageal intubation.
Esophageal stethoscopes and esophageal temperature probes should be avoided in patients with esophageal varices or strictures.
Techniques & Complications
A precordial stethoscope (Wenger chestpiece) is a heavy, bell-shaped piece of metal placed over the chest or suprasternal notch. Although its weight tends to maintain its position, double-sided adhesive disks provide an acoustic seal to the patient’s skin. Various chestpieces are available, but the child size works well for most patients. The bell is connected to the anesthesiologist’s ear by extension tubing.
The esophageal stethoscope is a soft plastic catheter (8–24FR) with balloon-covered distal openings (Figure 6–1). Although the quality of breath and heart sounds is much better than with a precordial stethoscope, its use is limited to intubated patients. Temperature probes, electrocardiogram (ECG) leads, ultrasound probes, and even atrial pacemaker electrodes have been incorporated into esophageal stethoscopes. Placement through the mouth or nose can occasionally cause mucosal irritation and bleeding. Rarely, the stethoscope slides into the trachea instead of the esophagus, resulting in a gas leak around the tracheal tube cuff.
The information provided by a precordial or esophageal stethoscope includes confirmation of ventilation, quality of breath sounds (eg, stridor, wheezing), regularity of heart rate, and quality of heart tones (muffled tones are associated with decreased cardiac output). The confirmation of bilateral breath sounds after tracheal intubation, however, is best made with a binaural stethoscope.