A pilot study of pharyngeal pulse oximetry with the laryngeal mask airway: a comparison with finger oximetry and arterial saturation measurements in healthy anesthetized patients

Successful use of pharyngeal pulse oximetry with the oropharyngeal airway in severely shocked patients

We describe the successful use of pharyngeal oximetry with the oropharyngeal airway in two patients with severe shock in whom finger pulse oximetry failed. One patient was a 50-year-old man with septic shock and the other a 32-year-old woman with haemorrhagic shock. In both patients, an oropharyngeal airway with a paediatric pulse oximeter probe was inserted adjacent to the tracheal tube. A good waveform was obtained and oxygen saturation was 0-2% lower than arterial samples whereas finger pulse oximetry saturation was unobtainable or much lower than arterial oxygen saturation. Pharyngeal oxygen saturation with the oropharyngeal airway is feasible and more accurate than finger oximetry in low perfusion states.

A preliminary study on the monitoring of mixed venous oxygen saturation through the left main bronchus

Introduction

The study sought to assess the feasibility and accuracy of measuring mixed venous oxygen saturation (SvO₂) through the left main bronchus (SpO_2trachea)

Methods

Twenty hybrid pigs of each sex were studied. After anesthesia, a Robertshaw double-lumen tracheal tube with a single-use pediatric pulse oximeter attached to the left lateral surface was introduced toward the left main bronchus of the pig by means of a fibrobronchoscope. Measurements of SpO_2trachea and oxygen saturation from pulmonary artery samples (SvO_2blood) were performed with an intracuff pressure of 0 to 60 cmH₂O. After equilibration, hemorrhagic shock was induced in these pigs by bleeding to a mean arterial blood pressure of 40 mmHg. With the intracuff pressure maintained at 60 cmH₂O, SpO_2trachea and SvO_2blood were obtained respectively during the pre-shock period, immediately after the onset of shock, 15 and 30 minutes after shock, and 15, 30, and 60 minutes after resuscitation.

Results

SpO_2trachea was the same as SvO_2blood at an intracuff pressure of 10, 20, 40, and 60 cmH₂O, but was reduced when the intracuff pressure was zero (p < 0.001 compared with SvO_2blood) in hemodynamically stable states. Changes of SpO_2trachea and SvO_2blood corresponded with varieties of cardiac output during the hemorrhagic shock period. There was a significant correlation between the two methods at different time points.

Conclusion

Measurement of the left main bronchus SpO₂ is feasible and provides similar readings to SvO_2blood in hemodynamically stable or in low saturation states. Tracheal oximetry readings are not primarily derived from the tracheal mucosa. The technique merits further evaluation.

Comparison of a prototype esophageal oximetry probe with two conventional digital pulse oximetry monitors in aortocoronary bypass patients

OBJECTIVE

Pulse oximetry (SpO2) is the non-invasive standard for monitoring arterial oxygen saturation in patients undergoing anesthesia, but is subject to external interference by motion artifact, peripheral vasoconstriction, and low cardiac output. We hypothesized that oximetry signals could be acquired from the esophagus when peripheral pulse oximetry is unobtainable. Therefore, we tested an esophageal stethoscope which incorporates transverse oximetry photodetectors and emitters in patients undergoing coronary bypass surgery.

METHODS

Immediately after induction of general anesthesia in 10 coronary artery bypass (CABG) patients, Criticare and Nellcor digital probes were positioned on the left hand, concurrent with placement of an esophageal SpO2 probe. A computer recorded 5,910 matched oximetry signals every 15 sec during an average of 2.5 hrs. All SpO2 measurements were before, and immediately after non-pulsatile, hypothermic cardiopulmonary bypass. Data represent the percentage (median value [range]) of the total monitored time that a SpO2 value was displayed.

RESULTS

The Nellcor (99.8%, range 6.5-100%) and Criticare (99.7%, range 36.6-100%) acquired and displayed saturation signals more frequently (p = 0.003) than the esophageal monitor (75.3%, range 42.1-95.8%). The two standard digital oximeters had a mean difference of 0.9%, with a standard deviation of the differences of 0.9. The esophageal probe had a mean difference of -5.2% and -4.8%, with standard deviation of differences of 8.0 and 7.7 (compared to the Nellcor and Criticare monitors, respectively). A second-generation prototype shielded from electrocautery interference was tested in an additional 4 patients. The shielded prototype displayed signals more frequently (96.7%, range 68.4-100%) than the original esophageal prototype.

CONCLUSIONS

Digital pulse oximetry failure is common in CABG patients, probably because of marginal cardiac output and peripheral vasoconstriction associated with hypothermia. Our study could not confirm that esophageal technology, which utilizes the esophagus as a site of transflectance oximetry, was superior to conventional digital pulse oximetry.