Extending the oesophageal Doppler into the peri‐operative period

Abstract

The oesophageal Doppler monitor is a fairly new tool in assessing cardiac output [1]. It is a rapid and relatively non-invasive way of measuring cardiovascular variables and requires minimal training [2]. Studies have validated its accuracy as measured by thermodilution using the pulmonary artery flotation catheter [3]. Clinical studies have also shown that its use and proper interpretation leads to shorter postoperative hospital stay and decreased morbidity [4, 5]. Apart from the expense, one of the main drawbacks of this technique is that the patient needs to be fully sedated to tolerate the oral oesophageal Doppler probe. Nasogastric and nasopharyngeal tubes are better tolerated than orogastric and oropharyngeal tubes, respectively. However, the oesophageal Doppler probe is difficult to place nasally as the distal part of the probe is fairly rigid and is unable to safely and easily navigate the nasopharynx. By using the nasopharyngeal airway as a guide and utilising a modified Seldinger technique, it is possible to safely insert the oesophageal Doppler probe nasally, so that it is tolerated by the awake patient. The oesophageal probe is initially prepared by gently easing the 35- and 40-cm bands off the probe. The original position of the bands is then marked with ink. A size 7 nasopharyngeal airway is then gently inserted into one of the patient's nostrils in the usual fashion whilst the patient is under general anaesthesia; this then acts as the guide for the probe and protects the nasopharynx from traumatic insertion of the probe. The tip of the oesophageal probe is lubricated with a water-soluble lubricant and then it can be inserted easily into the oesophagus via the nasopharyngeal airway. The optimal aortic signal is still obtained with the probe at 35–40 cm. Once the probe is satisfactorily placed, the nasopharyngeal airway can be withdrawn over the probe, leaving only the probe within the nose. The probe can then be taped to the forehead. Reproducible results are obtained from the probe even when inserted nasally. Once the patient is extubated and awake, the oesophageal Doppler probe is exceedingly well tolerated by the patient and appears to cause no greater discomfort than a size 16F nasogastric tube. By using this technique, the use of the oesophageal Doppler can be extended into the high-dependency unit from theatre. This is clinically important, as the use of the oesophageal Doppler monitor is one of the few monitors that has been validated by clinical trials to reduce morbidity [4, 5].