Accuracy of Zero-flux and Ingestible Thermometers

Summary:

The study has been designed to provide information on the suitability and accuracy of two methods of temperature measurement in the perioperative period.

Background:

Good perioperative temperature management is an important means of improving patient outcome [1].

An essential part of optimal management is accurate temperature measurement. The gold standard is pulmonary artery catheter (PAC) measurement. However, these are used infrequently in British practice due to the high rates of associated complications. Urinary bladder and oesophageal temperatures are sufficiently accurate but are unsuitable for many patients [2]. For example it is not possible to use oesophageal probes in awake patients and many patients are not catheterised.

Although non-invasive and relatively cheap means of measuring temperature (such as aural canal probes and infrared scanners) exist, they are neither accurate nor consistent enough to distinguish the 0.5˚C differences which have a significant effect on patient outcomes [2].

In this study, the investigators plan to look at two methods of temperature measurement which potentially offer significant improvements to surgical care.

The first is a new method known as zero-flux thermometry. This is completely non-invasive, involving no more than placing an adhesive pad to the forehead. Connected up to a monitor, this will equilibrate with the patient's core temperature and give a constant read-out.

The second is an ingestible capsule. These have become an important tool for measuring both hypothermia and hyperthermia in other settings. Their accuracy has not, however, been tested in hospital patients. This technology, although too expensive for routine use, offers significant advantages for research as they can provide a constant record of temperature throughout the patient's stay in hospital. For example, the investigators' audit data show that if patients admitted with fractured neck of femur become hypothermic at any time, their mortality increases. Subsequent to this we showed that patient temperatures drop significantly between ambulance, A&E and admission to the ward. These parts of the patient journey are possible targets for the prevention of hypothermia and the continuous monitoring offered by these devices will allow us to accurately test the efficacy of the interventions.

Aims and objectives:

The aim of this study is to determine the accuracy in the perioperative period of zero-flux and ingestible temperature readings.

Previous studies have shown that oesophageal and nasopharyngeal measurements can be taken as an accurate reflection of core temperature [2]. The consistency and accuracy of the other two will be compared to this.

Plan of investigation:

This study will be purely observational. There will be no interference with current practice. Nasopharyngeal/oesophageal probes are routinely placed, according to NICE guidelines, in these patients. The zero-flux thermometer is non-invasive and the ingestible capsule no bigger than a pill, so neither provide any additional risk to the patient.

Temperature readings will be downloaded from each of the three devices with a maximum interval of 1 minute. The investigators have calculated that readings from 15 subjects will provide sufficient power. The investigators plan to recruit 20 patients. Analysis of agreement between the methods will be performed as suggested by Bland and Altman[3].

Inclusion criteria

Participants will be patients undergoing elective gynaecological, vascular or urological surgery at the Royal Sussex County Hospital, and as such will be seen at a pre-operative assessment clinic as part of their normal work up for theatre.

Exclusion criteria

• Lacking mental capacity
• Not speaking English
• Malignancy in medical history
• Undergoing open abdominal surgery