Transcutaneous Gases Research Articles

Cavitas Sensors: Contact Lens Type Sensors & Mouthguard Sensors

Abstract“Cavitas sensors” attached to body cavities such as the contact lens and mouthguard (“no implantable”, “no wearable”) are attracted attention as self‐detachable devices for daily medicine. Many types of contact lens (CL) sensors using electrical and optical methods have been developed for monitoring not only chemicals (glucose, lactate) and electrical conductivity in tear fluid, but also transcutaneous gases at eyelid mucosa. A CL intraocular pressure telemetric sensor has been also commercialized and applied to patients for monitoring the intraocular pressure. Some mouthguard sensors have been investigated for a real‐time measurement of salivary chemicals. A graphene based sensor on tooth enamel was reported to be capable of salivary bacterium detection. Here we review the challenges regarding the integration of biosensors into monitoring for biological information of body cavities. The self‐detachable cavitas sensors are expected to improve the quality of life in the near future.

A novel approach toward noninvasive monitoring of transcutaneous CO2

The continuous monitoring of transcutaneous gases is an integral part of neonatal intensive care. Present monitors measure the equilibrating values of these gases by raising the skin temperature to 42°C or above. Because neonatal skin is very sensitive and delicate, this often leads to serious skin injuries. In this work, we present a new approach to the noninvasive measurement of transcutaneous partial pressure of carbon dioxide (tcpCO2) based on the initial pseudo steady state diffusion rates instead of the mass-transfer equilibrium. Because we are following initial diffusion rates, each measurement takes no more than a few minutes. Additionally, raising the surface temperature is not required, thus, skin irritation and burns are highly unlikely. A dual-chamber diffusion vessel with either porcine skin or dialysis membrane placed between the two chambers was used to mimic neonatal skin. LI-820 CO2 Analyzer was used to measure the CO2 diffusing through the membrane or skin. Initial experiments on adult human skin under varying physical activities, food intake and breathing patterns showed a strong influence of the various conditions on the amount of CO2 diffusing through skin. These initial findings suggest that this method can be used not only on neonates but to a wider population of patients.

Preamputation evaluation of limb perfusion with laser Doppler imaging and transcutaneous gases

We studied 31 subjects with severe leg ischemia and 29 age-matched nonischemic control subjects to compare preamputation assessments of leg ischemia using laser Doppler imaging (LDI), transcutaneous partial pressure of oxygen (TcPO(2)), and transcutaneous partial pressure of carbon dioxide (TcPCO(2)). TcPO(2) and TcPCO(2) were evaluated with Novametrix Medical Systems, Inc, monitors (Wallingford, Connecticut) and perfusion (flux) of skin topically heated to 44 degrees C, and adjacent nonheated areas were evaluated with a Moor Laser Doppler Imager (Moor Instruments, Ltd; Devon, England). LDI flux of heated areas, its ratio to nonheated areas, and TcPO(2) (not TcPCO(2)) were lower in ischemic subjects than in control subjects. LDI flux ratio performed better than TcPO(2) in identifying ischemia, with fewer false positive and false negative results. Moreover, LDI flux of heated skin detected a proximal to a distal gradient of perfusion in ischemic subjects, while TcPO(2) did not. LDI was superior to TcPO(2) in discriminating correctly between ischemic and nonischemic skin. The results suggest that an LDI ratio below 5 indicates nonviable skin.

Exploring the influence of skin perfusion on transepidermal water loss

Eventual relationships between the vascular function and transepidermal water loss (TEWL), in vivo,have not been entirely explored. By promoting local perfusion alterations through a well-known challenge test, the'tourniquet-cuff occlusion' manoeuvre, the present study searches for other dynamical factors influencing the cutaneous barrier, further exploring the applicability of these flow-related variables in dermatological research. By applying the tourniquet-cuff manoeuvre to a group of healthy volunteers (n= 20), transcutaneous (tc)gases (pO2-pCO2), LDF (laser doppler flowmetry) and TEWL were considered as representing the dynamical aspects under study and measured non-invasively. An haemodynamical relationship between tcpO2 and LDF in the post-occlusive period was clearly identified, defining the autoregulatory index as a numerical descriptor of the local metabolic-flow adjustment under stress. TEWL was also significantly affected by the manoeuvre, especially during the post-occlusive period,although no significant relationships between TEWL and other tc variables could be found. The present findings seem to suggest that, under the present experimental conditions, local haemodynamics may also influence TEWL measurements and the skin barrier.

Assessment of alternating-pressure air mattresses using a time-based pressure threshold technique and continuous measurements of transcutaneous gases

Alternating-pressure air mattresses (APAMs) are used increasingly for the prevention and treatment of pressure sores. Laboratory evaluation techniques have centred largely on interface pressure (IP) measurement, typically analysing discrete maximum and minimum levels, or average pressure. However, since pressure relief varies with time, a time-based analysis technique has been developed for performance assessment. IP was recorded continuously, and the duration of pressures below three thresholds (30, 20 and 10 mmHg) was calculated automatically using a computerized rig. Fifteen healthy volunteers were used to evaluate the pressure-relieving characteristics of four APAMs, including one overlay. Results indicated significant differences (P < 0.001) between products when durations below the 20 and 10 mmHg thresholds were analysed, showing that some devices were only capable of momentarily relieving pressure. Maximum contact pressures on the sacrum were significantly lower (P < 0.0001) on devices whose inflation pressure was adjusted according to subject's body mass. This technique could assist in the selection of alternating or dynamic surfaces of any description with further clinical validation.

Cardiovascular and Catecholamine Changes After Administration of Pancuronium in Distressed Neonates

Heart rate, blood pressure, transcutaneous gases, and catecholamine changes following intravenous injection of pancuronium were evaluated in seven ill newborn infants (birth weight: 1,280 to 4,500 g; gestational age, 29 to 42 weeks). Each infant was monitored continuously for 30 minutes before and 50 minutes after infusion of the paralyzing agent. There were no significant changes in transcutaneous gases, whereas significant increases in heart rate; systolic, diastolic, and mean blood pressures; and blood norepinephrine and epinephrine levels were found. The increase in heart rate lasted for 30 minutes, and the increase in blood pressure persisted for 50 minutes after administration of the drug. Because of the potential relationship between increased blood pressure and intraventricular hemorrhage and myocardial dysfunction, heart rate and blood pressure must be monitored during infusion of pancuronium in distressed newborns. These data suggest that pancuronium stimulates sympathetic activity in distressed newborns.

Evaluation of a single transcutaneous PO2-PCO2 sensor in adult patients.

We evaluated a new transcutaneous gas monitor designed to measure simultaneously transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) tensions. A total of 514 simultaneous transcutaneous and arterial gases were obtained in 47 adult ICU patients. Mean PtcCO2 was close (SEE less than 4 torr) to mean PaCO2, but mean PtcO2 was considerably less than mean PaO2. However, PtcO2 changes larger than 15 torr virtually always indicated respective increases or decreases in PaO2. Similarly, PtcCO2 changes larger than 5 torr almost invariably indicated a parallel change in PaCO2. From this study we conclude that monitoring of transcutaneous gases yields reliable trend information on arterial gases and that it is a valuable noninvasive adjunct in the monitoring of gas exchange in adult patients.