Monitoring for neuroprotection. New technologies for the new millennium

Monitoring for neuroprotection, like surgery, has placed on emphasis on minimal or non-invasiveness. Monitoring of parameters that truly reflect the degree of injury to the nervous system is another goal. Thus, two themes for the coming decade in neuromonitoring will be: (1) less-invasive monitoring; and (2) parameters that more closely reflect the etiological factors in ischemic or other neuroinjury. In this paper, we review neuromonitoring techniques and devices that can be used readily in the operating room or intensive care unit setting. Those that require transport of the patient to a special facility (e.g., for computed tomography or magnetic resonance imaging/spectroscopy) and those that have been in standard practice for neuromonitoring (e.g., electrophysiological monitoring--EEG, evoked potentials) are not considered. The two techniques considered in detail are (1) continuous multiparameter local brain tissue monitoring with microprobes, and (2) non-invasive continuous local brain tissue oxygenation monitoring by near infrared spectroscopy. Both techniques have been cleared by the Food and Drug Administration (FDA) for clinical use. The rationale for their use, the nature of the devices, and clinical results to date are reviewed. It is expected that both techniques will gain wide acceptance during the coming decade; further advances in neuromonitoring that can be expected further into the twenty-first century are also discussed.

[Comparison between the Eppendorf histograph and the Licox system for determination oxygen partial pressure in tumor tissue]

BACKGROUND

The oxygenation of a tumor is certainly one of the major facts influencing the response to treatment. pO2 measurement in tumor tissue can be done by using the Eppendorf-histograph. In recent years the Licox-system (GMS) was developed for oxygen tension measurement in tissues and fluids under clinical routine conditions and for research work. Aim of the present study was to assess the suitability of the Licox-system in drawing up histograms of pO2 values in tumor tissues.

METHOD

Histograms of the distribution of oxygen tension in twelve tumors were prepared with both measuring systems in parallel. Investigations were performed on rats with isotransplanted R1H rhabdomyosarcomas in continuous intravenous anesthesia with Fentanyl and Dormicum. Ventilation with a mixture of air and oxygen was applied through a tracheostoma. Arterial pressure and body temperature were analysed and balanced continuously.

RESULTS

No correspondence between data of both measuring methods could be found.

CONCLUSIONS

Because of constructional advantages the Eppendorf-histograph seems to be comparatively more suitable in drawing up histograms of oxygen tension tumor tissue.

Transcutaneous oxygen measurements: implications for nursing

Transcutaneous oxygen measurement is a noninvasive diagnostic technique that records the partial pressure of oxygen at the skin surface. This measurement provides information regarding the supply and delivery of oxygen to the underlying microvascular circulation. It can be used for adults in wound evaluation, hyperbaric therapy, plastic surgery, amputation level determination, and peripheral vascular disease assessment, including the status of limb revascularization procedures. This article presents an overview of transcutaneous oxygen measurement and situations that influence measurement levels, including environmental, dermal, physiologic, and mechanical factors. Nursing considerations and indications for further research are also discussed.

Monitoring tissue oxygenation during resuscitation of major burns

BACKGROUND

Because subcutaneous and splanchnic oxygenation indices are sensitive indicators of evolving hemorrhagic shock and adequacy of resuscitation, we postulated that these indices might have an equivalent role in the monitoring of severely burned patients. This observational study was undertaken to examine changes in tissue oxygenation indices during burn resuscitation.

METHODS

Seven patients with major burns (54 +/- 21% total body surface area) were studied during the first 36 hours of fluid resuscitation. Silastic tubing was placed in the subcutaneous tissue just beneath both normal skin and deep partial thickness burn. Fiberoptic sensors inserted into the tubing measured subcutaneous oxygen and carbon dioxide tensions in the burnt skin (PO2scb and PCO2scb) and normal skin (PO2scn and PCO2scn) continuously. Gastric intramucosal pH (pHi) and the mucosal CO2 (PCO2m) gap were calculated using gastric tonometers. Mean arterial pressure, arterial pH, lactate, and pHi measurements were obtained for 36 hours.

RESULTS

There were no significant differences in mean arterial pressure, arterial pH, or lactate concentrations throughout the study period, whereas indices of tissue oxygenation showed deterioration: pHi decreased from 7.2 +/- 0.1 to 6.7 +/- 0.3 (p = 0.06), the PCO2m gap increased from 12 +/- 17 to 108 +/- 123 mm Hg (p < 0.01), PO2scn decreased from 112 +/- 18 to 50 +/- 11 mm Hg (p < 0.01), PO2scb decreased from 62 +/- 23 to 29 +/- 16 mm Hg (p < 0.01), PCO2scn increased from 42 +/- 4 to 46 +/- 10 mm Hg (p = 0.2), and PCO2scb increased from 42 +/- 10 to 52 +/- 5 mm Hg (p = 0.05).

CONCLUSION

Despite adequate global indices of tissue perfusion after 36 hours of resuscitation, tissue monitoring indicated significant deterioration in the splanchnic circulation and in the normal and burnt skin.

Comparison of invasive and noninvasive measurements of indocyanine green plasma disappearance rate in critically ill patients with mechanical ventilation and stable hemodynamics

OBJECTIVES

We studied the correlation between invasive (aortic fiberoptic) and noninvasive (transcutaneous sensor) measurements of indocyanine green (ICG) plasma disappearance rate (PDR) in critically ill patients.

DESIGN AND SETTING

Prospective clinical study in a surgical intensive care unit of a university hospital.

PATIENTS

16 critically ill patients with adult respiratory distress syndrome (n = 8), sepsis/septic shock (n = 6), subarachnoid hemorrhage (n = 1), or severe head injury (n = 1).

MEASUREMENTS AND RESULTS

We analyzed 16 pairs of simultaneous ICG PDR measurements. All patients were deeply sedated and mechanically ventilated. Each patient received a 4-F aortic catheter with an integrated fiberoptic and thermistor connected to a computer system for automatic calculation of invasive ICG PDR (PDRINV). An ICG sensor was also attached to the nose wing and connected to a DDG2001 analyzer for noninvasive measurement (PDRNINV). Linear regression analysis revealed PDRNINV = 0.98 PDRINV +0.11%/min (r = 0.94, p < 0.0001) with a mean bias of 0.2 +/- 2.0%/min.

CONCLUSION

Noninvasive measurements of ICG PDR are very highly correlated with values derived from an invasive fiberoptic-based reference technique.

Comparison of two commercially available near-infrared spectroscopy instruments for cerebral oximetry. Technical note

Two near-infrared spectroscopy (NIRS) devices were compared with regard to their responses to changes in cerebral hemoglobin oxygenation induced by hypoxia and hypercapnia in five healthy volunteers. Sensors belonging to each NIRS device were placed on opposite sides of the volunteer's forehead. The INVOS-3100A device, approved by the United States Food and Drug Administration, records the percentage of oxyhemoglobin (HbO2) saturation and the investigational NIRO500 device records absolute changes in HbO2, deoxyhemoglobin, and total hemoglobin in micromolar concentrations referenced to an arbitrary baseline. The volunteers breathed separate mixtures of 7% CO2 in O2 and 10% O2 for 5 minutes in random order. Arterial blood pressure, end-tidal CO2 (ETCO2), arterial O2 saturation, and electrocardiographic data were continuously monitored. Hypercapnia increased (p < 0.01) ETCO2 from 42+/-2 to 56+/-3 mm Hg (mean +/- standard deviation), resulting in a 7.3+/-0.2% increase (p < 0.005) in cerebral HbO2 saturation detected by the INVOS3100A device and an 11.6+/-3 microM increase (p < 0.0008) in HbO2 detected by the NIRO500. Hypoxia decreased (p < 0.01) arterial HbO2 saturation from 98+/-1 to 87+/-3%, causing a 5.1+/-1.2% decrease (p < 0.01) in the percentage of HbO2 saturation detected by the INVOS3100A device and a 9.7+/-6.3 microM decrease in HbO2 detected by the NIRO500. The responses of the NIRO500 and the INVOS3100A instruments to changes in cerebral oxygenation resulting from hypercapnia and hypoxia were generally similar; however, responses tended to be greater when recorded by the NIRO500 device, perhaps because, unlike the INVOS3100A device, the NIRO500 does not correct for skin and bone contamination.

Use of transcutaneous oxygen and carbon dioxide tensions for assessing indices of gas exchange during exercise testing

The slow response characteristics of the combined transcutaneous electrode have been viewed as a major disadvantage when compared with other types of non-invasive assessment of gas exchange during exercise testing. We have previously shown that by using the highest recommended temperature of 45 degrees C to reduce response times, and combining this with an exercise protocol of gradual work load increments, that this allows changes in arterial blood gases to be closely followed by transcutaneous values. In the present study we have validated the use of a transcutaneous electrode for estimation of alveolar-arterial oxygen gradient (AaO2) and dead space to tidal volume ratio (V(D)/V(T)) during exercise, against values calculated from direct arterial blood gas analysis. One hundred measurements were made in 20 patients with various cardiopulmonary disorders who underwent exercise testing. Exercise testing was performed by bicycle ergometry with a specific protocol involving gradual work load increments at 2 min intervals. Transcutaneous gas tensions were measured by a heated combined O2 and CO2 electrode. Arterial blood was sampled at the midpoint of each stage of exercise and transcutaneous tensions noted at the end of each stage. The mean difference of the AaO2 gradient calculated from blood gas tensions obtained by the two methods was 0.14 kPa. The limits of agreement were -0.26 and 0.63 kPa. The same values for V(D)/V(T) calculated from gas tensions measured by the two methods were: mean difference 0001; limits of agreement -0.0242 and 0.0252. For both these parameters there was an even scatter around the mean value on Bland and Altman analysis. The findings of this study suggest that estimation of parameters of gas exchange using transcutaneous values during exercise testing is reliable, provided the electrode is heated to a slightly higher temperature than usual and the work load increments are gradual, allowing for the latency in the response time of the system. This system allows the assessment of the contribution of ventilation/perfusion inequality to breathlessness on exertion in patients, provided an initial arterial or ear lobe capillary sample is obtained for calibration purposes. This technique is particularly valuable in patients undergoing repeat exercise tests as it circumvents the need for arterial cannulation.

[Four new instrument for blood gas analysis are tested: handy cassettes for easier use]

An entirely new type of blood gas analyser has made its way into the marketplace, to be used, for example, in emergency rooms, intensive care units, ambulances, and bedside with quarantined patients in infectious diseases units. The instruments reviewed here employ new miniaturised analysis circuitry, integrated into the cassette on which the blood sample is applied. These instruments are designed for use by care-givers without specific laboratory training. Four point-of-care blood gas analysers are tested: OPTI 1 (AVL), I-STAT (HP), IRMA (Infiniti) och ABL 70 (Radiometer).

Transcutaneous oxygen tension in subjects with tetraplegia with and without pressure ulcers: a preliminary report

This study compared transcutaneous oxygen tension (TcpO2) in subjects with paraplegia and pressure ulcers (PU), those with paraplegia and no pressure ulcer (NPU), and ambulatory controls. TcpO2 was measured using a surface-electrode monitoring system, recorded at 1-min intervals for 5 min and averaged. Mean TcpO2 was significantly lower in the PU than the NPU and control groups (23.53+/-1.83 vs. 58.93+/-2.53 and 79.70+/-6.77 mmHg, respectively, p<0.05). In a PU subgroup (n=4) mean TcpO2 of the pressure ulcer and nonpressure ulcer sides (trochanter or ischium) were significantly different (21.05+/-2.98 vs. 67.65+/-2.11 mmHg, respectively, p<0.001). Additionally, the NPU group demonstrated significantly lower TcpO2 than the controls. PUs had a greater reduction in TcpO2 levels relative to controls than NPUs. No association was found between TcpO2 and duration of injury, completeness of lesion, or smoking history. Thus, TcpO2 may be an effective method to identify individuals who are susceptible to pressure ulcers. The further attenuation of TcpO2 observed in the PU group may be useful to help predict whether ulcers will heal with local care or will require additional treatment.

Prognostic aspects of TcPO2 in iloprost treatment as an alternative to amputation

To help in determining management strategy as an alternative to amputation by using a synthetic prostacycline, a preliminary study was undertaken in 12 patients (11 men and one woman), with a mean age of 71.08 years, ie, 13 limbs evaluated at the stage of amputation. All patients were treated with a combination of iloprost and physical therapy (massage, specific exercises, cardiorespiratory training). Static transcutaneous oxygen pressure (TcPO2) was measured, with a sensitization test by verticalization and inhalation of oxygen, on day (D) D0, D15, D28, D60, D180, and D365. Results were analyzed in absolute terms and by tissue oxygenation ratio (TOR) (ratio between absolute values of TcPO2 in the foot and those of a reference chest electrode). Supine TOR and vertical TOR, with values of 36.67 and 65.08, respectively, appeared to be significantly linked to the variable "preservation of limb". At 1 year, seven limbs were preserved (53.85%) while amputation had been scheduled for all the patients treated. Evidence was found in all patients who kept their limb of stability (7.69%) and a decrease in (30.77%) or disappearance of pain (15.38%) at 1 year.

[Fiberoptic measurement of arterial oxygen saturation in premature and term neonates]

BACKGROUND

Non-invasive oxygen monitoring with pulse oximetry or transcutaneous monitoring has gained widespread use in neonatology. Different factors like arterial hypotension, peripheral vasoconstriction and edema adversely affect the accuracy of both methods. To ensure reliable monitoring of oxygen saturation in critically ill patients we measured oxygen saturation with a fiberoptic catheter via umbilical artery.

METHODS

In ventilated premature infants (FiO2 > 0.4) a 4F-fiberoptic catheter (Oximetrix)-3, Abbott) was inserted to the descending aorta (Th 6-8). Simultaneously pulse oximetry (SaPO2) was performed with the Ohmeda Biox 3700. To compare the reliability of both methods, blood was analysed for arterial partial oxygen pressure (PaO2), fetal hemoglobin (HbF) and arterial oxygen saturation (SaO2) by complete co-oximetry (Radiometer Copenhagen OSM3) as reference.

RESULTS

In 10 premature infants (median gestational age 30.5 weeks; median birth weight 1360 g) oxygen saturation was measured with the fiberoptic catheter (SaFO2) over a total period of 935 hours. In all, 137 blood samples were analysed for arterial saturation (SaO2) by co-oximetry. The mean difference between the SaO2 and SaFO2 was -1.89% (+/- 1.53); the mean difference between SaO2 and the values obtained by pulse oximetry (SaPO2) was -3.09% (+/- 2.33). The SaFO2 results correlated closely with the co-oximetry values (r = 0.97; p < 0.0001).

CONCLUSION

In critically ill patients, if non-invasive oxygen monitoring fails, a fiberoptic catheter offers the possibility of continuous and reliable measurement of oxygen saturation.

Clinical investigation of a new combined pulse oximetry and carbon dioxide tension sensor in adult anaesthesia

OBJECTIVE

To test the accuracy of a new combined oxygen saturation and cutaneous carbon dioxide tension (SPO2-PCO2) sensor in a routine adult clinical environment. This probe provides a non-invasive and continuous monitoring of the arterial oxyhaemoglobin saturation, arterial carbon dioxide tension and pulse rate at the ear lobe. The sensor is intended to measure both relevant respiration/ventilation parameters in one single probe.

METHODS

Ten adult patients were consecutively studied during general anaesthesia. During the first 5 min after sensor placement at the ear lobe, arterial blood samples were drawn each minute. Carbon dioxide tension and oxygen saturation measurements were obtained simultaneously at 1-min intervals. After this period, patients were hyper-, normo- and hypoventilated. After 15 min at each setting, the simultaneously obtained cutaneous and arterial carbon dioxide tension values were compared.

RESULTS

A total of 80 comparisons between ear lobe SpO2-PCO2 measurement, finger clip pulse oximetry and arterial blood gas values were analysed. Three minutes after sensor placement, there were no significant differences between ear probe (cutaneous) and arterial carbon dioxide tensions (p = 0.367). Comparison of arterial with cutaneous carbon dioxide values demonstrated an excellent linear correlation (r2 = 0.92), and showed a standard error of estimate (SDEE) of 0.26 kPa (1.95 mmHg) only. The mean difference was -0.08 kPa (-0.60 mmHg) with a limits of agreement range of -0.38 kPa to +0.22 kPa (-2.85 mmHg to +1.65 mmHg). Concerning oxygen saturation measurements, the absolute SpO2 value deviated 1% or less from standard pulse oximetry.

CONCLUSIONS

During general anaesthesia, postoperative recovery and critical care treatment, both monitoring of oxygenation and ventilation is important. Since pulse oximetry estimates only arterial oxygen saturation, periodic blood sampling is still necessary to determine the patient's arterial carbon dioxide status. We could demonstrate that the difference between cutaneous and arterial PCO2 was clinically unimportant, and therefore we conclude that the two methods of estimating the patient's carbon dioxide status may be used interchangeably. Our results demonstrated that 3 min after sensor placement, the new SpO2-PCO2 sensor prototype proved to be a reliable tool for continuous non-invasive monitoring of oxygenation and ventilation.

Transcutaneous PCO2 to monitor noninvasive mechanical ventilation in adults: assessment of a new transcutaneous PCO2 device

The present study was designed to analyze the usability of a commercially available, transcutaneous PCO2 (TcPCO2) sensor for monitoring noninvasive positive pressure ventilation (NPPV). Twenty-six hemodynamically stable patients with intra-arterial radial catheters were assessed. After stabilization of TcPCO2, arterial blood was analyzed and results were compared with TcPCO2 at time of sampling. To evaluate the drift of the signal, samples were taken hourly in five patients for 4 h while continuously recording TcPCO2. Finally, to assess for the response of the sensor to changes in PaCO2, six patients underwent continuous TcPCO2 recording while initiating or interrupting NPPV; arterial samples were analyzed before the event, and 1, 3, 5, 7, 9, and 20 min afterwards.

RESULTS

TcPCO2 and PaCO2 were tested over a range of 26 to 71 mm Hg, and were found to be closely correlated (r=0.968, p<0.0001); mean bias was 0.75 mm Hg. There was no significant drift of TcPCO2 as compared with PaCO2 over 4 h. The time of response of TcPCO2 to initiation or interruption of NPPV was <60 s. An estimation of the lag time averaged 5+/-3 min (range, 1 to 9 min).

CONCLUSION

TcPCO2 in hemodynamically stable adults was in excellent agreement with arterial measurements. The time of response to a change in ventilation was compatible with the aim of clinical monitoring of patients under NPPV.

Effects of motion, ambient light, and hypoperfusion on pulse oximeter function

STUDY OBJECTIVE

To compare the performance of five pulse oximeters during hypoperfusion, probe motion, and exposure to ambient light interference.

DESIGN

Prospective study.

SETTING

Laboratory facility at a university medical center.

PATIENTS

8 unanesthetized, ASA physical status I volunteers.

INTERVENTIONS

We evaluated five common pulse oximeters with respect to three scenarios: (1) an operating room light was shone on oximeter probes, (2) a motion generator was used to generate 2 Hz and 4 Hz hand motion, and (3) a pneumatic compression device overlying the brachial artery was used to simulate hypoperfusion. Electrocardiographic (ECG) and arterial blood gas values were considered gold standards for heart rate (HR) and oxygen saturation (SpO2) respectively. SpO2 nondisplay and values greater than 4% from simultaneous arterial SaO2-oximeter values were defined as errors. Nondisplay of HR, or HR greater than 5% from ECG values, were also considered errors.

MEASUREMENTS AND MAIN RESULTS

The Ohmeda and Nellcor N200 with finger probe had the highest total failure rates with respect to both SpO2 and HR due to ambient light interference (p < 0.05). The Nellcor N200 with finger probe and N200 with C lock were the most accurate with regard to SpO2 during 2 Hz and 4 Hz motion (p < 0.05). However, all oximeters failed dramatically during 4 Hz motion when measuring HR. In the hypoperfusion model, the Nellcor N200 with finger probe and the Nellcor C Lock oximeters performed significantly better than all others in terms of both HR and SpO2 (P < 0.05), while the Criticare oximeter failed 100% of the time.

CONCLUSION

There are significant differences in the accuracy of commercially available pulse oximeters during nonideal circumstances, with failure rates varying from approximately 5% to 50% depending on the oximeter and source of interference. Furthermore, no single oximeter performed the best under all conditions.

Pulse oximeter performance during desaturation and resaturation: a comparison of seven models

STUDY OBJECTIVE

To compare pulse oximeter performance during induced hypoxemia.

DESIGN

Prospective investigation in human volunteers.

SETTING

Laboratory facility at a university medical center.

PATIENTS

8 unanesthetized, healthy ASA physical status I volunteers.

INTERVENTIONS

We evaluated the accuracy and response times of seven popular pulse oximeters during induced hypoxemia. Arterial blood fractional oxygen saturation (SaO2) measurements were performed simultaneously and considered a gold standard.

MEASUREMENTS AND MAIN RESULTS

All oximeters were accurate (+/-2%) while subjects were breathing room air. During maximal hypoxemia (induced by breathing a FIO2 = 10% in nitrogen), large differences were noted between oxygen saturation as measured by pulse oximetry (SpO2) and SaO2 values, with pulse oximeters consistently underreporting SpO2 when actual SaO2 values were 75% or less. The Ohmeda 3740 (Ohmeda, Boulder, CO) using an ear probe was the first to detect desaturation (change in SpO2 > 3%) in 4 of 8 subjects (p < 0.05), and the Nellcor N200 reflectance oximeter (Nellcor, Inc., Pleasanton, CA) was first in 3 of 8 subjects (p < 0.05). During resaturation (after administering 100% oxygen), the Novametrix Oxypleth (Novametrix, Wallingford, CT) was significantly faster than other oximeters (p < 0.05) to return to baseline (SpO2 = 98%).

CONCLUSION

Most models of oximeters tested performed well when hemoglobin oxygen saturation was high, but all were inaccurate when SaO2 was approximately 75%. During induced hypoxemia, there were significant differences in the response times of oximeters tested, with no model demonstrably superior to others in all measures of performance.

[Simultaneous measurements of end-expiratory and transcutaneous carbon dioxide partial pressure in ventilated premature and newborn infants]

BACKGROUND

The aim of the present trial was to study the relationship between end-tidal pCO2 (p(et)CO2) and transcutaneous pCO2 (ptcCO2) after in-vivo calibration in ventilated newborns.

PATIENTS

61 end-tidal and transcutaneous pCO2 measurements were simultaneously performed in 30 ventilated preterm and term newborn infants (weight at birth 1862.6 +/- 981.9 g).

METHOD

End-tidal pCO2 was measured in mainstream mode at the end of the endotracheal tubus (Novametrix 7000 Medical Systems Inc., USA, dead volume of the chamber 0.6 ml). Transcutaneous pCO2 was measured by means of a Servomed (SMK 365 Hellige, FRG) analyser.

RESULTS

The statistical analysis demonstrated a good correlation (r = 0.72, p < 0.001) between ptcCO2 (mean +/- SD, 44.3 +/- 11.2 mmHg) and p(et)CO2 (32.4 +/- 10.4 mmHg). A considerable difference between transcutaneous and end-tidal pCO2 values was observed (p(tc-et)CO2 = +11.9 +/- 8.7 mmHg). This phenomenon was probably caused by ventilation-perfusion disturbances in the studied critically ill neonates. The statistical analysis revealed that the absolute magnitude of the P(tc-et)CO2 difference was independent from disease, episodes of spontaneous respiration or of respiratory frequency.

CONCLUSIONS

Capnographic determination of P(et)CO2 provides informations about alveolar ventilation-perfusion-disturbances. Capnography enables the on-line control of end-tidal pCO2 in neonates with respiratory failure. It cannot replace transcutaneous pCO2 measurements or blood gas analysis but it can reduce its frequency in clinically stable patients. The analysis of the capnogram can be used to optimise artificial ventilation. A quantitative evaluation of the capnogram by calculation of Murányi's-CO2-Index was possible only in 28% of the ventilated newborns which limits its value in such patients.

Validation of reflectance pulse oximetry: an evaluation of a new sensor in piglets

OBJECTIVE

A new reflectance pulse oximetry sensor, developed for intrapartum estimation of arterial oxygen saturation (SaO2), was calibrated and evaluated. The sensor contains two light emitting diodes of 735 and 890 nm, and a photodetector at a distance of 14 mm from both light emitting diodes.

METHODS

In seven Yorkshire/Hampshire piglets, the reflectance sensor (Nellcor Puritan Bennett Inc.) was calibrated using blood sample SaO2 values. The resulting calibration line was evaluated in four Dutch piglets, by comparing pulse oximetry saturation readings (SpO2) with blood sample and intravascular fiberoptic oximetry SaO2 values. Several reflectance sensors were fixed on each animal. Desaturation levels were obtained by changing the gas mixture of oxygen/ nitrous oxide via a tracheal catheter.

RESULTS

In the Yorkshire/ Hampshire piglets, the standard deviation of difference (SpO2-SaO2) was 4.7% (n = 364), over an SaO2 range of 17% to 100%. In the Dutch piglets, the mean difference (SpO2-SaO2) was -1.6% and the standard deviation of difference was 5.4%, over the same SaO2 range (n = 254). Comparisons of continuous recordings of reflectance SpO2 and fiberoptic SaO2 revealed variation in individual regression lines.

CONCLUSIONS

This new 735/890 nm reflectance sensor demonstrates acceptable accuracy in piglets. A further evaluation during labor should assess its feasibility for fetal surveillance.

Doctors and the health industry: a case study of transcutaneous oxygen monitoring in neonatal intensive care

This case study presents an industry perspective on medical innovation. Introduced as a scientific breakthrough in the late 1970s, transcutaneous oxygen monitoring was rapidly adopted for routine use in neonatal intensive care. But plagued by technical problems, it was within a decade being replaced by pulse oximetry, a still more recent technology. Its use in efforts to prevent retinopathy of prematurity, an eye disease of preterm newborns often leading to blindness, proved disappointing. The project included interviews with executives and design engineers of companies marketing the device, with investigators who had pioneered the technology, and with senior practicing neonatologists. The findings, reflecting complexity and uncertainty, are relevant to issues concerning health care in the United States and other developed nations. They centre on the key role and ultimate responsibility of the medical profession, with a need for greater attention to the scientific training of health care workers, as perceived by members of the medical device industry. The views of senior investigators are integrated into the picture, with discussion of major challenges faced by the medical community.