Tribute to Dr. Takuo Aoyagi, inventor of pulse oximetry.

INTRODUCTION: Dr. Takuo Aoyagi invented pulse oximetry in 1974. Pulse oximeters are widely used worldwide, most recently making headlines during the COVID-19 pandemic. Dr. Aoyagi passed away on April 18, 2020, aware of the significance of his invention, but still actively searching for the theory that would take his invention to new heights. METHOD: Many people who knew Dr. Aoyagi, or knew of him and his invention, agreed to participate in this tribute to his work. The authors, from Japan and around the world, represent all aspects of the development of medical devices, including scientists and engineers, clinicians, academics, business people, and clinical practitioners. RESULTS: While the idea of pulse oximetry originated in Japan, device development lagged in Japan due to a lack of business, clinical, and academic interest. Awareness of the importance of anesthesia safety in the US, due to academic foresight and media attention, in combination with excellence in technological innovation, led to widespread use of pulse oximetry around the world. CONCLUSION: Dr. Aoyagi's final wish was to find a theory of pulse oximetry. We hope this tribute to him and his invention will inspire a new generation of scientists, clinicians, and related organizations to secure the foundation of the theory.

Pressure-limited sustained inflation vs. gradual tidal inflations for resuscitation in preterm lambs.

Support of the mechanically complex preterm lung needs to facilitate aeration while avoiding ventilation heterogeneities: whether to achieve this gradually or quickly remains unclear. We compared the effect of gradual vs. constant tidal inflations and a pressure-limited sustained inflation (SI) at birth on gas exchange, lung mechanics, gravity-dependent lung volume distribution, and lung injury in 131-day gestation preterm lambs. Lambs were resuscitated with either 1) a 20-s, 40-cmH2O pressure-limited SI (PressSI), 2) a gradual increase in tidal volume (Vt) over 5-min from 3 ml/kg to 7 ml/kg (IncrVt), or 3) 7 ml/kg Vt from birth. All lambs were subsequently ventilated for 15 min with 7 ml/kg Vt with the same end-expiratory pressure. Lung mechanics, gas exchange and spatial distribution of end-expiratory volume (EEV), and tidal ventilation (electrical impedance tomography) were recorded regularly. At 15 min, early mRNA tissue markers of lung injury were assessed. The IncrVt group resulted in greater tissue hysteresivity at 5 min (P = 0.017; two-way ANOVA), higher alveolar-arterial oxygen difference from 10 min (P < 0.01), and least uniform gravity-dependent distribution of EEV. There were no other differences in lung mechanics between groups, and the PressSI and 7 ml/kg Vt groups behaved similarly throughout. EEV was more uniformly distributed, but Vt least so, in the PressSI group. There were no differences in mRNA markers of lung injury. A gradual increase in Vt from birth resulted in less recruitment of the gravity-dependent lung with worse oxygenation. There was no benefit of a SI at birth over mechanical ventilation with 7 ml/kg Vt.

Pressure- versus volume-limited sustained inflations at resuscitation of premature newborn lambs.

BACKGROUND: Sustained inflations (SI) are advocated for the rapid establishment of FRC after birth in preterm and term infants requiring resuscitation. However, the most appropriate way to deliver a SI is poorly understood. We investigated whether a volume-limited SI improved the establishment of FRC and ventilation homogeneity and reduced lung inflammation/injury compared to a pressure-limited SI. METHODS: 131 d gestation lambs were resuscitated with either: i) pressure-limited SI (PressSI: 0-40 cmH2O over 5 s, maintained until 20 s); or ii) volume-limited SI (VolSI: 0-15 mL/kg over 5 s, maintained until 20 s). Following the SI, all lambs were ventilated using volume-controlled ventilation (7 mL/kg tidal volume) for 15 min. Lung mechanics, regional ventilation distribution (electrical impedance tomography), cerebral tissue oxygenation index (near infrared spectroscopy), arterial pressures and blood gas values were recorded regularly. Pressure-volume curves were performed in-situ post-mortem and early markers of lung injury were assessed. RESULTS: Compared to a pressure-limited SI, a volume-limited SI had increased pressure variability but reduced volume variability. Each SI strategy achieved similar end-inflation lung volumes and regional ventilation homogeneity. Volume-limited SI increased heart-rate and arterial pressure faster than pressure-limited SI lambs, but no differences were observed after 30 s. Volume-limited SI had increased arterial-alveolar oxygen difference due to higher FiO2 at 15 min (p = 0.01 and p = 0.02 respectively). No other inter-group differences in arterial or cerebral oxygenation, blood pressures or early markers of lung injury were evident. CONCLUSION: With the exception of inferior oxygenation, a sustained inflation targeting delivery to preterm lambs of 15 mL/kg volume by 5 s did not influence physiological variables or early markers of lung inflammation and injury at 15 min compared to a standard pressure-limited sustained inflation.

Histologic chorioamnionitis and severity of illness in very low birth weight newborns.

OBJECTIVE: Estimating the risk of in-hospital mortality in the neonatal intensive care unit provides important information for health care providers, and several neonatal illness severity scores have been developed. Histologic chorioamnionitis (HCA) is a known cause of neonatal morbidity and mortality. To date, the relationship between HCA and neonatal illness severity scores has not been rigorously tested. In this study, the relationships among HCA, initial illness severity, and neonatal outcomes were analyzed in very low birth weight (VLBW) newborns admitted to the neonatal intensive care unit. DESIGN: Prospective. SETTING: Neonatal intensive care unit. PATIENTS: A total of 116 VLBW inborn infants (gestational age, 28.1 +/- 2.82 wks; birth weight, 1009 +/- 312 g) were categorized as HCA-positive (n = 67) and HCA-negative (n = 49). INTERVENTIONS: Placental histology was performed to identify HCA. Illness severity evaluation included several different neonatal illness severity scores-Clinical Risk Index for Babies (CRIB), CRIB-II, Score for Neonatal Acute Physiology-II (SNAP-II), and Score for Neonatal Acute Physiology Perinatal Extension-II (SNAPPE-II)-as well as the recording of severe morbidity and in-hospital mortality. MEASUREMENTS AND MAIN RESULTS: HCA-positive VLBW newborns showed significantly lower gestational age (p < .0001) and birth weight (p = .0010), together with higher CRIB, CRIB-II, SNAP-II, and SNAPPE-II scores at admission to the NICU (p 5 (odds ratio [OR], 21.37; 95% confidence interval [CI], 6.24-73.21); CRIB-II > 10 (OR, 56.17; 95% CI, 6.75-467.2); SNAP-II > 22 (OR, 43.05; 95% CI, 11.9-155.7), and SNAPPE-II > 42 (OR, 48.95; 95% CI, 10.18-235.4) (all p values <.0001). CONCLUSIONS: Our findings indicate that HCA is a major predictor of morbidity and mortality in VLBW newborns.

Recent findings in the use of reflectance oximetry: a critical review.

PURPOSE OF REVIEW: Pulse oximetry is ubiquitous but detailed understanding of the technology is poor. This is illustrated by publications addressing knowledge of pulse oximetry and those warning against the use of transmission pulse oximeter sensors in a reflectance manner, unintended by the manufacturers, owing to the potential for iatrogenic problems. Reflectance oximetry sensors are distinct and their application rather specific. Users must adhere to the manufacturer's guidelines to be assured of approximating the claimed accuracy and other specifications. Moreover, a thorough understanding of the device's shortcomings will optimize performance and avoid misuse. Cautious skepticism is appropriate with use of any technology but particularly with indirect measures of vital signs. RECENT FINDINGS: The studies of reflectance sensors described here illustrate a diversity of successful applications and opportunities for further research. The genesis of applications for some sensors, for example fetal sensors, has proven helpful in other clinical settings where low mean arterial pressure and need for accurate monitoring of a SpO2 of less than 80% is poorly provided by transmittance sensors. Reflectance sensors are more prone to placement over contaminating sources (for example arteries and pigmentation), but their more sophisticated design can provide greater versatility than transillumination methods. SUMMARY: This invited review highlights recent developments and applications of reflectance oximetry with an emphasis on the potential clinical and research advantages.

Oral mucosal microvascular abnormalities: an early marker of bronchopulmonary dysplasia.

An abnormal pulmonary vasculature has been reported as an important component of bronchopulmonary dysplasia (BPD). We tested the hypothesis of an early abnormal vascular network pattern in infants with BPD. Fifteen infants with BPD (nine boys and six girls; gestational age 27.5 +/- 2.0 wk; birth weight 850 +/- 125 g) and 15 sex- and gestational age-matched infants (nine boys and six girls; gestational age 27.6 +/- 2.6 wk; birth weight 865 +/- 135 g) were examined on postnatal days 1 and 28. BPD infants showed a significantly higher prevalence of histologic chorioamnionitis (p = 0.009), as well as higher intubation duration (p = 0.0004), oxygen supplementation (p < 0.0001), and initial illness severity (p = 0.0002) than the BPD-negative population. The lower gingival and vestibular oral mucosa was chosen as the study area. The blood vessel area was determined, and the oral vascular networks were characterized by analyzing their complexity (D, at two scales: D 1-46, D 1-15), tortuosity (Dmin), and randomness (L-Z) of the vascular loops. Infants with BPD showed a significantly lower blood vessel area as well as a higher vascular network complexity (D 1-46, D 1-15, and L-Z) than control subjects (p < 0.0001). Our findings provide a new early clinical sign in BPD and stress the importance of an early disorder in the oral mucosal vascularization process in the disease pathogenesis.

Assessing high-risk infants in the delivery room with pulse oximetry.

Heart rate and oxygenation status are essential to the delivery room assessment of newborn infants. Pulse oximetry (PO) can capture these two variables but low peripheral perfusion, patient motion and the presence of ambient lighting can challenge the technology. New generation pulse oximeters claim to measure through these conditions. The objective of this study was to assess the performance of new generation pulse oximeters during the delivery room assessment and management of high-risk newborns. Part one (study A) compared the outcome of 25 infants simultaneously monitored with two new PO technologies (experimental group) to a matched population of 25 infants without PO-monitoring (control group). Findings from the experimental group revealed a significant difference between new PO technologies and an improvement in patient outcome compared to the control group. Part two (study B) evaluated the affects of PO-monitoring on 15 very immature infants. Use of Masimo SET PO was associated with a rapid acquisition and near continuous display of PO values, which proved valuable for initial respiratory care and to determine the need for more intensive procedures. Both studies revealed that near immediate postnatal PO monitoring of newborns in the delivery room was feasible and valuable.