ORi™: a new indicator of oxygenation

In the perioperative period, hypoxemia and hyperoxia are crucial factors that require attention, because they greatly affect patient prognoses. The pulse oximeter has been the only noninvasive monitor that can be used as a reference of oxygenation in current anesthetic management; however, in recent years, a new monitoring method that uses the oxygen reserve index (ORi™) has been developed by Masimo Corp. ORi is an index that reflects the state of moderate hyperoxia (partial pressure of arterial oxygen [PaO2] between 100 and 200 mmHg) using a non-unit scale between 0.00 and 1.00. ORi monitoring performed together with percutaneous oxygen saturation (SpO2) measurements may become an important technique in the field of anesthetic management, for measuring oxygenation reserve capacity. By measuring ORi, it is possible to predict hypoxemia and to detect hyperoxia at an early stage. In this review, we summarize the method of ORi, cautions for its use, and suitable cases for its use. In the near future, the monitoring of oxygen concentrations using ORi may become increasingly common for the management of respiratory function before, after, and during surgery.

New Device for Noninvasive Telemetric Monitoring of Vital Signs in Healthy and Newly Operated Piglets

Measuring vital signs is central to medical practice, but they are difficult to monitor in awake laboratory animals. We examined the feasibility of a noninvasive device for telemetric assessment of respiration rate, heart rate, temperature and movement in pigs. Awake piglets were monitored continuously for 31 h (interquartile range, 7) before (n = 4) and after (n = 3) surgery. Data quality was sufficient for determination of all parameters. We conclude that continuous, noninvasive monitor- ing of pigs is possible by using the evaluated device.

Incidence, Severity, and Detection of Blood Pressure Perturbations after Abdominal Surgery

Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Intraoperative and postoperative hypotension are associated with myocardial and kidney injury and 30-day mortality. Intraoperative blood pressure is measured frequently, but blood pressure on surgical wards is usually measured only every 4 to 6 h, leaving long intervals during which hypotension and hypertension may be undetected. This study evaluated the incidence and severity of postoperative hypotension and hypertension in adults recovering from abdominal surgery and the extent to which serious perturbations were missed by routine vital-sign assessments. Methods Blood pressure was recorded at 1-min intervals during the initial 48 h in adults recovering from abdominal surgery using a continuous noninvasive monitor. Caregivers were blinded to these measurements and depended on routine vital-sign assessments. Hypotension and hypertension were characterized as time under and above various mean arterial pressure thresholds. Results Of 502 available patients, 312 patients with high-quality records were analyzed, with a median measurement time of 48 [interquartile range: 41, 48] postoperative hours. Nearly a quarter experienced an episode of mean arterial pressure of less than 70 mm Hg lasting at least 30 min (24%; 95% CI, 20%, 29%), and 18% had an episode of mean arterial pressure of less than 65 mm Hg lasting at least 15 min. Nearly half the patients who had mean arterial pressure of less than 65 mm Hg for at least 15 min (47%; 95% CI, 34%, 61%) were undetected by routine vital-sign assessments. Episodes of mean arterial pressure greater than 110 mm Hg lasting at least 30 min were observed in 42% (95% CI, 37%, 48%) of patients; 7% had mean arterial pressure greater than 130 mm Hg for at least 30 min, 96% of which were missed by routine assessments. Episodes of mean arterial pressure less than 65 mm Hg and mean arterial pressure greater than 110 mm Hg captured by routine vital-sign assessments but not by continuous monitoring occurred in 34 and 8 patients, respectively. Conclusions Postoperative hypotension and hypertension were common, prolonged, profound, and largely undetected by routine vital-sign assessments in a cohort of adults recovering from abdominal surgery. Frequent or continuous blood pressure monitoring may detect hemodynamic perturbations more effectively and potentially facilitate treatment.

Monitoring Pressure Augmentation in Patients With Ischemic Penumbra Using Continuous Electroencephalogram: Three Cases and a Review of the Literature

Background: Continuous electroencephalography (CEEG) is a sensitive, noninvasive surrogate monitor of cerebral blood flow (CBF). Changes in CBF can be seen as changes in the frequencies on the CEEG. This case series suggests that increase in CEEG frequencies may be used to detect improved CBF following pressure augmentation such as with treatment of vasospasm from subarachnoid hemorrhage (SAH) or acute thrombosis from ischemic stroke. The application of this observation to clinical decision-making has not been clearly defined and requires further study. Methods: Case series and imaging. Results: We present 3 patients with ischemic penumbras either from vasospasm from SAH or thrombosis from acute ischemic stroke. All patients were monitored on CEEG and found to have lateralized slowing. During pressure augmentation, the lateralized slowing improved in frequency, which corresponded with improvement in the patients’ neurological examinations. Conclusion: Continuous electroencephalography may be used as a noninvasive monitor to allow for individualization of pressure augmentation in cases of vasospasm from SAH or in cases of acute ischemic strokes. This customized approach may allow for less morbidity associated with pressure augmentation in patients who otherwise may have dysfunction of their intracerebral autoregulation.

Noninvasive Monitoring of Cerebrovascular Autoregulation Response to Resistance Exercises

Background and Objective. A novel noninvasive monitor is presented by demonstrating its capabilities to perform the real-time estimation of dynamics in cerebrovascular autoregulation in athletes during their training. The aim was to explore the characteristics of human cerebrovascular autoregulation by performing the monitoring of cerebrovascular autoregulation responses to resistance exercises in healthy volunteer athletes. Material and Methods. Cerebrovascular autoregulation status was monitored in 20 amateur and 20 elite male athletes (weightlifters and bodybuilders) in the supine position at rest during and after the resistance exercises by using a novel noninvasive monitor “Vittamed.” Blood pressure and heart rate were also measured noninvasively. During the exercises, the athletes lifted 50 kg and 80% of 1RM (repetition maximum) weights in a dynamic and static manner in separate tests. Results. The cerebrovascular autoregulation reactivity index showed a temporal improvement in the cerebrovascular autoregulation status for almost all sportsmen after the exercises. No disturbances of cerebrovascular autoregulation response occurred in the weightlifters and amateur athletes after the static and dynamic exercises. However, an unstable status of cerebrovascular autoregulation was observed for the elite bodybuilders during the interval of 400 to 600 s after the exercises. Conclusions. The data of this study demonstrated significant differences in cerebrovascular autoregulation response to the resistance exercises between the elite bodybuilders and other subjects (amateurs and weightlifters) – a temporarily unstable status of cerebrovascular autoregulation was observed in the group of elite bodybuilders. This study also demonstrated the applicability of the noninvasive device for exploring the physiology of cerebrovascular autoregulation mechanism in elite athletes and healthy volunteers.

The Correlation of Near-Infrared Spectroscopy with Changes in Oxygen Delivery in a Controlled Model of Altered Perfusion

Alterations in regional tissue perfusion may precede global indications of shock. This study compared regional tissue oxygenation saturation (StO2) using near-infrared spectroscopy with standard hemodynamic and biochemical variables in 40 patients undergoing cardiopulmonary bypass (CPB). Mean arterial pressure, cardiac output, oxygen delivery, arterial blood gases, and lactate were recorded at specific intervals during surgery. Data were organized by stage of procedure, and the relationship of StO2 to established parameters was investigated. With initiation of CPB, StO2 declined by 12.9 per cent (standard deviation ± 14.75%) with a delayed increase in lactate from 0.9 (interquartile range [IQR], 0.6–1.5) mmol/L to 2.3 (IQR, 1.8–2.5) mmol/L. The minimum StO2 value preceded the maximum lactate level by an average time of 93.9 (standard deviation ± 86.3) minutes. Additionally, a decrease in StO2 corresponded with an increase in base deficit of 4.84 (standard deviation ± 2.37) mEq/L over the same period. Calculated oxygen delivery decreased from a baseline value of 754 (IQR, 560–950) mL/min to 472 (IQR, 396–600) mL/min with initiation and maintenance of CPB. For patients undergoing CPB, StO2 is a reliable, noninvasive monitor of perfusion, which correlates well with oxygen delivery and identifies perfusion deficits earlier than lactate or base deficit.