Low Perfusion Index Research Articles

Perfusion index monitoring and its correlation with outcome in neonates undergoing surgery

Background: The perfusion index (PI) has been found to be a reliable indicator of peripheral perfusion and can be used to monitor perfusion in neonates undergoing surgical procedures. To study correlation of perfusion index with the need for post op mechanical ventilation, ICU care and inotropic support in neonates undergoing surgery. Methods: Eighty neonates posted for surgery were enrolled after taking proper written informed consent from the parents. HR, BP and SPO2 and PI were recorded at 3 minutes interval for the first 30 minutes of surgery, followed by every 5 minutes till the end of procedure. Neonates requiring admission in the Department of Pediatrics were shifted to the Neonatal ICU or ward. Post-operative vitals were monitored initially every 30 minutes for first 24 hours followed by 2 hourly. Results: There was a statistically significant association between PI and need for post-op mechanical ventilation (MV). Duration of post-operative MV based on PI showed no significant difference. A lower PI was strongly correlated with an increased likelihood of requiring ICU-level care post-operatively, but not the duration of ICU stay. There was a potential association between PI and the requirement for inotropic support. Mortality rate was higher in patients with low PI, but not statistically significant. Conclusions: Low PI in neonates is associated with poor outcome in terms of need for ICU stay, need of postoperative mechanical ventilation and inotropic support.

Normal Value of Perfusion Index in Healthy Neonates Born in Iran.

Perfusion index is a dependable indicator for assessing the perfusion status of newborns. A low perfusion index indicates compromised hemodynamic function. The study aims to investigate perfusion index in asymptomatic newborns aged 35 to 41 weeks who did not require medical support. Healthy neonates born in four major maternity hospitals of Tehran University from 2019 to 2021 were selected. To ensure consistency and reliability in data collection, a detailed manual was developed and distributed, along with comprehensive training sessions for all personnel involved. A total of 994 newborns entered the study. Among them, echocardiography was adversely affected in 218 neonates due to abnormal screening pulse oximetry. Of these 218 neonates, 53 were found to have abnormal echocardiography results. The median perfusion index value in healthy neonates was 1.6%, and the median oxygen saturation was 97%. A percentile perfusion index curve was developed for healthy neonates to establish a normal reference range. Developing a percentile perfusion index curve specific to healthy neonates provides a useful reference range for healthcare providers to assess perfusion status in this population, but further research is needed to confirm its accuracy.

Evaluation of lateral sagittal infraclavicular block according to inferior vena cava collapsibility index (VCI-CI): An observational study.

Depending on the total amount of fluid, changes occur in the amount of fluid in the peripheral area. The aim of this study was to observe the differences caused by hemodynamic changes after lateral sagittal infraclavicular block (LS-ICB) according to the inferior vena cava collapsibility index (VCI-CI). In this prospective, observational study (Clinical Trial Number: NCT05968105), patients undergoing elective hand and wrist surgery with LS-ICB were classified according to VCI-CI, with Group 1 defined as inferior vena cava (VCI) diameter < 1.5 cm and VCI-CI > 50% and Group 2 defined as VCI diameter > 1.5 cm and VCI-CI < 50%. Groups were compared for demographic characteristics, defined durations, rescue analgesics, and complications. Continuous hemodynamic parameters and pulsed wave Doppler were evaluated within groups. Demographic characteristics and time periods were comparable between the groups. Hemodynamic parameters and pulsed wave Doppler measurements showed no significant differences. However, while Group 1 remained consistent, Group 2 exhibited differences in axillary artery diastolic diameter and axillary artery contractility index. A significant statistical difference was observed in Group 1 for the perfusion index at 30 minutes and postoperatively, whereas Group 2 remained consistent. The dosage and number of patients requiring rescue analgesics were similar across both groups, and no complications were reported. Blood flow increased after LS-ICB without a corresponding increase in axillary artery diameter. Group 1 showed a tendency toward a lower perfusion index in the postoperative period.

Peripheral Perfusion Index in Ugandan Children With Plasmodium falciparum Severe Malaria: Secondary Analysis of Outcomes in a 2014-2017 Cohort Study.

Continuous, noninvasive tools to monitor peripheral perfusion, such as perfusion index (PI), can detect hemodynamic abnormalities and assist in the management of critically ill children hospitalized with severe malaria. In this study of hospitalized children with severe malaria, we aimed to assess whether PI correlates with clinical markers of perfusion and to determine whether combining PI with these clinical measures improves identification of children with greater odds of mortality. Post hoc analysis of a prospective, multicenter, cohort study conducted between 2014 and 2017. Two referral hospitals in Central and Eastern Uganda. Six hundred children younger than 5 years old with severe malaria and 120 asymptomatic community children. None. PI was measured at 6-hour intervals for the first 24 hours of hospitalization. We compared PI to standard clinical perfusion measures such as capillary refill time, presence of cold peripheral limbs, or temperature gradient. Admission PI was highly correlated with clinical measures of perfusion. Admission PI was lower in children with severe malaria compared with asymptomatic community children; and, among the children with severe malaria, PI was lower in those with clinical features of poor perfusion or complications of severe malaria, such as shock and hyperlactatemia (all p < 0.02). Among children with severe malaria, lower admission PI was associated with greater odds of mortality after adjustment for age, sex, and severe malaria criteria (adjusted odds ratio, 2.4 for each log decrease in PI [95% CI, 1.0-5.9]; p = 0.045). Diagnostically, the presence of two consecutive low PI measures (< 1%) predicted mortality, with a sensitivity of 50% and a specificity of 76%. In severe malaria, PI correlates with clinical complications (including shock and elevated serum lactate) and may be useful as an objective, continuous explanatory variable associated with greater odds of later in-hospital mortality.

Exploring the bias: how skin color influences oxygen saturation readings via Monte Carlo simulations.

Our goal is to understand the root cause of reported oxygen saturation ( ) overestimation in heavily pigmented skin types to devise solutions toward enabling equity in pulse oximeter designs. We aim to gain theoretical insights into the effect of skin tone on curves using a three-dimensional, four-layer tissue model representing a finger. A finger tissue model, comprising the epidermis, dermis, two arteries, and a bone, was developed using a Monte Carlo-based approach in the MCmatlab software. Two skin tones-light and dark-were simulated by adjusting the absorption and scattering properties within the epidermal layer. Following this, curves were generated in various tissue configurations, including transmission and reflection modes using red and infrared wavelengths. In addition, the influence of source-detector (SD) separation distances on both light and dark skin tissue models was studied. In transmission mode, curves did not deviate with changes in skin tones because both pulsatile and non-pulsatile terms experienced equal attenuation at red and infrared wavelengths. However, in reflection mode, measurable variations in curves were evident. This was due to differential attenuation of the red components, which resulted in a lower perfusion index at the red wavelength in darker skin. As the SD separation increased, the effect of skin tone on curves in reflection mode became less pronounced, with the largest SD separation exhibiting effects similar to those observed in transmission mode. Monte Carlo simulations have demonstrated that different light pathlengths within the tissue contribute to the overestimation of in people with darker skin in reflection mode pulse oximetry. Increasing the SD separation may mitigate the effect of skin tone on readings. These trends were not observed in transmission mode; however, further planned research using more complex models of the tissue is essential.

Mean airway pressure as a parameter of lung-protective and heart-protective ventilation

Mean airway pressure (MAP) is the mean pressure generated in the airway during a single breath (inspiration + expiration), and is displayed on most anaesthesia and intensive care ventilators. This parameter, however, is not usually monitored during mechanical ventilation because it is poorly understood and usually only used in research. One of the main determinants of MAP is PEEP. This is because in respiratory cycles with an I:E ratio of 1:2, expiration is twice as long as inspiration. Although MAP can be used as a surrogate for mean alveolar pressure, these parameters differ considerably in some situations. Recently, MAP has been shown to be a useful prognostic factor for respiratory morbidity and mortality in mechanically ventilated patients of various ages. Low MAP has been associated with a lower incidence of 90-day mortality, shorter ICU stay, and shorter mechanical ventilation time. MAP also affects haemodynamics: there is evidence of a causal relationship between high MAP and low perfusion index, both of which are associated with poor prognosis in mechanically ventilated patients. Elevated MAP values have also been associated with high central venous pressure and lactate, which are indicative of ventilator-associated right ventricular failure and tissue hypoperfusion, respectively. MAP, therefore, is an important parameter to measure in clinical practice. The aim of this review has been to identify the determinants of MAP, the pros and cons of using MAP instead of traditional protective ventilation parameters, and the evidence that supports the use of MAP in clinical practice.

Presión media de la vía aérea: ¿parámetro integrador de ventilación pulmonar y circulatoria protectoras?

Mean airway pressure (MAP) is the mean pressure generated in the airway during a single breath (inspiration+expiration), and is displayed on most anaesthesia and intensive care ventilators. This parameter, however, is not usually monitored during mechanical ventilation because it is poorly understood and usually only used in research. One of the main determinants of MAP is PEEP. This is because in respiratory cycles with an I:E ratio of 1:2, expiration is twice as long as inspiration. Although MAP can be used as a surrogate for mean alveolar pressure, these parameters differ considerably in some situations. Recently, MAP has been shown to be a useful prognostic factor for respiratory morbidity and mortality in mechanically ventilated patients of various ages. Low MAP has been associated with a lower incidence of 90-day mortality, shorter ICU stay, and shorter mechanical ventilation time. MAP also affects haemodynamics: there is evidence of a causal relationship between high MAP and low perfusion index, both of which are associated with poor prognosis in mechanically ventilated patients. Elevated MAP values have also been associated with high central venous pressure and lactate, which are indicative of ventilator-associated right ventricular failure and tissue hypoperfusion, respectively. MAP, therefore, is an important parameter to measure in clinical practice. The aim of this review has been to identify the determinants of MAP, the pros and cons of using MAP instead of traditional protective ventilation parameters, and the evidence that supports the use of MAP in clinical practice.

Perfusion Index as a Predictor of Hemodynamically Significant Patent Ductus Arteriosus in Preterm Newborns

Aim To assess the value of perfusion index (PI) and arrive at the ideal cut-off value of delta PI (DPI) (pre and postductal difference in PI) in identifying hemodynamically significant patent ductus arteriosus (HsPDA). Methods Prospective observational study was conducted on 156 preterm newborns of &lt;37 weeks in the NICU of tertiary care center, from August 2019 to March 2020 after ethical clearance. 156 preterm babies were classified into noPDA, HsPDA and Non-HsPDA based on echocardiogram findings and compared with DPI value on Day 1 to 3 of life. Receiver operating characteristic (ROC) curve was constructed to establish cut-offs for DPI in diagnosing HsPDA. A P value &lt;.05 is considered for statistical significance. Results There was a significantly lower PI in both preductal and post ductal limbs with HsPDA compared to other groups. A DPI Cut-off of 0.75 on day 2 of life has a sensitivity of 75%, specificity of 100% and positive predictive value (PPV) of 100% and a negative predictive value of 89%. Conclusion PI is a simple non-invasive bedside index predict the presence of a HsPDA in preterm newborns and DPI of &gt;0.75 indicates for presence of HsPDA.

Racial effects on masimo pulse oximetry: impact of low perfusion index

Purpose: Evaluate the SpO2-SaO2 difference between Black and White volunteer subjects having a low perfusion index (Pi) compared to those having a normal Pi. Methods: The Pi data were abstracted from electronic files collected on 7183 paired SpO2-SaO2 samples (3201 Black and 3982 White) from a recently reported desaturation study of 75 subjects (39 Black and 36 White) where SaO2 values were sequentially decreased from 100 to 70%. The Pi values from that dataset were divided into two groups (Pi ≤ 1 or Pi > 1) for analysis. A Pi value ≤ 1 was considered “low perfusion” and a Pi value > 1 was considered “normal perfusion”. Statistical calculations included values of bias (mean difference of SpO2-SaO2), precision (standard deviation of the difference), and accuracy (root-mean-square error [ARMS]). During conditions of low perfusion (Pi ≤ 1, range [0.1 to 1]), overall bias and precision were + 0.48% ± 1.59%, while bias and precision were + 0.19 ± 1.53%, and + 0.91 ± 1.57%, for Black and White subjects, respectively. Results: During normal perfusion (Pi > 1, range [1 to 12]), overall bias and precision were + 0.18% ± 1.34%, while bias and precision were -0.26 ± 1.37%, and − 0.12 ± 1.31%, for Black and White subjects, respectively. ARMS was 1.37% in all subjects with normal perfusion and 1.64% in all subjects with low perfusion. Conclusion: Masimo SET® pulse oximeters with RD SET® sensors are accurate for individuals of both Black and White races when Pi is normal, as well as during conditions when Pi is low. The ARMS for all conditions studied is well within FDA standards. This study was conducted in healthy volunteers during well-controlled laboratory desaturations, and results could vary under certain challenging clinical conditions.

Comparing Non-Invasive Spectrophotometry to Hematology Analysis for Hemoglobin Measurements in Sickle Cell Disease Patients.

Patients with sickle cell disease (SCD) require repeated blood sampling for hemoglobin (Hb) concentration measurements. The primary aim of this study was to compare non-invasive spectrophotometric hemoglobin (SpHb, g/dL) measurements to those taken via an automated hematology analyzer (Hb, g/dL) in patients with SCD visiting outpatient clinics and to investigate the correlations and agreements between both measurement techniques. Secondarily, we aimed to identify the SpHb cut-off concentration for the diagnosis of anemia and to monitor the effects of the pleth variability index (PVI, %) and perfusion index (PI) on SpHb measurements. The results gained from the examination of one hundred and fifty-eight patients indicated that the SpHb measurements overestimated the lab Hb concentrations, with a mean (SpHb-Hb) bias of 0.82 g/dL (SD 1.29). The SpHb measurements were positively correlated with the Hb measurements (Kendall's tau correlation (τ), n = 158, τ = 0.68, p < 0.001), with an intra-class correlation (ICC) of 0.67 and a 95% CI from 0.57 to 0.74 (p = 0.000). The SpHb cut-off concentration to diagnose anemia was 11.4 and 11.7 g/dL for males and females, respectively. SpHb sensitivity was low for males and females at 64.4% and 57.1%; however, the specificity was higher at 90.9% and 75%, with positive predictive values (PPVs) of 95.6 and 85.7, respectively. No correlation existed between SpHb measurements and the PVI (%) in contrast with a moderate correlation with the PI (r = 0.049, p = 0.54, and r = 0.36, p < 0.001, respectively). The mean PI was low at 2.52 ± 1.7. In conclusion, the SpHb measurements were consistently higher than the lab Hb concentrations, with a positive correlation. The sensitivity and precision of the SpHb measurements were lower than expected. However, the SpHb specificity and its positive predictive values (PPVs) indicated that it is less likely for a patient with a positive SpHb test result for anemia to be non-anemic. These results will allow SpHb measurement to play a role in excluding the presence of anemia. In light of the low PI values determined, the SpHb measurements were challenging to take and, thus, require further technological improvements.

Effect of Norepinephrine on Peripheral Perfusion Index and Its Association With the Prognosis of Patients With Sepsis.

Background: To evaluate whether the use of norepinephrine during the management of patients with sepsis affects the perfusion index (PI) and patient outcomes. Methods: We retrospectively studied patients with septic shock between January 2014 and December 2018 who had undergone Pulse index Continuous Cardiac Output-Plus cardiac output monitoring and received norepinephrine during the management. We collected data regarding basic clinical characteristics. Hemodynamic parameters, including lactate, PI, and norepinephrine dose at T0 and 24 h after Pulse index Continuous Cardiac Output catheterization (T24) were obtained. Results: The PI of the nonsurvivor group (n = 44) was significantly lower than that of the survivor group (n = 144) at T24, and the lactate level of the nonsurvivor group was significantly higher than that of the survivor group. The multiple logistic regression analysis suggested that the norepinephrine dose and PI were the most independent risk and protective factors, respectively, for intensive care unit mortality. The area under the curve for a poor prognosis was 0.847 (95% confidence interval, 0.782-0.912). The optimal cutoff value of the PI at T24 to predict intensive care unit mortality was 0.6, with a sensitivity of 77.1% and a specificity of 80%. Based on this optimal cutoff value, we divided patients into groups with PI ≥ 0.6 (n = 125) and PI < 0.6 (n = 59). The lactate level of the PI < 0.6 group was higher than that of the PI ≥ 0.6 group at T24. The PI < 0.6 group showed a significantly higher sublingual dose of norepinephrine indicators than the PI ≥ 0.6 group. The PI showed a strong negative correlation with norepinephrine dose (r = -0.344, P < .001) and lactate (r = -0.291, P < .001). Conclusions: A higher PI is a protective factor, and a higher dose of norepinephrine is a risk factor for the prognosis of critically ill patients with septic shock. A lower PI was associated with a higher dose of norepinephrine.

Role of perfusion index and plethysmography variability index for predicting outcomes in neonatal sepsis.

(i) To compare perfusion index (PI) and plethysmography variability index (PVI) between neonates with proven or probable sepsis versus no-sepsis, (ii) to examine an association of PI and PVI with in-hospital mortality. We enrolled neonates with clinically presumed sepsis. Culture-proven or probable sepsis were categorised as 'cases' and no-sepsis as 'controls'. PI and PVI were recorded hourly for 120 h and averaged in 20-time epochs (0-6 h to 115-120 h). We analysed 148 neonates with sepsis (proven sepsis = 77, probable sepsis = 71) and 126 with no-sepsis. Neonates with proven/probable sepsis and no-sepsis had comparable PI and PVI values. Among 148 neonates with sepsis, 43 (29%) died. Non-survivors had significantly lower PI values than survivors (mean difference 0.21 [95% CI 0.14-0.29], p-value <0.001). PI had a significant but modest discriminative ability to identify non-survivors. However, PI did not independently predict mortality. Neonates with proven/probable sepsis and no-sepsis had comparable PI and PVI values in the first 120 h of sepsis. PI but not PVI values were significantly lower in non-survivors than survivors. PI did not independently predict in-hospital mortality. Due to modest discriminative ability, PI should be interpreted along with other vital signs to take clinical decisions.

Initial 24-h perfusion index of ICU admission is associated with acute kidney injury in perioperative critically ill patients: A retrospective cohort analysis

BackgroundThe relationship between perfusion index (PI) and organ dysfunction in patients in the intensive care unit (ICU) is not clear. This study aimed to explore the relationship between PI and renal function in the perioperative critical care setting and evaluate the predictive efficiency of PI on patients with acute kidney injury (AKI) in the ICU. MethodsThis retrospective analysis involved 12,979 patients who had undergone an operation and were admitted to the ICU in Peking Union Medical College Hospital from January 2014 to December 2019. The distribution of average PI in the first 24 h after ICU admission and its correlation with AKI was calculated by Cox regression. Receiver operating characteristic (ROC) curves were generated to compare the ability of PI, mean arterial pressure (MAP), creatinine, blood urea nitrogen (BUN), and central venous pressure (CVP) to discriminate AKI in the first 48 h in all perioperative critically ill patients. ResultsAverage PI in the first 24 h served as an independent protective factor of AKI (Odds ratio [OR]=0.786, 95% confidence interval [CI]: 0.704–0.873, P <0.0001). With a decrease in PI by one unit, the incidence of AKI increased 1.74 times. Among the variables explored for the prediction of AKI (PI, MAP, creatine, BUN, and CVP), PI yielded the highest area under the ROC curve, with a sensitivity of 64.34% and specificity of 70.14%. A cut-off value of PI ≤2.12 could be used to predict AKI according to the Youden index. Moreover, patients in the low PI group (PI ≤2.12) exhibited a marked creatine elevation at 24–48 h with a slower decrease compared with those in the high PI group (PI >2.12). ConclusionsAs a local blood flow indicator, the initial 24-h average PI for perioperative critically ill patients can predict AKI during their first 120 h in the ICU.

Comparative effects of desflurane and sevoflurane on intraoperative peripheral perfusion index: a retrospective, propensity score matched, cohort study

Desflurane is known to have a larger vasodilatory effect than that of sevoflurane. However, its generalizability and effect size in actual clinical practice are yet to be proven. Patients aged ≥ 18 years who underwent noncardiac surgery under general anesthesia using inhalation anesthetics (desflurane or sevoflurane) were matched 1:1 by propensity score. The mean intraoperative perfusion index (PI) of each patient were compared between the two groups. Propensity score matching of 1680 patients in the study cohort identified 230 pairs of patients. PI was significantly higher in the desflurane group (median of paired difference, 0.45; 95% CI 0.16 to 0.74, p = 0.002). PI durations below 1.0 and 1.5 were significantly longer in the sevoflurane group. Mean arterial pressure (MAP) and durations of low MAP did not differ significantly between the two groups. Generalized linear mixed models revealed that the use of sevoflurane, mean MAP, mean heart rate, age, and duration of anesthesia had significant negative effects (lower PI), whereas mean age-adjusted minimum alveolar concentration of inhalation agent had a positive effect on PI (higher value). Intraoperative PI was significantly higher in patients administered desflurane than sevoflurane. However, the impact of the choice between desflurane and sevoflurane on intraoperative PI in this clinical setting was minimal.

A low peripheral perfusion index can accurately detect prolonged capillary refill time during general anesthesia: A prospective observational study.

Capillary refill time (CRT) is the gold standard for evaluating peripheral organ perfusion; however, intraoperative CRT measurement is rarely used because it cannot be conducted continuously, and it is difficult to perform during general anesthesia. The peripheral perfusion index (PI) is another noninvasive method for evaluating peripheral perfusion. The PI can easily and continuously evaluate peripheral perfusion and could be an alternative to CRT for use during general anesthesia. This study aimed to determine the cutoff PI value for low peripheral perfusion status (prolonged CRT) by exploring the relationship between CRT and the PI during general anesthesia. We enrolled 127 surgical patients. CRT and the PI were measured in a hemodynamically stable state during general anesthesia. A CRT >3 s indicated a low perfusion status. Prolonged CRT was observed in 27 patients. The median PI values in the non-prolonged and prolonged CRT groups were 5.0 (3.3-7.9) and 1.5 (1.2-1.9), respectively. There was a strong negative correlation between the PI and CRT (r = -0.706). The area under the receiver operating characteristic curve generated for the PI was 0.989 (95% confidence interval, 0.976-1.0). The cutoff PI value for detecting a prolonged CRT was 1.8. A PI <1.8 could accurately predict a low perfusion status during general anesthesia in the operating room. A PI <1.8 could be used to alert the possibility of a low perfusion status in the operating room. University Hospital Medical Information Network (UMIN000043707; retrospectively registered on March 22, 2021, https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno = R000049905).

Effect of intraoperative operating table rotation on lower limb perfusion index in patients in the lithotomy position.

We focused on “returning to the horizontal position,” one of the measures for preventing well leg compartment syndrome implemented at our hospital, and aimed to clarify the effect of intraoperative positional changes by operating table rotation on blood perfusion in the lower extremities during lithotomy in patients under general anesthesia. This prospective observational study examined 64 patients scheduled to undergo general anesthesia in the lithotomy position from March 2021 to May 2022. The primary endpoint was the perfusion index (PI) of the lower limb before and after operating table rotation. The baseline lower limb PI before the operating table rotation was 2.376 (1.591), and the lower limb PI after the change from Trendelenburg to the horizontal position was as follows: immediately after, 2.123 (1.405); 5 minutes, 1.894 (1.138); 10 minutes, 1.915 (1.167); and 15 minutes, 1.993 (1.218). Compared with the baseline, no significant difference was noted in the change in the lower limb PI due to the Trendelenburg to horizontal positional change. The baseline lower leg pressure before the operating table rotation was 51.4 (13.4) mm Hg, and the lower leg pressure after the change from the Trendelenburg to the horizontal position was as follows: immediately after, 36.6 (10.3) mm Hg; 5 minutes, 36.5 (10.2) mm Hg; 10 minutes, 36.4 (10.0) mm Hg; and 15 minutes, 36.5 (10.2) mm Hg. Compared with the baseline, the change in lower leg pressure due to the Trendelenburg to horizontal positional change showed a significant decrease immediately afterward (P < .001). After operating table rotation from the Trendelenburg to the horizontal position, the lower limb PI did not change significantly after 15 min. However, lower leg pressure showed a significant decrease immediately after returning to the horizontal position. This result provides evidence for operating table rotation as a preventive measure for well leg compartment syndrome.

RENAL MICROPERFUSION RESPONSE TO A COLD PRESSURE TEST IS DECREASED IN HYPERTENSIVE PATIENTS

Objective: Microcirculation is essential to supply oxygen and nutriments to tissue. Alteration in the microcirculation is often proposed as a mechanistic link between hypertension and target organ damage. The recent developments in contrast-enhanced ultrasonography (CEUS) have enable the quantification of renal microcirculation. The objective of this study was to compare the microcirculatory response during a cold pressure test (CPT) in hypertensive (HT) patients with those in healthy normotensive (NT) participants. Design and method: This was a prospective case-control study. Hypertensive (HT) and normotensive (NT) participants underwent two separate CPT of 2 minutes. Doppler ultrasound was used to measure renal resistive index (RRI) and CEUS to measure the perfusion index (PI) as a proxy of renal tissue microcirculation. Renal Doppler and CEUS were performed before and during the CPT. We compared baseline measures and responses to CPT of HT and NT groups using a Wilcoxon test. Results: Sixteen hypertensive and nineteen normotensive male participants were included. HT participants were older and had higher blood pressure and body mass index. Baseline RRI was similar in both group, but HT had lower PI (median with interquartile range): 1083 U(447–1476) vs 1772 U(1295–2557), p = 0.016. The CPT decreased the RRI in NT and increased the RRI in HT, resulting in a different CPT response -0.026 [CI -0.045; -0.008, p = 0.006]. The CPT increased the PI in both groups but the response was blunted in HT patients - 755U ± 518, (p = 0.01). Conclusions: Compared to healthy participants, hypertensive patients show a paradoxal RRI response and a lower increase in perfusion index during CPT suggesting that microcirculation and possibly renal autoregulation is altered. This is the first demonstration showing that CEUS enables the detection of microcirculatory differences between healthy participants and hypertensive patients.

A study to evaluate perfusion index as a predictor of hypotension following spinal anesthesia for caesarean section.

Background and Aims:The perfusion index (PI) has been used as a marker of peripheral perfusion. A lower PI indicates greater peripheral vascular tone and increased risk of hypotension following spinal anesthesia. The present study was conducted to evaluate and correlate perfusion index (PI) with incidence of hypotension following spinal anesthesia for caesarean section.Material and Methods:The present prospective, double blind, observational study included sixty full term parturients in the age group 18-35 years belonging to American Society of Anesthesiologists (ASA) physical status I and II, having singleton pregnancy undergoing caesarean section under spinal anesthesia. On the basis of baseline PI, patients were allocated into one of the two groups: Group I (n = 30) Patients with baseline PI ≤.3.5 and Group II (n = 30) Patients with PI >3.5.Results:The incidence of hypotension in group I was 40% as compared to 73.3% in group II (p = 0.009). Thus, the incidence of hypotension in group II with baseline PI >.3.5 was more as compared to group I. Patients in group II with baseline PI >.3.5 had significantly more episodes of hypotension as compared to those in group I with baseline PI ≤3.5.Conclusion:PI can be used as a useful tool for predicting hypotension in parturients undergoing elective caesarean section under spinal anesthesia in everyday practice.

Low peripheral perfusion index values may indicate the need for antivenom in the early phase of scorpion envenomation

BackgroundScorpion envenomation may cause local symptoms as well as life-threatening situations including shock, and death. Antivenom administration is the cornerstone of therapy, meticulous patient selection is needed because of the possible side effects of the antivenom including anaphylaxis. Peripheral perfusion index (PPI) is a simple, non-invasive test that is widely used for the detection of peripheral hypoperfusion. We aimed to investigate the value of using PPI to predict the need for antivenom administration for scorpion envenomation. MethodsThis prospective observational study was conducted in the ED of a tertiary care center. We consecutively enrolled patients with scorpion envenomation on the extremities who are over 18 years old without pregnancy and a peripheral arterial disease between March 1, 2021, to October 31, 2021. Demographics included age, sex, sting zone, the time between sting and the ED admission, and vital parameters, we blindly measured PPI both on affected and contralateral extremities before any therapeutic intervention. We compared PPI levels, vital parameters, and the outcome including discharge from the ED, admission to ward or ICU, and death between patients who received antivenom and those who did not. ResultsTwenty-nine male (58.0%) and 21 (42.0%) female patients with scorpion envenomation were enrolled in the study. The median age was 46.5 [IQR 33.3]. Thirty-eight (76.0%) patients had Class I, 12 (24.0%) patients had Class II and III envenomation. The median duration of the ED admission after the sting was 90 [IQR 120] minutes. Antivenom was administered in 13 (26.0%) patients. PPI was significantly lower both on the affected and the contralateral extremities (p = 0.043 and p = 0.045, respectively) in patients who required antivenom. With a cut-off value of 2.4, PPI can predict the need for antivenom with a sensitivity of 61.54%, a specificity of 86.5%, a positive likelihood ratio of 4.55, a negative likelihood ratio of 0.44, a positive predictive value of 61.54%, a negative predictive value of 86.49%, and an accuracy of 80% (AUC 0.691, p < 0.05). ConclusionPPI can better reflect the ongoing systemic inflammation and the need for antivenom compared to other vital parameters. Therefore, we suggest this noninvasive and objective test may have a significant role in detecting patients who need antivenom in the early phase of scorpion envenomation. However, more studies are needed to elucidate the role of PPI in scorpion envenomation.

A Low-Noise Analog Front End with Interstage Systematically Ambient Interference Cancellation for Pulse Oximeter

This paper presents a low-noise analog front end (AFE) with interstage systematically ambient interference cancellation for a pulse oximeter, which is suitable for clinical oxygen saturation (SPO2) detection with a low perfusion index. The fully differential implementation is adopted to have a better rejection performance of common mode interference and noise. Firstly, the proposed interstage systematically ambient interference cancellation is placed in the two gain stages to decrease low frequency noise in the bandwidth of interest (0.1–20 Hz), so that the larger signal-to-noise ratio (SNR) can be achieved to increase the detection accuracy of this system. Secondly, due to the additional gain stage compared with traditional implementation, the current-reuse OTA is employed to have better noise and power efficiency. Thirdly, the auto zero technique is utilized in the LED Driver to decrease the offset voltage and acquire a larger dynamic range (DR) in the low frequency bandwidth of interest. This PPG AFE chip is designed and fabricated in a 180 nm standard CMOS process. The receiver (RX) of this AFE consumes 220 μW from a 1.8 V supply, and the power consumption of the transmitter (TX) is 60 μW from a 3 V supply. The measurement results show that the input-referred noise current of 2.3 pA/sqrt(Hz) is achieved in RX and 110 dB peak DR is obtained in TX.