Randomized evaluation of pulse oximetry in 20,802 patients: I. Design, demography, pulse oximetry failure rate, and overall complication rate

Causes of Perioperative Cardiac Arrest: Mnemonic, Classification, Monitoring, and Actions

Perioperative cardiac arrest (POCA) is a catastrophic complication that requires immediate recognition and correction of the underlying cause to improve patient outcomes. While the hypoxia, hypovolemia, hydrogen ions (acidosis), hypo-/hyperkalemia, and hypothermia (Hs) and toxins, tamponade (cardiac), tension pneumothorax, thrombosis (pulmonary), and thrombosis (coronary) (Ts) mnemonic is a valuable tool for rapid differential diagnosis, it does not cover all possible causes leading to POCA. To address this limitation, we propose using the preload-contractility-afterload-rate and rhythm (PCARR) construct to categorize POCA, which is comprehensive, systemic, and physiologically logical. We provide evidence for each component in the PCARR construct and emphasize that it complements the Hs and Ts mnemonic rather than replacing it. Furthermore, we discuss the significance of utilizing monitored variables such as electrocardiography, pulse oxygen saturation, end-tidal carbon dioxide, and blood pressure to identify clues to the underlying cause of POCA. To aid in investigating POCA causes, we suggest the Anesthetic care, Surgery, Echocardiography, Relevant Check and History (A-SERCH) list of actions. We recommend combining the Hs and Ts mnemonic, the PCARR construct, monitoring, and the A-SERCH list of actions in a rational manner to investigate POCA causes. These proposals require real-world testing to assess their feasibility.

Signaling Patient Oxygen Desaturation with Enhanced Pulse Oximetry Tones

Manufacturers could improve the pulse tones emitted by pulse oximeters to support more accurate identification of a patient's peripheral oxygen saturation (SpO2) range. In this article, we outline the strengths and limitations of the variable-pitch tone that represents SpO2 of each detected pulse, and we argue that enhancements to the tone to demarcate clinically relevant ranges are feasible and desirable. The variable-pitch tone is an appreciated and trusted feature of the pulse oximeter's user interface. However, studies show that it supports relative judgments of SpO2 trends over time and is less effective at supporting absolute judgments about the SpO2 number or conveying when SpO2 moves into clinically important ranges. We outline recent studies that tested whether acoustic enhancements to the current tone could convey clinically important ranges more directly, without necessarily using auditory alarms. The studies cover the use of enhanced variable-pitch pulse oximeter tones for neonatal and adult use. Compared with current tones, the characteristics of the enhanced tones represent improvements that are both clinically relevant and statistically significant. We outline the benefits of enhanced tones, as well as discuss constraints of which developers of enhanced tones should be aware if enhancements are to be successful.

Signaling Patient Oxygen Desaturation with Enhanced Pulse Oximetry Tones

Manufacturers could improve the pulse tones emitted by pulse oximeters to support more accurate identification of a patient's peripheral oxygen saturation (SpO2) range. In this article, we outline the strengths and limitations of the variable-pitch tone that represents SpO2 of each detected pulse, and we argue that enhancements to the tone to demarcate clinically relevant ranges are feasible and desirable. The variable-pitch tone is an appreciated and trusted feature of the pulse oximeter's user interface. However, studies show that it supports relative judgments of SpO2 trends over time and is less effective at supporting absolute judgments about the SpO2 number or conveying when SpO2 moves into clinically important ranges. We outline recent studies that tested whether acoustic enhancements to the current tone could convey clinically important ranges more directly, without necessarily using auditory alarms. The studies cover the use of enhanced variable-pitch pulse oximeter tones for neonatal and adult use. Compared with current tones, the characteristics of the enhanced tones represent improvements that are both clinically relevant and statistically significant. We outline the benefits of enhanced tones, as well as discuss constraints of which developers of enhanced tones should be aware if enhancements are to be successful.

Apophenia and anesthesia: how we sometimes change our practice prematurely

Human beings are predisposed to identifying false patterns in statistical noise, a likely survival advantage during our evolutionary development. Moreover, humans seem to prefer "positive" results over "negative" ones. These two cognitive features lay a framework for premature adoption of falsely positive studies. Added to this predisposition is the tendency of journals to "overbid" for exciting or newsworthy manuscripts, incentives in both the academic and publishing industries that value change over truth and scientific rigour, and a growing dependence on complex statistical techniques that some reviewers do not understand. The purpose of this article is to describe the underlying causes of premature adoption and provide recommendations that may improve the quality of published science.

Complications and survival after subcutaneous ureteral bypass device placement in 24 cats: a retrospective study (2016-2019)

OBJECTIVES

The aim of this study was to document survival, complications and risk factors for the development of complications and mortality prior to discharge after placement of a subcutaneous ureteral bypass (SUB) device in cats.

METHODS

The medical records of cats with SUB placement between January 2016 and August 2019 were retrospectively analysed. The development of complications (overall, intraoperative, perioperative, short- and long-term complications) and risk factors for mortality prior to discharge were statistically assessed with univariate binary logistic regression. All variables with a P value ⩽0.10 in the univariate analysis were assessed in a multivariate model. Variables were significant if P <0.05.

RESULTS

Twenty-four cats were included; 12 (50.0%) received a unilateral SUB, 11 (45.8%) a bilateral nephrostomy tube with single cystostomy catheter and the remaining cat (4.2%) two unilateral SUBs. Nearly 80% of the cats developed complications, ranging from mild to fatal, including (partial) SUB obstruction (33.3% of complications), lower urinary tract infection (20.8%), pyelonephritis (20.8%) and sterile cystitis (12.5%). Five cats (20.8%) died prior to discharge. Six cats (25.0%) underwent revision surgery. The overall median survival time (MST) was 274 days (range 1-311 days). Complications were most common in the long-term period (14/16 cats), followed by the short-term (9/18 cats), perioperative (10/23 cats) and intraoperative (4/24 cats) periods. Older cats had an increased risk for developing perioperative complications (P = 0.045) and were less likely to survive to discharge (P = 0.033). An increased haematocrit at presentation was a risk factor for the occurrence of short-term complications (P = 0.03).

CONCLUSIONS AND RELEVANCE

Although complications similar to those previously described were observed, the complication rate was higher and the MST shorter than previously reported in cats undergoing SUB placement. Despite good short-term survival, the development of complications may necessitate regular and intensive control visits. Owners that consider SUB placement should be informed that follow-up can be strenuous and expensive.

Injectable, thermosensitive, fast gelation, bioeliminable, and oxygen sensitive hydrogels

The decrease of tissue oxygen content due to pathological conditions leads to severe cell death and tissue damage. Restoration of tissue oxygen content is the primary treatment goal. To accurately and efficiently assess efficacy of a treatment, minimally invasive, and long-term detection of oxygen concentration in the same tissue location represents a clinically attractive strategy. Among the different oxygen concentration measurement approaches, electron paramagnetic resonance (EPR) has the potential to accomplish this. Yet there lacks injectable EPR probes that can maintain a consistent concentration at the same tissue location during treatment period to acquire a stable EPR signal, and can finally be eliminated from body without retrieval. Herein, we developed injectable and bioeliminable hydrogel-based polymeric EPR probes that exhibited fast gelation rate, slow weight loss rate, and high oxygen sensitivity. The probe was based on N-Isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), dimethyl-γ-butyrolactone acrylate (DBA), and tetrathiatriarylmethyl (TAM) radical. The injectable probes can be implanted into tissues using a minimally invasive injection approach. The high gelation rate (~10 s) allowed the probes to quickly solidify upon injection to have a high retention in tissues. The polymeric probes overcame the toxicity issue of current small molecule EPR probes. The probes can be gradually hydrolyzed. Upon complete hydrolysis, the probes became water soluble at 37 °C, thus having the potential to be removed from the body by urinary system. The probes showed slow weight loss rate so as to maintain EPR signal intensity for extended periods while retaining in a certain tissue location. The probes remained their high oxygen sensitivity after in vitro hydrolysis and in vivo implantation for 4 weeks. These hydrogel-based EPR probes have attractive properties for in vivo oxygen detection.

Evaluation of key design parameters for mitigating motion artefact in the mobile reflectance PPG signal to improve estimation of arterial oxygenation

OBJECTIVE

Pulse oximetry, a widely accepted method for non-invasive estimation of arterial oxygen saturation (SpO₂) and pulse rate (PR), is increasingly being adapted for mobile applications. Previous work in mitigating motion artefact, which corrupts the photoplethysmogram (PPG) used in pulse oximetry, has focused on reducing noise using signal processing algorithms or through sensor design that controlled only one variable at a time. In this work, we have investigated the effect of several variables such as sensor weight, relative motion, placement, and contact force against the skin that can impact motion artefact independently or by interacting with each other.

APPROACH

We have identified a unique combination of these variables that is most optimal in reducing motion artefacts using a full factorial design of experiments methodology and evaluated the effect of these factors on PPG readings with and without motion.

MAIN RESULTS

Data collected on 10 diverse subjects showed that placement (p  =  0.03), contact force (p  =  0.004), and sensor-to-skin adhesion or relative motion when combined with force (p  <  0.001) had the most significant effect on reducing the motion artefact signal. Sensor weight (p  =  0.822) by itself had no significant effect, however when combined with sensor adhesion (p  <  0.001) had a significant impact.

SIGNIFICANCE

This lays the foundation for future development of more robust sensors that can significantly reduce the effect of motion artefacts in reflectance-based pulse oximetry and could have great clinical value due to significant reduction of SpO₂ errors and false alarms associated with motion artefact, making wearable pulse oximetry more reliable in mobile applications.

Increasing body mass index and the incidence of intraoperative hypoxemia

STUDY OBJECTIVE

Obese patients regularly present for surgery and have greater hypoxemia risk. This study aimed to identify the risk and incidence of intraoperative hypoxemia with increasing body mass index (BMI).

DESIGN

This was a retrospective cohort study.

SETTING

Operating room.

PATIENTS

A total of 15,238 adult patients who underwent general anesthesia for elective noncardiac surgery at a single large urban academic institution between January 2013 and December 2014.

INTERVENTIONS

Unadjusted and risk-adjusted logistic regression analyses explored the relationship between increasing categories of BMI and intraoperative hypoxemia, severe hypoxemia, and prolonged hypoxemia.

MEASUREMENTS

Intraoperative pulse oximeter readings and preoperative patient characteristics.

MAIN RESULTS

With normal BMI, 731 (16%) patients experienced hypoxemia compared with 1150 (28%) obese patients. Adjusted odds ratio (AOR) of intraoperative hypoxemia increased with each category of BMI from 1.27 (95% confidence interval [CI], 1.12-1.44) in overweight patients to 2.63 (95% CI, 2.15-3.23) in patients with class III obesity. AOR of severe hypoxemia was significant with class I obesity (AOR, 1.32; 95% CI, 1.08-1.60), class II obesity (AOR, 2.01; 95% CI, 1.59-2.81), and class III obesity (AOR, 2.27; 95% CI, 1.75-2.93). AOR of prolonged hypoxemia increased with BMI from 3.29 (95% CI, 1.79-6.23) with class I obesity to 9.20 (95% CI, 4.74-18) with class III obesity.

CONCLUSIONS

Despite existing practices to limit hypoxemia in obese patients, the odds of experiencing intraoperative hypoxemia increase significantly with increasing categories of BMI. Further practices may need to be developed to minimize the risk of intraoperative hypoxemia in obese patients.

Continuous Noninvasive Hemoglobin Monitoring: A Measured Response to a Critical Review

Supplemental Digital Content is available in the text.

Published ahead of print March 5, 2015

Recommendations for standards of monitoring during anaesthesia and recovery 2015: Association of Anaesthetists of Great Britain and Ireland

This guideline updates and replaces the 4th edition of the AAGBI Standards of Monitoring published in 2007. The aim of this document is to provide guidance on the minimum standards for physiological monitoring of any patient undergoing anaesthesia or sedation under the care of an anaesthetist. The recommendations are primarily aimed at anaesthetists practising in the United Kingdom and Ireland. Minimum standards for monitoring patients during anaesthesia and in the recovery phase are included. There is also guidance on monitoring patients undergoing sedation and also during transfer of anaesthetised or sedated patients. There are new sections discussing the role of monitoring depth of anaesthesia, neuromuscular blockade and cardiac output. The indications for end-tidal carbon dioxide monitoring have been updated.

Pulse oximetry

Pulse oximetry is universally used for monitoring patients in the critical care setting. This article updates the review on pulse oximetry that was published in 1999 in Critical Care. A summary of the recently developed multiwavelength pulse oximeters and their ability in detecting dyshemoglobins is provided. The impact of the latest signal processing techniques and reflectance technology on improving the performance of pulse oximeters during motion artifact and low perfusion conditions is critically examined. Finally, data regarding the effect of pulse oximetry on patient outcome are discussed.

Detection of hypoxia in the early postoperative period

The aim of this study was to determine the incidence of early postoperative hypoxia after general anesthesia and to evaluate the need of oxygen supplementation. A total of 150 patients aged between 18-60 years belonging to ASA I or II were studied. Patients were alternately allocated to two groups of 75 each. Group-I (n=75) patients received 2 L of oxygen via nasopharyngeal catheter during transfer from operation theatre to recovery room and in the recovery room for a period of 4 h. Group-II (n=75) patients did not receive oxygen either during transfer or in the recovery room. Twenty percent in Group-II developed hypoxaemia during transfer from operation theatre to recovery room out of which 24% developed mild (SaO2 86-90%), 2.66% moderate (SaO2 85-81%), and 1.33% extreme (SaO2 <76%) hypoxaemia. None of the patients in Group - I, who received oxygen supplementation, developed hypoxaemia in the early postoperative period.

Pulse oximetry for perioperative monitoring

BACKGROUND

This is an update of a review last published in Issue 9, 2009, of The Cochrane Library. Pulse oximetry is used extensively in the perioperative period and might improve patient outcomes by enabling early diagnosis and, consequently, correction of perioperative events that might cause postoperative complications or even death. Only a few randomized clinical trials of pulse oximetry during anaesthesia and in the recovery room have been performed that describe perioperative hypoxaemic events, postoperative cardiopulmonary complications and cognitive dysfunction.

OBJECTIVES

To study the use of perioperative monitoring with pulse oximetry to clearly identify adverse outcomes that might be prevented or improved by its use.The following hypotheses were tested.1. Use of pulse oximetry is associated with improvement in the detection and treatment of hypoxaemia.2. Early detection and treatment of hypoxaemia reduce morbidity and mortality in the perioperative period.3. Use of pulse oximetry per se reduces morbidity and mortality in the perioperative period.4. Use of pulse oximetry reduces unplanned respiratory admissions to the intensive care unit (ICU), decreases the length of ICU readmission or both.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2013, Issue 5), MEDLINE (1966 to June 2013), EMBASE (1980 to June 2013), CINAHL (1982 to June 2013), ISI Web of Science (1956 to June 2013), LILACS (1982 to June 2013) and databases of ongoing trials; we also checked the reference lists of trials and review articles. The original search was performed in January 2005, and a previous update was performed in May 2009.

SELECTION CRITERIA

We included all controlled trials that randomly assigned participants to pulse oximetry or no pulse oximetry during the perioperative period.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed data in relation to events detectable by pulse oximetry, any serious complications that occurred during anaesthesia or in the postoperative period and intraoperative or postoperative mortality.

MAIN RESULTS

The last update of the review identified five eligible studies. The updated search found one study that is awaiting assessment but no additional eligible studies. We considered studies with data from a total of 22,992 participants that were eligible for analysis. These studies gave insufficient detail on the methods used for randomization and allocation concealment. It was impossible for study personnel to be blinded to participant allocation in the study, as they needed to be able to respond to oximetry readings. Appropriate steps were taken to minimize detection bias for hypoxaemia and complication outcomes. Results indicated that hypoxaemia was reduced in the pulse oximetry group, both in the operating theatre and in the recovery room. During observation in the recovery room, the incidence of hypoxaemia in the pulse oximetry group was 1.5 to three times less. Postoperative cognitive function was independent of perioperative monitoring with pulse oximetry. A single study in general surgery showed that postoperative complications occurred in 10% of participants in the oximetry group and in 9.4% of those in the control group. No statistically significant differences in cardiovascular, respiratory, neurological or infectious complications were detected in the two groups. The duration of hospital stay was a median of five days in both groups, and equal numbers of in-hospital deaths were reported in the two groups. Continuous pulse oximetry has the potential to increase vigilance and decrease pulmonary complications after cardiothoracic surgery; however, routine continuous monitoring did not reduce transfer to an ICU and did not decrease overall mortality.

AUTHORS' CONCLUSIONS

These studies confirmed that pulse oximetry can detect hypoxaemia and related events. However, we found no evidence that pulse oximetry affects the outcome of anaesthesia for patients. The conflicting subjective and objective study results, despite an intense methodical collection of data from a relatively large general surgery population, indicate that the value of perioperative monitoring with pulse oximetry is questionable in relation to improved reliable outcomes, effectiveness and efficiency. Routine continuous pulse oximetry monitoring did not reduce transfer to the ICU and did not decrease mortality, and it is unclear whether any real benefit was derived from the application of this technology for patients recovering from cardiothoracic surgery in a general care area.

Accuracy of the Lifebox pulse oximeter during hypoxia in healthy volunteers

Pulse oximetry is a standard of care during anaesthesia in high-income countries. However, 70% of operating environments in low- and middle-income countries have no pulse oximeter. The 'Lifebox' oximetry project set out to bridge this gap with an inexpensive oximeter meeting CE (European Conformity) and ISO (International Organization for Standardization) standards. To date, there are no performance-specific accuracy data on this instrument. The aim of this study was to establish whether the Lifebox pulse oximeter provides clinically reliable haemoglobin oxygen saturation (Sp O2 ) readings meeting USA Food and Drug Administration 510(k) standards. Using healthy volunteers, inspired oxygen fraction was adjusted to produce arterial haemoglobin oxygen saturation (Sa O2 ) readings between 71% and 100% measured with a multi-wavelength oximeter. Lifebox accuracy was expressed using bias (Sp O2 - Sa O2 ), precision (SD of the bias) and the root mean square error (Arms). Simultaneous readings of Sa O2 and Sp O2 in 57 subjects showed a mean (SD) bias of -0.41% (2.28%) and Arms 2.31%. The Lifebox pulse oximeter meets current USA Food and Drug Administration standards for accuracy, thus representing an inexpensive solution for patient monitoring without compromising standards.

Perioperative complications in obstructive sleep apnea patients

BACKGROUND

Perioperative complications in obstructive sleep apnea (OSA) patients are described in a small series of case reports. No study to date systematically evaluates perioperative complications in a large number of OSA patients receiving surgeries other than those involving the pharynx.

METHODS

Names of the 860 OSA patients seen in a hospital-based sleep disorders center was cross-referenced with a list of the names of the 2,350 patients receiving surgeries in hospital during an 18 month period. In-patient and sleep center records of the 57 OSA patients receiving surgery were reviewed.

RESULTS

Nine perioperative complications occurred in eight of 48 OSA patients (17%) receiving general anesthesia. All of these complications were related to difficulties with airway management both pre- and postoperatively. Clinical characteristics including body mass index and Polysomnographie measurements of OSA severity did not prove to be useful predictors of perioperative complications.

CONCLUSIONS

The incidence of respiratory complications related to difficulties in airway management in OSA patients was higher than that reported in a recent study for all patients receiving general anesthesia (4%). The perioperative complications observed in these OSA patients are consistent with the underlying pathogenesis of OSA, pharyngeal obstruction. The absence of observed perioperative arrhythmias and myocardial ischemia is consistent with previous findings that sleep-related cardiac ischemia is uncommon in OSA patients. Our results suggest it is prudent to cautiously manage all OSA patients receiving surgeries involving general anesthesia.

Clinical review: Does it matter which hemodynamic monitoring system is used?

Hemodynamic monitoring and management has greatly improved during the past decade. Technologies have evolved from very invasive to non-invasive, and the philosophy has shifted from a static approach to a functional approach. However, despite these major changes, the critical care community still has potential to improve its ability to adopt the most modern standards of research methodology in order to more effectively evaluate new monitoring systems and their impact on patient outcome. Today, despite the huge enthusiasm raised by new hemodynamic monitoring systems, there is still a big gap between clinical research studies evaluating these monitors and clinical practice. A few studies, especially in the perioperative period, have shown that hemodynamic monitoring systems coupled with treatment protocols can improve patient outcome. These trials are small and, overall, the corpus of science related to this topic does not yet fit the standard of clinical research methodology encountered in other specialties such as cardiology and oncology. Larger randomized trials or quality improvement processes will probably answer questions related to the real impact of these systems.

Evaluation of Masimo signal extraction technology pulse oximetry in anaesthetized pregnant sheep

OBJECTIVE

Evaluation of the accuracy of Masimo signal extraction technology (SET) pulse oximetry in anaesthetized late gestational pregnant sheep.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Seventeen pregnant Merino ewes.

METHODS

Animals included in study were late gestation ewes undergoing general anaesthesia for Caesarean delivery or foetal surgery in a medical research laboratory. Masimo Radical-7 pulse oximetry (SpO(2) ) measurements were compared to co-oximetry (SaO(2) ) measurements from arterial blood gas analyses. The failure rate of the pulse oximeter was calculated. Accuracy was assessed by Bland & Altman's (2007) limits of agreement method. The effect of mean arterial blood pressure (MAP), perfusion index (PI) and haemoglobin (Hb) concentration on accuracy were assessed by regression analysis.

RESULTS

Forty arterial blood samples paired with SpO(2) and blood pressure measurements were obtained. SpO(2) ranged from 42 to 99% and SaO(2) from 43.7 to 99.9%. MAP ranged from 24 to 82 mmHg, PI from 0.1 to 1.56 and Hb concentration from 71 to 114 g L(-1) . Masimo pulse oximetry measurements tended to underestimate oxyhaemoglobin saturation compared to co-oximetry with a bias (mean difference) of -2% and precision (standard deviation of the differences) of 6%. Accuracy appeared to decrease when SpO(2) was <75%, however numbers were too small for statistical comparisons. Hb concentration and PI had no significant effect on accuracy, whereas MAP was negatively correlated with SpO(2) bias.

CONCLUSIONS AND CLINICAL RELEVANCE

Masimo SET pulse oximetry can provide reliable and continuous monitoring of arterial oxyhaemoglobin saturation in anaesthetized pregnant sheep during clinically relevant levels of cardiopulmonary dysfunction. Further work is needed to assess pulse oximeter function during extreme hypotension and hypoxaemia.

Prediction of rate and severity of adverse perioperative outcomes: "normal accidents" revisited

The American Society of Anesthesiologists Physical Status classification system has been shown to predict the frequency of perioperative morbidity and mortality despite known subjectivity, inconsistent application, and exclusion of many perioperative confounding variables. The authors examined the relationship between the American Society of Anesthesiologists Physical Status and both the frequency and the severity of adverse events over a 10-year period in an academic anesthesiology practice. The American Society of Anesthesiologists Physical Status is predictive of not only the frequency of adverse perioperative events, but also the severity of adverse events. These nonlinear mathematical relationships can provide meaningful information on performance and risk. Calculated odds ratios allow discussion about individualized anesthesia risks based on the American Society of Anesthesiologists Physical Status because the added complexity of the surgical or diagnostic procedure, and other perioperative confounding variables, is indirectly factored into the Physical Status classification. The ability of the American Society of Anesthesiologists Physical Status to predict adverse outcome frequency and severity in a nonlinear relationship can be fully explained by applying the Normal Accident Theory, a well-known theory of system failure that relates the interactive complexity of system components to the frequency and the severity of system failures or adverse events.

[Reliability of pulsatile saturometry in patients with shock. Digital standard sensors are not reliable for facial measurement!]

INTRODUCTION

Non-invasive monitoring of oxygen saturation by pulse oxymetry (SpO(2)) is sometimes perturbed on fingers during shock states. Other sites are possible (toes, forehead, nose, ear). Self-adhesive standard digital sensors are commonly used off-label in these sites. We have assessed their reliability for all of these sites.

METHODS

We have studied patients presenting a stabilized shock state and receiving vasoconstrictive catecholamines. When an arterial blood gas was ordered, six SpO(2) were measured quasi-simultaneously (self-adhesive standard sensors): right and left index, toe, forehead, nose and ear. SpO(2) at "finger", "toe", "forehead", "nose" and "ear" were compared to the arterial oxygen saturation (SaO(2)) by using the Bland and Altman method. The plethysmographic curve was assessed as "correct" or "unsatisfactory".

RESULTS

Hundred and ten patients were included (63 ± 15 years, SAPSII 46 ± 16, catecholamines: 0.6 ± 0.5 μg/kg/min). Plethysmographic curves are more often of "correct" quality for fingers (90%) than for the other locations (50 to 70%). Bias are low for all the locations (-0.1 to +1.5%). Limits of agreement are around ±5% for fingers and toes, but as high as ±15% for the face locations. When the analysis is restricted to plethysmographic curves of "good" quality, the limits of agreement are unchanged for fingers and toes, but improved (between ±5 to ±10%) for face locations.

CONCLUSION

In patients with a shock receiving vasoconstrictive catecholamines, the reliability of SpO(2) measurements with standard sensors appears better for fingers than for toes and face locations. These standard sensors should be discouraged for facial measurement because of their low reliability, even when the plethysmographic curve seems correct. Sensors specifically designed for each facial site exist, and their reliability should be estimated in patients receiving vasoconstrictive catecholamines.

Clinical predictors and outcome of hypoxaemia among under-five diarrhoeal children with or without pneumonia in an urban hospital, Dhaka, Bangladesh

OBJECTIVE

To explore the predictors and outcome of hypoxaemia in children under 5 years of age who were hospitalized for the management of diarrhoea in Dhaka, where comorbidities are common.

METHODS

In a prospective cohort study, we enrolled all children <5 years of age admitted to the special care ward (SCW) of the Dhaka Hospital of ICDDR,B from September to December 2007. Those who presented with hypoxaemia (SpO(2) < 90%) constituted the study group, and those without hypoxaemia formed the comparison group.

RESULTS

A total of 258 children were enrolled, all had diarrhoea. Of the total, 198 (77%) had pneumonia and 106 (41%) had severe malnutrition (<-3 Z-score of weight for age of the median of the National Centre for Health Statistics), 119 (46%) had hypoxaemia and 138 children did not have hypoxaemia at the time of admission. Children with hypoxaemia had a higher probability of a fatal outcome (21%vs. 4%; P < 0.001). Using logistic regression analysis, the independent predictors of hypoxaemia at the time of presentation were lower chest wall indrawing [OR 6.91, 95% confidence intervals (CI) 3.66-13.08, P < 0.001], nasal flaring (OR 3.22, 95% CI 1.45-7.17, P = 0.004) and severe sepsis (OR 4.48, 95% CI 1.62-12.42, P = 0.004).

CONCLUSION

In this seriously ill population of children with diarrhoea and comorbidities, hypoxaemia was associated with high case-fatality rates. Independent clinical predictors of hypoxaemia in this population, identifiable at the time of admission, were lower chest wall indrawing, nasal flaring and the clinical syndrome of severe sepsis.

Cardiac arrest in anesthetized children: recent advances and challenges for the future

Over the past 50 years the incidence of anesthesia-related cardiac arrest has declined, despite increased patient co-morbidities, the most significant determinant of anesthetic risk. Multiple factors have contributed to this improvement including safer anesthetic agents, better monitoring devices and the development of a specialized pediatric environment. Provider skill has benefitted from improved training and recognition of high-risk situations. Further improvements will depend on international, multispecialty efforts to standardize terminology and analyze large numbers of these infrequent adverse events.

[Pharmacoeconomics: basic concepts and applications to clinical anesthesia]

The economic evaluation of medications and health care technology has gained importance in recent years. Health care resources are limited and their use must be optimized so that we can take the greatest possible advantage. Pharmacoeconomics seeks to analyze the best therapeutic drug choices to obtain the desired outcome in specific cases or in populations. The 4 approaches used in pharmacoeconomics are cost-minimization analysis, cost-benefit analysis, cost-effectiveness analysis, and cost-utility analysis. This review examines the characteristics of each type of study using examples from anesthesiology, a field in which pharmacoeconomics is beginning to play a role.

The impact of increasing oximetry usage in India: A pilot study

The overall goal of the global oximetry (GO) project was to increase patient safety during anaesthesia and surgery in low and middle income countries by decreasing oximetry costs and increasing oximetry utilisation. Results from the overall project have been previously published. This paper reports specifically on pilot work undertaken in four hospitals in one Indian State. The aim of this work was to assess the impact of increasing oximetry provision in terms of benefits to anaesthetists and in the identification of patient problems during anaesthesia, to identify training needs and to explore perceptions regarding barriers to more comprehensive oximetry coverage. Data collection was by interview with hospital staff, use of a log-book to capture data on desaturation episodes and a follow-up questionnaire at 10 months after the introduction of additional oximeters. Increasing oximetry utilisation in the four hospitals was viewed positively by the anaesthetic staff and enabled improvement in monitoring patients. Of the 939 monitored patients studied, 214 patients (23%) experienced a total of 397 desaturation episodes. For nearly half of the patients undergoing caesarean section under regional anaesthesia following a desaturation event supplementary oxygen was required. In 53 of the 379 female sterilisations (14%) desaturation episodes occurred and in eight patients, there were 17 episodes of desaturation due to obstruction. In the recovery room, 91 of the 939 patients were monitored using the oximeters with 12 patients (13%) requiring oxygen. This study has highlighted that pulse oximetry must be used even in patients having surgical procedures or caesarean section under regional or local anaesthesia as these procedures are associated with hypoxic episodes. Anaesthetists must ensure they are complying with the Indian Society of Anaesthesiologists monitoring standards for anaesthesia and ensure patients are monitored by pulse oximetry.

Anesthesia care in a medium-developed country: a nationwide survey of Mongolia

STUDY OBJECTIVE

To evaluate the current status of anesthesia and its allied disciplines in Mongolia.

DESIGN

Nationwide questionnaire survey.

SETTING

Two university hospitals.

MEASUREMENTS

A total of 44 hospitals that include a department of surgery and that were registered at the Mongolian Ministry of Health were queried. The questionnaire included 44 questions in two sections. The first section consisted of 6 general questions about the hospital, and the second section included 40 questions on anesthesia and perioperative patient care. The Mann-Whitney U-test, Chi²-tests, and a bivariate correlation analysis were used for statistical analysis.

MAIN RESULTS

44 (100%) questionnaires were returned. Twenty-two (50%) hospitals were located in the capital city of Ulaanbaatar. Nine hundred (median; interquartile range: 413-1,468) surgical interventions were performed annually in the study hospitals. Physician anesthesiologists delivered anesthesia in all hospitals. Techniques for general anesthesia included endotracheal intubation (95.5%), laryngeal mask ventilation (13.6%), mask ventilation (27.3%), dissociative ketamine anesthesia (84.1%), and combined general/regional anesthesia (63.6%). Regional anesthetic techniques included spinal (97.7%), epidural (43.2%), axillary plexus (40.9%), peripheral nerve (13.6%), and local anesthesia (15.9%). The most frequently used hypnotics were ketamine (86.4%) and thiopental sodium (70.5%). Halothane was available in all hospitals. Oxygen was available during anesthesia in 95.5% of hospitals. The most widely available intraoperative monitoring equipment were a stethoscope (84.1%), oximeter (81.8%), and sphygmomanometer (84.1%). A recovery room was available in 22 (50%) hospitals.

CONCLUSIONS

Anesthesia is an underdeveloped and under-resourced medical specialty in Mongolia.

Prevalence of undiagnosed hypoxemia in adults and children in an under-resourced district hospital in Zambia

Background

In adequately resourced clinical environments, diagnosis of hypoxemia via pulse oximetry is routine. Unfortunately, pulse oximetry is rarely utilized in under-resourced hospitals in developing countries.

Aim

The prevalence of undiagnosed hypoxemia among adults and children with illnesses other than pneumonia in these environments remains poorly described.

Methods

This cross-sectional analysis of the prevalence of hypoxemia was conducted in Kapiri Mposhi, Zambia, at the 60-bed District Hospital, which serves a population of 320,000. The resting room air oxygen saturations of two consecutive samples of all adult and pediatric inpatients were measured in December 2008 and March 2009 using handheld pulse oximetry. Hypoxemia was defined as resting room air SpO₂ less than 90%.

Results

A total of 192 patients were enrolled: 68 young children (<5 years old), 15 older children (5–17 years old), and 109 adults (≥18 years old). Five young children (7%), 0 older children (0%), and 10 adults (9%) were hypoxemic. No hypoxemic patients were receiving oxygen therapy at the time of diagnosis. Pneumonia, tuberculosis, and malnutrition were the most common conditions among those with hypoxemia. Oximetry data changed clinical management in all observed cases of hypoxemia and several cases of normoxemia, leading to application of supplemental oxygen, initiation of further diagnostic testing, prolongation of inpatient stay, or expedited discharge home.

Conclusions

Undiagnosed hypoxemia is present among inpatients at this district hospital in rural Zambia with high prevalence in both adults and young children. These results support routine screening for hypoxemia in similar facilities in both age groups. Further investigation is warranted into the clinical impact and cost-effectiveness of pulse oximetry, provision of oxygen concentrators, and training on their use in developing countries.

The incidence of hypoxemia during surgery: evidence from two institutions

PURPOSE

The incidence of hypoxemia in patients undergoing surgery is largely unknown and may have a clinical impact. The objective of this study was to determine the incidence of intraoperative hypoxemia in a large surgical population.

METHODS

We performed a retrospective study of electronically recorded pulse oximetry data obtained from two large academic medical centres. All adults (age ≥ 16 yr) undergoing non-cardiac surgery during a three-year period at the two hospitals were included in the analysis. Our main outcome measure was the percentage of patients with episodes of hypoxemia (SpO(2) < 90) or severe hypoxemia (SpO(2) ≤ 85) for two minutes or longer during the intraoperative period (induction of anesthesia, surgery, and emergence).

RESULTS

We evaluated 95,407 electronic anesthesia records at the two hospitals. During the intraoperative period, 6.8% of patients had a hypoxemic event, and 3.5% of patients had a severely hypoxemic event of two consecutive minutes or longer. Seventy percent of the hypoxemic episodes occurred during either induction or emergence- time periods that represent 21% of the total intraoperative time. From induction to emergence, one episode of hypoxemia occurred every 28.9 hr, and one episode of severe hypoxemia occurred every 55.7 hr of intraoperative time.

CONCLUSION

Despite advances in monitoring technology, hypoxemia continues to occur commonly in the operating room and may be a serious safety concern because of its potential impact on end organ function and long-term outcomes. Further studies are needed to improve our understanding of the clinical impact of intraoperative hypoxemia and the strategies that will be most useful in minimizing its occurrence.

Arterial line for monitoring SpO2 in patients with ischemic peripheries

Monitoring the oxygenation status of patients with poor peripheral perfusion or ischemic peripheries is challenging in view of unreliable or unrecordable pulse oximeter data. In this article we describe a very simple and innovative technique of using the arterial line for reliable recording of arterial oxygen saturation (SpO(2)) in such patients. We conclude that the arterial line can be used as an extension of the artery and SpO(2) may be reliably measured using the arterial line in such patients as long as the blood in the arterial tubing is pulsatile and a good contact is ensured between the arterial tubing and the sensor of the pulse oximeter.

Monitoring with head-mounted displays in general anesthesia: a clinical evaluation in the operating room

BACKGROUND

Patient monitors in the operating room are often positioned where it is difficult for the anesthesiologist to see them when performing procedures. Head-mounted displays (HMDs) can help anesthesiologists by superimposing a display of the patient's vital signs over the anesthesiologist's field of view. Simulator studies indicate that by using an HMD, anesthesiologists can spend more time looking at the patient and less at the monitors. We performed a clinical evaluation testing whether this finding would apply in practice.

METHODS

Six attending anesthesiologists provided anesthesia to patients undergoing rigid cystoscopy. Each anesthesiologist performed 6 cases alternating between standard monitoring using a Philips IntelliVue MP70 and standard monitoring plus a Microvision Nomad ND2000 HMD. The HMD interfaced wirelessly with the MP70 monitor and displayed waveform and numerical vital signs data. Video was recorded during all cases and analyzed to determine the percentage of time, frequency, and duration of looks at the anesthesia workstation and at the patient and surgical field during various anesthetic phases. Differences between the display conditions were tested for significance using repeated-measures analysis of variance.

RESULTS

Video data were collected from 36 cases that ranged from 17 to 75 minutes in duration (median 31 minutes). When participants were using the HMD, compared with standard monitoring, they spent less time looking toward the anesthesia workstation (21.0% vs 25.3%, P = 0.003) and more time looking toward the patient and surgical field (55.9% vs 51.5%, P = 0.014). The HMD had no effect on either the frequency of looks or the average duration of looks toward the patient and surgical field or toward the anesthesia workstation.

CONCLUSIONS

An HMD of patient vital signs reduces anesthesiologists' surveillance of the anesthesia workstation and allows them to spend more time monitoring their patient and surgical field during normal anesthesia. More research is needed to determine whether the behavioral changes can lead to improved anesthesiologist performance in the operating room.

Blood lactate monitoring in critically ill patients: a systematic health technology assessment

OBJECTIVE

To decide whether the use of blood lactate monitoring in critical care practice is appropriate. We performed a systematic health technology assessment as blood lactate monitoring has been implemented widely but its clinical value in critically ill patients has never been evaluated properly.

DATA SOURCE

PubMed, other databases, and citation review.

STUDY SELECTION

We searched for lactate combined with critically ill patients as the target patient population. Two reviewers independently selected studies based on relevance for the following questions: Does lactate measurement: 1) perform well in a laboratory setting? 2) provide information in a number of clinical situations? 3) relate to metabolic acidosis? 4) increase workers' confidence? 5) alter therapeutic decisions? 6) result in benefit to patients? 7) result in similar benefits in your own setting? 8) result in benefits which are worth the extra costs?

DATA EXTRACTION AND SYNTHESIS

We concluded that blood lactate measurement in critically ill patients: 1) is accurate in terms of measurement technique but adequate understanding of the (an)aerobic etiology is required for its correct interpretation; 2) provides not only diagnostic but also important prognostic information; 3) should be measured directly instead of estimated from other acid-base variables; 4) has an unknown effect on healthcare workers' confidence; 5) can alter therapeutic decisions; 6) could potentially improve patient outcome when combined with a treatment algorithm to optimize oxygen delivery, but this has only been shown indirectly; 7) is likely to have similar benefits in critical care settings worldwide; and 8) has an unknown cost-effectiveness.

CONCLUSIONS

The use of blood lactate monitoring has a place in risk-stratification in critically ill patients, but it is unknown whether the routine use of lactate as a resuscitation end point improves outcome. This warrants randomized controlled studies on the efficacy of lactate-directed therapy.

Critical monitoring issues outside the operating room

There is no need to reinvent the wheel to determine the need for vigilant monitoring in outside of the operating room (OOR) settings. Anesthesiologists have evolved a robust system of monitoring standards based on decades of experience in operating room environments. Every OOR location should be thoroughly evaluated and monitoring standards implemented. The standards should be periodically reviewed to avert morbidity.

A simulation design for research evaluating safety innovations in anaesthesia*

SUMMARY

It is notoriously difficult to obtain evidence from clinical randomised controlled trials for safety innovations in healthcare. We have developed a research design using simulation for the evaluation of safety initiatives in anaesthesia. We used a standard and a modified scenario in a human-patient simulator, involving a potentially life-threatening problem requiring prompt attention--either a cardiac arrest or a failure in oxygen supply. The modified scenarios involved distractions such as loud music, a demanding and uncooperative surgeon, telephone calls and frequent questions from a medical student. Twenty anaesthetics were administered by 10 anaesthetists. A mean (SD) of 11.3 (2.8) errors per anaesthetic were identified in the oxygen failure scenarios, compared with 8.0 (3.4) in the cardiac arrest scenarios (ANOVA: p = 0.04). The difference between the combined standard scenarios and the combined modified scenarios was not significant. The mean rate of errors overall was 9.7 per simulation, with a pooled SD of 4.46, so in future studies 21 subjects would provide 80% statistical power to show a reduction in error rate of 30% from baseline with p<or=0.05. Our research design will facilitate the evaluation of safety initiatives in anaesthesia.

Patient monitoring during gastrointestinal endoscopy: why, when, and how?

Patient monitoring is intended to reduce the risk of sedation-related cardiopulmonary complications. Physiological monitoring and visual assessment by a qualified individual should be routine during endoscopic procedures. Additionally, ventilatory monitoring should be considered for high-risk patients and those receiving sedation with propofol.

Outcomes of pediatric anesthesia

Improvement in anesthesia outcomes has derived from advances in safety science related to equipment, drugs, human factors analysis, professional standardization and organization, subspecialty care, and regionalization. Outcomes of pediatric anesthesia have improved, but universal outcome measures are lacking. Because of the limitations of small numbers, future improvement efforts will necessarily involve multiple disciplines, institutions, and regions, and will require sophisticated systems approaches.