Patients Breathing Room Air Research Articles

Tachypnea in response to hypoxemia decreases with age in older patients.

To investigate if tachypneic response to hypoxia is decreased in older patients. We included all patients ≥65 years of age attending 52 Spanish emergency departments (EDs) for whom peripheral arterial oxygen saturation (SatO2) measured by pulsioxymetry and respiratory rate (RR) were registered at ED arrival. We assessed the relationship between SatO2 and RR in different models, and with the best-fitting model, we independently analyzed this relationship in four subgroups according to patient age (65-69, 70-79, 80-89, and ≥90 years). Five sensitivity analyses using different subsets of patients were carried out to check for the consistency of the results. We included 7126 patients, with medians for SatO2 and RR of 97% (interquartile range [IQR]: 94-98) and 15 bpm (IQR: 15-16), respectively. We found significant associations (P < 0.001) between SatO2 and RR in every model tested (P < 0.001 for all), with the quadratic model obtaining the best fit (R2: 0.098) over those obtained with linear (R2: 0.096) and logarithmic (R2: 0.092) models. The same was observed in sensitivity analyses, with R2 for quadratic models ranging from 0.069 in patients with low comorbidity and 0.102 in patients breathing room air. The mean RR for 100% SatO2 was 15 bpm and increased as SatO2 decreased, although with a progressive slowing of the slope, with a mean RR of 27 at 50% SatO2. We detected a decreased RR response to increasing hypoxemia according to age and, while the RR curve was higher and with a progressively steepening slope in the 972 patients aged 65-69 (mean RR of 42 bpm with 50% SatO2), a progressive slowing of slope was observed in the 2693 patients aged 70-79 (mean RR of 28 with 50% SatO2), the 2582 aged 80-89 (mean RR of 25) and the 879 aged ≥90 (mean RR of 23). Sensitivity analyses provided very similar results. Tachypneic response to hypoxemia in older patients decreases as age advances, regardless of the reason leading to hypoxemia. Geriatr Gerontol Int 2024; ••: ••-••.

Remdesivir is Associated with Reduced Mortality in Patients Hospitalized for COVID-19 Not Requiring Supplemental Oxygen.

Remdesivir has demonstrated benefit in some hospitalized patients with coronavirus disease 2019 (COVID-19) on supplemental oxygen and in nonhospitalized patients breathing room air. The durability of this benefit across time periods with different circulating severe acute respiratory syndrome coronavirus 2 variants of concern (VOC) is unknown. This comparative effectiveness study in patients hospitalized for COVID-19 and not receiving supplemental oxygen at admission compared those starting remdesivir treatment in the first 2 days of admission with those receiving no remdesivir during their hospitalization across different VOC periods. Using a large, multicenter US hospital database, in-hospital mortality rates were compared among patients hospitalized for COVID-19 but not requiring supplemental oxygen at admission between December 2020 and April 2022. Patients receiving remdesivir at hospital admission were matched 1:1 to those not receiving remdesivir during hospitalization, using propensity score matching. Cox proportional hazards models were used to assess 14- and 28-day in-hospital mortality rates or discharge to hospice. Among the 121 336 eligible patients, 58 188 remdesivir-treated patients were matched to 17 574 unique patients not receiving remdesivir. Overall, 5.4% of remdesivir-treated and 7.3% in the non-remdesivir group died within 14 days, and 8.0% and 9.8%, respectively, died within 28 days. Remdesivir treatment was associated with a statistically significant reduction in the in-hospital mortality rate compared with non-remdesivir treatment (14-day and 28-day adjusted hazard ratios [95% confidence interval], 0.75 [0.68-0.83] and 0.83 [0.76-0.90], respectively). This significant mortality benefit endured across the different VOC periods. Remdesivir initiation in patients hospitalized for COVID-19 and not requiring supplemental oxygen at admission was associated with a significantly reduced in-hospital mortality rate. These findings highlight a potential survival benefit when clinicians initiated remdesivir on admission across the dominant variant eras of the evolving pandemic.

Neutrophil extracellular traps in COVID-19.

In severe cases of coronavirus disease 2019 (COVID-19), viral pneumonia progresses to respiratory failure. Neutrophil extracellular traps (NETs) are extracellular webs of chromatin, microbicidal proteins, and oxidant enzymes that are released by neutrophils to contain infections. However, when not properly regulated, NETs have the potential to propagate inflammation and microvascular thrombosis - including in the lungs of patients with acute respiratory distress syndrome. We now report that sera from patients with COVID-19 have elevated levels of cell-free DNA, myeloperoxidase-DNA (MPO-DNA), and citrullinated histone H3 (Cit-H3); the latter 2 are specific markers of NETs. Highlighting the potential clinical relevance of these findings, cell-free DNA strongly correlated with acute-phase reactants, including C-reactive protein, D-dimer, and lactate dehydrogenase, as well as absolute neutrophil count. MPO-DNA associated with both cell-free DNA and absolute neutrophil count, while Cit-H3 correlated with platelet levels. Importantly, both cell-free DNA and MPO-DNA were higher in hospitalized patients receiving mechanical ventilation as compared with hospitalized patients breathing room air. Finally, sera from individuals with COVID-19 triggered NET release from control neutrophils in vitro. Future studies should investigate the predictive power of circulating NETs in longitudinal cohorts and determine the extent to which NETs may be novel therapeutic targets in severe COVID-19.

26-Year-Old Woman With Shortness of Breath and Chest Pain

26-Year-Old Woman With Shortness of Breath and Chest Pain

57-Year-Old Man With Vertigo

57-Year-Old Man With Vertigo

Characteristics of Desaturation and Respiratory Rate in Postoperative Patients Breathing Room Air Versus Supplemental Oxygen: Are They Different?

Routine monitoring of postoperative patients with pulse oximetry-based surveillance monitoring has been shown to reduce adverse events. However, there is some concern that pulse oximetry is limited in its ability to detect deterioration quickly enough to allow for intervention in patients receiving supplemental oxygen. To address such concerns, this study expands on the current limited knowledge of differences in desaturation and respiratory rate characteristics between patients breathing room air and those receiving supplemental oxygen. Pulse oximetry-derived data and patient characteristics were used to examine overnight desaturation patterns of 67 postoperative patients who were receiving either supplemental oxygen or breathing room air. The 2 modalities with respect to the speed of desaturation, in addition to magnitude and duration of desaturation events, are compared. Night-time pulse rate, oxygen saturation, respiratory rate, and the transition times from normal oxygen saturation levels to desaturated states are also compared. The behavior of respiratory rate in proximity to desaturation events is described. Statistical methods included multivariable regression and inverse probability of treatment weighted to adjust for any imbalance in patient characteristics between the oxygen and room air patients and linear mixed effect models to account for clustering by patient. The study included 33 patients on room air and 34 receiving supplemental oxygen. The speed of desaturation was not different for room air versus oxygen for 2 types of desaturation (adjusted % difference, 95% confidence interval [CI]: type I; 22.4%, -51.5% to 209%; P = .67, type II; -17.3%, -53.8% to 47.6%; P = .52). Patients receiving supplemental oxygen had a higher mean oxygen saturation (adjusted difference, 95% CI, 2.4 [0.7-4.0]; P = .006). No differences were found for the average overnight respiratory or pulse rate, or proportion of time in desaturation states between the 2 groups.The time to transition from a normal oxygen saturation (92%) to 88% or below was not longer for supplemental oxygen patients (P = .42, adjusted difference 26.1%: 95% CI, -28.1% to 121%). Respiratory rates did not differ between the overall mean and desaturation or recovery phases or between the oxygen and room air group. In this study, desaturation characteristics did not differ between patients receiving supplemental oxygen and breathing room air with regard to speed, depth, or duration of desaturation. Transition time for desaturations to reach low oxygen saturation alarms was not different, while respiratory rate remained in the normal range during these events. These findings suggest that pulse oximetry-based surveillance monitoring for deterioration detection can be used equally effectively for patients on supplemental oxygen and for those on room air.

66-Year-Old Woman With Falls and Confusion

66-Year-Old Woman With Falls and Confusion

Changes in Brain Oxygenation in Response to Inhaled 100% Oxygen Are Different in Sickle Cell Disease Patients

Introduction: The prevalence of silent stroke increases monotonically with age in SCD patients, with more than 50% developing detectable white matter hyperintensities on MRI by adulthood. We are exploring the use of inhaled oxygen as a contrast agent to try to identify individuals at risk for silent stroke and to better understand how the brain regulates its own oxygen delivery. In this study, we report changes of brain Blood Oxygen Level Dependent (BOLD) signal and frontal Near Infrared Spectroscopy (NIRs) to 5 minutes of inhaled 100% oxygen in patients with sickle cell disease (SCD), non sickle anemia (ACTL), and control subjects.Method: The study was approved by the institutional review board and performed at Children’s Hospital Los Angeles (CHLA); all patients provided informed consent. Patients with previous stroke, pregnancy, and acute chest pain and crisis hospitalization within one month were excluded. 19 SCD patients (age = 20.7 ± 8.8), 12 patients with non sickle anemia syndromes (age = 25.1 ± 6.9) and 20 ethnicity matched control (CTL) subjects (age = 30.5 ± 12.7) were studied. Peripheral oxygen saturation (SpO2%) was measured by MRI compatible pulse oximeter. A five minute BOLD sequence was acquired with the patient breathing room air for 50 seconds, followed by 100% oxygen for 250 seconds. NIRS recordings of oxygenated hemoglobin change (DOHB), deoxygenated hemoglobin change (DDHB) and tissue oxygenation index (TOI) were recorded from the patient’s forehead. Average BOLD signal was from a 6 cm slab in the middle of the brain. CBC, hemoglobin electrophoresis, and markers of hemolysis were also measured.Results: A representative frontal DOHB signal, and the parameters used to characterize its time-course, are shown in Figure 1. DOHB remained stable until oxygen was administered and then increased over several minutes to a maximum. In many patients, the DOHB signal subsequently declined back toward baseline, representing the effects of compensatory cerebral vasoconstriction. The delay time was shorter in anemic subjects because of increased cerebral blood flow, but the rise times were not different. Peak DOHB increase was greater in SCD patients than in ACTL or non anemic control subjects (1.4 mM ± 0.2mM, 0.8 mM ± 0.2 mM and 0.6 mM ± 0.4 mM, respectively, p <0.0001 by ANOVA). There was no difference in the DOHB vasoconstriction response among the three patient groups.DOHB was highly correlated with DDHB and DTOI in all three patient groups. Consequently, both DDHB and DTOI changes were also larger in SCD patients. All three NIRs signal changes were larger in non-transfused SCD patients than in patients on chronic transfusions. Non-transfused SCD patients had more significant increases in SpO2% than chronically transfused subjects and the effect was proportional to hemoglobin F%, suggesting a p50 effect. After controlling for SpO2%, SCD patients still exhibited larger NIRs changes than ACTL or CTL patients, but the differences between transfused and non transfused SCD patients disappeared.Whole brain %BOLD was also correlated with changes in DOHB, DDHB, TOI, and SpO2%. The relationship between DOHB versus %BOLD is illustrated in Figure 2. %BOLD changes were also significantly higher in SCD patients. However, unlike the NIRS changes, whole brain %BOLD differences could entirely be explained by differences in SpO2% with hyperoxia.Conclusion:100% oxygen administration increases brain oxygenation in SCD patients to a greater degree than in control subjects or patients with anemia of other etiologies. Some of the differences can be explained by differences in resting oxygen saturations but disparities between BOLD and NIRs response suggest regional variation of brain oxygenation in response to this challenge. [Display omitted] [Display omitted] DisclosuresWood:Apopharma: Consultancy; AMAG: Consultancy; World Care Clinical: Consultancy; AMAG: Consultancy; Celgene: Consultancy; Apopharma: Consultancy; Biomed Informatics: Consultancy; Celgene: Consultancy; Ionis Pharmaceuticals: Consultancy; Vifor: Consultancy; Vifor: Consultancy; Ionis Pharmaceuticals: Consultancy; Biomed Informatics: Consultancy; World Care Clinical: Consultancy.

Neuromonitoring during adult cardiac surgery.

Available online at www.jbr-pub.org Open Access at PubMed Central The Journal of Biomedical Research, 2016, 30(3):171-173 Perspective Neuromonitoring during adult cardiac surgery Anna K. Kowalczyk, Bradlee J. Bachar, Hong Liu  Department of Anesthesiology and Pain Medicine, University of California Davis, Sacramento, CA 95817, USA. Introduction Cerebral oximetry The brain has been considered an index organ for global tissue perfusion because of the physiological processes aimed at flow preservation to vital organs of the body [1] .When cerebral perfusion is compromised, other organs are likely inadequately perfused as well. It would therefore be prudent to monitor cerebral perfu- sion based on the proposition that interventions aimed at its preservation will likely result in adequate tissue perfusion of the whole body and reduced complications related to ischemia of various organs. It is worth emphasizing the difference between tissue perfusion and tissue oxygen supply. It is a consensus that the normal oxygen supply/demand ratio is impor- tant to normal tissue metabolic physiology at the molec- ular level. Because oxygen demand is largely related to perfusion, it is perfusion that remains the main focus of all clinicians in the cardiac operating room [1] . Very brief periods of cerebral hypoperfusion occur fre- quently during cardiac surgery due to a multitude of fac- tors (reduced cardiac output, low pump flow, decreased perfusion pressure, etc.) but are of minute clinical sig- nificance. It is prolonged or cumulative hypoperfusion, particularly in watershed areas of the brain, undetected by standard monitors such as arterial blood pressure or pulse oximetry, that leads to brain tissue injury and adverse outcomes [2] . To date, no device has been devel- oped that can reliably, continuously and non-invasively monitor global cerebral tissue perfusion directly. A num- ber of existing monitors can indirectly assess regional cerebral perfusion and provide information useful in managing cerebral blood flow and oxygen supply. Cerebral tissue oximetry operates via measurement of hemoglobin saturation of the mixed arterial, cap- illary and venous blood in superficial frontal lobe being illuminated by near-infrared light. The number represents the ratio of the oxygenated hemoglob in to total hemoglobin, with the frequently reported range of 50-80 and bilateral (right and left) hemisphere difference of no more than 10 points. Desaturation below 50% or more than 20% below baseline, obtained in an awake, non-sedated patient breathing room air, has been used as the threshold of interven- tion in cardiac patients. Previous evidence shows that interventions aimed at maintaining cerebral sat- uration at baseline correlate with reduced neuropsy- chological complications and decreased length of hospital stay [2-4] . The benefit of the monitor is that it is non-invasive and as such poses virtually no known harm to the patient. It is portable, easy to apply and operate as well as interpret. The cost is moderate and can be jus- tified by the beneficial outcome it associates with. It is now considered by many experts in the field as a standard of monitoring during cardiac surgery [2] . Given that both hemispheres are monitored, it can differen- tiate between global and unilateral causes of hypop- erfusion, such as head position or unilateral vessel occlusion. Because the technology does not require pulsatile flow, it offers an advantage during cardio- pulmonary bypass or in patients with non-pulsatile arterial flow (e.g. patients with left ventricular assist devices). Corresponding author: Hong Liu, MD, Professor of Anesthesiology, Department of Anesthesiology and Pain Medicine,University of California Davis Health System, 4150 V Street, Sacramento, CA 95817, USA, Tel: 1-916-734-2413, email: hualiu@ucdavis.edu. Received 20 November 2015, Revised 08 December 2015, Accepted 03 February 2016, Epub 10 March 2016 CLC number: R614, Document code: B The authors reported no conflict of interests. © 2016 by the Journal of Biomedical Research. All rights reserved. doi: 10.7555/JBR.30.20150159

Baseline cerebral oximetry values depend on non-modifiable patient characteristics

ObjectiveThe aim of the present study was to evaluate baseline regional cerebral oxygen saturation (rSO2) values and identify factors influencing preoperative rSO2 in elective minor surgery. Study designObservational analysis post-hoc. Patients and methodsObservational post-hoc analysis of data for the patient sample (n=50) of a previously conducted clinical trial in patients undergoing tumourectomy for breast cancer or inguinal hernia repair. Exclusion criteria included pre-existing cerebrovascular diseases, anaemia, baseline pulse oximetry <97% and low quality rSO2 sensor signals. Demographic data, comorbidities, and ASA physical status as well as height and weight were collected prospectively from all patients. Baseline rSO2 values were recorded while the patient breathed room air, using the INVOS 5100C monitor™ (Covidien, Dublin, Ireland). ResultsThirty-seven women (72%) and 13 men (28%) 48±13 years of age were enrolled in this study. Baseline rSO2 was 62.01±10.38%. Baseline rSO2 was significantly different between men (67.6±11.2%) and women (60±9.4%), (P=0.023). There were also differences between baseline rSO2 and ASA physical status (ASA I: 67.6±10.7%, ASA II: 61.6±8.4%, ASA III: 55.8±13.9%, P=0.045). Baseline rSO2 had a positive correlation with body weight (r=0.347, P=0.014) and height (r=0.345, P=0.014). We also found significant differences in baseline rSO2 among patients with and without chronic renal failure (P=0.005). No differences were found in any other studied variables. ConclusionsNon-modifiable patient characteristics (ASA physical status, sex, chronic renal failure, body weight and height) influence baseline rSO2.

65-Year-Old Woman With Intermittent Fevers, Lower Extremity Paresthesia, Weight Loss, and Malaise

65-Year-Old Woman With Intermittent Fevers, Lower Extremity Paresthesia, Weight Loss, and Malaise

Chronic Lung Allograft Dysfunction: Oxygen-enhanced T1-Mapping MR Imaging of the Lung.

To evaluate oxygen-enhanced T1-mapping magnetic resonance (MR) imaging of the lungs for detection of chronic lung allograft dysfunction (CLAD) in patients who have undergone double lung transplantation. The local ethics committee approved this study. Seventy-six recipients of double lung allografts who underwent MR imaging of the lungs during an outpatient visit between 2011 and 2013 were included in this study after they provided written informed consent. Patients were classified as having CLAD on the basis of spirometric results and were divided into three groups: no CLAD (bronchiolitis obliterans syndrome level 0 [BOS 0]), early CLAD (BOS 0p), and late-stage CLAD (BOS 1-3). Coronal T1 maps of the lungs were acquired with the patient breathing room air and 100% oxygen by using an inversion-recovery snapshot fast low-angle shot sequence at 1.5 T. The median and interquartile range of T1 values at room air and at 100% oxygen and the oxygen transfer function were calculated. Statistical analysis was performed with analysis of variance and the Tukey honestly significant difference test or the Kruskal-Wallis test and the Mann-Whitney U test (α = 0.05). Bonferroni correction was applied for multiple comparisons. The oxygen transfer function was significantly lower in patients in the BOS 0p (P = .025) and BOS 1-3 groups (P = .003) than it was in the patients with BOS 0. Absolute T1 values (room air, P = .66; 100% oxygen, P = .67) did not differ significantly among the groups. The heterogeneity of T1 values, measured by using the interquartile range, showed a strong trend toward higher values in patients with BOS (room air, P = .06; 100% oxygen, P = .08). Oxygen transfer function may serve as an early marker for detection of CLAD.

Impact of medical training and clinical experience on the assessment of oxygenation and hypoxaemia after general anaesthesia: an observational study.

In Germany it is common practice to use pulse oximetry and supplementary oxygen only on request in patients breathing spontaneously transferred to the post-anaesthesia care unit (PACU) following surgery under general anaesthesia. The main aim was to study the influence of medical training and clinical experience on assessing SpO(2) and detecting hypoxaemia in these patients. The second aim was to do a preliminary assessment whether this practice can be found in countries other than Germany. Anaesthetists, nurses and medical students estimated SpO(2) in patients breathing room air at the end of transfer to the PACU following surgery (including all major surgical fields) under general anaesthesia. Estimated SpO(2) was compared to SpO(2) measured by pulse oximetry. A survey was carried out among European anaesthesists concerning the use of pulse oximetry and supplementary oxygen during patient transfer to the PACU. Hypoxaemia (SpO(2) < 90 %) occurred in 154 (13.5 %) out of 1,138 patients. Anaesthetists, nurses, and medical students identified only 25, 23, and 21 patients of those as being hypoxaemic, respectively. Clinical experience did not improve detection of hypoxaemia both in anaesthetists (p = 0.63) and nurses (p = 0.18). Use of pulse oximetry and supplemental oxygen during patient transfer to the PACU in European countries differs to a large extent. It seems to be applied only on request in many hospitals. Considering the uncertainty about deleterious effects of transient, short lasting hypoxaemia routine use of pulse oximetry is advocated for patient transfer to the PACU.

Capnography monitoring in procedural sedation for bronchoscopy.

Capnography monitoring in procedural sedation for bronchoscopy.

76-Year-Old Woman With Pruritis and Lip Swelling

Resident in Internal Medicine, Mayo School of Graduate Medical Education, Mayo Clinic, Rochester, MN (J.C.S.-V., B.K.); Advisor to residents and Consultant in Allergy and Immunology, Mayo Clinic, Rochester, MN (M.A.P.). A 76-year-old woman presented to her local emergency department for evaluation of lip swelling and pruritis. She was seen earlier that morning at the outpatient clinic with symptoms of earache and mild fever. Her medical history was remarkable for seropositive rheumatoid arthritis treated with long-term immunosuppression with methotrexate and prednisone, gastroesophageal reflux disease, pulmonary fibrosis, chronic obstructive pulmonary disease, idiopathic bronchiectasis, microcytic anemia, and no penicillin allergy. Physical examination revealed a well appearing patient. Otoscopy showed a bulging right tympanicmembranewith evidence offluid.Otitis media was diagnosed, and a 7-day course of amoxicillin, 500 mg twice daily, was prescribed. The patient returned home after filling the prescription and took one amoxicillin tablet around 5 PM. About 10 minutes after ingestion, the patient noted pruritus involving her upper extremities and trunk as well as mild lip swelling. She immediately proceeded to the emergency department, where she arrived 5 minutes after symptom onset. Initial evaluation by the triage nurse revealed the following: temperature, 38.1 C; heart rate, 105 beats/min and regular; blood pressure, 91/53 mm Hg; respiratory rate, 24 breaths/min; and oxygen saturation, 94% while the patient breathed room air. The patient was in mild distress and complained of tingling in her throat. Pertinent positive examination findings included visibly swollen upper and lower lips, mild expiratory wheezing on chest auscultation, and wheals on the upper trunk. The patient was taken to a treatment room, and the attending emergency physician was called to the bedside.

Oxygenation in cervical cancer and normal uterine cervix assessed using blood oxygenation level‐dependent (BOLD) MRI at 3T

Hypoxia is reported to be a biomarker for poor prognosis in cervical cancer. However, a practical noninvasive method is needed for the routine clinical evaluation of tumor hypoxia. This study examined the potential use of blood oxygenation level-dependent (BOLD) contrast MRI as a noninvasive technique to assess tumor vascular oxygenation at 3T. Following Institutional Review Board-approved informed consent and in compliance with the Health Insurance Portability and Accountability Act, successful results were achieved in nine patients with locally advanced cervical cancer [International Federation of Gynecology and Obstetrics (FIGO) stage IIA to IVA] and three normal volunteers. In the first four patients, dynamic T₂*-weighted MRI was performed in the transaxial plane using a multi-shot echo planar imaging sequence whilst patients breathed room air followed by oxygen (15 dm³/min). Later, a multi-echo gradient echo examination was added to provide quantitative R₂* measurements. The baseline T₂*-weighted signal intensity was quite stable, but increased to various extents in tumors on initiation of oxygen breathing. The signal in normal uterus increased significantly, whereas that in the iliacus muscle did not change. R₂* responded significantly in healthy uterus, cervix and eight cervical tumors. This preliminary study demonstrates that BOLD MRI of cervical cancer at 3T is feasible. However, more patients must be evaluated and followed clinically before any prognostic value can be determined.

Hypoxämie nach Allgemeinanästhesie

Studies conducted shortly after the implementation of pulse oximetry (PO) into clinical practice 20-25 years ago revealed that many patients breathing room air during transfer from the operating room (OR) to the post-anesthesia care unit (PACU) directly after general anesthesia (GA) had a peripheral oxygen saturation (S(p)O(2)) below 90%. Moreover, it was shown that the detection of hypoxemia by clinical criteria is extremely unreliable. Meanwhile, the use of PO has become part of the obligatory standard monitoring during GA in Germany and many other countries. Likewise, the use of PO is standard care in the PACU although there are no official recommendations. However, for the time period in between, i.e. immediately after GA during transportation of patients from the OR to the PACU, monitoring of the S(p)O(2) in patients breathing room air is neither obligatory in Germany nor are there any official recommendations or guidelines in this respect. Given the introduction of shorter acting anesthetic agents within the last 25 years, the main goal of this study was to explore whether the incidence of hypoxemia in the immediate period after GA is still so high. Additional aims of this study were to examine whether the detection of hypoxemia based on clinical criteria can be confirmed to be very unreliable, what the risk factors for hypoxemia following GA are and how common it is in Germany to transport patients from the OR to the PACU without PO and supplemental oxygen. In a prospective observational study 970 patients who underwent a broad spectrum of elective surgery under GA in a university hospital setting were included. The S(p)O(2) was measured at the end of the transfer from the OR to the PACU immediately after the anesthetist who had taken care of the patient during the operation had estimated the S(p)O(2). The association between biometric, surgical and anesthesiological variables on the one hand and hypoxemia as well as a decrease of S(p)O(2) on the other hand were studied using multivariate methods. Finally, a survey including all university hospitals was carried out to find out about the use of PO and oxygen during patient transfer from the OR to the PACU. Of the 959 patients who were eligible for analysis 17% had a S(p)O(2) < 90% and 6.6% a S(p)O(2) < 85%. Hypoxemia was not recognized in 82% of the patients in whom an assessment based on clinical grounds was carried out. Variables with an independent influence on hypoxemia and decrease of S(p)O(2) were as follows: saturation before induction of GA, body mass index, age, American Society of Anesthesiologists (ASA) physical status, difference between maximum and minimum inspiratory pressure, mode of ventilation, the choice of opioid and muscle relaxant as well as the use of nitrous oxide. Patient-dependent risk factors had the strongest impact on hypoxemia. In about 80% of the university hospitals neither PO nor supplemental oxygen is used during transportation of the patient from the OR to the PACU. The use of opioids and relaxants with short duration of action may have favorable effects on preventing hypoxemia and decreases of S(p)O(2). These measures will, however, not be sufficient to solve this problem because the highest risk factors for hypoxemia are patient-related. Despite knowing risk factors for oxygen desaturation, it is currently not possible to reliably predict which patients will become hypoxemic or have a decrease of S(p)O(2). Therefore, transportation of patients breathing room air from the OR to the PACU directly after GA without use of PO or supplemental oxygen seems to be questionable in terms of patient safety.

The Effect of Supplemental Oxygen on Hypercapnia in Subjects with Obesity-associated Hypoventilation: A Randomized, Crossover, Clinical Study: Wijesinghe M, Williams M, Perrin K, Weatherall M, Beasley R. Chest 2011;139:1018–24.

It is well known that supplemental oxygen can cause worsening hypercapnia in patients with chronic obstructive pulmonary disease. This study sought to determine if the same effect is seen in patients with obesity-associated hypoventilation (OAH). In this double-blind, randomized, controlled, crossover trial of 24 patients newly diagnosed with OAH, subjects inhaled either 100% oxygen or room air via full-face continuous positive airway pressure mask, without positive airway pressure, for 20 min on 2 separate days. Baseline measurements of transcutaneous carbon dioxide tension (PtCO2), minute ventilation, and volume of dead-space-to-tidal-volume ratio were compared to the same values at 20 min by mixed linear model to determine differences between the two treatments. All subjects who completed the study (23 of 24) participated in both of the treatments on separate days within 7 days. Testing was terminated early in 3 subjects while breathing 100% oxygen secondary to a rise in PtCO2 of ≥ 10 mm Hg, whereas none of the patients breathing room air required early termination of the treatment protocol. PtCO2 increased by 5.0 mm Hg (95% confidence interval [CI] 3.1–6.8, P < 0.001) with oxygen compared to room air. Minute ventilation decreased by 1.4 L/min (95% CI 0.11–2.6 L/min; p < 0.03), and volume-of-dead-space-to-tidal-volume ratio increased by 0.067 (95% CI 0.035–0.1; p < 0.001), with oxygen compared to room air. This study demonstrated that breathing 100% oxygen worsens hypercapnia in stable patients with OAH.

Postoperative Monitoring of Obese Patients with Obstructive Sleep Apnea

To the Editor: We have serious concerns about the conclusion by Ahmad et al.1 that obese patients with obstructive sleep apnea (OSA) require no closer postoperative surveillance than obese patients without OSA. Their conclusion is based on statistically (as well as clinically) insignificant differences of oxygen desaturation index (ODI), and other derived measures of oxygen desaturation postoperatively. The authors acknowledge that the ODI is a highly sensitive and specific test for the obstructive apneas and hypopneas that characterize OSA. The likely reason the two groups had dissimilar ODI’s preoperatively (ODI correlates with the apnea- hypopnea index -AHI- which diagnoses OSA2) but indistinguishable ODI’s postoperatively is that the ability of the ODI to reliably discriminate OSA patients who intermittently obstruct their airway, from those without OSA, depends on using both a high fidelity pulse oximeter and the patient breathing room air. The American Academy of Sleep Medicine demands pulse oximeters used during polysomnography have a maximum signal averaging time of 3 s.3 Oximeters with a longer averaging time underestimate the brief desaturations associated with airway obstruction. Zafar found diagnostic differences in the AHI (and by extension ODI) by using different pulse oximeters.4 Schumann found supplemental oxygen partly responsible for a paradoxical decrease in the respiratory disturbance index (analogous to the AHI) in bariatric surgery patients monitored with a portable polysomnography in the 24 h following surgery.5 We have also found oximetry patterns pathognomonic for airway obstruction attenuated in the setting of supplemental oxygen.6 OSA is extremely prevalent in the bariatric surgery population, and patients with ODI’s ≥5 preoperatively are at greater risk for complications.7 Clinicians should be aware that timely warning of recurrent airway obstruction in OSA patients breathing supplemental oxygen may not be provided by conventional pulse oximetry. Frank J. Overdyk, MSEE, MD Department of Anesthesia and Perioperative Medicine Medical University of South Carolina Charleston, South Carolina [email protected] Qanta Ahmed, MD, FAASM Division of Pulmonary and Critical Care Medicine, Allergy and Sleep Medicine Medical University of South Carolina Charleston, South Carolina

Increased Oxygen Administration Improves Cerebral Oxygenation in Patients Undergoing Awake Carotid Surgery

During regional anesthesia for carotid endarterectomy (CEA), 10% to 15% of patients develop signs of cerebral hypoxia after cross-clamping, manifested as changes in speech, cerebration or contralateral motor power. Reversal of such neurological deficits using administration of 100% O2 has been described. We used near-infrared cerebral oximetry to assess whether 100% O2 reliably improves regional cerebral oxygenation (rSO2) during carotid cross-clamping. Sixteen patients undergoing awake CEA were studied. Bilateral rSO2 optodes were applied before the initiation of sedation and the conduct of the regional blockade. Patients received 28% oxygen by Venturi facemask. Perioperative blood pressure was maintained at or within 10% above the patient's normal limits during carotid cross-clamping. After cross-clamping, 100% O2 was administered for 5 min by a close-fitting anesthetic facemask. The O2 mask was then removed and the patient breathed room air. The effects on rSO2 readings and arterial blood gases were observed after each intervention. Data were analyzed for 15 patients. Ipsilateral rSO2 values decreased by 7.4% +/- 5% after carotid cross-clamping. Administration of 100% O2 resulted in an increase in ipsilateral rSO2 in all patients of 6.9% +/- 3.3% (range, 1%-12%) (paired t-test, P < 0.001) over the cross-clamped value while receiving 28% O2. Hemodynamic variables and arterial PaCO2 values were unaltered. With the carotid cross-clamped, ipsilateral rSO2 was reliably increased by the administration of 100% O(2) compared with 28% O2. The etiology of this increase is unclear, but may relate to the associated increase in O2 content of the blood or to an improvement in cerebral blood flow. Thus administration of 100% O2 during carotid cross-clamping may be beneficial for all patients undergoing CEA.