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1.  Use of a Combined SpO2/PtcCO2 Sensor in the Delivery Room 
Sensors (Basel, Switzerland)  2012;12(8):10980-10989.
Arterial oxygen saturation (SaO2) and partial arterial pressure of carbon dioxide (PaCO2) are important respiratory parameters in critically ill neonates. A sensor combining a pulse oximeter with the Stow-Severinghaus electrode, required for the measurement of peripheral oxygen saturation (SpO2) and transcutaneous partial pressure of carbon dioxide (PtcCO2), respectively, has been recently used in neonatal clinical practice (TOSCA500ÒRadiometer). We evaluated TOSCA usability and reliability in the delivery room (DR), throughout three different periods, on term, late-preterm, and preterm neonates. During the first period (period A), 30 healthy term neonates were simultaneously monitored with both TOSCA and a MASIMO pulse oximeter. During the second period (period B), 10 healthy late-preterm neonates were monitored with both TOSCA and a transcutaneous device measuring PtcCO2 (TINAÒ TCM3, Radiometer). During the third period (period C), 15 preterm neonates were monitored with TOSCA and MASIMO after birth, during stabilization, and during transport to the neonatal intensive care unit (NICU). Blood gas analyses were performed to compare transcutaneous and blood gas values. TOSCA resulted easily and safely usable in the DR, allowing reliable noninvasive SaO2 estimation. Since PtcCO2 measurements with TOSCA required at least 10 min to be stable and reliable, this parameter was not useful during the early resuscitation immediately after birth. Moreover, PtcCO2 levels were less precise if compared to the conventional transcutaneous monitoring. However, PtcCO2 measurement by TOSCA was useful as trend-monitoring after stabilization and during transport to NICU.
doi:10.3390/s120810980
PMCID: PMC3472870  PMID: 23112642
oxygen saturation; partial pressure of carbon dioxide; pulse oximeter; delivery room; TOSCA sensor; neonate
2.  Randomized controlled trial of high concentration oxygen in suspected community-acquired pneumonia 
Objective
To determine whether high concentration oxygen increases the PaCO2 in the treatment of community-acquired pneumonia.
Design
Randomized controlled clinical trial in which patients received high concentration oxygen (8 L/min via medium concentration mask) or titrated oxygen (to achieve oxygen saturations between 93 and 95%) for 60 minutes. Transcutaneous CO2 (PtCO2) was measured at 0, 20, 40 and 60 minutes.
Setting
The Emergency Departments at Wellington, Hutt and Kenepuru Hospitals.
Participants
150 patients with suspected community-acquired pneumonia presenting to the Emergency Department. Patients with chronic obstructive pulmonary disease (COPD) or disorders associated with hypercapnic respiratory failure were excluded.
Main outcome variables
The primary outcome variable was the proportion of patients with a rise in PtCO2 ≥4 mmHg at 60 minutes. Secondary outcome variables included the proportion of patients with a rise in PtCO2 ≥8 mmHg at 60 minutes.
Results
The proportion of patients with a rise in PtCO2 ≥4 mmHg at 60 minutes was greater in the high concentration oxygen group, 36/72 (50.0%) vs 11/75 (14.7%), relative risk (RR) 3.4 (95% CI 1.9 to 6.2), P < 0.001. The high concentration group had a greater proportion of patients with a rise in PtCO2 ≥8 mmHg, 11/72 (15.3%) vs 2/75 (2.7%), RR 5.7 (95% CI 1.3 to 25.0), P = 0.007. Amongst the 74 patients with radiological confirmation of pneumonia, the high concentration group had a greater proportion with a rise in PtCO2 ≥4 mmHg, 20/35 (57.1%) vs 5/39 (12.8%), RR 4.5 (95% CI 1.9 to 10.6) P < 0.001.
Conclusions
We conclude that high concentration oxygen therapy increases the PtCO2 in patients presenting with suspected community-acquired pneumonia. This suggests that the potential increase in PaCO2 with high concentration oxygen therapy is not limited to COPD, but may also occur in other respiratory disorders with abnormal gas exchange.
doi:10.1258/jrsm.2012.110084
PMCID: PMC3360531  PMID: 22532661
3.  Use of transcutaneous oxygen tension, arterial oxygen saturation, and respiratory resistance to assess the response to inhaled methacholine in asthmatic children and normal adults. 
Thorax  1991;46(6):433-437.
Respiratory resistance (Rrs6), transcutaneous oxygen tension (PtcO2), and oxygen saturation (SaO2) were measured during methacholine challenge in 15 asthmatic children and six normal adults. During bronchoconstriction, induced by a wide range of inhaled methacholine concentrations (0.5-256 g/l), the rise in Rrs6 was reflected by a fall in PtcO2 in all subjects. Although there was a significant mean fall in SaO2 at maximum bronchoconstriction there was no consistent relation between changes in SaO2 and Rrs6. The inhaled dose of methacholine causing a 40% increase in Rrs6 (PD40Rrs6) and a 20% fall in PtCO2 (PD20PtcO2) was calculated for each subject. There was no significant difference in mean PD40Rrs6 and PD20PtcO2, and the relation between the two was similar in the asthmatic children and the normal adults. It was therefore concluded that the measurement of PtcO2, but not SaO2, during methacholine challenge can be used for the assessment of bronchial responsiveness, and that it could prove particularly useful for children too young to cooperate with lung function tests.
PMCID: PMC463191  PMID: 1858082
4.  Effect of early goal directed therapy on tissue perfusion in patients with septic shock 
BACKGROUND:
This study aimed to observe the effect of early goal directed therapy (EGDT) on tissue perfusion, microcirculation and tissue oxygenation in patients with septic shock.
METHODS:
Patients with early septic shock (<24 hours) who had been admitted to the ICU of Zhongda Hospital Affiliated to Southeast University from September 2009 through May 2011 were enrolled (research time: 12 months), and they didn’t meet the criteria of EGDT. Patients who had one of the following were excluded: stroke, brain injury, other types of shock, severe heart failure, acute myocardial infarction, age below 18 years, pregnancy, end-stage disease, cardiac arrest, extensive burns, oral bleeding, difficulty in opening the mouth, and the onset of septic shock beyond 24 hours. Patients treated with the standard protocol of EGDT were included. Transcutaneous pressure of oxygen and carbon dioxide (PtcO2, PtcCO2) were monitored and hemodynamic measurements were obtained. Side-stream dark field (SDF) imaging device was applied to obtain sublingual microcirculation. Hemodynamics, tissue oxygen, and sublingual microcirculation were compared before and after EGDT. If the variable meets the normal distribution, Student's t test was applied. Otherwise, Wilcoxon's rank-sum test was used. Correlation between variables was analyzed with Pearson's product-moment correlation coefficient method.
RESULTS:
Twenty patients were involved, but one patient wasn’t analyzed because he didn’t meet the EGDT criteria. PtcO2 and PtcCO2 were monitored in 19 patients, of whom sublingual microcirculation was obtained. After EGDT, PtcO2 increased from 62.7±24.0 mmHg to 78.0±30.9 mmHg (P<0.05) and tissue oxygenation index (PtcO2/FiO2) was 110.7±60.4 mmHg before EGDT and 141.6±78.2 mmHg after EGDT (P<0.05). The difference between PtcCO2 and PCO2 decreased significantly after EGDT (P<0.05). The density of perfused small vessels (PPV) and microcirculatory flow index of small vessels (MFI) tended to increase, but there were no significant differences between them (P>0.05). PtcO2, PtcO2/FiO2, and PtcCO2 were not linearly related to central venous saturation, lactate, oxygen delivery, and oxygen consumption (P>0.05).
CONCLUSION:
Peripheral perfusion was improved after EGDT in patients with septic shock, and it was not exactly reflected by the index of systemic perfusion.
doi:10.5847/wjem.j.issn.1920-8642.2013.02.006
PMCID: PMC4129837  PMID: 25215104
Transcutaneous pressure of oxygen; Transcutaneous pressure of carbon dioxide; Microcirculation; Septic shock; EGDT; Tissue perfusion; Tissue oxygenation; Sidestream dark field imaging
5.  Optimal Clinical Time for Reliable Measurement of Transcutaneous CO2 with Ear Probes: Counterbalancing Overshoot and the Vasodilatation Effect 
Sensors (Basel, Switzerland)  2010;10(1):491-500.
OBJECTIVES:
To determine the optimal clinical reading time for the transcutaneous measurement of oxygen saturation (SpO2) and transcutaneous CO2 (TcPCO2) in awake spontaneously breathing individuals, considering the overshoot phenomenon (transient overestimation of arterial PaCO2).
EXPERIMENTAL SECTION:
Observational study of 91 (75 men) individuals undergoing forced spirometry, measurement of SpO2 and TcPCO2 with the SenTec monitor every two minutes until minute 20 and arterial blood gas (ABG) analysis. Overshoot severity: (a) mild (0.1–1.9 mm Hg); (b) moderate (2–4.9 mm Hg); (c) severe: (>5 mm Hg). The mean difference was calculated for SpO2 and TcPCO2 and arterial values of PaCO2 and SpO2. The intraclass correlation coefficient (ICC) between monitor readings and blood values was calculated as a measure of agreement.
RESULTS:
The mean age was 63.1 ± 11.8 years. Spirometric values: FVC: 75.4 ± 6.2%; FEV1: 72.9 ± 23.9%; FEV1/FVC: 70 ± 15.5%. ABG: PaO2: 82.6 ± 13.2; PaCO2: 39.9.1 ± 4.8 mmHg; SaO2: 95.3 ± 4.4%. Overshoot analysis: overshoot was mild in 33 (36.3%) patients, moderate in 20 (22%) and severe in nine (10%); no overshoot was observed in 29 (31%) patients. The lowest mean differences between arterial blood gas and TcPCO2 was −0.57 mmHg at minute 10, although the highest ICC was obtained at minutes 12 and 14 (>0.8). The overshoot lost its influence after minute 12. For SpO2, measurements were reliable at minute 2.
CONCLUSIONS:
The optimal clinical reading measurement recommended for the ear lobe TcPCO2 measurement ranges between minute 12 and 14. The SpO2 measurement can be performed at minute 2.
doi:10.3390/s100100491
PMCID: PMC3270853  PMID: 22315552
transcutaneous CO2; optimal reading time; overshoot phenomenon
6.  The peripheral perfusion index and transcutaneous oxygen challenge test are predictive of mortality in septic patients after resuscitation 
Critical Care  2013;17(3):R116.
Introduction
The peripheral perfusion index (PI) is a noninvasive numerical value of peripheral perfusion, and the transcutaneous oxygen challenge test (OCT) is defined as the degree of transcutaneous partial pressure of oxygen (PtcO2) response to 1.0 FiO2. The value of noninvasive monitoring peripheral perfusion to predict outcome remains to be established in septic patients after resuscitation. Moreover, the prognostic value of PI has not been investigated in septic patients.
Methods
Forty-six septic patients, who were receiving PiCCO-Plus cardiac output monitoring, were included in the study group. Twenty stable postoperative patients were studied as a control group. All the patients inspired 1.0 of FiO2 for 10 minutes during the OCT. Global hemodynamic variables, traditional metabolic variables, PI and OCT related-variables were measured simultaneously at 24 hours after PiCCO catheter insertion. We obtained the 10min-OCT ((PtcO2 after 10 minutes on inspired 1.0 oxygen) - (baseline PtcO2)), and the oxygen challenge index ((10min-OCT)/(PaO2 on inspired 1.0 oxygen - baseline PaO2)) during the OCT.
Results
The PI was significantly correlated with baseline PtcO2, 10min-OCT and oxygen challenge index (OCI) in all the patients. The control group had a higher baseline PtcO2, 10min-OCT and PI than the septic shock group. In the sepsis group, the macro hemodynamic parameters and ScvO2 showed no differences between survivors and nonsurvivors. The nonsurvivors had a significantly lower PI, 10min-OCT and OCI, and higher arterial lactate level. The PI, 10min-OCT and OCI predicted the ICU mortality with an accuracy that was similar to arterial lactate level. A PI <0.2 and a 10min-OCT <66mmHg were related to poor outcome after resuscitation.
Conclusions
The PI and OCT are predictive of mortality for septic patients after resuscitation. Further investigations are required to determine whether the correction of an impaired level of peripheral perfusion may improve the outcome of septic shock patients.
doi:10.1186/cc12788
PMCID: PMC4057372  PMID: 23787173
Peripheral perfusion index (PI); transcutaneous oxygen/carbon dioxide tensions (PtcO2/PtcCO2); oxygen challenge test (OCT); septic shock; prognosis
7.  Repeatability of methacholine challenge in asthmatic children measured by change in transcutaneous oxygen tension. 
Thorax  1992;47(10):804-808.
BACKGROUND: The airway response to bronchial provocation may be evaluated by monitoring the fall in transcutaneous oxygen tension (PtcO2) but the repeatability of this method has not been rigorously assessed. METHODS: To determine the repeatability of this indirect method of assessment, bronchial challenge was performed with methacholine in nine children with stable asthma (age range 6-12 years) and was repeated 24 hours later. The response was determined by the fall both in forced expiratory volume in one second (FEV1) and in PtcO2. A modified tidal inhalation protocol was used in which quadrupling concentrations of methacholine were given, thereby reducing the time taken for the full challenge by almost half. The concentrations of methacholine that provoked a 20% decrease in FEV1 (PC20FEV1) and 15% and 10% falls in PtcO2 (PC15PtcO2, PC10PtcO2) were calculated. RESULTS: Repeatability measures, assessed as the 95% range for a single determination, were +/- 0.96 and +/- 1.12 doubling concentration differences respectively for PC15PtcO2 and PC10PtcO2 and +/- 0.80 for PC20FEV1. CONCLUSION: This challenge method using quadrupling concentrations and an indirect assessment of the response by PtcO2 was sufficiently repeatable for clinical use and compared favourably with repeated challenge assessed by FEV1. The PtcO2 method is simple and effort independent, and should prove particularly useful for measuring bronchial reactivity in young children.
PMCID: PMC464053  PMID: 1481181
8.  Monitoring of end tidal carbon dioxide and transcutaneous carbon dioxide during neonatal transport 
Objective: To assess the accuracy of measurements of end tidal carbon dioxide (CO2) during neonatal transport compared with arterial and transcutaneous measurements.
Design: Paired end tidal and transcutaneous CO2 recordings were taken frequently during road transport of 21 ventilated neonates. The first paired CO2 values were compared with an arterial blood gas. The differences between arterial CO2 (PaCO2), transcutaneous CO2 (TcPCO2), and end tidal CO2 (PetCO2) were analysed. The Bland-Altman method was used to assess bias and repeatability.
Results: PetCO2 correlated strongly with PaCO2 and TcPCO2. However, PetCO2 underestimated PaCO2 at a clinically unacceptable level (mean (SD) 1.1 (0.70) kPa) and did not trend reliably over time within individual subjects. The PetCO2 bias was independent of PaCO2 and severity of lung disease.
Conclusions: PetCO2 had an unacceptable under-recording bias. TcPCO2 should currently be considered the preferred method of non-invasive CO2 monitoring for neonatal transport.
doi:10.1136/adc.2004.064717
PMCID: PMC1721963  PMID: 15863489
9.  The Application of Transcutaneous CO2 Pressure Monitoring in the Anesthesia of Obese Patients Undergoing Laparoscopic Bariatric Surgery 
PLoS ONE  2014;9(4):e91563.
To investigate the correlation and accuracy of transcutaneous carbon dioxide partial pressure (PTCCO2) with regard to arterial carbon dioxide partial pressure (PaCO2) in severe obese patients undergoing laparoscopic bariatric surgery. Twenty-one patients with BMI>35 kg/m2 were enrolled in our study. Their PaCO2, end-tidal carbon dioxide partial pressure (PetCO2), as well as PTCCO2 values were measured at before pneumoperitoneum and 30 min, 60 min, 120 min after pneumoperitoneum respectively. Then the differences between each pair of values (PetCO2–PaCO2) and. (PTCCO2–PaCO2) were calculated. Bland–Altman method, correlation and regression analysis, as well as exact probability method and two way contingency table were employed for the data analysis. 21 adults (aged 19–54 yr, mean 29, SD 9 yr; weight 86–160 kg, mean119.3, SD 22.1 kg; BMI 35.3–51.1 kg/m2, mean 42.1,SD 5.4 kg/m2) were finally included in this study. One patient was eliminated due to the use of vaso-excitor material phenylephrine during anesthesia induction. Eighty-four sample sets were obtained. The average PaCO2–PTCCO2 difference was 0.9±1.3 mmHg (mean±SD). And the average PaCO2–PetCO2 difference was 10.3±2.3 mmHg (mean±SD). The linear regression equation of PaCO2–PetCO2 is PetCO2 = 11.58+0.57×PaCO2 (r2 = 0.64, P<0.01), whereas the one of PaCO2–PTCCO2 is PTCCO2 = 0.60+0.97×PaCO2 (r2 = 0.89). The LOA (limits of agreement) of 95% average PaCO2–PetCO2 difference is 10.3±4.6 mmHg (mean±1.96 SD), while the LOA of 95% average PaCO2–PTCCO2 difference is 0.9±2.6 mmHg (mean±1.96 SD). In conclusion, transcutaneous carbon dioxide monitoring provides a better estimate of PaCO2 than PetCO2 in severe obese patients undergoing laparoscopic bariatric surgery.
doi:10.1371/journal.pone.0091563
PMCID: PMC3974655  PMID: 24699267
10.  Atopy, bronchial responsiveness, and symptoms in wheezy 3 year olds. 
Archives of Disease in Childhood  1992;67(4):491-495.
Fifty children with at least one hospital admission for acute lower airway obstruction in the first 2.5 years of life were assessed at 3 years of age to determine the relationship between atopy, bronchial responsiveness, and the pattern of their symptoms. Bronchial responsiveness was measured by assessing the effect of inhaled metacholine, using the change in transcutaneous oxygen tension (PtCO2) as an indirect measure of response. Symptom patterns were defined by the number of wheezing episodes associated with colds and the presence or absence of cough or wheeze unrelated to viral infections. Forty per cent of the children were found to be atopic by skin prick test or history. In contrast to the situation found in older children and adults, the non-atopic children had significantly greater bronchial responsiveness (lower mean concentration of methacholine causing a 20% fall in PtCO2, the PC20) than the atopic children and significantly more of them had an onset of respiratory symptoms in the first year of life. Cough and wheeze in the absence of colds was more frequently found in the atopic children as was the use of continuous medication. However, the number of reported acute episodes of wheeze associated with colds was the same in the two groups. The findings of the study suggest that in this hospital based group of children, acute wheeze associated with colds in the first three years of life is independent of the finding of atopy and that bronchial responsiveness in this age group may have a different pathogenesis from that in older subjects.
PMCID: PMC1793338  PMID: 1580678
11.  Peripheral venous blood gases and pulse-oximetry in acute cardiogenic pulmonary oedema 
Background:
The role of venous blood gases as an alternative to arterial blood gases in patients with severe acute heart failure has not been established.
Objective:
To assess the correlation between arterial and peripheral venous blood gases together with pulse-oximetry (SpO2), as well as to estimate arterial values from venous samples in the first hours upon admission of patients with acute cardiogenic pulmonary oedema.
Methods:
Simultaneous venous and arterial blood samples were extracted on admission and over the next 1, 2, 3, 4, and 10 hours. SpO2 was also registered at the same intervals.
Results:
A total of 178 pairs of samples were obtained from 34 consecutive patients with acute cardiogenic pulmonary oedema. Arterial and venous blood gases followed a parallel course in the first hours, showing high correlation rates at all time intervals. Venous samples underestimated pH (mean difference −0.028) and overestimated CO2 (+5.1 mmHg) and bicarbonate (+1 mEq/l). Conversely, SpO2 tended to underestimate SaO2 (mean±SD: 93.1±9.1 vs. 94.2±8.4). Applying simple mathematical formulae based on these differences, arterial values were empirically calculated from venous samples, showing acceptable agreement in the Bland−Altman test. Likewise, a venous pH <7.32, pCO2 >51.3 mmHg, and bicarbonate <22.8 mEq/l could fairly identify arterial acidosis, either respiratory or metabolic, with a test accuracy of 92, 68, and 91%, respectively.
Conclusions:
In patients with cardiogenic pulmonary oedema, arterial blood gas disturbances may be estimated from peripheral venous samples. By monitoring SpO2 simultaneously, arterial punctures could often be avoided.
doi:10.1177/2048872612457087
PMCID: PMC3760566  PMID: 24062917
Acute heart failure; arterial blood gases; pulmonary oedema; oxygen saturation; venous blood gases
12.  Evaluation of PO2 and PCO2 Changes During Surgical Removal of Third Molars Utilizing Enflurane Anesthesia 
Anesthesia Progress  1985;32(3):93-97.
This study investigated the changes in partial pressure of oxygen during surgical removal of wisdom teeth utilizing a spontaneous ventilation general anesthesia technique with enflurane. Simultaneous transcutaneous and arterial blood gas determination confirmed the presence of two oxygen patterns. Normal preoperative pulmonary function tests, coupled with the stability of the Paco2 between surgery and extubation, indicates that the 23±10 mmHg increase in transcutaneous oxygen (Ptco2) reported in 14 of 27 patients evaluated, was due to ventilation perfusion defects, since 13 of the 27 patients showed a 149±22 mmHg increase in Ptco2 during the same time period.
PMCID: PMC2148505  PMID: 3935011
13.  Increased blood glycohemoglobin A1c levels lead to overestimation of arterial oxygen saturation by pulse oximetry in patients with type 2 diabetes 
Background
Non-enzymatic glycation increases hemoglobin-oxygen affinity and reduces oxygen delivery to tissues by altering the structure and function of hemoglobin.
Objectives
We investigated whether an elevated blood concentration of glycosylated hemoglobin (HbA1c) could induce falsely high pulse oximeter oxygen saturation (SpO2) in type 2 diabetic patients during mechanical ventilation or oxygen therapy.
Methods
Arterial oxygen saturation (SaO2) and partial pressure of oxygen (PO2) were determined with simultaneous monitoring of SpO2 in 261 type 2 diabetic patients during ventilation or oxygen inhalation.
Results
Blood concentration of HbA1c was >7% in 114 patients and ≤ 7% in 147 patients. Both SaO2 (96.2 ± 2.9%, 95% confidence interval [CI] 95.7-96.7% vs. 95.1 ± 2.8%, 95% CI 94.7-95.6%) and SpO2 (98.0 ± 2.6%, 95% CI 97.6-98.5% vs. 95.3 ± 2.8%, 95% CI 94.9-95.8%) were significantly higher in patients with HbA1c >7% than in those with HbA1c ≤ 7% (Data are mean ± SD, all p < 0.01), but PO2 did not significantly differ between the two groups. Bland-Altman analysis demonstrated a significant bias between SpO2 and SaO2 (1.83 ±0.55%, 95% CI 1.73% -1.94%) and limits of agreement (0.76% and 2.92%) in patients with HbA1c >7%. The differences between SpO2 and SaO2 correlated closely with blood HbA1c levels (Pearson’s r = 0.307, p < 0.01).
Conclusions
Elevated blood HbA1c levels lead to an overestimation of SaO2 by SpO2, suggesting that arterial blood gas analysis may be needed for type 2 diabetic patients with poor glycemic control during the treatment of hypoxemia.
doi:10.1186/1475-2840-11-110
PMCID: PMC3489581  PMID: 22985301
Glycohemoglobin A1c; Diabetes mellitus; Arterial blood gas analysis; Pulse oxygen saturation
14.  Accuracy of pulse oximetry and capnography in healthy and compromised horses during spontaneous and controlled ventilation 
The objective of this prospective clinical study was to evaluate the accuracy of pulse oximetry and capnography in healthy and compromised horses during general anesthesia with spontaneous and controlled ventilation. Horses anesthetized in a dorsal recumbency position for arthroscopy (n = 20) or colic surgery (n = 16) were instrumented with an earlobe probe from the pulse oximeter positioned on the tip of the tongue and a sample line inserted at the Y-piece for capnography. The horses were allowed to breathe spontaneously (SV) for the first 20 min after induction, and thereafter ventilation was controlled (IPPV). Arterial blood, for blood gas analysis, was drawn 20 min after induction and 20 min after IPPV was started. Relationships between oxygen saturation as determined by pulse oximetry (SpO2), arterial oxygen saturation (SaO2), arterial carbon dioxide partial pressure (PaCO2), and end tidal carbon dioxide (P(et)CO2), several physiological variables, and the accuracy of pulse oximetry and capnography, were evaluated by Bland–Altman or regression analysis. In the present study, both SpO2 and P(et)CO2 provided a relatively poor indication of SaO2 and PaCO2, respectively, in both healthy and compromised horses, especially during SV. A difference in heart rate obtained by pulse oximetry, ECG, or palpation is significantly correlated with any pulse oximeter inaccuracy. If blood gas analysis is not available, ventilation to P(et)CO2 of 35 to 45 mmHg should maintain the PaCO2 within a normal range. However, especially in compromised horses, it should never substitute blood gas analysis.
PMCID: PMC227048  PMID: 12889721
15.  A survey of transcutaneous blood gas monitoring among European neonatal intensive care units 
BMC Pediatrics  2005;5:30.
Background
PCO2 and PO2 are important monitoring parameters in neonatal intensive care units (NICU). Compared to conventional blood gas measurements that cause significant blood loss in preterms, transcutaneous (tc) measurements allow continuous, non-invasive monitoring of blood gas levels. The aim of the study was to survey the usage and opinions among German speaking NICUs concerning tc blood gas monitoring.
Methods
A questionnaire was developed and sent to 56 head nurses of different NICUs in Germany, Switzerland and Austria.
Results
A completely answered questionnaire was obtained from 41 NICUs. In two of these units tc measurements are not performed. In most NICUs (77%), both PtcO2 and PtcCO2 are measured simultaneously. Most units change the sensors every 3 hours; however, the recommended temperature of 44°C is used in only 15% of units. In only 8% of units are arterial blood gases obtained to validate tc values. Large variations were found concerning the targeted level of oxygen saturation [median upper limit: 95% (range 80–100%); median lower limit: 86% (range 75–93%)] and PO2 [median upper limit: 70 mmHg (range 45–90 mmHg); median lower limit: 44 mmHg (range 30–60 mmHg)].
Conclusion
Our survey shows that the use of tc monitors remains widespread among German speaking NICUs, despite earlier data suggesting that their use had been abandoned in many NICUs worldwide. In addition, we suggest that the current method of monitoring oxygenation may not prevent hyperoxemia in preterm infants.
doi:10.1186/1471-2431-5-30
PMCID: PMC1192805  PMID: 16092957
16.  The accuracy of pulse oximetry in emergency department patients with severe sepsis and septic shock: a retrospective cohort study 
Background
Pulse oximetry is routinely used to continuously and noninvasively monitor arterial oxygen saturation (SaO2) in critically ill patients. Although pulse oximeter oxygen saturation (SpO2) has been studied in several patient populations, including the critically ill, its accuracy has never been studied in emergency department (ED) patients with severe sepsis and septic shock. Sepsis results in characteristic microcirculatory derangements that could theoretically affect pulse oximeter accuracy. The purposes of the present study were twofold: 1) to determine the accuracy of pulse oximetry relative to SaO2 obtained from ABG in ED patients with severe sepsis and septic shock, and 2) to assess the impact of specific physiologic factors on this accuracy.
Methods
This analysis consisted of a retrospective cohort of 88 consecutive ED patients with severe sepsis who had a simultaneous arterial blood gas and an SpO2 value recorded. Adult ICU patients that were admitted from any Calgary Health Region adult ED with a pre-specified, sepsis-related admission diagnosis between October 1, 2005 and September 30, 2006, were identified. Accuracy (SpO2 - SaO2) was analyzed by the method of Bland and Altman. The effects of hypoxemia, acidosis, hyperlactatemia, anemia, and the use of vasoactive drugs on bias were determined.
Results
The cohort consisted of 88 subjects, with a mean age of 57 years (19 - 89). The mean difference (SpO2 - SaO2) was 2.75% and the standard deviation of the differences was 3.1%. Subgroup analysis demonstrated that hypoxemia (SaO2 < 90) significantly affected pulse oximeter accuracy. The mean difference was 4.9% in hypoxemic patients and 1.89% in non-hypoxemic patients (p < 0.004). In 50% (11/22) of cases in which SpO2 was in the 90-93% range the SaO2 was <90%. Though pulse oximeter accuracy was not affected by acidoisis, hyperlactatementa, anemia or vasoactive drugs, these factors worsened precision.
Conclusions
Pulse oximetry overestimates ABG-determined SaO2 by a mean of 2.75% in emergency department patients with severe sepsis and septic shock. This overestimation is exacerbated by the presence of hypoxemia. When SaO2 needs to be determined with a high degree of accuracy arterial blood gases are recommended.
doi:10.1186/1471-227X-10-9
PMCID: PMC2876142  PMID: 20444248
17.  Prediction of arterial blood gas values from arterialized earlobe blood gas values in patients treated with mechanical ventilation 
Background/Objective:
Arterial blood gas (ABG) analysis is useful in evaluation of the clinical condition of critically ill patients; however, arterial puncture or insertion of an arterial catheter may sometimes be difficult and cause many complications. Arterialized ear lobe blood samples have been described as adequate to gauge gas exchange in acute and chronically ill pediatric patients.
Purpose:
This study evaluates whether pH, partial pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2), base excess (BE), and bicarbonate (HCO3) values of arterialized earlobe blood samples could accurately predict their arterial blood gas analogs for adult patients treated by mechanical ventilation in an intensive care unit (ICU).
Setting:
A prospective descriptive study
Methods:
Sixty-seven patients who were admitted to ICU and treated with mechanical ventilation were included in this study. Blood samples were drawn simultaneously from the radial artery and arterialized earlobe of each patient.
Results:
Regression equations and mean percentage-difference equations were derived to predict arterial pH, PCO2, PO2, BE, and HCO3-values from their earlobe analogs. pH, PCO2, BE, and HCO3 all significantly correlated in ABG and earlobe values. In spite of a highly significant correlation, the limits of agreement between the two methods were wide for PO2. Regression equations for prediction of pH, PCO2, BE, and HCO3- values were: arterial pH (pHa) = 1.81+ 0.76 × earlobe pH (pHe) [r = 0.791, P < 0.001]; PaCO2 = 1.224+ 1.058 × earlobePCO2 (PeCO2) [r = 0.956, P < 0.001]; arterial BE (BEa) = 1.14+ 0.95 × earlobe BE (BEe) [r= 0.894, P < 0.001], and arterial HCO3- (HCO3-a) = 1.41+ earlobe HCO3(HCO3-e) [r = 0.874, P < 0.001]. The predicted ABG values from the mean percentage-difference equations were derived as follows: pHa = pHe × 1.001; PaCO2 = PeCO2 × 0.33; BEa = BEe × 0.57; and HCO3-a = HCO3-e × 1.06.
Conclusions:
Arterialized earlobe blood gas can accurately predict the ABG values of pH, PCO2, BE, and HCO3- for patients who do not require regular continuous blood pressure measurements and close monitoring of arterial PO2 measurements.
doi:10.4103/0972-5229.43677
PMCID: PMC2738313  PMID: 19742254
Arterialized earlobe blood gas; critically illness; mechanical ventilation
18.  Alveolar partial pressures of carbon dioxide and oxygen measured by a helium washout technique. 
Thorax  1990;45(7):520-524.
A non-invasive technique was developed for measuring alveolar carbon dioxide and oxygen tension during tidal breathing. This was achieved by solving the Bohr equations for mean alveolar carbon dioxide and oxygen tensions (PACO2, PAO2) from known values of the dead-space:tidal volume ratio measured by helium washout, and from the mixed expired partial pressure of carbon dioxide and oxygen. The derived values of wPACO2 and wPAO2 were compared with PaCO2 obtained from arterial gas analysis and PAO2 calculated from the ideal air equation. Four normal subjects and 58 patients were studied. Calculated and measured PCO2 values agreed closely with a difference in mean values (wPACO2 - PaCO2) of 0.01 kPa; the SD of the differences was 0.7 kPa. The difference in mean values between wPAO2 and PAO2 was 0.02 kPa; the SD of the differences was 0.93 kPa. The method is simple and not time consuming, and requires no special cooperation from the patients. It can be applied in the laboratory or at the bedside to any subject breathing tidally. Physiological deadspace:tidal volume ratio, PAO2 and PACO2, static lung volumes, respiratory exchange ratio, carbon dioxide production, oxygen uptake, tidal volume, and total ventilation can be measured with acceptable accuracy and reproducibility in one test. An arterial blood sample is needed initially to provide an independent measure of PaCO2 and for measurement of the alveolar-arterial PO2 difference. Subsequently, PaCO2 can be estimated from wPACO2 sufficiently well for clinical purposes and PaO2 or SaO2 can be monitored by non-invasive methods.
Images
PMCID: PMC462581  PMID: 2118690
19.  Performance of capnometry in non-intubated infants in the pediatric intensive care unit 
BMC Pediatrics  2014;14:163.
Background
Assessing the ventilatory status of non-intubated infants in the Pediatric Intensive Care Unit (PICU) is a constant challenge. Methods to evaluate ventilation include arterial blood gas analysis (ABG), which is invasive and intermittent, and transcutaneous carbon dioxide monitoring (PtcCO2), which, while non-invasive, is also intermittent. A method that is non-invasive and continuous would be of great benefit in this population. We hypothesized that non-invasive capnometry via sidestream monitoring of exhaled carbon dioxide (CO2) would provide an acceptable measurement of ventilatory status when compared to ABG or PtcCO2.
Methods
Preliminary prospective study of infants less than one year of age admitted to the PICU in a large urban teaching hospital. Infants not intubated and not requiring non-invasive ventilation were eligible. A sidestream CO2 reading was obtained in a convenience sample of 39 patients. A simultaneous ABG was collected in those with an arterial catheter, and a PtcCO2 was obtained in those without.
Results
Correlation of sidestream CO2 with ABG was excellent (r2 = 0.907). Sidestream correlated less well with PtcCO2 (r2 = 0.649). Results were not significantly altered when weight and respiratory rate were added as independent variables. Bland-Altman analysis revealed a bias of -2.7 with a precision of ±6.5 when comparing sidestream CO2 to ABG, and a bias of -1.7 with a precision of ±9.9 when comparing sidestream CO2 to PtcCO2.
Conclusions
Performance of sidestream monitoring of exhaled CO2 is acceptable clinical trending to assess the effectiveness of ventilation in non-intubated infants in the PICU.
doi:10.1186/1471-2431-14-163
PMCID: PMC4080582  PMID: 24965523
Capnometry; Ventilation; Monitoring; Infants; Microstream; Carbon dioxide
20.  Use of a combined oxygen and carbon dioxide transcutaneous electrode in the estimation of gas exchange during exercise. 
Thorax  1993;48(6):643-647.
BACKGROUND--Accurate and reliable measurement of gas exchange during exercise has traditionally involved arterial cannulation. Non-invasive devices to estimate arterial oxygen (O2) and carbon dioxide (CO2) tensions are now available. A method has been devised and evaluated for measuring gas exchange during exercise with a combined transcutaneous O2 and CO2 electrode. METHODS--Symptom limited exercise tests were carried out in 24 patients reporting effort intolerance and breathlessness. Exercise testing was performed by bicycle ergometry with a specifically designed protocol involving gradual two minute workload increments. Arterial O2 and CO2 tensions were measured at rest and during exercise by direct blood sampling from an indwelling arterial cannula and a combined transcutaneous electrode heated to 45 degrees C. The transcutaneous system was calibrated against values obtained by direct arterial sampling before each test. RESULTS--In all tests the trend of gas exchange measured by the transcutaneous system was true to the trend measured from direct arterial sampling. In the 140 measurements the mean difference between the O2 tensions estimated by direct sampling and the transcutaneous method was 0.08 kPa (0.62 mm Hg, limits of agreement 4.42 and -3.38 mm Hg). The mean difference between the methods for CO2 was 0.02 kPa (0.22 mm Hg, limits of agreement 2.20 and -1.70 mm Hg). There was no morbidity associated with the use of the transcutaneous electrode heated to 45 degrees C. CONCLUSIONS--A combined transcutaneous O2 and CO2 electrode heated to 45 degrees C can be used to provide a reliable estimate of gas exchange during gradual incremental exercise in adults.
PMCID: PMC464594  PMID: 8346496
21.  Correlation between end-tidal and arterial carbon dioxide partial pressure in patients undergoing craniotomy 
Journal of Injury and Violence Research  2012;4(3 Suppl 1): Paper No. 32.
Abstract:
Background:
Both end-tidal carbon dioxide pressure (ETCO2) is used routinely as an indicator of arterial partial pressure of carbon dioxide (PaCO2) and thus adequacy of ventilation. Accurate determination of the PaCO2 level in neuroanesthesia is quite important because of its effect on cerebral blood flow and also hyperventilation is often used to reduce intracranial pressure in neurosurgical patients. This study was aimed to evaluate the relationship between ETCO2 and arterial PaCO2 in neurosurgical patients undergoing craniotomy to assess the predictive value of ETCO2 as an indicator of PaCO2 level.
Methods:
Forty-five consecutive adult patients with inclusion criteria, scheduled to undergo elective craniotomy surgery were enrolled in this prospective study. Measurements of PaCO2 and ETCO2 were performed at three different intervals: Time 1: 10 min after induction of general anesthesia; time 2: after cranium opening prior to dural incision; and at time 3: start of dural closure. All patients received the same anesthetic agent (propofol, sufentanil, atracurium, oxygen). Data were initially analyzed using Pearson’s Correlation to assess the relationship between PaCO2 and ETCO2 at different stages of the operation. A p-value (P) of less than 0.05 was considered significant. The agreement between the measures of CO2 was assessed using Bland-Altman method, where mean difference and average between PaCO2 and ETCO2 were calculated. The 95% confidence intervals for the lower and upper limits of agreement were presented.
Results:
A total of 44 patients, aged 18 to 65 years, ASA grades 1 and 2 were participated in the study. Mean difference, standard deviation and correlation coefficient of the parameters were calculated for three time periods. The values for PaCO2, ETCO2, (PaCO2- ETCO2), and correlation coefficient for 10 min after anesthetic induction, prior to dural incision, and start of dural closure were 35.4 ± 3.2, 32.1 ± 3.2, 3.8 ± 2.1, and 0.565, 36.2 ± 3.1, 32.6 ± 3.2,4.8 ± 3.1, and 0.574, and 36.7 ± 2.4, 33 ± 3.2,3.8 ± 2.3, and 0.627, respectively (p less than 0.01 for all analyses). The greatest mean difference occurred just prior to dural incision. The lowest mean difference was observed at 10 min post-anesthetic induction.
Conclusions:
To the present study was aimed to correlate between End-tidal and arterial carbon dioxide partial pressure in neurosurgical patients undergoing craniotomy. Findings of this study showed that ETCO2 consistently underestimates the value of PaCO2 during craniotomy indicating that ETCO2 value can be used instead of PaCO2.
Keywords:
End-tidal carbon dioxide pressure, Arterial partial pressure of carbon dioxide, Craniotomy
PMCID: PMC3571558
22.  Chest physiotherapy in preterm infants with lung diseases 
Background
In neonatology the role of chest physiotherapy is still uncertain because of the controversial outcomes.
Methods
The aim of this study was to test the applicability in preterm infants of 'reflex rolling', from the Vojta method, in preterm neonates with lung pathology, with particular attention to the effects on blood gases and oxygen saturation, on the spontaneous breathing, on the onset of stress or pain. The study included 34 preterm newborns with mean gestational age of 30.5 (1.6) weeks - mean (DS) - and birth weight of 1430 (423) g - mean (DS) -, who suffered from hyaline membrane disease, under treatment with nasal CPAP (continuous positive airways pressure), or from pneumonia, under treatment with oxygen-therapy. The neonates underwent phase 1 of 'reflex rolling' according to Vojta method three times daily. Respiratory rate, SatO2, transcutaneous PtcCO2 e PtcO2 were monitored; in order to evaluate the onset of stress or pain following the stimulations, the NIPS score and the PIPP score were recorded; cerebral ultrasound scans were performed on postnatal days 1-3-5-7, and then weekly.
Results
In this population the first phase of Vojta's 'reflex rolling' caused an increase of PtcO2 and SatO2 values. No negative effects on PtcCO2 and respiratory rate were observed, NIPS and PIPP stress scores remained unmodified during the treatment; in no patient the intraventricular haemorrhage worsened in time and none of the infants developed periventricular leucomalacia.
Conclusions
Our experience, using the Vojta method, allows to affirm that this method is safe for preterm neonates, but further investigations are necessary to confirm its positive effects and to evaluate long-term respiratory outcomes.
doi:10.1186/1824-7288-36-65
PMCID: PMC2955600  PMID: 20868518
23.  Non-invasive proportional assist and pressure support ventilation in patients with cystic fibrosis and chronic respiratory failure 
Thorax  2002;57(1):50-54.
Background: Patients with advanced cystic fibrosis can benefit from non-invasive positive pressure ventilation (NPPV) for the treatment of acute decompensation as well as for the management of chronic respiratory failure. This study was undertaken to compare the physiological effects of non-invasive proportional assist ventilation (PAV) and pressure support ventilation (PSV) on ventilatory pattern, transcutaneous blood gas tensions, and diaphragmatic effort in stable patients with cystic fibrosis and chronic CO2 retention.
Methods: In 12 patients two periods of spontaneous breathing were followed randomly by PSV (12 (3) cm H2O) and PAV (flow assist 4.9 (1.3) cm H2O/l.s, volume assist 18.9 (5.1) cm H2O/l) set for the patient's comfort and administered for 40 minutes with 2 cm H2O continuous positive airway pressure. Ventilatory pattern, transcutaneous blood gas tensions, and surface diaphragmatic electromyography were measured in the last 10 minutes of each application.
Results: On average, both PSV and PAV improved ventilation (+30%), tidal volume (+30%), and transcutaneous CO2 (-7%) while reducing diaphragmatic activity (-30% with PSV, -20% with PAV). Mean inspiratory airway pressure was lower during PAV than during PSV (9.7 (1.9) and 12.9 (2.7) cm H2O, respectively; p<0.05). The mean coefficient of variation of tidal volume was about 20% (range 11–39%) during spontaneous breathing and did not change with either PAV or PSV.
Conclusions: These results show that short term administration of nasal PAV and PSV to patients with stable cystic fibrosis with chronic respiratory insufficiency is well tolerated, improves ventilation and blood gas tensions, and unloads the diaphragm.
doi:10.1136/thorax.57.1.50
PMCID: PMC1746175  PMID: 11809990
24.  Repeatability of lung function tests during methacholine challenge in wheezy infants 
Thorax  1998;53(11):933-938.
BACKGROUND—The repeatability of lung function tests and methacholine inhalation tests was evaluated in recurrently wheezy infants over a one month period using the rapid thoracic compression technique.
METHODS—Eighty one wheezy, symptom free infants had pairs of methacholine challenge tests performed one month apart. Maximal flow at functional residual capacity (V̇maxFRC) and transcutaneous oxygen tension (PtcO2) were measured at baseline and after methacholine inhalation. Provocative doses of methacholine causing a 15% fall in PtcO2 (PD15PtcO2) or a 30% fall in V̇maxFRC (PD30V̇maxFRC) were determined.
RESULTS—Large changes in V̇maxFRC were measured from T1 to T2 with a mean difference between measurements (T2—T1) of 7 (113) ml/s and a 95% range for a single determination for V̇maxFRC of 160 ml/s. The mean (SD) difference between pairs of PD30V̇maxFRC measurements was 0.33 (1.89) doubling doses with a 95% range for a single determination of 2.7 doubling doses. Repeatability of PD15PtcO2 was similar. A change of 3.7 doubling doses of methacholine measured on successive occasions represents a significant change.
CONCLUSIONS—Baseline V̇maxFRC values are highly variable in wheezy, symptom free infants. Using either V̇maxFRC or PtcO2 as the outcome measure for methacholine challenges provided similar repeatability. A change of more than 3.7 doubling doses of methacholine is required for clinical significance.


PMCID: PMC1745105  PMID: 10193390
25.  Noninvasive Optical Quantification of Cerebral Venous Oxygen Saturation in Humans 
Academic radiology  2014;21(2):162-167.
Rationale and Objectives
Cerebral oxygen extraction, defined as the difference between arterial and venous oxygen saturations (SaO2 and SvO2), is a critical parameter for managing intensive care patients at risk for neurological collapse. Although quantification of SaO2 is easily performed with pulse oximetry or moderately invasive arterial blood draws in peripheral vessels, cerebral SvO2 is frequently not monitored because of the invasiveness and risk associated with obtaining jugular bulb or super vena cava (SVC) blood samples.
Materials and Methods
In this study, near-infrared spectroscopy (NIRS) was used to noninvasively measure cerebral SvO2 in anesthetized and mechanically ventilated pediatric patients (n = 10). To quantify SvO2, the NIRS signal component that fluctuates at the respiration frequency is isolated. This respiratory component is dominated by the venous portion of the interrogated vasculature. The NIRS measurements of SvO2 were validated against the clinical gold standard: invasively measured oxygen saturations from SVC blood samples. This technique was also applied in healthy volunteers (n = 5) without mechanical ventilation to illustrate its potential for use in healthy populations with natural airways.
Results
Ten pediatric patients with pulmonary hypertension were studied. In these patients, SvO2 in the SVC exhibited good agreement with NIRS-measured SvO2 (R2 = 0.80, P = .001, slope = 1.16 ± 0.48). Furthermore, in the healthy adult volunteers, mean (standard deviation) NIRS-measured SvO2 was 79.4 (6.8)%. This value is in good agreement with the expected average central venous saturation reported in literature.
Conclusion
Respiration frequency-selected NIRS can noninvasively quantify cerebral SvO2. This bedside technique can be used to help assess brain health in neurologically unstable patients.
doi:10.1016/j.acra.2013.10.013
PMCID: PMC4126245  PMID: 24439329
Near-infrared spectroscopy; cerebral venous oxygenation; pediatrics; validation; noninvasive

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