Transcutaneous PCO2 Monitoring Research Articles

Complex home assessment of long-term non-invasive ventilation efficacy using transcutaneous monitoring of PCO2 and polygraphy – A feasibility study

PurposeHome non-invasive ventilation (HNIV) during sleep is a standard treatment for chronic hypercapnic respiratory failure (CHRF). The aim of this study was to evaluate the feasibility of the complex overnight assessment of HNIV in adults performed at home and the efficacy of HNIV after one year of treatment. MethodsStable patients with CHRF on HNIV for more than 12 months had unattended polygraphy (PG) with transcutaneous monitoring of PCO2 (tcPCO2) at home during one night. The recording quality was regarded as excellent when 100% and good if 80–99% of the analysis time was registered. The following efficacy criteria were approved: (1) SpO2<90% for <10% of analysis time, (2) increase in PtcCO2 ≤7.5 ​mmHg between baseline and average value at night, (3) apnea-hypopnea index (AHI) ≤5/h. ResultsEighteen patients with CHRF (median age 66 [60–74] years, 10 female) were included. The quality of the PG tracings was good to excellent in 16 (89%) patients and the quality of the tcPCO2 data was good to excellent in 14 (78%) patients. There was no difference in the quality of tcPCO2 between patients who lived alone and those who lived with family (100 [50–100]% vs. 100 [90–100]% of analysis time, respectively). Only 4 (22%) patients fulfilled all three efficacy criteria. ConclusionsHome-based monitoring using PG and tcPCO2 is a feasible and adequate tool to assess the efficacy of HNIV. In most of the patients on HNIV for more than 12 months, the treatment was not effective based on the predefined efficacy criteria.

Transcutaneous Carbon Dioxide Measurement in Adult Patients with Neuromuscular Disorders: A quality Level Assessment

Carbon dioxide tension (PCO2) monitoring during sleep, is crucial to identify respiratory failure in patients with neuromuscular disorders (NMD). Transcutaneous PCO2 monitoring is an available technique to measure PCO2. To assess the quality level of transcutaneous blood gas measurements via SenTec monitor. A 12-month analysis of SenTec measurements was conducted in a Belgian Centre for Home Mechanical Ventilation (HMV). Over two consecutive nights; SpO2 and PCO2 measurements, the presence of PCO2 drift and drift correction with SenTec, were reviewed and scores (0, 1, 2 for poor, medium and high level) were assigned to estimate the quality of measurements. Sixty-nine NMD patients met the inclusion criteria, of which 48/69 used HMV. PCO2 drift and drift correction were present in 15% and 68% of the 138 recordings, respectively. The quality level of measurements throughout night 1, scored 1.55 (0-2). The relevance of our clinical findings from SenTec scoring 1.94 (1-2); was considered highly satisfactory. HMV was ineffective in 24/48 patients. Among 12 patients with hypercapnia, 8 patients improved PCO2 between night 1 and 2. Among 12 patients with hypocapnia, PCO2 improved in 4/12 patients, who reached the range of normal PCO2 (35-47 mmHg). The quality of SenTec measurements was acceptable in the majority of recordings and clinical findings were deemed satisfactory in all cases. A single SenTec measurement was sufficient to determine the need for NIV. However, two SenTec registrations were insufficient to both improve NIV effectiveness in 50% of cases, and, to ensure follow-up of our interventions.

Transcutaneous blood gas monitoring among neonatal intensive care units in Japan.

This study aimed to investigate the utility of transcutaneous (tc) measurements of partial pressure of oxygen (tcPO2 ) and carbon dioxide (tcPCO2 ) monitoring in neonatal intensive care units (NICUs) in Japan. At the end of 2016,we sent a survey questionnaire on tc monitoring to all 106 NICUs registered with the Japanese Neonatologist Association. The questions included usage, subjects, methods, management, and the practical usefulness of tc monitoring. The questionnaire was returned by 69 NICUs (65.1% of response rate). Seventeen institutions (24.6%) measured both tcPCO2 and tcPO2 , and 42 (60.9%) measured tcPCO2 alone. Transcutaneous PCO2 or tcPO2 monitoring was applied for "pre-viable" infants born at 22-23weeks' gestational age (18.6% vs 23.5%), and infants of <500g birthweight (30.5% vs 17.6%). The tcPCO2 and tcPO2 monitoring was started at birth in 49.2% and 70.6% of the newborn infants, respectively. The temperature of the sensor was set at <38°C for tcPCO2 in 54.3% and >42°C for tcPO2 in 58.9% of NICUs. The accuracy for tcPO2 was rated as good in 35.3% or moderate in 64.7%, of institutions but or for tcPCO2 as 1.7% or 93.2%of institutions , respectively. Transcutaneous monitoring was widely, but limitedly, used for preterm infants. The lower temperature of the tcPCO2 sensor compared to that reported in other developed countries might compromise the accuracy but increase the feasibility of tc monitoring in Japan.

Respiratory acidosis during bronchoscopy-guided percutaneous dilatational tracheostomy: impact of ventilator settings and endotracheal tube size

BackgroundThe current study investigates the effect of bronchoscopy-guided percutaneous dilatational tracheostomy (PDT) on the evolution of respiratory acidosis depending on endotracheal tube (ET) sizes. In addition, the impact of increasing tidal volumes during the intervention was investigated.MethodsTwo groups of ICU-patients undergoing bronchoscopy-guided PDT with varying tidal volumes and tube sizes were consecutively investigated: 6 ml/kg (N = 29, mean age 57.4 ± 14.5 years) and 12 ml/kg predicted body weight (N = 34, mean age 59.5 ± 12.8 years).ResultsThe mean intervention time during all procedures was 10 ± 3 min. The combination of low tidal volumes and ETs of 7.5 mm internal diameter resulted in the most profound increase in PaCO2 (32.2 ± 11.6 mmHg) and decrease in pH-value (− 0.18 ± 0.05). In contrast, the combination of high tidal volumes and ETs of 8.5 mm internal diameter resulted in the least profound increase in PaCO2 (8.8 ± 9.0 mmHg) and decrease of pH (− 0.05 ± 0.04). The intervention-related increase in PaCO2 was significantly lower when using higher tidal volumes for larger ET: internal diameter 7.5, 8.0 and 8.5: P > 0.05, =0.006 and = 0.002, respectively. Transcutaneous PCO2 monitoring revealed steadily worsening hypercapnia during the intervention with a high correlation of 0.87 and a low bias of 0.7 ± 9.4 mmHg according to the Bland-Altman analysis when compared to PaCO2 measurements.ConclusionsProfound respiratory acidosis following bronchoscopy-guided PDT evolves in a rapid and dynamic process. Increasing the tidal volume from 6 to 12 ml/kg PBW was capable of attenuating the evolution of respiratory acidosis, but this effect was only evident when using larger ETs.Trial registrationDRKS00011004. Registered 20th September 2016.

Transcutaneous PCO2 monitoring in critically ill patients: update and perspectives.

The physiology of venous and tissue CO2 monitoring has a long and well-established physiological background, leading to the technological development of different tissue capnometric devices, such as transcutaneous capnometry monitoring (TCM). To outline briefly, measuring transcutaneous PCO2 (tcPCO2) depends on at least three main phenomena: (I) the production of CO2 by tissues (VCO2), (II) the removal of CO2 from the tissues by perfusion (wash-out phenomenon), and (III) the reference value of CO2 at tissue inlet represented by arterial CO2 content (approximated by arterial PCO2, or artPCO2). For this reason, there are, at present, roughly two clinical uses for tcPCO2 measurement: a respiratory approach where tcPCO2 is likely to estimate and non-invasively track artPCO2; and a hemodynamic under-estimate use where tcPCO2 can reflect tissue perfusion, summarized by a so-called "tc-art PCO2 gap". Recent research shows that these two uses are not incompatible and could be combined. The spectrum of indications and validation studies in ICUs is summarized in this review to give a survey of the potential applications of TCM in critically ill patients, focusing mainly on its potential (micro)circulatory monitoring contribution. We strongly believe that the greatest benefit of measuring tcPCO2 is not to only to estimate artPCO2, but also to quantify the gap between these two values, which can then help clinicians continuously and noninvasively assess both respiratory and hemodynamic failures in critically ill patients.

VaPER: The Development of Spaceflight Associated Neuro‐ocular Syndrome (SANS) During Hypercapnic 6° Head‐Down Tilt Bed Rest; sans Sufficient Sleep?

OBJECTIVETo determine whether the combination of a cephalad fluid shift induced by headdown tilt (HDT) bed rest and chronic exposure to mild hypercapnia for 30 days will alter sleep architecture and circadian rhythm, contributing to characteristics of Spaceflight Associated Neuro‐ocular Syndrome (SANS).METHODSAfter 14 days of ambulatory normocapnic familiarization with the facility and baseline data collection (BDC), eleven subjects (5 female) breathed mild, ambient hypercapnia (0.5% CO2) throughout 30 days of 6° HDT at the German Aerospace Center (DLR): envihab facility. Following HDT, subjects were monitored for an additional 14 days of ambulatory, normocapnic recovery (R). Overnight polysomnography (PSG) was measured using a type‐2 sleep monitoring system, and the PSG was scored by a Polysomnographic Technologist to assess sleep duration, staging, latency, and arousals. Circadian rhythm was assessed by monitoring 24‐hour core body temperature with rectal temperature probes. Arterial PCO2 levels were estimated from transcutaneous PCO2 monitoring throughout sleep. Retinal thickness was measured via optical coherence tomography (OCT); those with increased thickness &gt;50μ in the nasal quadrant were classified as RET+, those &lt;50μ were classified as RET‐. After one night of familiarization with the instrumentation, measurements were collected at six different time points (one BDC, three HDT, and two R).RESULTSWhen comparing RET+ to RET‐, subjects had: significantly less total sleep time (TST) in BDC (345 ± 25 min vs 401 ± 23 min, p &lt; 0.05), HDT4 (303 ± 64 min vs 375 ± 20 min, p &lt; 0.05), HDT28 (344 ± 59 min vs 407 ± 32 min, p &lt; 0.05), and R+4 (344 ± 68 min vs 421 ± 21 min, p &lt; 0.05); significantly less stage 2 (N2) sleep in HDT4 (157 ± 43 min vs 220 ± 9 min, p &lt; 0.05), HDT28 (198 ± 32 min vs 256 ± 21 min, p &lt; 0.05), and R+4 (187 ± 74 min vs 271 ± 32, p &lt; 0.05); significantly more wake after sleep onset (WASO) in HDT4 (147 ± 85 min vs 57 ± 27 min, p &lt; 0.05) and R+4 (134 ± 106 min vs 41 ± 12 min, p &lt; 0.05); and a significantly reduced core body temperature amplitude at BDC (0.3 ± 0.1 deg vs 0.5 ± 0.1 deg, p &lt; 0.05), HDT4 (0.2 ± 0.1 deg vs 0.4 ± 0.1 deg, p &lt; 0.05), HDT28 (0.3 ± 0.1 deg vs 0.4 ± 0.1 deg, p &lt; 0.05), and R+10 (0.3 ± 0.0 deg vs 0.4 ± 0.1 deg, p &lt; 0.05).CONCLUSIONSPrior to and throughout the experimental conditions, when compared to RET‐, RET+ subjects were “short” sleepers and in general had less N2 sleep, greater WASO, and had a lower amplitude of core body temperature. We conclude that insufficient sleep may predispose certain individuals to the development of retinal thickening, a finding of SANS. Objective PSG may be a potential variable to consider when determining astronaut spaceflight duration.Support or Funding InformationNASA Human Research Program NNJ14ZSA001NThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Transcutaneous versus blood carbon dioxide monitoring during acute noninvasive ventilation in the emergency department - a retrospective analysis.

Transcutaneous measurement of carbon dioxide (PtCO2) has been suggested as an alternative to invasively obtained PaCO2 for the monitoring of patients with hypercapnic respiratory failure during noninvasive ventilation (NIV). Current data on monitoring in hypoxaemic respiratory failure are scarce and show conflicting results in hypercapnic patients in the emergency department. We performed a retrospective comparison of real-time PtCO2 (SenTec Digital Monitor) and arterial/venous carbon dioxide tension (PaCO2/PvCO2) measurements in patients with severe hypoxaemic and/or hypercapnic respiratory failure during NIV. Agreement between PtCO2 and PaCO2/PvCO2 was the primary endpoint. Bland-Altman analysis and linear regression were used. 102 patients had at least one matched measurement of PtCO2 and PaCO2/PvCO2. For patients with arterial blood gas analysis, the mean difference was 0.46 kPa at baseline (95% confidence interval [CI] 0.23 to 0.60, limits of agreement 95% CI -0.54 to 1.45) and 0.12 kPa after NIV (95% CI -0.04 to 0.29, limits of agreement 95% CI: -0.61 to 0.86). The linear regression analysis found a correlation R2 of 0.88 (p <0.001) at baseline and an R2 of 0.99 (p <0.001) after initiating NIV. For patients with venous blood gas analysis, the mean difference was 0.64 kPa at baseline (95% CI 0.04 to 1.24, limits of agreement 95% CI -0.72 to 2) and 0.80 kPa after NIV (95% CI 0.51 to 1.10, limits of agreement 95% CI 0.29 to 1.32), R2 0.78 (p <0.001) at baseline and R2 0.91 (p <0.001) after initiating NIV. A PaCO2/PvCO2 >8 kPa was associated with a lesser degree of agreement between the levels of PtCO2 and PaCO2/PvCO2 (p <0.001). Transcutaneous PCO2 monitoring shows a good concordance with PaCO2 and is a reliable, feasible, patient-friendly and safe alternative to repeated blood gas analysis for patients with severe hypoxaemic and/or hypercapnic respiratory failure receiving emergency NIV in the emergency department. An initial blood gas analysis to evaluate the respiratory and metabolic state and to rule out a significant discrepancy compared with the transcutaneous measurement is recommended.

Transcutaneous PCO2 Monitoring in Newborn Infants During General Anesthesia Is Technically Feasible.

Transcutaneous (TC) measurement of PCO2 (TC PCO2) is a well-established method to monitor assisted ventilation in neonatal intensive care, but its use in the operating room is limited, and the data regarding its performance during general anesthesia of the newborn are lacking. The aim of this study is to evaluate the performance of continuous TC PCO2 monitoring during general anesthesia in newborn infants. Infants (n = 25) with a gestational age of 23 to 41 weeks and a birth weight of 548 to 4114 g were prospectively enrolled. During general anesthesia and surgery, TC PCO2 was measured continuously and recorded at 1-minute intervals. Five-minute mean values were compared with simultaneously obtained blood gas (BG) analyses of PCO2. Only the first paired TC and BG samples were used in this analysis. We defined precision as 2.1 times the standard deviation of the difference of the 2 samples. P < .01 was considered statistically significant. We obtained samples from 25 infants. The difference between TC and BG was 0.3 ± 0.7 kPa (mean ± standard deviation) giving a precision of 1.47 kPa. Nineteen of twenty-five (76%) sample pairs displayed a difference of <1 kPa (99% confidence interval, 48%-92%, P = .016). The difference in paired samples was similar for different gestational and postnatal ages and did not appear to be affected by electrocautery. In this small study, we did not demonstrate that TC CO2 monitoring was accurate at P < .01. This partly reflects the small size of the study, resulting in wide 99% confidence bounds.

A case of behavioural hyperventilation associated with severe central sleep apnoea and follow-up management

YL (Junior Doctor): A 36-year-old man was observed by his wife to have irregular breathing with sighs followed by recurrent episodes of prolonged breathing cessation while falling asleep. The longest...

P173 The role of transcutaneous carbon dioxide monitoring in acute non-invasive ventilation

BackgroundTranscutaneous carbon dioxide monitoring is rarely used in the acute hospital setting, where samples of arterial blood are used to measure pCO2. This is a pilot observational study to assess...

A reply

We are grateful to Drs McCormack and Kelly for their interest in our publication on the accuracy of non-invasive carbon dioxide monitoring. They correctly point out that transcutaneous Pco2 (Ptcco2) measurement may be influenced by low cardiac output, and that we did not obtain cardiac index values at the time of the measurements. Because most of our study patients had normal cardiac function, insertion of a pulmonary arterial catheter was rarely indicated or justified. Therefore, cardiac index values were available only in a small minority of our patients. However, pre-existing normal cardiac function and haemodynamic stability make low cardiac output a very unlikely confounder of our study. Drs McCormack and Kelly have also missed data on the effects of vasopressor therapy on Ptcco2 values in our study. We have not reported these data in detail but stated in the Results section that vasopressors did not influence the accuracy of Ptcco2 monitoring in our study patients. As mentioned in the discussion, these findings are in agreement with those of two recent studies [1, 2] that also failed to find an influence of administered of vasopressors on Ptcco2 measurements. Drs McCormack and Kelly postulate that interpretation of data from patients with pulmonary pathologies may be difficult because of the disturbed pulmonary carbon dioxide transfer. We agree that pulmonary pathologies may influence the arterial Pco2 level. However, why should transcutaneous carbon dioxide transfer be influenced by pulmonary disease, unless the latter is combined with major haemodynamic consequences? The same holds true for low PEEP (2–8 mmHg), as used in our patients. PEEP has been found to influence Ptcco2 measurements only at higher PEEP levels [3]. Drs McCormack and Kelly correctly state that findings of industry-sponsored trials may not necessarily be invalid. However, conflicts of interest may arise at various levels when industry representatives perform or co-author studies involving their own products, thus questioning the reliability of their study results [4]. We are grateful to the manufacturers for providing the monitors and all disposables based on a contract that confirmed our unrestricted right to interpret and publish the data. We fully support Drs McCormack and Kelly's call for further scientific evaluation of transcutaneous Pco2 monitoring. We only tested its usefulness in the specific setting of patients during and shortly after major surgery. Our conclusion may not apply to patients in different clinical settings.

Transcutaneous Pco2 monitoring in critically ill adults: Clinical evaluation of a new sensor*

In critically ill patients, arterial blood gas analysis is the gold standard for evaluating systemic oxygenation and carbon dioxide partial pressure. A new miniaturized carbon dioxide tension Pco2-Spo2 single sensor (TOSCA, Linde Medical Sensors AG, Basel, Switzerland) continuously and noninvasively (transcutaneously) monitors both Paco2 and oxygen saturation by pulse oximetry (Spo2). The present study was designed to investigate the usability and the accuracy of this device in critically ill patients. Prospective clinical investigation. A 20-bed, university-affiliated, surgical intensive care unit. Patients admitted after major surgery, multiple trauma, or septic shock equipped with an arterial catheter. The heated (42 degrees C) sensor was fixed at the earlobe using an attachment clip. Transcutaneous Pco2 (TcPco2) measurements were correlated with Paco2 values (measured using a blood gas analyzer). In addition, the differences between Paco2 and TcPco2 values were evaluated using the method of Bland-Altman. We studied 55 patients, aged 18-80 (mean 57 +/- 15) yrs. A total of 417 paired measurements were compared. Correlation between TcPco2 and Paco2 was r = .86 (p < .01) in the Paco2 range of 24-101 mm Hg. Mean bias (+/-sd) between the two methods of measurement (Bland-Altman analysis) was 1.2 +/- 6.0 mm Hg with TcPco2 slightly overestimating arterial carbon dioxide tension. Nineteen percent of the measured values were outside of the acceptable clinical range of agreement of +/-7.5 mm Hg. The present study suggests that Paco2 can be acceptably assessed by measuring TcPco2 using the TOSCA Pco2-Spo2 sensor.

Non-Invasive (Transcutaneous) Monitoring of PCO2 (TcPCO2) in Older Adults

Background: Transcutaneous measurements of arterial blood gases (ABG) may decrease the need for repeated arterial puncture in older patients treated for acute cardiac or pulmonary disorders. However, age-related changes in skin perfusion, metabolism, or thickness may alter the validity of the technique. Objective: To analyse the agreement between transcutaneous and arterial measurement of PaO₂ and PaCO₂ in older adults. Design: Prospective descriptive study performed in the intermediate-care unit of a geriatric university hospital and a pulmonary rehabilitation centre. Methods: 40 patients, aged 82.5 ± 8 years (66–97), hemodynamically stable, without vasopressor treatment, underwent simultaneous measurement of arterial blood gases (ABG) and transcutaneous CO₂ (TcPCO₂) and O₂ (TcPO₂) with a Radiometer TINA TCM3^® capnograph, and a probe T° set at 43°C. Results: Correlation between PaCO₂ and TcPCO₂ was high (r² = 0.86) with a low bias (–0.1 mm Hg) and limits of agreement quite compatible with clinical use: (8.3; –8.5 mm Hg). The probe was well tolerated without any cutaneous lesion even after prolonged recordings (up to 8 h). Conversely, although TcPO₂ and PaO₂ were significantly correlated, the variability around the regression line precludes the use of transcutaneous measurements for monitoring PaO₂in a clinical setting. Conclusion: In older subjects, TcPCO₂ (but not TcPO₂) measurements are reliable when repeated assessment of ABG is warranted.

Oxygénothérapie du nouveau-né : matériels de surveillance non invasive

In newborn and premature infants whose lung immaturity entails a limited capacity for O2 detoxification, the use of supplemental oxygen should be continuously and non-invasively monitored. Pulse oximetry and transcutaneous O2 monitoring are the systems most used in the NICU. Major limitations of pulse oximetry are motion artifact, sensitivity to excessive light, cutaneous hypoperfusion, hypothermia, venous congestion, arterio-venous shunting, strong skin pigmentation, anemia and high percentage of abnormal hemoglobin. Alarm habituation is a further major risk. New oxymeters show less motion, artifact and higher accuracy during low oxygen saturation. The accuracy during high oxygen saturation is very dependent on the specific oxymeter model used. Transcutaneous O2 monitoring is usually combined with transcutaneous PCO2 monitoring, hence enabling evaluation of oxygenation as well as ventilation. A major risk of this method is related to the heated electrode sensor, which can induce skin burns. A combined ear sensor for pulse oximetry and PCO2 monitoring seems promising.

Respiratory monitoring

Monitoring is essential to patient care in the intensive care unit. Although arterial blood gas analysis is often considered the gold standard for evaluation of gas exchange, blood gases may be used excessively in many intensive care units. Pulse oximetry is commonly used to assess arterial oxygenation in critically ill patients. Capnometry is useful to detect esophageal intubation, but use of end-tidal PCO2 as a noninvasive indicator of arterial PCO2 is often unreliable. Transcutaneous monitoring of PO2 and PCO2 is commonly used in the neonatal intensive care unit but not with critically ill adults. A wealth of information is provided by ventilator waveforms such as the risk of alveolar overdistension and the presence of auto-positive end-expiratory pressure. There has been increasing enthusiasm recently for the use of pressure-volume curves to properly set the ventilator.

The Efficiency of CO2 Elimination During High-Frequency Jet Ventilation for Laryngeal Microsurgery

For adequate and safe use of high-frequency jet ventilation (HFJV), reliable monitoring of the PCO2 status and course is necessary. Because of improved handling and performance, recently available transcutaneous PCO2 monitoring devices such as MicroGas 7650[trade mark sign] (Kontron Instruments Medical Sensors, Basel, Switzerland) should enable more effective surveillance of CO2 elimination and, subsequently, better control of subglottic HFJV. Adult patients (n = 164) undergoing laryngeal microsurgery during total IV anesthesia were assessed. The resulting transcutaneous PCO2 values, as well as the necessary driving pressure settings, were analyzed to define the CO2 elimination capacity of each patient. Therefore, an individual CO2 elimination coefficient (ECCO2) was calculated. The frequency distribution of the obtained ECCO2 values showed a normal distribution with a median at 0.79 and a range between 0.30 and 2.17. A significant difference in the frequency of obstructive lung disease was found between two patient subpopulations separated by the 25th percentile at an ECCO2 value of 0.63. Other co-factors of CO2 elimination during HFJV were age, gender, and body weight, whereas height and ventilation duration were not involved. We conclude that the individual assessment of ECCO2 enables one to find adequate ventilator settings, resulting in lower airway pressure and less cooling and drying of the tracheobronchial mucosa. Implications: CO2 elimination during high-frequency jet ventilation can be assessed by calculating the CO2 elimination coefficient (ECCO2) of each patient from the required driving pressure and the resulting transcutaneous CO2 partial pressure. The frequency distribution of ECCO2 in a typical laryngological patient population was analyzed, and a value of 0.63 was found to be a characteristic limit between sufficient and difficult CO (2) elimination. The individual assessment of ECCO2 enables one to find adequate ventilator settings, resulting in lower airway pressure and less cooling and drying of the tracheobronchial mucosa. (Anesth Analg 1998;87:180-4)

Double-blind placebo-controlled study of the hyperventilation provocation test and the validity of the hyperventilation syndrome

Hyperventilation syndrome (HVS) describes a set of somatic and psychological symptoms thought to result from episodic or chronic hyperventilation. Recognition of symptoms during the hyperventilation provocation test (HVPT) is the most widely used criterion for diagnosis of HVS. We have investigated the validity of the HVPT and of the concept of HVS. In a randomised, double-blind, crossover design, the ability of 115 patients with suspected HVS to recognise symptoms during the HVPT was compared with the ability to recognise symptoms during a placebo test (isocapnic overbreathing, with carbon dioxide levels maintained by manual titration). 30 patients who had positive results on the HVPT underwent ambulatory transcutaneous monitoring of pCO2 to ascertain whether they hyperventilated during spontaneous symptom attacks. Of the 115 patients who underwent the HVPT and the placebo test, 85 (74%) reported symptom recognition during the HVPT (positive diagnosis HVS). Of that subset, 56 were also positive on the placebo test (false-positive), and 29 were negative on the placebo test (true-positive). False-positive and true-positive patients did not differ in symptom profile or in physiological variables. During ambulatory monitoring (15 true-positive, 15 false-positive) 22 attacks were registered. Transcutaneous end-tidal, pCO2 decreased during only seven. The decreases were slight and apparently followed the onset of the attack, which suggests that hyperventilation is a consequence rather than a cause of the attack. There were no apparent differences between false-positive and true-positive patients. The HVPT is invalid as a diagnostic test for HVS. Hyperventilation seems a negligible factor in the experience of spontaneous symptoms. The term HVS should be avoided.

Pathogenesis of Cheyne-Stokes Respiration in Patients With Congestive Heart Failure: Relationship to Arterial Pco2

In order to determine which patients with congestive heart failure (CHF) develop Cheyne-Stokes respiration (CSR) during sleep, we compared the cardiorespiratory profiles of CHF patients with CSR to those of CHF patients without CSR. Overnight polysomnography and continuous transcutaneous PCO2 (tc PCO2) monitoring, estimation of left ventricular ejection fraction (LVEF), pulmonary function tests, and chest radiograph were performed on 16 consecutive patients with chronic, stable CHF. The tc PCO2 monitor (Kontron 7640) was calibrated so that measurements reflected arterial PCO2 values. A mean value was calculated for wakefulness (W) and total sleep time (TST). Circulation time (CT) from the lung to the carotid body was estimated from the end of an apnea or voluntary breath-hold to the nadir of oxygen desaturation recorded on an ear oximeter. The duration of CSR was expressed as a percent of TST. Nine patients developed CSR during sleep (52.5 +/- 31.6 percent TST) (group 1) and 7 did not (group 2). All patients were male and both groups were a similar age (64 +/- 8 vs 63 +/- 4 years) and weight (body mass index, 28.1 +/- 3.5 vs 25.4 +/- 3.4 kg/m2). There were no significant intergroup differences between LVEF (22 +/- 5.2 vs 24.1 +/- 5.2 percent), CT (19.1 +/- 3.6 vs 15.9 +/- 6.7 s), SaO2 (W) (94 +/- 1.2 vs 92.4 +/- 2.1 percent), and SaO2 (TST) (90.8 +/- 2.7 vs 92.4 +/- 2.1 percent). The tc PCO2 (W) was lower in group 1 (34.4 +/- 3.5 vs 38.1 +/- 1.9 mm Hg), increased during sleep by a similar amount in both groups (1.6 +/- 1.5 vs 2.1 +/- 2.2 mm Hg), and was significantly lower during sleep in group 1 (36.1 +/- 3.4 vs 40.2 +/- 2.2 mm Hg). We conclude that CHF patients with CSR hyperventilate during sleep and wakefulness and that CHF patients with awake hypocapnia are more likely to develop CSR during sleep. These findings indicate that arterial PCO2 is important in determining which CHF patients develop CSR.

Hyperventilation: Is It a Cause of Panic Attacks?

During transcutaneous PCO2 (PtcCO2) monitoring of 15 freely ambulant patients suffering from panic attacks, all the patients experienced a typical attack. Seven were identified as hyperventilators, as PtcCO2 fell to abnormally low levels during the attack. This group could not be distinguished on the basis of either their usual symptoms of panic or the hyperventilation provocation test. There was no apparent association between absolute levels of PCO2 and the nature of symptoms. The anxiety ratings of hyperventilators were lower than those of non-hyperventilators. These data do not support the hypothesis that hyperventilation causes panic attacks or contributes to their severity. Hyperventilation may be better understood as a consequence of panic.

Noninvasive Monitoring of Oxygen and Carbon Dioxide

New technologies for the noninvasive assessment of oxygen and carbon dioxide are transforming clinical practice. Transcutaneous monitoring of PO2 (PtcO2) and PCO2 (PtCO2) provides an approximation of PaO2 and PaCO2 values in hemodynamically normal individuals, but both PtcO2 and PtcCO2 diverge from the corresponding arterial values when cardiac output is reduced, even in the absence of hypotension. Transcutaneous monitors also have relatively slow equilibration and response times. Pulse oximeters rapidly assess arterial O2 saturation, but give spurious results when dyshemoglobins (for example, carboxyhemoglobin, methemoglobin) are present in significant quantity. End-tidal CO2 (PetCO2) monitoring tracks breath-by-breath changes in ventilation, and PetCO2 approximates PaCO2 when significant physiologic dead-space is not present. Respiratory inductive plethysmography provides a semiquantitative assessment of tidal volume and the relative contribution of the thorax and abdomen to ventilation; among other uses, this technology may allow for the early detection of respiratory muscle fatigue prior to the onset of respiratory failure.