Effect of continuous positive airway pressure on central sleep apnea and nocturnal PCO2 in heart failure

We have previously shown that hypocapnia triggers Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) in patients with congestive heart failure (CHF). Nasal continuous positive airway pressure (NCPAP) may attenuate CSR-CSA in patients with CHF and CSR-CSA. Accordingly, we hypothesized that attenuation of CSR-CSA by NCPAP would be related to an increase in PCO2. Therefore, we examined the effect of NCPAP on the frequency of apneas and hypopneas, transcutaneous PCO2 (PtcCO2), and minute volume of ventilation (VI) in 12 consecutive patients with CHF and CSR-CSA during stage 2 sleep. A control group of six patients, who did not receive NCPAP, was also studied. In the control group, there were no changes from baseline to 1 mo in the frequency of central apneas and hypopneas, mean PtcCO2, mean VI, or mean SaO2 during stage 2 sleep. In contrast, from baseline to 1 mo the NCPAP group experienced a decrease in the frequency of apneas and hypopneas (58.7 +/- 5.2 to 23.2 +/- 6.0/h of sleep, p < 0.001), an increase in mean PtcCO2 (34.6 +/- 1.4 to 40.8 +/- 1.1 mm Hg, p < 0.001), a reduction in mean VI (8.1 +/- 1.0 to 5.2 +/- 0.5 L/min, p < 0.01) and an increase in mean SaO2 (91.6 +/- 1.1 to 95.0 +/- 0.5%, p < 0.025) during stage 2 sleep while on 10.2 +/- 0.5 cm H2O nasal CPAP. We conclude that likely mechanisms through which NCPAP reduces CSR-CSA are by increasing SaO2 and raising PaCO2 during sleep toward or above the apneic threshold.

An evaluation of iodine-123 iodoazomycinarabinoside as a marker of localized tissue hypoxia in patients with diabetes mellitus

Peripheral vascular disease is a serious and common complication in patients with diabetes mellitus (DM). Evaluation is, conventionally, by transcutaneous oxygen tension measurements (TcpO2), although this technique has some limitations in the evaluation of tissue viability. We have evaluated a new, radiolabelled, in vivo marker of tissue hypoxia, iodoazomycinarabinoside (IAZA), by comparing TcpO2 measurements with patterns of iodine-123 IAZA uptake in ten patients (19 lower limbs) with DM and peripheral vascular disease using conventional gamma camera imaging techniques. Normal uptake patterns were seen in limbs in which normal TcpO2 measurements were obtained. Diffusely increased uptake of [123I]IAZA was seen in limbs with reduced TcpO2. Focally increased uptake was seen in ulcers or in areas of atrophic skin change. A semi-quantitative measure showed an inverse correlation between [123I]IAZA and TcpO2 values. These data suggest that tissue hypoxia can be imaged in this population of patients and that severity of disease can be assessed. A longitudinal prospective trial is now being developed.

Sleep polygraphic parameters in neuromuscular diseases

In a polysomnographic study of 32 neuromuscular patients-22 with a form of muscular dystrophy, 3 with a form of congenital myopathy, 4 with a form of spinal muscular atrophy, 1 with a recurrent form of polymyositis and 1 with osteogenesis imperfecta syndrome--of which 21 were nonambulatory, we observed sleep related respiratory disturbances represented by: drops in oxygen saturation (SaO2), cardiac arrhythmia, sleep disruption, apneas, tachypnea, tachycardia and snoring. Nine out of the cohort of 32 patients presented with significant desaturations periods. These patients presented with an associated restrictive syndrome and thoracic deformities, some with tachypnea and/or SaO2 below 90% during wakefulness. In this group, snoring was observed in those patients with a form of muscular dystrophy while tachypnea was observed in patients who presented the highest desaturations levels. Sleep quantification revealed an increase of stage 1 sleep coupled with a decrease or even total absence of REM sleep. This is, we believe, a likely consequence of episodic desaturations that may accompany sleep hypoventilation which is potentialised during REM sleep stage.

Normal transcutaneous oxygen pressure in skin after radiation therapy for cancer

BACKGROUND

Chronic deleterious changes in human skin after radiation therapy often have been ascribed to progressive ischemia (decreased blood supply and oxygenation). Recent studies suggest, however, that damaged irradiated skin is not ischemic. Transcutaneous oxygen pressure (TCPO2), that accurately reflects skin oxygenation, was studied in 100 patients who had undergone prior extensive radiation therapy for cancer.

METHODS

In the 100 patients, the mean time since radiation was 7.86 +/- 10.56 years (mean, +/- SD) (range, 1-58 years). Radiation skin effects were graded (0-4+), and TCPO2 was measured in irradiated and control nonirradiated sites, with patients first breathing room air, then 100% O2 6 l/min for 10 minutes. Data were stratified according to skin grades, sex, time since irradiation, site, type, and dose of radiation.

RESULTS

The mean TCPO2 in patients breathing room air was 52.0 17.8 mm Hg (mean +/- SD) for all irradiated skin, compared with 131.8 +/- 51.1 at the same irradiated sites in response to oxygen breathing (P < 0.0001); the mean TCPO2 for normal, nonirradiated skin was 56.5 +/- 12.6 when patients were breathing room air, compared with 151.5 +/- 48.1 when breathing 100% oxygen (P < 0.0001). Higher skin damage grades correlated with increasing time after radiation therapy. However, neither increasing time after irradiation nor grade of skin damage correlated with TCPO2, which was normal in 88% of the patients.

CONCLUSIONS

Human skin, even many decades after radiation therapy, retains normal tissue oxygenation and TCPO2 response to inspired oxygen. Postradiation scarring, poor healing, and rare ulceration are not solely due to ischemia and may be caused by other radiation effects, such as permanent changes in fibroblasts.

Ability of new lung function tests to assess methacholine-induced airway obstruction in infants

We assessed the ability of innovative lung function tests to detect bronchial obstruction induced by methacholine bronchial challenge. Fifty-five recurrently wheezy infants (mean age 16 +/- 5.2 months) free of respiratory symptoms underwent baseline lung function tests. Forty-two completed the methacholine challenge. Maximal flow at functional residual capacity (VmaxFRC) was obtained using the squeeze technique; compliance and resistance of the respiratory system (Crs, Rrs) was measured with the passive expiatory flow volume technique; tidal volume breathing patterns were analyzed from recordings of respiratory rate (RR), tidal volume (VT), and inspiratory time divided by total cycle of duration (Ti/Ttot). Expiratory tidal flow volume (V/VT) curves were described with multiple indices such as the ratio of expiratory time necessary to reach peak tidal expiratory flow (Fpet) to expiratory time (Tme/Te). Transcutaneous oxygen tension (PtCO2) was measured as an indicator of response to methacholine challenge. Of 42 infants 41 responded to methacholine by a change > or = 2 standard deviations from baseline values. The mean SD unit changes were 9.8 in PtCO2, 3.7 for VmaxFRC, 2.8 for Crs, 2.09 for Rrs, 3.1 for RR, 1.6 for Ti/Ttot, 2.2 for Tme/Te 3.9 for PFVt. We conclude that these noninvasive lung function tests, especially VmaxFRC and Fpet, can be used to detect minor or moderate airway obstruction. Further studies are needed to determine the value of the tests in assessing bronchial disease and effects of its treatment.

The practical management of artifact in computerised physiological data

Computerised physiological data contains artifact that needs to be identified and possibly removed. Whilst computers may eventually satisfactorily perform this function, at present only manual removal is possible for the majority of intensive care computer groups. We assessed the effects of artifact and its removal on the physiological data of 3 patients. Artifact was manually removed from 7 days of data in 4 parameters (heart rate, respiratory rate, systolic blood pressure [sbp] and transcutaneous oxygen [tcpO2]) by 3 independent observers. Six hour time periods were analysed. Median and mean values before and after the manual removal of artifact were compared. Overall 6.5% of data was removed as artifact. This was greatest for tcpO2 (9.9%) and sbp (10.6%), with smaller amounts for respiratory rate (2.8%) and heart rate (2.4%). Sbp showed a marked difference in the amount of data removed between patients, whereas tcpO2 data contained quite large volumes of artifact, but this was fairly consistent between patients. Removal of artifact affected mean values more than median values. One observer considered that both physiological and non-physiological artifact should be removed, whereas the other two observers removed only non-physiological artifact. Agreement in results between the latter was good. Our results suggest that inter-observer variability should have a minimal effect on values, once rules identifying the type of artifact to be removed are agreed. Removal of artifact did not have a clinically significant effect on results, but may be an important consideration in the statistical analysis of computerised physiological data.

Abnormal hypoxemia after life-threatening events in infants born before term

This study aimed to determine whether preterm infants who have a history of apparent life-threatening events (ALTE) have abnormalities in oxygenation and, if so, whether the ALTE would stop with oxygen therapy. We assessed 92 patients (median gestational age at birth, 32 weeks (range, 24 to 36 weeks); median birth weight, 1840 gm (650 to 3500 gm)) who had had a single (n = 20) or recurrent ALTE. Median postnatal age at referral was 3.2 months (0.5 to 44.7 months). All had been considered otherwise free of symptoms and adequately oxygenated in air at the time of discharge from their neonatal unit, before the ALTE. Fifty-two patients had received mouth-to-mouth resuscitation, and 40 vigorous stimulation. Ninety-one patients underwent 8- to 12-hour recordings of arterial oxygen saturation, the plethysmographic waveforms from the oximeter, breathing movements, and electrocardiograms. These recordings were compared with previously published data from 110 "healthy" preterm infants made at around 6 weeks after discharge from hospital. Compared with these data, 49 recordings (54%) were normal, 19 showed abnormal hypoxemic episodes, 6 had abnormally low baseline arterial oxygen saturation (< 95%), and 17 had both. In 31 of 33 patients, ALTE stopped or were reduced in frequency or severity after additional inspired oxygen (0.1 to 1.0 L/min via nasal cannulas) was given. Oxygen was given for a median duration of 3.9 months (range, 0.8 to 17.2 months). Persistent events in the remaining two patients were subsequently found to be due to intentional suffocation in one and epileptic seizures in the other. Monitoring of transcutaneous oxygen tension at home was undertaken in 84 patients. To date, this has been discontinued in 81 after a median duration of 7.3 months (0.3 to 18.9 months). We conclude that recognition and treatment of abnormalities in episodic or baseline hypoxemia may reduce the risk of further ALTE in previously preterm infants.

Non invasive recording of CO2 cerebrovascular reactivity in normal subjects and patients with unilateral internal carotid artery stenosis

CO2 cerebrovascular reactivity has been recorded in 12 healthy volunteers and 10 patients with unilateral > 70% extracranial internal carotid artery (ICA) stenosis, using non invasive techniques. The relative changes of middle cerebral artery blood flow velocity (VMCA) and velocity waveform pulsatility (PIMCA) after that hypocapnia was induced by spontaneous hyperventilation were recorded. 35.5% average VMCA reduction and 63% PIMCA increment of basal values was produced in healthy subjects after hyperventilation. The percentage variation of CO2 Reactivity Index (RI), expressed in terms of VMCA (V-RI) and PIMCA (PI-RI), per mmHg change in pCO2, presents a good right-left side correlation (r = 0.82 and r = 0.83 respectively) in healthy subjects, while a dissociation between V-RI and PI-RI was found in our patients. A significant reduction of PI-RI was also recorded in the group of patients on the side of ICA stenosis. From our data CO2 reactivity index recorded in terms of PI seems to allow a better separation between pathology and normality, without the need to assume a close relationship between velocity and blood flow under the condition considered. Furthermore, PI-RI seems to be a valid index in the evaluation of some attribute pertaining to the distal vascular bed.

[Intraoperative cortical PO2 measurement in kidney transplantation. the effect of the calcium antagonist diltiazem]

A local measurement of the partial pressure of oxygen in the renal cortex was performed during renal transplantation in 40 patients aged between 10 and 62 years. During the measurement, 20 of the patients received the calcium channel blocker diltiazem. Accurate knowledge of the renal microcirculation in the postischemic phase became possible when PO2 tissue polarography was performed. Moreover, measurement in four live donors before removal of the kidneys allowed an exact comparison between the postischemic microcirulation and the native in situ perfusion. A good postischemic baseline histogram (similar to the situation in a live donor) or quick stabilization of the histogram during the course was found to correlate with a prompt initial renal function. Intra-arterial administration of diltiazem led to an insignificant improvement of the primary function rate. In the case of kidneys with longer cold ischemic periods and initially indifferent baseline histograms there was an especially pronounced benefit of diltiazem administration. Not only macroscopic examination, but also polarographic measurements revealed an improvement in the renal microcirculation throughout, with higher mean values for PO2 and homogeneity of all PO2 values measured after administration of diltiazem. In keeping with this, in such cases the incidence of primary renal function was distinctly higher. In cases with improved cortical circulation the a-v oxygen difference was less pronounced, so that evaluation of the avDO2 determinations suggests distinct perfusion improvement following diltiazem.

[The effect of different types of anesthetic respirators on oxygenation and ventilation in infants during short-term anesthesia. A study using transcutaneous PO2 and PCO2 monitoring]

Monitoring of ventilation in infants is difficult and often not very reliable. In this study, transcutaneous measurement of blood gas tensions was used to investigate the influence of four different modes of ventilation on oxygenation and ventilation in anaesthetized infants. METHODS. In a randomised study, transcutaneously measured PO2 (tc-PO2) and PCO2 (tcPCO2) tensions were continuously registered in 42 ASA class I and II infants between 3 and 24 weeks of age undergoing minor surgical procedures (inguinal hernia repair). Two breathing systems combined with different modes of ventilation were evaluated: manual ventilation with Kuhn's T-piece system and face mask (group A; n = 11) or endotracheal tube (group B; n = 10); manual ventilation with paediatric circuit system and face mask (group C; n = 11); and mechanical ventilation with paediatric circle system, endotracheal tube, and positive end-expiratory pressure (PEEP) 3 cm H2O (group D; n = 10). Transcutaneous values were measured by a combined tcPO2/PCO2 electrode (E 5277, Radiometer). Anaesthesia was maintained by controlled ventilation with N2O/O2 (67%/33%) and halothane 0.5-1.5 vol.%. Surgical and anaesthetic techniques were standardized and the anaesthetist was blinded to the measured values. RESULTS. Preoperative mean tcPO2 values while spontaneously breathing air ranged between 69 and 75 mmHg in all patients. During anaesthesia and controlled ventilation (FiO2 = 0.33), there was a significant increase in tcPO2 (P < 0.01) in 3 groups: in groups A and D mean tcPO2 increased to 90-100 mmHg and in group C to 110-120 mmHg. In contrast, tcPO2 in group B reached only 75-80 mmHg, which was not considered significant. Postoperatively, tcPO2 immediately reached baseline values in all patients (Fig. 2). Compared to preoperative values, the alveolar-tcPO2 difference (AtcDO2) significantly increased during anaesthesia in all groups (Fig. 3). The tcPCO2 measurements revealed marked alveolar dysventilation, with hyperventilation supervening in groups A, B, and D; in group C, however, most (7 of 11) infants were normoventilated (Fig. 4). CONCLUSIONS. Adverse effects of anaesthesia on pulmonary function in infants are caused by loss of the PEEP effect induced by the physiological subglottic stenosis. Endotracheal intubation and the increase in chest wall compliance during anaesthesia lead to a decrease in functional residual capacity (FRC) associated with premature airway closure and ventilation/perfusion mismatch. These pathophysiological disturbances result in a marked increase in AaDO2 and low arterial PO2 values despite high FiO2, as could be observed when intubated infants had been ventilated with a high-flow T-piece system (group B). Mechanical ventilation with a paediatric circuit system and endotracheal tube allows the use of low PEEP levels (group D), which may replace the lost subglottic function and partially restore the FRC. Ventilation by mask does not disturb the functional subglottic stenosis, and the impairment of pulmonary function will depend solely on the decrease in FRC caused by increased chest wall compliance (group A). If mask ventilation is combined with a paediatric circuit system (group C), the pressure relief valve produces a low PEEP of 2 to 3 cm H2O, which may partially counteract the decrease in FRC. With regard to oxygenation, the paediatric circle system proved to be superior to the high-flow T-piece system independent of whether children were ventilated via a face mask or an endotracheal tube. The group-specific differences in degree of dysventilation with manual ventilation show that the type of breathing system is important with regard to the size of the tidal volume delivered. Thus, tidal volumes will be unintentionally increased by the high fresh gas flow needed when a T-piece system is used. The lower flow and preadjusted pressure limit may prevent the delivery of excessive tidal volumes with the paediatric circuit system...

Epileptic seizure-induced hypoxemia in infants with apparent life-threatening events

OBJECTIVE

To describe the physiologic changes that occur during epileptic seizure (ES)-induced apparent life-threatening events (ALTE) and to provide an explanation for the mechanism whereby the hypoxemia characterizing these events occurred.

PATIENTS AND DESIGN

Six infants were retrospectively selected from a group of 17 because they had ALTE documented on physiologic recordings where the first change in signals was in the electroencephalogram (EEG). The 17 infants had clinical features suggestive of partial seizures (but normal standard EEGs) and were from a sample of 172 infants with recurrent ALTE. All 17 infants underwent continuous recordings of breathing, electrocardiogram (ECG), oxygenation, and EEG, but only in 6 was an ES-induced ALTE recorded and the physiologic changes described.

RESULTS

Twenty-three ALTE were documented in six infants. Events commenced with an abnormality in the EEG, followed by a decrease in SaO2 after a median interval of 27 seconds (range 2 to 147). Despite resuscitation, the median duration of severe hypoxemia (SaO2 < or = 60%) was 40 seconds (range 8 to 74). In 18 events (five infants) there was a median of four apneic pauses (range 1 to 9) preceding the decrease in SaO2 by a median duration of 24 seconds (range 3 to 48). The longest apneic pause per event lasted a median of 19 seconds (range 8 to 47). Breathing movements continued in five events (four infants), and expiratory airflow in one. Sinus tachycardia was found in 19 of the 23 events (six infants), but there were no cardiac arrhythmias.

CONCLUSIONS

ES in infants can manifest as ALTE and be accompanied by potentially life-threatening episodes of severe hypoxemia and apnea, despite a normal EEG between events.

Effect of preanesthetic medication on carbon dioxide tension in children with congenital heart disease

Hypercarbia during the postoperative period following repair of congenital heart defects in children has been associated with acute pulmonary hypertension. Because decreases in respiratory rate (RR) and digital pulse oximetry (SpO2) have been observed after preanesthetic medication of similar children, it is possible that hypercarbia and pulmonary hypertension may be unappreciated risks in premedicated children during the preoperative period. As the first step in addressing this question, changes in transcutaneous and end-tidal PCO2 (PtcCO2 and PetCO2) were examined after preanesthetic medication of children prior to cardiac surgery. Forty-four children were randomly assigned to receive either intramuscular morphine, 0.2 mg/kg, and scopolamine, 0.01 mg/kg, or oral midazolam, 0.75 mg/kg, 1 hour before anesthetic induction. PtcCO2, PetCO2, SpO2, RR, and sedation score were monitored. Significant sedation occurred after both premedication regimens. Following morphine/scopolamine, PtcCO2 increased from 36 +/- 4 (mean +/- SD) to 43 +/- 6 mmHg (P < 0.01), PetCO2 increased from 35 +/- 3 to 40 +/- 5 mmHg (P < 0.01), SpO2 decreased from 93 +/- 2 to 91 +/- 4% (P < 0.01), and RR decreased from 30 +/- 10 to 24 +/- 7 breaths/minute (P < 0.01). After midazolam, PtcCO2 increased from 35 +/- 4 to 40 +/- 6 mmHg (P < 0.01), PetCO2 increased from 34 +/- 5 to 39 +/- 3 mmHg (P < 0.01), SpO2 decreased from 93 +/- 6 to 90 +/- 7% (P < 0.01), and RR decreased from 33 +/- 13 to 30 +/- 13 breaths/minute (P < 0.01). Clinically significant increases in PtcCO2 (> 45 mmHg) occurred in nine patients, including five with pulmonary hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of end-tidal and transcutaneous PCO2 monitoring during sleep

STUDY OBJECTIVE

Although it is intuitively desirable, the measurement of arterial carbon dioxide tension (PaCO2) during diagnostic polysomnography and nocturnal trials of positive pressure therapy is invasive and potentially expensive. The accuracy of end-tidal carbon dioxide tension (PETCO2) and transcutaneous carbon dioxide (tcPCO2) monitoring in these contexts has not been systematically evaluated. This investigation was undertaken to evaluate the accuracy of PETCO2 and tcPCO2 in patients undergoing polysomnography.

METHODS AND PROCEDURES

Values of PETCO2 were compared with PaCO2 in 19 patients spontaneously breathing room air (condition 1), in 13 patients receiving supplemental oxygen via nasal cannula (condition 2), and in 22 patients receiving nocturnal positive pressure ventilatory assistance (all but one with continuous positive airway pressure or bilevel positive airway pressure) (condition 3). The accuracy of tcPCO2 monitoring during sleep was also examined by comparing tcPCO2 values with simultaneously recorded PaCO2 values obtained during sleep in patients undergoing nocturnal polysomnography. Data were collected using three commercially available brands of tcPCO2 monitors (capnograph R, n = 17 patients; capnograph S, n = 17; and capnograph N, n = 15).

RESULTS

Accuracy of PETCO2--There was significant scatter in the PaCO2 vs PETCO2 relationship such that only 23 percent of the variability in PaCO2 was explained by variation of PETCO2 during condition 1 and only 15 percent and 20 percent of the variability in PaCO2 was explained by variation of PETCO2 during conditions 2 and 3, respectively. 21.3 percent of patients had average PETCO2 values in error by > 10 mm Hg during condition 1, while during conditions 2 and 3, 46.2 and 63.7 percent of patients had average values in error by > 10 mm Hg, respectively. Accuracy of tcPCO2--While capnographs S and N generally overestimated PaCO2 with a wide scatter, capnograph R tended to have offsetting overestimations and underestimations of PaCO2 with a wide scatter. With each capnograph, a relatively small portion of the variability of the PaCO2 was explained by variability of the tcPCO2 (r2 = 0.2, 0.45 and 0.64 for capnographs S, N, and R, respectively). Across the three capnographs, 43.1 to 66.7 percent of measurements were in error by > 10 mm Hg, and 5 to 20 percent of measurements reflected errors > 20 mm Hg. There was no consistent relationship between the tcPCO2 error and the level of PaCO2, nor was the tcPCO2 error consistent in individual patients. There was no relationship between tcPCO2 accuracy and body mass index.

CONCLUSION

Neither PETCO2, measured within a face mask, nor tcPCO2 is a consistently accurate reflection of PaCO2. This limits the utility of these variables in monitoring patients during diagnostic and therapeutic sleep studies, and in particular, during trials of nocturnal ventilatory assistance where adequate levels of support are to be established and unacceptable hyperventilation and respiratory alkalosis must be recognized.

Hypoxaemia during transoesophageal echocardiography

OBJECTIVES

To establish the incidence and severity of arterial oxygen desaturation during transoesophageal echocardiography performed under light intravenous sedation; to determine which patients are at greatest risk; and to assess the effects of supplementary oxygen treatment.

DESIGN

Prospective study of 150 patients referred for transoesophageal echocardiography.

SETTING

Echocardiography laboratory in a tertiary cardiothoracic referral centre.

MAIN OUTCOME MEASURE

Transcutaneous arterial oxygen saturation.

RESULTS

During transoesophageal echocardiography mean (SD) arterial oxygen saturation (SaO2) fell in 144 of 150 patients (96%) from 95.4%(2.6%) to 90.7%(6.3%) (p < 0.001). Significant hypoxaemia, defined as SaO2 < 90%, was found in 27 of 150 patients (18%); in this group SaO2 fell from 92.9%(3.5%) to 81.8%(9.6%) (p < 0.001), but rose rapidly on oxygen to 95.5%(2.4%) (p < 0.001). Two patients became profoundly hypoxaemic with SaO2 values of 35% and 74%. The principal risk factors for hypoxaemia during transoesophageal echocardiography were mitral valve disease, severe mitral regurgitation, and New York Heart Association symptomatic class III or IV.

CONCLUSIONS

Transcutaneous oximetry and supplementary oxygen should be available routinely during transoesophageal echocardiography.

[The usefulness of transcutaneous gas monitoring during hemorrhagic shock; discrepancy between the two transcutaneous gas tensions of anterior thorax and femur]

We measured transcutaneous gas tensions of both anterior thorax and femur. The differences between the two transcutaneous gas tensions were compared, as well as the relationship between the two transcutaneous and mixed venous blood gas tensions, in 10 dogs during hemorrhagic shock. The changes in femoral transcutaneous gas tensions correlated better with the changes in mixed venous gas tensions. The correlation between the two transcutaneous gas tensions were fairly good (oxygen tensions; r = .827, carbon dioxide tensions; r = .867). However, the discrepancy between the two gas tensions became greater in severe shock. Hence, oxygen tensions became smaller and carbon dioxide tensions became greater on femur than on anterior thorax. This indicates the possibility of "maldistribution of blood flow", which has already been detected between vital organs and skin, also exists between peripheral and central skin. Therefore, transcutaneous gas tensions should be monitored at peripheral skin, where gas tensions show greater changes and reflect systemic perfusion precisely than at central skin, during shock.

Effect of fetal brainsparing on the early neonatal cerebral circulation

The effect of antenatal brainsparing on subsequent neonatal cerebral blood flow velocity (CBFV) was studied in very preterm infants. CBFV was determined, using a pulsed Doppler technique, both in the fetal and neonatal period. Neonatally, blood pressure and transcutaneous carbon dioxide tension (TcPCO2) was monitored simultaneously; daily cranial ultrasound examinations were performed. In infants with evidence of brainsparing a higher mean value of CBFV and a different pattern of changes of CBFV during the first week of life was demonstrated compared with infants with normal fetal cerebral haemodynamics. No differences were found in blood pressure and TcPCO2. The incidence of intracranial haemorrhages and of ischaemic echo-dense lesions was also the same for both groups. In a multivariate statistical model gestational age, antepartum brainsparing, and TcPCO2 all contributed significantly in explanation of variation in CBFV. It is speculated that a different setting of cerebral autoregulation related to differences in gestational age or to brainsparing might explain the difference in changes found in neonatal CBFV.

Relationship between hemorheological and microcirculatory abnormalities in diabetes mellitus

From numerous studies, it is now well known that diabetes mellitus is usually accompanied by miscellaneous hemorheological disturbances. These may alter the microcirculatory flow and lead ultimately to tissue chronic hypoxia. In this report, red blood cell aggregation characteristics and transcutaneous oxygen pressure (TcPO2) have been evaluated in diabetic patients without any sign of angiopathy. Results showed a tendency towards erythrocyte hyperaggregation in diabetic patients, even when under good glycaemic control. TcPO2 measurements, were found to be significantly lower in diabetic patients than in control subjects. Furthermore, the TcPO2 values were related with the aggregation parameters, confirming thereby the existence of an inter-relationship and thus the possible role played by hemorheological parameters in oxygen transport to tissues and hence in the pathogenesis of microangiopathy at the functional level.

Transcutaneous oxygen pressure measurements in patients with intermittent claudication

Transcutaneous oxygen pressure (TcPO2) measurements were performed on 10 male patients with moderate-to-severe intermittent claudication. The TcPO2 electrode was attached to the dorsum of the foot. TcPO2 response to a standardized treadmill exercise test was evaluated, as was the reproducibility of TcPO2 measurements at rest and during exercise. Reproducibility was assessed using a similar exercise test within 2-5 days. Treadmill exercise induced a marked decrease in TcPO2 in all patients, from 9.3 +/- 0.9 to 2.8 +/- 2.0 kPa. Maximal walking distance was 280 +/- 127 m at the first treadmill test and 272 +/- 113 m at the second. Blood lactate and heart rates at rest and at end of exercise were also unchanged. TcPO2 at rest was highly reproducible, but considerable variation was found for measurements during and after exercise. This variation was most obvious for measurements during exercise and no direct or reproducible relation was found between ischaemic calf pain and TcPO2 values. Post-exercise measurements were slightly more reproducible and somewhat easier to assess. In contrast to standard TcPO2 measurements, total exercise-induced ischaemia expressed as area under the post-exercise TcPO2 curve was highly reproducible. In summary, our results with TcPO2 measurements in patients with intermittent claudication showed a marked exercise-induced decrease in all patients. However, the variation in TcPO2 values when the test was repeated after 2-5 days under stable clinical and circulatory conditions limits its application as a quantitative measure of lower-limb ischaemia. Thus, measurements of area under the TcPO2 curve might be preferred for this purpose.

Upper airway stability and respiratory muscle activity during inspiratory loading in full-term neonates

To investigate the role of genioglossus and posterior cricoarytenoid (PCA) activity in stabilizing the extrathoracic airway (ETA) of full-term infants during inspiratory flow-resistive loading (IRL), 10 unsedated full-term infants were evaluated in quiet sleep. IRLs were randomly imposed (L2, 125 cmH2O.l-1.s; L3, 250 cmH2O.l-1.s). Ventilation, total respiratory resistance (a correlate of ETA resistance), and moving time averages of PCA, submental activity of the genioglossus (SM), and diaphragm electromyogram were obtained. Results revealed no phasic activity in the SM during baseline breathing or with either IRL. Phasic PCA activity was always observed; burst duration increased with L2 and L3 (P < 0.01) and commenced earlier in relation to the onset of inspiratory airflow with both loads (P < 0.05). PCA activity always preceded that of the diaphragm and invariably outlasted it other than with L3. The upper airway negative pressure changes induced by IRL were insufficient to recruit SM activity; other potential stimuli such as transcutaneous PO2, transcutaneous PCO2, and pulmonary stretch receptor activation (increase in tidal volume) remained unchanged. Ventilation decreased with both loads (L3: P < 0.01), esophageal and mouth pressures increased (P < 0.01), and inspiratory time and inspiratory time divided by total time were both prolonged (P < 0.01). Total respiratory resistance remained unchanged with L2 but increased with L3 (P < 0.01). We concluded that ETA narrowing may be induced in full-term infants during quiet sleep with moderately large-sized IRL and that it is not entirely ameliorated by activation of the SM or PCA or by arousal.

Assessment of soft tissue injury in open tibial shaft fractures by transcutaneous oximetry

Transcutaneous oximetry was performed on 32 patients with 33 open tibial shaft fractures in an attempt to identify those patients at risk for the subsequent development of serious complications. Oxygen electrodes were placed on areas of intact skin, over viable compartments at the fracture site (wound) as well as on the anterior chest wall (control). Simultaneous wound and chest wall measurements were obtained after equilibration (30 minutes) on both room air and 100% oxygen. Values obtained were expressed as absolute values and as percentages of the wound measurement divided by the chest measurement. The study group consisted of 27 male and five female patients with an average age of 37 years (range, 17-63 years). There were 8 Grade I, 12 Grade II, and 13 Grade III fractures as described by Gustilo et al. Complications requiring medical or surgical intervention occurred in six patients: four deep infections, one deep vein thrombosis, and one superficial infection with severe bone and soft tissue loss requiring multiple procedures. Transcutaneous oximetry with patients breathing 100% oxygen was found to correlate with the development of complications in this study group. Five (42%) of 12 patients with transcutaneous oximetry values < or = 85 mm Hg and a wound-to-chest ratio < or = 25% developed a complication, whereas only one of 19 patients with either a fracture site value greater than 85 mm Hg or a wound to chest ratio greater than 25% developed a complication (p = 0.007).

Role of respiratory muscles in upper airway narrowing induced by inspiratory loading in preterm infants

Extrathoracic airway (ETA) narrowing is induced in preterm infants by inspiratory flow-resistive loading (IRL), which reduces intraluminal pressure within the region. Neuromuscular load compensation was evaluated over time in 10 infants [body wt 1.5 +/- 0.17 (SD) kg, gestational age 33 +/- 2.3 wk, age 12 +/- 5.2 days] during quiet sleep. Baseline (BL) studies were followed by IRL (125 cmH2O.l-1.s at 1 l/min). Minute ventilation, changes in esophageal pressure (Pes) and proximal airway pressure, and moving time averages of posterior cricoarytenoid (PCA), submental genioglossus (SM), and diaphragm (DIA) electromyograms were obtained during BL and 1 and 5 min of IRL. Total respiratory resistance was calculated from pressure and flow changes and was used to estimate ETA narrowing: there was an increase in total respiratory resistance from 90 +/- 15 to 120 +/- 34 and 151 +/- 86 cmH2O.l-1.s after 1 and 5 min of IRL, respectively (P < 0.05, 1-min IRL vs. BL), in association with a sustained decline in minute ventilation (P < 0.05) and increases in Pes and proximal airway pressure (P < 0.05). Phasic PCA activity was always present, but its duration was only transiently prolonged with IRL (P < 0.05, 1-min IRL vs. BL). SM activity was present in only one infant during BL and was recruited in two additional infants during IRL. The decline in Pes from 1 to 5 min of IRL occurred despite continuing increases in peak and average activities of the DIA moving time average, which may reflect an onset of DIA fatigue. The transient prolongation of phasic PCA activity and occasional recruitment of SM activity with sustained loading explain, in part, the ETA instability detectable by moderate IRL in sleeping preterm infants.

Study of the antiischemic action of EGb 761 in the treatment of peripheral arterial occlusive disease by TcPo2 determination

In a randomized, placebo-controlled, double-blind, parallel study of 20 patients, the antiischemic effect of EGb 761 (Ginkgo biloba Extract) was studied by measuring the transcutaneous partial pressure of oxygen (TcPo2) during exercise. Transcutaneous oximetry during exercise provides a good, noninvasive estimation of local arterial perfusion and constitutes a real index of local and regional capillary perfusion. Twenty patients between the ages of forty-four and seventy-three years suffering from claudicating atherosclerotic arterial occlusive disease in stage II according to the Leriche and Fontaine classification, diagnosed for more than a year and stable for three months, were included. The eligible patients received placebo for fifteen days under single-blind conditions. At the end of this preinclusion period, the eligibility criteria were checked and the patients were randomized to two treatment groups. The first group received 320 mg per day of EGb 761 for four weeks and the second group received placebo. The treadmill walking test was performed under standardized conditions at the same time of day and by the same investigator. In a comparison of the differences before and after treatment, the areas of ischemia decreased by 38% in the EGb 761 group but remained essentially stable (+5%) in the placebo group. This difference between groups is significant (F [1.18] = 4.91; P = 0.04) and the 95% confidence interval for the difference ranges from 0.89 to 3.87. This study confirmed significantly the rapid antiischemic action of EGb 761 and its value in the management of peripheral arterial occlusive disease at the stage of intermittent claudication.