The Use of Iso-Shunt Lines for Control of Oxygen Therapy

Benatar, Solomon R.; Hewlett, A.M.; Nunn, J.F.

doi:10.1093/bja/45.7.711

Cited by 142 publications

(67 citation statements)

References 6 publications

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“…The alveolar to arterial oxygen gradient (D A–a O 2 ) was calculated by standard formula using the value of R obtained from the metabolic measurements. Venous admixture (Q s /Q t ) was estimated noninvasively using an assumed arterial-venous O 2 difference of 4.5 ml/100 ml [19]. Dead space fraction (V D /V T ) was derived form the Enghoff modification of the Bohr equation using mixed expired and arterial CO 2 tensions [20] with adjustments made for the breathing valve dead space.…”

Section: Methodsmentioning

confidence: 99%

Iloprost Improves Gas Exchange and Exercise Tolerance in Patients with Pulmonary Hypertension and Chronic Obstructive Pulmonary Disease

Dernaika

Beavin

Kinasewitz³

2009

Respiration

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Background: Nonselective systemic vasodilators worsen ventilation perfusion (V/Q) matching and gas exchange in patients with chronic obstructive pulmonary disease (COPD). Inhaled iloprost has the potential to act preferentially in ventilated regions of the lung, thereby reducing pulmonary hypertension (PH) while alveolar ventilation is still maintained. Objectives: To investigate the acute effects of inhaled iloprost on V/Q matching in patients with COPD and PH. Methods: Ten males with COPD and PH on echocardiography were evaluated before and after inhaling 2 doses of iloprost (2.5 µg). Measurements included lung function, arterial blood gas, 6-min walk test (6MWT) as well as ventilatory equivalents for oxygen (V_E/VO₂) and carbon dioxide (V_E/VCO₂) taken at baseline, 30 min following each dose of iloprost, and 2 h after the second dose. Results: Mean differences in V_E/VCO₂ and V_E/VO₂ were –13.3 (95% CI –36.5 to –2.7; p = 0.002) and –15.0 (95% CI –36.7 to –0.4; p = 0.02), respectively, and the mean change in (A-a) gradient was –3.7 mm Hg (95% CI –6.1 to –1.0; p = 0.01) after a single dose of iloprost, whereas mean improvement in 6MWT was 49.8 m (95% CI 14.8 to 84.7; p = 0.02). Arterial blood gas, venous admixture, dead space fraction and lung functions were maintained after iloprost. The effects of iloprost were reproducible after the second dose. All measurements returned to baseline 2 h after the last dose. No adverse effects on systemic blood pressure or oxygen saturation were seen. Conclusions: Iloprost inhalation was safe in patients with COPD and PH, and was associated with improved V/Q matching and exercise tolerance.

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Section: Methodsmentioning

confidence: 99%

Iloprost Improves Gas Exchange and Exercise Tolerance in Patients with Pulmonary Hypertension and Chronic Obstructive Pulmonary Disease

Dernaika

Beavin

Kinasewitz³

2009

Respiration

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“…An increase in Fi Ol to 28% caused an increase in (Cc' O2 -Ca Oz ) in three patients and a decrease in eight, and 35% oxygen caused an increase in two and a decrease in nine. If the hypoxaemia found after operation was caused by shunting of blood, and if the effect of this shunting was not influenced by oxygen therapy, then the response to oxygen administration could be predicted (Benatar, Hewlett and Nunn, 1973). Table VI oxygen that is better than predicted.…”

Section: Resultsmentioning

confidence: 99%

Oxygen Therapy After Thoracotomy

Drummond¹,

Milne²

1977

British Journal of Anaesthesia

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SUMMARYArterial blood samples were taken from patients before thoracotomy, and on the 1st day after operation, with the patient breathing first air, and then 24%, 28% and 35% oxygen from a venturitype mask. Pao t was reduced markedly by operation, the reduction being related to the value before operation. Oxygen therapy restored P&o t to a value greater than the value before operation in nine of 11 patients and was not associated with significant increases in Paco,. The effect of administration of oxygen on Pao, could be predicted from the Pao t when breathing air. The pattern of response to oxygen suggested that the hypoxaemia was caused by ventilation/perfusion mismatch in most of the patients.Lung function is impaired severely after thoracotomy; arterial oxygen tension is reduced, and carbon dioxide tension may be increased, particularly within hours of the operation (Maier and Cournand, 1943; Bjork and Hilty, 1954;Hood and Beall, 1958;Knudsen, 1970). Opiate analgesia may increase the respiratory acidosis (Pandit, Galway and Dundee, 1973).Patients studied on the day after thoracotomy have persistent hypoxaemia, but reduced .Pa COl! values (Hatch, 1966;Bergh et al., 1966). In this respect, they resemble patients recovering from upper abdominal surgery, whose gas exchange is impaired by ventilation/perfusion (l?y$) mismatch rather than respiratory depression. Nevertheless, it is possible that, after thoracotomy, patients remain susceptible to respiratory depression, and that this is masked by the stimulus of hypoxaemia. The influence of controlled oxygen therapy on arterial oxygen and carbon dioxide tensions in such patients has not been reported.This study was designed to assess the effects of oxygen therapy after thoracotomy. The response of Pa Oa to different oxygen fractions (Fi Oi ) might indicate the mechanism of impairment of gas transfer (Kerr, 1975; Drummond and Wright, 1977). The difference between the calculated oxygen content of blood leaving the pulmonary capillaries (Cc'o 2 ) and the oxygen content of arterial blood (Ca Oj ) can be used as an index of impaired gas transfer, in the same way as the difference between alveolar and arterial oxygen tensions (PA 02 -Pa 02 ) has been used. The advantage of the former expression is that it is not changed by changes in alveolar oxygen tension if the impaired oxygenation is caused by the shunting of a constant fraction of blood through regions where it is not exposed to gas exchange. A reduction in the value of the index during administration of oxygen shows that increasing the alveolar oxygen tension improves the efficiency of oxygen transfer, which is characteristic of impaired exchange caused by fjQ mismatch (West, 1969). This analysis depends upon the assumption that the oxygen content difference between arterial and mixed venous blood (Ca 02 -Cv 02 ) is not changed by oxygen administration.If oxygen therapy were associated with an increase in PacQj,, this would suggest that respiration had been stimulated by hypoxia when the patient was breathing ai...

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“…Measurements must be corrected for intrapulmonary shunts. The NICO-monitor compensates for this by using a shunting fraction based on Nunn's iso-shunt tables [33]. However, in ICU patients with important cardiopulmonary disease (pneumonia, atelectasis, intracardial shunts), this may be a problem.…”

Section: Respiratory Derived Cardiac Output Monitoring System: Partiamentioning

confidence: 99%

Hemodynamic monitoring: To calibrate or not to calibrate? Part 2 — Non-calibrated techniques

Bernards¹,

Mekeirele²,

Hoffmann³

et al. 2015

Anaesthesiol Intensive Ther

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There is much evidence that fluid overload leads to adverse outcomes in perioperative and critically ill patients. Cardiac output monitoring can help us guiding initial and ongoing fluid resuscitation and can help us to assess whether a patient will be responsive to fluids when hypotensive. In recent years, many sophisticated devices that measure a variety of hemodynamic parameters have evolved on the market. We wanted to provide an overview of the different techniques available today, including their validation in different patient populations. In this second part of the review, we focus on non-calibrated techniques, both invasive and non-invasive. For each technique a short overview of the working principle, together with the advantages, disadvantages and the available validation literature is listed. Many promising minimal invasive monitoring devices can help us to further optimize our hemodynamic treatment in both the perioperative and critical care setting. However, the validation data are scarce for many of these techniques, especially in complex circumstances with changing hemodynamics (preload, afterload and contractility), as with the use of fluids and vasoactive medication. The measurements made by these devices, therefore, need to be interpreted with caution. Further improvements and more validation data are needed before these techniques can be implemented in common day practice. Moreover, in severely shocked hemodynamic unstable patients, calibrated techniques are to be preferred over those which are uncalibrated. Hence, the new techniques not only need to be accurate, but also need to be precise in order to keep track of changes.

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The Use of Iso-Shunt Lines for Control of Oxygen Therapy

Cited by 142 publications

References 6 publications

Iloprost Improves Gas Exchange and Exercise Tolerance in Patients with Pulmonary Hypertension and Chronic Obstructive Pulmonary Disease

Iloprost Improves Gas Exchange and Exercise Tolerance in Patients with Pulmonary Hypertension and Chronic Obstructive Pulmonary Disease

Oxygen Therapy After Thoracotomy

Hemodynamic monitoring: To calibrate or not to calibrate? Part 2 — Non-calibrated techniques

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