Catheter position and blood gases during constant-flow ventilation

1987 ◽  
Vol 62 (2) ◽  
pp. 513-519 ◽  
Author(s):  
A. S. Slutsky ◽  
A. S. Menon
Keyword(s):  
Steady State ◽  
Flow Rate ◽  
Blood Gases ◽  
Constant Flow ◽  
Arterial Blood Gases ◽  
Catheter Position ◽  
Flow Rates ◽  
Arterial Blood ◽  
Tracheal Carina ◽  
Co2 Elimination

We studied the effect of catheter position and flow rate on gas exchange during constant-flow ventilation (CFV) in eight anesthetized, paralyzed dogs. The distal tips of the insufflation catheters were positioned 0.5, 2.0, 3.5, and 5.0 cm from the tracheal carina. Flow rates were varied between 10 and 55 l/min and steady-state arterial blood gases were measured. At a given flow rate, arterial CO2 pressure (PaCO2) decreased as CFV was administered further into the lung up to a distance of 3.5 cm from the carina; there were no significant differences in PaCO2 at 3.5 and 5.0 cm. For a given catheter position, PaCO2 decreased with increasing flow rate up to a flow rate of 40 l/min. Further increases in flow rate had no significant effect on PaCO2. Arterial O2 pressure (PaO2) was relatively constant at all flow rates and catheter positions. We conclude that, up to a point, CO2 elimination can be improved by positioning the catheters further into the lung; advancing the catheters further than 3.5 cm from the carina may cause over-ventilation of specific lung regions resulting in a relative plateau in CO2 elimination and relatively constant PaO2's. Positioning the catheters further into the lung permits the use of lower flow rates, thus potentially minimizing the risk of barotrauma.

Constant-flow ventilation in pigs

1986 ◽  
Vol 61 (6) ◽  
pp. 2238-2242 ◽  
Author(s):  
P. Webster ◽  
A. S. Menon ◽  
A. S. Slutsky
Keyword(s):  
Steady State ◽  
Gas Exchange ◽  
Gas Flow ◽  
Blood Gases ◽  
Maximum Flow ◽  
Constant Flow ◽  
Catheter Position ◽  
Flow Rates ◽  
Co2 Partial Pressure ◽  
Flow Through

Constant-flow ventilation (CFV) is a ventilatory technique in which physiological blood gases can be maintained in dogs by a constant flow of fresh gas introduced via two catheters placed in the main-stem bronchi (J. Appl. Physiol. 53: 483–489, 1982). High-velocity gas exiting from the catheters can create uneven pressure differences in adjacent lung segments, and these pressure differences could lead to gas flow through collateral channels. To examine this hypothesis, we studied CFV in pigs, animals known to have a high resistance to collateral ventilation. In three pigs we examined steady-state gas exchange, and in six others we studied unsteady gas exchange at three flow rates (20, 35, and 50 l/min) and three catheter positions (0.5, 1.5, and 2.5 cm distal to the tracheal carina). During steady-state runs we were unable to attain normocapnia; the arterial CO2 partial pressure (PaCO2) was approximately 300 Torr at all flow rates and all catheter positions, compared with 20–50 Torr at similar flows and positions in dogs studied previously. The initial unsteady gas-exchange experiments indicated no consistent effect of catheter position or flow rate on the rate of rise of PaCO2. In three other pigs, the rates of rise of PaCO2 were compared with the rates observed with apneic oxygenation (AO). At the maximum flow and deepest position, the rate of rise of PaCO2 was lower during CFV than during AO. These data suggest that flow through collateral channels might be important in producing adequate gas transport during CFV; however, other factors such as airway morphometry and the effects of cardiogenic oscillations may explain the differences between the results in pigs and dogs.

Arterial blood gases and acid-base status of dogs during graded dynamic exercise

1986 ◽  
Vol 61 (5) ◽  
pp. 1914-1919 ◽  
Author(s):  
T. I. Musch ◽  
D. B. Friedman ◽  
G. C. Haidet ◽  
J. Stray-Gundersen ◽  
T. G. Waldrop ◽  
...  
Keyword(s):  
Steady State ◽  
Blood Gases ◽  
Respiratory Alkalosis ◽  
Submaximal Exercise ◽  
O2 Consumption ◽  
Arterial Blood Gases ◽  
Acid Base ◽  
Vo2 Max ◽  
Arterial Blood ◽  
Acid Base Status

The objective of this study was to determine whether arterial PCO2 (PaCO2) decreases or remains unchanged from resting levels during mild to moderate steady-state exercise in the dog. To accomplish this, O2 consumption (VO2) arterial blood gases and acid-base status, arterial lactate concentration ([LA-]a), and rectal temperature (Tr) were measured in 27 chronically instrumented dogs at rest, during different levels of submaximal exercise, and during maximal exercise on a motor-driven treadmill. During mild exercise [35% of maximal O2 consumption (VO2 max)], PaCO2 decreased 5.3 +/- 0.4 Torr and resulted in a respiratory alkalosis (delta pHa = +0.029 +/- 0.005). Arterial PO2 (PaO2) increased 5.9 +/- 1.5 Torr and Tr increased 0.5 +/- 0.1 degree C. As the exercise levels progressed from mild to moderate exercise (64% of VO2 max) the magnitude of the hypocapnia and the resultant respiratory alkalosis remained unchanged as PaCO2 remained 5.9 +/- 0.7 Torr below and delta pHa remained 0.029 +/- 0.008 above resting values. When the exercise work rate was increased to elicit VO2 max (96 +/- 2 ml X kg-1 X min-1) the amount of hypocapnia again remained unchanged from submaximal exercise levels and PaCO2 remained 6.0 +/- 0.6 Torr below resting values; however, this response occurred despite continued increases in Tr (delta Tr = 1.7 +/- 0.1 degree C), significant increases in [LA-]a (delta [LA-]a = 2.5 +/- 0.4), and a resultant metabolic acidosis (delta pHa = -0.031 +/- 0.011). The dog, like other nonhuman vertebrates, responded to mild and moderate steady-state exercise with a significant hyperventilation and respiratory alkalosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Work With Chemical Additives Advances Understanding of Relative Permeability Shifts

2021 ◽  
Vol 73 (09) ◽  
pp. 37-38
Author(s):  
Chris Carpenter
Keyword(s):  
Steady State ◽  
Relative Permeability ◽  
Flow Rate ◽  
Pressure Difference ◽  
Effective Permeability ◽  
Constant Flow ◽  
Chemical Additives ◽  
Flow Rates ◽  
Steady State Method ◽  
Tight Rocks

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201520, “Advances in Understanding Relative Permeability Shifts by Imbibition of Surfactant Solutions Into Tight Plugs,” by Mohammad Yousefi, Lin Yuan, and Hassan Dehghanpour, SPE, University of Alberta, prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, Colorado, 5–7 October. The paper has not been peer reviewed. Various chemical additives have been proposed recently to enhance imbibition oil recovery from tight formations during shut-in periods after hydraulic fracturing operations. In the complete paper, the authors develop and apply a laboratory protocol mimicking leakoff, shut-in, and flowback processes to evaluate the effects of fracturing-fluid additives on oil regained permeability. A conventional coreflooding apparatus is modified to measure oil effective permeability (koeff) before and after the surfactant-imbibition experiments. Methodology Proposed Technique for Measuring Oil Effective Permeability. Despite the simplicity of the steady-state method, measuring permeability of tight rocks with this technique is challenging because of its time-consuming nature and the fact that accurate measurement is necessary of extremely low flow rates corresponding to low injectivity of tight rocks. The authors use a pair of plugs from a well drilled in the Montney formation that is a stratigraphic unit of the Lower Triassic age in the western Canadian sedimentary basin located in British Columbia and Alberta. It is mainly a low-permeability siltstone reservoir. In the modified coreflooding apparatus, the authors reduce the effect of compressibility in order to reduce the duration of the transient period by approximately one order of magnitude. Because monitoring changes in pressure is much easier and more accurate than monitoring flow-rate changes, a constant flow-rate mode is used and pressure is recorded with time. Oil is injected at different constant flow rates (qo), and the inlet pressure is monitored. The stable pressure difference across the plug is recorded for each flow rate. After steady-state conditions are reached based on the pressure profile, the qo is increased. This process is repeated until four stable pressure differences corresponding to four different qo are obtained. After the highest qo is reached, it is decreased in similar steps to check the repeatability of each data point. The permeability is calculated with the Darcy equation and slope of the qo vs. stable pressure difference across the plug.

Constant-flow ventilation of apneic dogs

1982 ◽  
Vol 53 (2) ◽  
pp. 483-489 ◽  
Author(s):  
B. E. Lehnert ◽  
G. Oberdorster ◽  
A. S. Slutsky
Keyword(s):  
Gas Flow ◽  
Blood Gases ◽  
Constant Flow ◽  
Blood Gas ◽  
Total Flow ◽  
Flow Rates ◽  
Arterial Blood Gas ◽  
Arterial Blood ◽  
Humidified Air ◽  
Upper Third

The adequacy of constant airway gas flow sustenance of arterial blood gas tensions was investigated in anesthetized-paralyzed mongrel dogs. Gas delivery was achieved via a main-stem bronchi cannulation system constructed of two polyethylene tubes bifurcating at the carina, which rested on the posterior surface of the trachea outside of an endotracheal tube positioned in the upper third of the trachea. Equal flows (total flow = Vin) of humidified air were delivered through each limb of the cannulation system at constant flow rates with Vin ranging from 8 to 28 l/min. Intratracheal pressures at these flows characteristically ranged from 0.1 to 1 cmH2O. Arterial O2 tension varied directly (PaO2 = 0.72 Vin + 74.6), and arterial CO2 tension varied inversely (PaCO2 = -0.73 Vin + 51.2) with Vin during ambient gas, constant-flow ventilation (CFV). During prolonged CFV (greater than 2 h), no evidence of CO2 accumulation or deterioration of PaO2, was observed. This study demonstrates that in apneic dogs normal blood gases can be achieved and maintained over prolonged periods with constant airway flow at low intratracheal pressures.

Influence of indomethacin on ventilatory and cerebrovascular responsiveness to CO2 and breathing stability: the influence of Pco2 gradients

2010 ◽  
Vol 298 (6) ◽  
pp. R1648-R1658 ◽  
Author(s):  
Jui-Lin Fan ◽  
Keith R. Burgess ◽  
Kate N. Thomas ◽  
Karen C. Peebles ◽  
Samuel J. E. Lucas ◽  
...  
Keyword(s):  
Steady State ◽  
Blood Gases ◽  
Cerebrovascular Reactivity ◽  
Arterial Blood Gases ◽  
Ventilatory Control ◽  
Arterial Blood ◽  
Steady State Method ◽  
Variability Index ◽  
State Method

Indomethacin (INDO), a reversible cyclooxygenase inhibitor, is a useful tool for assessing the role of cerebrovascular reactivity on ventilatory control. Despite this, the effect of INDO on breathing stability during wakefulness has yet to be examined. Although the effect of reductions in cerebrovascular CO2 reactivity on ventilatory CO2 sensitivity is likely dependent upon the method used, no studies have compared the effect of INDO on steady-state and modified rebreathing estimates of ventilatory CO2 sensitivity. The latter method includes the influence of Pco2 gradients and cerebral perfusion, whereas the former does not. We examined the hypothesis that INDO-induced reduction in cerebrovascular CO2 reactivity would 1) cause unstable breathing in conscious humans and 2) increase ventilatory CO2 sensitivity during the steady-state method but not during rebreathing methods. We measured arterial blood gases, ventilation (V̇e), and middle cerebral artery velocity (MCAv) before and 90 min following INDO ingestion (100 mg) or placebo in 12 healthy participants. There were no changes in resting arterial blood gases or V̇e following either intervention. INDO increased the magnitude of V̇e variability (index of breathing stability) during spontaneous air breathing (+4.3 ± 5.2 Δl/min, P = 0.01) and reduced MCAv (−25 ± 19%, P < 0.01) and MCAv-CO2 reactivity during steady-state (−47 ± 27%, P < 0.01) and rebreathing (−32 ± 25%, P < 0.01). The V̇e-CO2 sensitivity during the steady-state method was increased with INDO (+0.5 ± 0.5 l·min−1·mmHg−1, P < 0.01), while no changes were observed during rebreathing ( P > 0.05). These data indicate that the net effect of INDO on ventilatory control is an enhanced ventilatory loop gain resulting in increased breathing instability. Our findings also highlight important methodological and physiological considerations when assessing the effect of INDO on ventilatory CO2 sensitivity, whereby the effect of INDO-induced reduction of cerebrovascular CO2 reactivity on ventilatory CO2 sensitivity is unmasked with the rebreathing method.

scholarly journals Pathophysiology and clinical consequences of arterial blood gases and pH after cardiac arrest

2020 ◽  
Vol 8 (S1) ◽  
Author(s):  
Chiara Robba ◽  
Dorota Siwicka-Gieroba ◽  
Andras Sikter ◽  
Denise Battaglini ◽  
Wojciech Dąbrowski ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Mechanical Ventilation ◽  
Cardiac Arrest ◽  
Oxygen Demand ◽  
Blood Gases ◽  
Metabolic Energy ◽  
High Morbidity ◽  
Arterial Blood Gases ◽  
Arterial Blood ◽  
Clinical Consequences

AbstractPost cardiac arrest syndrome is associated with high morbidity and mortality, which is related not only to a poor neurological outcome but also to respiratory and cardiovascular dysfunctions. The control of gas exchange, and in particular oxygenation and carbon dioxide levels, is fundamental in mechanically ventilated patients after resuscitation, as arterial blood gases derangement might have important effects on the cerebral blood flow and systemic physiology.In particular, the pathophysiological role of carbon dioxide (CO2) levels is strongly underestimated, as its alterations quickly affect also the changes of intracellular pH, and consequently influence metabolic energy and oxygen demand. Hypo/hypercapnia, as well as mechanical ventilation during and after resuscitation, can affect CO2 levels and trigger a dangerous pathophysiological vicious circle related to the relationship between pH, cellular demand, and catecholamine levels. The developing hypocapnia can nullify the beneficial effects of the hypothermia. The aim of this review was to describe the pathophysiology and clinical consequences of arterial blood gases and pH after cardiac arrest.According to our findings, the optimal ventilator strategies in post cardiac arrest patients are not fully understood, and oxygen and carbon dioxide targets should take in consideration a complex pattern of pathophysiological factors. Further studies are warranted to define the optimal settings of mechanical ventilation in patients after cardiac arrest.

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