Assessment Of Gas Exchange Research Articles

Venous air embolism and cervical microdiscectomy.

Venous air embolism and cervical microdiscectomy.

Intravenacaval Membrane Oxygenation and Carbon Dioxide Removal in Severe Acute Respiratory Failure

To characterize the physiologic response to, and safety of, intravenacaval membrane oxygenation and carbon dioxide removal. Interventional before-after study. University teaching hospital ICU. Twenty-two patients with severe acute respiratory distress syndrome (ARDS). Implantation of a hollow-fiber membrane oxygenator (IVOX; CardioPulmonics; Salt Lake City, Utah) into the superior and inferior venae cavae by venotomy of the right femoral or right internal jugular vein for a duration of up to 20 days. Hemodynamic measurements using pulmonary artery and systemic artery catheters, ventilator settings (FIO2, minute ventilation, peak inspiratory pressure, and positive end-expiratory pressure), arterial and mixed venous blood gases (pH, PCO2, PO2, and measured saturation), and clinical laboratory determinations (CBC, fibrinogen, plasma hemoglobin, complement C3 and C5) were obtained. Calculations of PaO2/FIO2 ratio and PaCO2-VE product were used to assess gas exchange efficacy. Microbiologic cultures were obtained from the device and wound following explantation. Survival to ICU discharge and hospital discharge were recorded. Implantation was successful in 20 of 22 patients. Gas exchange rates averaged 50.4 +/- 15.8 mL.min-1 for carbon dioxide and 71.1 +/- 20.2 mL.min-1 for oxygen. A reduction in FIO2 from 0.78 +/- 0.16 to 0.63 +/- 0.21 and in VE from 177 +/- 94 mL.kg-1.min-1 to 127 +/- 58 mL.kg-1.min-1 was possible within 4 h post-implantation. By 12 h, FIO2 was reduced to 0.57 +/- 0.18. Indices of gas exchange improved significantly after implantation, with PaO2/FIO2 ratio increasing from 79 +/- 20 to 112 +/- 47 and PaCO2-VE product decreasing from 7.6 +/- 4.2 to 4.9 +/- 2.5 within 4 h. A significant reduction in peak inspiratory pressure was achieved (45 +/- 10 to 38 +/- 9 cm H2O). Major complications were blood loss during implantation requiring transfusion in 11 patients, a retroperitoneal bleed in 1 patient, and femoral deep venous thrombosis in 4 patients, but there were no long-term sequelae or IVOX-related deaths. The ICU and hospital survival were 10/20 (50%) and 8/20 (40%), respectively. Intravenacaval membrane oxygen and carbon dioxide removal can provide partial respiratory support during severe respiratory failure and permit reductions in the level of mechanical ventilator support, with an acceptable safety profile.

Measurement of carbon monoxide transfer and lung volume in ventilated subjects

A simple method for measuring lung volume and carbon monoxide transfer factor (TLCO) by a rebreathing technique was assessed in nine healthy volunteers undergoing intermittent positive pressure ventilation (IPPV). Measurements of TLCO, alveolar volume (VA) and carbon monoxide transfer coefficient (KCO) made at three inspired oxygen concentrations (21, 35 and 70%) during IPPV were compared to those obtained during spontaneous breathing. The effects of 10 cmH2O positive end expiratory pressure (PEEP) were also studied. Pulmonary capillary blood volume (Vc) and the diffusing capacity of the alveolar capillary membrane (Dm) were derived. There was a close correlation between measurements of TLCO during IPPV (TLCOIPPV) and spontaneous breathing (TLCOSV) (r = 0.92). Ventilated TLCO was 64 +/- 8% of spontaneously breathing TLCO. There was a close agreement between ventilated and spontaneously breathing measurements of KCO (r = 0.95; mean difference 0.14, 95% limits of agreement +0.37 to -0.09 mmol.min-1 x kPa-1 x l-1). Vc was 92 +/- 23 ml during spontaneous breathing and 72 +/- 21 ml during IPPV (p < 0.05). PEEP of 10 cmH2O significantly increased functional residual capacity (2.3 +/- 0.5 to 3.5 +/- 0.6 l) and decreased TLCO (5.9 +/- 1.0 to 5.3 +/- 1.2 mmol.min-1 x kPa-1), KCO (1.7 +/- 0.2 to 1.1 +/- 0.3 mmol.min-1 x kPa-1 x l-1) and Vc (82 +/- 22 to 56 +/- 20 ml). Dm did not change with PEEP. This simple method may be a useful means of assessing gas exchange and lung volume in ventilated subjects. It showed that PEEP increased lung volume but reduced TLCO and that this reduction appeared to be due to a reduction in capillary blood volume.

Cardiorespiratory response to exercise after the Fontan procedure for tricuspid atresia.

Noninvasive exercise testing was used to assess gas exchange in 13 patients age 6-25 yr who had undergone Fontan procedures for tricuspid atresia, five of whom had preexisting Glenn shunts. The results were compared to 28 age- and sex-matched controls. Oxygen saturation was measured by ear oximetry at rest and after exercise. Ventilation, oxygen consumption (VO2), carbon dioxide production (VCO2), and heart rate were measured during progressive exercise. The ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2), mixed expired pCO2 (PECO2) end-tidal pCO2 (PETCO2), and dead space to tidal volume ratio (VD/VT) were determined during steady state exercise on a cycle ergometer. Heart rate was higher for VO2 by 15% (p less than 0.02) and ventilation was higher for both VO2 (by 37%, p less than 0.001) and VCO2 (by 27%, p less than 0.002) in the patients than the controls. Mean VE/VO2 was 35.4 +/- 7.8 (SD) compared to 25.8 +/- 3.1 (p less than 0.001) and mean VE/VCO2 was 41.7 +/- 9.0 compared to 31.6 +/- 4.3 (p less than 0.001). Mean PECO2 was 21.4 +/- 4.4 torr with controls at 27.9 +/- 3.8 (p less than 0.001) and mean PETCO2 was 33.0 +/- 5.3 torr compared to 40.0 +/- 3.3 (p less than 0.001). The patients had a mean oxygen saturation of 92 +/- 5% at rest and abnormal saturation after exercise (87 +/- 9, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of high-frequency ventilation on gas exchange and pulmonary vascular resistance in lambs.

We studied the effects of conventional mechanical ventilation (CMV) (15 ml/kg tidal volume delivered at 18-25 breaths/min) and high-frequency oscillatory ventilation (HFOV) (less than or equal to 2 ml/kg delivered at 10 Hz) on pulmonary hemodynamics and gas exchange during ambient air breathing and hypoxic gas breathing in 10 4-day-old lambs. After instrumentation and randomization to either HFOV or CMV the animals breathed first ambient air and then hypoxic gas (inspired O2 fraction = 0.13) for 20 min. The mode of ventilation was then changed, and the normoxic and hypoxic gas challenges were repeated. The multiple inert gas elimination technique was utilized to assess gas exchange. There was a significant increase with HFOV in mean pulmonary arterial pressure (Ppa) (20.1 +/- 4.2 vs. 22 +/- 3.8 Torr, CMV vs. HFOV, P less than 0.05) during ambient air breathing. During hypoxic gas breathing Ppa was also greater with HFOV than with CMV (29.5 +/- 5.7 vs. 34 +/- 3.1 Torr, CMV vs. HFOV, P less than 0.05). HFOV reduced pulmonary blood flow (Qp) during ambient air breathing (0.33 +/- 0.11 vs. 0.28 +/- 0.09 l . kg-1 . min-1, CMV vs. HFOV, P less than 0.05) and during hypoxic gas breathing (0.38 +/- 0.11 vs. 0.29 +/- 0.09 l . kg-1 . min-1, P less than 0.05). There was no significant difference in calculated venous admixture for sulfur hexafluoride or in the index of low ventilation-perfusion lung regions with HFOV compared with CMV.(ABSTRACT TRUNCATED AT 250 WORDS)

104 RESPONSE TO EXERCISE AFTER FONTAN PROCEDURE

Previous studies demonstrating maldistribution of pulmonary blood flow in patients who had undergone Fontan procedures (FP) predict high physiologic dead space during exercise. We used non-invasive exercise testing to assess gas exchange in 5 patients age 10-19, compared to 11 age and sex matched controls. Oxygen saturation was measured by ear oximetry at rest and after exercise. The ventilatory equivalents for oxygen (Ve/VO2) and carbon dioxide (Ve/VCO2) were measured during progressive exercise and mixed expired pCO2 (PeCO2) and end-tidal pCO2 (PetCO2) were measured during steady state exercise on a cycle ergometer. We obtained the following results: In addition, the patients had a mean oxygen saturation of 89±6% at rest and desaturated further during exercise (81±11, p<0.05). These data show high ventilation for O2 consumption and CO2 production, low expired CO2 concentrations and oxygen desaturation during exercise. The results strongly indicate elevated physiologic dead space and ventilation perfusion mismatch consistent with maldistribution of pulmonary blood flow.

Large airway response to cemented arthroplasty: relationship to hypoxaemia. An experimental study in dogs.

Alteration in airway smooth muscle tone has been implicated in the mechanism of hypoxemia, pulmonary hypertension and changes in dynamic thoracic compliance after total hip arthroplasty (THA). We used the pressure within a water-filled cuff of an endotracheal tube as a continuous measure of changes in tracheomotor tone during THA in mongrel dogs, while intermittently assessing gas exchange abnormalities. In all 16 dogs the instillation of polymethylmethacrylate (PMMA) into the femoral medullary shaft resulted in tracheal dilation. In ten dogs we demonstrated simultaneous hypotension, hypoxemia and increase in shunt fraction (Qs/Qt) after THA. In six dogs the medullary canal was thoroughly lavaged prior to PMMA injection, and no hypoxemia, hypotension or increased Qs/Qt was found in spite of persisting tracheomotor relaxation. We conclude that these well-documented gas-exchange abnormalities are not mediated by changes in large airway tone. Since the hypoxemia was abolished by medullary lavage in our animal model, we suggest that this syndrome is mediated by alterations in lung perfusion and associated small airway constriction and not by changes in large airway smooth muscle tone.

Ventilation/perfusion relationships.

Over the last 10 years the investigation of VA/Q relationships has been significantly advanced as a result of the application of computer-assisted engineering techniques to the traditional concepts and equations of gas exchange. The price paid for this increase in ability to measure VA/Q relationships has been an increase in the complexity of technique, especially as seen by clinicians without a special interest in mathematics. Advances have taken place in the understanding of mechanisms of altered gas exchange in disease, but just as importantly in this author's mind, advances have taken place in our understanding of the problem of indirectly obtaining information from an inaccessible organ. This has been illustrated at some length in this review, and has been applied not only to the newer, more complex approaches to gas exchange, but also to the more traditional methods for assessing gas exchange such as the measurement of venous admixture. Thus, one must have a good understanding of the basic information content of any method before it can be used appropriately.