Acid-base response to acute carbon dioxide changes in chronic obstructive pulmonary disease.

New FindingsWhat is the central question of this study?The relationship between changes in cerebral blood flow and arterial carbon dioxide tension is used to assess cerebrovascular function. Hypercapnia is generally evoked by two methods, i.e. steady-state and transient increases in carbon dioxide tension. In some cases, the hypercapnia is immediately preceded by a period of hypocapnia. It is unknown whether the cerebrovascular response differs between these methods and whether a period of hypocapnia blunts the subsequent response to hypercapnia.What is the main finding and its importance?The cerebrovascular response is similar between steady-state and transient hypercapnia. However, hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.Cerebral vasomotor reactivity (CVMR) to changes in arterial carbon dioxide tension () is assessed during steady-state or transient changes in . This study tested the following two hypotheses: (i) that CVMR during steady-state changes differs from that during transient changes in ; and (ii) that CVMR during rebreathing-induced hypercapnia would be blunted when preceded by a period of hyperventilation. For each hypothesis, end-tidal carbon dioxide tension () middle cerebral artery blood velocity (CBFV), cerebrovascular conductance index (CVCI; CBFV/mean arterial pressure) and CVMR (slope of the linear regression between changes in CBFV and CVCI versus) were assessed in eight individuals. To address the first hypothesis, measurements were made during the following two conditions (randomized): (i) steady-state increases in of 5 and 10 Torr above baseline; and (ii) rebreathing-induced transient breath-by-breath increases in . The linear regression for CBFV versus (P = 0.65) and CVCI versus (P = 0.44) was similar between methods; however, individual variability in CBFV or CVCI responses existed among subjects. To address the second hypothesis, the same measurements were made during the following two conditions (randomized): (i) immediately following a brief period of hypocapnia induced by hyperventilation for 1 min followed by rebreathing; and (ii) during rebreathing only. The slope of the linear regression for CBFV versus (P < 0.01) and CVCI versus (P < 0.01) was reduced during hyperventilation plus rebreathing relative to rebreathing only. These results indicate that cerebral vasomotor reactivity to changes in is similar regardless of the employed methodology to induce changes in and that hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.

Arterial and alveolar carbon dioxide tension at end-tidal and maximal expiration were measured simultaneously in 104 patients with chronic obstructive respiratory disease. Regardless of the degree of abnormality of distribution of ventilation, there was a consistent relationship between arterial and maximal expiratory carbon dioxide tension. Therefore, close approximation of arterial carbon dioxide tension was obtained from the measurement of carbon dioxide tension at maximal expiration by rapid infrared carbon dioxide analysis. An infrared carbon dioxide analyzer might be used at the bedside or in the laboratory for frequent monitoring of arterial carbon dioxide tension without repeated arterial punctures.

&#x0D; Nowadays, laparoscopic surgeries are being performed under subarachnoid block (SAB) safely.&#x0D; Aims: This study was to compare the arterial and end-tidal carbon dioxide (CO2) tension changes during spinal and general anaesthesia (GA) in CO2 pneumoperitoneum for upper abdominal laparoscopic surgeries.&#x0D; Settings and Design: This was a prospective randomized comparative clinical study.&#x0D; Materials and Methods: Eighty patients posted for upper abdominal laparoscopic surgeries were randomly allocated to two groups either to receive standard GA or lumbar SAB.&#x0D; Results: The demographic profiles of both the groups were comparable. The PaCO2 was increased gradually and sustained at its peaks within 20±4.37 minutes in both the groups. The mean±SD revealed to be higher in Group B (41.5500±2.1315) than Group A (40.8460±2.1136), but the difference between the two was not statistically significant (P=0.6142). There was a gradual increase in ETCO2 over the initial 10±2.07 minutes and reached a plateau within 20±5.74 minutes in both the groups and declined faster after deflation of pneumoperitoneum in SAB group. The mean±SD was found to be higher in Group B (33.923±1.642) than Group A (33.408±1.772), but it was also not statistically significant (P=0.4492). The difference of the arterial blood pH between the groups was not statistically significant. Three (7.5%) patients developed transient urinary retention and 2 (5%) patients suffered from post-dural puncture headache in SAB group.&#x0D; Conclusions: Arterial and end-tidal CO2 tension changes during upper abdominal laparoscopic surgery under SAB remain within physiological limit and comparable to the CO2 tensions under GA. However, per-operative complications in SAB are greater, while it is lesser in postoperative period in comparison to GA. SAB may be adopted in ASA physical status I patients with proper preoperative counselling.&#x0D; J Bangladesh Coll Phys Surg 2019; 37(1): 13-18&#x0D; &#x0D;

1. The pH of a natural water is determined by the temperature, solids in solution and its carbon dioxide tension. 2. A change in the carbon dioxide tension of a water causes a definite and predictable change in pH, provided the carbon dioxide in solution is the only factor modifying the system. The amount of change in pH with a given change in carbon dioxide tension is determined by the water itself as a chemical system. That is, the pH at a definite carbon dioxide tension and temperature and the amount of change with a definite change in carbon dioxide tension are determined by the characteristics of the natural water itself. 3. Aquatic organisms are able to withstand wide ranges in pH. 4. Aquatic animals are affected in their physiological processes and behavior by changes in carbon dioxide and oxygen tensions. Of the two, a change in carbon dioxide tension is the more effective. 5. All aquatic animals can regulate their internal environment to bring them into harmony with their external environment. Th...

This study investigated the hypothesis that hypercapnia in some chronic obstructive pulmonary disease (COPD) patients may be related to a high cerebrovascular response to carbon dioxide (CO2). The relationship between responses of ventilation and of cerebral blood volume (CBV) to acute changes in carbon dioxide tension in arterial blood (Pa,CO2) was measured in 17 chronic hypercapnic (Pa,CO2 >6.0 kPa) and 16 normocapnic (Pa,CO2 < or = 6.0 kPa) COPD patients, who were matched for degree of airway obstruction (forced expiratory volume in one second 27% predicted). Results were compared with 15 age-matched healthy subjects. CBV was measured using near infrared spectroscopy during normo- and hypercapnia and related to inspired minute ventilation (V'I) and mouth occlusion pressure (P0.1). Hypercapnia (end-tidal pressure of carbon dioxide (deltaPET,CO2) > 1 kPa) was induced by giving adequate amounts of CO2 in the inspired air. During normocapnia, CBV (mL x 100 g(-1)) was 2.41+/- 0.66 and 2.90 +/- 0.60 (mean +/- SD) in the normocapnic and chronic hypercapnic patients, respectively, which was significantly lower compared to healthy subjects (3.53 +/- 0.77). All slopes of CO2 responsiveness (deltaCBV/deltaPa,CO2, deltaV'I/deltaPa,CO2, deltaP0.1/deltaPa,CO2) were significantly lower in both COPD groups relative to healthy subjects, but were not significantly different between the COPD groups. A poor but positive correlation between ventilatory and cerebrovascular CO2 responsiveness (deltaCBV/deltaPa,CO2 and deltaV'I/deltaPa,CO2) was found in COPD patients and healthy subjects. The findings do not support the hypothesis of abnormal cerebrovascular responses to carbon dioxide in hypercapnic chronic obstructive pulmonary disease patients.

Local effects of O2 and CO2 on limb, renal, and coronary vascular resistances.

To evaluate the efficacy and safety of oral theophylline versus placebo in patients with stable chronic obstructive pulmonary disease (COPD). The databases Medline, Embase, Web of Science, Cochrane Central Register of Controlled Trials and Chinese Biomedical Database were retrieved by using the key words "Uniphyl or Theophylline or Theo-Dur or theo or Theotrim or Elixophyllin or Elixophyllin or Phyllocontin or aminophylline or Methylxanthine or nuelin or doxofylline" and "obstructive or bronchitis or pulmonary emphysema or bronchial hyperreactivity or COPD or COLD or emphysema" so as to search the materials about the randomized controlled clinical trials comparing the effectiveness of stable COPD treated by oral theophylline and placebo. A meta-analysis was conducted. For continuous variables, the results of individual studies were pooled using fixed-effect weighted mean difference (WMD) with a corresponding 95% confidence interval (CI). Where the results were expressed as dichotomous variables, the relative risk (RR) with 95%CI was calculated. Thirty-four documents about randomized controlled clinical trials, including a total of 2087 patients, from the retrieved 2010 documents accorded to the demand of enrollment. The results of meta-analysis showed that theophylline significantly improved the forced expiratory volume in 1 s, forced vital capacity and peak expiratory flow rate (WMD 0.09 L, 95%CI 0.09 - 0.09; WMD 0.14 L, 95%CI 0.13 - 0.14; WMD 17.0 L/min and 95%CI 6.9 - 27.2 respectively). Arterial oxygen tension and arterial carbon dioxide tension at rest both improved with treatment (WMD 2.89 mm Hg, 95%CI 1.11 - 4.66; WMD -2.05 mm Hg and 95%CI -3.59 to -1.42 respectively). Six-minute walk distance significantly improved (WMD 38.89 meters, 95%CI 21.55 - 56.22) in treatment group. The RR of acute exacerbations was smaller between both groups (RR 0.74, 95%CI 0.59 - 0.93). The RR of total adverse events was similar (RR 1.05, 95%CI 0.95 - 1.16) while RR of drug-related adverse events was greater (RR 2.54, 95%CI 1.37 - 4.70). And there was significant statistical difference. Compared with the placebo, theophylline can improve lung function, arterial blood gas tensions and walking distance while the incidence of drug-related adverse events is higher.

In contrast to previous studies in which arterial hypoxia in patients with chronic obstructive pulmonary disease did not appear to be a major factor influencing their subsequent ventilatory response to an oxygen test, the degree of pre-existing hypoxia in this study of 151 patients was significantly correlated with the amount of ventilatory depression observed during subsequent oxygen administration. On the other hand, arterial pH, which was of high significance in other studies, had the lowest correlation in this study. The variability of ventilatory responses observed by others in smaller groups of patients has been confirmed, and no combination of factors related to arterial carbon dioxide tension, arterial oxygen tension, or pH could be identified to account for this variability. Patients who manifested a priority for diminution of dyspnea rather than a constancy of arterial carbon dioxide tension did not correspond to the bronchitic type B patients of Burrows and associates, because in this study, pa...

The effect of endotracheal suctioning on cerebral haemodynamics was investigated in 29 newborn infants with a mean gestational age of 31 weeks (range 25-40 weeks). Prior to one of two suctioning procedures, the inspiratory fraction of oxygen was increased by 10%. Brain oxygenation and total haemoglobin concentration were estimated continuously by near infrared spectroscopy. Mean arterial blood pressure, arterial blood oxygen saturation and carbon dioxide tension were recorded simultaneously. Brain oxygenation decreased in parallel with arterial oxygen saturation during suctioning. Preoxygenation ameliorated the decrease in brain oxygenation and arterial oxygen saturation whereas there was no benefit with regard to the changes in total haemoglobin concentration, carbon dioxide tension or mean arterial pressure. Changes in total haemoglobin concentration were related closely to concomitant changes in carbon dioxide tension (p less than 0.0001) but unrelated to changes in mean arterial pressure or arterial oxygen saturation. Our findings suggest that cerebral blood volume may react to changes in carbon dioxide tension during endotracheal suctioning in mechanically ventilated neonates. Apparently, preoxygenation prior to suctioning does not ameliorate the stress in normoxic infants.

The influence of changes in pH and the partial pressure of carbon dioxide in arterial blood on the neuromuscular blocking effect of a single dose of tubocurarine or dimethyl tubocurarine was investigated in rabbits. The sciatic nerve was stimulated supramaximally at a rate of 3 per second and the electrical response of the gastrocnemius muscle was recorded; the amplitude of the first and fourth response was measured. During the period of spontaneously subsiding block after a single injection of the blocking agent, a shift in the arterial pH was produced either with or without a change in carbon dioxide tension. An increase of the block during this period was always considered significant but a decrease of the block only if it was followed by a spontaenous increase. The action of tubocurarine increased during acidosis and diminished during alkalosis. This effect was greater during metabolic alkalosis and acidosis, corresponding to a more rapid shift in pH, than during respiratory alkalosis and acidosis, but no qualitative difference was observed. The effect of a shift in pH is explained by changes in the potency of tubocurarine. The action of dimethyl tubocurarine was not influenced by changes in pH or carbon dioxide tension.

Dilution acidosis and contraction alkalosis: Review of a concept

The results of pulmonary function tests in 663 patients and pulmonary vascular resistance in 136 patients were evaluated in relation to prognosis. The studies included spirogram, lung volumes, arterial blood gases, nitrogen washout, lung recoil at total lung capacity, airway resistance, diffusing capacity, and pulmonary vascular resistance. Forced expired volume in 1 second contributed significantly to predicting survival. Other tests probably contributed to predicting survival independent of 1-second forced expiratory volume. These tests were diffusing capacity for carbon monoxide, recoil pressure at total lung capacity, radiographic emphysema, arterial carbon dioxide tension, and single breath nitrogen washout. Decrease in 1-second forced expiratory volume averaged 52 ml per year. Changes from one follow-up period to another in any 1 patient showed considerable variability.

The dose effect of propofol on cerebrovascular reactivity to carbon dioxide in rabbits.

Monitored arterial and end-tidal carbon dioxide during in-flight mechanical ventilation

Neurological impairment may occur following cardiopulmonary bypass (CPB) and the effect of CPB on cerebrovascular control may be important in the mechanism of cerebral injury. We have used near infrared spectroscopy (NIRS) to observe cerebral haemodynamics non-invasively before and during CPB. We measured the change in cerebral blood volume (CBV) associated with changing PaCO2 (CBVR). Patients (n = 19) were aged from 1 to 135 (median 14) months. The cerebral blood volume response was determined pre-operatively at normothermia under the influence of standardised anaesthesia employing isoflurane (up to ET conc 0.5%) and during steady-state hypothermic bypass (22-32 degrees C) at an arterial pump flow rate of 1.9-2.4 lm-2.min-1. Complete data was available for 10 patients. The relation between CBV, arterial carbon dioxide tension (PaCO2), mean arterial pressure (MAP) and central venous pressure (CVP) was examined using analysis of covariance (P < or = 0.05) was accepted as significant). The change in CBV associated with changing PaCO2 was corrected for the effects of MAP and CVP. Preoperatively the median CBVR was 0.130 (25th-75th percentile 0.079-0.243) ml.100 g-1.kPa-1 and during hypothermic bypass the median CBVR was 0.093 (25th-75th percentile 0.026-0.255) ml.100 g-1.kPa-1. These values were compared with our reference range derived for normal conscious children using the Kruskal-Wallis test. There was not statistically significant difference between the three groups (P = 0.35). These results, indicating preservation of CBVR during the conditions of anaesthesia and bypass used, are consistent with the observations of previous authors who measured cerebral blood flow response to carbon dioxide by a variety of other methods. Near infrared spectroscopy is proving to be a reliable, non-invasive technique for the investigation of cerebral haemodynamics during CPB.