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PubMed1978

[Analysis of the mechanism of action of carbonic acid on tissue chemoreceptors].

Perfusion of the small intestine of anesthetized cats with a solution imitating metabolic acidosis (pH = 7.3; [HCO-3] = =20.2 mM; PCO2 = 38 mm Hg) produced a threshold reflex increase in the blood pressure. The subsequent decrease of [HCO-3] to 3.2 mM and pH to 6.5 evoked a gradual raise of the blood pressure followed by a sharp increase of pressor reflexes amplitude within the range of pH 6.5--6.3. Solutions imitating metabolic acidosis (pH = 7.1; [HCO-3] = 12.7 mM) were found to increase the concentration of H+ ions in the outflow perfusate and blood pressure to larger extent than solutions imitating respiratory acidosis (pH = 7.1; PCO2 = 75 mm Hg). If the solution pH was held constantly at 7.4 by simultaneous decreasing PCO2 and [HCO-3] by a factor of two, a reflex increase in the blood pressure and decrease of perfusate pH had no effect either on blood pressure or perfusate pH. The data obtained suggest that one of the primary determinants of different responses of the tissue chemoreceptors to CO2 is the interstitial pH.

Acid-Base Imbalance↗
PubMed2004

Effect of extracellular acid-base disturbances on the intracellular pH of neurones cultured from rat medullary raphe or hippocampus.

Previous reports suggest that an important characteristic of chemosensitive neurones is an unusually large change of steady-state intracellular pH in response to a change in extracellular pH (DeltapH(i)/DeltapH(o)). To determine whether such a correlation exists between neurones from the medullary raphe (a chemosensitive brain region) and hippocampus (a non-chemosensitive region), we used BCECF to monitor pH(i) in cultured neurones subjected to extracellular acid-base disturbances. In medullary raphe neurones, respiratory acidosis (5%--> 9% CO(2)) caused a rapid fall in pH(i) (DeltapH(i) approximately 0.2) with no recovery and a large DeltapH(i)/DeltapH(o) of 0.71. Hippocampal neurones had a similar response, but with a slightly lower DeltapH(i)/DeltapH(o) (0.59). We further investigated a possible link between pH(i) regulation and chemosensitivity by following the pH(i) measurements on medullary raphe neurones with an immunocytochemistry for tryptophan hydroxylase (a marker of serotonergic neurones). We found that the DeltapH(i)/DeltapH(o) of 0.69 for serotonergic neurones (which are stimulated by acidosis) was not different from either the DeltapH(i)/DeltapH(o) of 0.75 for non-serotonergic neurones (most of which are not chemosensitive), or from the DeltapH(i)/DeltapH(o) of hippocampal neurones. For both respiratory alkalosis (5%--> 3% CO(2)) and metabolic alkalosis (22 mm--> 35 mm HCO(3)(-)), DeltapH(i)/DeltapH(o) was 0.42-0.53 for all groups of neurones studied. The only notable difference between medullary raphe and hippocampal neurones was in response to metabolic acidosis (22 mm--> 14 mm HCO(3)(-)), which caused a large pH(i) decrease in approximately 80% of medullary raphe neurones (DeltapH(i)/DeltapH(o)= 0.71), but relatively little pH(i) decrease in 70% of the hippocampal neurones (DeltapH(i)/DeltapH(o)= 0.09). Our comparison of medullary raphe and hippocampal neurones indicates that, except in response to metabolic acidosis, the neurones from the chemosensitive region do not have a uniquely high DeltapH(i)/DeltapH(o). Moreover, regardless of whether neurones were cultured from the chemosensitive or the non-chemosensitive region, pH(i) did not recover during any of the acid-base stresses.

Acidosis, Respiratory↗
PubMed1973

The interrelationship of the concentration of hydrogen ions, bicarbonate ions, carbon dioxide and calcium ions in the regulation of renal gluconeogenesis in the rat.

1. The interrelationship of acidosis and Ca(2+) on the stimulation of gluconeogenesis by rat kidney-cortex slices was studied. 2. Ca(2+) stimulated gluconeogenesis from glutamine, glutamate, 2-oxoglutarate, succinate, malate, pyruvate, lactate and fructose, but not from galactose. 3. The [Ca(2+)] needed for optimum gluconeogenesis was about 2mm, but at this concentration, acidosis, produced in vitro by a decrease of [HCO(3) (-)] in the medium at constant pCO(2) or by an increase in pCO(2) at constant [HCO(3) (-)], did not stimulate gluconeogenesis. 4. In the absence of Ca(2+), acidosis (low [HCO(3) (-)]) stimulated gluconeogenesis from glutamine, glutamate, 2-oxoglutarate, succinate, malate, pyruvate and lactate but not from fructose or galactose. With succinate as substrate, the stimulatory effect of acidosis (low [HCO(3) (-)]) disappeared at Ca(2+) concentrations above 1.0mm. 5. The [HCO(3) (-)] was the most important determinant of the acidosis effect since a decrease of pH caused by an increase in pCO(2) did not uniformly stimulate gluconeogenesis, whereas a decrease in [HCO(3) (-)] without a change in pH consistently stimulated glucose formation in a way similar to the stimulation produced by acidosis (low [HCO(3) (-)]) in the absence of Ca(2+). 6. Acidosis in vitro inhibited the rate of decrease of activity of phosphoenolpyruvate carboxylase in slices, and Ca(2+) caused an increase in the activity of fructose 1-phosphate aldolase. 7. Respiratory acidosis in vitro caused an increase in the activity of phosphoenolpyruvate carboxylase in kidney cortex and an increase in gluconeogenesis from glutamine. 8. Possible points of interaction between Ca(2+), H(+) and HCO(3) (-) with the gluconeogenic sequence are discussed.

Acidosis↗
PubMed1975

[Effect of hypercapnia on the acid base states of the blood in the crab Carcinus maenas (L.) (Crustacea-Decapoda)].

When the crab Carcinus maenas respires in hypercapnic water, a respiratory acidosis occurs, which is progressively compensated by a rise of the blood bicarbonate concentration. The CO2 partial pressure in the blood increases in proportion to the change in ambient CO2 partial pressure. Therefore, the regulation of the acid-base status depends mainly on non-respiratory adjustments of the blood bicarbonate concentrations.

Acid-Base Equilibrium↗
PubMed1993

Acidosis and metabolic rate in golden mantled ground squirrels (Spermophilus lateralis).

In this study, three series of experiments were conducted on euthermic, anesthetized, artificially ventilated golden mantled ground squirrels (Spermophilus lateralis), each of which altered pHa in a different fashion. In Series I, animals were randomly hypo- or hyper-ventilated. On average, pHa changed from 7.13 to 7.59, PaCO2 from 59.2 to 23.6 Torr, and PaO2 from 45.8 to 57.2 Torr between the two conditions, respectively. VO2 showed a significant positive correlation with pHa (r = +0.84) as well as PaO2 (r = + 0.60). In Series II, respiratory acidosis was produced by pump-ventilating animals with up to 10% inspired CO2 to reduce pHa to within the range 7.40 to 7.20. On average, pHa was reduced to 7.30, PaO2 to 50.1 Torr and PaCO2 was increased to 56.7 Torr. As in Series I, there was a significant positive correlation between VO2 and pHa (r = +0.78) and between VO2 and PaO2 (r = +0.71). In Series III, metabolic acidosis was produced by infusing lactic or acetic acid intravenously for 20 to 30 min. This reduced pHa from 7.56 to 7.32, PaO2 from 70.2 to 58.9 Torr, and elevated PaCO2 from 26.9 to 37.9 Torr (P < 0.05 in all cases). Contrary to Series I and II, VO2 increased with a decline in pHa (r = -0.65, P < 0.05) and PaO2 (r = -0.55, P < 0.05). Thus, despite a significant decline in pHa and PaO2 and an elevation of PaCO2 during all three series, VO2 changed in opposite directions during respiratory and metabolic acidosis. We conclude that whatever the mechanism involved, hypoventilation during the early stages of entrance into hibernation can contribute to the fall in metabolic rate.

Acidosis↗
PubMed1986

Mechanical ventilation. Physiology, equipment design, and management.

The major goals of mechanical ventilation are the prevention of significant respiratory acidosis and the correction of arterial hypoxemia. Ventilators are categorized as negative- or positive-pressure types, depending on their effect on airway pressure. Positive-pressure ventilators, which are used in the treatment of acute respiratory failure, may be subclassified as pressure-, volume-, or time-cycled. Volume types provide stable tidal volumes and inspiratory oxygen concentrations over the range of changing ventilatory conditions seen in acute respiratory failure. Ventilation may be provided in a number of modes. No clear-cut advantage of intermittent mandatory ventilation over assisted mechanical ventilation has been demonstrated. By following simple guidelines, the clinician can initiate mechanical ventilation that provides an ideal ventilatory pattern.

Acidosis, Respiratory↗
PubMed2005

Intratracheal pulmonary ventilation improves gas exchange during laparoscopy in a pediatric lung injury model.

BACKGROUND/PURPOSE: This study was aimed at determining whether intraoperative intratracheal pulmonary ventilation (ITPV) could prevent/treat respiratory complications of laparoscopy in a model of pediatric pulmonary insufficiency. METHODS: Severe lung injury was induced in 0- to 2-month-old lambs (n = 5) by endotracheal saline lavage. Animals then underwent establishment of CO2 pneumoperitoneum. Intraperitoneal pressures were progressively raised from 0 to 15 mm Hg, at intervals of 5 mm Hg. At each interval, blood gas and hemodynamic data were recorded, 20 minutes after initiation of both conventional ventilation and pure ITPV. All ventilatory parameters were constant and identical on both modes of ventilation. RESULTS: On conventional ventilation, severe respiratory acidosis and hypoxemia ensued at intraperitoneal pressures of 5 mm Hg and 10 mm Hg or more, respectively. Compared with conventional ventilation, ITPV led to statistically significant decreases in PCO2 at intraperitoneal pressures of 5 mm Hg (43.2 +/- 5.2 vs 56.1 +/- 6.6 mm Hg) and 10 mm Hg (45.1 +/- 3.2 vs 61 +/- 6.3 mm Hg) and to significant increases in PO2 at 10 mm Hg (92 +/- 10.2 vs 61 +/- 8.1 mm Hg), resolving the acidosis and hypoxemia at those pressure levels. CONCLUSIONS: Compared with conventional ventilation, ITPV improves both CO2 removal and oxygenation during CO2 pneumoperitoneum in a pediatric lung injury model. Intratracheal pulmonary ventilation may be a safer intraoperative mode of ventilation for neonates and children with respiratory failure who require laparoscopy.

Acidosis, Respiratory↗
PubMed1993

The effect of hypoxia and acidosis on propranolol clearance in the isolated perfused rat liver preparation.

The effect of hypoxia and acidosis on the elimination of an oxidatively metabolized drug, S-propranolol, was examined in the single-pass isolated perfused rat liver (IPRL). The experiments (N = 6) consisted of four consecutive 30 min phases: normal pH (pH 7.4)/normal oxygen delivery, normal pH/hypoxia, hypercapnic acidosis (pH 7.1)/normal oxygenation and hypercapnic acidosis/hypoxia. Hypoxia and acidosis were produced by equilibrating the perfusate with appropriate mixtures of O2, N2 and CO2. With normal oxygen delivery there was no difference in hepatic clearance of propranolol between normal pH and acidosis (9.65 +/- 0.34 and 9.78 +/- 0.11 mL/min, respectively. P < 0.05). During hypoxia, propranolol clearance was impaired to a similar extent under both pH conditions (7.41 +/- 0.97 and 8.06 +/- 0.81 mL/min, respectively, P > 0.05). Therefore, respiratory acidosis does not affect the clearance of propranolol by the IPRL, nor does it influence the sensitivity of propranolol clearance to hypoxia. Neither acidosis nor hypoxia resulted in a significant reduction in bile flow compared with the normal pH/normal oxygen phase and there was no correlation between bile flow and perfusate bicarbonate concentration (P > 0.05).

Acidosis, Respiratory↗
PubMed1979

Pre-ejection period of cardiac cycles in fetal lamb.

The pre-ejection period (PEP) of the fetal cardiac cycle was studied on 22 chronically instrumented pregnant ewes. The PEP was measured from the onset of the Q wave on fetal electrocardiogram to the onset of the upstroke on the fetal arterial blood pressure curve. Lengthening of the PEP was observed in association with an increase in gestational age, fetal body weight, fetal brow-rump length, and fetal heart weight. Consequently, the PEP values were calculated to those at fetal heart weight of 10 grams. The PEPc (calculated) was prolonged by acidosis but no significant relationship was found between the PEPc and arterial blood pO2. An increase in coronary blood flow was associated with a shortening of the PEPc in the fetuses under normal physiologic conditions. Fetal hypoxemia and respiratory acidosis created by administration of 10 per cent O2 and 20 per cent CO2 with 20 per cent O2 to the mother increased fetal coronary flow and was in general associated with a prolonged pre-ejection period.

Acidosis, Respiratory↗
PubMed1996

[Acidosis in severe acute asthma].

On admission to intensive care units, the acid-base profile in acute severe asthma appears to be more diverse than previously. Especially a mixed or less frequently metabolic acidosis is eventually observed, which is not always caused by elevated lactate. On the other hand, hyperlactatemia is actually rather common, not necessarily accompanied by acidosis. This finding is as a rule related to massive doses of beta 2 adrenergic agents given parenterally: subsequent elevated lactate is in no way a marker of cellular hypoxia and has no pejorative meaning in this event. Hypercapnia with severe respiratory acidosis implies less and less mechanical ventilation; however, when mandatory, it has to be carried out using permissive hypercapnia, giving more favorable outcome while lowering side-effects.

Acidosis↗
PubMed2004

Hypercapnia: what is the limit in paediatric patients? A case of near-fatal asthma successfully treated by multipharmacological approach.

We describe a case of prolonged severe hypercapnia with respiratory acidosis occurring during an episode of near-fatal asthma in an 8-year-old boy, followed by complete recovery. After admission to the intensive care unit, despite treatment with maximal conventional bronchodilatative therapy, the clinical picture deteriorated with evident signs of respiratory muscle fatigue. The child was sedated, intubated and mechanically ventilated. Magnesium sulphate, ketamine and sevoflurane were gradually introduced together with deep sedation, curarization and continuous bronchodilatative therapy. Ten hours after admission, arterial pCO2 reached 39 kPa (293 mmHg), pH was 6.77 and pO2 8.6 kPa (65 mmHg). Chest radiograph showed severe neck subcutaneous emphysema, with signs of mediastinal emphysema. No episode of haemodynamic instability was seen despite severe prolonged hypercapnia lasting more than 14 h. Oxygenation was maintained and successful recovery followed without neurological or cardiovascular sequelae. This case shows the cardiovascular and neurological tolerance of a prolonged period of supercarbia in a paediatric patient. The most important lesson to be learned is the extreme importance of maintaining adequate tissue perfusion and oxygenation during an asthma attack. The second lesson is that when conventional bronchodilators fail, the intensivist may resort to the use of drugs such as ketamine, magnesium sulphate and inhalation anaesthesia. In this context deep sedation and curarization are important not only to improve oxygenation, but also to reduce cerebral metabolic requirements.

Acidosis, Respiratory↗
PubMed1977

[Influence of ventilatory pattern on the functional situation of the lung during inhalation anaesthesia. Part I: Spontaneous breathing versus IPPB (author's transl)].

After five hours breathing spontaneously enflurane, halothane and methoxyflurane only the rabbits under enflurane showed, apart from a mild respiratory acidosis, no deterioration of pulmonary functional situation. Halothane and methoxyflurane exhibited under the same conditions a significant worsening of elastic behaviour of the lung. The structural bases of the mechanical impairment were atelectasis, dystelectasis and interstitial edema. Postnarcotic examination of lung extracts in the wilhelmy balance showed no abnormalities in the spontaneously breathing animals. If one compares these findings, indicating an irritation of surfactant by halothane and methoxyflurane with the results after IPPB the conclusion can be made that under these circumstances IPPB represents an additional stress for the alveolar lining layer. From the theoretical point of view therefore it would be advisable in patients with surfactant deficiencies to avoid the combination of halothane or methoxyflurane with IPPB. The use of PEEP will be discussed in part II. The value of periodical sighs could not be established under our conditions. Longer periods of spontaneous breathing seem only advisable under halothane but not under enflurane or methoxyflurane because their respiratory depressant properties.

Acidosis, Respiratory↗
PubMed2001

Acid-base imbalance and the skeleton.

Humans generally consume a diet that generates metabolic acids leading to a reduction in the concentration of systemic bicarbonate and a fall in pH. In vitro experiments indicate that this metabolic acidosis causes a release of calcium from bone that initially is simply due to physicochemical dissolution of the mineral. On a more chronic basis metabolic acidosis alters bone cell function; there is an increase in osteoclastic bone resorption and a decrease in osteoblastic bone formation. Concomitant with the dissolution and resorption of the bone mineral there is buffering of the addition protons by bone leading to restoration of the systemic pH. Interestingly respiratory acidosis, caused by an increase in the partial pressure of carbon dioxide induces far less bone dissolution and resorption and the additional hydrogen ions are not buffered by bone. As we age we are less able to excrete these metabolic acids due to the normal decline in renal function. We hypothesize that a slight, but significant, metabolic acidosis leads to greater loss of bone mineral and increase potential to fracture.

Acid-Base Imbalance↗
PubMed1991

Ionized calcium in blood: studies on patients with pulmonary disease.

A new automatic ionized calcium analyser ICA 2 (Radiometer, Copenhagen, Denmark) was used for studies of ionized calcium (cCa2+) in the arterial blood of patients with a compensated respiratory acidosis due to chronic lung disease. The data for 16 patients showed an unexpectedly high level of variation in cCa2+ (range, 1.01-1.25 mmol l-1) despite the fact that there was only a small degree of variability in pH (range, 7.38-7.51). cCa2+ was not correlated with pH as has been observed in acute respiratory disturbances. A highly significant negative correlation was found between cCa2+ and base excess (BE) (r = -0.81, P less than 0.0001), and between cCa2+ and carbon dioxide tension (PCO2) (r = 0.71, P less than 0.002). These correlations differed from those reported previously in acute respiratory disturbances. CCa2+ showed a significant positive correlation with oxygen tension (PO2) (r = 0.71, P less than 0.002). It is concluded that cCa2+ in arterial blood from patients with chronic lung disease is correlated with acid-base and gas quantities in an entirely different manner to that observed in acute acid-base disturbances in normal adults.

Acidosis, Respiratory↗
PubMed1995

Maternal and fetal effects of laparoscopic insufflation in the gravid baboon.

STUDY OBJECTIVE: To test the hypothesis that intraabdominal pressures (IAP) associated with abdominal insufflation for laparoscopic procedures can alter pulmonary and hemodynamic values in the pregnant baboon and hemodynamic values in the fetus. DESIGN: A descriptive physiologic study. SETTING: Animal research facility at Scott and White Memorial Hospital, Temple, TX. PARTICIPANTS: Four pregnant baboons at 120 +/- 7 days' gestation. INTERVENTIONS: The baboons underwent general anesthesia, Swan-Ganz and arterial catheter placement, and abdominal insufflation at 10 and 20 mm Hg IAP for 20-minute intervals at each pressure. The following end points were measured: maternal heart rate (MHR), mean arterial pressure (MAP), cardiac output (CO), pulmonary capillary wedge pressure (PCWP), pulmonary artery pressures (PAP), central venous pressure (CVP), systemic vascular resistance (SVR), ventilator rate (VR), oxygen saturation, and end-tidal carbon dioxide (CO2). Fetal heart rate and fetal growth values were measured, and umbilical artery Doppler flow studies were performed. MEASUREMENTS AND MAIN RESULTS: The PCWP (p <0.026), CVP (p <0.0012), and PAP (p <0.046) were significantly increased at 20 mm Hg IAP; CO decreased as IP increased. The MAP, MHR, and SVR did not change significantly with increased IAP. The only significant change in pulmonary values was the increase in peak airway pressure (p <0.001). The VR was increased from an average of 18 to 41 breaths/minute in an attempt to maintain adequate oxygen saturation and to normalize end-tidal CO2 when IAP was increased to 20 mm Hg. Respiratory acidosis (pH <7. 35, partial pressure of carbon dioxide >50 torr) was demonstrated in three of four animals within 20 minutes at an IAP of 20 mm Hg. Results of Doppler flow studies on the effects of the fetuses were unaltered immediately after this procedure compared with baseline measurements. Normal interval growth was demonstrated 2 weeks after the procedure. CONCLUSION: The baboon mothers and fetuses had no adverse effects at an IAP of 10 mm Hg, but may have significant cardiovascular and respiratory alterations associated with IAP of 20 mm Hg.

Acidosis, Respiratory↗
PubMed1983

Correlation of the one-minute Apgar score and the pH value of umbilical arterial blood.

The one-minute Apgar score, proven useful for rapid assessment of the neonate, is often poorly correlated with other indicators of intrauterine well-being. Fetal asphyxia is directly associated with neonatal acidosis. A low Apgar score in the face of normal pH and base deficit does not, therefore, indicate an asphyxiated infant. We performed a study at Vanderbilt University Hospital to ascertain the feasibility of combining the pH value of umbilical arterial blood with the one-minute Apgar score for neonatal assessment. The pH values and Apgar scores were obtained on 172 singleton neonates. When the Apgar score was less than 7, over one half (56%) of the neonates had a normal pH value. Of this group 46% had undergone intubation and nasopharyngeal suctioning, procedures known to be associated with lowered Apgar scores. We recommend, therefore, that neonates with a one-minute Apgar score of less than 7 be further evaluated with umbilical arterial blood gas studies to ascertain the presence of acidosis and to differentiate between metabolic and respiratory acidosis. More precise confirmation of the diagnosis of fetal distress and neonatal asphyxia, for both treatment and medicolegal purposes, is possible with this information.

Apgar Score↗
PubMed1995

Effects of hypoxia and hypercapnia on whole body release and clearance of choline.

We have recently demonstrated an increase in arterial blood choline (Ch) concentration in normocapnic hypoxia and apnea. This could be due to enhanced release of free Ch from tissues, to decreased Ch clearance, or both. The present investigations was undertaken to determine the individual contributions of these processes to the whole body balance of Ch, using an intravenous infusion of tracer quantities of [2H4]Ch to assess the bidirectional flux between the central pool and peripheral pools. Rats were subjected to normocapnic hypoxia or hypercapnia; release and clearance of Ch were calculated using a simple model. Hypoxia caused an increase in Ch production and a decrease in Ch clearance. At severe levels of hypoxia, Ch clearance was essentially zero. Hypoxia was attended by progressive acidosis that was related to the magnitude of the hypoxic challenge. To determine the possible effects of acidosis per se on the variables measured, respiratory acidosis with normoxia was provoked by controlled administration of CO2. Under these conditions, parallel decreases in Ch production and Ch clearance were observed.

Acidosis↗
PubMed1982

Immediate adaptation of the dog kidney to acute hypercapnia.

Studies were performed to determine whether ammoniagenesis could adapt instantaneously to acidosis in the dog kidney. Following acute respiratory acidosis, renal glutamine extraction rose acutely in dogs with stable renal blood flow but did not change when the renal blood flow fell by more than 25%. Acute hypercapnia immediately increased renal ammonia production in both groups of dogs. The rate of both glutamine extraction and ammonia production in acutely hypercapnic dogs without hemodynamic changes was comparable to the rates observed in dogs with chronic metabolic acidosis. Furthermore, the renal metabolite profile observed in acute hypercapnia was similar to the pattern described in chronic metabolic acidosis, i.e., a marked fall in renal glutamate and alpha-ketoglutarate concentrations and a fivefold increase in malate and oxaloacetate concentrations. In the liver and muscle, acute hypercapnia induced no significant change in glutamine concentration but glutamate and alpha-ketoglutarate concentrations decreased. Our findings demonstrate that the dog kidney can adapt immediately to acidosis but that hemodynamic change may mask this adaptation.

Acute Disease↗