Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. We recorded phrenic nerve activities and single unit firing of mesencephalic neurones in unanaesthetized supracollicularly decerebrated, paralysed and ventilated cats, in which vagi and carotid sinus nerves had been ablated. We made these measurements first at low levels of respiratory drive associated with normal PCO2 levels, then with increased respiratory drive and levels of phrenic activity produced by hypercapnia or by carotid sinus nerve stimulation. 2. We found that at least a quarter of the neurones in the central tegmental field of the mesencephalon, which were irregularly tonic or silent at low respiratory drives, developed a rhythmic increase of firing associated with each respiration. There appeared to be a threshold at about 50% of maximum respiratory activity, below which the respiratory-associated rhythm did not occur. Above this level, neuronal firing increased in graded fashion with increasing magnitude of respiratory activity. The latency from onset of phrenic activity to onset of increased neuronal firing was quite long (1.0 s) at drives just above the threshold but shortened to as little as 0.3 s as drive increased towards its maximum. 3. Cutting the spinal cord at C1-C2 had no effect on the ability of increased respiratory activity to generate a respiratory-associated rhythm in mesencephalic neurones. 4. Short-lasting anaesthesia with the agent Saffan caused mesencephalic neurones to lose the respiratory-associated rhythm with little change in phrenic activity and no change in respiratory cycle timing. 5. We also found a mesencephalic response to ventilator-induced chest expansion. The latency of the response from onset of expansion, indexed by fall of airway PCO2, to onset of neurone firing was shorter (0.2 s) than that found with the respiratory-associated rhythm. In seventeen neurones we found both the respiratory-associated rhythm and the independent ventilator-associated rhythm. 6. We interpret our findings to show that the respiratory-associated rhythmic firing of midbrain neurones is not primarily involved in generation or modulation of the motor function of the respiratory oscillator. We believe, instead, that these neurones are part of a sensory pathway conveying information about the magnitude of central neural respiratory drive, as well as spinally transmitted information from receptors in the chest wall, to thalamus and cortex. We suggest that the sensation ultimately generated may be that of 'air hunger' or dyspnoea.
 ...
PMID:Respiratory-associated rhythmic firing of midbrain neurones in cats: relation to level of respiratory drive. 189 Jun 37

This retrospective study was undertaken to examine the management and outcome of children who developed isolated masseter muscle spasm (MMS) after the administration of intravenous succinylcholine during anesthetic induction. The inhalation anesthetics used for induction were continued in all of these cases. The medical records of 68 patients (male/female ratio, 1.7:1), identified from approximately 42,000 anesthetics given during the period 1980-1989, were reviewed. Fifty-seven children (2.3-12 yr old) were diagnosed as having isolated MMS, i.e., MMS without spasm of other muscles; 11 experienced generalized rigidity in combination with MMS. Anesthetic and postoperative management of these two groups differed. The overall incidence of MMS was 0.3% of inhalation anesthetics during which succinylcholine was given. Intraoperative arrhythmias occurred in 33% of the patients who developed isolated MMS and more frequently in older children. Most children experienced some degree of hypercarbia and/or metabolic acidosis, but the significance of these abnormalities in the spontaneously ventilating, fasting child is unknown. Serum creatine kinase levels when measured 18-24 h postoperatively were elevated in all but one child (n = 45). There was no long-term morbidity and no mortality. We conclude that failure of the masseter muscles to relax after succinylcholine is not uncommon in children. Based on our experience, and accepting that MMS may be part of the clinical spectrum of malignant hyperthermia, we believe that anesthesia can be continued safely in cases of isolated MMS when careful monitoring accompanies diagnostic evaluation. This differs from the current practice of discontinuing the anesthetic or switching to a nontriggering anesthetic technique.
 ...
PMID:Masseter muscle spasm in children: implications of continuing the triggering anesthetic. 186 39

Cerebral hemorrhagic insults are common in neonates. However, the consequences of intracranial blood on cerebral hemodynamics are poorly understood. We examined the effects of perivascular blood on cerebrovascular dilator responses in 29 piglets. Fresh, autologous blood (n = 15) or cerebrospinal fluid (n = 14) was placed under the dura mater over the parietal cortex, and the piglets were allowed to recover from anesthesia. One to four days later, a closed cranial window was placed over the parietal cortex and pial arteriolar responses to arterial hypercapnia (PaCO2 greater than 55 mm Hg), hemorrhagic hypotension (mean arterial blood pressure less than 35 mm Hg), or topical application of 10(-6) and 10(-4) M isoproterenol were determined. Pial arterioles in the cerebrospinal fluid group dilated 27 +/- 4% (mean +/- SEM) (n = 11) in response to hypercapnia, 26 +/- 5% (n = 9) in response to hypotension, and 26 +/- 3% in response to 10(-6) M and 40 +/- 4% in response to 10(-4) M isoproterenol (n = 11). In the group in which blood was placed on the parietal cortex, pial arterioles did not dilate significantly in response to hypercapnia (8 +/- 3%, n = 11) or hypotension (2 +/- 5%, n = 13) but dilated normally in response to isoproterenol (25 +/- 5% in response to 10(-6) M and 36 +/- 7% in response to 10(-4) M, n = 13). We conclude that prolonged contact of pial arterioles with extravascular blood selectively attenuates cerebrovascular dilation in piglets.
 ...
PMID:Selective attenuation by perivascular blood of prostanoid-dependent cerebrovascular dilation in piglets. 190 99

The effects of acute changes in arterial carbon dioxide and oxygen tension, produced by altering the inspired gas mixtures while maintaining constant-volume intermittent positive pressure ventilation, on global function, regional left ventricular function, and coronary hemodynamics were studied in eight sheep during halothane anesthesia. Hypercapnia (Paco2, 73.5 +/- 2.3 mm Hg, mean +/- SD) increased heart rate, stroke volume, and cardiac output but decreased systolic shortening in the base of the left ventricle. Hypocapnia (PaO2, 24 +/- 1.5 mm Hg) decreased cardiac output and coronary flow below levels seen with hypercapnia but not below levels seen with normocapnia. Systolic shortening decreased in both apical and basal regions, and left ventricular relaxation was impaired as evidenced by a reduction of the nadir of LV dP/dt. Hypoxemia (PaO2, 39 +/- 1.5 mm Hg) elicited a hyperdynamic response of the circulation, increased coronary blood flow, and exhausted the coronary flow reserve. Neither changes in PaCO2 nor changes in PaO2 caused postsystolic shortening, although hypercapnia caused nonuniformity of contraction in the left ventricle. Thus, marked alterations in oxygen and carbon dioxide tensions do not cause left ventricular dysfunction, even though moderate hypoxia reduces the coronary flow reserve.
 ...
PMID:Effects of altered PaO2 and PaCO2 on left ventricular function and coronary hemodynamics in sheep. 190 14

The effects of variation of arterial CO2 tension (PaCO2) on the electroencephalogram (EEG) and posterior tibial nerve somatosensory cortical evoked potentials (PTN-SCEP) during opioid/N2O anesthesia have not been well documented. We studied the effects of hypocapnia (PaCO2 approximately 23 mmHg) and hypercapnia (PaCO2 approximately 50 mmHg) during steady-state alfentanil/N2O anesthesia in 16 patients. EEG and PTN-SCEP were recorded continuously, while PaCO2 was altered in 15-min intervals by varying the inspired CO2 concentration. Hypocapnia caused significant increases in power in the delta, theta, and beta bands (P less than 0.01), with the greatest increase observed in the alpha band. Relative power increased in the alpha band but remained unchanged in the delta, theta, and beta bands. Median frequency and 95% spectral edge frequency were unaltered during hypocapnia. In contrast, hypercapnia caused a significant decrease of power in the alpha and beta bands, whereas delta and theta power remained unchanged. This was reflected in a significant decrease of the 95% spectral edge frequency, from 8.9 (6.7-11.6) to 7.0 (5.6-8.6) Hz. All EEG parameters returned to normal upon restoration of normocapnia. There was a significant negative correlation between power in the alpha band and end-tidal CO2 in all patients (r = 0.47 to -0.89). PTN-SCEP latencies and amplitudes were not significantly different from control values during hypocapnia and hypercapnia. It is concluded that variations in PaCO2 within the limits 20-50 mmHg produce substantial changes in the EEG power spectrum, especially in the alpha band (8-12 Hz), but do not alter PTN-SCEP.
 ...
PMID:Influence of changes in arterial carbon dioxide tension on the electroencephalogram and posterior tibial nerve somatosensory cortical evoked potentials during alfentanil/nitrous oxide anesthesia. 190 85

Haemodynamic responses to the apnoea test for the diagnosis of brain death were investigated in nine patients with severe head injury or cerebrovascular disease. To prove apnoea, the ventilator was disconnected for ten minutes and oxygen was insufflated to avoid hypoxaemia. No respiratory movement was seen in any patient. Ten minutes after disconnecting the ventilator, PaCO2 was increased to 78 +/- 3 mmHg and pH was reduced to 7.17 +/- 0.02. Adequate oxygenation was maintained in all patients. Cardiac output increased from 4.8 +/- 0.7 to 5.7 +/- 0.8 L.min-1 (P less than 0.05), and mean pulmonary artery pressure increased from 11 +/- 1 to 17 +/- 2 mmHg (P less than 0.01). However, mean arterial pressure, heart rate, pulmonary artery wedge pressure and right atrial pressure did not change. Plasma catecholamines were measured in three patients. Plasma norepinephrine concentrations increased in all three patients but the changes in plasma epinephrine were minimal. These circulatory responses to acute hypercapnia were less than those reported in awake volunteers and in patients during general anaesthesia. However, since plasma norepinephrine concentration increased during the test, some sympathoadrenal response, probably of spinal origin, was present, and may have prevented the direct depressant circulatory effects of acute hypercapnia. In conclusion, the apnoea test did not produce haemodynamic disturbances when respiratory acidosis was limited to a pH 7.17 +/- 0.02 and PaCO2 60-80 mmHg.
 ...
PMID:Haemodynamic changes during the apnoea test for diagnosis of brain death. 190 87

The efficacy of acupuncture and transcutaneous stimulation analgesia, supplemented by small doses of fentanyl (mean 1.2 micrograms/kg, SD 1.7) was compared with moderate-dose fentanyl anaesthesia (mean 22.9 micrograms/kg, SD 2.8) in 29 patients who underwent surgery for retroperitoneal lymph node dissection. The present study describes the anaesthetic techniques and comparison of haemodynamics, demand for analgesics after surgery, recovery and blood gases, restoration of urinary and bowel functions, convalescence in terms of self-reliance and the postoperative course in respect of fatigue and morbidity. A more rapid return of consciousness, an absence of hypercapnia and a smaller decrease in pH were observed in patients who received acupuncture and transcutaneous stimulation (p less than 0.05). No clinically relevant disadvantages attributable to the method were demonstrated.
Anaesthesia 1991 Feb
PMID:Acupuncture and transcutaneous stimulation analgesia in comparison with moderate-dose fentanyl anaesthesia in major surgery. Clinical efficacy and influence on recovery and morbidity. 188 9

The presence of persistent arrhythmias was correlated with hypercarbia (end-tidal CO2 greater than or equal to 55 mm Hg for greater than or equal to 60 s). A continuous strip chart recording of oxygen saturation, a capnogram, and an electrocardiogram were obtained from 402 children. No episodes of arrhythmia occurred in 153 patients younger than 2 yr compared with 24 patients 2 yr of age or older (P = 0.0001). Older patients whose airways were managed via a mask had a higher incidence (13.2% [21 of 159 patients]) than tracheally intubated patients (3.3% [3 of 90 patients]) (P = 0.01). In older patients whose tracheas were intubated, hypercarbia was associated with arrhythmia in 1 of 20 hypercarbia episodes. Seven of 16 patients with hypercarbia, whose airways were managed via a mask, had an arrhythmia (P = 0.0014); in eight, arrhythmias were associated with light anesthesia; in seven, arrhythmias were not associated with either hypercarbia or light anesthesia. Arrhythmias developed in 13 of 55 patients 2 yr old or older whose airways were managed via a mask and who were undergoing orchiopexy or herniorrhaphy as compared with 1 of 30 tracheally intubated patients (P = 0.016). There was a higher incidence of arrhythmias during halothane anesthesia compared with that during all other techniques (P = 0.035). The authors conclude that the incidence of arrhythmias is extremely low in infants younger than 2 yr. Hypercarbia is associated with arrhythmias in pediatric patients whose airways are managed via a mask but not in patients whose tracheas are intubated.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Persistent cardiac arrhythmias in pediatric patients: effects of age, expired carbon dioxide values, depth of anesthesia, and airway management. 195 67

Severe hypercarbia was documented by arterial blood gas analysis in 2 adult horses anesthetized for exploratory laparotomy. Both horses appeared to be adequately anesthetized, but continued to breathe against the ventilator. In both cases, the inspiratory valve on the anesthesia machine was found to be stuck open, permitting expired CO2 to return to the inspiratory limb of the anesthetic circuit and to be inhaled with the next breath. Correction of the malfunctioning valve alleviated the hypercarbia. Problems with the flow valves of the anesthesia machine should be suspected when anesthetized horses breathe against the ventilator and develop severe hypercarbia.
 ...
PMID:Severe hypercarbia resulting from inspiratory valve malfunction in two anesthetized horses. 199 68

The electroencephalographic (EEG) effects of a new inhaled anesthetic are of interest because of the potential of such agents to produce excitatory (convulsant) activity and because of the potential usefulness of the EEG as an indicator of anesthetic depth and cerebral activity. Accordingly, we examined the EEG in 12 healthy, young male volunteers during desflurane anesthesia. Each subject had a baseline recording and then steady-state exposure to 6, 9, and 12% (0.83, 1.24, and 1.66 MAC) desflurane in O2 alone, and to 3, 6, and 9% desflurane in O2 with 60% N2O. The sequence of doses and the presence of N2O were randomized. We used mechanical ventilation to maintain normocapnia at each dose level. We also tested the effects of hypercapnia secondary to spontaneous ventilation. Additionally, at 1.24 MAC, subjects' lungs were hyperventilated to a PCO2 of 25.8 +/- 0.7 mmHg and exposed to rhythmic, loud clapping to attempt to provoke excitatory phenomena. Finally, after at least 6 h exposure to desflurane, we repeated measurements at 0.83 and 1.66 MAC to assess possible tolerance. Four channels of EEG were monitored visually, and at each dose, a quantitative EEG analysis was performed. Desflurane produced EEG changes comparable to those observed with equipotent levels of isoflurane. No epileptiform activity was seen. Desflurane significantly suppressed EEG activity; prominent burst suppression was seen at 1.24 MAC and higher. Substitution of N2O for 0.42 MAC desflurane reduced the degree of EEG suppression relative to the equipotent administration of desflurane and O2. Quantitative EEG measures for the early doses and for the later, repeated exposures did not differ.
 ...
PMID:The electroencephalographic effects of desflurane in humans. 200 Oct 21


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>