Experimental cerebral venous oxygen tension under very high intracranial pressure

Summary The cerebral circulation in rabbits was monitored by continuous recording of the cerebral venous oxygen tension (Pcvo₂). The intracranial pressure was raised by applying hydrostatic pressure through a catheter introduced into the lumbar subarachnoid space. In the experiments reported here, very high pressures, generally 140 mmHg, were investigated. It was found that in most cases the experimental animals could maintain their cerebral circulation reasonably well for some time, even with such high pressures, and that their tolerance could be raised by infusion of vasopressors. Periodic breathing and oscillations in blood pressure seemed to indicate that the animal had reached its limit of tolerance. When the application of high intracranial pressure was stopped, the Pcvo₂ often rose higher than before the application of pressure; considering the report ofHäggendal, Löfgren, Nilsson, andZwetnow (1966) this presumably indicated cerebral hyperaemia.

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Zusammenfassung Die zerebrale Zirkulation bei Kaninchen wurde durch fortlaufende Registrierung des zerebro-venösen Sauerstoffdruckes gemessen. Der intrakranielle Druck wurde auf hydrostatische Weise durch einen in den lumbalen Subarachnoidalraum eingeführten Katheter erhöht. In den hier dargestellten Versuchen wurden sehr hohe Drucke, im allgemeinen um 140 mmHg, untersucht. Dabei wurde festgestellt, daß die meisten Versuchstiere selbst bei so hohen Drucken ihre Hirndurchblutung für einige Zeit verhältnismäßig gut aufrecht erhalten konnten und daß die Toleranz durch Infusion vasopressorisch wirkender Pharmaka verbessert werden konnte. Periodische Atmung und Schwankungen des Blutdruckes schienen anzuzeigen, daß das Tier die Grenze seiner Toleranzfähigkeit erreicht hatte. Wenn die intrakranielle Drucksteigerung beendet wurde, stieg der Sauerstoffdruck in den zerebralen Venen oft höher als vor Beginn der Drucksteigerung; unter Berücksichtigung der Arbeit vonHäggendal, Löfgren, Nilsson undZwetnow (1966) spricht dieses wahrscheinlich für eine zerebrale Hyperämie.

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Resumen Se midió la circulación cerebral en conejos mediante registros continuos de la tensión de oxígeno venoso del cerebro. La presión intracraneal se elevó de forma hidrostática mediante la introducción de un cateter en el espacio subaracnoideo lumbar. En las pruebas aquí expuestas se probaron presiones muy elevadas, en general de 140 mm de Hg. Se demostró que la mayor parte de los animales prueba, aun en caso de presiones elevadas, podian mantener bien su circulación cerebral durante un cierto tiempo y que la tolerancia podia mejorarse con la infusión de fármacos de acción vasopresiva. La respiración periodica y las oscilaciones de la presión sanguinea parecen indicar el límite de su capacidad de tolerancia. Cuando se concluyó con el aumento de la presión intracraneal, la presión de oxígeno de las venas cerebrales se elevó con frecuencia mas intensamente que al comienzo del aumento de la presión; bajo consideracíon a los trabajos deHäggendal, Löfgren, Nilsson y Zwetnow (1966) esto habla con gran probabilidad en favor de una hiperemia cerebral.

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Résumé La circulation cérébrale chez les lapins fut contrôlée par un enregistrement continu de la tension de l'oxygène dans les veines cérébrales (PcvO₂). La tension intracranienne fut augmentée en appliquant une pression hydro-statique au moyen d'un cathéter introduit dans l'espace sous-arachnoidien. Dans les expériences rapportées des tensions très hautes, en général 140 mmHg, ont été réalisées. Dans la plupart des cas les animaux d'expérience pouvaient maintenir leur circulation cérébrale relativement bien pendant quelque temps, même avec une si haute pression et leur tolérance pouvait être élevée par la perfusion de «vasopresseurs». La respiration périodique et les oscillations de la pression sanguine semblaient indiquer que l'animal avait atteint sa limite de tolérance. Quand l'hypertension intracranienne fut supprimée le PcvO₂ montait souvent plus haut qu'avant. D'après l'étude deHäggendal, Löfgren, Nilsson etZwetnow (1966), ceci indique vraisemblablement une hyperémie·cérébrale.

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Riassunto Si osservò sistematicamente la circolazione cerebrale nei conigli con continue rilevazioni della tensione di ossigeno nel sangue venoso cerebrale (Pcvo₂). La pressione cerebrale fu aumentata, applicando una pressione idrostatica mediante l'introduzione di un catetere nello spazio subaracnoideo lombare. La pressione applicata era di 140 mmHg. Si osservò nella maggior parte dei casi che la circolazione cerebrale si mantenne bene per un certo tempo in limiti normali, malgrado l'alta pressione, e che la tollerabilità si poteva accrescere con l'infusione di un vasocostrittore. Disturbi respiratori periodici ed oscillazioni della pressione sanguigna dettero il segno che l'animale aveva raggiunto il limite di tolleranza. Con la sospensione della pressione endocranica il Pcvo₂ sali spesso ad un livello superiore a quello precedente all'applicazione; tenuto conto di quanto riferito daHäggendal, Löfgren, Nilsson eZwetnow (1966) ciò è probabilmente segno di iperemia cerebrale.

     

Arterial and transcutaneous oxygen tension measurement during hypotensive anaesthesia.

The values of oxygen tension (PO2) as measured by transcutaneous (at two different sites) and invasive methods were compared during hypotensive anaesthesia with sodium nitroprusside (SNP) in 15 patients. Generally the PO2 significantly decreased during and increased after SNP-induced hypotensive anaesthesia (p less than 0.001). A positive correlation was found between the ratios of change of invasive arterial oxygen tension (PaO2) and supraclavicular transcutaneous oxygen tension (tcPO2) both during (r = 0.64) and after (r = 0.83) hypotension. A similar correlation existed between the ratios of change of PaO2 and forearm tcPO2 only after (r = 0.66) but not during (r =0.33) hypotensive anaesthesia. It is concluded that any of the above methods can be used to give an assessment of PO2 changes during SNP-induced hypotension provided the prehypotensive value is measured. For quantitative measurement of PO2 the invasive method is the first choice. Supraclavicular tcPO2, however, can give an accurate result, while the forearm tcPO2 is the least sensitive.     

Arterial/alveolar oxygen tension ratio: a critical appraisal

A critical analysis of the arterial/alveolar oxygen tension ratio (a/APO2) is presented by rearranging the terms of the pulmonary shunt equation. The influence of the shunt and inspired oxygen concentration on a/APO2 are illustrated. It is shown that, despite reports to the contrary, a/APO2 varies with F1O2, particularly at high shunt levels.     

Arterial and respiratory influences on intracranial pressure in infancy.

Ventricular and subdural pressures have been monitored in 23 infants. Pressure waves which were influenced by respiratory and cardiac activity were noted. These were rather long lasting and were influenced more by respiration than by cardiac activity, when the intracranial pressure is low. Respiration and arterial pressure have similar effects when the intracranial pressure is normal, but when the intracanial pressure is increased the effects of respiratory activity are diminished.     

Arterial oxygen partial pressure and cardiovascular surgery in elderly patients

Arterial blood gas assessment is still routinely performed in candidates for a cardiovascular surgery. Whether sampling arterial blood is useful in an elderly patient with a near normal lung function and who meets all other criteria for operability, is unknown. Therefore, it was our purpose to provide reference values for arterial blood gases in these patients and to examine how the level of arterial oxygen partial pressure (PaO(2)) might influence postoperative outcome. We retrospectively studied arterial blood gases in 201 patients, aged 70-92 years with normal or near normal ventilatory function awaiting a planned cardiovascular surgery. PaO(2) averaged 81.6+/-7.6 mmHg and PaCO(2) averaged 37.7+/-3.2 mmHg. Both were independent of age. Factors associated with mortality according to bivariate analysis were: gender (female), type of surgery (valve replacement), and a low PaO(2) with strictly no ventilatory abnormality. In conclusion, PaO(2) values in elderly patients with cardiac disease and normal ventilatory function are greater than those obtained by extrapolation from healthy younger subjects. PaO(2) measurement should be recommended prior to cardiovascular surgery in elderly patients since a low PaO(2) with strictly normal ventilatory function is significantly associated with an increased risk for postoperative mortality.     

Internal pressure and oxygen tension of bone tumors and tumorous conditions

Summary Internal pressure and oxygen tension were measured in 24 patients with bone tumors and tumorous conditions. High internal pressures were observed in most of the rapidly growing lesions. The internal pressures of slowly growing and non-growing lesions were not different from those of normal bone marrow. Oxygen tension was commonly higher in the rapidly growing lesions than in simulataneously obtained peripheral venous samples from the same patients. The oxygen tension of the fluid from simple bone cysts was lower than that in venous samples from the same patients. There is a good correlation between internal pressure and the growth rate of the bone lesions in this study. It is suggested that internal pressure and oxygen tension of the lesions demonstrated the degree of blood supply to the bone tumors and tumorous conditions.     

Internal pressure and oxygen tension of bone tumors and tumorous conditions

Internal pressure and oxygen tension were measured in 24 patients with bone tumors and tumorous conditions. High internal pressures were observed in most of the rapidly growing lesions. The internal pressures of slowly growing and non-growing lesions were not different from those of normal bone marrow. Oxygen tension was commonly higher in the rapidly growing lesions than in simultaneously obtained peripheral venous samples from the same patients. The oxygen tension of the fluid from simple bone cysts was lower than that in venous samples from the same patients. There is a good correlation between internal pressure and the growth rate of the bone lesions in this study. It is suggested that internal pressure and oxygen tension of the lesions demonstrated the degree of blood supply to the bone tumors and tumorous conditions.     

Arterial oxygen content regulates plasma erythropoietin independent of arterial oxygen tension: a blinded crossover study

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Arterial oxygen tension increase 2-3 h after hyperbaric oxygen therapy: a prospective observational study

BACKGROUND: Inhalation of hyperbaric oxygen (HBO) has been reported to decrease arterial oxygen tension (PaO(2)) in the early period after exposure. The current investigation aimed at evaluating whether and to what extent arterial blood gases were affected in mechanically ventilated intensive care patients within 6 h after HBO treatment. METHODS: Arterial blood gases were measured in 11 ventilated subjects [nine males, two females, synchronized intermittent mandatory ventilation (SIMV) mode] undergoing HBO therapy for necrotizing soft tissue infection (seven patients), burn injury (two patients), crush injury (one patient) and major abdominal surgery (one patient). Blood gases were obtained with the patients in the supine position under continuous analgesia and sedation before the hyperbaric session (baseline), during isopression, after decompression, after each transport, and 1, 2, 3 and 6 h after exposure. Heart rates and blood pressures were recorded. Intensive care unit (ICU) ventilator settings remained unchanged. Transport and chamber ventilator settings were adjusted to baseline with maintenance of tidal volumes and positive end-expiratory pressure (PEEP) levels. The hyperbaric protocol consisted of 222.9 kPa (2.2 absolute atmospheres) and a 50-min isopression phase. The paired Wilcoxon's test was used. RESULTS: Major findings (median values, 25%/75% quartiles) as per cent change of baseline: PaO(2) values decreased by 19.7% (7.0/31.7, P < 0.01) after 1 h and were elevated over baseline by 9.3% (1.5/13.7, P < 0.05) after 3 h. SaO(2), alveolar-arterial oxygen tension difference and PaO(2)/FiO(2) ratio behaved concomitantly. Acid-base status and carbon dioxide tension were unaffected. CONCLUSION: Arterial oxygen tension declines transiently after HBO and subsequently improves over baseline in intensive care patients on volume-controlled mechanical ventilation. The effectiveness of other ventilation modes or a standardized recruitment manoeuvre has yet to be evaluated.     

Effect of hyperventilation on brain tissue oxygen pressure, carbon dioxide pressure, pH value and intracranial pressure during intracranial hypertension in pigs

ＨＤｅｐａｒｔｍｅｎｔｏｆＮｅｕｒｏｓｕｒｇｅｒｙ ,ＣｈａｎｇｚｈｅｎｇＨｏｓｐｉｔａｌ,ＳｅｃｏｎｄＭｉｌｉｔａｒｙＭｅｄｉｃａｌＵｎｉｖｅｒｓｉｔｙ ,Ｓｈａｎｇｈａｉ 2 0 0 0 0 3,Ｃｈｉｎａ (ＢａｏＹＨ ,ＪｉａｎｇＪＹ ,ＺｈｕＣ ,ＬｕＹＣ ,ＣａｉＲＪａｎｄＭａＣＹ)ｙｐｅｒｖｅｎｔｉｌａｔｉｏｎ (ＨＶ )ｈａｓｂｅｅｎｗｉｄｅｌｙｕｓｅｄｔｏｄｅｃｒｅａｓｅｔｈｅｉｎｔｒａｃｒａｎｉａｌｐｒｅｓｓｕｒｅ (ＩＣＰ)ｉｎｔｈｅｐａｔｉｅｎｔｓｗｉｔｈｓｅｖｅｒｅｔｒａｕｍａｔｉｃｂｒａｉｎｉｎｊｕｒｙ…     

Intra-osseous pressure and oxygen tension in avascular necrosis and osteoarthritis of the hip

The intra-osseous pressure, PO2, and PCO2 were measured in 32 hips (21 patients) which were painful but showed no severe degenerative changes. Pre-operative scintigraphy and radiography was performed in all patients. Thirteen hips showed early osteoarthritis, eight had early osteonecrosis, and 11 had no changes. Core biopsies were performed and the bone was examined histologically and graded for necrosis. Histologically, necrosis was present in 27 specimens. Scintigraphic findings did not correlate with the histological results but were more closely related to the radiographic findings. The intra-osseous pressure in hips with histological necrosis (mean 47 mmHg) was significantly higher than in hips without necrosis (mean 26 mmHg). The PO2 was lower in bone with histological necrosis (mean 44 mmHg) than in bone without (mean 71 mmHg). PO2 increased and intra-osseous pressure decreased after decompression. The results confirm that ischaemia plays a central role in the development of necrotic changes in bone. Histological necrosis was found in hips with radiographic signs of osteonecrosis and in those with osteoarthritis. Radiography, and scintigraphy are shown to be insensitive methods for differentiating between those disorders.     

Arterial hypertension increases intracranial pressure in cat after opening of the blood-brain barrier

BACKGROUND: Increased permeability for small solutes in brain capillaries means that a change in hydrostatic capillary pressure may influence transcapillary fluid exchange according to the Starling fluid equilibrium, and a high arterial pressure may cause transcapillary fluid filtration and raised intracranial pressure. This could be of clinical relevance in states of disrupted blood-brain barrier such as meningitis and after a severe head injury, especially since these patients quite often are spontaneously hypertensive, and hypertensive therapy is sometimes used to increase cerebral perfusion pressure. This study on cat investigated the long-term relation between arterial pressure and intracranial pressure in a state of disrupted blood-brain barrier. METHOD: Endotoxin was given intrathecally to open the blood-brain barrier and depress cerebral autoregulation. Arterial pressure was increased by about 30 mm Hg during 5 hours by dopamine and angiotensin II infusion. The immediate fall in intracranial pressure after normalization of blood pressure reflects the blood volume component of an intracranial pressure increase. RESULTS: Increased arterial pressure had no effect on intracranial pressure before endotoxin. Endotoxin infusion increased intracranial pressure from the normal value of 10 to 12 mm Hg. and at steady state by almost 10 mm Hg. Intracranial pressure increased further after the arterial pressure increase. At steady state (achieved within 5 hours), this increase was almost as great as the arterial pressure increase, and about 80% persisted when measured directly after normalization of the arterial pressure. CONCLUSION: Increased arterial pressure in a state of disrupted blood-brain barrier increases intracranial pressure, mainly because of brain edema. This stresses that arterial hypertension may be deleterious in conditions such as meningitis or after a brain trauma.