ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

An animal model and experimental protocol were developed to elucidate the pathogenesis of coma and convulsions observed during artificial hyperventilation of patients with chronic hypercarbia. Compensated hypercarbia was simulated by sustained elevation of PaCO2to 80 torr and normalization of pHa by bicarbonate given i.v. Arterial [HCO3-] eqilibrated with CSF [HCO3-] within about 2 hrs CBF, CMRO2, CMRL, CSFpH and lactate concentration and other variables were determined at PaCO240 and 20 torr, before and after bicarbonate loading. Rapid normalization of PaCO2in compensated hypercarbia resulted in CSF alkalosis (CSFpH 7.52), cerebral hypoxia (CBF 50 percent of control) and evidence of cerebral hypoxia (increased cerebral lactate production, cerebral venous Po2of about 20 torr, abnormal EEG with convulsive patterns) without a significant change in CMRO2. CSF alkalosis and cerebral hypoxia were augmented by further reduction in PaCO2to 20 torr. Under light halothane anesthesia CBF was higher, CMRO2was the same and cerebral lactate production was greater than in awake dogs with comparable PaCO2.The results indicate that CNS failure during rapid normalization of PaCO2in compensated hypercarbia is due to cerebral hypoxia, which is caused by cerebral vasoconstriction from CSF alkalosis and a shift of the hemoglobin oxygen dissociation curve to the left from alkalemia; both effects result in impaired oxygen delivery to brain cells. Thus, to avoid these dangerous effects in patients with chronic hypercarbia and acute decompensation, oxygenation should be prompt, but PaCO2should be corrected gradually to avoid alkalemia; base excess, hypochloremia and hypokalemia also should be corrected.

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Oxygen delivery to the tissues, studied as oxygen availability, does not take account of the changes in oxyhemoglobin dissociation. Oxygen at a tension of less than 20 torr is considered relatively unavailable. This paper presents a clinical methodology for the analysis of oxyhemoglobin dissociation so that oxygen avail-ability can be mathematically modified by subtracting the calculated mixed venous content at a tension of 20 torr (consumable oxygen). Similar modification of the arterial oxygen content and oxygen utilization coefficient give more realistic indices of oxygen delivery. Examples are given to show how the use of these indices give a better understanding and quantification of the effects of changes in oxyhemoglobin dissociation characteristics on oxygen transport. The conventional estimations of oxygen avail-ability, arterial oxygen content and utilization coefficient do not change with shifts of the dissociation curve. A rightward shift of the curve gives a higher consumable oxygen, consumable arterial oxygen content, and a lower consumable oxygen coefficient, reflecting that more oxygen is available to the tissues before significant anaerobic metabolism is initiated.

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

A forceful blow to the precordium has long been recommended as the first resuscitative measure following cardiac arrest. It has been shown sometimes to cause slowing of ventricular tachycardia. However, reports maintaining that cardiac standstill responded to chest thumping failed to establish the cardiocirculatory conditions at the time of treatment. This study evaluated the maneuver in resuscitating asphyxiated dogs with cardiac standstill, ventricular fibrillation, severe hypotension clinically resembling cardiac arrest, and post-resuscitation tachyarrhythmias.In animals with ventricular tachycardia, precordial thumping caused ventricular fibrillation as often as reversion to sinus rhythm. Used during severe hypotension it had no effect; nor did it precipitate cardiac asystole, ventricular fibrillation or ventricular tachycardia. No animal with cardiac standstill or ventricular fibrillation was benefited by thumping while artificial ventilation, external cardiac massage, intravenous epinephrine and external countershock restored 14 of 15 animals.It would appear that precordial thumping should be utilized in the management of ventricular tachycardia only when equipment for external defibrillation is immediately available. The measure should be deleted from the recommended treatment of cardiac arrest.

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Shock following acute myocardial infarction is closely related to the volume of damaged myocardium. For this reason, the main therapeutic effort should be directed towards improvement of myocardial oxygenation rather than improvement of cardiac performance. Hemodynamics and cardiac energetics were studied in 25 patients in myocardial infarction shock. Hemodynamic abnormalities associated with shock were emphasized when compared to data from 40 patients with acute myocardial infarction but not in shock.Isoproterenol increased cardiac index an average of 0.87 1/min/M2and heart rate by 20 beats/min; coronary blood flow rose an average of 12 ml/100g/min in face of decreased diastolic aortic (coronary perfusion) pressure; rate of myocardial lactate production increased. L-norepinephrine increased mean aortic pressure and coronary blood flow an average of 21 mm Hg and 27 ml/100g/min; mean myocardial oxygen consumption rose 2.24 ml/100g/min; myocardial lactate production shifted to extraction (mean, 12%); myocardial oxygen extraction remained abnormally high (mean, 73%); cardiac index did not change. Intra-aortic counterpulsation in-creased mean aortic pressure and coronary blood flow an average of 14 mm Hg and 23 ml/100g/ min; myocardial oxygen consumption remained essentially unchanged; both myocardial lactate and oxygen extraction improved toward normal values (15% and 61%); cardiac index in-creased an average of 0.48 1/min/M2.Isoproterenol appears to be harmful in myocardial infarction shock in that it increased myocardial oxygen demand more than oxygen supply. L-norepinephrine seems to be the vasoactive agent of choice in the initial treatment of shock because it improved myocardial perfusion and metabolism but not cardiac index. Intra-aortic counterpulsation improved both coronary and peripheral circulation and the myocardial metabolism changed towards normal. Mortality remained unchanged during the three different therapeutic interventions; emphasizing the importance of early recognition of the pre-shock state and of further aggressive diagnositc and therapeutic measures.

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Small residual-volume, small-contact area, high-pressure cuffs and disk “cuffs” are to be condemned. Large-volume, large-contact area, low-pressure cuffs are recommended as intracuff pressures equal tracheal mucosa pressures and airway pressures during positive pressure inflation. Tracheal mucosa pressure can be kept at 15 torr during exhalation to prevent aspiration without mucosal ischemia. The sponge cuff may fail to provide no-leak ventilation and protection against aspiration when used open. However, if a large enough sponge cuff is chosen and the pilot tube is clamped, it performs as a safe, low-pressure cuff. The McGinnis balloon effectively limits tracheal mucosa pressure to 25 torr despite accidental overinflation. With proper use of currently available large cuffs, serious cuff-induced tracheal wall damage should be totally preventable.

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:1973

数据来源: OVID