Hyperventilation in the management of cerebral oedema

Sexual intercourse and cerebral aneurysmal rupture: potential mechanisms and precipitants

Aneurysmal subarachnoid hemorrhage (SAH) is a significant cause of death in young and middle-aged individuals and causes tremendous morbidity in affected patients. Despite the identification of various risk factors, the series of events leading to the formation, growth, and rupture of intracranial aneurysms is poorly understood. Cerebral aneurysm rupture has been associated with sexual intercourse and other forms of physical exercise. In fact, multiple case series reported that coitus was the immediate preceding activity in 3.8–14.5% of patients suffering from aneurysmal SAH. This may be related to the large elevations in mean arterial blood pressure that occur in both males and females during sexual intercourse (130–175 and 125–160 mm Hg, respectively). While coitus and physical exercise share important physiological similarities, each may differentially affect the probability that a preformed aneurysm will rupture. In this literature review and synthesis, the authors analyze the physiological human response to sexual intercourse in an effort to delineate those factors that may precipitate aneurysmal rupture. The authors' analysis is based on the original data collected by Masters and Johnson. To the authors' knowledge, this is the first review to address the link between sexual intercourse and intracranial aneurysmal rupture. While actual measurements of the physiological variables relevant to SAH were not performed in this article, the authors make reasonable assumptions based on the available data to help elucidate the mechanism of sexually induced aneurysmal rupture.

Hypocapnia does not alter hepatic blood flow or oxygen consumption in patients with head injury

OBJECTIVE

To evaluate the effects of hypocapnia on the systemic and hepatic circulations and oxygenation values in patients with head injury.

DESIGN

Open-label, prospective study.

SETTING

University hospital, department of anesthesiology and intensive care unit.

PATIENTS

Eleven mechanically ventilated patients with isolated head trauma and stable hemodynamic status.

INTERVENTIONS

At the beginning of the study, each patient presented with normocapnic ventilation. Mechanical hyperventilation was then adjusted to obtain stable hypocapnia over an interval of 24 hrs. Cardiac output and other systemic hemodynamic parameters were measured, using a pulmonary artery catheter. Hepatic parameters were measured via a catheter inserted into the hepatic vein. Total hepatic blood flow was determined by the Fick principle using a continuous infusion of indocyanine green. Arterial and hepatic venous blood gases were sampled to determine systemic and hepatic-splanchnic oxygenation. Measurements were done at the end of the four phases: a) 30 mins of normocapnia (N); b) 30 mins of hypocapnia (H0); c) 3 hrs of hypocapnia (H3); and d) 24 hrs of hypocapnia (H24). Intracranial pressure and cerebral perfusion pressure were hourly monitored throughout the study.

MEASUREMENTS AND MAIN RESULTS

There were no significant changes in systemic hemodynamic parameters. The hepatic blood flow index did not differ from normocapnia (N 1.8 +/- 0.4 L/min/m2) to hypocapnia (H0 1.6 +/- 0.3 L/min/m2; H3 1.7 +/- 0.4 L/min/m2; H24 1.7 +/- 0.4 L/min/m2). The ratio of hepatic blood flow index to cardiac index remained stable throughout the study. Hypocapnia did not affect hepatic-splanchnic oxygen delivery and consumption.

CONCLUSIONS

Hypocapnic hyperventilation does not alter hepatic hemodynamic parameters in patients with head injury. This result may be related to the lack of changes in cardiac output or in the hepatic vasoreactivity. Moreover, hypocapnia does not modify hepatic-splanchnic oxygenation. Thus, in case of intracranial hypertension, hypocapnia might be used without undesirable effect on the hepatic-splanchnic perfusion.

Acute post-traumatic respiratory physiology and insufficiency

This article reviews the physiologic mechanisms by which acute injury results in respiratory insufficiency. It delineates the need for oxygenation versus ventilatory support and provides a pragmatic approach to dealing with the proper early respiratory support of the victim of chest trauma as well as the rationale for various immediate treatment modalities. In addition, it discusses various assessment techniques and clinical clues that predict the onset of late respiratory complications in the patient with serious injuries.

Prehospital endotracheal intubation: rationale for training emergency medical personnel

Endotracheal intubation by emergency medical services (EMS) personnel in the prehospital setting decreases morbidity and helps to improve the outcome of critically ill patients, especially those with cardiac or respiratory arrest, multiple injuries, or severe head trauma. The endotracheal tube facilitates better oxygenation and ventilation because it enhances lung inflation and protects the lungs from aspiration. No other alternative modality is as efficacious. Compared to physicians in general, properly instructed, well-supervised paramedics can be trained to perform this procedure safely and more efficiently in the emergency setting. The use of the endotracheal tube in the prehospital setting should be strongly encouraged and the training of EMS personnel in this skill should be given high priority.