Successful management of venous air embolism with inotropic support.

PURPOSE: Since venous air embolism may occur during many different types of surgery, management of this clinical emergency can be required in patients who do not have a previously established central venous access for aspiration of air. Recent reviews suggest that management of right heart syndromes in patients with embolism is critical in improving outcome. CLINICAL FEATURES: Abrupt decreases in oxygen saturation (from 98% to 40%) and end-tidal carbon dioxide tension (from 24 to 6 mm Hg), compatible with venous air embolism were observed in a 73-yr-old woman during craniotomy for meningioma in the supine position. Since no access for aspiration of air was readily available, therapy was directed at inotropic support of the right heart using a bolus of ephedrine. Cardiorespiratory variables rapidly returned to normal, and the patient recovered from anesthesia and surgery without sequelae. CONCLUSIONS: Venous air embolism places an acute load on the right ventricle and may provoke right heart failure, even in the absence of total cardiovascular collapse. Treatment that supports right heart function may allow sufficient time for redistribution of embolized air and produce a good outcome when access for central aspiration of air is not available.

Anaesthetic management of a parturient with severe muscular dystrophy, lumbar lordosis and a difficult airway.

PURPOSE: This case describes the management of a 19-yr-old wheelchair bound primigravida with severe muscular dystrophy who presented for Caesarean section after spontaneous rupture of membranes. Anaesthesia was influenced by several features of her systemic disease which were impediments to both neuraxial and general anaesthesia. CLINICAL FEATURES: Other than for a prenatal record and the history obtainable from the patient, little additional medical information was available. Physical examination showed diffuse muscular weakness and an anatomically abnormal airway. Examination of the spine showed slight 10-15 degrees thoracolumbar scoliosis and > 45 degrees lumbar lordosis. Fetal assessment was normal. Echocardiography revealed mildly decreased left ventricular function and was consistent with pulmonary hypertension. After discussion with the patient and her obstetrician, elective Caesarean delivery was deemed the best management. Neuroaxial anaesthesia was at an increased risk of failure due to the profound lumbar lordosis. A plan for awake intubation and general anaesthesia was described to the patient in case regional anaesthesia could not be initiated. A fibreoptic bronchoscope and difficult intubation kit were made available. General anaesthesia was expected to have increased risk of postoperative pulmonary complications, hence epidural anaesthesia was attempted. After difficult catheter insertion, a sensory block was titrated to a T4 level. This was well tolerated by both mother and fetus. A healthy baby was delivered with Apgar scores of 9 and 9. Postoperatively the mother was transferred to the intensive care unit. After 72 hr, the patients respiratory status allowed transfer to the word. CONCLUSION: This case illustrates the use of epidural anaesthesia in the successful management of a severely compromised patient with limb-girdle muscular dystrophy undergoing elective Caesarean section.

Maternal halothane anesthesis reduces cerebral blood flow in the acidotic sheep fetus.

Cerebrovascular autoregulation is lost during fetal asphyxia as cerebral vessels undergo compensatory vasodilation. In such a situation, maternal anesthetics, which decrease fetal arterial blood pressure and cardiac output, may further aggravate cerebral hypoxia. To examine this possibility, we prepared six pregnant ewes in such a manner as to be able to measure fetal regional cerebral blood flow in utero during acidosis produced by partial umbilical cord compression both before and after 15 minutes of halothane anesthesia given to the mother. Umbilical cord compression in the absence of anesthesia caused fetal metabolic and respiratory acidosis as evidenced by a decrease in arterial pH from 7.34 to 7.05; fetal arterial oxygen saturation simultaneously decreased from 29 to 17%. Halothane anesthesia administered to the mother of the acidotic fetus caused further aggravation of fetal acidosis (arterial pH 6.85) and oxygen desaturation (10%) and the fetus became markedly hypotensive. Blood flow to four cerebral areas increased 27 to 69% above control levels in the fetus during acidosis in the absence of maternal anesthesia but decreased to levels 30 to 42% below acidosis values when maternal anesthesia was combined with fetal acidosis. These data suggest that potent cardiovascular depressant anesthetics administered to the mother in the presence of fetal acidosis could decrease fetal cerebral oxygen delivery by interfering with fetal cardiovascular compensation during acidosis and reducing fetal cerebral blood flow.

Tissue albumin and water content in the early stages of vasogenic brain edema formation.

Brain edema (BE) research lacks quantitative regional methods. We modified the method of Pappius and McCann (1969), who used radioactive iodinated I125 serum albumin (RISA) as a label for vasogenic BE fluid. To correct for intravascular plasma volume we used Cr51 labelled red blood cells and calculated equivalent extravascular plasma volume (EVPV). The modified RISA method was compared with a standard method for measuring increased tissue water, i.e. the change in wet:dry weights. Anesthetized rabbits were subjected to unilateral cortical freeze injury and sacrificed three hours later. The lesion corresponding to the area of blood brain barrier (BBB) breakdown was delineated by Evan's blue staining. That area and the two adjacent poles were sectioned. The contralateral hemisphere was used as the control. Good agreement was found between the two methods. By the modified RISA method, 4.08% of the wet weight of the injured hemisphere was EVPV while the decrease in dry weight corresponded to 5.56% edema. In the freeze lesion, however, where BBB breakdown occurred extravascular (EV) protein exceeded EV water, while adjacent to the lesion in the area with intact BBB, EV water exceeded EV protein. This suggests that the diffusion rate for water through brain tissue exceeds that of albumin in the early stages of vasogenic BE formation. We conclude that the modified RISA method is a satisfactory measure of regional vasogenic BE in acute animal experiments.