The value of circular reasoning: what Harvey taught and we forgot.

William Harvey discovered that the cardiovascular system is a closed hydraulic circle. Since that discovery, many haemodynamic models have strayed by dividing the circulation into segments, which can be misleading. An alternative model is presented that both preserves circular hydraulics and provides a comprehensive picture of overall cardiovascular function using a novel cardiovascular vector graphic. The practical value of this approach resides in its ease of visualising critical physiological variables and ease of predicting and communicating how changes in those variables affect function.

The hemodynamic management of 5177 neurosurgical and orthopedic patients who underwent surgery in the sitting or "beach chair" position without incidence of adverse neurologic events.

BACKGROUND: A small number of highly publicized case reports describe ischemic brain or spinal cord injury after surgery in the sitting ("beach chair") position. The incidence of such catastrophic outcomes remains unknown, as does the relationship between arterial blood pressure management and injury, because few hemodynamic details were included with those 4 cases. To add quantitative data to the discussion of anesthesia in the sitting position, we examined the detailed hemodynamics of a large number of patients managed at our institution who sustained no similar catastrophic outcomes. METHODS: A comprehensive, retrospective, interrogation was performed of the electronic hemodynamic record for all 5177 patients who underwent either orthopedic shoulder surgery or neurological surgery in the sitting position at Mayo Clinic Rochester between January 1, 2002 and December 31, 2009. RESULTS: No immediate postoperative catastrophic outcomes occurred in 5177 sitting patients undergoing surgery and general anesthesia in the sitting position. For orthopedic shoulder surgery patients, intraoperative systolic blood pressures obtained from an arterial line referenced to heart level decreased 14.4% ± 12.7% (mean ± SD), and those obtained from a noninvasive blood pressure (NIBP) cuff referenced to heart level decreased 19.3% ± 12.6%. For neurosurgical patients, the average reductions in intraoperative mean arterial blood pressures from baseline were 17.6% ± 11.5% and 19.7% ± 10.7% for patients with heart- and head-level transducer placement, respectively. The absolute intraoperative mean arterial blood pressures (mean ± SD) for orthopedic patients measured by NIBP referenced to heart level were 75 ± 8 mm Hg; for orthopedic patients measured from an arterial line referenced to heart level were 74 ± 7 mm Hg; for neurosurgical patients measured with an arterial line referenced to heart level were 78 ± 7 mm Hg; and for neurosurgical patients measured with an arterial line referenced to head level were 75 ± 7 mm Hg. Over the entire duration of surgery, 52% (95% confidence interval [CI], 49%-56%) of neurosurgical patients, 51% (95% CI, 47%-55%) of orthopedic patients monitored with an A-line, and 48% (95% CI, 46%-50%) of orthopedic patients monitored with NIBP experienced ≥1 episodes of systolic blood pressure reduction >40% below baseline. CONCLUSION: This study provides a descriptive summary of intraoperative blood pressure changes, measured either invasively or noninvasively, and referenced to either head or heart level, but never lower than heart level, in patients under general anesthesia in the sitting position who sustained no catastrophic outcomes.

Neurosurgical management of intracranial lesions in the pregnant patient: a 36-year institutional experience and review of the literature.

OBJECT: A review of the literature has revealed scant data related to neurosurgical treatment of gravid patients. The authors reviewed their experience with the neurosurgical treatment of pregnant women to better characterize the optimal management strategies for intracranial pathological entities in this population. METHODS: Between July 1969 and July 2005, 34 patients with documented pregnancy and concomitant intracranial pathological entities were treated at the authors' institution. The average age of the gravid patients at presentation was 27 +/- 6 years. Twelve patients harbored vascular and 14 patients harbored neoplastic lesions. Four gravid patients suffered from traumatic intracranial hemorrhage, 2 had primary intracerebral hemorrhage, and 2 had hydrocephalus. The medical records of these patients were reviewed to assess the outcome for the mothers and fetuses. RESULTS: Nineteen pregnant patients (56%) underwent a neurosurgical procedure after induction of general anesthesia. Of these, 14 (74%) underwent craniotomies for clipping/resection of their lesion, 2 (10%) underwent stereotactic biopsies, and 3 (16%) underwent CSF shunting procedures. Three patients (9%) delivered by cesarean section followed by their neurosurgical procedure, and 5 (15%) underwent therapeutic abortion preoperatively to allow for radiation therapy early in their pregnancy (4 of these patients underwent surgery prior to their therapeutic abortion). Eleven patients (32%) were treated nonoperatively while pregnant, and 3 of these received their treatment after delivery. There was no operative maternal mortality or permanent morbidity. The fetuses did not suffer from any complications related to the mother's neurosurgical procedure. CONCLUSIONS: Based on the authors' experience and a review of the literature, surgery for intracranial lesions in pregnant patients is generally well tolerated by both mother and fetus. Preoperative delivery by cesarean section of term or near-term babies is reasonable. Some patients treated conservatively may deteriorate and require an operation.

Delayed emergence from anesthesia associated with absent brainstem reflexes following suboccipital craniotomy.

One of the most feared complications after intracranial surgery is development of acute intracranial pathology, which may result in hypoperfusion and brain injury. Thus, early neurological assessment, performed in the operating room immediately after emergence from anesthesia, is a practice that may contribute to timely diagnosis of neurosurgical complications. Failure to awake after general anesthesia precludes conductance of neurological assessment. We report a patient who failed to emerge from anesthesia after suboccipital craniotomy and had absent brain-stem reflexes with fixed and dilated pupils consistent with severe brain injury. Approximately 60 minutes after termination of surgery, the patient suddenly woke up. After the fact, we discovered that the neurosurgeon performed a generous field block with bupivacaine along the neck incision line. We presume that our patient's failure to awaken was caused by paralysis of brain-stem caused by migration of bupivacaine from the site of the injection.

Peripheral venous pressure as a measure of venous compliance during pheochromocytoma resection.

Venous pressures measured from peripheral venous catheters (PVP) closely estimate the central venous pressure (CVP) in surgical and critically ill patients. CVP is often used to estimate intravascular volume; however, fluctuations of CVP may also be induced by changes in venous tone caused by alpha-adrenergic catecholamine stimulation. We simultaneously monitored PVP, CVP, and mean arterial blood pressure during resection of pheochromocytoma in a 63-yr-old woman and found excellent correlation between the three pressure variables, suggesting that fluctuations of PVP reflect overall changes in vascular tone.