Biomedical subjects

W E Hoffman

Publications and source records attributed to W E Hoffman.

At least 37 records · Page 2Linked to original sources

PubMed1999

Quantitative assessment of vessel flow integrity for aneurysm surgery. Technical note.

Quantitative measurement of blood flow in cerebral vessels during aneurysm surgery can help prevent ischemic injury and improve patient outcome. The authors report a case of a superior cerebellar artery (SCA) aneurysm in which perivascular microflow probes were used to measure blood flow quantitatively in both the SCA and the posterior cerebral artery before and after aneurysm clipping. Following aneurysm clipping, blood flow in the SCA was reduced to less than 25% of its initial baseline value. Prompt detection of compromised blood flow gave the surgeon the opportunity to adjust the clip and restore SCA flow to its preclipping value within 5 minutes of initial clip placement. Quantitative vessel-flow measurements were integral to the safe progression of the operation and may have prevented an adverse neurological outcome in this patient. The recommended surgical technique and the principle of operation are described.

Aged↗

PubMed1998

Comparison of brain tissue metabolic changes during ischemia at 35 degrees and 18 degrees C.

BACKGROUND: We evaluated brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2) and pH during ischemia with brain temperature at 35 degrees and 18 degrees C in the same patient. METHODS: Surgery was performed in a 60-year-old woman to clip a large aneurysm in the left internal carotid artery (ICA). A Paratrend 7 probe measuring PO2, PCO2, and pH was inserted into tissue at risk for ischemia during ICA occlusion and brain protection was provided with 9% desflurane. One week later, hypothermic circulatory arrest with brain temperature at 18 degrees C was performed for aneurysm clipping and tissue measurements were obtained during ischemia and rewarming. RESULTS: At 35 degrees C, ICA occlusion for 16 minutes produced tissue hypoxia (PO2 = 0) and acidosis (pH = 6.70). The rate of increase of hydrogen ion (H+) reached 50 nEq.L(-1).min(-1) during ICA occlusion and there was a slow recovery of acidosis at the end of the ischemic period. During hypothermic circulatory arrest, tissue PO2 was sensitive to decreases in blood pressure and decreased rapidly during exsanguination. Although tissue pH decreased to 6.5 with 30 min of no pump flow, the rate of H+ increase during hypothermic arrest was one-third of that seen during ischemia at 35 degrees C. During rewarming from profound hypothermia, two phases of recovery from acidosis were observed, one during CO2 clearance and one after tissue reoxygenation. Recovery of acidosis occurred sooner at 18 degrees C than at 35 degrees C. CONCLUSIONS: These results show that tissue acidosis develops more slowly and recovers more rapidly with hypothermic ischemia. This may be an important mechanism of reduced ischemic injury during hypothermia.

Brain↗

PubMed1998

Ultra-rapid opioid detoxification increases spontaneous ventilation.

STUDY OBJECTIVE: To evaluate the effect of ultra-rapid opioid detoxification on spontaneous respiration. DESIGN: Prospective study. SETTING: University of Illinois, Chicago, Hospital. PATIENTS: 20 ASA physical status I and II patients undergoing ultra-rapid opioid detoxification, and 5 ASA physical status I and II control patients undergoing surgical procedures. INTERVENTIONS: Ultra-rapid opioid detoxification patients were anesthetized with propofol, intubated, and spontaneously ventilating. Opioid detoxification was achieved by giving repeated increasing intragastric doses of naltrexone. Control patients were anesthetized with propofol and 70% nitrous oxide and were time-based controls for opioid detoxification. MEASUREMENTS AND MAIN RESULTS: Respiratory rate and minute ventilation were measured and increased 80% to 100% during opioid detoxification (p < 0.05). Respiratory rate and minute ventilation did not change in controls. Oxygen consumption and carbon dioxide (CO2) production were measured in separate studies and increased during ultra-rapid opioid detoxification with increases in spontaneous ventilation, but not when the patients were paralyzed. CONCLUSIONS: Spontaneous ventilation increases during opioid detoxification without a change in end-tidal CO2. An increase in metabolism is produced in opioid withdrawal that is mediated by elevated muscle activity.

Anesthetics, Inhalation↗

PubMed1998

Ultrasonic perivascular flow probe: technique and application in neurosurgery.

Documentation and measurement of intraoperative cerebral blood flow during various neurosurgical procedures is not only valuable but also very informative. There are various methods by which qualitative and quantitative measurement of blood flow have been developed over the years. The use of perivascular ultrasonic flow more recently is fast gaining popularity. We describe the technique, principle and application of ultrasonic perivascular micro-flow probe quantitative measurement of selective vessel flow in neurosurgery.

Blood Flow Velocity↗

PubMed1998

Comparison of the effect of etomidate and desflurane on brain tissue gases and pH during prolonged middle cerebral artery occlusion.

BACKGROUND: The authors compared the effects of etomidate and desflurane on brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH in patients who had middle cerebral artery occlusion for > 15 min. METHODS: After a craniotomy, a probe that measures PO2, PCO2, and pH was inserted into cortical tissue at risk for ischemia during middle cerebral artery occlusion. A burst suppression pattern of the electroencephalogram was induced with etomidate (n = 6) or 9% end-tidal desflurane (n = 6) started before middle cerebral artery occlusion. Mean blood pressure was supported with phenylephrine to 90-95 mmHg. RESULTS: During baseline conditions, tissue PO2, PCO2, and pH were similar between the two groups (PO2 = 15 mmHg, PCO2 = 60 mmHg, pH = 7.1). During administration of etomidate before middle cerebral artery occlusion, tissue PO2 decreased in five of six patients without a change in PCO2 or pH. During administration of 9% desflurane, tissue PO2 and pH increased before middle cerebral artery clipping. Middle cerebral artery occlusion for an average of 33 min with etomidate and 37 min with desflurane produced a decrease in pH with etomidate (7.09 to 6.63, P < 0.05) but not with desflurane (7.12 to 7.15). CONCLUSION: These results suggest that tissue hypoxia and acidosis are often observed during etomidate treatment and middle cerebral artery occlusion. Treatment with desflurane significantly increases tissue PO2 alone and attenuates acidotic changes to prolonged middle cerebral artery occlusion.

Adult↗

PubMed1998

Thiopental and desflurane treatment for brain protection.

OBJECTIVE: Thiopental produces cerebral metabolic depression and cerebral vasoconstriction. However, the effect of thiopental on brain tissue oxygen pressure (PO2), carbon dioxide pressure, and pH is not known. In a prospective study, we measured brain tissue gases and pH during thiopental or desflurane treatment that was administered for brain protection during brain artery occlusion. METHODS: After institutional review board approval, 20 patients undergoing craniotomies for cerebrovascular surgery were tested; 10 were randomized to receive thiopental and 10 to receive desflurane. After each craniotomy, a Neurotrend probe (Diametrics Medical, Minneapolis, MN) was inserted to measure tissue PO2, carbon dioxide pressure, and pH in a tissue region at risk to develop ischemia during temporary brain artery occlusion. Thiopental or desflurane was administered to produce burst suppression of electroencephalography, and then temporary artery occlusion was performed during aneurysm or extracerebral-to-intracerebral bypass surgery. RESULTS: Thiopental produced no change in tissue gases or pH, but temporary artery clipping in thiopental-treated patients decreased PO2 30% (P < 0.05). Desflurane increased PO2 70% (P < 0.05), and tissue oxygenation remained elevated during temporary artery occlusion. Tissue pH did not decrease in either group during temporary brain artery occlusion. CONCLUSION: Thiopental has a metabolically neutral effect on brain tissue gases and pH, even though it is known to decrease cerebral oxygen consumption. The metabolic depressant and vasodilator effects of desflurane enhance tissue oxygenation and attenuate tissue PO2 reductions produced by artery occlusion. Both thiopental and desflurane inhibit ischemic lactic acidosis and decreases in pH.

Acid-Base Equilibrium↗

PubMed1998

Simultaneous increases in respiration and sympathetic function during opiate detoxification.

This study evaluated the relationship between the sympathetic withdrawal response and increases in spontaneous ventilation during naltrexone treatment in opioid-dependent patients. Naltrexone was given in repeated increasing doses by orogastric tube to 16 opioid-dependent patients during propofol anesthesia. Sympathetic activity was evaluated in 64-second segments by low frequency heart rate variability (0.02-0.10 Hz) and minute ventilation was measured every 15 minutes. During naltrexone treatment, heart rate and blood pressure increased with no change in the electroencephalogram as measured by the bispectral index. Sympathetic activity increased five-fold and minute ventilation increased by 50% during naltrexone administration. There was a significant correlation between the time of the peak sympathetic response and peak ventilation (r = 0.83, p < 0.001). In three control patients, who received anesthesia for surgery without naltrexone treatment, no increases in sympathetic or respiratory parameters were seen. These results indicate that peak sympathetic and respiratory stimulation occur together during opiate receptor antagonism in opioid addicts.

Adult↗

PubMed1998

Increased brain tissue oxygenation during arteriovenous malformation resection.

The purpose of this study was to determine if baseline oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH in brain tissue adjacent to an arteriovenous malformation (AVM) is different from measures in control patients. In addition, PO2, PCO2, and pH changes were measured during the course of AVM resection. Two groups were studied. Group 1 (n = 8) were non-ischemic patients scheduled for cerebral aneurysm clipping. Group 2 (n = 13) were patients undergoing neurosurgery for AVM resection. Following craniotomy, the dura was retracted and a PO2, PCO2, pH sensor inserted into non-ischemic brain tissue in Group 1. In Group 2, the sensor was inserted into tissue adjacent to the AVM. Following equilibration, tissue gases and pH were measured during steady state anesthetic conditions in Group 1 and during AVM resection in Group 2. The results show that under baseline conditions before the start of surgery, tissue PO2 was decreased in AVM compared to control patients but PCO2 and pH were not changed. During AVM resection, PO2 increased, PCO2 decreased, and pH increased compared to baseline measures. These parameters did not change in control patients over a similar time period. The results suggest that chronic cerebrovascular adaptation occur in AVM patients with decreased tissue perfusion pressure as an adjustment for decreased oxygen delivery. During AVM resection, this adaptation produces a hyperemic environment with relative tissue hyperoxia, hypocapnia, and alkalosis which is not corrected by the end of surgery.

Arteriovenous Malformations↗

PubMed1998

Role of a perivascular ultrasonic micro-flow probe in aneurysm surgery.

There are various intraoperative monitoring devices available today for helping the neurosurgeons the progress of the intracranial aneurysm surgery. Till now the intraoperative ultrasonic blood flow probes has been used only in vascular, cardiac, and transplant surgery. In the University of Illinois at Chicago we have been able to use the same technology in various neurovascular surgeries. We describe the use of the ultrasonic perivascular blood flow probes in patients operated for clipping of intracranial aneurysm. The use of this perivascular micro-flow probe and its importance in cerebral aneurysm will be discussed.

Brain↗

PubMed1998

Regional tissue pO2, pCO2, pH and temperature measurement.

We compared the difference in brain tissue oxygen pressure (pO2), carbon dioxide pressure (pCO2), pH and temperature with 2 probes inserted 1 cm apart, in 7 patients. Following a craniotomy for cerebrovascular surgery, two Neurotrend probes which measure pO2, pCO2, pH and temperature were inserted into the brain 1 cm apart. Measures were compared between the probes under baseline anesthetic conditions and during the course of surgery. Under baseline conditions, tissue pO2, pCO2, pH and temperature were not different between the 2 probes. A significant correlation was seen between the probes in pH and temperature. During the course of surgery, variation in tissue gases and pH occurred with changes in ventilation and blood pressure but the difference between the probes remained stable. Ischemic changes in pO2, pCO2 and pH were seen in one of the 2 probes during brain artery occlusion or retractor placement. These results show that tissue pO2, pCO2 and pH are consistent in local brain regions during steady state conditions. The relationship between local measures is disrupted by regional ischemia.

Body Temperature↗

PubMed1997

Brain tissue acid-base changes during ischemia.

It is likely that brain tissue acidosis during ischemia is associated with neuronal injury. The authors measured brain extracellular H+, PCO2 and HCO3- concentrations during an ischemic event produced by temporary occlusion of the middle or anterior cerebral arterial distributions, with a 10-minute recovery period. Patients who were to undergo craniotomy for cerebrovascular surgery were recruited for the study. A probe that measures PCO2, pH, and temperature was inserted into tissue at risk for ischemia during temporary arterial occlusion. As a control for this treatment, PaCO2 was increased 10 mm Hg in five patients over a 10-minute period. Under baseline conditions, there was no difference in arterial blood pressure, blood gas levels, or brain temperature between patients who underwent temporary arterial occlusion or those in whom hypercapnia was induced. In patients in whom hypercapnia was induced, H+, PCO2, and HCO3- concentrations increased and all values returned to baseline levels within 10 minutes. In 10 patients who underwent a median 9-minute arterial occlusion, transient ischemia was seen with an increase in tissue H+ and PCO2 levels of 100% and 60%, respectively, and a 20% decrease in HCO3- levels. After a 10-minute postischemic recovery, only PCO2 had returned to baseline levels. These results are consistent with a rapid equilibration of lactic acidosis across the cell membrane during ischemia which decreases HCO3- concentration. After ischemia, extracellular acidosis may be prolonged because of the extrusion of H+ from the cell by membrane ion exchange.

Journal Article↗

PubMed1997

Cerebral interstitial tissue oxygen tension, pH, HCO3, CO2.

BACKGROUND: There are many techniques for monitoring the injured brain following trauma, subarachnoid hemorrhage, or surgery. It is thought that the major determinants for recovery of injured cerebral tissue are oxygen, glucose delivery, and the clearance of metabolites. These factors, at optimal levels, are probably responsible for the regaining of neuronal functions. These parameters are in turn dependent on the tissue's blood flow and metabolism. METHODS: We have been using a single, compact, polyethylene sensor, the Paratrend 7 for the measurement of cerebral oxygen tension, CO2, pH, and temperature. This sensor is designed for continuous blood gas analysis to aid in monitoring neurosurgical patients, both during surgery and in the intensive care unit. RESULTS: Using the Paratrend 7 sensor, we found the normal range of values to be: PO2 33 +/- 11 mm Hg; PCO2 48 +/- 7 mm Hg; pH 7.19 +/- 0.11. Critical measurements are considered to be tissue PO2 < 10 mm Hg; PCO2 > 60 mm Hg, and pH < 6.8. We have had no complications with this device; the risks are similar to those of placing a parenchymal intracranial pressure monitor. CONCLUSIONS: We believe that assessment of interstitial cerebral oxygen saturation can be of great value both intraoperatively and postoperatively. In our experience, the Paratrend 7 system is an effective method of measuring tissue cerebral oxygen tension, along with carbon dioxide levels, pH, and temperature.

Bicarbonates↗

PubMed1997

Regional ischemia during cerebral bypass surgery.

BACKGROUND: We evaluated brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH during regional ischemia produced by temporary brain artery occlusion. METHODS: This 45-year-old woman with cerebral occlusive disease was scheduled for right superficial temporal artery (STA) to middle cerebral artery (MCA) bypass. Two Paratrend 7 sensors measuring PO2, PCO2, and pH were inserted into the cortex in the distribution of the MCA at a distance of 1 cm from each other. Jugular bulb oxygen saturation was measured by oximetry. Local perfusion was measured with a flow probe on the MCA and using a laser Doppler. Tissue responses were recorded during: (1) 100% oxygen ventilation, (2) hypercapnia, and (3) an 18 minute occlusion of the right MCA. RESULTS: Under baseline conditions, tissue PO2, PCO2, and pH suggested that ischemia was present in tissue measured by both sensors. Tissue PO2 rose 40%-50% in both regions during 100% oxygen ventilation. During hypercapnia, blood flow increased in the MCA, but local perfusion did not increase in region 2. During temporary occlusion of the MCA, ischemic changes in PO2, PCO2, and pH were seen in region 2 but not in region 1. Local perfusion decreased 80% in region 2, where ischemic changes were seen. CONCLUSIONS: These results show that changes in tissue PO2, PCO2, and pH are consistent with local perfusion. The use of multiple tissue sensors can detect the presence of watershed ischemia that is not demonstrated by jugular bulb measurement.

Brain↗

PubMed1997

Cerebral blood flow and metabolic response to etomidate and ischemia.

The purpose of this study was to measure the cerebrovascular and metabolic effects of etomidate during cerebral aneurysm surgery. Flow probes were placed on brain arteries to measure regional tissue perfusion. Cerebral oxygen consumption (CMRO2) was determined from blood flow measures and arterial-jugular bulb oxygen content differences. CBF and CMRO2 decreased 40% during etomidate infusion to suppress the electroencephalogram. During temporary brain artery occlusion, measurement of arterial blood flow in the circle of Willis provides an indication of collateral blood flow to potentially ischemic territory. The use of multiple flow probes can provide information on the effect of anesthetic drugs and surgical manipulation on cerebral circulation.

Anesthetics, Intravenous↗

PubMed1997

Brain tissue oxygenation in patients with cerebral occlusive disease and arteriovenous malformations.

It is not clear if ventilation with oxygen increases brain tissue oxygen pressure (PO2) during ischaemia. We have measured brain tissue PO2, carbon dioxide pressure (PCO2) and pH during baseline anaesthesia and oxygen ventilation in non-ischaemic control patients (n = 9), patients with cerebral occlusive disease (n = 11) and patients with arteriovenous malformations (AVM, n = 12). The same anaesthetic treatment was given to all groups and anaesthesia was constant during the study. Arterial pressure, brain temperature and arterial blood-gas tensions were similar between groups. Under baseline conditions, brain tissue PO2 was mean 4.2 (SD 1.4) kPa in the controls and was 70% lower in patients with ischaemia and AVM. Patients with occlusive disease also had elevated tissue PCO2 and acidosis. During oxygen ventilation, PO2 increased to 7.5 (2.9) kPa in controls and this was 50% greater than the increase in the ischaemia and AVM patients. The results showed that baseline tissue oxygenation and increases in PO2 during hyperoxia were attenuated in patients with ischaemia or AVM.

Anesthesia, General↗

PubMed1997

Cerebral hypoxia after etomidate administration and temporary cerebral artery occlusion.

UNLABELLED: Neurovascular surgical procedures often require temporary cerebral arterial occlusion. Although clinical validation is lacking, etomidate has often been used to attenuate the effects of cerebral ischemia in this setting. The purpose of this study was to evaluate the effects of etomidate and temporary cerebral arterial occlusion on human brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH during intracranial aneurysm surgery. We studied nine patients presenting for cerebral aneurysm surgery. A Paratrend probe was used to determine brain tissue pH and gas tensions. Etomidate was administered to produce electroencephalographic burst suppression before temporary cerebral arterial occlusion. After etomidate administration in nine patients, brain tissue PO2 decreased 30% compared with baseline (P < 0.05). During temporary brain artery occlusion in 8 patients, tissue PO2 decreased 32% below preclip values (P < 0.05) in conjunction with a tissue PCO2 increase of 23% (P < 0.05) and a 0.1-unit decrease in pH (P < 0.05). In patients in whom PO2 decreased below 10 mm Hg during temporary clipping, tissue pH decreased, compared with patients in whom PO2 remained above 10 mm Hg (P < 0.05). These results demonstrate that etomidate administration during cerebral aneurysm surgery decreases tissue PO2 and that in these patients, tissue PO2 does not increase with increases in inspired oxygen concentration. Low tissue PO2 during temporary clipping significantly increases the risk of tissue acidosis. IMPLICATIONS: Etomidate administration alone resulted in cerebral deoxygenation. Subsequent temporary cerebral artery occlusion resulted in additional tissue deoxygenation and acidosis. These results suggest that etomidate enhances hypoxic risk in the setting of cerebral ischemia.

Adult↗

PubMed1997

Brain tissue gases and pH during arteriovenous malformation resection.

OBJECTIVE: The purpose of this study was to determine whether baseline partial pressure of oxygen (PO2), partial carbon dioxide pressure (PCO2), and pH in brain tissue adjacent to arteriovenous malformations (AVMs) are different from those in control patients. In addition, PO2, PCO2, and pH changes were measured during resection of the AVMs. METHODS: Two groups were studied. Group 1 (n = 8) was composed of nonischemic patients scheduled for cerebral aneurysm clipping. Group 2 (n = 13) was composed of patients undergoing neurosurgery for resection of AVMs. After the craniotomy, the dura was retracted and a combined PO2, PCO2, and pH sensor was inserted into nonischemic brain tissue in Group 1. In Group 2, the sensor was inserted into tissue 2 to 3 cm from the margin of the AVMs, within the same arterial blood supply. After equilibration of the sensor, tissue gases and pH were measured during steady-state anesthetic conditions in Group 1 and during resection of AVMs in Group 2. RESULTS: Under baseline conditions before the start of surgery, tissue PO2 was decreased in patients with AVMs compared with control patients, but PCO2 and pH were not changed. During resection of the AVMs, PO2 and pH increased and PCO2 decreased compared with baseline measurements. These parameters did not change in control patients during a similar time period. CONCLUSION: The results suggest that cerebrovascular or metabolic adaptation occurs in patients with AVMs with decreased tissue perfusion pressure as an adjustment for decreased oxygen delivery. During resection of AVMs, this adaptation produces a relative hyperemic environment with tissue hyperoxia, hypocapnia, and alkalosis that is not corrected by the end of surgery.

Acid-Base Equilibrium↗

PubMed1997

Desflurane increases brain tissue oxygenation and pH.

BACKGROUND: Desflurane anesthesia can produce cerebral metabolic depression and increase cerebral blood flow. We evaluated the effect of desflurane on brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2) and pH during neurosurgery. METHODS: Following a craniotomy, the dura was opened and a Paratrend 7 sensor, which measures PO2, PCO2, pH and temperature, was inserted into brain tissue. In 6 control patients in group 1, anesthesia was maintained constant with 3% end-tidal desflurane over 60 min, including a 30-min stabilization period. In group 2, 9 patients were ventilated with 3% desflurane under baseline conditions. After a 30-min stabilization period, baseline tissue gases and pH were measured and end-tidal desflurane was increased to 6% and then 9% for 15-min intervals. Mean arterial pressure (MAP) was maintained with intravenous phenylephrine. RESULTS: Under baseline conditions, cardiovascular and brain tissue measures were similar between the 2 groups. Increasing end-tidal desflurane from 3% to 9% produced burst-suppression EEG in all patients and significantly increased tissue PO2 and pH and decreased PCO2. No parameters changed significantly in the control group during steady-state anesthesia. CONCLUSION: These results show that 9% desflurane can improve brain tissue metabolic status before temporary brain artery occlusion if cerebral perfusion pressure is maintained. This may be particularly important in patients with symptoms of ischemia before surgery.

Adult↗