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PubMed1987

Preservation of hearing in surgical removal of acoustic neuromas of the internal auditory canal and cerebellar pontine angle.

The surgical results in 69 patients with unilateral tumors of the cerebellopontine angle or internal auditory canal in whom total tumor removal was accomplished, and in whom an attempt was made to preserve hearing, are presented. The success rate of preservation of hearing and facial nerve function was correlated with the size of the tumor. Useful hearing, as defined by speech reception threshold no poorer than 70 dB and a discrimination score of at least 15%, was preserved in 73% of cases in which the tumor extension to the posterior fossa was no greater than 0.5 cm. In contrast, useful hearing was preserved in 22% of cases in which posterior fossa extension was greater than 2.5 cm. No significant correlation was found between preoperative evoked responses and success in preservation of hearing. The techniques and value of intraoperative monitoring of electrocochleogram (ECoG) and brain stem evoked responses are discussed. A theory of pathogenesis of intraoperative hearing loss, based on correlation of changes in evoked responses and simultaneous surgical events, is presented.

Adult↗

PubMed2005

Oximetry-derived perfusion index for intraoperative identification of successful thoracic sympathectomy.

BACKGROUND: Endoscopic thoracic sympathectomy treats patients with hyperhidrosis. Laser Doppler flow and changes in palmar temperature have been advocated for intraoperative monitoring. The pulse oximetry-derived perfusion index (PI) is used to quantify pulsatile blood flow at the pulse oximeter. Upper limb sympathectomy is associated with increased flow to the ipsilateral extremity; thus we postulate that it will increase PI. We evaluated changes in intraoperative PI as a monitor of successful thoracic sympathectomy. METHODS: After institutional review board approval and informed consent, 10 adult patients undergoing bilateral endoscopic thoracic sympathectomy under general anesthesia were studied. Finger pulse-oximetry probes were placed on each hand, and reference probes on each earlobe. Hemodynamic variables and PI were continuously monitored. Data were collected immediately before and every minute after sympathectomy for 5 minutes. Anesthetic management remained constant throughout. A successful sympathectomy was defined by a twofold increase in PI on the ipsilateral arm. Data were analyzed with analysis of variance and Student's t tests; a p < 0.05 was considered significant. RESULTS: Baseline oximetric waveforms were adequate in all subjects. Right sympathectomy was associated with a 372% increase in PI (p < 0.0001), and left sympathectomy with a 316% increase in PI (p < 0.029). This occurred as early as 1 minute after transection of the sympathetic chain. The PI in the reference probes as well as the hemodynamics remained constant. All patients had postoperative resolution of their hyperhidrosis symptoms. CONCLUSIONS: In patients with hyperhidrosis of the upper extremity, the intraoperative PI derived from pulse oximetry is an additional indicator of successful thoracic sympathectomy.

Adolescent↗

PubMed2001

Microdialytical monitoring of uric and ascorbic acids in the brains of patients after severe brain injury and during neurovascular surgery.

OBJECTIVES: Microdialysis has been extensively used to monitor brain metabolism in the extracellular fluid of patients with severe head injury, to detect the onset of secondary ischaemic damage. The aim was to investigate whether concentrations of uric and ascorbic acids were altered in such patients. Both these compounds play a part in free radical metabolism, which is accelerated after ischaemia and brain injury. METHODS: Patients with aneurysm or bypass operations were monitored intraoperatively to assess concentrations in minimally disturbed tissue. Afterwards, 13 patients with severe head trauma were monitored for up to 13 days in the intensive care unit. RESULTS: Intraoperatively, concentrations of both ascorbic and uric acids were significantly higher in the bypass group than in patients with aneurysm, which might be attributed to chronic ischaemic conditions caused by the unilateral occlusion of the carotid artery. In the patients with trauma, mean values of uric acid, varying between 6 microM and 180 microM, did not correlate with type of injury (contusion or diffuse) or duration of monitoring time. Patients who died had significantly higher concentrations of uric acid than those with a good outcome. Ascorbic acid could be detected only intermittently, probably due to technical problems. Concentrations of these two compounds could not be correlated with clinical findings during the course of monitoring. CONCLUSIONS: Although uric and ascorbic acids are influenced by ischaemic conditions-for example, in bypass patients, neither compound is suitable for monitoring for free radical activity after severe head injury. Patients with a bad outcome tended to have higher concentrations of uric acid.

Adult↗

PubMed1997

The usefulness of the spinal and subcortical components of the posterior tibial nerve SEPs for spinal cord monitoring during aortic coarctation repair.

This study examines how the recording of the lumbar and subcortical components of the posterior tibial nerve (PTN) SEPs may usefully replace that of cortical components in situations in which these components cannot be reliably obtained (infants, high concentrations of halogenated gasses). Lumbar, brain-stem, and cortical PTN SEPs were intraoperatively monitored in 7 patients undergoing repair of aortic coarctation under variable isoflurane concentration (up to 1.2%). Four patients were less than 1 year old. Two distinct activities were evidenced at the lumbar level in all of the patients: the dorsal root component (DRC) and the dorsal horn negativity (DHN). The equivalent of the adult P30 (lemniscal positivity; LP) was also present in all of the patients, whatever their age or the concentration of isoflurane. By contrast, the parietal activities were absent intraoperatively in the youngest patients. Spinal-cord ischemia consecutive to aortic cross-clamping gave rise to early DHN changes and later alterations of the LP in the two patients in which it occurred, while the DRC and the peripheral nerve activities remained unchanged. This elective sensitivity of the DHN is likely due to it being dependent on the gray matter of the spinal cord, the basal metabolism of which is greater than that of the white matter and to the situation of the DHN generator in a watershed zone of the spinal cord. This study emphasizes the interest of PTN SEPs for spinal-cord monitoring in vascular surgery and the importance of combining the recording of parietal activities with that of the lumbar spinal components.

Adult↗

PubMed2001

Stroke from carotid endarterectomy: when and how to reduce perioperative stroke rate?

OBJECTIVES: To analyse four years of CEA with respect to the underlying mechanisms of perioperative stroke and the role of intraoperative monitoring in the prevention of stroke. PATIENTS AND METHODS: From January 1996 through December 1999, 599 CEAs were performed in 404 men and 195 women (mean age: 65 years, range: 39-88). All operations were performed under general anaesthesia using computerised electroencephalography (EEG) and transcranial Doppler (TCD). Any new or any extension of an existing focal cerebral deficit, as well as stroke-related death were registered. Perioperative strokes were classified by time of onset (intraoperative or postoperative), outcome (minor or major stroke), and side (ipsilateral or contralateral). Stroke aetiology was assessed intraoperatively by means of EEG, TCD, completion arteriography or immediate re-exploration, and postoperatively by duplex sonography, computerised tomography (CT) or magnetic resonance imaging (MRI) of the head. RESULTS: Perioperative stroke or death occurred in 20 (3.3%) patients. In four operations stroke was apparent immediately after surgery. Mechanisms of these strokes were ipsilateral carotid artery occlusion (1) and embolisation (3). In 16 patients stroke developed after a symptom-free interval (2-72 h, mean 18 h) due to occlusion of the internal carotid artery on the side of surgery (9). Other mechanisms were: contralateral occlusion of the internal carotid artery (1), postoperative hyperperfusion syndrome (1), intracerebral haemorrhage (1), and contralateral ischaemia due to prolonged clamping (1). In three procedures the cause was unknown. CONCLUSIONS: In our experience most strokes from CEA developed after a symptom-free interval and mainly due to thromboembolism of the operated artery. We suggest the introduction of additional TCD monitoring during the immediate postoperative phase.

Adult↗

PubMed2006

Intraoperative dynamic infrared thermography and free-flap surgery.

Flap failure in free-tissue transfer relates strongly to technical failure of the anastomosis or to kinking as well as to external compression of the donor or recipient vessels. Intraoperative monitoring of flap perfusion has shown to prevent flap failure. This prospective, clinical study presents the results of intraoperative dynamic infrared thermography as a novel method to monitor reperfusion indirectly in 10 free flaps. This noninvasive technique provided a fast and reliable method to register partial or total arterial occlusion due to anastomotic failure, as well as due to external compression or kinking of the vessels. The dynamic infrared image sequences showed an improved rate and pattern of rewarming of the flap after an additional venous anastomosis was opened. The state of reperfusion of the flap at the end of the operation could easily be determined. The authors conclude that dynamic infrared thermography provides the surgeon with valuable information on flap reperfusion during free flap surgery.

Adult↗

PubMed2006

Neurosurgical operations with the patient in sitting position: analysis of risk factors using transcranial Doppler sonography.

BACKGROUND: One major risk factor of the sitting position for neurosurgery is air embolism, especially in patients with persistent foramen ovale (PFO). The first aim of this prospective study was to evaluate a bedside method for detecting PFO using transcranial Doppler sonography (TCD) with contrast medium. A second aim was to address intraoperative monitoring, patient positioning and the occurrence and clinical relevance of air embolism. METHODS: Ninety patients with a mean age of 56.5 yr (range 14-81 yr) undergoing surgery in sitting position were investigated by TCD with contrast agent to detect functional PFO, that is PFO that can be provoked with a Valsalva manoeuvre. In patients in whom TCD was not possible, transcranial duplex sonography, duplex sonography of the carotid artery at the neck or transoesophageal ECG was performed. RESULTS: In 26 patients PFO was detected. Thirteen of them presented a persistent PFO with high-intensity transient signal in both middle cerebral arteries without Valsalva manoeuvre. The intraoperative positioning in these patients was adapted to the risk for a paradoxical air embolism, although, after surgical recommendations, three patients with a persistent PFO underwent surgery in sitting position. Intraoperative air embolisms were seen in 8 of 80 patients in sitting or semi-sitting position with air aspirable through the central venous catheter. CONCLUSION: To address the risk of a paradoxical air embolism, especially in patients undergoing surgery in sitting position, preoperative detection of PFO is advisable. If surgery is performed in seated PFO patients, additional monitoring and special care are warranted.

Adolescent↗

PubMed1980

Continuous measurement of transcutaneous oxygen tension of neonates under general anesthesia.

Neonates present unique challenges to the anesthesiologist because of their susceptibility to oxygen toxicity and because clinical assessment of the degree of an infant's hypoxia is more difficult than in the adult. Equipment is now available for the continuous noninvasive measurement of transcutaneous oxygen tension. We used this equipment to monitor nine different neonates undergoing ten surgical procedures requiring general anesthesia. We found that certain of the infants were above and below what we considered to be a safe range for the transcutaneous oxygen tension for a significant portion of the surgery. Additionally, the manipulations of the surgeon and anesthesiologists were seen to cause sudden and large fluctuations in the transcutaneous oxygen tension. By providing the anesthesiologist with continuous and immediate data on the cardiorespiratory status of the infant, transcutaneous oxygen monitoring makes itself a valuable addition to the equipment used in the intraoperative monitoring of the neonate.

Anesthesia, General↗

PubMed2004

[Clinical features and surgical treatment of posttraumatic epilepsy].

OBJECTIVE: To study the clinical features of posttraumatic epilepsy and evaluate the surgical procedures for anti-epileptic treatment and their therapeutic effects. METHODS: Neurological and scalp EEGs were performed in 35 patients with posttraumatic epilepsy, who also underwent CT, MRI examination, single photon emission computerized tomography (SPECT) and positron emission tomography (PET) prior to intracranial surgery, with intraoperative monitoring of the cortical EEG. RESULTS: With the cortical EEG monitoring, 16 patients underwent surgical resection of the epileptogenic foci identified by intraoperative EEG, 7 had multiple subpial transection and 12 received stereotactic radiosurgery for the epileptogenic foci localized by PET. In most of the cases, the epileptogenic foci were located around the lesions of encephalomalacia. During the follow-up of 32 patients varying from 1 to 4 years, 18 patients became seizure free, 10 had obvious reduction in the frequency of seizure while 4 failed to respond favorably to the treatment. CONCLUSIONS: Seizures of posttraumatic epilepsy may aggravate the brain dysfunction due to primary trauma, and surgical treatment often yields good effect and lessens the toxic and adverse effect of antiepileptic drugs. Stereotactic radiosurgery guided by PET is safe and effective in the treatment of patients with posttraumatic epilepsy.

Adolescent↗

PubMed1989

[Prevention of spinal cord ischemia after cross-clamping of the thoracic aorta--monitoring of spinal cord perfusion pressure and somatosensory evoked potentials].

The pressure difference between the mean distal aortic pressure (MDAP) and the cerebrospinal fluid pressure (CSFP), defined as the spinal cord perfusion pressure (SCPP), as well as somatosensory evoked potentials (SEP) were monitored intraoperatively to detect and prevent intraoperative spinal cord ischemia in 24 patients who required cross-clamping of the descending thoracic aorta. A temporary axillo-femoral shunt, utilizing a 10 mm woven Dacron tube graft, was employed in 10 patients and partial cardiopulmonary bypass was employed in fourteen. Ischemic SEP changes were seen in six patients. Two patients, whose SCPPs were 32 and 35 mmHg, showed a complete loss of SEP and subsequently developed paraplegia. In the other four cases, increase of the MDAP and/or withdrawal of cerebrospinal fluid were performed to increase the SCPP to more than 60 mmHg when ischemic SEP changes occurred. The SEP gradually recovered in two of these cases. The ischemic SEP changes seen in one patient, who had the longest aortic cross-clamping time, (175 minutes) returned to normal immediately after unclamping. In another case, who had a thoracoabdominal aortic aneurysm, the intercostal arteries were reimplanted since the ischemic SEP changes did not revert. These four patients recovered without any neurological deficit. In the other 18 cases without ischemic SEP change, SCPP was kept at more than 40 mmHg during aortic cross-clamping. We conclude that the SCPP should be maintained at more than 40 mmHg during aortic occlusion, and increased to more than 60 mmHg when ischemic SEP changes occur, by increasing MDAP and/or withdrawing cerebrospinal fluid in order to prevent postoperative paraplegia.

Adult↗

PubMedDate not supplied

The risk of fat embolism during cemented total hip replacement in the elderly patient.

The increase in intramedullary pressure in the femur is the most decisive pathogenic factor for the development of embolic phenomena during total hip replacement. The aim of this study was to assess the risk of embolism and its clinical relevance during surgery by means of transesophageal echocardiography, hemodynamic and hemogasanalytic monitoring. A total of 65 arthroplasties entered the clinical trial. Total hip arthroplasty was cemented conventionally. The right heart was monitored intraoperatively by an echocardiography probe positioned in the patient's esophagus. Hemodynamic and hemogasanalytic monitoring were performed. Severe embolism occurred in 91% of the cases during implantation of the femoral component. Emodynamic and respiratory parameters showed significant changes after major embolism. The timing suggests a nearly immediate cause-and-effect relationship. Acute hypotension was observed in 62% of the cases. Mean pulmonary shunt values increment was 30.5%. Patients with intraoperative embolism who had pre-existing associated diseases showed more severe and persistent cardiopulmonary dysfunction than healthy patients. The surgeon's proclivity to deny the clinical relevance of fat and bone marrow during during total hip arthroplasty is directly related to his awareness of and attempt to avoid embolism. Patients at risk require more intensive monitoring to obtain detailed information about hemodynamic and oxymetric parameters.

Age Factors↗

PubMed1993

Relationship between oxygen consumption and oxygen delivery during anesthesia in high-risk surgical patients.

OBJECTIVE: To identify critical oxygen delivery (DO2) and oxygen extraction ratio in high-risk surgical patients studied preoperatively and intraoperatively. DESIGN: Prospective study. Consecutive series of intraoperatively monitored patients. SETTING: The surgical ICU in a tertiary care center. PATIENTS: High-risk surgical patients undergoing major noncardiac surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Twenty high-risk patients were studied during the preoperative and intraoperative periods. All patients were monitored with triple-lumen thermodilution catheters. Hemodynamic profiles consisted of determinations of intravascular pressures, cardiac output, and arterial and venous pulmonary gases. Oxygen transport variables were calculated by standard formulas. Multiple determinations were carried out during the perioperative period in each patient. The critical levels of DO2, determined by a polynomial regression method, were 375 and 390 mL/min/m2 in the preoperative and intraoperative periods, respectively. Oxygen extraction reached at the critical level of DO2 was significantly (p < .01) lower during the intraoperative period (31 +/- 4.5% vs. 18 +/- 2.3%). Critical mixed venous oxygen tension was significantly (p < .01) higher in the intraoperative period (36 +/- 5 vs. 46 +/- 4 torr [4.8 +/- 0.7 vs. 6.1 +/- 0.5 kPa]). CONCLUSIONS: Our data show that the intraoperative period might be associated with a reduction in tissue ability to extract oxygen. If this reduction in oxygen extraction is proportionately higher than the reduction in metabolic oxygen demand produced by anesthetic agents and hypothermia, then the critical value for DO2 may be similar to, or higher than, that value in the preoperative period. Thus, the intraoperative period represents, for this patient population, a high-risk condition for the development of a tissue oxygenation debt in the presence of a limitation in DO2. Cautious dosing of inhaled agents, maintenance of normothermia, and early optimization of the oxygen delivery/oxygen consumption relationship seem to constitute reasonable measures in the intraoperative handling of these patients in order to reduce perioperative morbidity and mortality.

Adult↗

PubMed1982

Brain stem and somatosensory evoked potentials: application in the operating room and intensive care unit.

Intraoperative monitoring of the brain's electrical function with evoked potentials (EPs) may prove as valuable as cardiac monitoring in detecting abnormalities before permanent damage occurs. To date, evoked potential monitoring has only been employed in select neurological cases, where the significance of electrical changes can be related to postoperative deficits. If EP intraoperative techniques are to be useful in preventing these postoperative deficits, they must be able to predict impending brain dysfunction during surgery. There is strong clinical and experimental data relating EP changes to critical blood flow, brain retraction, and CNS manipulation. However, little is known of the normal fluctuations in electrical activity during routine non-neurological surgery. The data we have collected in control patients (non-neurological) will be a guide to the interpretation of neurological cases (carotid endarterectomy, aneurysm, and cervical spine and cord lesions). We have concentrated on monitoring somatosensory and auditory short-latency EPs since they appear to be the most stable, reproducible and the most applicable to patient monitoring during neurosurgical, vascular and orthopedic procedures.

Animals↗

PubMed1989

Neurophysiologic monitoring in posterior fossa surgery. II. BAEP-waves I and V and preservation of hearing.

Of 135 cases operated upon for posterior fossa lesions 103 showed preoperative hearing. In 34 acoustic neurinomas 14 had postoperative initially preserved hearing, in 20 microvascular decompressions 19 had preserved postoperative hearing and in 49 other lesions 5 lost hearing. The relationship between preservation of hearing and the preservation or loss of brainstem auditory evoked potentials (BAEP) waves I and V in the three groups of namely: acoustic neurinomas, microvascular decompressions and other lesions are presented. It is noteworthy that only patients with preserved waves I or V are suitable candidates for intraoperative monitoring. The loss of wave V is usually associated with hearing loss (10 out of 13 cases). But hearing loss is also possible despite preservation of wave I (3 out of 60) or despite preservation of wave V (2 out of 68). The predictive value of the preservation of waves I and V is not an absolute one, but it strongly suggests preserved hearing postoperatively. The dilemma remains that once waves I or V are lost during surgery there is no certainty as to postoperative hearing. If wave V recovers after an initial loss, hearing is usually preserved but not in all cases. In wave I amplitude changes alone were more frequent than in wave V, where latency changes alone were more frequently observed. Particular surgical manoeuvres could be found to be often associated with a wave deterioration. Hearing preservation could never be achieved in patients who already preoperatively had no BAEP. It is concluded that BAEP monitoring is of great value in surgery for microvascular decompression and cerebello-pontine-angle (CPA) tumours with preserved hearing.

Audiometry, Evoked Response↗

PubMed1984

[Visual evoked potentials (VEP) in anesthesia and intensive care].

Methodological considerations and different stimulation techniques of visual evoked potentials (VEP) are described. VEP can provide information about neurological function during anaesthesia, surgery and in the unconscious patient after head injury. The feasibility of the method for intraoperative monitoring in neuro- and cardiac surgery and the influence of general anaesthetics and other contributing factors such as temperature, paCO2, pO2, part are discussed.

Anesthesia↗

PubMed1984

Cerebral monitoring of somatosensory evoked potentials during profoundly hypothermic circulatory arrest.

The factors that influence the functional integrity of the central nervous system during clinical procedures involving profoundly hypothermic circulatory arrest (PHCA) have not been objectively evaluated. Intraoperative monitoring of somatosensory evoked potentials (SEPs) was performed in nine infants undergoing PHCA during repair of congenital cardiac anomalies to investigate the short-term effects of this intervention on neurophysiologic function. Latency prolongation of the primary cortical (N18,P22) and cervical spinal cord (N13) responses, reflecting slowing of neural transmission with hypothermia, occurred as a power function of decreasing systemic temperature (p less than .01). The cortical evoked response disappeared during profound hypothermia (less than 18 degrees C), remaining absent throughout the period of circulatory arrest and for a variable period of time after reperfusion. Regression analysis indicated that the time required for the recovery of the cortical evoked response on reperfusion was a linear function of the time-temperature integral of the arrest period (p less than .001) and the pH at the onset of circulatory arrest (p less than .001). Neurologic complications occurred in three patients and included cortical blindness (n = 2) and a generalized seizure disorder (n = 1). Visual dysfunction was not reflected in the intraoperative SEP recordings, whereas prolonged delay of SEP recovery, indicative of global central nervous system injury, was observed in the patient who experienced seizures after the surgery. This preliminary experience with SEP monitoring during PHCA suggests a role for this modality in determining the short-term effects of this procedure on neurophysiologic function. The recovery characteristics of somatosensory neural transmission appear to be modulated by the duration of, and temperature and pH maintained during, the arrest period.

Body Temperature↗

PubMed1983

Noninvasive intraoperative assessment of arterial reconstruction. Experimental validation of the role of central and regional hemodynamics.

We developed an experimental model of graded arterial stenosis to emulate conditions that might be encountered immediately following arterial grafting. Noninvasive measurements of systolic BP and limb blood flow were recorded with a Doppler probe and segmental air plethysmography, respectively, under conditions of different cardiac output and local arterial resistance. These measurements were correlated with direct intra-arterial pressure recordings and flow measurements taken with an electromagnetic flowmeter. There was an excellent correlation between noninvasive and intra-arterial measurements of systolic pressure over a range of cardiac outputs and degree of arterial stenosis. Pulse volume recordings correlated with direct measurements of blood flow at high and baseline cardiac outputs, but the calibration of pulse volume amplitude varied between cuff applications in this canine model. Noninvasive intraoperative monitoring techniques can faithfully represent known physiologic responses to graded arterial stenoses, irrespective of a high cardiac output or peripheral vasodilation.

Animals↗

PubMed1987

Technical controversies in carotid artery surgery.

Carotid endarterectomy has become a routine and safe therapeutic strategy in most neurovascular centers. Wide diversity of opinion and considerable debate, however, persists concerning the ideal methods of anesthetic management, cerebral protection, intraoperative monitoring, and arterial repair. We have examined and summarized the current status of these controversies and have identified several new techniques that hold promise for further development.

Anesthesia↗