Neurologic deficits after cervical laminectomy in the prone position

New neurologic deficits are known to occur after spine surgery. We present four patients with cervical myeloradiculopathy who underwent cervical laminectomy, fusion, or both in the prone position, supported by chest rolls. Three patients were intubated and positioned while awake, whereas the fourth patient was positioned after induction. Surgeries were successfully carried out, except for transient episodes of relative hypotension intraoperatively. On recovery from anesthesia, all patients were noted to have new neurologic deficits. Immediate CT myelography or surgical reexploration was unremarkable. All patients improved gradually with administration of high-dose steroids and induction of hypertension. Use of the prone position with abdominal compression may compromise spinal cord perfusion and lead to spinal cord ischemia. The use of frames that prevent abdominal compression, as well as avoidance of perioperative arterial hypotension, is important in maintaining adequate spinal cord perfusion during and after decompressive spinal cord surgery.

Effects of positive end-expiratory pressure ventilation on cerebral venous pressure with head elevation in dogs

Mechanical ventilation with positive end-expiratory pressure (PEEP) may prevent venous air embolism in the sitting position because cerebral venous pressure (Pcev) could be increased by the PEEP-induced increase in right atrial pressure (Pra). Whereas it is clear that there is a linear transmission of the PEEP-induced increase in Pra to Pcev while the dog is in the prone position, the mechanism of the transmission with the dog in the head-elevated position is unclear. We tested the hypothesis that a Starling resistor-type mechanism exists in the jugular veins when the head is elevated. In one group of dogs, increasing PEEP linearly increased Pcev with the dog in the prone position (head at heart level, slope = 0.851) but did not increase Pcev when the head was elevated. In another group of dogs, an external chest binder was used to produce a larger PEEP-induced increase in Pra. Further increasing Pra increased Pcev only after Pra exceeded a pressure of 19 mmHg (break pressure). This sharp inflection in the upstream (Pcev)-downstream (Pra) relationship suggests that this may be caused by a Starling resistor-type mechanism. We conclude that jugular venous collapse serves as a significant resistance in the transmission of Pra to Pcev in the head-elevated position.

Antioxidant LY231617 enhances electrophysiologic recovery after global cerebral ischemia in dogs

OBJECTIVE

The potent antioxidant LY231617 (2,6-bis(1,1-dimethylethyl)-4-[[(1-ethyl)amino]methyl]phenol hydrochloride) is cytoprotective in models of focal and global cerebral ischemia. We tested the hypothesis that administration of LY231617, before the insult, would improve recovery of cerebral electrical activity and metabolic function after transient global cerebral ischemia by improving cerebral blood flow (CBF) during the reperfusion period.

DESIGN

Randomized, controlled, prospective study.

SETTING

Research laboratory at a university teaching hospital.

SUBJECTS

Twenty-four male beagle dogs.

INTERVENTIONS

All experiments were performed under pentobarbital anesthesia and controlled conditions of normoxia, normocarbia, and normothermia. Twelve control dogs received 20 mL/kg saline (vehicle) bolus into the right atrium and 0.01 mL/kg/min i.v., beginning 20 mins before 13 mins of global cerebral ischemia (by aortic occlusion). The dogs in the drug-treated group received LY231617 as a 10-mg/kg bolus 20 mins before ischemia and 5 mg/kg/hr throughout reperfusion (n = 12). CBF was measured using radiolabeled microspheres.

MEASUREMENTS AND MAIN RESULTS

Total CBF, cerebral oxygen consumption, and somatosensory evoked potentials (SEP) were measured during 240 mins of reperfusion. CBF was similar in both vehicle- and LY231617-treated animals at baseline and throughout the experimental period. In all animals, SEP became isoelectric between 60 and 100 secs after cross-clamping of the ascending aorta. SEP amplitude recovery was significantly higher in drug-treated animals compared with controls (73%+/-15% vs. 39%+/-14% [mean+/-SEM] from baseline at 120 mins [p<.05] and 86%+/-12% vs. 49%+/-14% from baseline at 240 mins [p< .05]).

CONCLUSIONS

LY231617 improves recovery of cerebral electrical function after complete transient global ischemia via mechanisms unrelated to cerebral circulatory effects.

Neuroprotective FK506 does not alter in vivo nitric oxide production during ischemia and early reperfusion in rats

BACKGROUND AND PURPOSE

Previous studies have demonstrated that the immunosuppressant FK506 provides neuroprotection in experimental brain injury and suggest that this action may be mediated by suppression of neuronal nitric oxide synthase activation that occurs after ischemic depolarization. We sought to determine whether FK506 reduces histological injury after middle cerebral artery occlusion (MCAO) in the rat and whether the neuroprotective effect is mediated via suppression of in vivo nitric oxide (NO) production during ischemia or early reperfusion.

METHODS

Under controlled conditions of normoxia, normocarbia, and normothermia, halothane-anesthetized male Wistar rats were subjected to 2 hours of MCAO by the intraluminal occlusion technique in a blinded, randomized experimental trial. Ipsilateral parietal cortical laser-Doppler flowmetry was monitored throughout ischemia. Animals were randomly assigned to 4 pretreatment groups: intravenous FK506 0.3 mg/kg or 1. 0 mg/kg, vehicle (cremaphor), or an equivalent volume of saline administered 30 minutes before MCAO. Infarction volume was assessed by a triphenyltetrazolium chloride staining at 22 hours of reperfusion. In separate experiments, microdialysis probes were placed bilaterally into the striatum. Rats were perfused with artificial cerebrospinal fluid containing 3 micromol/L [14C]- L-arginine for 3 hours and then subjected to 2 hours of right MCAO. Intravenous 0.3 mg/kg FK506 or cremaphor was given 30 minutes before right MCAO. Right-left differences between [14C]-L-citrulline in the effluent were assumed to reflect differences in NO production.

RESULTS

All values are mean+/-SE. FK506 at 0.3 mg/kg reduced infarction volume in cortex: 40+/-12 mm3 compared with saline (109+/-15 mm3) and cremaphor vehicle (148+/-23) (P<0.05). Striatal infarction was also reduced by low-dose FK506: 16+/-4 mm3 versus 36+/-4 mm3 and 34+/-4 mm3 in saline and vehicle groups, respectively (P<0.05). High-dose treatment reduced infarction volume in cortex (61+/-14 mm3, P<0.05 from saline and vehicle groups) and in striatum (22+/-5 mm3, P<0.05 from saline and vehicle groups). [14C]-L-citrulline recovery via microdialysis was markedly enhanced in ischemic compared with nonischemic striatum. However, ischemia-evoked [14C]-L-citrulline recovery was not different in FK506-treated rats compared with vehicle-treated animals.

CONCLUSIONS

These data demonstrate that FK506 provides robust neuroprotection against transient focal cerebral ischemia in the rat. The mechanism of protection in vivo is not through attenuation of ischemia-evoked NO production during MCAO and early reperfusion.

The effect of the prone position on pulmonary mechanics is frame-dependent

By compressing the abdomen and restricting chest wall movement, the prone position compromises pulmonary compliance. For spine surgery, placing the anesthetized patient into the prone position increases the risk of improper ventilation. In this study, we tested the hypothesis that the compromise in pulmonary compliance is related to the patient's body habitus and the surgical frame used to support the patient while in the prone position. Seventy-seven adult patients were divided into three groups according to body mass index: normal (n = 36) < or = 27 kg/m2, heavy (n = 21) 28-31 kg/m2, and obese (n = 20) > or = 32 kg/m2. Patients were placed in the prone position supported by chest rolls, a Wilson frame, or the Jackson spinal surgery table (Jackson table) according to the surgeon's preferences. Peak airway pressure (at the proximal endotracheal tube), pleural pressure (esophageal balloon), and mean arterial pressure were recorded in the supine position and prone position within 15 min of the turn. Dynamic mean (+/- SD) pulmonary compliance (mL/cm H2O) decreased when turning from the supine to the prone position in all three body mass groups when using chest rolls (normal 37+/-5 to 29+/-6; heavy 43+/-2 to 34+/-4; obese 42+/-8 to 32+/-6) or the Wilson frame (normal 39+/-6 to 32+/-7; heavy 43+/-16 to 34+/-10; obese 36+/-11 to 28+/-9). The dynamic pulmonary compliance was not altered in patients positioned on the Jackson table. Regardless of body habitus, using the Jackson table for prone positioning was not associated with a significant alteration in pulmonary or hemodynamic variables. We conclude that moving patients from the supine to the prone position during anesthesia results in a decrease in pulmonary compliance that is frame-dependent but that is not affected by body habitus.

IMPLICATIONS

We hypothesized that compromise in pulmonary compliance in the prone position is related to the patient's body mass index and the surgical frame used. In this study, we demonstrated that prone positioning during anesthesia results in a decrease in pulmonary compliance that is frame-dependent but that is not affected by body mass index.

Estrogen-mediated neuroprotection after experimental stroke in male rats

BACKGROUND AND PURPOSE

We have previously shown that 17beta-estradiol reduces infarction volume in female rats. The present study determined whether single injection or chronic implantation of estrogen confers neuroprotection in male animals with middle cerebral artery occlusion (MCAO) and whether there is an interaction with endogenous testosterone.

METHODS

Male Wistar rats were treated with 2 hours of reversible MCAO. In protocol 1, acute versus chronic estrogen administration was examined in groups receiving the following: Premarin (USP) 1 mg/kg IV, immediately before MCAO (Acute, n=13, plasma estradiol=171+/-51 pg/mL); 7 days of 25 microg (E25, n=10, 10+/-3 pg/mL) or 100 microg 17beta-estradiol (E100, n=12, 69+/-20 pg/mL) by subcutaneous implant; or saline (SAL, n=21, 3+/-1 pg/mL). Laser-Doppler flowmetry was used to monitor the ipsilateral parietal cortex throughout the ischemic period and early reperfusion. At 22 hours of reperfusion, infarction volume was determined by 0 2,3,5-triphenyltetrazolium chloride staining and image analysis. In protocol 2, rats were castrated to deplete endogenous testosterone and then treated with estradiol implants: castration only (CAST, n= 13, estradiol=5+/-2 pg/mL), sham-operated (SHAM, n= 10, 4+/-2 pg/mL), estradiol implant 25 microg (CAST+E25, n=16, 7+/-2 pg/mL) or 100 microg (CAST+E100, n=14, 77+/-14 pg/mL).

RESULTS

Cortical infarct volumes were reduced in all estrogen-treated groups: Acute (21+/-4% of ipsilateral cortex), E25 (12+/-5%), and E100 (12+/-3%) relative to SAL (38+/-5%). Caudate infarction was similarly decreased: Acute (39+/-7% of ipsilateral striatum), E25 (25+/-7%), and E100 (34+/-6%) relative to SAL (63+/-4%). Castration did not alter ischemic outcome; cortical and caudate infarction (percentage of respective ipsilateral regions) were 37+/-5% and 59+/-5% in CAST and 39+/-7% and 57+/-5% in SHAM, respectively. Estrogen replacement reduced infarction volume in castrated animals in cortex (19+/-4% in CAST+E25 and 12+/-4% in CAST+E100) and in caudate (42+/-6% in CAST+25 and 20+/-7% in CAST + 100). Laser-Doppler flowmetry results during ischemia and reperfusion was not different among groups.

CONCLUSIONS

Both acute and chronic 17beta-estradiol treatments protect male brain in experimental stroke. Testosterone availability does not alter estradiol-mediated tissue salvage after MCAO.

Hemodynamics of pancreatic ischemia in cardiogenic shock in pigs

BACKGROUND & AIMS

Previous studies have shown that the renin-angiotensin axis plays a pivotal role in vasoconstriction of the gastric, intestinal, and hepatic circulations during cardiogenic shock. The aim of this study was to evaluate the fundamental hemodynamic mechanism of pancreatic ischemia during cardiogenic shock induced by pericardial tamponade.

METHODS

Cardiogenic shock was induced by pericardial tamponade. Cardiac output (and total peripheral vascular resistance) was determined by thermodilution. Pancreatic blood flow (and vascular resistance) was determined with radiolabeled microspheres.

RESULTS

Graded increases in pericardial pressure produced corresponding decreases in cardiac output to 42% +/- 1% and arterial pressure to 67% +/- 3% of baseline and increases in total peripheral vascular resistance to 146% +/- 5% of baseline. Pancreatic blood flow decreased disproportionately to 30% +/- 3% of baseline, because of a disproportionate increase in pancreatic vascular resistance to 220% +/- 19% of baseline. Previously confirmed blockade of the renin-angiotensin axis ablated this response, whereas confirmed blockade of the alpha-adrenergic system or vasopressin system had no significant effect. Without shock, central intravenous infusions of angiotensin II closely mimicked this selective vasoconstriction.

CONCLUSIONS

Angiotensin-mediated selective pancreatic vasoconstriction results in significant pancreatic ischemia during cardiogenic shock.

Enhanced recovery of brain electrical activity by adenosine 3',5'-cyclic monophosphate following complete global cerebral ischemia in dogs

OBJECTIVE

To test the hypothesis that adenosine 3',5'-cyclic monophosphate (cAMP) or dibutyl-cAMP (a more lipid-soluble, less rapidly metabolized analog of cAMP) would improve recovery of cerebral electrical activity and metabolic function after transient global cerebral ischemia by improving cerebral blood flow during the reperfusion period.

DESIGN

Randomized, controlled, prospective study.

SETTING

University research laboratory.

SUBJECTS

Twenty-five male beagle dogs.

INTERVENTIONS

Nine control dogs received saline (20-mL/kg bolus and 0.01 mL/kg/min) intravenously, beginning 25 mins before 12 mins of cerebral global ischemia (by aortic occlusion). The dogs in the experimental groups received either cAMP (40 mg/kg 25 mins before ischemia and 0.2 mg/kg/min throughout reperfusion, n = 7), or dibutyl-cAMP (6 mg/kg 25 mins before ischemia and 3 mg/kg at 60, 90, and 120 mins of reperfusion, n = 9).

MEASUREMENTS AND MAIN RESULTS

Total and regional cerebral blood flow, cerebral oxygen consumption, and somatosensory evoked potentials were measured during 180 mins of reperfusion. Pretreatment with dibutyl-cAMP resulted in increased postischemic hyperemia at 30 mins of reperfusion (e.g., whole brain: control 40 +/- 6; cAMP 56 +/- 9; dibutyl-cAMP 67 +/- 10 mL/min/100 g [mean +/- SEM, p < .05 control vs. dibutyl-cAMP group]) but no difference in total cerebral blood flow or oxygen consumption during later points of reperfusion. All groups demonstrated rapid ablation of the amplitude of somatosensory evoked potentials during ischemia, with no difference between the groups. At 180 mins of reperfusion, somatosensory evoked potentials recovered to 28 +/- 4% of the preischemic baseline value in dogs treated with saline, whereas the somatosensory evoked potentials recovered to 58 +/- 4% of preischemic baseline value in the cAMP-pretreated group (p < .05), and to 70 +/- 6% of preischemic baseline value in dogs treated with dibutyl-cAMP (p < .05).

CONCLUSIONS

cAMP and dibutyl-cAMP improve recovery of cerebral electrical function after complete transient global cerebral ischemia. Although hyperemia was more prolonged in cAMP- and dibutyl-cAMP-treated dogs, there was no difference between groups in degree of postischemic delayed hypoperfusion. Therefore, we believe that the mechanism for cerebral protection afforded by cAMP and dibutyl-cAMP is not related to cerebral circulatory effects.

Effects of pentoxifylline on cerebral blood flow, metabolism, and evoked response after total cerebral ischemia in dogs

OBJECTIVE

To test the hypothesis that pentoxifylline improves recovery of cerebral electrical activity and metabolic function after a transient cerebral global ischemia by improving cerebral blood flow during the reperfusion period.

DESIGN

Randomized, controlled, prospective study.

SETTING

University research laboratory.

SUBJECTS

Forty male beagle dogs.

INTERVENTIONS

Six control dogs received pentoxifylline (40 mg/kg bolus followed by infusion at 0.2 mg/kg/hr) without ischemia. Thirteen dogs received Ringer's lactate solution with 12 mins of cerebral global ischemia (by aortic occlusion). Nine dogs received pentoxifylline before ischemic insult. Six dogs received pentoxifylline on reperfusion, and six dogs received pentoxifylline 30 mins after reperfusion.

MEASUREMENTS AND MAIN RESULTS

Total and regional cerebral blood flow, cerebral oxygen consumption, and somatosensory evoked potentials were measured during 180 mins of reperfusion. Pentoxifylline did not affect cerebral blood flow, oxygen consumption, or somatosensory evoked potentials without ischemia. Pretreatment with pentoxifylline resulted in attenuated postischemic hyperemia at 10 mins of reperfusion (94 +/- 15 vs. 133 +/- 11 [SEM] mL/min/100 g; p < .05), but there was no difference in total cerebral blood flow or oxygen consumption during later points of reperfusion. Pentoxifylline treatment during reperfusion resulted in no recovery of cerebral blood flow or oxygen consumption. All ischemic groups demonstrated a rapid ablation of somatosensory evoked potential amplitude and there were no differences in the decrement of the amplitude on ischemia. At 180 mins of reperfusion, somatosensory evoked potentials recovered to the following percentages of the baseline control values: 28 +/- 4% in dogs treated with Ringer's lactate solution; 58 +/- 4% in the pentoxifylline pretreated group (p < .05); 40 +/- 5% in dogs receiving pentoxifylline at reperfusion (p > .05); and 53 +/- 8% in dogs receiving pentoxifylline at 30 mins of reperfusion (p < .05).

CONCLUSIONS

Pentoxifylline treatment improves recovery of cerebral electrical function after complete transient cerebral global ischemia by a mechanism that does not involve improvement in cerebral blood flow or global oxygen consumption.

Incidence and perioperative management of tension pneumocephalus following craniofacial resection

This study is a retrospective review to evaluate factors associated with the risk of pneumocephalus following craniofacial resection and the management of tension pneumocephalus. Twenty-two craniofacial operative procedures were reviewed in 18 patients entered into the Neurosciences Critical Care Unit, Johns Hopkins Hospital, during a 54 month period, from 1986-1991. Pneumocephalus developed after 7 of 22 operations; of these seven, two developed tension pneumocephalus. The use of lumbar cerebral spinal fluid (CSF) drainage during the operation correlated most strongly with the development of pneumocephalus. The diagnosis of esthesioblastoma also correlated significantly. Both episodes of tension pneumocephalus occurred after craniofacial resection in which lumbar drainage of CSF was performed. Tension pneumocephalus was successfully treated in these two patients with a combination of air evacuation and medical management of raised intracranial pressure. Transient diabetes insipidus developed in both patients. The risk of pneumocephalus following craniofacial procedures is significant, and may be increased by the use of lumbar drainage of CSF intraoperatively. Rapid neurologic deterioration following craniofacial resection may be caused by the development of tension pneumocephalus. Early diagnosis of tension pneumocephalus and aggressive management of raised intracranial pressure may be important in preventing serious neurological complications.

Sucralfate does not reduce the risk of acid aspiration pneumonitis

OBJECTIVE

To study the pulmonary effects of aspirating a mixture of sucralfate in water and sucralfate in hydrochloric acid in an animal model of aspiration pneumonia.

DESIGN

Prospective, randomized, controlled study with repeated measures.

SETTING

University research laboratory.

SUBJECTS

Thirty-two in situ, isolated, blood perfused porcine lung preparations.

INTERVENTIONS

Five control preparations received no aspiration. Twenty-seven preparations received a standard aspiration of 1.5 mL/kg body of a) distilled water (n = 5), b) sucralfate in distilled water (n = 8), c) 1/10 normal hydrochloric acid (n = 6), and d) mixture of sucralfate in distilled water and hydrochloric acid (n = 8).

MEASUREMENTS

The pH measurements were made of all aspirates. Lung weight, airway pressures, and pulmonary artery pressures were continuously monitored before and for 4 hrs after aspiration. Lung wet/dry weight ratio was measured at the completion of the study.

RESULTS

The pH of sucralfate mixed with distilled water was 4.9, pH of 1/10 normal hydrochloric acid was 1.0, and pH of equal volumes of a sucralfate-water suspension mixed with hydrochloric acid was 1.5. Airway pressures and pulmonary arterial pressures increased in all aspirate groups over time compared with those values of control lungs. Control lungs gained 18 +/- 3 (SEM) g over 4 hrs and the wet/dry ratio was 4.951 +/- 0.310. Lungs aspirating distilled water gained 147 +/- 49 g and the wet/dry ratio was 5.198 +/- 0.120. Lungs aspirating sucralfate and distilled water increased their weight by 109 +/- 30 g and the wet/dry ratio was 5.380 +/- 0.076. Lungs aspirating a suspension of sucralfate and water and hydrochloric acid were similar to lungs aspirating hydrochloric acid alone with weight increases of 265 +/- 30 g and 346 +/- 81 g, and the wet/dry ratio of 7.011 +/- 0.273 and 7.230 +/- 0.390, respectively.

CONCLUSIONS

Sucralfate has minimal acid buffering effect. Aspiration of sucralfate mixed with distilled water causes lung edema similar to aspiration of water alone. Aspiration of a sucralfate-water suspension mixed with hydrochloric acid causes severe lung edema. These results suggest that patients given sucralfate prophylaxis for stress ulceration are at risk for acid aspiration.

Lung injury produced by pancreatic proteases in dogs

With an isolated, blood-perfused canine lung-lobe preparation, the potential role of reactive oxygen metabolites and neutrophils in pancreatic protease (alpha-chymotrypsin)-induced acute lung injury was studied. Administration of alpha-chymotrypsin caused a low-pressure pulmonary edema (mean lung lobe weight increased from 71 to 197 gm). Pretreatment with superoxide dismutase alone did not attenuate the injury (58 to 166 gm), but when combined with catalase, the injury was significantly ameliorated (64 to 107 gm). However, depletion of circulating leukocytes did not attenuate the injury (69 to 200 gm). These findings suggest that circulatory proteases can cause lung injury by a mechanism that is mediated, at least in part, by toxic oxygen metabolites that are not of neutrophil origin.

Preoperative risks predict neurological outcome of carotid endarterectomy related stroke

The aim of this study was to determine if preoperative risk factors are predictors of poor stroke outcome after carotid endarterectomy. In addition, the effect of other stroke risk factors on stroke severity was determined. A retrospective review of carotid endarterectomy results spanning 10 years, encompassing 561 patients, and reporting the combined results of all surgeons at our institution was performed. Patients were assigned to one of four groups. There were 227 patients with no preoperative risks (Group 1), 61 with angiographic risks (Group 2), 196 with medical risks with or without angiographic risks (Group 3), and 77 with neurological risks with or without medical/angiographic risks (Group 4). Other risks associated with stroke occurrence were recorded including: intraoperative risks (cross-clamp time, use of shunt, use of glucose solutions), surgical complications (carotid occlusion/thrombus or ligation), and medical complications (hypoxia, myocardial infarct). Stroke incidence was 5% with 2% (11 patients) and 3.4% (19 patients) having good and poor outcomes, respectively. Stroke incidence was highest in Groups 2 and 4 (10 and 14%, respectively), and Group 4 had the highest incidence of poor-outcome stroke (12%). Cross-clamp time, intraoperative shunt placement, and intraoperative glucose administration were similar among preoperative risk groups and were not primary determinants of stroke severity. The most common medical complication was myocardial infarction, which had the highest incidence in Groups 3 and 4 (6.1 and 5%, respectively). The highest incidence of surgical complications occurred in Groups 2 and 4, carotid thrombosis being the most common event (16 patients). Surgical complications were more commonly associated with stroke than were medical complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cyclosporine on cerebral blood flow and metabolism in dogs

Neurological side effects associated with cyclosporine immunosuppressive therapy are generally believed to occur with CsA blood concentrations above the therapeutic range. The effects of high blood CsA levels on cerebral hemodynamics, metabolism, and electrophysiologic activity were studied in acute (no CsA prior treatment) and chronic (with CsA prior treatment) dogs. In acute animals, when parenteral CsA (10 mg/kg or 25 mg/kg) was administered intravenously (CsA blood level 2000-22,000 ng/ml), slight but significant time-dependent decreases in cerebral blood flow (CBF), prolongation of absolute latencies of somatosensory-evoked potential (SSEP), and brainstem auditory-evoked responses (BAER) were noted. In the CsA chronically administered animals (oral CsA 25 mg/kg/24 hr for 14 days, CsA blood level 1077 ng/ml), baseline cerebral physiologic parameters were normal, and the cerebral responses to further administration of CsA (25 mg/kg, CSA blood level 56,000 ng/ml) intravenously were similar to those of the acute animals. Animals given Cremophor EL, the solvent for parenteral CsA preparation, showed similar cerebral responses to those observed in animals given CsA. Thus this study showed that CsA, regardless of the dose given, whether chronically or acutely administered, or the solvent for CsA all induced similar cerebral physiologic responses. We suggest that the cerebral physiologic and functional changes associated with parenteral CsA administration were small and were likely caused by its solvent, Cremophor EL, rather than CsA itself. Furthermore on the basis of our results, it is unlikely that high blood CsA per se can account for neurological side effects that occur in immunosuppressed patients.

Pentoxifylline attenuates edema formation in proteolytic enzyme-induced lung injury

Ex vivo canine lung lobes were exposed to a pancreatic proteolytic enzyme (chymotrypsin) alone or chymotrypsin after pretreatment with a continuous infusion with pentoxifylline. The lobes exposed to chymotrypsin gained 133 g, while the pentoxifylline-treated lobes gained only 65 g (p less than .05) over the 3-h experimental period. These results suggest that pentoxifylline significantly attenuates the lung weight gain associated with chymotrypsin.

Age-related cerebrovascular response to global ischemia in pigs

We tested the hypothesis that 1- to 2-wk-old pigs (piglet) have improved recovery of cerebral blood flow (CBF), cerebral oxygen consumption (CMRO2), and somatosensory-evoked potentials (SEP) compared with 6- to 8-mo-old pigs (pig) after transient global cerebral ischemia. All animals were anesthetized with pentobarbital sodium. After tracheostomy ventilation was adjusted to maintain normoxia (arterial oxygen pressure, 100-150 mmHg) and normocarbia (arterial carbon dioxide pressure, 35-40 mmHg). Arterial blood gases, blood pressure, and hemoglobin concentration remained within physiological limits throughout the experiment. Cerebral ischemia was produced by sequentially tightening ligatures around the inferior vena cava and ascending aorta. During ischemia the electroencephalogram and SEP became isoelectric within 40 and 120 s, respectively. At 10 min of reperfusion hyperemia occurred in most brain regions (e.g., whole brain: piglet, 270 +/- 45%; pig, 316 +/- 48%). In pigs delayed hypoperfusion occurred in all regions except white matter. In contrast, piglets only had delayed hyperperfusion to the brain stem and caudate nucleus. Throughout reperfusion CMRO2 was decreased in pigs (3.3 +/- 0.4 to 1.9 +/- 0.2 ml.min-1.100 g-1) but was not different from control (2.7 +/- 0.3 ml.min-1.100 g-1) in piglets. By the end of reperfusion SEP amplitude was closer to control in piglets than pigs (55 +/- 9 vs. 32 +/- 4% of control). We conclude that 1- to 2-wk-old piglets have quicker return of CBF, CMRO2, and SEP to control values after global ischemia, which mechanistically may explain previous reports of improved neurological recovery in young animals after transient ischemia.

Effect of PEEP and jugular venous compression on canine cerebral blood flow and oxygen consumption in the head elevated position

Cerebral blood flow (CBF) (radiolabelled microspheres) and oxygen consumption (CMRO2) were studied in nine dogs during 30 min of either neck vein compression or application of positive end-expiratory pressure (PEEP) ventilation. With the animal in the prone position, elevation of the head from horizontal to 30 cm above the heart markedly decreased cisterna magna (PCSF) and dorsal sagittal sinus pressure (PCV). With the head elevated, compression of neck veins using neck tourniquet (pressure 40 mmHg) increased PCSF and PCV from 3.6 +/- 2.2 to 6.8 +/- 4.8 and -2.5 +/- 2.7 to 2.3 +/- 2.3 mmHg (mean +/- SE, P less than 0.05), respectively, while total or regional CBF and CMRO2 remained unchanged. Application of PEEP (15 cm H2O) increased right atrial pressure (-4.7 +/- 1.7 to -0.1 +/- 3.4 mmHg, P less than 0.05), but did not affect PCSF or PCV (3.4 +/- 3.3 to 3.3 +/- 3.7 and -3.5 +/- 2.6 to -4.1 +/- 2.4 mmHg, respectively, P greater than 0.05). Total or regional CBF and CMRO2 were also unaffected. These data demonstrate that, although neither maneuver affects CBF or CMRO2, neck vein compression elevates PCV above atmospheric pressure, but PEEP does not. In patients at risk for cerebral venous embolism, intermittent neck vein compression should be used as a prophylactic measure to prevent air embolism.

O2 radicals mediate reperfusion lung injury in ischemic O2-ventilated canine pulmonary lobe

This study was undertaken to determine whether lung injury after a period of ischemia reperfusion is caused by O2 ventilation during ischemia and whether this injury is mediated by reactive O2 metabolites. Isolated canine left lower pulmonary lobes were subjected to room temperature ischemia for 6 h while being ventilated with either 100% O2, room air, or 100% N2. After the ischemic period, all lobes were perfused with autologous blood and ventilated with 100% O2 for an additional 4 h. In lobes ventilated with 100% O2 during the ischemic period, massive weight gain (228%) occurred 4 h after reperfusion. A marked increase in pulmonary shunt was noted. Lobes ventilated with room air behaved similarly. In contrast, lobes ventilated with 100% N2 gained significantly less weight (54%) and did not manifest any increase in pulmonary shunt. When lobes ventilated with 100% O2 or room air were pretreated with superoxide dismutase (SOD), the injury was significantly reduced. Pressure-volume deflation study of lobes, after ischemia only, demonstrated that ventilation with 100% O2 and with 100% N2 both equally decreased pulmonary compliance. We conclude that lung ischemia-reperfusion injury is related to O2 ventilation during ischemia and that injury can be prevented by administration of SOD or ventilation with 100% N2. This suggests that the injury is related to O2 metabolites produced during O2 ventilation in the absence of the circulation.

Pneumocephalus: effects of patient position on the incidence and location of aerocele after posterior fossa and upper cervical cord surgery

The incidence of pneumocephalus and factors contributing to its occurrence were studied retrospectively in 100 consecutive patients who underwent posterior fossa or cervical cord surgery in the sitting, park-bench, and prone positions. Supine skull x-ray films taken immediately postoperatively were used to determine the presence of intracranial air. Surgery in the sitting position uniformly resulted in pneumocephalus (32/32 patients). Pneumocephalus also occurred frequently among patients in the park-bench (29/40) and prone positions (16/28). Intraventricular air occurred more frequently when patients were in the sitting position (25/32) than in the two other surgical positions (3/29 and 4/16, respectively, P less than 0.001). The high incidence of pneumocephalus and of intraventricular air that occurred when patients were in the sitting position is attributed to the large amount of cerebrospinal fluid drained due to gravitational effect. When surgical position is considered one of the contributing factors, only positions significantly affected the frequencies of pneumocephalus and intraventricular air accumulation. None of the 77 patients with pneumocephalus suffered neurologic change related to the presence of intracranial air. We conclude the following: pneumocephalus commonly occurs after posterior fossa or cervical cord surgeries, particularly when the surgery is performed in the sitting position; neurologic change caused by pneumocephalus is a rare complication after posterior fossa craniotomy; when a patient with coexisting hydrocephalus undergoes surgery, if the patient is in the sitting position, there is an increased risk of trapping a large amount of intracranial air.

Effect of intra-alveolar meconium on pulmonary surface tension properties

To evaluate the effect of meconium on pulmonary surface tension properties, the mechanics of 30 excised, separated canine pulmonary lobes were studied. Meconia were blended in normal saline to produce solutions of 10% and 20%. Solutions were filtered to remove large particles and instilled endobronchially into the canine lobes. The static pressure-volume deflation curve of each lobe was determined before and 4 h after instillation of either normal saline or meconium solution. In the saline control group (eight lobes), the curve was essentially unchanged before and after instillation. In the 10% meconium group (14 lobes), the curve was significantly depressed after instillation, especially at a transpulmonary airway pressure of 10 cm H2O (p less than .05) and 5 cm H2O (p less than .005). In the 20% meconium group (eight lobes), the depression of the pressure-volume curve was essentially the same as that of the 10% solution group. It is concluded that meconium depresses the surface-active properties of the alveolar linings.

Evaluation of the efficacy of Alka-Seltzer Effervescent in gastric acid neutralization

A commercially available antacid, a mixture of sodium and potassium bicarbonates and citric acid (Alka-Seltzer Effervescent), was evaluated experimentally and clinically for its efficacy in neutralizing 0.1 N HCl and gastric contents. In an in vitro titration study, Alka-Seltzer Effervescent buffered 5-30 times the volume of HCl with a pH between 1.0 and 2.0 to above a pH of 2.5. In an isolated canine pulmonary lobe model, aspiration of the antacid or acid-antacid mixture caused only a mild increase in lobe weight and did not increase intrapulmonary shunting. In the clinical study, when the antacid was given 5-40 min before administration of general anesthesia in a group of patients for emergency surgery, the pH of the gastric contents in each patient was increased to above 4.0. This contrasts with the control group of patients, which showed 50% (P less than 0.05) of the patients were at risk when no antacid was administered. Preoperative administration of Alka-Seltzer effectively increases the pH of the gastric contents in patients undergoing emergency surgery.

Aspiration pneumonia: treatment with pulmonary vasodilators

Experimental aspiration pneumonia induced in the isolated perfused ventilated canine pulmonary lobe by the intrabronchial instillation of hydrochloric acid is characterized by pulmonary edema, intrapulmonary shunting, and loss of lung compliance. In addition, pulmonary artery pressure increases. In an attempt to modify the injury response, we restricted the increase in pulmonary artery pressure in the isolated lobe model by administering vasodilator drugs. In control lobes perfused for 4 hours there was minimal weight gain (14 gm), pulmonary artery pressure remained stable (13 mm Hg), and intrapulmonary shunting did not occur. Following intrabronchial instillation of 0.2 ml of 0.1N HCl/gm of lobe weight, lobe weight tripled (183 gm), pulmonary artery pressure (20 mm Hg) was significantly increased, and significant intrapulmonary shunting (32%) developed. When sodium nitroprusside (2 micrograms/min/kg of dog body weight) was infused into the pulmonary artery 3 minutes after HCl instillation, the pulmonary artery pressure was significantly reduced (13 mm Hg) compared to that in untreated acid lobes. This was accompanied by a significant reduction in mean weight gain (100 gm) and intrapulmonary shunting (15%) compared to untreated acid lobes. Similarly, when isoproterenol (0.04 micrograms/min/kg dog body weight) was infused into the pulmonary artery following acid instillation, the pulmonary artery pressure (12.5 mm Hg) was significantly reduced compared to that in untreated acid lobes. This was also accompanied by a significant reduction in weight gain (60 gm) and intrapulmonary shunting (6%) compared to untreated acid lobes. These data demonstrate that the increase in pulmonary artery pressure following acid injury can be lowered pharmacologically and that a significant decrease in injury response follows. This suggests that the magnitude of the injury response is in part a function of pulmonary artery pressure.

Measurement of carotid blood flow in man and its clinical application

With the use of a new ultrasonic volume flow meter (VFM), over 8000 measurements of common carotid blood flow were made in 120 normal control subjects and 550 patients with various neurological disease. The accuracy of the flow meter in measuring blood flow on an experimental model ranged from 93 to 97%. In normal subjects, common carotid blood flow varies with age. It increased from newborn to age 20 and gradually decreased thereafter. In normal healthy subjects, the flow varies within +/- 6.7% (2SD) at one sitting (intrasession) and +/- 21.2% (2SD) from week to week (intersession study). Carotid blood flow varies linearly with PaCO2 and increased markedly in response to endotracheal intubation. In healthy adults, the flow ratio between the two common carotid arteries is 1.07 +/- 0.052. This ratio increases in patients with transient ischemic attacks to 1.28 +/- 0.23 (p less than 0.05) and in patients with intracranial space occupying lesions to 1.46 +/- 0.39, (p less than 0.01). In 26 consecutive cases of carotid endarterectomies, the preoperative common carotid blood volume flow was 5.1 +/- 1.0 cc/sec. All cases preoperatively had at least 30% stenosis and ranged from 30 to 100% stenosis. The carotid blood volume was significantly increased post-operatively (p less than 0.001). The overall accuracy in detecting carotid and cerebral arterial disease is 89% with sensitivity of 96% and the specificity of 71%. Our clinical experience indicates that this device is not only a valuable noninvasive diagnostic tool for evaluation of carotid disease but also appears to be useful in assessing cerebral blood flow.

Aspiration pneumonia: treatment with osmotically active agents

Utilizing the ex vivo perfused ventilated canine pulmonary lobe, we evaluated the effects of three osmotically active agents on pulmonary function after acid aspiration. Control lobes were stable during a 44-hour perfusion with minimal weight gain, stable pulmonary artery and end-inspiratory pressures, and no increase in intrapulmonary shunting. After acid aspiration during a 44-hour perfusion period, massive weight gain occurred (228 gm), pulmonary artery and end-inspiratory pressure increased, and marked intrapulmonary shunting (44%) developed. When mannitol (molecular weight 182) or dextran 40 (molecular weight 40,000) were added to the perfusate of the acid-instilled lobes, no significant modifications of the acid-induced response were seen during the 44-hour perfusion. The administration of albumin (molecular weight 69,000), however, markedly modified the acid-induced response. Weight gain (53 gm) was almost completely eliminated, pulmonary artery and end-inspiratory pressures were stable, and intrapulmonary shunting increased only minimally (10%). It is concluded that despite the permeability change in the capillary-alveolar membrane produced by acid aspiration, albumin is retained within the vascular space and is effective in reducing the injury response.

Pulmonary injury caused by free fatty acid: evaluation of steroid and albumin therapy

Intrapulmonary free fatty acid (FFA) release has been suggested as a pathogenetic mechanism in respiratory failure caused by acute pancreatitis and fat embolism. Utilizing the isolated perfused ventilated canine pulmonary lobe, we evaluated the effects of FFA infusion and its subsequent modification by albumin and steroid therapy. In control lobes perfused for a 4-hour period, there was minimal weight gain (11 gm), intrapulmonary shunting did not occur, and compliance remained within normal limits. When 1 ml of oleic acid was infused into the pulmonary artery lobe weight tripled (188 gm), intrapulmonary shunting (20%) developed, and compliance was significantly decreased compared to controls. When 30 gm of human salt-poor albumin was added to the perfusate immediately after FFA infusion, the lobe response was similar to that of untreated oleic acid lobes. In contrast, when 400 mg of methylprednisolone succinate was added to the perfusate immediately after FFA infusion, lobe weight gain was significantly reduced (94 gm) compared to oleic acid lobes, intrapulmonary shunting did not occur, and compliance was within normal limits. This study suggests that steroids may be of benefit in the treatment of respiratory insufficiency secondary to acute pancreatitis and fat embolism.

The beneficial and harmful effects of positive end expiratory pressure

The effects of increasing levels of positive end expiratory pressure on gas exchange and pulmonary mechanics were determined utilizing an ex vivo ventilated perfused canine pulmonary lobe. When zero positive end expiratory pressure was used, shunting, weight gain and a decrease in compliance occurred over the four and one-half hour experiment. Shunting was eliminated when 5, 10 or 15 centimeters of water of positive end expiratory pressure were used. However, increasing extravascular fluid sequestration and decreasing pulmonary compliance occurred progressively with increasing levels of positive end expiratory pressure above 5 centimeters of water. Pulmonary artery pressure increased immediately along with end inspiratory pressure, an amount approximately equal to the increase in positive end expiratory pressure, and this is thought to be the primary cause of the increased rate of fluid sequestration. These experiments suggest that an optimal level of positive end expiratory pressure exists when the shunt can be reduced and oxygenation improved without increasing the rate of extravascular fluid accumulation to the point where long time deleterious effects could outweigh immediate benefits.

Aspiration pneumonia: experimental evaluation of albumin and steroid therapy

An experimental model using an ex vivo perfused ventilated canine pulmonary lobe was used to study aspiration pneumonia. After intrabronchial acid instillation, the lobe weight tripled, air way pressure and pulmonary artery pressure doubled, and intrapulmonary shunting increased from 5.5% to 53.4%. If large quantities of albumin were added to the lobe perfusate 5 minutes after intrabronchial acid instillation, weight gain, air way and pulmonary artery pressure, and intrapulmonary shunting were unchanged from control levels. If large quantities of steroid were added to the lobe perfusate 5 minutes after intrabronchial acid instillation, the lobe weight doubled but air way pressure and pulmonary artery pressure, and intrapulmonary shunting were not significantly different from control values. It is surmised that intrapulmonary acid aspiration causes an immediate and marked changed in pulmonary capillary permeability. Albumin administration by counteracting this permeability change, and steroid administration by modifying the permeability change, are both beneficial following acid aspiration.