Clinical features, intestinal histopathology, and outcome in protein-losing enteropathy in Yorkshire Terrier dogs.

BACKGROUND: A poorly understood protein-losing enteropathy (PLE) disorder has been reported in Yorkshire Terrier dogs. OBJECTIVES: To describe clinical features, intestinal histopathology, and outcome in Yorkshire Terrier dogs with PLE, and to identify variables predictive of outcome. ANIMALS: Thirty client-owned Yorkshire Terrier dogs with PLE. METHODS: Retrospective study. Records of dogs with a diagnosis of PLE were reviewed. Intestinal histopathology was interpreted using the World Small Animal Veterinary Association gastrointestinal histopathology classification system. Discriminate analysis techniques were used to identify variables predictive of outcome. RESULTS: Females outnumbered males (20/30). Median age was 7 years (range 1-12). Common clinical signs were diarrhea (20/30), vomiting (11), ascites and abdominal distension (11), and respiratory difficulty (8). Histopathologic abnormalities included villous lymphatic dilatation, crypt lesions, villous stunting, and variable increases in cellularity of the lamina propria. All dogs were treated with glucocorticoids. Of 23 dogs with long-term follow-up, 9 had complete, and 3 had partial, resolution of signs, and 11 failed to respond to treatment. Median survival of responders was 44 months and of nonresponders was 12 months, with 4 dogs experiencing peracute death. Vomiting, monocytosis, severity of hypoalbuminemia, low blood urea nitrogen concentration, and villous blunting were predictive of survival <4 months. CONCLUSIONS: In addition to classic GI signs, Yorkshire Terriers with PLE often show clinical signs associated with hypoalbuminemia and low oncotic pressure. Lymphatic dilatation, crypt lesions, and villous stunting are consistent histopathologic findings. Clinical outcomes are variable, but many dogs experience remission of clinical signs and prolonged survival.

Applicability of 3T body MRI in assessment of nonfocal bone marrow involvement of hematopoietic neoplasia in dogs.

BACKGROUND: The utility of whole body magnetic resonance imaging (MRI) in detecting bone marrow infiltration in dogs with cancer has not been investigated. OBJECTIVES: To assess the feasibility of 3T body MRI for bone marrow assessment in dogs with hematopoietic neoplasia. ANIMALS: Seven dogs with B-cell lymphoma, 3 dogs with myelodysplastic syndrome (MDS), and 2 clinically normal dogs. METHODS: A prospective study of dogs with hematopoetic cancer was conducted using T1W, T2W, In-Phase, Out-of-Phase and STIR pulse sequences of the body excluding the head prior to bone marrow sampling. The relative signal intensity of a midlumbar vertebral body and a midshaft femoral bone marrow was compared by visual and point region of interest analysis to regional skeletal muscle. RESULTS: Similarity of femoral diaphyseal and vertebral body marrow signal intensity to that of skeletal muscle on the Out-of-Phase sequence was useful in distinguishing the 3 dogs with hypercellular marrow because of MDS from the 7 dogs with B-cell lymphoma and from the 2 clinically normal dogs. 1/7 dogs with lymphoma had proven bone marrow involvement but normal cellularity and less than 5% abnormal cells. Unaffected midfemoral marrow had greater signal intensity than skeletal muscle and unaffected vertebral marrow had less signal intensity than skeletal muscle on the Out-of-Phase sequence. CONCLUSIONS AND CLINICAL IMPORTANCE: 3T, Out-of-Phase MR pulse sequence was useful in distinguishing diffuse bone marrow infiltrate (MDS) from minimally or unaffected marrow using skeletal muscle for signal intensity comparison on whole body MRI.

External-beam Co-60 radiotherapy for canine nasal tumors: a comparison of survival by treatment protocol.

A retrospective analysis of survival times in dogs with intranasal tumors was performed comparing those treated using hypofractionated or full course Co-60 radiotherapy protocols alone or with surgical adjuvant therapy and those receiving no radiation treatment. One hundred thirty-nine dogs presented to the University of Minnesota Veterinary Medical Center for treatment of histologically-confirmed nasal neoplasia between July 1983 and October 2001 met the criteria for review. Statistically analyzed parameters included age at diagnosis, tumor histologic classification, fractionation schedule (number of treatments, and number of treatment days/week) (classified as hypofractionated if 2 or less treatments/week); calculated minimum tumor dose/fraction; calculated total minimum tumor dose (classified as hypofractionated if less than 37 Gy in six or fewer fractions); number of radiotherapy portals, a treatment gap of more than 7 days in a full course (3-5 treatments/week, 3-3.5 week treatment time) radiotherapy protocol, the influence of eye shields on survival following single portal DV fields, the survey radiographic extent of the disease, and the presence or absence of cytoreductive surgery. There was a significant relationship only between protocols using 3 or more treatments/week and at least 37 Gy cumulative minimum tumor dose and survival. However, there was no significant relationship between either total minimum tumor dose or dose/fraction and survival and there were no significant relationships between survival and any of the other variables analyzed including tumor histologic type.

An integrated epidemiologic and radiographic algorithm for canine urocystolith mineral type prediction.

Research involved 2 databases. One database (occurrence frequency) comprised the age, breed, gender and urocystolith mineral type (pure chemical types only) from 2041 canine patients submitted to the Minnesota Urolith Center. The other database (imaging) comprised the maximum size, surface (rough, smooth, and smooth with blunt tips), shape (faceted, irregular, jackstone, ovoid, and round) and internal architecture (lucent center, random-nonuniform, and uniform) from 434 canine patients imaged in a urinary bladder phantom. The imaging database was a partial subset of the occurrence frequency database. Imaging techniques simulated were survey radiography and double contrast cystography. The databases were compared using multivariate analysis techniques. Equations were developed to use clinically-relevant characteristics (age, breed, gender, maximum size, surface, shape, and internal architecture) to predict urocystolith mineral types. The goal was to assess the accuracy of the various techniques in predicting the urocystolith mineral types. The combination of signalment (age, breed, gender) and simulated survey radiographic findings does not improve mineral type prediction accuracy (average across all mineral types is 69.9%) beyond that achievable with signalment alone (average across all mineral types is 69.8%). However, the combination of signalment and double contrast cystography does improve mineral type prediction accuracy (average across all mineral types is 75.3%). For comparison, mineral type prediction accuracy without signalment from survey radiographs only was 65.7% across all mineral types. The clinical utility of the algorithm is the option to distinguish urocystolith mineral types requiring surgical vs. medical treatment.

Relevance of sonographic artifacts observed during in vitro characterization of urocystolith mineral composition.

Nine pure mineral type canine uroliths (bladder or urethral origin only) were imaged ultrasonographically using 3.5 MHz, 5.0 MHz, and 7.5 MHz fixed focus, mechanical sector transducers in a urinary bladder phantom. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (brushite), ammonium acid urate, sodium acid urate, cystine, and silica. The occurrence of both reverberation/streak and acoustic shadowing artifacts were compared to urocystolith mineral type (classified by effective atomic number), urocystolith width, urocystolith height (thickness), and ultrasonographic imaging frequency. No predictable relationship was found between either of the artifacts seen beyond the urocystolith (reverberation/streak or the acoustic shadowing) and urocystolith mineral type. There was no statistical relationship between the occurrence of reverberation/streak artifact and the size (width or height) of the urocystolith or the ultrasonographic frequency. There was, however, a statistically relevant relationship between ultrasonographic imaging frequency and the occurrence of acoustic shadowing and between urocystolith height (thickness) and the occurrence of acoustic shadowing. However, regardless of ultrasound frequency, acoustic shadowing was observed less than 35% of the time in any of the urocystolith mineral types examined. Based on the imaging of the bladder phantom supporting apparatus (7.0 mm bolts covered by plastic), the accurate characterization of a curved object surface directly facing the transducer was found to be directly related to the frequency of sound used for imaging and at best predictably limited to curved vs flat. Accurate measurement of the maximum transverse dimension of an echogenic curved object or accurate characterization of the lateral borders of such an object was considered unlikely with general ultrasonographic equipment of the frequencies studied. Therefore, detailed architectural characterization of urocystoliths suitable for mineral composition prediction is considered highly unlikely with general pulse-echo ultrasonographic techniques.

Contrast medium-related artifacts observed during in vitro radiographic characterization of urocystolith mineral composition.

Nine pure mineral types of canine uroliths (bladder or urethral origin only) were exposed to sequential increasing concentrations of iodinated, radiographic contrast medium in petri dishes. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (Brushite), ammonium acid urate, sodium acid urate, cystine, and silica. Two phenomena were observed. First, there was a tendency for selected urocystoliths to undergo radiopacity augmentation beyond that expected for just contrast medium superimposition. This was termed, contrast medium adhesion, which persisted despite repeated washing of the urocystoliths. Second, there was a tendency for bubbles to form on or near selected urocystolith chemical types. These observations prompted careful scrutiny for their occurrence in subsequent clinical simulation of radiographic procedures using these same urocystoliths in a urinary bladder phantom. Imaging techniques simulated were survey radiography, pneumocystography, double contrast cystography (two iodine concentrations). The contrast medium adhesion occurrence found in the petri dish studies was compared to urocystolith mineral type. Similar comparisons were made for contrast medium adhesion occurrence in the bladder phantom. The detection of contrast medium adhesion in the bladder phantom differed from that observed in the petri dish experiments. While contrast adhesion occurred across a fairly broad range of the urocystolith mineral types in the petri dish studies, it was observed primarily for sodium acid urate and cystine urocystoliths in the bladder phantom. Prompted by the observation of bubbles in association with a limited number of urocystolith types in the petri dish studies, bubble occurrence in the bladder phantom was compared to the urocystolith type. Bubble formation on or near the urocystoliths, although uncommonly observed, was seen only with either cystine or silica urocystoliths. The potential clinical utility and clinical caveat aspects of these phenomena are discussed.

Loss of urocystolith architectural clarity during in vivo radiographic simulation versus in vitro visualization.

Urocystoliths of 9 mineral types from 434 canine patients submitted to the University of Minnesota Urolith Bank were imaged in a urinary bladder phantom. Imaging techniques simulated were survey radiography and double contrast cystography. Morphologic characteristics visually observed in vitro or by interpretation of high-resolution specimen radiographs were compared to those seen using the simulated in vivo imaging techniques. Shape characteristics that were accurately detected > or = 25% of the time on simulated survey or double contrast radiography were faceted, irregular, jackstone, ovoid, and round. Surface characteristics that were accurately detected > or = 25% of the time on simulated survey or double contrast radiography were rough, smooth, and smooth with blunt tips. Internal architecture characteristics that were accurately detected > or = 25% of the time on simulated survey or double contrast radiography were lucent center, random-nonuniform, and uniform. Shapes such as bosselated, faceted-ovoid, and rosette; surfaces such as botryoidal, and knife-edged; and internal architecture characteristics such as dense center, dense shell, laminated, and fissures were of almost no value either due to poor detectability or poor accuracy of recognition. Based on optimized simulated survey and double contrast radiographic procedures, it appears that a number of shape, surface, and internal architecture characteristics may be of limited or no value in discriminating among urocystolith mineral types under clinical circumstances. Shapes and surfaces were more accurately characterized by the simulated double contrast technique, but for internal architecture, the simulated survey radiographic technique seemed slightly superior overall.

Urocystolith detection: comparison of survey, contrast radiographic and ultrasonographic techniques in an in vitro bladder phantom.

Urocystoliths of 9 mineral types from 437 canine patients submitted to the University of Minnesota Urolith Bank were imaged in a urinary bladder phantom. Imaging techniques simulated were survey radiography, pneumocystography, double contrast cystography (two iodine concentrations) and real-time ultrasonography (3.5 MHz, 5.0 MHz, 7.5 MHz). Imaging techniques were compared for accuracy of urocystolith detection, accuracy of urocystolith enumeration, and tendencies for over or undercounting. Across urocystolith mineral types, the false negative rates (no urocystoliths detected in a given case) for survey radiographs range from 2 to 27%. Pneumocystographic techniques are one-half as likely to yield false negative results as are survey radiographic techniques. Underestimates of urocystolith numbers and false negatives are likely using 80 mg iodine/ml double contrast cystography because calcium-based urocystoliths are isopaque in this contrast medium dilution. The 200 mg iodine/ml double contrast cystographic techniques are unlikely to yield false negative diagnoses even for very small (< or = 1.0 mm) urocystoliths and is comparable to pneumocystography for detection and slightly better for enumeration. The likelihood of an ultrasonographic false negative for urocystoliths decreases with increasing MHz. Under optimal conditions using a 7.5 MHz mechanical sector transducer, the false negative rates were comparable to double contrast cystography, but rates increased notably with lower MHz transducers.

Imaging canine urocystoliths. Detection and prediction of mineral content.

The role of survey radiography, contrast radiography, and ultrasonography in the assessment of urocystolithiasis has been primarily one of detection. Information about the radiographic characteristics of uroliths (size, shape, radiopacity, surface characteristics, number detected) for characterization and diagnosis of urocystolithiasis is emerging; however, there are no studies on the accuracy or sensitivity of these techniques. In this article, the intent is to update knowledge about available imaging techniques used in the detection and characterization of urocystoliths based on recent studies designed to evaluate their accuracy in prediction of different urocystoliths mineral content.

In vitro evaluation of contrast medium concentration and depth effects on the radiographic appearance of specific canine urolith mineral types.

Nine pure mineral types of canine uroliths (bladder or urethral origin only) identified in a chronologic sample from the Minnesota Urolith Center were compared to sequential dilutions of iodinated radiographic contrast medium in vitro. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, calcium hydrogen phosphate dihydrate (brushite), ammonium acid urate, sodium acid urate, cystine, and silica. The radiopacity of the uroliths was classified as radiolucent, isopaque, or radiopaque, as compared to the radiopacity of the contrast medium solutions in which they were placed, using 2.0 mm and 5.0 mm depths in petri dishes radiographed using a table-top technique. A statistically significant relationship was found between the effective atomic number of the uroliths and the effective atomic number of the contrast medium solutions to which they were compared for the endpoints of isopacity, first lucency (in increasing iodine concentration sequence), and optimal visualization of internal architecture. In general, uroliths isopaque or radiolucent in contrast medium solutions weaker than 23.5 mgI2/ml are most likely ammonium acid urate or sodium acid urate. Uroliths isopaque or radiolucent in contrast medium solutions between 23.5 mgI2/ml and 44.4 mgI2/ml are probably magnesium ammonium phosphate, cystine, or silica. Uroliths that remained radiopaque in solutions stronger than 44.4 mgI2/ml, and particularly those radiopaque in contrast medium solutions stronger than 80 mgI2/ml, almost always contained calcium. This relative opacity assessment is proposed for use in double contrast cystography as an aid in differentiating urolith mineral types clinically to facilitate appropriate use of medical protocols to dissolve uroliths or to prevent their growth or recurrence.

Evaluation of the morphologic characteristics and prevalence of canine urocystoliths from a regional urolith center.

OBJECTIVE: To determine whether morphology of single-mineral urocystoliths and age, sex, or breed data could be applied to facilitate radiographic and clinical urocystolith mineral type prediction, respectively, in dogs. SAMPLE POPULATION: Database of 2,041 dogs with pure mineral composition urocystoliths. PROCEDURE: All uroliths were characterized according to geologic descriptive terminology and by breed, sex, and age of dog at time of sample submission. Summary statistics were used to compare features with specific mineral types. Observed trends were analyzed for statistical relevance between observed and expected frequencies for age, sex, color, size, shape, and surface, using the null hypothesis that differences by urocystolith mineral type did not exist. On the basis of expected breed occurrence derived by equations, the null hypothesis that urocystolith occurrence paralleled canine breed popularity was tested. RESULTS: Urocystoliths > 10 mm in any dimension were > 92% likely to be magnesium ammonium phosphate hexahydrate (MAP). Smooth, blunt-edged or faceted, and pyramidal urocystoliths were usually MAP. Jackstone shapes were almost always silica. Botryoidal (grape-like clusters) urocystoliths were likely to be oxalates. Breeds with high relative likelihood of urocystoliths included: English Bulldog, Pekingese, Pug, Welsh Corgi, and West Highland White Terrier. Breeds with low relative likelihood of urocystolith production included: German Shepherd Dog, Shar-Pei, and German Shorthaired Pointer. About 94% of urocystoliths produced in females or spayed females were MAP, whereas males and neutered males produced a greater assortment. CONCLUSIONS AND CLINICAL RELEVANCE: For pure mineral composition urocystoliths, trends in mineral type among breeds and between sexes can be exploited clinically in the diagnosis and management of urolith-related disease. Size and shape, used in conjunction with age, breed, and sex, can facilitate pure urocystolith mineral type prediction.

Case-control study of canine malignant lymphoma: positive association with dog owner's use of 2,4-dichlorophenoxyacetic acid herbicides.

A hospital-based case-control study of companion dogs examined the risk of developing canine malignant lymphoma associated with the use of chemicals in and about the home. Information from a self-administered owner questionnaire and/or a telephone interview of about 491 cases, 466 nontumor controls, and 479 tumor controls indicated that owners in households with dogs that developed malignant lymphoma applied 2,4-dichlorophenoxyacetic acid (2,4-D) herbicides to their lawn and/or employed commercial lawn care companies to treat their yard significantly more frequently than control owners (odds ratio = 1.3). In addition, the risk of canine malignant lymphoma rose to a twofold excess with four or more yearly owner applications of 2,4-D. The findings in this study are consistent with occupational studies in humans, which have reported modest associations between agricultural exposure to 2,4-D and increased risk of non-Hodgkin's lymphoma, the histology and epidemiology of which are similar to those of canine malignant lymphoma. The present study suggests that human health implications of 2,4-D exposure in the home environment should receive further investigation.

Effects of urinary bladder distention on location of the urinary bladder and urethra of healthy dogs and cats.

Evaluation of the anatomic location of the distended and empty urinary bladders and urethras of healthy adult male and female dogs and cats by retrograde urethrocystography revealed substantial variations. In 15 dogs in lateral recumbency with empty bladder lumens, the caudal portion of the urinary bladder was within the pelvic canal in 5 of 7 male and 5 of 8 female dogs. In female dogs examined in ventrodorsal recumbency, only 4 of 8 had the empty urinary bladders in part within the pelvic canal. After luminal distention, 3 of 7 male and 3 of 8 female dogs, while in lateral recumbency, had the urinary bladders in part intrapelvically. However, when female dogs were placed in ventrodorsal recumbency, only 1 of 7 urinary bladders was in part within the pelvis. The urinary bladders of 14 cats were consistently within the abdominal cavity, irrespective of whether the bladder lumen was distended or empty. Urethral flexures occurred in dogs with intrapelvic bladders that were distended or empty. Urethral flexures were not found in cats. The urethras of dogs and cats in lateral recumbency were generally closer to the floor of the pelvis after urinary bladder distention than when the bladder was empty. The urethra of the dogs and cats in ventrodorsal recumbency was to the left or right of or on the midsagittal plane, whether the urinary bladder was empty or distended. A greater degree of lateral displacement was encountered in ventrodorsal recumbency after urinary bladder distention.

Effects of intravesical hydrostatic pressure and volume on the distensibility of the canine prostatic portion of the urethra.

Positive-contrast retrograde urethrocystograms were obtained serially on 12 male dogs weighing 11.4 to 23.2 kg before, during, and after the injection of contrast medium until the urinary bladder neck and prostatic and membranous portions of the urethra remained open and distended as viewed by fluoroscopy. Correlations of intravesical volumes and pressures required to achieve maximum distension of the midprostatic portion of the urethra with body weight and surface area were not significant. Because of the variability in intravesical volumes and pressures encountered at maximum distension of the prostatic portion of the urethra, a dose of contrast material expressed relative to body weight or surface area could not be determined for consistently providing maximum distension of the prostatic portion of the urethra.

Effects of urinary bladder distension on the length of the dog and cat urethra.

Urethral lengths were determined in male and female cats and in female dogs from positive contrast retrograde urethrocystograms at 2 levels of urinary bladder distension. Urethral lengths were longer on urethrograms obtained after urinary bladder distension in female cats and in 7 of 8 female dogs. The intrapelvic and penile urethra were longer after bladder distension in 4 of 6 male cats. In female cats, urethral lengths significantly increased (P less than 0.05) after urinary bladder distension.

Orthovoltage radiation of normal canine nasal passages: assessment of depth dose.

Frozen heads of 9 clinically normal dogs were irradiated with orthovoltage x-rays. Surface doses and nasal cavity depth doses were measured, and the percentage of surface dose (depth dose) was calculated at random depths from the dorsal cutaneous surface in transverse planes through the medial and lateral canthi. Depth dose of 2 orthovoltage x-ray beams having half-value layers of 1.5 mm of Cu (96 keV) and 2.6 mm of Cu (134 keV) were compared with and found to resemble that reported in depth dose tables based on soft tissue equivalent material. Any differences (identified graphically) in depth dose, compared with that described using a uniform (soft tissue equivalent) phantom, were explained by the variations in tissue composition and the presence of air within the normal nasal and paranasal cavities.

Complications of retrograde contrast urethrography in dogs and cats.

Urinary bladder lesions varying histologically from a focal hemorrhagic cystitis to a diffuse transmural fibrinonecrotic cystitis were encountered in 11 of 14 dogs and cats euthanatized 1 day after retrograde urethrography. Focal-to-diffuse hemorrhagic urethritis was histologically encountered in 14 of 14 dogs and cats euthanatized 1 day after retrograde urethrography. Lesions in the urinary bladder and urethra were not reversible within 14 days and were evident histologically in 10 of 15 urinary bladders and 11 of 15 urethras of dogs and cats euthanatized 14 days after retrograde urethrography. During urethrography, iatrogenic mural leakage of contrast media into the bladder wall or bladder wall rupture was encountered radiographically in 6 of 15 dogs and 3 of 14 cats. However, macroscopic evidence of bladder rupture was encountered in only 1 male dog at necropsy. Immediately after retrograde urethrography, macroscopic hematuria occurred in 12 of 15 dogs and 9 of 14 cats. Microscopic hematuria was not encountered in dogs or cats euthanatized 14 days after urethrography. Pyuria was encountered less frequently and was present in only 2 cats euthanatized 14 days after urethrography. One day after urethrography, urinary tract infection characterized by urine cultures with greater than 10(5) microbes/ml was encountered in 4 of 29 dogs and cats. All animals with urinary tract infection were female dogs or cats. At day 14, only 1 female cat had a positive urine culture. Seemingly, the technique of retrograde urethrography was the cause of the encountered lesions.

Effects of prolonged distention of retention catheters on the urethra of dogs and cats.

The effects of inflation of a balloon-tipped catheter in the distal part of the urethra of clinically healthy male and female dogs and cats were evaluated. Tissues were evaluated at 1 and 14 days after balloon inflation. Macroscopic and microscopic lesions were limited to the distal part of the urethra occupied by the inflated balloon in animals which were euthanatized 1 day after balloon inflation. The lesions were characterized by submucosal urethral hemorrhage. This investigation indicates that balloon inflation for 15 minutes duration in the distal part of the urethra of dogs and cats results in a mild reversible inflammatory reaction.

Malignant hyperthermia-triggering liability of selected inhalant anesthetics in swine.

Twenty pigs, known to be malignant hyperthermia (MH)-susceptible by previous MH-positive [MH(+)] reactions to halothane testing, were given 5 inhalant anesthetics. The number of MH(+) responses evoked by the different anesthetics varied. In response to halothane, isoflurane, and enflurane, MH(+) reactions were exhibited by 12, 11, and 7 pigs, respectively. The number of MH(+) reactions to nitrous oxide (0) and methoxyflurane (1) was significantly (P = 0.02) less. In the present study, all 4 halogenated-hydrocarbon volatile liquid inhalant anesthetics were capable of evoking a MH(+) reaction in susceptible pigs.

Protection from halothane-induced porcine malignant hyperthermia syndrome by droperidol.

A group of 43 pigs from eight litters of purebred Pietrains were identified as malignant hyperthermia susceptible by halothane testing, and their reaction time (measured in seconds from the onset of halothane administration of the onset of skeletal muscle rigidity) was recorded. One week later, these pigs were treated with 0.02, 0.2, 0.5, 1.0 or 2.0 mg/kg of droperidol 1 hour prior to a second halothane test. Pigs with a post-droperidol reaction time of greater than 100.4 seconds (mean + 2.021 SD of initial reaction time) were considered to be protected from malignant hyperthermia. Droperidol afforded some degree of protection at all doses tested. The effective dose50 was determined to be 0.055 with 95% confidence limits of 0.017 to 0.183 mg/kg.