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PREGNANCY DIAGNOSIS AND TIMING ELECTIVE C-SECTIONS

January 6, 2012 Leave a comment

C. Scott Bailey, DVM, MS, DACT

Consultant, Veterinary Answers

Veterinarians are often asked to perform pregnancy diagnosis and time a c-section with very little information from the owner. Often, the only information provided is the breeding-dates and occasionally even those are hard to come by. Consequently there is a need for veterinarians to be familiar different with methods of estimating gestational age. This is particularly important when an elective caesarean section is desirable. Elective c-sections can carry an excellent prognosis for maternal and fetal viability when timed correctly and may be less stressful to the bitch, puppies and attending veterinarian than waiting for a potential dystocia. Animals that are particularly good candidates are those with a history of dystocia or a c-section and animals that have small (less than 3 pups) or large (more than 8 pups) litter sizes. Dogs of certain breeds have a known predisposition to dystocia, such as Boxers, Bulldogs, Scottish Terriers, Great Danes and Bernese Mountain Dogs [1].

A number of factors play critical roles in the ultimate success-rate of elective c-sections, including fetal maturity, patient preparation, selection of anesthesia protocol and surgical technique as well as neonatal care of the pups. In this review we focus on only the first of these – Timing of c-section to maximize fetal maturity.

Three basic methods exist to predict parturition in the bitch:

Hormonal Assay

While the easiest methods for timing involve breeding management, breeding dates provided by owners are notoriously unreliable. Parturition may occur anywhere from 57 to 72 days after a single observed breeding [2]. On the contrary, the easiest and most accurate way to predict whelping is to diagnose or estimate the time of LH surge. Bitches reliably whelp 64-66 days post LH surge [2,3], which can be diagnosed by repeated LH assay (every 12 hours due to the short duration of the LH surge in the bitch). LH-peak may also be estimated by observing serum progesterone levels that achieve 2-3ng/ml and continue to rise thereafter [3,8]. Shortly after this period, vaginal cytology may be used to diagnose the onset of diestrus, occurring approximately 51-60 days before whelping [4].

Thereafter a variety of measures represent guides to estimate gestational stage within 2-3 days [4-6]. Further, equations have been developed to calculate gestational age in a variety of breeds [6,7].

A brief summary of useful ultrasonographic and radiographic markers of gestational age is listed below:

Ultrasonographic examination [5-8]

The fetal heartbeat is visible at approximately 22-26 days.

Limbuds, fetal movement and a fluid filled stomach may be seen on day 29, 30 and 33.

Fetal length exceeds chorionic width at approximately day 42.

Radiographic examination [5,7,9]

Pregnancy can first be reliably diagnosed radiographically day 45-48 post LH surge. More specific information is also available describing the appearance of specific structures in relation to whelping.

The scapula, humerus and femur are first detectable 17 days (15-18) prepartum.

The pelvis and 13 pairs of ribs are visible 11 days (9-13) prepartum.

Teeth are visible 4 days (3-8) prepartum.

During the final days of gestation, cortisol is produced and released from the maturing fetal adrenal gland in response to space-constraint and other physiologic stressors. This results in production of prostaglandin F2α in the placenta and endometrium, which in turn induces luteolysis and starts the cascade of events that ultimately result in fetal expulsion [10]. At the same time the cortisol also has critical effects on the fetus, resulting in rapid maturation of vital organ systems, including the musculoskeletal system, gastrointestinal system and lungs. Prior to these final maturation processes, puppy survival may be decreased due to weakness, poor mobility and respiratory distress after removal from the uterus. On the contrary, if these processes have occurred and the bitch experiences a dystocia, survival may also be decreased. Consequently, the goal of gestational timing should be to predict whelping accurately enough to intervene after final maturation has occurred but before the bitch is in active labor. To do this, repeated monitoring of hormone levels during the final week of gestation, in combination with fetal monitoring via ultrasound or tocometry, may improve fetal viability and prevent dystocias [11-13].

Progesterone [11]:

Progesterone measures below 2ng/ml indicate imminent parturition within 18-36 hours.

A temperature drop by 1-3F from previous measures occurs in 75-85% of bitches within 8-18 hours prior to parturition.

Fetal heart-rate can accurately diagnose fetal distress during late gestation [12,13]

Normal late pregnancy: 200 beats/min

Fetal Stress: 180 beats/min – Values in this range indicate readiness for parturition

Fetal distress: 150 beats/min – values of 150 or below indicate the urgent need for emergency intervention to save the puppy.

References:

1) Bergström A, Nødtvedt A, Lagerstedt AS, Egenvall A. Incidence and breed predilection for dystocia and risk factors for cesarean section in a Swedish population of insured dogs. Vet Surg 2006 Dec;35(8):786-91.

2) Concannon PW, Whaley S, Leid D, Wissler R. Canine Gestation length: vacioation related to time of mating and fertile life of sperm. Am J Vet Res 1983;44:1819-21.

3) Cohen JA, Holle DM, Meyers-Wallen VN. Accuracy of canine parturition date prediction from LH peak. Clin Theriogenology 2009;1:570

4) Holst PA, Phemister RD. Onset of diestrus in the Beagle bitch: definition and significance. Am J Vet Res 1974;35:401-6

5) Aissi A and Slimani C. Ultrasonographic appearance of the gestational structures throughout pregnancy in bitches. Am J Anim Vet Sciences 2008;3(1):32-35

6) Yeager AE  and Concannon PW. Association between preovulatory LH surge and the early ultrasonographic detection of pregnancy and fetal hearteats in beagle dogs. Theriogenology 1990;34:655-665.

7) Lopate C. Estimation of gestational age and assessment of canine fetal marutation using radiology and ultrasonography: A review. Theriogenology 2008;70:397-402

8) Luvoni GC and Beccaglia M. The Prediction of Parturition Date in Canine Pregnancy. Reprod Dom Anim 2006;41:27-32.

9) Rendano VT. Radiographic evaluation of fetal development in the bitch and fetal death in the bitch and queen. In: Current veterinary therapy vol VIII. WB Saunders Co 1983; 947-52

10) Concannon PW, Butler WR, Hansel W, Knight PJ, Hamilton JM. Parturition and lactation in the bitch: serum progesterone, cortisol and prolactin. Biol Reprod 1978 Dec;19(5):1113-8.

11) Verstegen-Onclin K, Verstegen J. Endocrinology if pregnancy in the dog: A review. Theriogenology 2008;70:291-199.

12) Verstegen JP, Silvia LDM, Onclin K, Donnay I. Echocardiographic study of heart rate in dog and cat fetuses in utero. J Reprod Fertil Suppl 1993;47:174-80

13) Zone MA and Wanke MM. Diagnosis of canine fetal death by ultrasonography J. Reprod Fertil 2001;57:215-9.

Does Ultrasound Miss Abdominal Lesions?

November 7, 2008 Leave a comment
Of course it does. But big question is how often? Are some findings more or less reliable?

An interesting article in the recent JAAHA looks at the correlation of abdominal ultrasound findings with gross surgical exploration. Whenever I have access to the ex lap findings of a patient undergoing an explore after one of my ultrasounds, I am anxious to find out how my findings compare. We all fear a negative explore, although almost every patient I can think of who had a negative gross explore, had microscopic lesions that were helpful in patient management. Following up on the ultrasound findings is an essential part of the learning process for anyone performing ultrasound or ordering one for their patient.

This was a retrospective study looking at cases from The Queen Mother Hospital for Animals in the UK. The ultrasounds were performed by experienced radiologists or radiology residents. They looked at 100 cases who had an ex lap within 48 hours of an abdominal ultrasound. There were only 19 cats, so one has wonder whether this was an adequate sample size for this particular species. There were no stats looking at cats versus dogs. However, they did note that there was “no apparent relationship…detected between body size of animal and the sensitivity of ultrasound for the primary lesion.” I find cats much easier to ultrasound than similarly-sized dogs (perhaps that is my bias towards this fabulous species), but I do feel this is a weakness in the study.

Their results are similar to what I have found in my clinical practice:

100 primary lesions & 67 secondary lesions were found at surgery.

Ultrasound did not detect the primary lesion in 24 of these animals and secondary lesions in 11 animals.

“A total of 36 animals [out of 100] had discordant ultrasonographic and surgical findings of their primary and secondary lesions.”

Ultrasound detected peritonitis lesions in 89% of cases.

Ultrasound detected intestinal obstruction in 64% of cases.

Ultrasound detected hepatic or splenic nodules in 63% of cases.

GI lesions were most likely to be missed by ultrasound (perforations, ulcerations) followed by organomegaly.

Although not statistically significant, ultrasound missed 5 GI foreign bodies.

Gross visualization at surgery missed some lesions seen on ultrasound – prostatic cysts, renal lesions, bladder lesions, splenic/liver lesions, and a gall bladder polyp.

This study brings to light my own experience.

If I am presented with a persistently vomiting animal with radiographs that are very suspicious for a GI obstruction but my ultrasound findings do not suggest obstruction – I ALWAYS err on the side of suspecting obstruction. Depending on the status of the animal and the level of suspicion from the radiographs, the next step may be to continue supportive care and repeat rads in 6-12 hours or it may be an exploratory laparotomy. My own cat had a negative explore and a number of my patients have as well. We have always learned something from the biopsies obtained and I have been fortunate to never have an owner be angry about it. The possibility of a negative explore is an important part of my conversation with the owner prior to surgery.

When ultrasound is used as part of check for metastasis, again, I always warn owners that we may be missing something. Ultrasound is notoriously poor at seeing all lesions in a liver or spleen. It may miss a focal intestinal lesion. I cannot count how many times over the course of my residency that Mike Willard showed me pictures of horrid livers at laparoscopy that were deemed normal by very experienced radiologists. Likewise, as was seen in this study, ultrasound may be able to detect architectural irregularities in an organ (especially liver, spleen, kidney) that are not seen on the surface of the organ at surgery. In these cases, a biopsy of a “normal” organ may reveal significant pathology.

This is why I am an annoyance to the surgeons when they explore the abdomens of my patients. Ultrasound is so subjective. It helps to have the objective look at surgery (or necropsy) to verify what I have seen. I am quick to recommend surgery (unless it would be detrimental to the patient) when I have any doubt about what I am seeing with ultrasound or if the animal’s signs are worse than expected based on ultrasound. Until we get a hold of one of Dr. Crusher’s tricorders, we’re stuck with histopathology for a diagnosis in many patients.

Jennifer S. Fryer, DVM

www. veterinaryanswers.com

PetRays Affiliation

March 12, 2008 Leave a comment

Veterinary Answers is now partnering with PetRays to provide our clients with rapid access to quality radiology consultations with a 4 hour turnaround on routine requests and 30 minutes on STAT requests.  Soon, all Veterinary Answers consultants will be available at the click of button via your PetRays account software.  This will speed up our turnaround on consults and provide you with an archive of both your radiology and medicine reports. 

Call 1-888-4PetRays to set up an account to start receiving rapid radiology consults.

PetRays Affiliation

March 12, 2008 Leave a comment
Veterinary Answers is now partnering with PetRays to provide our clients with rapid access to quality radiology consultations with a 4 hour turnaround on routine requests and 30 minutes on STAT requests. Soon, all Veterinary Answers consultants will be available at the click of button via your PetRays account software. This will speed up our turnaround on consults and provide you with an archive of both your radiology and medicine reports.

Call 1-888-4PetRays to set up an account to start receiving rapid radiology consults.

Canine Adrenal Testing – Which Test Should I Run?

November 28, 2007 2 comments

By Dr. Jennifer S. Fryer

Urine Cortisol:Creatinine Ratio:

· Screening test for Hyperadrenocorticism (Cushing’s or HAC)

· Low Cost, Easy to collect (voided morning urine at home)

· Normal value rules out Hyperadrenocorticism

· Elevated values can indicate stress or Hyperadrenocorticism & adrenal function testing is necessary.

Baseline Cortisol:

· Screening test for Hypoadrenocorticism (Addison’s)

· Values >2 mcg/dl rule out Hypoadrenocorticism (Addison’s)

· Cannot be used to diagnose Hyperadrenocorticism (Cushing’s)

ACTH Stimulation Test:

· Test of choice to diagnose Hypoadrenocorticism (Addison’s)

· Screening test for Hyperadrenocorticism (Cushing’s)

· Used to monitor Trilostane or Lysodren Therapy

· Can be used to differentiate spontaneous vs. iatrogenic HAC

· 60-85% of dogs with HAC will have a positive result on this test.

· 85-90% of dogs without HAC will have a negative result on this test.

· Advantages:

o Can be completed in 1 hour

o No special handling of samples

o Submit for extended Adrenal Panel to document Atypical HAC

· Disadvantages:

o High cost of Cosyntropin

o Low Sensitivity (false negatives are possible)

Low-Dose Dexamethasone Suppression Test:

· Screening test for Hyperadrenocorticism (Cushing’s)

· Helps differentiate pituitary vs. adrenal origin

· 85-95% of HAC dogs have a positive result.

· 70-75% of dogs without HAC have a negative result.

· 40% of dogs with PDH and all adrenal tumor dogs have dexamethasone resistance and will require another differentiating test.

· Advantages:

o Low cost

o Higher sensitivity than ACTH Stim

o No special handling of samples

· Disadvantages:

o All day test requiring three blood samples at 0, 4, 8 hours

o The dog should be kept as minimally stressed as possible during this 8 hour period

High-Dose Dexamethasone Suppression Test:

· Theoretically helps differentiate Hyperadrenocorticism of pituitary vs. adrenal origin.

· Similar results to Low-Dose Dexamethasone Suppression Test at 8 hours.

· Rarely performed.

Endogenous ACTH Measurement:

· Helps differentiate pituitary vs. adrenal HAC

· Single plasma sample required

· Sample handling is difficult & critical to accurate measurement.

· With proper sample handling, this test is very reliable at differentiating pituitary vs. adrenal HAC.

Abdominal Ultrasound:

· Helps differentiate pituitary vs. adrenal HAC.

· May identify adrenal tumor, local invasion or metastasis.

· High cost

· Adrenals can be normally sized in PDH

· Adrenals can be difficult to visualize in some animals

· Ultrasound does not always accurately identify extent of metastasis or local invasion of an adrenal tumor

Computed Tomography (CT Scan):

· Screening test for Pituitary Tumor or Primary Adrenal Tumor and abdominal metastasis &/or local invasion

· Brain CT is not indicated unless a macroadenoma is suspected.

· Very high cost.

· Requires anesthesia.

· Cannot detect 50% of pituitary masses.

· Cannot differentiate between functional and non-functional tumors. Adrenal function tests are still required.

Brain Magnetic Resonance Imagine (MRI):

· Screening test for Pituitary Tumor

· Brain MRI is not necessary unless a macroadenoma is suspected.

· More reliable than CT at detecting small pituitary masses.

· Very high cost.

· Requires anesthesia.

· Not indicated unless a macroadenoma is suspected.

· Cannot differentiate between functional and non-functional tumors. Adrenal function tests are still required.

 

 

References

Lennon EM, Boyle TE, Hutchins RG, et al. Use of basal serum or plasma cortisol concentrations to rule out a diagnosis of hypoadrenocorticism in dogs: 123 cases (2000-2005). J Am Vet Med Assoc 2007;231(3):413-6.

Nelson RW, Turnwald GH, Willard MD. Endocrine, Metabolic, and Lipid Disorders. In: Willard MD and Tvedten H, eds. Small Animal Clinical Diagnosis by Laboratory Methods. 4th edition. St. Louis: Elsevier Saunders, 2004:165-207.

Reusch, CE. Hyperadrenocorticism. In: Ettinger SJ and Feldman EC, eds. Textbook of Veterinary Internal Medicine. 6th edition. St. Louis: Elsevier Saunders, 2005:1592-1611.

 

Does Ultrasound Miss Abdominal Lesions?

November 7, 2007 Leave a comment

Of course it does. But big question is how often? Are some findings more or less reliable?

An interesting article in the recent JAAHA looks at the correlation of abdominal ultrasound findings with gross surgical exploration. Whenever I have access to the ex lap findings of a patient undergoing an explore after one of my ultrasounds, I am anxious to find out how my findings compare. We all fear a negative explore, although almost every patient I can think of who had a negative gross explore, had microscopic lesions that were helpful in patient management. Following up on the ultrasound findings is an essential part of the learning process for anyone performing ultrasound or ordering one for their patient.

This was a retrospective study looking at cases from The Queen Mother Hospital for Animals in the UK. The ultrasounds were performed by experienced radiologists or radiology residents. They looked at 100 cases who had an ex lap within 48 hours of an abdominal ultrasound. There were only 19 cats, so one has wonder whether this was an adequate sample size for this particular species. There were no stats looking at cats versus dogs. However, they did note that there was “no apparent relationship…detected between body size of animal and the sensitivity of ultrasound for the primary lesion.” I find cats much easier to ultrasound than similarly-sized dogs (perhaps that is my bias towards this fabulous species), but I do feel this is a weakness in the study.

Their results are similar to what I have found in my clinical practice:

100 primary lesions & 67 secondary lesions were found at surgery.

Ultrasound did not detect the primary lesion in 24 of these animals and secondary lesions in 11 animals.

“A total of 36 animals [out of 100] had discordant ultrasonographic and surgical findings of their primary and secondary lesions.”

Ultrasound detected peritonitis lesions in 89% of cases.

Ultrasound detected intestinal obstruction in 64% of cases.

Ultrasound detected hepatic or splenic nodules in 63% of cases.

GI lesions were most likely to be missed by ultrasound (perforations, ulcerations) followed by organomegaly.

Although not statistically significant, ultrasound missed 5 GI foreign bodies.

Gross visualization at surgery missed some lesions seen on ultrasound – prostatic cysts, renal lesions, bladder lesions, splenic/liver lesions, and a gall bladder polyp.

This study brings to light my own experience.

If I am presented with a persistently vomiting animal with radiographs that are very suspicious for a GI obstruction but my ultrasound findings do not suggest obstruction – I ALWAYS err on the side of suspecting obstruction. Depending on the status of the animal and the level of suspicion from the radiographs, the next step may be to continue supportive care and repeat rads in 6-12 hours or it may be an exploratory laparotomy. My own cat had a negative explore and a number of my patients have as well. We have always learned something from the biopsies obtained and I have been fortunate to never have an owner be angry about it. The possibility of a negative explore is an important part of my conversation with the owner prior to surgery.

When ultrasound is used as part of check for metastasis, again, I always warn owners that we may be missing something. Ultrasound is notoriously poor at seeing all lesions in a liver or spleen. It may miss a focal intestinal lesion. I cannot count how many times over the course of my residency that Mike Willard showed me pictures of horrid livers at laparoscopy that were deemed normal by very experienced radiologists. Likewise, as was seen in this study, ultrasound may be able to detect architectural irregularities in an organ (especially liver, spleen, kidney) that are not seen on the surface of the organ at surgery. In these cases, a biopsy of a “normal” organ may reveal significant pathology.

This is why I am an annoyance to the surgeons when they explore the abdomens of my patients. Ultrasound is so subjective. It helps to have the objective look at surgery (or necropsy) to verify what I have seen. I am quick to recommend surgery (unless it would be detrimental to the patient) when I have any doubt about what I am seeing with ultrasound or if the animal’s signs are worse than expected based on ultrasound. Until we get a hold of one of Dr. Crusher’s tricorders, we’re stuck with histopathology for a diagnosis in many patients.

Jennifer S. Fryer, DVM

www. veterinaryanswers.com