Urolithiasis is considered a surgical emergency as they may complicate with cystorrhexis and uroabdomen when urine is retained for more than 32 to 48 hours. Clinical cases of urolithiasis are mostly recorded in male animals and the incidence is more in older animals compared to younger age groups (Fromsa et al. 2019). The average age of animals presented was 8.5 years and five out of six animals were male dogs. The severity of clinical signs depends on the duration of obstruction and whether the obstruction is complete or partial. In the present study, animals exhibited signs of uremia viz. vomiting, lethargy, dehydration and symptoms pertaining to the lower urinary tract pathology including stranguria, pollakiuria, hematuria, pain and overflow incontinence which may be attributed to long-standing obstruction (Gisselman et al. 2009). Haematological evaluation revealed mild anaemia and neutrophilic leucocytosis, which might be due to concurrent urinary tract infections and cystitis in three out of six cases. A similar observation was recorded by Fromsa et al. (2019) that the mean total leucocyte count value was elevated significantly in partial and completely obstructed animals. Serum biochemical analysis revealed elevated blood urea nitrogen and creatinine in cases with complete obstruction indicating post renal azotemia (Sithanukul S et al. 2010). The values were within normal range in unobstructed and partially obstructed dogs.
Blood gas analysis was crucial for identification of electrolyte status of the animals. Hyperkalemia and metabolic acidosis were the most significant abnormalities associated with complete urinary obstruction. Impired urinary excretion and defective reabsorption of potassium from the retained urine resulted in hyperkalemia (Balakrishnan et al. 2013). Hyperkalemia might complicate with life threatening cardiac disarrhythmia due to cardiac conduction abnormalities, demonstrated with the help of electrocardiogram (Tag et al. 2008). Increased amplitude of T wave was a consistant finding in ECG of animals with hyperkalemia. Decreased level of HCO3- and negative base excess values indicated primary metabolic acidosis (Freitas et al. 2012) in all the cases except case V. Reduced blood pH value below 7.35 indicated metabolic acidosis due to defective renal function. Radiographic evaluation was helpful to specifically focus the site of obstruction as the stones were radio opaque in nature except cystiene and urate (Lulich et al. 2008). Urine pH was consistently towards alkaline side when the major stone composition was struvite but was acidic in COM and calcium phosphate urolithiasis (Palma et al. 2013).
Treatment was directed to immediately relieve the obstruction, correction of post-renal azotemia, hyperkalemia, acid-base imbalance and dehydration. Alleviation of primary causes of the disease by dietary modification, medical management and fluid therapy were also followed. Cystotomy, urethrotomy or combination of both were the surgical options depending on the site of calculi once the retro grade urohydropropulsion failed. In the present study, three out of six cases were managed with urethrotomy alone, one with cystotomy and two cases by urethrotomy combined with cystotomy.
Characterization of urinary calculi by Fourier Transform Infrared Spectroscopy (FT-IR)
FTIR is a modern physical chemical method suitable for investigation of urinary stone composition (Sofia et al. 2010). The working principle of FT-IR is that every molecule gives a characteristic absorption spectrum in the infrared region depending on the chemical bonding conditions and structure. The vibration motions of atoms in bonds (bond stetching/ contracting/ bond wagging) are measured by passing FT-IR through the powdered stone sample, which has been compressed in to a nearly transparent wafer with adequate quantity of potassium bromide. In the FT-IR region (4000–200cm− 1), characteristic attenuation of incident energy occurs depending on the ability of molecules in the compound to oscillate at certain wavelengths (Kanchana et al. 2009).
On FT-IR, 3 samples were identified as combination of struvite, COD and apatite crystals. Struvite has a characteristic infrared spectrum easily recognizable even in mixed stone samples by strong band at 1010 cm− 1 due to absorption of PO4 group and presence of other bands at 2377, 1476, 1437, 872, 770 and 574 cm− 1. The bands at 1476 and 1435 cm− 1are because of vibration of NH4 group (Sofia et al. 2010). Similar absorption values with comparable wave numbers could be obtained for struvite crystals in the present study. When struvite was in association with apatite, the presence of later was deduced by absorption at 600cm− 1 and by a shift of bands at 1010 cm− 1 towards higher frequencies. The broad absorption band at 3000 cm− 1 was due to the presence of O-H group in the dihydrate form of calcium oxalate (Kanjana et al. 2009).
Rest of the three samples were identified as mixture of COM and calcium phosphate. The important spectral characteristics of COM was grouping of five bands between 3477 and 3047cm− 1, due to symmetric and asymmetric O-H stretch (Kanchana et al. 2009).The staircase pattern of five absorption bands between 3477 and 3047cm− 1 in the present study confirmed the presence of COM crystals (Table 5). The absorptions at 2291cm− 1 and 885cm− 1was due to C-Cstretching mode, two bands at 662 and 781cm− 1were due to the out of plane O-H bending and C-CH bending mode respectively and absorption at 517cm− 1arised due to O-C-O in plane bending (Sundaramoorthi et al. 2007). The absorption band at 1620 cm− 1 and 1320 cm− 1 was due to the vibration of C = O and C-O respectively (Tsay 1982). Hence, in addition to the grouping of 5 bands, the presence of COM was confirmed with the presence of absorption bands at all the above specified wave numbers for COM. The discrete formation of two bands at 780 and 517cm− 1was important in differentiating COM from COD (Kanchana et al. (2009). Presence of phosphorous group was detected by absorption at 1040 cm− 1(Kanchana et al. 2009), phosphorous groups usually shows an absorption range of 1000-1100cm − 1. Thus the presence of Calcium phosphate crystals was confirmed by identifying Calcium and Phosphorous groups together.
All the stone samples analyzed in the present study were composed of mixed compounds, 50 percent being a combination of struvite, COD and apatite and 50 percent COM and calcium phosphate. Quantitative characterization of urolith composition was effective in understanding the etiology, planning proper management and prevent recurrence of the disease. Proper dietary modifications guided by the urolith composition would considerably decrease morbidity and complications associated with recurrent urolithiasis (Bhattacharyya et al. 2014).