• View in gallery

    Box plot of the preoperative, abdominal wall closure, and postoperative IAP (mmHg), APP (mmHg), DBP (mmHg), and TP (g/dL) measured in dorsal recumbency in late-term pregnant queens and nonpregnant controls undergoing elective ovariohysterectomy. The box plot displays the first quartile, median, and third quartile variable. Whiskers display the minimum and maximum variable that do not exceed 1.5 times the IQR, represented by the vertical axis of the box plot. Points plotted beyond the maximum whisker value represent single data points that exceeded 1.5 times the IQR. APP = Abdominal perfusion pressure (Doppler blood pressure – intra-abdominal pressure). DBP = Doppler blood pressure. IAP = Intra-abdominal pressure; IQR = Interquartile range. TP = Total protein.

  • View in gallery

    Bland Altman agreement and graphic representation of the concordance correlation coefficient for pre- and postoperative IAP (mmHg) measurements in dorsal and right lateral recumbency in late-term pregnant and control cats undergoing elective ovariohysterectomy.

  • 1.

    Chun R, Kirkpatrick AW. Intra-abdominal pressure, intra-abdominal hypertension, and pregnancy: a review. Ann Intensive Care. 2012;2(suppl 1):S5.

  • 2.

    Lozada MJ, Goyal V, Levin D, et al. Management of peripartum intra-abdominal hypertension and abdominal compartment syndrome. Acta Obstet Gynecol Scand. 2019;98(11):13861397.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3.

    Malbrain ML, De Keulenaer BL, Oda J, et al. Intra-abdominal hypertension and abdominal compartment syndrome in burns, obesity, pregnancy, and general medicine. Anaesthesiol Intensive Ther. 2015;47(3):228240.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Bosch L, Rivera del Álamo MM, Andaluz A, et al. Effects of ovariohysterectomy on intra-abdominal pressure and abdominal perfusion pressure in cats. Vet Rec. 2012;171(24):622.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    Rader RA, Johnson JA. Determination of normal intra-abdominal pressure using urinary bladder catheterization in clinically healthy cats. J Vet Emerg Crit Care. 2010;20(4):386392.

    • Search Google Scholar
    • Export Citation
  • 6.

    Lozada MJ, Goyal V, Osmundson SS, Pacheco LD, Malbrain MLNG. It's high time for intra-abdominal hypertension guidelines in pregnancy after more than 100 years of measuring pressures. Acta Obstet Gynecol Scand. 2019;98(11):14861488.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Cheatham ML, Malbrain ML, Kirkpatrick A, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. II. Recommendations. Intensive Care Med. 2007;33(6):951962.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Tyagi A, Singh S, Kumar M, Sethi AK. Intra-abdominal pressure and intra-abdominal hypertension in critically ill obstetric patients: a prospective cohort study. Int J Obstet Anesth. 2017;32:3340.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Staelens AS, Van Cauwelaert S, Tomsin K, Mesens T, Malbrain ML, Gyselaers W. Intra-abdominal pressure measurements in term pregnancy and postpartum: an observational study. PLoS One. 2014;9(8):e104782.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10.

    Schorn MN. Measurement of blood loss: review of the literature. J Midwifery Womens Health. 2010;55(1):2027.

  • 11.

    Vitello DJ, Ripper RM, Fettiplace MR, Weinberg GL, Vitello JM. Blood density is nearly equal to water density: a validation study of the gravimetric method of measuring intraoperative blood loss. J Vet Med. 2015;2015:152730.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    Duthie SJ, Ven D, Yung GL, Guang DZ, Chan SY, Ma HK. Discrepancy between laboratory determination and visual estimation of blood loss during normal delivery. Eur J Obstet Gynecol Reprod Biol. 1991;38(2):119124.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13.

    Borden FW. Loss of blood at operation; a method for continuous measurement. Calif Med. 1957;87(2):9197.

  • 14.

    Lee MH, Ingvertsen BT, Kirpensteijn J, Jensen AL, Kristensen AT. Quantification of surgical blood loss. Vet Surg. 2006;35(4):388393.

  • 15.

    Paramore RH. The intra-abdominal pressure in pregnancy. Proc R Soc Med. 1913;6:291334.

  • 16.

    Kirkpatrick AW, Roberts DJ, De Waele J, et al. Intra-abdominal hypertension and the abdominal compartment syndrome: updated consensus definitions and clinical practice guidelines from the World Society of the Abdominal Compartment Syndrome. Intensive Care Med. 2013;39(7):11901206.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17.

    Malbrain ML, Cheatham ML, Kirkpatrick A, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. I. Definitions. Intensive Care Med. 2006;32(11):17221732.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18.

    Nielsen LK, Whelan M. Compartment syndrome: pathophysiology, clinical presentations, treatment, and prevention in human and veterinary medicine. J Vet Emerg Crit Care. 2012;22(3):291302.

    • Search Google Scholar
    • Export Citation
  • 19.

    Hoareau GL MM. Intraabdominal pressure monitoring. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 2nd ed. Elsevier Saunders; 2015:982987.

    • Search Google Scholar
    • Export Citation
  • 20.

    Smith SE, Sande AA. Measurement of intra-abdominal pressure in dogs and cats. J Vet Emerg Crit Care. 2012;22(5):530544.

  • 21.

    Al-Khan A, Shah M, Altabban M, et al. Measurement of intraabdominal pressure in pregnant women at term. J Reprod Med. 2011;56(1–2):537.

  • 22.

    van Nimwegen SA, Kirpensteijn J. Laparoscopic ovariectomy in cats: comparison of laser and bipolar electrocoagulation. J Feline Med Surg. 2007;9(5):397403.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23.

    Dorn M, Becher-Deichsel A, Bockstahler B, Peham C, Dupré G. Pressure-volume curve during capnoperitoneum in cats. Animals (Basel). 2020;10(8):1408.

    • Search Google Scholar
    • Export Citation
  • 24.

    Noel-Morgan J, Muir WW. Anesthesia-associated relative hypovolemia: mechanisms, monitoring, and treatment considerations. Front Vet Sci. 2018;5:53. doi: 10.3389/fvets.2018.00053.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25.

    Cheatham ML, White MW, Sagraves SG, Johnson JL, Block EF. Abdominal perfusion pressure: a superior parameter in the assessment of intra-abdominal hypertension. J Trauma. 2000;49(4):621626. doi: 10.1097/00005373-200010000-00008.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26.

    Klevans LR, Hirkaler G, Kovacs JL. Indirect blood pressure determination by Doppler technique in renal hypertensive cats. Am J Physiol. 1979;237(6):H720H723.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27.

    Grandy JL, Dunlop CI, Hodgson DS, Curtis CR, Chapman PL. Evaluation of the Doppler ultrasonic method of measuring systolic arterial blood pressure in cats. Am J Vet Res. 1992;53(7):11661169.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28.

    Caulkett NA, Cantwell SL, Houston DM. A comparison of indirect blood pressure monitoring techniques in the anesthetized cat. Vet Surg. 1998;27(4):370377.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29.

    Jones TJ. Inter- and intraindividual variation in Doppler ultrasonic indirect blood pressure measurements in healthy cats. J Vet Intern Med. 1999;13(4):314318. doi: 10.1892/0891-6640(1999)013<0314:iaivid>2.3.co;2.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 30.

    Binns SH, Sisson DD, Buoscio DA, Schaeffer DJ. Doppler ultrasonographic, oscillometric sphygmomanometric, and photoplethysmographic techniques for noninvasive blood pressure measurement in anesthetized cats. J Vet Intern Med. 1995;9(6):405414.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 31.

    Jepson RE, Hartley V, Mendl M, Caney SM, Gould DJ. A comparison of CAT Doppler and oscillometric Memoprint machines for non-invasive blood pressure measurement in conscious cats. J Feline Med Surg. 2005;7(3):147152.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32.

    Sawchuck DJ, Wittmann BK. Pre-eclampsia renamed and reframed: Intra-abdominal hypertension in pregnancy. Med Hypotheses. 2014;83(5):619632.

  • 33.

    Seal JB, Gewertz BL. Vascular dysfunction in ischemia-reperfusion injury. Ann Vasc Surg. 2005;19(4):572584.

  • 34.

    Chun R, Baghirzada L, Tiruta C, Kirkpatrick AW. Measurement of intra-abdominal pressure in term pregnancy: a pilot study. Int J Obstet Anesth. 2012;21(2):135139.

    • PubMed
    • Search Google Scholar
    • Export Citation

Advertisement

Assessment of changes in intra-abdominal pressure and abdominal perfusion pressure in late-term pregnant queens undergoing elective ovariohysterectomy

View More View Less
  • 1 Department of Clinical Sciences and Advanced Medicine, University of Pennsylvania, School of Veterinary Medicine, Philadelphia, PA
  • | 2 Surgery, Hill Country Animal League, Boerne, TX

Abstract

OBJECTIVE

Compare changes in intra-abdominal pressure (IAP), abdominal perfusion pressure (APP), hemodynamics, and clinicopathological variables in nonpregnant and late-term pregnant queens undergoing elective ovariohysterectomy (OHE) and evaluate the effect of patient positioning on IAP and APP measurements.

ANIMALS

18 late-term pregnant queens and 25 nonpregnant controls.

PROCEDURES

Temperature, heart rate (HR), Doppler blood pressure (DBP), IAP (dorsal and right lateral), PCV, total protein (TP), and lactate were recorded preoperatively, at abdominal wall closure (dorsal IAP only), and postoperatively under general anesthesia. Uterine weight, blood loss, and surgical duration were recorded. Abdominal perfusion pressure was calculated as DBP minus IAP.

RESULTS

Pre- and postoperatively, pregnant queens had lower DBP, APP, and PCV compared to controls (P < 0.001). IAP was higher in pregnant queens preoperatively (P < 0.001). Controls had a decrease in HR and increase in IAP, while both groups had a decrease in body temperature, DBP, APP, and lactate over time (P < 0.05). Pregnant queens had a decrease (P = 0.029), and controls had an increase in TP (P = 0.001). Blood loss and surgical time were greater for pregnant queens (P < 0.001). Dorsal IAP and APP were higher and lower than right lateral measurements (P < 0.001), respectively, and correlation was strong.

CLINICAL RELEVANCE

Hemodynamics and APP are impaired in late-term pregnant queens undergoing OHE, and increased monitoring is warranted. Although strongly correlated, feline IAP and APP measurements in dorsal and right lateral recumbency are not interchangeable.

Abstract

OBJECTIVE

Compare changes in intra-abdominal pressure (IAP), abdominal perfusion pressure (APP), hemodynamics, and clinicopathological variables in nonpregnant and late-term pregnant queens undergoing elective ovariohysterectomy (OHE) and evaluate the effect of patient positioning on IAP and APP measurements.

ANIMALS

18 late-term pregnant queens and 25 nonpregnant controls.

PROCEDURES

Temperature, heart rate (HR), Doppler blood pressure (DBP), IAP (dorsal and right lateral), PCV, total protein (TP), and lactate were recorded preoperatively, at abdominal wall closure (dorsal IAP only), and postoperatively under general anesthesia. Uterine weight, blood loss, and surgical duration were recorded. Abdominal perfusion pressure was calculated as DBP minus IAP.

RESULTS

Pre- and postoperatively, pregnant queens had lower DBP, APP, and PCV compared to controls (P < 0.001). IAP was higher in pregnant queens preoperatively (P < 0.001). Controls had a decrease in HR and increase in IAP, while both groups had a decrease in body temperature, DBP, APP, and lactate over time (P < 0.05). Pregnant queens had a decrease (P = 0.029), and controls had an increase in TP (P = 0.001). Blood loss and surgical time were greater for pregnant queens (P < 0.001). Dorsal IAP and APP were higher and lower than right lateral measurements (P < 0.001), respectively, and correlation was strong.

CLINICAL RELEVANCE

Hemodynamics and APP are impaired in late-term pregnant queens undergoing OHE, and increased monitoring is warranted. Although strongly correlated, feline IAP and APP measurements in dorsal and right lateral recumbency are not interchangeable.

Pregnancy encompasses numerous physiological changes associated with the maternal adaptation to increased intra-abdominal contents. While an acute elevation in intra-abdominal pressure (IAP) has the potential to result in significant organ dysfunction that may require emergent decompression, the pregnant individual is able to accommodate the gravid uterus via expansion of the thoracic wall, softening of intra-abdominal ligaments, and the development of collateral blood flow.13 These gradual changes result in the permission of IAP levels among this patient population that might otherwise result in significant end-organ compromise in nonpregnant individuals.3

Normal IAP is reported to be 10.9 ± 4.7 to 17.8 ± 3.6 mmHg in otherwise healthy term human parturients and decreases to values between 9.6 ± 0.89 and 10.7 mmHg (SD unavailable) 24 hours postpartum.2 Previous investigations of IAP in relation to pregnancy among veterinary patients are limited to a single study4 of predominantly early term pregnant queens (4 to 5 weeks gestation), where a mean IAP of 3.51 ± 0.56 mmHg and 2.66 ± 0.56 mmHg was reported before and 4 hours after ovariohysterectomy (OHE), respectively. Comparatively, median IAP in a population of clinically healthy nonpregnant cats has been reported to be 5.15 mmHg (interquartile range, 3.85 to 6.49 mmHg).5 In addition to the relative scarcity of reports documenting changes in IAP before and after parturition, its potential clinical implications remain unclear.3,6

Increased IAP in critically ill human patients is well recognized as a pertinent finding triggering rapid intervention via techniques to improve abdominal wall compliance, the evacuation of intraluminal contents or abdominal fluid, correction of a positive fluid balance, and ultimately, surgical decompression in many cases.7 Comparatively, the clinical significance of increases in IAP and its use as a monitoring tool among parturient patients in the intensive care unit remains an area of active research with numerous unknowns.3,6,8,9 Similarly, the role of changes in abdominal perfusion pressure (APP), defined as the difference between the mean arterial blood pressure (MAP) and the IAP, remains to be elucidated as a clinically significant monitoring parameter.2,7

The primary objective of this study was to compare changes in IAP and APP between nonpregnant and late-term pregnant queens undergoing elective ovariohysterectomy. Secondary objectives were to compare concurrent hemodynamic (heart rate [HR] and Doppler blood pressure [DBP]) and clinicopathological (PCV, total protein [TP], and lactate) changes, assess potential correlations between these variables, and evaluate the significance of patient positioning on IAP and APP measurements. The authors hypothesized that late-term pregnant queens would have higher IAP and lower APP compared to nonpregnant queens. It was also hypothesized that IAP would rapidly decrease and APP would increase following elective ovariohysterectomy in pregnant queens.

Materials and Methods

Female cats presented to the Hill Country Animal League clinic for elective ovariohysterectomy (OHE) were considered for prospective enrollment in the study. This study was reviewed and approved by the Hill Country Animal League Institutional Animal Care and Use Committee (approval no. 21-043; approval date: February 12, 2021). Cats were excluded if they had significant comorbidities precluding elective surgery at the time of presentation. Owner/agent consent was obtained for all owned cats at the time of study enrollment. Cats were weighed and confirmed to be ≥ 2.75 kg body weight, and ≥ 6 months of age as reported by owner/agent, and confirmed by dentition and body condition of the cat during the presurgical physical exam. Cats were included in a continuous fashion as they were presented if they met enrollment criteria. Cats were defined as late-term pregnant queens if the excised gravid uterus weighed ≥ 10% of the body weight recorded at admission. Pregnant cats were excluded if the gravid uterus weighed < 10% of body weight. Cats were enrolled in the negative control group if they were classified by the veterinary surgeon intraoperatively as a nonpregnant queen in estrus or anestrus.

Animal data were collected pertaining to age, body weight, breed, abdominal circumference (cm), abdominal width (cm) in dorsal and right lateral recumbency, and owned or feral status at admission to the clinic. Rectal body temperature was recorded prior to surgery and immediately postoperatively. Data were recorded pertaining to HR, noninvasive DBP (mmHg; Ultrasonic Doppler Flow Detector; Parks Medical Electronics, Inc), IAP (mmHg), PCV (%), TP (g/dL), and whole blood lactate (mmol/L; Lactate Plus Meter; Nova Biomedical) at baseline prior to surgery, following removal of the gravid uterus at the time of abdominal wall closure, and immediately postoperatively. Uterine weight (kg) and blood loss (mL) were recorded in addition to the time from preoperative evaluation to the start of surgery, start of surgery to abdominal wall closure, preoperative evaluation to postoperative evaluation, and surgical time. All cats were standardized to have blood pressure measured from a single forelimb. A modified APP was calculated retrospectively at all time points, defined as DBP minus IAP.

Cats were anesthetized with a standardized protocol including buprenorphine, ketamine, dexmedetomidine, and isoflurane. Equal volumes of ketamine (100 mg/ml) and dexmedetomidine (0.5 mg/ml) were mixed in a single sterile vial. Anesthesia was induced by intramuscular injection of 0.4 ml of this mixture. Total dosage of induction drugs ranged from 3.9 to 8.8 mg/kg for ketamine and 0.02 to 0.04 mg/kg for dexmedetomidine. Buprenorphine (0.01 mg/kg IM) was administered after anesthetic induction, during surgical preparation. Each animal was intubated, and isoflurane was administered to assist in maintaining a surgical plane of anesthesia with a vaporizer setting range of 0.5 to 1%. Oxygen flow rate was 2 L/min using a nonrebreathing circuit.

Ovariohysterectomies were performed by a standard midline celiotomy by 1 of 2 veterinary surgeons experienced in high-volume, high-quality feline OHEs.

A previously reported gravimetric method was used to determine blood loss.10 Dry, sterile, 4 X 4-inch cotton surgical gauze sponges were weighed on a previously zeroed electronic scale before and after attempting to saturate the gauze with free blood. The difference in their weight was used to estimate blood loss, based on the assumption that the density of blood is 1 g/ml.1014 If upon entering the abdominal cavity, peritoneal effusion fluid was identified, this was absorbed using a separate surgical sponge to avoid inclusion in the measured blood loss.

Intra-abdominal pressure was measured using a standardized intravesical technique. For the first 11 pregnant cats enrolled in the study, a 3.5Fr Mila Tomcat catheter (Small Animal/Tomcat Catheter Kit 3.5Fr; Mila International, Inc) was inserted into the urinary bladder via sterile technique following induction. A 4Fr Mila Foley catheter (Foley Catheter with Wire Stylet in a Procedure Kit 4Fr; Mila International, Inc.) was used for the remaining pregnant and all nonpregnant cats. The urinary bladder was fully emptied with the use of a 20-mL syringe. Once negative pressure was obtained, 1 mL/kg of sterile 0.9% NaCl was instilled into the urinary bladder. A sterile urine collection system was attached with the use of a 3-way stopcock with a water manometer attached to the upright stopcock port. The manometer was subsequently zeroed to the cat's symphysis pubis, and the manometer was filled with 0.9% NaCl. The stopcock was then opened to the urinary bladder, and the meniscus of the manometer was allowed to equilibrate. Once the meniscus appeared to be at a steady state, an additional 20 seconds were allowed to confirm to the measured IAP. The IAP was then recorded in centimeters of H2O and converted to millimeters of mercury (1 cm H2O = 0.736 mmHg). Cats had IAP measurements obtained in both right lateral and dorsal recumbency at baseline prior to surgery and immediately postoperatively. The manometer was rezeroed following all positional changes. A single IAP measurement was obtained in dorsal recumbency following removal of the uterus at the time of abdominal wall closure. The urinary catheter was removed following the postoperative IAP measurement.

All pregnant cats received 22 mL/kg warmed subcutaneous 0.9% NaCl over the dorsolateral thorax caudal to the scapulae following their final IAP measurement.

Statistical analysis

An a priori sample size calculation was performed based on the results of a similar prospective study4 evaluating the effect of OHE on IAP and APP in cats. A preoperative IAP of 3.51 ± 0.56 mmHg and 2.08 ± 0.53 was reported in pregnant and nonpregnant queens, respectively. Using a 2-sample independent means t test, assuming a 0.05 type I error and a statistical power level of 90%, the same magnitude of IAP difference between pregnant and nonpregnant queens could be detected with a total sample size of 10 cats with 5 per group.

The Shapiro-Wilk test was used to assess continuous variables for normality. Descriptive statistics consisted of the mean ± SD for normally distributed variables and the median (range) for variables that were not normally distributed and for variables where distribution differed between groups. The count and percentage (%) were used to report frequency data. Continuous variables were compared between groups using the 2-sample independent t test for normally distributed variables and the Wilcoxon rank sum test for data that were not normally distributed. Paired continuous variables were compared within groups using a paired t test for normally distributed data and a signed rank test for data that were not normally distributed. Correlation between variables was assessed using Pearson's correlation coefficient for normally distributed variables and Spearman's rank correlation for variables that were not normally distributed. Bonferroni's correction was applied to account for multiple comparisons when applicable.

To evaluate change in IAP and APP measured in dorsal recumbency over time, a multilevel mixed-effects generalized linear model was computed for each group including “Time” considered as a fixed categorical variable (0 = preoperative, 1 = abdominal wall closure, 2 = postoperative), and individuals and catheter type as random effects: Y (pregnant or control) = (IAP or APP) + Time + (1|Individual:) + (1|Catheter:). To test the association between change in IAP and APP and pregnancy over time, a multilevel mixed-effects generalized linear model was computed including “Group” (pregnant queen vs control group), “Time” considered as a categorical variable (0 = preoperative, 1 = abdominal wall closure, 2 = postoperative), and the interaction between “Group” and “Time” as fixed effects, and individuals and catheter type as random effects nested within the variable “Group” (pregnant queen vs control group): Y = (IAP or APP) + Group + Group#Time + (1|Group:Individual) + (1|Group:Catheter). All models were also computed with IAP and APP measured in right lateral recumbency, excluding the time of abdominal closure. Similar models were created to evaluate change in body temperature, HR, DBP, PCV, TP, and lactate over time and the association between the change and pregnancy, with the exclusion of “catheter type” as a random effect. Maximum likelihood was used to estimate the variance and covariance parameters for all models. The assumption of homoscedasticity and normality of residuals were visually assessed using scatterplots of generated residuals and predicted values and histograms of generated residuals, respectively.

The agreement between IAP and APP measurements obtained in dorsal recumbency and right lateral recumbency was further evaluated using Bland-Altman analysis to calculate both the average difference with 95% confidence intervals and the limits of agreement (average difference ± 1.960 standard deviation) between simultaneous results obtained at preoperative and postoperative time points. For all comparisons, P < 0.05 was considered statistically significant. A commercial software program (STATA IC, version 16.1; StataCorp LLC) was used for all statistical analyses.

Results

A total of 18 late-term pregnant queens and 25 controls were enrolled in the study. Patient characteristics are outlined in Table 1. Body temperature, HR, DBP, IAP, APP, PCV, TP, lactate, and times for pregnant queens and controls measured at preoperative, abdominal wall closure, and postoperative time points are also summarized in Table 1 and depicted in Figure 1.

Table 1

Characteristics and measurements at preoperative, abdominal wall closure, and postoperative time points in late-term pregnant queens and nonpregnant controls undergoing elective ovariohysterectomy.

PregnantControl
VariableMedianRangeMedianRangeP-valueBonferroni corrected P value
Age (months)16.512–3676–36< 0.001a0.016a
Weight (kg)3.222.90–5.142.812.27–3.46< 0.001a< 0.001a
MeanSDMeanSD
Abdominal circumference (cm)39.973.8228.833.31< 0.001b< 0.001b
Right lateral abdominal width (cm)6.860.685.810.560.001b0.039b
MedianRangeMedianRange
 Uterus weight (grams)560290–1,00421–5< 0.001a< 0.001a
 Blood loss (mL)3< 1–7< 1< 1–2< 0.001a< 0.001a
PreoperativeMeanSDMeanSD
Body temperature (°C [°F])37.7 (99.9)0.8 (1.4)38.1 (100.6)0.6 (1.1)0.100b1b
HR124.8318.97120.818.820.493b1b
DBP (mmHg)8012.31108.1221.75< 0.001b< 0.001b
Dorsal IAP (mmHg)7.521.815.080.74< 0.001b< 0.001b
Right lateral IAP (mmHg)5.821.383.460.77< 0.001b< 0.001b
Dorsal APP (mmHg)72.4812.79103.0421.76< 0.001b< 0.001b
Right lateral APP (mmHg)74.1812.59104.6621.83< 0.001b< 0.001b
PCV (%)25.394.3131.924.32< 0.001b< 0.001b
TP (g/dL)6.620.616.610.350.975b1b
Lactate (mmol/L)1.070.291.020.300.602b1b
Abdominal wall closure
HR129.1113.94115.9216.320.009b0.343b
DBP (mmHg)73.5616.8396.1720.03< 0.001b0.016b
Dorsal IAP (mmHg)6.462.266.241.340.693b1b
Dorsal APP (mmHg)67.1016.4289.8819.84< 0.001b0.012b
PCV (%)23.714.2731.674.70< 0.001b< 0.001b
TP (g/dL)6.540.606.710.420.293b1b
Lactate (mmol/L)0.960.400.860.250.323b1b
Postoperative
Body temperature (°C [°F])36.3 (97.3)c35.6–37.4 (96–99.4)c36.4 (97.6)c34.4–37.7 (93.9–99.8)c0.096a1a
HR126.7814.13113.9617.340.014b0.530b
DBP (mmHg)71.5613.859618.22< 0.001b< 0.001b
Dorsal IAP (mmHg)5.70c3.68–11.77c5.88c4.41–10.3c0.569a1a
Right lateral IAP (mmHg)5.582.095.211.630.517b1b
Dorsal APP (mmHg)64.7913.7489.3817.70< 0.001b< 0.001b
Right lateral APP (mmHg)65.9813.9890.7918.09< 0.001b< 0.001b
PCV (%)244.0631.125.13< 0.001b< 0.001b
TP (g/dL)6.520.636.770.430.136b1b
Lactate (mmol/L)0.910.300.860.310.631b1b
Time
Surgical (min)24.465.0914.083.74< 0.001b< 0.001b
Preoperative to postoperative (min)38.176.1529.124.94< 0.001b< 0.001b
MedianRangeMedianRange
Preoperative to start of surgery (min)11.56–17157–310.045a1a
Start of surgery to abdominal wall closure (min)127–2562–10< 0.001a< 0.001a

APP = Abdominal perfusion pressure (Doppler blood pressure – intra-abdominal pressure). DBP = Doppler blood pressure. HR = Heart rate. IAP = intra-abdominal pressure. TP = Total protein.

a

Nonparametric distribution, Wilcoxon rank sum test.

b

Parametric distribution, 2-sample independent t test.

c

Median and range reported. Bonferroni correction for multiple comparisons, α < 0.001.

Figure 1
Figure 1

Box plot of the preoperative, abdominal wall closure, and postoperative IAP (mmHg), APP (mmHg), DBP (mmHg), and TP (g/dL) measured in dorsal recumbency in late-term pregnant queens and nonpregnant controls undergoing elective ovariohysterectomy. The box plot displays the first quartile, median, and third quartile variable. Whiskers display the minimum and maximum variable that do not exceed 1.5 times the IQR, represented by the vertical axis of the box plot. Points plotted beyond the maximum whisker value represent single data points that exceeded 1.5 times the IQR. APP = Abdominal perfusion pressure (Doppler blood pressure – intra-abdominal pressure). DBP = Doppler blood pressure. IAP = Intra-abdominal pressure; IQR = Interquartile range. TP = Total protein.

Citation: American Journal of Veterinary Research 83, 8; 10.2460/ajvr.22.02.0023

Pregnant cats had a significant decrease in IAP measured in dorsal recumbency at the time of abdominal wall closure (P = 0.017), but not postoperatively (P = 0.088). Control cats had a significant increase in IAP measured in dorsal recumbency at both the time of abdominal wall closure and postoperatively (P < 0.001). This change in IAP over time was significantly different between pregnant and control cats at both time points, independent of catheter type (P = 0.002). Pregnant cats had a significant decrease in APP postoperatively (P = 0.016), but not at the time of abdominal wall closure (P = 0.092). Comparatively, control cats had a significant decrease in APP at both time points (P < 0.001). These findings remained true when measured in right lateral recumbency.

No significant correlations were identified between abdominal circumference or abdominal width and change in IAP or APP for either pregnant or control groups.

Both pregnant (P < 0.001) and control (P < 0.001) cats had a significant decrease in body temperature over time. Pregnant cats had no significant change in HR over time (abdominal wall closure, P = 0.153; postoperatively, P = 0.516), while control cats had a significant decrease in HR postoperatively (P = 0.023). This change in HR over time was not significantly different between pregnant and control cats. Both pregnant (abdominal wall closure, P = 0.047; postoperatively, P = 0.009) and control (P < 0.001) cats had a significant decrease in DBP over time. Both pregnant (abdominal wall closure, P = 0.059; postoperatively, P = 0.155) and control (abdominal wall closure, P = 0.421; postoperatively, P = 0.251) cats had no significant change in PCV over time. Pregnant cats had a significant decrease in TP postoperatively (P = 0.029), but not at the time of abdominal wall closure (P = 0.164). Control cats had a significant increase in TP at both the time of abdominal wall closure (P = 0.016) and postoperatively (P = 0.001). This change in TP over time was not significantly different between pregnant and control cats. Both pregnant (abdominal wall closure, P = 0.005; postoperatively, P < 0.001) and control (abdominal wall closure, P = 0.001; postoperatively, P < 0.001) cats had a significant decrease in lactate over time.

Change in dorsal and right lateral APP was significantly correlated with DBP in both pregnant and control groups (P < 0.001). No other significant correlations were identified between change in IAP or APP and change in HR, DBP, PCV, TP, or lactate for either pregnant or control groups.

Comparison of IAP and APP measurements obtained in dorsal compared to right lateral recumbency at pre- and postoperative time points in pregnant and control cats is summarized in Table 2. Dorsal IAP measurements were significantly higher than right lateral IAP measurements for pregnant and control groups, both preoperatively (average difference, 1.651 mmHg) and postoperatively (average difference, 1.317 mmHg) (P < 0.001). Similarly, dorsal APP measurements were significantly lower than right lateral APP measurements for pregnant and control groups, both preoperatively and postoperatively (P < 0.001). Bland Altman agreement and graphic representation of the concordance correlation coefficient for pre- and postoperative IAP and APP measurements in dorsal and right lateral recumbency are depicted in Figure 2. Pearson's correlation coefficient, slope, concordance correlation coefficient, average difference, standard deviation, and 95% limits of agreement for pre- and postoperative IAP and APP measurements in dorsal and right lateral recumbency are summarized in Table 3. Correlation was considered to be strong for both preoperative and postoperative measurements of IAP and APP in dorsal and right lateral recumbency.

Table 2

Comparison of preoperative and postoperative IAP (mmHg) and APP (mmHg) measurements obtained in dorsal compared to right lateral recumbency in pregnant and nonpregnant control groups undergoing elective ovariohysterectomy.

GroupDorsal IAP (mmHg)Right Lateral IAP (mmHg)P valueBonferroni corrected P valueDorsal APP (mmHg)Right lateral APP (mmHg)P valueBonferroni corrected P value
PreoperativeMeanSDMeanSDMeanSDMeanSD
Pregnant7.521.815.821.38< 0.001a< 0.001a72.4812.7974.1812.59< 0.001a< 0.001a
Control5.080.743.460.77< 0.001a< 0.001a103.0421.76104.6621.83< 0.001a< 0.001a
PostoperativeMedianRangeMedianRangeMeanSDMeanSD
Pregnant5.703.68–11.774.782.94–10.30< 0.001b0.002b64.7913.7465.9813.97< 0.001a< 0.001a
Control5.884.41–10.305.152.94–8.09< 0.001b< 0.001b89.3817.7090.7918.09< 0.001a< 0.001a
a

Parametric distribution, paired t test.

b

Nonparametric distribution, signed rank test. Bonferroni correction for multiple comparisons, α < 0.00625.

Figure 2
Figure 2

Bland Altman agreement and graphic representation of the concordance correlation coefficient for pre- and postoperative IAP (mmHg) measurements in dorsal and right lateral recumbency in late-term pregnant and control cats undergoing elective ovariohysterectomy.

Citation: American Journal of Veterinary Research 83, 8; 10.2460/ajvr.22.02.0023

Table 3

Pearson's correlation coefficient, slope, concordance correlation coefficient, average difference, standard deviation, and 95% limits of agreement for pre- and postoperative IAP (mmHg) and APP (mmHg) measurements in dorsal and right lateral recumbency in late-term pregnant and nonpregnant control cats undergoing elective ovariohysterectomy.

ComparisonPearson's correlation coefficientSlopeConcordance correlation coefficient (95% CI)Average differenceSD95% LOA
Preoperative
 Dorsal IAP vs right lateral IAP (mmHg)0.9051.1180.601 (0.463–0.711)1.6510.7540.172, 3.129
 Dorsal APP vs right lateral APP (mmHg)1.0001.0010.997 (0.995–0.998)−1.6510.754−3.129, −0.172
Postoperative
 Dorsal IAP vs right lateral IAP (mmHg)0.9001.0600.718 (0.586–0.812)1.3170.846−0.342, 2.976
 Dorsal APP vs right lateral APP (mmHg)0.9990.9840.997 (0.995–0.998)−1.3170.846−2.976, 0.342

LOA = Limits of agreement.

Discussion

This prospective study is the first to evaluate changes in IAP, APP, hemodynamics, and clinicopathological variables in late-term pregnant queens undergoing elective OHE. The aim of the study was to evaluate potential changes during pregnancy that may be of clinical concern for cats in a veterinary setting, while also contributing to the evidence-based information regarding the physiology of intra-abdominal pressure changes in all species, including humans. While changes in IAP and APP were previously evaluated in predominantly early stage pregnant queens, pregnancy did not significantly affect abdominal pressures in that population.4 This lack of significance was hypothesized to be related to the relatively small size of embryo vesicles in the majority of cats.4 In the current study, cats were defined as late-term pregnant queens if the gravid uterus weighed ≥ 10% of body weight. This resulted in the inclusion of only cases where the gravid uterus was anticipated to have the greatest impact on the variables of interest.

Despite IAP being first measured in pregnant women in 1913,15 clinical recommendations pertaining to intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) were not published until over 100 years later in 2019.2,6 As intensivists are commonly faced with critical illnesses such as obstetric hemorrhage and preeclampsia throughout the course of pregnancy, the novelty of IAP and APP assessment in pregnancy and the scarcity of research pertaining to its potential physiological implications provide a niche to improve morbidity and mortality in this population.1 Prior to delivery, IAH was recently defined as an IAP ≥ 14 mmHg in pregnant women compared to a threshold of ≥ 12 mmHg in postpartum in women.2,6

The World Society of the ACS updated their definitions of IAP and ACS in 2013 to define IAP in nonpregnant individuals as a sustained or repeated pathological elevation in IAP ≥ 12 mmHg and ACS as a sustained IAP ≥ 20 mmHg (with or without an APP < 60 mmHg) that is associated with new organ dysfunction or failure.16,17 Animals are frequently used in experimental research to elucidate pathophysiological mechanisms, and the application of clinical veterinary patients as translational research models has become increasingly widespread. Given that normal IAP in dogs, cats, and horses appears similar to values measured in people, it was suggested that application of these thresholds to veterinary medicine may be reasonable.18 Veterinary-specific guidelines are published, although are a direct application of the human guidelines and lack evidence-based validation.1820 This is the first study to investigate IAP in otherwise healthy late-term pregnant queens and has identified substantially lower median preoperative IAPs of 5.82 to 7.52 mmHg compared to 22 mmHg reported in pregnant women at term undergoing scheduled caesarean delivery.21 The flexibility and compliance associated with the feline abdominal wall in addition to the constant pressure associated with a quadruped stance may contribute to the low IAPs observed in these late-term pregnant queens compared to parturient women.22,23 The latter study23 reported a significant decrease in IAP postoperatively to 16 mmHg in contrast to the current study, which failed to identify a significant decrease in IAP.21 Contrarily, IAP significantly increased in a population of predominantly early stage pregnant queens following OHE in a previous study.4 These findings are mirrored in the control population of the current study, likely reflecting the early stage of pregnancy in the majority of patients in the prior study.4 Potential explanations for an increase in IAP following OHE in either early or nonpregnant queens include an inadequate anesthetic plane at the time of postoperative assessment, iatrogenic pneumoperitoneum, gastrointestinal gas accumulation, tissue edema formation, pain, or tremors from hypothermia.4,19 It is possible that the IAP of pregnant queens may have continued to decrease in the current study following the immediate postoperative period; however, continued measurement was unfortunately not feasible in this population of cats. Alternatively, the effect of pregnancy on IAP in queens may be inferior to that seen in parturient women as is evidenced by the relatively low preoperative IAPs obtained in this study, although not all cats in this study were at full term. Of further support, the median preoperative IAPs of 5.82 to 7.52 mmHg in the pregnant queen population of the current study were only slightly above the median (interquartile range) of 5.15 mmHg (3.85 to 6.49 mmHg) previously reported in clinically healthy nonpregnant sedated cats.5

Both injectable and general anesthetics are known to have vasodilatory properties that may contribute to systemic hypotension.24 As expected, DBP significantly decreased in both pregnant and control groups throughout surgery with no difference in the magnitude of this change. However, DBP was significantly lower among pregnant queens both pre- and postoperatively. Pregnant queens were noted to have increased surgical blood loss compared to controls; however, the median volume was 3 mL in the pregnant group compared to < 1 mL in the controls. Unaccounted blood loss associated with removal of gravid uterus may have contributed to this postoperative finding. While hypovolemia secondary to surgical blood loss cannot be entirely ruled out, this is considered unlikely as the highest estimated blood loss observed throughout the study was 7 mL and would equate to 2.4 mL/kg for even the smallest of the pregnant cats (2.90 kg). Increased anesthetic and surgical time among the pregnant cat population may contribute to a lower postoperative DBP but is unlikely to have contributed to this preoperative finding. Supine-hypotension syndrome is characterized by breathlessness and decreased blood pressure observed in the second and third trimester of pregnancy in women when patients are placed in dorsal recumbency.1,3 Compression of the caudal vena cava occurs in this position and contributes to reduced preload, cardiac output, and subsequent hypotension.3 All DBP measurements were standardized to a single forelimb in the current study; however, patient positioning (i.e. dorsal vs right lateral recumbency) was not specifically standardized during DBP measurement. Despite this lack of standardization, the majority of measurements were obtained in dorsal recumbency. The supine-hypotension syndrome observed in women is likely applicable to the late-term pregnant cats in this study, thus contributing to their lower pre- and postoperative DBP. The preoperative DBP among pregnant cats of 80 ± 12.31 mmHg was slightly lower than the 88.3 ± 10.5 mmHg previously reported in predominantly early stage pregnant queens, while the postoperative DBP of 71.56 ± 13.85 mmHg was almost half of the 147.1 ± 11.9 reported in the same study.4 Possible explanations for this marked postoperative discrepancy in DBP include differences in preoperative volume status, variable planes of anesthesia at the postoperative assessment period, stress, or pain.4 Furthermore, cats did not have an intravenous catheter placed in the current study and were not administered intravenous fluids. While pregnant cats received subcutaneous, this was provided after postoperative DBP measurement. Comparatively, all cats received intraoperative isotonic crystalloids at a rate of 10 mL/kg/h in the previous study, which may have resulted in excessive intravascular volume and a subsequently hypertensive mean postoperative DBPs.4

Abdominal perfusion pressure is cited to be a potentially useful marker in the management of patients with IAH and ACS, and a target of 55 to 60 mmHg was previously suggested as it correlates with improved survival in human patients with IAH.2,25 However, most recent updated consensus definitions and clinical practice guidelines from the World Society of the ACS were unable to make evidence-based recommendations pertaining to the use of APP in the resuscitation or management of critically ill patients with IAP or ACS.16 A modified APP was applied in this study using the difference between the DBP and the IAP, similar to a previous study4 evaluating APP in pregnant cats. Doppler blood pressure does not necessarily equate to a direct mean arterial or systolic blood pressure in cats, although is generally accepted as the most reliable technique to measure blood pressure in low flow states.2631 As such, the blood pressure readings and APP reported in the current study may be higher than those where mean arterial pressures are used and are not directly comparable to those discussed in human medicine. The APPs observed in the current study ranged from 72.48 to 74.18 mmHg and 64.79 to 65.98 mmHg pre- and postoperatively in pregnant queens, respectively. Bosch et al4 reported higher pre- and postoperative APPs of 84.8 ± 10.5 mmHg and 140.6 ± 11.9 mmHg in a population of predominantly early staged pregnant cats, respectively. Although the ranges reported in the current study are above the recommended target of 55 to 60 mmHg, it is possible that postoperative APPs among pregnant queens may have dropped below this threshold if a true mean arterial pressure was measured. Blood lactate concentrations remained low and decreased over time for both pregnant and control groups, although peripheral lactate may not be an appropriate assessment of rapid intra-abdominal perfusion changes. Contrary to the hypothesis, APP decreased following removal of the gravid uterus in pregnant queens. This was likely a reflection of the significant decrease in DBP as IAP did not significantly change in this group throughout surgery. This highlights the potential to prevent decreases in APP with additional blood pressure support in late-term pregnant queens undergoing OHE, as interstitial edema and intraluminal splanchnic congestion may continue to prevent adequate perfusion despite restoration of APP.32,33

Intra-abdominal pressures are significantly lower in term parturient women positioned at a 10° left lateral tilt compared to supine, and this tilt is argued to prevent elevated IAPs associated with the weight of the gravid uterus.34 Left uterine displacement is also thought to alleviate the risks of supine-hypotension syndrome.1,2 However, the optimal position for IAP measurements in parturient women remains unclear and left uterine displacement may contribute to a reduction in accuracy.2 Intra-abdominal pressures were significantly higher in dorsal recumbency compared to right lateral recumbency in all cats in this study, although measurements in both positions were strongly correlated. Comparatively, right lateral IAP is higher than that obtained in sternal recumbency in awake clinically healthy cats.5 While compression from the gravid uterus may explain the difference in IAP measurements among late-term pregnant queens, the effect of abdominal contents on IAP appears to also increase IAP in dorsal recumbency among cats in estrus or anestrus. Lateral recumbency and consistent positioning for serial measurement of IAP are recommended in veterinary medicine and appear appropriate given the findings of the current study.19

This study has several limitations that are important to consider when interpreting and extrapolating findings to clinical practice. A standardized general anesthesia protocol was applied throughout the course of this study, although variations in patient response and depth of anesthesia may have played a confounding role. Of note, epidural or spinal anesthesia was not applied to the cats undergoing elective OHE in this study, while this is commonplace in women undergoing caesarean sections and may have additional cardiovascular implications.1,2,32 As discussed above, a left-sided tilt was not investigated in the current study.1,2 As such, the IAPs in dorsal recumbency may be elevated.

The IAP protocol was adjusted following the inclusion of 11 pregnant cats in the study to use a 4Fr Mila Foley catheter in the place of a 3.5Fr red rubber catheter to improve the efficiency of data collection. While this may have contributed to variability in IAP and APP measurements among the pregnant queen population, the inclusion of catheter type as a covariate served to control for this potential confounding effect. Finally, postoperative assessments were limited to the immediate postoperative period given patient temperament and the high-volume nature of the spay and neuter clinic, and it remains unknown whether variables of interest would have continued to change throughout the recovery period.

The results of this prospective study evaluating changes in IAP, APP, hemodynamics, and clinicopathological variables in late-term pregnant queens undergoing elective OHE have identified unique features among this patient population. Pregnant queens had higher preoperative IAPs and did not exhibit an increase in these pressures following OHE, unlike that observed in predominantly early staged and nonpregnant queens.4 Abdominal perfusion pressure decreased in both pregnant queens and controls; however, APP was significantly lower postoperatively among the pregnant group, approaching the recommended target of 55 to 60 mmHg.2,25 Results of this study support the current veterinary guidelines recommending that abdominal pressure monitoring be performed in lateral recumbency, as values obtained in dorsal recumbency were significantly higher than right lateral. Furthermore, a consistent recumbent position is imperative for serial measurements. As future studies continue to advance our understanding of the mechanisms underlying IAP and APP changes, there is great potential to reduce both morbidity and mortality, particularly among critically ill subgroups in human and veterinary medicine.

Acknowledgments

No external funding was used in this study. The authors declare that there were no conflicts of interest.

The authors thank Devin Angelucci, Katherine Cano, Faith Northcutt, and Will Northcutt for their technical support in model development, operating room procedures, sample collection, lab processing, and data collation. Grateful acknowledgement is offered to Dr. Kenneth J. Drobatz for statistical analyses consultation. Furthermore, authors extend their gratitude to Bernadette Vogel for study administrative support.

References

  • 1.

    Chun R, Kirkpatrick AW. Intra-abdominal pressure, intra-abdominal hypertension, and pregnancy: a review. Ann Intensive Care. 2012;2(suppl 1):S5.

  • 2.

    Lozada MJ, Goyal V, Levin D, et al. Management of peripartum intra-abdominal hypertension and abdominal compartment syndrome. Acta Obstet Gynecol Scand. 2019;98(11):13861397.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3.

    Malbrain ML, De Keulenaer BL, Oda J, et al. Intra-abdominal hypertension and abdominal compartment syndrome in burns, obesity, pregnancy, and general medicine. Anaesthesiol Intensive Ther. 2015;47(3):228240.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Bosch L, Rivera del Álamo MM, Andaluz A, et al. Effects of ovariohysterectomy on intra-abdominal pressure and abdominal perfusion pressure in cats. Vet Rec. 2012;171(24):622.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    Rader RA, Johnson JA. Determination of normal intra-abdominal pressure using urinary bladder catheterization in clinically healthy cats. J Vet Emerg Crit Care. 2010;20(4):386392.

    • Search Google Scholar
    • Export Citation
  • 6.

    Lozada MJ, Goyal V, Osmundson SS, Pacheco LD, Malbrain MLNG. It's high time for intra-abdominal hypertension guidelines in pregnancy after more than 100 years of measuring pressures. Acta Obstet Gynecol Scand. 2019;98(11):14861488.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Cheatham ML, Malbrain ML, Kirkpatrick A, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. II. Recommendations. Intensive Care Med. 2007;33(6):951962.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Tyagi A, Singh S, Kumar M, Sethi AK. Intra-abdominal pressure and intra-abdominal hypertension in critically ill obstetric patients: a prospective cohort study. Int J Obstet Anesth. 2017;32:3340.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Staelens AS, Van Cauwelaert S, Tomsin K, Mesens T, Malbrain ML, Gyselaers W. Intra-abdominal pressure measurements in term pregnancy and postpartum: an observational study. PLoS One. 2014;9(8):e104782.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10.

    Schorn MN. Measurement of blood loss: review of the literature. J Midwifery Womens Health. 2010;55(1):2027.

  • 11.

    Vitello DJ, Ripper RM, Fettiplace MR, Weinberg GL, Vitello JM. Blood density is nearly equal to water density: a validation study of the gravimetric method of measuring intraoperative blood loss. J Vet Med. 2015;2015:152730.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    Duthie SJ, Ven D, Yung GL, Guang DZ, Chan SY, Ma HK. Discrepancy between laboratory determination and visual estimation of blood loss during normal delivery. Eur J Obstet Gynecol Reprod Biol. 1991;38(2):119124.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13.

    Borden FW. Loss of blood at operation; a method for continuous measurement. Calif Med. 1957;87(2):9197.

  • 14.

    Lee MH, Ingvertsen BT, Kirpensteijn J, Jensen AL, Kristensen AT. Quantification of surgical blood loss. Vet Surg. 2006;35(4):388393.

  • 15.

    Paramore RH. The intra-abdominal pressure in pregnancy. Proc R Soc Med. 1913;6:291334.

  • 16.

    Kirkpatrick AW, Roberts DJ, De Waele J, et al. Intra-abdominal hypertension and the abdominal compartment syndrome: updated consensus definitions and clinical practice guidelines from the World Society of the Abdominal Compartment Syndrome. Intensive Care Med. 2013;39(7):11901206.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17.

    Malbrain ML, Cheatham ML, Kirkpatrick A, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. I. Definitions. Intensive Care Med. 2006;32(11):17221732.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18.

    Nielsen LK, Whelan M. Compartment syndrome: pathophysiology, clinical presentations, treatment, and prevention in human and veterinary medicine. J Vet Emerg Crit Care. 2012;22(3):291302.

    • Search Google Scholar
    • Export Citation
  • 19.

    Hoareau GL MM. Intraabdominal pressure monitoring. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 2nd ed. Elsevier Saunders; 2015:982987.

    • Search Google Scholar
    • Export Citation
  • 20.

    Smith SE, Sande AA. Measurement of intra-abdominal pressure in dogs and cats. J Vet Emerg Crit Care. 2012;22(5):530544.

  • 21.

    Al-Khan A, Shah M, Altabban M, et al. Measurement of intraabdominal pressure in pregnant women at term. J Reprod Med. 2011;56(1–2):537.

  • 22.

    van Nimwegen SA, Kirpensteijn J. Laparoscopic ovariectomy in cats: comparison of laser and bipolar electrocoagulation. J Feline Med Surg. 2007;9(5):397403.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23.

    Dorn M, Becher-Deichsel A, Bockstahler B, Peham C, Dupré G. Pressure-volume curve during capnoperitoneum in cats. Animals (Basel). 2020;10(8):1408.

    • Search Google Scholar
    • Export Citation
  • 24.

    Noel-Morgan J, Muir WW. Anesthesia-associated relative hypovolemia: mechanisms, monitoring, and treatment considerations. Front Vet Sci. 2018;5:53. doi: 10.3389/fvets.2018.00053.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25.

    Cheatham ML, White MW, Sagraves SG, Johnson JL, Block EF. Abdominal perfusion pressure: a superior parameter in the assessment of intra-abdominal hypertension. J Trauma. 2000;49(4):621626. doi: 10.1097/00005373-200010000-00008.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26.

    Klevans LR, Hirkaler G, Kovacs JL. Indirect blood pressure determination by Doppler technique in renal hypertensive cats. Am J Physiol. 1979;237(6):H720H723.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27.

    Grandy JL, Dunlop CI, Hodgson DS, Curtis CR, Chapman PL. Evaluation of the Doppler ultrasonic method of measuring systolic arterial blood pressure in cats. Am J Vet Res. 1992;53(7):11661169.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28.

    Caulkett NA, Cantwell SL, Houston DM. A comparison of indirect blood pressure monitoring techniques in the anesthetized cat. Vet Surg. 1998;27(4):370377.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29.

    Jones TJ. Inter- and intraindividual variation in Doppler ultrasonic indirect blood pressure measurements in healthy cats. J Vet Intern Med. 1999;13(4):314318. doi: 10.1892/0891-6640(1999)013<0314:iaivid>2.3.co;2.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 30.

    Binns SH, Sisson DD, Buoscio DA, Schaeffer DJ. Doppler ultrasonographic, oscillometric sphygmomanometric, and photoplethysmographic techniques for noninvasive blood pressure measurement in anesthetized cats. J Vet Intern Med. 1995;9(6):405414.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 31.

    Jepson RE, Hartley V, Mendl M, Caney SM, Gould DJ. A comparison of CAT Doppler and oscillometric Memoprint machines for non-invasive blood pressure measurement in conscious cats. J Feline Med Surg. 2005;7(3):147152.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32.

    Sawchuck DJ, Wittmann BK. Pre-eclampsia renamed and reframed: Intra-abdominal hypertension in pregnancy. Med Hypotheses. 2014;83(5):619632.

  • 33.

    Seal JB, Gewertz BL. Vascular dysfunction in ischemia-reperfusion injury. Ann Vasc Surg. 2005;19(4):572584.

  • 34.

    Chun R, Baghirzada L, Tiruta C, Kirkpatrick AW. Measurement of intra-abdominal pressure in term pregnancy: a pilot study. Int J Obstet Anesth. 2012;21(2):135139.

    • PubMed
    • Search Google Scholar
    • Export Citation

Contributor Notes

Corresponding author: Dr. Fudge (mackfudge@hotmail.com)