The intra-abdominal pressure (IAP) is the constant pressure within the abdominal cavity that ranges from 0 to 7.4 mmHg in dogs (13). Intra-abdominal hypertension (IAH) of more than 20 mmHg caused by sustained increases in IAP can impair normal perfusion and function of the surrounding tissues due to closed anatomic abdominal space (1,10). IAH causes significant dysfunction of the cardiovascular, respiratory, and abdominal organ systems, which contributes significantly to increased mortality in critically ill patients (3,5). Despite the fact that IAH is studied as an independent cause of morbidity and mortality in the intensive care unit (ICU) in humans, it is rarely described in veterinary medicine outside of experimental models (6). Although there have been studies that have measured IAP after surgery (3,5), studies on continuous measurement of IAP and stabilization of IAH in the ICU are limited. This report describes a case of IAH development and stabilization by administration of tranquilizer in a dog in which IAP was continuously measured for 12 hours after cervical ventral slot decompression surgery.

A castrated male Yorkshire Terrier (8 years old, 3.7 kg) with a history of tetraplegia was referred to Kyungpook National University’s Veterinary Medical Teaching Hospital for Magnetic Resonance Imaging (MRI). The dog’s right forelimb paresis began 48 days before, and after three weeks, the dog with tetraplegia was presented for MRI and cervical ventral slot decompression.

On presentation, the dog’s heart rate was 124 beats/min (reference range, 80-160 beats/min), respiratory rate was 44 breaths/min, and rectal temperature (39.4°C) were all within normal ranges. Except for albumin (4.1 g/dL; reference range, 2.6-4.0 g/dL), Bun/creatinine ratio (61.2 rate; reference range, 12.5-31.8 rate), GGT (26 U/L; reference range, 5-14 U/L), and cholesterol (316 mg/dL; reference range, 111-312 mg/dL), all complete blood cell count and biochemistry results were within normal ranges. Neurologic assessment revealed nonambulatory tetraplegia with normal deep pain and conscious proprioception was absent in all four limbs. Cranial and spinal nerve reflexes were unremarkable.

An MRI of the cervical spine was performed under anesthesia. A 24-gauge catheter was inserted into the right cephalic vein and butorphanol (0.2 mg/kg, IV) was administered. Midazolam (0.2 mg/kg, IV) was used to pre-oxygenate the patient using the flow-by method. Propofol (5 mg/kg, IV) was used to induce anesthesia, which was then followed by intubation. Anesthesia was maintained with 2% isoflurane and a 2 L/min oxygen rate. During anesthesia, a normal saline solution (0.9% NaCl, 5 mL/kg/h) was administered via an infusion pump. The MRI results revealed 5th cervical vertebra (C5) and 6th cervical vertebra (C6) spinal cord compression due to disc extrusion on the right side of the spinal cord, which was considered a possible cause of the symptoms.

Ventral slot surgery on the C5-6 side and penetration on the C6-7 side were performed two days later. Premedication included fentanyl (3 µg/kg, IV) and midazolam (0.2 mg/kg, IV). Pre-oxygenation lasted 5 minutes, followed by induction with propofol (5 mg/kg, IV). As a maintenance fluid, Plasma solution (5 mL/kg/h) was used. During the operation, fentanyl (4-10 µg/kg/hr, IV) and ketamine (0.6-1.2 mg/kg/hr, IV) constant rate infusion (CRI) were used for analgesia. Anesthesia lasted 134 minutes, and the operation took 70 minutes. Extradural material was discovered and removed from the right and ventral sides of the C5-6 spinal cord.

Following surgery, a 6-Fr Foley urinary catheter was inserted into the urethra for urination and the patient was transferred to the ICU. Every hour, respiratory rate, heart rate, arterial pressure and IAP was measured (Table 1). Intravesicular pressure was used to measure IAPs in this dog (8,15), IAP and abdominal perfusion pressure (APP), which can be calculated as mean arterial pressure minus IAP, and the results are summarized in Table 1. During the postoperative monitoring period, IAP was normal and within the reference range one hour after surgery (0-7.4 mmHg) (Fig. 1).

Table 1 . Patient clinical variables of time intervals within 12 hours.

Parameter
After surgery (hour)	HR (min)	RR (min)	SAP (mmHg)	MAP (mmHg)	DAP (mmHg)	IAP (mmHg)	APP (MAP-IAP) (mmHg)
1	98	58	171	139	55	5	135
2	116	86	191	148	101	4	144
3	120	86	151	77	56	12	65
4	125	76	159	78	59	4	74
5	110	20	150	59	49	5	54
6	107	44	177	89	61	5	84
7	93	32	166	83	50	5	78
8	119	36	153	81	63	8	73
9	110	20	138	80	60	6	74
10	85	20	144	83	63	6	76
11	134	20	152	120	98	6	114
12	96	20	120	82	71	5	77

HR, heart rate; RR, respiratory rate; SAP, systolic arterial pressure; MAP, mean arterial pressure; DAP, diastolic arterial pressure; IAP, intra-abdominal pressure; SYS, systolic; DIA, diastolic; APP, abdominal perfusion pressure..

Figure 1. Photographs of a patient in the intensive care unit with a urinary catheter and an intravesicular pressure (A). Intra-abdominal pressure (IAP) is measured using an invasive blood pressure transducer and displayed on a multiparameter monitor (B). IAP were all measured at 5 mmHg one hour after surgery.

Despite the administration of fentanyl (2 µg/kg/hr, IV) and ketamine (0.6 mg/kg/hr, IV), three hours after surgery, abdominal distension with agitation and respiratory distress were observed and IAP increased to 12 mmHg, indicating mild IAH (Fig. 2A). It was presumed that the dog’s pain response and fentanyl (4 µg/kg/hr, IV) and ketamine (1.2 mg/kg/hr, IV) was increased, the blood pressure was measured oscillometrically at that time and was 151/56 (77) mmHg, while APP was 65 mmHg. Although the fentanyl and ketamine CRI doses were increased, clinical signs had not abated, and acepromazine (0.01 mg/kg, IV) was administered to try to alleviate the respiratory distress. After acepromazine administration, abdominal distention had stopped, IAP had dropped to 4 mmHg (Fig. 2B), and respiratory rate had returned to normal after another hour. During the next 24 hours, the patient’s vital signs and IAP remained stable, with normal urine output. The patient was discharged four days after surgery because there were no postoperative complications. We are still following up with the patient for a neurologic exam, and no other clinical signs have been observed.

Figure 2. Three hours after surgery, intra-abdominal pressure (IAP) were measured to be 12 mmHg, respectively (A). Following acepromazine administration, IAP were all 4 mmHg (B).

In this case, a transient increase in IAP of 12 mmHg was observed despite the administration of appropriate analgesics in the ICU following cervical spine surgery. According to the guidelines for IAP and IAH in veterinary medicine, an IAP of 0-7.4 mmHg is considered normal in a dog, 7.4-14.7 mmHg is considered mild IAH, 14.7-25.7 mmHg is considered moderate-to-severe IAH, and an IAP >25.7 mmHg is considered severe IAH and requires immediate surgical decompression (2,13). The IAP in this dog was 12 mmHg, indicating mild IAH. Even in mild IAH, especially in the presence of edema, abdominal compliance is reduced or systemic disease exceeds vascular hydrostatic pressure, resulting in loss of APP induced ischemia and reperfusion injury (4,6). In the normovolemic patient, the effects of mild IAH are usually mild symptoms (eg, hypoxia, hypercarbia, and decreased cardiac output); therefore, less invasive medical treatment options should be prioritized (7,10). The dog in this study had mild IAH during the postoperative monitoring period and additional fentanyl and ketamine CRI did not alleviate the clinical signs despite no apparent underlying disease in either dog. Although it is difficult to explain this mild IAH, it might be associated with an agitation and/or postoperative pain.

To treat mild IAH, various treatments have been proposed, which are based on improving abdominal wall compliance, evacuation of intraluminal contents, evacuation of abdominal fluid collections, and correction of the capillary leak and positive fluid balance (9,14). Although IAH occurred after surgery, in this case, the patient did not have IAH due to intra-abdominal organ edema. Postoperative pain and excitability are thought to have inhibited abdominal cavity compliance and caused mild IAH in this dog. The dog in this study fentanyl and ketamine CRI did not alleviate IAH and acepromazine (0.01 mg/kg, IV) was administered to alleviate excitement. Sedation treatment that improves abdominal wall compliance is recommended as the recommended treatment for patients with mild IAH (6,9).

By increasing abdominal wall compliance, Sedatives and muscle relaxants can help control IAH (9). Acepromazine is a promazine 2-acetyl derivative that is widely used in veterinary medicine to provide mild-to-moderate sedation at low doses (12). In this case, the dog displayed IAH symptoms, including agitation, and acepromazine was administered. As a result, the IAH was stabilized. Following that, IAP was continuously measured in the ICU, and there was no further increase in IAP. There is currently no case in veterinary medicine where IAP stabilization was induced by sedative administration when IAP was increased. In this case, as in human medicine (9), the administration of sedatives when IAP rises is regarded as the therapeutic option for stabilizing IAH.

The IAP was measured in dogs in lateral positions using urinary bladder catheterization and volumes of saline instillation before measurement while sedated and awake. Because decreasing interfaces in body position will also affect IAP (13), staff should ensure consistency of IAP measurement with each consecutive value. In veterinary medicine, the most commonly recommended method is IAP measurement in the lateral position (5,11). All IAP were measured continuously in the lateral position in this case, and measurement errors were kept to a minimum.

This study has several limitations. First, the relationship between cervical ventral slot decompression and intra-abdominal pressure elevation is not clear. Although cervical ventral slot decompression surgery does not directly IAH, IAP can be increased, and even if there is no abdominal problem as in this case, IAH can be caused by increased muscle tension, excitement, and post operative pain (1-3,5,6,10). Second, it was not clear how the acepromazine that was administered affected the severity of the dog’s IAH because the exact mechanism has not been introduced to veterinary medicine. However, additional fentanyl and ketamine CRI did not alleviate IAH and acepromazine (0.01 mg/kg, IV) was administered to alleviate excitement and decrease IAP. Although the exact mechanism has not been introduced to veterinary medicine, acepromazine provide mild-to-moderate sedation and improves abdominal wall compliance, the IAH was stabilized. Finally, one case is an obvious limitation. However, in the current veterinary literature, it is difficult to find a case that describes an increase in IAP by continuously measuring IAP for 12 hours, and it is meaningful because there is no study that lowers IAP by administering sedative drugs.

In conclusion, in dogs, postoperative pain and excitability are thought to have inhibited abdominal cavity compliance and postoperative mild IAH can be induced, and additional analgesics and acepromazine administration can be considered a therapeutic option to stabilize mild IAH. However, considering the nature of a single surgical case of cervical ventral slot, further study is required for indication of IAH monitoring.

This research was supported by Kyungpook National University Research Fund, 2020.

The authors have no conflicting interests.