An update on the anaesthetic management of gastric dilatation-volvulus in dogs
MeSH keywords:anaesthesia, dilatation, dog, stomach, stomach volvulus
Gastric dilatation - volvulus (GDV) is a complex and multifactorial condition that requires urgent treatment. The aim of this study is to assess the steps for the anaesthetic management of GDV in dogs. The first step of the GDV management is the stabilization of the patient, so that the surgery can be performed with the less possible risk. Resuscitation with isotonic crystalloid or colloid fluids in order to correct the electrolyte abnormalities, the administration of lidocaine or other antiarrhythmic drugs to treat ventricular arrhythmias and the administration of analgesics are essential in the treatment. Oxygen therapy is also needed. After stabilization, gastric decompression should be performed through an orogastric tube or by gastrocentesis. There are few drugs that can be used in the anaesthetic protocol, with minimal effects on the cardiovascular and respiratory system. Electrolyte and acid-base disorders, electrocardiographic abnormalities, and haemodynamic changes must be closely monitored.
Gastric dilatation - volvulus (GDV) is a life-threatening condition in dogs, with high morbidity and mortality, which requires immediate surgical and anaesthetic management (Sharp & Rozanski 2014, O’Neill et al. 2017). In this situation, the stomach is distended with gas and ingesta and it is rotated along its mesenteric axis (Broome & Walsh 2003, Green et al. 2011, Gazzola & Nelson 2014). As a result, the intragastric pressure is increased and the venous flow, cardiac output and arterial pressure are decreased (Green et al. 2011, Gazzola & Nelson 2014). The main pathological events are rapid accumulation of gas in the stomach, gastric volvulus, increased intragastric pressure and decreased venous return (Bruchim & Kelmer 2014, O’Neill et al. 2017).
GDV seems to be a clinical concern in affected dogs, as it is a combination of acute pain and high mortality. According to Evans & Adams (2010), GDV was the cause of 2.5% deaths in UK pedigree dogs, with a median age of 7.9 years. Another epidemiological study has shown that GDV cases have a survival rate of less than 50%, but 80% of dogs that underwent surgery were successfully discharged from the clinic. Although the aetiology and pathophysiology of this disease is not yet fully known, a lot of predisposing factors have been identified (O’Neill et al. 2017).
Large and giant breeds, like Great Danes, German shepherds, Labrador retrievers, Golden retrievers and Dobermanns, appear to be at high risk. This fact does not eliminate the risk for small breeds, like Pinchers or Poodles (Green et al. 2011, Goodrich et al. 2013, Gazzola & Nelson 2014, O’Neill et al. 2017). Dogs with deep and narrow chest structure are more prone to develop GDV, as the body conformation seems to play an important role to the development of GDV (Green et al. 2011, Goodrich et al. 2013, Gazzola & Nelson 2014).
Diets that are composed of particles larger than 30 mm, have been shown to increase the risk of GDV. On the other hand, the use of dry diets is controversial. Although they have been identified as a potential risk factor, because of their basic components, oil and fat, that reduce gastric emptying, studies have shown that dry food offered according to the company guidelines does not cause any problems (Broome & Walsh 2003). Irrespectively of the quality and the components of the food, dogs that are fed with large volume of food once per day have increased risk of developing GDV (Tivers & Brockman 2009, Green et al. 2011, Goodrich et al. 2013, Gazzola & Nelson 2014). Moreover, there is limited evidence on whether dogs that eat rapidly or from a height are at an increased risk to develop GDV compared with dogs that are fed from a bowl on the floor (Buckley 2017). Furthermore, another question seems to be if the dogs that eat quickly are more likely to develop GDV in comparison with the dogs that eat slowly, but the answer is unclear and inconclusive (Buckley 2016). Age seems also to be a serious predisposing factor for GDV. Finally, dogs with fearful temperament, kennelling or having a long journey the day before the appearance of GDV, have higher chances of developing GDV (Tivers & Brockman 2009, Green et al. 2011, Goodrich et al. 2013, Gazzola & Nelson 2014).
The aim of this study is to assess the steps for the anaesthetic management of GDV in dogs.
A literature research was performed using Google Scholar and PubMed online platforms. Search terms included the following, in an “OR” or “AND” combination where it was deemed applicable: gastric dilatation, volvulus, dog, canine, anaesthesia, management.
Manipulations prior to anaesthesia
Before any sedation, dogs with GDV should be stabilized by administration of fluids intravenously (IV). According to the literature, the stabilization for a prolonged period is not suitable, as gastric ischemia and necrosis may develop. The surgery is preferred to be performed when the patient is stable for anaesthesia (Broome & Walsh 2003). In many cases, this goal is not fully achieved, so anaesthesia may be induced without the complete stabilization of the patient (Mathews 2006, Tivers & Brockman 2009).
In these patients, fluid therapy is very aggressive in order to reverse hypovolaemia and improve perfusion. Two venous catheters (14-18G) are placed in the cephalic veins, but not in the saphenous, because of the possible coexisting compression of the vena cava. In hypovolemic patients with a mean arterial pressure (MAP) below 60 mmHg or systolic arterial pressure (SAP) below 90 mmHg, isotonic crystalloid solutions, usually Lactated Ringer’s, are administered at a rate of 50-90 mL kg-1 h-1 IV. As MAP increases, the rate of administration is reduced down to 50% gradually. If hypotension remains, dopamine or norepinephrine can be administered as a continuous rate infusion. In non-dehydrated patients with MAP below 60 mmHg or SAP below 90 mmHg, fluids are given at a rate of 20 mL kg-1 h-1 IV. If the patient is in a very critical condition, hypertonic saline solution 5% (6-10 mL kg-1) or 7.5% (4-8 mL kg-1) can be administered at a rate of 1 mL kg-1 min-1 IV (Broome & Walsh 2003, Tivers & Brockman 2009, Frikis & Zlateva 2018).
The second very important step is to stabilize the respiratory status of the patient. As respiratory dysfunction usually occurs in dogs with GDV, the gastric dilation and the high intra-abdominal pressure can cause hypoventilation and ventilation- perfusion mismatch. Tachypnoea, hypercapnia and hypoxia may eventually occur. The decreased cardiac output can further aggravate the pulmonary blood flow impairment and contribute to the ventilation-perfusion mismatch. Therefore, gastric decompression is mandatory, in order to further stabilize the patient and improve the respiratory function, either by gastric intubation or gastrocentesis (Goodrich et al. 2013). Additionally, the oxygen administration can be performed through a mask without causing further stress to the animal (Mathews 2006, Tivers & Brockman 2009, Sharp & Rozanski 2014).
In most of the cases, the choices of anaesthetic protocols are limited. Drugs that do not affect the cardiovascular and respiratory systems are preferred. Agents which are known to cause arrhythmias and hypotension, such as α2-agonists and thiopentone, should be avoided.
Opioids seem to be the best choice as agents for premedication because of their analgesic effect. There is a wide range of opioids that can be used in dogs such as fentanyl at a dose of 0.5-2 μg kg-1 IV, every 30 minutes, morphine at 0.1-0.3 mg kg-1 IM, methadone at 0.2-0.3 mg kg-1 IM, butorphanol at 0.1-0.4 mg kg-1 IM and tramadol at 2-3 mg kg-1 IM. Moreover, the use of benzodiazepines, such as midazolam at 0.2-0.3 mg kg-1 IM, can be helpful as they have low effect on arterial blood pressure. On the other hand, acepromazine at 0.05-0.1 mg kg-1 IM is not commonly used as it causes vasodilatation and it has no analgesic effect (Self 2016).
Generally, the goal is a smooth induction and a rapid intubation of the patient. Propofol, despite its short duration of action, has been experimentally found that at 6 mg kg-1or more in dogs with hypovolemia causes hypotension. Therefore, it is recommended that it is carefully administered at low doses, 2-4 mg kg-1 IV, slowly to effect, as it is also a very strong respiratory depressant (Broome & Walsh 2003, Tivers & Brockman 2009). Etomidate at a dose of 1-2 mg kg-1 IV, is also a good choice. In contrast to propofol, etomidate has little effect on the circulatory and respiratory system when given to hypovolemic dogs. Benzodiazepines, like midazolam (0.5 mg kg-1 IV), can be used in combination with the above anaesthetics to reduce their dose and their effects on circulation and respiration. Combinations of fentanyl and midazolam can be used for sedation to introduce the gastric tube for decompression, and/or to induce anaesthesia (Broome & Walsh 2003, Mathews 2006, Tivers & Brockman 2009).
Maintenance of anaesthesia
Anaesthesia is maintained with inhalational anaesthetics, such as isoflurane or sevoflurane (Dugdale 2020) in 100% oxygen, through a rebreathing system (Broome & Walsh 2003, Mathews 2006, Tivers & Brockman 2009), as they have a little effect on cardiovascular system, except from hypotension (Mathews 2006). Low depth of anaesthesia is also achieved by the administration of a fast onset and short duration opioid, such as fentanyl as constant rate infusion (CRI). Fentanyl reduces the minimum alveolar concentration (MAC) of isoflurane by 53%. Moreover, nitrous oxide (N2O) can be used, which also reduces the needs of the inhaled anaesthetic, but should not be used until a permanent gastric decompression occurs (Broome & Walsh 2003, Mathews 2006).
Based on the above, we recommend the following anaesthetic protocols for GDV:
Induction: Fentanyl 2-4 μg kg-1 & midazolam 0.2- 0.3 mg kg-1 IV. If needed, low doses of propofol to effect (1 mg kg-1) to help with intubation.
Maintenance: Isoflurane in 100% oxygen.
Premedication: Midazolam 0.2-0.3 mg kg-1 IM & pethidine at 3 mg kg-1 IM.
Induction: Propofol 1 mg kg-1 IV until intubation (to effect).
Maintenance: Isoflurane in 100% oxygen & fentanyl as CRI at 0.1 μg kg-1 min-1.
Premedication: Midazolam 0.2-0.3 mg kg-1 IM & pethidine at 3 mg kg-1 IM.
Induction: Propofol 1 mg kg-1 IV until intubation (to effect).
Maintenance: Propofol as CRI at 0.1 mg kg-1 min-1 alone or in combination with fentanyl as CRI at 0.05 μg kg-1 min-1.
Ventricular cardiac arrythmias have been reported in up to 40% of dogs with GDV because of myocardial ischemia (Brockman et al. 1995, Homer 2020). Moreover, the increased circulation of catecholamines and cytokines contributes to the formation of arrythmias and this may lead to the cardiovascular instability after the gastric decompression (Sharp & Rozanski 2014). Therefore, ECG is highly recommended to identify cardiac arrythmias and the response to the therapy. There are different approaches for the use of antiarrhythmics. According to Brockman et al. (1995) and Volk (2009), antiarrhythmics should be used when arrythmias are associated with poor myocardial function, low cardiac output and electrolyte imbalance. Bruchim (2012) believes that the early administration of lidocaine, initially as bolus and then as CRI, reduces the incidence of acute kidney injury (AKI), cardiac arrythmias and mortality.
Measures must be taken peri-operatively, if arrhythmia persists, at a rate of more than 130 beats min-1. In these cases, the administration of lidocaine may help to reduce the heart rate to about 120 beats min-1, as well as to reduce abnormal morphology of the ECG. Specifically, lidocaine can be administered at a dose of 2 mg kg-1 IV. If the first administration is not successful, it can be repeated after 2-3 minutes. Moreover, lidocaine can be administered at a rate of 20-80 μg kg-1 min-1 as CRI, if arrhythmia responds to its bolus administration (Bruchim et al. 2012). Failure to treat arrhythmias with lidocaine requires a reassessment of the ECG and the general condition of the patient (electrolytes, acid-base balance, pain), possibly by choosing an alternative antiarrhythmic treatment. Generally, regardless of the success of the treatment, the complete disappearance of arrhythmias is not expected. If there is atrial tachycardia, it is usually corrected after fluid resuscitation and administration of analgesics (Bruchim et al. 2012). The use of ECG should be continued 24-48 hours post-operatively
Arterial blood pressure measurement and fluid therapy
Hypovolemic-distributive and cardiogenic shock, inadequate tissue perfusion and ischemia characterize the patients with GDV (Mathews 2006, Tivers & Brockman 2009, Bruchim & Kelmer 2014, Sharp & Rozanski 2014, O’Neill et al. 2017). The primary therapy is the administration of fluids measurement while monitoring the arterial blood pressure, giving attention in geriatric patients or animals with cardiovascular problems.
Arterial blood pressure measurement, invasive or non-invasive, is a useful tool in estimating the haemodynamic status and tissue perfusion. Invasive blood pressure measurement can be achieved with the placement of an arterial catheter attached to a pressure transducer and therefore, it is thought to be the golden standard method for the most accurate measurements of arterial blood pressure (Haskins 2011). On the other hand, Doppler and oscillometric techniques can be used for the non-invasive arterial blood pressure measurement, with the second one to be preferred, as it gives information on systolic, diastolic and mean arterial pressure (Cooper & Cooper 2012).
If hypotension is present, even after administration of fluids, dopamine should be administered at a rate of 7-10 μg kg-1 min-1 and it can be increased by 1 μg kg-1 min-1 every 1 to 3 minutes (maximum dose rate 10 μg kg-1 min-1) until the desired MAP is achieved (over 60 mmHg). If the desired MAP is not achieved, norepinephrine can be given at a rate of 0.1-0.5 μg kg-1 min-1 (Tivers & Brockman 2009).
According to Williams (2016), colloids should be given when high volumes of fluids are not effective to resuscitate a patient. They also help in increasing tissue perfusion with concomitant administration of oxygen at the same time.
Capnography and pulse oximetry
As the respiratory function is affected during GDV, capnography and pulse oximetry are two parameters that should be monitored during anaesthesia. The first one is a non-invasive method for the measurement of the respiratory carbon dioxide and the second one estimates the saturation of arterial haemoglobin in oxygen (Homer 2020).
Acid-base and electrolyte disturbances
Increased lactate concentration (Green et al. 2011, Mooney et al. 2014), metabolic acidosis, metabolic alkalosis and respiratory acidosis can develop in animals with GDV (Rauserova-Lexmaulova et al. 2020). Hypokalaemia is the most usual electrolyte disturbance and it can deteriorate cardiac arrythmias and therefore, it is important to be measured (Mooney et al. 2014). Potassium supplement solutions can be administered IV, separately from the rapid administration of isotonic crystalloids, at a concentration of 30-80 mEq L-1. The potassium solutions are administered at a maximum rate of 0.5-1 mEq kg-1 h-1 when serum potassium is below 3 mEq L-1 (Mathews 2006).
Complications of GDV during anaesthesia
The most usual complications of GDV are the ischemia- reperfusion injury (IRI), systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS). Organ and/or systemic dysfunctions that have been reported in dogs with GDV include hypotension, AKI, disseminated intravascular coagulation (DIC), gastric ulceration and cardiac arrhythmias (Bruchim & Kelmer 2014, O’Neill et al. 2017).
GDV is a life threating condition, but early admission (Song et al. 2020) and treatment improves survival rates (Tivers & Brockman 2009, Bruchim & Kelmer 2014). Lactate concentration is thought to be a prognostic factor with high reliability. Concentrations below 4 mmol L-1 indicate high survival rate and reduced risk of complications. On the other hand, concentrations of lactate above 6 mmol L-1 may indicate gastric necrosis and sepsis, and survival rate is reduced significantly (Tivers & Brockman 2009, Green et al. 2011, Mooney et al. 2014). The owner must always be informed about the outcome of every possible treatment followed.
Conflict of interest
The authors declared no conflicts of interest.
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