A haemangiosarcoma is a type of cancer that is common in dogs. Cancers that are visceral in nature, in this case the spleen, are difficult to treat (Kim et al, 2015). They generally originate from the vascular endothelial cells, and are highly metastatic, commonly spreading to the liver, lymph nodes and lungs (Wendelburg et al, 2015). Alexander et al (2019) state that 50–65% of incidences of canine hemangiosarcoma originate from the spleen, and patients typically present with lethargy, vomiting, acute collapse and hypovolaemic shock as a result of internal haemorrhage. Alvarez et al (2013) suggest that treatment of splenic hemangiosarcomas by splenectomy only achieved a median survival time of 65–86 days, whereas the cases that were treated surgically and then delivered a course of chemotherapy achieved a median survival time of 172–202 days, suggesting these patients benefit from multi-modal treatment options depending on their staging. Anaesthesia of these cases for splenectomy is likely to be challenging, as stabilisation of patients with haemoabdomen prior to surgery greatly reduces the risks of anaesthesia-related complications; however, in these cases surgical intervention forms part of the stabilisation process (Mills and Welsh, 2016a).
Pre-anaesthetic assessment
On presentation to the practice the patient should have their basic parameters assessed, including heart rate, respiratory rate, temperature, mucous membrane colour, capillary refill time and blood pressure. In the case of a dog with a bleeding splenic hemangiosarcoma, the patient would be expected to be tachycardic, with pale mucous membranes and prolonged capillary refill time, caused by an increase in catecholamines triggered by low-pressure stretch receptors in vessels (Nolan and Pullinger, 2014). Blood pressure measurement should be prioritised when triaging the patient. The patient will likely be hypotensive due to the loss in circulating blood volume, and venous return will therefore be reduced (Ouston, 2011). Tabor (2016) describes how this loss in circulating blood volume also leads to a loss in haemoglobin, resulting in reduced oxygen carrying capacity. The oxygen saturation (SpO2) should be monitored closely and supplemental oxygen provided in the pre- and post-operative period. As a compensatory mechanism to preserve oxygen use, thermoregulation is also reduced and so hypothermia can be expected (Oncken et al, 2001).
The oxygenation of the patient can be monitored more reliably with the use of blood gas analysis. Obtaining an arterial sample can give an indication of the patient's ability to oxygenate, while the levels of carbon dioxide in the sample reflect the patient's ability to ventilate (Hara et al, 2019). Kules et al (2015) state that blood gases are also useful to detect acid–base imbalances and electrolyte abnormalities. Hyperlactataemia could be expected as a byproduct of anaerobic respiration. Thomas and Boller (2018) describe that lactate can be used to determine prognosis, and values above 2.5 mmol/l are suggestive of a poor outcome, though regular measurement to monitor lactate clearance is more indicative than a singular result. Packed cell volume (PCV) and total solids (TS) should also be measured in cases with haemoabdomen to assess the extent of anaemia; however, the PCV reading may not be reliable and may still produce a normal value due to the loss of whole blood rather than just packed cells. In cases of acute haemorrhage, the TS would be expected to decrease. Samples of free abdominal fluid achieved by abdominocentesis can also have PCV and TS measured, as this will give an idea of whether there is still active haemorrhage when compared with venous samples (Mills and Welsh, 2016b).
The above assessments and diagnostic tools should be used in conjunction with the patient signalment in order to assign an appropriate American Society of Anaesthesiologists (ASA) Physical Status Classification. These patients would typically be assigned an ASA grade of 5E, as survival would be unlikely without surgical intervention and the ‘E’ denotes emergency surgery (Abouleish et al, 2015). Due to the high incidence of cardiac and lung metastasis in cases of splenic neoplasia, thoracic radiographs are also recommended prior to surgery (Marino et al, 1994). Mills and Welsh (2016a) state that pre-operative fluid resuscitation should be approached with caution, as treatment of shock and stabilisation of blood pressure promotes a more stable anaesthetic; however, high volume fluid rates may displace clots that have formed and lead to further haemorrhage. Low normotensive values should be aimed for, with a mean arterial pressure of 60 mmHg considered ideal.
High volumes of crystalloid fluids would be required, as only one-third stay in the intravascular space. Colloids may be considered as they stay within the circulatory system and so smaller volumes would be required for resuscitation (Martin and Bassett, 2019). Should the PCV drop below 25%, blood transfusion should be considered using either whole blood or packed red blood cells. In this case, autotransfusion should be avoided due to the potential presence of neoplastic cells.
Anaesthetic equipment
Patients presenting for emergency surgery are at higher risk of anaesthesia-related complications due to their unstable physiological condition, as well as a number of other factors. They will not have undergone the usual pre-operative precautions that is common in planned surgery, such as a period of starvation, so it could be that there is still stomach contents. Alternatively, they could have been inappetant for a period of time. Jolliffe (2011) states that the optimal starvation time prior to anaesthetic to minimise the effects of regurgitation is 6–8 hours, and prolonged starvation times are associated with increased risks of oesophagitis due to an increase in stomach acidity. Due to this, it is important to have suction available for induction, and to intubate the patient with an appropriately sized, cuffed, endotracheal tube in order to reduce the risk of aspiration pneumonia. It is also important to have a spare endotracheal tube, laryngoscope and a Yankauer suction tip available to clear the airway should regurgitation occur and reintubate if necessary. The endotracheal tube should be cuffed using a manometer to a pressure of 20–30 cmH2O (Kumar et al, 2021). Hung et al (2020) explain that underinflation of the cuff can lead to aspiration of gastric content if regurgitation occurs and therefore pneumonia, as well as leakage of anaesthetic gases into the atmosphere, whilst overinflation can cause ischemic damage to the airway. During induction, the patient should be positioned in sternal recumbency with their head elevated, and only moved when the airway is secured and the cuff inflated.
Table 1.
Normal values for packed cell volume and total solids
| Species | Packed cell volume | Total solids |
|---|---|---|
| Dog | 35–57% | 5.4–7.5 g/dL |
| Cat | 30–45% | 6.0–7.9 g/dL |
As discussed previously, the patient is likely to present with hypothermia, which can be exacerbated when placed under general anaesthesia. Pottie et al (2007) describe how inhalational anaesthetic agents cause vasodilation which, with contributions from cold anaesthetic gases, a large surgical clip, and exposure of the abdominal cavity, all predispose to a decrease in body temperature. In their study, Kanda et al (2020) showed that the use of a heat–moisture exchanger helped to maintain temperature and humidity of inhaled anaesthetic gases, and so this piece of equipment could be beneficial to this patient. The use of a rebreathing system, such as a circle, will also help to prevent a further decrease in body temperature, as lower gas flow rates of cold anaesthetic gas can be used. A circle is able to be used when delivering intermittent positive pressure ventilation to a patient (Thurston, 2021). Given the complications a dog with a bleeding splenic hemangiosarcoma may have with ventilation, being able to mechanically ventilate them is an advantage. Pre-oxygenation is imperative for these patients, and Mathis (2017) explains how delivering 100% oxygen via a tightly fitting face mask for at least 3 minutes prior to induction will increase oxygen reserve and decrease the time to desaturation. Once induced and positioned in dorsal recumbency, the table should be tilted to raise the thoracic cavity above the abdomen. Mosing (2016) describes how this position prevents the abdominal contents applying pressure to the diaphragm and preventing the patient from ventilating sufficiently; however, tilting the table in excess of 30° can cause a reduction in cerebral perfusion and so care must be taken.
Monitoring equipment
In order to monitor the patient effectively under general anaesthesia, a multi-parameter monitor should be used that at minimum includes electrocardiography (ECG), SpO2, capnography, temperature and blood pressure, whether that is invasive or non-invasive. ECG is particularly important in patients with splenic haemangiosarcoma, as arrhythmias, usually ventricular tachycardias, are common (Adams, 2014). Panissidi and Robinson (2021) explain that this is due to hypoxia causing ischaemic damage. They also state that the right atrium is a common site of metastasis in these patients, which can lead to arrhythmias. Panissidi and Robinson (2021) also state that dogs with splenic neoplasia are likely to be thrombocytopenic, which has been shown to have a correlation with the presentation of premature ventricular contractions (VPCs). Miller and Flaherty (2017) describe how tachyarrhythmias have a negative impact on stroke volume and cardiac output, as diastolic relaxation time is reduced and the ventricles are unable to fill sufficiently. Reduction in cardiac output results in decreased myocardial blood flow and hypoperfusion of vital organs in these already compromised patients, highlighting the importance of ECG monitoring.
Capnography is another important tool when monitoring patients under anaesthesia and is a measure of the partial pressure of carbon dioxide in inspired and expired gases (Waugh et al, 2012). Immediately following induction, the capnograph should be used to confirm endotracheal intubation (Long et al, 2017). The patient should not be inspiring any carbon dioxide, and so the presence of this can indicate a problem with equipment, such as excessive dead space in the circuit or exhaustion of the carbon dioxide absorber (Anderson and Breen, 2000). Scales and Clancy (2019) add that the waveform can indicate a number of things, such as whether there is any obstruction of the airways from mucous in the endotracheal tube. An end tidal carbon dioxide value is indicative of whether ventilation is adequate or not, and therefore also provides information on the patient's perfusion and metabolic state. Capnography relies on adequate circulation to deliver carbon dioxide from the blood stream to the lungs, and so an abnormal end-tidal carbon dioxide reading could indicate poor systemic perfusion. Hypocapnia may be as a result of tachypnoea, hyperventilation, hypovolaemia, hypotension or decreased cardiac output, whereas hypercapnia can be caused by hypoventilation (Marshall, 2004). In a dog with a bleeding splenic hemangiosarcoma, the patient is haemodynamically unstable and may have compromised ventilation, thus mechanical ventilation may be required to maintain normocapnia (35–45 mmHg). Should this be the case, high inspiratory pressures should be avoided as this increase in intrathoracic pressure will result in reduced venous return, negatively impacting cardiac output (Beckett, 2016). Instead, increasing the respiratory rate could lower the endtidal carbon dioxide and aid in achieving normocapnia. Capnography is essential here in order to ensure the peak inspiratory pressures and respiration rate used is appropriate for the patient. Finally, capnography is particularly beneficial in critical patients under general anaesthesia, as it can be the first sign of impending cardiac arrest. Due to the correlation of end tidal carbon dioxide and pulmonary blood flow, a sudden decrease in expired carbon dioxide suggests a change in cardiac output (Kerslake and Kelly, 2017). During cardiopulmonary resuscitation, a low end tidal could be as a result of inadequate chest compressions, and a value of less than 10 mmHg dictates that return of spontaneous circulation is unlikely (Nassar and Schmidt, 2016).
Measuring blood pressure in patients with internal haemorrhage is imperative, and invasive blood pressure monitoring would be the gold standard as it provides continuous, accurate, real-time readings (Summerfield, 2019). MacFarlane et al (2010) conducted a study that proves non-invasive blood pressure monitoring provides trends that can be interpreted for that individual patient, but the actual values obtained may not be accurate due to a number of factors, such as selection of cuff sizes and placement of the cuff either above or below the level of the heart. Some oscillometric devices will also fail to read if there is interference from electrocautery or from movement within the vicinity of the cuff (Seliškar et al, 2013). Placing an arterial catheter can be technically challenging, especially in cases with poor pulses, and recognised complications include infection and failure to maintain function due to clotting (Trim et al, 2017). However, in critical patients the benefits outweigh the risks, as Waddell (2000) states that invasive blood pressure monitoring is beneficial in hypovolaemic patients as it provides a guide on the effectiveness of fluid volume replacement, as well as enables drugs such as vasopressors to be titrated appropriately. The placement of an arterial catheter to monitor blood pressure also facilitates the collection of blood samples for arterial blood gas analysis, meaning this can be monitored more frequently peri-operatively (Aldridge and O'Dwyer, 2013).
Conclusions
Patients presenting for emergency surgery that are haemodynamically unstable, such as those with a bleeding hemangiosarcoma, are at higher risk of anaesthetic complications, and require careful assessment and stabilisation prior to anaesthesia. They also require intense intraoperative monitoring to detect changes in physiology and assess effectiveness of interventions.
KEY POINTS
- Patients presenting for emergency surgery with haemoabdomen require a thorough clinical examination and diagnostic tests before anaesthetising.
- Consideration should be taken into the equipment needed prior to the induction of anaesthesia.
- Careful monitoring during the anaesthetic period should include ECG, blood pressure, SpO2, temperature and capnography.