Anaesthesia requirements and considerations can drastically change depending on the patient's presenting problem, comorbid conditions and individual characteristics, making the need for patient-specific care essential (Grubb et al, 2020). These changes are best anticipated and mitigated in advance of the anaesthetic event to improve patient outcomes and reduce mortality rates (Redondo et al, 2024). However, preparation and management of these changes can be challenging in the event of an emergency presentation (Shoop-Worrall et al, 2022; Redondo et al, 2024).
Emergency presentations are, by definition, unpredictable in their occurrence and require urgent treatment to preserve life (Fages et al, 2021). Furthermore, these cases often present outside regular working hours, and the impacts of reduced staffing numbers and increased team fatigue may contribute to higher peri-anaesthetic mortality rates (Grubb et al, 2020; Fages et al, 2021; Shoop-Worrall et al, 2022).
This article discusses the peri-anaesthetic considerations for some of the most common emergency case presentations while exploring the physiological changes that may impact peri-anaesthetic care.
Triage and preparation
Triage is the assessment of urgency and is a vital tool in identifying conditions or problems that pose the greatest risk to the patient's life (Newfield, 2018). This identification and assessment process is often second nature to the clinical veterinary team once the patient arrives at the clinic (Covey, 2018). However, triage begins at the point of first contact with the practice; therefore, all staff should have a basic understanding of how to perform a telephone triage (Covey, 2018).
It is beyond the scope of this article to discuss the art of triage in depth; however, it is important to recognise the difference between a primary and secondary survey of the patient before discussing case-specific examples.
A primary survey of the patient includes an assessment of cardiorespiratory status and stability, neurological status or level of consciousness and identification of any imminent threats to life, such as uncontrolled haemorrhage (Covey, 2018; Ho-Le, 2024). This primary survey enables the most urgent needs to be attended to promptly and facilitates stabilisation of the patient's condition (Ho-Le, 2024). The secondary survey can only begin once the patient is stabilised or the effects of any life-threatening conditions have been mitigated or managed (Ho-Le, 2024). It includes a thorough physical examination, assessment of response to initial therapy, and performance of diagnostic procedures (Ho-Le, 2024). Anaesthetising patients for the management of emergency cases is most likely to occur during or following this period of the secondary survey.
Urethral obstruction
Urethral obstruction (UO) is most commonly seen in male dogs and cats as their urethral lumen is longer and narrower compared to that of females (Kulendra, 2018; Beeston et al, 2022). While disease aetiology may differ between species, the physiological impacts of being unable to void urine are largely the same in both cats and dogs (Figure 1) (Rioja Garcia, 2016).
Fluid therapy
Following the primary survey, biochemical and haematological samples should be taken to assess the patient's hydration status and evaluate the presence of hyperkalaemia or acid-base disturbances (Kershaw, 2019; Canei et al, 2021; Beeston et al, 2022). Ideally, patient stabilisation should be achieved through fluid therapy and management of hyperkalaemia before anaesthesia (Rioja Garcia, 2016; Kulendra, 2018; Beeston et al, 2022). Isotonic crystalloids are most often used for initial stabilisation in these cases, including 0.9% sodium chloride and lactated Ringer's/Hartmann's solution (Beiter, 2016; Breheny et al, 2022).
Historically, 0.9% sodium chloride has been the more popular fluid choice owing to its reduced potassium content compared to Hartmann's (Breheny et al, 2022). However, Hartmann's may be the superior choice, as its low potassium content contributes minimally to exacerbating hyperkalaemia, while its administration provides a dilutional effect on serum potassium levels and an alkalinising effect to assist in the correction of metabolic acidosis (Breheny et al, 2022; Grint et al, 2023). While both 0.9% sodium chloride and Hartmann's will reduce serum potassium levels, Hartmann's has been shown to correct acid-base and electrolyte imbalances more rapidly (Cunha et al, 2010; Breheny et al, 2022).
If crystalloid administration alone is insufficient to reduce serum potassium levels to <6 mmol/L before anaesthesia, additional therapies such as glucose (± insulin) administration should be considered (Grint, 2023). Sodium bicarbonate may be used in cases of severe acidosis; however, this treatment is not without risks and can cause side effects including hypernatraemia, hypocalcaemia and hypokalaemia (Grint, 2023).
Anaesthesia
Placement of a urinary catheter is usually required to facilitate deobstruction. This is most commonly performed under general anaesthesia (GA) to ensure adequate muscle relaxation and patient comfort, as well as to provide analgesia (Beeston et al, 2022). Sedation can also be used to facilitate urinary catheter placement; however, to prevent voluntary patient movement and achieve an adequate level of muscle relaxation, heavy sedation is likely required, which may increase the risk of peri-anaesthetic death (Grubb et al, 2020; Simon and Steagall, 2020). Patients are not considered adequately sedated if voluntary movement is present, which in these cases is often identified by kicking off the hindlimbs during catheterisation attempts. In such instances, further sedation or conversion to GA should be used (Murrell, 2016; Simon and Steagall, 2020).
GA is advocated in the majority of cases as it eradicates voluntary patient movement, enabling local anaesthetic administration via epidural or sacrococcygeal block. It also prevents the patient from responding to catheterisation attempts, which could otherwise trigger stress-induced catecholamine release and increase the risk of cardiac arrhythmias. Additionally, GA facilitates endotracheal (ET) intubation, providing airway protection in case of regurgitation and enabling intermittent positive pressure ventilation (IPPV) during cardiopulmonary arrest (CPA). (O'Hearn and Wright, 2011; Beiter, 2016; Warne et al, 2018; Simon and Steagall, 2020; Canei et al, 2021).
The choice of anaesthetic or sedation drugs should be tailored to each individual patient according to their needs, condition and presentation. However, certain considerations should be made when selecting drugs for cases of UO. The use of alpha-2 adrenoreceptor agonists, such as medetomidine, can exacerbate hyperkalaemia induced bradycardia, increase diuresis and inhibit insulin release, which may impair the patient's ability to respond to treatment efforts to correct hyperkalaemia (Rioja Garcia, 2016). Acepromazine should be used with great caution in dehydrated patients because of its vasodilatory effects, even when only mild sedation has been achieved (Rioja Garcia, 2016; Costa et al, 2021).
Ketamine may be included within the anaesthetic protocol but should be avoided in cases where renal damage is suspected or where tachycardia is to be avoided, such as in a patient with hypertrophic cardiomyopathy (Perkowski and Oyama, 2015). Additionally, ketamine should not be used as a sole agent because it can induce muscle rigidity (Grint et al, 2023). Benzodiazepines, such as midazolam, can be used alongside an opioid or as part of an anaesthetic co-induction to reduce the amount of induction agent required. These drugs have minimal impact on the cardiovascular system and provide a good level of muscle relaxation (Kershaw, 2019; Grint et al, 2023). The use of an opioid in combination with a sedative agent is recommended to provide adequate analgesia and sedation. Table 1 summarises the benefits and uses of different opioids in these cases.
| Opioid | Use/method of action |
|---|---|
| Butorphanol | Poor analgesic effect in mammals, any analgesic effects that may be experienced are short-lived |
| Buprenorphine | Long duration of action (6-8 hours) and provision of moderate analgesia; however, if use of a more potent opioid becomes necessary, its action may be impeded until the agonist/antagonist effect of buprenorphine has worn off |
| Methadone | Excellent analgesic effect but shorter duration of action (4-6 hours) |
| Fentanyl | Excellent analgesic effect with some intrinsic antispasmodic properties that may reduce urethral spasms |
Anaesthetic induction agent choice is not significantly influenced in UO cases, except when repeated anaesthetic events may be required in cats. In such cases, alfaxalone is favoured over propofol, as consecutive use of propofol has been associated with oxidative damage to erythrocytes, leading to Heinz body formation (Grint et al, 2023).
Peri-anaesthetic monitoring should include pulse oximetry, capnography, blood pressure monitoring, temperature and electrocardiography (ECG), alongside hands-on monitoring techniques (Kershaw, 2019; Grubb et al, 2020). ECG changes and bradyarrhythmias, as shown in Figure 2, are likely to be seen in these cases secondary to hyperkalaemia above 7 mmol/L. However, the absence of these changes is not indicative of normal serum potassium levels (Canei et al, 2021; Teymouri et al, 2022).
Gastric dilatation and volvulus
Often seen in deep-chested dogs, gastric dilatation and volvulus (GDV) is a life-threatening condition requiring urgent surgical intervention (Frikis and Zlateva, 2018; McCagherty and Woods, 2022). The primary treatment goals in these cases are to restore normovolaemia, decompress the stomach via percutaneous and/or surgical means, correct acid-base disturbances and identify and manage cardiac arrhythmias (Rauserova-Lexmaulova et al, 2020).
The exact aetiology of this condition is not fully understood, and it remains unclear whether dilatation or volvulus occurs first. However, the presence of a large gas-filled stomach is known to result in tissue ischaemia, compromised venous return and reduced ventilatory ability (O'Neill et al, 2017; Frikis and Zlateva, 2018; Homer, 2020).
Stabilisation
Initial stabilisation before anaesthesia is advised to restore tissue perfusion, correct hypovolaemic shock and resolve acid-base abnormalities. However, stabilisation efforts should not significantly delay surgical intervention (Homer, 2020; White et al, 2021). Percutaneous decompression of the stomach can reduce intra-abdominal pressure and provide temporary restoration of blood flow to surrounding tissues (White et al, 2021). Passage of an orogastric or large-bore nasogastric tube can also enable rapid decompression of the stomach in cases without volvulus (Self, 2016; McCagherty and Woods, 2022).
Placement of large-bore intravenous catheters in the cranial half of the body allows for rapid fluid resuscitation (Self, 2016; Fullagar, 2019; Lhuillery et al, 2021). While most are placed bilaterally in the cephalic veins, the jugular veins can also be used (Fullagar, 2019). Catheterisation and fluid administration via the caudal half of the body are not advised because of compression of the caudal vena cava, which can impair venous return (Frikis and Zlateva, 2018; McCagherty and Woods, 2022).
Isotonic crystalloids are often the fluid of choice in these cases, with Hartmann's solution favoured for its buffering effect in the presence of metabolic acidosis (Self, 2016; Frikis and Zlateva, 2018; Rauserova-Lexmaulova et al, 2022). Hypertonic saline (7.2%) can be administered to aid the rapid expansion of circulating volume but should be followed by isotonic crystalloids to replace the fluid drawn from the interstitial space into the intravascular compartment (Grint et al, 2023).
Blood samples should be taken to measure packed cell volume (PCV), total protein (TP) and lactate at a minimum, although ideally a full biochemical and haematological profile should be performed to assess these values and provide a complete clinical picture before anaesthesia or surgical intervention (Self, 2016; Homer, 2020; Grint et al, 2023). Assessment of acid-base balance through blood gas analysis is advantageous and, in conjunction with plasma lactate levels, can serve as a prognostic indicator (Rauserova-Lexmaulova et al, 2020).
Anaesthesia
Patients that present in a severely debilitated state may require no pre-medication, although pre-emptive analgesia should be provided in the form of a full muagonist opioid (Self, 2016; McCagherty and Woods, 2022). Patients that are distressed or agitated before induction may benefit from the addition of a benzodiazepine in their pre-medicant combination or the use of a co-induction technique (Lhuillery et al, 2021). Phenothiazines, such as acepromazine, should be avoided due to the patient's hypovolaemic shock (Rioja Garcia, 2016; Costa et al, 2021). Similarly, alpha-2 adrenergic agonists are contraindicated due to their significant cardiovascular effects (Pan et al, 2021).
Peri-anaesthetic monitoring should include ECG and, if available, invasive blood pressure monitoring. However, surgery should not be delayed if access to the latter proves difficult (Homer, 2020). The most commonly identified ECG abnormalities in GDV cases are ventricular premature complexes (VPCs), accelerated idioventricular rhythm (AIVR) and ventricular tachycardia (Figure 3), likely owing to myocardial ischaemia, coupled with circulating catecholamines and cytokines (Homer, 2020; McCagherty and Woods, 2022). While intermittent VPCs are unlikely to significantly impact cardiac output, AIVR and ventricular tachycardia reduce ventricular filling time, which may compromise cardiac output and blood pressure (Homer, 2020).
Treatment of significant cardiovascular arrhythmias includes an initial bolus of lidocaine followed by a constant rate infusion (CRI) (Adams, 2024). Lidocaine CRIs have also been found to reduce volatile agent requirements, provide anti-inflammatory and prokinetic effects, and are associated with improved post-anaesthetic outcomes in these cases (Homer, 2020; McCagherty and Woods, 2022; Adams, 2024).
Caesarean
While more common in dogs than cats, dystocia can occur in either species, and caesarean section may be required to improve outcomes for both the dam and the offspring (Robertson, 2016). Many patients present after several hours of labour and may be dehydrated, experiencing biochemical or haematological abnormalities, electrolyte imbalances or relative volume loss (Claude and Meyer, 2016). Evaluation of blood gases, biochemistry, PCV and TP provides a rapid assessment of cardiovascular status, enabling effective stabilisation before anaesthesia (Aarnes and Murdock, 2022).
Physiology
During pregnancy, physiological changes occur to support the growth of the foetuses (Cameron-Blackie, 2023). Cardiac output increases because of an increase in both erythrocyte production and plasma volume, meaning the patient's ability to respond to hypotensive episodes by increasing heart rate or improving cardiac contractility may be reduced (Cameron-Blackie, 2023). While red blood cell mass increases by up to 25%, plasma volume increases by approximately 40%, resulting in dilutional anaemia (Grint et al, 2023). The large abdominal contents decrease functional residual capacity, leading to an increase in minute volume and, consequently, oxygen consumption (Robertson, 2016; Grint et al, 2023). This dilutional anaemia, combined with an increased metabolic oxygen requirement and reduced functional residual capacity, highlights the importance of pre-oxygenation before anaesthetic induction (Cameron-Blackie, 2023; Grint et al, 2023).
The gravid uterus is likely to cause compression of the caudal vena cava when the patient is positioned in dorsal recumbency. Adopting a ‘modified dorsal’ recumbency, with the patient tilted to the left, can reduce compression of this major vessel, improving venous return and blood pressure (Grint et al, 2023). Clipping the patient before anaesthesia, if tolerated, may minimise the time spent in dorsal recumbency under anaesthesia (Cameron-Blackie, 2023). If conscious clipping is not tolerated, the abdomen can be clipped following anaesthetic induction with the patient positioned in lateral recumbency (Grint et al, 2023).
Hypotension under anaesthesia can cause uterine ischaemia and may increase foetal mortality (Schmidt et al, 2021; Aarnes and Murdock, 2022). Management of intraoperative hypotension includes multimodal analgesia to reduce dose-dependent cardiorespiratory depression associated with volatile agents; administration of anticholinergics in the presence of bradycardia, with glycopyrrolate favoured over atropine because of its lower placental transfer; use of ephedrine or phenylephrine to induce vasoconstriction and increase systemic vascular resistance; and correction of fluid deficits with crystalloids and/or colloids (Robertson and White, 2020; Cameron-Blackie, 2023).
During pregnancy, reduced cardiac sphincter tone and prolonged gastric emptying time increase the risk of regurgitation (Aarnes and Murdock, 2022). To minimise this risk, a ‘head-up’ induction technique should be used, supporting the patient's head above the body until intubation is achieved and the endotracheal tube cuff is inflated where necessary (Aarnes and Murdock, 2022; Grint et al, 2023). In the event of regurgitation under anaesthesia, the patient's head should be positioned below the body (such as hanging off the edge of the table), the oral cavity should be suctioned to remove liquid debris (Figure 4), and anti-emetic and antacid therapy should be considered (Adams, 2024).
Analgesia
As many products are not licensed for use in pregnant or lactating animals, informed consent for off-licence use should be obtained from the client before drug administration (Cameron-Blackie, 2023). The pre-anaesthetic use of full mu-opioids in caesarean management is not associated with increased neonatal mortality and should not be withheld for this reason (Robinson, 2016; Schmidt et al, 2021; Navarro-Altuna et al, 2024).
While historically controversial, the use of pre-medication in caesarean sections provides pre-emptive analgesia, reduces patient stress, decreases the amount of induction and volatile agent required and contributes to a balanced anaesthetic (Grint et al, 2023). If an opioid alone does not provide sufficient sedation to allow intravenous access for induction, a low dose of acepromazine may be effective and is not associated with increased maternal or foetal mortality (Aarnes and Murdock, 2022). Low doses of dexmedetomidine have also been shown to have no impact on fetal mortality rates (Groppetti et al, 2019; Navarro-Altuna et al, 2024). Local anaesthesia can be incorporated into a multimodal analgesia plan in the form of line blocks, splash blocks or epidurals (Cameron-Blackie, 2023).
Once the neonates have been delivered, additional analgesic agents, such as paracetamol, can be administered (Raffe and Goudie-DeAngelis, 2024). NSAIDs, such as meloxicam, should only be given once hypotension has been resolved, often during recovery from anaesthesia (Raffe and Goudie-DeAngelis, 2024). Pain scoring and ongoing analgesic management are essential for patient welfare, as untreated pain not only has detrimental effects on the dam but also causes uterine vasoconstriction and reduced milk production (Grint et al, 2023).
Conclusions
The successful anaesthetic management of emergency cases requires veterinary nurses to understand disease physiology, patient impacts and strategies to mitigate these effects. The ability to anticipate, recognise and manage anaesthetic challenges in emergency cases can help improve peri-anaesthetic mortality rates (Redondo et al, 2024). While not all emergency presentations can be predicted, a thorough understanding of normal anatomy and physiology provides the foundation for veterinary nurses to advocate for their patients and deliver high-quality, holistic care.