Enemy at the Gates: Hypothermia, the underestimated anesthesia complication

denDr Denica Djiodjeva

Central Vet Clinic

Sofia, Bulgaria

Hypothermia is one of the most frequent and major anesthetic complications, occurring in at least 40% of patients. Unfortunately, too little attention is paid to this condition, which is associated with many pathophysiological changes that affect the patient before, during and after surgery. In a dog, hypothermia is considered a temperature below 37° C. As with prolonged procedures and operations, the risk increases. These are operations in which the abdominal cavity is open for a long time, in small animals under 2 kg, weak, cachectic, pediatric and geriatric patients.

Cat and dog lying on the snow in cold winter

Thermoregulation is a process in which the body strives to maintain a constant body temperature, regardless of external conditions, which ensures normal functioning of enzymes, coagulation and immune response. The normal physiological limits for a dog and a cat are 37.5˚ C to 39.2˚ C for a dog and 37.8˚ C to 39.5˚ C for a cat. For mild hypothermia, 37.0˚ C to 37.7˚ C is accepted; moderate, 35.8˚ C to 37.0˚ C ; severe, 33.6˚ C to 35.8˚  C ; and critical, less than 33.6˚ C or less. The normal body temperature (head and body) is about 38° C, and that of the peripheral parts is 2-4° C lower. Animals and humans, in addition to maintaining their body temperature within certain limits, can also produce it. Their body is conditionally divided into two parts, central (core), which generates heat, and peripheral, which regulates. The body’s regulatory mechanisms work to keep heat within normal limits. Under normal conditions, the production of heat is the result of the metabolic processes of the internal organs. When the blood passes through them, it warms up and reaches the periphery of the body through the cardiovascular system. The main organ that plays the role of a thermostat is the hypothalamus. When the blood passes through it, its temperature depends on what the body’s response will be in order to maintain the balance between heat gain and loss. From the hypothalamus, through afferent and efferent nerve pathways, vasoconstriction is induced, which occurs before the activation of other energy-consuming reactions, such as shivering. It is important to mention that the efferent response includes both types of regulation – behavioral and autonomic. Behavioral is the strongest response to rewarming, but requires awareness, which is absent during anesthesia. For this reason, the patient must rely on autonomic defense mechanisms, such as maintaining normal blood pressure, vasoconstriction, etc. When local anesthesia is used, vasoconstriction is reduced in the area, where it is administered and this increases heat loss. In addition to central thermoreceptors for heat and cold (in the hypothalamus, spinal cord, abdominal organs, brain stem, muscles), there are also peripheral ones in the skin.

images (2)

According to the second law of thermodynamics heat can only flow by temperature gradient from the body that is warmer towards the periphery or the environment that is colder, therefore, the body can never be heated from the periphery to the core which is usually warmer than the outside.

As already mentioned, when the animal is under anesthesia, the thermoregulatory mechanisms are blocked. Anesthesia slows down behavioral defense mechanisms, reduces metabolic needs, hypothalamic function and muscle tone. Heat loss begins within the first minutes of premedication because all sedatives and tranquilizers block the hypothalamus. The highest heat loss is during the first 20 minutes of induction, due to its distribution from the center to the periphery of the body. For this reason, it is very important to prevent heat loss at the beginning of the anesthesia, through various methods that will be mentiont later.images (4)

At first, the main mechanisms of heat loss are four.


Convection- This is one of the most common ways of losing heat, which occurs when body heat is dissipated into the surrounding space through the air. The larger the surface of the body, the greater the heat loss. In animals, hair greatly interferes with this mechanism and it is important, with a larger shaved area and an open abdominal cavity during prolonged surgery.         Conduction – occurs in direct contact of surfaces with different temperatures. For example, when lying on a cold operating table. This mechanism is especially important, when the patient is lying on a wet and cold surface.  Temp-4a-1140x778 (1)

Radiation- The transfer of heat from one surface (e.g. the body) to another without direct physical contact. Radiation is received from the sun by any object exposed to sunlight. The heat load from solar radiation,  can be significant in hot environments, where animals are exposed to sunlight for prolonged periods. When an animal is standing in bright sunlight, the amount of solar radiation absorbed may substantially exceed its own metabolic heat production.

Evaporation – evaporation of water at the surface of the body or respiratory tract results in heat loss and it’s approximately 22% of total body loss. 0.58 kilocalories of heat is lost for each gram of evaporated water. In human the evaporation is manifested like sweating but in animals due to the lack of sweat glands, it is expressed by panting. To prevent evaporation from the respiratory tract and a drop in body temperature during anesthesia, the oxygen flow can be reduced if this is compatible with the circuit used and the needs of the patient.

The main physiological disorders that occur with hypothermia are related to reduced liver metabolism, compromised cardiovascular system, reduced ventilation and oxygenation, compromised renal function, reduced cerebral flow. All these factors also influence the slower post-anesthesia recovery. In human medicine, there are many more studies on the subject and more specifically on the direct impact of hypothermia on the body. The most frequently observed are delayed pharmacokinetic and dynamics of anesthetics, impaired coagulation, a threefold increase in the risk of cardiac problems in high-risk patients, an increased likelihood of difficult wound healing and infection, leukocyte migration and suppression along with impaired phagocytosis and neutropenia.

When liver metabolism and enzyme systems are reduced, the metabolism of most anesthetics such as acepromazine, propofol is also impaired. As well as anesthetics can directly block the hypothalamus, such as acepromazine and morphine. Inhalational anesthetics are affected by hypothermia by increasing their solubility but not slowing their potency. They also reduce the intensity of shivering, as a mechanism to conserve heat. It has not been proven, whether that hypothermic patients may take longer to recover from anesthesia because of larger amounts of anesthetic that need to be exhaled. But it’s for sure known that propofol, as one of the most commonly used anesthetics, is also affected by body temperature, as for hypothermia with 3° C down, its plasma concentration increases by 30%. The only drug tested so far, which does not effect thermoregulatory responses, is midazolam. The vasodilator effect of most of the anesthetics surpasses physiological vasoconstriction, which supports thermoregulation. As with vasodilation, there is a large loss of heat that comes from the center of the body and is lost to the periphery.

The negative effect of hypothermia on coagulation and blood has three main factors. It affects – platelet function, coagulation enzyme function and fibrinolytic function. As a rule, hypothermia increases blood viscosity, which leads to deterioration of perfusion. For every 1° C decrease, the hematocrit rises by 2%. This accordingly leads to false results that can be interpreted as blood loss. Since the function of the enzyme systems is disturbed, this also affects blood clotting. PTT, PT increase significantly, there is temporary thrombocytopenia and reduced platelet function occur due to impaired synthesis of thromboxane B2. The morphology of the platelets  also changes. There is a hypothesis according to which hypothermia results in coagulopathy by reducing the availability of platelet activators. This hypothesis is supported by the following observations: (a) The generation of thrombin, a potent platelet agonist, decreases under hypothermic conditions, and (b) hypothermia results in the release of a circulating anticoagulant with heparin-like effects. (1)

Due to the vasoconstriction that occurs, the oxygenation of the tissues is reduced and hence their slower healing. Direct suppression of neutrophil function is also a factor influencing healing in addition to the immunosuppressive effect, reducing leukocyte migration, neutrophil phagocytosis and production of ILF 1, 2, 6 and TNF.

In order to avoid all complications of hypothermia, different methods are used for pre-during and post-operative warming of patients. Typically, in the preparation of the animal for surgery, towels are used to cover the table or the animal is wrapped. A heating pad is often placed on the surgical table. The use of fluid-warming devices, which largely support normothermia, is also appropriate. Various methods can be used such as putting socks on the paws, wrapping in bubble rap, placing hot water bottles, red infrared lamps. After surgery, the animal can be wrapped with a blanket and any of the methods of warming can be used. But some of the most effective methods of maintaining a normal body temperature are warm air devices and warm water beds. According to a study comparing several methods of warming and prevention of heat loss, warm air is the most effective. (2) In addition to all the listed methods, it is important to reduce the time of the operation, especially in longer abdominal operations. Avoiding placing animals on cold metal tables, warm operating room.

It is advisable to warm up by 1-2° C per hour and under constant monitoring, because complications can occur from trivial burns to more serious systemic complications. Some of the underestimated ones are the so-called “afterdrop”, in which, despite the warming, the temperature of the animal continues to fall. This is caused by the return of cold blood from the peripheral limbs to the body, which makes it difficult to reach a normal temperature. It is important in such moments to warm up the body (chest, abdomen), and not the extremities. Afterdrop can cause deterioration of physiological parameters, cardiac arrhythmias and arrest.

Rewarming shock is very unknown and underestimated complicaton, which manifests itself in a sudden vasodilation with following drop in blood pressure and cardiac output. This results in increased metabolic demands and increased perfusion requirements. In this regard, there may also be areas of impaired perfusion that are hypoxic and lactate begins to form. During rewarming, these areas are reperfused and lactate re-enters normal oxidative pathways, consuming oxygen in the process. Because of the rewarming acidosis that has occurred, appropriate fluid therapy may be considered. Shivering is a normal response of the body, with which it tries to normalize its temperature, but on the other hand, it can also lead to additional complications, because additional oxygen consumption is needed and this can cause additional hemodynamic instability. The suppression of shivering by neuromuscular blockade is an effective method for decreasing O2 consumption. This method has been described in some human studies. (3) Monitoring during the warm-up should include as many indicators as possible, such as saturation, blood pressure, ECG, lactate, glucose.images (1)

Basic anaesthesia of brachycefalic dog

denicaDr Denica Djodjeva

Blue Cross Veterinary Clinic

Sofia, Bulgaria




Quite often in our practice we have to sedate or keep under anaesthesia brachycephalic dogs and cats. This is associated with some stress for us, given the peculiarities of the breed. In this article I will try to briefly present the main key points in the anesthesia of brachycephalic breeds, which has gained great popularity in recent years. Will pay attention to their anatomical and physiological features, which are a prerequisite for complications during anesthesia, and how to avoid them and reduce the risk.


The main specificity of them is the so-called brachycephalic syndrome ( BOAS). It may include narrowed nostrils, a long soft palate, a hypoplastic trachea, or an inverted laryngeal sac. It can be re-applied and used for prolonged trauma to the pharyngeal soft tissues and trachea, which can cause soft tissue outflow or tracheal collapse. This trauma most often occurs when the animal is intubated. Gastroesophageal reflux should not be forgotten, also high vagal tone.

In severe cases of BOAS, airway obstruction may benefit from the development of pulmonary edema. The pathophysiology of post-obstructive pulmonary edema includes the effect of negative intrathoracic pressure on fluid distribution and subsequent hypoxia. High negative intrathoracic pressure causes an increase in venous return to the right atrium, which increases the pulmonary artery, while left ventricular function is reduced and afterload is increased. The end result is increased hydrostatic pressure, which aids in the movement of fluids from the capillaries in the interstitium and thus causes pulmonary outflow. Rapid recognition of this condition and taking temporary measures, such as maintaining airway patency, adequate oxygen supply and, if necessary, PPV administration. Diuretics may also be used, but it should be anticipated that hypovolaemia and hypoperfusion may occur during anesthesia and clinical delivery should be considered. And because of the risk of soft tisuue and pulmonary oedema, it’s beneficial to add an corticosteroid in low dose, as prevention. Unless there are a serious contraindications. There are different anaesthesia protocols with dexamethason or methylprednisolon, it’s a matter of personal choice.

Deep sedation in these patients is performed with excessive relaxation of the pectoral muscles and aggravation of airway obstruction. Even if the patient is aggressive, it is good to adhere to lower doses of premedication. The most commonly used combination is of a sedative component, for example an alpha-2-agonist and an opioid. A tranquilizer such as acepromazine and benzodiazepines such as diazepam or midazolam may also be used. Accordingly, the doses are at the discretion and according to the desired effect and treatment.  In the table below I quote some of the most commonly used pre- anaesthetic drugs with the value of the dose. There are no restrictions and contraindications to the use of narcotic drugs in this breed. For induction you can use a different combinations, as benzodiazepine+ propofol or benzodiazepine+ ketamine. Your choice mainly depends on what the end result you whant. In brachycefalic breeds it is recommended the induction to be smooth and fast, so the most suitable drug in this case is propofol.

Given the peculiarity of the birth, it is very important to monitor the brachycephalic patient during the pre-aesthetic period, as relaxation of the pectoral muscles further complicates breathing, reduces the number of respiratory movements and the appropriate patient does not fall into hypoxia. It is recommended that the patient be preoxygenated during the pre-anesthetic period. The administration of 100% oxygen before induction of anesthesia prolongs the time to the onset of arterial hypoxemia.

When intubating a brachycephalic patient, prepare several tube sizes, apparently up to two sizes smaller than you think would be appropriate. It will be useful if you use a laryngoscope, especially when your patient has a long soft palate, as it will help ensure good visibility to the airways.

It is common practice to maintain the patient under inhalation anesthesia during the operation. Isoflurane is most commonly used for this purpose. It should be borne in mind that, like other inhaled anesthetics, it produces a dose-dependent reduction in myocardial contractility, systemic vascular resistance and cardiac preload, followed by a reduction in mean arterial pressure (MAP) and cardiac output in a dose-dependent manner; therefore, the evaporator settings should be kept as low as possible while maintaining an adequate depth of anesthesia.

In brachycephalic breeds, there is a very strong vasovagal tone, which can cause bradycardia, which in turn can lead to AV block or even cardiac arrest. The most common reason for increased vagal tone is severe pain. Advice on this reason for good pain relief of this breed is extremely important. However, if the patient develops severe bradycardia, a use of anticholinergic in an appropriate emergency dose is indicated.

As mentioned earlier, another common complication is gastroesophageal reflux, which can occur at any stage of anesthesia. This can lead to airway obstruction and aspiration pneumonia. Advice for this reason is recommended in the anesthesia protocol to include antiemetics, unless there are serious contraindications. It is recomended to be applied proton pump inhibitors as omeprasole, 4 hours before the planed anaesthesia.

d1 d3

The recovery period is also not to be underestimated. Here it is important to constantly monitor the patient and be extubated, when we are sure that all reflexes have returned. Especially the swallowing one. The best time to extubate is when our patient has muscle tone in the lower jaw and tries to cough up the endotracheal tubus itself or even better if the patient is tring to chews it. It is important to be positioned in a sternal position with appropriate continuous monitoring.

The anaesthesia of these specific breeds is not so complicated, if know their features and for what to watch out for. With more carefulness and knowinge there is nothing to be afraid of.

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Tabl. Most commonly used pre- anaesthetic drugs

Drug Benefit Side effects Peak onset/duration of action IM dose


Profound sedation, reversible, some analgesic properties, drug sparing (reduction in induction drugs needed) Dose dependent bradycardia 5-15 min IM

2- 3 min IV

Dexmedetomidine 5-15 µg/  kg



3- 10 µg/ kg

Butorphanol Mild analgesia, good sedation Poor analgesia and should not be used for surgical patients 10–15min/lasts for 60–90min 0.1–0.4mg/kg
Buprenorphine Moderate analgesia, mild sedation Moderate analgesia 10- 15 min IV

15-30min IM

/can be given q 6–8 h

Methadone Good analgesia If given too fast, IV can cause bradycardia and respiratory depression 30min/can be given q 4 – 6 h 0.1–0.4mg/kg
Acepromazine Good anxiolytic, sedation improved when administered with an opioid Hypotension, unreliable sedation when used alone, not reversible 35–40min IM

10- 15 IV

/can be given q 4–6h






Alternative anesthesia protocols without use of the neuromuscular block for phacoemulsification in dogs and cats

4 (1)Authors: Stroe M.S., DVM, Ionașcu I. DVM PhD, Ion L., DVM


Correspondence: Stroe Marina-Stefania, DVM, Marina-Stefania.Stroe-Giurca@uliege.be



Cataracts may occur at any age and in any location in the lens. Cataracts can block tapetal reflection and fundic examination partially or completely and are often classified by stage of maturation and cause.

Cataract surgery are facilitated by a central position of the eye ball within the palpebral fissure. A centrally positioned eye is normally achieved by using of neuromuscular blocking agents (NMBAs). NMBAs also decrease the ocular muscle tone and that is very useful because an increased tonus may cause ocular structures to become displaced and distorted and can also influence IOP. Use of these agents necessitates intermittent positive pressure ventilation (IPPV).


Objective: Offering alternatives for anesthesia to perform cataract surgery in dogs and cats without using the neuromuscular block.

The safety of anesthetic protocols consisting of midazolam, tramadol, lidocaine, propofol, fentanyl, ketamine, isoflurane without using the neuromuscular block was studied in 16 cataract surgeries in dogs and cats. The protocol’s safety was expressed by monitoring heart rate, oxygen saturation and pulse rate using pulse oximetry, respiratory rate, end-tidal carbon dioxide provided by capnography, arterial blood pressure using oscillometric method. Assessments were made for quality of induction, maintenance and recovery from anesthesia.


Animals: Sixteen animals, eleven dogs and five cats, all client-owned.


Methods: All animals were examined prior to premedication, were performed blood tests hemoleucogram and biochemistry and monitored during induction, surgery and recovery. Blood samples were analyzed for standard biochemistry panel including glucose, creatinine, ureea, hepatic transaminases and hemoleucogram. Before anesthesia, HR was measured using cardiac auscultation and MAP was measured using automated oscillometry, respectively. Protocols consisting of midazolam, tramadol, or lidocaine iv was performed. IV propofol was administered to abolish the palpebral reflex, produce jaw relaxation and facilitate ETI. Topical ocular administration of oxybuprocaine (Benoxicaine®) 0.4% drops to anesthetize cornea was performed before general anesthesia. All patients received topically sprayed laryngeal 2% lidocaine. The cough response at ETI was recorded.

After intubation, auscultation of heart and lung sounds was possible by means of an oesophageal stethoscope. Pulse oximetry was used to monitor oxygen saturation of hemoglobin in arterial blood and pulse rate. The patient was connected to the inhalational anesthesia machine. The maintenance of anesthesia was achieved using isoflurane like inhalant agent and fentanyl or mixture of fentanyl, lidocaine and ketamine. Respiratory rate and end-tidal carbon dioxide was provided by capnography. Assessments were made for quality of induction, maintenance and recovery from anesthesia by evaluation of the animal’s eye position, jaw tone, heart and respiratory rates and autonomic responses to surgical stimulation.


Results: The purpose of this work was to perform anesthesia protocols without use of the neuromuscular block for phacoemulsification in dogs and cats and make preliminary investigation into safety for patient and to record the advantages and disadvantages. Cataract surgery are facilitated by a central position of the globe within the palpebral fissure. A centrally positioned eye is normally achieved by using neuromuscular blocking agents (NMBAs). NMBAs also decrease the ocular muscle tone and that is very useful because an increased tonus may cause ocular structures to become displaced and distorted and can also influence IOP. But if there is no possibility of using NMBAs solutions must be found.


Conclusion: The aim of the project was to test several variants of anesthetic protocols to compare the various effects of molecules including lidocaine, ketamine, fentanyl, tramadol, propofol, isoflurane have on the organism.

The use of anesthetic drugs without using of neuromuscular block for cataract surgery may be challenging bringing both advantages and disadvantages. The recovery period after a classic anesthesia without neuromuscular block probably is much shorter than that achieved after a curarisation and the probability for hypotension is less likely. On the other hand, without neuromuscular blocking agents we can`t obtain the central position of the eye globe and that implicate make some compromises for the surgery.


Keywords:  cataract, anesthesia, phacoemulsification, cat, dog,



Patients with ophthalmic disease, such as cataract, vary from young, healthy animals with congenital cataract to geriatric patients, which may have significant diseases like diabetus mellitus. When planning anesthesia for cataract surgery is important to consider the general health status because there are many patients with concurrent disease and that may present significant challenges for the anesthetist [4]. It required investigations before anesthesia like blood tests and if there are changes ideally their condition should be stabilized before anesthesia. Also need to consider that animals that are blind are more likely to be stressed and fearful compared with patients that have vision, especially if the onset of blindness was acute [4].

A complete ophthalmic examination should be performed and should include examination of PLR and menace response, Schirmmer tear test, fluorescein stain test, intraocular pressure (IOP) and a fundic examination if possible. A complete physical examination is also pertinent, as cataracts may be related to extra-ocular disease.

Electroretinography and ocular ultrasonography are standard pre-operative screening tools to confirm an eye’s candidacy for cataract surgery. Although pre-operative preparation and postoperative management can be intensive, canine cataract surgery is often successful and rewarding. Risks, time commitment, and financial demands of phacoemulsification should be discussed with the pet owner.


 1 (2) 2 (1)

Materials and methods

Eleven dogs and five cats presenting to the ophthalmology service with ophtalmological conditions that cause blindness. All patients received the cataract diagnosis after a full ophthalmic examination. Once a cataract forms, surgery is the only treatment method to restore vision. Phacoemulsification uses ultrasonic energy to fragment and extract cataractous lens material from its capsular bag.  Exclusion criteria of the patients were concurrent diseases that could not be stabilized before anesthesia. Any pre-existing medical conditions and drugs administered were recorded.

Food and water were withheld from all patients for a minimum of 12 hours prior to surgery

Animals were gently restrained in a sitting or standing position for drug administration and data collection.

Mydriasis is obtained with topical mydriatic agents (Tropicamide) applied with 2-3 hours before intraocular surgery. Also, topical ocular administration of oxybupracaine (Benoxicaine®) 0.4% drops to anesthetized cornea was performed before general anesthesia. Topical local anesthetics are effective because of a direct action on the cornea and minimizing systemic side effects but their use is limited to diagnostic procedures and intra-operatively as they delay corneal healing, are epitheliotoxic and have a short duration of action [5].

The position of the animals during surgery was in lateral position for unilateral cataract and dorsal for bilateral cataract (Fig.1). HR was measured using cardiac auscultation and MAP was measured using automated oscillometry.5

Anesthesia was maintained with isoflurane in a oxygen delivered via a rebreathing anesthetic circuit with the oxygen flow rate set at 60 ml/kg/min and vaporizer setting of 2%. Oxygen saturation as measured by pulse oximetry, pulse rate and respiratory rate were recorded every 5 minutes after anesthetic induction until the end of anesthesia (vaporizer turned off). Pulse quality was established by manual palpation of the femoral artery and respiratory rate was recorded by observation of the capnogram and chest movement.

Measurement of rectal and esophageal temperature was performed by use of 2 thermistor probes. Rectal temperatures were measured at initial hospital intake and after the end of anesthesia. Once each patient had been induced esophageal temperature was measured by placement of an esophageal thermistor probe and was removed at the end of anesthesia.

The premedication has been achieved with lidocaine 2 mg/kg iv or tramadol 2 mg/kg iv (Fig. 2). All the patients received the propofol-midazolam combination for anesthetic induction. The dose utilized for midazolam was 0,4 mg/kg iv.

The use of ketamine was accomplished in combination with lidocaine and fentanyl for dogs and for one cat was used the ketamine-propofol combination. There is significant interest in this combination of propofol and ketamine because has several benefits in the terms of hemodynamic stability, absence of respiratory depression, post-operative analgesia and recovery [6]. The ketamine dose that was used was low at 0,6 mg/kg iv and was mixed in the same syringe with propofol 3 mg/kg.

The extubation was performed when the coughing and swallowing reflexes had returned.3

Steroidal anti-inflammatory drug (Betametazone, Diprophos®) was administered intraconjuctival at the end of the surgery.



In total sixteen animals (eleven dogs and five cats) were enrolled in the project.

All patients were in good condition of general health just 2/11 dogs were stable diabetic patients and for they measurements have been taken to monitoring the blood glucose level before, during and after surgery.

Premedication with lidocaine 2 mg/kg was performed for 6 dogs and was made observation about cough during endotracheal intubation. IV lidocaine can decrease the incidence of cough during endotracheal intubation but does not appear to have a sparing effect on the dose of propofol required for endotracheal intubation.

Two patients receive tramadol 2 mg/kg iv in premedication, one in combination with lidocaine 2 mg/kg iv and the other just the tramadol. For the patient that receive just tramadol was not observed any changes in the propofol dose.

One dog received fentanyl in premedication and after induction was observed significant respiratory depression compared with the others. Two dogs and 6 cats did not receive anything for premedication.

The diabetic protocol for phacoemulsification consist in tramadol 2 mg/kg iv for premedication, induction with midazolam 0,4 mg/kg and propofol at effect. Maintenance of anesthesia has been achieved using isoflurane like inhalant agent and mixture of fentanyl, lidocaine and ketamine. The glucose level was measured before and every hour during anesthesia.

For all patients, cats and dogs, the induction was performed with propofol and midazolam 0,4 mg/kg and topical laryngeal lidocaine was used prior to intubation. One cat received the ketamine-propofol combination for induction.

The cough response at ETI was observed for 3 dogs, the patient that receive tramadol in premedication and the others that was not premedicated and 2 cats. In propofol anaesthetized dogs iv and topical laryngeal lidocaine attenuated the pressor response to ETI where iv lidocaine reduced the cough response.

Duration of the anesthesia from intubation to extubation was 80 min ±10 min depending of the surgical procedure, unilateral/bilateral cataract.

After induction, a rotation of the eyes towards the internal angle was observed. To achieve the phacoemulsification surgery, the eye was brought to the central position by means of the traction sutures.


Cardiovascular and respiratory parameters were well maintained during induction, maintenance and recovery periods for all patients. All patients receive Ringer Lactate infusion at 5 ml/kg/h. The anesthesia was maintained with isoflurane delivered via a rebreathing anesthetic circuit with the oxygen flow rate set at 60 ml/kg/min and vaporizer setting of 2%. This was completed by analgesia offered by combination of fentanyl-lidocaine-ketamine for dogs and fentanyl CRI for cats. The doses utilized for fentanyl was 4 μg/kg/h in combination with lidocaine 2 mg/kg/h and ketamine 0,6 mg/kg/h and when fentanyl was used alone, the dose was between 5-10 μg/kg/h.

Pulse oximetry was used to monitor oxygen saturation of hemoglobin in arterial blood and was maintained at >95%. MAP was measured using automated oscillometry and was stabilized at 80-110 mmHg.

Respiratory rate, end-tidal carbon dioxide was provided by capnography. The respiratory rate was maintained at 10 ± 5 rpm and the level of CO2 was 45-60 mmHg. All patients breathed themselves spontaneously, just one cat need the controlled ventilation because of the elevated level of EtCO2, up to 65 mmHg and the low respiratory rate.

For all patients the recovery from anesthesia was fast and without any complication. The temperature at the end of anesthesia was 37,2 ± 5ºC.



The ideal anesthetic protocol for cataract surgery should provide central position of the eye, decrease the ocular muscle tone, provide analgesia and narcosis for optimal operating conditions, be safe for the patient and comfortable for the surgeon [4] (Fig. 5).

Good communication with the surgeon before the procedure and an understanding of the surgeon’s requirements are essential when formulating an anesthesia plan. The patient position with the head lower than the heart should also be avoided and at 15 degrees head-up position during intraocular surgery has been recommended in humans.

Also, the position of the animal during surgery may influence the choice of breathing system and endotracheal tube (ETT). Related to intubation should be remembered that the mouth during tracheal intubation can increase IOP as the choroid process of the mandible moves into the orbit. Care must be taken when positioning patients for tracheal intubation, as pressure may be exerted on the globe while the maxilla is held; this is especially the case for brachycephalic breeds. An armored ETT is recommended to use[4].

The ability to influence IOP is very important part of anesthesia management. Is necessary to avoid increased IOP because in these circumstances may result in a globe rupture, risk for intraocular bleeding or retinal detachment.

The use of ketamine, a dissociative anesthetic, for ophthalmologic procedures is controversial. Ketamine used alone is likely to significantly increase IOP because it causes an increase in extraocular muscle tone [4]. The good benefits of ketamine administration consist in increased of the amount of circulating norepinephrine, increase in peripheral arteriolar resistance and muscle activity and decrease the extent of redistribution hypothermia [3]. The use of ketamine has beneficial effects on the blood pressure, cardiac output, corporal temperature and contributes to realization of a balanced anesthesia based on a multimodal analgesia. On the other hand, ketamine can increase IOP but considering that in the protocols used in this study was never used alone and the fact that the surgical procedure involves making a break through the incision of the cornea and penetrating the eye globe this pressure can be adjusted naturally without becoming hazardous for the structures of the eye.

Is mandatory to avoid coughing, sneezing, vomits when there is a risk of globe rupture because this can result in an increased central venous pressure [2]. Therefore, drugs like morphine that causes vomiting should be avoided. On the other hand, the use of alpha 2 adrenergic agonist is not prohibited; although may induce vomiting especially in cats the alpha 2 adrenergic agonist can be very useful when we are dealing with uncooperative patients and the risk of globe rupture is bigger because of the stress and manipulation. In this study, for avoiding the coughing response was used lidocaine. Both iv and topical laryngeal lidocaine attenuated the pressor response to ETI and iv lidocaine 2 mg/kg reduced the cough response to ETI in propofol anaesthetized dogs [1] [2].

Intraocular blood volume is influenced by intraocular vascular tone (vasodilatation or vasoconstriction), arterial blood pressure (ABP) and outflow of the blood from the globe [4]. Is well known that exist an inverse proportional relationship between arterial carbon dioxide tension (PaCO2) and vascular tone. Increased carbon dioxide tension causes choroidal vessel vasodilatation and an increase in IOP. Hypoxaemia can be detect using pulse oximetry and should be avoided by oxygen supplementation and ventilation. PaCO2 can be monitored by capnography or arterial blood gas analysis and controlled using IPPV. However, inappropriate use of IPPV can increase CVP by increasing intrathoracic pressure during inspiration, resulting in an increase in IOP.

Cataract phacoemulsification is not a very painful procedure except during the incision and suturing of the corneal limbus. Traditionally, most anesthetic molecules mildly decrease IOP by increasing the outflow of aqueous humor. The use of anesthetic induction agents such as propofol, alfaxalone, ketamine and etomidate may all increase IOP. All are ameliorated by co-induction agents like opioids,  midazolam or diazepam [4].

One limitation to the present study was the small number of the patients (sixteen animals – eleven dogs and five cats) used.

In conclusion, if the realization of the neuromuscular block for phacoemulsification is not possible, we can perform anesthesia for this procedure using just the standard molecules like lidocaine, propofol, midazolam, fentanyl, ketamine and tramadol. The recovery period after a classic anesthesia without neuromuscular block is much shorter than that achieved after a curarisation and the probability for hypotension is less likely. On the other hand, after induction, a basculation of the eyes towards the internal angle was observed for all studied cases. In order to achieve the phacoemulsification surgery, the eye was brought to the central position by means of the traction sutures.

The great disadvantage is the fact that without neuromuscular blocking agents we can`t obtain the central position of the eye globe and that implicate make some compromises from the surgeon.



6 (1)The project was provided by Di-Vet Medical – pet emergency and critical care clinic, Bucharest, Romania.