One of the most underestimated aspects of perioperative patient management during veterinary ophthalmic surgery is maintaining normal body temperature. While ophthalmic
procedures are often perceived as minimally invasive, many are lengthy, require
profound anesthesia, and are performed on patients that are inherently susceptible to
hypothermia. Cataract surgery, corneal transplantation, glaucoma procedures, retinal
surgery, enucleation, and complex reconstructive surgeries frequently last one to
several hours, creating ideal conditions for significant heat loss.
Perioperative hypothermia, which is defined as a core body temperature below 36°C
(96.8°F) is not merely a comfort issue. Even mild reductions in body temperature can
alter cardiovascular function, delay anesthetic recovery, impair immune function,
increase oxygen consumption during recovery, and complicate postoperative care.
These risks are especially relevant in veterinary ophthalmology where patients are
commonly geriatric, pediatric, or affected by systemic diseases that already compromise
thermoregulation.

As veterinary medicine increasingly adopts advanced microsurgical techniques and
higher standards of anesthesia monitoring, effective patient warming has become an
essential component of quality perioperative care rather than an optional accessory.

Why Ophthalmic Patients Are Especially Vulnerable to Hypothermia

Several characteristics of ophthalmic procedures make patients particularly susceptible
to hypothermia.

General Anesthesia Suppresses Thermoregulation

General anesthetic agents impair the body's normal thermoregulatory responses by
decreasing metabolic heat production and causing peripheral vasodilation. Upon
anesthetic induction, heat stored within the body's core rapidly redistributes toward
cooler peripheral tissues due to peripheral vasodilation. A temperature gradient of 2.5
degrees C to 7 degrees C between the core and peripheral compartments can exist in
the typical patient. The core compartment comprises the head, chest and abdomen and
the peripheral compartment comprises the legs, skin and tail. Unless preemptive
warming measures are taken, the patient can lose 81 percent of the heat loss it will
ultimately lose, during the course of that anesthetic, in the first 30 to 45 minutes after
induction.

Long Surgical Times

Although some ophthalmic procedures are brief, many advanced surgeries routinely
extend beyond one hour. Bilateral cataract extraction, complicated lens luxation repair,
retinal procedures, corneal grafting, orbital surgeries, and revision procedures may
require prolonged periods under anesthesia predisposing the patient to hypothermia.
Even modest heat losses accumulate over time, making active warming increasingly
important as procedure duration increases.

Small Patient Size

Small animals possess a much higher surface-area-to-body-mass ratio than larger
patients, causing heat to dissipate rapidly into the environment. The smaller the patient,
the faster hypothermia can develop unless active warming is provided.
Veterinary ophthalmology frequently treats small patients like:

• Cats
• Toy breed dogs
• Rabbits
• Exotic mammals
• Birds

Large Body Surface Exposure

Although the surgical incision itself is small, patients are typically clipped extensively,
positioned on operating tables that conduct heat away from the patient, and covered
only with thin sterile drapes that leave large body areas exposed to room air.
Alcohol-based skin preparations, ophthalmic irrigation fluids, and cool operating room
temperatures further increase evaporative and conductive heat loss.

Clinical Consequences of Perioperative Hypothermia

Delayed recovery also increases nursing workload, lengthens occupancy of recovery
areas and decreases overall postoperative clinic efficiency.

Cardiovascular Effects

Cooling increases sympathetic stimulation and may contribute to:

• bradycardia
• arrhythmias
• altered blood pressure regulation
• increased myocardial oxygen demand during recovery
  

Geriatric patients and patients with pre-existing cardiac disease may tolerate these
changes poorly.

Respiratory Effects

Hypothermia suppresses respiratory drive and may result in an increase in
intraoperative end tidal CO2 requiring ventilatory support. It can also prolong
postoperative ventilatory depression, especially following inhalant anesthesia or opioid
administration.

Hematologic Effects

Hypothermia causes slowing of blood clotting enzymes, reduction of platelet counts by
aggregating them in the spleen and liver and increasing blood viscosity. This increases
the incidence of severe bleeding. Because of hypothermia induced increase in
sympathetic tone, blood vessels constrict and can decrease oxygen delivery to the
tissues. This can lead to increased post operative infections and poor wound healing.

Impaired Drug Metabolism

Numerous anesthetic drugs exhibit prolonged duration at lower body temperatures due
to decrease in hepatic enzymatic activity. Reduced renal clearance may complicate
anesthetic management and delay return to normal physiologic function.

Impaired Immune Function

Experimental and clinical studies have demonstrated that hypothermia impairs
leukocyte function, decreases tissue oxygen delivery, and slows wound healing.
Although ophthalmic surgeries generally involve relatively small incisions, optimal tissue
healing remains critical for preserving vision and minimizing postoperative
complications.

Challenges Specific to Ophthalmic Surgery

Despite the availability of warming technologies, ophthalmic surgery presents unique
implementation challenges.

Limited Surgical Access

The surgeon requires unrestricted access to the patient's head while preserving
microscope positioning, anesthesia circuits, intravenous lines, monitoring equipment,
and sterile draping. Large warming devices positioned near the surgical field may
interfere with ergonomics or sterile technique.

Small Patient Positioning

Toy breeds and cats often occupy only a small portion of standard operating tables.
Obtaining sufficient surface contact with a warming source without creating pressure
points requires careful positioning.

Microsurgical Environment

Operating microscopes, phacoemulsification equipment, laser systems, and delicate
ophthalmic instrumentation create crowded workspaces. Warming systems must
integrate seamlessly without increasing clutter or obstructing equipment movement.

Airflow Considerations

Although extensive research has generally not demonstrated increased surgical site
infection associated with properly used forced-air warming, some surgical teams remain
cautious regarding airflow within highly controlled operating environments.
Consequently, warming technologies that provide airflow away from the surgical field
may be preferred in certain facilities.

Practical Strategies for Maintaining Normothermia

Successful warming usually begins before anesthesia induction.

Preoperative Warming

As was stated earlier, a temperature gradient of from 2.5 degrees C to 7 degrees C can
exist between the patient’s core and peripheral compartments. Prewarming patients for
30 minutes in the cage before induction reduces the core-to-peripheral temperature
gradient. This limits the redistribution hypothermia during the first 30 to 45 minutes of
anesthesia due to peripheral vasodilation.

Preoperative Warming in the Cage

A proven effective preoperative warming method consists of using the HoverHeat Cage
Warming Combo and a warm air blower. Warm air is distributed in the cage to warm the
patient’s periphery thereby decreasing the core-to-peripheral temperature gradient.

HoverHeat Cage Warming Combo

Preoperative Warming During Anesthetic Induction and Prep

It is imperative that continued active warming occurs during anesthetic induction and
prep to decrease the core-to-peripheral temperature gradient and prevent redistribution
hypothermia. Clipping of the patient’s insulating fur and prep solutions contribute to
convective and evaporative heat loss.

Use of an actively functioning HoverHeat patient warming pad has been proven
effective in continuing preoperative warming during anesthetic induction and prep.

HoverHeat Patient Warming Pad

Intraoperative Warming

The transition from preoperative warming to intraoperative warming must be made as
quickly and seamlessly as possible. If the preoperative anesthetic induction area is
separate from the operating room, an effective method of preventing heat loss during
transfer is to wrap the patient in a thermal retention blanket like the ConRad Thermal
Blanket. Upon entry into the operating room an actively functioning heat source should
already be available to prevent any delay in patient warming because heat stored in the
peripheral compartment is transient.

The EyeCare Warming Combo uses a medley of ConRad Thermal Blankets, a
HoverHeat Patient Warming Pad and a HUG-U-VAC Head Positioner to provide precise
positioning and the ultimate in patient warming.

1. Place a ConRad Thermal Blanket on your ophthalmology table surface to prevent conductive heat loss from the HoverHeat pad to the table
   
2. Place a HoverHeat pad and HUG-U-VAC Head Positioner on the ConRad Thermal Blanket
   
   
3. Place the patient on the HoverHeat pad in the position for your procedure and position the head with the HUG-U-VAC Head Positioner
   
   
4. Cover the patient with a ConRad Thermal Blanket to prevent convective and radiant heat loss from the patient and the HoverHeat pad.
   
   

Upon transfer to the OR continue patient warming and monitoring.

Continue Active Warming

During intraoperative warming it is important to prevent conductive heat loss to the
underlying table surface. This again can be accomplished by placing the ConRad
Thermal Blanket underneath the patient. It is also imperative to expose as much body
surface area to your active warming device as possible. The HoverHeat patient warming
system provides the greatest exposure to body surface area by underbody warming.
Prevent as much convective and radiant heat loss to the OR environment as possible
by covering nonsurgical areas with a thermal retention blanket.

Warm IV Fluids

Warmed IV fluids are essential in long cases with the IV line insulated along its length
from the IV warmer to the patient.

Operating Room Temperature

Convective heat loss can be curtailed by having the operating room temperature as high
as the operating room personnel and surgeon find comfortable.

Postoperative Warming

The end of the procedure does not mean that active warming can be discontinued.

Maintain active warming until the patient emerges from anesthesia.
Postoperative return to normothermia occurs when hypothalamic anesthetic
concentration decreases sufficiently to again trigger normal thermoregulatory defenses.
These defenses include compensatory vasoconstriction and the return to normal
metabolic heat production, which enable a return to normal core body temperature.

In-cage postoperative warming using a warm air blower, HoverHeat Cage Warming
Combo, HoverHeat pad and ConRad Thermal Blankets.

Continuous Temperature Monitoring

Core temperature should be monitored throughout anesthesia using esophageal or
rectal temperature probes. Continuous monitoring allows clinicians to detect downward
trends before severe hypothermia develops.

Combine Multiple Warming Methods

No single intervention eliminates hypothermia. The EyeCare Warming Combo is an
excellent example of combining multiple warming methods
Best practice combines:

• Preoperative warming – HoverHeat Cage Warming Combo
  
• Active patient warming – HoverHeat Patient Warming System
  
• Warmed IV fluids
  
• Thermal retention blankets – ConRad Thermal Blankets
  
• Continuous temperature monitoring
  
• Efficient anesthetic management
  

Together, these strategies provide additive protection against heat loss.

Emerging Trends in Veterinary Ophthalmology

As veterinary ophthalmology continues to advance, expectations regarding perioperative care continue to rise.

Modern practices increasingly emphasize:

• enhanced recovery protocols
• evidence-based anesthesia
• shorter recovery times
• improved patient comfort
• standardized temperature management

Active warming systems designed specifically for veterinary patients are becoming more
ergonomic, easier to disinfect, and better suited for diverse patient sizes.

Reusable conductive warming platforms like the HoverHeat Patient Warming Pad and improved temperature monitoring technologies are helping practices deliver more
consistent perioperative thermal care.

Conclusion

Patient warming during veterinary ophthalmological procedures is far more than a
comfort measure; it is a critical component of safe anesthesia and successful surgical
outcomes. Small body size, prolonged anesthesia, exposed body surfaces, cool
operating environments, and impaired thermoregulation combine to place ophthalmic
patients at significant risk of perioperative hypothermia.

Fortunately, these risks are largely preventable. Evidence from both human and veterinary anesthesia demonstrates that proactive warming strategies, including preoperative warming, intraoperative warming and postoperative warming as well as continuous temperature monitoring, active warming systems, and minimization of heat loss can substantially improve temperature maintenance throughout surgery.

As veterinary ophthalmology continues to embrace increasingly sophisticated
microsurgical procedures, effective perioperative warming must remain an integral part
of every anesthetic protocol. By prioritizing thermal management alongside
cardiovascular monitoring, analgesia, and meticulous surgical technique, veterinary teams can promote faster recoveries, improve physiologic stability, and ultimately
support better patient outcomes.

References

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9. National Institute for Health and Care Excellence (NICE). (2022). Hypothermia:
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10. Mosley CAE, Shaw DJ. (2013). A longitudinal cohort study of perioperative hypothermia
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EyeCare Warming Combo - Super Set

EyeCare Warming Combo - Mini Set