Align-ju STUDENT
If a drop in the level of oxygen is detected in the body , the respiratory centre will increase the rate and depth of respiration . However , if oxygen levels continue to drop and the patient becomes hypoxic , or remains below that critical level , the respiratory centre can become depressed and unable to effectively signal that more oxygen is needed .
An increase in respiratory rate can decrease the carbon dioxide level in the blood , which is detected by chemoreceptors that will trigger a reduction in the respiratory rate to increase carbon dioxide levels [ 3 ] . An unwanted side effect of an animal breathing 100 % oxygen instead of room air is that these chemoreceptors will register the change in the oxygen level and will depress respiration to allow the carbon dioxide level to return to normal , in some cases totally inhibiting respiration . Carbon dioxide and hydrogen ion ( H + ) concentrations have a greater impact on respiratory drive than the requirement for oxygen [ 3 ] .
Nursing considerations
When veterinary nurses assess patients , their respiratory rate , depth and effort are observed , often numerous times a day as part of routine observations . It is preferable to assess respiration while the patient is settled in its kennel or crate , before the door is opened . This is not always possible when compromised patients are rushed through from the consultation room , but we should assess respiration before attempting any nursing care .
When handling patients with respiratory compromise , stress should be minimised as these patients are at high risk of a potentially fatal decompensation . A slow and steady approach to handling is advised , so as not to cause their respiratory rate to increase further .
The normal ranges for the respiratory rates of dogs , cats and rabbits are shown in Table 1 [ 4 ] . Questions to consider when assessing a patient ' s respiration include :
• Is the patient ventilating effectively ?
• Are there signs of increased respiratory effort ?
• Is the patient ' s chest moving as expected ?
• Is the patient breathing with its mouth open ? ( Remember that panting is not a true indicator of respiratory rate .)
• Does the patient ' s position indicate respiratory distress ? ( An animal in respiratory distress will often adopt a position that aids breathing : neck extended , elbows out , breathing through its mouth and it may also show signs of abdominal effort .)
Table 1 . Respiratory rates [ 4 ] .
Species
Breaths per minute
Dog 10 – 30 ( small dogs will have a higher rate ) Cat 20 – 30 Rabbit 30 – 60
Supplemental oxygen
There are many methods of delivering supplemental oxygen to a patient , including flow-by oxygen , nasal cannulas , face masks , oxygen collars , oxygen tents / kennels and intubation . The least stressful method should be adopted wherever possible .
Oxygen can have a drying effect on the respiratory tract , which can lead to respiratory infections [ 5 ] . The drying effect is less likely to cause a problem in short-term oxygen delivery , but longer-term oxygen supplementation should be humidified via a water canister filled with sterile saline or water .
In small animals , such as cats and smaller dogs , the use of oxygen tents or kennels can help minimise stress . It is important to remember that every time the tent or kennel is opened , oxygen will disperse into the room .
Oxygen tents and kennels can quickly become hot ; if the unit is not temperature controlled , regularly monitor the temperature inside with a room thermometer and use ice packs to cool it , as necessary .
When using a circle circuit to deliver oxygen , the system should be flushed to ensure there is no residual volatile agent present . Consideration must also be given to where the oxygen enters the circuit : before or after the adjustable pressure-limiting ( APL ) valve . The APL valve may need to be closed , to prevent oxygen being lost down the scavenging hose before reaching the patient . It is important to reopen the APL valve afterwards .
In practice I have witnessed the oxygen supply being turned up and the end of an anaesthetic circuit waved in the general direction of a patient ; this will not work . A well-fitting mask should be used , ideally , but in cases where a mask causes the patient excessive stress , steady flow-by oxygen is better than nothing .
A glossary of terms relating to respiration , which are not covered in this article but which you may find useful , can be found in Table 2 on page 58 .
• Is the patient eating and drinking normally ? ( An animal in respiratory distress may not eat or drink , as doing so can further compromise its breathing .)
Volume 39 ( 3 ) • June 2024
57