Case Management

Chapter 7 Case Management



CANINE “HIT-BY-CAR” LIMB FRACTURE


Patients that have been hit by a car may have damage not externally visible. Rule out pneumothorax, bladder rupture, head trauma, and myocardial injury before administration of anesthesia.



Preanesthesia



▪ With regard to blood work, at a minimum, packed cell volume (PCV), total protein (TP), blood glucose, and blood urea nitrogen (BUN) should be measured

▪ Anemia secondary to hemorrhage must be corrected before anesthesia; any patient with PCV < 20% should receive blood transfusion

▪ Perform electrocardiography (ECG); any bodily trauma may produce myocardial injury and result in traumatic myocarditis that manifests as ventricular arrhythmias (premature ventricular contractions or ventricular tachycardia)

▪ Examine chest radiograph for signs of pneumothorax or pulmonary damage

▪ An intravenous (IV) catheter is placed for the administration of anesthetic agents and resuscitation fluids; patients in shock are administered “shock-dose” fluids at 90 ml/kg IV; in addition, hypertonic saline or colloids may be administered



Premedication



Agents (mg/kg IM; use half if administering IV)


Oxymorphone* 0.03-0.08 + midazolam (or diazepam)† 0.1-0.3 ± glycopyrrolate 0.01


Morphine* 0.4-0.8 + midazolam (or diazepam)† 0.1-0.3 ± glycopyrrolate 0.01


Buprenorphine 0.01-0.02 + midazolam (or diazepam)† 0.1-0.3 ± glycopyrrolate 0.01



* Mu-opiate and benzodiazepine administration may lead to hypoventilation; use with caution in patients with respiratory trauma or pneumothorax.


† Acepromazine (0.02-0.05) can be substituted as a sedative only if patient is well hydrated, as vasodilation and hypotension may result.



Induction



▪ Propofol may induce respiratory depression; use with caution in patients with respiratory trauma; give half the calculated induction dose over 60 seconds; preoxygenate (with oxygen administered via face mask for 5 minutes) before induction to prevent hypoxemia

▪ Thiopental may exacerbate cardiac arrhythmias and induce ventricular arrhythmias

▪ Ketamine and benzodiazepine induction may lead to tachycardia or arrhythmias and should be avoided in patients with cardiac trauma; use is recommended in patients with respiratory disease or with pneumothorax, as ventilation is minimally depressed

▪ Opiate and benzodiazepine induction may lead to hypoventilation or apnea; use with caution in patients with respiratory trauma; bradycardia may result and can be prevented or treated with anticholinergic agents

▪ Inhalant induction by face mask is acceptable only if patient is not vomiting and pneumothorax is not present



Induction



Agents (mg/kg IV); give only until effective


Propofol 4-6 (use caution if hypovolemia or hypotension is present)


Thiopental 10 (watch for ventricular arrhythmias)


Ketamine 5 + diazepam (or midazolam) 0.25 (watch for arrhythmias)


Oxymorphone (or hydromorphone) 0.1 + diazepam 0.2


Mask with isoflurane or sevoflurane



Analgesia



▪ Brachial plexus block if fracture is present in forelimb

▪ Epidural administration if fracture present in forelimb or hindlimb; if performed before surgery, decreases inhalant requirement during surgery and provides postoperative analgesia for up to 24 hours (if preservative-free morphine is used)

▪ Fentanyl patch placement before surgery (blood levels of fentanyl and therefore analgesia are not present for 8 to 12 hours after placement; provides only postoperative analgesia)

▪ Constant-rate infusion of analgesic agent during surgery


Constant-Rate Infusion




image


Maintenance



▪ The most rapidly acting, minimally metabolized inhalant agents are preferred

▪ Isoflurane and sevoflurane are preferred over halothane; halothane sensitizes myocardium to catecholamine-induced arrhythmias (exercise caution in patients with traumatic myocarditis)

▪ IV fluids must be administered during anesthesia at a rate of 10 ml/kg/hr


Monitoring



▪ ECG: watch for arrhythmias (particularly ventricular premature contractions [PVCs] and ventricular tachycardia)
□ Prevent bradycardia (heart rate [HR] < 60 beats per minute [bpm])
• Treat bradycardia with atropine 0.01 mg/kg IM or IV

□ Prevent tachycardia (HR > 200 bpm)
• Consider source of tachycardia

• Treat pain with analgesic (e.g., oxymorphone 0.05 mg/kg IM or IV)

• Ensure adequate anesthetic depth

• Evaluate blood pressure (hypotension can result in reflex tachycardia)

▪ Blood pressure should be monitored; mean arterial pressure (MAP) should be maintained above 60 mm Hg and systolic arterial pressure (SAP) above 90 mm Hg
□ Hypotension = MAP < 60 mm Hg, SAP < 90 mm Hg
• Treat hypotension

• Decrease anesthetic depth (by decreasing vaporizer concentration)

• Administer IV fluid bolus (10 ml/kg)

• Administer IV colloids (10 to 20 ml/kg; use only if hemostasis adequate)

• Ensure adequate surgical hemostasis

• Replace surgical blood loss at 1:3 ratio—for every milliliter of blood lost during surgery, 3 ml of crystalloid (e.g., lactated Ringer’s solution [LRS]) is administered IV

• Hemorrhage resulting in PCV < 20% requires blood transfusion or hemoglobin-substitute administration

• Administration of inotrope (e.g., dopamine) IV

▪ Ventilation
□ Exercise caution with manual or mechanical ventilation unless the absence of pneumothorax is confirmed radiographically

□ Capnography (measures amount of expired carbon dioxide [CO2] at the end of expiration [end-tidal CO2, or Etco2])
• Normal Etco2 = 35 to 45 mm Hg

• Hypoventilation (Etco2 > 45 mm Hg) may require assisted or mechanical ventilation; if any degree of pneumothorax is present, consider placement of chest tube and continuous suction during ventilation


CANINE OPHTHALMIC SURGERY



Preanesthesia



▪ With regard to blood work, at a minimum, PCV, TP, blood glucose, and BUN should be measured

▪ An IV catheter is placed for the administration of anesthetic agents and fluids

▪ Exercise caution with restraint and handling, especially if globe is open



Premedication



Agents (mg/kg IM; use half if administering IV)


Oxymorphone* 0.5-0.2 + acepromazine 0.02-0.05 ± glycopyrrolate 0.01


Morphine* 0.5-1 + acepromazine 0.02-0.05 ± glycopyrrolate 0.01


Buprenorphine 0.01-0.02 + acepromazine 0.02-0.05 ± glycopyrrolate 0.01


Midazolam† (or diazepam) 0.1-0.3 can be substituted as a sedative



* Mu-opiate administration can lead to long-lasting miosis, which can prohibit intraocular surgery.


† Benzodiazepines combined with opiates as premedicants frequently cause vomiting, which increases intraocular pressure. Acepromazine has antiemetic effects and lowers the incidence of vomiting.



Induction



▪ Propofol lowers intraocular pressure

▪ Thiopental lowers intraocular pressure

▪ Ketamine and benzodiazepine induction may lead to increased intraocular pressure and is not recommended

▪ Opiate and benzodiazepine induction has no direct effect on intraocular pressure but may lead to hypoventilation or apnea, which indirectly increases intraocular pressure

▪ Inhalant induction by face mask is acceptable if patient is not struggling



Five Induction Methods for Anesthesia for Ophthalmic Surgery



Agents (mg/kg IV); give only until effective


Propofol 4–6


Thiopental 10


Ketamine 5 + diazepam (or midazolam) 0.25


Oxymorphone (or hydromorphone) 0.1 + diazepam 0.2


Mask with inhalant



Analgesia



▪ Constant-rate infusion of analgesic agent during surgery

▪ Patients given a neuromuscular blocking agent will not move in response to painful surgical stimulation; administer analgesics and monitor HR and blood pressure for indications of pain


Constant-Rate Infusion




image


Maintenance



▪ IV fluids must be administered during anesthesia at a rate of 10 ml/kg/hr


Neuromuscular Blockade



▪ Intraocular surgery requires centrally located pupil

▪ Nondepolarizing neuromuscular blocking agents paralyze skeletal muscle

▪ Mechanical ventilation is necessary; set tidal volume to 10 to 20 ml/kg, respiratory rate to 6 to 12 breaths per minute, and peak inspiratory pressure to < 20 cm Hg

▪ Monitor degree of neuromuscular blockade with a peripheral nerve stimulator


Nondepolarizing Neuromuscular Blocking Agents





















Agent Initial Dose (mg/kg IV) Repeat Dose (mg/kg IV)
Atracurium 0.25 0.1
Pancuronium 0.06–0.1 0.05
Vecuronium 0.1–0.2 0.05


Monitoring



▪ Neuromuscular paralysis monitored with peripheral nerve stimulator
□ Objectively monitors degree of skeletal muscle paralysis by determining percentage of neuromuscular receptors “blocked” by the paralytic agent

□ Place nerve stimulator contact heads around the peripheral nerve to be stimulated

□ Place one of the two contacts on each side of the nerve

□ Most commonly used nerves are peroneal, ulnar, and facial

□ Train-of-four (TOF): stimulus for TOF is delivered as a total of four pulses (low frequency, 2 to 4 Hz, for 2 seconds at 0.5-second intervals); aim is to keep only one or two twitches (of a possible four) visible

□ Four twitches are present with no or up to 75% blockade

□ Three twitches are present with 75% blockade

□ Two twitches are present with 80% blockade

□ One twitch is present with 90% blockade

□ Zero twitches indicate 100% blockade

□ Tetany: continuous stimulation at either 50 or 100 Hz; sensitive to both residual and deep paralysis; the presence of any persisting strength during tetany is good indicator of the patient’s ability to maintain muscle tone

□ Reversal of blockade is difficult unless at least one twitch in TOF is present

▪ Reversal of neuromuscular blockade
□ Requires accumulation of acetylcholine at neuromuscular junction and competitive inhibition

□ Use anticholinesterase inhibitors
• Neostigmine and edrophonium

□ These agents are also muscarinic agonists and may cause bradycardia

□ Administer anticholinergic (atropine 0.02 mg/kg or glycopyrrolate 0.01 mg/kg IV) before anticholinesterase inhibitor to prevent bradycardia


Anticholinesterase Agents














Agent Dose (mg/kg IV)
Edrophonium* 0.5–1
Neostigmine* 0.1–0.2

* Duration of action shorter than that of nondepolarizing neuromuscular agents; may need to readminister.



▪ ECG:
□ Tachycardia (HR > 200 bpm)
• Consider source of tachycardia

• Ensure adequate anesthetic depth

• Treat pain with analgesic (e.g., oxymorphone 0.05 mg/kg IM or IV)

• Evaluate blood pressure (hypotension can result in reflex tachycardia)

▪ Blood pressure
□ Hypertension in paralyzed patient indicates inadequate anesthetic depth

□ Administer analgesic (e.g., oxymorphone 0.05 mg/kg IM or IV)

▪ Ventilation
□ Mechanical ventilation imperative if using neuromuscular blockade

□ Arterial blood gas analysis
• Normal arterial CO2 = 35 to 45 mm Hg

□ Capnography (measures Etco2)
• Normal Etco2 = 35 to 45 mm Hg


CESAREAN SECTION IN DOGS AND CATS


General anesthesia is needed to induce pain relief, unconsciousness, and relaxation during cesarean section. In a typical case the pet receives a preanesthetic sedative-analgesic combination and an induction agent and, subsequently, inhalation anesthesia.



Preanesthesia



▪ Preoperative tests depend in part on the age and general health of the pet; in younger otherwise healthy females, minimal tests are needed

▪ With regard to blood work, at a minimum, PCV, TP, and blood glucose should be measured

▪ In older or unhealthy animals it may be necessary to perform a routine blood count, serum biochemical tests, a urinalysis, and possibly a chest x-ray examination or ECG before anesthesia; the need for such tests varies on a case-by-case basis and depends on the overall health of the pet at the time of anesthesia

▪ Administer analgesic with or without a sedative agent

▪ Anticholinergics (glycopyrrolate or atropine) decrease salivation and prevent excess vagal tone during uterine traction

▪ Fetal cardiac output is dependent on fetal HR (not blood pressure), and it is imperative to prevent bradycardia by administering an anticholinergic

▪ Atropine crosses the placental barrier and increases fetal HR; glycopyrrolate does not; atropine is the agent of choice in patients undergoing cesarean section

▪ An IV catheter is placed for the administration of anesthetic agents and fluids


Premedication














Species Agents (mg/kg IM; Use Half if Administering IV)
Dogs Oxymorphone 0.05–0.1 ± midazolam (or diazepam) 0.1–0.3 + glycopyrrolate 0.01
Cats Oxymorphone 0.02–0.08 ± midazolam (or diazepam) 0.1–0.3 + glycopyrrolate 0.01


Induction



▪ Propofol is the agent of choice because of rapid clearance, minimal hepatic metabolism, and minimal cardiac depression

▪ Respiratory depression or apnea may occur with large boluses of propofol given rapidly IV; it is recommended that half the calculated induction dose be given over 60 seconds; preoxygenation (oxygen administered via face mask for 5 minutes) before induction prevents maternal and fetal hypoxemia

▪ Inhalant induction by face mask is acceptable only if patient is not vomiting

▪ Monitor ventilation after induction and once patient is placed in dorsal recumbency, as increased abdominal volume may inhibit diaphragmatic movement

▪ Mechanical ventilation may be required in large-breed dogs or patients that have great abdominal distention


Induction


























Species Agents (mg/kg IV)
Dogs Propofol 4–6
Ketamine 5 + diazepam 0.25
Thiopental 10
Mask with isoflurane or sevoflurane
Cats Propofol 4–6
Ketamine 5 + diazepam 0.25
Thiopental 10
Mask with isoflurane or sevoflurane


Maintenance



▪ Before surgery an epidural block can be performed, but care should be taken not to prolong anesthetic time, as the risk of increased anesthetic time outweighs the benefit of epidural analgesia

▪ All inhalant anesthetics cross the placental barrier and will reach the fetus

▪ The most rapidly acting, minimally metabolized inhalant agents are preferable

▪ Isoflurane and sevoflurane are preferred over halothane


Monitoring



▪ ECG
□ Prevent bradycardia (HR < 60 bpm in large dogs; HR < 80 bpm in small dogs and cats)
• Treat bradycardia with atropine 0.01 mg/kg IM or IV

□ Prevent tachycardia (HR > 160 bpm in large dogs; HR > 200 in small dogs and cats)
• Consider source of tachycardia

• Treat pain with analgesic (e.g., oxymorphone 0.01 mg/kg IM or IV)

• Ensure adequate anesthetic depth

• Evaluate blood pressure (hypotension can result in reflex tachycardia)

▪ Blood pressure should be monitored, and MAP maintained above 60 mm Hg
□ Hypotension = MAP < 60 mm Hg
• Treat hypotension
▪ Decrease anesthetic depth (by decreasing vaporizer concentration)

▪ Administer IV fluid bolus 10 ml/kg

▪ Ensure adequate surgical hemostasis

▪ Replace surgical blood loss at 1:3 ratio—for every milliliter of blood lost during surgery, 3 ml of crystalloid (e.g., LRS) is administered IV

▪ Administer ephedrine 0.025 to 0.05 mg/kg IV

▪ Ventilation
□ Capnography (measures Etco2)
• Normal Etco2 = 35 to 45 mm Hg

• Most cesarean section patients hypoventilate during anesthesia and have Etco2 > 45 mm Hg; treat with assisted or mechanical ventilation

▪ Depth of anesthesia


Newborns



▪ Dry immediately after delivery

▪ Ensure presence of heartbeat and breathing
□ Weak or absent heartbeat: treat with atropine, one drop from 25-gauge needle under tongue

□ Minimal respiratory efforts: treat with 100% oxygen by face mask and doxapram (Dopram), one drop from 25-gauge needle under tongue

□ No suckle reflex, weak heartbeat, and minimal respiratory efforts: treat with naloxone + atropine + doxapram, one drop of each via 25-gauge needle under tongue

▪ Ensure normothermia
□ Place in box with recirculation heating pad and dry towels

□ Use forced-air heating unit if available (or carefully use blow-dryer to warm and dry newborns)

▪ Place newborns with dam as soon as she is awake from anesthesia

▪ Monitor dam and newborns for cannibalism until discharge from hospita


FELINE DIABETIC PATIENTS



Preanesthesia



▪ With regard to blood work, at a minimum, PCV, TP, and blood glucose should be measured

▪ Patient should be fasted no longer than 6 hours

▪ Administer half the normal dose of insulin before premedication or induction

▪ Perform anesthesia early in day

▪ Place IV catheter for administration of anesthetic agents, fluids, and glucose if necessary

▪ Use of sterile technique for catheter placement and surgery is imperative, as diabetic patients are prone to infection



Premedication



Agents (mg/kg IM; use half if administering IV)


Oxymorphone 0.03-0.08 + midazolam (or diazepam)* 0.1-0.3 ± glycopyrrolate 0.01


Morphine 0.4-0.8 + midazolam (or diazepam)* 0.1-0.3 ± glycopyrrolate 0.01


Buprenorphine 0.01-0.02 + midazolam (or diazepam)* 0.1-0.3 ± glycopyrrolate 0.01



* Acepromazine 0.02-0.05 can be substituted as a sedative only if patient is well hydrated; vasodilation and hypotension may result.



Induction



▪ Propofol has no effect on blood glucose concentration or glucose metabolism; give half the calculated induction dose over 60 seconds; preoxygenate (with oxygen administered via face mask for 5 minutes) before induction to prevent hypoxemia

▪ Thiopental may increase plasma glucose concentration

▪ Ketamine and benzodiazepine induction may lead to tachycardia or arrhythmias and should be used with caution; contraindicated in cats that also have hyperthyroidism

▪ Opiate and benzodiazepine induction is acceptable

▪ Inhalant induction by face mask is acceptable



Induction



Agents (mg/kg IV); give only until effective


Propofol 4-6 (use caution if hypovolemia or hypotension is present)


Thiopental 10


Ketamine 5 + diazepam (or midazolam) 0.25 (watch for arrhythmias)


Oxymorphone (or hydromorphone) 0.1 + diazepam 0.2


Mask with inhalant



Maintenance



▪ Achievement of rapid induction and recovery is the goal; isoflurane and sevoflurane are preferable to halothane

Related posts:

  1. Blood and Blood Substitutes
  2. Cardiopulmonary Resuscitation
  3. Fluids
  4. Drug Combinations

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Oct 14, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Case Management

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