Intrathecal morphine for postoperative analgesia: Current trends

Table 1 Comparison of intrathecal morphine with hydrophilic opioids (Fentanyl and Sufentanil)[9]

Opioid	IT/iv potency ratio	Onset of IT analgesia (min)	Duration of analgesia (h)	Time of peak respiratory depression	Clinical dose range
Morphine	200-300:1	60-120	18-24	8-10 h	0.1-0.5 mg
Fentanyl	10-20:1	< 10	1-4	5-20 min	6-30 mcg
Sufentanil	10-20:1	< 10	2-6	5-20 min	2.5-10 mcg

IT: Intrathecal; iv: Inravenous.

Table 2 Recommended intrathecal morphine dosages for various surgical procedure[17]

Low dose (with LA or RA)	Moderate dose (with GA)	High dose (with GA)
TURP: 0.05 mg	Abdominal hysterectomy: 0.2 mg (plus LA)	Thoracotomy surgery: 0.5 mg
Caesarian section: 0.1 mg	Abdominal colon surgery: 0.3 mg	Abdominal aortic surgery and cardiac surgery: 7-10 mcg/kg
Hip replacement: 0.1 mg	Spinal surgery: 0.4 mg
Knee replacement: 0.2 mg

LA: Local anesthesia; RA: Regional anesthesia; GA: General anesthesia.

Table 3 Concomitant use of other intrathecal drugs with intrathecal morphine

Additional IT drug to IT morphine	Effect
Local anesthetic-bupivacaine	Improved pain score and lower requirement of additional analgesia
Fentanyl	May induce acute tolerance to IT morphine and no real advantage
Clonidine	Increased duration of analgesia with better pain scores but higher incidence of hypotension
Ketorolac	Increased duration of analgesia without significant side effects

IT: Intrathecal.

Table 4 Summary of side effects of intrathecal morphine

	Serious	Not serious
Common	Respiratory depression	Pruritus
	Sedation	Nausea and vomiting
		Urinary retention
Uncommon	Bradycardia	Sweating
		Delayed gastric emptying
		Constipation
		Headache
		Persistent hiccups
		Resistant hypothermia
		Priapism
		Nystagmus

Table 5 Guidelines by American Society of Anaesthesiologists task force for the prevention, detection, and management of respiratory depression associated with intrathecal morphine administration[58,75]

Identification of patients who may have increased risk respiratory depression	Prevention of respiratory depression	Detection of respiratory depression	Treatment of respiratory depression
• History of sleep apnea or OSA • Diabetes • Obesity • Concurrent systemic opioids • History of opioid intolerance • Physical examination of airway, heart, lung, cognitive function and vital signs	• NIPPV should be used for known OSA patients • Single shot neuraxial opioid preferred over systemic continuous opioids • IT morphine is not to be given in outpatient settings • Minimal effective dose to be used • Cautious use of parenteral opioids and hypnotics in the presence of neuraxial opioid • Concomitant use of parenteral hypnotics, opioids, magnesium, or sedatives will require increased monitoring in terms of duration, intensity or additional methods	• Monitor, respiration (rate and depth), oxygenation (SaO2%) and sedation (Sedation score) • Monitor for at least 24 h every hour for the first 12 h then every 2 h for the next 12 h • After 24 h check the patient’s condition and concurrent medication and decide on frequency of monitoring	• O2 therapy when altered level of consciousness, respiratory depression, or hypoxemia • Routine O2 therapy not advised as it may prolong the duration of apneic episodes and prevent detection of atelectasis, transient apnea and hypoventilation • Use of reversal agents like naloxone •Iv access should be maintained at all times • NIPPV should be considered and initiated when there is frequent and severe airway obstruction or hypoxemia

OSA: Obstructive sleep apnea; NIPPV: Noninvasive positive pressure ventilation; iv: Intravenous.