From the Guidelines
High Acuity Low Occurrence (HALO) events in Obstetrics and Gynecology are primarily caused by several critical complications that occur rarely but require immediate intervention, including postpartum hemorrhage, severe preeclampsia progressing to eclampsia, amniotic fluid embolism, placental abruption, and uterine rupture, as well as complications during laparoscopic surgery and severe pelvic infections leading to sepsis. In obstetrics, the most common causes of HALO events include:
- Postpartum hemorrhage (blood loss exceeding 500ml after vaginal delivery or 1000ml after cesarean section) 1
- Severe preeclampsia progressing to eclampsia (characterized by seizures) 1
- Amniotic fluid embolism
- Placental abruption
- Uterine rupture Shoulder dystocia, where the anterior shoulder of the fetus cannot pass below the pubic symphysis, is another significant HALO event. In gynecology, causes of HALO events include:
- Complications during laparoscopic surgery such as major vessel injury, bowel perforation, and anesthetic emergencies
- Severe pelvic infections leading to sepsis
- Ectopic pregnancy rupture causing hemorrhagic shock
- Complications from gynecologic oncology procedures These situations are dangerous because their rarity means healthcare providers may have limited experience managing them, yet they require rapid recognition and intervention to prevent maternal morbidity and mortality, as highlighted in recent studies 1. Regular simulation training and clear institutional protocols are essential for maintaining readiness to address these uncommon but life-threatening scenarios, and guidelines such as those from the Society for Maternal-Fetal Medicine 1 and the Association of Anaesthetists 1 provide valuable recommendations for management.
From the FDA Drug Label
OVERDOSAGE Overdosage with oxytocin injection (synthetic) depends essentially on uterine hyperactivity whether or not due to hypersensitivity to this agent Hyperstimulation with strong (hypertonic) or prolonged (tetanic) contractions, or a resting tone of 15 to 20 mm H2O or more between contractions can lead to tumultuous labor, uterine rupture, cervical and vaginal lacerations, postpartum hemorrhage, uteroplacental hypoperfusion and variable deceleration of fetal heart, fetal hypoxia, hypercapnia or death PRECAUTIONS General All patients receiving intravenous oxytocin must be under continuous observation by trained personnel with a thorough knowledge of the drug and qualified to identify complications. A physician qualified to manage any complications should be immediately available. When properly administered, oxytocin should stimulate uterine contractions similar to those seen in normal labor Overstimulation of the uterus by improper administration can be hazardous to both mother and fetus. Even with proper administration and adequate supervision, hypertonic contractions can occur in patients whose uteri are hypersensitive to oxytocin Except in unusual circumstances, oxytocin should not be administered in the following conditions: prematurity, borderline cephalopelvic disproportion, previous major surgery on the cervix or uterus including Caesarean section, overdistention of the uterus, grand multiparity or invasive cervical carcinoma Maternal deaths due to hypertensive episodes, subarachnoid hemorrhage, rupture of the uterus and fetal deaths due to various causes have been reported associated with the use of parenteral oxytocic drugs for induction of labor and for augmentation in the first and second stages of labor
The common causes of HALO (High Acuity Low Occurrence) events in Obstetrics (O&G) and Gynecology (Gyne) include:
- Uterine hyperactivity due to oxytocin overdose or hypersensitivity
- Hyperstimulation of the uterus with strong or prolonged contractions
- Hypertonic contractions in patients with hypersensitive uteri
- Improper administration of oxytocin
- Pre-existing conditions such as prematurity, borderline cephalopelvic disproportion, previous major surgery on the cervix or uterus, overdistention of the uterus, grand multiparity, or invasive cervical carcinoma 2 2 These conditions can lead to severe complications, including tumultuous labor, uterine rupture, cervical and vaginal lacerations, postpartum hemorrhage, and fetal deaths.
From the Research
Common Causes of HALO Events in O&G
The common causes of High Acuity Low Occurrence (HALO) events in Obstetrics (O&G) and Gynecology (Gyne) include:
- Hypertensive disorders of pregnancy, such as preeclampsia, eclampsia, and HELLP syndrome 3
- Postpartum hemorrhage, which can be caused by uterine atony, retained placental tissue, or lacerations 4, 5
- Severe maternal morbidity, including adult respiratory distress syndrome, shock, disseminated intravascular coagulation, acute renal failure, and pituitary necrosis (Sheehan syndrome) 4
- Uterine atony, which is a common cause of primary postpartum hemorrhage and can be treated with uterotonic medications such as oxytocin, methylergonovine, and carboprost 5
- Intrapartum administration of magnesium sulfate, which has been associated with an increased risk of postpartum hemorrhage, uterine atony, and red blood cell transfusion 6
- Reversible cerebral vasoconstrictive syndrome (RCVS), which is a pregnancy-related cause of seizure that can be provoked by vasoconstrictive agents such as methergine 7
Risk Factors and Management
Risk factors for HALO events in O&G include:
- Hypertensive disorders of pregnancy
- Previous history of postpartum hemorrhage or uterine atony
- Multiple gestations
- Placental abruption
- Uterine rupture Management of HALO events in O&G involves a multidisciplinary team approach, including:
- Early diagnosis and treatment of hypertensive disorders of pregnancy
- Active management of postpartum hemorrhage, including uterotonic medications and blood transfusions
- Close monitoring of patients with risk factors for HALO events
- Avoidance of vasoconstrictive agents in patients with RCVS
- Use of calcium channel blockers and magnesium sulfate in patients with RCVS 7